A light-field image projection system that generates a time-continuous virtual image using a single narrow-band light source for each color.

Abstract

To make a light field image projection device using multiple light sources more compact. The light source (10) comprises a single narrowband point source (10) for each color emitting narrowband light (200); a splitting device (20, 30, 70, 80) for sequentially generating an incident light beam (220) and forming a virtual light source (50); a spatial light modulator (40) for generating a modulated beam of light (240) and a virtual image for each incident light beam (220); a combiner (100) for projecting virtual images at virtual viewpoints (60) within an eyebox region (121) and transmitting natural light from the real world (80) toward the eyebox (121), each virtual viewpoint (60) including an image of a virtual scene as seen from that viewpoint (60); A light field image projection system comprising: a splitter for directing an incident light beam (220) to a spatial light modulator (40) such that the incident light beam (220) is incident at different angles of incidence (θ) on a surface of the spatial light modulator (40); a ratio of the illuminance of the single virtual light source (50) to the illuminance of the narrow band light (200) is at least 1%.

Description

[Technical field]

[0001] The present disclosure relates to near-eye, light field image projection systems, and more particularly to light field image projection systems having small form factors. The present disclosure relates to wearable devices that include light field image projection systems. [Background technology]

[0002] Known light field image projection devices typically comprise a light source consisting of an array of point sources collimated into parallel light beams. The collimated light beams illuminate a spatial light modulator (SLM) at different angles of incidence. Each reflected (or transmitted) beam carries a specific image information generated by the modulation of the SLM. An intermediate optic (which may include a combiner optic) reprojects the point sources to the viewpoints. The multiple viewpoints form a light field eyebox, allowing the user to view a realistic 3D rendering of the digital scene. The point source array typically uses LED sources to sequentially generate the viewpoints that form the light field. Summary of the Invention [Problem to be solved by the invention]

[0003] A large number of spatially separated light sources makes it difficult to build a compact and cost-effective light field image projection device. [Means for solving the problem]

[0004] The present disclosure relates to a light source comprising a single narrowband point light source for each color, the point light source being configured to emit narrowband light having a narrow wavelength spectrum of the narrowband light; a splitter configured to sequentially generate a plurality of incident light beams to form a plurality of virtual light sources at different locations within a first image plane; A spatial light modulator (SLM) configured to generate a modulated beam of light and a virtual image for each incident light beam; a combiner configured to project virtual images of virtual viewpoints within an eyebox region and transmit natural light from the real world towards the eyebox, each (virtual) viewpoint including an image of a virtual scene as seen from that viewpoint; The present invention relates to a light field image projection system comprising: The splitting device is further configured to direct the (multiple) incident light beams to the SLM so that the incident light beams are incident on a surface of the SLM at different angles of incidence and to sequentially select at least one of the virtual viewpoints visible within the eyebox.

[0005] In one embodiment, the splitting device comprises: a diffractive element configured to generate a plurality of incident light beams at different angles of incidence from a narrowband light source; an optical lens configured to form a plurality of virtual light sources; an active shutter array configured to sequentially select at least one of the virtual viewpoints visible within the eyebox; Equipped with.

[0006] In another embodiment, the splitting device comprises a lens array comprising a number of lenslets (lenslets), each lenslet generating an incident light beam at an angle of incidence different from the angles of incidence of the incident light beams generated by other lenses, the lenslets generating focused or defocused beams.

[0007] In yet another embodiment, the splitting device comprises: A beam steering device and a lens array comprising a plurality of lenslets. Equipped with The beam steering device steers narrowband light towards one of the lenslets to generate an incident light beam at an incidence angle.

[0008] The point light sources may comprise laser light sources, in particular a red laser point source configured to generate red light, a green laser point source configured to generate green light, and a blue laser point source configured to generate blue light.

[0009] The combiner may comprise a reflective holographic combiner.

[0010] The present disclosure is further directed to wearable devices comprising a light field image projection system, such as augmented or mixed reality glasses, or smart glasses.

[0011] The light field image projection system disclosed herein is compact. When used with a holographic reflection holographic combiner, the light field image projection system can be made more compact and has a high degree of freedom in shape. The light field image projection system has very good see-through performance.

[0012] A light field image projection system does not require an array of point sources, but may use only a single point source or a small number of point sources, in either case the number of point sources required by the light field image projection system is less than the total number of viewpoints.

