Homogenizing lens arrays for display imaging

Abstract

The present application relates to a uniformized lens array for display imaging. In the described example, a system (e.g., projection system 100) may include a diffractive optical element (e.g., 104) adapted to be illuminated by at least one coherent light beam. A lens array (140) is coupled to receive a diffracted light beam from the diffractive optical element (e.g., 104). The lens array (140) includes a first (e.g., 140A) array lens and a second (e.g., 140C) array lens. The first (e.g., 140A) array lens is coupled to receive a first segment of an illumination pattern of the diffracted light beam, and the second (e.g., 140C) array lens is coupled to receive a second segment of the illumination pattern of the diffracted light beam. A spatial light modulator (e.g., 168) is coupled to receive overlapping diffracted light beams from the first (e.g., 140A) array lens and the second (e.g., 140C) array lens to form an image beam.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and more particularly to a uniformizing lens array for display imaging. Background Art

[0002] The projection system may include a device such as a spatial light modulator (SLM). The SLM may modulate light (including beam-steering light) for projection on a display surface. Some SLMs are arranged as digital micromirror devices (DMDs) with tiltable micromirrors. To project an illuminated pixel, the corresponding micromirror is tilted in a first direction so that light is reflected toward the display surface. When the pixel is not to be illuminated, the corresponding micromirror is tilted in a second direction so that light is reflected into a light trap. Trapping light reduces the efficiency of such a system, and the trapped light is dissipated as heat. Summary of the invention

[0003] In the described examples, a system (e.g., a projection system) may include a diffractive optical element adapted to be illuminated by at least one coherent light beam. A lens array is coupled to receive a diffracted light beam from the diffractive optical element. The lens array includes a first array lens and a second array lens. The first array lens is coupled to receive a first segment of an illumination pattern of the diffracted light beam, and the second array lens is coupled to receive a second segment of the illumination pattern of the diffracted light beam. A spatial light modulator is coupled to receive overlapping diffracted light beams from the first array lens and the second array lens to form an image beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 is a front view of the example lighting system.

[0005] Figure 2A The display includes Figure 1 Representation of an example diffraction image (e.g., a zero phase shift diffraction pattern) of visible diffraction order effects produced by an example illumination system.

[0006] Figure 2B The display includes Figure 1 Representation of an example diffraction image (e.g., a half-field shifted diffraction pattern) with reduced zero-order effects produced by an example illumination system.

[0007] Figure 2C Show by Figure 1 Representation of an example diffraction image (e.g., a superimposed half-field shifted diffraction pattern) produced by a composite diffracted light beam with a superimposed holographic half-field shift produced by an example illumination system.

[0008] Figure 3 is a front view of an example phase light modulator.

[0009] Figure 4is a flow chart of an example method for homogenizing light intensity distribution in a diffraction image.

[0010] Figure 5 is a front view of an example time-division multiplexing lighting system. DETAILED DESCRIPTION

[0011] In the drawings, like reference numerals refer to like elements, and the various features are not necessarily drawn to scale.

[0012] A phase hologram—e.g., produced by a phase spatial light modulator (PSLM or PLM)—can include a two-dimensional array of pixels. Each pixel of the PLM pixel array (e.g., a mechanical element for modulating a picture element) can change the path length of an incident coherent light wavefront, such that the optical phase of the incident coherent light wavefront can be controlled pixel by pixel. In one example, the PLM array can include pixels, wherein each pixel includes a corresponding movable micromirror, such that the micromirror can be moved in a direction perpendicular to the plane of the pixel array. The vertical movement of the micromirror can be about half the wavelength of the incident coherent light, such that the reflected wavefront can be displaced by about a full wavelength.

[0013] Some PLMs can be used to generate a distribution of arbitrary intensity (e.g., spatial distribution) across a projected image, where light modulated for the projected image has propagated from the PLM to the SLM and then to the far field for display. Some PLMs can also be used to scan a laser beam to an arbitrary location and / or for generating an arbitrary image. Scanning a laser beam can be used to efficiently direct light in the direction of illuminating an image.

[0014] Some applications of PLM include lighting high dynamic range (HDR) image displays. In such applications, the PLM can be configured to receive coherent light and selectively reflect the incident coherent light toward a DMD or liquid crystal (LC) so that the light is directed more to illuminate bright areas of the projected image and less toward dark areas of the projected image.

[0015] In one example, the zero-order beam (e.g., the zero-order beam intensity) appears at the center of a far-field image that has been generated by illuminating the SLM with coherent light modulated by the PLM (e.g., as Figure 2A). The zero-order diffraction beam illumination pattern is a result of some non-ideal properties of the PLM and the displayed hologram data, which may result in useless light in the image area. Zero-order effects are visible in the central portion of the far-field image, some of which include "over-illumination" portions of the far field. Such zero-order effects reduce the fidelity of the projected picture to the original image to be displayed. In addition, the uniformity of pixel illumination in the far-field image is determined by the Fourier transform of each pixel of the PLM and / or the effective surface of the mirror, so that (for example) the maximum brightness occurs near the zero-order phase position (e.g., as a function of wavelength) and falls off according to a sin(x / x)-type envelope (e.g., for an ideally flat, square PLM pixel). Such zero-order effects and the falloff in illumination intensity of the sin(x / x) envelope contribute to the formation of a non-uniform illumination gradient, which can reduce the uniformity of pixel illumination, making it potentially more difficult to project a high-quality image.

[0016] In the example techniques described herein, a far-field image is generated by illuminating a (e.g., amplitude-only) SLM with hologram-induced, phase-shifted coherent light received from a PLM. By applying a 2D linear phase ramp—e.g., exp(2πj(xm+yn))—to the phase-only hologram, the far-field image can be shifted so that the zero-order effects are at the image corners (e.g., instead of the center: see Figure 2B , which is described below). The resulting diffraction image includes four segment (e.g., quadrant) images, where each quadrant image includes a shifted version of the zero-order image. The area around four adjacent (e.g., mutually consecutive) corners of the quadrant images is illuminated more brightly, and the opposite corner of each respective quadrant image is illuminated less brightly.

