RU2782886C2 - Systems and methods for digital laser projection with enhanced contrast, using fourier filter - Google Patents

Abstract

FIELD: laser equipment.

SUBSTANCE: invention relates to laser projection systems. The system contains a spatial light modulator configured to modulate a light signal with formation of a repeated sequence of the first, the second, and the third modulated light signals; a lens configured for spatial Fourier transform; and a disc with light filters, located on the Fourier plane and containing a set of optical filter masks. Each mask filters one of the first, the second, and the third modulated light signals by passage of at least one diffraction order of a corresponding one of the first, the second, and the third modulated light signals and blocking of the rest part of the corresponding one of the specified signals. The disc with light filters is configured so that to rotate synchronously with the modulated light signal, so that each mask is located in the modulated light signal with time multiplexing on the Fourier plane, where the modulated light signal is the corresponding one of the first, the second, and the third modulated light signals.

EFFECT: increase in a contrast coefficient.

32 cl, 38 dwg

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of U.S. Provisional Application No. 62/651657, filed April 2, 2018, and European Patent Application No. EP18180390.9, filed June 28, 2018, each of which is incorporated herein in its entirety by links.

BACKGROUND OF THE INVENTION

Projector contrast indicates the ratio of the brightest projector output to the darkest projector output. The contrast ratio is a quantifiable measure of contrast, defined as the ratio of the brightness of the brightest projector output to the brightness of the darkest projector output. This ratio of contrast ratio is also referred to as the "static" or "natural" contrast ratio.

Due to the visual adaptation of the human visual system, the range of brightness values perceptible to the viewer corresponds to a contrast ratio of approximately 1000,000,000:1, although at any time the perceptible range of brightness values corresponds to a contrast ratio that is less than this value. For example, in scotopic vision performed solely by rod cells in the human eye, the apparent contrast ratio at any given moment for some viewers can be as high as 1,000,000:1, depending on the scene being observed, the user's adaptation state, and biological factors.

Viewers in a movie theater setting may be in different states of adaptation at any given moment, and therefore may see the same scene with different contrast ratios. Differences in adaptation states between viewers can be explained by different seating positions relative to the screen, where each viewer is focused on the screen, and when and how often each viewer closes their eyes. Because a movie theater is used by many viewers, an ideal projector has a contrast ratio that is high enough to accurately reproduce images for all viewers.

Some projectors that are compliant with the Digital Cinema Initiatives (DCI) specification have contrast ratios of 2000:1 or less. For these digital projectors, dark and/or black areas of images can be projected at a brightness high enough that these areas are brighter than they should be.

The essence of the invention

In a first aspect, an optical filter for enhancing the contrast of an image generated by a spatial light modulator comprises a lens configured to spatially Fourier transform a modulated light signal from the spatial light modulator, wherein the modulated light signal contains a plurality of diffraction orders. The optical filter also includes an optical filter mask located on the Fourier plane of the lens and configured to filter the modulated light signal that has undergone a spatial Fourier transform by the lens by passing at least one order of diffraction of the modulated light signal and blocking the remainder of the modulated light signal. .

In certain embodiments of the first aspect, at least one diffraction order is the zero diffraction order.

In certain embodiments of the first aspect, the optical filter mask has a pass region configured to pass zero order diffraction of the modulated light signal.

In certain embodiments of the first aspect, at least one diffraction order includes a zero diffraction order and one or more first diffraction orders.

In certain embodiments of the first aspect, the optical filter mask has a pass region configured to pass zero order diffraction and the first two diffraction orders.

In certain embodiments of the first aspect, the modulated light signal is one of red light, green light, and blue light.

In the second aspect, the modulator system for generating a contrast enhanced image comprises an optical filter of the first aspect and a digital micromirror device that implements a spatial light modulator.

In a third aspect, the modulator system for generating a contrast enhanced image comprises an optical filter of the first aspect and a collimator lens positioned to collimate at least one order of diffraction of the modulated light signal transmitted by the optical filter mask.

In a fourth aspect, a modulator system for generating a contrast enhanced image comprises first, second, and third spatial light modulators configured to modulate, in accordance with the image, respective first, second, and third light signals to generate respective first, second, and third modulated light signals. signals. The modulator system also comprises three instances of the first aspect optical filter forming respective first, second and third optical filters configured to pass at least one order of diffraction of the respective first, second and third modulated light signals to generate the respective first, second and third filtered light signals and block the rest of the respective first, second and third modulated light signals. The modulator system also includes a beam combiner configured to combine the first, second, and third filtered light signals into an output light signal.

In certain embodiments of the fourth aspect, each of the first, second, and third optical filter masks of the respective first, second, and third optical filters has at least one pass region configured to pass zero diffraction order and one or more first, second, and second diffraction orders. and third modulated light signals, respectively.

In certain embodiments of the fourth aspect, each of the first, second, and third spatial light modulators is a digital micromirror device.

In certain embodiments of the fourth aspect, the first, second, and third lights are red, green, and blue, respectively.

In certain embodiments of the fourth aspect, the modulator system further comprises first, second, and third output lenses positioned to collimate the first, second, and third filtered light signals, respectively, before being combined by the beam combiner.

In certain embodiments of the fourth aspect, the modulator system further comprises a projection lens configured to project a light output onto a screen.

In a fifth aspect, a time-multiplexed modulator system for generating a contrast-enhanced image comprises a spatial light modulator configured to modulate, in accordance with the image, a time-multiplexed light signal into a time-multiplexed modulated light signal to generate a repeating sequence of first, second, and third modulated light signals. signals. The time-multiplexed modulator system also includes a lens configured to perform a spatial Fourier transform of the modulated light signal time-multiplexed onto a Fourier plane, and a filter disk located on the Fourier plane and containing a plurality of optical filter masks, each of the optical filter masks configured to filter the respective one of the first, second, and third modulated light signals that have been spatially Fourier transformed by the lens by passing at least one diffraction order of the respective one of the first, second, and third modulated light signals and blocking the remainder of the respective one from the first, second and third modulated light signals. The filter disk is configured to rotate in synchronization with the time-multiplexed modulated light signal such that each of the optical filter masks is located in the time-multiplexed modulated light signal on a Fourier plane when the time-multiplexed modulated light signal is a respective one of the first, second, and third modulated light signals.

In certain embodiments of the fifth aspect, the spatial light modulator is a digital micromirror device.

масок оптического фильтра, где

является положительным целым числом, при этом каждый из трех наборов сконфигурирован так, чтобы фильтровать соответствующий один из первого, второго и третьего модулированных световых сигналов.In certain embodiments of the fifth aspect, the plurality of optical filter masks are three sets of

masks of the optical filter, where

is a positive integer, with each of the three sets configured to filter a corresponding one of the first, second, and third modulated light signals.

In certain embodiments of the fifth aspect, the plurality of optical filter masks comprises first, second, and third optical filter masks respectively configured to filter the first, second, and third modulated light signals.

In certain embodiments of the fifth aspect, the first optical filter mask has a pass region configured to pass zero diffraction order and one or more first diffraction orders of the first modulated light signal, the second optical filter mask has a pass region configured to pass zero diffraction order and one or more first diffraction orders of the second modulated light signal, and the third optical filter mask has a pass region configured to pass zero diffraction order and one or more first diffraction orders of the third modulated light signal.

In certain embodiments of the fifth aspect, the first, second, and third modulated light signals are red, green, and blue, respectively.

In certain embodiments of the fifth aspect, the filter disc is further configured to rotate non-uniformly to stop when each of the first, second, and third optical filter masks is positioned in the time-multiplexed modulated light signal.

In certain embodiments of the fifth aspect, the time-multiplexed modulator system further comprises a projection lens configured to project onto the screen at least one diffraction order of the respective first, second, and third modulated light signals transmitted by the filter disk.

In a sixth aspect, a method for enhancing the contrast of an image generated by a spatial light modulator includes a spatial Fourier transform of a modulated light signal from a spatial light modulator to a Fourier plane, wherein the modulated light signal contains a plurality of diffraction orders. The method also includes filtering the modulated light signal by passing at least one order of diffraction of the modulated light signal on the Fourier plane and blocking the remainder of the modulated light signal on the Fourier plane.

In certain embodiments of the sixth aspect, at least one diffraction order is a zero diffraction order.

In certain embodiments of the sixth aspect, the transmission includes the transmission of zero order diffraction through the transmission region of the optical filter mask.

In certain embodiments of the sixth aspect, at least one diffraction order includes a zero diffraction order and one or more first diffraction orders.

In certain embodiments of the sixth aspect, transmission includes passing zero diffraction orders and one or more first diffraction orders through the transmission region of the optical filter mask.

In certain embodiments of the sixth aspect, the modulated light signal is one of red light, green light, and blue light.

In certain embodiments of the sixth aspect, the method further includes driving a plurality of micromirrors of the spatial light modulator so as to generate a modulated light signal.

In certain embodiments of the sixth aspect, the method further includes collimating, after passing through, at least one order of diffraction.

In a seventh aspect, a method for projecting a contrast enhanced color image includes spatially modulating first, second, and third input light signals, in accordance with the color image, to generate respective first, second, and third modulated light signals, wherein each of the first, second, and third modulated light signals contains many orders of diffraction. The method also includes filtering the first, second and third modulated light signals into the respective first, second and third filtered light signals by (i) passing at least one of the diffraction orders of the respective first, second and third modulated light signals, (ii) blocking the remainder of the respective first, second and third modulated light signals; and (iii) combining the first, second and third filtered light signals into an output light signal.

In certain embodiments of the seventh aspect, the first, second, and third input lights are red, green, and blue, respectively.

In certain embodiments of the seventh aspect, the method further includes projecting the light output onto a screen.

In an eighth aspect, a time-multiplexing method for generating and projecting a contrast-enhanced image includes modulating, according to an image, a time-multiplexing light signal with a spatial light modulator to generate a time-multiplexing modulated light signal forming a repeating sequence of first, second, and third modulated light signals. The method also includes a spatial Fourier transform of the modulated light signal with time multiplexing using a lens and filtering the modulated light signal with time multiplexing by rotating the disk with filters in synchronism with the modulated light signal with time multiplexing. The filter disc contains a plurality of optical filter masks, each of the optical filter masks configured to filter a respective one of the first, second, and third modulated light signals that have been spatially Fourier transformed by the lens. The rotation involves locating each of the optical filter masks in the temporally multiplexed modulated light signal on the Fourier plane of the lens when the temporally multiplexed modulated light signal is a respective one of the first, second, and third modulated light signals.

In certain embodiments of the eighth aspect, the spatial light modulator is a digital micromirror device.

масок оптического фильтра, где

является положительным целым числом, при этом каждый из трех наборов сконфигурирован так, чтобы фильтровать соответствующий один из первого, второго и третьего модулированных световых сигналов.In certain embodiments of the eighth aspect, the plurality of optical filter masks are three sets of

masks of the optical filter, where

is a positive integer, with each of the three sets configured to filter a corresponding one of the first, second, and third modulated light signals.

In certain embodiments of the eighth aspect, the plurality of optical filter masks are first, second, and third optical filter masks, respectively configured to filter the first, second, and third modulated light signals.

In certain embodiments of the eighth aspect, filtering includes passing the zero diffraction order and one or more first diffraction orders of the first modulated light signal through the mask pass region of the first optical filter, passing the zero diffraction order and one or more first diffraction orders of the second modulated light signal through the mask pass region. a second optical filter; and passing a zero diffraction order and one or more first diffraction orders of the third modulated light signal through the bandwidth of the mask of the third optical filter.

In certain embodiments of the eighth aspect, the first, second, and third modulated light signals are red, green, and blue, respectively.

In certain embodiments of the eighth aspect, the rotation further includes uneven rotation and stop when each of the masks of the first, second, and third optical filters are located in the time-multiplexed modulated light signal.

In certain embodiments of the eighth aspect, the post-filtering method further comprises projecting the time-multiplexed filtered modulated light signal onto a screen.

Brief description of graphic materials

In FIG. 1 is a functional diagram of an optical filter that enhances the contrast of an image generated by a spatial light modulator in embodiments.

In FIG. 2 and 3 are front and side views, respectively, of a digital micromirror device (DMD) used for image generation, which is part of a digital projector.

In FIG. 4 is a side view of an optical filter that spatially filters the modulated light signal from the DMD shown in FIG. 2 and 3 in embodiments.

In FIG. 5 and 6 are side views of an example of a digital projector that contains the DMD shown in FIG. 2 and 3 and a projection lens, but does not include the optical filter shown in FIG. one.

In FIG. Figures 7 and 8 show intensity graphs of examples of Fraunhofer diffraction patterns of ON and OFF modulated light signals, respectively.

In FIG. 9-14 are front views of examples of the optical filter mask shown in FIG. 4 showing examples of configurations of the bandwidth area(s) in the embodiments.

In FIG. 15 is a block diagram of an example of a multicolor digital projector that achieves increased projector contrast ratio by optically filtering each color channel with spatial multiplexing, in embodiments.

In FIG. 16 is a block diagram of an example of a multi-colored digital projector that achieves increased projector contrast ratio by time-multiplexing optical filtering of different color channels, in embodiments.

In FIG. 17 is a plot of optical power versus time for a time-multiplexed light signal used as the input light signal of the multi-colored digital projector shown in FIG. 16 according to one embodiment.

