Near eye sequential light-field projector displaying images with variable resolution and depth of field

Abstract

The present disclosure concerns a near eye sequential light-field projector comprising a light source (1), including a plurality of point-light sources (11-13) sequentially generating incident light beams (110), a spatial light modulator (40) modulating the incident light beams (110) and generating modulated light beams (120), an intermediate optical element (22) projecting the modulated light beams (120) and forming a plurality of light source images (31-33) in a Fourier plane (60) and virtual images (41, 42). A tunable spatial filter (61) in the Fourier plane (60) interacts with the modulated light beams (120). The tunable spatial filter (61) comprises a filter SLM and is controllable to display a filter image pattern (600) comprising a plurality of apertures (62, 641-645). The tunable spatial filter (61) is configured to define the arrangement of the apertures (62, 641-645) in the filter image pattern (600) and individually vary the shape and size of each aperture (62, 641-645) to adjust the depth of field and resolution of the virtual images (41, 42).

Description

Near eye sequential light-field projector displaying images with variable resolution and depth of fieldTechnical domain

[0001] The present disclosure concerns a near-eye image projection system having a variable depth of field and resolution. More particularly, the present disclosure concerns a near-eye light-field projection system with an improved image resolution over a larger depth of field.Background

[0002] There is a trade-off between resolution and depth of field in imaging using a light field display comprising a spatial light modulator (SLM). Although a light field display can display virtual images at different distances and defocus, the highest resolution of the image is always achieved in the plane of the SLM. Usually, this plane is located optically at infinity, but it can be moved closer or further away if needed. The higher the resolution of the SLM (or of the image), the shorter the depth of field and inversely. Often a light field display has a fixed image resolution and therefore a fixed depth of field at the image resolution.

[0003] The depth of field can be changed by adding a spatial filter in the Fourier plane of the SLM.

[0004] A phoropter has a very small depth of field and a high resolution. Changing the focus in a phoropter requires physically switching lenses in order to correct for the user's eye refractive error. The phoropter can display patterns with high resolution at a given correction, allowing to determine the visual acuity of the user.

[0005] Recently, light field displays have been used in replacement of a phoropter as an ophthalmic testing device. In contrast, phoropter using aCreal3-17-PCTlight-field has a larger depth of field and lower resolution. The advantage of the light field phoropter is that it can display simultaneously different corrections for the user, whereas the classical phoropter is limited to one at a given time. However, the resolution of the light field phoropter is too low to allow the measurement of high visual acuities.Summary

[0006] The present disclose concerns a near eye sequential light-field projector, comprising a light source including a plurality of point-light sources, each point-light source being configured to generate an incident light beam, an illumination control unit configured to control the light device to time sequentially activate and deactivate the individual pointlight sources and sequentially generate the incident light beam. The lightfield projector further comprises an SLM, configured to modulate the incident light beams and generate modulated light beams, an intermediate optical element, configured to project the modulated light beams and form a plurality of light source images in a Fourier plane, and a relay optics configured to form virtual images. A tunable spatial filter is arranged in the Fourier plane and configured to interact with the modulated light beams. The tunable spatial filter is controllable by a filter control unit to display a filter image pattern comprising a plurality of apertures. The filter control is further configured to control the tunable spatial filter to define the arrangement of the apertures in the filter image pattern and to individually vary the shape and size of each aperture to adjust the depth of field and resolution of the virtual images.

[0007] The tunable spatial filter removes higher frequencies of the virtual images while increasing the depth of field and resolution of the viewpoints. This allows for the light-field projector to display viewpoints having both high resolution and large depth of field. The tunable spatial filter allows for varying the resolution and depth of field by the individual adjustment of the shape and size of each aperture.Creal3-17-PCT

[0008] The light-field projector can then be advantageously used as an ophthalmic testing device (to replace a phoropter) whereby the image quality at different optical distances or for different ophthalmic corrections can be improved.Brief description

