WO2025111387A1 - Filters for high contrast projection systems - Google Patents

Abstract

Optical filters for projection assemblies. One optical filter includes a transmissive portion configured to transmit modulated light toward a downstream optical element and a reflective portion. The reflective portion is configured to receive unmodulated light from a modulator at a first angle, and reflect the unmodulated light toward a light dump at a second angle, wherein an angle different between the first angle and the second angle is between 90° and 180°. The optical filter is disposed at a Fourier plane of the modulated light.

Description

FILTERS FOR HIGH CONTRAST PROJECTION SYSTEMS

1. Cross-Reference to Related Applications

[0001] This application claims the benefit of priority from U.S. Provisional Application No. 63/601,557, filed November 21, 2023 and U.S. Provisional Application No. 63/550,120, filed February 6, 2024, each of which is incorporated by reference herein in its entirety.

2. Field of the Disclosure

[0002] This application relates generally to filters and, more particularly to filters for blocking zero angle (DC) light in high contrast projection systems.

3. Background

[0003] Spatial light modulators (SLMs) are typically sectioned into pixels, with each pixel being driven separately to introduce a spatially varying change in an incident lightfield. Through spatial variation of lightfields, SLMs can be used to generate a pre-defined image from a spatially homogenous lightfield. SLMs include amplitude modulators, which attenuate the amplitude of incident light, and phase modulators, which alter the phase of incident light. Both amplitude modulators and phase modulators have significant drawbacks.

[0004] Amplitude modulators utilize liquid crystals, for example, to variably darken areas within the incident lightfield that correspond to individual pixels of the modulator. An image is formed by darkening each pixel in an amount that corresponds to the brightness of a corresponding region of the desired image. Liquid crystals control amplitude by varying phase, which varies polarization due to the birefringent nature of the liquid crystals, and utilizing external polarizers (or polarizers built into the modulator) to convert the polarization change to an amplitude change. Typical amplitude modulators have a relatively low limit for achievable contrast, because, among other things, reflections (i.e., 0^th order light) from various refractive interfaces within the devices brighten regions on the resultant image that are intended to be dark.

[0005] Phase modulators utilize, for example, liquid crystals or piston mirror devices to variably introduce phase change to areas of the incident light that correspond to individual pixels of the modulator. The phase changes introduce interference between light from different pixels, effectively steering the modulated light in a predictable manner. An image is formed by steering light toward brighter areas of the image and away from darker areas of the image. Known phase modulators have a relatively low limit for achievable contrast in images with a total irradiance that is significantly dimmer than the incident lightfield, because unwanted light is not attenuated, as in an amplitude modulator.

BRIEF SUMMARY OF THE DISCLOSURE

[0006] FIG. 1 is a cross-sectional view of an example SLM 100 according to the prior art. SLM 100 includes a cover glass 102, an electrode 104, a liquid crystal layer 106, a dielectric layer 108, and a plurality of pixel mirrors 110 formed on a substrate 112. Light is incident on cover glass 102 at an angle. Most of the incident light is transmitted into cover glass 102, but a portion of the incident light is reflected at an angle 3 with respect to the normal to cover glass 102, which is equal to the angle of the incident light with respect to the normal to cover glass 102. Another portion of the transmitted light is reflected from the bottom surface of cover glass 102 and is transmitted from cover glass 102 at an identical angle 3. The rest of the transmitted light travels through the various layers of SLM 100 (being modulated by liquid crystal layer 106 on the way), reflects off pixel mimors 110, travels back through the various layers of SLM 100, and is transmitted into the surrounding area at an identical angle 3. Because each of the unwanted, reflected portions of light arc traveling at the same angle with respect to cover glass 102 as the desired, modulated light, they will follow the same path, thus, decreasing the overall contrast of the resultant image.

[0007] Additionally, when fiber-coupled coherent illumination is used as a light source, the interference of the multiple modes travelling down the fiber creates a speckle pattern (also known as modal noises). This modal noise is sensitive to fiber movement. This modal noise creates a small amount of reflection within the modulated light from the plurality of pixels mirrors 110. The modal noise within the modulated light may be hidden by quickly changing the driving pattern of the plurality of pixel mirrors 110 in a temporal fashion. For modal noises in the unmodulated fraction of light with small angles 0, a filter can be used to block the light.

[0008] Embodiments described herein relate to a filter for filtering unmodulated, reflected light after a phase modulator for enhancing the black level of an output image. For example, the filter may filter out unmodulated DC light reflected off the cover glass 102. In some instances, the filter blocks higher diffraction orders that corrupt reconstructed output images, allowing for reconstruction distances where the high diffraction orders overlap with the zeroth (DC) order.

[0009] In one exemplary aspect of the present disclosure, there is provided an optical filter for a projection assembly. The optical filter includes a transmissive portion configured to transmit modulated light toward a downstream optical element and a reflective portion. The reflective portion is configured to receive unmodulated light from a modulator at a first angle, and reflect the unmodulated light toward a light dump at a second angle, wherein an angle different between the first angle and the second angle is between 90° and 180°. The optical filter is disposed at a Fourier plane of the modulated light.

