Laser-integrated balance detection for self-mixing interferometry

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.

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.

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.

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.