US20240004346A1 - Holographic display apparatus for providing expanded viewing window - Google Patents

Abstract

Provided is a holographic display apparatus capable of providing an expanded viewing window when reproducing a holographic image via an off-axis technique. The holographic display apparatus includes a spatial light modulator comprising a plurality of pixels arranged two-dimensionally; and an aperture enlargement film configured to enlarge a beam diameter of a light beam coming from each of the plurality of pixels of the spatial light modulator. The beam diameter of each light beam enlarged by the aperture enlargement film may be greater than the width of an aperture of each pixel of the spatial light modulator.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. application Ser. No. 17/011,080, filed Sep. 3, 2020, which claims priority from Korean Patent Application Nos. 10-2019-0164803 and 10-2020-0039707, filed on Dec. 11, 2019 and Apr. 1, 2020, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entireties by reference.
BACKGROUND1. Field
• Example embodiments of the present disclosure relate to holographic display apparatuses, and more particularly to, holographic display apparatuses capable of providing an expanded viewing window when reproducing a holographic image via an off-axis technique.
2. Description of the Related Art
• Methods such as glasses-type methods and non-glasses-type methods are widely used for realizing 3D images. Examples of glasses-type methods include deflected glasses-type methods and shutter glasses-type methods, and examples of non-glasses-type methods include lenticular methods and parallax barrier methods. When these methods are used, there is a limitation with regard to the number of viewpoints that may be implemented due to binocular parallax. Also, these methods make the viewers feel tired due to the difference between the depth perceived by the brain and the focus of the eyes.
• Holographic 3D image display methods, which provide full parallax and are capable of making the depth perceived by the brain consistent with the focus of the eyes, have been considered. According to such a holographic display technique, when light is irradiated onto a hologram pattern having recorded thereon an interference pattern obtained by interference between object light reflected from an original object and reference light, the light is diffracted and an image of the original object is reproduced. When a currently considered holographic display technique is used, a computer-generated hologram (CGH), rather than a hologram pattern obtained by directly exposing an original object to light, is provided as an electrical signal to a spatial light modulator. Then, the spatial light modulator forms a hologram pattern and diffracts light according to an input CGH signal, thereby generating a 3D image.
SUMMARY
• One or more example embodiments provide holographic display apparatuses capable of providing an expanded viewing window.
• Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of example embodiments.
• According to an aspect of an example embodiment, there is provided a holographic display apparatus including a spatial light modulator including a plurality of pixels disposed two-dimensionally, and an aperture enlargement film configured to enlarge a beam diameter of a light beam transmitted from each of the plurality of pixels of the spatial light modulator.
• The spatial light modulator may include a plurality of apertures and a black matrix surrounding each of the plurality of apertures.
• An intensity distribution of the enlarged light beam may decrease from a center of the enlarged light beam to a periphery of the enlarged light beam.
• A beam diameter of the enlarged light beam may be greater than a width of each of the plurality of apertures of the spatial light modulator.
• A beam diameter of the enlarged light beam may be greater than a pixel period of the spatial light modulator.
• The aperture enlargement film may include a light guide layer disposed to face a light exiting surface of the spatial light modulator and a grating layer disposed on an upper surface of the light guide layer opposite to the spatial light modulator.
• A thickness of the light guide layer may range from 1 μm to 5 μm.
• The grating layer may be configured to transmit a portion of a light beam vertically incident on a lower surface of the grating layer from the light guide layer in a direction perpendicular to an upper surface of the grating layer, and may be configured to reflect a remaining portion of the light beam to propagate obliquely in the light guide layer.
• The light guide layer may be configured to obliquely propagate the light beam reflected from the grating layer along an inside of the light guide layer based on total reflection.
• The grating layer may be configured to transmit a portion of the light beam obliquely incident on a lower surface of the grating layer from the light guide layer to propagate in a direction perpendicular to an upper surface of the grating layer.
• A first light beam perpendicularly incident on the lower surface of the grating layer and transmitted in the direction perpendicular to the upper surface of the grating layer and a second light beam obliquely incident on the lower surface of the grating layer and transmitted in the direction perpendicular to the upper surface of the grating layer may at least partially overlap.
• The aperture enlargement film may include a substrate configured to support the light guide layer and the grating layer such that the light guide layer and the grating layer do not bend, and a refractive index of the light guide layer may be greater than a refractive index of the substrate.
• The aperture enlargement film may include a first grating layer disposed to face a light exiting surface of the spatial light modulator, a light guide layer disposed on the first grating layer, and a second grating layer disposed on the light guide layer opposite to the first grating layer.
• The aperture enlargement film may include a grating layer disposed to face a light exiting surface of the spatial light modulator and a light guide layer disposed on an upper surface of the grating layer opposite to the spatial light modulator.
• The holographic display apparatus may further include a backlight unit configured to provide a coherent collimated illumination light to the spatial light modulator, and a Fourier lens configured to focus a holographic image reproduced by the spatial light modulator on a space.
• The holographic display apparatus may further include a Gaussian apodization filter array disposed between a light exiting surface of the spatial light modulator and the aperture enlargement film or disposed to face a light entering surface of the spatial light modulator.
• The Gaussian apodization filter array may include a plurality of Gaussian apodization filters configured to convert an intensity distribution of a light beam into a curved Gaussian distribution.
• The holographic display apparatus may further include a prism array disposed between the spatial light modulator and the aperture enlargement film or disposed to face a light exiting surface of the aperture enlargement film.
• The prism array may be divided into a plurality of unit regions that are two-dimensionally disposed, and each of the plurality of unit regions may include a plurality of prisms configured to propagate an incident light in different directions.
• The plurality of prisms included in the prism array may correspond one-to-one to a plurality of pixels included in the spatial light modulator.
• A first pixel of the spatial light modulator corresponding to a first prism of each of the plurality of unit regions of the prism array may be configured to reproduce a holographic image of a first viewpoint, and a second pixel of the spatial light modulator corresponding to a second prism of each of the plurality of unit regions of the prism array may be configured to reproduce a holographic image of a second viewpoint different from the first viewpoint.
• According to another aspect of an example embodiment, there is provided a holographic display apparatus including a spatial light modulator including a plurality of pixels disposed two-dimensionally, the plurality of pixels including a plurality of apertures, respectively, and an aperture enlargement film configured to enlarge a beam diameter of a light beam transmitted from each of the plurality of pixels of the spatial light modulator, wherein a beam diameter of the enlarged light beam is greater than a width of each of the plurality of apertures.
• The aperture enlargement film may include a light guide layer disposed to face a light exiting surface of the spatial light modulator and a grating layer disposed on an upper surface of the light guide layer opposite to the spatial light modulator.
BRIEF DESCRIPTION OF THE DRAWINGS
• The above and/or other aspects, features, and advantages of example embodiments will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:
• FIG.1 is a schematic diagram showing a configuration of a holographic display apparatus according to an example embodiment;
• FIG.2 is a cross-sectional view schematically showing the configuration and operation of an aperture enlargement film according to the example embodiment of the holographic display apparatus shown inFIG.1;
• FIG.3A shows the intensity distribution of illumination light transmitted through an aperture of a spatial light modulator when only the spatial light modulator is used without an aperture enlargement film,FIGS.3B and3C show a light intensity distribution formed by the illumination light transmitted through the aperture of the spatial light modulator on the focal plane of a Fourier lens in the case ofFIG.3A, andFIG.3D shows the distribution of light formed on the focal plane of the Fourier lens by a holographic display apparatus according to a related example in the case ofFIG.3A.