In FIG. 18 is a front view of an example filter disk having three sectors each containing one optical filter mask, in embodiments.

In FIG. 19 is a front view of an example filter disc having six sectors each containing one optical filter mask, in embodiments.

In FIG. 20 shows a method for enhancing the contrast of an image generated by a spatial light modulator in embodiments.

In FIG. 21 shows a method for projecting a contrast-enhanced color image by optically filtering each color channel with spatial multiplexing, in embodiments.

In FIG. 22 shows a time-multiplexing method for generating and projecting a contrast-enhanced color image, in embodiments.

In FIG. 23 is a side view of the model experiment.

In FIG. 24–26 are plots of contrast ratio and optical efficiency versus half angle obtained numerically for the model experiment shown in FIG. 23.

In FIG. 27 is a Fraunhofer diffraction pattern for the model experiment shown in FIG. 23 when the light wavelength is 532 nm and all DMD micromirrors are in the ON position.

In FIG. 28 is a Fraunhofer diffraction pattern for the model experiment shown in FIG. 23 when the light wavelength is 617 nm and all DMD micromirrors are in the ON position.

In FIG. 29 is a plot of contrast ratio and optical efficiency obtained numerically for the model experiment shown in FIG. 23, when operating at a wavelength of 617 nm, when the tilt angles in the ON and OFF modes of the micromirrors are +12.1° and -12.1°, respectively.

In FIG. 30 and 31 are graphs of the dependence of the contrast ratio on the tilt angle of the micromirrors obtained numerically for the model experiment shown in FIG. 23.

In FIG. 32 is a plot of contrast ratio and optical efficiency versus input light angular separation obtained numerically for the model experiment shown in FIG. 23, at a wavelength of 532 nm.

In FIG. 33 and 34 are Fraunhofer diffraction patterns of the model experiment shown in FIG. 23 showing the broadening of the diffraction peaks caused by the angular separation of the input light signal.

In FIG. 35 shows a time sequence of exemplary bit planes that determines how the micromirrors of the DMD shown in FIG. 2 and 3 to display one video frame.

In FIG. 36 is a reconstructed frame showing what one video frame looks like when the exemplary bit planes shown in FIG. 35 control the DMD shown in FIG. 2 and 3 to display one video frame.

In FIG. 37 shows one example of a randomized bitplane that forms part of a sequence of randomized bitplanes that can be used with embodiments of the present invention to reduce artifacts in the reconstructed frame shown in FIG. 36 in embodiments.

In FIG. 38 is a reconstructed frame showing what a single video frame looks like when a sequence of randomized bit planes controls the DMD shown in FIG. 2 and 3 to display one video frame.

Detailed description of embodiments

In FIG. 1 is a block diagram of an optical filter 110 that enhances the contrast of an image generated by a spatial light modulator (SLM). In FIG. 1, optical filter 110 is shown in one application scenario in which optical filter 110 is implemented in digital projector 100 to enhance the contrast of an image projected by digital projector 100 onto screen 116. Digital projector 100 includes an SLM 102 that modulates an input light signal 106 to a modulated light signal. 104 according to the input representing the image to be projected by the digital projector 100.

The optical filter 110 filters the modulated light signal 104 by blocking the part 114 of the modulated light signal 104 that the digital projector 100, in the absence of the optical filter 110, would project onto the screen 116 even when the SLM 102 is instructed not to emit light in the direction of the screen 116. Optical filter 110 outputs, in the form of filtered light signal 108, the transmitted portion of modulated light signal 104. Digital projector 100 includes a projection lens 112 that projects filtered light signal 108 onto screen 116. In the absence of optical filter 110, the blocked portion 114 of modulated light signal 104 corresponds to the bottom the luminous intensity limit of the digital projector 100 and therefore determines how dark the projected image is. By blocking the blocked portion 114 of the modulated light signal 104, the optical filter 110 reduces the lower limit, thereby increasing the contrast of the digital projector 100.

As described in more detail below, the blocked portion 114 of the modulated light signal 104 corresponds to one or more diffraction orders of the modulated light signal 104 produced when the input light signal 106 is diffracted by the SLM 102. The SLM 102 may be any type of spatial light modulator that (1 ) has a periodic structure acting as a diffraction grating, and (2) modulates the optical phase of the input light signal 106 so as to redirect the light signal between two states (eg, ON and OFF states). In one example, the SLM 102 is a digital micromirror device (DMD) that directs a light signal by tilting a plurality of micromirrors so as to modulate the optical phase of an input light signal 106. In other examples, the SLM 102 is a phase modulator based on a reflective liquid crystal on silicon ( LCOS) or transmission liquid crystal (LC) phase modulator, each of which directs light by modulating the refractive index of the liquid crystal.

In FIG. 2 and 3 are front and side views, respectively, of a DMD 200 used for image generation as part of a digital projector (eg, digital projector 100). DMD 200 is one example of SLM 102. FIG. 2 and 3 in the following description are best considered together.

The DMD 200 is a micro-optoelectromechanical system (MOEMS) SLM having a plurality of square micromirrors 202 arranged in a two-dimensional rectangular array on a substrate 204 lying in the x-y plane (see right hand coordinate system 220). In certain embodiments, the DMD 200 is a digital light signal processor (DLP) available from Texas Instruments. Each of the micromirrors 202 may correspond to one image pixel and may be tilted about a rotation axis 208 oriented at -45° to the x-axis by electrostatic activation to direct the input light signal 206. For clarity, FIG. 2 shows only the respective micromirrors 202 at the corners and center of the DMD 200, and not all micromirrors 202 are indicated in FIG. 3.

In FIG. 3 shows micromirrors 202 tilted to direct input light 206. Micromirror 202(1) is activated in the ON position so as to mirror input light 206 into ON reflected light 306 parallel to the z-axis (see system 220 coordinates). The micromirror 202(2) is activated in the OFF position so as to mirror the input light signal 206 into the OFF-mode reflected light 320 towards a beam trap (not shown) that absorbs the OFF-mode reflected light 320. The micromirror 202( 3) is not activated when lying parallel to the substrate 204 (eg, the x-y plane) in a flat state. The front surface 304 of each of the micromirrors 202 may be coated with a deposited metal layer (such as aluminum) that acts as a reflective surface to reflect the input light signal 206. The gaps 310 between adjacent micromirrors 202 may be absorbent, i.e., the input light signal 206, that enters the gaps 310 is absorbed by the substrate 204. For clarity, the mechanical structures that physically connect the micromirrors 202 to the substrate 204 are not shown. Without departing from the scope of the present invention, DMD 200 may be implemented to direct ON-mode reflected light 306 and OFF-mode reflected light 320 in respective directions other than those shown in FIG. 3. In addition, the DMD 200 may be configured such that each of the micromirrors 202, when not activated, lies at any angle to the substrate 204.

A digital projector utilizing DMD 200 can be designed with only specular reflections of input light 206 from micromirrors 202. However, micromirrors 202 and gaps 310 interact to form a two-dimensional grating that diffracts input light 206. Therefore, the modulated light, propagating from the DMD 200 can form multiple diffraction orders observed as Fraunhofer diffraction patterns (see diffraction patterns 700 and 800 in FIGS. 7 and 8, respectively) in the far field of the DMD 200 or in the focal plane of the lens. Each order of diffraction corresponds to one light beam propagating from the DMD 200 in a unique corresponding direction. By design, most of the optical power of the modulated light signal from the DMD 200 is in the zero diffraction order corresponding to the ON and OFF specularly reflected lights 306 and 320.

Diffraction of the input light signal 206 by the DMD 200 may reduce the projector contrast ratio (PCR) of a digital projector using the DMD 200 (eg, the digital projector 100 shown in FIG. 1 in the absence of the optical filter 110). The PCR of a projector is defined herein as the ratio of ON and OFF light intensities (or, equivalently, first and second photometric luminance values) measured on a projection screen (e.g., screen 116 of FIG. 1) illuminated by the projector. The ON and OFF light intensity values are generated when the projector is controlled to output its brightest output (eg white) and its darkest output (eg black) respectively. When the DMD 200 is used in a digital projector, the ON and OFF mode luminous intensity values are generated when all the micromirrors 202 are in the ON and OFF positions, respectively.

How the DMD 200 diffracts the input light signal 206 can be determined by a variety of parameters such as (1) wavelength of the input light signal 206, (2) direction of the input light signal 206, (3) pitch 212 of the DMD 200, (4) width 210 of the gaps 310 of the DMD 200 and (5) the ON and OFF tilt angles of the micromirror 202. In both the x and y directions of the DMD 200, the pitch 212 is equal to the sum of the width 210 and the length 218 of the edge of the micromirror, as shown in FIG. 2. Pitch 212 may be 5 to 15 microns. Width 210 may be less than 1 micron. In one example, pitch 212 is 7 to 8 microns and width 210 is 0.7 to 0.9 microns.

In FIG. 4 is a side view of an optical filter 400 that spatially filters the modulated light signal 402 from the DMD 200 to enhance the PCR of the digital projector 100. The optical filter 400 is one example of an optical filter 110. Without departing from the scope of the present invention, in the optical filter 400, the DMD 200 may be replaced by another type of SLM 102 (eg, phase modulator based on reflective LCOS or pass LC). The optical filter 400 includes a lens 404 that spatially Fourier transforms the modulated light signal 402 by focusing the modulated light signal 402 onto a Fourier plane 408. The modulated light signal 402 is shown in FIG. 4 as a plurality of arrows each corresponding to one diffraction order and pointing in a unique direction in which one diffraction order propagates. In one embodiment, DMD 200 is centered on optical axis 422 defined by lens 404, as shown in FIG. 4. In another embodiment, the DMD 200 is located eccentric with respect to the optical axis 422. The lens 404 has a focal length of 410 and the Fourier plane 408 lies on the focal plane of the lens 404. An optical filter mask 412 located on the Fourier plane 408 performs spatial filtering of the modulated Fourier-transformed light signal 402 in lens 404. The spatial Fourier transform performed by lens 404 converts the propagation angle of each order of diffraction of the modulated light signal 402 to the corresponding spatial position on the Fourier plane 408. Thus, lens 404 provides the ability to select the desired diffraction orders and screening out unwanted diffraction orders by spatial filtering on a Fourier plane 408. The spatial Fourier transform of a modulated light signal 402 on a Fourier plane 408 is equivalent to the Fraunhofer diffraction pattern of the modulated light signal a 402.

Optical filter mask 412 has at least one pass region 416 that completely or partially passes at least one diffraction order of modulated light signal 402 through optical filter mask 412 as filtered light signal 414. In certain embodiments, optical filter mask 412 is opaque there. where the unwanted diffraction orders of the modulated light signal 402 fall. In some embodiments, the optical filter mask 412 is opaque where the optical filter mask 412 does not have a bandwidth 416. In other embodiments, the optical filter mask 412 is configured to reflect rather than skip desired diffraction orders to spatially separate desired diffraction orders from unwanted diffraction orders.

In one embodiment, optical filter 400 includes a collimator lens 418 that collimates filtered light signal 414 into collimated light signal 420. Collimator lens 418 may facilitate integration of optical filter 400 with other optical elements or systems. For example, lens 418 may couple filtered light signal 414 to additional optical devices located behind optical filter 400 (eg, projection lens 112 or beam combiner 1504, which is discussed below with reference to FIG. 15). Collimator lens 418 has a focal length of 424 and is positioned such that the focal plane of collimator lens 418 coincides with Fourier plane 408. Although focal lengths 410 and 424 are shown in FIG. 4 as being equal, the focal lengths 410 and 424 may be different from each other without departing from the scope of the present invention. In another embodiment, optical filter 400 includes a lens, like collimator lens 418, that optically couples filtered light 414 to additional optical devices located behind optical filter 400 (eg, projection lens 112).

For clarity, in FIG. 4 shows only diffracted beams diffracting in one dimension (eg in the x direction). However, the DMD 200 diffracts in two dimensions, so that the modulated light signal 402 also contains diffracted beams that have been diffracted by the DMD 200 in a second dimension perpendicular to the optical axis 422 (eg, in the y direction). Each diffracted beam in the two-dimensional diffraction pattern may be denoted by a pair of integers identifying the diffraction order of the diffracted beam for each of the two directions. As used herein, "zero order" refers to a single diffracted beam that has zero order in both of the two directions. Also without departing from the scope of the present invention, each arrow shown in FIG. 4 as part of the modulated light signal 402 may indicate a group of adjacent diffraction orders, such as a group consisting of a zero diffraction order and a plurality of first diffraction orders.

In FIG. 5 and 6 are side views of an example digital projector 500 that includes a DMD 200 and a projection lens 112 but does not include an optical filter 110. FIG. 5 and 6 show how the diffraction orders of the modulated light signal 402 from the DMD 200 attenuate the PCR of the digital projector 500. FIG. 5, the digital projector 500 generates light intensity in the ON mode by activating all of the micromirrors 202 of the DMD 200 in the ON position (see enlarged micromirror 202(1) 516). In FIG. 6, the digital projector 500 generates luminous intensity in the OFF mode by activating all the micromirrors 202 of the DMD 200 in the OFF position (see enlarged micromirror 202(1) 616). In FIG. 5 and 6, DMD 200 and projection lens 112 are centered in the x and y directions (see coordinate system 220) on optical axis 422. FIG. 5 and 6 in the following description are best considered together.