[0009] Exemplar embodiments of the invention are disclosed in the description and illustrated by the drawings in which:Fig. 1a schematically shows a near eye sequential light-field projector projecting modulated light beams and comprising a tunable spatial filter, according to an embodiment;Fig. 1 b shows virtual images formed by the near eye sequential light-field projector of Fig. 1a;Fig. 1c shows a simplified representation of the light field projector of Fig. 1a;Fig. 2a shows an example of the tunable spatial filter comprising a plurality of apertures;Figs. 2b and c illustrate a movable tunable spatial filter, arranged in a rotating wheel 410, in a position where the tunable spatial filter is the optical path of the modulated light beams (Fig. 2b) and outside the optical path of the modulated light beams (Fig. 2c);Fig. 3a shows a simplified representation of the light field projector wherein the tunable spatial filter comprises an SLM, according to an embodiment;Fig. 3b shows an example of the tunable spatial filter displaying a filter image pattern comprising a plurality of aperture patterns, according to an embodiment;Fig. 3c shows the tunable spatial filter of Fig. 3b where the aperture patterns define apertures having different apertures sizes and shapes;Creal3-17-PCTFigs. 4a to 4d illustrate the tunable spatial filter comprising circular-shaped aperture within a sub pattern, where the sub pattern is moved in synchronization with activation of point-light sources of the light field projector;Fig. 5 shows the tunable spatial filter comprising a pixelated SLM, according to an embodiment;Fig. 6a shows the tunable spatial filter comprising an image pattern defining a checkered motif comprising square-shaped linear polarizers with alternating polarization, according to an embodiment;Fig. 6b shows the tunable spatial filter of Fig. 6a further comprising an array of apertures, each located at a position corresponding to one of the linear polarizers;Fig. 6c shows an arrangement of a polarization switching element with the linear polarizers and the array of transparent areas, according to an embodiment;Fig. 7a compares the qualitative performance of the tunable spatial filter according to the different configurations; andFig. 7b shows the tunable spatial filter with an array of apertures viewed along a row, column or diagonally.Detailed description

[0010] Fig. 1a schematically shows a near eye sequential light-field projector (thereafter called light-field projector) 100 comprising a light source 1 including a plurality of point-light sources 11, 12, 13 arranged in a light source plane 10. Each of the point-light sources 11-13 is configured to sequentially generate an incident light beam 110. The light source 1 can comprise less or more than the three point-light sources represented in Fig.1a. The point-light sources 11-13 can comprise LEDs, pLEDs, lasers, or any other point-light-sources capable of emitting an incident light beam 110. The light-field projector display 100 can further comprise an illumination control unit 51 configured to control the light device 1 such as to timeCreal3-17-PCTsequentially activate and deactivate the individual point-light sources 11-13.

[0011] The light-field projector 100 further comprises an SLM 40 comprising a plurality of pixels to display an SLM image pattern. An SLM control unit 52 can be configured to control the pixels of the SLM 40 to provide the SLM image pattern such that the incident light beam 110 illuminating the SLM 40 are modulated according to the SLM image pattern, generating modulated light beams 120. An example of such a near-eye light field projector is described in European patent EP3542206B1 by the present applicant. The light-field projector 100 can further comprise a light source optical element 21 configured to project the incident light beams 110 on the SLM 40.

[0012] The light-field projector 100 can further comprise an intermediate optical element 22 configured to project the modulated light beams 120 along an optical path 170 and form a plurality of light source images 31, 32, 33 of the modulated light beams 120 in a Fourier plane 60 along the optical path 170. In some embodiments, the light source optical element 21 can be configured to collimate the incident light beams 110.

[0013] The light field projector 100 can further comprise relay optics configured to form virtual images 41, 42 (see Fig. 1b) and virtual viewpoints 81, 82, 83. For example, the relay optics may comprise a first relay optical element 23 configured to project the modulated light beams 120 and form intermediate images (not shown) in an intermediate image plane 231 and a second relay optical element 24 configured to project the modulated beam light 120 to form the viewpoints 81-83 in an exit pupil plane 80 and the virtual images 41, 42. In Fig. 1 b, the virtual images 41, 42 are represented in the prolongation of the optical path 170, before the viewpoints 81-83.

[0014] In the absence of diffraction by the SLM 40, the viewpoints 81-83 appear to be coming from a single point in space with a specific direction.Creal3-17-PCTSince the light source 1 sequentially generates the incident light beams 110, the viewpoints 81-83 are sequentially generated.

[0015] The light source and intermediate optical elements 21, 22 and the first and second relay optical elements 23, 24 can comprise lenses or metalenses.

[0016] Fig. 1c shows a simplified representation of the light field projector 100 without the relay optics 23, 24.

