Multi-mode sensor for object identification
Optical sensing apparatus includes a transmitter, which transmits outgoing FM coherent optical radiation toward a target scene, and a receiver, including an array of detectors, which output electrical signals in response to photons that are incident on the detectors, and optics to image the target scene onto the array while diverting a part of the outgoing FM coherent optical radiation to form a local beam, which mixes with incoming optical radiation from the target scene. Processing circuitry processes the electrical signals output by the detectors to produce a 2D image of the target scene, to identify an object of interest in the 2D image, which is imaged onto an area within the array, to extract beat frequencies in response to the mixed optical radiation from the electrical signals output by the detectors in the area, and to measure a feature of the object of interest responsively to the beat frequencies.
1 . Optical sensing apparatus, comprising:
a transmitter, which is configured to transmit outgoing frequency-modulated (FM) coherent optical radiation toward a target scene;
a receiver, comprising:
an array of detectors, which are configured to output electrical signals in response to photons that are incident on the detectors, wherein the detectors are single-photon detectors, which are configured to output electrical pulses in response to the incident photons; and
optics configured to image the target scene onto the array while diverting a part of the outgoing FM coherent optical radiation to form a local beam, which mixes with incoming optical radiation from the target scene; and
processing circuitry configured to process the electrical signals output by the detectors to produce a two-dimensional (2D) image of the target scene, to identify an object of interest in the 2D image, which is imaged onto an area within the array, to extract beat frequencies in response to the mixed optical radiation from the electrical signals output by the detectors in the area, and to measure a three-dimensional feature of the object of interest responsively to the beat frequencies,
wherein the processing circuitry is configured to compute counts of the electrical pulses output as a function of time by the single-photon detectors, wherein the counts of the electrical pulses as the function of time define temporal waveforms, and wherein the processing circuitry is configured to extract the beat frequencies by processing the temporal waveforms.
2 . The apparatus according to claim 1 , wherein the transmitter is configured to project the FM coherent optical radiation as flood radiation over a region of the target scene.
3 . The apparatus according to claim 1 , wherein the processing circuitry is configured to produce the 2D image responsively to total counts of the electrical pulses output by each of the single-photon detectors during a given exposure time.
4 . The apparatus according to claim 1 , wherein the processing circuitry is configured to select groups of the single-photon detectors within the area and to compute the counts as collective counts of the electrical pulses output by each of the selected groups of the single-photon detectors.
5 . The apparatus according to claim 1 , wherein the single-photon detectors comprise single-photon avalanche diodes (SPADs).
6 . The apparatus according to claim 1 , wherein the transmitter is configured to apply a frequency chirp to the outgoing coherent optical radiation, and the processing circuitry is configured to measure a three-dimensional shape of the object of interest based on the beat signals that arise due to the frequency chirp.
7 . The apparatus according to claim 1 , wherein the processing circuitry is configured to detect, based on the beat signals, a Doppler shift indicative of movement of a feature of the object of interest.
8 . The apparatus according to claim 7 , wherein the object of interest is a part of a living body, and wherein the processing circuitry is configured to detect the Doppler shift due to flow of blood in blood vessels in the living body and to identify the blood vessels responsively to the detected Doppler shift.
9 . The apparatus according to claim 1 , wherein the processing circuitry is configured to identify a face in the 2D image and to generate a three-dimensional (3D) map of the face based on the beat frequencies.
10 . The apparatus according to claim 9 , wherein the processing circuitry is configured to apply the 3D map in verifying an identity of a person whose face appears in the 2D image.
11 . A method for optical sensing, comprising:
transmitting outgoing frequency-modulated (FM) coherent optical radiation toward a target scene;
imaging the target scene onto an array of detectors, which output electrical signals in response to photons that are incident on the detectors, while diverting a part of the outgoing FM coherent optical radiation to form a local beam, which mixes on the array of detectors with incoming optical radiation from the target scene, wherein the detectors are single-photon detectors, which are configured to output electrical pulses in response to the incident photons;
processing the electrical signals output by the detectors to produce a two-dimensional (2D) image of the target scene;
identifying an object of interest, which is imaged onto an area within the array, in the 2D image;
extracting beat frequencies in response to the mixed optical radiation from the electrical signals output by the detectors in the area,
wherein extracting the beat frequencies comprises computing counts of the electrical pulses output as a function of time by the single-photon detectors, wherein the counts of the electrical pulses as the function of time define temporal waveforms, and wherein the beat frequencies are extracted by processing the temporal waveforms; and
measuring a three-dimensional feature of the object of interest responsively to the beat frequencies.
12 . The method according to claim 11 , wherein the transmitting the outgoing FM coherent optical radiation comprises projecting the FM coherent optical radiation as flood radiation over a region of the target scene.
13 . The method according to claim 11 , wherein processing the electrical signals comprises producing the 2D image responsively to total counts of the electrical pulses output by each of the single-photon detectors during a given exposure time.
14 . The method according to claim 11 , wherein transmitting the outgoing FM coherent optical radiation comprises applying a frequency chirp to the outgoing coherent optical radiation, and wherein measuring the feature comprises measuring a three-dimensional shape of the object of interest based on the beat signals that arise due to the frequency chirp.
15 . The method according to claim 11 , wherein extracting the beat frequencies comprises detecting, based on the beat signals, a Doppler shift indicative of movement of a feature of the object of interest.
16 . The method according to claim 15 , wherein the object of interest is a part of a living body, and wherein detecting the Doppler shift comprises sensing a flow of blood in blood vessels in the living body and identifying the blood vessels responsively to the detected Doppler shift.
17 . The method according to claim 11 , wherein identifying the object of interest comprises identifying a face in the 2D image, and wherein measuring the feature comprises generating a three-dimensional (3D) map of the face based on the beat frequencies.