In FIG. 5, the DMD 200 diffracts the input light signal 206 into an ON modulated light signal 502 having a plurality of ON diffracted beams 504. FIG. 6, the DMD 200 diffracts the input light signal 206 into an OFF-modulated light signal 602 having a plurality of OFF-mode diffracted beams 604. In the far field of the DMD 200, each of the ON-mode diffracted beams 504 corresponds to one diffraction order or peak of the Fraunhofer diffraction pattern, 502, and each of the OFF-diffracted beams 604 corresponds to one diffraction order or peak of the Fraunhofer pattern generated by the OFF-modulated light 602. In the far-field DMD 200, each of the diffracted ON and OFF beams 504, 604 corresponds to a k-vector having one of a plurality of propagation directions 510. In the example in FIG. 5 and 6 propagation directions 510 are represented as thin lines; each of the ON and OFF diffracted beams 504, 604 is aligned with one of the propagation directions 510 and is represented by a thick arrow having a length corresponding to its power or intensity.

One aspect of the present embodiments is to understand that for a fixed direction of the input light signal 206, the power/intensity of the ON and OFF diffracted beams 504, 604 changes when the DMD 200 micromirrors 202 are switched between ON and OFF, while the propagation directions 510 of the ON and OFF diffracted beams 504, 604 remain unchanged when the micromirrors 202 of the DMD 200 are switched between ON and OFF.

In the example in FIG. 5, the input light signal 206 is a monochromatic plane wave illuminating the DMD 200 and propagating towards the DMD 200 such that the ON-diffracted beam 504(1) propagates along the optical axis 422. The ON-diffracted beam 504(1) contains a large a fraction of the power of the ON-modulated light signal 502. The ON-diffracted beam 504(1) may represent the zero diffraction order or a plurality of adjacent diffraction orders (e.g., zero diffraction order and several first diffraction orders) of the ON-modulated light signal 502.

In FIG. 5 also shows an ON-diffracted beam 504(2) propagating in a different direction than the ON-diffracted beam 504(1) but still passing through a transparent aperture 508 of the projection lens 112. Power in the ON-diffracted beam 504 (2) less than the power in the ON-diffracted beam 504(1). A plurality of ON-diffracted beams 518, including ON-diffracted beams 504(1) and 504(2), pass through a transparent aperture 508 of a projection lens 112 that projects the ON-diffracted beams 518 onto the projection screen as projected in ON mode. light signal 514.

In FIG. 5 also shows the ON-diffracted beam 504(3) propagating in the direction past the transparent aperture 508. The projection lens 112 does not project the ON-diffracted beam 504(3) onto the projection screen. The power in the ON-diffracted beam 504(3) is a small fraction of the power of the ON-modulated light signal 502. Therefore, excluding the ON-diffracted beam 504(3) from the ON-projected light signal 514 has little effect on the light efficiency of the digital projector 500 .

In FIG. 6 shows OFF-mode diffracted beams 604(1), 604(2), 604(3) corresponding to corresponding ON-mode diffracted beams 504(1), 504(2), 504(3) shown in FIG. 5. The OFF-diffracted beam 604(3) propagates away from the optical axis 422 passing the transparent aperture 508. Most of the power of the OFF-modulated light signal 602 is in the OFF-diffracted beam 604(3) and therefore will projected onto a projection screen.

In FIG. 6, the OFF-mode diffracted beams 604(1) and 604(2) pass through the transparent aperture 508 and are projected as part of the OFF-mode projected light signal 614. The power in the OFF-mode diffracted beams 604(1) and 604(2) is low. compared to the power in the diffracted OFF mode beam 604(3). However, the power in the OFF-diffracted beams 604(1) and 604(2) increases the luminous intensity in the OFF mode of the digital projector 500, thereby reducing the PCR of the digital projector 500.

Since most of the optical power of the ON-modulated light signal 502 resides in the ON-diffracted beam 504(1), the other ON-diffracted beams 504 in the plurality of ON-diffracted beams 518 passing through the transparent aperture 508 to form the projected ON-mode ON light signal 514 contain relatively low power and therefore have little effect on the power of the projected light signal 514 in ON mode. , reducing the PCR of the digital projector 500.

Another aspect of the present embodiments is the understanding that the diffraction orders corresponding to ON-diffracted beams with low optical powers, such as the ON-diffracted beam 504(2) described above, can be filtered to increase PCR with a minimum reducing the optical power output and efficiency of the digital projector 500. In order to find the diffraction orders to be filtered out, the diffraction order contrast ratio (DOCR) can be used. For each of the propagation directions 510 passing through the transparent aperture 508, DOCR is defined herein as the ratio of the optical powers of a pair of respective ON and OFF diffracted beams with the same diffraction order and propagation direction. For example, the diffraction order corresponding to the ON and OFF diffracted beams 504(1) and 604(1) has a high DOCR. High DOCR diffraction orders are advantageous for increasing PCR and may advantageously be chosen for projection onto a projection screen. On the other hand, ON and OFF diffracted beams 504(2) and 604(2) correspond to a low DOCR diffraction order. Low DOCR diffraction orders reduce PCR and can be advantageously filtered to increase the PCR of a 500 digital projector.

For clarity, in FIG. 5 and 6 show only diffracted beams 504, 604 diffracting in one dimension (eg, in the x direction). However, the DMD 200 diffracts the input light signal 206 in two dimensions, so that the modulated light signals 502 and 602 also contain diffracted beams that have been diffracted by the DMD 200 in a second dimension perpendicular to the optical axis 512 (eg, in the y direction).

In FIG. 7 and 8 are intensity graphs of exemplary Fraunhofer diffraction patterns 700 and 800 of ON and OFF modulated light signals 502 and 602, respectively. Diffraction patterns 700 and 800 correspond to the Fourier transforms produced by lens 404 on Fourier plane 408 when digital projector 100 operates with DMD 200 and optical filter 400. Diffraction patterns 700 and 800 were generated numerically in accordance with the procedure described in more detail below in section "Numerical analysis". Each of the diffraction patterns 700 and 800 contains a plurality of equally spaced diffraction maxima corresponding to diffracted beams 504 and 604, respectively. In FIG. 7 and 8, horizontal axis 704 and vertical axis 706 denote the direction cosines of the diffraction peaks about the x and y axes of the coordinate system 220, respectively. In FIG. 7 and 8, the intensities of the diffraction patterns 700 and 800 are indicated according to the intensity scale 708.

Circle 702 in FIG. 7 and 8 represent the transparent aperture 508 shown in FIG. 5 and 6. The diffraction peaks within circle 702 represent diffracted beams 518, 618 that are projected by projection lens 112 as ON and OFF projected light signals 514, 614, respectively. In FIG. 7, the brightest (eg, highest intensity) diffraction peak 710 at the center of circle 702 corresponds to ON-diffracted beam 504(1) shown in FIG. 5 and/or the zero order of the ON modulated light signal 502. Diffraction maxima lying outside the circle 702 are not projected onto the projection screen.

In FIG. 8, the most diffractive peak 810 corresponding to the OFF-diffracted beam 604(3) is at higher directivity cosines outside the circle 702 and is therefore not projected onto the projection screen. However, a plurality of low power diffraction peaks 812 in circle 702 are projected onto the projection screen as OFF-mode projected light 614, increasing OFF-mode light intensity and decreasing PCR.

To increase PCR, optical filter 400 can be implemented to reduce OFF mode luminous intensity by blocking diffraction orders lying within circle 702 that contribute relatively more to OFF mode luminous intensity than to ON mode luminous intensity. The Fraunhofer diffraction patterns 700 and 800 represent the Fourier transforms of the modulated light signal 402 and illustrate how pass regions 416 can be configured so that the optical filter mask 412 passes the desired diffraction orders for projection and blocks all other undesired diffraction orders that would otherwise would be projected. More specifically, using the parameters of the lens 404, the directivity cosines associated with each desired diffraction peak can be converted to a spatial position on the optical filter mask 412 at which a pass region 416 can be located to pass the desired diffraction peak through the optical filter mask 412. Similarly, the directivity cosines associated with each unwanted diffraction peak can be translated into a spatial position on the optical filter mask 412 at which the optical filter mask 412 is opaque to block (eg, filter out) the unwanted diffraction peak.

In one embodiment, the optical filter mask 412 comprises a single pass region 416 having a size, geometry, position, and orientation chosen to optimize the PCR and/or luminous efficiency of a digital projector. In another embodiment, the optical filter mask 412 has a plurality of pass regions 416 and the size, geometry, position and/or orientation is chosen for each pass region 416 so as to optimize the PCR and/or light efficiency of the digital projector.

In FIG. 9-14 are front views of examples of the optical filter mask 412 shown in FIG. 4 showing examples of configurations of throughput area(s) 416. In each of FIGS. 9-14, a plurality of positions 902 of diffraction orders, such as diffraction orders associated with different pairs of respective ON and OFF diffracted beams 504 and 604, are denoted by "X"s forming a two-dimensional grating. For example, in FIG. 9, position 902(2) denotes one diffraction order blocked by the optical filter mask 900, while position 902(1) denotes one diffraction order missed by the optical filter mask 900.

In FIG. 9 and 10 show examples of optical filter masks 900 and 1000 having circular pass areas 904 and 1004, respectively. Each of the circular passage areas 904 and 1004 may be an opening or a material that is at least partially translucent. Circular pass regions 904 and 1004 are examples of pass region 416. Circular pass region 904 is sized to pass one order of diffraction through the optical filter mask 900. The circular pass area 1004 is sized to allow multiple diffraction orders to pass through the optical filter mask, such as nine diffraction orders forming a 3 x 3 grating as shown in FIG. 9. Although FIG. 9 and 10, the circular gates 904 and 1004 are shown as being centered on the respective optical filter masks 900 and 1000 and thus centered on the optical axis 422, the circular gates 904 and 1004 may be positioned eccentrically without departing from the scope of the present invention.

In FIG. 11 and 12 show examples of optical filter masks 1100 and 1200 having square pass regions 1104 and 1204, respectively. Each of the square passage areas 1104 and 1204 may be a square hole or a square-shaped material that is at least partially translucent. The square pass regions 1104 and 1204 are examples of the pass region 416. The square pass region 1104 is centered on the optical filter mask 1100 and is sized to allow multiple diffraction orders to pass through the optical filter mask 1100, such as nine diffraction orders forming a 3 x 3 grating, as shown in FIG. 11. A square pass region 1204 is located eccentrically on the optical filter mask 1200 and is sized to allow multiple diffraction orders to pass through the optical filter mask 1200, such as four diffraction orders forming a 2 x 2 grating.

In FIG. 13 shows an example of an optical filter mask 1300 having an irregular rectangular pass region 1304 adapted to pass three adjacent diffraction orders through the optical filter mask 1300. The irregular rectangular passage area 1304 is an example of the passage area 416 and may be an opening or a material that is at least partially transparent to light.

In FIG. 14 shows an example of an optical filter mask 1400 having a plurality of circular pass regions 1404, each spaced and sized to pass one order of diffraction through the optical filter mask 1400, such as four pass regions 1404. The circular pass regions 1404 are an example multiple pass areas 416.

Passage area 416 may have a different shape, size, and/or position than those shown in the examples in FIG. 9-14 without departing from the scope of the present invention. In one class of implementations, each of the examples of gap regions 416 shown in FIG. 9-14 is a hole formed in the optical filter mask 412 (eg, by drilling, milling, or etching). In another class of implementations, each of the examples of gap regions 416 shown in FIG. 9-14 is an optically transparent window, an optically translucent window, or a color filter (eg, dichroic filter or thin film filter) physically connected to or embedded in the optical filter mask 412. In the examples shown in FIG. 9-14, optical filter masks (eg, optical filter mask 900) are circular in shape; each of these optical filter masks may instead have a different shape (eg, square or rectangular) without departing from the scope of the present invention. In some of the examples shown in FIG. 9-14 (eg, optical filter masks 900 and 1000) the optical filter masks are configured to be centered on the optical axis 422; each of these optical filter masks may instead be configured to be eccentric about optical axis 422 without departing from the scope of the present invention.

The optical filter mask 412 may be made of metal such as aluminum or stainless steel. The metal may be anodized or blackened to increase the absorption of light blocked by the optical filter mask 412. Alternatively, the optical filter mask 412 may be made from a semiconductor substrate, such as silicon, into which the pass region 416 may be etched or machined. (e.g., black paint) to block light in areas that do not coincide with the pass area(s) 416. In another embodiment, the optical filter mask 412 is an active optical filter mask having dynamically configurable pass areas 416, such as an array of mirrors with electronic control.

