Holographic projectors with size correction and beam alignment of different wavelengths of light.

Abstract

Holographic projection system (500) comprising: a first light source (504, 600) configured to produce a first light beam (620); a second light source (506, 602) configured to produce a second light beam (622); a third light source (508, 604) configured to produce a third light beam (624), wherein the first light beam (620), the second light beam (622) and the third light beam (624) have respective wavelengths; a plurality of spatial light modulators (510, 512, 514, 610, 612, 614) configured to diffract the first light beam (620), the second light beam (622) and the third light beam (624), respectively;a first lens (606) arranged to set a divergence angle of the first light beam (620), the second light beam (622), or the third light beam (624) such that diffracted light from each of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614) has the same diffraction angle, wherein the plurality of spatial light modulators (510, 512, 514, 610, 612, 614) is configured to encode phase holograms including respective versions of a graphic image based on light produced by the first light source (504, 600), the second light source (506, 602), and the third light source (508, 604), including the light emitted by the first lens (606) to provide phase hologram beams;a combiner (516) configured to combine the phase hologram beams to provide a combined phase hologram beam that is projected for viewing a combined graphic image; and a control module (502) configured to encode a prism hologram on one of the multiple spatial light modulators (510, 512, 514, 610, 612, 614) to align the outputs of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614);characterized in that the control module (502) is configured to dimension the first light beam (620), the second light beam (622) and the third light beam (624) so ​​that they do not fill an available image area, and to adjust the position of one or more of the first light beam (620), the second light beam (622) and the third light beam (624) in order to align the first light beam (620), the second light beam (622) and the third light beam (624).

Description

Introduction The information provided in this section serves to present the general context of the disclosure. Works of the inventors currently named, insofar as they are described in this section, as well as aspects of the description that may not have been prior art at the time of filing, are neither expressly nor implicitly recognized as prior art with respect to the present disclosure. This disclosure relates to holographic projection systems and head-up display systems for vehicles. Comparable and related systems can be found, for example, in US 2018 / 0 120 768 A1 and DE 10 2018 221 438 A1. Display devices are used in a wide variety of applications. Some examples include flat panel displays, projection displays, and head-up displays. Display devices can be either transmission-based or reflection-based. The driver of a vehicle typically sees the vehicle's surroundings through windows, the windshield, and other vehicle glass. The driver can control the vehicle's acceleration, braking, and steering based on this visual observation. The vehicle may contain one or more displays that show the driver various types of information. For example, some vehicles have an infotainment system that includes a display showing various infotainment and other vehicle information. The vehicle may also include a head-up display (HUD), which projects information by creating a virtual image at a certain distance, reflected off the windshield. The HUD can display, for example, the vehicle's speed and other vehicle information (such as lane departure warnings and collision avoidance alerts). Summary A holographic projection system according to the invention comprises a first light source, a second light source, a third light source, spatial light modulators, a first lens, a combiner, and a control module. The first light source is configured to generate a first light beam. The second light source is configured to generate a second light beam. The third light source is configured to generate a third light beam. The first, second, and third light beams each have specific wavelengths. The spatial light modulators are configured to diffract the first, second, and third light beams, respectively. The first lens is arranged to adjust the divergence angle of the first, second, or third light beam such that the diffracted light from each of the spatial light modulators has the same diffraction angle.The spatial light modulators are configured to encode phase holograms containing respective versions of a graphic image based on light generated by the first, second, and third light sources, including light emitted by the first lens, to provide phase hologram beams. The combiner is configured to combine the phase hologram beams to provide a combined phase hologram beam, which is projected for viewing a combined graphic image. The control module is configured to encode a prism hologram on one of the spatial light modulators to align the outputs of the spatial light modulators. Preferably, the first light beam is a red laser beam, the second light beam is a green laser beam, and the third light beam is a blue laser beam. Preferably, the holographic projection system also includes a second lens. The first lens adjusts the divergence angle of the green laser beam so that it matches the divergence angle of the red laser beam diffracted by one of the spatial light modulators. The second lens adjusts the divergence angle of the blue laser beam so that it matches the divergence angle of the red laser beam diffracted by one of the spatial light modulators. Preferably, the first lens adjusts the divergence angle of the red laser beam such that it matches a divergence angle of the green laser beam that is diffracted by one of the spatial light modulators. The holographic projection system preferably does not have a lens for adjusting the divergence angle of the blue laser beam. Preferably, one or more of the spatial light modulators includes a non-periodic photon sieve layer to set a divergence angle of one or more of the first light beam, the second light beam and the third light beam. Preferably, the control module is configured to encode a lens hologram on one or more of the spatial light modulators to set a size of one or more of the first