[0017] The hologram-induced shifted coherent light is spatially divided into four beam segments (e.g., quadrants), where each beam segment includes light for illuminating a corresponding image quadrant. A lens array (e.g., a two-by-two lens array) includes an array of lenses, where the array lenses are arranged in a plane so that each array lens can receive a mutually different quadrant of the beam segment. A mask (e.g., an optical mask adjacent to the lens array) can be optically configured to mask (e.g., block) portions of the zero-order phase image to reduce zero-order effects that may otherwise be visible in the far-field shifted image.

[0018] The lens array is configured to combine (e.g., superimpose) light from each of the four beam quadrants to form a combined phase hologram for illuminating the SLM. When the combined phase hologram illuminates the SLM, the brightest illuminated angle of each quadrant is (e.g.) superimposed over (e.g., optically averaged with) the least brightly illuminated angle of each quadrant (e.g., the respective diagonally opposite angles). The superposition of the four beam quadrants produces a uniformly illuminated far-field image, which is suitable for projecting an HDR image (for example).

[0019] Figure 1 1 is a front view of an example illumination system. Illumination system 100 generally includes the following elements, such as: light sources 101 (e.g., red lasers), 102 (e.g., green lasers), and 103 (e.g., blue lasers); optical fibers 110, 120, and 130 (for carrying coherent light of corresponding wavelengths, respectively); source lenses 112, 122, and 132; PLMs 114, 124, and 134; hologram output lenses 116, 126, and 136; prisms 128 (e.g., color combining prisms); and mirrors 118 and 138; lens array 140; mask 142 (optional); inverting lens 144; diffuser 146; relay imaging lenses 148, 150, and 152; prisms 154, 156, 160, 170, and 180; DMDs 158, 168, and 178; and projection focusing element 190. A phase hologram generator (e.g., hologram generator 104) is configured to program a PLM (e.g., 114, 124, or 134) to generate a phase hologram, and an image processor 182 (which may also include hologram generator 104) may program an SLM to generate a selected image to be projected as part (all or part) of a far-field image 199.

[0020] Light sources 101, 102, and 103 may include independently controllable lasers, such as laser diodes. Light from a first light source (e.g., light source 101) is optically coupled to a first diffractive optical element (e.g., PLM 114) via an optical fiber 110 and a source lens 112. Light from a second light source (e.g., light source 102) is coupled to a diffractive optical element PLM (e.g., PLM 124) via an optical fiber 120 and a source lens 122. Light from a third light source (e.g., light source 103) is coupled to a third diffractive optical element (e.g., PLM 134) via an optical fiber 130 and a source lens 132.

[0021] The coherent beam illuminator includes at least one of a light source (for example, a coherent light source such as a laser), an optical fiber, and a source lens, wherein the diffractive optical element is adapted to be optically coupled to (for example, corresponding to) the coherent beam illuminator. In an example, a first coherent beam illuminator may include a first light source configured to generate a first incident coherent beam, and a second coherent beam illuminator may include a second light source configured to generate a second incident coherent beam, wherein the first coherent beam illuminator and the second coherent beam illuminator are optically coupled to the lens array.

[0022] Light sources 101, 102, and 103 may be formed in separate substrates or in the same substrate. In various examples, the various light emitting portions of light sources 101, 102, and 103 may be individually and selectively controlled. Light sources 101, 102, and 103 may be tuned to produce corresponding coherent light beams having primary color wavelengths (e.g., to produce white light in a controlled combination), and some applications may include light sources of mutually different colors and / or color temperatures for additive (or subtractive) color synthesis in different applications. Although three light sources are described, various examples may include a greater or lesser number of light sources and include different corresponding color gamuts. (Various example light sources may include light sources for emitting wavelengths of invisible light.)

[0023] Coherent light optically coupled (e.g., received) from the corresponding optical fiber is focused onto the effective surface of the corresponding PLM by the corresponding source lens. The source lens may be configured to direct light onto the effective surface of the corresponding PLM at an angle (e.g., selected from a range of 20 to 30 degrees from the vertical). For example: source lens 112 is configured to focus light coupled by optical fiber 110 onto the effective surface of PLM114; source lens 122 is configured to focus light coupled by optical fiber 120 onto the effective surface of PLM124; and source lens 132 is configured to focus light coupled by optical fiber 130 onto the effective surface of PLM 134. In various examples, the PLM may be a diffractive optical element configured to generate a diffracted light beam in response to an incident coherent light beam, wherein the diffracted light beam includes a diffracted illumination pattern (e.g., see Figure 2B The diffracted illumination pattern comprises diffracted light having spatially varying intensity at right angles to the projection axis of the diffracted illumination pattern in at least one cross-sectional plane.

[0024] The PLM is configured to generate a corresponding hologram (e.g., a corresponding phase hologram) for phase shifting a received wavefront of coherent light (e.g., where the received wavefront has the same selected frequency and phase of the light received from the corresponding source lens). The corresponding hologram may have a viewing angle range of 5 to 10 degrees. For example: PLM 114 is coupled to generate a first hologram for phase shifting the coherent light generated by light source 101; PLM 124 is coupled to generate a second hologram for phase shifting the coherent light generated by light source 102 and PLM 134 is coupled to generate a third hologram for phase shifting the coherent light generated by light source 103. Each PLM may be programmed (e.g., by hologram generator 104) with a phase hologram to generate a profile of an effective surface of the corresponding PLM, such that the effective surface is configured to selectively diffract incident coherent light. The hologram generator may determine the phase hologram in response to the wavelength of the coherent light beam optically coupled to the corresponding PLM.

[0025] As referenced below Figure 3As described, the active surface of an example PLM includes an array of micromirrors (e.g., which may be actuated by independently controllable pistons). The PLM may be programmed (by creating a physical surface for diffracting received light) to phase shift (e.g., selectively phase shift) the received wavefront. The received wavefront is phase shifted by a selected fraction of the wavelength of the received coherent light so that the distance the mirror travels to produce the phase shift may be determined in response to the wavelength of the received wavefront (e.g., assuming the same propagation speed of light). The wavefront may be phase shifted by one wavelength by a respective PLM by actuating a selected piston of the PLM to move the respective micromirror by a distance of half the wavelength of the coherent light (e.g., movement of the micromirror achieves a double phase shift because the reflected light traverses a bidirectional path of the same distance "increment" traversed by the micromirror from a zero phase shift position).

