# US 11,994,672 B2 · Optical systems with light-expanding couplers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,994,672 B2 - Document ID: US11994672B2 - Status: Granted - Kind: B2 - Application number: 17/423,196 - Filed: 2020-05-26 - Published: 2022-03-03 - Granted: 2024-05-28 - Earliest claimed: 2019-05-30 - Assignees: Apple Inc. - Applicants: Apple Inc. - Inventors: Jonathan B. Pfeiffer; Francesco Aieta; Se Baek Oh; Friso Schlottau; Adam C. Urness - Web page: https://patentgrep.com/patent/US11994672B2 ## CPC - G02B 27/0081: {with means for altering, e.g. enlarging, the entrance or exit pupil} - G02B 5/1814: {structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings (G02B5/189 takes precedence)} - G02B 5/32: Holograms used as optical elements - G02B 6/0016: {Grooves, prisms, gratings, scattering particles or rough surfaces} - G02B 6/125: Bends, branchings or intersections - G02B 27/0101: {characterised by optical features (G02B27/0172 takes precedence)} - G02B 27/0103: {comprising holographic elements} - G02B 27/0172: {characterised by optical features} - G02B 27/4211: {correcting chromatic aberrations (G02B27/0056, G02B27/4222, G02B27/4227 take precedence)} - G02B 27/4272: {having plural diffractive elements positioned sequentially along the optical path} - G02B 6/0011: {the light guides being planar or of plate-like form} - G02B 6/0015: {provided on the surface of the light guide or in the bulk of it} - G02B 6/124: Geodesic lenses or integrated gratings - G02B 2006/12107: {Grating} - G02B 2006/12114: {Prism} - G02B 2006/12147: {Coupler} - G02B 2027/0123: {comprising devices increasing the field of view} - G02B 2027/0134: {of stereoscopic type} - G02B 2027/0174: {holographic} - G02B 2027/0178: {Eyeglass type (eyeglass details G02C)} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract An electronic device may include a display that generates light for an optical system that redirects the light towards an eye box. The optical system may include a waveguide, a non-diffractive input coupler, a cross coupler, and an output coupler. The cross coupler may expand the light in a first direction. The cross coupler may perform an even number of diffractions on the light and may couple the light back into the waveguide at an angle suitable for total internal reflection. The output coupler may expand the light in a second direction while coupling the light out of the waveguide. The cross coupler may include surface relief gratings or holographic gratings embedded within the waveguide or formed in a separate substrate. The optical system may direct the light towards the eye box without chromatic dispersion and while supporting an expanded field of view and optical bandwidth. ## Claims ### Claim 1 An optical system configured to redirect light, the optical system comprising: a waveguide, wherein the waveguide comprises a first waveguide substrate, a second waveguide substrate, and a medium interposed between the first and second waveguide substrates; an input coupler configured to couple the light into the waveguide; a cross coupler on the waveguide, wherein the cross coupler comprises a first surface relief grating and a second surface relief grating that at least partially overlaps the first surface relief grating, wherein the first surface relief grating is formed in the first waveguide substrate, wherein the second surface relief grating is formed in the second waveguide substrate, wherein the cross coupler is configured to expand the light coupled into the waveguide by the input coupler in a first direction, and wherein the waveguide is configured to propagate the light expanded in the first direction via total internal reflection; and an output coupler on the waveguide, wherein the output coupler is configured to couple the light expanded in the first direction by the cross coupler out of the waveguide while expanding the light in a second direction that is different from the first direction. ### Claim 2 (depends on 1) The optical system of claim 1, wherein the first surface relief grating has fringes oriented in a first direction. ### Claim 3 (depends on 2) The optical system of claim 2, wherein the second surface relief grating has fringes oriented in a second direction different from the first direction. ### Claim 4 (depends on 3) The optical system of claim 3, wherein the first surface relief grating overlaps the second surface relief grating within an overlap region of the cross coupler. ### Claim 5 (depends on 4) The optical system defined in claim 4, wherein the overlap region has a non-uniform width. ### Claim 6 (depends on 1) The optical system of claim 1, wherein the first surface relief grating has a non-binary profile. ### Claim 7 (depends on 1) The optical system of claim 1, wherein the output coupler has a diffraction efficiency that varies as a function of position along the first direction, wherein the output coupler has a first diffraction efficiency along a central axis of the output coupler and a second diffraction efficiency at a peripheral edge of the output coupler that is greater than the first diffraction efficiency. ### Claim 8 (depends on 1) The optical system of claim 1, wherein the cross coupler has a diffraction efficiency that varies as a function of position. ### Claim 9 (depends on 1) The optical system of claim 1, further comprising: a partially reflective beam splitter embedded in the waveguide, wherein the light coupled into the waveguide by the input coupler is configured to hit the partially reflective beam splitter prior to being received at the cross coupler. ### Claim 10 (depends on 1) The optical system of claim 1, wherein the cross coupler comprises a meta-grating on the waveguide. ### Claim 11 (depends on 1) The optical system of claim 1, wherein the input coupler comprises diffractive gratings. ### Claim 12 (depends on 1) The optical system of claim 1, wherein the output coupler comprises diffractive grating structures. ### Claim 13 An optical system configured to redirect light, the optical system comprising: a waveguide; an input coupler configured to couple the light into the waveguide; a cross coupler on the waveguide, wherein the cross coupler comprises a first surface relief grating having fringes oriented in a first direction and a second surface relief grating having fringes oriented in a second direction different from the first direction, wherein the first surface relief grating overlaps the second