• FIG.4A shows an intensity distribution of illumination light transmitted through an aperture of a spatial light modulator and an aperture enlargement film when the spatial light modulator and the aperture enlargement film are used,FIGS.4B to4D show light intensity distributions that the illumination light transmitted through the aperture and the aperture enlargement film of the spatial light modulator forms on the focal plane of a Fourier lens in the case ofFIG.4A, andFIG.4E shows the distribution of light formed on the focal plane of the Fourier lens by a holographic display apparatus according to an embodiment in the case ofFIG.4A;
• FIG.5 is a cross-sectional view schematically showing the configuration and operation of an aperture enlargement film according to another example embodiment;
• FIG.6 is a cross-sectional view schematically showing the configuration and operation of an aperture enlargement film according to another example embodiment;
• FIG.7 is a cross-sectional view schematically showing the configuration and operation of an aperture enlargement film according to another example embodiment;
• FIG.8 is a cross-sectional view schematically showing the configuration and operation of an aperture enlargement film according to another example embodiment;
• FIGS.9A and9B are configuration diagrams schematically showing a configuration of holographic display apparatuses according to another example embodiment;
• FIGS.10A and10B are configuration diagrams schematically showing a configuration of holographic display apparatuses according to another example embodiment;
• FIG.11 shows an arrangement of a plurality of prisms of a prism array of the holographic display apparatuses shown inFIGS.10A and10B;
• FIG.12 shows an arrangement of a plurality of pixels of a spatial light modulator of the holographic display apparatuses shown inFIGS.10A and10B; and
• FIG.13 shows the distribution of light formed on the focal plane of a Fourier lens by the holographic display apparatuses shown inFIGS.10A and10B.
DETAILED DESCRIPTION
• Reference will now be made in detail to example embodiments of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the example embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. For example, the expression, “at least one of a, b, and c,” should be understood as including only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.
• Hereinafter, with reference to the accompanying drawings, a holographic display apparatus for providing an expanded viewing window will be described in detail. Like reference numerals refer to like elements throughout, and in the drawings, sizes of elements may be exaggerated for clarity and convenience of explanation. The example embodiments described below are merely exemplary, and various modifications may be possible from the example embodiments. In a layer structure described below, an expression “above” or “on” may include not only “immediately on in a contact manner” but also “on in a non-contact manner”.
• FIG.1 is a schematic diagram showing a configuration of aholographic display apparatus100 according to an example embodiment. Referring toFIG.1, theholographic display apparatus100 according to an example embodiment may include a spatiallight modulator120 having a plurality of pixels arranged two-dimensionally and anaperture enlargement film130 disposed to enlarge the beam diameter of light emitted from each pixel of the spatiallight modulator120.
• In addition, theholographic display apparatus100 may further include abacklight unit110 that provides coherent collimated illumination light to the spatiallight modulator120, aFourier lens140 that focuses a holographic image on the space, and animage processor150 that generates and provides a hologram data signal based on the holographic image to be reproduced to the spatiallight modulator120. InFIG.1, although theFourier lens140 is disposed on the light entering surface of the spatiallight modulator120, that is, between thebacklight unit110 and the spatiallight modulator120, the position of theFourier lens140 is necessarily not limited thereto. For example, theFourier lens140 may be disposed between the spatiallight modulator120 and theaperture enlargement film130 or on the light exiting surface of theaperture enlargement film130.
• Thebacklight unit110 may include a laser diode to provide illumination light having high coherence. In addition to the laser diode, thebacklight unit110 may include any of other light sources configured to emit light having spatial coherence. In addition, thebacklight unit110 may further include an optical system that enlarges light emitted from the laser diode to generate collimated parallel light having a uniform intensity distribution. Accordingly, thebacklight unit110 may provide parallel coherent illumination light having the uniform intensity distribution to the entire region of the spatiallight modulator120.
• The spatiallight modulator120 may be configured to diffract and modulate the illumination light, according to the hologram data signal, for example, a computer-generated hologram (CGH) data signal, provided by theimage processor150. For example, the spatiallight modulator120 may use any one of a phase modulator for performing phase modulation, an amplitude modulator for performing amplitude modulation, and a complex modulator performing both phase modulation and amplitude modulation. Although the spatiallight modulator120 ofFIG.1 is a transmissive spatial light modulator, a reflective spatial light modulator may also be used. The spatiallight modulator120 may include a plurality of display pixels arranged two-dimensionally to display a hologram pattern for diffracting the illumination light. For example, the spatiallight modulator120 may use a liquid crystal device (LCD), a semiconductor modulator, a digital micromirror device (DMD), liquid crystal on silicon (LCoS), etc.
• The spatiallight modulator120 may include a two-dimensional grating-shaped black matrix and a plurality of apertures surrounded by the black matrix. A driving circuit for controlling the operation of each aperture is disposed below the black matrix, and each aperture is an active region that changes the intensity or phase of transmissive light or reflective light. The intensity or phase of light passing through each aperture or light reflected by the aperture may be adjusted under the control of the driving circuit. For example, when the spatiallight modulator120 displays the hologram pattern according to the CGH data signal provided from theimage processor150, the intensity or phase of the illumination light may be adjusted differently in the plurality of apertures. When light beams of the illumination light whose intensity or phase is modulated in the plurality of apertures of the spatiallight modulator120 cause interference and focus on theFourier lens140, the holographic image may be seen by an observer's eye E. Accordingly, the reproduced holographic image may be determined by the CGH data signal provided from theimage processor150 and the hologram pattern displayed by the spatiallight modulator120 based on the CGH data signal.
• Theaperture enlargement film130 is configured to enlarge the beam diameter of the light beam of the illumination light passing through or reflected from each aperture of the spatiallight modulator120. For example,FIG.2 is a cross-sectional view schematically showing the configuration and operation of theaperture enlargement film130 according to the example embodiment of theholographic display apparatus100 shown inFIG.1. Referring toFIG.2, theaperture enlargement film130 is disposed to face the light exiting surface of the spatiallight modulator120. The spatiallight modulator120 includes a plurality ofapertures121 and ablack matrix122 surrounding the plurality ofapertures121. Accordingly, a plurality of light beams transmitted from the plurality ofapertures121 of the spatiallight modulator120 respectively is incident on theaperture enlargement film130.
• Theaperture enlargement film130 may include alight guide layer132 disposed to face the light exiting surface of the spatiallight modulator120 and agrating layer133 disposed on an upper surface of thelight guide layer132. In addition, theaperture enlargement film130 may further include asubstrate131 for supporting thelight guide layer132 and thegrating layer133 such that thelight guide layer132 and thegrating layer133 do not bend. However, thesubstrate131 may be omitted if thelight guide layer132 is supported without bending itself. InFIG.2, although the thickness of thesubstrate131 is similar to the thickness of thelight guide layer132, thelight guide layer132 may be much thinner than thesubstrate131. For example, the thickness of thesubstrate131 may be about 0.5 mm to about 1 mm, and the thickness of thelight guide layer132 may be about 1 μm to about 5 μm. Thesubstrate131 may include glass or a transparent polymer material of a solid material, and thelight guide layer132 may include a transparent material having a higher refractive index than thesubstrate131 to transmit light therein.
