Beam expanding device for reflective spatial light modulator display

Abstract

An apparatus for achieving beam expansion without affecting the image quality of a reflective spatial light modulator (SLM), such as an LCOS matrix (10), comprises a polarization selective dispersion element (70) covering the SLM. The polarization selective dispersive element (70) is configured to be dispersive against light of a first polarization corresponding to the illumination polarization and non-dispersive against light of a second polarization corresponding to the image light. In an alternative embodiment, a modified LCOS matrix is provided in which a cover layer (113) between a pixel electrode (112) and a liquid crystal layer (110) and / or a surface of the pixel electrode is shaped to provide a reflected beam expansion effect such that collimated illumination incident on each pixel electrode (110) is reflected as diverging pixel image light.

Description

Technical Field

[0001] The present invention relates to displays and in particular to displays employing a reflective SLM such as an LCOS matrix for image generation. Background Art

[0002] Near-eye displays typically include an image projector that injects image light into a light guide. Even when projecting large field-of-view images, the projector needs to be small and light. For example, a reflective spatial light modulator (SLM) image generator with a Liquid Crystal on Silicon (LCOS) matrix is ​​commonly used for image modulation within the projector. A polarizing beam splitter (PBS) can be used to illuminate the LCOS.

[0003] The reflection from the LCOS matrix is ​​typically spectral along its direction, which requires various design considerations. Specifically, in order to uniformly illuminate and "fill" the entrance aperture of the light guide, the reflected light from each pixel should be divergent. However, to provide uniform illumination over a correspondingly large range of illumination angles would require large illumination optics, and this is especially true if the preferred illumination source is a scanning laser, where the illumination beam is typically a narrow beam that does not provide sufficient divergence. Summary of the invention

[0004] The present invention is a reflective SLM image generator with a beam expansion device and its components.

[0005] According to the teachings of an embodiment of the present invention, a beam-expanding liquid crystal on silicon (LCOS) chip for spatial light modulation is provided, the LCOS chip comprising: (a) a two-dimensional array of pixel electrodes; (b) a liquid crystal layer covering the pixel electrodes; and (c) a transparent electrode covering the liquid crystal layer, wherein the covering layer between the pixel electrode and the liquid crystal layer and / or the surface of the pixel electrode is configured to provide a reflective beam-expanding effect, so that collimated illumination incident on each of the pixel electrodes is reflected as divergent pixel image light.

[0006] According to another feature of an embodiment of the invention, the plurality of pixel electrodes are implemented using a concave reflective surface.

[0007] According to another feature of an embodiment of the present invention, the plurality of pixel electrodes are implemented using convex reflective surfaces.

[0008] According to another feature of an embodiment of the present invention, there is further provided a dispersive reflective cover layer disposed between the pixel electrode and the liquid crystal layer.

[0009] According to the teachings of an embodiment of the present invention, there is also provided an image generator, comprising: (a) the above-mentioned beam expansion LCOS chip; (b) an illumination device, which is deployed to illuminate the beam expansion LCOS chip, the illumination device comprising at least one light source and a scanning device, the scanning device comprising at least one scanning mirror, the at least one scanning mirror being deployed to scan the illumination spot along at least one direction across the beam expansion LCOS chip; and (c) a collimating optical device, which is deployed to collimate the image light reflected from the beam expansion LCOS chip.

[0010] According to the teachings of an embodiment of the present invention, there is also provided an image generator, comprising: (a) a polarization-modifying spatial light modulator (SLM), comprising a pixel array, for modifying the polarization of incident illumination of a first polarization based on pixel data loaded into the SLM to selectively rotate the first polarization toward a second polarization orthogonal to the first polarization; (b) an illumination device, the illumination device being disposed to illuminate the SLM with illumination of the first polarization; and (c) a polarization-selective dispersive element covering the SLM, the polarization-selective dispersive element being configured to be dispersive for light of the first polarization and substantially non-dispersive for light of the second polarization.

[0011] According to another feature of an embodiment of the invention, the illumination device comprises: at least one low etendue illumination source and a scanning device comprising at least one scanning mirror, the at least one scanning mirror being deployed for scanning the illumination spot in at least one direction across the SLM.

[0012] According to another feature of an embodiment of the invention, the polarization selective dispersive element includes a metasurface formed using elongated nanostructures.

