DISPLAY SYSTEM[Technical Field]The present invention relates to a display system.
[Background Art]
A display system for realizing augmented reality (AR) may transmit light from the outside world toward an eyeball of a user by a light guide member. Along with that, the display system may convert light from a display device into collimated light by a collimating optical system and guide the collimated light toward the eyeball of the user by the light guide member. To accomplish a practical size, that is, an eyeglasses-like shape with these AR optical units, it is required to downsize the above-mentioned display system.
[Disclosure of Invention]
[Problem to be Solved by the Invention]
For example, the collimating optical system may include a lens that heavily uses aspherical shapes on its lens surface. In this case, if materials included in lenses of the collimating optical system are unified to a single kind of easily-shapable material (e.g., plastic) , a characteristic of the collimating optical system such as a refractive index may vary depending on changes of ambient temperature, and a parallelism of light emitted from the collimating optical system may degrade. Therefore, an AR image to be displayed on the display device may be subject to a distortion by the collimating optical system and the light guide member and the distorted light may be guided to the eyeball of the user. As a result, it is difficult for the user to watch a suitable AR image on the display system. Furthermore, it can be considered that, for a less-variable refractive index, etc., of each lens of the collimating optical system in response to change in the ambient temperature, all the lenses may be configured with a material (e.g., glass) that is less variable in response to temperature change. In this case, the glass lenses may increase the weight and enlarge the shape, which makes it impossible to design a light and compact optical system. Accordingly, it is difficult to apply this to practical AR glasses.
The present invention has been made in view of the above-described problem, and an aim of the invention is to provide a display system that can suppress a variation of characteristics in accordance with changes of ambient temperature.
[Means for Solving Problem]
To solve the problem described above and achieve the object, there is provided a display system including a display device and an optical system. The display device includes a display surface and a pixel array. The pixel array is arranged in a region including the display surface. The pixel array has a plural pixels. The plural pixels corresponds to plural colors. The plural pixels are arranged three-dimensionally in the pixel array. The optical system has a lens group. The lens group includes a first lens and a second lens. The optical system is configured to convert light from the display device into collimated light. The first lens has different thermal characteristic from the second lens in the lens group.
[Effect of the Invention]
According to one aspect of the present invention, it is possible to suppress a variation of characteristics in accordance with changes of ambient temperature.
[Brief Description of Drawings]
FIG. 1 is a diagram illustrating a schematic configuration of a display system according to an embodiment;
FIG. 2 is a perspective view illustrating a configuration of a display device according to the embodiment;
FIG. 3 is a cross-sectional view illustrating a configuration of a pixel group according to the embodiment;
FIG. 4 is a cross-sectional view illustrating a configuration of an optical system according to the embodiment;
FIG. 5 is a diagram illustrating sizes of the display device and a lens diaphragm according to the embodiment;
FIG. 6 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system according to the embodiment;
FIG. 7 is a diagram illustrating the configuration and configuration variation responsive to temperature change of the optical system according to the embodiment;
FIG. 8 is a diagram illustrating a lens shape of the optical system according to the embodiment;
FIG. 9 is a diagram illustrating imaging characteristics and its variation responsive to temperature change of the optical system according to the embodiment;
FIG. 10 is a diagram illustrating characteristics of the optical system according to the embodiment;
FIG. 11 is a wave diagram illustrating drive current of a pixel group according to a first modification example of the embodiment;
FIG. 12 is a wave diagram illustrating operations of a drive circuit according to the first modification example of the embodiment;
FIG. 13 is a cross-sectional view illustrating a configuration of a display device according to a second modification example of the embodiment;
FIG. 14 is a cross-sectional view illustrating a configuration of an optical system according to a third modification example of the embodiment;
FIG. 15 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system according to the third modification example of the embodiment;
FIG. 16 is a diagram illustrating a lens shape of the optical system according to the third modification example of the embodiment;
FIG. 17 is a diagram illustrating characteristics of the optical system according to the third modification example of the embodiment;
FIG. 18 is a cross-sectional view illustrating a configuration of an optical system according to a fourth modification example of the embodiment;
FIG. 19 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system according to the fourth modification example of the embodiment;
FIG. 20 is a diagram illustrating a lens shape of the optical system according to the fourth modification example of the embodiment;
FIG. 21 is a diagram illustrating characteristics of the optical system according to the fourth modification example of the embodiment;
FIG. 22 is a cross-sectional view illustrating a configuration of an optical system according to a fifth modification example of the embodiment;
FIG. 23 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system according to the fifth modification example of the embodiment;
FIG. 24 is a diagram illustrating a lens shape of the optical system according to the fifth modification example of the embodiment;
FIG. 25 is a diagram illustrating characteristics of the optical system according to the fifth modification example of the embodiment;
FIG. 26 is a cross-sectional view illustrating a configuration of an optical system according to a sixth modification example of the embodiment;
FIG. 27 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system according to the sixth modification example of the embodiment;
FIG. 28 is a diagram illustrating a lens shape of the optical system according to the sixth modification example of the embodiment; and
FIG. 29 is a diagram illustrating characteristics of the optical system according to the sixth modification example of the embodiment.
[Embodiment (s) of Carrying Out the Invention]
Hereinafter, a display system according to an embodiment will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to this embodiment.
(Embodiment)
The display system according to the embodiment is, for example, a system (e.g., AR glasses) for realizing a multi-color AR image and is configured by combining a display device and an optical system, and some improvements to suppress its variation responsive to ambient temperature is made. For example, a display system 1 is configured as illustrated in FIG. 1. FIG. 1 is a diagram illustrating a configuration of the display system 1.
The display system 1 includes a display device 10, an optical system 20, a light guide member 30, and a drive circuit 50. The display device 10 is arranged on the object side of the optical system 20. The light guide member 30 is arranged on the image side of the optical system 20. The light guide member 30 is, for example, a light guide plate 31. The optical system 20 is arranged between a side surface 31c of the light guide plate 31 and a display surface 10a of the display device 10. The side surface 31c of the light guide plate 31 substantially coincides with an exit pupil surface of the optical system 20. The side surface 31c has a wedge shape in which the side surface inclines toward a back surface 31b as the side surface heads from a front surface 31a to the back surface 31b. By employing such a wedge shape, the light collimated by the optical system 20 can be incident into the light guide plate 31 to be guided by the total reflection. Note that, instead of a wedge shape, by arranging a diffractive optical element DOE (Diffractive Optical Element) , a holographic optical element HOE (Holographic Optical Element) , or the like on the front surface 31a or the back surface 31b, for example, the light collimated by the optical system 20 may be incident to the DOE and HOE within the light guide plate 31 and make the DOE and HOE change an angle for guide so as to guide the light within the light guide plate 31 by the total reflection.
The display system 1 may transmit light from the outside world toward an eyeball 100 of a user by using the light guide member 30. Along with that, the display system drives the display device 10 with the drive circuit 50 to display an image on the display device 10. Light corresponding to the image from the display device 10 is guided to the optical system 20. The display system may convert the light from the display device 10 into collimated light by using the optical system 20, and guide the collimated light toward the eyeball 100 of the user by using the light guide member 30. The collimated light injected from the side surface 31c of the light guide plate 31 proceeds through the light guide plate 31 while being reflected by the front surface 31a and the back surface 31b of the light guide plate 31. The diffractive optical element DOE is formed in a region indicated by a thick line on the front surface 31a of the light guide plate 31. The diffractive optical element DOE has a diffraction grating structure such as periodic unevenness, and is configured so that light having a predetermined wavelength injected by a predetermined angle among light rays proceeding through the light guide plate 31 is reflected toward the eyeball 100. The light diffracted by the diffractive optical element DOE among the light rays proceeding through the light guide plate 31 may be guided toward the eyeball 100 of the user. As a result, the exit pupil is enlarged simulatively, and the user distant from the light guide member 30 may visually recognize the AR image according to the image of the display device 10 that is enlarged by the optical system 20, without chipping. Moreover, the light guide plate 31 may easily expand an image to cause the user to visually recognize the image as the AR image by receiving the image of the display device 10 as the collimated light.
As illustrated in FIG. 2, the display device 10 may be configured to be able to display a multi-color (e.g., full-color) image. FIG. 2 is a perspective view illustrating a configuration of the display device 10.
The display device 10 includes the display surface 10a, a pixel array 10b, and a board 11. In FIG. 2, a direction perpendicular to the surface of the board 11 is defined as a Z direction, and two directions orthogonal to each other on the surface perpendicular to the Z direction are defined as X and Y directions. The display surface 10a extends along the XY direction. The image by the display device 10 is displayed on the display surface 10a. The optical system 20 is arranged on the+Z side of the display surface 10a. The display device 10 emits light according to an image from the display surface 10a to the optical system 20.
The pixel array 10b is arranged in a region that includes the display surface 10a and is arranged between the display surface 10a and the board 11. In the pixel array 10b, a plural pixel groups 13 (1, 1) to 13 (m, n) are arranged in the XY direction. The configuration that the pixel groups 13 (1, 1) to 13 (m, n) constituting m rows and n columns are arranged is exemplified in FIG. 2. Each of the pixel groups 13 is arranged on the+Z side of the board 11. A plural pixels 12 are arranged in the Z direction in each of the pixel groups 13. As a result, in the pixel array 10b, the plural pixels 12 are arranged three-dimensionally in the XYZ direction on the display surface 10a.
Each of the pixel groups 13 includes a plural pixels 12r, 12g, and 12b. In the pixel group 13, the pixels 12b, 12g, and 12r are arranged in the Z direction from a direction close to the optical system 20. In the plural pixels 12r, 12g, and 12b, central axes passing through the centers of the light emitting surfaces and being perpendicular to the light emitting surfaces may substantially coincide with each other. An axis that roughly approximates the central axes of the plural pixels 12r, 12g, and 12b may be considered as the central axis of the pixel group 13. The plural pixels 12r, 12g, and 12b corresponds to plural colors. The pixel 12r corresponds to a first color, the pixel 12g corresponds to a second color, and the pixel 12b corresponds to a third color. The first color corresponds to light in the first wavelength range. The second color corresponds to light in the second wavelength range shorter than the first wavelength range. The third color corresponds to light in the third wavelength range shorter than the second wavelength range. For example, the first color is red (R) , the second color is green (G) , and the third color is blue (B) . In FIG. 2, a pixel corresponding to blue is 12b, a pixel corresponding to green is 12g, and a pixel corresponding to red is 12r. In each of the pixel groups 13, the pixels 12r, 12g, and 12b are stacked onto the board 11 by bonding etc. A stacking order is not limited to the stacking order illustrated in FIG. 2, and an arbitrary stacking order may be employed.
