Light-field projector having an expanded eye box and virtual reality or augmented reality device comprising the light field projector

Abstract

A near-eye light field projector (1), comprising a light source (10) generating a plurality of incident light beams (100) illuminating a SLM (20), configured to project a plurality of modulated light-beams (110). A first imaging element (32) is configured to project the plurality of modulated light beams (110) and form first images (31) at a first image plane (30). A second imaging element (40) is configured to project the modulated light beams (110) and form second images (123) at a second image plane (124). The modulated light beams (110) are incident onto a numerical aperture expander (NAE) (60) arranged between the first and second imaging elements (32, 40). The NAE (60) comprises a first plurality of expanding elements (61) and is configured to project each expanded image light beam (111) with increased numerical aperture and beam divergence angle relative to those of the modulated light beams (110). Each expanding element (61) has an element lateral size (LE) that is between 0.8 and 1.5, the beam lateral size (LB) of each of the modulated light beams (110).

Description

Light-field projector having an expanded eye box and virtual reality or augmented reality device comprising the light field projectorField

[0001] The present disclosure relates to a near-eye light-field projector and virtual reality or augmented reality device comprising the light field projector. More particularly, the present disclosure relates to a near-eye light-field projector having an expanded eye box.Background

[0002] Etendue is a property of light in an optical system, which characterizes how "spread out" the light is in area and angle. It corresponds to the beam parameter product (BPP) in Gaussian beam optics. The conservation of the Etendue of the light in a projector links the size of the projector to other parameters of the projector such as the field of view, the resolution, and the eye box. Due to conservation of Etendue, obtaining an eye box that is comfortably large for a user requires increasing the size of the light-field projector.

[0003] Etendue can be increased but not decreased. For a non-light- field projector, Etendue can be increased simply by projecting an intermediate image plane onto a diffuser or a replicating optical element such as a diffraction grating. Another solution is to project the image into a pupil replicating waveguide. For a light-field projector, any replication of the exit pupil destroys the light-field perspectives information.Summary

[0004] The present disclosure relates to a near-eye light field projector comprising a light source, comprising an array of a plurality of point-light sources, and generating a plurality of incident light beams illuminating aCreal3-13-PCTspatial light modulator (SLM). The SLM is configured to modulate the incident light beams and project a plurality of modulated light-beams. A first imaging element is configured to project the plurality of modulated light beams and form first images at a first image plane. A second imaging element is configured to project the modulated light beams and form second images at a second image plane, the second images defining an exit pupil. The modulated light beams are incident onto a numerical aperture expander (NAE) arranged between the first and second imaging elements. The NAE comprises a first plurality of expanding elements and is configured to project expanded image light beams, each expanded image light beam having a larger numerical aperture (NA) and beam divergence angle relative to those of the modulated light beams. Each expanding element has an element lateral size that is between 0.8 and 1.5, the beam lateral size of each of the modulated light beams.

[0005] The present disclosure further relates to a wearable device configured to be used as a virtual reality or augmented reality device and comprising the light field projector.

[0006] The light field projector disclosed herein has a small form factor and a large eye box.

[0007] The light field projector allows for increasing the Etendue of a head mounted display by increasing the eye box size while conserving the light-field information of the light-field projector. The light field projector further allows obtaining augmented reality glasses having small Etendue and a large eye box for a comfortable viewing size.Brief description

[0008] The foregoing features of this disclosure may be more fully understood from the following description of the drawings in which:Fig. 1 illustrates a time sequential light field display;Creal3-13-PCTFig. 2 shows the light field projector comprising a NAE, according to an embodimentFig. 3 shows the NAE according to an embodiment;Fig. 4 shows the NAE of Fig. 3 wherein a plurality of modulated light beams are incoming at different incidence angles;Fig. 5 shows a partial view of the light field projector where the NAE comprises holographic optical element (HOE), according to an embodiment;Figs. 6a-c illustrate different beam sizes of the modulated light beams incoming on the NAE;Fig. 7 represents a transmission hologram recording setup configured to record an optical function into a HOE;Fig. 8 illustrates a variant of the light field projector of Fig. 5, wherein the NAE forms a pancake lens arrangement, according to an embodiment;Fig. 9 is a detailed view of the pancake lens arrangement of the NAE shown in Fig. 8;Figs. 10a and 10b show the NAE according to another embodiment;Fig. 11 shows an implementation of the NAE of Figs 10a-b onto a holographic film; andFig. 12 shows a wearable device comprising the near-eye light field projector, according to an embodiment.Detailed description