[0013] According to another feature of an embodiment of the present invention, a polarization selective dispersion element includes: (a) a first layer, the first layer is formed of a birefringent material having a first refractive index along a first principal axis and a second refractive index along a second principal axis; and (b) a second layer, the second layer is formed of an isotropic optical material having a refractive index matching one of the first refractive index and the second refractive index, and an interface between the first layer and the second layer has a relief corresponding to a microlens array or a diffuser.

[0014] According to another feature of embodiments of the invention, the illumination device is configured to illuminate the entire SLM simultaneously.

[0015] According to another feature of an embodiment of the invention, the polarization selective dispersive element includes a metasurface formed using elongated nanostructures.

[0016] According to another feature of an embodiment of the present invention, a polarization selective dispersion element includes: (a) a first layer, the first layer is formed of a birefringent material having a first refractive index along a first principal axis and a second refractive index along a second principal axis; and (b) a second layer, the second layer is formed of an isotropic optical material having a refractive index matching one of the first refractive index and the second refractive index, and an interface between the first layer and the second layer has undulations corresponding to a microlens array or a diffuser. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is herein described, by way of example only, with reference to the accompanying drawings, in which:

[0018] Figure 1A is a schematic side view of a reflective SLM image generator constructed and operated in accordance with one aspect of the present invention, showing a polarization selective dispersive element for expanding an illumination beam of scanning laser illumination via a polarizing beam splitter (PBS) prism;

[0019] Figure 1B is with Figure 1A A similar view showing the path of image light reflected from the reflective SLM image generator and collimated toward the exit aperture;

[0020] Figure 1C yes Figure 1A A magnified view of the surrounded area shows the beam-broadening effect of the polarization-selective dispersive element on the illumination beam.

[0021] Figure 1D yes Figure 1B A magnified view of the surrounded area shows the non-dispersive effect of the polarization-selective dispersive element on the reflected image light.

[0022] Figure 2A and Figure 2B Based on birefringent materials Figures 1A to 1D Schematic side view of an implementation of a polarization selective dispersion element, showing the optical effects of the birefringent material on s-polarized light and p-polarized light respectively;

[0023] Figure 3A is a schematic side view of a portion of an LCOS matrix having contoured reflective pixel electrodes to provide a beam-expanding effect, constructed and operative in accordance with one aspect of the present invention;

[0024] Figure 3B is with Figure 3A similar schematic side view showing a modified transparent electrode for achieving enhanced electric field uniformity;

[0025] Figure 3C is with Figure 3A A similar schematic side view showing an embodiment with buried electrodes and a shaped dielectric dispersive reflector layer;

[0026] Figure 4 is a schematic diagram of steps (a) to (h) of an implementation of a production method for producing an LCOS matrix according to the principle of FIG. 3 .

[0027] Figure 5A and Figure 5B are schematic side and front views, respectively, of another aspect of the invention including scanning laser illumination of LCOS via a light guide;

[0028] Fig. 6A is with Figure 1A A similar view modified to perform flood illumination of the LCOS matrix; and

[0029] Fig. 6A is with Figure 5B A similar view is modified to perform flood illumination of the LCOS matrix. DETAILED DESCRIPTION

[0030] The present invention is a reflective SLM image generator with a beam expansion device and its components.

[0031] The principles and operation of an image generator according to the present invention may be better understood with reference to the drawings and accompanying description.

[0032] As an introduction, the present invention provides various methods for achieving beam expansion in a reflective SLM image generator (e.g., an LCOS-based image generator). In principle, beam expansion can be achieved by inserting a micro-lens array (MLA) or another diffuser at the image plane of the LCOS matrix. However, in practice, the structure of the LCOS matrix is ​​such that any additional optical elements applied on the LCOS matrix are sufficiently spaced apart from the effective image plane, which will distort the generated image and impair image quality.

[0033] The present invention provides two methods for achieving beam expansion without affecting the image quality of the LCOS matrix. According to a first aspect of the present invention, a polarization selective dispersive element is deployed to cover the SLM, wherein the polarization selective dispersive element is configured to be dispersive for light of a first polarization (corresponding to the illumination polarization) and substantially non-dispersive for light of a second polarization (corresponding to the modulated light of the image). According to an alternative aspect of the present invention, a modified LCOS matrix is ​​provided, in which the cover layer between the pixel electrode and the liquid crystal layer and / or the surface of the pixel electrode is configured to provide a reflective beam expansion effect, so that the collimated illumination incident on each pixel electrode is reflected as divergent pixel image light. Another aspect of the present invention relates to a compact scanning laser illumination device using a light guide. These aspects of the present invention will now be described in detail with reference to the various drawings.