[0013] Exemplary embodiments of the present invention are disclosed in the description and illustrated in the drawings herein. [Brief description of the drawings]

[0014] [Figure 1a] FIG. 1a illustrates a schematic diagram of a light field image projection system according to one embodiment. [Figure 1b] FIG. 1b shows a light field image projection system according to an alternative configuration. [Figure 2a] FIG. 2a illustrates a light field image projection system according to one embodiment. [Figure 2b] FIG. 2b shows an alternative configuration of the light field image projection system of FIG. 2a. [Figure 2c] FIG. 2c shows another alternative configuration of the light field image projection system of FIG. 2a. [Diagram 3] FIG. 3 illustrates a light field image projection system according to yet another embodiment. [Figure 4] FIG. 4 illustrates a light field image projection system including projection optics and a combiner according to one embodiment. [Figure 5a] 5a to 5c show different embodiments of the light source comprising three narrowband point sources (FIG. 5a). [Figure 5b] 5a to 5c show different embodiments of the light source comprising three narrowband point sources (FIG. 5a). [Figure 5c] 5a to 5c show different embodiments of the light source comprising three narrowband point sources (FIG. 5a). [Figure 6a] FIG. 6a reports the temporal sequence of switching states of a ferroelectric liquid crystal on silicon (FLCoS) based spatial light modulator in a light field image projection system according to one embodiment. [Figure 6b] FIG. 6b reports the temporal sequence of the switching states of a FLCoS-based spatial light modulator of a light field image projection system according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 1a illustrates a schematic diagram of a near-eye light field image projection system according to one embodiment. The light field image projection system comprises a light source 10. The light source 10 comprises a single narrowband point source for each color, the point sources being configured to emit narrowband light 200 having a narrow wavelength spectrum.

[0016] The light field image projection system further comprises a splitting device 20 , 30 , 70 , 80 configured to sequentially generate a plurality of incident light beams 220 to form a plurality of virtual light sources 50 at different positions in the first image plane 31 .

[0017] The light field image projection system further comprises an SLM 40 configured to generate a modulated beam of light 240 and a virtual image for each incident light beam 220 .

[0018] The light field image projection system includes a combiner 100 (see FIG. 4). The combiner 100 is configured to project virtual images at virtual viewpoints 60a-60c within an eyebox region 121, and transmits natural light from the real world 180 toward the eyebox 121. Each virtual image generated by the spatial light modulator 40 corresponds to a viewpoint as seen at the location of the virtual viewpoint, from which a light field image can be formed. Thus, each virtual viewpoint 60a-60c includes a virtual image of a virtual scene as seen from that virtual viewpoint 60a-60c.

[0019] In the configuration of FIG. 1a, the splitting arrangement comprises a diffractive element 20 configured to generate a number of incident light beams 220 which are incident on the surface of the SLM 40 at different angles of incidence θ.

[0020] The diffractive element 20 may comprise a diffractive optical element (DOE), a holographic optical element (HOE), a liquid crystal polarization grating (LCPG), a semi-reflective surface, a Fresnel lens array, a mirror, or a metasurface (a two-dimensional arrangement of structures much smaller than the wavelength of light, which has properties that do not exist in nature, such as a negative refractive index). The splitting device further comprises a first optical lens 70 configured to form a plurality of virtual light sources 50a to 50c. The first optical lens 70 focuses the incident light beam 220, which forms the incident light beam 220, on the first image plane 31 to form an array of virtual light sources 50a to 50c. In FIG. 1a, three incident light beams 220 are depicted, forming three virtual light sources 50a to 50c at different positions on the first image plane 31. The diffractive element 20 and the first optical lens 70 may be configured to generate any number of incident light beams 220 and virtual light sources 50a to 50c. Virtual light sources 50a to 50c can further be formed in any two-dimensional arrangement at first image plane 31.

[0021] 1a, the first optical lens 70 is a single lens. Each incident light beam 220 passes through a portion of the first optical lens 70 depending on the incidence angle θ of the incident light beam 220. The portion of the first optical lens 70 focuses the incident light beam 220 passing therethrough to form the light sources 50a to 50c at the first image plane 31.

[0022] In one aspect, the splitting device further comprises a pixelated active shutter array 30 configured to sequentially select at least one of the virtual viewpoints 60a-60c visible in the eyebox 121. The active shutter array 30 allows each incident light beam 220 to be transmitted or not transmitted to the remainder of the optical system. The active shutter 30 may comprise a transparent or reflective ferroelectric liquid crystal device. Alternatively, the active shutter 30 may comprise a liquid crystal array or an active micromirror array. The choice of type of active shutter 30 may depend on the required shutter speed. The active shutter array may be configured to function in transmission or reflection.