• Thegrating layer133 disposed on the upper surface of thelight guide layer132 may emit a portion of light incident on thegrating layer133 from thelight guide layer132 in a direction parallel a direction parallel to a direction normal to the upper surface of thegrating layer133, which is a direction perpendicular to the upper surface of thegrating layer133, and may reflect the remaining portion of the light incident on thegrating layer133 to travel obliquely toward thelight guide layer132. Thegrating layer133 may include various types of surface gratings or volume gratings. The surface grating may include, for example, a diffractive optical element (DOE) such as a binary phase grating, a blazed grating, etc. In addition, the volume grating may include, for example, a holographic optical element (HOE), a geometric phase grating, a Bragg polarization grating, a holographically formed polymer dispersed liquid crystal (H-PDLC), etc. Such a volume grating may include periodic fine patterns of materials with different refractive indices. According to the size, height, period, duty ratio, shape, etc. of the periodic grating patterns constituting thegrating layer133, thegrating layer133 may diffract the incident light to cause extinctive interference and constructive interference and change the traveling direction of the incident light.
• The light beam transmitted from theaperture121 of the spatiallight modulator120 may be incident perpendicularly to the lower surface of thesubstrate131 and may pass through thesubstrate131 and thelight guide layer132, and may be incident perpendicularly to the lower surface of thegrating layer133. Thegrating layer133 may emit a 0th order diffracted light beam among incident light beams incident perpendicularly or obliquely to the lower surface of thegrating layer133 in the direction parallel to the direction normal to the upper surface of thegrating layer133, and may reflect a 1st order diffracted light beam to travel obliquely toward thelight guide layer132. Thelight guide layer132 is configured to propagate the light beam obliquely reflected from thegrating layer133 along the inside of thelight guide layer132 through total reflection. Therefore, the 1st order diffracted light beam may be totally reflected between the upper surface and the lower surface of thelight guide layer132 and travel along the inside of thelight guide layer132. For example, as indicated by the arrow inFIG.2, a +1st order diffracted light beam may travel along the right direction of thelight guide layer132, and a −1st order diffracted light beam may travel along the left direction of thelight guide layer132. The arrow inFIG.2 represents the center of the light beam, and an actual light beam may have a beam diameter equal to a width W1 of theaperture121. In addition, in the cross-sectional view ofFIG.2, although the −1st order diffracted light beam traveling to the left and the +1st order diffracted light beam traveling to the right are representatively indicated, the first diffracted light beam may travel in all radial directions with respect to the incident position of thegrating layer133.
• The 1st order diffracted light beam by thegrating layer133 is totally reflected from the lower surface of thelight guide layer132, and again obliquely incident on the upper surface of thelight guide layer132. Thereafter, a portion of the first diffracted light beam is totally reflected again from the upper surface of thelight guide layer132, while the remaining portion is diffracted by thegrating layer133, and emitted in the direction parallel to the direction normal to the upper surface of thegrating layer133.
• Accordingly, the light beam emitted from thegrating layer133 includes a light beam L0 emitted by the 0th order diffraction and a light beam L1 emitted by the 1st order diffraction. In the cross-sectional view ofFIG.2, although light beams −L1 and +L1 emitted by a ±1 order diffraction are respectively shown on the left and right sides of light beam L0 emitted by the 0th order diffraction, the light beam L1 emitted by the 1st order diffraction continuously surrounds the circumference of the light beam L0 emitted by the 0th order diffraction in the shape of a ring. Thegrating layer133 may be configured as a two-dimensional grating film capable of diffracting incident light in all directions. Thegrating layer133 may be configured by stacking two one-dimensional grating films having orthogonal directions to each other. In this case, for example, the light beam may be enlarged and emitted in the horizontal direction by the one-dimensional grating film in the horizontal direction, and the light beam may be enlarged in the vertical direction by the one-dimensional grating film in the vertical direction, and then the ring-shaped light beam L1 may be finally emitted.
• The light beam L1 emitted by the 1st order diffraction may overlap at least partially with the light beam L0 emitted by the 0th order diffraction. The degree to which the light beam L1 emitted by the 1st diffraction and the light beam L0 emitted by the 0th diffraction overlap may vary according to the thickness of thelight guide layer132. When the thickness of thelight guide layer132 is too large, the light beam L1 emitted by the 1st order diffraction may not overlap with the light beam L0 emitted by the 0th order diffraction, and a gap may exist between the light beam L0 emitted by the 0th order diffraction and the light beam L1 emitted by the 1st order diffraction. When the thickness of thelight guide layer132 is gradually reduced, the boundary of the light beam L1 emitted by the 1st order diffraction coincides with the boundary of the light beam L0 emitted by the 0th order diffraction. When the thickness of thelight guide layer132 is further reduced, the light beam L1 emitted by the 1st order diffraction may overlap with the light beam L0 emitted by the 0th order diffraction. Therefore, the maximum thickness of thelight guide layer132 may be selected such that the boundary of the light beam L1 emitted by the 1st order diffraction coincides with the boundary of the light beam L0 emitted by the 0th order diffraction.
• As described above, the light beam incident on theaperture enlargement film130 from eachaperture121 of the spatiallight modulator120 passes through theaperture enlargement film130 and is divided into the light beam L0 emitted by the 0th order diffraction and the light beam L1 emitted by the 1st order diffraction. These light beams may be combined to be viewed as one enlarged light beam. As a result, theaperture enlargement film130 may enlarge the beam diameter of the light beam incident from theaperture121 of the spatiallight modulator120. The beam diameter of the light beam incident on theaperture enlargement film130 from theaperture121 of the spatiallight modulator120 is equal to the width W1 of theaperture121. However, the beam diameter of the light beam enlarged while passing through theaperture enlargement film130 may be the same as a beam diameter W3 of a light beam combining the light beam L0 emitted by the 0th order diffraction and the light beam L1 emitted by the 1st order diffraction, and may be greater than the width W1 of theaperture121 of the spatiallight modulator120.
• The beam diameter W3 of the light beam enlarged by theaperture enlargement film130 may vary according to the degree to which the light beam L0 emitted by the 0th order diffraction and the light beam L1 emitted by the 1st order diffraction overlap. As the degree of overlap is based on the thickness of thelight guide layer132, the beam diameter W3 of the light beam enlarged by theaperture enlargement film130 may be determined by the thickness of thelight guide layer132. For example, the thickness of thelight guide layer132 may be selected such that the beam diameter W3 of the light beam enlarged by theaperture enlargement film130 is greater than a pitch W2 of a pixel of the spatiallight modulator120. The pitch W2 of the pixel of the spatiallight modulator120 is equal to the sum of the width W1 of theaperture121 and the width of theblack matrix122.
• In the related example, due to theblack matrix122 existing between theapertures121, there is a gap having no image information between the plurality of light beams transmitted from the plurality ofapertures121 of the spatiallight modulator120. The gap between the light beams may increase the intensity of a higher order diffraction pattern. Meanwhile, according to the example embodiment, because theaperture enlargement film130 enlarges the beam diameter of each light beam, the intensity of the high order diffraction pattern may decrease and ultimately the high order diffraction pattern may be removed.
• Meanwhile, the intensity of the light beam L0 emitted by the 0th order diffraction is greater than the intensity of the light beam L1 emitted by the 1st order diffraction. Therefore, the light beam enlarged by theaperture enlargement film130 has a shape in which the intensity decreases from the center of the light beam to the periphery, and has a shape approximately similar to a Gaussian distribution. According to the example embodiment, due to the enlarged light beam having a distribution having a beam diameter greater than the width W1 of theaperture121 of the spatiallight modulator120 and having the intensity decreasing from the center to the periphery, the spatiallight modulator120 may reduce high order noise generated in the focal plane of theFourier lens140 such that a viewing window through which a holographic image is visible may be enlarged.
• As described above, because the spatiallight modulator120 is configured with an array of the plurality ofapertures121 and theblack matrix122, a physical structure of the spatiallight modulator120 may function as a regular diffraction grating. Thus, the illumination light may be diffracted and interfered with by the hologram pattern formed by the spatiallight modulator120 and also by a regular structure constituting the spatiallight modulator120. Also, some of the illumination light may not be diffracted by the hologram pattern, but may pass through the spatiallight modulator120 as is. As a result, a plurality of lattice spots may appear on the focal plane or the pupil plane of theFourier lens140 on which the holographic image is converged to a point. The plurality of lattice spots may function as image noise that degrades quality of the reproduced holographic image and makes it uncomfortable to observe the holographic image. For example, a 0th order noise formed by the illumination light which is not diffracted may appear on an axis of theFourier lens140.