[0034] Polarization Selective Dispersion Element

[0035] Turning now to the first aspect of the present invention, Figure 1A and Figure 1B An image generator is shown that employs a polarization modifying spatial light modulator (SLM) 10 (e.g., an LCOS matrix) having an array of pixels for modifying the polarization of incident illumination of a first polarization to selectively rotate the first polarization toward a second polarization orthogonal to the first polarization according to the pixels loaded into the SLM. The SLM 10 is shown only schematically here, and various associated components including power supplies, data processing components, data storage components, drivers, and communication components are well known to those of ordinary skill in the art and are omitted here for simplicity of presentation. An illumination device is deployed to illuminate the SLM 10 with illumination of a first polarization.

[0036] According to this aspect of the invention, the polarization selective dispersive element 70 covering the SLM 10 is configured to selectively dissipate light of a first polarization (eg, s-polarized light illuminating the SLM, such as Figure 1A As shown in FIG. 1 ), the light of the second polarization (eg, the p-polarization modulated image light reflected from the SLM 10, as shown in FIG. 1 ) is dispersed. Figure 1B This ensures that the angular spread of the illumination is expanded before reaching the SLM, while the image light from each pixel is not distorted by element 70, thereby maintaining image quality.

[0037] Various particularly preferred implementations of the present invention are specifically directed to illumination devices that employ low etendue illumination sources, where etendue is the product of beam width and the divergence angle of the beam. In the present example, the product of beam width and beam divergence angle can be converted to the product of the illumination spot size of the same beam at the image plane (i.e., the illumination spot size at the LCOS, which may be, for example, about 50 microns) and the illumination size at the aperture plane (which is derived from the divergence angle and may be, for example, about 30 degrees). In a typical implementation of the present invention, the etendue of the image illumination returned from the LCOS may need to be about 50 microns x 30 degrees = 1,500 microns. degrees.

[0038] In the context of the present invention, the term "low etendue illumination" or "low etendue illumination source" refers to illumination whose etendue is insufficient to fill the exit aperture, i.e., a predefined illumination spot on the LCOS, the illumination from the same beam will not fill the desired aperture (entrance of the waveguide).

[0039] Examples of light sources that exhibit low etendue include illumination derived from:

[0040] Lasers: Typically very narrow and low divergence, typically producing an etendue of about 100 microns.

[0041] SLED (can be thought of as a laser without resonance): A narrow light source with moderate divergence, typically producing an etendue of about 200 microns.

[0042] Micro-LEDs: Small (narrow) and have a wider divergence, typically producing an etendue of about 500 microns.

[0043] In each of these examples, the light source itself is insufficient to fill the exit aperture without the various beam expansion (etendue increase) solutions of the present invention, and thus the light source is referred to in context as a "low etendue illumination source." The various beam expansion solutions described herein increase etendue sufficiently to allow the illumination device to illuminate the desired spot size on the LCOS and simultaneously fill the exit aperture, which typically corresponds to the approximately 1,500 micrometers.degrees noted above.

[0044] Thus, in a particularly preferred but non-limiting exemplary implementation shown herein, the illumination device comprises at least one laser light source 56 and a scanning device comprising at least one scanning mirror 60, the at least one scanning mirror 60 being deployed for scanning the illumination spot in at least one direction across the SLM 10. The low dispersion of the laser beam facilitates precise selective illumination of the SLM, which has been found to provide many advantages, including but not limited to: energy savings, where only a sub-portion of the display needs to be active at certain times; enhanced dynamic range, where the overall output is modulated in a region-by-region manner by the laser illumination and further modulated by the pixels of the SLM; and concave or other dynamic resolution adjustment, where full resolution is provided by the SLM only in certain regions of interest defined by the image content or by the user's current viewing direction, while a lower resolution peripheral image is generated only by modulation of the scanning laser. Laser scanning on the LCOS matrix also facilitates rapid and continuous color scanning on the LCOS matrix during a single scanning cycle (e.g., as described in PCT Patent Application Publication No. WO2019 / 111237A1), thereby avoiding color break-up.