The display device 10 is a micro LED (light emission diode) display, for example. As illustrated in FIG. 3, in the pixels 12r, 12g, and 12b, P-type semiconductor films 12rp, 12gp, and 12bp extending in the XY direction and N-type semiconductor films 12rn, 12gn, and 12bn extending in the XY direction are stacked in the Z direction. FIG. 3 is a cross-sectional view illustrating the configuration of the pixel group 13. The pixels 12r, 12g, and 12b may be stacked with a direct bonding (epi-film bonding) using intermolecular force. P-type semiconductor films 12rp, 12gp, and 12bp and N-type semiconductor films 12rn, 12gn, and 12bn are respectively formed on other boards with epitaxial growth technique. After that, each semiconductor film 12rp, 12gp, 12bp, 12rn, 12gn, and 12bn are peeled from the other boards. N-type semiconductor film 12rn, P-type semiconductor film 12rp, N-type semiconductor film 12gn, P-type semiconductor film 12gp, N-type semiconductor film 12bn, and P-type semiconductor film 12bp are stacked in turn on the board 11 and are applied with pressure and bonded to each other. At this time, due to the action of the intermolecular force, each semiconductor films 12rp, 12gp, 12bp, 12rn, 12gn, and 12bn are bonded while reducing compressive strain in each bonding interface 15r, 15g, and 15b.
Each pixel 12r, 12g, and 12b is applied with a current in a forward direction of PN junction from the drive circuit 50, and thus emit light from bonding interfaces 15r, 15g, and 15b between the P-type semiconductor films 12rp, 12gp, and 12bp and the N-type semiconductor films 12rn, 12gn, and 12bn. At this time, in each of the pixel groups 13, red light generated from the bonded outer surface 15r in the pixel 12r transmits the pixels 12g and 12b and is emitted from the display surface 10a to the optical system 20, green light generated from the bonded outer surface 15g in the pixel 12g transmits the pixel 12b and is emitted from the display surface 10a to the optical system 20, and blue light generated from the bonded outer surface 15b in the pixel 12b is emitted from the display surface 10a to the optical system 20. The emission intensities of the pixels 12r, 12g, and 12b may be respectively adjusted by the drive circuit 50 in accordance with target brightness of colors to be displayed.
At this time, the pixels 12r, 12g, and 12b may be stacked using epi-film bonding, for example. Usage of epi-film bonding enables bonding of the pixel group 13 onto the board 11 using intermolecular force. Usage of intermolecular force enables bonding of the pixel group 13 to the board 11 with the compressive strain in the laminated structure of the pixel group 13 being reduced sufficiently. Because the pixel group 13 is bonded to the board 11 with the compressive strain being reduced sufficiently, the occurrence of Piezoelectric effect is suppressed and therefore EQE (External Quantum Efficiency) may be enhanced.
Note that reflecting members 14R and 14L may be arranged on side walls 13R and 13L of the pixel group 13 as illustrated in FIG. 3. The reflecting member 14R and 14L may be formed of materials (e.g., metal) having reflectance properties or materials (e.g., silicon oxide) having a large refractive index difference from materials of the P-type semiconductor films 12rp, 12gp, and 12bp and the N-type semiconductor films 12rn, 12gn, and 12bn. As a result, the reflecting member 14R is arranged on the side wall 13R of the pixel group 13 to be able to form a reflective interface on the side wall 13R. The reflecting member 14L is arranged on the side wall 13L of the pixel group 13 to be able to form a reflective interface on the side wall 13L. As a result, in each of the pixel groups 13, light toward the side walls 13R and 13L among light rays emitted from the bonding interfaces 15r, 15g, and 15b in the pixels 12r, 12g, and 12b may be reflected and be guided in a direction heading for the optical system 20.
As illustrated in FIGS. 2 and 3, in the display device 10, because the plural pixels 12 corresponding to the plural colors in the pixel array 10b are arranged three-dimensionally, the number of pixels of each color in a predetermined area may be easily improved and an image by the display device 10 may be made high definition. Alternatively, an aperture ratio of a pixel of each color in the predetermined area and the predetermined number of pixels may be easily improved, and the brightness of an image by the display device 10 may be increased.
As illustrated in FIG. 4, the optical system 20 is configured to convert the light from the display device 10 into the collimated light. FIG. 4 is a cross-sectional view illustrating a configuration of the optical system 20. In FIG. 4, the optical axis is illustrated with a dashed-dotted line.
The optical system 20 includes a protection member 28 and a lens group 20a. The protection member 28 is a member that extends in a plate-like shape in XY directions. The protection member 28 has substantially rectangular shape in XY plan view. The lens group 20a has an incident surface 20b and an exit pupil surface 20c. The incident surface 20b faces the display surface 10a via the protection member 28. The exit pupil surface 20c substantially coincides with the side surface 31c of the light guide member 30 (e.g., the light guide plate 31) .
The optical system 20 receives light emitted from the display surface 10a of the display device 10 on the incident surface 20b, refracts the light to convert the light into collimated light substantially parallel to an optical axis PA, and emits the collimated light from the exit pupil surface 20c.
The lens group 20a includes a plural lenses 21 to 26 and a lens diaphragm 27 in sequence from the display-surface side to the AR-image side. The plural lenses 21 to 26 and the lens diaphragm 27 are arranged along the optical axis PA, and each of them intersects with the optical axis PA. The incident surface of the lens 21 closest to the display-surface side among the plural lenses 21 to 26 forms the incident surface 20b of the optical system 20. The lens diaphragm 27 is arranged on the exit pupil surface 20c of the optical system 20.
The plural lenses 21 to 26 are configured by combining lens having positive refractive power and lens having negative refractive power to correct an aberration of the lens group 20a. The plural lenses 21 to 26 may have different cross-sectional shapes including the optical axis PA. In FIG. 4, a lens configuration that the lenses 22 and 26 have positive refractive power and the other lenses 21, 23, 24, and 25 have negative refractive power in a paraxial region is exemplified.
It is desirable that the number of lenses included in the lens group 20a is 5 or more and 8 or less. When the number of lenses is 4 or less, it may be difficult to correct aberration characteristics so as to be within an allowable range. When the number of lenses is 9 or more, the optical system 20 may grow in size beyond an allowable range.
The lens group 20a may include a convex lens on the AR-image side. The lens group 20a may include a meniscus lens or a concave lens on the display-surface side. In the example illustrated in FIG. 4, the AR-image-side lens 26 is a convex lens, and the display-surface-side lens 21 is a meniscus lens.
In the lens group 20a, the diameter of the lens close to the incident surface 20b may be larger than the diameter of the lens close to the exit pupil surface 20c. In FIG. 4, the diameter of the lens 21 is larger than the diameter of the lens 26.
The lens diaphragm 27 is arranged between the light guide member 30 (e.g., the light guide plate 31) and the lens 26 in the Z direction. The lens diaphragm 27 has an aperture 27a. The aperture 27a is a substantially circular shape in an XY plan view.
Each of the lenses 21 to 26 is formed of translucent material. The lens diaphragm 27 may be formed of a light-shielding material, or may be formed of an arbitrary material to paint a color suitable for light shielding such as black color on its surface.
In the optical system 20, the lens group 20a may include a hybrid of a first lens and a second lens having different thermal characteristic from each other. For example, the lens group 20a may be configured with a hybrid of a first material of the first lens and a second material of the second lens, each material having different thermal characteristic from each other. A temperature change coefficient of a refractive index of the first material is smaller than a temperature change coefficient of a refractive index of the second material. A line expansion coefficient of the first material is smaller than a line expansion coefficient of the second material. The number of an inflection point at a cross-section of the first lens is equal to or less than the number of an inflection point at a cross-section of the second lens. The first material includes glass or quartz, and the second material includes plastic such as translucent plastic.
The optical system 20 may be configured to attenuate characteristic variation of the lens group 20a with characteristic variation of the first lens with the first material in response to a change in the ambient temperature. The optical system 20 may be configured such that characteristic variation of the first lens with the first material and characteristic variation of the second lens with the second material may attenuate with each other. In the lens group 20a, the first lens with the first material may be arranged at least closest to the AR-image side in the lens group 20a. The second lens with the second material may be arranged between the first lens with the first material and the display device 10.
In this way, it is possible to configure the optical system 20 so as to reduce variations in parallelism of light emitted from the optical system 20 in accordance with a change in the ambient temperature and therefore possible to enhance image quality by lights guided by the light guide member 30.
Herein, it is assumed that a distance between the display surface 10a and the exit pupil surface 20c is DTTL. It is assumed that a focal length of the lens 26 closest to the AR-image side among the lenses 21 to 26 is DEFL1. It is assumed that an Abbe number of the lens 26 closest to the AR-image side among lenses 21 to 26 isνL1. It is assumed that a distance between the display surface 10a and a point at which the optical axis PA of the optical system 20 intersects with the incident surface 20b of the lens 21 closest to the display-surface side among the lenses 21 to 26 is DBL.
As illustrated in (a) of FIG. 5, the display surface 10a of the display device 10 may have a rectangular shape in which the X direction is a longitudinal direction in an XY plan view, and the length of the diagonal line is the maximum size. It is assumed that the half of the maximum size of the display surface 10a is WDISD. It is assumed that the half of the size of the display surface 10a in the short direction is EDISV. (a) of FIG. 5 is a diagram illustrating a size of the display surface 10a of the display device 10.
As illustrated in (b) of FIG. 5, the aperture 27a of the lens diaphragm 27 has a substantially circular shape in an XY plan view and its diameter is an aperture diameter. It is assumed that an aperture diameter of the lens diaphragm 27 is WEXA. (b) of FIG. 5 is a diagram illustrating a size of the aperture 27a of the lens diaphragm 27. It is assumed that a viewing angle on the exit pupil surface is θDFOV.
At this time, the optical system 20 satisfies the following Expressions (1) to (8) .
0.4<DEFL1/DEFL<0.8 (1)
νL1>65 (2)
1/DEFL1>0 (3)
DEFL/WDISD>1.3 (4)
DBL<EDISV (5)
DEFL/WEXA<3.5 (6)
DTTL/DEFL<1.7 (7)
-4< {WDISD-DEFL·tan (θDFOV/2) } / {DEFL·tan (θDFOV/2) } x 100<4 (8)
By satisfying Expression (1) in the optical system 20, for temperature variation in the focus position of the lens group 20a, temperature variation in the focus position of the lens 26 in the direction opposite that of the lens group 20a may be acted. With this action, it is possible to suppress variation of focus position of the lens group 20a in accordance with changes in ambient temperature and thereby possible to suppress variation of characteristics of the lens group 20a.
By satisfying Expression (2) in the optical system 20, since low dispersion material (e.g., low dispersion glass or low dispersion quartz) may be used as a material of the lens 26, chromatic aberration of the lens group 20a may be effectively suppressed.
By satisfying Expression (3) in the optical system 20, the lens 26 has a positive refractive power and, at the same time, for temperature variation in the focus position of the lens group 20a, temperature variation in the focus position of the lens 26 in the direction opposite that of the lens group 20a may be acted.
By satisfying Expression (4) in the optical system 20, since a viewing angle θDFOV on the exit pupil surface 20c may fall within a suitable range (e.g., smaller than 75°) and in accordance with this a size of the optical system 20 may fall within a suitable size range. With this configuration, a fashionable external shape may be realized for the display system 1 (e.g., AR glass) .