[0010] In another exemplary aspect of the present disclosure, there is provided a projector comprising a light source, a modulator, and an optical filter. The light source is configured to emit a light in response to an image signal, the image signal including image data. The modulator is configured to receive the light from the light source and to apply a spatially-varying modulation on the light, thereby to steer the light and to generate a steered light. The modulator includes a cover glass. The steered light includes unmodulated light and modulated light. A lens is configured to spatially Fourier transform the steered light to generate a transformed light. The optical filter is configured to filter the transformed light to generate a filtered light output. The optical filter includes a transmissive portion configured to transmit the modulated light toward a downstream optical element. The reflective portion is configured to receive the unmodulated light from the modulator at a first angle and reflect the unmodulated light toward a light dump at a second angle. An angle difference between the first angle and the second angle is between 90° and 180°.

[0011] In yet another exemplary aspect of the present disclosure, there is provided a projector comprising a light source, a modulator, and an optical fdter. The light source is configured to emit a light in response to an image signal, the image signal including image data. The modulator is configured to receive the light from the light source and to apply a spatially-varying modulation on the light, thereby to steer the light and to generate a steered light. The modulator includes a cover glass. The steered light includes a plurality of diffraction orders and unmodulated light. A lens is configured to spatially Fourier transform the steered light to generate a transformed light. The optical filter is configured to filter the transformed light to generate a filtered light output. The optical filter is disposed at an image reconstruction plane of the steered light. The optical filter is configured to receive the steered light including the plurality of diffraction orders and the unmodulated light, transmit zeroth order light included in the plurality of diffraction orders, and reflect the unmodulated light.

[0012] In this manner, various aspects of the present disclosure provide for the display of images having a high dynamic range and high resolution, and effect improvements in at least the technical fields of image projection, holography, signal processing, and the like.

DESCRIPTION OF THE DRAWINGS

[0013] These and other more detailed and specific features of various embodiments are more fully disclosed in the following description, reference being had to the accompanying drawings, in which:

[0014] FIG. 1 illustrates a cross-sectional view of an example spatial light modulator (SLM);

[0015] FIG. 2 illustrates a block diagram showing an example projection system;

[0016] FIG. 3 illustrates an optical diagram showing light reflected by an example modulator;

[0017] FIG. 4 illustrates a block diagram showing one example of lightfield optics/filters of the projection system of FIG. 2;

[0018] FIG. 5A illustrates a cross-sectional view showing one example of the lightfield optics/filters of FIG. 4 in greater detail;

[0019] FIG. 5B illustrates a cross-sectional view showing potential undesirable filtering of modulated light;

[0020] FIG. 5C illustrates a cross-sectional view illustrating the avoidance of undesirable filtering by steering all modulated light by a predetermined angle;

[0021] FIG. 6A illustrates a front view of the optical filter of FIG. 5A in greater detail;

[0022] FIG. 6B illustrates a front view of an alternate optical filter;

[0023] FIG. 6C illustrates a front view of another alternate optical filter; [0024] FIG. 7 illustrates a cross-sectional view of alternate lightfield optics/filters;

[0025] FIG. 8 illustrates a front view of the optical filter of FIG. 7 in greater detail;

[0026] FIG. 9A illustrates a perspective view of a conical optical filter;

[0027] FIG. 9B illustrates a side view of the conical optical filter of FIG. 9A; and

[0028] FIG. 10 illustrates a side view of another alternate optical filter.

DETAILED DESCRIPTION

[0029] This disclosure and aspects thereof can be embodied in various forms, including hardware, devices or circuits controlled by computer-implemented methods, computer program products, computer systems and networks, user interfaces, and application programming interfaces; as well as hardware-implemented methods, signal processing circuits, memory arrays, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and the like. The foregoing is intended solely to give a general idea of various aspects of the present disclosure, and does not limit the scope of the disclosure in any way.

[0030] In the following description, numerous details are set forth, such as optical device configurations, timings, operations, and the like, in order to provide an understanding of one or more aspects of the present disclosure. It will be readily apparent to one skilled in the art that these specific details are merely exemplary and not intended to limit the scope of this application.

[0031] Moreover, while the present disclosure focuses mainly on examples in which the various circuits are used in digital projection systems, it will be understood that these arc merely examples. It will further be understood that the disclosed systems and methods can be used in any device in which there is a need to project light; for example, cinema, consumer, and other commercial projection systems, heads-up displays, virtual reality displays, and the like. Disclosed systems and methods may be implemented in additional display devices, such as with an OLED display, an LCD display, a quantum dot display, or the like.