[0045] For more details, refer to Figure 1A , laser light 56 ​​is directed by lens 58 onto scanning mirror 60 where it is scanned through a series of positions in one or preferably two dimensions (as represented by the different positions of beams 62). These beams pass through polarizing beam splitter (PBS) 50 and are focused by reflective lens 52 onto SLM 10 (via reflection at PBS 50 in this example - phase plate omitted). The scanned beams pass through polarization selective dispersive element 70. Figure 1C A magnified view is shown to illustrate that incident S polarization is diffused and scattered into a predetermined angular range. For example: a typical polarization selective dispersion element at 0.7 mm from a 5 micron pixel LCOS10 generates a 15 degree divergence (as required for the system to achieve full aperture illumination). This will illuminate a spot about 35 pixels wide, which is acceptable and, in many cases, is required for selective illumination when the matrix (LCOS) pixels produce fine image resolution. Although other sizes are possible, such spot illumination is practical for this application.

[0046] Figure 1B The optical path of the reflected light beam from the LCOS is shown. The divergent light beams from several specific pixels are shown here. Figure 1D In an enlarged view it is shown that the reflected P-polarized light beam passes through the polarization selective surface without being diffused.Thus, the projected image has a high resolution defined by the LCOS resolution and the exit aperture 26 is fully illuminated.

[0047] As a non-limiting but particularly preferred embodiment, the collimating optics may be implemented as a pancake lens 72 (also called "polarization catadioptric optics") based on a wave plate combined with a partial reflector and a polarizing reflector to generate a light path that passes through the lens multiple times. This option may be preferred due to its compactness, but other collimating optics, for example based on reflective lenses or refractive lenses, may also be used, all of which are known in the art.

[0048] Without limiting the broad scope of this aspect of the invention in any way, the invention will be illustrated with reference to two specific techniques which are considered suitable for realizing a polarization selective dispersive element having the described properties. A first exemplary implementation employs a meta-surface formed using elongated nanostructures.

[0049] Nanostructure-based optical elements with a pattern periodicity smaller than the wavelength of light are called metasurfaces. By employing elongated nanostructures, such surfaces can produce polarization-dependent manipulation of a transmitted light beam. Gradual changes in this fine structure (depth, width, shape or a combination of these parameters) produce phase changes of the light beam and thereby deflect the propagation direction of the light beam in addition to polarization manipulation.

[0050] Such an element can be modified to create a polarization-selective surface diffuser, where the S polarization is diffused (spread) to a predetermined angle, while the P polarization passes through undisturbed.

[0051] Design considerations and production methods for metasurfaces with such properties are described in various textbooks known in the art. As an example, one can refer to the article Zeyang Liu, Danyan Wang, Hao Gao, Moxin Li, Huixian Zhou, Cheng Zhang, “Metasurface-enabled augmented reality display: a review,” Adv. Photon. 5(3)034001 (May 15, 2023) https: / / doi.org / 10.1117 / 1.AP.5.3.034001 Finding the appropriate information, for example, referring to Figure 3, shows the principles that can be used to manipulate polarization, while Figure 6(e) shows that manipulating polarization can be combined with control of refractive / diffractive properties.

[0052] Figure 2A and 2BThe second method of implementing the polarization selective dispersion element 70 shown uses birefringent materials. Specifically, the element 70 is formed here by a first layer 82, which is formed of a birefringent material having a first refractive index along a first principal axis and a second refractive index along a second principal axis. The second layer 80 is formed of an isotropic optical material having a refractive index that matches one of the first refractive index and the second refractive index. The interface 86 between the first layer 82 and the second layer 80 is formed using a relief (i.e., a surface shape or texture) corresponding to a microlens array or a diffuser.

[0053] Figure 2A and Figure 2B The same structure is shown, but the first layer 82 is shaded differently to convey the different polarizations of light in use: S polarization ( Figure 2A ) and P polarization ( Figure 2B ) different optical properties when illuminated by light. The material in layer 80 is isotropic, so the refractive index of layer 80 is independent of the polarization of the light, while the birefringent material in layer 82 has different refractive indices (also called the principal axes "ordinary" and "extraordinary") for different polarizations. This is schematically shown in the two figures as different shading of the first layer 82.

[0054] The interface 86 between layer 80 and layer 82 may include an MLA structure or a diffuse pattern. By selecting the material of layer 80 to have a refractive index equal to the refractive index of the principal axis of the P polarization in layer 82, the P polarized light beam will encounter the interface 86 as an optical continuum and thus pass through the structure without beam expansion ( Figure 2B ). In contrast, when S-polarized light passes through the element ( Figure 2A ), the difference in refractive index causes the interface to act as an MLA or diffuser, thereby refracting and / or dispersing the light beam.