light beam, the second light beam, and the third light beam. Preferably, the control module is configured to encode two prism holograms each onto two of the spatial light modulators in order to shift the position of two of the first light beam, the second light beam and the third light beam. According to the invention, the control module is configured to dimension the first light beam, the second light beam and the third light beam so that they do not fill an available image area, and to adjust the position of one or more of the first light beam, the second light beam and the third light beam in order to align the first light beam, the second light beam and the third light beam. A holographic projection system is also provided, comprising a first light source, a second light source, a third light source, spatial light modulators, a combiner, and a control module. The first light source is configured to generate a first beam of light. The second light source is configured to generate a second beam of light. The third light source is configured to generate a third beam of light, with the first, second, and third beams having respective wavelengths. The spatial light modulators are configured to encode phase holograms containing respective versions of a graphic image, based on the light generated by the first, second, and third light sources to provide phase hologram beams. One of the spatial light modulators contains a first non-periodic photon sieve layer.The first non-periodic photon sieve layer is configured to adjust the divergence angle of one of the first, second, or third light beams so that the diffracted light from each of the spatial light modulators has the same diffraction angle. The combiner is configured to combine the phase hologram beams to produce a combined phase hologram beam, which is projected for viewing a combined graphic image. The control module is configured to encode a prism hologram on one of the spatial light modulators to align the outputs of the spatial light modulators. Preferably, the first of the spatial light modulators containing the first non-periodic photon sieve layer is the same spatial light modulator for which the control module has encoded the prism hologram. Preferably, the first of the spatial light modulators containing the first non-periodic photon sieve layer is another spatial light modulator for which the control module has encoded the prism hologram. Preferably, the first light beam is a red laser beam, the second light beam is a green laser beam, and the third light beam is a blue laser beam. The first of the spatial light modulators preferentially receives the green laser beam. A second spatial light modulator receives the blue laser beam and contains a second non-periodic photon sieve layer. The first non-periodic photon sieve layer adjusts the divergence angle of the green laser beam so that it matches the divergence angle of the red laser beam, which is diffracted by a third of the spatial light modulators. The second non-periodic photon sieve layer adjusts the divergence angle of the blue laser beam so that it matches the divergence angle of the red laser beam, which is diffracted by the third of the spatial light modulators. Preferably, the first non-periodic photon sieve layer sets a divergence angle of the red laser beam such that it matches a divergence angle of the green laser beam, which is diffracted by the first of the spatial light modulators. Preferably, the holographic projection system does not include a non-periodic photon sieve layer for adjusting a divergence angle of the blue laser beam. Furthermore, a holographic projection system is provided, comprising a first light source, a second light source, a third light source, spatial light modulators, and a control module. The first light source is configured to generate a first beam of light. The second light source is configured to generate a second beam of light. The third light source is configured to generate a third beam of light. The first, second, and third beams each have specific wavelengths. The spatial light modulators are configured to encode phase holograms containing a graphic image generated based on a combination of light from the first, second, and third beams.The control module is configured to encode one or more lens holograms on one or more of the spatial light modulators to adjust the size of one of the first light beam, the second light beam, or the third light beam relative to another of the first light beam, the second light beam, or the third light beam, and to encode one or more prism holograms on one or more of the spatial light modulators to align the first light beam, the second light beam, and the third light beam. Preferably, the holographic projection system further includes a combiner to combine the outputs of three of the spatial light modulators to provide a combined phase hologram beam that is projected for viewing a combined graphic image, or to combine the outputs of the first light source, the second light source and the third light source before the first light beam, the second light beam and the third light beam are received at the spatial light modulators. Preferably, the spatial light modulators comprise a first spatial light modulator and a second spatial light modulator downstream of the first spatial light modulator. The control module is configured to encode at least one lens hologram or prism hologram on the first spatial light modulator and to encode the graphic image on the second spatial light modulator. Preferably, the spatial light modulators comprise a third spatial light modulator and a fourth spatial light modulator downstream of the first spatial light modulator. The first spatial light modulator receives the first light beam. The third spatial light modulator receives the second light beam. The control module is configured to encode at least one lens hologram or prism hologram on the third spatial light modulator and to encode the graphic image on the second and fourth spatial light modulators. Further applications of the present disclosure will become apparent from the detailed description, the claims, and the drawings. The detailed description and specific examples serve only for illustration and are not intended to limit the scope of the disclosure. Brief description of the drawings The present disclosure is more fully understood from the detailed description and the accompanying drawings, wherein: Fig. 1 is an