CN111399321B - Small-size projection optical assembly and projection optical system suitable for near-eye display - Google Patents

Abstract

The invention provides a miniaturized projection optical assembly suitable for near-eye display, which comprises a lens group, a lens group and a lens group, wherein the lens group is used for correcting aberrations such as chromatic aberration and the like in a system; a prism for correcting off-axis aberrations and a deflection optical axis angle in the system; a wedge angle prism for slightly controlling the angle of the optical axis with respect to the exit pupil plane; the image light passing through the projection optics is coupled into a predetermined waveguide at the exit pupil plane. The projection optical assembly has the advantages of small volume, small vertical axis size not more than 7mm, compact structure and excellent optical performance.

Description

Small-size projection optical assembly and projection optical system suitable for near-eye display

Technical Field

The present invention relates to projection systems in the optical field, and more particularly, to a compact projection optical assembly and projection optical system suitable for use in a near-eye display.

Background

The concept of Augmented Reality (AR) technology is widely spread, and the technology can provide additional superimposed information for users while not shielding the normal observation of the real world by human eyes, effectively broaden the information capacity visible to the human eyes, and has wide application prospects in the fields of education, medical treatment, entertainment and the like. As an important device for realizing augmented reality, the development of a transmissive head-mounted near-eye display has become a hot spot. At present, companies such as EPSON, Google, Microsoft, etc. have been put into development of related technologies and have introduced related products such as ESPON-BT series, Google Glass, Hololens, etc. Patents related to AR have also been issued by Apple inc, which was a major development in the detonation industry in the mobile phone age, with a beneficial market layout.

Among the AR-related technologies, a technology has been developed that can realize enhanced see-through display in the form of a waveguide type element having a flat appearance based on the diffraction principle of physical optics, and this technology has been focused on the merit that the display effect is excellent, the flat state is similar to that of corrective glasses, and the device is suitable for wearing and modeling. The above-mentioned so-called waveguide near-eye display system is mainly composed of two parts: a waveguide type element and a projection section. Due to the limitation of optical principle, the planar waveguide type element cannot provide any focal power and cannot optically amplify an image, so that the performance of the projection part largely determines the quality of the displayed image of the waveguide near-eye display system. Therefore, how to design a light-weight, small-sized and excellent-performance projection unit is a technical problem that needs to be solved urgently.

Disclosure of Invention

In view of the above, the main objective of the present invention is to provide a projection optical assembly suitable for a waveguide type optical element, which is small, light, and compact, and a projection optical system using the same.

A compact projection optics assembly for a near-eye display according to the invention comprises:

a lens group for receiving image light from the microdisplay;

the prism is arranged behind the lens group along the optical path direction and used for correcting off-axis aberration in the system, and comprises at least one effective optical surface which is an aspheric surface or a free-form surface;

the wedge angle prism is arranged on the light emergent side of the prism along the direction of the light path and is used for controlling the angle of the image light relative to the exit pupil plane of the optical component;

the image light passing through the projection optical assembly is coupled to a predetermined waveguide type optical sheet at the exit pupil plane.

Further, the lens assembly comprises at least one cemented lens, wherein the cemented lens comprises at least one negative lens with high refractive index and small abbe number and at least one positive lens with low refractive index and large abbe number.

Preferably, the prism bends the optical axis, and the angle of the optical axis bending is 45-75 degrees.

According to an embodiment of the invention, the effective optical surface of the prism is configured such that total reflection of the image light occurs at least once while propagating therein. The wedge angle prism has the same shape as two adjacent surfaces of the prism.

Preferably, the maximum outer diameters of the lens group and the prism in the vertical axis direction do not exceed 7mm, and the wedge angle prism is smaller than the volume of the prism.

Optionally, the effective optical surface of the wedge prism comprises at least one aspheric surface.

