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    • 专利摘要:
    An image projecting device (30) comprising: at least one waveguide (32i) formed in a substrate (34); and at least one extraction device (37i) comprising a plurality of extraction cells (39ij) coupled to distinct areas of the guide (32i), each cell (39ij) being electrically activatable to extract light from the guide and project this light in a predetermined direction of projection (d39ij), in which different extraction cells (39ij) have directions of projection (d39ij) of distinct orientations.
    公开号:FR3022642A1
    申请号:FR1455845
    申请日:2014-06-24
    公开日:2015-12-25
    发明作者:Christophe Martinez
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    [0001] B13228 - DD14953JBD 1 DEVICE FOR PROJECTING AN IMAGE Domain The present application relates to a device for projecting an image. It relates in particular to a projection device that can be used in an augmented reality image display device intended to be worn on the head, without however being limited to this particular application domain. PRIOR ART DISCLOSURE The augmented reality image display consists in superimposing, on an image of the real world, an image containing additional information for an observer, for example information on his environment, his position, speed of movement, etc. Augmented reality image display devices intended to be worn on the head are generally designated by the acronym HMD, of the English "Head Mounted Display". Such devices may include a semitransparent blade placed a few millimeters or centimeters from the eye of a user and inclined at 45 degrees to the average optical axis of the eye, through which the user can see in transparency a real scene. A miniaturized projection device is provided to display information on the semi-transparent slide so that this information is perceived by the user as being integrated into the actual scene viewed through the slide. The existing devices, however, have various drawbacks, especially in their relatively large size, as well as in the relatively low light output and the relatively small angular field of the projection device. SUMMARY An object of an embodiment is to provide an image projection device overcoming all or part of the disadvantages of the existing projection devices, this device being particularly suitable for use in an image display device in reality. augmented to be worn on the head, or able to be used for other applications. Thus, an embodiment provides an image projection device comprising: at least one waveguide formed in a substrate; and at least one extraction device comprising a plurality of extraction cells coupled to discrete areas of the guide, each cell being electrically activatable for extracting light from the guide and projecting the light in a predetermined projection direction, wherein different extraction cells have separate orientation projection directions. According to one embodiment, each extraction cell comprises: a diffraction grating coating a portion of a face of the guide; an electrically controllable refractive index layer covering the array; and at least one control electrode of the refractive index of said layer. According to one embodiment, separate extraction cell diffraction gratings have distinct pitches or orientations with respect to a longitudinal direction of the guide. According to one embodiment, each extraction cell comprises a holographic element superimposed on the controllable refractive index layer, adapted to orient, in the projection direction of the cell, the light extracted from the guided by the diffraction grating of the cell. According to one embodiment, the diffraction gratings of the different cells have the same pitch and the same orientation with respect to a longitudinal direction of the guide. According to one embodiment, the projection device comprises a plurality of waveguides formed in the substrate and a plurality of extraction devices, each waveguide being coupled to one of the extraction devices.
    [0002] According to one embodiment, the different extraction devices all have the same number of extraction cells, and the cells of the same rank of the different extraction devices have their control electrodes connected, the rank of a cell of extraction corresponding to its positioning order, relative to the other cells of the same extraction device, between first and second ends of the guide which is coupled the extraction device. According to one embodiment, several waveguides 20 are optically connected, that is to say they are adapted to be supplied with light by the same light source. According to one embodiment, a plurality of extraction cells coupled to distinct optically connected waveguides have parallel projection directions.
    [0003] According to one embodiment, in each extraction device, several extraction cells are electrically connected, these cells having parallel projection directions. According to one embodiment, the extraction cells are distributed unevenly over the surface of the device. BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages will be set forth in detail in the following description of particular embodiments in a non-limiting manner with reference to the accompanying figures, in which: FIGS. and 1B schematically illustrate optical vision principles conditioning the perception of a scene by an observer; Fig. 2 is a perspective view schematically illustrating an example of an embodiment of an image projection device; FIGS. 3A and 3B are partial perspective views illustrating in more detail, in two operating configurations, an exemplary embodiment of the projection device of FIG. 2; Fig. 4 is a partial perspective view illustrating in more detail another embodiment of the projection device of Fig. 2; Figures aA-5C are diagrams illustrating the behavior in the eye of an observer of different types of light beams; Fig. 6 is a top view schematically illustrating an example of an embodiment of an image projection device; FIGS. 7A-7C schematically show various configurations of an image projection device, and for each configuration, the perception, for an observer, of the projection of a point image; Fig. 8 is a top view schematically illustrating an example of an embodiment of an image projection device; and Figs. 9A and 9B are sectional views schematically and partially illustrating an example of a method of making an image projection device. DETAILED DESCRIPTION For the sake of clarity, the same elements have been designated with the same references in the various figures and, in addition, the various figures are not drawn to scale. Otherwise, in the remainder of the description, unless otherwise