(например, пропускные области 904 и 1004), постепенный край может представлять собой кольцо, которое центрировано на окружности, имеет внутренний диаметр

и имеет наружный диаметр от, например, 1,1

до 1,2

; при этом любая часть маски 412 оптического фильтра, которая расположена от центра окружности дальше, чем наружный диаметр, может быть непрозрачной.In some embodiments, the optical filter mask 412 comprises a gradual, or “thin”, edge between the pass area 416 (eg, pass areas 904, 1004, 1104, 1204, 1304, and/or 1404) and surrounding opaque areas of the optical filter mask 412 (eg, , 900, 1000, 1100, 1200, 1300 and 1400 optical filter masks). The gradual edge may be made of a material (e.g., glass, plastic) with an optical density that increases monotonically in space from a relatively low value (e.g., 0) at points close to the passage area 416 to a relatively high value (e.g., 10 or above) at points close to the surrounding opaque areas. In the presence of a gradual edge, the passage area 416 does not have a sharp edge at which the transparency drops sharply (for example, a step change in transparency in space). Advantageously, the gradual edge reduces the precision of the optical filter mask 412 on the Fourier plane 408. This is particularly advantageous when the input light 106 comes from a laser with a low geometry factor, for which the point spread function is small. By comparison, a high geometric factor laser has a wide point spread function that smears the light source, thereby reducing the precision needed to position the optical filter mask 412. In embodiments where the passage area 416 is a circle of diameter

(e.g., gap areas 904 and 1004), the gradual edge may be a ring that is centered on a circle, has an inside diameter

and has an outer diameter from, for example, 1.1

up to 1.2

; however, any part of the mask 412 of the optical filter, which is located further from the center of the circle than the outer diameter, may be opaque.

In FIG. 15 is a block diagram of an example multicolor digital projector 1500 that achieves increased PCR by optically filtering each color channel with spatial multiplexing. The multicolor digital projector 1500 has a plurality of optical filters 400 and a corresponding number of DMDs 200. Each optical filter 400 is paired with a respective DMD 200 so as to work with a different respective base color. Without departing from the scope of the present invention, in the digital projector 1500, each DMD 200 may be replaced by a different type of SLM 102 (eg, a phase modulator based on a reflective LCOS or throughput LC). In FIG. 15, a multicolor digital projector 1500 is shown as having three color channels, and the following description refers to these three color channels. However, it should be understood that the multicolor digital projector 1500 may instead be configured with only two color channels or more than three color channels.

DMDs 200(1), 200(2), and 200(3) modulate respective input lights 206(1), 206(2), and 206(3) into respective modulated lights 402(1), 402(2), and 403 (3) which are optically filtered by respective optical filters 400(1), 400(2) and 400(3) into respective filtered light signals 414(1), 414(2) and 414(3). Multi-color digital projector 1500 further includes a beam combiner 1504 that combines filtered light signals 414(1), 414(2), and 414(3) into a composite light 1510. The projection lens 112 is configured to project complex light 1510 onto a projection screen ( for example, screen 116 shown in Fig. 1). The multicolor digital projector 1500 is one embodiment of the digital projector 100 extended to operate with three separate color inputs to produce complex light.

In one embodiment, the multicolored digital projector 1500 includes collimator lenses 418(1), 418(2), and 418(3) that collimate respective filtered light signals 414(1), 414(2), and 414(3) into respective collimated light signals. signals 420(1), 420(2), and 420(3). In this embodiment, the beam combiner 1504 combines the collimated light signals 420(1), 420(2), and 420(3), as shown in FIG. 15. In embodiments of multicolored digital projector 1500 that do not include collimator lenses 418, beam combiner 1504 combines filtered light signals 414(1), 414(2), and 414(3) that are not collimated.

In one embodiment, a multi-colored digital projector 1500 includes total internal reflection (TIR) prisms 1502(1), 1502(2), and 1503(3) that reflect input light signals 206(1), 206(2), and 206(3). ) to the respective DMDs 200(1), 200(2) and 200(3) and pass the respective modulated light signals 402(1), 402(2) and 402(3) to the respective optical filters 400(1), 400(2 ) and 400(3). Multicolor digital projector 1500 may be configured with mirrors 1506 and 1508 that direct collimated light signals 420(1) and 420(3) to beam combiner 1504 as shown in FIG. 15. Although shown in FIG. 15 as a transverse dichroic or x-cubic prism, the beam combiner 1504 may be another type of beam combiner known in the art.

In one implementation of the multicolored digital projector 1500, the first, second, and third primary colors are red, green, and blue, respectively. When the input lights 206(1), 206(2) and 206(3) are monochromatic, the wavelength of each input light 206(1), 206(2) and 206(3) can be selected such that the input lights 206 (1), 206(2), and 206(3) respectively represent red, green, and blue primaries, which are spectrally pure. In one such example, the wavelength of the input light signal 206(1) representing the red primary color is one of 615 nm, 640 nm, and 655 nm, the wavelength of the input light signal 206(2) representing the green primary color is one of 525 nm, 530 nm, and 545 nm, and the wavelength of the input light signal 206(3) representing the primary color blue is one of 445 nm, 450 nm, and 465 nm. Alternatively, the input lights 206(1), 206(2), and 206(3) may be polychromatic such that the red, green, and blue primaries are not spectrally pure colors. Without departing from the scope of the present invention, the three primary colors may be a set of colors other than red, green and blue.

Multicolor digital projector 1500 increases the PCR by increasing the PCR of each primary color (eg, red, green, and blue). Several optical processes used by multicolored digital projector 1500 are wavelength dependent, including diffraction of input light signal 206 by DMD 200, refraction of modulated light signal 402 by TIR prism 1502, and focusing of modulated light signal 402 by lens 404. Therefore, the Fraunhofer diffraction pattern of each of modulated light signals 402(1), 402(2) and 402(3) depends on the wavelength. In one embodiment, the optical filter masks 412(1), 412(2), and 412(3) are individually configured based on the wavelength of each of the respective input light signals 206(1), 206(2), and 206(3) such that to increase the PCR of the first, second, and third primary colors, respectively.

In FIG. 16 is a block diagram showing an example of a multicolor digital projector 1600 that achieves increased PCR by time multiplexing optical filtering of different color channels. The digital projector 1600 includes one DMD 200 and one optical filter 1610 having a filter disc 1612. In FIG. 17 is a plot of optical power versus time for a time-multiplexed light signal 1601 used as the input light signal of a multi-colored digital projector 1600. FIG. 18 and 19 show examples of a filter disc 1612. Fig. 16-19 in the following description are best taken together.

The time-multiplexed light signal 1601 comprises a repeating sequence 1702 of time-separated input light signals 206. Although multicolored digital projector 1600 can be configured to receive and output any number of different color input light signals, FIG. 17-19 and the following discussion considers a three-color embodiment of a multi-colored digital projector 1600. In this embodiment, the time-multiplexed light signal 1601 comprises time-separated input lights 206(1), 206(2), and 206(3). In FIG. 17 shows one example of a time-multiplexed light signal 1601, where sequence 1702 comprises a first input light pulse 206(1), a second input light pulse 206(2), and a third input light pulse 206(3). Light inputs 206(1), 206(2), and 206(3) may represent, for example, red, green, and blue primary colors. The input light pulses 206(1), 206(2), and 206(3) overlap in space to use the same DMD 200, optical filter 1610, and projection lens 112. FIG. 17, pulses of input light signals 206(1), 206(2), and 206(3) are represented as having the same power (eg, pulse height), duration (eg, pulse width), and "off" time between pulses (eg, interval between impulses). Without departing from the scope of the present invention, the multi-colored digital projector 1600 may receive input light signals 206 having other configurations of power, duration, and "off" time. For example, a selected one of the first, second, and third input light pulses 206(1), 206(2), and 206(3) may have a higher power to compensate for the lower diffraction efficiency of the DMD 200 at the input light wavelength corresponding to selected impulse.

The DMD 200 is configured to synchronously modulate, according to the image, the input lights 206(1), 206(2) and 206(3) of the time multiplex light signal 1601 into the time multiplex modulated light signal 1602. In other words, the DMD micromirrors 202 200 are translated into a first configuration when the temporally multiplexed modulated light signal 1602 is the first input light signal 206(1), to a second configuration when the temporally multiplexed modulated light signal 1602 is the second input light signal 206 (2), and in a third configuration, when the modulated light signal 1602 with time multiplexing is the third input light signal 206(3). The first, second and third configurations may be different. Without departing from the scope of the present invention, in the digital projector 1600, the DMD 200 may be replaced by another type of SLM 102 (eg, a phase modulator based on a reflective LCOS or throughput LC).

The optical filter 1610 is similar to the optical filter 400 shown in FIG. 4, except that the filter disk 1612 replaces the optical filter mask 412. The filter disc 1612 includes a plurality of optical filter masks 412 configured to synchronously filter the input light signals 206(1), 206(2), and 206(3) of the time-multiplexed modulated light signal 1602. For example, in an embodiment where the filter disc 1612 comprises first, second, and third optical filter masks corresponding to the first, second, and third light inputs 206(1), 206(2), and 206(3), the motor 1614 rotates the disc 1612 with filters so that the first optical filter mask 412 intercepts and filters the temporally multiplexed modulated light signal 1602 on the Fourier plane 408, when the temporally multiplexed modulated light signal 1602 is the first input light signal 206(1), the second optical filter mask 412 intercepts and filters the time-multiplexed modulated light signal 1602 on the Fourier plane 408 when the time-multiplexed modulated light signal 1602 is the second input light signal 206(2), and the third optical filter mask 412 intercepts and filters the time-multiplexed modulated light signal 1602 multiplexed Fourier plane 408 when the time-multiplexed modulated light 1602 is the third input light 206(3).

In one embodiment of multi-colored digital projector 1600, motor 1614 rotates the color filter wheel 1612 in stages so as to switch between different optical filter masks 412 in synchronization with the pulse train of input light signals 206(1), 206(2), and 206(3), with while maintaining a fixed position of the disk 1612 with filters during the propagation of each of these pulses through the Fourier plane 408. In this embodiment, the motor 1614 operates as follows. Before the pulse of input light signals 206(1), 206(2) and 206(3) reaches the Fourier plane 408, the motor 1614 rotates the filter disk 1612 to the position of the corresponding optical filter mask 412 in the path of the modulated light signal 1602 with time multiplexing on the Fourier plane 408. After the corresponding pulse of filtered light signal has completed its propagation through the optical filter mask 412, the motor 1614 rotates the filter disk 1612 to the position of the next optical filter mask 412 in the path of the modulated light signal 1602 with time multiplexing on the Fourier plane 408.

In certain embodiments, lens 404, as implemented in optical filter 1610 for focusing modulated light signal 1602 with time multiplexing, can be configured to reduce chromatic aberrations that cause the focal length of lens 404 to vary with wavelength. In one such embodiment, lens 404 is an achromatic lens designed to focus equally on the wavelengths of input light signals 206(1), 206(2), 206(3) such that the Fourier planes corresponding to each of the three wavelengths are located in the same way. In another such embodiment, lens 404 is an apochromatic lens, a superachromatic lens, an objective lens, a compound lens with multiple lens elements, an assembly of multiple lenses and/or other optical elements, or another type of lens known in the art. Lens 404 may have one or more anti-reflection coatings that enhance the transmission of modulated time-multiplexed light 1602 through lens 404 at wavelengths of input light signals 206(1), 206(2), 206(3).

In one embodiment, a multicolored digital projector 1600 is configured with a collimating lens 1618 that collimates the time-multiplexed filtered light signal that is passed by the filter disk 1612 into a time-multiplexed collimated light signal 1606 that is projected onto a screen by the projection lens 112. In another embodiment, In an embodiment, projection lens 112 is configured to receive a time-multiplexed light signal that is not collimated, and collimator lens 1618 is not included in multicolor digital projector 1600.

In FIG. 18 is a front view of an example filter disk 1800 having three sectors 1802 each containing one optical filter mask. The filter disc 1800 is an example of a filter disc 1612. The motor 1614 rotates the filter disk 1800 around the axis 1804, with each rotation of the filter disk 1800 corresponding to one sequence 1702 of the light signal 1602 with time multiplexing. In some embodiments, the implementation of the motor 1614 rotates the disk 1800 with filters in stages, as described previously. In the example in FIG. 18, the first optical filter mask of the first sector 1802(1) is shown as the optical filter mask 900 shown in FIG. 9, the second optical filter mask of the second sector 1802(2) is shown as the optical filter mask 1300 shown in FIG. 13 and the third sector third optical filter mask 1802(3) is shown as the optical filter mask 1400 shown in FIG. 14. However, the sector optical filter masks 1802 may be configured with pass areas (eg, pass area 416) having different shapes, sizes, and positions than those shown in FIG. 18 without departing from the scope of the present invention.

In one embodiment, multi-colored digital projector 1600 is configured to display images without certain temporal artifacts, and to this end, the duration of sequence 1702 is shorter than the response time of the human visual system. For example, the time multiplexing frequency of the light signal 1601, which is the reciprocal of the duration of the sequence 1702, may be higher than the flicker fusion frequency to exploit the inertia of visual perception. The multiplexing frequency may be 1 kHz or higher, corresponding to a pulse width of less than 1 millisecond for each of the light inputs 206(1), 206(2), and 206(3).