By satisfying Expression (5) in the optical system 20, when the display device 10 is made with a small size, since back focus can be shortened accordingly, the focal length of the optical system 20 may be reduced and the optical system is easy to be configured to have a wide field of view and a compact size.
By satisfying Expression (6) in the optical system 20, since effective F-number (≈DEFL/WEXA) may be reduced, a combined image by the optical system 20 may easily have high brightness.
By satisfying Expression (7) in the optical system 20, since an angle of view may be widely secured while downsizing the optical system 20, a fashionable external shape may be realized for the display system 1, and also a wide-field image may be realized and realistic sensation in use may be increased. When Expression (7) is not satisfied, since a viewing angle becomes large and thus the light guide member 30 also becomes large, it becomes difficult to fit in an appropriate size when the display system is mounted on the AR glasses having a highly fashionable glass shape, for example.
By satisfying Expression (8) in the optical system 20, aberration amount of distortion aberration of the lens group 20a may fall within an allowable range (e.g., larger than-4%and smaller than 4%) and thereby the performance of the display system 1 may be enhanced.
Next, a mounting configuration and its variation responsive to temperature change of the optical system 20 will be described with reference to FIGS. 4 to 8. FIG. 6 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system 20. FIG. 7 is a diagram illustrating the configuration, and configuration variation responsive to temperature change of the optical system 20. FIG. 8 is a diagram illustrating surface shapes of lenses 21 to 26 in the lens group 20a.
In FIG. 4, the configuration that an effective diameter for light flux of a lens on the AR-image side in the lens group 20a is smaller than an effective diameter for light flux of a lens on the display-surface side in the lens group 20a is exemplified. For example, an effective diameter for light flux of the lens 26 on the AR-image side is smaller than an effective diameter for light flux of the lens 21 on the display-surface side. In FIG. 4, the optical axis PA is illustrated with a dashed-dotted line, and passes through the substantial center of the aperture 27a of the lens diaphragm 27. Optical paths of light emitted from a center CP (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with solid lines. Optical paths of light emitted from a maximum display-height position PP2 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dotted lines. Optical paths of light emitted from a maximum display-height position PP1 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dashed-two dotted lines.
The number of an inflection point in an incident surface or an exit surface of each of the lenses 25, 26 when seen in a cross-section including the optical axis PA is equal to or less than the number of an inflection point in an incident surface or an exit surface of each of the lenses 21 to 24 when seen in a cross-section including the optical axis PA. The number of an inflection point in an incident surface or an exit surface of each of the lenses 25, 26 when seen in a cross-section including the optical axis PA is one to two within an effective-area surface through which the light rays pass. The number of an inflection point in incident surface or exit surface of each of the lenses 21 to 24 when seen in a cross-section including the optical axis PA is two or more within an effective-area surface through which the light rays pass.
(a) of FIG. 6 illustrates that the optical system 20 satisfies all of Expressions (1) to (8) . This allows to suppress the characteristic variation of the optical system 20 in accordance with change in the ambient temperature and to easily downsize the optical system 20. In the optical system 20, an entire length (the Z-direction length) can be set to around 9.061 mm, an angle of view can be secured to be "θDFOV=around 59.785 [°] " , and effective F-number (≈DEFL/WEXA) can be reduced to around 1.836.
In (a) of FIG. 7, there is shown that the lens group 20a is configured with a hybrid of glass and plastic. In (a) of FIG. 7, the configuration where the lenses 26, 25 are formed of glass and the lenses 24, 23, 22, 21 are formed of plastic is exemplified. With this configuration, for each of the light wavelengths of 653.3 nm, 546.1 nm,and 435.8 nm, a temperature change coefficient of a refractive index of each lens 21 to 26 and protection member 28 as illustrated in (c) of FIG. 6 may be achieved for refractive indices of each lens 21 to 26 and protection member 28 as illustrated in (b) of FIG. 6. In (c) of FIG. 6, there are a positive temperature change coefficient and a negative temperature change coefficient in a mixed manner. The temperature change coefficients of the lenses 26, 25 with glass material is smaller than the temperature change coefficients of the lenses 24, 23, 22, 21 with plastic material. With this configuration, it is possible to configure the optical system 20 such that the characteristic variations of the lenses 26, 25 and the characteristic variations of the lenses 24, 23, 22, 21 in response to changes in ambient temperature may attenuate with each other.
In (a) and (b) of FIG. 7 and (a) and (b) of FIG. 8, surface numbers are assigned as follows:
Surface number: 1: Exit surface of the lens diaphragm 27;
Surface number: 3: Exit surface of the lens 26;
Surface number: 4: Incident surface of the lens 26;
Surface number: 5: Exit surface of the lens 25;
Surface number: 6: Incident surface of the lens 25;
Surface number: 7: Exit surface of the lens 24;
Surface number: 8: Incident surface of the lens 24;
Surface number: 9: Exit surface of the lens 23;
Surface number: 10: Incident surface of the lens 23;
Surface number: 11: Exit surface of the lens 22;
Surface number: 12: Incident surface of the lens 22;
Surface number: 13: Exit surface of the lens 21; and
Surface number: 14: Incident surface of the lens 21.
Surface number: 15: Incident surface of the protection member 28.
(a) of FIG. 7 exemplifies a shape and a characteristic of each lens 21 to 26 in ambient temperature of 25℃. (b) of FIG. 7 exemplifies a shape and a characteristic of each lens 21 to 26 in ambient temperature of 60℃.
In (a) of FIG. 7, a curvature radius R [mm] , a surface separation D [mm] , a refractive index Nd, an Abbe number Vd, a material, a focal length, and a compound lens focal length are indicated for each surface of surface numbers 1 to 15. A lens configuration is indicated with the curvature radius R. The lens group 20a is configured to include, in a paraxial region, the positive convex lens 26, the negative meniscus lens 25 with a convex surface facing the image side, the negative meniscus lens 24 with a convex surface facing the image side, the negative meniscus lens 23 with a convex surface facing the image side, the positive convex lens 22, and the negative meniscus lens 21 with a convex surface facing the image side, in order from the image side. It is possible to preferably correct a chromatic aberration by causing the lenses 21 to 26 to have the different refractive indices Nd and Abbe numbers Vd. In (a) of FIG. 7, a curvature radius R [mm] , a surface separation D [mm] may show surface shape in ambient temperature of 25℃.
In (b) of FIG. 7, a curvature radius R [mm] , a surface separation D [mm] are indicated for each surface of surface numbers 1 to 15. In (b) of FIG. 7, a refractive index Nd, an Abbe number Vd, a material, a focal length, and a compound lens focal length are similar to that of (a) of FIG. 7 and omitted. In (b) of FIG. 7, a curvature radius R [mm] , a surface separation D [mm] may show surface shape in ambient temperature of 60℃.
By comparing the surface shape shown in (a) of FIG. 7 with the surface shape shown in (b) of FIG. 7, it is possible to understand variation in the shape of the optical system 20 in response to change in the ambient temperature. In other words, it may be understood that line expansion coefficients of the lenses 26, 25 with glass are smaller than line expansion coefficients of the lenses 24, 23, 22, 21 with plastic. Also, with this configuration, it is possible to configure the optical system 20 such that the characteristic variations of the lenses 26, 25 with glass and the characteristic variations of the lenses 24, 23, 22, 21 with plastic in response to changes in ambient temperature may attenuate with each other.
In (a) and (b) of FIG. 8, an aspherical shape is indicated for each surface of surface numbers 3 to 14. Assuming that the Z position (position in the direction of the optical axis PA) is z, the curvature radius is R, the XY direction distance from the optical axis PA is H, the conical constant is k, and the aspherical coefficients are A3, A4, ..., A19, and A20, the aspherical shape is expressed by the following Expression (9) .
In (a) and (b) of FIG. 8, the aspherical coefficients A3, A4, ..., A19, and A20 are indicated for each surface of surface numbers 3 to 14 in ambient temperature of 25℃. Each surface of surface numbers 3 to 14 is obtained by rotating a curved line expressed by an expression obtained by substituting the aspherical coefficients A3 to A20 of (a) and (b) of FIG. 8 into Expression (9) around the optical axis PA. Note that, in (a) and (b) of FIG. 8, "E-i" is an exponential notation with a base of 10. Herein, "i" is an integer number. A spherical aberration can be preferably corrected by making each surface of surface numbers 3 to 14 an aspheric surface as illustrated in (a) and (b) of FIG. 8. Note that the aspherical coefficients A3 to A20 for each surface of surface numbers 3 to 14 in ambient temperature of 60℃ differ from the aspherical coefficients A3 to A20 for each surface of surface numbers 3 to 14 in ambient temperature of 25℃; however, those are not illustrated and their explanation is omitted for simplicity.
The optical system 20 configured as illustrated in FIGS. 4 to 8 exhibits imaging characteristics as illustrated in FIG. 9. FIG. 9 is a diagram illustrating imaging characteristics and its variation responsive to temperature change of the optical system 20. Note that the imaging characteristics of the optical system 20 are to present a characteristic when parallel rays corresponding to an angle of view of the AR image are caused to be injected from the lens diaphragm 27 that is an exit pupil of the optical system 20 and the parallel rays are reversely traced and virtually imaged on the display surface 10a of the display device 10.
(a) of FIG. 9 illustrates imaging characteristic of the lens group 20a in ambient temperature of 25℃. (b) of FIG. 9 illustrates imaging characteristic of the lens group 20a in ambient temperature of 60℃. In respective of (a) and (b) of FIG. 9, the vertical axis indicates MTF (Modulation Transfer Function) and the horizontal axis indicates a defocus position. In respective of (a) and of (b) of FIG. 9, F1 indicates a position at the center CP (see (a) of FIG. 5) , F2 indicates a position of a maximum display-height position PP1 or PP2, and F3 indicates a maximum image-height position PP2 or PP1 that is symmetric to F2 with respect to the center CP. F2_R indicates a radial direction at F2. F3_T indicates a tangential direction at F3. F3_R indicates a radial direction at F3. The radial direction means a direction along a radial, in a plain perpendicular to the optical axis PA, whose center is a cross point of the plain and the optical axis PA. The tangential direction means that a direction vertical to the radial direction in the plain perpendicular to the optical axis PA.
In (a) and (b) of FIG. 9, the imaging characteristic curve at F1 is illustrated with a solid line, the imaging characteristic curves at F2_T, F3_T are illustrated with dashed-dotted lines, the imaging characteristic curves at F2_R, F3_R are illustrated with dotted lines. The imaging characteristic curves at F2_T, F3_T substantially overlap with each other in the figures. The imaging characteristic curves at F2_R, F3_R substantially overlap with each other in the figures. In each curve, the peak defocus position indicates a focus position. With regard to respective of F1, “F2_T, F3_T” , and “F2_R, F3_R” , by comparing (a) and (b) of FIG. 9, it may be understood that shift amounts of the focus position are small between the ambient temperatures 25℃ and 60℃.