indicated, the terms "approximately", "substantially", "about", "almost" and "of the order of", mean "at 10%". "or, when referring to angular or assimilated references," within 5 degrees ", and directional references such as" lateral "," below "," above "," upper ", "Lower", "overcoming", etc., apply to devices oriented in the manner illustrated in the corresponding views, it being understood that, in practice, these devices may be oriented differently. Figures 1A and 1B schematically illustrate optical vision mechanisms conditioning the perception of a scene by an observer. Figure lA illustrates the path of light rays 15 between a real object 10 and an eye 12 of an observer. As shown in the figure, each point of the object 10 produces a beam 14 of light rays captured by the pupil 16 of the eye. The beam 14 is focused by the eye at a point of the retina 18. A viewing angle α of a point of the object 10 is called the angle formed between the main optical axis X of the gaze and the direction main d14 of the beam 14 emitted by the object point - that is to say the direction passing through the object point and the optical center of the eye (point by which the incoming rays are not deflected). The angle α determines the size of the image of the object formed on the retina. Furthermore, the physiological modifications allowing the eye 12 to ensure the sharpness of the images formed on the retina 18 for different viewing distances between the object 10 and the eye 12 are called accommodation. By way of example, if the distance d is sufficiently large, the radii of the beam 14 emitted by a point of the object 10 can be considered as being parallel. On the other hand, if the distance d is small, the beam 14 may have a certain angle of divergence. The human eye is naturally capable, by physiological modifications, in particular by the deformation of the crystalline lens, of accommodating so as to ensure the sharpness of the image formed on the retina for different distances d, that is that is, to ensure that the image of a point of the object 10 is always punctual or considered as such. The feeling of accommodation allows the observer to evaluate the size of the object vis-à-vis the viewing angle of the object. In particular, it allows the observer to discriminate a small object located near the eye of a larger object located at a greater distance from the eye. As illustrated in FIG. 1B, if it is desired to artificially generate the vision of a scene by means of a projection device 20 situated at an arbitrary distance from the eye, it is desirable that the device 20 be adapted to generate light beams 14 'of substantially the same angular orientation α and of the same degree of divergence as the beams 14 emitted by the points of the real object, in order to give the illusion of the two aforementioned effects of angle of vision and accommodation at a desired distance d.
    [0004] Existing projection devices generally comprise an imager adapted to form an artificial image of the object in a display plane located outside the eye (for example a matrix of pixels of light display or a device adapted to project an image on a diffuser screen), and an optical system located between this display plane and the eye, adapted to shape the artificial image of the object so as to give the illusion of the aforementioned effects of angle of vision and accommodation. According to one aspect of the described embodiments, there is provided here an image projection device not comprising an imager in the conventional sense of the term, that is to say an imager adapted to generate an artificial image of a scene in a plane outside the eye. More particularly, there is provided here a projection device adapted to form an image directly on the retina of the observer, by a suitable set of laser emissions. Fig. 2 is a perspective view schematically illustrating an example of an embodiment of an image projection device 30. The projection device 30 comprises N optical waveguides 32i formed in a transparent substrate 34, for example a glass substrate, where N is an integer greater than or equal to 1 and i is an integer in the range of from 1 to N. In the example shown, N is equal to 3. However, the described embodiments are not limited to this particular case. In this example, each waveguide 32i is in the form of a straight ribbon extending in the longitudinal direction of the guide between first and second ends 35a and 35b of the guide, and the different guides 32i are substantially identical and parallel. between them. In this example, the waveguides 32i are located in a same mean plane approximately parallel to a face 34a of the substrate 34, that is to say that each guide has its main faces 35ci and 35di, or faces of more large areas, approximately parallel to the face 34a of the substrate, the 35ci faces of the different guides on the one hand and the faces 35di of the various guides on the other hand being approximately coplanar. The reference 35ci here designates the main face of the guide 32i the closest to the face 34a of the substrate, and 35di reference designates the main face of the guide 32i farthest from the face 34a of the substrate. In this example, the end faces 35ai of the different guides on the one hand and the end faces 35bi of the various guides on the other hand are substantially coplanar, orthogonal to the face 34a of the substrate, and orthogonal to the longitudinal direction guides. The projection device 30 further comprises N light extraction devices 37i, each extraction device 37i being coupled to the waveguide 32i of the same index 35 i via the main face 35ci of the guide. Each light extracting device 37i comprises M extraction cells 39ij coupled to discrete areas of the 35ci face of the guide 32i, where M is an integer greater than or equal to 2 and j is a whole number in the range from 1 to M. In the example shown, M is equal to 4. However, the described embodiments are not limited to this particular case. In this example, in each extraction device 37i, the cells 39ij are arranged at a regular spacing along substantially the entire length of the corresponding guide 32i, in order of index increasing between the end 35ai and the end 35bi of the guide. . In this example, the extraction cells 39ij of the same index or rank j are aligned in a direction approximately orthogonal to the longitudinal direction of the guides. Each cell 39ij is electrically activatable and is adapted, when activated, to extract light propagating in the guide 32i and to project this light to the outside of the device 30 in a predetermined direction dij. When a cell 39ij is deactivated, it has no effect on the light flowing in the guide 32i.