According to the projection optical system constituted by the optical assembly of the embodiment of the present invention, the image source can be selected from: one of a reflective liquid crystal display (LCoS) type Micro display, a MEMS (Micro electro mechanical System) laser scanning mirror, an organic light emitting semiconductor display (OLED) type, a Micro light emitting diode display (Micro led) type, and a Liquid Crystal Display (LCD) type Micro display. Accordingly, the rear intercept of the projection optics is less than 15 mm.

According to the projection optical assembly and the projection optical system, the volume is remarkably reduced due to the introduction of the prism, and the optical axis angle can be adjusted to a proper position to meet the requirements of integral modeling and arrangement. The projection system has the advantages of small number of units, further help for weight reduction, short overall optical path and compact structure, effectively solves the contradiction of small volume and high optical performance of the projection system for the waveguide type optical element in the near-to-eye display device, and ensures that the volume and the weight of the overall device are more suitable for head wearing.

Drawings

FIG. 1 is a schematic view of a projection optical system in a first embodiment of the present invention;

FIG. 1A is a schematic diagram of the optical performance of the system of FIG. 1;

FIG. 2 is a partial view of an illumination optical path and a projection optical path of the projection optical system in the first embodiment of the present invention;

FIG. 3 is a schematic view of the illumination path of a common LCoS chip of a projection optical system;

FIG. 4 is a schematic view of an illumination optical path of the projection optical system in the first embodiment of the present invention;

FIG. 5 is a schematic view of a microlens array in the illumination path shown in FIG. 4;

FIG. 6 is a schematic view of a projection optical system in a second embodiment of the present invention;

FIG. 6A is a schematic diagram of the optical performance of the system of FIG. 6;

FIG. 7 is a schematic view of a projection optical system in a third embodiment of the present invention;

fig. 8 is a schematic view of a projection optical system of the present invention configured as a near-eye display device.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

First embodiment

According to the projection optical assembly of the first embodiment of the present invention, the optical path is as shown in fig. 1. Anexemplary image source 15 is implemented as an LCoS-type microdisplay, where theimage source 15 provides image light to the projection optics, which passes through alens assembly 14, an off-axiscatadioptric prism 13, and awedge prism 12, and then onto theexit pupil plane 11. According to the use of the projection optical assembly of the present invention, the image light passing through the projection optical assembly is coupled to a predetermined waveguide type optical sheet at theexit pupil plane 11.

In the first embodiment, as shown in fig. 1, thelens group 14 is constructed in the form of a cemented lens including a negative lens on the side close to the image source and a positive lens cemented to the negative lens, preferably such that the negative lens is formed of a material having a relatively high refractive index and a small abbe number and the positive lens is formed of a material having a relatively low refractive index and a large abbe number. Thefront surface 110 of the negative lens is adjacent to the image source side, theback surface 109 is cemented to thefront surface 109 of the positive lens, and image light is transmitted out of thelens group 14 from theback surface 108 of the positive lens.

Theprism 13 is configured to be off-axis catadioptric, and includes three optical surfaces 107,104/106,105, wherein thesurface 104/106 is a multiplexing surface, that is, thesurface 104 is defined as the first pass after the image light passes through thesurface 107 of theprism 13 closest to thelens group 14 and is transmitted into theprism 13, and the image light is totally internally reflected on thesurface 104, so that the light energy is not lost, and thesurface 104/106 does not need to be coated to perform the reflection function; transmission occurs when the image light passes a second time after traveling in theprism 13, denoted assurface 106. Whilesurface 105 is also formed as a reflective surface, and preferably, a total reflection coating is plated to achieve high efficiency reflection.

Thelens group 14 is disposed coaxially with the image light emission surface, and the off-axiscatadioptric prism 13 realizes main optical axis folding, and off-axis aberration due to the optical axis folding can be corrected by using an aspherical surface or a free-form surface. Preferably, the three surfaces (107,104/106,105) ofprism 13 can be described as aspherical or free-form surfaces.

