Patent ID: 12210155

DETAILED DESCRIPTION

As mentioned in document WO2018102834, augmented reality and virtual reality devices use waveguide device that comprises input gratings. The present disclosure relates to a technique that can be implemented within input gratings for a polychromatic image input. The role of the input grating according to one embodiment of the disclosure is to take the image coming from the light engine (named Field of view on the figure), and deviate the light beam in such a way to tunnel it into the waveguide (which is a flat glass plate) by TIR.

FIG.1presents part of an optical device (such as augmented reality glasses) according to one embodiment of the disclosure. Such optical device aims at guiding a polychromatic image represented by light rays or beams referenced101generated a light engine.

A first waveguide element referenced102receives these light rays or beams101. The first waveguide element102comprises a diffraction grating (not represented) that only deviates blue color component within the light beams101. The light beams associated with the blue color component are reflected within the first waveguide element102in order to reach a first output that delivers the deviated “blue” light toward said eye box of the user referenced107. The other components of the light beams101(i.e. all the other color components, except the blue component color) are transmitted via a second output, referenced105, of the diffraction grating, without being altered in term of propagation direction (i.e. with the same direction of the light beams101) to a second waveguide element referenced103. However, the second output comprises an achromatic half-wave plate for modifying the polarization of the remaining light. In one embodiment of the disclosure a diffraction grating structure, in the first waveguide, comprises the diffraction grating and the second output.

The second waveguide element referenced103receives these light rays or beams that do not comprise blue color light component. The second waveguide element103comprises a diffraction grating (not represented) that only deviates green color component within the received light beams. The light beams associated with the green color component are reflected within the second waveguide element103in order to reach a first output that delivers the deviated “green” light toward said eye box of the user107. The other components of the light beams101(i.e. all the other color components, except the blue and the green component color) are transmitted via a second output, referenced106, of the diffraction grating, without being altered in term of propagation direction (i.e. with the same direction of the light beams101) to a third waveguide element referenced104. In addition, the second output106comprises an achromatic half-wave plate for modifying the polarization of the remaining light that is transmitted to another waveguide element.

The third waveguide element referenced104receives these light rays or beams that do not comprise blue and green colors light components.

The third waveguide element104comprises a diffraction grating (not represented) that only deviates red color component within the received light beams. The light beams associated with the red color component are reflected within the third waveguide element104in order to reach a first output that delivers the deviated “red” light toward said eye box of the user107. Hence, the third waveguide element104does not comprise an achromatic half-wave plate.

FIG.2presents in the left part, a schematic corresponding to the features ofFIG.1(but without the references), and in the right part, a schematic corresponding to the features of the optical device according to one embodiment of the disclosure, for delivering to the second eye of the user an image.

Such optical device aims at guiding a polychromatic image represented by light rays or beams referenced201generated a light engine.

A first waveguide element referenced202receives these light rays or beams201. The first waveguide element202comprises a diffraction grating (not represented) that only deviates blue color component within the light beams201. The light beams associated with the blue color component are reflected within the first waveguide element202in order to reach a first output that delivers the deviated “blue” light toward said eye box of the user referenced207. The other components of the light beams201(i.e. all the other color components, except the blue component color) are transmitted via a second output, referenced205, of the diffraction grating, without being altered in term of propagation direction (i.e. with the same direction of the light beams201) to a second waveguide element referenced203. In addition, the second output205comprises an achromatic half-wave plate for modifying the polarization of the remaining light that is transmitted to another waveguide element.

The second waveguide element referenced203receives these light rays or beams that do not comprise blue color light component. The second waveguide element203comprises a diffraction grating (not represented) that only deviates green color component within the received light beams. The light beams associated with the green color component are reflected within the second waveguide element203in order to reach a first output that delivers the deviated “green” light toward said eye box of the user207. The other components of the light beams201(i.e. all the other color components, except the blue and the green component color) are transmitted via a second output, referenced206, of the diffraction grating, without being altered in term of propagation direction (i.e. with the same direction of the light beams201) to a third waveguide element referenced204. In addition, the second output206comprises an achromatic half-wave plate for modifying the polarization of the remaining light that is transmitted to another waveguide element.

The third waveguide element referenced204receives these light rays or beams that do not comprise blue and green colors light components.

The third waveguide element204comprises a diffraction grating (not represented) that only deviates red color component within the received light beams. The light beams associated with the red color component are reflected within the third waveguide element204in order to reach a first output that delivers the deviated “red” light toward said eye box of the user207.

The multi-layer waveguide elements ofFIG.1and in the left part ofFIG.2comprise 1-order diffraction gratings, whereas the multi-layer waveguide elements of the right part ofFIG.2comprise −1-order diffraction gratings.

FIG.3illustrates an example of a diffraction grating used in a waveguide element according to one embodiment of the disclosure.

Such diffraction grating is also detailed in the European patent application no 18305263.

FIG.4illustrates an example of a diffraction grating used in a waveguide element according to another embodiment of the disclosure.

In such embodiment, the dimensions of the part made of a single material with refractive index n2, and the dimensions of the part made of a single material with refractive index n3are not the same contrary to the embodiment ofFIG.3.

FIG.5illustrates a part of an optical device (such as augmented reality glasses) according to another embodiment of the disclosure.

In another embodiment of the disclosure, the light engine used to deliver light beams101and201can generate light beams with n color components [C1, . . . , Ci, . . . , Cn] referenced501, each color component Cjbeing associated with a wavelength λj, and wherein λi+1>λifor all the i∈[1, n], and wherein the polarization of the color component fulfills the following property: pol(Ci)=TE if i=2k+1, and pol(Ct)=TM otherwise.

In addition, the wavelength should satisfy the following property:

λi+2>2⁢n4n4+1⁢λi+ε
with ε being around 10 nm.

Hence, in one embodiment of the disclosure, the optical device comprises n waveguide elements (stacked on each other as in the embodiment ofFIGS.1and2, with three waveguide elements), and the waveguide element that can deviate only the smallest wavelength, referenced502, is positioned closer to the light engine. The arrangement of the n waveguide elements follows the order of the n color components [C1, . . . , Ci, . . . , Cn]. Therefore, the i-waveguide element referenced503can only deviate the color component Ciand transmits the color components [Ci+1, . . . , Cn]. The last waveguide element, that is positioned closer to the eye of the user referenced505, only deviates the color component Cnof the received light beams.

As in the embodiment ofFIGS.1and2, the waveguide elements inFIG.5comprise a diffraction grating as previously detailed, and also achromatic half-wave plates, as the achromatic half-wave plate referenced506and the achromatic half-wave plate referenced507.