    [0005] According to one aspect of the described embodiments, in each extraction device 37i, separate extracting cells 39ij having projection directions of ij of distinct orientations with respect to the face 35ci of the corresponding guide 32i. In the example shown, the orientations 25 of the projection directions d1ij extraction cells 39ij with respect to the upper face 34a are all different from each other. The projection device 30 is intended to be positioned in front of an observer so that the beams projected by the different extraction cells 39j1 all reach the pupil of an eye 12 of the observer. The projection device 30 further comprises N laser emission sources 41i individually controllable in intensity. Each laser source 41i is adapted to inject into the guide 32i of the same rank i, a monochromatic or polychromatic light beam 35 of constant orientation adapted to propagate in the guide, for example a beam of parallel radii to the longitudinal direction of the guide 32i. In the example shown, each laser source 41i is coupled to the guide 32i of the same rank i via the end 35ai of this guide.
    [0006] The operation of the projection device 30 is as follows. During the projection of an image, the N laser sources 41i are fed, and in each extraction device 37i, the extraction cells 39ij are successively activated by a control circuit (not shown) to project, in the different projection directions dij of the extraction device 37i, the light emitted by the corresponding source 41i. When activating a cell 39ij, the control circuit controls the transmission power of the corresponding laser source 41i, so as to modulate the light intensity emitted by the device 30 as a function of the projection angle . Each extraction cell 39ij, when activated, projects a light beam corresponding to a pixel of the image. The orientation of the projection direction dij of each cell 39ij is chosen according to the desired viewing angle for the corresponding pixel. The device 30 of FIG. 2 is thus adapted to project an image of N * M pixels. In this example, in each extraction device 37i, a single extraction cell 39ij is activated at a time. The extraction cells 39j of the same rank of the different extraction devices 37i can for example be activated simultaneously so as to project the image line by line. FIGS. 3A and 3B are perspective views illustrating in more detail a portion of an exemplary embodiment of the projection device 30 of FIG. 2 in two distinct operating configurations. More particularly, FIGS. 3A and 3B show a portion of a waveguide 32i of the device 30 and an exemplary embodiment of an extraction cell 39j coupled to this waveguide. Fig. 3A shows the cell 39ij in the idle state, and Fig. 3B shows the cell 39ij in the active state. In the example of FIGS. 3A and 3B, the extraction cell 39ij comprises a diffraction grating 51ij coupled to the guide 32i by an area of its face 35ci. The diffraction grating 51ij consists essentially of a structure made of a transparent material having a first flat face in contact with the face 35ci of the guide, and a second face opposite to the first face having parallel grooves that are regularly spaced, for example approximately orthogonal to the longitudinal direction of the guide 32i. The diffraction grating 51ij may be formed in the substrate material 34 on the side of the substrate face 34a if the waveguide 32i is buried under the face 34a of the substrate. Alternatively, the diffraction grating 51ij may comprise a grooved layer of a transparent material coating the face 34a of the substrate. The cell 39ij further comprises a layer 53ij of a transparent material coating the grooved surface of the diffraction grating 51ij, and whose face opposite to the grooved surface of the grating 51ij is approximately flat. The layer 53ij is made of a material whose refractive index can be electrically controlled by applying a bias voltage. The layer 53ij is for example a liquid crystal layer. The cell 39ij further comprises electrodes for applying a bias voltage to the layer 53ij to modify its refractive index. For the sake of clarity, these electrodes have not been shown in Figures 3A and 3B. By way of example, the grooved layer of the diffraction grating 51ij may be made of an electrically conductive material, for example indium tin oxide (ITO), and serve as an electrode for the application of a voltage of polarization at layer 53ij. A second, approximately flat transparent electrode, for example made of ITO, can coat the flat face of the layer 5ij. Other arrangements of the bias electrodes of the layer 53 may, however, be provided. For example, the electrodes may be disposed on the lateral faces of the layer 53ij. When a suitable bias voltage Voff 5 (FIG. 3A), for example equal to 0 V, is applied to the layer 53ij, the refractive index of the layer 53ij is identical or almost identical to that of the grooved layer of the grating 51ij, which causes the inactivation of the optical diopter formed between the grooved face of the network 51ij and the layer 53ij. The cell 39ij is then in a state that is called here inactive state, that is to say that the laser beam guided by the waveguide 32i, when it passes through the coupling zone between the guide 32i and the cell 39ij is not disturbed by the cell 39ij and continues to propagate in the guide to the next extraction cell. When a suitable bias voltage Von (FIG. 3B), different from VOff, is applied to the layer 53ij, the refractive index of the layer 53ij is modified, which causes the activation of the diopter formed between the grooved face of the Network 51ij and the layer 53ij. The cell 39ij is then in a state that is called here active state, that is to say that the laser beam guided by the waveguide 32i interacts with the network 51ij when it passes through the coupling zone between the guide 32i and the cell 39ij. Part of the guided wave is then extracted from the guide, and is projected in a direction forming an angle R (of the order of 90 degrees in the example shown) with the longitudinal direction of the guide. For a given wavelength of the guided light, the angle R depends in particular on the pitch of the grating 51ij of the cell.