example diagram representing a diffraction angle for a spatial light modulator (SLM); Fig. 2 is an example intensity-diffraction-angle diagram showing the differences in diffraction angles for red and blue light; Fig. 3 is an example bar chart illustrating the differences in the orientation and size of the blue, green, and red light rays due to different diffraction angles; Fig. 4 is an example diagram illustrating the misalignment of various red-green-blue (RGB) images due to diffraction angle differences and a resulting image after correction of the misalignment according to the present disclosure; Fig.5 is a functional block diagram of an example of a holographic projection system with RGB SLMs and an X-cube combiner according to the present disclosure; Fig. 6A is a side view of a red laser and an SLM, illustrating the laser divergence of red light according to the present disclosure; Fig. 6B is a side view of a green laser, a lens, and an SLM, illustrating the laser divergence of green light according to the present disclosure; Fig. 6C is a side view of a blue laser, a lens, and an SLM, illustrating the laser divergence of blue light according to the present disclosure; Fig. 7A is a diffraction diagram showing the diffraction angle and the size of the viewing area without the use of a non-periodic photon sieve; Fig.7B is an example diagram illustrating the diffraction angle and viewing area size when using a non-periodic photon sieve according to the present disclosure; Fig. 8 is a diagram of an exemplary hologram illustrating the introduction of prism and lens holograms via software and SLM(s) for position and size adjustments of RGB images according to the present disclosure; Fig. 9 is a functional block diagram of an example holographic projection system incorporating dual SLMs and introducing prism and lens holograms as well as focal plane distance compensation according to the present disclosure; Fig. 10 is a perspective view of an exemplary vehicle interior with a HUD; Fig. 11 is a functional block diagram of an exemplary implementation of the holographic projection system of Fig. 9; Fig.Figure 12 illustrates an example of a holographic projection method according to the present disclosure; Figure 13 is a cross-sectional view of an example of a liquid crystal-on-silicon (LCoS) SLM according to the present disclosure; and Figure 14 is a functional block diagram of an example of part of an LCoS SLM and a control module according to the present disclosure. Reference numbers can be reused in the drawings to identify similar and / or identical elements. Detailed description A vehicle can contain a holographic HUD, which includes a single-light module (SLM) and a coherent or partially coherent light source. The phase hologram is encoded on the SLM. Light from the coherent or partially coherent light source illuminates the SLM, which is encoded with a phase hologram, and the light is diffracted in a manner specified by the hologram. The diffracted light is reflected off the vehicle's windshield and forms a real image on the driver's retina. Holographic display systems often use a source of coherent light, such as a laser, in conjunction with the other display components. Coherent light can refer to light that is spatially and temporally in phase. When coherent light is reflected from a surface, different points on the surface are considered secondary light waves. When independent RGB channels are used, as in a holographic 3-LCoS HUD, it becomes necessary to provide three spatially aligned RGB images within an eye field or eyebox; otherwise, the viewer will see three misaligned images. The eyebox can refer to a rectangular planar area within which a viewer can see an image. Figures 1 and 2 show diagrams illustrating a diffraction angle θ for an SLM 100 and intensity-diffraction angle curves 206, 208 for red and blue light, respectively, for the SLM 100. As shown, an incident light beam 102 is directed onto the SLM 100 and reflected by it. The reflection of the incident light beam 102 provides (i) a central maximum at 0, which has a peak along a central axis, and (ii) additional maxima of decreasing magnitude, arranged symmetrically around the central axis of the central maximum in a diffraction order. The maxima can be represented by Equation 1, where Λ is the pitch or division of the SLM 100, m is an integer, and λ is the wavelength of the light. The division Λ refers to a distance between the grooves 110 of the SLM 100. The resulting diffraction light distribution for different wavelengths (RGB) depends on the wavelength-dependent diffraction angle at the SLM 100 and the misalignment of the optical components of the corresponding holographic projection system. Misalignment of the optical components can refer to any optical component within a holographic projection system. This misalignment can be caused, for example, by the windshield angle, the angles of lenses, the angles and / or positions of the SLMs, the angle of a beam spreader, etc. Different reflected light spectra associated with the first (-1 and 1) maxima are represented by "pie slice" shapes 112, 114. The intensity modulation is shown in Fig. 2 by dashed curves 216, 218 for red and blue light, respectively. First minima 220, 222 are shown between the central maximum and the first maxima. The image size and position of a holographic display varies with the wavelength. This is illustrated in Figures 3 and 4. Figure 3 shows a bar chart illustrating differences in the orientation and size of blue, green, and red light due to different diffraction angles of the respective colored light beams. For example, the first stripes 300a, 300b, 302a, 302b, 304a, and 304b of the respective blue, green, and red light are shown, differing in their position relative to a central axis 310 and in their width (or size). Figure 4 shows (i) a misalignment of a red image 400, a green image 402, and a blue image 404 due to differences in the respective diffraction angles, and (ii) a resulting image 410 after correction of the misalignment using the techniques disclosed herein.The resulting image 410 can be a white image provided as a result of a combination of RGB images 400, 402, 404 of the same size. In a holographic display system, aligning three primary color image-generating units presents a challenge. Misalignment can be caused (i) by the different diffraction angles of the different colored light beams reflected by the respective SLMs, (ii) by