• Also, multiple high order noise of a regular lattice pattern may appear around a 0th order noise by interference between light diffracted by the regular pixel structure of the spatiallight modulator120. However, as shown inFIG.2, when theaperture enlargement film130 is used together with the spatiallight modulator120, the multiple high order noise having the regular lattice structure may be reduced to enlarge a viewing window.
• For example,FIG.3A shows the intensity distribution of illumination light transmitted through theaperture121 of the spatiallight modulator120 without theaperture enlargement film130, andFIGS.3B and3C show a light intensity distribution formed by the illumination light ofFIG.3A on the focal plane of theFourier lens140. In particular,FIG.3B shows the light intensity distribution formed by one pixel, andFIG.3C shows the light intensity distribution formed when a plurality of adjacent pixels are simultaneously turned on.
• InFIG.3A, graph B indicates the intensity distribution of the illumination light of a uniform distribution transmitted through theaperture121 of the spatiallight modulator120, and has a uniform distribution across the width W1 of theaperture121. InFIG.3A, graph A indicates the intensity distribution when the illumination light of the uniform distribution indicated by graph B passes through a Gaussian apodization filter, and shows a Gaussian distribution. In the absence of theaperture enlargement film130, the beam diameter of the illumination light transmitted through theaperture121 of the spatiallight modulator120 is substantially the same as the width W1 of theaperture121 of the spatiallight modulator120. Because the width W1 of theaperture121 of the spatiallight modulator120 is smaller than the pixel period of the spatiallight modulator120, the beam diameter of the illumination light transmitted through theaperture121 of the spatiallight modulator120 is also smaller than the pixel period of the spatiallight modulator120.
• The graph A inFIG.3B showing the light intensity distribution formed by one pixel shows an intensity distribution after the illumination light having the Gaussian distribution indicated by graph A inFIG.3A expands on the focal plane of theFourier lens140 due to the diffraction phenomenon by theaperture121 of the spatiallight modulator120. In addition, a graph B inFIG.3B shows a light intensity distribution formed on the focal plane of theFourier lens140 due to the diffraction when the illumination light having the uniform intensity distribution indicated by graph B inFIG.3A passes through theaperture121 of one pixel of the spatiallight modulator120.
• The graph B inFIG.3C showing the light intensity distribution formed on the focal plane of theFourier lens140 by a plurality of adjacent pixels shows a light intensity distribution formed on the focal plane of theFourier lens140 due to the diffraction when the illumination light having the uniform intensity distribution indicated by graph B inFIG.3A passes through theapertures121 of the plurality of adjacent pixels of the spatiallight modulator120. The central peak of the graph B inFIG.3C is generated by the 0th order diffraction, and surrounding peaks are generated by high order diffraction of ±1st order or higher. Accordingly, an interference pattern formed by the illumination light having the Gaussian distribution indicated by graph A in FIG.3A may be the same as the product of the graph A inFIG.3B and the graph B inFIG.3C, and is indicated by a graph D inFIG.3C. As shown by the graph D inFIG.3C, because the distribution of the graph A expanded on the focal plane includes the peaks by high order diffraction of the graph B, even if the illumination light having the Gaussian distribution indicated by graph A inFIG.3A is used, the interference pattern due to 0th order diffraction and high order diffraction is generated.
• FIG.3D shows the distribution of light formed in the focal plane of theFourier lens140 by a holographic display apparatus according to the related example shown inFIG.3A. The holographic display apparatus according to the related example may have a structure without theaperture enlargement film130 in the configuration shown inFIG.1. Referring toFIG.3D, 0th order noise NO due to 0th order diffraction is formed on the center of the focal plane, that is, on the optical axis. In addition, in the periphery of the 0th order noise NO, high order noises N1 generated by high order diffraction of ±1st order or higher are regularly formed in the form of a lattice. InFIG.3D, a rectangle indicated by a thick solid line surrounded by the high order noises N1 becomes a viewing window of the holographic display apparatus determined by the resolution of the spatiallight modulator120.
• In order to prevent or reduce such the multiple noises NO and N1 from being visible by an observer, a holographic image may be reproduced via an off-axis technique such that the spot of the holographic image is reproduced by avoiding the multiple noises NO and N1. Because the multiple noises NO and N1 are generated by the physical internal structure of the spatiallight modulator120 and are independent of the hologram pattern displayed by the spatiallight modulator120, the positions of the noises NO and N1 are always fixed. Because the spot position of the holographic image is determined by the hologram pattern displayed by the spatiallight modulator120, a holographic pattern may be formed such that the holographic image is reproduced on a position that does not include the multiple noises NO and N1. For example, theimage processor150 may add a prism phase to CGH data including holographic image information. Then, the holographic image may be reproduced away from the optical axis by a prism pattern displayed together with the hologram pattern by the spatiallight modulator120. Therefore, the reproduced holographic image may be away from the 0th order noise NO.
• For example, as illustrated inFIG.3D, a holographic image signal S may be positioned slightly away from the 0th order noise NO in a diagonal direction by using an off-axis technique. In the case of the off-axis technique, a complex conjugate image signal S* may be generated in the opposite direction of the holographic image signal S with respect to the 0th order noise NO. However, even when using the off-axis technique, because the expression limit of the prism phase is smaller than the pixel period of the spatiallight modulator120, the holographic image signal S may not be positioned farther away than the high order noise N1 as shown inFIG.3D. Therefore, the high order noise N1 makes it difficult to enlarge the viewing window and interferes with the viewing of the holographic image. In addition, holographic image signals S1 by a high order diffraction in the diagonal direction with respect to the high order noises N1 and their complex conjugate image signals S1* may be generated together. The holographic image signal S1 by the high order diffraction and its complex conjugate image signal S1* may also interfere with the viewing of the holographic image.
• FIG.4A shows an intensity distribution of illumination light transmitted through theaperture121 of the spatiallight modulator120 and theaperture enlargement film130. In addition,FIGS.4B to4D show light intensity distributions that the illumination light ofFIG.4A forms on the focal plane of theFourier lens140. In particular,FIG.4B shows the light intensity distribution formed by one pixel,FIG.4C shows the light intensity distribution formed when a plurality of adjacent pixels are simultaneously turned on, andFIG.4D shows a light intensity distribution formed on the focal plane of theFourier lens140 due to the diffraction of the illumination light transmitted through theaperture121 of the spatiallight modulator120 and theaperture enlargement film130.
• InFIG.4A, graph B indicates the intensity distribution of the illumination light transmitted through theaperture121 of the spatiallight modulator120, and a graph C indicates the intensity distribution of the illumination light transmitted through theaperture121 of the spatiallight modulator120 and theaperture enlargement film130. As shown inFIG.4A, it is assumed that the intensity of the illumination light transmitted through theaperture121 of the spatiallight modulator120 and theaperture enlargement film130 has the Gaussian distribution. When using theaperture enlargement film130, the beam diameter of the illumination light may be greater than the width W1 of theaperture121 of the spatiallight modulator120 and may be greater than the pixel period of the spatiallight modulator120. This may have the same effect that optically theaperture121 of thelight modulator120 through which the illumination light passes is greater than the pixel period of the spatiallight modulator120. For example, theaperture enlargement film130 may provide an effect such as enlarging theaperture121 of the spatiallight modulator120.
• The graph B inFIG.4B showing the light intensity distribution formed by one pixel is the same as the graph B inFIG.3B. For example, the graph B inFIG.4B is the light intensity distribution formed on the focal plane of theFourier lens140 due to the diffraction of the illumination light having a uniform intensity distribution that passes through theaperture121 of the spatiallight modulator120 but does not pass through theaperture enlargement film130. The graph C inFIG.4B shows the light intensity distribution formed by the illumination light having the intensity distribution indicated by graph C inFIG.4A on the focal plane of theFourier lens140 without considering interference. The illumination light having the intensity distribution indicated by graph C inFIG.4A is rarely enlarged on the focal plane of theFourier lens140, as shown inFIG.4B, due to an optical effect such that theaperture121 of the spatiallight modulator120 is enlarged.
