Waveform design for a LiDAR system with closely-spaced pulses

1. Depth-sensing apparatus, comprising:

a laser, which is configured to emit pulses of optical radiation toward a scene;

one or more detectors, which are configured to receive the optical radiation that is reflected from points in the scene and to output signals indicative of respective times of arrival of the received radiation; and

control and processing circuitry, which is coupled to drive the laser to emit a succession of output sequences of the pulses such that successive output sequences within the succession have different, respective temporal spacings between the pulses within each of the successive output sequences, and to match the times of arrival of input sequences of the signals to the temporal spacings of the output sequences in order to find respective times of flight for the points in the scene.

2. The depth-sensing apparatus according to claim 1 , wherein the output sequences comprise temporally-separated tuples of the pulses.

3. The depth-sensing apparatus according to claim 1 , wherein the output sequences are mutually overlapping.

4. The depth-sensing apparatus according to claim 3 , wherein each output sequence comprises a number N of pulses, such that N>1, and wherein consecutive output sequences have N−1 pulses in common, such that a second pulse of any given output sequence is a first pulse of a succeeding output sequence.

5. The depth-sensing apparatus according to claim 1 , wherein the control and processing circuitry is configured to identify a signal output by the one or more detectors due to a stray-light pulse, to identify an emitted pulse in an input sequence that temporally coincides with the stray-light pulse, and to remove the identified pulse from the input sequence while adding to the input sequence a further pulse from a neighboring sequence in matching the times of arrival.

6. The depth-sensing apparatus according to claim 1 , wherein the control and processing circuitry is configured to construct a depth map of the scene based on the times of flight.

7. The depth-sensing apparatus according to claim 1 , wherein the control and processing circuitry is configured to match the times of arrival of the pulses in each input sequence to the temporal spacings of the output sequences by calculating a respective fit between the times of arrival of the input sequence and each output sequence within a selected time period, calculating a residual of each respective fit, and identifying the output sequence yielding a minimum value of the residual among all residuals as the output sequence associated with the input sequence.

8. The depth-sensing apparatus according to claim 7 , wherein the control and processing circuitry is configured, in calculating the respective fit, to apply a linear transformation to each output sequence to account for a tilt of a planar region of the scene relative to a line of sight of the apparatus, and to calculate the respective fit between the times of arrival of each input sequence and each output sequence following the linear transformation.

9. A method for depth sensing, comprising:

emitting a succession of output sequences of pulses of optical radiation toward a scene, such that successive output sequences within the succession have different, respective temporal spacings between the pulses within each of the successive output sequences;

receiving the optical radiation that is reflected from points in the scene at one or more detectors, which output signals indicative of respective times of arrival of the received radiation; and

matching the times of arrival of input sequences of the signals to the temporal spacings of the output sequences in order to find respective times of flight for the points in the scene.

10. The method according to claim 9 , wherein the output sequences comprise temporally-separated tuples of the pulses.

11. The method according to claim 9 , wherein the output sequences are mutually overlapping.

12. The method according to claim 11 , wherein each output sequence comprises a number N of pulses, such that N>1, and wherein consecutive output sequences have N−1 pulses in common, such that a second pulse of any given output sequence is a first pulse of a succeeding output sequence.

13. The method according to claim 9 , wherein matching the times of arrival comprises identifying a signal output by the one or more detectors due to a stray-light pulse, identifying an emitted pulse in an input sequence that temporally coincides with the stray-light pulse, and removing the identified pulse from the input sequence while adding to the input sequence a further pulse from a neighboring sequence in matching the times of arrival.

14. The method according to claim 9 , and comprising constructing a depth map of the scene based on the times of flight.

15. The method according to claim 9 , wherein matching the times of arrival comprises calculating a respective fit between the times of arrival of the input sequence and each output sequence within a selected time period, calculating a residual of each respective fit, and identifying the output sequence yielding a minimum value of the residual among all residuals as the output sequence associated with the input sequence.

16. The method according to claim 15 , wherein calculating the respective fit comprises applying a linear transformation to each output sequence to account for a tilt of a planar region of the scene relative to a line of sight of the apparatus, and calculating the respective fit between the times of arrival of each input sequence and each output sequence following the linear transformation.