[0055] Beam expansion LCS matrix

[0056] Another aspect of the present invention provides an alternative method for beam expansion without compromising the image quality of the LCOS matrix based on manufacturing an LCOS chip with a specifically modified internal structure, which will now be referred to FIG. 3A to FIG. 4 Describe this.

[0057] Specifically, Figure 3A As shown, a beam expansion liquid crystal on silicon (LCOS) chip for spatial light modulation is implemented using a two-dimensional array of pixel electrodes 112, a liquid crystal layer 110 covering the pixel electrodes, and a transparent electrode 106 covering the liquid crystal layer. According to this aspect of the invention, the cover layer between the pixel electrode and the liquid crystal layer and / or the surface of the pixel electrode is configured to provide a reflective beam expansion effect, so that the collimated illumination incident on each of the pixel electrodes is reflected as divergent pixel image light. Various options for achieving these characteristics will now be described in detail.

[0058] exist Figure 3A In the cross-sectional view of FIG. 1 , the structure of the LCOS matrix is ​​preferably as follows. Under the transparent window 104 there is a transparent conductive electrode 106. Under this layer is an alignment coating 108a which determines the static orientation of the liquid crystal molecules. The liquid crystal is a layer 110 which has a thickness of, for example, a few microns and under the layer 110 is another alignment layer 108b.

[0059] The pixel electrodes 112 are optically reflective and are located above the wafer carrier 114. According to a first implementation option, these electrodes are concave so that when a low divergence light beam 116 (solid arrow) is incident on these electrodes, the low divergence light beam 116 is reflected at a larger divergence angle 118. For a twenty degree reflective divergence (typical requirement) in a filling medium 109 (which can be the same as 108b or can be the liquid crystal 110 itself) with a refractive index of the order of 1.5 and a pixel size of a few microns, the depression (depression) of the curved electrode is on the order of a few tenths of a micron or less. Therefore, in many cases, the impact on the electric field uniformity and LCOS contrast can be ignored.

[0060] Figure 3B An alternative is shown in which the transparent electrode 106b is periodically bent to compensate for the bent electrode 112 and thereby achieve better field uniformity.

[0061] Figure 3C Another alternative is shown where the electrode 112B is embedded and reflectivity is achieved by a periodically shaped layer 113, which is preferably a dielectric. This layer may deflect the light by a refraction or diffraction pattern so as to reflect dispersively, i.e. reflect light with a greater angular spread than that incident on the layer. Using a dielectric (non-conductive) layer in place of the periodically shaped layer 113 will not generally significantly perturb the electric field between the electrode 106 and the electrode 112B. If it is found necessary to perform any correction to the electric field, this can be done in a manner similar to Figure 3B way to complete it.

[0062] As is known in the art, the alignment layers 108a and 108b may be implemented in various ways depending on the liquid crystal activation method.

[0063] The reflective electrode 112 or layer 113 may be concave, convex, diffractive or diffuse (random pattern). Optionally, the selected surface geometry may additionally be tilted to compensate for non-telecentric beams (either in incident or reflected mode).

[0064] Various methods can be used to generate Figure 3A and Figure 3BThe most practical method can be based on multi-step photolithography. Figure 4 Steps (a) to (h) in schematically illustrate examples. Step (a) shows a wafer coated with a photoresist developed for the openings (pre-processed for the rest of the system). Step (b) shows that these openings are used to etch and apply the conductors into the wafer (another conductor may be located below, not shown for clarity). Step (c) shows the photoresist applied and developed for the electrode itself, while step (d) shows the layout coated with electrode material (shown between the photoresist gaps). Step (e) shows the layout of the electrodes and conductors left after the photoresist has been removed. It should be understood that the above photolithography process can be performed with a positive photoresist or a negative photoresist. Alternatively, as known in the art, the electrode pattern can be achieved by applying an electrode pattern and then etching the electrode pattern.

[0065] At this stage, the layout can be heated to a high temperature, partially melting the electrodes so that surface tension causes bending, as shown in step (g). Alternatively, a photoresist can be developed on top of the electrodes having the shape shown in step (f). Applying an etching process to the form will imprint the shape onto the electrodes (as in step (g)). Alternatively, a patterned etch can be performed on the electrodes, resulting in a concave upper surface for each electrode, corresponding to the upper surface in step (g). Figure 3A The form of the electrode shown in corresponds to.

