# US 11,909,171 B2 · Laser-integrated balance detection for self-mixing interferometry > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,909,171 B2 - Document ID: US11909171B2 - Status: Granted - Kind: B2 - Application number: 17/219,744 - Filed: 2021-03-31 - Published: 2022-10-06 - Granted: 2024-02-20 - Earliest claimed: 2021-03-31 - Assignees: Apple Inc. - Applicants: Apple Inc. - Inventors: Tong Chen; Fei Tan; Mingzhou Jin - Web page: https://patentgrep.com/patent/US11909171B2 ## CPC - H01S 5/026: Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers (stabilisation of output H01S5/06) - H01S 5/0262: {Photo-diodes, e.g. transceiver devices, bidirectional devices (H01S5/0265 takes precedence)} - G01B 9/02041: {characterised by particular imaging or detection techniques} - G01B 9/02092: {Self-mixing interferometers, i.e. feedback of light from object into laser cavity} - G01S 7/4812: {transmitted and received beams following a coaxial path} - G01S 7/4813: {Housing arrangements} - G01S 7/4814: {of transmitters alone} - G01S 7/4913: Circuits for detection, sampling, integration or read-out - G01S 7/4916: {using self-mixing in the laser cavity} - G01S 7/4917: {superposing optical signals in a photodetector, e.g. optical heterodyne detection} - G01S 17/58: Velocity or trajectory determination systems; Sense-of-movement determination systems - H01S 5/18361: {Structure of the reflectors, e.g. hybrid mirrors} - H01S 5/34: comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers (H01S5/36 takes precedence) - H10F 77/146: {Superlattices; Multiple quantum well structures} - G01B 2290/45: Multiple detectors for detecting interferometer signals - H01S 5/0264: {for monitoring the laser-output} - H01S 5/0656: {Seeding, i.e. an additional light input is provided for controlling the laser modes, for example by back-reflecting light from an external optical component (H01S5/14, H01S5/4062 and H01S5/4006 take precedence)} - H01S 5/183: having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION ## Abstract An optical sensor system includes a set of epitaxial layers formed on a semiconductor substrate. The set of epitaxial layers defines a semiconductor laser having a first multiple quantum well (MQW) structure. Electromagnetic radiation is generated by the first MQW structure, emitted from the first MQW structure, and self-mixed with a portion of the emitted electromagnetic radiation that is returned to the first MQW structure. The set of epitaxial layers also defines a second MQW structure operable to generate a first photocurrent responsive to detecting a first emission of the semiconductor laser, and a third MQW structure operable to generate a second photocurrent responsive to detecting a second emission of the semiconductor laser. The optical sensor system also includes a circuit configured to generate a self-mixing interferometry (SMI) signal by combining the first photocurrent and the second photocurrent. ## Claims ### Claim 1 An optical sensor system, comprising: a semiconductor substrate; a set of epitaxial layers formed on the semiconductor substrate and defining, a semiconductor laser having a first multiple quantum well (MQW) structure, wherein electromagnetic radiation is generated by the first MQW structure, emitted from the first MQW structure, and self-mixed with a portion of the emitted electromagnetic radiation that is returned to the first MQW structure; a second MQW structure, positioned on a first side of the first MQW structure and operable to generate a first photocurrent responsive to detecting a first emission of the semiconductor laser; and a third MQW structure, positioned on a second side of the first MQW structure and operable to generate a second photocurrent responsive to detecting a second emission of the semiconductor laser, the second side opposite the first side; and a circuit configured to generate a self-mixing interferometry (SMI) signal by combining the first photocurrent and the second photocurrent. ### Claim 2 (depends on 1) The optical sensor system of claim 1, wherein the first MQW structure, the second MQW structure, and the third MQW structure are disposed along an emission axis of the semiconductor laser. ### Claim 3 (depends on 1) The optical sensor system of claim 1, wherein: the semiconductor laser is a vertical cavity surface-emitting laser (VCSEL); and the VCSEL comprises a distributed Bragg reflector (DBR) in which the first MQW structure and the second MQW structure are formed. ### Claim 4 An optical sensor system, comprising: a semiconductor substrate; a set of epitaxial layers formed on the semiconductor substrate and defining, a semiconductor laser having a first multiple quantum well (MQW) structure, wherein electromagnetic radiation is generated by the first MQW structure, emitted from the first MQW structure, and self-mixed with a portion of the emitted electromagnetic radiation that is returned to the first MQW structure; a second MQW structure operable to generate a first photocurrent responsive to detecting a first emission of the semiconductor laser; and a third MQW structure operable to generate a second photocurrent responsive to detecting a second emission of the semiconductor laser; and a circuit configured to generate a self-mixing interferometry (SMI) signal by combining the first photocurrent and the second photocurrent; wherein, the second MQW structure and the third MQW structure share a same set of one or more epitaxial layers. ### Claim 5 (depends on 1) The optical sensor system of claim 1, wherein the circuit comprises: a first transimpedance amplifier (TIA) configured to receive the first photocurrent; a second TIA configured to receive the second photocurrent; and a set of one or more circuit components configured to combine a first output of the first TIA and a second output of the second TIA. ### Claim 6 (depends on 1) The optical sensor system of claim 1, wherein the second MQW structure is alternatively operable to, generate the