[0026] The diffracted light beams generated by the PLMs 114, 124, and 134 are focused by hologram output lenses 116, 126, and 136, respectively, and optically coupled to the lens array 140 through at least one of the mirrors 118 and 138 (e.g., color combining mirrors) and the prism 128 (e.g., color combining mirror / prism). The lens array 140 is a two-by-two lens array including array lenses 140A (e.g., upper left quadrant lens), 140B (e.g., upper right quadrant lens), 140C (e.g., lower right quadrant lens), and 140D (e.g., lower left quadrant lens).

[0027] Array lenses 140A, 140B, 140C, and 140D are respectively optically coupled to receive a respective segment (e.g., quadrant) of each of the diffracted light beams generated by a respective one of the PLMs 114, 124, and 134 (e.g., in response to coherent illumination of at least one of the PLMs 114, 124, and 134). For example: array lens 140A (e.g., an upper left quadrant lens) is configured to receive an upper left portion (e.g., a first beam quadrant) of corresponding diffracted light beams generated by PLMs 114, 124, and 134; array lens 140B (e.g., an upper right quadrant lens) is configured to receive an upper right portion (e.g., a second beam quadrant) of corresponding diffracted light beams generated by PLMs 114, 124, and 134; array lens 140C (e.g., a lower right quadrant lens) is configured to receive a lower right portion (e.g., a third beam quadrant) of corresponding diffracted light beams generated by PLMs 114, 124, and 134; and array lens 140D (e.g., a lower left quadrant lens) is configured to receive a lower left portion (e.g., a fourth beam quadrant) of corresponding diffracted light beams generated by PLMs 114, 124, and 134. In other example cases where more (or fewer) PLMs are used, the array lenses of lens array 140 each receive a respective segment of the diffracted light beam received from each optically coupled PLM.

[0028] In at least one example system, lens array 140 is illuminated by a diffracted light beam from a diffractive optical element (e.g., 114). Lens array 140 includes a first array of lenses (e.g., 140A) illuminated by a first segment of the illumination pattern of the diffracted light beam. The lens array further includes a second array of lenses (e.g., 140C) illuminated by a second segment of the illumination pattern of the diffracted light beam. The second segment of the illumination pattern of the diffracted light beam includes a light intensity distribution that is different from the light intensity distribution of the first segment of the illumination pattern of the diffracted light beam.

[0029] In at least one example system, a lens array (e.g., 140) is optically coupled to a diffractive optical element, the lens array including a first array lens (e.g., 140A) configured to receive a first segment of a diffracted illumination pattern, and wherein the lens array includes a second array lens (e.g., 140C) configured to receive a second segment of the diffracted illumination pattern, the first array lens and the second array lens being configured to generate overlapping diffracted beams (e.g., as a composite diffracted light beam) in response to the diffracted illumination pattern. At least one example system may further include a third array lens configured to receive a third segment of the diffracted illumination pattern and a fourth array lens configured to receive a fourth segment of the diffracted illumination pattern.

[0030] Array lenses 140A, 140B, 140C, and 140D are respectively configured to superimpose (e.g., overlap) each of the received respective segments (e.g., quadrants) of the diffracted light beams so that a composite diffracted light beam is generated. For example: array lens 140A is configured to focus the first beam segment onto a common area (e.g., the same portion of inverting lens 144); array lens 140B is configured to focus the second beam segment onto a common area; array lens 140C is configured to focus the third beam segment onto a common area; and array lens 140D is configured to focus the fourth beam segment onto a common area. Inverting lens 144 is configured to generate an inverted composite diffracted light beam that is optically coupled to at least one spatial light modulator.

[0031] In an example, each array lens of the lens array is optically coupled to (e.g., where each array lens is configured to focus a corresponding diffracted light beam onto a common area of ​​the inverted lens) an inverted lens, such that the inverted lens is optically coupled to the lens array. The lens array is configured to focus a first segment and a second segment of a diffracted illumination pattern onto the same portion of the inverted lens (e.g., where the same portion may be an intersection of the focused first segment and the second segment of the diffracted illumination pattern). A spatial light modulator (e.g., one of the DMDs 158, 168, and 178 for final imaging) is optically coupled to the lens array (e.g., lens array 140, via the inverted lens), which is configured to form an image beam in response to overlapping diffracted beams.

[0032] The composite diffracted light beam is optically coupled to (eg, directed to) an inverting lens 144. The inverting lens 144 is a combination lens configured to combine with a lens array to produce a diffracted light beam such that the composite diffracted light beam converges according to the focal length and / or focus of the inverting lens 144.

[0033] The lens array 140 optionally includes a mask 142. The mask 142 is arranged between adjacent array lenses to mask (e.g., cover or obscure) the area that interfaces with adjacent quadrant lenses. For example, the masked area may include the area between each pair of adjacent quadrant lenses and may include a central boundary area (e.g., a "four corner" area). The central boundary area includes the central axis (e.g., the intersection of the projected central axis and the plane containing all array lenses of the lens array 140) between the first, second, third, and fourth array lenses (array lenses 140A, 140B, 140C, and 140D). The mask 142 is configured to mask the central boundary area (e.g., see the central axis 222) and is configured to prevent the propagation of zero-order effects and higher diffraction order effects, which may otherwise be visible (e.g., displayed) when a far-field image is generated in response to an unmasked diffracted light beam.