That is, for temperature variation of focus position of the lens group 20a, temperature variation of focus position of the lens 26 with glass in the direction opposite that of the lens group 20a may be acted. In addition, temperature variation of focus position of the lenses 26, 25 with glass and temperature variation of focus position of the lenses 24, 23, 22, 21 with plastic may be acted in the directions to attenuate with each other.
It may be understood that this action allows to suppress characteristic variation of the lens group 20a in accordance with changes in ambient temperature.
The optical system 20 configured as illustrated in FIGS. 4 to 8 exhibits aberration characteristics as illustrated in FIG. 10. FIG. 10 is a diagram illustrating aberration characteristics of the optical system 20. Note that the aberration characteristics of the optical system 20 are to present an aberration when parallel rays corresponding to an angle of view of the AR image are caused to be injected from the lens diaphragm 27 that is an exit pupil of the optical system 20 and the parallel rays are reversely traced and virtually imaged on the display surface 10a of the display device 10.
(a) of FIG. 10 illustrates an aberration diagram of astigmatism with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (a) of FIG. 10, the case where an angle of view θDFOV of 59.78° is a maximum image height is exemplified. In the aberration diagram of the optical system 20 illustrated in (a) of FIG. 10, an aberration amount on a tangential surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on a sagittal surface is illustrated with a dotted line. The tangential surface is a surface including a principal ray and the optical axis PA. The sagittal surface is a surface including a principal ray and perpendicular to the tangential surface. In (a) of FIG. 10, the case where astigmatism is suppressed within an allowable range is illustrated.
(b) of FIG. 10 illustrates an aberration diagram of distortion aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (b) of FIG. 10, the case where the angle of view θDFOV of 59.78° is a maximum image height is exemplified. In the aberration diagram of the optical system 20 illustrated in (b) of FIG. 10, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line. In (b) of FIG. 10, the case where distortion aberration is suppressed within an allowable range is illustrated.
(c) of FIG. 10 illustrates an aberration diagram of spherical aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an eye image height and the horizontal axis indicates the size of an aberration. In (c) of FIG. 10, the case where the F-number Fno is 1.836 is exemplified. In the aberration diagram of the optical system 20 illustrated in (c) of FIG. 10, an aberration amount for c-line (wavelength: 656.28 nm) is illustrated with a dashed-dotted line, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount for g-line (wavelength: 435.84 nm) is illustrated with a dotted line. In (c) of FIG. 10, the case where spherical aberration is suppressed within an allowable range is illustrated.
(d) of FIG. 10 illustrates an aberration diagram of chromatic aberration of magnification with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (d) of FIG. 10, the case where the angle of view θDFOV of 59.78° is a maximum image height is exemplified. In the aberration diagram of the optical system 20 illustrated in (d) of FIG. 10, an aberration amount on the sagittal surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on the tangential surface is illustrated with a dotted line. In (d) of FIG. 10, the case where chromatic aberration of magnification is suppressed within an allowable range is illustrated.
As described above, in the embodiment, in the optical system 20 of the display system 1, the lens group 20a include a hybrid of lenses 25, 26 and lenses 21 to 24 having different thermal characteristic from each other. For example, the lens group 20a is configured with a hybrid of a first material (e.g., glass or quartz) of lenses 25, 26 and a second material (e.g., plastic such as translucent plastic) of lenses 21 to 24. The lens 26 with the first material may be arranged closest to the image side among the plural lenses 21 to 26 included in the lens group 20a. The temperature change coefficient of a refractive index of the first material is smaller than the temperature change coefficient of a refractive index of the second material. The optical system 20 may be configured to attenuate characteristic variation of the lens group 20a with characteristic variation of lens with the first material in response to change in the ambient temperature. The optical system 20 may be configured such that characteristic variation of the lens with the first material and characteristic variation of the lens with the second material may attenuate with each other in response to change in the ambient temperature. With this configuration, it is possible to configure the optical system 20 so as to reduce variations in parallelism of light emitted from the optical system 20 in accordance with change in the ambient temperature, and therefore possible to enhance image quality by lights guided by the light guide member 30.
Note that the light guide member 30 can be applied with an arbitrary member that can transmit light from the outside world toward the eyeball 100 of the user and can guide light from the display device 10 toward the eyeball 100 of the user, and is not limited to the light guide plate 31 illustrated in FIG. 1. For example, instead of the diffractive optical element DOE, a holographic optical element may be provided on the light guide plate 31. The holographic optical element has an interference fringe pattern and is configured so that light having a predetermined wavelength injected by a predetermined angle among light rays proceeding through the light guide plate 31 is reflected toward the eyeball 100. Alternatively, instead of the diffractive optical element DOE, a light-guide optical element may be provided on the light guide plate 31. The light-guide optical element has a multi-stage halfmirror to intersect with an optical path of light proceeding through the light guide plate 31, and is configured to reflect some of light rays incident on the multi-stage halfmirror toward the eyeball 100. Alternatively, instead of the diffractive optical element DOE, a pin mirror may be provided on the light guide plate 31. The pin mirror has a multi-stage mirror with a small reflecting surface to intersect with the optical path of light proceeding through the light guide plate 31, and is configured to reflect light rays incident on the multi-stage mirror toward the eyeball 100.
Further, as a first modification example of the embodiment, as illustrated in FIGS. 11, 12, the drive circuit (see FIG. 1) may PWM-control a drive current of each pixel 12b, 12g, 12r of the pixel group 13 (see FIG. 3) in accordance with a target brightness when driving the display device 10. FIG. 11 is a wave diagram illustrating drive current of the pixel group 13 according to the first modification example of the embodiment. FIG. 12 is a wave diagram illustrating operations of the drive circuit 50 according to the first modification example of the embodiment.
As mentioned before, in the display device 10, each pixel 12r, 12g, and 12b of the pixel group 13 may be stacked with a direct bonding (epi-film bonding) using intermolecular force and this allows the pixel group 13 to be configured to with compressive strain of each bonding interface 15r, 15g, and 15b reduced. With this configuration, when a forward direction current (a drive current) is supplied from the drive circuit 50 to each pixel 12r, 12g, and 12b, efficiency of light emission by the recombination of an electron and a hole in the bonding interface 15r, 15g, and 15b may be improved. Therefore, it is possible to lower current density of the drive current of each of the pixels 12r, 12g, and 12b and also possible to enhance EQE.
For example, the drive circuit 50 may perform the PWM-control such that a drive current provided to at least one pixel among the pixels 12r, 12g, and 12b of the pixel group 13 is lower than a drive current provided to other pixel among the pixels 12r, 12g, and 12b.
With regard to each pixel 12r, 12g, and 12b, relationships between current density of drive current and EQE were reviewed. According to the result, the pixel 12g corresponding to the second color (e.g., green) showed the peak of EQE at around a first current density (e.g., 100A/cm2) . The pixel 12b corresponding to the third color (e.g., blue) showed the peak of EQE at around the first current density (e.g., 100A/cm2) . On the other hand, the pixel 12r corresponding to the first color (e.g., red) showed the peak of EQE at around a second current density (e.g., 1A/cm2) lower than the first current density.
In view of this, as illustrated in FIG. 11, the drive circuit 50 may perform the PWM-control such that, among the plural pixels 12r, 12g, and 12b of the pixel group 13, a current density Jr of the drive current Ir provided to the pixel 12r is lower than current densities Jg, Jb of the drive currents Ig, Ib provided to the other pixels 12g, 12b. With regard to the drive currents Ig, Ib of the pixels 12g, 12b, the drive circuit 50 sets pulse height as H1 and pulse width as W1 in one frame period TFR. The pule height H1 is decided to correspond to the current density Jg=Jb=J1. The pulse width W1 is decided such that H1×W1 is commensurate to a power corresponding to the target brightness of the pixels 12g, 12b.
For example, in the case where the target brightness corresponds to a relatively large gradation value GR1, as illustrated in (a) of FIG. 12, the pulse width W1 is decided to a relatively large value W11. In the case where the target brightness corresponds to a smaller gradation value GR2 (<GR1) , as illustrated in (b) of FIG. 12, the pulse width W1 is decided to a smaller value W12. In the case where the target brightness corresponds to a smaller gradation value GR3 (<GR2) , as illustrated in (c) of FIG. 12, the pulse width W1 is decided to a smaller value W13.
With regard to the drive current Ir of the pixel 12r, the drive circuit 50 sets pulse height as H2 (<H1) and pulse width as W2 (>W1) in one frame period TFR. The pule height H2 is decided to correspond to the current density Jr=J2 (<J1) . The pulse width W2 is decided such that H2×W2 is commensurate to a power corresponding to the target brightness of the pixel 12r.
For example, in the case where the target brightness corresponds to the relatively large gradation value GR1, as illustrated in (d) of FIG. 12, the pulse width W2 is decided to a relatively large value W21. In the case where the target brightness corresponds to the smaller gradation value GR2 (<GR1) , as illustrated in (e) of FIG. 12, the pulse width W2 is decided to a smaller value W22. In the case where the target brightness corresponds to the smaller gradation value GR3 (<GR2) , as illustrated in (f) of FIG. 12, the pulse width W2 is decided to a smaller value W23.
In this way, the drive circuit 50 may perform the PWM-control such that a drive current provided to at least one pixel among the pixels 12r, 12g, and 12b is lower than a drive current provided to other pixel among the pixels 12r, 12g, and 12b. With this operation, it is possible to lower the current density of drive current of each pixels 12r, 12g, and 12b while enhancing EQE. As a result, it is possible to reduce power consumption of driving the display device 10.
Alternatively, the drive circuit 50 may perform the PWM-control such that the difference between the drive current density Jr and the drive current density Jg, Jb is lowered as long as EQE fall within allowable range while maintaining the drive operation where the drive current density Jr of the pixel 12r is made to be less than the drive current densities Jg, Jb of the pixels 12g, 12b. With this performance, the pulse width of drive current of pixel 12r in accordance with target brightness and the pulse widths of drive currents of the pixels 12g, 12b in accordance with target brightness may come close to each other. According to this, it is possible to shorten one frame period TFR, and for example, possible to increase the frame rate when the display device 10 displays the moving image.
For example, assume that wall-plug efficiencies (WPEs) of the pixels 12r, 12g, and 12b are expressed as WPEr, WPEg, and WPEb, respectively. Note that there is a correlation between the WPE and the EQE such that when the EQE is enhanced, the WPE is enhanced.
If the drive of pixel 12 is performed under Jr=1A/cm2 and Jg=Jb=100A/cm2, then WPEr= 5.6%, WPEg=14%, and WPEb=10.5%, which means that each WPEr, WPEg, WPEb fall within the allowable range, is achieved and the frame rate is obtained at 60 Hz.
If the drive of pixel 12 is performed under Jr=5A/cm2 and Jg=Jb=100A/cm2, then the difference between the drive current density Jr and the drive current density Jg, Jb may become smaller. WPEr= 4.9%, WPEg=14%, WPEb=10.5%, which means that each WPEr, WPEg, WPEb fall within the allowable range, is achieved and the frame rate is enhanced to 240 Hz.
