Close-range measurement of time of flight using parallax shift

1. An optical sensing device, comprising:

a light source, which is configured to emit one or more beams of light pulses toward a target scene at respective angles about a transmit axis of the light source;

a first array of single-photon detectors, which are configured to output electrical pulses in response to photons that are incident thereon;

a second array of counters, which are coupled to count the electrical pulses output during respective count periods by respective sets of one or more of the single-photon detectors;

light collection optics configured to form an image of the target scene on the first array along a receive axis, which is offset transversely relative to the transmit axis, thereby giving rise to a parallax shift as a function of distance between the target scene and the device; and

control circuitry, which is configured to set the respective count periods of the counters, responsively to the parallax shift, to cover different, respective time intervals following each of the light pulses.

2. The device according to claim 1 , wherein the light collection optics are configured to image a respective area of the target scene that is illuminated any given beam among the one or more beams onto a respective region containing a plurality of the single-photon detectors in the first array, and the control circuitry is configured, responsively to the parallax shift, to apply the different time intervals in setting the counters that are coupled to different, respective sets of the single-photon detectors within the respective region.

3. The device according to claim 2 , wherein the respective region in the first array is elongated due to the parallax shift, and the plurality of the singe-photon detectors includes at least a first single-photon detector at a first end of the elongated region and at least a second single-photon detector at a second end of the elongated region, opposite the first end, and

wherein the control circuitry is configured to initiate a first count period of a first counter that is coupled to the first single-photon detector at an earlier start time following each of the light pulses than a second count period of a second counter that is coupled to the second single-photon detector.

4. The device according to claim 3 , wherein the control circuitry is configured to initiate the respective count periods of one or more of the counters that are coupled to one or more of the single-photon detectors that are disposed within the elongated region between the first and second single-photon detectors at respective start times that are graduated between the first and second count periods.

5. The device according to claim 3 , wherein the control circuitry is configured to cause the first counter to aggregate and count all the electrical pulses output by the first single-photon detector during the first count period, while causing at least the second counter to count the electrical pulses in different time bins within the second count period so as to generate a histogram of the electrical pulses.

6. The device according to claim 3 , wherein the elongated region in the first array is defined such that the light collecting optics image objects disposed at a short distance from the device within the respective area of the target scene that is illuminated by the given beam onto the first end of the elongated region, while imaging objects disposed at a long distance from the device within the respective area of the target scene that is illuminated by the given beam onto the second end of the elongated region.

7. The device according to claim 1 , wherein the control circuitry is configured to process count values generated by the counters during the respective count periods in order to compute a depth map of the target scene using times of flight of the photons that are incident on the first array together with triangulation based on the parallax shift.

8. The device according to claim 1 , wherein the single-photon detectors comprise single-photon avalanche diodes (SPADs).

9. The device according to claim 1 , wherein the light source comprises a plurality of emitters, which are configured to emit a corresponding plurality of the beams concurrently toward different, respective areas of the target scene.

10. The device according to claim 1 , wherein each of the counters is configured to aggregate and count the electrical pulses output by a respective set of two or more of the single-photon detectors that are mutually adjacent in the first array.

11. A method for optical sensing, comprising:

emitting one or more beams of light pulses toward a target scene at respective angles about a transmit axis;

forming an image of the target scene on a first array of single-photon detectors along a receive axis, which is offset transversely relative to the transmit axis, thereby giving rise to a parallax shift as a function of distance to the target scene;

counting electrical pulses that are output by respective sets of one or more of the single-photon detectors in response to photons that are incident thereon during respective count periods; and

setting the respective count periods, responsively to the parallax shift, to cover different, respective time intervals following each of the light pulses.

12. The method according to claim 11 , wherein forming the image comprises imaging a respective area of the target scene that is illuminated by any given beam among the one or more beams onto a respective region containing a plurality of the single-photon detectors in the array, and wherein setting the respective count periods comprises applying the different time intervals, responsively to the parallax shift, in setting counters that are coupled to different, respective sets of the single-photon detectors within the respective region.

13. The method according to claim 12 , wherein the respective region in the first array is elongated due to the parallax shift, and the plurality of the singe-photon detectors includes at least a first single-photon detector at a first end of the elongated region and at least a second single-photon detector at a second end of the elongated region, opposite the first end, and

wherein applying the different time intervals comprises initiating a first count period of a first counter that is coupled to the first single-photon detector at an earlier start time following each of the light pulses than a second count period of a second counter that is coupled to the second single-photon detector.

14. The method according to claim 13 , wherein applying the different time intervals comprises initiating the respective count periods of one or more of the counters that are coupled to one or more of the single-photon detectors that are disposed within the elongated region between the first and second single-photon detectors at respective start times that are graduated between the first and second count periods.

15. The method according to claim 13 , wherein applying the different time intervals comprises causing the first counter to aggregate and count all the electrical pulses output by the first single-photon detector during the first count period, while causing at least the second counter to count the electrical pulses in different time bins within the second count period so as to generate a histogram of the electrical pulses.

16. The method according to claim 13 , wherein the elongated region in the array is defined such that objects disposed at a short distance from the array within the respective area of the target scene that is illuminated by the given beam onto the first end of the elongated region, while imaging objects disposed at a long distance from the method within the respective area of the target scene that is illuminated the given beam onto the second end of the elongated region.

17. The method according to claim 11 , wherein the method comprises processing count values generated during the respective count periods in order to compute a depth map of the target scene using times of flight of the photons that are incident on the array together with triangulation based on the parallax shift.

18. The method according to claim 11 , wherein the single-photon detectors comprise single-photon avalanche diodes (SPADs).

19. The method according to claim 11 , wherein emitting the one or more beams comprises operating a plurality of emitters to emit a corresponding plurality of the beams concurrently toward different, respective areas of the target scene.

20. The method according to claim 11 , wherein counting electrical pulses comprises aggregating and counting the electrical pulses output by sets of two or more of the single-photon detectors that are mutually adjacent in the array.