секторов, где

является положительным целым числом. Каждый набор из трех секторов содержит маски трех оптических фильтров, и каждый полный поворот диска 1900 со светофильтрами соответствует

последовательным итерациям последовательности 1702, тем самым позволяя мотору 1614 и диску 1612 со светофильтрами поворачиваться с

частоты мультиплексирования светового сигнала 1601 с временным мультиплексированием. В одном сценарии использования мотор 1614 поворачивает диск 1900 со светофильтрами поэтапно, так, что каждая маска оптического фильтра диска 1900 со светофильтрами является неподвижной во время фильтрования соответствующего импульса входного светового сигнала 206.In FIG. 19 is a front view of an example filter disk 1900 that has six sectors 1902 each containing one optical filter mask. The motor 1614 rotates the filter wheel 1900 about the axis 1804 such that each full turn of the filter wheel 1900 corresponds to two consecutive iterations of the sequence 1702. frequency multiplexing of the light signal 1601 with time multiplexing, thereby reducing the power consumption and speed requirements of the motor 1614. In another embodiment, the filter disk 1612 has

sectors where

is a positive integer. Each set of three sectors contains masks of three optical filters, and each complete rotation of the filter disk 1900 corresponds to

successive iterations of sequence 1702, thereby allowing motor 1614 and filter disc 1612 to rotate with

multiplexing frequency of the light signal 1601 with time multiplexing. In one use case, motor 1614 rotates the color wheel 1900 in stages such that each optical filter mask of the color wheel 1900 is stationary while filtering the corresponding input light pulse 206.

In FIG. 20 shows a method 2000 for enhancing the contrast of an image generated by a spatial light modulator. Method 2000 may be performed by optical filter 400. Method 2000 includes step 2002 for performing a spatial Fourier transform of the modulated light signal from the spatial light modulator onto a Fourier plane. The modulated light signal contains a plurality of diffraction orders. In one example of step 2002, lens 404 spatially Fourier transforms modulated light signal 402 onto Fourier plane 408. Method 2000 also includes a step 2004 of filtering the modulated light signal that has been Fourier transformed in step 2002. Step 2004 includes two steps, 2006 and 2008, which can happen at the same time. Step 2006 includes passing at least one order of diffraction of the modulated light signal on a Fourier plane. Step 2008 includes blocking the rest of the modulated light signal on the Fourier plane. In one example of steps 2006 and 2008, the optical filter mask 412 passes at least one order of diffraction of the modulated light signal 402 through the pass region(s) 416 on the Fourier plane 408 and blocks the rest of the modulated light signal 402 on the Fourier plane 408. In another In an example of steps 2006 and 2008, the optical filter mask 412 passes at least the zero order of diffraction of the modulated light signal 402 through the pass region(s) 416 on the Fourier plane 408 and blocks the remainder of the modulated light signal 402 on the Fourier plane 408. In another exemplary method 2000 modulated light signal 402 is monochromatic light. In another example of method 2000, modulated light signal 402 is one of red light, green light, and blue light. In another example of method 2000, modulated light 402 is a composite light formed by combining red light, green light, and blue light. In this example, the modulated light signal 402 may be white light. In one embodiment, method 2000 further includes the step 2010 of collimating, after step 2006, at least one order of diffraction of the transmitted modulated light signal. In one example of step 2010, collimator lens 418 collimates filtered light 414.

In FIG. 21 shows a method 2100 for projecting a color image with enhanced contrast by optically filtering each color channel with spatial multiplexing. Method 2100 may be performed by multi-colored digital projector 1500. Method 2100 includes 2102 spatially modulating first, second, and third input light signals according to a color image to generate respective first, second, and third modulated light signals. The first, second, and third light inputs may represent light for three different respective color channels of a color image, as discussed above with reference to FIG. 15. Each of the first, second and third modulated light signals contains a plurality of diffraction orders. In one example of step 2102, DMDs 200(1), 200(2), and 200(3) shown in FIG. 15 spatially modulate the respective first, second, and third input lights 206(1), 206(2), and 206(3) into the respective first, second, and third modulated lights 402(1), 402(2), and 402( 3). The method 2100 also includes a step 2104 of filtering the first, second, and third modulated light signals (generated in step 2102) into respective first, second, and third filtered light signals. In one embodiment, at 2104, method 2000 is performed for each of the first, second, and third modulated light signals to obtain first, second, and third filtered light signals. In one example of such an embodiment of step 2104, the optical filter masks 412(1), 412(2), and 412(3) of the multicolor digital projector 1500 filter the respective first, second, and third modulated light signals 402(1), 402(2), and 402 (3) Fourier-transformed into the respective first, second and third filtered light signals 414(1), 414(2) and 414(3). Step 2104 includes steps 2106 and 2108, which may occur simultaneously. Step 2106 includes passing at least one diffraction order of each of the first, second, and third modulated light signals. Step 2108 includes blocking the rest of the first, second and third modulated light signals. In one example of steps 2106 and 2108, the optical filter masks 412(1), 412(2), and 412(3) of the multicolor digital projector 1500 pass at least one diffraction order of each of the first, second, and third modulated light signals 402(1), 402(2) and 402(3) that have undergone a Fourier transform and block the rest of the first, second and third modulated light signals 402(1), 402(2) and 402(3). Method 2100 also includes step 2110 of combining the first, second, and third filtered light signals generated at step 2104 to generate an output light signal. In one example of step 2110, beam combiner 1504 combines first, second, and third filtered light signals 414(1), 414(2), and 414(3) into output light signal 1510. In one embodiment, method 2100 further includes a step 2112 of projecting output light signal on the screen. In one example of step 2112, projection lens 112 projects light output 1510 onto a screen, such as projection screen 116.

Without departing from the scope of the present invention, method 2100 can be extended to process only two light channels or more than three light channels, such as four light channels.

In FIG. 22 shows a time multiplexing method 2200 for generating and projecting a contrast enhanced color image. The method 2200 may be performed by a multi-colored digital projector 1600. The method 2200 includes the step of modulating a time-multiplexed light signal 2202 according to the color image to be projected with a spatial light modulator to generate a time-multiplexed modulated light signal having a repeating sequence of the first, second and third modulated light signals. The first, second, and third modulated light signals may represent light for three different color channels of a color image, as discussed above with reference to FIG. 16. In one example of step 2202, the DMD 200 of the multicolor digital projector 1600 modulates a time multiplex light signal 1601 into a time multiplex modulated light signal 1602. The method 2200 also includes a step 2204 of spatially Fourier transforming the time-multiplexed modulated light signal (generated in step 2202) with the lens. In one example of step 2204, lens 404 performs a spatial Fourier transform of the modulated light signal 1602 with time multiplexing. The method 2200 further includes a step 2206 of filtering the time-multiplexed modulated light signal that has undergone a spatial Fourier transform in step 2204 by rotating the filter wheel in synchronism with the time-multiplexed modulated light signal. The filter disk comprises a plurality of optical filter masks, each configured to filter a respective one of the first, second, and third modulated light signals spatially Fourier transformed by the lens in step 2204. Step 2206 includes rotating the filter disk to position each of masks of the optical filter in the Fourier-transformed light signal when the time-multiplexed modulated light signal is the corresponding one of the first, second, and third modulated light signals. In one example of step 2206, motor 1614 rotates filter wheel 1612 in synchronization with time-multiplexed light signal 1602, as discussed above with reference to FIG. 16. In another example of step 2206, motor 1614 rotates the filter wheel 1612 in stages so that each optical filter mask is stationary when it filters the respective modulated light signal. In one embodiment, the method 2200 further includes a step 2208 of projecting the time-multiplexed modulated light signal, after filtering, onto a screen. As an example of step 2208, projection lens 112 projects a time-multiplexed light signal filtered by optical filter mask 1612 and optionally collimated by collimator lens 1618 onto a projector screen.

Without departing from the scope of the present invention, method 2200 can be extended to process only two light channels or more than three light channels, such as four light channels.

NUMERICAL ANALYSIS

The following discussion relates to a numerical analysis to study how the contrast ratio of a digital projector equipped with a DMD 200 depends on various parameters, including wavelength, tilt angles in ON and OFF modes of the micromirror 202, tilt angle tolerances in ON and OFF modes, geometric shapes the bandwidth 416 of the optical filter mask 412, the angular and spectral separations of the input light signal 206, and the effective size of the light source generating the input light signal 206. The digital projectors 100, 500, 1500, and 1600 can be configured according to the parameters learned in this numerical analysis. .

In FIG. 23 is a side view of the 2300 model experiment for which the numerical results are presented in this section. In simulation experiment 2300, DMD 200 modulates input light signal 206 into a modulated light signal 402 containing multiple diffraction orders. The Fraunhofer diffraction pattern of the modulated light signal 402 is calculated and a spatial filter 2302 is modeled, designating each diffraction order of the Fraunhofer diffraction pattern as either transmitted or blocked by the spatial filter 2302, depending on the geometry and configuration of the spatial filter 2302. The spatial filter 2302 is one example of a mask 412 optical filter. The contrast ratio of the model experiment 2300 is obtained by numerically integrating the diffraction orders designated as being passed by the spatial filter 2302 once when the DMD 200 micromirrors 202 are turned ON and again when the DMD 200 micromirrors 202 are turned OFF. These two numerical integration values correspond to the ON and OFF light intensity values, respectively, whose ratio determines the contrast ratio.

The Fraunhofer diffraction pattern can be calculated for the 2300 model experiment using the formal Rayleigh-Sommerfeld description for the scalar theory of diffraction. This formal description is based on the Rayleigh-Sommerfeld integral, which expresses the complex amplitude of a diffracted electric field as an integral (eg, sum) over spherical waves.

It should be understood that the numerical analysis presented herein is not limited to DMD 200, but is easily extended to other SLM 102 embodiments such as a reflective LCOS phase modulator or a pass LC phase modulator.

In FIG. 24-26 are plots of contrast ratio and optical efficiency versus half angle obtained numerically for the 2300 model experiment. To obtain the results shown in FIG. 24-26, the spatial filter 2302 was modeled as a circular aperture centered on the optical axis 422 and having an aperture diameter of 2304. The spatial filter 2302 was centered on the zero diffraction order of the modulated light signal 402 (eg, the first ON and OFF diffracted beams 504(1) and 604(1)). The circular aperture of the spatial filter 2302 forms the base of a cone having an apex located at the center of the face of the DMD 200, the cone having an axis coinciding with the optical axis 422. The half angle 2308 here is defined as the half angle at the apex of the cone.

In FIG. 24–26 for the light signal in Model Experiment 2300, wavelengths of 532 nm, 465 nm, and 617 nm, respectively, were used. For micromirrors 202 DMD 200, nominal ON and OFF position angles of +12° and -12°, respectively, were used. For DMD 200, dimension and area fill factors of 81% and 90%, respectively, were used.

With decreasing half angle 2308 in FIG. 24, the green contrast ratio 2402 increases as a series of "steps" as the diffraction orders of the modulated light signal 402 are increasingly blocked by the spatial filter 2302. The highest green contrast ratio of 757,000:1 is obtained when only the zero diffraction order of the modulated light signal 402 is passed by the spatial filter 2302. As the half-angle 2308 increases, the optical efficiency 2404 of green increases as a series of "steps" as diffraction orders are more and more passed by the spatial filter 2302. Since most of the optical power of the green modulated light signal is in low diffraction orders (e.g. , zero, first and second orders of diffraction), the largest steps in the efficiency of 2404 green occur at small values of the half angle 2308. At the highest green contrast ratio, the optical efficiency of 2404 green is approximately 80%, i.e. 80% of the modulated light signal 402 is passed through the spatial filter 2302.

In FIG. 25, the blue contrast ratio 2502 and the blue optical efficiency 2504 have behavior similar to the green contrast ratio 2402 and the green optical efficiency 2404, respectively. The highest blue contrast ratio of 850,000:1 is obtained when only the zero diffraction order of the modulated light signal 402 is passed by the spatial filter 2302. At the highest blue contrast ratio, the blue optical efficiency 2504 drops rapidly from 80% to less than 50%.

In FIG. 26, the red contrast ratio 2602 and red optical efficiency 2604 have behavior similar to green and blue contrast ratios 2402, 2502 and green and blue optical efficiency 2404, 2504, respectively. However, the highest red contrast ratio is only 450,000:1. One reason that the highest contrast ratio of red is lower than the corresponding contrast ratios of green and blue is that at 617 nm red light, the DMD 200 is illuminated far from the glare state. At the highest red contrast ratio, the optical efficiency of red 2604 is approximately 80%.

In FIG. 27 shows the Fraunhofer diffraction pattern for model experiment 2300 when the light wavelength is 532 nm and all micromirrors 202 DMD 200 are in the ON position. In FIG. 27, each of the four lightest diffraction orders is surrounded by one of the frames 2702. The frame 2702(1) contains the highest optical power and corresponds to the zero diffraction order of the modulated light signal 402. For each frame 2702, the DOCR was calculated using the frame 2702 as a rectangular aperture (e.g., bandwidth 416) of the spatial filter 2302. The numerically obtained DOCR is printed inside each frame. For example, in frame 2702(1), the zero diffraction order of the modulated light signal 402 has a DOCR of 758075:1. In one embodiment, the optical filter mask 412 is configured to pass the zero diffraction order and block all other diffraction orders of the modulated light signal 402; the optical filter mask 900 is one example of an optical filter mask 412 that can be used with this embodiment. In another embodiment, each optical filter mask 412(1), 412(2), and 412(3) of the multicolor digital projector 1500 may be configured to pass zero diffraction order and block all other diffraction orders of modulated light signals 402(1), 402(2) and 402(3).