[0017] In an embodiment, the light field projector 100 further comprises a tunable spatial filter 61 arranged in the Fourier plane of the SLM 40.Since there are a plurality of point-light sources 11-13, the tunable spatial filter 61 should comprise a plurality of apertures (or pinholes) corresponding to the light source images 31-33. Because of diffraction, the light source images 31-33 do not focus on a single spot, but rather will produce a distributed pattern of light in the Fourier plane 60. Each apertures of the tunable spatial filter 61 allows the desired light to pass, while blocking light that corresponds to undesired structure in the distributed pattern of light, resulting in a "filtered" light source images 31-33.

[0018] Fig. 2a shows an example of the tunable spatial filter 61 comprising a plurality of apertures 62 (here substantially circular apertures or pinholes) arranged in an array such that the position of the apertures 62 in the array corresponds to the positions of the light source images 31-33 formed in the Fourier plane 60. Each of the apertures 62 has an aperture size D. Hereafter, the array of apertures 62 in the tunable spatial filter 61 configuration of Fig. 2a will be called single-pitch array.

[0019] In an embodiment, the tunable spatial filter 61 can be configured to be movable between an active position, where the tunable spatial filter 61 is arranged through the optical path 170 in the Fourier plane 60, as shown in Fig. 1b, and an inactive position where the tunable spatial filterCreal3-17-PCT61 is removed outside the optical path 170. In the active position, the tunable spatial filter 61 interacts with the modulated light beams 120 to change the depth of field and resolution of the virtual images 41, 42. In the inactive position, the tunable spatial filter 61 does not interact with the modulated light beams 120.

[0020] For example, the movable tunable spatial filter 61 can be arranged in a rotating wheel 410 that rotate about a wheel axis 411 that is eccentric relative to the optical path 170 (see Figs. 2b and 2c). The rotating wheel 410 about the wheel axis 411 to place the tunable spatial filter 61 through the optical path 170 and in the Fourier plane 60 (active position, Fig. 2b) or to place the tunable spatial filter 61 outside the optical path 170 (inactive position, Fig. 2c). The rotating wheel 410 can comprise a window 412 opposite the tunable spatial filter 61 such that when the tunable spatial filter 61 is in the inactive position, the window 412 is in the optical path 170 and let the modulated light beams 120 pass through the rotating wheel 410 unaffected. Other arrangements of the movable tunable spatial filter 61 are possible.

[0021] When the tunable spatial filter 61 is switched off, the light field projector 100 can display the light source image 31-33 with a short depth of field. The tunable spatial filter 61 switched on allows for increasing the depth of field of the virtual images 41, 42, depending on the aperture size D of aperture 62.

[0022] Depending on the aperture size D of the apertures 62, the lateral size L of the light source images 31-33 can be larger than the aperture size D of the apertures 62. In the case the tunable spatial filter 61 comprises large number of aperture 62, such as the tunable spatial filter 61 shown in Fig. 2a, the light of one of the light source images 31-33 may overlap neighboring apertures 62 and pass through the neighboring apertures 62. Indeed, the light source images 31-33 can be enlarged due to diffraction of modulated light beams 120 when modulated by the SLM 40 (the modulation of the incident light beams 110 by the SLM 40 can generateCreal3-17-PCTdiffraction in the modulated light beams 120). Fig. 2a shows an example of one of the light source images 31-33 (dashed circle) centered on one of the apertures 62 and which lateral size L is larger than the aperture size D and overlap at least partially with some of the neighboring apertures 62. This configuration results in each aperture 62 creating a filtered light source images 31-33 that has a lateral size L that is larger than the aperture size D of the aperture 62.

[0023] Advantageously, the tunable spatial filter 61 should be configured to avoid the overlap of the light of one of the light source images 31-33 with neighboring apertures 62. Moreover, the tunable spatial filter 61 should be configured to actively tune each aperture 62 to allow different modes of operation, namely, to allow for the virtual images 41, 42 to have high or low resolution and / or low or high depth of field, as required by the application. In particular, the aperture 62 of the tunable spatial filter 61 can be configured to provide either a large depth of field or a high resolution of the virtual images 41, 42.

[0024] In another embodiment shown in Figs. 3a to 3c, the tunable spatial filter 61 comprises a filter SLM including a plurality of pixels configured to display a filter image pattern 600. A filter control unit 53 can be configured to control the pixels of the tunable spatial filter 61 to provide the filter image pattern 600.