Further, the first embodiment of the present invention further includes awedge prism 12 disposed close to theprism 13 to realize a slight optical axis folding, and for better controlling the balanced aberration, the surface of thewedge prism 12 may be described by using an aspheric surface/a free-form surface. Thesurface 103 of the wedge-angle prism is adjacent to thesurface 104/106 of theprism 13 and has the same shape, and in order not to obstruct the occurrence of surface total internal reflection, thesurface 103 and thesurface 104/106 need to keep a certain air space, preferably, the space is 0.1-0.5 mm.

Fig. 1a (a) shows an optical Modulation Transfer Function (MTF) of a projection optical assembly according to a first embodiment of the present invention shown in fig. 1, and fig. 1a (b) shows a corresponding distortion, which indicates that the assembly has excellent optical performance. In the projection optical assembly of the first embodiment, the optical axis is folded at least once due to the prism, and although the deflection angle can be set to be between-90 ° and 90 °, it is preferable that the angle of folding the optical axis is controlled to be between 45 ° and 80 ° in the first embodiment.

For the requirement of miniaturization, in the first embodiment, the maximum outer diameters in the vertical axis direction of the lens group and the prism are each limited to not more than 7 mm; whereas wedge-angle prism mirror image encompasses a volume that is generally masked under thesurface 104/106 of the prism, the wedge-angle prism volume is also significantly smaller than the volume of the prism.

Exemplary specific optical surface parameters are given in table 1-1, wheresurface 101 is the plane ofexit pupil 11 andsurfaces 103 and 104/106 have the same surface shape, and althoughsurfaces 107 and 105 are formed as free-form surfaces andsurfaces 108 and 110 are shown as spherical surface shapes in table 4-1, it is understood that aspheric surfaces may be used as the surface shapes. The front and back surfaces of the beam splitting prism, which are typically required to fit LCoS type microdisplays, are designated assurfaces 111, 112, which are planar.

TABLE 1-1

Wherein the surface formed as a sphere satisfies the equation:

where c is the inverse of the radius of curvature and r is the radial distance of a point on the surface.

A surface configured as an aspheric surface satisfies the equation:

where c is the inverse of the radius of curvature, r is the radial distance of a point on the surface, k is the conic constant, and Ai is the coefficient of the higher order term, seeTables 1-2;

the free-form surface constituted as an XY polynomial satisfies the equation:

where c is the inverse of the radius of curvature, r is the radial distance of a point on the surface, k is the conic constant, and Cj is the polynomial coefficient, see tables 1-3.

Tables 1 to 2

Tables 1 to 3

In the first embodiment of the present invention, as shown in fig. 1, theimage source 15 is implemented by an LCoS type microdisplay, and according to the image light generation principle of LCoS, a corresponding illumination optical path needs to be added to provide collimated and uniform illumination light for the Display chip 113(Display panel) of the LCoS type microdisplay. Due to the necessary arrangement of the illumination beam path, the rear intercept (BFL) of the projection optics should accordingly have: 6mm < BFL <15mm to accommodate the illumination light path.

As shown in fig. 2, the manner in which the illumination beam is coupled into the projection light path when using an LCoS-type microdisplay is illustrated. Wherein, Path2 represents the optical Path of the projection optical assembly, which has been described in detail in the embodiment, Path1 represents the optical Path of the illumination for the LCoS display chip, the illumination light beam firstly passes through the splitting surface M1 of the splitting prism BS1, and is reflected to the display chip of the LCoS type micro display, then the light beam is modulated, the reflected light beam carries the information of the image to form the image light, and the image light is transmitted again through the splitting surface M1 to enter the projection optical assembly.

Before entering the splitting plane, some exemplary ways to satisfy the illumination requirement can be shown in fig. 3, where fig. 3(a) is implemented as a simple LED lamp panel, which is compact and small, but can provide limited optical power; the illumination light path composed of the LED and the shaping lens shown in fig. 3(b) has a volume slightly larger than that of the LED lamp panel, so that the optical power can be effectively increased; further, as shown in fig. 3(c), the illumination light path composed of the LED, the light guide rod, and the shaping lens has a larger volume, so that the light power can be effectively increased, and a more uniform illumination beam with better collimation can be provided. The manner shown in figure 3, however, adversely affects the control volume.