If the drive of pixel 12 is performed under Jr=10A/cm2 and Jg=Jb=100A/cm2, then the difference between the drive current density Jr and the drive current density Jg, Jb may become further smaller. WPEr=4.2%, WPEg=14%, WPEb=10.5%, which means that each WPEr, WPEg, WPEb fall within the allowable range, is achieved and the frame rate is further enhanced to 360 Hz.
In this way, the drive circuit 50 may perform the PWM-control such that the difference between the drive current density Jr and the drive current density Jg, Jb is lowered as long as EQE fall within allowable range while maintaining the drive operation where the drive current density Jr of the pixel 12r is made to be less than the drive current densities Jg, Jb of the pixels 12g, 12b. With this performance, it is possible to enhance the frame rate of the display device 10 and therefore possible to speed up the drive of the display device 10.
Further, as a second modification example of the embodiment, as illustrated in FIG. 13, a display device 110 of a display system 101 may further include a plural micro-lenses 14 (1, 1) to 14 (m, n) corresponding to the plural pixel groups 13 (1, 1) to 13 (m, n) , respectively. Each micro-lens 14 is also referred to as an on-chip lens. FIG. 13 is a cross-sectional view illustrating a configuration of the display device 110 according to the second modification example of the embodiment. FIG. 13 illustrates a cross section of the display device 110, cut along a line parallel to the Z axis that passes through the maximum display-height position PP2, the center CP, the maximum display-height position PP1 of the display surface 10a (see (a) of FIG. 5) .
For each micro-lens 14, the positional relation between the optical axis and the central axis of the corresponding pixel group 13 may correspond to the direction in which the light exits from the micro-lens 14 to the optical system 20.
Of the plural pixel groups 13 (1, 1) to 13 (m, n) , the pixel group 13 (1, 1) is near the maximum display-height position PP1, and it has the central axis AX (1, 1) . The central axis AX (1, 1) substantially coincides with an axis parallel to the Z axis that passes through the center of the light emitting surface of each of the pixel 12b (1, 1) , the pixel 12g (1, 1) , and the pixel 12r (1, 1) .
Of the plural micro-lenses 14 (1, 1) to 14 (m, n) , the micro-lens 14 (1, 1) is near the maximum display-height position PP1, and it has the optical axis OA (1, 1) . The optical axis OA (1, 1) is shifted in the+X direction/+Y direction so that the optical axis OA (1, 1) comes closer to the center CP than the central axis AX (1, 1) is. This shifting direction corresponds to inclination of the direction in which the light exits from the micro-lens 14 (1, 1) to the optical system 20, inclined from the+Z direction to the+X direction/+Y direction.
Of the plural pixel groups 13 (1, 1) to 13 (m, n) , the pixel group 13 (j, k) is near the center CP, and it has the central axis AX (j, k) , where j is an integer number greater than one and less than m, and k is an integer number greater than one and less than n. The central axis AX (j, k) substantially coincides with an axis parallel to the Z axis that passes through the center of the light emitting surface of each of the pixel 12b (j, k) , the pixel 12g (j, k) and the pixel 12r (j, k) .
Of the plural micro-lenses 14 (1, 1) to 14 (m, n) , the micro-lens 14 (j, k) is near the center CP, and it has the optical axis OA (j, k) . The optical axis OA (j, k) substantially coincides with the central axis AX (j, k) .
Of the plural pixel groups 13 (1, 1) to 13 (m, n) , the pixel group 13 (m, n) is near the maximum display-height position PP2, and it has the central axis AX (m, n) . The central axis AX (m, n) substantially coincides with an axis parallel to the Z axis that passes through the center of the light emitting surface of each of the pixel 12b (m, n) , the pixel 12g (m, n) and the pixel 12r (m, n) .
Of the plural micro-lenses 14 (1, 1) to 14 (m, n) , the micro-lens 14 (m, n) is near the maximum display-height position PP2, and it has the optical axis OA (m, n) . The optical axis OA (m, n) is shifted in the-X direction/-Y direction so that the optical axis OA (m, n) comes closer to the center CP than the central axis AX (m, n) is. This shifting direction corresponds to inclination of the direction in which the light exits from the micro-lens 14 (m, n) to the optical system 20, inclined from the+Z direction to the-X direction/-Y direction.
In this way, in the display device 110 of the display system 101, the distance between the optical axis OA of one micro-lens 14 of the plural micro-lenses 14 and the central axis AX of the corresponding pixel group 13 is greater than the distance between the optical axis OA of another micro-lens 14 closer to the center CP and the central axis AX of the corresponding pixel group 13. With this configuration, it becomes possible to incline the direction in which the light exits from the pixel group 13 in line with the direction in which the light travels to the optical system 20 (see FIG. 4) in accordance with the position of the pixel group 13 on the display surface 10a, which enables efficient incidence of the light from the display device 110 to the optical system 20. Moreover, because the central axis AX (m, n) substantially coincides with an axis that is parallel to the Z axis and that passes through the centers of the light emitting surfaces of the pixel 12b (m, n) , the pixel 12g (m, n) , and the pixel 12r (m, n) , it is possible to emit the light rays of the respective pixels in the same direction with a single micro-lens, and the light rays of the respective pixels are not dispersed, which makes it possible to improve the image quality.
Further, as a third modification example of the embodiment, an optical system 220 of a display system 201 may be configured as illustrated in FIGS. 14 to 16. FIG. 14 is a cross-sectional view illustrating a configuration of the optical system 220 according to the third modification example of the embodiment. FIG. 15 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system 220. FIG. 16 is a diagram illustrating a lens shape of each of lenses 221 to 226 of a lens group 220a.
In FIG. 14, the configuration that an effective diameter for light flux of a lens on the AR-image side in the lens group 220a is smaller than an effective diameter for light flux of a lens on the display-surface side in the lens group 220a is exemplified. For example, an effective diameter for light flux of the lens 226 on the AR-image side is smaller than an effective diameter for light flux of the lens 221 on the display-surface side. In FIG. 14, the optical axis PA is illustrated with a dashed-dotted line, and passes through the substantial center of an aperture 227a of a lens diaphragm 227. Optical paths of light emitted from the center CP (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with solid lines. Optical paths of light emitted from the maximum display-height position PP2 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dotted lines. Optical paths of light emitted from the maximum display-height position PP1 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dashed-two dotted lines.
The number of an inflection point in an incident surface or an exit surface of each of the lenses 225, 226 when seen in a cross-section including the optical axis PA is equal to or less than the number of an inflection point in an incident surface or an exit surface of each of the lenses 221 to 224 when seen in a cross-section including the optical axis PA. The number of an inflection point in an incident surface or an exit surface of each of the lenses 225, 226 when seen in a cross-section including the optical axis PA is one to two within an effective-area surface through which the light rays pass. The number of an inflection point in incident surface or exit surface of each of the lenses 221 to 224 when seen in a cross-section including the optical axis PA is two or more within an effective-area surface through which the light rays pass.
(a) of FIG. 15 illustrates that the optical system 220 satisfies all of Expressions (1) to (8) . This allows to suppress the characteristic variation of the optical system 220 in accordance with change in the ambient temperature and to easily downsize the optical system 220. In the optical system 220, an entire length (the Z-direction length) can be set to around 8.563 mm, an angle of view can be secured to be "θDFOV=around 49.237 [°] " , and effective F-number (≈DEFL/WEXA) can be reduced to around 1.810.
In (b) of FIG. 15, there is shown that the lens group 220a is configured with a hybrid of glass and plastic. In (b) of FIG. 15, the configuration where the lenses 226, 225 are formed of glass and the lenses 224, 223, 222, 221 are formed of plastic is exemplified. With this configuration, for each of the light wavelengths of 653.3 nm, 546.1 nm, and 435.8 nm, a temperature change coefficient of a refractive index of each lens 221 to 226 and protection member 28 as illustrated in (d) of FIG. 15 may be achieved for refractive indices of each lens 221 to 226 and protection member 28 as illustrated in (c) of FIG. 15. In (d) of FIG. 15, there are a positive temperature change coefficient and a negative temperature change coefficient in a mixed manner. The temperature change coefficients of the lenses 226, 225 with glass material is smaller than the temperature change coefficients of the lenses 224, 223, 222, 221 with plastic material. With this configuration, it is possible to configure the optical system 220 such that the characteristic variations of the lenses 226, 225 and the characteristic variations of the lenses 224, 223, 222, 221 in response to changes in ambient temperature may attenuate with each other.
In (b) of FIG. 15, (a) of FIG. 16, and (b) of FIG. 16, surface numbers are assigned as follows:
Surface number: 1: Exit surface of the lens diaphragm 227;
Surface number: 3: Exit surface of the lens 226;
Surface number: 4: Incident surface of the lens 226;
Surface number: 5: Exit surface of the lens 225;
Surface number: 6: Incident surface of the lens 225;
Surface number: 7: Exit surface of the lens 224;
Surface number: 8: Incident surface of the lens 224;
Surface number: 9: Exit surface of the lens 223;
Surface number: 10: Incident surface of the lens 223;
Surface number: 11: Exit surface of the lens 222;
Surface number: 12: Incident surface of the lens 222;
Surface number: 13: Exit surface of the lens 221; and
Surface number: 14: Incident surface of the lens 221.
Surface number: 15: Incident surface of the protection member 28.
(b) of FIG. 15 exemplifies a shape and a characteristic of each lens 221 to 226 in ambient temperature of 25℃. In (b) of FIG. 15, a curvature radius R [mm] , a surface separation D [mm] , a refractive index Nd, an Abbe number Vd, a material, a focal length, and a compound lens focal length are indicated for each surface of surface numbers 1 to 14. A lens configuration is indicated with the curvature radius R. The lens group 220a is configured to include, in a paraxial region, the positive convex lens 226, the negative meniscus lens 225 with a convex surface facing the image side, the negative meniscus lens 224 with a convex surface facing the image side, the negative meniscus lens 223 with a convex surface facing the image side, the positive convex lens 222, and the negative meniscus lens 221 with a convex surface facing the image side, in order from the image side. It is possible to preferably correct a chromatic aberration by causing the lenses 221 to 226 to have the different refractive indices Nd and Abbe numbers Vd.
In (a) and (b) of FIG. 16, an aspherical shape is indicated for each surface of surface numbers 3 to 14 in ambient temperature of 25℃. Assuming that the Z position (position in the direction of the optical axis PA) is z, the curvature radius is R, the XY direction distance from the optical axis PA is H, the conical constant is k, and the aspherical coefficients are A3, A4, ..., A19, and A20, the aspherical shape is expressed by the above Expression (9) .
In (a) and (b) of FIG. 16, the aspherical coefficients A3, A4, ..., A19, and A20 are indicated for each surface of surface numbers 3 to 14. Each surface of surface numbers 3 to 14 is obtained by rotating a curved line expressed by an expression obtained by substituting the aspherical coefficients A3 to A20 of (a) and (b) of FIG. 16 into Expression (9) around the optical axis PA. Note that, in (a) and (b) of FIG. 16, "E-i" is an exponential notation with a base of 10. Herein, "i" is an integer number. A spherical aberration can be preferably corrected by making each surface of surface numbers 3 to 14 an aspheric surface as illustrated in (a) and (b) of FIG. 16.