[0025] Fig. 3a shows a simplified representation of the light field projector 100 without the relay optics 23, 24 wherein the tunable spatial filter 61 comprises the filter SLM.

[0026] Fig. 3b shows an example of the tunable spatial filter 61 displaying a filter image pattern 600 comprising a plurality of aperture patterns 640. The filter control unit 53 can be configured to control the tunable spatial filter 61 such that each aperture pattern 640 correspond to a substantially circular aperture having a predetermined aperture size D by defining transparent and opaque areas on the aperture pattern 640.Creal3-17-PCT

[0027] Fig. 3c shows the tunable spatial filter 61 of Fig. 3b being controlled in such a way that the aperture patterns 640 define apertures 641, 642, 643, 644, 645 having different apertures sizes D and shapes by controlling the transparent areas 65 and opaque areas 66 of the aperture patterns 640. For example, the transparent and opaque areas 65, 66 of the aperture patterns 640 can be controlled such as to define substantially circular apertures 641, 642, 643 having different apertures sizes D and / or define apertures 644, 645 having a substantially annular shape. The tunable spatial filter 61 can be further controlled such that the aperture pattern 640 contains only opaque areas 66 such that the aperture pattern 640 does not form an aperture. The annular-shaped apertures 644, 645 makes the virtual images 41, 42 consist of nearly non-diverging Bessel-like beams and considerably extends the depth of field.

[0028] In the tunable spatial filter 61 configuration of Figs. 3b and 3c, the aperture size D of the circular apertures (apertures 641-643) and the shape (annular apertures 644, 645) can be dynamically modified, allowing for dynamically tuning the resolution and / or depth of field of the virtual images 41, 42 provided by each aperture 641-645 of the tunable spatial filter 61. For example, an aperture 641-645 can be tuned to obtain a high or low resolution of one of the virtual images 41, 42 and / or to obtain a small or large depth of field of another virtual image 41, 42.

[0029] The tunable spatial filter 61 can comprise a transmissive liquid crystal display (LCD) containing LC pixels.

[0030] In another configuration illustrated in Figs.4a to d, the illumination control unit 51 can be configured to control the light device 1 such as to time sequentially activate the point-light sources 11-13, such as to sequentially generate the modulated light beams 120. The tunable spatial filter 61 can be controlled by the filter control unit 53 to display the filter image pattern 600 wherein the filter image pattern 600 comprises at least one transparent area 65, forming an aperture 62 (for example a substantially circular aperture represented by the white circle in Figs. 4a-d)Creal3-17-PCTand / or comprising at least one opaque area 66, corresponding to no aperture (represented by the black circle in Figs. 4a-d). The filter control unit 53 can control the tunable spatial filter 61 such that each transparent area 65 is generated in synchronization with the sequential activation of the point-light sources 11-13 and thus, the sequential generation of the modulated light beams 120.

[0031] In particular, the tunable spatial filter 61 can be controlled by the filter control unit 53 such that the position of each formed aperture 62 on the tunable spatial filter 61 corresponds to the position of one of the light source images 31-33 formed by the modulated light beams 120. The tunable spatial filter 61 can be further controlled such that each aperture 62 is formed simultaneously with the light source images 31-33 formed at the same position. The tunable spatial filter 61 can be further controlled such that only one aperture 62 is formed at a given time.

[0032] As shown in Figs. 4a-d, the tunable spatial filter 61 can be controlled by filter control unit 53 such that the filter image pattern 600 comprises at least one sub pattern 610 comprising a plurality of the transparent areas 65 generated simultaneously. At least one of the transparent areas 65 in the sub pattern 610 can be generated at a position of the tunable spatial filter 61 that corresponds to the position of one of the light source images 31-33 in the Fourier plane 60, the position of the light source images 31-33 being determined by the activated point-light sources 11-13.

[0033] The tunable spatial filter 61 can be controlled by the filter control unit 53 such that the whole filter image pattern 600 comprises an array of transparent areas 65, wherein the transparent areas 65 are located at the positions of the light source images 31-33 formed in the Fourier plane 60 when all the point-light sources 11-13 are activated. The tunable spatial filter 61 having such filter image pattern 600 is then similar to the tunable spatial filter 61 of Fig. 2a. The tunable spatial filter 61 can be further controlled by the filter control unit 53 such that the sub pattern 610Creal3-17-PCTcomprises an array of transparent areas 65, wherein the transparent areas 65 are located at the positions of the light source images 31-33 formed in the Fourier plane 60 when only some of the point-light sources 11-13 are activated.