[0009] Fig. 1 shows a near-eye light field projector 1 comprising a light source 10 comprising an array of a plurality of point-light sources, generating a plurality of incident light beams 100 illuminating a SLM 20, configured for modulating the incident light beams 100. In Fig. 1, three point-light sources 11 are represented, although the light source 10 couldCreal3-13-PCTcomprise less or more than three point-light sources. The light source 10 can be configured to time sequentially activate and deactivate the individual point-light sources. An example of such near-eye light field projector is described in European patent EP3542206B1 by the present applicant. The light-field projector 1 can further comprise a projection element 70 configured to project an image of the light source 10 to a lightsource image plane 71. Optionally, the light-field projector 1 can further comprise a collimating element 50 configured to collimate the incident light beams 100 illuminating the SLM 20.

[0010] Fig. 2 shows the light field projector 1, according to an embodiment, wherein the light field projector 1 further comprises a numerical aperture expander (NAE) 60 arranged substantially parallel to the first image plane 30. The NAE 60 is configured to increase the numerical aperture (NA) of each modulated light beam 110 interacting with NAE 60, increase the divergence angle between each modulated light beam 110, and forming expanded image light beams 111. The exit pupil 121 formed by the expanded image light beams 111 is larger than the exit pupil 121 formed by the light field projector 1 without the NAE 60.

[0011] The first image plane 30 can be arranged in proximity of the focal length of the second imaging element 40. In that case, the expanded image light beams 111, after traversing the second imaging element 40, are approximately collimated and form the exit pupil 121.

[0012] The NAE 60 further allows for increasing the resolution of the first and second images 31, 123 formed by the expanded image light beams 111, relative to the resolution obtained by the light field projector 1 in the absence of the NAE 60. The resolution of the of the first and second images 31, 123 is increased due to the larger beam size of the expanded image light beams 111 that has higher diffraction limit.

[0013] It should be noted that the NAE 60 does not split the incoming modulated light beam 110 into more beams but increases the NA andCreal3-13-PCTchanges the propagation direction of the modulated light beams 110 when forming the expanded image light beams 111. Other parameters of the light field projector 1, such as the field of view (FOV) and pixel density, are not affected by the NAE 60.

[0014] Fig. 3 shows the NAE 60 according to an embodiment, wherein the NAE 60 comprises a refractive lens array comprising a plurality of expanding elements 61 (first plurality of expanding elements). Here, the plurality of expanding elements 61 corresponds to a plurality of lenslets 61 . In Fig. 3, the modulated light beams 110 incidents onto the NAE 60 are represented by a single modulated beam chief ray 116 (dashed line). The expanded image light beams 111 outgoing from the NAE 60 are represented by a single expanded beam chief ray 117 (dashed lines). The modulated and expanded beam chief rays 116, 117 correspond to a single pixel of a particular viewpoint. More generally, the plurality of expanding elements 61 can comprise refractive elements, diffractive elements, or holographic elements.

[0015] After the refraction through the lens array, the outgoing expanded image light beams 111 have an output NA 113 and a refraction angle 115 that are larger than the incident NA 112 and the incident angle 114 of the modulated light beams 110.

[0016] Fig. 4 shows the NAE 60 of Fig. 3 wherein a plurality of modulated light beams 110 are incoming from different viewpoints, thus incoming at different incident angles 114.

[0017] In an embodiment, the NAE 60 comprises a holographic optical element (HOE), wherein the optical function of the NAE 60 is recorded into the HOE. In other words, the plurality of expanding elements 61 are recorded into the HOE. The recorded plurality of expanding elements 61 recorded in the HOE has the same optical function as the plurality of lenslets 61 in the example of Fig. 3. An advantage of having the NAECreal3-13-PCTfunction recorded into an HOE is that the so-configured NAE 60 appears transparent to the user.