• The graph B inFIG.4C showing the light intensity distribution formed on the focal plane of theFourier lens140 by a plurality of adjacent pixels is the light intensity distribution formed on the focal plane of theFourier lens140 due to the diffraction when the illumination light having a uniform intensity distribution indicated by graph B inFIG.4A passes through theapertures121 of the plurality of adjacent pixels of the spatiallight modulator120. The central peak of the graph B inFIG.3C is generated by the 0th order diffraction, and surrounding peaks are generated by high order diffraction of ±1st order or higher.
• An interference pattern formed by the illumination light having the Gaussian distribution indicated by graph C inFIG.4A may be the same as the product of the graph C inFIG.4B and the graph B inFIG.4C, and is indicated by a graph D inFIG.4D. The distribution of the graph C inFIG.4B may include only peak due to a 0th order diffraction of the graph B inFIG.4C, as shown inFIG.4C. Therefore, when using the illumination light of a wide beam diameter having the Gaussian distribution indicated by graph C inFIG.4A, as shown inFIG.4D, only the interference pattern due to the 0th order diffraction occurs, and an interference pattern due to a high order diffraction does not appear.
• FIG.4E shows the distribution of light formed on the focal plane of theFourier lens140 by the holographic display apparatus according100 ofFIG.4A. Referring toFIG.4E, on the focal plane of theFourier lens140, only the 0th order noise NO, the holographic image signal S, and the complex conjugate image signal S* appear, and the high order noises N1, the holographic image signals S1 by the high order diffraction and their complex conjugate image signals S1* illustrated inFIG.3D hardly appear. Therefore, by using theaperture enlargement film130, the observer may view the holographic image without being disturbed by the high order noise N1 and in a wider region.
• Theaperture enlargement film130 may be manufactured in various other structures in addition to the structure shown inFIG.2. For example,FIG.5 is a cross-sectional view schematically showing the configuration and operation of anaperture enlargement film130aaccording to another example embodiment. Referring toFIG.5, theaperture enlargement film130amay include a firstgrating layer133adisposed to face the light exiting surface of the spatiallight modulator120, thelight guide layer132 disposed on the firstgrating layer133a, and a secondgrating layer133bdisposed on thelight guide layer132. Thelight guide layer132 is disposed between the firstgrating layer133aand the secondgrating layer133b. The firstgrating layer133aand the secondgrating layer133bmay include various types of surface gratings or volume gratings. For example, the firstgrating layer133aand the secondgrating layer133bmay have different periodic grating patterns in the size, height, period, duty ratio, and shape from thegrating layer133 illustrated inFIG.2.
• Theaperture enlargement film130amay be disposed such that the firstgrating layer133afaces the light exiting surface of the spatiallight modulator120. A light beam transmitted from theaperture121 of the spatiallight modulator120 is first incident perpendicularly on the lower surface of the firstgrating layer133a. The firstgrating layer133amay be configured to diffract an incident light that is incident perpendicularly on the lower surface. For example, the firstgrating layer133amay be configured to 0th diffract a portion of the incident light that is incident perpendicularly on the lower surface and travel in a direction parallel to the direction normal to the upper surface. Therefore, the traveling direction of a light beam that is 0th diffracted by the firstgrating layer133adoes not change. Also, the firstgrating layer133amay be configured to 1st diffract a portion of the incident light that is incident perpendicularly on the lower surface and travel in an inclined direction with respect to the upper surface.
• The light beam that is 0th diffracted by the firstgrating layer133amay be incident perpendicularly on the upper surface of thelight guide layer132, and the light beam that is 1st diffracted may be obliquely incident on the upper surface of thelight guide layer132. The secondgrating layer133bis disposed on the upper surface of thelight guide layer132. The secondgrating layer133bmay be configured to propagate a portion of the incident light that is incident on the lower surface in the direction parallel to the direction normal to the upper surface. Therefore, the light beam perpendicularly incident on the upper surface of thelight guide layer132 from the firstgrating layer133ais emitted through the secondgrating layer133bwithout changing the traveling direction. A portion of the light beam obliquely incident on the upper surface of thelight guide layer132 from the firstgrating layer133ais emitted in the direction parallel to the direction normal to the upper surface of the secondgrating layer133bthrough the secondgrating layer133b. The remaining portion of the light beam obliquely incident on the upper surface of thelight guide layer132 from the firstgrating layer133ais totally reflected from the upper surface of thelight guide layer132 and travels in a lateral direction along the inside of thelight guide layer132. In this process, a portion of the light beam is emitted through the secondgrating layer133bwhenever the light beam is incident on the upper surface of thelight guide layer132.
• Therefore, the light beam incident on theaperture enlargement film130ais divided into a plurality of light beams −L2, −L1, L0, +L1, and +L2 and is emitted from theaperture enlargement film130a. The thickness of thelight guide layer132 may be selected such that the plurality of light beams −L2, −L1, L0, +L1, and +L2 overlap at least partially. Then, the plurality of light beams −L2, −L1, L0, +L1, and +L2 emitted from theaperture enlargement film130amay be viewed as one enlarged light beam. As a result, theaperture enlargement film130amay enlarge the beam diameter of the light beam incident from theaperture121 of the spatiallight modulator120. Further, because the intensity of the light beam L0 is greater than the intensity of the surrounding light beams −L1 and +L1, and the intensity of the light beams −L1 and +L1 is greater than the intensity of the surrounding light beams −L2 and +L2, the light beam enlarged by theaperture enlargement film130amay have a shape similar to the Gaussian distribution in which the intensity decreases from the center to the periphery.
• FIG.6 is a cross-sectional view schematically showing the configuration and operation of anaperture enlargement film130baccording to another example embodiment. Referring toFIG.6, theaperture enlargement film130bmay include a thirdgrating layer133c, thelight guide layer132, and a fourthgrating layer133d. Thelight guide layer132 is disposed between the thirdgrating layer133cand the fourthgrating layer133d. The thirdgrating layer133cand the fourthgrating layer133dmay have different periodic grating patterns in the size, height, period, duty ratio, and shape from the first and second grating layers133aand133bshown inFIG.5.
• Theaperture enlargement film130bmay be disposed such that the thirdgrating layer133cfaces the light exiting surface of the spatiallight modulator120. Then, a light beam transmitted from eachaperture121 of the spatiallight modulator120 is first incident perpendicularly on the lower surface of the thirdgrating layer133c. The thirdgrating layer133cmay be configured to transmit an incident light that is incident perpendicularly on the lower surface as is. Accordingly, the light beam incident on the lower surface of the thirdgrating layer133cmay be incident perpendicularly on the lower surface of the fourthgrating layer133dthrough thelight guide layer132. In addition, the thirdgrating layer133cmay be configured to reflect a portion of an incident light obliquely incident on the upper surface in a direction perpendicular to the upper surface.
• The fourthgrating layer133dmay 0th and 1st diffract the incident light perpendicularly incident on the lower surface to travel in different directions. For example, the light beam that is 0th diffracted by the fourthgrating layer133dmay be emitted in a direction parallel to the direction normal to the upper surface of the fourthgrating layer133d, and the light beam that is 1st diffracted may obliquely travel toward thelight guide layer132. Then, the light beam that is 1st diffracted by the fourthgrating layer133dtravels in a lateral direction inside thelight guide layer132 through total reflection.
• In a process of traveling inside thelight guide layer132 in the lateral direction, a portion of the light beam may be diffracted by the upper surface of the thirdgrating layer133cand again be incident perpendicularly on the lower surface of the fourthgrating layer133d. The light beam incident on theaperture enlargement film130bfrom the spatiallight modulator120 is divided into the plurality of light beams −L2, −L1, L0, +L1, and +L2 in this manner, and is output from theaperture enlargement film130b.
• In addition,FIG.7 is a cross-sectional view schematically showing the configuration and operation of anaperture enlargement film130caccording to another example embodiment. Referring toFIG.7, theaperture enlargement film130cmay include a fifthgrating layer133e, a fourthgrating layer133d, and thelight guide layer132 disposed between the fifthgrating layer133eand the fourthgrating layer133d.