[0034] As illustrated in the example of Figs. 4a-d, the tunable spatial filter 61 can further be controlled such that the transparent areas 65 in the sub pattern 610 form nonadjacent apertures 62 (the apertures 62 are separated by at least one opaque area 66). In the example of Figs. 4a-d, each aperture 62 in the sub pattern 610 is separated by an opaque area 66. The nonadjacent apertures 62 allows for increasing the distance between two simultaneously apertures 62 (doubling the distance for the sub pattern 610 of Figs. 4a-d) compared to the tunable spatial filter 61 of Fig. 2a. Such an array can be called double-pitch array.

[0035] The configuration of Figs. 4a-d allows for compensating the reaction time of the tunable spatial filter 61, i.e., the time required for generating the apertures 62, that is larger than the reaction time of the point-light sources 11-13 (the activation / deactivation of the point-light sources 11-13). For example, the tunable spatial filter 61 can be configured to display the sub pattern 610 shown in Fig. 4a for a display period during which the illumination control unit 51 controls the light device 1 to time sequentially activate the point-light sources 11-13 and time sequentially project a light source image 31-33 at each of the apertures 62 in the sub pattern 610 during the display period.

[0036] During a subsequent display period, the sub pattern 610 can be moved around the surface area of the tunable spatial filter 61 in synchronization with each light source image 31-33, such that the apertures 62 in the sub pattern 610 are at different locations than in the previous display period. The illumination control unit 51 can control the light device 1 to time sequentially activate the point-light sources 11-13 to time sequentially project a light source image 31-33 at each of the apertures 62 in the sub pattern 610 during the subsequent display period. ThisCreal3-17-PCTconfiguration allows for changing the filter image pattern 600 at a lower rate than the activation rate of the point-light sources 11-13 while each light source image 31-33 is sequentially formed at an aperture 62.

[0037] In the example of Figs 4a-d, the sub pattern 610 comprises four apertures 62, each separated by an opaque area 66. During a first display period, the sub pattern 610 is in the above right corner of the filter image pattern 600. During a second, third, and fourth display period, the sub pattern 610 is moved, respectively, in the below right corner, the below left corner and the above left corner of the filter image pattern 600. During each of the first, second, third, and forth display periods, the illumination control unit 51 can control the light device 1 to time sequentially activate the point-light sources 11-13 to time sequentially project a light source image 31-33 at each of the four apertures 62 in the sub pattern 610. The configuration of Figs. 4a-d is this advantageous when the tunable spatial filter 61 has a time of formation of the filter image pattern 600 comprising the transparent areas 65 is slower than the time for sequentially activating the point-light sources 11-13.

[0038] In another configuration shown in Fig. 5, the tunable spatial filter 61 is pixelated, i.e., comprises pixels having a size that is smaller than the aperture size of the transparent areas 65 comprised in the filter image pattern 600.

[0039] In the example of Fig. 5, the tunable spatial filter 61 comprises a plurality of pixels 67. The filter control unit 53 controls the pixels 67 such that the filter image pattern 600 comprises four transparent areas 65, each encompassing a plurality of pixels 67. The rest of the filter image pattern 600 comprises black pixels 67 forming an opaque area 66. The four transparent areas 65 have substantially the shape of, respectively, a circular aperture, a semi-circular aperture, an elliptical aperture, and an annular aperture.Creal3-17-PCT

[0040] The pixels 67 of the tunable spatial filter 61 can be controlled by the filter control unit 53 to display one or a plurality of transparent areas 65, wherein each transparent area 65 can have any defined or arbitrary shape. For example, the pixels 67 can be controlled by the filter control unit 53 such that the filter image pattern 600 comprises an array of substantially circular apertures 62, such as in the example of Figs. 2 and 4, or an array of substantially annular-shaped apertures 62.

[0041] The tunable spatial filter 61 can be controlled such as to display the transparent areas 65 in synchronization with the sequential activation of the point-light sources 11-13 and thus, the sequential generation of the modulated light beams 120 and light source image 31-33. Alternatively, the transparent areas 65 can be displayed independently of the point-light sources 11-13 activation (fixed filter image pattern 600).