[0032] FIG. 2 is a block diagram of an image projector 200 capable of producing high contrast images. Image projector 200 includes an illumination source 202, lightfield optics/filters 204, high contrast imaging SLM(s) 206, imaging optics 208, and a controller 210. In this particular example embodiment, projector 200 is a dual modulation projector. Dual modulation increases the dynamic range of projector 200 by reducing light leakage at imaging SLM(s) 206. For example, the pixels of imaging SLM(s) 206 that are displaying darker areas of an image are illuminated with less intense light, thereby decreasing the amount of required attenuation by imaging SLM(s) 206. As a result, the light output of dark pixels is closer to 0%, which improves the dynamic range of projector 200.

[0033] Illumination source 202 includes a plurality of individually controllable light valves, which facilitate the emission of a modulated illumination beam 214. In this example embodiment, illumination source 202 includes a light source 209, illumination optics 211, and high contrast illumination SLM(s) 220. Light source 209 generates a raw illumination beam 222, and directs raw illumination beam 222 toward illumination optics 211. Illumination optics 211 conditions raw illumination beam 222 to generate a conditioned illumination beam 224 and directs conditioned illumination beam 224 to evenly impinge on illumination SLM(s) 220. Illumination SLM(s) 220 modulate conditioned illumination beam 224 to produce modulated illumination beam 214 responsive to illumination data provided by controller 210. In this example embodiment, the individually controllable light valves of illumination source 202 are pixels (or groups of pixels) of illumination SLM(s) 220, which is/are reflective liquid crystal phase modulators capable of steering light beams at desired angles.

[0034] Lightfield optic s/filters 204 receives modulated imaging beam 214 and alters/redirects modulated imaging beam 214 in a predetermined way, in order to illuminate high contrast imaging SLM(s) 206 with a desired lightfield 216. Although shown as a beam transmitted from lightfield optic s/filters 204 to imaging SLM(s) 206 for illustrative purposes, lightfield 216 is more accurately described as the light impinging on the modulating surface(s) of imaging SLM(s) 206.

[0035] Imaging SLM(s) 206, responsive to image data from controller 210, modulate(s) lightfield 216 to infuse an imaging beam 218 with an image corresponding to the image data, and directs imaging beam 218 to imaging optics 208. Imaging optics 208 focuses imaging beam 218 on a viewing surface 225, where the projected images can be viewed (e.g., on a movie theater screen). Controller 210 receives image/video data from a source (not shown) via data input 226, adjusts the image data depending on lightfield 216, which is simulated by controller 210, and provides the adjusted image data to imaging SLM(s) 206. [0036] In the example embodiment, illumination SLM(s) 220 and imaging SLM(s) 206 are high contrast spatial light modulators. SLM(s) 220 and 206 increase contrast by redirecting unwanted light that reflects from optical interfaces of SLM(s) 220 and 206 (i.e. 0^th order light) away from the desired, modulated light (i.e. 1^st order light). The present disclosure presents various particular embodiments of SLM(s) 220 and 206 that generate high contrast images as illustrative examples, but it should be understood that the illustrative examples disclosed are not limiting. For example, SLM(s) 220 and 206 are shown in the following examples as liquid crystal SLMs. However, SLM(s) 220 and 206 can be any SLMs having a cover glass or other front reflective surface, including, but not limited to, digital micro-mirror devices, multi-element mirror devices, microelectromechanical devices, and/or any other spatial light modulators, including those yet to be invented.

[0037] In some implementations, a second path is provided on which the light bypasses the illumination SLM(s) 220 before the light arrives at the imaging SLM(s) 206. In such an implementation, a second light source and second illumination optics may be provided before the imaging SLM(s) 206. Light from the second light source is combined with light from the light source 209 prior to being provided to the imaging SLM(s) 206. In other instances, a portion of the raw illumination beam 222 projected by the light source 209 is split off before the raw illumination beam 222 is modulated by the illumination SLM(s) 220 and is recombined prior to modulation at the imaging SLM(s) 206.

[0038] As previously mentioned, when fiber-coupled coherent illumination is used as a light source, the interference of the multiple modes travelling down the fiber creates a speckle pattern (also known as modal noises). This modal noise is sensitive to fiber movement. This modal noise is detected within unmodulated light from the cover glass 102, adding distortion to generated images.

[0039] For modulators with flat mirrors (such as the SLM 100), most of the reflected light is in the 0^th order direction. However, as shown in optical diagram 300 of FIG. 3, the 0^th order light reflected by SLM 220 at a distance less than/o is mixed with other diffraction orders, such as 1^st order light. The distance fo is the distance at which the diffraction orders just separate and is a distance at which an image 302 (e.g., a reconstruction image) is formed with only 0^th order light (e.g., the shortest reconstruction distance). The image is reconstructed on image reconstruction plane 304. Should the image reconstruction plane 304 be situated at a distance less than fo, the image 302 may be corrupted by diffraction orders greater than the 0^th order. However, due to the etendue of the light reflected by the SLM 220, the resolution of the image 302 reduces as the distance between the SLM 220 and the image reconstruction plane 304 increases. Accordingly, it is desirable to reconstruct the image 302 at a distance less than / to increase the resolution of the image 302.

