US-12619078-B2 - Device for projecting an image formed by a screen

US12619078B2US 12619078 B2US12619078 B2US 12619078B2US-12619078-B2

Abstract

The invention relates to a device for projecting an image onto an eye, the device comprising: a light emitter, configured to emit light waves along various respective emission axes; an optical combiner, optically coupled to the light emitter, and configured to form, from each light wave emitted by the light emitter, a collimated light wave that propagates to the pupil of the eye; the device being characterized in that: the light emitter comprises a screen, comprising various pixels, each pixel being configured to emit a divergent light wave that propagates around an emission axis, the various pixels emitting respective divergent light waves that propagate along various emission axes, respectively; the optical combiner is configured to receive each light wave emitted by a pixel and to form a collimated light wave that propagates towards a central position corresponding to the centre of the pupil of the eye.

Inventors

Christophe Martinez

Assignees

COMMISSARIAT A L'ENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES

Dates

Publication Date: 20260505
Application Date: 20231229
Priority Date: 20221229

Claims (14)

1 . A device for projecting an image onto an eye, the device comprising: a light emitter, configured to emit light waves along various respective emission axes; an optical combiner, optically coupled to the light emitter, and configured to form, from each light wave emitted by the light emitter, a collimated light wave that propagates towards a pupil of the eye; wherein: the light emitter comprises a directional screen, comprising various pixels, each pixel being configured to emit a divergent light wave that propagates around an emission axis of the pixel, the various pixels emitting respective divergent light waves that propagate along various emission axes, respectively, each light wave propagating such as to make a divergence angle of the pixel to the emission axis of the pixel; the optical combiner is configured to receive each light wave emitted by a pixel and to form a collimated light wave that propagates towards a central position corresponding to the centre of the pupil of the eye; the device comprises a convergent lens interposed between the directional screen and the optical combiner, the convergent lens extending around a centre, the centre of the lens forming, with a centre of the combiner, an optical axis of the device; wherein the image of the directional screen, as generated by the convergent lens, is formed in an object focal plane of the optical combiner; the image of the centre of the convergent lens, as generated by the combiner, is formed at the central position; so that the collimated light wave, resulting from the combiner, reaches the central position at an angle dependent on the position of the pixel of the screen; and wherein the respective emission axes of the pixels converge to the centre of the convergent lens.
2 . The device of claim 1 , wherein the screen comprises a stack comprising: light guides, each light guide being coupled to a plurality of diffraction gratings, which are distributed over the length of the light guide, each diffraction grating being electrically modulatable, each diffraction grating being configured to be electrically modulated so as to extract light propagating through the light guide; electrodes, each electrode being associated with a plurality of diffraction gratings coupled to various light guides, respectively, each electrode being configured to modulate each diffraction grating with which it is associated; wherein: each pixel of the screen corresponds to an association between an electrode and a diffraction grating coupled to a light guide; when illuminated by light extracted from the light guide, each pixel is configured to emit a divergent light wave that propagates around the emission axis of the pixel, thereby forming an emission cone, defined by the divergence angle of the pixel around the emission axis of the pixel.
3 . The device of claim 2 , wherein the screen comprises a holographic film, which is subdivided into various elementary zones, each elementary zone being associated with the diffraction grating of one pixel, and configured to emit the divergent light wave, along the emission axis and at the divergence angle of the pixel, under an effect of light extracted by the diffraction grating with which it is associated.
4 . The device of claim 2 , wherein: a plurality of light guides are connected to the same light source; a light modulator lies between the light source and each light guide, so as to modulate an intensity of the light emitted by the light source and fed to each light guide.
5 . The device of claim 2 , comprising a plurality of light sources, each light source being optically connected to a plurality of light guides.
6 . The device of claim 2 , wherein various light sources are configured to emit light at various respective wavelengths.
7 . The device of claim 2 , wherein the pixels are arranged in: rows, each row being defined by one light guide, the light guide extending over the length of various pixels in the row; columns, each column being defined by one electrode, the electrode extending over the length of various pixels over the length of the column.
8 . The device of claim 1 , comprising: a plurality of convergent lenses aligned parallel to the directional screen, each convergent lens extending around a centre and having the same object focal plane; wherein the screen is placed parallel to each convergent lens; each convergent lens is associated with pixels of the directional screen; the emission axis of each pixel associated with the lens converges to the centre of the convergent lens with which said pixels is associated.
9 . The device of claim 1 , wherein: two adjacent pixels are separated by a spatial pitch; the screen comprises a central part, encircled by a peripheral part; the spatial pitch between two adjacent pixels of the central part is smaller than the spatial pitch between two adjacent pixels of the peripheral part.
10 . The device of claim 1 , wherein the combiner is a holographic combiner.
11 . The device of claim 10 , wherein: the screen emits light in at least one emission spectral band; the holographic combiner is transparent outside of the at least one emission spectral band; the holographic combiner forms a convergent lens in the at least one emission spectral band.
12 . The device of claim 11 , wherein the holographic combiner forms a reflector in the or each emission spectral band.
13 . The device of claim 1 , wherein the convergent lens is movable translationally with respect to the screen, along the optical axis.
14 . The device of claim 1 , wherein the convergent lens has a variable focal length.