[0066] Step (h) shows the system after covering with liquid crystal, transparent electrodes and other layers (as described above with reference to Figure 3A This structure is functionally equivalent to Figure 3A But in this example, the electrodes are protruding to serve the same purpose of dispersing the light beam without compromising the image quality.

[0067] Can be Figure 1A and Figure 1B These beam expansion LCOS chip configurations are advantageously used in an image projector configuration, which are deployed as shown at LCOS10 and do not require element 70. Then, Figure 1A The illumination light remains at a low divergence until it reaches the LCOS10 surface, while the reflected image light has a higher divergence (e.g. Figure 1B ), until the reflected image light reaches the collimating optics 72, thereby providing sufficient field angle width to fill the exit aperture 26 corresponding to the entrance optical aperture of the display's light guide.

[0068] Functionally similar to Figure 1A and Figure 1BThe configuration of the configuration can be implemented in a more compact configuration, in a more compact configuration, such as Figure 5A and Figure 5B As shown, the PBS is replaced by multiple polarizers in a plate-like light guide. In this case, when a scanning laser is used as the illumination source, the illumination is linear and scanned in only one direction, thus reducing complexity compared to a two-axis scanning device. Figure 5A and Figure 5B Side and front views, respectively, of an illumination and projector system according to the present method.

[0069] Specifically, light from the laser 56 is reflected from a uniaxial (one-dimensional) scanning mirror 150 onto a curved reflector 152, which is preferably a parabolic reflector with a focus at the scanning mirror. The illumination optics (not shown) and the curved mirror 152 (the lens is not shown and the mirror can be replaced by a lens) are preferably configured to generate a parallel scanning beam 153. The scanning beam 153 enters the plate 156 through a coupling prism or mirror 154 to propagate by total internal reflection. The partial reflector 158 within the plate 156 gradually partially reflects one polarization (and transmits for the orthogonal polarization) onto the reflective SLM (e.g., LCOS) 10.

[0070] As is apparent from this configuration, each scanning beam 153 illuminates light across the modulator 10. The power of the laser 56 and the modulation of the matrix 10 are synchronized to generate the desired image, for example, according to the method described in the PCT patent application publication No. WO2019 / 111237A1 cited above. The modulated image light reflected from the LCOS 10 has an orthogonal polarization and will therefore pass through the plate 156 and the face 158 to be filtered by the polarizer 160. The filtered image is collimated by the optical device 162 (which can use a refractive optical device, a reflective optical device, or a pancake lens, as described above) to enter the waveguide through the aperture 26. The various beam expansion configurations and methods described above can be used in Figure 5A and Figure 5B is implemented in the configuration.

[0071] Although the description so far has focused on the case of scanning laser illumination, it should be noted that various solutions for angular beam expansion (also known as increasing optical etendue) are also applicable to illumination devices that are configured to illuminate the entire SLM simultaneously (also known as flood illumination). Fig. 6A and Figure 6B Two examples of flood illumination are shown by expanding light from a single narrow illumination source 168 (e.g., a laser, a superluminescent light emitting diode (SLED), or a collimated micro-LED). Fig. 6A In the case of Figure 1A A modification of the PBS prism-based illumination optics in which the scanning mirror is replaced by a convex (diverging) mirror or other beam expander to simultaneously illuminate the entire LCOS 10, exemplary simultaneous illumination beams are shown as divergent beam 172 and collimated beam 174. Optical Path and Figure 1A The optical path described in is similar and the various options for enhancing beam divergence described above can be used.

[0072] Figure 6B Shows the concept and Figure 5A and Figure 5B A similar light guide based illumination device, but where the two-dimensional aperture expansion is achieved by two stages of light guide based aperture expansion, includes a light guide 178 for laterally expanding illumination from a source 168, which is formed into a beam by an illumination optic 176. Other architectures such as refractive and diffractive lenses are also possible. In all configurations described herein and variations thereof, the optical processes are substantially similar to those described in the detailed embodiments above.

[0073] In certain particularly preferred implementations:

[0074] 1. It may be preferred to output incoherent image light to avoid interference effects. In the case of an LED light source, the light source is incoherent at the origin. In the case of a laser, the light is preferably made incoherent (or pseudo-incoherent) by electronic modulation or by introducing mechanical jitter of the optical components.