[0023] Each virtual viewpoint 60a-60c can be projected in a time sequence. For example, the pixelated shutter array 30 can block virtual light sources 50b and 50c, and thus virtual viewpoints 60b and 60c, while virtual light source 50a reaches virtual viewpoint 60a. At this moment, only virtual viewpoint 60a is seen and transmitted or reflected through the optical system. At a later moment, only virtual light source 50b is transmitted by the active shutter 30, and virtual viewpoint 60b is seen, and similarly for virtual light source 50c.

[0024] The SLM 40 generates images corresponding to each virtual viewpoint 60a to 60c. For example, when the shutter array 30 allows the virtual light source 50a to reach the virtual viewpoint 60a, the SLM 40 generates a 2D image of the virtual scene corresponding to the viewpoint seen at the virtual viewpoint location 60a. The same process is repeated in a time sequence for the other virtual viewpoint locations 60b and 60c. Each time, the 2D image of the virtual scene corresponds to the viewpoint seen from the virtual viewpoint location 60b or 60c. Then, a light field image is formed. It should be noted that since any number of virtual light sources 50a to 50c can be generated, the light field image projection system can project any number of virtual viewpoints 60a to 60c in a time sequence.

[0025] The refresh rate of the sequence that generates the virtual viewpoints 60a to 60c may be fast enough to occur within the eye's integration time, which is typically between 20 Hz and 1000 Hz.

[0026] The light field image projection system enables the generation of temporally continuous virtual viewpoints by using at least a single narrowband point light source per color, based on the passive light splitting device 20 and active shutter array 30 sequentially selecting visible virtual viewpoints 60a to 60c. Light field image projection systems further enable the projection of 3D images with monocular depth of field that allows virtual content to be placed at any depth plane.

[0027] The light field image projection system may further include a first projection optical system 27 disposed between the splitting devices 20, 30, 70, 80 and the SLM 40. The first projection optical system 27 is configured to collimate and project the incident light beam 220 to form an intermediate image at an intermediate image plane 127 that coincides with the position of the SLM 30. The light field image projection system may further include a second projection optical system 90 disposed between the SLM 40 and the eyebox 121. The projection system is also configured to project the modulated light beam 240 to form the virtual viewpoints 60a-60c.

[0028] The incident light beam 220 has an illuminance (light output weighted by the wavelengths emitted by the incident light beam 220), which is essentially the luminance of the narrowband light 200 divided by the number of virtual light sources 50. If we assume that the intensity profile of the narrowband light 200 is a Gaussian distribution, then the intensity profile of the envelope of each virtual light source 50 will also be a Gaussian distribution, and the intensities of each of the separated virtual light sources 50 will not be equal but will follow the Gaussian envelope.

[0029] For the light field image projection system shown in FIG. 1a, the numerical aperture NA of the system can be defined by NA=D / 2f, where f is the focal length of the first optical lens 70 and D is the size of the incident light beam 220.

[0030] Assuming a 10 mm incident light beam 220 and 25 virtual light sources 50 (e.g., a 5×5 array of virtual light sources 50), the ratio of the illuminance of a single virtual light source 50 to the illuminance of the narrowband light 200 is 4%. In this configuration, the numerical numerical aperture NA of the virtual light sources 50 corresponds to 0.2 (f=5 mm and D=2 mm).

[0031] 1b shows an alternative configuration of a light field image projection system in which the first optical lens 70 is a lens array comprising a number of lenslets 71 (lenslets 71). In this configuration, each incident light beam 220 passes through one of the lenslets 71 depending on the incidence angle θ. Each lenslet 71 focuses the incident light beam 220 passing therethrough to form light sources 50a-50c at the first image plane 31. Optionally, the light field image projection system may further comprise a second optical element 25. The second optical element 25 allows the main rays (or first order rays) of each incident light beam 220 to be arranged parallel to each other before reaching the first optical lens 70. Without the second optical element 25, the main rays of the incident light beams 220 would diverge from each other, which would require not only a larger first optical lens 70, but also a larger active shutter 30 and first projection optics 27, resulting in a larger projection system.

[0032] As shown in FIG. 1b, the size of the narrowband light 200 can be made to substantially match the size of the lenslet 71.