[0040] First, by implementing a high-pass (or, in some instances, a band-pass) DC-blocking Fourier filter, all modulated light that is steered in small angles (e.g., angles less than approximately ±1°) is effectively blocked. The high-pass Fourier filter may be implemented as part of the lightfield optic s/filters 204. This blocked light includes the “DC” noise and modal noise previously described, but may also contain a portion of the desired reconstruction image. Without adjusting the algorithm that generates the PLM phase-drive signals that drive the plurality of mirrors 110, the high-pass Fourier filter may attenuate light that is willingly steered at small angles. To overcome the undesired attenuation, phase-drive signals may be implemented that avoid the steering angles that would be blocked by the high-pass Fourier filter. Example beam-steering algorithms that may be implemented are found in U.S. Patent No. 10,904,495, the full disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

[0041] Additionally, by implementing a low-pass (or, in some instances a band-pass) Fourier filter, shorter reconstruction distances for the image 302 may be utilized. The low-pass Fourier filter may be implemented as part of the lightfield optics/filters 204. For example, the locations on the Fourier plane correspond to angles of light. Instead of blocking the DC (or 0 angle) light, the Fourier filter may instead block light at angles of unwanted diffraction orders. By blocking unwanted diffraction orders, the image 302 may be reconstructed at a distance less than o from the SLM 220 without higher-order light corrupting the image 302.

[0042] FIG. 4 is a block diagram showing one example of lightfield optics/filters 204 of projection system 200 in greater detail. Illumination SLM(s) 220 provide(s) a spatially modulated lightfield to SLM(s) 206, through lightfield optics/filters 204. SLM(s) 220 is/are (a) reflective phase modulator(s) that effectively steer(s) selected portions of the incident light to generate a spatially variant lightfield. The steered light traverses lightfield optics/filters 204, which include a first optical element 402, an optical filter 404, and a second optical element 406. First optical element 402 is, in the example embodiment, a Fourier lens, which produces a Fourier transform of the steered light in the Fourier plane. Optical filter 404 is located at or near the Fourier plane of first optical element 402. Optical filter 404 selectively filters portions of the Fourier transform corresponding to reflected, unmodulated light from SLM(s) 220, and second optical element 406 focuses the filtered lightfield on SLM(s) 206. Each of the first optical element 402, the optical filter 404, and the second optical element 406 may include only a single lens or multiple lenses. SLM(s) 206 is/are (an) amplitude modulating SLM(s), which generate(s) images by spatially modulating the lightfield produced by SLM(s) 220. Filtering the reflected, unmodulated light from the lightfield generated by SLM(s) 220 results in higher contrast images being generated by SLM(s) 206.

[0043] FIG. 5A is a cross-sectional view showing lightfield optic s/filters 204 in more detail. Light incident on SLM(s) 220 is steered toward first optical element 402, which, in this embodiment, is a convex lens 502. Lens 502 focuses a Fourier transform of the steered light onto an optical filter 504 by directing rays to corresponding points of the filter, based on the angle of those rays with respect to the normal of SLM(s) 220. For example, the two rays 505 having angles equal to O with respect to the normal of SLM(s) 220 are redirected to an off-center point on optical filter 504. The other rays (two unmodulated, reflected rays 507 and one intentionally un-steered ray 509), all of which have an angle of 0° with respect to the normal, are redirected to the center of optical filter 504. The light that is redirected to the center of optical filter 504 includes the “DC term” of the modulated lightficld and the unmodulated, reflected light. Optical filter 504 is a transparent optical element having an opaque, light block disc 506 positioned in the center, which blocks the “DC term” of the modulated lightfield and the unmodulated, reflected light. Thus, a user can eliminate unwanted light from the system by leaving it un-steered. Light that is not blocked continues onto second optical element 506, which, in this embodiment, is a convex lens 508. Lens 508 focuses the, now diverging, light from lens 502 back to its initial trajectory toward SLM(s) 206 (FIG. 4).

[0044] In some implementations, the lightfield optics/filters 204 may include filters and optical components to filter other diffraction orders and undesired, excess light. For example, the lightfield optics/filters 204 may include a low-pass filter to block high diffraction orders instead of or in addition to the “DC term” of the modulated lightfield and the unmodulated, reflected light. In such an instance, a portion of the upper steerable angles of the SLM(s) 220 may be directed to a light dump. [0045] In the example embodiment, optical filter 504 is placed at the Fourier plane of lightfield optic s/filters 204 to allow precise spatial filtering of the steered lightfield. In alternate embodiments, optical filter 504 can be placed in other locations between lenses 502 and 508, in order to filter less of the DC term light. Additionally, optical filter 504 can be made slidable with respect to lenses 502 and 508, in order to filter more or less of the DC term, as needed for each particular application. In addition, light block disc 506 can be a light block of various shapes and sizes, such as one or more concentric rings.