    [0007] Furthermore, the direction of projection of the light extracted by the cell forms an angle γ (of the order of 90 degrees in the example shown) with the transverse direction of the guide. This angle depends in particular on the orientation of the grooves of the network 51ij.
    [0008] In an exemplary embodiment of the projection device of FIG. 2, the gratings 51ij of the various extraction cells 39ij of the device have different steps and / or different orientations with respect to the longitudinal direction of the waveguide. , which makes it possible to obtain the different desired orientations of the projection directions of 39ij cells. FIG. 4 is a perspective view schematically and partially illustrating another embodiment of the projection device of FIG. 2. More particularly, FIG. 4 represents a portion of a waveguide 32i of the device 30, and three extraction cells 39ij-1, 39ij and 39ij + 1 coupled to distinct areas of the 35ci face of the guide 32i.
    [0009] In the example of FIG. 4, each extraction cell 39ij comprises the same elements as in the example of FIGS. 3A and 3B, that is to say a diffraction grating 51ij coupled to the guide 32i by a zone its face 35ci, a layer 53ij of electrically controllable refractive index, coating the grooved face of the grating 51ij, and at least one electrode 55ij for controlling the refractive index of the layer 53ij, or activation electrode / inactivation of the cell. For the sake of simplification, only a control electrode 55ij of the cell 39ij has been shown in FIG. 4.
    [0010] A difference between the exemplary embodiment of FIGS. 3A and 3B and the exemplary embodiment of FIG. 4 is that, in the example of FIG. 4, the networks 51ij of the different extraction cells 39ij of the projection device are all substantially identical, i.e. they all have the same pitch and orientation with respect to the longitudinal direction of the guide. Thus, in the example of FIG. 4, the directions of projection of the light at the output of the networks 51ij of the different cells 39ij all have substantially the same orientation with respect to the 35ci faces of the guides. In the nonlimiting example shown, the projection direction of the light at the output of the gratings 51ij is approximately orthogonal to the plane of the faces 35ci of the guides. In the exemplary embodiment of FIG. 4, each cell 39ij further comprises a holographic element 60ij disposed opposite the variable index layer 53ij, in the path of the light extracted from the guide by the network 51ij when the cell is in the active state. The holographic element 60ij is adapted to orient the light beam extracted from the guide 32i in the projection direction dij desired for the cell 39ij. In the case of the projection device 30 of FIG. 2, the holographic elements 60ij of the different cells 39ij all have different orientation properties. In the example shown in FIG. 4, the holographic orientation elements 60ij are reflective orientation elements. Alternatively, transmissive orientation holographic elements may be used. An advantage of the embodiment of Figure 4 is related to the fact that the diffraction gratings 51ij of the projection device are all substantially identical, which facilitates their realization. An exemplary method for manufacturing the holographic orientation elements 60ij of the device of FIG. 4 will be described below in relation to FIGS. 9A and 9B.
    [0011] As a nonlimiting example of dimensioning, the waveguides 32i may be refractive index guides of the order of 1.52, formed in a substrate 34 of index of the order of 1, 5, and having a width of about 800 nm and a thickness of about 500 nm. The sources 41i are, for example, adapted to emit a laser beam at a wavelength of the order of 650 nm. In the embodiment of FIG. 4, the diffraction gratings 51ij may have a pitch of approximately 430 nm. The area of the emission zone of each of the extraction cells 39ij is, for example, between 1 and 20 gm 2.
    [0012] The inventors have found that, for certain sizing of the projection device, especially when the emission zones of the extraction cells 39ij of the projection device are small, for example when they have a surface. less than or equal to 5 pm2, the beams projected by the various extraction cells 39ij of the device may have a non-negligible divergence angle, which the eye may be unable to accommodate. In this case, the image on the retina of a light beam projected by an extraction cell 39ij of the device will not be a dot, but a relatively large spot that the observer will perceive as a hazy halo. FIGS. 5A to 5C illustrate this phenomenon as well as an example of a solution that can be implemented so that the user perceives sharp images even when the emission zones of the extraction cells of the projection device are short. Figure aA shows the shape taken, inside the eye, by a light beam 70 issuing from a point of an object on which the eye is able to accommodate its vision, for example a point d 'an object located at infinity. FIG. 5A further represents, in the form of a diagram, the spatial distribution of the light energy of the beam 70 received by the retina 18 at the bottom of the eye. As it appears in the figure, the eye transforms the wavefront of the incident beam (which is for example a plane wavefront in the case of an infinite object) into a wavefront. The beam energy 70 is then concentrated in a point zone or considered as such of the retina 18. The observer thus actually perceives a point. The angle of vision a (see FIG. LA) of the incident beam fixes the position of this point (or center of convergence of the circular wavefront) on the retina. FIG. 5B shows the shape taken, inside the eye, by a light beam 72 having a divergence angle that the eye is unable to accommodate, for example a beam divergent light emitted by an extraction cell 39ij a projection device of the type described in relation to Figures 2 to 4 when the emission surface 5 of this cell is small. FIG. 5B also represents the spatial distribution of the light energy of the beam 72 received by the retina 18 at the bottom of the eye. The eye transforms the wavefront of the incident beam (which is for example a circular wavefront centered on the beam emission source) into a plane wavefront or a centered circular wavefront. on a point behind the retina 18 - that is to say on the side of the retina 18 opposite the pupil. The energy of the beam 72 is thus distributed in a relatively wide area of the retina 18. The observer therefore does not perceive a point but a hazy halo whose position on the retina is fixed by the angle of vision a. emission point. FIG. 5C illustrates a solution that can be implemented to reconstitute, within the eye, the illusion of a circular wavefront centered on a point of the retina, from a plurality beams each having, outside the eye, a relatively large divergence angle, for example beams emitted by extraction cells with a small emission surface of a projection device of the type described in connection with Figures 2 to 4.