[0018] Fig. 5 shows a partial view of the light field projector 1, according to an embodiment. Here, the NAE 60 comprises a HOE with the recorded optical function of the NAE 60, as described above. In Fig. 5, the modulated light beams 110 incidents onto the NAE 60 are represented by the modulated beam chief ray 116 and the expanded image light beams 111 outgoing from the NAE 60 are represented by the expanded beam chief ray 117. The modulated and expanded beam chief rays 116, 117 correspond to a single pixel of a particular viewpoint.

[0019] Since the NAE optical function is recorded in the HOE at specific wavelengths and angles, real world light 118 incoming from the real world and transmitted through the NAE 60 can reach the user's eye 90 mostly unaffected. The NAE 60 appears transparent to the user and can be placed in proximity to the second imaging element 40 (acting as a combiner).More generally, the NAE 60 can be implemented as a highly transparent and efficient image combiner allowing high efficiency for the projector and a good see-through experience of the real world for the user.

[0020] Other optical functions, in addition to the optical function of the NAE 60 can be recorded into the NAE 60 comprising the HOE. Fig. 5 shows an example of where a turning function is also recorded in the NAE 60. The turning function is configured to change the direction of the incident modulated light beams 110 such that the expanded image light beams 111 are directed towards the second imaging element 40 following an optical path that differs from that of the modulated light beam 110.

[0021] In the example of Fig. 5, the NAE 60 is arranged in a plane substantially perpendicular to the projection axis 170. The modulated light beams 110 are incident on the NAE 60 with an angle of incidence 0i smaller than 90° and greater than 0°. The expanded image light beams 111 transmitted by the NAE 60 are projected substantially parallel to theCreal3-13-PCTnormal of the NAE 60 (substantially parallel to the projection axis 170), towards the second imaging element 40 (acting as a combiner).

[0022] The configuration of the light field projector 1 of Fig. 5 allows for arranging the light field projector 1 in the temples of a pair of glass, and the projection the expanded image light beam 111 from the top in a headset like configuration.

[0023] In some embodiments, the NAE 60 comprising a HOE can comprise additional recorded optical functions, including any one alone or in combination: aperture array, mirrors array, axicon array, Fresnel lens array, meta lens array, or angularly multiplexed holograms.

[0024] In some embodiments, the second imaging element 40 can comprise an optical combiner, for example an optical combiner of holographic type or of reflective type. For instance, the second imaging element 40 can comprise a combiner of reflective type having a broadband semi reflective coating (half-mirror) allowing some light of the projector to be reflected to the user (such as shown in Fig. 5) and to transmit light incoming from the real world to each the user's eye 90.

[0025] In the case the point-light sources of the light source 10 comprise narrow wavelength light sources (such as lasers), the second imaging element 40 can comprise a wavelength-sensitive reflective coating to its reflectivity for the selected wavelengths, while the second imaging element 40 remains transparent for all other wavelengths of the visible light.

[0026] Figs. 6a to 6c illustrate different possible beam sizes of the modulated light beams 110 incidents on the NAE 60. In Figs. 6a-6c the expanding elements 61 are represented as a plurality of lenslets forming a lens array. However, the expanding elements 61 could also comprises any other element having the optical function that the one of the lenslets forming a lens array, for example the plurality of expanding elements 61 recorded in the HOE.Creal3-13-PCT