[0033] 2a shows a light field image projection system according to another embodiment. The splitting device comprises a lens array 70 comprising a plurality of lenslets 71. The lens array 70 is configured to focus at least a portion of the narrowband light 200 to generate an incident light beam 220 and form an array of virtual light sources 50a to 50c at the first image plane 31. In particular, each lenslet 71 generates an incident light beam 220 and forms a corresponding virtual light source 50a to 50c. The generated incident light beams 220 are incident on the surface of the SLM 40 at different angles of incidence θ. The lenslets 71 may comprise converging or diverging lenses.

[0034] The splitting device may further comprise the active shutter array 30 described above.

[0035] The active shutter array 30 may be located at different positions in the optical path of the incident light beam 220 or the modulated beam of light 240 .

[0036] 1a and 2a, the active shutter array 30 is disposed substantially at a first image plane 31 and is positioned such that at least one of the virtual light sources 50a to 50c is transmitted or reflected at any one time.

[0037] In the arrangement of FIG. 1 b , active shutter array 30 is located near the focal point of lenslets 71 , specifically between lens array 70 and first image plane 31 .

[0038] Figure 2b shows an alternative configuration of the light field image projection system of figure 2a, in which an active shutter array 30 is provided between the light source 10 and the splitting device 20.

[0039] Figure 2c shows an alternative configuration of the light field image projection system of Figure 2a, in which an active shutter array 30 is provided between the SLM 40 and the eyebox 121. For example, the active shutter array 30 may be provided near the virtual viewpoints 60a to 60c.

[0040] As shown in FIGS. 2a-2c, the size of the narrowband light 200 may substantially correspond to the size of the lens array 70.

[0041] The active shutter array 30 arrangement shown in Figures 2a to 2c may be implemented in the light field image projection system configuration shown in Figures 1a and 1b.

[0042] This position can also be used in configurations with splitter 20. Note that one or more light sources 10 can be passed simultaneously. This can be used to create a brighter image, a perimeter image, or to fill in the color of an object.

[0043] For the light field image projection system shown in Figures 1b, 2a-2c, the numerical numerical aperture NA of the virtual light source 50 can be defined by NA = D / 2f, where f is the focal length of the first optical lens 70 and D is the size of the lenslet 71 diameter when the beam fills the lenslet aperture. As mentioned above, assuming a 10 mm incident light beam 220 and 25 virtual light sources 50 (e.g., a 5x5 array of virtual light sources 50), the ratio of the illuminance of a single virtual light source 50 to the illuminance of the narrowband light 200 is 4%. The size of the lenslet 71 gives the numerical numerical aperture NA (for a lenslet diameter of 2 mm, NA = 0.2).

[0044] More generally, for the light field image projection systems shown in Figures 1a, 1b, 2a-2c, the ratio of the illuminance of the narrowband light 200 to the illuminance of a single virtual light source 50 depends on the number of virtual light sources 50. In one embodiment, the ratio of the illuminance of the single virtual light source 50 to the illuminance of the narrowband light 200 is at least 1%. Alternatively, the ratio of the illuminance of the single virtual light source 50 to the illuminance of the narrowband light 200 may be at least 5%, 10% or 20%.

[0045] A light field image projection system is shown in Fig. 3 according to yet another embodiment. In this configuration, the splitting device comprises a beam steering device 80 and a lens array 70 comprising a number of lenslets 71. The beam steering device 80 is steerable to direct narrowband light 200 towards one of the lenslets 71, generating an incident light beam 220 at a predetermined angle of incidence θ.

[0046] Beam steering device 80 may include a tilting mirror that is tiltable to direct narrowband light 200 towards one of the lenslets 71 .

[0047] Beam steering device 80 may be configured to be steered in a first position and stop its motion in a first position while light source 10 is on, such that incident light beam 220 is directed towards one of the lenslets 71. Beam steering device 80 may be further configured to be steered in a second position and stop its motion in a second position while light source 10 is on, such that incident light beam 220 is directed towards another lenslet 71. While steering beam steering device 80, light source 10 is turned off. Beam steering device 80 may be configured to be steered to any number of positions corresponding to the number of lenslets 71 in lens array 70, and to stop its movement so that incident light beam 220 is directed towards one of the lenslets 71. Each time light source 10 is turned on and incident light beam 220 is directed towards one of the lenslets 71, virtual viewpoints 60a-60c are generated.