In FIG. 28 shows the Fraunhofer diffraction pattern for the Model Experiment 2300 when the light wavelength is 617 nm and all micromirrors 202 of the DMD 200 are in the ON position. In FIG. 28, the four diffraction orders comprise most of the optical power of the modulated light signal 402. Compared to FIG. 27, where a wavelength of 532 nm has been used, the optical power is more evenly distributed among the four diffraction orders because the wavelength of 617 nm is farther from the blaze state of DMD 200. A contrast ratio up to a value of 852000:1 can be obtained by forming a spatial filter only the order of diffraction in the 2802(1) frame. However, by blocking the diffraction orders within 2802(2), 2802(3), and 2802(4), the optical efficiency will be significantly degraded.

As a compromise between contrast ratio and optical efficiency, spatial filter 2302 can be configured to pass three diffraction orders with the highest DOCR corresponding to frames 2802(1), 2802(2), and 2802(4). In this example of spatial filter 2302, the apertures corresponding to frames 2802(1), 2802(2), and 2802(4) are not symmetrical about optical axis 422. In one embodiment, optical filter 400 is configured to pass three orders of modulated light diffraction. signal 402, as shown in FIG. 28; an optical filter mask 1300 is one example of an optical filter mask 412 that can be used with this embodiment. In other embodiments, the optical filter 412 is configured to pass a non-zero integer number of diffraction orders of the modulated light signal 402, up to a maximum number determined by the transparent aperture of the lens 404.

In FIG. 29 is a graph of the contrast ratio 2902 and optical efficiency 2904 obtained numerically for the model experiment 2300 operating at a wavelength of 617 nm, when the ON and OFF tilt angles of the micromirrors 202 are +12.1° and -12.1°, respectively. The contrast ratio can be sensitive to small changes in the tilt angle of the micromirrors. Compared to FIG. 26, a 0.1° change in tilt angles more than doubles the highest contrast ratio of red to almost 1,000,000:1, while the optical efficiency of red 2904 remains at about 80%. By comparison, commercial DMDs typically have a tilt tolerance of ±0.5°.

In FIG. 30 and 31 are plots of the contrast ratio versus the tilt angle of the micromirrors obtained numerically for the model experiment 2300. FIG. 30, the tilt angle in the OFF position is fixed at -12°, and the tilt angle in the ON position varies from 11.5° to 12.5°. In FIG. 31, the tilt angle in the ON position is fixed at +12°, and the tilt angle in the OFF position varies from -12.5° to -11.5°. In FIG. 30, contrast ratios 3002, 3004, and 3006 correspond to wavelengths of 617 nm, 465 nm, and 532 nm, respectively. In FIG. 31, contrast ratios 3102, 3104, and 3106 correspond to wavelengths of 617 nm, 465 nm, and 532 nm, respectively. Fig. 30 and 31 in the following description are best considered together.

Contrast ratio values are generally more sensitive to variations in luminous intensity in OFF mode than luminous intensity in ON mode. Therefore, the contrast ratio may vary more depending on the tilt angle in OFF mode than the tilt angle in ON mode. As shown in FIG. 30, the contrast ratios 3002, 3004, and 3006 show little variation for an ON-mode tilt angle within a tilt angle tolerance range of ±0.5°. On the other hand, the contrast ratios 3102, 3104, and 3106 shown in FIG. 31 change more strongly for the tilt angle in the OFF mode being in a similar tilt angle tolerance range.

In one embodiment, a digital micromirror device optimized for green light modulation is provided that has a nominal OFF tilt angle of greater than -12°, such as greater than -11.8° or greater than -11.6°. In one example, the digital micromirror device has a nominal tilt angle in the OFF position of -11.5° or more.

The digital micromirror device according to this embodiment can improve the ON-OFF contrast ratio by modulating green light.

In one example, a digital micromirror device optimized for green light modulation has a nominal tilt angle in the ON position ranging from +11.5° to +12.5°, such as +12°.

In one embodiment, a digital micromirror device optimized for modulating red or blue light is provided that has a nominal OFF tilt angle of less than -12°, such as less than -12.2° or less than -12.4°. In one example, the digital micromirror device has a nominal tilt angle in the OFF position of -12.5° or less.

The digital micromirror device according to this embodiment can improve the ON-OFF contrast ratio by modulating red or blue light.

In one example, a digital micromirror device optimized for modulating red or blue light has a nominal tilt angle in the ON position ranging from +11.5° to +12.5°, such as +12°.

In one embodiment, a modulator system for generating an image is provided, this modulator system comprises:

a first digital micromirror device configured to modulate a red light signal to generate a modulated red light signal;

a second digital micromirror device configured to modulate a green light signal to generate a modulated green light signal; and

a third digital micromirror device configured to modulate a blue light signal to generate a modulated blue light signal,

wherein the nominal tilt angle in the OFF position of the second digital micromirror device is different from the nominal tilt angle in the OFF position of the first and third digital micromirror devices. For example, the first and third digital micromirror devices may be of a first type having a first nominal tilt angle at the OFF position, and the second digital micromirror device may be of a second type having a second nominal tilt angle at the OFF position that is different from the nominal tilt angle at the OFF position. OFF of the first type. For example, the first and third digital micromirror devices are the red or blue light modulation optimized digital micromirror devices described above, while the second digital micromirror device is the green light modulation optimized digital micromirror device described above.

The modulator system may further comprise:

- first, second and third optical filters, each containing:

a lens configured to spatially Fourier transform the modulated light signal from the respective first, second and third spatial light modulators, the modulated light signal comprising a plurality of diffraction orders; and

- an optical filter mask located on the Fourier plane of the lens and configured to filter the modulated light signal that has undergone a spatial Fourier transform by the lens, by passing at least one order of diffraction of the modulated light signal, generating the corresponding first, second and third filtered light signals and blocking the rest of the modulated light signal; and

- a beam combiner configured to combine the first, second and third filtered light signals into an output light signal.

In addition, the modulator system may optionally also contain any of the features described herein, such as the features described with respect to Figures 9-15.

In FIG. 32 is a plot of the contrast ratio 3202 and the optical efficiency 3204 as a function of the angular separation of the input light signal 206 obtained numerically for the simulation experiment 2300 at a wavelength of 532 nm. In FIG. 33 and 34 are Fraunhofer diffraction patterns of Model Experiment 2300 showing the broadening of the diffraction peaks caused by the angular separation of the input light signal 206. FIG. 33, the input light signal 206 is a plane wave with no angular separation. In FIG. 34, input light 206 has an 8° half-angle angle of angular separation. To obtain the data in Fig. 32, the spatial filter 2302 has been configured with the rectangular aperture represented by box 3302 in FIG. 33 and 34. FIG. 32-34 in the following description are best taken together.

In cinema and other environments where viewing quality is important, digital laser image projection benefits from the angular spacing and reduced coherence of the laser irradiation as it reduces the visibility of dust and other unwanted scattering artifacts. Also advantageous for laser irradiation is the presence of an increased spectral width in order to reduce the visibility of speckle patterns on the screen.

Increasing the angular separation and spectral width of laser irradiation can lead to deterioration in the contrast ratio of the optical filtering systems and methods presented herein. Namely, in the Fourier plane, increased angular separation and spectral width can widen the diffraction peaks, leading to mixing of their edges with other edges of neighboring peaks. This broadening of the maxima can prevent individual diffraction orders from passing through the spatial filter 2302 without passing a portion of adjacent diffraction orders that need to be blocked. As shown in FIG. 32, the contrast ratio is halved, from 721,000:1 to 346,000:1, when the light input half angle 206 is increased to 8°.

Therefore, when considering angular separation and spectral width, there is a trade-off between (1) dust visibility and speckle reduction and (2) contrast ratio.

It is understood that deterioration in contrast may result from factors other than diffraction of the input light signal 206 by the DMD 200, such as scattering of the input light signal 206 by the surfaces of the micromirrors 202, unwanted stray light and reflections in the cinema room, optical aberrations, and/or polarization effects. However, for most digital projectors, diffraction by the DMD 200 is expected to be the predominant source, or at least one of the predominant sources, of contrast degradation. The systems and methods disclosed herein are easily extended to cases in which contrast is degraded by other factors in addition to diffraction, such as those listed above. The systems and methods disclosed herein can improve contrast even in the presence of other such factors.

EXPERIMENTAL RESULTS

The numerical analysis presented above was verified using an experimental setup similar to that shown in FIG. 4. To demonstrate the greatest contrast, the experimental setup was configured to filter zero order diffraction at 532 nm. The optical filter mask 412 was configured with a circular aperture centered on the optical axis 422. The diameter of the circular aperture and the lens (eg, lens 404) were chosen to form a 2° half angle on the Fourier plane. Light input to the DMD 200 was provided by a polarized 532 nm laser with M ² < 1.1. The input light signal was expanded to fill the face of the DMD 200 using a Galilean beam expander formed from two doublets that provided diffraction limited performance. For simplicity, TIR did not use a prism to supply light to the DMD 200. The DMD 200 was used with the lightest (eg white level) and darkest (eg black level) outputs and the contrast was measured with a spectrometer.

The contrast ratios of two identical 4K DMDs were measured. At 532 nm and 2° half angle, the contrast ratio predicted by the 2300 model experiment is approximately 757,000:1 (see highest green contrast ratio in FIG. 24). Contrast ratios of 254234:1 and 277966:1 were measured. These values are approximately three times smaller than the predicted value; the discrepancy is attributed to stray light originating from the overflow of the DMD, stray light originating from the gaps between the DMD micromirrors, and scattering from the surface and edges of the micromirrors.

It has also been observed that the direction of propagation of the input light signal 206 towards the DMD 200 has an effect on the contrast ratio, as would be expected given the dependence of the contrast ratio on the tilt angle in the OFF mode. In addition, it has been observed that the polarization of the input light signal 206 affects the black level of the DMD 200, thereby affecting the contrast ratio. For the experimental results described above, the polarization of the input light signal was rotated by a waveplate to maximize contrast.

Given the sensitivity of the contrast ratio to the tilt angles of the micromirrors and the direction of propagation of the input light signal 206, spacing can be used to group DMDs having similar tilt angles. In one embodiment of the three-color digital projector 1500, three-spacing DMDs having similar tilt angles are used for DMDs 200(1), 200(2), and 200(3). In another embodiment, three-interval DMDs having different inclination angles (e.g., from three different intervals) are used for DMDs 200(1), 200(2), and 200(3), with each DMD device having an inclination selected so as to maximize the contrast ratio for a particular wavelength of the input light signal 206 used with this DMD.

DLP BIT SEQUENCES

In FIG. 35 shows a time sequence 3500 of exemplary bit planes 3502 that determines how the micromirrors 202 of the DMD 200 are controlled to display a single video frame. In FIG. 36 is a reconstructed frame 3600 showing what a single video frame looks like when the exemplary bit planes 3502 shown in FIG. 35 control the DMD 200 to display one video frame. Fig. 35 and 36 are best read in conjunction with the following description.

-битные целые числа, где 0 представляет самый низкий уровень интенсивности, а

представляет самый высокий уровень интенсивности. При таком представлении кадр может быть образован как сумма

битовых плоскостей 3502. Белый бит на любой из битовых плоскостей 3502 представляет ВКЛ для соответствующего микрозеркала 202 DMD 200, тогда как черный бит представляет ВЫКЛ для соответствующего микрозеркала 202. Устройством DMD 200 последовательно управляют в соответствии с каждой из битовых плоскостей 3502 в течение временного интервала

, где

представляет минимальный временной интервал, а

= 0…

представляет индексы битовых плоскостей 3502. Таким образом, в примере, представленном на фиг. 35, где пиксельные уровни представлены как 6-битные целые числа, устройством DMD 200 управляют в соответствии с первой битовой плоскостью 3502(0) в течение первого временного интервала

, второй битовой плоскостью 3502(1) в течение второго временного интервала

и так далее, аж до шестой битовой плоскости 3502(5) в течение шестого временного интервала

. Биты битовых плоскостей 3502 выбирают (например, 0 или 1 для каждого бита, соответствующие ВЫКЛ и ВКЛ, соответственно, для соответствующего микрозеркала 202) таким образом, что взвешенная по времени сумма битовых плоскостей 3502 дает желаемые пиксельные значения для кадра. Кадр отображается достаточно быстро, так что зрительная система человека отвечает на интеграл по времени отображаемой последовательности 3500 битовых плоскостей 3502. Each pixel in a digital video frame is assigned a corresponding pixel level that represents a desired pixel intensity level. Pixel levels can be represented as

-bit integers, where 0 represents the lowest intensity level, and

represents the highest intensity level. With this representation, the frame can be formed as the sum

bit planes 3502. A white bit on any one of the bit planes 3502 represents ON for the corresponding micromirror 202 of the DMD 200, while a black bit represents OFF for the corresponding micromirror 202. The DMD 200 is sequentially controlled in accordance with each of the bitplanes 3502 during the time interval

, where

represents the minimum time interval, and

= 0…

represents bit plane indices 3502. Thus, in the example shown in FIG. 35, where the pixel levels are represented as 6-bit integers, the DMD 200 is controlled in accordance with the first bit plane 3502(0) during the first time interval.