[0027] More particularly, Fig. 6a shows an example of a modulated light beam 110 incident on the NAE 60, wherein the beam lateral size LB of the modulated light beam 110 incoming at the surface of the NAE 60 is larger than the element lateral size LE of a single expanding element 61 and encompasses more than a single expanding element 61. Here, the transmitted expanded image light beam 111 shows an interference pattern that is visible in the second image 123 as a Moire effect. Thus, the configuration of Fig. 6a does not yield a good quality image. Fig. 6b shows a modulated light beam 110 incident on the NAE 60, wherein the beam lateral size LB is smaller than the element lateral size LE. In this case, the modulated light beam 110 encompasses a very small surface area of an expanding element 61 and is substantially not influenced by its passage through the expanding element 61. Thus, the lateral size of the transmitted expanded image light beam 111 is substantially the same as the beam lateral size LB. The output NA 113 and refraction angle 115 of the transmitted expanded image light beam 111 are also substantially the same as the incident NA 112 and incident angle 114 of the incoming modulated light beam 110. Fig. 6c shows a modulated light beam 110 incident on the NAE 60, wherein the beam lateral size LB is substantially the same as the element lateral size LE. Here, the modulated light beam 110 encompasses a surface area that substantially corresponds to the surface area of an expanding element 61. The outgoing expanded image light beam 111 has a larger output NA 113 and refraction angle 115 than the incident NA 112 and incident angle 114, without showing any interference pattern.

[0028] In some embodiments, the NAE 60 can be arranged in proximity of the first image plane 30 or at the first image plane 30. Such location of the NAE 60 allows chromatic dispersion generated by the NAE 60 to be cancelled by the collimating effect of the second imaging element 40. Even if the light source 10 comprises laser point-light sources having a narrow spectrum of emission wavelength, this spectrum can spread over 1 to 5 nm. This spread in wavelength is sufficient to disperse the expanded image light beams 111 that are diffracted by the NAE 60. When the NAE 60 is in proximity to the focal length of the second imaging element 40, the dispersed expanded image light beams 111 are collimated by the secondCreal3-13-PCTimaging element 40 and the pixel formed on the retina 92 is devoid of chromatic dispersion.

[0029] More generally, each expanding element 61 has a lateral size along the first image plane 30 (hereinafter called element lateral size LE) and the expanded image light beam 111 has a lateral size along the first image plane 30 (hereinafter called beam lateral size LB). It has been shown that good quality image (substantially no interference pattern) can be obtained for a ratio R of the element lateral size LE to the beam lateral size LB. The ratio R can be between 0.5 and 1.5, or between 0.8 and 1.5. In an advantageous embodiment, the beam lateral size LB can be smaller than element lateral size LE, for example, the ratio R can be between 0.5 and 1.0, or between 0.5 and 0.9, or between 0.8 and 1.0, or between 0.8 and 0.9.

[0030] The beam lateral size LB of the modulated light beam 110 between the first and second imaging elements 32, 40 depends on the properties of the light field projector 1. For instance, the beam lateral size LB between the first and second imaging element 32, 40 depends on the properties of the first imaging element 32, and possibly on the properties of the collimating element 50 and projection element 70.

[0031] In an embodiment, the NAE 60 is arranged at a distance D between the first and second imaging element 32, 40 such as to obtain the ratio R. For example, the NAE 60 can be arranged at a distance of 10 cm or less on each side of the first image plane 30. In a possible configuration, the NAE 60 can be arranged at a distance D corresponding to the location of the first image plane 30.

[0032] In the case a turning function is also recorded in the NAE 60, the NAE 60 is arranged at a distance D corresponding to 10 cm or less on each side of the first image plane 30, but not at the location of the first image plane 30. This position of the NAE 60 allows for obtaining the ratio R and the correct functioning of the turning function.Creal3-13-PCT

[0033] The second imaging element 40 can be located at a second distance from the first image plane 30 which corresponds approximately to the focal length of the second imaging element 40. In Fig. 5, the second distance is indicated by the numeral 33 in Fig 5.

[0034] Fig. 7 illustrates a detail of a variant of the configuration of the light field projector 1 shown in Fig. 5. In the configuration of Fig. 7, the NAE 60 and the second imaging element 40 form a so-called pancake lens arrangement. In such pancake lens arrangement, the second imaging element 40 is located at a second distance 33 from the first image plane 30 which corresponds substantially to the focal length of the second imaging element 40. In the configuration of Fig. 7, the NAE 60 further comprises a polarizer element 62 such as wire-grid polarizer and quarter wave plate 63. The polarizer element 62 can comprise a wire-grid polarizer.