The optical system 220 configured as illustrated in FIGS. 14 to 16 exhibits aberration characteristics as illustrated in FIG. 17. FIG. 17 is a diagram illustrating aberration characteristics of the optical system 220. Note that the aberration characteristics of the optical system 220 are to present an aberration when parallel rays corresponding to an angle of view of the AR image are caused to be injected from the lens diaphragm 227 that is an exit pupil of the optical system 220 and the parallel rays are reversely traced and virtually imaged on the display surface 10a of the display device 10.
(a) of FIG. 17 illustrates an aberration diagram of astigmatism with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (a) of FIG. 17, the case where an angle of view θDFOV of 49.24° is a maximum image height is exemplified. In the aberration diagram of the optical system 220 illustrated in (a) of FIG. 17, an aberration amount on a tangential surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on a sagittal surface is illustrated with a dotted line. The tangential surface is a surface including a principal ray and the optical axis PA. The sagittal surface is a surface including a principal ray and perpendicular to the tangential surface. In (a) of FIG. 17, the case where astigmatism is suppressed within an allowable range is illustrated.
(b) of FIG. 17 illustrates an aberration diagram of distortion aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (b) of FIG. 17, the case where the angle of view θDFOV of 49.24° is a maximum image height is exemplified. In the aberration diagram of the optical system 220 illustrated in (b) of FIG. 17, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line. In (b) of FIG. 17, the case where distortion aberration is suppressed within an allowable range is illustrated.
(c) of FIG. 17 illustrates an aberration diagram of spherical aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an eye image height and the horizontal axis indicates the size of an aberration. In (c) of FIG. 17, the case where the F-number Fno is 1.81 is exemplified. In the aberration diagram of the optical system 220 illustrated in (c) of FIG. 17, an aberration amount for c-line (wavelength: 656.28 nm) is illustrated with a dashed-dotted line, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount for g-line (wavelength: 435.84 nm) is illustrated with a dotted line. In (c) of FIG. 17, the case where spherical aberration is suppressed within an allowable range is illustrated.
(d) of FIG. 17 illustrates an aberration diagram of chromatic aberration of magnification with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (d) of FIG. 17, the case where the angle of view θDFOV of 49.24° is a maximum height is exemplified. In the aberration diagram of the optical system 220 illustrated in (d) of FIG. 17, an aberration amount on the sagittal surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on the tangential surface is illustrated with a dotted line. In (d) of FIG. 17, the case where chromatic aberration of magnification is suppressed within an allowable range is illustrated.
As described above, in the optical system 220 of the display system 201, the lens group 220a include a hybrid of lenses 225, 226 and lenses 221 to 224 having different thermal characteristic from each other. For example, the lens group 220a is configured with a hybrid of a first material (e.g., glass or quartz) of lenses 225, 226 and a second material (e.g., plastic) of lenses 221 to 224, as well. The lens 226 with the first material may be arranged closest to the image side among the plural lenses 221 to 226 included in the lens group 220a. The temperature change coefficient of a refractive index of the first material is smaller than the temperature change coefficient of a refractive index of the second material. The optical system 220 may be configured to attenuate characteristic variation of the lens group 220a with characteristic variation of lens with the first material in response to change in the ambient temperature. The optical system 220 may be configured such that characteristic variation of the lens with the first material and characteristic variation of the lens with the second material may attenuate with each other in response to change in the ambient temperature. With this configuration, it is possible to configure the optical system 220 so as to reduce variations in parallelism of light emitted from the optical system 220 in accordance with change in the ambient temperature, and therefore possible to enhance image quality by lights guided by the light guide member 30.
Further, as a fourth modification example of the embodiment, an optical system 320 of a display system 301 may be configured as illustrated in FIGS. 18 to 20. FIG. 18 is a cross-sectional view illustrating a configuration of the optical system 320 according to the fourth modification example of the embodiment. FIG. 19 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system 320. FIG. 20 is a diagram illustrating a lens shape of each of lenses 321 to 326 of a lens group 320a.
In FIG. 18, the configuration that an effective diameter for light flux of a lens on the AR-image side in the lens group 320a is smaller than an effective diameter for light flux of a lens on the display-surface side in the lens group 320a is exemplified. For example, an effective diameter for light flux of the lens 326 on the AR-image side is smaller than an effective diameter for light flux of the lens 321 on the display-surface side. In FIG. 18, the optical axis PA is illustrated with a dashed-dotted line, and passes through the substantial center of an aperture 327a of a lens diaphragm 327. Optical paths of light emitted from the center CP (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with solid lines. Optical paths of light emitted from the maximum display-height position PP2 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dotted lines. Optical paths of light emitted from the maximum display-height position PP1 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dashed-two dotted lines.
The number of an inflection point in an incident surface or an exit surface of each of the lenses 325, 326 when seen in a cross-section including the optical axis PA is equal to or less than the number of an inflection point in incident surface or exit surface of each of the lenses 321 to 324 when seen in a cross-section including the optical axis PA. The number of an inflection point in an incident surface or an exit surface of each of the lenses 325, 326 when seen in a cross-section including the optical axis PA is one to two within an effective-area surface through which the light rays pass. The number of an inflection point in incident surface or exit surface of each of the lenses 321 to 324 when seen in a cross-section including the optical axis PA is two or more within an effective-area surface through which the light rays pass.
(a) of FIG. 19 illustrates that the optical system 320 satisfies all of Expressions (1) to (8) . This allows to suppress the characteristic variation of the optical system 320 in accordance with change in the ambient temperature and to easily downsize the optical system 320. In the optical system 320, an entire length (the Z-direction length) can be set to around 9.387 mm, an angle of view can be secured to be "θDFOV=around 39.664 [°] " , and effective F-number (≈DEFL/WEXA) can be reduced to around 2.108.
In (b) of FIG. 19, there is shown that the lens group 320a is configured with a hybrid of glass and plastic. In (b) of FIG. 19, the configuration where the lenses 326, 325 are formed of glass and the lenses 324, 323, 322, 321 are formed of plastic is exemplified. With this configuration, for each of the light wavelengths of 653.3 nm, 546.1 nm, and 435.8 nm, a temperature change coefficient of a refractive index of each lens 321 to 326 and protection member 28 as illustrated in (d) of FIG. 19 may be achieved for refractive indices of each lens 321 to 326 and protection member 28 as illustrated in (c) of FIG. 19. In (d) of FIG. 19, there are a positive temperature change coefficient and a negative temperature change coefficient in a mixed manner. The temperature change coefficients of the lenses 326, 325 with glass material is smaller than the temperature change coefficients of the lenses 324, 323, 322, 321 with plastic material. With this configuration, it is possible to configure the optical system 320 such that the characteristic variations of the lenses 326, 325 and the characteristic variations of the lenses 324, 323, 322, 321 in response to changes in ambient temperature may attenuate with each other.
In (b) of FIG. 19, (a) of FIG. 20, and (b) of FIG. 20, surface numbers are assigned as follows:
Surface number: 1: Exit surface of the lens diaphragm 327;
Surface number: 3: Exit surface of the lens 326;
Surface number: 4: Incident surface of the lens 326;
Surface number: 5: Exit surface of the lens 325;
Surface number: 6: Incident surface of the lens 325;
Surface number: 7: Exit surface of the lens 324;
Surface number: 8: Incident surface of the lens 324;
Surface number: 9: Exit surface of the lens 323;
Surface number: 10: Incident surface of the lens 323;
Surface number: 11: Exit surface of the lens 322;
Surface number: 12: Incident surface of the lens 322;
Surface number: 13: Exit surface of the lens 321; and
Surface number: 14: Incident surface of the lens 321.
Surface number: 15: Incident surface of the protection member 28.
(b) of FIG. 19 exemplifies a shape and a characteristic of each lens 321 to 326 in ambient temperature of 25℃. In (b) of FIG. 19, a curvature radius R [mm] , a surface separation D [mm] , a refractive index Nd, an Abbe number Vd, a material, a focal length, and a compound lens focal length are indicated for each surface of surface numbers 1 to 14. A lens configuration is indicated with the curvature radius R. The lens group 320a is configured to include, in a paraxial region, the positive convex lens 326, the negative meniscus lens 325 with a convex surface facing the image side, the negative meniscus lens 324 with a convex surface facing the image side, the negative meniscus lens 323 with a convex surface facing the image side, the positive convex lens 322, and the negative meniscus lens 321 with a convex surface facing the image side, in order from the image side. It is possible to preferably correct a chromatic aberration by causing the lenses 321 to 326 to have the different refractive indices Nd and Abbe numbers Vd.
In (a) and (b) of FIG. 20, an aspherical shape is indicated for each surface of surface numbers 3 to 14 in ambient temperature of 25℃. Assuming that the Z position (position in the direction of the optical axis PA) is z, the curvature radius is R, the XY direction distance from the optical axis PA is H, the conical constant is k, and the aspherical coefficients are A3, A4, ..., A19, and A20, the aspherical shape is expressed by the above Expression (9) .
In (a) and (b) of FIG. 20, the aspherical coefficients A3, A4, ..., A19, and A20 are indicated for each surface of surface numbers 3 to 14. Each surface of surface numbers 3 to 14 is obtained by rotating a curved line expressed by an expression obtained by substituting the aspherical coefficients A3 to A20 of (a) and (b) of FIG. 20 into Expression (9) around the optical axis PA. Note that, in (a) and (b) of FIG. 20, "E-i" is an exponential notation with a base of 10. Herein, "i" is an integer number. A spherical aberration can be preferably corrected by making each surface of surface numbers 3 to 14 an aspheric surface as illustrated in (a) and (b) of FIG. 20.
The optical system 320 configured as illustrated in FIGS. 18 to 20 exhibits aberration characteristics as illustrated in FIG. 21. FIG. 21 is a diagram illustrating aberration characteristics of the optical system 320. Note that the aberration characteristics of the optical system 320 are to present an aberration when parallel rays corresponding to an angle of view of the AR image are caused to be injected from the lens diaphragm 327 that is an exit pupil of the optical system 320 and the parallel rays are reversely traced and virtually imaged on the display surface 10a of the display device 10.
(a) of FIG. 21 illustrates an aberration diagram of astigmatism with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (a) of FIG. 21, the case where an angle of view θDFOV of 39.66° is a maximum image height is exemplified. In the aberration diagram of the optical system 320 illustrated in (a) of FIG. 21, an aberration amount on a tangential surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on a sagittal surface is illustrated with a dotted line. The tangential surface is a surface including a principal ray and the optical axis PA. The sagittal surface is a surface including a principal ray and perpendicular to the tangential surface. In (a) of FIG. 21, the case where astigmatism is suppressed within an allowable range is illustrated.
(b) of FIG. 21 illustrates an aberration diagram of distortion aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (b) of FIG. 21, the case where the angle of view θDFOV of 39.66° is a maximum image height is exemplified. In the aberration diagram of the optical system 320 illustrated in (b) of FIG. 21, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line. In (b) of FIG. 21, the case where distortion aberration is suppressed within an allowable range is illustrated.