, the second bit plane 3502(1) during the second time interval

and so on, up to the sixth bit plane 3502(5) during the sixth time interval

. The bits of the bit planes 3502 are selected (eg, 0 or 1 for each bit, corresponding to OFF and ON, respectively, for the respective micromirror 202) such that the time-weighted sum of the bit planes 3502 gives the desired pixel values for the frame. The frame is displayed fast enough that the human visual system responds to the time integral of the displayed sequence of 3500 bit planes 3502.

250 пикселей, битовые плоскости 3502 могут иметь такой размер, чтобы управлять всеми микрозеркалами 202 DMD 200 без отступления от объема настоящего изобретения.Although in FIG. 35 and 36 show an example where pixel values are represented as 6-bit integers, pixel values can be represented by a different number of bits and the same number of bit planes without departing from the scope of the present invention. Although in FIG. 35 shows bit planes 3502 having a size of 250 pixels for clarity.

250 pixels, bit planes 3502 may be sized to drive all of the micromirrors 202 of the DMD 200 without departing from the scope of the present invention.

In prior art digital projection systems in which many orders of diffraction are projected onto a screen, the desired pixel level of a pixel is proportional to the ON time for the micromirror that the pixel generates. However, when the diffraction orders from the DMD 200 are blocked by an optical filter (eg, optical filter 412) to enhance contrast, the amount of light passing through the optical filter (eg, zero diffraction order) also depends on the spatial structure of the micromirror 202. structure affects how much power is diffracted into each order, and hence how much power passes through the optical filter. In some frames, this combination of spatial structure and optical filter may generate artifacts 3602 in reconstructed frame 3600. For example, in FIG. The 35 bit planes 3502 drive the DMD 200 to form ON and OFF "bands" having pronounced spatial frequencies, and the phase shifts resulting from this spatial pattern change the amount of light passing through the optical filter, thereby creating artifacts 3602 that appear like vertical stripes. Although only three artifacts 3602 are indicated in the reconstructed frame 3600, the reconstructed frame 3600 contains other bands of different levels of obscuration, which are also artifacts. Artifacts 3602 appear as vertical streaks on reconstructed frame 3600 due to bit planes 3502 forming vertical ON and OFF streaks with pronounced horizontal spatial frequency. However, the artifacts 3602 will be horizontal stripes when the bit planes 3502 form horizontal ON and OFF stripes with a pronounced vertical spatial frequency.

In FIG. 37 shows one example of a randomized bitplane 3700 that forms part of a sequence of randomized bitplanes that can be used with embodiments of the present invention to reduce the presence of artifacts 3602. FIG. 38 is a reconstructed frame 3800 showing what a single video frame looks like when a sequence of randomized bit planes controls the DMD 200 to display a single video frame. Advantageously, the visibility of artifacts in the reconstructed frame 3800 is significantly reduced in comparison to the reconstructed frame 3600. FIG. 37 and 38 are best read in conjunction with the following description.

рандомизированных битовых плоскостей, одним примером которых является рандомизированная битовая плоскость 3700.

рандомизированных битовых плоскостей являются визуально похожими (хотя не обязательно идентичными), и поэтому только одна показана на фиг. 37 для ясности. Как и для битовых плоскостей 3502 на фиг. 35, белый бит указывает, что соответствующее микрозеркало 202 DMD 200 находится в положении ВКЛ, а черный бит указывает, что соответствующее микрозеркало 202 DMD 200 находится в положении ВЫКЛ. В отличие от последовательности 3500 битовых плоскостей, где временные интервалы битовых плоскостей 3502 увеличиваются на степени 2, каждая из

рандомизированных битовых плоскостей имеет одинаковый временной интервал

.The sequence of randomized bit planes is formed from

randomized bit planes, one example of which is randomized bit plane 3700.

randomized bitplanes are visually similar (though not necessarily identical) and therefore only one is shown in FIG. 37 for clarity. As with bit planes 3502 in FIG. 35, a white bit indicates that the corresponding DMD 200 micromirror 202 is in the ON position, and a black bit indicates that the corresponding DMD 200 micromirror 202 is in the OFF position. Unlike the bit plane sequence 3500, where the time intervals of the bit planes 3502 are incremented by a power of 2, each of

randomized bit planes has the same time interval

.

The random distribution of bits ON and OFF on the randomized bit plane 3700 replaces pronounced spatial structures like those shown in FIG. 35 with randomized spatial structures, thereby spreading the effects of diffraction across all pixels of the frame and advantageously reducing the visibility of artifacts 3602.

битовых плоскостей таким образом, что все биты всех битовых плоскостей представляют ВЫКЛ.

битовых плоскостей затем случайным образом заполняют (т. е. переключают биты в «ВКЛ»), при этом убеждаясь, что для каждого пикселя сумма

битов для этого пикселя никогда не превышает соответствующего пиксельного значения. Заполнение

битовых плоскостей останавливают, когда для каждого пикселя в кадре сумма

битов равняется соответствующему пиксельному значению.In one embodiment, a sequence of randomized bitplanes is generated for one frame by initializing

bit planes such that all bits of all bit planes represent OFF.

the bit planes are then randomly populated (i.e., toggle the bits "ON") while making sure that for each pixel the sum

bits for that pixel never exceeds the corresponding pixel value. filling

bit planes stop when for each pixel in the frame the sum

bits equals the corresponding pixel value.

The randomized bitplane sequence described above contains more bitplanes than the 3500 bitplane sequence shown in FIG. 35. However, these two approaches can be combined, i.e. a sequence of hybrid planes can be formed with some of the 3502 bitplanes (i.e. for shorter time intervals) and some of the randomized bitplanes, provided that for each pixel a weighted in time, the sum of all bits in the hybrid sequence equals the corresponding pixel level. In addition, sequences of randomized and hybrid bitplanes can be combined with other techniques for adjusting output power levels, such as dithering micromirrors 202.

The sequence of randomized bit planes may result in a pixel response that is less linear than the pixel response obtained when the DMD 200 optical filter is not used. A non-linear pixel response may be desirable in display devices because human visual perception is a non-linear process, and the non-linearity introduced by a sequence of randomized bit planes more closely matches the non-linearity of human visual perception. Where a non-linear response is desired, it may be possible to reduce the number of bits used to represent pixel values as the projection system displays frames with better perceptual capability.

The benefits gained from a sequence of randomized or hybrid bitplanes depend on the quality of the input light signal illuminating the DMD 200. when the input light signal has a large geometric factor and/or low coherence (for example, from a lamp). Thus, sequences of randomized and hybrid bit planes become more important in reducing the visibility of artifacts 3602 when the input light signal is of "high quality".

BENEFITS

Advantageously, the embodiments presented herein increase the contrast ratio without the use of additional DMDs. For example, as an alternative to the systems and methods disclosed herein, the contrast ratio can be increased by using multi-stage modulation, i.e., two or more DMDs connected in series such that OFF-mode diffracted beams from the first DMD are blocked by the second DMD. As a way to increase the contrast ratio, multi-stage modulation disadvantageously increases the cost and complexity of a digital projector due to the second DMD and related electronics. In addition, one type of digital projector uses three DMDs, one DMD for each of red light, green light, and blue light; the use of two DMDs for each light in this type of digital projector increases the total number of DMDs from three to six, further increasing cost and complexity.

Another advantage of the embodiments presented herein is that the optically filtered projected light signal can reduce the appearance of moiré patterns caused by interference between the unfiltered projected light signal and periodic perforations of the screen onto which the projected light signal is projected. More specifically, optical filtering can be configured to reduce the high frequency components of the projected light signal, thereby "smoothing out" sharp edges between pixels as they appear on the screen. This smoothing reduces the interaction between the periodic intensity of the projected light and the periodic screen perforations.

Another advantage of the optical filtering systems and methods presented herein is that optical filtering can enhance the contrast ratio of a digital projector using a Tilt-and-roll pixel (TRP) DLP chip available from Texas Instruments. ". The micromirrors of the DLP TRP chip do not tilt about an axis oriented at an angle of 45° (for example, the axis of rotation of the mirrors 208 shown in Fig. 2). As a result, compared to other types of DMD chips, the modulated light signal propagates away from the TRP chip so that the diffracted OFF-state light signal orders (e.g., the OFF-mode diffracted beams 604 shown in FIG. 6) are brighter, the thereby increasing the light intensity in OFF mode and decreasing the contrast ratio. By reducing light intensity in OFF mode, the optical filtering systems and methods presented herein advantageously allow TRP chips to be included in projectors for high contrast ratio applications such as Digital Cinema Initiatives (DCI) specification projection.

Changes may be made to the methods and systems described above without departing from the scope of the present invention. Therefore, it should be noted that the subject matter contained in the description above or shown in the accompanying graphics should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all derivatives and special features described herein, as well as all wordings of the scope of the method and system according to the invention that can be said to fall within their scope.

Various aspects of the present invention can be understood from the following numbered exemplary embodiments (NEPs):

1. An optical filter for enhancing the contrast of an image generated by a spatial light modulator, comprising:

a lens configured to spatially Fourier transform the modulated light signal from the spatial light modulator, the modulated light signal comprising a plurality of diffraction orders; and

an optical filter mask located on the Fourier plane of the lens and configured to filter the modulated light signal that has undergone a spatial Fourier transform by the lens by passing at least one order of diffraction of the modulated light signal and blocking the rest of the modulated light signal.

2. Optical filter according to ATIR 1, in which at least one diffraction order is the zeroth order.

3. An optical filter according to APVO2, wherein the optical filter mask has a pass region configured to pass a zero order modulated light signal.

4. Optical filter according to ATIR 1, wherein at least one diffraction order includes a zero order and a plurality of first orders.

5. An optical filter according to ATOP 4, wherein the optical filter mask has a pass region configured to pass the zero order and two of the first orders of the modulated light signal.

6. An optical filter according to any one of ATOPs 1 to 5, wherein the modulated light signal is one of red light, green light, and blue light.

7. A modulator system for generating an image with enhanced contrast, comprising:

an optical filter according to any of APVO 1-6; and

a digital micromirror device that implements a spatial light modulator.

8. A modulator system for generating an image with enhanced contrast, comprising:

an optical filter according to any of APVO 1-7; and

a collimating lens positioned to collimate at least one diffraction order of the modulated light signal transmitted by the optical filter mask.

9. A modulator system for generating an image with enhanced contrast, comprising:

first, second and third spatial light modulators configured to modulate respective first, second and third light signals according to the image to generate respective first, second and third modulated light signals;

three instances of an optical filter according to any one of AFTRs 1-6, forming respective first, second, and third optical filters configured to pass at least one order of diffraction of the respective first, second, and third modulated light signals to generate the respective first, second, and third filtered light signals and block the rest of the respective first, second and third modulated light signals; and

a beam combining unit configured to combine the first, second and third filtered light signals into an output light signal.

10. A modulator system according to ATFR9, wherein each of the first, second, and third optical filter masks of the respective first, second, and third optical filters has at least one pass region configured to pass a zero diffraction order and a plurality of first diffraction orders, respectively. first, second and third modulated light signals.

11. A modulator system according to TFOP 9 or TFFT 10, wherein each of the first, second, and third spatial light modulators is a digital micromirror device.

12. A modulator system according to any one of PPVO 9-11, wherein the first, second, and third light signals are respectively red light, green light, and blue light.

13. A modulator system according to any of the APVOs 9-12, which further comprises first, second, and third output lenses positioned to collimate the first, second, and third filtered light signals, respectively, before being combined by a beam combiner, respectively.

14. A modulator system according to any one of APVOs 9-13, which further comprises a projection lens configured to project a light output onto a screen.

15. A time-multiplexed modulator system for generating an image with enhanced contrast, comprising:

a spatial light modulator configured to modulate, in accordance with the image, a time multiplexed light signal into a time multiplexed modulated light signal comprising a repeating sequence of first, second and third modulated light signals;

a lens configured to spatially Fourier transform the modulated light signal with time multiplexing on a Fourier plane; and

a filter disk disposed on a Fourier plane and comprising a plurality of optical filter masks, each optical filter mask configured to filter a respective one of the first, second, and third modulated light signals space-Fourier-transformed by the lens by passing at least at least one order of diffraction of the respective one of the first, second and third modulated light signals and blocking the remainder of the respective one of the first, second and third modulated light signals, wherein the filter disk is configured to rotate in synchronism with the modulated light signal with time multiplexing so that each optical filter mask is located in a fourier-plane time-multiplexed modulated light signal when the time-multiplexed modulated light signal is one of the first, second and third modulated light signals.

16. The ATDM 15 time-multiplexed modulator system in which the spatial light modulator is a digital micromirror device.

17. A time multiplexing modulator system according to TFEP 15 or FTOP 16, wherein the plurality of optical filter masks are three optical filter masks respectively configured to filter the first, second, and third modulated light signals.

является положительным целым числом, при этом каждый из трех наборов сконфигурирован так, чтобы фильтровать соответствующий один из первого, второго и третьего модулированных световых сигналов.18. A time-multiplexed modulator system according to any one of TFEP 15-17, wherein the set of optical filter masks are three sets of optical filter masks, where

is a positive integer, with each of the three sets configured to filter a corresponding one of the first, second, and third modulated light signals.