[0034] In response to mask 142 being located (e.g., disposed) between (e.g., adjacent to and / or overlying) adjacent lenses of the first, second, third, and fourth array lenses, each of the segments of each respective received diffracted light beam is a mutually distinct segment relative to other segments in the respective received diffracted light beam (e.g., such that the beam segments do not overlap when the respective array lens is initially illuminated). Mask 142 may optionally be included to block portions of the zero-order phase image of the diffracted illumination pattern of the diffracted light beam (e.g., optically coupled from the respective diffractive optical element: see, e.g., Figure 2A and Figure 2B). Adjacent lenses of the lens array (e.g., between which corresponding portions of the mask are disposed) may include: a first array lens adjacent to a second array lens and a fourth array lens; a second array lens adjacent to the first array lens and the third array lens; a third array lens adjacent to the second array lens and the fourth array lens; and a fourth array lens adjacent to the third array lens and the first array lens.

[0035] Diffuser 146 is an optional diffuser arranged with a movable aperture that is optically coupled to the composite diffracted beam (e.g., in the path of the composite diffracted beam) (e.g., at the focus of the inverting lens 144). The aperture is configured to move (e.g., fluctuate in position) and diffuse the received composite diffracted beam, which reduces laser "speckle". Because the diffuser is located at the far-field image plane, the diffuser does not need to adversely blur the image produced at the imaging SLM. Laser speckle is visible (and reduces image quality) when the imaged laser beam is reflected from a display surface that has surface features that are larger than the wavelength of the light from the laser. Diffuser 146 produces a composite diffracted beam with reduced speckle in response to receiving the composite diffracted beam from the inverting lens 144.

[0036] The composite diffracted beam (e.g., the reduced-speckle composite diffracted beam) is optically coupled to relay imaging lenses 148, 150, and 152. Relay imaging lenses 148, 150, and 152 are configured to re-image the PLM image onto a corresponding final imaging DMD (e.g., one of 158, 168, and 178).

[0037] Relay imaging lenses 148, 150 and 152 are optically coupled to prisms 156, 160, 170 and 180 via prism 154. Prisms 156, 160, 170 and 180 include, for example, dichroic mirrors so that selected colors (e.g., each respective color of light sources 101, 102 and 103) can be selectively (e.g., individually) optically coupled to respective DMDs 158, 168 and 178. Each of the respective DMDs is optically coupled to receive overlapping diffracted light beams from at least two array lenses to form an image beam. The image beams (e.g., if there are more than one image beam) can be combined to form an image beam (e.g., a combined image beam) that is optically coupled to projection focusing element 190.

[0038] For example, prism 160 is configured to direct a diffracted light beam (e.g., generated by PLM 114 in response to illumination by a red laser) toward DMD 158, which images a first color holographic illumination image frame of an image to be displayed in the far field. Prism 170 is configured to direct a diffracted light beam (e.g., generated by PLM 124 in response to illumination by a green laser) toward DMD 158, which images a second color holographic illumination image frame of an image to be displayed in the far field. Prism 180 is configured to direct a diffracted light beam (e.g., generated by PLM 134 in response to illumination by a blue laser) toward DMD 158, which images a third color holographic illumination image frame of an image to be displayed in the far field.

[0039] DMDs 158, 168, and 178 may each include a two-dimensional array of reflective elements (e.g., micromirrors) arranged in rows and columns, where each such reflective element controls illumination relative to a "pixel" (e.g., a micromirror for individually controlling a corresponding portion of an incident light beam for projection). The reflective elements of DMDs 158, 168, and 178 are individually responsive to input data received from image processor 182. In an example, the input data includes a bit frame generated in response to pixel hues and intensity information data of an image frame of an image input signal. The bit frame may be projected using pulse width modulation. The pulse width modulation scheme includes a weighted time interval for projecting pixels having a pixel hue and intensity corresponding to a corresponding pixel in the input data. The weighted time interval is long enough to allow the human eye to integrate within a given image frame display period.

[0040] Prisms 156, 160, 170 and 180 are optically coupled to receive and superimpose first, second and third color holographic illumination image frames from respective DMDs, and optically merge the holographic illumination image frames (e.g., superimposed when color images are generated by at least two DMDs) to projection focusing element 190.

[0041] The projection focusing element 190 is optically configured to relay an image beam from a spatial light modulator and to focus the image beam for viewing. In an example, the projection focusing element 190 is optically coupled to a spatial light modulator (e.g., DMD 168), and the projection focusing element 190 is configured to focus the image beam for viewing (e.g., to be projected on a display screen for viewing by a human observer). The projection focusing element 190 is configured to project (several) holographic illumination image frames onto a display surface such that the holographic illumination image frames are displayed as displayed images (e.g., far-field images 199). The holographic illumination image frames include increased resolution and contrast, for example, compared to an image projected using incoherent light (e.g., from an equivalent DMD).

[0042] Figure 2AThe display includes Figure 1 2 is a representation of an example diffraction image of visible diffraction order effects (e.g., a zero phase shift diffraction pattern) produced by an example illumination system of . For example, diffraction image 210 includes field 210A (which includes zero order effects), and fields 210B, 210C, 210D, and 210E (which include higher order integer diffraction effects). The diffraction image can be produced by directing coherent light on an effective surface of a PLM (for example) to produce a holographic diffraction beam including a light intensity distribution. The diffracted beam is optically coupled to illuminate a DMD imager that has been programmed (for example) to produce an image of an uppercase letter "I". Diffraction image 210 is a representation of a far field image displayed by directing light from a DMD imager to a display screen (e.g., where the directed light is produced without the lens array 140 described herein).

[0043] An image of the capital letter "I" (e.g., illuminated by a diffracted beam induced by a Fahrenhofer / Fourier hologram) is displayed as a zeroth order diffraction image in field 210A, while higher order (e.g., integer order) diffraction images of the capital letter "I" exist in an infinite (theoretically infinite) order that extends vertically and horizontally (e.g., as partially shown in fields 210B, 210C, 210D, and 210E). The intensity of the diffraction images decreases (e.g., varies according to a sin(x / x) envelope) such that the intensity of the far-field zeroth order diffraction image decreases radially from a central axis 212 of diffraction image 210. For example, the illumination intensity of the central portion of the zeroth order illumination effect is bright enough (e.g., overexposed) to at least perceptibly lose displayed information, while the illumination intensity of fields 210B, 210C, 210D, and 210E decreases (all the way to infinity) and becomes more difficult to perceive in directions extending outward from the central axis.