misalignment of the optical components of the corresponding holographic imaging system, and / or (iii) by a diffractional optical expander. Misalignment due to optical components can relate to the SLMs themselves, the distances between light beams from the SLMs and the optical expander, and the distances between the optical expander and the viewer's eyes. Furthermore, the image-generating hardware of the holographic imaging system controls light diffraction, which is wavelength-dependent. The size of a projected image is proportional to the diffraction angle of the light in that projected image. The diffraction angle is directly related to the wavelength of the light. If a hologram is illuminated with different wavelengths, a single output image is perceived as three images of different sizes and positions. The misalignment of different color images and size differences can become more noticeable to a viewer as the distance between the image-generating hardware and the viewer's eyes increases. For displays positioned close to the eyes, such as virtual reality or augmented reality headsets, where images are projected near the viewer's eyes, the problem of color misalignment is minimal.This problem of misalignment and size differences for various colors is exacerbated when the holographic system's optics are scaled and holograms are projected over long distances before reaching the viewer's eyes, such as in a vehicle using a head-up display (HUD). The distances between the image-generating hardware and the viewer's eyes also vary between different vehicles. The examples disclosed herein correct for and account for differences in color alignment and image size. The examples include holographic projection display systems that adjust the size and position of RGB images to produce overlapping images of the same size. When adjusting the size of a monochrome light beam, the divergence angle and / or cross-sectional area of ​​the light beam is adjusted perpendicular to the emission direction of the light beam (or to the path of the light beam). When adjusting the position of a monochrome image, and thus the position of a corresponding light beam, the vertical and / or horizontal position relative to an eyebox is set. The image can be shifted vertically or horizontally within the image plane in front of the viewer's eyes, for example.The RGB images are aligned so that they share a common, overlapping center point and are vertically and horizontally aligned to provide a single image where no image extends beyond any of the others. An example of this is shown in Fig. 4, where the respective center points 412, 414, 416 of images 400, 402, 404 overlap and are represented by point 418. Several different examples of color error correction are provided. Some of these include matching or adjusting diffraction angles to achieve image resizing and software prism coding for spatial alignment. For example, one holographic display system adjusts RGB laser divergence to compensate for diffraction angle differences using RGB LCoS SLMs to produce equally sized RGB images using fixed lenses, electrically tunable lenses, and / or SLMs with pin-hole layers. One or more prism function holograms are then used to adjust the alignment of one or more of the RGB images to align them relative to each other at the eyebox. Different virtual image distances can be accommodated in these examples to maintain varying color image alignments. Fig. 5 shows an example of a holographic projection system 500 comprising a control module 502, a red light source 504, a green light source 506, a blue light source 508, RGB SLMs 510, 512, 514, an X-cube combiner 516, and an optical expander 518. The light sources 502, 504, 506 can be lasers or other suitable light sources. In one embodiment, the RGB SLMs 510, 512, 514 are implemented as LCoS SLMs. The light beams generated by the light sources 502, 504, 506 are supplied to the RGB SLMs 510, 512, 514. During operation, the RGB SLMs 510, 512, and 514 receive control signals from the control module 502, which provides the phase hologram of the graphic to be projected. The phase hologram beams 520, 522, and 524 from the RGB SLMs 510, 512, and 514 are a multiplication of wavefronts and phase holograms of the graphic to be projected in the frequency domain. The outputs of the RGB SLMs 510, 512, and 514 are combined by the X-cube combiner 516. The output of the X-cube combiner 516 is provided to the optical expander 518, which expands the beam received by the X-cube combiner 516 before it is reflected by a windscreen 530 and received on a retina 532 of the viewer. The viewer perceives an image 534 of an object in front of the windshield 530. The example in Fig. 5 can be modified to include features described below in relation to Fig. 6A-8 and / or other disclosed features. The example in Fig. 5 can be modified to include features from more than one of Fig. 6A-8 and / or other disclosed features. As a first example, Figures 6A-C (together Figure 6) show a red light source 600, a green light source 602, and a blue light source 604, lenses 606, 608, and SLMs 610, 612, 614. The light sources 600, 602, 604 and SLMs 610, 612, 614 can represent the light sources 504, 506, 508 and RGB SLMs 510, 512, 514 of Figure 5. In one embodiment, the system 500 of Figure 5 is modified to include the lenses 606, 608. The system 500 can be modified to include one or more lenses for one or more of the corresponding light sources 504 (or 600), 506 (or 602), 508 (or 604). Figures 6A-6C are provided as an embodiment for adjusting the diffraction angle of light rays to produce resultant light rays 620, 622, 624 of the same magnitude. Figure 6A shows an example of red light divergence. Figure 6B shows an example of green light divergence. Figure 6C shows an example of blue light divergence. The term divergence, as used here, refers to beam divergence, which is an angular measure of the increase in beam diameter or radius with distance. Although lenses 606 and 608 are shown as being used for the green and blue light rays, lenses can be included for each of the red, green, and blue light rays. The lenses can be fixed lenses or electrically tunable lenses. If they are electrically tunable, the control module 502 from Figure 5 can be connected to the lenses and control their state. As shown in Figures 6B and 6C, the lenses can be fixed lenses or electrically tunable lenses.As shown in Figure 6C, the lenses can be positioned between