    [0013] In this example, several diverging light beams 74 corresponding to the same pixel of the image to be displayed, are emitted simultaneously in the direction of the eye, from distinct areas of the projection device (i.e. separate extraction cells of the device), with parallel projection directions converging at one and the same point of the retina. FIG. 5C shows the shape taken, inside the eye, by each of the beams 74. FIG. 5C also represents the spatial distribution of the light energy of the beams 74 received by the retina 18 at the bottom of the beam. 'eye. As shown in the figure, the eye transforms the wavefront of each beam 74 (which is for example a circular wavefront centered on the beam emission source) into a front edge. plane wave or a circular wavefront centered on a point located behind the retina 18. If the different beams 74 are coherent and suitably tuned in phase, the wave fronts constructively interfere at the point of convergence on the retina 18. This gives a focusing effect by multiple interferences. The energy of the beams 74 is thus concentrated in a point zone or can be considered as such of the retina 18. In other words, by multiplying the beams 74, it is possible to reconstitute, inside the eye, an assembly of wave fronts that espouses a circular wavefront shape of the type described in connection with FIG. The observer then perceives a point whose position on the retina depends on the orientation of the incident beams. Figure 6 is a top view schematically illustrating an exemplary embodiment of an image projection device 80 adapted to perform an operation of the type described in connection with Figure 5C. The projection device 80 is adapted to project an image of N * M pixels. In the illustrative and nonlimiting example shown, N = M = 4. The projection device 80 comprises k * N optical waveguides 82p formed in a transparent substrate (not shown), where k is an integer greater than or equal to 2 and p is an integer in the range of 1 at k * N. In the example shown, k is equal to 3. The waveguides 82p of the projection device 80 of FIG. 6 have, for example, substantially the same straight ribbon shape as the guides 32i of the device of FIG. 2, and may be arranged substantially in the same manner (ie parallel to each other, aligned, arranged in the same middle plane, and regularly distributed along a direction orthogonal to the length of the guides).
    [0014] The projection device 80 further comprises k * N light extraction devices 87p, each extraction device 87p being coupled to the waveguide 82p of the same index p. Each extraction device 87p comprises the electrically activatable / electrically deactivatable extractor cells 85Pq, coupled to distinct areas of the guide 82p, where 1 is an integer greater than or equal to 2 and q is an integer within the range of ranging from 1 to 1 * M. In the example shown, 1 is equal to 3. The extraction cells 89pq are, for example, cells of the type described with reference to FIGS. 3A, 3B or 4. In this example, the 89pq cells of the same device extraction 87 are regularly distributed along the corresponding guide 82p, and 89pq cells of the same rank q are aligned in a direction orthogonal to the length of the guides 82p. In the example shown, the 89pq cells of the same rank q can be activated or deactivated simultaneously via the same control electrode 91q, to allow line-by-line display of the images. Each cell 89pq is adapted, when activated, to extract light propagating in the guide 82p and to project this light out of the device in a predetermined direction d89pq (not shown in FIG. 6). When a 89pq cell is turned off, it has no effect on the light flowing in the guide 82p. The projection device 80 further comprises N 25 intensity-controllable laser emission sources 93i, each laser source 93i being coupled to k waveguides selected from the k * N waveguides 82p of the device. Each laser source 93i is adapted to inject simultaneously, into the k waveguides to which it is coupled, a constant orientation light beam 30 adapted to propagate in these guides. In the example shown, the k waveguides coupled to the same laser source 93i are arranged at regular spacing along the dimension of the device 80 orthogonal to the length of the guides. More particularly, in the example shown, the waveguides 14 coupled to the same laser source 93i are the guides 82i, 82i + k, 82i + s * k, with s integer such that i + s kk * * N. Moreover, in the projection device 80 of FIG. 6, each extraction device 87p comprises M 5 groups of 1 extraction cells 89pq connected - that is to say, activatable or deactivatable simultaneously via the same control electrode . In the example shown, each group of 1 89pq cells connected to the same extraction device 87 has its cells regularly distributed over the entire length of the corresponding guide. More particularly, in the example shown, in each extraction device 87p, each group of 1 connected cells of index j (j ranging from 1 to M) comprises