[0042] This configuration allows for using an existing off-the-shelf SLM, without the need to pre-customize any specific filter image pattern 600 and / or aperture pattern 640 on the tunable spatial filter 61. The pixelated tunable spatial filter 61 further allows for generating a filter image pattern 600 containing arbitrarily shaped aperture patterns 640 or transparent area 65. The shape of the aperture patterns 640 can be configured in order to optimize the sharpness of the viewpoints 81-83, for example along specific axis. The shape of the tunable spatial filter 61 can be adapted according to the content to be displayed.

[0043] More generally, the filter SLM can comprise any type of SLM, including a reflective such as DLP, transmissive, LCOS, or FLCOS. The tunable spatial filter 61 can also be a phase modulator SLM.

[0044] Figs. 6a and 6b illustrate another configuration of the tunable spatial filter 61 comprising a filter image pattern 600 defining a checkered motif comprising square-shaped linear polarizers 63 with alternating polarization (Fig. 6a). For example, the axis of polarization of one of the linear polarizers 63 can have an axis of polarization that differs (e.g., beingCreal3-17-PCTorthogonal) from the axis of polarization of the adjacent linear polarizer 63. As shown in Fig. 6b, the filter image pattern 600 can further comprise an array of transparent areas 65, wherein each transparent area 65 defines an aperture 62 (for example a circular aperture) and is located at a position corresponding to one of the linear polarizers 63. The transparent areas 65 (apertures 62) can be formed by performing openings in a layer of opaque material 66. This configuration allows for doubling the period of the aperture array for a given polarization (doubling the distance between two adjacent apertures 62), allowing a better filtering of higher frequencies.

[0045] The linear polarizer 63 is configured to let pass the modulated light beams 120 having a specific polarization and not the other polarizations. For example, depending on its polarization the modulated light beams 120 passes through the linear polarizer 63 that acts as an aperture 62 or is blocked by the linear polarizer 63. In the case of the checkered motif comprising square-shaped linear polarizers 63 with alternating polarization (Fig. 6a), the tunable spatial filter 61 can comprise the double-pitch array of apertures 62.

[0046] The tunable spatial filter 61 in the configuration of Figs. 6a-b may function as a polarization switch. To that end, a polarization switching element 68 may be configured to control the polarization of the modulated light beams 120 incoming on the spatial filter 61. For example, the polarization switching element 68 may be configured to switch the polarization of the modulated light beams 120, incoming on the spatial filter 61, between two orthogonal polarizations. The polarization switching element 68 can be controlled by the filter control unit 53. The polarization switching element 68 can be configured to be controlled by the filter control unit 53 such that the polarization of the modulated light beams 120 is synchronized with the sequential generation of the modulated light beams 120 and light source image 31-33. The polarization switching element 68 can be further configured to be controlled by the filter control unit 53 such that the polarization of the modulated light beams 120 is synchronized with the generation of the transparent areas 65.Creal3-17-PCT

[0047] Fig. 6c shows a possible arrangement of the spatial filter 61, wherein the linear polarizers 63 is between the polarization switching element 68 and the array of transparent areas 65. Other configurations of the spatial filter 61 can be contemplated. For example, the array of transparent areas 65 can be between the polarization switching element 68 and the linear polarizers 63. The polarization switching element 68 can be arranged in contact with the transparent areas 65 or the linear polarizers 63. Alternatively, the polarization switching element 68 can be physically separated from the transparent areas 65 or the linear polarizers 63.

[0048] The polarization switching element 68 can comprise a liquid crystal, a metamaterial, a diffractive optical element, or a magneto-optical crystal.

[0049] In summary, the tunable spatial filter 61 with the double-pitch array of apertures 62, can be achieved by the configurations illustrated in Figs. 4a to d, in Fig. 5 but also with the tunable spatial filter 61 of Figs. 6a-b.

[0050] In the configurations of Figs. 3a to 6b, the tunable spatial filter 61 is controllable by the filter control unit 53 to display a filter image pattern 600 comprising a plurality of apertures 62, 641-645. The filter control unit 53 is further configured to control the tunable spatial filter 61 to define the arrangement of the apertures 62, 641 -645 in the filter image pattern 600 and to individually vary the shape and size of each aperture 62, 641-645 to adjust the depth of field and resolution of the virtual images 41,42.