In order to keep the volume small, the specific illumination light path according to the first embodiment of the present invention is preferably in the form shown in fig. 4, and includes at least one microlens array. Specifically, light emitted by the LED light source passes through the Lens1, the divergence angle of the light beam is adjusted, the light beam further passes through the microlens array LA1 and the microlens array LA2, and the microlens arrays LA1 and LA2 homogenize the light beam passing through the shaping Lens. Preferably, the Lens1 can be formed by an aspheric surface, a free-form surface shaping Lens or a catadioptric mirror, and is produced by a resin material and an injection molding process, and a glass or resin material can be selected to design the microlens array, each small Lens in the microlens array can be described by a spherical surface, an aspheric surface and a free-form surface, although not shown, the microlens array can be a plane surface on one side, and the small Lens array on the other side; or both sides are small lens arrays; with the same or different arrangements. For simplicity, fig. 5 shows microlens arrays LA1, LA2 used in the first embodiment of the present invention, having the same design parameters.

Tables 1-4 present exemplary design parameters for Lens1, LA1, and LA2, where the faces (surface markers 9,10) of the shaping Lens1 are formed as aspheric faces, and the individual lenslets of the microlens arrays LA1, LA2 are formed as spherical faces.

Tables 1 to 4

Surface marking	Type (B)	Radius of curvature	Thickness of	Properties	Micro-lens aperture	Pitch ofmicro-lenses
							1	Spherical surface	Infinite number of elements	Infinite number ofelements
2	Spherical surface	0.60	1	Lens array 1	0.2×0.2	0.2
							3	Spherical surface	Infinite number ofelements	0
4	Spherical surface	Infinite number ofelements	1
							5	Spherical surface	Infinite number ofelements	0
6	Spherical surface	Infinite number ofelements	1	Lens array 2	0.2×0.2	0.2
							7	Spherical surface	-0.60	0
8	Spherical surface	Infinite number of elements	0.5
							9	Aspherical surface	2.86	4.17	Shaping lens
10	Aspherical surface	-10.02	0

Second embodiment

According to a second embodiment of the invention, a similar projection optical assembly is used as in the first embodiment of the invention, but with an OLED type microdisplay as theimage source 25, as shown in fig. 6.

According to the projection optical assembly of the second embodiment of the present invention, compared with using an LCoS type micro display as an image source, the OLED type micro display is a self-light emitting device, an additional illumination optical path is not required for illumination, the complexity of image light formation is simplified, and the entire projection optical system can be further reduced in weight because an additional illumination system is not required.

Fig. 6a (a) shows the optical Modulation Transfer Function (MTF) of the projection optics, and fig. 6a (b) shows the corresponding distortion. The system has similar optical performance as compared with the first embodiment, and the maximum outer diameters in the vertical axis direction of the same lens group and prism are each limited to not more than 7 mm.

The parameters of the respective optical surfaces are given in table 2-1, in which thesurface 201 is the plane in which theexit pupil 21 of the projection optical assembly of the second embodiment of the present invention is located, and thesurface 203 and themultiplexing surface 204/206 of theprism 23 have the same surface shape, although thesurfaces 207 and 205 are formed as the surface types of the free curved surfaces and thesurfaces 208 and 210 are shown as the surface shapes of the spherical surfaces in table 2-1, it is understood that the aspherical surfaces may be used as the shapes of the above surfaces.

TABLE 2-1

Wherein the surface constituted as a sphere satisfies the equation:

where c is the inverse of the radius of curvature and r is the radial distance of a point on the surface.

A surface configured as an aspheric surface satisfies the equation:

where c is the inverse of the radius of curvature, r is the radial distance of a point on the surface, k is the conic constant, and Ai is the high order term coefficient, as shown in Table 2-2.