[0035] Fig. 8 is a detailed view of the pancake lens arrangement of the NAE 60 of Fig. 7 and the optical path of the modulated light beams 110 and expanded light beams 111 in the light field projector 1. For simplicity, Fig. 8 represents the modulated light beams 110 incidents onto the NAE 60 by a single modulated beam chief ray 116 and the expanded image light beams 111 outgoing from the NAE 60 by a single expanded beam chief ray 117. The modulated and expanded beam chief rays 116, 117 correspond to a single pixel of a particular viewpoint.

[0036] The optical paths of the modulated and expanded light beams 110, 111 can be described as follows. In (A), the linearly polarized modulated light beams 110 are incident on the NAE 60. After interacting with the NAE 60, the expanded light beams 111 are directed towards the polarizer element 62 and transmitted through the polarizer element 62 and the quarter wave plate 63 (B). Transmission of the expanded light beams 111 through the polarizer element 62 is possible since the linear polarization state of the expanded light beams 111 are aligned with the transmission polarization axis of the polarizer element 62. After a transmission through the quarter wave plate 63, the polarization of theCreal3-13-PCTexpanded light beams 111 is circular. The polarization of the expanded light beams 111 could also be right-hand circular polarization.

[0037] After a transmission through the quarter wave plate 63, the expanded light beams 111 are reflected on the second imaging element 40 towards the quarter wave plate 63 and polarizer element 62 (C). After the reflection on the second imaging element 40, the handedness of the polarization of the expanded light beams 111 is changed to left-hand circular.

[0038] The left-hand circular polarized expanded light beams 111 are then transmitted through the quarter wave plate 63 and becomes linear but with an axis that is perpendicular to the entrance polarization and, thus, not aligned with the transmission axis of the polarizer element 62. Due to this not alignment, the expanded light beams 111 are reflected at the polarizer element 62, toward the quarter wave plate 63 (D).

[0039] The linear polarization then becomes left-hand circular polarization, and the expanded light beams 111 are reflected by the second imaging element 40 into a right-hand circular polarization, towards the NAE 60 (E). After the expanded light beams 111 have pass through the quarter wave plate 63, the polarization of the expanded light beams 111 is changed to a linear polarization with a linear axis close to the input polarization. The expanded light beams 111 can finally be transmitted through the polarizer element 62 and the NAE 60 such as to reach the eye 90 of the user (see Fig. 7).

[0040] The lens arrangement of the NAE 60 has a compact size owing to the use of optical path folding. In comparison to a non-pancake NAE 60, the second distance 33 can be reduced by a factor of a least two or three by the folding the optical path between the NAE 60 and the second imaging element 40, yielding a more compact optical arrangement.Creal3-13-PCT

[0041] Fig. 9 shows an example of a transmission hologram recording setup configured to record an optical function into a HOE 60. The recording setup comprises an object 64 comprising the optical function that is to be recorded into the HOE 60 and a holographic film 66. The object 64 is illuminated with a collimated coherent recording light beam 67, 68 and imaged through an imaging lens element 65 to obtain interferences on the holographic film 66. The imaging lens element 65 allow for adapting the size of the image of the object 64 to be recorded onto the holographic film 66. The recording light beam 67, 68, object 64 and imaging lenses 64 form the object arm of the holographic recording setup.

[0042] The recording light beam comprises an object beam 67, which illuminates the object 64, and a reference beam 68, which illuminates the holographic film 66 from a different angle than the one of the object beams 67. The light waves reflected from the object 64 and the waves from the reference beam 68 overlap to form an interference pattern on the holographic film 66. After development and illumination, the original object 64 is recreated as a fully three-dimensional image on the so produced holographic NAE (HOE) 60.

[0043] The object 64 can comprise lens array (as illustrated on Fig. 9) or any other types of NAE optical function such as an aperture array, mirrors array, axicon array, Fresnel lens array, meta lens array, angularly multiplexed holograms, diffractive optical element (DOE).