[0046] An advantage of some embodiments of the present invention is the ability to preserve the DC term of the desired lightfield, while at the same time filtering out the reflected unmodulated light (0^th order light) from the lightfield. An example method for preventing the desired DC term light from being blocked by optical filter 504 includes steering the entire image at a non-zero angle with respect to the normal of SLM 220. To form an image, a steering solution is calculated by determining a steering angle for light from each region of SLM 220 (e.g., one or more pixels). The range of steering angles for the solution is constrained to the interval \-3, 3], where 3 is some fraction of the maximum steering angle that SLM 220 is capable of producing. In most examples, the solution will include some steering angles that are parallel to the normal of SLM 220. However, adjusting the steering angles of the solution to steer the entire lightfield by a predetermined amount can ensure that the adjusted solution will include some steering angles that arc parallel to the normal of SLM 220. However, adjusting the steering angles of the solution to steer the entire lightfield by a predetermined amount can ensure that the adjusted solution will not include any angles that will be filtered out with the reflected, unmodulated (0^th order) light. This technique will be described in more detail with reference to FIGs. 5B and 5C.

[0047] FIG. 5B is a cross-sectional view illustrating the constrained range of steering angles available to SLM 220 in the initial image solution. Imaging beams 510 range in angle from -3 to 3, including a zero angle in between. Because the zero-angle light 511 is traveling perpendicular with respect to the surface of SLM 220, it is blocked by optical filter 504, along with reflected beams 512, which cannot be steered.

[0048] FIG. 5C is a cross-sectional view illustrating additional steering of the initial image solution of FIG. 5B. In order to retain the un-steered light 511 in the image solution, the entire image is steered by an additional angle ±<p, where <p > 3 and (p+3 is smaller than the maximum steering angle that SLM 220 is capable of producing. Imaging beams 510 are each steered at an additional angle -(p, and now range in angle from (O-(p) to ~(O+(p). Because the entire interval [(0- (pi), -(0+^)] is negative, none of the rays of the steered solution are normal to SLM 220 and, therefore, none of the image (including the DC term) is inadvertently blocked by optical filter 504. In this way, reflected (0^th order) light 512 can be removed from an image, without affecting the desired image itself.

[0049] This technique for preserving the DC term of the lightfield has been described as a two- step process for ease of understanding. In particular, the technique has been described as first calculating a steering angle within the confined range to generate the desired light field, and then steering the entire lightfield by adjusting the steering angles by a predetermined amount. However, it should be understood that these steps can be consolidated into a single steering angle computation that yields the adjusted steering angles in the first instance. It is not necessary to generate the initial steering angles, and then adjust those steering angles in a separate step.

[0050] FIG. 6A is a front view showing optical filter 504 in more detail. Optical filter 504 is a transparent, circular element with light block disc 506 centered in the middle. In a particular embodiment, optical filter 504 is positioned so that light block disc is centered on the optical axis of lens 502. Light block disc 506 blocks light corresponding to the DC term of the Fourier transform of the steered lightfield.

[0051] FIG. 6B is a front view showing an alternate optical filter 602 according to the present invention. Optical filter 602 is a transparent circular element with a polarizing disc 604 centered in the middle. For use in systems with some level of light polarization, optical filter 602 can provide adjustable attenuation of light corresponding to the DC term of the Fourier transform of the steered lightfield. Optical filter 602 is rotationally coupled to a rotary actuator 606, which selectively rotates in either direction. Actuator 606 rotates optical filter 602 between 0° and 90° in order to alter the polarization orientation of polarizing disc 604, with respect to the incident lightfield. Thus, the amount of light corresponding to the DC term that passes through optical filter 602 can be attenuated by driving actuator 606.

[0052] FIG. 6C is a front view showing an alternate optical filter 622 according to the present invention. In the example of FIG. 6C, the alternate optical filter 622 is a band-pass filter that includes a low-pass filter element 624, a transmissive element 626, and a high-pass filter element 628. In some implementations, the low-pass filter element 624 blocks all light that is not received by the transmissive element 626 or the low-pass filter element 628. The transmissive element 626 and the low-pass filter element 628 may then block modulated 1^st order light such that 0^th order light is transmitted. In some implementations, the low-pass filter element 624 includes a polarization coating such that attenuation of the 1^st order light is adjusted by driving actuator 606.

[0053] In some implementations, the high-pass filter element 628 blocks all unmodulated (0^th order, DC) light components. In other instances, the high-pass filter element 628 includes a polarization coating such that attenuation of the DC component is adjusted by driving actuator 606. While the high-pass filter element 628 is illustrated as being situated at a center of the optical filter 622, in some instances, the high-pass filter element 628 is displaced from the center of the optical filter 622.

[0054] While FIG. 6C illustrates the optical filter 622 as a band-pass filter, in other instances, the optical filter 622 may consist of only the high-pass filter element 628 or only the low-pass filter element 624. Additionally, the optical filter 622, the high-pass filter element 628, and the low-pass filter element 624 may take the form of other shapes, such as rectangles, ovals, crosshairs, and the like.