(c) of FIG. 21 illustrates an aberration diagram of spherical aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an eye image height and the horizontal axis indicates the size of an aberration. In (c) of FIG. 21, the case where the F-number Fno is 2.11 is exemplified. In the aberration diagram of the optical system 320 illustrated in (c) of FIG. 21, an aberration amount for c-line (wavelength: 656.28 nm) is illustrated with a dashed-dotted line, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount for g-line (wavelength: 435.84 nm) is illustrated with a dotted line. In (c) of FIG. 21, the case where spherical aberration is suppressed within an allowable range is illustrated.
(d) of FIG. 21 illustrates an aberration diagram of chromatic aberration of magnification with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (d) of FIG. 21, the case where the angle of view θDFOV of 39.66° is a maximum image height is exemplified. In the aberration diagram of the optical system 320 illustrated in (d) of FIG. 21, an aberration amount on the sagittal surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on the tangential surface is illustrated with a dotted line. In (d) of FIG. 21, the case where chromatic aberration of magnification is suppressed within an allowable range is illustrated.
As described above, in the optical system 320 of the display system 301, the lens group 320a include a hybrid of lenses 325, 326 and lenses 321 to 324 having different thermal characteristic from each other. For example, the lens group 320a is configured with a hybrid of a first material (e.g., glass or quartz) of lenses 325, 326 and a second material (e.g., plastic) of lenses 321 to 324, as well. The lens 326 with the first material may be arranged closest to the image side among the plural lenses 321 to 326 included in the lens group 320a. The temperature change coefficient of a refractive index of the first material is smaller than the temperature change coefficient of a refractive index of the second material. The optical system 320 may be configured to attenuate characteristic variation of the lens group 320a with characteristic variation of lens with the first material in response to change in the ambient temperature. The optical system 320 may be configured such that characteristic variation of the lens with the first material and characteristic variation of the lens with the second material may attenuate with each other in response to change in the ambient temperature. With this configuration, it is possible to configure the optical system 320 so as to reduce variations in parallelism of light emitted from the optical system 320 in accordance with change in the ambient temperature, and therefore possible to enhance image quality by lights guided by the light guide member 30.
Further, as a fifth modification example of the embodiment, an optical system 420 of a display system 401 may be configured as illustrated in FIGS. 22 to 24. FIG. 22 is a cross-sectional view illustrating a configuration of the optical system 420 according to the fifth modification example of the embodiment. FIG. 23 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system 420. FIG. 24 is a diagram illustrating a lens shape of each of lenses 421 to 426 of a lens group 420a.
In FIG. 22, the configuration that an effective diameter for light flux of a lens on the AR-image side in the lens group 320a is substantially equal to an effective diameter for light flux of a lens on the display-surface side in the lens group 420a is exemplified. For example, an effective diameter for light flux of the lens 426 on the AR-image side is substantially equal to an effective diameter for light flux of the lens 421 on the display-surface side. In FIG. 22, the optical axis PA is illustrated with a dashed-dotted line, and passes through the substantial center of an aperture 427a of a lens diaphragm 427. Optical paths of light emitted from the center CP (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with solid lines. Optical paths of light emitted from the maximum display-height position PP2 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dotted lines. Optical paths of light emitted from the maximum display-height position PP1 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dashed-two dotted lines.
The number of an inflection point in an incident surface or an exit surface of each of the lenses 425, 426 when seen in a cross-section including the optical axis PA is equal to or less than the number of an inflection point in incident surface or exit surface of each of the lenses 421 to 424 when seen in a cross-section including the optical axis PA. The number of an inflection point in an incident surface or an exit surface of each of the lenses 425, 426 when seen in a cross-section including the optical axis PA is one to two within an effective-area surface through which the light rays pass. The number of an inflection point in incident surface or exit surface of each of the lenses 421 to 424 when seen in a cross-section including the optical axis PA is two or more within an effective-area surface through which the light rays pass.
(a) of FIG. 23 illustrates that the optical system 420 satisfies all of Expressions (1) to (8) . This allows to suppress the characteristic variation of the optical system 420 in accordance with change in the ambient temperature and to easily downsize the optical system 420. In the optical system 420, an entire length (the Z-direction length) can be set to around 8.342 mm, an angle of view can be secured to be "θDFOV=around 29.702 [°] " , and effective F-number (≈DEFL/WEXA) can be reduced to around 1.525.
In (b) of FIG. 23, there is shown that the lens group 420a is configured with a hybrid of glass and plastic. In (b) of FIG. 23, the configuration where the lenses 426, 425 are formed of glass and the lenses 424, 423, 422, 421 are formed of plastic is exemplified. With this configuration, for each of the light wavelengths of 653.3 nm, 546.1 nm, and 435.8 nm, a temperature change coefficient of a refractive index of each lens 421 to 426 and protection member 28 as illustrated in (d) of FIG. 23 may be achieved for refractive indices of each lens 421 to 426 and protection member 28 as illustrated in (c) of FIG. 23. In (d) of FIG. 23, there are a positive temperature change coefficient and a negative temperature change coefficient in a mixed manner. The temperature change coefficients of the lenses 426, 425 with glass material is smaller than the temperature change coefficients of the lenses 424, 423, 422, 421 with plastic material. With this configuration, it is possible to configure the optical system 420 such that the characteristic variations of the lenses 426, 425 and the characteristic variations of the lenses 424, 423, 422, 421 in response to changes in ambient temperature may attenuate with each other.
In (b) of FIG. 23, (a) of FIG. 24, and (b) of FIG. 24, surface numbers are assigned as follows:
Surface number: 1: Exit surface of the lens diaphragm 427;
Surface number: 3: Exit surface of the lens 426;
Surface number: 4: Incident surface of the lens 426;
Surface number: 5: Exit surface of the lens 425;
Surface number: 6: Incident surface of the lens 425;
Surface number: 7: Exit surface of the lens 424;
Surface number: 8: Incident surface of the lens 424;
Surface number: 9: Exit surface of the lens 423;
Surface number: 10: Incident surface of the lens 423;
Surface number: 11: Exit surface of the lens 422;
Surface number: 12: Incident surface of the lens 422;
Surface number: 13: Exit surface of the lens 421; and
Surface number: 14: Incident surface of the lens 421.
Surface number: 15: Incident surface of the protection member 28.
(b) of FIG. 23 exemplifies a shape and a characteristic of each lens 421 to 426 in ambient temperature of 25℃. In (b) of FIG. 23, a curvature radius R [mm] , a surface separation D [mm] , a refractive index Nd, an Abbe number Vd, a material, a focal length, and a compound lens focal length are indicated for each surface of surface numbers 1 to 14. A lens configuration is indicated with the curvature radius R. The lens group 420a is configured to include, in a paraxial region, the positive convex lens 426, the negative meniscus lens 425 with a convex surface facing the image side, the negative meniscus lens 424 with a convex surface facing the image side, the negative meniscus lens 423 with a convex surface facing the image side, the positive convex lens 422, and the negative meniscus lens 421 with a convex surface facing the image side, in order from the image side. It is possible to preferably correct a chromatic aberration by causing the lenses 421 to 426 to have the different refractive indices Nd and Abbe numbers Vd.
In (a) and (b) of FIG. 24, an aspherical shape is indicated for each surface of surface numbers 3 to 14 in ambient temperature of 25℃. Assuming that the Z position (position in the direction of the optical axis PA) is z, the curvature radius is R, the XY direction distance from the optical axis PA is H, the conical constant is k, and the aspherical coefficients are A3, A4, ..., A19, and A20, the aspherical shape is expressed by the above Expression (9) .
In (a) and (b) of FIG. 24, the aspherical coefficients A3, A4, ..., A19, and A20 are indicated for each surface of surface numbers 3 to 14. Each surface of surface numbers 3 to 14 is obtained by rotating a curved line expressed by an expression obtained by substituting the aspherical coefficients A3 to A20 of (a) and (b) of FIG. 24 into Expression (9) around the optical axis PA. Note that, in (a) and (b) of FIG. 24, "E-i" is an exponential notation with a base of 10. Herein, "i" is an integer number. A spherical aberration can be preferably corrected by making each surface of surface numbers 3 to 14 an aspheric surface as illustrated in (a) and (b) of FIG. 24.
The optical system 420 configured as illustrated in FIGS. 22 to 24 exhibits aberration characteristics as illustrated in FIG. 25. FIG. 25 is a diagram illustrating aberration characteristics of the optical system 420. Note that the aberration characteristics of the optical system 420 are to present an aberration when parallel rays corresponding to an angle of view of the AR image are caused to be injected from the lens diaphragm 427 that is an exit pupil of the optical system 420 and the parallel rays are reversely traced and virtually imaged on the display surface 10a of the display device 10.
(a) of FIG. 25 illustrates an aberration diagram of astigmatism with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (a) of FIG. 25, the case where an angle of view θDFOV of 29.70° is a maximum image height is exemplified. In the aberration diagram of the optical system 420 illustrated in (a) of FIG. 25, an aberration amount on a tangential surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on a sagittal surface is illustrated with a dotted line. The tangential surface is a surface including a principal ray and the optical axis PA. The sagittal surface is a surface including a principal ray and perpendicular to the tangential surface. In (a) of FIG. 25, the case where astigmatism is suppressed within an allowable range is illustrated.
(b) of FIG. 25 illustrates an aberration diagram of distortion aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (b) of FIG. 25, the case where the angle of view θDFOV of 29.70° is a maximum image height is exemplified. In the aberration diagram of the optical system 420 illustrated in (b) of FIG. 25, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line. In (b) of FIG. 25, the case where distortion aberration is suppressed within an allowable range is illustrated.
(c) of FIG. 25 illustrates an aberration diagram of spherical aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an eye image height and the horizontal axis indicates the size of an aberration. In (c) of FIG. 25, the case where the F-number Fno is 1.53 is exemplified. In the aberration diagram of the optical system 420 illustrated in (c) of FIG. 25, an aberration amount for c-line (wavelength: 656.28 nm) is illustrated with a dashed-dotted line, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount for g-line (wavelength: 435.84 nm) is illustrated with a dotted line. In (c) of FIG. 25, the case where spherical aberration is suppressed within an allowable range is illustrated.
(d) of FIG. 25 illustrates an aberration diagram of chromatic aberration of magnification with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (d) of FIG. 25, the case where the angle of view θDFOV of 29.70° is a maximum image height is exemplified. In the aberration diagram of the optical system 420 illustrated in (d) of FIG. 25, an aberration amount on the sagittal surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on the tangential surface is illustrated with a dotted line. In (d) of FIG. 25, the case where chromatic aberration of magnification is suppressed within an allowable range is illustrated.