[0044] Figs. 10a and 10b show the NAE 60 according to another embodiment. The NAE 60, configured in a telescopic arrangement, comprises a first plurality of expanding elements 61a having a first focal length f 1 , and a second plurality of expanding elements 61 b having a second focal length f2. The first focal length f1 is larger than the second focal length f2 in order to increase the NA and form the expanded image light beams 111. In some aspects, the first image plane 30 can be coincident with the first focal plane f1. The distance D between the first and second expanding elements 61a and 61 b can be close or substantiallyCreal3-13-PCTequal to the sum of the first and second focal lengths (f 1 + f2). The first expanding elements 61a can have a different element lateral size LE than the one of the second expanding elements 61 b. Preferably, the element lateral sizes LE of the first and second expanding elements 61 a, 61 b are substantially identical. The first and second expanding elements 61a, 61 b can comprise refractive elements, diffractive elements, or holographic elements.

[0045] Fig 10b shows two modulated light beams 110 incoming with an angle of incidence 0i (relative to the projection axis 170) smaller than 90° and greater than 0°. The two modulated light beams 110 are mot aligned. In other words, the two modulated light beams 110 are not coincident and do not hit the lenslet of the first expanding element 61a at the same location. In such configuration, the output chief rays 117a and 117b exiting the second expanding element 61 b are substantially parallel to each other. The NAE 60 in the configuration of Figs. 10a-b is thus not substantially sensitive to the alignment of the incoming beams 110. This is in contrast with the NAE 60 comprising a single expanding element 61 where a misalignment of the modulated beams 110 can have a steering effect on the expanded image beam 111.

[0046] Fig. 11 shows the implementation of the NAE 60 comprising the first and second expanding elements 61a-b in the configuration of Figs. 10a-b onto a holographic film 66. The expanding function can be combined with the turning function as in the previous examples.

[0047] In an embodiment, a wearable device comprises the near-eye light field projector 1 disclosed herein. The wearable device can be configured to be used as a virtual reality or augmented reality device and, in particular, as an augmented reality head mounted display. The wearable device can comprise virtual reality or augmented reality glasses. As illustrated in Fig. 12, the wearable device can be embodied in an eyeglass form factor that includes the light source 10, the SLM 20, the NAE 60, and the second imaging element 40. The second imaging element 40 isCreal3-13-PCTintegrated in the lenses of the glasses (the second imaging element 40 functions as a combiner that is transparent for the light from the real world, while it projects the expanded light beams 111 towards the user's eye 90).

[0048] In the case the optical function of the NAE 60 and the turning optical function are recorded in the NAE 60, the light source 10 can be arranged on the temples 201 / end pieces / hinges 202 of the glasses and the the optical function of the NAE 60 and the tuning optical function can be arranged into the lenses 203. In this configuration, the light source 10 projects the incident light beams 100 from the temples / end pieces / hinges towards the lenses 203 containing the NAE 60. The NAE 60 redirects the expanded light beams 111 towards the second imaging element 40 and the exit pupil 121, without using traditional optics. The second imaging element 40 can also be comprised in the lenses 203 of the glasses.Creal3-13-PCTReference Numbers and1 near-eye light field projector10 light source11 point-light source20 spatial light modulator (SLM)30 first image plane31 first image32 first imaging element33 second distance40 second imaging element, combiner50 collimating element60 numerical aperture expander (NAE)61 expanding element, lens 61a first expanding element 61b second expanding element 62 polarizer element63 quarter wave plate64 optical function65 imaging lens element66 holographic film67 object beam68 reference beam70 projection element71 light-source image plane90 eye92 retina 100 incident light beam110 modulated light beams 111 expanded light beams 112 incident numerical aperture (NA) 113 output numerical aperture (NA)114 incident angle 115 refraction angle 116 modulated beam chief ray 117 expanded beam chief ray118 real world light 121 exit pupil 123 second image 124 second image plane130 pupil 170 projection axis 201 temple 202 hinge6i incidence angleLB beam lateral sizeLE element lateral size R ratio D distanceCreal3-13-PCT