The surface of the free-form surface constituted as an XY polynomial satisfies the equation:

where c is the inverse of the radius of curvature, r is the radial distance of a point on the surface, k is the conic constant, and Cj is the polynomial coefficient, as shown in tables 2-3.

Tables 2 to 2

Tables 2 to 3

Although the second embodiment of the present invention is shown with an OLED-type microdisplay as the image source, it will be appreciated by those skilled in the art that other types of microdisplays, such as micro led-type microdisplays, which are self-emitting or do not require additional illumination to be inserted in front of the light exit surface of the image, and LCD-type microdisplays, which are backlit, can be used as the image source in the second embodiment, accommodating the projection optics shown in the second embodiment. Since the location of the extra illumination path does not have to be taken into account, the back-intercept (BFL) of the projection optics assembly can satisfy 2mm < BFL <15mm when using a microdisplay of the type described above.

Third embodiment

According to a third embodiment of the present invention, the embodiment is different from the first embodiment in that it uses a MEMS (Micro electro mechanical System) laser scanning mirror as an image source.

Compared with an OLED type micro-display used as an image source, the MEMS laser scanning mirror has high power, and the display brightness of image light can be effectively improved; compared with an LCoS type micro display used as an image source, the MEMS laser scanning mirror used as the image source can omit an illumination light path comprising a shaping lens, the weight of the projection optical system is further effectively reduced, and the light efficiency of laser is also higher than that of an LED.

Fig. 7(a) shows a projection optical assembly and a projection optical system optical path using the same according to a third embodiment of the present invention, where the projection optical assembly is similar to the first and second embodiments and will not be repeated.

FIG. 7(b) is an enlarged schematic diagram of the operation of the MEMS Laser scanning mirror, according to the solution of the third embodiment of the present invention, a Laser first emits a fine collimated Laser beam, wherein, in case of monochromatic application, only one Laser is needed; if the laser is applied in a complex color mode, at least three lasers of red, green and blue are needed, and three-color lasers need to be combined through a prism and modulated through a color wheel.

For an image source of the MEMS Laser scanning mirror, a Laser beam emitted by a Laser enters the MEMS scanning mirror, which is a planar mirror capable of two-dimensional rotational movement, i.e., can rotate around an x axis or a z axis, and reflects a Laser emitted by the Laser to an imagesource position surface 311 of the projection system; for example, when the MEMS is in the P1 position, the reflected laser beam will reach point a onsurface 311, and then the MEMS rotates about the x-axis, and when the MEMS is in the P2 position, the reflected laser beam will reach point B onsurface 311. The MEMS scanning mirror can scan a complete image onsurface 311 by rotation in both directions about the x-axis and z-axis. In order for the light to enter the projection optics, thesurface 311 should have reflective/scattering properties and be formed substantially as a plane.

According to the projection optical assembly and the projection optical system using the same shown in the embodiments of the present invention, an image displayed on a microdisplay near the user's eye (e.g., at the side of the eye, approximately the position of the temple) is projected with magnification to the exit pupil position and then coupled into a waveguide type optical element arranged based on the principle of physical optics, and the transmission and one-dimensional or two-dimensional expansion of the light entering optical element are propagated to the user's eye, so that the user can see the magnified image displayed on the microdisplay, and if the projection optical system of the present invention is implemented with both eyes, the user can see the magnified 3D display image, as shown in fig. 8. The projection optical unit according to the present invention can be miniaturized and can be accommodated in a substantially temple position on the side with the aid of a support and protection structure (not shown), and the flat waveguide type optical element is realized in front of the eye as a lens and is configured as a complete near-eye display device in a form similar to spectacles as a whole. The image displayed on the microdisplay can be transmitted by the central processor by means of a wired, e.g. USB-type C wired interface, which has been implemented as a general purpose, or a wireless network, e.g. a 5G network with large bandwidth and low delay transmission characteristics.

