Frequency chirp for lidar for high-velocity targets

Abstract

A device includes a controller with a processor and memory with instructions for controlling power to a light source such that the light source emits a frequency-modulated continuous light beam that, over time, includes an up region, a down region, and a flat region. The up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency.

We claim: 
     
         1 . A method comprising:
 emitting a frequency-modulated continuous light beam according to a repeating first light pattern that includes an up region, a down region, and a flat region, wherein the up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency;   detecting backscattered light responsive to the first light pattern;   detecting a target based, at least in part, on the backscattered light; and   in response to detecting the target, emitting the frequency-modulated continuous light beam according to a second light pattern.   
     
     
         2 . The method of  claim 1 , wherein the second light pattern has a higher frame rate than the first light pattern. 
     
     
         3 . The method of  claim 1 , wherein a length of the flat region is shorter during the second light pattern compared to the first light pattern. 
     
     
         4 . The method of  claim 1 , wherein the second light pattern includes the up region and the down region but does not include the flat region. 
     
     
         5 . The method of  claim 1 , further comprising:
 determining a magnitude of a Doppler frequency shift on the backscattered light responsive to the flat region; and   determining, based at least in part on the magnitude, a velocity of the target.   
     
     
         6 . The method of  claim 5 , further comprising:
 determining that the magnitude of the Doppler frequency shift is greater than or less than a range frequency shift; and   determining the velocity of the target based further on the determining that the magnitude is greater than or less than the range frequency shift.   
     
     
         7 . The method of  claim 1 , further comprising:
 determining a slope of calculated frequency differences plotted against ramp rate; and   determining whether the calculated frequency differences fall along the determined slope; and   determining, based only on the calculated frequency differences that fall along the determined slope, a velocity of the target.   
     
     
         8 . A system comprising:
 a light source controlled to emit a frequency-modulated continuous light beam according to a repeating first light pattern that includes an up region, a down region, and a flat region, wherein the up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency;   an optical detector arranged to detect backscattered light response to the first light pattern; and   circuitry configured to:
 identify a target based, at least in part, on the backscattered light, and 
 in response to detecting the target, emitting the frequency-modulated continuous light beam according to a second light pattern. 
   
     
     
         9 . The system of  claim 8 , wherein the light source and the optical detector are packaged in a shared housing. 
     
     
         10 . The system of  claim 8 , wherein the second light pattern has a higher frame rate than the first light pattern. 
     
     
         11 . The system of  claim 8 , wherein a length of the flat region is shorter during the second light pattern compared to the first light pattern. 
     
     
         12 . The system of  claim 8 , wherein the second light pattern includes the up region and the down region but does not include the flat region. 
     
     
         13 . The system of  claim 8 , further comprising:
 a light source driver coupled to the light source and configured to apply a power signal to modulate the frequency of the emitted light of the light source.   
     
     
         14 . The system of  claim 8 , wherein the circuitry is further configured to:
 determining a magnitude of a Doppler frequency shift on the backscattered light responsive to the flat region, and   determining, based at least in part on the magnitude, a velocity of the target.   
     
     
         15 . A device comprising:
 one or more controllers including a processor and memory with instructions for controlling power to a light source such that the light source emits a frequency-modulated continuous light beam according to a repeating first light pattern that includes an up region, a down region, and a flat region, wherein the up region includes increasing a frequency of the continuous light beam, the down region includes decreasing the frequency of the continuous light beam, and the flat region includes maintaining the frequency of the continuous light beam at a constant frequency,   wherein the memory further stores instructions for:
 controlling power to the light source such that the light source emits the frequency-modulated continuous light beam according to a second light pattern after a target is identified. 
   
     
     
         16 . The device of  claim 15 , wherein the second light pattern has a higher frame rate than the first light pattern. 
     
     
         17 . The device of  claim 15 , wherein a length of the flat region is shorter during the second light pattern compared to the first light pattern. 
     
     
         18 . The device of  claim 15 , wherein the second light pattern includes the up region and the down region but does not include the flat region. 
     
     
         19 . The device of  claim 15 , wherein the memory further stores instructions for:
 determining a magnitude of a Doppler frequency shift on the backscattered light responsive to the flat region, and   determining, based at least in part on the magnitude, a velocity of the target.   
     
     
         20 . The device of  claim 19 , wherein the memory further stores instructions for:
 determining that the magnitude of the Doppler frequency shift is greater than or less than a range frequency shift, and   determining the velocity of the target based further on the determining that the magnitude is greater than or less than the range frequency shift.