• A light beam transmitted from eachaperture121 of the spatiallight modulator120 is first incident perpendicularly on the lower surface of the fifthgrating layer133e. The fifthgrating layer133emay be configured to 0th diffract a portion of the incident light that is incident perpendicularly on the lower surface and travel in a direction parallel to the direction normal to the upper surface of the fifthgrating layer133e. Also, the fifthgrating layer133emay be configured to 1st diffract a portion of the incident light that is incident perpendicularly on the lower surface and travel in an inclined direction with respect to the upper surface of the fifthgrating layer133e. Then, the light beam that is 0th diffracted by the fifthgrating layer133emay be incident perpendicularly on the lower surface of the fourthgrating layer133d, and the light beam that is 1st diffracted may be obliquely incident on the upper surface of thelight guide layer132.
• In addition, the fifthgrating layer133emay be configured to diffract a portion of the incident light that is obliquely incident on the upper surface and travel in the direction parallel to the direction normal to the upper surface. There is a common point between the fifthgrating layer133eillustrated inFIG.7 and the firstgrating layer133aillustrated inFIG.5 in that the 0th order diffracted light in the incident light incident perpendicularly on the lower surface travels in the direction perpendicular to the upper surface, and the 1st order diffracted light travels in the inclined direction with respect to the upper surface. However, the firstgrating layer133ais different from the fifthgrating layer133ein that the firstgrating layer133adoes not diffract the incident light obliquely incident on the upper surface in the direction normal to the upper surface. In addition, the thirdgrating layer133cillustrated inFIG.6 is different from the fifthgrating layer133ein that the incident light incident perpendicularly on the lower surface does not travel in the inclined direction with respect to the upper surface. To this end, the fifthgrating layer133emay have a periodic grating pattern different from the firstgrating layer133aand the thirdgrating layer133cin the size, height, period, duty ratio, shape, etc.
• The fourthgrating layer133dillustrated inFIG.7 is the same as the fourthgrating layer133dillustrated inFIG.6. Accordingly, a portion of the incident light incident perpendicularly on the lower surface of the fourthgrating layer133dis emitted in the direction parallel to the direction normal to the upper surface, and the remaining portion obliquely travels in the lateral direction along thelight guide layer132. In a process of traveling inside thelight guide layer132 in the lateral direction through total reflection, a portion of the light beam may be diffracted by the upper surface of the fifthgrating layer133eand again incident perpendicularly on the lower surface of the fourthgrating layer133d. The light beam incident on theaperture enlargement film130cfrom the spatiallight modulator120 is divided into a plurality of light beams −L3, -L2, −L1, L0, +L1, +L2, and +L3 in this manner, and is output from theaperture enlargement film130c.
• In addition,FIG.8 is a cross-sectional view schematically showing the configuration and operation of anaperture enlargement film130daccording to another example embodiment. Referring toFIG.8, theaperture enlargement film130dmay include the fifthgrating layer133eand thelight guide layer132 disposed on the upper surface of the fifthgrating layer133e. Theaperture enlargement film130dmay be disposed such that the fifthgrating layer133efaces the light exiting surface of the spatiallight modulator120. In addition, theaperture enlargement film130dmay further include thesubstrate131 for supporting the fifthgrating layer133eand thelight guide layer132 such that thelight guide layer132 and the fifthgrating layer133edo not bend. For example, thesubstrate131 may be disposed on the lower surface of the fifthgrating layer133e.
• The fifthgrating layer133eillustrated inFIG.8 is the same as the fifthgrating layer133eillustrated inFIG.5. Therefore, a portion of a light beam transmitted from eachaperture121 of the spatiallight modulator120 is 0th order diffracted on the lower surface of the fifthgrating layer133eand is perpendicularly incident on the lower surface of thelight guide layer132. The light beam perpendicularly incident on the lower surface of thelight guide layer132 passes through thelight guide layer132 as is, and is emitted in a direction normal to the upper surface of thelight guide layer132. Then, the remaining portion of the light beam transmitted from eachaperture121 of the spatiallight modulator120 is 1st diffracted on the lower surface of the fifthgrating layer133eand obliquely travels in the lateral direction along thelight guide layer132.
• In a process of traveling inside of thelight guide layer132 in the lateral direction through total reflection, a portion of the light beam may be diffracted by the upper surface of the fifthgrating layer133eand again be incident perpendicularly on the lower surface of thelight guide layer132. The light beam incident on theaperture enlargement film130dfrom the spatiallight modulator120 is divided into the plurality of light beams −L2, -L1, L0, +L1, and +L2 in this way, and is output from theaperture enlargement film130d.
• FIG.9A is a configuration diagram schematically showing a configuration of aholographic display apparatus200 according to another example embodiment. Referring toFIG.9A, theholographic display apparatus200 includes all of the components of theholographic display apparatus100 shown inFIG.1, and may further include a Gaussianapodization filter array210 which is disposed to face the light exiting surface of the spatiallight modulator120. For example, the Gaussianapodization filter array210 may be disposed between the spatiallight modulator120 and theaperture enlargement film130.
• As described above, thebacklight unit110 provides a collimated uniform coherent illumination light to the spatiallight modulator120. For example, the illumination light incident on the spatiallight modulator120 has a uniform intensity distribution. In addition, a light beam passing through theaperture121 of the spatiallight modulator120 also has a uniform intensity distribution. Accordingly, in the case of the example embodiment shown inFIG.1, the intensity distribution of the light beam enlarged by theaperture enlargement film130 may be a stepwise distribution, not a curved Gaussian distribution.
• The Gaussianapodization filter array210 may be configured to convert the uniform intensity distribution of the light beam emitted from theaperture121 of the spatiallight modulator120 into the curved Gaussian distribution. The Gaussianapodization filter array210 may include a plurality of Gaussian apodization filters arranged two-dimensionally. The Gaussian apodization filters may correspond one-to-one with theapertures121 of the spatiallight modulator120, respectively. Then, the intensity of each light beam that passes through the Gaussianapodization filter array210 and is incident on theaperture enlargement film130 may have the curved Gaussian distribution. Therefore, the intensity distribution of each light beam enlarged by theaperture enlargement film130 may also have the curved Gaussian distribution.
• For example, the Gaussian apodization filter may be a reverse apodizing filter with light reflection coating or light absorption coating. In the Gaussian apodization filter, the light reflection coating or the light absorption coating may be formed to have the highest transmittance in the center and a transmittance that gradually reduces in the radial direction such that the intensity distribution of a transmitted light may have a Gaussian profile. For example, the Gaussian apodization filter may be formed by coating a reflective metal such that the coating thickness gradually increases from the center toward the periphery in the radial direction. The size of the Gaussian apodization filter may be the same as the pixel size of the spatiallight modulator120.
• The Gaussianapodization filter array210 may be provided in the form of a separate layer or a separate film, but may be integrally formed with a color filter array of the spatiallight modulator120. For example, in a process of manufacturing the color filter array of the spatiallight modulator120, the Gaussianapodization filter array210 may be integrally formed on the surface of the color filter array by coating the reflective metal on the surface of each color filter corresponding to each pixel of the spatiallight modulator120 in the manner as described above.
• FIG.9B is a configuration diagram schematically showing a configuration of aholographic display apparatus200aaccording to another example embodiment. Referring toFIG.9B, theholographic display apparatus200aincludes all of the components of theholographic display apparatus100 shown inFIG.1, and may further include the Gaussianapodization filter array210 which is disposed to face the light entering surface of the spatiallight modulator120. For example, the Gaussianapodization filter array210 may be disposed between thebacklight unit110 and the spatiallight modulator120.