The foregoing is a detailed description of the invention with reference to specific preferred embodiments, and no attempt is made to limit the invention to the particular embodiments disclosed, or modifications and equivalents thereof, since those skilled in the art may make various alterations and equivalents without departing from the spirit and scope of the invention, which should be determined from the claims appended hereto.

Claims (12)

1. A compact projection optics assembly for a near-eye display, the projection optics assembly comprising:

a lens group (14) for receiving image light from the microdisplay;

a prism (13) which is configured to be of an off-axis catadioptric type, is disposed behind the lens group in an optical path direction, is used for realizing optical axis catadioptric and correcting off-axis aberration in the system, and comprises at least one effective optical surface which is an aspheric surface or a free-form surface, and one of the optical surfaces of the prism is provided with a total reflection film;

a wedge angle prism (12) disposed on a light exit side of the prism in an optical path direction for controlling an angle of image light with respect to an exit pupil plane (11) of the projection optical assembly; the effective optical surface of the wedge-angle prism comprises at least one aspheric surface or a free-form surface;

the image light passing through the projection optics is coupled to a predetermined waveguide type optical sheet at the exit pupil plane (11);

the maximum outer diameters of the lens group and the prism in the vertical axis direction are not more than 7 mm; the wedge-angle prism is covered under the prism in a bag-type manner, and the wedge-angle prism does not exceed the maximum outer diameter of the prism in the vertical axis direction; the volume of the wedge-angle prism is smaller than that of the prism;

the back intercept of the projection optics is less than 15 mm.

2. The projection optics assembly of claim 1 wherein the lens group comprises at least one cemented lens comprising at least one negative lens with a high refractive index and a small abbe number and at least one positive lens with a low refractive index and a large abbe number.

3. The projection optics assembly according to claim 1, wherein the prism (13) folds the optical axis at an angle of 45 to 75 degrees.

4. Projection optics assembly according to claim 3, wherein the effective optical surface of the prism (13) is configured to cause at least one total reflection of the image light as it propagates therein.

5. Projection optical assembly according to claim 1, wherein the wedge angle prism (13) has the same shape as two adjacent surfaces of the prism (12), the wedge angle prism (13) having a spacing between the two adjacent surfaces of the prism (12).

6. Projection optical assembly according to claim 5, wherein the faces of the wedge angle prism (13) adjacent to the prism (12) are aspherical.

7. A projection optical system comprising the projection optical assembly of any one of claims 1 to 6, characterized by further comprising a reflective liquid crystal display (LCoS) type image source.

8. Projection optical system according to claim 7, characterized in that the image source (45) comprises:

a reflective liquid crystal switching layer;

a polarization beam splitter disposed in front of the reflective light-emitting surface of the switching layer at a predetermined distance;

an LED light source for providing an initial light beam, and at least one shaping Lens (Lens1) disposed between the LED light source and the polarizing beam splitter for adjusting the divergence angle of the initial light beam and projecting the light onto a micro-Lens array (LA1, LA2) for further homogenizing the light beam.

9. The projection optical system according to claim 8, wherein the polarization beam splitter is a polarization beam splitting cube prism or a beam splitting film having a support structure.

10. The projection optical system of claim 9 wherein said shaping lens has aspheric front and back surfaces for coupling the illumination beam into the optical path.

11. A projection optical System comprising the projection optical assembly of any one of claims 1 to 6, further comprising a MEMS (Micro electro mechanical System) laser scanning mirror as an image source, said MEMS scanning mirror scanning a complete one-plane image on a reflection/scattering surface (311) at a predetermined position by a laser beam irradiated thereto, said predetermined position being an image source surface position of said projection optical assembly.

12. A projection optical system comprising the projection optical assembly of any one of claims 1 to 6, characterized in that said projection optical system further comprises an image source of a type selected from one of an organic light emitting semiconductor display (OLED) type, a micro light emitting diode display (micro led) type, a Liquid Crystal Display (LCD) type micro display.

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