[0048] In one aspect, the incident light beams 220 can pass through the second optical element 25 before reaching the lenslets 71 of the lens array 70. As discussed in conjunction with FIG. 1b, the second optical element 25 enables the chief rays of each incident light beam 220 to be aligned parallel to one another before they reach the first optical lens 70.

[0049] 3, the size of narrowband light 200 may substantially match the size of lenslet 71. In this configuration, a majority of narrowband light 200, and possibly the entirety of narrowband light 200, is used to generate incident light beam 220 and form virtual light source 50, and thus virtual viewpoints 60a-60c. In contrast, in the configurations of the light field image projection system shown in Figures 1a, 1b, and 2a-2c, when the narrowband light 200 is split, only a portion of the narrowband light 200 is used to generate the incident light beam 220 to form the virtual viewpoints 60a-60c, while the remaining portion of the narrowband light 200 is blocked by the active shutter 30. Thus, only a small portion of the initial narrowband light 200 is used to create the virtual viewpoints 60a-60c. Thus, the incident light beam 220 has an illuminance that substantially matches the illuminance of the narrowband light 200.

[0050] In one optional configuration, narrowband light 200 can be collimated (parallelized) by collimating optic 101 .

[0051] The light field image projection system in the configuration of Figures 1b to 3 comprises a first projection optical system 27 arranged between the splitting devices 20, 30, 70, 80 and the SLM 40, and the first projection optical system 27 is configured to collimate and project the incident light beam 220.

[0052] FIG. 4 shows a schematic of a light field image projection system including a second projection optical system 90 disposed between the SLM 40 and a combiner 100. The second projection optical system 90 is configured to form intermediate virtual viewpoints 60a-60c at an intermediate image plane 110 between the second projection optical system 90 and the combiner 100. The second projection optical system 90 may include a plurality of refractive, reflective, diffractive, or freeform surfaces. The combiner 100 is transparent or semi-transparent and projects virtual innerges (virtual images) at the virtual viewpoints 60a-60c within an eyebox region 121 and transmits natural light from the real world 180 towards the eyebox 121. The combiner 100 may include a reflective holographic, a transmission holographic, a refractive, a reflective, or a diffractive combiner.

[0053] In one preferred embodiment, combiner 100 comprises a holographic reflective combiner that selectively reflects the projector's RGB three color components while transmitting the remainder of the visible spectrum. Holographic reflective combiner 100 has a broadband acceptance angle of incident light from 15° to 80°.

[0054] In one embodiment, light source 10 comprises a laser point source. In one possible configuration, light source 10 may comprise a red laser point source configured to generate red light, a green laser point source configured to generate green light, and a blue laser point source configured to generate blue light. In another possible configuration, light source 10 may comprise a single narrowband point source configured to emit white light consisting of red, green, and blue light.

[0055] In contrast to LED sources, laser sources have sufficient optical power density to be split into multiple virtual sources. Thus, a split single laser point source may be advantageously used in combination with a holographic combiner. Alternatively, an array of small VCSEL (Vertical Cavity Surface Emitting) lasers may be provided, where each VCSEL laser is a single point source. When using a VCSEL laser array, no splitting device is needed to generate multiple incoming light beams 220. In fact, each incoming light beam 220 is generated by a VCSEL laser of the array. However, VCSEL laser arrays are currently only available emitting red light. Edge-emitting lasers, on the other hand, are technically challenging and too large and expensive to be integrated into an array.

[0056] Also, in contrast to LED light sources, laser light sources are essentially monochromatic, significantly reducing chromatic dispersion in the projection system, especially in the combiner. Using multiple laser light sources to replace the current multiple LEDs presents challenges in terms of device size, packaging, and power consumption. Therefore, a light field image projection system using a single narrowband light source for each color is advantageous.

[0057] Figures 5a to 5c show different embodiments of the light source 10. In particular, Figure 5a shows that the light source 10 comprises three narrowband point light sources 10a to 10c, for example one narrowband point light source for each colour. The light source 10 comprises a first narrowband point light source 10a emitting red narrowband light 200, a second narrowband point light source 10c emitting green narrowband light 200 and a third narrowband point light source 10c emitting blue narrowband light 200.