19. The ATTF 17 time-multiplexed modulator system, wherein the first optical filter mask has a pass region configured to pass a zero diffraction order and a plurality of first diffraction orders of the first modulated light signal, the second optical filter mask has a pass region configured as to pass the zero diffraction order and the plurality of first diffraction orders of the second modulated light signal, and the third optical filter mask has a pass region configured to pass the zero diffraction order and the plurality of first diffraction orders of the third modulated light signal.

20. An ATTP 19 time-multiplexed modulator system in which the first, second, and third modulated light signals are red light, green light, and blue light, respectively.

21. A TFAM 20 time-multiplexed modulator system in which the filter disk is further configured to rotate unevenly to stop when each optical filter mask is positioned in the time-multiplexed modulated light signal.

22. The ATTF 21 time-multiplexed modulator system, which further comprises a projection lens configured to project onto the screen at least one order of diffraction of the respective first, second, and third modulated light signals transmitted by the filter disk.

23. A method for enhancing the contrast of an image generated using a spatial light modulator, including:

spatial Fourier transform of the modulated light signal from the spatial light modulator to the Fourier plane, wherein the modulated light signal contains a plurality of diffraction orders; and

filtering the modulated light signal by:

transmitting at least one order of diffraction of the modulated light signal on the Fourier plane; and

blocking the rest of the modulated light signal on the Fourier plane.

24. The method according to WPTO 23, wherein at least one diffraction order is the zero diffraction order.

25. The method according to APTR 24, wherein the step of passing includes passing a zero order diffraction through the pass region of the optical filter mask.

26. The method according to ATIR 23, wherein at least one diffraction order includes a zero diffraction order and a plurality of first orders.

27. The method according to APTR 26, wherein the step of passing includes passing a zero diffraction order and a plurality of first diffraction orders through the pass region of the optical filter mask.

28. A method according to any one of TPVRs 23-27 wherein the modulated light signal is one of red light, green light and blue light.

29. The method according to any one of TPOPs 23-28, which further includes driving a plurality of micromirrors of a spatial light modulator so as to generate a modulated light signal.

30. A method according to any one of TFEP 23-29, which further comprises, after the transmission step, collimating at least one order of diffraction of the modulated light signal.

31. A method for projecting a color image with enhanced contrast, including:

spatial modulation of the first, second and third input light signals, in accordance with the image, to generate the respective first, second and third modulated light signals, each of the first, second and third modulated light signals contains a plurality of diffraction orders;

filtering the first, second and third modulated light signals into the respective first, second and third filtered light signals by:

transmitting at least one order of diffraction of the respective first, second and third modulated light signals; and

blocking the rest of the respective first, second and third modulated light signals; and

combining the first, second and third filtered light signals into an output light signal.

32. The method according to TPOP 31, wherein the first, second, and third input lights are red light, green light, and blue light, respectively.

33. The method according to TFOP 31 or TFFT 32, which further includes projecting the output light signal onto a screen.

34. A method with time multiplexing for generating and projecting an image with enhanced contrast, including:

according to the image, modulating the light signal with time multiplexing with a spatial light modulator to generate a modulated light signal with time multiplexing, containing a repeating sequence of the first, second and third modulated light signals;

spatial Fourier transform of the modulated light signal with time multiplexing using a lens; and

filtering the modulated light signal with time multiplexing by rotating the filter disk in synchronism with the modulated light signal with time multiplexing, while the filter disk contains a plurality of optical filter masks, each optical filter mask is configured to filter the corresponding one of the first, second and third modulated of light signals that have undergone a spatial Fourier transform by the lens, wherein said rotation includes locating each optical filter mask in the temporally multiplexed modulated light signal in the Fourier plane of the lens, when the temporally multiplexed modulated light signal is the respective one of the first, second, and third modulated light signals.

35. An ATTP 34 time-multiplexed modulator system in which the spatial light modulator is a digital micromirror device.

36. The method according to TFOP 34 or TFFT 35, wherein the plurality of optical filter masks are three optical filter masks respectively configured to filter the first, second, and third modulated light signals.

является положительным целым числом, при этом каждый из трех наборов сконфигурирован так, чтобы фильтровать соответствующий один из первого, второго и третьего модулированных световых сигналов.37. The method according to any of the TFAPs 34-36, wherein the plurality of optical filter masks are three sets of optical filter masks, where

is a positive integer, with each of the three sets configured to filter a corresponding one of the first, second, and third modulated light signals.

38. The method according to PPVO 36, in which the filtering step includes:

passing a zero order and a plurality of first orders of the first modulated light signal through the bandwidth of the mask of the first optical filter;

passing a zero order and a plurality of first orders of the second modulated light signal through the bandwidth of the mask of the second optical filter; and

passing the zero order and the plurality of first orders of the third modulated light signal through the bandwidth of the mask of the third optical filter.

39. A method according to FTOP 36 or FTOP 38, wherein the first, second, and third modulated light signals are red light, green light, and blue light, respectively.

40. The method according to FTOP 36, FTOP 38, or FTOP 39, wherein the turning further includes uneven turning and stopping when each optical filter mask is located in a time-multiplexed modulated light signal.

41. A method according to TFOP 36, FTOP 38, FTOP 39, or FTOP 40, which after the filtering step further comprises projecting the post-filtered time-multiplexed modulated light signal onto a screen.

Claims (54)

1. A time-multiplexed modulator system for generating an image, comprising: a spatial light modulator configured to modulate, in accordance with the image, a time multiplexed light signal into a time multiplexed modulated light signal to form a repeating sequence of first, second, and third modulated light signals; a lens configured to spatially Fourier transform the modulated light signal with time multiplexing on a Fourier plane; and a filter disk disposed on a Fourier plane and comprising a plurality of optical filter masks, each of the optical filter masks configured to filter a respective one of the first, second, and third modulated light signals spatially Fourier transformed by the lens by passing through at least one order of diffraction of the respective one of the first, second and third modulated light signals and blocking the remainder of the respective one of the first, second and third modulated light signals, wherein the filter disk is configured to rotate in synchronism with the modulated light signal with time multiplexing such that each of the optical filter masks is located in the Fourier plane time-multiplexed modulated light signal when the time-multiplexed modulated light signal is coo The corresponding one of the first, second and third modulated light signals. 2. The modulator system with time multiplexing according to claim 1, characterized in that the spatial light modulator is a digital micromirror device. 3. The modulator system with time multiplexing according to claim 1 or 2, characterized in that the set of masks of the optical filter is three sets of

masks of the optical filter, where

is a positive integer, with each of the three sets configured to filter a corresponding one of the first, second, and third modulated light signals. 4. System modulator with time multiplexing according to any one of paragraphs. 1-3, characterized in that the plurality of optical filter masks comprises first, second, and third optical filter masks respectively configured to filter the first, second, and third modulated light signals. 5. Modulator system with time multiplexing according to claim 4, wherein the first optical filter mask has a pass region configured to pass zero diffraction order and/or one or more first diffraction orders of the first modulated light signal; the second optical filter mask has a pass region configured to pass zero diffraction order and/or one or more first diffraction orders of the second modulated light signal; and the third optical filter mask has a pass region configured to pass zero diffraction order and/or one or more first diffraction orders of the third modulated light signal. 6. System modulator with time multiplexing according to any one of paragraphs. 1-5, characterized in that the first, second and third modulated light signals are respectively red, green and blue. 7. The time-multiplexed modulator system of claim 6, wherein each optical filter mask filtering the red light signal is configured to pass zero diffraction order and many, but not all, first diffraction orders. 8. The time-multiplexed modulator system according to claim 7, characterized in that each optical filter mask filtering the red light signal has an L-shaped bandwidth. 9. System modulator with time multiplexing according to any one of paragraphs. 6-8, characterized in that each optical filter mask filtering the green light signal is configured to pass only the zero order of diffraction. 10. System modulator with time multiplexing according to any one of paragraphs. 6-9, characterized in that each optical filter mask filtering the blue light signal is configured to pass many, but not all, first orders of diffraction, and optionally also passes the zero order of diffraction. 11. Modulator system with time multiplexing according to any one of paragraphs. 1-10, characterized in that the filter disk is further configured to rotate non-uniformly to stop when each optical filter mask is positioned in the time-multiplexed modulated light signal. 12. System modulator with time multiplexing according to any one of paragraphs. 1-11, characterized in that it further comprises a projection lens configured to project onto the screen at least one order of diffraction of the respective first, second and third modulated light signals transmitted by the filter disk. 13. A modulator system for generating an image, comprising: first, second and third spatial light modulators configured to modulate, in accordance with the image, the respective first, second and third light signals to generate the respective first, second and third modulated light signals; first, second and third optical filters, each containing: a lens configured to spatially Fourier transform the modulated light signal from the respective first, second, and third spatial light modulators, the modulated light signal comprising a plurality of diffraction orders; and an optical filter mask located on the Fourier plane of the lens and configured to filter the modulated light signal that has been spatially Fourier transformed by the lens by passing at least one diffraction order of the modulated light signal, generating the respective first, second, and third filtered light signals and blocking the rest of the modulated light signal, wherein the optical filter mask filtering the first modulated light signal has an L-shaped pass area; and a beam combining unit configured to combine the first, second and third filtered light signals into an output light signal. 14. The modulator system of claim 13, wherein each of the first, second, and third optical filter masks of the respective first, second, and third optical filters has at least one pass region configured to pass zero order diffraction and/or one or more first orders of diffraction, respectively, of the first, second and third modulated light signals. 15. The modulator system according to claim 13 or 14, characterized in that each of the first, second and third spatial light modulators is a digital micromirror device. 16. The modulator system according to any one of paragraphs. 13-15, characterized in that the first, second and third light signals are respectively red, green and blue. 17. The modulator system of claim 16, wherein each optical filter mask filtering the red light signal is configured to pass zero diffraction order and many, but not all, first diffraction orders. 18. The modulator system according to any one of paragraphs. 16, 17, characterized in that each optical filter mask filtering the green light signal is configured to pass only the zero order of diffraction. 19. The modulator system according to any one of paragraphs. 16-18, characterized in that each optical filter mask filtering the blue light signal is configured to pass many, but not all, first orders of diffraction, and optionally also passes the zero order of diffraction. 20. The modulator system according to any one of paragraphs. 13-19, characterized in that it additionally contains the first, second and third output lenses located so as to collimate the first, second and third filtered light signals, respectively, before combining by the beam combining unit. 21. The modulator system according to any one of paragraphs. 13-20, characterized in that it further comprises a projection lens configured to project an output light signal onto a screen. 22. Method for projecting a color image, including: spatial modulation of the first, second and third input light signals, in accordance with the color image, to generate the respective first, second and third modulated light signals, each of the first, second and third modulated light signals contains a plurality of diffraction orders; filtering the first, second and third modulated light signals into the respective first, second and third filtered light signals by: transmitting at least one of the diffraction orders of the respective first, second and third modulated light signals, the first modulated light signal being transmitted in an L-shape; blocking the rest of the respective first, second and third modulated light signals; and combining the first, second and third filtered light signals into an output light signal. 23. The method of claim 22, wherein the first, second, and third input lights are red, green, and blue, respectively. 24. The method according to claim 22 or 23, further comprising projecting the output light signal onto a screen. 25. A time multiplexing method for generating and projecting an image, comprising: modulating, in accordance with the image, the light signal with time multiplexing using a spatial light modulator to generate a modulated light signal with time multiplexing, containing a repeating sequence of the first, second and third modulated light signals; spatial Fourier transform of the modulated light signal with time multiplexing using a lens; and filtering the modulated light signal with time multiplexing by rotating the filter disk in synchronism with the modulated light signal with time multiplexing, while the filter disk contains a plurality of optical filter masks, each of the optical filter masks is configured to filter the corresponding one of the first, second and third modulated light signals that have undergone a spatial Fourier transform by a lens, wherein said rotation includes the location of each of the masks of the optical filter in the modulated light signal with time multiplexing in the Fourier plane of the lens, when the modulated light signal with time multiplexing is the corresponding one of the first, second and third modulated light signals. 26. The method according to claim 25, characterized in that the spatial light modulator is a digital micromirror device. 27. The method according to claim 25 or 26, characterized in that the set of masks of the optical filter is three sets of

masks of the optical filter, where

is a positive integer, with each of the three sets configured to filter a corresponding one of the first, second, and third modulated light signals. 28. The method according to any one of paragraphs. 25-27, characterized in that the plurality of optical filter masks comprises first, second, and third optical filter masks respectively configured to filter the first, second, and third modulated light signals. 29. The method according to any one of paragraphs. 25–28, characterized in that the filtering includes: passing zero diffraction order and/or one or more first diffraction orders of the first modulated light signal through the bandwidth of the first optical filter mask; passing zero diffraction order and/or one or more first diffraction orders of the second modulated light signal through the bandwidth of the mask of the second optical filter; and passing the zero order diffraction and/or one or more first orders of diffraction of the third modulated light signal through the pass region of the mask of the third optical filter. 30. The method according to any one of paragraphs. 25-29, characterized in that the first, second and third modulated light signals are respectively red, green and blue. 31. The method according to any one of paragraphs. 25-30, characterized in that the rotation further includes uneven rotation and stop, when each of the masks of the first, second and third optical filters is located in the modulated light signal with time multiplexing. 32. The method according to any one of paragraphs. 25-31, characterized in that, after filtering, it additionally includes the projection of a modulated light signal with time multiplexing after filtering onto the screen.

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