Description

TECHNICAL FIELD The technical field of the invention relates to a directional screen and use thereof in a device for projecting an image onto an eye, for example in augmented-reality applications. PRIOR ART Wearable augmented-reality devices, such as glasses, allow a real scene to be observed while complementary information is viewed. This type of device is frequently based on micro-displays, allowing an image to be formed in immediate proximity to an eye of a user. Such micro-displays may for example be integrated into a pair of glasses. An optical system, comprising a set of lenses, allows a clear image to be perceived by the eye. U.S. Pat. No. 6,963,2317, and the publication Martinez “See-through holographic retinal projection display concept”, Optica, Vol. 5 No. 10, October 2018, describe a device allowing projection, onto the retina of an eye, without a screen or an optical system. The device comprises a transparent integrated optical circuit composed of an array of nanoscale light guides, of an array of electrodes and of a holographic film. Such a device is compact, and allows a large field of view to be obtained. In addition, it makes it possible not to use bulky optical systems of complex design. The light guides allow a set of emission points to be defined on the holographic film, each point being capable of being illuminated by light extracted from one light guide. The set of emission points is subdivided into various subsets, each subset comprising emission points distributed, as randomly as possible, over the holographic film. The emission points of a given subset may be simultaneously illuminated by various light guides. Under the effect of illumination, each emission point of the same subset emits a light wave that propagates in the same direction to the pupil of the eye, so as to form a single spot of light on the retina. In this way, each subset of emission points allows a pixel of the image perceived by the user to be formed. An image may be formed by successively illuminating various subsets of points, so as to form an image comprising a high number of pixels. Such a configuration makes it possible to form a very compact device. However, this presupposes use of a high number of different laser sources. Other technologies have been described that allow an image to be projected onto an eye using a compact device. The U.S. Pat. No. 10,254,547 for example describes a pair of glasses comprising a device for projecting a virtual image. The operating principle is schematically shown in FIG. 1. A light emitter E is place on the frame M of a pair of glasses. The light emitter E generates light beams F that propagate to a holographic reflector H. The holographic reflector H is formed on the lens of the glasses. It is configured to reflect each light beam towards the pupil P of an eye O of a user. The light emitter is formed by a light source coupled to a movable mirror. The movable mirror is moved, so as to successively form light beams that scan the holographic reflector. Thus, the user perceives reflected light beams, of various angular directions. When the intensity of each beam is modulated during the scan, the user perceives an image. Other documents describe configurations in which a light beam scans a holographic reflector. Mention may for example be made of US2019/0285897 or US20180299680. One drawback of scan-based configurations is that the eye box is small in size. An eye box is a volume in which the eye may be moved while still perceiving a sharp image. The movement of the eye of a user may be dynamic, when the eye is rotated to scan the field of view. It may also vary from one user to another because of differences between interpupillary distances. With a small eye box, a device may be suitable for one user but not for another, for example if the two users have different interpupillary distances. Another drawback is related to the need to use a mechanical system to perform the scan. Use of a mechanical scanning system and of moving components increases the complexity and cost of the device. The inventors provide an alternative configuration to the aforementioned scanning-based projecting devices. The objective is to provide a solution free of moving components, while improving user comfort, by increasing the size of the eye box. SUMMARY OF THE INVENTION A first subject of the invention is a device for projecting an image onto an eye, the device comprising: a light emitter, configured to emit light waves along various respective emission axes;an optical combiner, optically coupled to the light emitter, and configured to form, from each light wave emitted by the light emitter, a collimated light wave that propagates to the pupil of the eye; wherein the light emitter comprises a screen, comprising various pixels, each pixel being configured to emit a divergent light wave that propagates around an emission axis, the various pixels emitting respective divergent light waves that propagate al