first photocurrent; or generate electromagnetic radiation contemporaneously with the first MQW structure. ### Claim 7 (depends on 1) The optical sensor system of claim 1, wherein the first MQW structure and the second MQW structure are phase-matched. ### Claim 8 An optical sensor system, comprising: a substrate; a first photodetector on the substrate; a second photodetector on the substrate, laterally offset from the first photodetector; an epitaxial stack; a semiconductor laser formed in an epitaxial stack, the epitaxial stack attached to the substrate, the semiconductor laser aligned with the first photodetector and configured to make a first emission of electromagnetic radiation toward the first photodetector, the semiconductor laser having a resonant cavity in which emitted electromagnetic radiation and returned electromagnetic radiation is self-mixed; an optical subsystem configured to, receive a second emission of the semiconductor laser; and redirect a portion of the second emission toward the second photodetector; and a noise-mitigating self-mixing interferometry (SMI) signal channel configured to combine a first photocurrent from the first photodetector and a second photocurrent from the second photodetector; wherein, the first photodetector is outside of the epitaxial stack. ### Claim 9 (depends on 8) The optical sensor system of claim 8, wherein a set of epitaxial layers in the epitaxial stack extends over the second photodetector. ### Claim 10 (depends on 8) The optical sensor system of claim 8, wherein the optical subsystem comprises at least one grating that helps redirect the portion of the second emission toward the second photodetector. ### Claim 11 (depends on 8) The optical sensor system of claim 8, wherein: the substrate is a first substrate; the semiconductor laser is formed on a second substrate, with the first substrate positioned on a first side of the semiconductor laser and the second substrate positioned on a second side of the semiconductor laser; and at least a part of the optical subsystem is formed on the second substrate. ### Claim 12 An optical sensor system, comprising: a semiconductor substrate; a set of epitaxial layers formed on the substrate and defining, a semiconductor laser having a resonant cavity parallel to the semiconductor substrate and parallel or orthogonal to a primary electromagnetic radiation emission axis of the semiconductor laser; a first photodetector positioned adjacent a first end of the resonant cavity and configured to receive a secondary electromagnetic radiation emission of the semiconductor laser; and a second photodetector positioned adjacent a second end of the resonant cavity and configured to receive a tertiary electromagnetic radiation emission of the semiconductor laser; and a circuit configured to generate an SMI signal by combining a first photocurrent generated by the first photodetector and a second photocurrent generated by the second photodetector; wherein, the first photocurrent and the second photocurrent have opposite SMI excess phases. ### Claim 13 (depends on 12) The optical sensor system of claim 12, wherein: the resonant cavity is a first resonant cavity; and the set of epitaxial layers comprises a multiple quantum well structure, subdivided between, the first resonant cavity of the semiconductor laser; a second resonant cavity of the first photodetector; and a third resonant cavity of the second photodetector. ### Claim 14 (depends on 12) The optical sensor system of claim 12, wherein: the first photodetector is separated from the semiconductor laser by a trench extending through at least a subset of epitaxial layers in the set of epitaxial layers. ### Claim 15 (depends on 14) The optical sensor system of claim 14, further comprising: at least one of a coating, a fill material, or a surface treatment within the trench; wherein, the first photodetector is resonance-coupled to the semiconductor laser. ### Claim 16 (depends on 12) The optical sensor system of claim 12, wherein the semiconductor laser is a distributed feedback laser. ### Claim 17 (depends on 16) The optical sensor system of claim 16, wherein the resonant cavity of the distributed feedback laser has periodic changes in refractive index that regulate secondary electromagnetic radiation emission received by the first photodetector. ### Claim 18 (depends on 4) The optical sensor system of claim 4, wherein: the second MQW structure is disposed along an emission axis of the semiconductor laser; and the third MQW structure does not intersect the emission axis of the semiconductor laser. ### Claim 19 (depends on 4) The optical sensor system of claim 4, wherein the circuit comprises: a first transimpedance amplifier (TIA) configured to receive the first photocurrent; a second TIA configured to receive the second photocurrent; and a set of one or more circuit components configured to combine a first output of the first TIA and a second output of the second TIA. ### Claim 20 An optical sensor system, comprising: a substrate; a first photodetector on the substrate; a second photodetector on the substrate, laterally offset from the first photodetector; a semiconductor laser attached to the substrate, the semiconductor laser aligned with the first photodetector and configured to make a first emission of electromagnetic radiation toward the first photodetector, the semiconductor laser having a resonant cavity in which emitted electromagnetic radiation and returned electromagnetic radiation is self-mixed; an optical subsystem comprising at least one grating and configured to, receive a second emission of the semiconductor laser; and redirect a portion of the second emission toward the second photodetector, the redirection occurring at least in part because of the at least one grating; and a noise-mitigating self-mixing interferometry (SMI) signal channel configured to combine a first photocurrent from the first photodetector and a second photocurrent from the second photodetector.