[0044] Figure 2B The display includes Figure 11 is a representation of an example diffraction image (e.g., a half-field shifted diffraction pattern) with reduced zero-order effects produced by an example illumination system of . For example, diffraction image 220 includes fields 220A, 220B, 220C, and 220D. Fields 220A, 220B, 220C, and 220D are vertically and horizontally shifted by half a field from a central axis. Diffraction image 220 can be generated by directing coherent light on an active surface of a PLM programmed to produce a half-field phase-shifted hologram. When illuminated by coherent light of a selected wavelength, the phase hologram produces a diffraction pattern with an intensity that is vertically and horizontally shifted by half a field. Due to the non-ideal implementation of the hologram for shifting the diffraction image by half a field, the zero-order effect is reduced (e.g., and not necessarily eliminated) and can be further reduced by using an optional blocking mask (e.g., mask 142). Mask 142 can be arranged between adjacent array lenses of lens array 140. The diffraction orders (and hence the replicated far-field PLM images) are approximately spaced apart by an angle θ:

[0045]

[0046] where λ is the wavelength of coherent light guided on the active surface of the PLM (e.g., hologram), and the PLM pitch is the piston pitch (e.g., 5 μm to 10 μm) used to generate the effective surface profile of the PLM (hereinafter referred to as Figure 3 described).

[0047] The phase hologram used to shift the image half field produces a diffracted illumination pattern. The diffracted illumination pattern is directed on a DMD imager that has been programmed (for example) to produce an image of the capital letter "I". Diffraction image 220 is a representation of a far-field image that would be displayed by directing light from the DMD imager to a display screen (for example, where the directed light is produced without the lens array 140 described herein).

[0048] The intensity of the diffraction image of the capital letter "I" decreases (e.g., also varies according to the sin(x / x) envelope) so that the intensity of the far-field zero-order diffraction image decreases radially from the central axis 222 of the diffraction image 220. For example, the illumination intensity is: brightest at the radial central corners of fields 220A, 220B, 220C, and 220D (e.g., the lower right, lower left, upper left, and upper right corners of each corresponding field, respectively); intermediate in brightness at the radial intermediate corners of fields 220A, 220B, 220C, and 220D (e.g., lower left / upper right, upper left / lower right, upper right / lower left, and lower right / upper left, respectively); and dimmest at the radial far corners of fields 220A, 220B, 220C, and 220D (e.g., upper left, upper right, lower right, and lower left, respectively). As described below with respect to Figure 2CAs described, fields 220A, 220B, 220C, and 220D may be optically superimposed (eg, effectively superimposed) to produce a superimposed field where a uniform illumination gradient exists throughout.

[0049] In an example, a phase hologram is configured to diffractively shift a Fourier transform phase image (e.g., diffraction image 230) to a position between diffraction orders. A phase hologram may be configured to diffractively shift a Fourier transform phase image vertically and horizontally to a position between diffraction orders of a phase image of a Fourier series.

[0050] Figure 2C Show by Figure 1 2 is a representation of an example diffraction image (e.g., a superimposed half-field shifted diffraction pattern) produced by a composite diffracted light beam with superimposed holographic half-field shifts produced by an example illumination system. For example, diffraction image 230 is produced in response to a composite hologram (e.g., a composite image hologram) produced by superimposing phase-shifted beam quadrants produced by at least one hologram. The quadrants are phase-shifted by increments of half-field.

[0051] Diffraction image 230 is a representation of a far-field image displayed by directing the composite diffracted beam produced by lens array 140 onto a DMD (e.g., programmed to image a capital letter "I") and directing the composite hologram image as modulated by the DMD to a display screen.

[0052] The diffraction image 230 is produced by a uniform distribution of light intensity (e.g., by a composite hologram that produces a uniform distribution of light intensity) such that the capital letter "I" is displayed with uniform illumination (horizontally and vertically). The composite hologram effectively averages the non-uniform distribution of light intensity from the corresponding portion (e.g., field) of the half-field shifted hologram (e.g., the non-uniform distribution would otherwise be present without using a composite hologram such as Figure 2B ) as produced in the case of the hologram combiner described in .

[0053] Figure 3 3 is a front view of an example phase light modulator, such as PLM 300. PLM 300 generally includes elements, such as pistons 310 and 320. For example, for clarity, the displacement (e.g., extension) of pistons 310 and 320 is not to scale and is exaggerated. The extension of pistons 310 and 320 is controlled by a PLM actuator (not shown) in response to information (e.g., programming) received from a phase hologram generator (e.g., hologram generator 104). Piston 310 is shown as fully extended to a distance 360 ​​(e.g., height) labeled λ (lambda), while piston 320 is shown as partially extended to a distance (e.g., height) that is one quarter wavelength shorter than distance 360 ​​(e.g., λ).

[0054] The visible portions (e.g., tops) of pistons 310 and 320 are reflective (e.g., mirrored) such that the piston array forms an effective surface of a PLM configured to generate (e.g., programmable to) present a profile of a selected phase hologram. In an example where coherent light (e.g., from laser 350) is directed obliquely (e.g., 20 to 30 degrees from vertical) onto the effective surface of PLM 300, a phase hologram may be optically generated in response to a phase hologram by which the effective surface of PLM 300 is programmed. The generated phase hologram includes dimensional features determined in response to the wavelength of the incident coherent light beam. The dimensional features may be determined, for example, in response to calculations performed by a phase hologram generator.

[0055] As described herein, the PLM 300 can be programmed (by creating a physical surface contoured to diffract the received coherent light) to phase shift the received wavefront. The received wavefront is phase shifted, for example, by half the wavelength of the received coherent light, so that the degree of mirror travel used to produce a selected phase shift (e.g., assuming the propagation speed of light is the same) can be determined in response to the wavelength of the received wavefront. The wavefront can be phase shifted by the wavelength of the PLM by actuating a selected piston of the corresponding PLM to move the corresponding micromirror by a distance of half the wavelength of the coherent light (e.g., movement of the micromirror achieves a double phase shift because the reflected light traverses a bidirectional path of the same distance "increment" traversed by the micromirror from a zero phase shift position).