[0058] In one aspect, the first point light source 10a can be collimated by the collimating optical element 101 and then reflected by the mirror 102. Similarly, the second point light source 10b and the third point light source 10c can be collimated by the collimating optical element 101 and then reflected by the dichroic plate 103. The dichroic plate 103 reflects a certain color and transmits another color. For example, the first point light source 10a transmits through the dichroic plate 102 and the second point light source 10b is reflected by the dichroic plate 102, effectively combining the first point light source 10a and the second point light source 10b. At the exit of the light source 10, the first point light source 10a, the second point light source 10b, and the third point light source 10c are combined into a single narrowband light 200. An aperture lens 105 can be added to expand the numerical aperture of the light source 10.

[0059] In the configuration of FIG. 5b, the light source 10 does not include a lens 105 and the narrowband light 200 remains collimated or has a small numerical aperture.

[0060] In the configuration of Fig. 5c, the point light sources 10a to 10c are combined using a single collimating optical element 106. The point light sources 10a, 10b and 10c may be arranged along a line (as shown in Fig. 5c), overlapping each other in a triangle or a square. When the single collimating optical element 106 is positioned at a distance close to the focal length f of the point light sources 10a to 10c from the single collimating optical element 106, the latter overlap at the focal plane 107 of the collimating optical element 106 at the distance f on the side of the collimating optical element 106 opposite the light source 10.

[0061] Returning to the projection system configuration shown in Figure 3, the SLM 40 may comprise a ferroelectric liquid crystal on silicon (FLCoS). The light field image projection system may further comprise a controller 300 configured to control the switching state of the SLM 40 in synchronization with the beam steering device 80 and the light source 10.

[0062] Figure 6a reports the switching states of the FLCoS-based SLM 40 as a function of time t. The FLCoS can display image information as a display corresponding to the illumination of the light sources, which in Figure 6a are shown in colours such as red (R), green (G) and blue (B), corresponding to the narrowband point light sources 10a to 10c emitting red, green and blue narrowband light 200, respectively. In Figure 6a, the numbers 0, 1 and 2 correspond to the positions of the virtual light sources 50a to 50c, respectively.

[0063] As shown in Fig. 6a, for one image information R1, for example red image information, the FLCoS takes a certain time (or positive setup time t11) to switch to the correct state. The positive setup time t11 is the time corresponding to the positive data of the FLCoS R channel of the virtual light sources 50a to 50c. The FLCoS maintains the correct state during the positive illumination time t111, which corresponds to the time when the light source 10 is actually turned on to project the image. Illuminating the FLCoS before or after the window of illumination time t111 will reduce the contrast of the image.

[0064] After the positive illumination time t111, negative image information is sent to the FLCoS at approximately the same timing as the positive image information to balance the charge level of the FLCoS (indicated by the negative setup time T11 and the dashed step -R1 during the negative illumination time T111). Without this charge balance, the SLM of the FLCoS could be damaged. During the negative setup time T11 and the negative illumination time T111, there is no illumination of the light source. In other words, the controller 300 turns on the light source 10 during the positive illumination times t111, t121, t131 when the beam steering device 80 is not moving, to shine the narrowband light 200 towards one of the lenslets 71, and turns off the light source 10 at other times.

[0065] The same lighting sequence described above can be done in the following way: green (G1) having a positive setup time t12 and a negative setup time T12 and a positive illumination time t121 and a negative illumination time T121; Blue (B1) with positive setup time t13 and negative setup time T13 and positive illumination time t131 and negative illumination time T131; Also applies to other colors, including

[0066] Looking at the global RGB sequence illumination of a given virtual light source position 50a to 50c (e.g., R1 / G1 / B1), the beam steering device 80 (e.g., tilt mirror) needs to be in a stable position for at least a stabilization time t3, which includes the three RGB illumination times t111, t121, and t131. After that, the beam steering device 80 needs a certain time, a switching time t4, to switch to the next position corresponding to the next virtual light source 50a to 50c in the virtual point source array 50, before another image information R2, e.g., red image information, is turned on during t211. The switching time t4 is shown here as the sum of times T13, T131, and t21, which are essentially related to the entire projection data flow of the high-level system architecture. As such, the switching time t4 can be very short, in the range of 50 ps to 500 ps. Therefore, the beam steering device 80 needs to switch at least as fast as the switching time t4, which can be a very severe physical constraint.

[0067] Fig. 6b reports an alternative time sequence of the switching states of the FLCoS-based SLM 40. The timings of the positive setup time t11 and the positive illumination time t111 and the negative illumination times T11 and T111 are inverted compared to the timings of Fig. 6a. In other words, at least one positive setup time t11, t12, t13 and positive illumination times t111, t112, t113 of a color has a corresponding negative setup time T11, T12, T13 and negative illumination times T111, T112, T113.