the light sources and the corresponding SLMs. The lenses are contained and / or controlled to adjust the beam divergence and thus the beam size. The lenses modify the divergence of the received light beam. In the example shown, lenses are provided for the green and blue light sources to further diverge the output of the light sources so that it matches the divergence of the red light. To maximize the field of view, in this example the longest of the three wavelengths of RGB light is red and is referred to as the baseline (or reference), and compensation components (e.g., lenses and / or SLMs with pin-hole layers as described above and / or lens holograms as described below) are applied to the green and blue light beams. In another embodiment, to minimize the number of compensation components, the mean wavelength (green) is selected as the baseline (or reference). Blue is not compensated because the diffraction angle of blue is close to that of green. Compensation components (e.g., a lens and / or an SLM with a pin-hole layer as described above and / or a lens hologram as described below) are applied to the red light. In one embodiment, a control module, such as one of the control modules disclosed herein, selects the color light source (or wavelength) to be used as the baseline and then adjusts the diffraction angle of one or more of the other light sources. Alternatively or additionally to the use of lenses, one or more of the SLMs 610, 612, 614 can contain a "pin-hole" layer (or a non-periodic photon sieve) with "pin" holes to widen the diffraction of light passing through the SLMs. This is illustrated in Fig. 7A and Fig. 7B. Fig. 7A illustrates a diffraction angle φ1 of an SLM 700 and a corresponding size of the viewing area in an observation plane 702. The SLM 700 does not contain a non-periodic photon sieve (or a pin-hole layer). Fig. 7B shows a diffraction angle φ2 of an SLM 710 and a corresponding size of the viewing zone in an observation plane 711 when using a non-periodic photon sieve (or a pin-hole layer) 712. The pin-hole layer 712 is arranged on a base layer 714 and contains pinholes 716 for the passage of light. The dashed lines 720, 722 in Fig.Figures 7B correspond to (or coincide with) the solid lines 724 and 726 in Figure 7A and serve to illustrate the differences in divergence and the size of the viewing area. The focal points for the examples in Figures 7A and 7B are labeled z1 and z2. The pinholes 716 transmit and diffract the light. The remaining parts of the pinhole layer 712 are absorbing and prevent the passage of light. The pinholes 716 change the divergence of the received light. Fig. 8 illustrates the introduction of a prism hologram 800 and a lens hologram 802 via software or one or more SLMs for positioning and resizing RGB images. The examples in Fig. 8 can be used alternatively and / or in combination with the examples described here, including those described above with reference to Fig. 5-7B. The control module 502 can encode a prism hologram and / or a lens hologram on one or more of the SLMs 510, 512, 514, 610, 612, and 614. This can be done in addition to a graphic hologram, such as the graphic holograms 804 and 806, which can also be encoded on one or more of the SLMs 510, 512, 514, 610, 612, and 614 via the control module 502. A prism hologram shifts the corresponding image upwards, downwards, left and / or right. A lens hologram changes the size of the image.The prism holograms and lens holograms are multiplied with the graphic holograms as shown to obtain a resulting image. Various prism and lens functions can be incorporated to remove and / or compensate for different alignment and / or positional errors. Fig. 9 shows a holographic projection system 910 comprising one or more light (or laser) sources 912, a beam expander 914, a reflector 916, an LCoS-SLM 918, and a control module 920. The laser 912 generates a laser beam 922, which is received at the beam expander 914. The beam expander 914 expands a portion of the laser beam 922 to produce a expanded beam 924. The reflector 916 receives the expanded beam 924 and produces a reflected expanded beam 928, which is received at the LCoS-SLM 918. The SLM 918 is encoded with a graphic hologram via the control module 920 and delivers a projected beam 930 which is seen by the retina 932 of an eye 934 of a viewer.The control module 920 can include a display driver 940 for controlling the states of the reflective device 916 and / or the LCoS-SLM 918. The LCoS-SLM 918 can include a limiting aperture 950 for attenuating stray light. The limiting aperture 950 can be implemented as a frame holding the LCoS-SLM 918. The reflection device 916 can be a reflection SLM or a micromirror array. If it is an SLM, the reflection device 916 is used to adjust the divergence angle of the light source 912 and / or the image size. In one embodiment, the reflection device (or the SLM) 916 is used for fine-tuning the beam size and position. This includes using the reflecting device 916 to (i) adjust the divergence angle of the light beam with a lens hologram encoded on the reflecting device 916 by the control module 920, (ii) shift a projected graphic (up, down, left and / or right) with a prism hologram encoded on the reflecting device 916 by the control module 920, and / or (iii) compensate for a focal plane difference induced by the software encoding of the lens phase hologram.An example of a focal plane 921 is shown. The reflecting device 916 reflects and diffractes the received expanded light beam at the LCoS-SLM 918. In one embodiment, the reflecting devices for each RGB light beam can be equipped with a lens function to maintain the correct (equal) sizes of the RGB light beams. The lens functions can be used to compensate for the virtual image distance in order to maintain the same focal plane at the viewer's eyes. This compensation can be provided for size errors that occur at the LCoS-SLMs downstream of the reflecting devices. The LCoS-SLMs may have different focal planes, and the lens functions implemented at the reflecting devices can be used to adjust the focal planes so that they are located in the same position relative to the viewer's eyes and / or the reference plane. In one embodiment, the configuration of Fig. 9 can be implemented for each of the three RGB light sources, with divergence and position being controlled independently for each of the three light sources. In this example, three light sources (red, green, and blue light sources) are provided, as shown in Fig. 5, and six SLMs are included. A pair of SLMs is provided for each light source. Each pair of SLMs comprises a first SLM (a reflecting device) similar to reflecting device 916 and a second SLM similar to SLM 918. The second SLMs in the pairs can be LCoS SLMs, the outputs of which can be supplied to an X-cube combiner, as shown in Fig. 5. The number of SLMs included depends on their speeds. One embodiment includes 6 SLMs. Another embodiment includes 4 SLMs. A further embodiment includes 2 SLMs. In the 4-SLM embodiment, the configuration shown is used for one light source, and a different version of the same configuration is used for two light sources, with the outputs of the two light sources being provided, for example, via a combiner of the same beam-spreading device. In the 2-SLM embodiment, a single version of the configuration shown is used for all three light sources, with the outputs of the three light sources being provided, for example, via a combiner of the same beam-spreading device. Fig. 10 shows an exemplary perspective view from the driver's seat of a vehicle 1000. The vehicle 1000 includes a windshield 1004 located in a front opening of the vehicle 1000. Passengers in a passenger cabin 1008 of the vehicle 1000 can look through the windshield 1004 to see in front of the vehicle 1000. Although the example described is of a land vehicle, the present application is also applicable to aircraft (e.g., airplanes, helicopters, etc.) and watercraft (e.g., boats, etc.). Although some examples are disclosed here relating to vehicle implementations, the examples are also applicable to non-vehicle-related implementations. As shown in Fig. 10, the windshield 1004 is optically located above a dashboard 1006 of the vehicle 1000. The vehicle 1000 may include a steering wheel 1010. The vehicle 1000 may be an autonomous vehicle, a semi-autonomous vehicle, or a non-autonomous vehicle. A HUD system, such as the one described above with reference to Figures 5-9, projects a hologram 1012, shown in Figure 10, through an opening 1016 in the dashboard 1006 onto a portion of the windshield 1004. The hologram 1012 contains various vehicle information, such as the vehicle's current speed 1000, the current gear of the vehicle's transmission 1000, the engine speed, the vehicle's direction of travel 1000, current infotainment system settings, and / or other vehicle information. The hologram 1012 presents data to the driver without requiring the driver to look away from the objects in front of the vehicle. As discussed further below, the hologram 1012 contains several colored, overlapping images of the same size and spatially aligned to produce a single image seen by the viewer, as described herein. Fig. 11 shows a HUD system 1100 comprising a vehicle reflector 1102 and the holographic projection system 910 of Fig. 9 with a modified version of the control module 920 (designated as control module 920'). In the example shown, the reflector is implemented as a windshield, but it can also be a different reflector. The control module 920' can perform the operations described above and additional operations, such as determining vehicle information for display via the reflector (or the windshield 1102). The holographic projection system 910 comprises one or more light sources (a laser 912 is shown), the beam expander 914, the reflector 916, the LCoS-SLM 918, and the control module 920'. The laser 912 generates a laser beam 922, which is received at the device 914 for beam expansion.The beam-expanding device 914 expands the width of the laser beam 922 to produce a expanded beam 924. The reflection device 916 reflects the expanded beam 924 to produce the beam 928, which is received by the LCoS-SLM 918. The LCoS-SLM 918 provides the projected beam 930. The control module 920' can contain one or more display drivers 940 from Fig. 9. The display drivers 940 can be used to control the states of the reflection device 916 and / or the LCoS-SLM 118. The display drivers 940 can be implemented on the control module 920' and / or on the switching SLM 916 and / or the LCoS-SLM 918. The LCoS-SLM 918 can contain a limiting aperture 950 to reduce stray light. The limiting aperture 950 can be implemented as a frame containing the LCoS-SLM 918. Fig. 12 shows a holographic projection method that can be implemented by the holographic projection systems disclosed above and one of the corresponding control modules. Although the following operations are primarily described with reference to the implementations of Figs. 5-9, they can easily be modified to be applicable to other implementations of the present disclosure. The operations are given as examples; one or more of the operations can be omitted and / or skipped. The operations can be performed iteratively. The process can begin at 1200. At 1202, a control module (e.g., one of the control modules 502, 920, or 920') activates RGB light sources to generate RGB light (or laser) beams. The light beams can be directed onto lenses, SLMs, or a beam expander (or optical expander), as shown above. At operation 1204, the control module can determine whether a separate SLM is used for each of the RGB light sources. If so, operation 1206 can be executed; otherwise, operation 1224 can be executed. At operation 1206, the control module can determine whether the size of one or more of the generated light beams should be adjusted using one or more lenses, as described above. If yes, operation 1208 can be executed; otherwise, operation 1216 can be executed. At operation 1208, the control module can adjust the divergence angle of one or more of the RGB light beams using one or more lenses, as described above. At operation 1210, the control module can determine whether the size of one or more of the RGB light beams should be adjusted via one or more SLMs. This can be done at one or more of the SLMS, LCoS-SLMs, and / or reflective devices mentioned above. If yes, operation 1212 can be executed; otherwise, operation 1214 can be executed. At 1212, the control module can (i) adjust the size of one or more of the RGB light beams with one or more lens holograms and (ii) adjust the position of one or more of the RGB light beams with one or more prism holograms. The one or more RGB light beams whose size is adjusted can be the same as, or different from, the one or more RGB light beams whose positions are adjusted. The positions can be adjusted relative