Multi-range time of flight sensing

Abstract

An electro-optical device includes at least one laser light source and a beam steering device, which transmits and scan the at least one beam across a target scene. One or more sensing elements output a signal indicative of a time of incidence of a single photon on the sensing element from the target scene. Circuitry processes the signal in order to determine respective distances to points in the scene and controls the light source to emit the beam at the low level during a first scan, to identify, based on the first scan, the points in the scene that are located at respective distances from the device that are greater than a predefined threshold distance, and to control the laser light source during a second scan to emit the beam at the high level while the beam steering device directs the beam toward the identified points.

1 . An electro-optical device, comprising:
 at least one laser light source configured to emit at least one beam of light pulses having an emissive power selectable between a low level and a high level;   a beam steering device configured to transmit and scan the at least one beam across a target scene;   one or more sensing elements configured to output a signal indicative of a time of incidence of a single photon on the sensing element;   light collection optics configured to image the target scene scanned by the at least one transmitted beam onto the one or more sensing elements; and   circuitry coupled to process signals output by the one or more sensing elements in order to determine respective distances to points in the target scene, to control the at least one laser light source to emit the at least one beam at the low level during a first scan of the beam steering device over the target scene, to identify, based on the first scan, the points in the scene that are located at respective distances from the device that are greater than a predefined threshold distance, and to control the at least one laser light source during a second scan of the beam steering device, subsequent to the first scan, to emit the at least one beam at the high level while the beam steering device directs the at least one beam toward the identified points.   
     
     
         2 . The device according to  claim 1 , wherein the at least one laser light source comprises a laser light source having an output selectable between the low level and the high level. 
     
     
         3 . The device according to  claim 1 , wherein the at least one laser light source comprises at least two lasers, comprising at least a first laser configured to emit the light pulses at the low level, and at least a second laser configured to emit the light pulses at the high level. 
     
     
         4 . The device according to  claim 1 , wherein the circuitry is configured to set at least one of a timing and a sensitivity of the sensing elements to different, respective values during the first scan and during the second scan. 
     
     
         5 . The device according to  claim 1 , wherein the circuitry is configured to control the at least one laser light source during the second scan to direct the at least one beam at the high level only at the points that were identified as being located at respective distances from the device that are greater than the predefined threshold distance. 
     
     
         6 . The device according to  claim 1 , wherein the one or more sensing elements comprise an array of the sensing elements, and wherein the circuitry is configured to actuate the sensing elements only in a selected region of the array and to sweep the selected region over the array in synchronization with scanning of the at least one beam. 
     
     
         7 . The device according to  claim 6 , wherein the circuitry is configured to select the region such that at any instant during the scan, the selected region contains a part of the array onto which the light collection optics image an area of the target scene that is illuminated by the at least one beam. 
     
     
         8 . The device according to  claim 6 , wherein the at least one laser light source is configured to emit at least two beams along different, respective beam axes, such that at any instant during the scan, the light collection optics image respective areas of the target scene that are illuminated by the at least two beams onto different, respective ones of the sensing elements. 
     
     
         9 . The device according to  claim 1 , wherein the sensing elements comprise single-photon detectors. 
     
     
         10 . The device according to  claim 9 , wherein the single-photon detectors are single-photon avalanche diodes (SPADs). 
     
     
         11 . A method for sensing, comprising:
 selecting a laser light source emissive power between a low level and a high level;   emitting at least one beam of light pulses having a selected emissive power;   transmitting and scanning the at least one beam across a target scene;   providing one or more sensing elements configured to output a signal indicative of a time of incidence of a single photon on the sensing element;   imaging the target scene scanned by the at least one transmitted beam onto the one or more sensing elements;   controlling the at least one laser light source to emit the at least one beam at the low level during a first scan of the beam steering device over the target scene;   processing signals output by the one or more sensing elements in order to determine respective distances to points in the target scene;   identifying, based on the first scan, the points in the scene that are located at respective distances from the device that are greater than a predefined threshold distance; and   controlling the at least one laser light source during a second scan of the beam steering device, subsequent to the first scan, to emit the at least one beam at the high level while directing the at least one beam toward the identified points.   
     
     
         12 . The method according to  claim 11 , wherein controlling the at least one laser light source switching an output level of a laser light source between the low level and the high level. 
     
     
         13 . The method according to  claim 11 , wherein controlling the at least one laser light source comprises alternately selecting the output of a first laser light source configured to emit the light pulses at the low level, and selecting the output of a second laser light source configured to emit the light pulses at the high level. 
     
     
         14 . The method according to  claim 11 , and comprising setting at least one of a timing and a sensitivity of the sensing elements to different, respective values during the first scan and during the second scan. 
     
     
         15 . The method according to  claim 11 , wherein controlling the at least one laser light source comprises setting the at least one laser light source during the second scan to direct the at least one beam at the high level only at the points that were identified as being located at respective distances from the device that are greater than the predefined threshold distance. 
     
     
         16 . The method according to  claim 11 , wherein the one or more sensing elements comprise an array of the sensing elements, and wherein the method comprises actuating the sensing elements only in a selected region of the array and to sweep the selected region over the array in synchronization with scanning of the at least one beam. 
     
     
         17 . The method according to  claim 16 , wherein actuating the sensing elements comprises selecting the region such that at any instant during the scan, the selected region contains a part of the array onto which the light collection optics image an area of the target scene that is illuminated by the at least one beam. 
     
     
         18 . The method according to  claim 16 , wherein emitting at least one beam comprises emitting at least two beams along different, respective beam axes, such that at any instant during the scan, the light collection optics image respective areas of the target scene that are illuminated by the at least two beams onto different, respective ones of the sensing elements. 
     
     
         19 . The method according to  claim 11 , wherein the sensing elements comprise single-photon detectors. 
     
     
         20 . The method according to  claim 15 , wherein the single-photon detectors are single-photon avalanche diodes (SPADs).