[0068] The beam steering device moves from one position to another between the negative setup times T11, T12, T13 of the previous illumination step, the negative illumination times T111, T121, T131, and the positive setup times of the next illumination step. Thus, the beam steering device 80 has a longer time to move from one position to another between the negative setup times and negative illumination times of the previous illumination step, and the negative setup times and negative illumination times and positive setup times of the next illumination step.

[0069] By reversing the timing, the switching time t4 can be increased by at least 30% (increased switching time t41) depending on the values ​​of illumination times t121 and t131. Compared with the timing of Fig. 6a, the reversed timing of Fig. 6b would cause irreversible damage to the FLCoS-based SLM 40, since sequential positive and negative image data of the same color and virtual light source position transmitted to the FLCoS SLM 40 would be preserved.

[0070] Optionally, For green, a positive setup time t12 and a positive exposure time t121, and a negative setup time T12 and a negative exposure time T121; For blue, positive setup time t13 and positive exposure time t131, negative setup time T13 and negative exposure time T131, The timing of may also be inverted compared to that of FIG. 6a.

[0071] It is understood that the invention is not limited to the exemplary embodiments described above, but that other implementations are possible within the scope of the claims. For example, the light source 10 may be Two or more narrowband point light sources 10a to 10c; Two or more virtual light sources 50a to 50c; The present invention may include both or one of the above. [Explanation of symbols]

[0072] 10 light source 10a First narrowband point light source 10b Second narrowband point source 10c Third narrowband point source 20 Beam splitter, splitting device 25 Second Optical Element 30 Active Shutter 31 1st image plane 40 Spatial Light Modulator 50, 50a, 50b, 50c Virtual Light Source 60, 60a, 60b, 60c Virtual Viewpoint 70 First optical lens, lens array 71 Lenses (lenslets, small lenses) 80 Beam steering device 90 Second projection optical system 100 Combiner 101 Collimating Optical Element 102 Mirror 103 Dichroic plate 105 Lens 106 Collimating Optical Elements 107 Focal plane 110 Intermediate image plane 180 Natural Light from the Real World 200 Narrowband Light 220 Incident light beam 240 Modulated Beam Light 300 Controller θ angle of incidence t11 Red R1 positive setup time t111 Red R1 positive illumination time T11 Negative setup time for red R1 T111 Negative illumination time of red R1 t12 Green G1 positive setup time t121 Green G1 positive illumination time T12 Green G1 negative setup time T121 Green G1 Negative Illumination Time T13 Blue B1 positive setup time t131 Blue B1 positive illumination time T13 Blue B1 negative setup time T131 Blue B1 Negative Illumination Time t3 Stabilization time t4 Switching time

Claims

1. A light source (10) configured to emit narrowband light (200) having a narrow wavelength spectrum, the light source having a single narrowband point light source for each color; a splitting device (20, 30, 70, 80) configured to sequentially generate a plurality of incident light beams (220) to form a plurality of virtual light sources (50) at different positions in a first image plane (31); a spatial light modulator (40) configured to generate a modulated beam of light (240) and a virtual image for each incident light beam (220); a combiner (100) configured to project the virtual image at virtual viewpoints (60) within an eyebox region (121) and transmit natural light from the real world (80) towards the eyebox (121), each viewpoint (60) including an image of the virtual scene as seen from that viewpoint (60); In a light field image projection system comprising: the splitting device (20, 30, 70, 80) is further configured to direct the incident light beam (220) to the spatial light modulator (40) such that the incident light beam (220) is incident on a surface of the spatial light modulator (40) at different angles of incidence (θ) and to sequentially select at least one of the virtual viewpoints (60) visible within the eyebox (121); The ratio of the illuminance of the single virtual light source 50 to the illuminance of the narrow band light (200) is at least 1%; Light field image projection system.

2. 2. The projection system of claim 1, wherein the incident light beam (220) has an illuminance substantially corresponding to an illuminance of the narrowband light (200) divided by the number of the virtual light sources (50).