• Compared to theholographic display apparatus200 shown inFIG.9A, theholographic display apparatus200ashown inFIG.9B differs only in the position of the Gaussianapodization filter array210. In the example embodiment shown inFIG.9B, the Gaussianapodization filter array210 generates an illumination light of a uniform intensity emitted from thebacklight unit110 into a plurality of light beams having an intensity distribution in the form of a Gaussian distribution. A plurality of light beams having the intensity distribution in the form of the Gaussian distribution may be respectively incident on the correspondingapertures121 of the spatiallight modulator120. Then, each light beam passing through theaperture121 of the spatiallight modulator120 and incident on theaperture enlargement film130 may have an intensity of a curved Gaussian distribution. Therefore, the intensity distribution of each light beam enlarged by theaperture enlargement film130 may also have a curved Gaussian distribution.
• FIG.10A is a configuration diagram schematically showing a configuration of aholographic display apparatus300 according to another example embodiment. Referring toFIG.10A, theholographic display apparatus300 includes all of the components of theholographic display apparatus200 shown inFIG.9A, and may further include aprism array310. For example, theprism array310 may be disposed between the Gaussianapodization filter array210 and theaperture enlargement film130. The Gaussianapodization filter array210 may be disposed to face the light entering surface of the spatiallight modulator120 as shown inFIG.9B or may be omitted as shown inFIG.1. In this case, theprism array310 may be disposed between the spatiallight modulator120 and theaperture enlargement film130.
• FIG.10B is a configuration diagram schematically showing a configuration of aholographic display apparatus300aaccording to another example embodiment. Compared to theholographic display apparatus300 shown inFIG.10A, theholographic display apparatus300ashown inFIG.10B differs only in the position of theprism array310. For example, referring toFIG.10B, theprism array310 may be disposed to face the light exiting surface of theaperture enlargement film130.
• Theprism array310 may include a plurality of prisms that allow incident light to travel in different directions. For example,FIG.11 shows an arrangement of a plurality of prisms P1, P2, and P3 of theprism array310 of theholographic display apparatuses300 and300ashown inFIGS.10A and10B. Referring toFIG.11, theprism array310 may be divided into a plurality ofunit regions310aarranged two-dimensionally. Eachunit region310amay include the plurality of prisms P1, P2, and P3 that allow incident light to travel in different directions. Accordingly, theprism array310 may include the plurality of prisms P1, P2, and P3 arranged repeatedly. For example, among the plurality of prisms P1, P2, and P3, the first prism P1 may be configured to change the traveling direction of the incident light to a first direction, the second prism P2 may be configured to change the traveling direction of the incident light to a second direction different from the first direction, and the third prism P3 may be configured to change the traveling direction of the incident light in a third direction different from the first and second directions.
• InFIG.11, eachunit region310aincludes prisms of a 1×3 arrangement, but is not necessarily limited thereto. As described later, the prism arrangement in eachunit region310amay be differently selected according to the number of holographic images of different viewpoints simultaneously provided by theholographic display apparatuses300 and300a. For example, when theholographic display apparatuses300 and300aprovide four holographic images of different viewpoints in the horizontal direction, eachunit region310amay include prisms of a 1×4 arrangement. Further, when theholographic display apparatuses300 and300aprovide four holographic images of different viewpoints in the transverse direction and the longitudinal direction, eachunit region310amay include prisms of a 2×2 arrangement.
• Each of the prisms P1, P2, and P3 of theprism array310 may correspond one-to-one with each pixel of the spatiallight modulator120. For example,FIG.12 shows an arrangement of a plurality of pixels of the spatiallight modulator120 of theholographic display apparatuses300 and300ashown inFIGS.10A and10B. Referring toFIG.12, the spatiallight modulator120 includes the plurality of pixels that are two-dimensionally arranged. In addition, the spatiallight modulator120 may include a plurality ofunit regions120aarranged two-dimensionally. Theunit regions120aof the spatiallight modulator120 may have the same arrangement form as theunit regions310aof theprism array310. For example, when theunit region310aof theprism array310 includes the prisms P1, P2, and P3 of a 1×3 arrangement, theunit region120aof the spatiallight modulator120 may include pixels X1, X2, and X3 of the 1×3 arrangement.
• The plurality of pixels X1, X2, and X3 may operate to reproduce holographic images having different viewpoints. For example, among the plurality of pixels X1, X2, and X3, the first pixel X1 may operate to reproduce a holographic image of a first viewpoint, the second pixel X2 may operate to reproduce a holographic image of a second viewpoint different from the first viewpoint, and the third pixel X3 may operate to reproduce a holographic image of a third viewpoint different from the first and second viewpoints. To this end, theimage processor150 may be configured to provide a first hologram data signal for the holographic image of the first viewpoint to the first pixel X1, a second hologram data signal for the holographic image of the second viewpoint to the second pixel X2, and a third hologram data signal for the holographic image of the third viewpoint to the third pixel X3.
• InFIG.12, eachunit region120aonly includes the pixels of the 1×3 arrangement, but is not necessarily limited thereto. The pixel arrangement in eachunit region120amay be differently selected according to the number of holographic images of different viewpoints to be simultaneously provided by theholographic display apparatuses300 and300a. For example, when theholographic display apparatuses300 and300aprovide four holographic images of different viewpoints in the horizontal direction, eachunit region120aonly includes pixels of a 1×4 arrangement. In addition, when theholographic display apparatuses300 and300aprovide four holographic images of different viewpoints in the horizontal and vertical directions, eachunit region120amay include pixels of a 2×2 arrangement.
• In the configuration of theprism array310 and the spatiallight modulator120 illustrated inFIGS.11 and12, the first pixel X1 may be disposed to face the first prism P1, the second pixel X2 may be disposed to face the second prism P2, and the third pixel X3 may be disposed to face the third prism P3. Then, the holographic image of the first viewpoint reproduced through the first pixel X1 travels in the first direction by the first prism P1, the holographic image of the second viewpoint reproduced through the second pixel X2 travels in the second direction by the second prism P2, and the holographic image of the third viewpoint reproduced through the third pixel X3 travels in the third direction by the third prism P3. As a result, three holographic images having different viewpoints are focused on the focal plane of theFourier lens140 at different positions.
• For example,FIG.13 shows the distribution of light formed on the focal plane of theFourier lens140 by theholographic display apparatuses300 and300ashown inFIGS.10A and10B. Referring toFIG.13, the 0th order noise NO appears in the center of the focal plane of theFourier lens140. InFIG.13, a square indicated by a solid line is a boundary of a viewing window determined by a pixel period of the spatiallight modulator120. As described above, using theaperture enlargement film130 may prevent the high order noise N1 from appearing along the boundary of the viewing window. Then, the first holographic image signal S1 by the first pixel X1 and the first prism P1, the second holographic image signal S2 by the second pixel X2 and the second prism P2, and the third holographic image signal S3 by the third pixel X3 and the third prism P3 appear. Also, first complex conjugate image signal S1*, the second complex conjugate image signal S2*, and the third complex conjugate image signal S3* appear at symmetrical positions with respect to the first holographic image signal S1, the second holographic image signal S2, and the third holographic image signal S3 around on the 0th order noise NO.
• As illustrated inFIG.13, the first holographic image signal S1 whose travel direction changes by the first prism P1 and the third holographic image signal S3 whose travel direction changes by the third prism P3 may be located outside the boundary of the viewing window determined by the pixel period of the spatiallight modulator120. Accordingly, using theprism array310 may further enlarge the viewing window determined by the pixel period of the spatiallight modulator120 beyond the limit range of the viewing window, and an observer may view the holographic image in a wider region Further, because the high order noise N1 does not appear between the first holographic image signal S1 and the second holographic image signal S2 and between the second holographic image signal S2 and the third holographic image signal S3, when the observer's eye E moves from the first holographic image signal S1 to the second holographic image signal S2 or from the second holographic image signal S2 to the third holographic image signal S3, the observer may view a holographic image of a naturally changed viewpoint without being disturbed by high order noise N1.
• It should be understood that example embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each example embodiment should typically be considered as available for other similar features or aspects in other embodiments.
• While example embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.