Claims

Claims1. A near-eye light field projector (1), comprising: a light source (10), comprising an array of a plurality of pointlight sources (11) and generating a plurality of incident light beams (100) illuminating a spatial light modulator (SLM) (20), the SLM (20) being configured to modulate the incident light beams (100) and project a plurality of modulated light-beams (110); a first imaging element (32), configured to project the plurality of modulated light beams (110) and form first images (31) at a first image plane (30); a second imaging element (40), configured to project the modulated light beams (110) and form second images (123) at a second image plane (124), the second images (123) defining an exit pupil (121); the modulated light beams (110) being incident onto a numerical aperture expander (NAE) (60) arranged between the first and second imaging elements (32, 40); wherein the NAE (60) comprises a first plurality of expanding elements (61) and is configured to project expanded image light beams (111), each expanded image light beam (111) having a larger numerical aperture and beam divergence angle relative to those of the modulated light beams (110); wherein a ratio (R) of the element lateral size (LE) of each of the expanding elements (61) to the beam lateral size (LB) of the expanded image light beam (111) is between 0.5 and 1.5.

2. The light field projector according to claim 1, wherein the NAE (60) is arranged at a distance between 10 cm on each side of the first image plane (30).Creal3-13-PCT3. The light field projector according to claim 2, wherein the NAE (60) is arranged at a first distance corresponding to the location of the first image plane (30).

4. The light field projector according to any one of claims 1 to 3, wherein the NAE (60) comprises a refractive lens array including a plurality of lenslets, said first plurality of expanding elements (61) corresponding to the lenslets.

5. The light field projector according to any one of claims 1 to 3, wherein the NAE (60) comprises holographic optical element (HOE), wherein the optical function of said first plurality of expanding elements (61) is recorded into the HOE.

6. The light field projector according to claim 5, wherein a turning function is further recorded in the NAE (60), such that the NAE (60) in configured to change the direction of the modulated light beams (110) incident on the NAE (60) such as to direct the expanded image light beam (111) towards the second imaging element (40) with an output angle (0out) relative to the projection axis (170).

7. The light field projector according to claim 6, configured such that the modulated light beams (110) is incident on the NAE (60) with an incidence angle (0i) smaller than 90° and greater than 0° relative to the plane of the NAE (60); and the expanded image light beams (111) transmitted by the NAE (60) are projected substantially perpendicular to the surface of the NAE (60).

8. The light field projector according to any one of claims 5 to 7, wherein the NAE (60) comprises at least one further recorded optical function other than that of said first plurality of expanding elements (61).Creal3-13-PCT9. The light field projector according to claim 8, wherein said at least one further recorded optical function comprises any one alone or in combination: aperture array, mirrors array, axicon array, Fresnel lens array, meta lens array, or angularly multiplexed holograms.

10. The light field projector according to any one of claims 1 to 9, wherein the second imaging element (40) comprises an optical combiner, such as to transmit light incoming from the real world.

11. The light field projector according to any one of claims 1 to 10, wherein the NAE (60) is arranged at a distance between 10 cm on each side of the first image plane (30).

12. The light field projector according to claim 11, wherein the NAE (60) is arranged at the first image plane (30).

13. The light field projector according to any one of claims 1 to 12, wherein the second imaging element (40) is arranged at a distance from the first image plane (30) that corresponds to the focal length of the second imaging element (40).

14. The light field projector according to any one of claims 5 to 13, wherein the NAE (60) and the second imaging element (40) are arranged as a pancake lens.

15. The light field projector according to claim 14, wherein the NAE (60) further comprises a polarizer element (62) and quarter wave plate (63).

16. The light field projector according to any one of claims 5 to 15, wherein the NAE (60) comprises said first plurality of expanding elements (61a) having a first focal length (f 1 ), and a second plurality of expandingCreal3-13-PCTelements (61 b) having a second focal length (f2); wherein the first focal length (f 1 ) is larger than the second focal length (f2).

17. The light field projector according to claim 16, wherein the distance between the first and second plurality of expanding elements (61a, 61 b) is substantially equal to the sum of the first and second focal lengths (f 1 , f2).

18. A wearable device configured to be used as a virtual reality or augmented reality device and comprising the light field projector (1) according to any one of claims 1 to 17.Creal3-13-PCT

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