3. The splitting device comprises: a diffractive element (20) configured to generate the plurality of incident light beams (220) at the different angles of incidence (θ) from the narrowband light (200); an optical lens (70) configured to form the plurality of virtual light sources (50); an active shutter array (30) configured to sequentially select at least one of the virtual viewpoints (60) visible within the eyebox (121); 3. The projection system of claim 1 , comprising:

4. 4. The projection system of claim 3, wherein the optical lens is a single lens (70) and each incident light beam (220) passes through a portion of the lens (70) depending on the angle of incidence (θ) of the incident light beam (220).

5. 4. The projection system of claim 3, wherein the optical lens (70) is a lens array comprising a plurality of lenslets (71), and each incident light beam (220) passes through one of the lenslets (71) depending on the incidence angle (θ).

6. The diffractive element (20) may be a diffractive optical element (DOE), a holographic optical element (HOE), 6. The projection system of claim 3, comprising a liquid crystal polarization grating (LCPG), a semi-reflective surface, a mirror, or a metasurface.

7. 3. The projection system of claim 1 or 2, wherein the splitting device comprises a lens array (70) comprising a plurality of lenslets (71), each lenslet (71) generating the incident light beam (220) at an angle of incidence (θ) different from the angle of incidence (θ) of the incident light beam (220) generated by another lens (71).

8. 8. The projection system of claim 5, wherein a size of the narrowband light (200) substantially matches a size of the lens array (70).

9. The splitting device comprises a beam steering device (80) and a lens array (70) comprising a plurality of lenslets (71); 2. The projection system of claim 1, wherein the beam steering device (80) is steerable to direct the narrowband light (200) toward one of the lenslets (71) and to generate the incident light beam (220) at the incidence angle (θ).

10. 10. The projection system of claim 9, wherein a size of the narrowband light (200) substantially matches a size of the lenslet (71), and the incident light beam (220) has an intensity that is substantially 100% of an intensity of the narrowband light (200).

11. 11. The projection system of claim 1, wherein the active shutter array (30) comprises a transparent or reflective ferroelectric liquid crystal device or an active micromirror array.

12. 11. The projection system of claim 1, wherein the active shutter array (30) is arranged substantially within the first image plane (31) and configured to transmit at least one of the virtual light sources (50) at a given time.

13. 11. The projection system of claim 1, wherein the active shutter array (30) is disposed between the light source (10) and the splitting device (70).

14. 11. The projection system of claim 1, wherein the active shutter array (30) is disposed between the spatial light modulator (40) and the eyebox (121).

15. 15. The projection system of any one of the preceding claims, wherein the light source (10) comprises a laser light source.

16. 16. The projection system of claim 1, wherein the light source (10) comprises a red laser point source configured to generate red light, a green laser point source configured to generate green light, and a blue laser point source configured to generate blue light.

17. 16. The projection system of any one of claims 1 to 15, wherein the light source (10) comprises a single narrowband point source configured to emit white light comprising red, green and blue light.

18. 17. The projection system of claim 1, wherein the combiner (100) comprises a reflective holographic combiner.

19. the spatial light modulator (SLM) (40) comprises ferroelectric liquid crystal on silicon; 19. The projection system of claim 9, wherein the light field image projection system comprises a control device (300) configured to control the switching state of the SLM (40) in synchronization with the beam steering device (80) and the light source (10).

20. The control device (300), configured to switch a color state of the SLM (40) during positive setup times (t11, t12, t13) and negative setup times (T11, T12, T13), and to place the SLM (40) in a switched color state during positive illumination times (t111, t121, t131) and negative illumination times (T111, T121, T131); The control device (300), further configured to turn on the light source (10) during positive illumination times (t111, t121, t131) while the beam steering device (80) is not moving and to direct the narrowband light (200) towards one of the lenslets (71), and to turn off the light source (10) at other times; The beam steering device comprises: moving from one position to another between the negative setup times (T11, T12, T13) and negative illumination times (T111, T121, T131) of a previous illumination step and the positive setup times of a subsequent illumination step; at least one positive setup time (t11, t12, t113) and positive illumination time (t111, t112, t113) per color is inverted for a corresponding negative setup time (T11, T12, T13) and negative illumination time (T111, T112, T113) so that the beam steering device (80) has a longer time to move from one position to another during the negative setup time and negative illumination time of a previous illumination step plus the negative setup time and negative illumination time of a next illumination step plus the positive setup time of the next illumination step; 20. The projection system of claim 19.

21. A wearable device comprising a light field image projection system according to any one of claims 1 to 20.

22. 22. The wearable device of claim 21, comprising an augmented or mixed reality device, or smart glasses.

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