surface relief grating within an overlap region of the cross coupler, wherein the first surface relief grating and the second surface relief grating are formed in a first surface relief grating substrate, wherein the cross coupler further comprises a second surface relief grating substrate that includes at least one additional surface relief grating and that is layered over the first surface relief grating substrate, wherein the cross coupler is configured to expand the light coupled into the waveguide by the input coupler in a first direction, and wherein the waveguide is configured to propagate the light expanded in the first direction via total internal reflection; and an output coupler on the waveguide, wherein the output coupler is configured to couple the light expanded in the first direction by the cross coupler out of the waveguide while expanding the light in a second direction that is different from the first direction. ### Claim 14 (depends on 13) The optical system of claim 13, wherein the waveguide comprises first and second waveguide substrates and a medium interposed between the first and second waveguide substrates, and wherein the first surface relief grating substrate is layered on the first waveguide substrate. ### Claim 15 (depends on 14) The optical system of claim 14, wherein the output coupler comprises a louvered mirror embedded in the medium. ### Claim 16 (depends on 14) The optical system of claim 14, wherein the medium comprises a grating medium and wherein the output coupler comprises a set of volume holograms recorded in the grating medium. ### Claim 17 (depends on 16) The optical system of claim 16, further comprising an antireflection layer on a surface of the first waveguide substrate at the output coupler. ### Claim 18 (depends on 13) The optical system defined in claim 13, wherein the waveguide comprises a medium having first and second surfaces and a waveguide substrate layered on the first surface, wherein the first surface relief grating substrate is layered on the second surface of the medium, and wherein the first surface relief grating is embedded in the medium. ### Claim 19 (depends on 18) The optical system defined in claim 18, wherein the medium comprises a grating medium and wherein the output coupler comprises a set of volume holograms recorded in the grating medium. ### Claim 20 (depends on 19) The optical system of claim 19, further comprising an optically transparent coating on the first surface relief grating and interposed between the first surface relief grating and the grating medium. ### Claim 21 (depends on 18) The optical system defined in claim 18, wherein the grating medium has a bulk index of refraction and wherein the surface relief grating substrate has an index of refraction that is greater than the bulk index of refraction of the grating medium. ### Claim 22 (depends on 13) The optical system of claim 13, wherein the input coupler comprises diffractive gratings. ### Claim 23 (depends on 13) The optical system of claim 13, wherein the output coupler comprises diffractive grating structures. ### Claim 24 (depends on 13) The optical system of claim 13, wherein the cross coupler has a diffraction efficiency that varies as a function of position. ### Claim 25 (depends on 13) The optical system of claim 13, wherein the output coupler has a diffraction efficiency that varies as a function of position along the first direction. ### Claim 26 An optical system configured to redirect light, the optical system comprising: a waveguide; an input coupler configured to couple the light into the waveguide; a cross coupler on the waveguide, wherein the cross coupler comprises a first surface relief grating and a second surface relief grating that at least partially overlaps the first surface relief grating, wherein the waveguide comprises a first waveguide substrate, a second waveguide substrate, and a medium interposed between the first and second waveguide substrates, wherein the first surface relief grating is formed in a surface relief grating substrate layered on the first waveguide substrate, wherein the second surface relief grating is formed in the second waveguide substrate, wherein the cross coupler is configured to expand the light coupled into the waveguide by the input coupler in a first direction, and wherein the waveguide is configured to propagate the light expanded in the first direction via total internal reflection; and an output coupler on the waveguide, wherein the output coupler is configured to couple the light expanded in the first direction by the cross coupler out of the waveguide while expanding the light in a second direction that is different from the first direction. ### Claim 27 (depends on 26) The head-mounted device of claim 26, wherein the first surface relief grating comprises first fringes with a first orientation, wherein the second surface relief grating comprises second fringes with a second orientation that is non-parallel with respect to the first orientation, and wherein the first and second surface relief gratings overlap within an overlap region of the cross coupler. ### Claim 28 (depends on 27) The head-mounted device of claim 27, further comprising an optically-transparent coating on the first and second surface relief gratings and interposed between the second waveguide substrate and the medium. ### Claim 29 (depends on 27) The head-mounted device of claim 27, further comprising a partially reflective beam splitter on the medium, wherein the cross coupler is configured to receive the image light from the partially reflective beam splitter. ### Claim 30 (depends on 26) The optical system of claim 26, wherein the second surface relief grating is embedded within the medium. ### Claim 31 (depends on 26) The optical system of claim 26, wherein the input coupler comprises diffractive gratings. ### Claim 32 (depends on 26) The optical system of claim 26, wherein the output coupler comprises diffractive grating structures. ### Claim 33 (depends on 26) The optical system of claim 26, wherein the medium comprises a grating medium and the output coupler comprises a set of volume holograms recorded in the grating medium. ### Claim 34 (depends on 26) The optical system of claim 26, wherein the cross coupler has a diffraction efficiency that varies as a function of position and the output coupler has a diffraction efficiency that varies as a function of position along the first direction.