# US 12,001,054 B2 · Wideband grating coupler > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,001,054 B2 - Document ID: US12001054B2 - Status: Granted - Kind: B2 - Application number: 17/511,427 - Filed: 2021-10-26 - Published: 2022-05-05 - Granted: 2024-06-04 - Earliest claimed: 2020-10-30 - Assignees: The Chinese University of Hong Kong - Applicants: The Chinese University of Hong Kong - Inventors: Xuetong Zhou; Hon Ki Tsang - Web page: https://patentgrep.com/patent/US12001054B2 ## CPC - G02B 6/124: Geodesic lenses or integrated gratings - G02B 6/30: for use between fibre and thin-film device - G02B 6/34: utilising prism or grating {(G02B6/293 takes precedence)} - G02B 6/29359: {Cavity formed by light guide ends, e.g. fibre Fabry Pérot [FFP]} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract An output coupler can be used to couple multiple channels of light from a semiconductor waveguide to an optical fiber for wavelength division multiplexing. To couple light of a wide bandwidth (e.g., equal to or greater than 100 nm), two symmetrical gratings on two sides of a Fabry Perot cavity is used. The two symmetrical gratings are optimized to both reflect light for a Fabry Perot resonator and couple light out of the semiconductor waveguide. ## Claims ### Claim 1 A system for optical communication, comprising: a waveguide having a semiconductor core, wherein the semiconductor core is configured to guide light along a first propagation direction; and a coupler comprising: a first grating, a second grating, and walls forming an optical cavity between the first grating and the second grating, wherein: there is no gain medium between the first grating and the second grating, the coupler is configured to couple light out of the waveguide along a second propagation direction, and the second propagation direction is not parallel to the first propagation direction. ### Claim 2 (depends on 1) The system of claim 1, further comprising an optical fiber positioned to receive light along the second propagation direction. ### Claim 3 (depends on 1) The system of claim 1, wherein: the first grating is symmetrical to the second grating, in a plane along the first propagation direction; the first grating is a first Bragg reflector; the second grating is a second Bragg reflector; the optical cavity is a Fabry Perot cavity, formed between the first Bragg reflector and the second Bragg reflector; ridges of the first grating and ridges of the second grating are elongated structures; and the ridges of the first grating and ridges of the second grating are curved along a length of the ridges. ### Claim 4 (depends on 1) The system of claim 1, wherein: the first grating is a first Bragg reflector; the second grating is a second Bragg reflector; and the optical cavity is a Fabry Perot cavity, formed between the first Bragg reflector and the second Bragg reflector. ### Claim 5 (depends on 1) The system of claim 1, wherein the coupler has etched feature sizes that are no less than 150 nm. ### Claim 6 (depends on 1) The system of claim 1, wherein the first grating is configured to have a first order diffraction along the second propagation direction and a second order reflection opposite the first propagation direction. ### Claim 7 (depends on 1) The system of claim 1, wherein the first grating has a non-uniform period. ### Claim 8 (depends on 1) The system of claim 1, wherein: ridges of the first grating and ridges of the second grating are elongated structures; and the ridges of the first grating and ridges of the second grating are curved along a length of the ridges. ### Claim 9 (depends on 8) The system of claim 8, wherein lengths of ridges of the first grating are longer than lengths of ridges of the second grating. ### Claim 10 (depends on 1) The system of claim 1, wherein the coupler has an optical bandwidth equal to or greater than 100 nm, measured as 1 dB optical bandwidth. ### Claim 11 A method for coupling light out of an optical waveguide, the method comprising: receiving light from a waveguide, wherein the light propagates in a first propagation direction in the waveguide; reflecting the light, using a first grating, so that the light passes through an optical cavity wherein light passing through the optical cavity does not pass through a gain medium; reflecting the light, using a second grating, after the light passes through the optical cavity; and directing the light, using the first grating or the second grating, in a second propagation direction, wherein the second propagation direction is not parallel with the first propagation direction. ### Claim 12 (depends on 11) The method of claim 11, wherein: light received from the waveguide is defined by a center wavelength, and an average period of the first grating is equal to the center wavelength. ### Claim 13 (depends on 11) The method of claim 11, wherein directing light in the second propagation direction is based on a first order diffraction of the first grating. ### Claim 14 (depends on 11) The method of claim 11, wherein the first grating, the second grating, the optical cavity, and the waveguide are formed in a device layer of a silicon-on-insulator wafer. ### Claim 15 An apparatus, comprising: a first grating, a second grating, and walls forming an optical cavity between the first grating and the second grating, wherein: there is no gain medium between the first grating and the second grating; the first grating and the second grating are configured to diffract light, propagating parallel to a first propagation direction, to propagate in a second propagation direction and reflect light in a direction parallel to the first propagation direction; the second propagation direction is not parallel to the first propagation direction; diffracting light uses a first order diffraction; and reflecting light uses a second order reflection. ### Claim 16 (depends on 15) The apparatus of claim 15, wherein: the first grating is a first Bragg reflector; the second grating is a second Bragg reflector; and the optical cavity is a Fabry Perot cavity, formed between the first Bragg reflector and the second Bragg reflector. ### Claim 17 (depends on 15) The apparatus of claim 15, wherein the first grating, the second grating are part of a coupler, and the coupler has etched feature sizes that are no less than 150 nm. ### Claim 18 (depends on 15) The apparatus of claim 15, wherein the first grating and the second grating are symmetrical Bragg gratings having an equal number of periods. ### Claim 19 (depends on 11) The method of claim 11, wherein lengths of ridges of the first grating are longer than lengths of ridges of the second grating. ### Claim 20 (depends on 15) The apparatus of claim 15, wherein lengths of ridges of the first grating are longer than lengths of ridges of the second grating.