[0051] Fig. 7a compares the qualitative performance of the tunable spatial filter 61 according to the different configurations described above. In particular, the contrast the viewpoints 81-83 is reported as a function of the defocus around the Fourier plane 60.Creal3-17-PCT

[0052] The virtual innages 41, 42 with the higher contrast (i.e. the sharpest image) around the intermediate image plane 231, or the plane where the SLM 40 is located, is obtained without the tunable spatial filter 61 (curve A). In the case the spatial filter 61 comprises a single pinhole, located at the light source image plane (curve B), the virtual images 41, 42 have a reduced contrast but remain sharper than without the tunable spatial filter 61 when the image is defocused.

[0053] When the tunable spatial filter 61 comprises the single-pitch array of apertures 62 (such as in the configuration of Fig. 2) with the apertures 62 located at the light source image 31-33 in the Fourier plane 60, the sharpness rapidly decreases with increasing defocus and then periodically fluctuate when the defocus is further increased (curve C).

[0054] When the tunable spatial filter 61 comprises the double-pitch array (curve F), for example, for the checkered motif comprising squareshaped linear polarizers 63 with alternating polarization, such as shown in Figs. 6a-b, or for the tunable spatial filter 61 comprising the double-pitch array of apertures 62 where each aperture 62 is separated by at least one opaque area 66, such as shown in Figs. 4a-d, the virtual images 41, 42 have a reduced contrast compared to the one of the tunable spatial filter 61 comprising a single pinhole but remains sharper than without the tunable spatial filter 61 when the image is defocused.

[0055] Curve C and E show the contrast of the virtual images 41, 42 when the tunable spatial filter 61 comprising the single-pitch array of apertures 62 is viewed along a row or column (curve C) and along a diagonal (curve E) (see Fig. 7b). The comparison between curves C and E shows an anisotropy between the virtual images 41, 42 viewed along a row or column and viewed diagonally. This may cause issues when attempting to display astigmatic content.

[0056] Curves D and F show the contrast of the virtual images 41, 42 when the double-pitch array of apertures 62 is viewed along a row orCreal3-17-PCTcolumn (curve F) and diagonally (curve D). The comparison of curves D and F shows less anisotropy between the virtual images 41, 42 viewed along a row or column and viewed along a diagonal. The double-pitch array of apertures 62 can diminish the anisotropy.

[0057] Curves C-F for the single-pitch and double-pitch array of apertures 62 also show a lower contrast compared to the contrast of the tunable spatial filter 61 comprising a single pinhole (curve A).Creal3-17-PCTReference Numbers and1 light source10 light source plane11, 12, 13 point-light source100 near eye sequential light-field projector 110 incident light beam120 modulated light beam170 optical path21 light source optical element22 intermediate optical element23 first relay optical element231 intermediate image plane24 second relay optical element31, 32, 33 light source image40 spatial light modulator41, 42 virtual image410 rotating wheel411 wheel axis412 window51 illumination control unit52 SLM control unit53 filter control unit60 Fourier plane600 filter image pattern610 sub pattern61 tunable spatial filter62 pinhole, aperture63 linear polarizer640 aperture pattern641, 642, 643 aperture pattern65 transparent area66 opaque area67 pixel68 polarization switching element80 exit pupil plane81, 82, 83 viewpointD aperture sizeL lateral size of the light source imageCreal3-17-PCT

Claims

Claims1. A near eye sequential light-field projector, comprising:a light source (1) including a plurality of point-light sources (11-13), each point-light source (11-13) being configured to generate an incident light beam (110);an illumination control unit (51) configured to control the light device (1) to time sequentially activate and deactivate the individual pointlight sources (11-13) and sequentially generate the incident light beam (110);a spatial light modulator (SLM) (40), configured to modulate the incident light beams (110) and generate modulated light beams (120);an intermediate optical element (22), configured to project the modulated light beams (120) and form a plurality of light source images (31-33) in a Fourier plane (60);a relay optics, configured to form virtual images (41, 42); and a tunable spatial filter (61), arranged in the Fourier plane (60) and configured to interact with the modulated light beams (120);wherein the tunable spatial filter (61) comprises a filter SLM and is controllable by a filter control unit (53) to display a filter image pattern (600) comprising a plurality of apertures (62, 641-645);wherein the filter control unit (53) is further configured to control the tunable spatial filter (61) to define the arrangement of the apertures (62, 641-645) in the filter image pattern (600) and to individually vary the shape and size of each aperture (62, 641-645) to adjust the depth of field and resolution of the virtual images (41, 42).