the cells 89pj, 89pj + 1, 89pj + t * 1, with integer t such that j + t * 11 * M. In the example shown, the projection device 80 comprises M control terminals Ej, each terminal Ej being connected to the electrodes 91j, 91j + 1, 91j + t * 1. The operation of the projection device 80 is as follows. To display a coordinate pixel i, j of the image, the laser source 93i is turned on at the desired intensity for that pixel, and the control terminal Ej is set to a potential to activate the 89pq cells to which it is connected. A group of k * 1 extraction cells regularly distributed over the entire surface of the device 80 is then in the active state and powered optically by the same laser source 93i. The set of beams projected by the cells of this group corresponds to the display of the pixel of coordinates i, j of the image. These beams coming from the same laser source 93i are coherent and can be adapted in phase. The cells in the group all have substantially the same projection orientation, chosen according to the desired viewing angle for the pixel. It is thus possible to obtain the effect described with reference to FIG. 5C for reconstituting a circular wavefront centered on a point of the retina whose position depends on the angle of vision desired for the pixel. By way of example, the N laser sources 93i can be switched on simultaneously and the M electrodes Ej can be successively turned on so as to project the image line by line. Preferably, in the same set of extraction devices 87p coupled to the same laser source 93i, only one group of interconnected extraction cells is activated at a time. FIGS. 7A-7C schematically show various configurations of an image projection device, and, for each configuration, the perception, for an observer, of the projection of a point image. FIG. 7A illustrates the case of a projection device 30 of the type described with reference to FIG. 2, in which the projection of a pixel of the image is carried out by a single extraction cell 39ij. We consider here the case where the emission surface of the cell 39ij is relatively small, typically less than or equal to 5 gm2. As it appears in the right-hand part of FIG. 7A, when a point image, ie a single-pixel image, is projected, the user perceives a blurry light halo spread over a large part of the image. of the retina. FIG. 7B illustrates the case of a projection device 80 of the type described in relation to FIG. 6, in which the projection of a pixel of the image is carried out by a group of several extraction cells 89 pq of the same type. orientation regularly distributed over the entire surface of the projection device, to obtain a multi-interference focusing effect of the type described in connection with Figure 5C. Consider the case where the emission area of each 89pq cell is relatively small, typically less than or equal to 5μm 2. As appears in the right-hand part of FIG. 7B, when a point image, that is to say a single-pixel image, is projected, the user perceives a point, at a position of the retina corresponding to the viewing angle wished for this pixel. However, as shown in Fig. 7B, the observer further perceives, in addition to this point, a plurality of parasitic dots evenly distributed on the surface of the retina. This parasitic repetition of the image point results from the periodic distribution of the emitted beams for the display of the same image pixel, which leads to a resonance effect on the phase chords. This effect is explained by the notion of decomposition of the circular wavefront (desired inside the eye) into an angular spectrum. The larger angle of the spectrum sets the focus point width, and the spectrum distribution step sets the repeat pitch of the projected pattern on the focus point. Depending on the angular distribution pitch chosen for the spectrum, parasitic resonances may occur on the observer's retina and thus be perceived by the observer, which may be problematic in some applications. FIG. 7C illustrates the case of a projection device 100 similar to the device 80 of FIGS. 6 and 7B, but in which the projection of a pixel of the image is carried out by a group of several interconnected extraction cells 89pq. irregularly distributed on the surface of the projection device, for example distributed randomly or pseudo-randomly on the surface of the projection device. As before, consider the case where the emission area of each cell 89pq is relatively small, typically less than or equal to 5 pm2. As appears in the right-hand part of FIG. 7C, when a point image, that is to say a single-pixel image, is projected, the user perceives a point, at a position of the retina corresponding to the viewing angle desired for this pixel, and the repetition effect of this observed point in the configuration of Figure 7B does not occur. The inventors have indeed found that when the distribution of the emission zones is irregular, the wave fronts all interpenetrate only at the point of convergence of the main axes of the beams on the retina.