to a reference (e.g., a reference point) and / or relative to one or more of the other RGB light beams whose position is not adjusted. At 1214, the control module can adjust the positions of one or more of the RGB light beams with one or more prism holograms. The positions can be adjusted relative to a reference (e.g., a reference point) and / or relative to one or more of the other RGB light beams whose positions are not being adjusted. At operation 1216, the control module can determine whether the size is to be set using a pin-hole layer of an SLM, as described above. If yes, operation 1218 is executed; otherwise, operation 1210 can be executed. At 1218, the control module can determine whether the size is to be set via an SLM. If yes, operation 1220 can be executed; otherwise, operation 1222 can be executed. This can be done on one or more of the aforementioned SLMS, LCoS-SLMs, and / or reflective devices. If yes, operation 1220 can be executed; otherwise, operation 1222 can be executed. At 1220, the control module can (i) adjust the divergence angle of one or more of the RGB light beams via one or more pin-hole layers of the respective SLMs for one or more respective RGB light beams, and (ii) adjust the size of one or more of the RGB light beams via one or more respective lens holograms. At 1222, the control module can set a divergence angle of one or more of the RGB light beams via one or more pin-hole layers of the respective SLMs for one or more respective RGB light beams. At operation 1224, the control module can determine whether a dual SLM is used for each of the RGB light sources, as in the examples described above with reference to Figures 9 and 11. If yes, operation 1226 can be executed; otherwise, operation 1228 can be executed. In operation 1226, the control module can adjust the size(s) of one or more of the RGB light beams using one or more corresponding lens holograms and the position(s) of the one or more RGB light beams using one or more corresponding prism holograms on the first SLMs (e.g., on the reflecting devices 916). Although not shown in Fig. 12, an additional lens and / or prism hologram can be encoded on the second SLM following operation 1226. At operation 1228, the control module can proceed to operation 1206 for single SLM paths and to operation 1226 for dual SLM paths. Operation 1230 can be executed after operations 1212, 1214, 1220, 1222, and 1226. In operation 1230, the control module manages the operation of one or more LCoS-SLMs to display the phase hologram of a graphic to be projected. Operation 1230 can be executed during operation 1212 and / or operation 1220. Each LCoS-SLM encoded with a phase hologram of a graphic is illuminated with a corresponding expanded laser beam, generating an encoded phase hologram beam. If more than one beam is projected, the projected beams can be combined using a combiner. This can be done before operation 1232. One or more of the display drivers 940 can be used to generate drive voltages to control the states of the one or more LCoS-SLMs. At 1232, RGB instances of the coded phase holograms can be directed at the viewer's eyes, so that the viewer sees a single graphic image. The phase holograms can be generated based on signals from a vehicle control module. The control module can be implemented as a vehicle control module or communicate with one. The control module generates the phase holograms based on vehicle data. The control module can obtain the vehicle data, for example, from a vehicle communication bus. The vehicle data can include, for example, the vehicle's current speed, the vehicle's current gear, the current engine speed, the vehicle's current direction of travel, the current infotainment system settings, and / or other vehicle information. The procedure can end at 1234. The operations described above are intended as illustrative examples. Depending on the application, the operations can be executed sequentially, synchronously, simultaneously, continuously, in overlapping time periods, or in any other order. Furthermore, depending on the implementation and / or event flow, one of the operations may not be executed or may be skipped. The examples disclosed here offer a flexibility in a display assembly that allows for imprecise alignment of the optical components and takes into account wavelength-dependent optical properties of the components. The imprecise alignment is compensated for by adjusting the sizes and positions of the RGB light beams. The examples eliminate color misalignment associated with the fact that images from independent RGB color channels do not perfectly overlap in a HUD eyebox. The examples achieve image size adjustment by resizing RGB graphics images through the selection and adjustment of the divergence angles of one or more RGB light beams to compensate for the wavelength-dependent difference to diffraction angle compensation. A software coding lens (e.g.,(a prism hologram) can be used for each of one or more RGB graphic holograms to spatially align the resized images on the HUD eyebox. The control modules revealed here can include graphics software to generate the images via the LCoS-SLMs in order to align the images with the HUD eyebox. This can be done, for example, on the LCoS-SLMs encoded with graphic holograms and involve using a reduced number of pixels or a reduced available image area for the corresponding generated light beams. For example, a light beam can be projected onto a portion of an available image area, and then the position of the light beam within that area can be shifted. This can be done for one or more of the RGB light beams. Fig. 13 shows an example of the LCoS-SLM 918 from Fig. 9. The LCoS-SLM 918 can be used in any of the embodiments disclosed herein. The LCoS-SLM 918 can comprise a silicon backplane layer 1302, an LCoS-SLM (or phase modulator) layer with a circuit (or pixelated electrode) layer 1304, a first alignment layer 1308, a liquid crystal layer 1310, a second alignment layer 1312, a transparent electrode layer 1314, and a glass substrate layer 1316. Circuit layer 1304 contains control circuits and / or pixel drivers for controlling the liquid crystal layer 1310. Circuit layer 1304 can contain one transistor for each pixel. Each pixel independently modulates the phase of the light exiting the LCoS-SLM. For example, if the voltages supplied to the pixels are different, then the phases of the light beams exiting the corresponding parts of the