2. The light-field projector according to claim 1,wherein the filter image pattern (600) comprises a plurality of aperture patterns (640);wherein the filter control unit (53) is configured to control the tunable spatial filter (61) to define for each aperture pattern (640) transparentCreal3-17-PCTand / or opaque areas; andwherein the transparent area form an aperture (62, 641-645) having a predefined shape and size or no aperture.

3. The light-field projector according to claim 2,wherein the aperture patterns (640) is configured to define a circularshaped aperture (641-643).

4. The light-field projector according to claim 2 or 3, wherein the aperture patterns (640) is configured to define an annularshaped aperture (641-643).

5. The light-field projector according to claim 3,wherein the plurality of aperture patterns (640) are arranged in a regular array.

6. The light-field projector according to claim 5,wherein the filter control unit (53) is configured to control the tunable spatial filter (61) for each aperture pattern (640) to form the circularshaped aperture (62) in synchronization with the sequential activation of the point-light sources (11-13), in a position in the array that corresponds to the position of one of the light source images (31-33).

7. The light-field projector according to claim 6,wherein the filter control unit (53) is configured to control the tunable spatial filter (61) for each aperture pattern (640) to form one aperture (62) at a given time.

8. The light-field projector according to claim 6,wherein the filter control unit (53) is configured to control the tunable spatial filter (61) for each aperture pattern (640) to form a plurality of apertures (62) at a given time.Creal3-17-PCT9. The light-field projector according to claim 6, wherein the filter control unit (53) is configured to control the tunable spatial filter (61) to form the apertures (62) only within a sub pattern (610) of the filter image pattern (600) comprising a subset of the aperture patterns (640) in the filter image pattern (600).

10. The light-field projector according to claim 9,wherein the filter control unit (53) is further configured to control the tunable spatial filter (61) to form the apertures (62) with non-adjacent aperture patterns (640).

11. The light-field projector according to claim 9,wherein each aperture (62) is separated form another by one opaque aperture patterns (640).

12. The light-field projector according to any one of claims 9 to 11, wherein the filter control unit (53) is configured to control the tunable spatial filter (61) to change the sub pattern (610) within the filter image pattern (600) in synchronization with the sequential activation of the pointlight sources (11-13).

13. The light-field projector according to claim 12,wherein the filter control unit (53) is configured to control the tunable spatial filter (61) to display the sub pattern (610) for at least a display period during which the illumination control unit (51) controls the light device (1) to time sequentially project a light source image (31-33) at each of the apertures (62) in the sub pattern (610) during the display period.

14. The light-field projector according to claim 13,wherein the filter control unit (53) is configured to control the tunable spatial filter (61) to display the sub pattern (610) for a plurality of display periods;wherein the apertures 62 in the sub pattern 610 are at different locations than in the previous display period.Creal3-17-PCT15. The light-field projector according to claim 1, wherein the filter SLM comprises a plurality of pixels (67), each pixel (67) having a size that is smaller than the size of the aperture (62, 641-645).

16. The light-field projector according to claim 1,wherein the filter image pattern (600) defines a checkered motif comprising linear polarizers (63);wherein each adjacent linear polarizers (63) have an orthogonal polarization.

17. The light-field projector according to claim 16,wherein the filter control unit (53) is further configured to control the tunable spatial filter (61) to define an array of the apertures (62), each aperture (62) being arranged at a position corresponding to one of the linear polarizers (63).

18. The light-field projector according to claim 17,wherein the filter control unit (53) is configured to control the tunable spatial filter (61) to define an array of the apertures (62) in synchronization with the sequential activation of the point-light sources (11-13).

19. a polarization switching element 68 may be configured to control the polarization of the modulated light beams 120 incoming on the spatial filter 61.

20. The light-field projector according to any one of claims 1 to 18, wherein the tunable spatial filter (61) can comprise a transmissive liquid crystal display (LCD) containing LC pixels.Creal3-17-PCT

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