    [0015] For an uneven distribution of the emission zones corresponding to the same pixel of the image, a first option is to adapt the device of FIG. 6 so that the waveguides 82p supplied with light. by a same laser source 93i are irregularly distributed along the dimension of the orthogonal device to the length of the guides, and / or so that, in each extraction device 87p, the cells 89pq of the same group activatable cells deactivatable simultaneously by the same control electrode 10 are irregularly distributed along the longitudinal dimension of the guides. A second option that may be provided in combination with the first option or independently is to provide non-rectilinear 82p waveguides, of irregularly shaped coils, and / or non-rectilinear 91q electrodes, of irregularly shaped coils. FIG. 8 is a top view schematically illustrating an exemplary embodiment of an image projection device 100 of the type described in connection with FIG. 6, adapted on the basis of the first and second options mentioned above so as to obtain an irregular distribution of 89pq extraction cells interconnected optically and electrically corresponding to the same pixel of the image to be displayed. In the nonlimiting example represented, N = 5, M = 4, 25 k = 7 and 1 = 4. In FIG. 8, the l * k extraction cells 89pq used for displaying the pixel of coordinates i = 1 and j = 1 of the image are represented by black dots. An advantage of the projection devices described in connection with FIGS. 2 to 8 is their small size, high light output, and the many possibilities they offer in terms of field of view and / or accommodation. It will be noted in particular that, in terms of size, an advantage of the proposed devices is that they can be placed directly in front of the eye of a user, without an intermediate optical system and without a semi-circular deflection blade. 22 reflective. In addition, the proposed devices are compatible with the visualization of a real scene by transparency through the device, in particular because of the transparency of the materials used to manufacture the device. In particular, the diffractive effects of the various optical components (networks or holograms) are limited with respect to the beams coming from the external scene. This is due in particular to the low pitch of the structures (for example of the order of 400 nm) and the small index differences involved. To increase the size of the eye box, that is to say the zone in which the eye of the user can move in front of the projection device while continuing to see the entire image, it can be expected to replicate the structures described, so that for each pixel of the image, several beams or sets of beams of the same angular orientation are emitted simultaneously from separate areas of the projection device, by separate extraction cells. By way of example, in the projection device 20 of FIG. 2, to increase the size of the eye box in the longitudinal direction of the guides 32i, it is possible to extend the guides 32i and to replicate one or more times the structure formed by the extraction devices 37i in the longitudinal direction of the guides.
    [0016] In order to increase the size of the eye box in the transverse direction of the guides 32i, provision may be made to replicate the entire device one or more times in the transverse direction of the guides. In the same way, it is possible to increase the size of the eye box in the longitudinal direction of the guides and / or in the transverse direction of the guides in a projection device of the type described in relation to FIGS. 6 and 8. by replicating the structures described on a larger surface. Figs. 9A and 9B are sectional views schematically and partially illustrating an example of a method of manufacturing an image projection device of the type described above. More particularly, FIGS. 9A and 9B illustrate an exemplary method of manufacturing the holographic orientation elements in a projection device comprising extraction cells of the type described with reference to FIG. 4. FIG. 9A illustrates a structure comprising in a transparent substrate 34, one or more waveguides 82i, and, coupled to each waveguide, a plurality of extraction cells 89pq each comprising a diffraction grating 51pq covered by a variable index layer 53pq, and a control electrode 55pq of the layer 53pq. Above this structure, on the path of the light at the output of the diffraction gratings 51pq, is disposed a layer 110 made of a holographic material. In the example shown, the layer 110 extends over substantially the entire surface of the projection device. Alternatively, the holographic material may be arranged only facing the emission surfaces of diffraction gratings 51pq.
    [0017] To form, in one or more extraction cells 89pq, a 60pq holographic element having a particular orientation angle, a laser beam emitted by the same source is split into two channels. A first channel 112 is shaped and injected into the waveguide (s) 32p to which the 89pq cells concerned by this angle are coupled. A second channel 114 is collimated and extended to cover substantially the entire surface of the projection device. This second channel is projected on the layer 110 with the desired viewing angle for the cells concerned. The cells concerned are then activated electrically via their control electrodes, so that the diffraction gratings 51pq ensure the extraction of the signal in the cells concerned. Opposite each of the optically and electrically activated cells, the holographic material of layer 110 records an interference pattern. At the end of this step, as shown in FIG. 9B, the exposed portions of the layer 110 have the desired orientation properties. These portions form the orientation elements 60Pq of the cells concerned.
    [0018] Optionally, in order not to expose the portions of the layer 110 that are not affected by the angle considered, the exposure of the device to the beam 114 can be achieved through a programmable matrix of micro-mirrors adapted to limit the extent of the beam 114 to the only areas concerned by the angular orientation of the beam 114. The process can be repeated as many times as necessary by changing each time the orientation of the beam 114 and the optical and electrical addressing of the active extraction cells , so as to form the different orientation elements of the projection device. It will be noted that for a given angular orientation of the projection device, if the dimensions of the optical paths between the laser emission source and the various extraction cells concerned by this orientation are not carefully chosen, the projected beams at the output of the diffraction gratings of these cells are not tuned in phase. An advantage of the manufacturing method described in relation with FIGS. 9A and 9B is that the holographic elements 60pq corresponding to the same emission angular orientation will naturally take into account the phase dispersion of the beams at the output of the networks 51pq. Thus, once the holograms have been recorded, the orientation elements 60pq will not only have the effect of orienting the light injected into the device at the desired angle, but also of tuning in phase the different beams emitted simultaneously by the device. with the same angular orientation, thus making it possible to obtain a focusing effect by multiple interferences of the type described with reference to FIG. 5C.