As described above, in the optical system 420 of the display system 401, the lens group 420a include a hybrid of lenses 425, 426 and lenses 421 to 424 having different thermal characteristic from each other. For example, the lens group 420a is configured with a hybrid of a first material (e.g., glass or quartz) of lenses 425, 426 and a second material (e.g., plastic) of lenses 421 to 424, as well. The lens 426 with the first material may be arranged closest to the image side among the plural lenses 421 to 426 included in the lens group 420a. The temperature change coefficient of a refractive index of the first material is smaller than the temperature change coefficient of a refractive index of the second material. The optical system 420 may be configured to attenuate characteristic variation of the lens group 420a with characteristic variation of lens with the first material in response to change in the ambient temperature. The optical system 420 may be configured such that characteristic variation of the lens with the first material and characteristic variation of the lens with the second material may attenuate with each other in response to change in the ambient temperature. With this configuration, it is possible to configure the optical system 420 so as to reduce variations in parallelism of light emitted from the optical system 420 in accordance with change in the ambient temperature, and therefore possible to enhance image quality by lights guided by the light guide member 30.
Further, as a sixth modification example of the embodiment, an optical system 520 of a display system 501 may be configured as illustrated in FIGS. 26 to 28. FIG. 26 is a cross-sectional view illustrating a configuration of the optical system 520 according to the sixth modification example of the embodiment. FIG. 27 is a diagram illustrating the configuration, characteristics, and characteristic variation responsive to temperature change of the optical system 520. FIG. 28 is a diagram illustrating a lens shape of each of lenses 521 to 526 of a lens group 520a.
In FIG. 26, the configuration that an effective diameter for light flux of a lens on the AR-image side in the lens group 320a is substantially equal to an effective diameter for light flux of a lens on the display-surface side in the lens group 520a is exemplified. For example, an effective diameter for light flux of the lens 526 on the AR-image side is substantially equal to an effective diameter for light flux of the lens 521 on the display-surface side. In FIG. 26, the optical axis PA is illustrated with a dashed-dotted line, and passes through the substantial center of an aperture 527a of a lens diaphragm 527. Optical paths of light emitted from the center CP (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with solid lines. Optical paths of light emitted from the maximum display-height position PP2 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dotted lines. Optical paths of light emitted from the maximum display-height position PP1 (see (a) of FIG. 5) of the display surface 10a of the display device 10 are illustrated with dashed-two dotted lines.
The number of an inflection point in an incident surface or an exit surface of the lens 526 when seen in a cross-section including the optical axis PA is equal to or less than the number of an inflection point in incident surface or exit surface of each of the lenses 521 to 525 when seen in a cross-section including the optical axis PA. The number of an inflection point in an incident surface or an exit surface of the lens 526 when seen in a cross-section including the optical axis PA is one to two within an effective-area surface through which the light rays pass. The number of an inflection point in incident surface or exit surface of each of the lenses 521 to 525 when seen in a cross-section including the optical axis PA is two or more within an effective-area surface through which the light rays pass.
(a) of FIG. 27 illustrates that the optical system 520 satisfies all of Expressions (1) to (8) . This allows to suppress the characteristic variation of the optical system 520 in accordance with change in the ambient temperature and to easily downsize the optical system 520. In the optical system 520, an entire length (the Z-direction length) can be set to around 8.206 mm, an angle of view can be secured to be "θDFOV=around 29.922 [°] " , and effective F-number (≈DEFL/WEXA) can be reduced to around 1.526.
In (b) of FIG. 27, there is shown that the lens group 520a is configured with a hybrid of glass and plastic. In (b) of FIG. 27, the configuration where the lens 526 is formed of glass and the lenses 525, 524, 523, 522, 521 are formed of plastic is exemplified. With this configuration, for each of the light wavelengths of 653.3 nm, 546.1 nm, and 435.8 nm, a temperature change coefficient of a refractive index of each lens 521 to 526 and protection member 28 as illustrated in (d) of FIG. 27 may be achieved for refractive indices of each lens 521 to 526 and protection member 28 as illustrated in (c) of FIG. 27. In (d) of FIG. 27, there are a positive temperature change coefficient and a negative temperature change coefficient in a mixed manner. The temperature change coefficients of the lens 526 with glass material is smaller than the temperature change coefficients of the lenses 525, 524, 523, 522, 521 with plastic material. With this configuration, it is possible to configure the optical system 520 such that the characteristic variations of the lens 526 and the characteristic variations of the lenses 525, 524, 523, 522, 521 in response to changes in ambient temperature may attenuate with each other.
In (b) of FIG. 27, (a) of FIG. 28, and (b) of FIG. 28, surface numbers are assigned as follows:
Surface number: 1: Exit surface of the lens diaphragm 527;
Surface number: 3: Exit surface of the lens 526;
Surface number: 4: Incident surface of the lens 526;
Surface number: 5: Exit surface of the lens 525;
Surface number: 6: Incident surface of the lens 525;
Surface number: 7: Exit surface of the lens 524;
Surface number: 8: Incident surface of the lens 524;
Surface number: 9: Exit surface of the lens 523;
Surface number: 10: Incident surface of the lens 523;
Surface number: 11: Exit surface of the lens 522;
Surface number: 12: Incident surface of the lens 522;
Surface number: 13: Exit surface of the lens 521; and
Surface number: 14: Incident surface of the lens 521.
Surface number: 15: Incident surface of the protection member 28.
(b) of FIG. 27 exemplifies a shape and a characteristic of each lens 521 to 526 in ambient temperature of 25℃. In (b) of FIG. 27, a curvature radius R [mm] , a surface separation D [mm] , a refractive index Nd, an Abbe number Vd, a material, a focal length, and a compound lens focal length are indicated for each surface of surface numbers 1 to 14. A lens configuration is indicated with the curvature radius R. The lens group 520a is configured to include, in a paraxial region, the positive convex lens 526, the negative meniscus lens 525 with a convex surface facing the image side, the negative meniscus lens 524 with a convex surface facing the image side, the negative meniscus lens 523 with a convex surface facing the image side, the positive convex lens 522, and the negative meniscus lens 521 with a convex surface facing the image side, in order from the image side. It is possible to preferably correct a chromatic aberration by causing the lenses 521 to 526 to have the different refractive indices Nd and Abbe numbers Vd.
In (a) and (b) of FIG. 28, an aspherical shape is indicated for each surface of surface numbers 3 to 14 in ambient temperature of 25℃. Assuming that the Z position (position in the direction of the optical axis PA) is z, the curvature radius is R, the XY direction distance from the optical axis PA is H, the conical constant is k, and the aspherical coefficients are A3, A4, ..., A19, and A20, the aspherical shape is expressed by the above Expression (9) .
In (a) and (b) of FIG. 28, the aspherical coefficients A3, A4, ..., A19, and A20 are indicated for each surface of surface numbers 3 to 14. Each surface of surface numbers 3 to 14 is obtained by rotating a curved line expressed by an expression obtained by substituting the aspherical coefficients A3 to A20 of (a) and (b) of FIG. 28 into Expression (9) around the optical axis PA. Note that, in (a) and (b) of FIG. 28, "E-i" is an exponential notation with a base of 10. Herein, "i" is an integer number. A spherical aberration can be preferably corrected by making each surface of surface numbers 3 to 14 an aspheric surface as illustrated in (a) and (b) of FIG. 28.
The optical system 520 configured as illustrated in FIGS. 26 to 28 exhibits aberration characteristics as illustrated in FIG. 29. FIG. 29 is a diagram illustrating aberration characteristics of the optical system 520. Note that the aberration characteristics of the optical system 520 are to present an aberration when parallel rays corresponding to an angle of view of the AR image are caused to be injected from the lens diaphragm 527 that is an exit pupil of the optical system 520 and the parallel rays are reversely traced and virtually imaged on the display surface 10a of the display device 10.
(a) of FIG. 29 illustrates an aberration diagram of astigmatism with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (a) of FIG. 29, the case where an angle of view θDFOV of 29.92° is a maximum image height is exemplified. In the aberration diagram of the optical system 520 illustrated in (a) of FIG. 29, an aberration amount on a tangential surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on a sagittal surface is illustrated with a dotted line. The tangential surface is a surface including a principal ray and the optical axis PA. The sagittal surface is a surface including a principal ray and perpendicular to the tangential surface. In (a) of FIG. 29, the case where astigmatism is suppressed within an allowable range is illustrated.
(b) of FIG. 29 illustrates an aberration diagram of distortion aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (b) of FIG. 29, the case where the angle of view θDFOV of 29.92° is a maximum image height is exemplified. In the aberration diagram of the optical system 520 illustrated in (b) of FIG. 29, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line. In (b) of FIG. 29, the case where distortion aberration is suppressed within an allowable range is illustrated.
(c) of FIG. 29 illustrates an aberration diagram of spherical aberration with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an eye image height and the horizontal axis indicates the size of an aberration. In (c) of FIG. 29, the case where the F-number Fno is 1.53 is exemplified. In the aberration diagram of the optical system 520 illustrated in (c) of FIG. 29, an aberration amount for c-line (wavelength: 656.28 nm) is illustrated with a dashed-dotted line, an aberration amount for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount for g-line (wavelength: 435.84 nm) is illustrated with a dotted line. In (c) of FIG. 29, the case where spherical aberration is suppressed within an allowable range is illustrated.
(d) of FIG. 29 illustrates an aberration diagram of chromatic aberration of magnification with reference to the display surface 10a (virtual image surface) . Herein, the vertical axis indicates an image height and the horizontal axis indicates the size of an aberration. In (d) of FIG. 29, the case where the angle of view θDFOV of 29.92° is a maximum image height is exemplified. In the aberration diagram of the optical system 520 illustrated in (d) of FIG. 29, an aberration amount on the sagittal surface for e-line (wavelength: 546.1 nm) is illustrated with a solid line, and an aberration amount on the tangential surface is illustrated with a dotted line. In (d) of FIG. 29, the case where chromatic aberration of magnification is suppressed within an allowable range is illustrated.
As described above, in the optical system 520 of the display system 501, the lens group 520a include a hybrid of lenses 525, 526 and lenses 521 to 524 having different thermal characteristic from each other. For example, the lens group 520a is configured with a hybrid of a first material (e.g., glass or quartz) of lenses 525, 526-and a second material (e.g., plastic) of lenses 521 to 524, as well. The lens 526 with the first material may be arranged closest to the image side among the plural lenses 521 to 526 included in the lens group 520a. The temperature change coefficient of a refractive index of the first material is smaller than the temperature change coefficient of a refractive index of the second material. The optical system 520 may be configured to attenuate characteristic variation of the lens group 520a with characteristic variation of lens with the first material in response to change in the ambient temperature. The optical system 520 may be configured such that characteristic variation of the lens with the first material and characteristic variation of the lens with the second material may attenuate with each other in response to change in the ambient temperature. With this configuration, it is possible to configure the optical system 520 so as to reduce variations in parallelism of light emitted from the optical system 520 in accordance with change in the ambient temperature, and therefore possible to enhance image quality by lights guided by the light guide member 30.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
[Explanations of Letters or Numerals]
1, 101, 201, 301, 401, 501: display system
10: display device
20, 120, 220, 320, 420, 520: optical system
50: drive circuit