[0075] 2. The optical device of the present invention preferably achieves beam expansion and collimation. Fig. 6A The collimated beam 174 is generated by the optical device 170 and then by the reflective lens 52, or the collimated beam 174 is generated by aperture multiplication in the light guide, such as in Figure 6B The medium collimated light beam 174 is produced by the light guide 178 and the light guide 156 .

[0076] 3. The optical device of the present invention preferably achieves beam expansion (increase in optical etendue) by any of the above alternatives:

[0077] a. Polarization selective diffuser ( Figure 1C , Figure 1D , Figure 2A and Figure 2B ),or

[0078] b. Bent pixels in a matrix or otherwise modified LCOS matrix ( FIG. 3A to FIG. 3C ).

[0079] c. The end result of the various configurations described above is preferably a high resolution projected image formed by collimated beams, each of which has the width required to fully illuminate the exit aperture 26 (the entrance to the waveguide).

[0080] It should be understood that the above description is intended to be exemplary only and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. A beam expansion liquid crystal on silicon (LCOS) chip for spatial light modulation, the LCOS chip comprising: (a) Two-dimensional array of pixel electrodes; (b) a liquid crystal layer covering the pixel electrode; as well as (c) a transparent electrode covering the liquid crystal layer, The covering layer between the pixel electrode and the liquid crystal layer and / or the surface of the pixel electrode is configured to provide a reflected light beam expansion effect, so that the collimated illumination incident on each of the pixel electrodes is reflected as divergent pixel image light.

2. The beam expansion LCOS chip according to claim 1, wherein: A plurality of the pixel electrodes are implemented using a concave reflective surface.

3. The beam expansion LCOS chip according to claim 1, wherein: The plurality of pixel electrodes are implemented using a convex reflective surface. 4 . The beam expansion LCOS chip according to claim 1 , further comprising a dispersive reflective cover layer disposed between the pixel electrode and the liquid crystal layer.

5. An image generator comprising: (a) A beam expansion LCOS chip according to any preceding claim; (b) an illumination device, the illumination device being arranged to illuminate the beam expansion LCOS chip, the illumination device comprising at least one light source and a scanning device, the scanning device comprising at least one scanning mirror, the at least one scanning mirror being arranged to scan an illumination spot in at least one direction across the beam expansion LCOS chip; as well as (c) A collimating optical device disposed to collimate image light reflected from the beam expansion LCOS chip.

6. An image generator comprising: (a) a polarization modifying spatial light modulator (SLM) comprising an array of pixels for modifying the polarization of incident illumination of a first polarization to selectively rotate the first polarization toward a second polarization orthogonal to the first polarization based on pixel data loaded into the SLM; (b) an illumination device arranged to illuminate the SLM with illumination of the first polarization; as well as (c) a polarization selective dispersive element covering the SLM, the polarization selective dispersive element being configured to be dispersive for light of the first polarization and substantially non-dispersive for light of the second polarization.

7. The image generator according to claim 6, wherein: The illumination arrangement comprises at least one low etendue illumination source and a scanning arrangement comprising at least one scanning mirror arranged for scanning an illumination spot in at least one direction across the SLM.

8. The image generator according to claim 7, wherein: The polarization selective dispersive element includes a metasurface formed using elongated nanostructures.

9. The image generator according to claim 7, wherein: The polarization selective dispersion element comprises: (a) a first layer formed of a birefringent material having a first refractive index along a first principal axis and a second refractive index along a second principal axis; and (b) a second layer formed of an isotropic optical material having a refractive index matching one of the first refractive index and the second refractive index, The interface between the first layer and the second layer has relief corresponding to a microlens array or a diffuser.

10. The image generator according to claim 6, wherein: The illumination device is configured to illuminate the entire SLM simultaneously.

11. The image generator according to claim 6, wherein: The polarization selective dispersive element includes a metasurface formed using elongated nanostructures.

12. The image generator according to claim 6, wherein: The polarization selective dispersion element comprises: (a) a first layer formed of a birefringent material having a first refractive index along a first principal axis and a second refractive index along a second principal axis; and (b) a second layer formed of an isotropic optical material having a refractive index matching one of the first refractive index and the second refractive index, The interface between the first layer and the second layer has relief corresponding to a microlens array or a diffuser.

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