Claims (20)

What is claimed is:

1. An aperture enlargement film comprising:

a light guide layer, and

a grating layer disposed on an upper surface of the light guide layer,

wherein the light guide layer and the grating layer are configured to transmit a 0th order diffracted light beam and a 1st order diffracted light beam among incident light beams,

wherein the grating layer is configured to transmit the 0th order diffracted light beam of a light beam vertically incident on the lower surface of the grating layer from the light guide layer in a direction perpendicular to an upper surface of the one grating layer, and is configured to reflect the 1st order diffracted light beam of the light beam incident on the lower surface of the grating layer from the light guide layer at an angle to propagate obliquely in the light guide layer,

wherein the grating layer transmits a portion of the 1st order diffracted light beam that is reflected by a lower surface of the light guide layer and obliquely incident on the one grating layer in the direction perpendicular to the upper surface of the one grating layer,

wherein a boundary of the transmitted 1st order diffracted light beam coincides with a boundary of the transmitted 0th order diffracted light beam or the transmitted 1st order diffracted light beam overlaps with the transmitted 0th order diffracted light beam based on a thickness of the light guide layer, and

wherein an intensity of the transmitted 0th order diffracted light beam is greater than the intensity of the transmitted 1st order diffracted light beam.

2. The aperture enlargement film ofclaim 1, wherein an intensity distribution of the enlarged light beam decreases from a center of the enlarged light beam to a periphery of the enlarged light beam.

3. The aperture enlargement film ofclaim 1, wherein a beam diameter of the enlarged light beam is greater than a beam diameter of each of the incident light beams.

4. The aperture enlargement film ofclaim 1, wherein a thickness of the light guide layer ranges from 1 μm to 5 μm.

5. The aperture enlargement film ofclaim 1, wherein the light guide layer is configured to obliquely propagate the second light beam from the one grating layer along an inside of the light guide layer based on total reflection.

6. The aperture enlargement film ofclaim 1, further comprising a substrate configured to support the light guide layer and the one grating layer such that the light guide layer and the one grating layer do not bend, and

wherein a refractive index of the light guide layer is greater than a refractive index of the substrate.

7. The aperture enlargement film ofclaim 1, further comprising a Gaussian apodization filter array disposed to face the lower surface of the light guide layer.

8. The aperture enlargement film ofclaim 7, wherein the Gaussian apodization filter array comprises a plurality of Gaussian apodization filters configured to convert an intensity distribution of a light beam into a curved Gaussian distribution.

9. The aperture enlargement film ofclaim 1, further comprising a prism array disposed to face the lower surface of the light guide layer or disposed to face a light exiting surface of the aperture enlargement film.

10. The aperture enlargement film ofclaim 9, wherein the prism array is divided into a plurality of unit regions that are two-dimensionally disposed, and

wherein each of the plurality of unit regions comprises a plurality of prisms configured to propagate an incident light in different directions.

11. An aperture enlargement film comprising:

a light guide layer;

a first grating layer disposed on an upper surface of the light guide layer; and

a second grating layer disposed on an lower surface of the light guide layer,

wherein the second grating layer is configured to transmit a light beam incident on a lower surface of the second grating layer,

wherein the first grating layer is configured to transmit a 0th order diffracted light beam in a direction perpendicular to an upper surface of the first grating layer and obliquely reflect a 1st order diffracted light beam toward the light guide layer,

wherein the second grating layer is further configured to reflect a portion of the 1st order diffracted light beam incident on an upper surface of the second grating layer in a direction perpendicular to the upper surface of the second grating layer,

wherein the first grating layer is further configured to transmit the portion of the 1st order diffracted light beam from the second grating layer,

wherein a boundary of the transmitted 1st order diffracted light beam coincides with a boundary of the transmitted 0th order diffracted light beam or the transmitted 1st order diffracted light beam overlaps with the transmitted 0th order diffracted light beam based on a thickness of the light guide layer, and

wherein an intensity of the transmitted 0th order diffracted light beam is greater than the intensity of the transmitted 1st order diffracted light beam.

12. The aperture enlargement film ofclaim 11, wherein the second grating layer is further configured to diffract the light beam incident on the lower surface of the second grating layer such that the diffracted light beam by the second grating layer obliquely travels with respect to the upper surface of the second grating layer.

13. The aperture enlargement film ofclaim 11, wherein an intensity distribution of the enlarged light beam decreases from a center of the enlarged light beam to a periphery of the enlarged light beam.

14. The aperture enlargement film ofclaim 11 wherein a beam diameter of the enlarged light beam is greater than a beam diameter of each of the incident light beams.

15. The aperture enlargement film ofclaim 11, wherein a thickness of the light guide layer ranges from 1 μm to 5 μm.

16. The aperture enlargement film ofclaim 11, wherein the light guide layer is configured to obliquely propagate the 1st order diffracted light beam from the first grating layer along an inside of the light guide layer based on total reflection.

17. The aperture enlargement film ofclaim 11, further comprising a Gaussian apodization filter array disposed to face the lower surface of the light guide layer.

18. The aperture enlargement film ofclaim 17, wherein the Gaussian apodization filter array comprises a plurality of Gaussian apodization filters configured to convert an intensity distribution of a light beam into a curved Gaussian distribution.

19. The aperture enlargement film ofclaim 11, further comprising a prism array disposed to face the lower surface of the light guide layer or disposed to face a light exiting surface of the aperture enlargement film.

20. The aperture enlargement film ofclaim 19, wherein the prism array is divided into a plurality of unit regions that are two-dimensionally disposed, and

wherein each of the plurality of unit regions comprises a plurality of prisms configured to propagate an incident light in different directions.

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