[0056] Figure 4 4 is a flow chart of an example method for homogenizing a light intensity distribution in a diffraction image. The process 410 of the example method 400 includes generating a diffracted light beam by a diffractive optical element by illuminating the diffractive optical element with at least one coherent light beam. For example, the diffracted light beam can be generated by illuminating a diffractive optical element (e.g., 114) with at least one coherent light beam (e.g., optically coupled from a light source 101 via an optical fiber 110).

[0057] Process 420 includes illuminating a lens array including a first array lens and a second array lens with a diffracted light beam coupled from a diffractive optical element. Illuminating the lens array with the diffracted light beam may include: focusing a first segment of an illumination pattern of the diffracted light beam by the first array lens to produce a first segment focused pattern; and focusing a second segment of the illumination pattern of the diffracted light beam by the second array lens to produce a second segment focused pattern. For example, a lens array (e.g., 140) may include (at least) a first array lens and a second array lens (e.g., 140A and 140C). The lens array may be illuminated with a diffracted light beam coupled from a diffractive optical element (e.g., 114). The first array lens is illuminated with a first segment of an illumination pattern of the diffracted light beam (see, e.g., illumination pattern in 220A), and the second array lens is illuminated with a second segment of an illumination pattern of the diffracted light beam (see, e.g., illumination pattern in 220C).

[0058] Process 430 optionally includes diffusing light from the first array lens and the second array lens. Diffusion of light from the first array lens and the second array lens may include: diffusing light from the first array lens and the second array lens through a diffuser. For example, light from the array lenses (e.g., 140A and 140C) is converged by a converging lens (e.g., 144) to illuminate a diffuser (e.g., 146). The diffuser may include at least one aperture. The diffuser may be moved during illumination to reduce speckle caused by a display surface of coherent light (e.g., of far field image 199) projected for display (e.g., by projection focusing element 190).

[0059] Process 440 includes forming an image beam by illuminating a spatial light modulator with a first distribution of light intensities from a first array lens and with a second distribution of light intensities from a second array lens. Forming an image beam by illuminating a spatial light modulator with the first distribution of light intensities and the second distribution of light intensities may include modulating a first segment focused pattern and a second segment focused pattern with the spatial light modulator, wherein portions of the first segment focused pattern and portions of the second segment focused pattern overlap on the spatial light modulator. For example, an image beam (e.g., for projection by projection focusing element 190) is formed by illuminating a spatial light modulator (e.g., 158) with a first distribution of light intensities from a first array lens (e.g., 140A) and with a second distribution of light intensities from a second array lens (e.g., 140C).

[0060] Portions (e.g., part or all) of the first and second distributions of light intensity overlap during illumination of the spatial light modulator. For example, a single pixel of the SLM may control both a stronger beam received from a first lens of the lens array (e.g., the first array lens) and a weaker beam received from a second lens of the lens array (e.g., the second array lens). The superposition of the stronger beam and the weaker beam effectively averages the intensities of the two beams to a normalized value. (As described above with respect to FIG. 2, four beams are combined, which increases the uniformity and brightness level of the displayed image.) When applied across an active portion of the SLM (which includes pixels for forming a displayed image), pixels of the displayed image are formed in response to incident light uniformized to the normalized value. The pixels of the displayed image formed in response to incident light uniformized to the normalized value effectively produce a uniformly illuminated displayed image (e.g., including linearized contrast in response to effectively averaging coherent light), higher resolution (e.g., in response to the coherence of the coherent light), and higher brightness (e.g., in response to the generation and coherence of the coherent light).

[0061] Figure 5 5 is a front view of an example time-division multiplexed illumination system. Illumination system 500 generally includes the following elements, such as: light sources 501 (e.g., red lasers), 502 (e.g., green lasers), and 503 (e.g., blue lasers); source lenses 512, 522, and 532; PLM 504; color combiners 518, 528, and 538; lens array 140; mask 142 (optional); inverting lens 144; diffuser 146; relay imaging lenses 148, 150, and 152; prisms 554 and 556; DMD 558; and projection focusing element 190.

[0062] Light sources 501, 502, and 503 may be lasers that are independently controllable from each other, such as laser diodes. Light from a first light source (e.g., light source 501) is optically coupled to a diffractive optical element (e.g., PLM 504) via a source lens 512 and a color combiner 518 (which reflects light incident from source lens 512 and passes light incident from color combiners 528 and 538). Light from a second light source (e.g., light source 502) is coupled to a diffractive optical element (e.g., PLM 504) via a source lens 522 and a color combiner 528 (which reflects light incident from source lens 522 and passes light incident from color combiner 538). Light from a third light source (e.g., light source 503) is coupled to a diffractive optical element (e.g., PLM 504) via a source lens 532 and a color combiner 538 (which reflects light incident from source lens 532).

[0063] Light sources 501, 502, and 503 are configured to be time-division multiplexed (e.g., where the light sources are individually activated in a repeatable time sequence) to illuminate the lens array at different times. For example, light sources 501, 502, and 503 are time-division multiplexed (e.g., activated at mutually exclusive times) during corresponding time periods of three times in a time-division multiplexing cycle. During a first time period: light source 501 is powered on (e.g., to emit coherent radiation); PLM 504 is programmed to generate a first hologram for diffracting a first wavelength of light (e.g., red) from light source 501; and DMD is programmed to image a first color frame (e.g., a red frame) for imaging a far-field image (e.g., far-field image 199). During a second time: light source 502 is powered on (e.g., to emit coherent radiation); PLM 504 is programmed to generate a second hologram for diffracting a second wavelength of light (e.g., green) from light source 502; and DMD is programmed to image a second color frame (e.g., green frame) for imaging a far-field image. During a third time: light source 503 is powered on (e.g., to emit coherent radiation); PLM 504 is programmed to generate a third hologram for diffracting a third wavelength of light (e.g., blue) from light source 503; and DMD is programmed to image a third color frame (e.g., blue frame) for imaging a far-field image.