    [0019] Particular embodiments have been described. Various variations and modifications will be apparent to those skilled in the art. In particular, the embodiments described are not limited to the numerical examples mentioned above, particularly in terms of the image size that can be projected by the proposed devices. In practice, devices capable of projecting images comprising several hundred to several tens of thousands of pixels may be provided. Alternatively, the projection device may comprise a single waveguide in the case where it is desired to project an image of a single line of pixels. In addition, the use of the projection devices proposed is not limited to the field of HMD augmented reality display devices 15. In particular, the projection devices proposed can be used to display images for the attention of a user without these images being intended to be superimposed on a real scene. In this case, it is not necessary for the projection device to be transparent.
    权利要求:
    Claims (11)
    [0001]
    REVENDICATIONS1. An image projection device (30; 80; 100) comprising: at least one waveguide (32i; 82p) formed in a substrate (34); and at least one extraction device (37i; 87p) comprising a plurality of extraction cells (39ii; 89pq) coupled to distinct regions of the guide (32i; 82p), each cell (39ii; 89pq) being electrically activatable for extracting light from the guide and projecting this light along a predetermined direction of projection (d39ij; d89pq), wherein different extraction cells (39ii; 89pq) have different directions of projection (d39ij; d89pq).
    [0002]
    The device of claim 1, wherein each extraction cell (39ii; 89pq) comprises: a diffraction grating (51) coating a portion of a face of the guide; an electrically controllable refractive index layer (53) overlying the array (51); and at least one refractive index control electrode (55) of said layer (53).
    [0003]
    The device (30; 80; 100) according to claim 2, wherein distinct diffraction gratings (51) of extraction cells (39ii; 89pq) have distinct pitches or orientations distinct from a longitudinal direction. of the guide (32i, 82p).
    [0004]
    The device (30; 80; 100) according to claim 2, wherein each extraction cell (39ii; 89pq) comprises a holographic element (60) superimposed on the controllable refractive index layer (53) adapted directing, in the direction (d39ij; d89pq) of projection of the cell, the light extracted from the guide (32i; 82p) by the diffraction grating (51) of the cell. 3022642 B13228 - DD14953JBD 27
    [0005]
    The device (30; 80; 100) according to claim 4, wherein the diffraction gratings (51) of the different cells (39ii; 89pq) have the same pitch and orientation with respect to a longitudinal direction of the guide (32i; 82p). 5
    [0006]
    The device (30; 80; 100) according to any one of claims 1 to 5, comprising a plurality of waveguides (32i; 82p) formed in the substrate (34) and a plurality of extraction devices (37i; 87p). each waveguide being coupled to one of the extraction devices.
    [0007]
    The device (30; 80; 100) according to claims 2 and 6, wherein the different extraction devices (37i; 87p) all have the same number of extraction cells (39ii; 89pq), and wherein the cells (39ii, 89pq) of the same rank of the different extraction devices (37i, 87p) have their control electrodes (55) connected, the rank of an extraction cell (39ii; 89pq) corresponding to its order of positioning, relative to the other cells of the same extraction device (37i; 87p), between first and second ends of the guide (32i; 82p) to which the extraction device is coupled.
    [0008]
    8. Device (80; 100) according to claim 6 or 7, wherein a plurality of waveguides (82p) are optically connected, that is to say they are adapted to be supplied with light by the same source luminous (93i). 25
    [0009]
    A device (80; 100) according to claim 8, wherein a plurality of extraction cells (89pq) coupled to distinct optically connected waveguides (82p) have parallel projection directions (d89pq).
    [0010]
    10. The device (80; 100) according to any one of claims 1 to 9, wherein in each extraction device (37i; 87p), a plurality of extraction cells (39ii; 89pq) are electrically connected; cells having parallel projection directions (d39ij; d89pq).
    [0011]
    Apparatus (100) according to any one of claims 1 to 10, wherein the extraction cells (89pq) are irregularly distributed over the surface of the device.
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    同族专利:
    公开号 | 公开日
    EP2960715B1|2018-10-24|
    FR3022642B1|2017-11-24|
    EP2960715A1|2015-12-30|
    US9632317B2|2017-04-25|
    US20150370073A1|2015-12-24|
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    2015-06-26| PLFP| Fee payment|Year of fee payment: 2 |
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    2016-07-08| PLFP| Fee payment|Year of fee payment: 3 |
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    2021-03-12| ST| Notification of lapse|Effective date: 20210205 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1455845A|FR3022642B1|2014-06-24|2014-06-24|DEVICE FOR PROJECTING AN IMAGE|FR1455845A| FR3022642B1|2014-06-24|2014-06-24|DEVICE FOR PROJECTING AN IMAGE|
    EP15172608.0A| EP2960715B1|2014-06-24|2015-06-17|Device for projecting an image|
    US14/743,628| US9632317B2|2014-06-24|2015-06-18|Image projection device|
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