[0055] FIG. 7 is a cross-sectional view showing an alternate lightfield optic s/filters 700. Lightfield optic s/filters 700 are substantially similar to lightfield optics/filters 204 of FIG. 5A, except that filter 706 is configured to additionally block light that is steered in a particular, predetermined direction. An example SLM 702 (e.g., SLM(s) 220) steers incident light to produce a desired lightfield. A first convex lens 704, which is substantially similar to lens 502, focuses the steered light toward an optical filter 706 located at or near the Fourier plane. Filter 706 is positioned with light blocking disc 708 at or near the optical axis of lens 704. Optical filter 706 is similar to optical filter 504, except that optical filter 706 includes a centered light blocking disc 708 in combination with an additional light blocking disc 710 that is spaced apart from light blocking disc 708 at a predetermined position. Light blocking disc 708 functions in the same manner as light blocking disc 506. Light blocking disc 710 is positioned to block light steered at a particular angle, such as, for example, light with an angle of (p with respect to the normal of SLM 702, as shown in FIG. 7. As a result, unwanted light can be steered at angle (p in order to remove the light from the lightfield, using light blocking disc 710 as a light dump. A second convex lens 712 then focuses the, now diverging, light from lens 704 back to its initial trajectory toward additional system optics (not shown).

[0056] FIG. 8 is a front view showing optical filter 706 in more detail. Optical filter 706 is a transparent, circular element with light blocking disc 708 located in the center and light block disc 710 located in predetermined position near peripheral portion of filter 706. Light blocking disc 708 blocks the reflected, unmodulated (0^th order) light, and light blocking disc 710 blocks light steered at the predetermined angle (p.

[0057] FIG. 9A is a perspective view showing another example optical filter 900. FIG. 9B is a side view of the optical filter 900 transmitting light. The optical filter 900 may be implemented as, for example, the optical filter 404. The optical filter 900 may be a transmissive refractive Fourier filter. The optical filter 900 includes an optically transmissive element, such as a window, at a base portion 902. At a center 904 of the optical filter 900 is a conical point which aligns with the undesired unmodulated DC (or near-DC) light. The conical point functions as an inverted axicon lens and refracts light away from the optical axis. In some instances, other shapes are implemented at the center 904 instead of a conical point to effectively diffuse or scatter light. For example, a smooth curved surface or complex surface shape that scatters light may be used. In some instances, the inverted axicon may be replaced with a positive lens such that light converges at a focal point before being spread.

[0058] In some embodiments, the optical filter 404 includes a reflective feature for the undesired DC light. For example, the optical filter 404 is a transmissive filter that consists of a window or other optically transmissive element. The region on the Fourier “face” of the element that coincides with the undesired DC region of the Fourier plane is covered with a reflective material such as deposited aluminum or silver. For example, with reference to FIG. 5A, the light block disc 506 is covered with a reflective material. The undesired light is reflected back upstream in the optical path such that the undesired light is reflected away from the reconstructed image 225.

[0059] The face with the reflective feature, such as the light block disc 506, may be at an angle such that the reflected undesired light does not reflect straight backwards, but is instead reflected backwards at an angle towards a light dump. The reflective feature may be geometrically flat, may be convex, may be concave, or may be a complex surface structure such that the reflected light angles are modified. For example, the reflective feature may be a smooth convex surface that reflects and spreads light at an angle towards a dedicated light dump.

[0060] FIG. 10 is a side view showing another example optical filter 1000. The optical filter 1000 includes a refractive portion 1002 (for example, the optical filter 900), a transmissive portion 1004, and a reflective portion 1006. The refractive portion 1002 is configured to refract the light towards the reflective portion 1006. The transmissive portion 1004 is an optically transmissive element (for example, silica) that transmits light without changing the angle of the light. For example, a portion of received light 1008 passes through the transmissive portion 1004 as a transmitted light 1010. An angle of the received light 1008 is the same as an angle of the transmitted light 1010.

[0061] The reflective portion 1006 may be, for example, a mirror or an element coated in reflective material such as aluminum or silver. The refractive portion 1002 refracts light to the reflective portion 1006 such that the reflective portion 1006 directs the light back towards the SLM 220. For example, a portion of the received light 1008 is refracted by the refractive portion 1002 to generate a refracted light 1012. The reflective portion 1006 receives the refracted light 1012 and reflects the refracted light 1012 as a reflected light 1014. The reflected light 1014 may be directed towards a light dump. The light is reflected by the reflective portion 1006 to avoid interaction with downstream optical elements (e.g., the imaging optics 208). Accordingly, if the received light 1008 is traveling at an angle of 0°, the reflected light 1014 has an angle between 90° (perpendicular to the received light 1008) and 180° (exactly opposite a direction of the received light 1008). In some embodiments, the light is first refracted at an angle to avoid the light traveling directly backwards toward the SLM 220. Accordingly, the reflected light 1014 may have an angle between 90° and 150°, or similar angular ranges.

[0062] In yet another example, with reference to FIG. 4, the Fourier plane coincides with a mirror functioning as the optical filter 404. The mirror includes an aperture where undesired light (e.g., DC light, unmodulated light, etc.) is located on the Fourier plane. The undesired light passes through the aperture to a light dump, while the desired light is reflected by the mirror toward the second optical element 406.

