Adaptive transmission power control for a LIDAR
An electro-optical device includes a laser, which is configured to emit toward a scene pulses of optical radiation. An array of detectors 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. A controller is coupled to drive the laser to emit a sequence of pulses of the optical radiation toward each of a plurality of points in the scene and to find respective times of flight for the points responsively to the output signals, while controlling a power of the pulses emitted by the laser by counting a number of the detectors outputting the signals in response to each pulse, and reducing the power of a subsequent pulse in the sequence when the number is greater than a predefined threshold.
1. An electro-optical device, comprising:
a laser, which is configured to emit toward a scene pulses of optical radiation;
an array of single-photon detectors, which are configured to:
receive the optical radiation that is reflected from points in the scene, and
emit, upon detecting a photon, one or more output signals indicative of respective times of arrival of received photons, while the single-photon detectors that have not detected any photon do not emit the output signals indicative of the respective times of arrival; and
a controller, which is coupled to drive the laser to emit a sequence of pulses of the optical radiation toward each of a plurality of points in the scene and to find respective times of flight for the points responsively to the output signals, while controlling a power of the pulses emitted by the laser by counting a number of the detectors that have emitted the output signals in response to each pulse, and when the number of the detectors that have emitted the output signals in response to a given pulse is greater than a threshold, reducing the power of a subsequent pulse in the sequence.
2. The electro-optical device according to claim 1 , wherein the single-photon detectors are single-photon avalanche detectors (SPADs).
3. The electro-optical device according to claim 1 , wherein the controller is configured to reduce the power of the subsequent pulse in the sequence by at least one predetermined attenuation factor.
4. The electro-optical device according to claim 3 , wherein the controller is configured to attenuate the power of subsequent pulses in multiple steps of a predetermined ratio until the number of the detectors outputting the signals falls below the predefined threshold.
5. The electro-optical device according to claim 1 , and comprising a scanner configured to scan the pulses of optical radiation across the scene.
6. The electro-optical device according to claim 5 , wherein the controller is configured to construct a depth map of the scene based on the respective time of flight found at the plurality of points while scanning the pulses.
7. The electro-optical device according to claim 5 , wherein the controller is configured to activate a respective subset of the detectors at a location in the array that receives the reflected optical radiation at each point in synchronization with scanning the pulses.
8. The electro-optical device according to claim 5 , wherein the controller is configured to set the power of the pulses at some of the points to the reduced power that was used at a preceding point while scanning the pulses.
9. The electro-optical device according to claim 1 , wherein the controller comprises:
an adder, which is coupled to receive the signals from the detectors and to output a numerical signal indicative of the number of the detectors outputting signals;
a comparator, which is configured to compare the numerical signal from the adder to the predetermined threshold and to generate a command signal when the signal exceeds the predetermined threshold; and
a pulse generator, which generates, in response to the command signal, an adaptive power control signal, which controls a drive current of the laser responsively to the adaptive power control signal.
10. A method for sensing, comprising:
emitting a sequence of pulses of optical radiation toward each of a plurality of points in the scene;
receiving the optical radiation that is reflected from points in the scene in an array of single-photon detectors, which emit, upon detecting a photon, one or more output signals indicative of respective times of arrival of received photons, while the single-photon detectors that have not detected any photon do not emit the output signals indicative of the respective times of arrival;
finding respective times of flight for the points responsively to the output signals; and
controlling a power of the emitted pulses by counting a number of the detectors outputting the signals in response to each pulse, and when the number of the detectors that have emitted the output signals in response to each pulse, and when the number of the detectors that have emitted the output signals in response to a given pulse is greater than a threshold, reducing the power of a subsequent pulse in the sequence.
11. The method according to claim 10 , wherein the single-photon detectors are single-photon avalanche detectors (SPADs).
12. The method according to claim 10 , wherein controlling the power comprises reducing the power of the subsequent pulse in the sequence by at least one predetermined attenuation factor.
13. The method according to claim 12 , wherein reducing the power comprises attenuating the power of subsequent pulses in multiple steps of a predetermined ratio until the number of the detectors outputting the signals falls below the predefined threshold.
14. The method according to claim 10 , wherein emitting the sequence of pulses comprises scanning the pulses of optical radiation across the scene.
15. The method according to claim 14 , and comprising constructing a depth map of the scene based on the time of flight found at the plurality of points while scanning the pulses.
16. The method according to claim 14 , wherein receiving the optical radiation comprises activating a respective subset of the detectors at a location in the array that receives the reflected optical radiation at each point in in synchronization with scanning the pulses.
17. The method according to claim 14 , wherein controlling the power comprises setting the power of the pulses at some of the points to the reduced power that was used at a preceding point while scanning the pulses.
18. The method according to claim 10 , wherein controlling the power comprises:
receiving the signals from the detectors and outputting a numerical signal indicative of the number of the detectors outputting signals;
comparing the numerical signal to the predetermined threshold and generating a command signal when the signal exceeds the predetermined threshold; and
generating, in response to the command signal, an adaptive power control signal, which controls a drive current of a laser emitting the pulses.