LCoS-SLM will be different. A specific voltage can be assigned to each pixel. The range of voltages supplied to each pixel can vary the phase of the corresponding part of the phase hologram beam 930 between, for example, 0 and 2π, in order to lead or retard the corresponding part of the light wave exiting the LCoS-SLM 918. The circuit layer 1304 controls the amount and phase of light emitted by the liquid crystal layer 1310. The orientations of the molecules in the liquid crystal layer 1310, and in conjunction with the pixels of the LCoS-SLM 918, change with the voltage. This voltage-dependent orientation of the molecules induces a spatially varying phase distribution at the LCoS-SLM 918. The ratio between the magnitude of the modulated phase and the applied voltage can be positive or negative, depending on the physical properties of the liquid crystals. The LCoS-SLM layer is further described with reference to Fig. 14. The LCoS-SLM 918 can include a reflective film layer if it is implemented as a reflective holographic projector. Fig. 14 shows a portion 1400 of an LCoS-SLM layer and the control module 920, which can be implemented in the embodiments of Fig. 9. The LCoS-SLM layer can contain pixels 1404 arranged in an array and connected to driver circuits 1406 and 1408. The LCoS-SLM layer can also contain an SLM control module 1410, which can control the driver circuits 1406 and 1408. The driver circuits 1406 and 1408 can receive power from the SLM control module 1410 or the control module 920 via switches 1407 and 1409. The SLM control module 1410 can receive signals directly from wavefront sensors and / or control signals from the control module 920. The control module 920 can receive phase detection signals and control the operation of the SLM control module 1410 to adjust the voltages supplied to the pixels 1404.In another embodiment, the SLM control module 1410 directly receives the phase detection signals and controls the driver circuits 1406, 1408 to generate the corresponding voltages that are applied to the pixels 1404.

Claims

Holographic projection system (500) comprising: a first light source (504, 600) configured to produce a first light beam (620); a second light source (506, 602) configured to produce a second light beam (622); a third light source (508, 604) configured to produce a third light beam (624), wherein the first light beam (620), the second light beam (622) and the third light beam (624) have respective wavelengths; a plurality of spatial light modulators (510, 512, 514, 610, 612, 614) configured to diffract the first light beam (620), the second light beam (622) and the third light beam (624), respectively;a first lens (606) arranged to set a divergence angle of the first light beam (620), the second light beam (622), or the third light beam (624) such that diffracted light from each of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614) has the same diffraction angle, wherein the plurality of spatial light modulators (510, 512, 514, 610, 612, 614) is configured to encode phase holograms including respective versions of a graphic image based on light produced by the first light source (504, 600), the second light source (506, 602), and the third light source (508, 604), including the light emitted by the first lens (606) to provide phase hologram beams;a combiner (516) configured to combine the phase hologram beams to provide a combined phase hologram beam that is projected for viewing a combined graphic image; and a control module (502) configured to encode a prism hologram on one of the multiple spatial light modulators (510, 512, 514, 610, 612, 614) to align the outputs of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614);characterized in that the control module (502) is configured to dimension the first light beam (620), the second light beam (622) and the third light beam (624) so ​​that they do not fill an available image area, and to adjust the position of one or more of the first light beam (620), the second light beam (622) and the third light beam (624) in order to align the first light beam (620), the second light beam (622) and the third light beam (624). Holographic projection system (500) according to claim 1, wherein the first light beam (620) is a red laser beam, the second light beam (622) is a green laser beam and the third light beam (624) is a blue laser beam. Holographic projection system (500) according to claim 2, further comprising a second lens (608), wherein the first lens (606) adjusts a divergence angle of the green laser beam (622) such that it matches a divergence angle of the red laser beam (620) which is diffracted by one of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614), and the second lens (608) adjusts a divergence angle of the blue laser beam (624) such that it matches the divergence angle of the red laser beam (620) which is diffracted by one of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614). Holographic projection system (500) according to claim 2, wherein the first lens adjusts a divergence angle of the red laser beam (620) such that it matches a divergence angle of the green laser beam (620) which is diffracted by one of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614). Holographic projection system (500) according to claim 4, wherein the holographic projection system (500) does not have a lens for adjusting a divergence angle of the blue laser beam (624). Holographic projection system (500) according to claim 1, wherein one or more of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614) comprise a non-periodic photon sieve layer to set a divergence angle of one or more of the first light beam (620), the second light beam (622) and the third light beam (624). Holographic projection system (500) according to claim 1, wherein the control module (502) is configured to encode a lens hologram on one or more of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614) to adjust a size of one or more of the first light beam (620), the second light beam (622) and the third light beam (624). Holographic projection system (500) according to claim 1, wherein the control module (502) is configured to encode two prism holograms each onto two of the plurality of spatial light modulators (510, 512, 514, 610, 612, 614) in order to shift a position of two of the first light beam (620), the second light beam (622) and the third light beam (624).

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