[0063] With reference to FIG. 3, optical filters described herein provide for the removal of unmodulated light and modal noise from the image 302 reconstructed at the image reconstruction plane 304. Additionally, optical filters described herein block higher-order diffraction orders, allowing for the image reconstruction plane 304 to be at a distance from the SLM 220 less than the distance fo, resulting in a higher resolution image than images reconstructed at the distance fo.

[0064] The above filters provide for blocking zero angle (DC) light in high contrast projection systems. Systems, methods, and devices in accordance with the present disclosure may take any one or more of the following configurations.

[0065] (1) An optical filter for a projection assembly, the optical filter comprising: a transmissive portion configured to transmit modulated light toward a downstream optical element; and a reflective portion configured to: receive unmodulated light from a phase light modulator at a first angle and reflect the unmodulated light toward a light dump at a second angle. An angle difference between the first angle and the second angle is between 90° and 180°. The optical filter is disposed at a Fourier plane of the modulated light.

[0066] (2) The optical filter according to (1), wherein the optical filter includes a conical shape.

[0067] (3) The optical filter according to any one of (1) to (2), wherein the reflective portion includes a coating selected from the group consisting of an aluminum coating and a silver coating.

[0068] (4) The optical filter according to any one of (1) to (3), wherein the reflective portion includes one selected from the group consisting of a convex surface, a concave surface, and a complex surface.

[0069] (5) The optical filter according to any one of (1) to (4), wherein the reflective portion includes a flat mirror.

[0070] (6) The optical filter according to any one of (1) to (5), wherein the modulated light includes a plurality of diffraction orders, and wherein the optical filter further includes: a filtering portion configured to block a subset of the plurality of diffraction orders.

[0071] (7) A projector comprising: a light source configured to emit a light in response to an image signal, the image signal including image data; a modulator configured to receive the light from the light source and to apply a spatial varying modulation on the light, thereby to steer the light and to generate a steered light, wherein the modulator includes a cover glass, and wherein the steered light includes unmodulated light and modulated light; a lens configured to spatially Fourier transform the steered light to generate a transformed light; and an optical filter configured to filter the transformed light to generate a filtered light output, wherein the optical filter includes: a transmissive portion configured to transmit the modulated light toward a downstream optical element; and a reflective portion configured to: receive the unmodulated light from the modulator at a first angle, and reflect the unmodulated light toward a light dump at a second angle, wherein an angle difference between the first angle and the second angle is between 90° and 180°.

[0072] (8) The projector according to (7), wherein the steered light includes a plurality of diffraction orders, and wherein the optical filter further includes: a filtering portion configured to block a subset of the plurality of diffraction orders.

[0073] (9) The projector according to any one of (7) to (8), wherein the optical filter includes a conical region configured to diffract the unmodulated light toward the reflective portion.

[0074] (10) The projector according to any one of (7) to (9), wherein the reflective portion includes a coating selected from the group consisting of an aluminum coating and a silver coating.

[0075] (11) The projector according to any one of (7) to (10), wherein the reflective portion includes one selected from the group consisting of a convex surface, a concave surface, and a complex surface.

[0076] (12) The projector according to any one of (7) to (11), wherein the reflective portion includes a flat mirror.

[0077] (13) A projector comprising: a light source configured to emit a light in response to an image signal, the image signal including image data; a modulator configured to receive the light from the light source and to apply a spatial varying modulation on the light, thereby to steer the light and to generate a steered light, wherein the modulator includes a cover glass, and wherein the steered light includes a plurality of diffraction orders and unmodulated light; a lens configured to spatially Fourier transform the steered light to generate a transformed light; and an optical filter configured to filter the transformed light to generate a filtered light output, wherein the optical filter is disposed at an image reconstruction plane of the steered light, and wherein the optical filter is configured to: receive the steered light including the plurality of diffraction orders and the unmodulated light, transmit zeroth order light included in the plurality of diffraction orders, and reflect the unmodulated light.

[0078] (14) The projector of claim 13, wherein the optical filter is further configured to receive the unmodulated light at a first angle, and wherein reflecting the unmodulated light includes reflecting the unmodulated light toward a light dump at a second angle, wherein an angle difference between the first angle and the second angle is between 90° and 180°.

[0079] (15) The projector according to any one of (13) to (14), wherein the optical filter includes a transmissive portion configured to transmit the zeroth order light and a reflective portion configured to reflect the unmodulated light.

[0080] (16) The projector according to (15), wherein the optical filter includes a conical shape, and wherein the conical shape is configured to steer the unmodulated light toward the reflective portion.

[0081] (17) The projector according to (15), wherein the optical filter includes one selected from the group consisting of a convex surface, a concave surface, and a complex surface configured to steer the unmodulated light toward the reflective portion.

[0082] (18) The projector according to any one of (13) to (17), wherein the optical filter includes a coating selected from the group consisting of an aluminum coating and a silver coating, wherein the coating is configured to reflect the unmodulated light.