[0064] For example, the human eye optically integrates the far field images produced by the first, second and third color frames so that the human viewer can perceive a full color image. When the time multiplexing cycle is iterated (and the advancement of the frame information of the video sequence is sequentially applied during each iteration of the time multiplexing cycle), a moving image can be perceived.

[0065] The diffracted light beams (e.g., time-division multiplexed diffracted light beams) generated by PLM 504 are optically coupled to lens array 140. Lens array 140 is a two-by-two lens array including array lenses 140A (e.g., upper left quadrant lens), 140B (e.g., upper right quadrant lens), 140C (e.g., lower right quadrant lens), and 140D (e.g., lower left quadrant lens).

[0066] In an example, lens array 140 is optically coupled to receive each of the diffracted beams (e.g., having different wavelengths at separate times), wherein each of the diffracted beams of different wavelengths is corrected for magnification prior to being received by lens array 140. For example, source lens 512 can adjust the magnification of the red diffracted beam, source lens 522 can adjust the magnification of the green diffracted beam, and source lens 532 can adjust the magnification of the blue diffracted beam.

[0067] Array lenses 140A, 140B, 140C, and 140D are respectively optically coupled to receive a respective segment (e.g., quadrant) of each of the time-multiplexed diffracted light beams generated by PLM 504. For example: lens 140A (e.g., upper left quadrant lens) is configured to receive an upper left portion (e.g., first beam quadrant) of the time-multiplexed diffracted light beams generated by PLM 504; array lens 140B (e.g., upper right quadrant lens) is configured to receive an upper right portion (e.g., second beam quadrant) of the time-multiplexed diffracted light beams generated by PLM 504; array lens 140C (e.g., lower right quadrant lens) is configured to receive a lower right portion (e.g., third beam quadrant) of the time-multiplexed diffracted light beams generated by PLM 504; and array lens 140D (e.g., lower left quadrant lens) is configured to receive a lower left portion (e.g., fourth beam quadrant) of the time-multiplexed diffracted light beams generated by PLM 504.

[0068] In at least one example system, the lens array 140 is illuminated by a diffracted light beam from a diffractive optical element (e.g., 514, which can be programmed by the hologram generator 104). The lens array 140 includes a first array of lenses (e.g., 140A) illuminated by a first segment of the illumination pattern of the diffracted light beam. The lens array further includes a second array of lenses (e.g., 140C) illuminated by a second segment of the illumination pattern of the diffracted light beam. The second segment of the illumination pattern of the diffracted light beam includes a light intensity distribution that is different from the light intensity distribution of the first segment of the illumination pattern of the diffracted light beam.

[0069] Array lenses 140A, 140B, 140C, and 140D are respectively configured to superimpose (e.g., overlap) each of the received corresponding segments (e.g., quadrants) of the diffracted light beams so that a composite diffracted light beam is generated. For example: array lens 140A is configured to focus the first beam segment onto a common area (e.g., the same portion of inverting lens 144); array lens 140B is configured to focus the second beam segment onto a common area; array lens 140C is configured to focus the third beam segment onto a common area; and array lens 140D is configured to focus the fourth beam segment onto a common area. Inverting lens 144 optically couples the time-multiplexed composite diffracted light beam to at least one spatial light modulator.

[0070] The time-multiplexed composite diffracted light beam is optically coupled to (eg, directed toward) an inverting lens 144. The inverting lens 144 is configured to invert the time-multiplexed composite diffracted light beam such that the time-multiplexed composite diffracted light beam is converged according to a focal length and / or focus.

[0071] The diffuser 146 is optionally arranged with a movable aperture that is optically coupled to the composite diffracted light beam (e.g., at the focus of the inverting lens 144). The aperture is configured to move and diffuse the received composite diffracted light beam, which reduces laser "speckle". The diffuser 146 generates a reduced-speckle, time-multiplexed composite diffracted light beam in response to receiving the composite diffracted light beam from the inverting lens 144.

[0072] The time-multiplexed composite diffracted beam (e.g., the reduced-speckle, time-multiplexed, and composite diffracted beam) is optically coupled to relay imaging lenses 148, 150, and 152. The relay imaging lenses 148, 150, and 152 focus the diverging wavefronts of the time-multiplexed composite diffracted beam into focused rays (e.g., including the time-multiplexed composite diffracted beam).

[0073] The focused light is optically coupled to DMD 558 via prism 554. DMD 558 is optically coupled to receive overlapping diffracted light beams from at least two array lenses to form an image beam (e.g., three primary color image frames are time-division multiplexed into the image beam). The image beam is optically coupled to projection focusing element 190.

[0074] The example system described herein includes: a diffractive optical element adapted to receive at least one coherent light beam and to generate a diffracted illumination pattern in response to the at least one coherent light beam; a lens array optically coupled to the diffractive optical element, the lens array including a first array lens and a second array lens, the first array lens being configured to focus a first segment of the diffracted illumination pattern, the second array lens being configured to focus a second segment of the diffracted illumination pattern, and the second segment of the diffracted illumination pattern including a light intensity distribution different from the light intensity distribution of the first segment of the diffracted illumination pattern, the lens array being configured to generate overlapping diffracted light beams; and a spatial light modulator optically coupled to the lens array, the spatial light modulator being configured to form an image beam in response to the overlapping diffracted light beams.

[0075] The example method described herein includes: generating a diffracted light beam by a diffractive optical element in response to at least one coherent light beam incident on the diffractive optical element; focusing a first segment of an illumination pattern of the diffracted light beam by a first array lens optically coupled to the diffractive optical element to generate a first segment focused pattern; focusing a second segment of the illumination pattern of the diffracted light beam by a second array lens optically coupled to the diffractive optical element to generate a second segment focused pattern; and modulating the first segment focused pattern and the second segment focused pattern by a spatial light modulator optically coupled to the diffractive optical element, portions of the first segment focused pattern and the second segment focused pattern overlapping on the spatial light modulator.