[0083] (19) The projector according to any one of (13) to (18), wherein the optical filter includes a flat mirror configured to reflect the unmodulated light.

[0084] (20) The projector according to any one of (13) to (19), wherein the optical filter further includes a filtering portion configured to block diffraction orders greater than the zeroth order light.

[0085] With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claims.

[0086] Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. The scope should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the technologies discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the application is capable of modification and variation.

[0087] All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.

[0088] The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments incorporate more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in fewer than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.

Claims

CLAIMS What is claimed is:

1. An optical filter for a projection assembly, the optical filter comprising: a transmissive portion configured to transmit modulated light toward a downstream optical element; and a reflective portion configured to: receive unmodulated light from a phase light modulator at a first angle, and reflect the unmodulated light toward a light dump at a second angle, wherein an angle difference between the first angle and the second angle is between 90° and 180°, wherein the optical filter is disposed at a Fourier plane of the modulated light.

2. The optical filter of claim 1, wherein the optical filter includes a conical shape.

3. The optical filter of claim 1 or 2, wherein the reflective portion includes a coating selected from the group consisting of an aluminum coating and a silver coating.

4. The optical filter of any one of claims 1 to 3, wherein the reflective portion includes one selected from the group consisting of a convex surface, a concave surface, and a complex surface.

5. The optical filter of any one of claims 1 to 4, wherein the reflective portion includes a flat miiTor.

6. The optical filter of any one of claims 1 to 5, wherein the modulated light includes a plurality of diffraction orders, and wherein the optical filter further includes: a filtering portion configured to block a subset of the plurality of diffraction orders.

7. A projector comprising: a light source configured to emit a light in response to an image signal, the image signal including image data; a modulator configured to receive the light from the light source and to apply a spatially- varying modulation on the light, thereby to steer the light and to generate a steered light, wherein the modulator includes a cover glass, and wherein the steered light includes unmodulated light and modulated light; a lens configured to spatially Fourier transform the steered light to generate a transformed light; and an optical filter configured to filter the transformed light to generate a filtered light output, wherein the optical filter includes: a transmissive portion configured to transmit the modulated light toward a downstream optical element; and a reflective portion configured to: receive the unmodulated light from the modulator at a first angle, and reflect the unmodulated light toward a light dump at a second angle, wherein an angle difference between the first angle and the second angle is between 90° and 180°.

8. The projector of claim 7, wherein the steered light includes a plurality of diffraction orders, and wherein the optical filter further includes: a filtering portion configured to block a subset of the plurality of diffraction orders.

9. The projector of claim 7 or 8, wherein the optical filter includes a conical region configured to diffract the unmodulated light toward the reflective portion.

10. The projector of any one of claims 7 to 9, wherein the reflective portion includes a coating selected from the group consisting of an aluminum coating and a silver coating.

11. The projector of any one of claims 7 to 10, wherein the reflective portion includes one selected from the group consisting of a convex surface, a concave surface, and a complex surface.

12. The projector of any one of claims 7 to 11, wherein the reflective portion includes a flat mirror.

13. A projector comprising: a light source configured to emit a light in response to an image signal, the image signal including image data; a modulator configured to receive the light from the light source and to apply a spatially- varying modulation on the light, thereby to steer the light and to generate a steered light, wherein the modulator includes a cover glass, and wherein the steered light includes a plurality of diffraction orders and unmodulated light; a lens configured to spatially Fourier transform the steered light to generate a transformed light; and an optical filter configured to filter the transformed light to generate a filtered light output, wherein the optical filter is disposed at an image reconstruction plane of the steered light, and wherein the optical filter is configured to: receive the steered light including the plurality of diffraction orders and the unmodulated light, transmit zeroth order light included in the plurality of diffraction orders, and reflect the unmodulated light.

14. The projector of claim 13, wherein the optical filter is further configured to receive the unmodulated light at a first angle, and wherein reflecting the unmodulated light includes reflecting the unmodulated light toward a light dump at a second angle, wherein an angle difference between the first angle and the second angle is between 90° and 180°.

15. The projector of claim 13 or 14, wherein the optical filter includes a transmissive portion configured to transmit the zeroth order light and a reflective portion configured to reflect the unmodulated light.

16. The optical filter of claim 15, wherein the optical filter includes a conical shape, and wherein the conical shape is configured to steer the unmodulated light toward the reflective portion.

17. The optical filter of claim 15, wherein the optical filter includes one selected from the group consisting of a convex surface, a concave surface, and a complex surface configured to steer the unmodulated light toward the reflective portion.

18. The optical filter of any one of claims 13 to 17, wherein the optical filter includes a coating selected from the group consisting of an aluminum coating and a silver coating, wherein the coating is configured to reflect the unmodulated light.

19. The optical filter of any one of claims 13 to 18, wherein the optical filter includes a flat miiTor configured to reflect the unmodulated light.

20. The optical filter of any one of claims 13 to 19, wherein the optical filter further includes a filtering portion configured to block diffraction orders greater than the zeroth order light.