[0076] The example method may further include: diffusing through a diffuser optically coupled to the diffractive optical element to produce diffused light in response to light received from the first array lens and the second array lens; and projecting the diffused light through a projection focusing element optically coupled to the diffractive optical element.

[0077] Modifications in the described embodiments are possible, and other embodiments are possible, within the scope of the claims.

Claims

1. An optical system, comprising: a phase light modulator PLM comprising a two-dimensional array of pixels, the PLM being adapted to be optically coupled to a coherent beam illuminator, the PLM being configured to generate a diffraction pattern in response to an incident coherent beam received from the coherent beam illuminator, the diffraction pattern comprising a first diffracted beam and a second diffracted beam; a lens array optically coupled to the PLM, the lens array comprising: a first array lens configured to receive the first diffracted light beam and generate a first overlapping diffracted light beam in response to the first diffracted light beam; and a second array lens configured to receive the second diffracted light beam and generate a second overlapping diffracted light beam in response to the second diffracted light beam; and A spatial light modulator is optically coupled to the lens array, the spatial light modulator being configured to form an image beam in response to the first overlapping diffracted light beams and the second overlapping diffracted light beams.

2. The optical system of claim 1, further comprising a projection focusing element optically coupled to the spatial light modulator, the projection focusing element configured to focus the image beam.

3. The optical system of claim 1, further comprising the coherent beam illuminator, the coherent beam illuminator comprising a light source configured to generate the incident coherent beam.

4. The optical system of claim 3, wherein the coherent beam illuminator is a first coherent beam illuminator, the light source is a first light source and the incident coherent beam is a first incident coherent beam, the optical system further comprises a second coherent beam illuminator, the second coherent beam illuminator comprises a second light source configured to generate a second incident coherent beam, and the second coherent beam illuminator is optically coupled to the lens array. 5 . The optical system of claim 4 , wherein the first light source and the second light source are configured to be time-division multiplexed to illuminate the lens array at different times.

6. The optical system of claim 4, wherein the PLM is a first PLM, the optical system further comprising a second PLM optically coupled to the second coherent beam illuminator, the second PLM being configured to generate a third diffracted beam and a fourth diffracted beam in response to the second incident coherent beam, the first array lens being configured to receive the third diffracted beam, and the second array lens being configured to receive the fourth diffracted beam.

7. The optical system according to claim 1, wherein the first diffracted light beam and the second diffracted light beam are different segments from each other.

8. The optical system of claim 1, wherein the PLM is configured to generate a phase hologram.

9. The optical system of claim 8, wherein the phase hologram comprises dimensional features determined in response to a wavelength of the incident coherent light beam.

10. The optical system of claim 9, wherein the phase hologram is configured to diffractively shift a Fourier transformed phase image to a position between diffraction orders.

11. The optical system of claim 9, wherein the phase hologram is configured to diffraction-shift a Fourier transformed phase image vertically and horizontally to a position between diffraction orders of the phase image in a Fourier series.

12. The optical system of claim 1, further comprising an inverting lens optically coupled to the lens array, the lens array configured to focus the first overlapping diffracted light beams and the second overlapping diffracted light beams on a same portion of the inverting lens.

13. An optical system according to claim 1, wherein the PLM is configured to generate a third diffraction beam and a fourth diffraction beam in response to the incident coherent light beam, and wherein the lens array further includes a third array lens configured to receive the third diffraction beam, and wherein the lens array further includes a fourth array lens configured to receive the fourth diffraction beam.

14. The optical system of claim 13, wherein the first array lens, the second array lens, the third array lens, and the fourth array lens are arranged as a two by two lens array.

15. The optical system according to claim 13 further comprises a mask adjacent to the lens array, wherein the mask is arranged between adjacent array lenses of the first array lens, the second array lens, the third array lens and the fourth array lens, the first array lens is adjacent to the second array lens and the fourth array lens, the second array lens is adjacent to the first array lens and the third array lens, the third array lens is adjacent to the second array lens and the fourth array lens, and the fourth array lens is adjacent to the third array lens and the first array lens.

16. The optical system of claim 13, further comprising a mask adjacent to the lens array, the mask configured to block portions of a zeroth order phase image of a diffracted illumination pattern.

17. The optical system of claim 1, further comprising the coherent beam illuminator, the coherent beam illuminator comprising a laser and an optical fiber coupled between the laser and the PLM.

18. The optical system of claim 1, further comprising a diffuser optically coupled to the lens array, the diffuser having a movable aperture.

19. An optical system comprising: a phase light modulator PLM comprising a two-dimensional array of pixels, the PLM being adapted to receive at least one coherent light beam and to generate a diffractive illumination pattern in response to the at least one coherent light beam, the diffractive illumination pattern comprising a first diffracted light beam and a second diffracted light beam; a lens array optically coupled to the PLM, the lens array comprising: a first array lens configured to focus the first diffracted light beam and generate a first overlapping diffracted light beam in response to the first diffracted light beam; a second array lens configured to focus the second diffracted light beam and generate a second overlapping diffracted light beam in response to the second diffracted light beam, the second diffracted light beam including a light intensity distribution different from that of the first diffracted light beam; and A spatial light modulator is optically coupled to the lens array, the spatial light modulator being configured to form an image beam in response to the first overlapping diffracted light beams and the second overlapping diffracted light beams.

20. A method for an optical system, the method comprising: generating a first diffracted light beam and a second diffracted light beam by a phase light modulator PLM in response to at least one coherent light beam incident on the PLM, the PLM comprising a two-dimensional pixel array; focusing the first diffracted light beams by a first array lens optically coupled to the PLM to generate first overlapping diffracted light beams; focusing the second diffracted beam by a second array lens optically coupled to the PLM to generate a second overlapping diffracted beam; and The first overlapping diffracted light beams and the second overlapping diffracted light beams are modulated by a spatial light modulator optically coupled to the PLM.

21. The method according to claim 20, further comprising: diffusing through a diffuser optically coupled to the PLM to produce diffused light in response to light received from the first array lens and the second array lens; and The diffused light is projected through a projection focusing element optically coupled to the PLM.

Images