Lidar devices with frequency and time multiplexing of sensing signals

Abstract

The subject matter of this specification can be implemented in, among other things, systems and methods of optical sensing that utilize time and frequency multiplexing of sensing signals. Described are, among other things, a light source subsystem to produce a first beam having a first frequency and a second beam having a second frequency, a modulator to impart a modulation to the second beam, and an optical interface subsystem to receive a third beam caused by interaction of the first beam with an object and a fourth beam caused by interaction of the second beam with the object. Also described are one or more circuits to determine, based on a first phase information carried by the third beam, a velocity of the object, and then determine, based on a second phase information carried by the third beam and the first phase information, a distance to the object.

What is claimed is: 
     
         1 . A system comprising:
 a light source subsystem configured to produce a first beam having a first frequency and a second beam having a second frequency;   a modulator configured to impart a modulation to the second beam;   an optical interface subsystem configured to:
 receive a third beam caused by interaction of the first beam with a first object, and 
 receive a fourth beam caused by interaction of the second beam with the first object; and 
   one or more circuits configured to:
 determine, based on a first phase information carried by the third beam, a velocity of the first object; and 
 determine, based on a second phase information carried by the third beam and the first phase information, a distance to the first object. 
   
     
     
         2 . The system of  claim 1 , wherein the modulation imparted to the second beam comprises a sequence of shifts characterized by a correlation function that is a peaked function of a time delay, wherein the sequence of shifts comprises at least one of a sequence of frequency shifts or a sequence of phase shifts. 
     
     
         3 . The system of  claim 2 , wherein the sequence of shifts is based on at least one of a maximum-length sequence, a Gold code, or a Barker code. 
     
     
         4 . The system of  claim 1 , wherein the optical interface subsystem is further configured to output, towards the first object, the first beam and the second beam along a same optical path. 
     
     
         5 . The system of  claim 1 , wherein to determine the velocity of the first object, the one or more circuits compare the first phase information with a phase information carried by a local oscillator (LO) beam, wherein the first frequency is shifted from a frequency of the LO beam by a first frequency offset. 
     
     
         6 . The system of  claim 5 , wherein the second frequency is shifted from the frequency of the LO beam by a second frequency offset. 
     
     
         7 . The system of  claim 1 , wherein the light source subsystem comprises:
 a light source configured to generate a common beam, wherein the first beam and the second beam are obtained from the common beam, and wherein at least one of the first beam or the second beam is shifted in frequency from the common beam.   
     
     
         8 . The system of  claim 1 , wherein the light source subsystem comprises:
 a first light source configured to output the first beam having a first frequency; and   a second light source configured to output the second beam having a second frequency; and   an optical feedback loop configured to lock one of the first frequency or the second frequency to another one of the second frequency or the first frequency.   
     
     
         9 . The system of  claim 8 , wherein the optical feedback loop (OFL) comprises:
 a coherent photodetector configured to:
 receive a copy of the first beam and a copy of the second beam; 
 generate an electrical signal representative of a phase difference between the copy of the first beam and the copy of the second beam; and 
 one or more OFL circuits configured to adjust, in view of the electrical signal, at least one of the first frequency or the second frequency. 
   
     
     
         10 . The system of  claim 1 , further comprising:
 a coherent photodetector configured to:
 receive a combined beam comprising the third beam and the fourth beam; 
 receive a local oscillator (LO) beam; 
 generate a first electrical signal representative of a phase difference of the combined beam and the LO beam; 
   wherein the one or more circuits are further configured to receive the first electric signal.   
     
     
         11 . The system of  claim 10 , wherein the one or more circuits comprise:
 a first filter to generate, based on the first electrical signal, a second electrical signal representative of a phase difference of the third beam and the LO beam;   a second filter to generate, based on the first electrical signal, a third electrical signal representative of a phase difference of the fourth beam and the LO beam; and   a signal processing stage configured to
 determine, based on the second electrical signal, the velocity of the first object; and 
 determine, based on the second electrical signal and the third electrical signal, the distance to the first object. 
   
     
     
         12 . The system of  claim 1 , wherein the light source subsystem is configured to generate a frequency comb comprising a plurality of comb teeth, and wherein the first beam and the second beam are associated with a first comb tooth of the plurality of comb teeth and at least one of the first frequency or the second frequency is obtained by shifting a frequency of the first comb tooth. 
     
     
         13 . The system of  claim 12 , further configured to determine a velocity of a second object and a distance to the second object using one or more beams generated based on a second comb tooth of the plurality of comb teeth. 
     
     
         14 . A system comprising:
 a light source configured to generate a first beam;   a first modulator configured to produce, based on the first beam, a second beam comprising a plurality of first portions interspersed with a plurality of second portions, wherein each of the plurality of second portions is modulated with a first sequence of shifts, the first sequence of shifts comprising at least one of a sequence of frequency shifts or a sequence of phase shifts;   an optical interface subsystem configured to:
 receive a third beam caused by interaction of the second beam with an object, the third beam comprising a plurality of third portions interspersed with a plurality of fourth portions, wherein each of the plurality of fourth portions is modulated with a second sequence of shifts that is time-delayed relative to the first sequence of shifts; and 
   one or more circuits configured to:
 determine a velocity of the object based on a Doppler frequency shift between the third beam and the second beam, identified using the plurality of first portions and the plurality of third portions; and 
 determine a distance to the object based on:
 a time delay between the first sequence of shifts and the second sequence of shifts, and 
 the identified Doppler frequency shift. 
 
   
     
     
         15 . The system of  claim 14 , wherein the first sequence of shifts is characterized by a correlation function that is a peaked function of a time delay. 
     
     
         16 . The system of  claim 14 , wherein each of the plurality of first portions of the second beam is unmodulated. 
     
     
         17 . The system of  claim 14 , further comprising:
 a beam splitter configured to produce a local oscillator (LO) copy of the first beam;   a second modulator configured to impart a frequency offset to the second beam relative to the first beam; and   a coherent photodetector configured to:
 input the third beam and the LO beam; and 
 generate one or more electrical signals representative of a phase difference between the third beam and the LO beam; and 
   a signal processing stage configured to determine the Doppler frequency shift and the time delay using the one or more electrical signals.   
     
     
         18 . A system comprising:
 a light source configured to generate a first beam;   one or more modulators configured to produce, using the first beam, a second beam comprising a plurality of chirped portions, wherein each of the plurality of chirped portions comprises a monotonic modulation and a sequence of shifts, wherein the sequence of shifts comprises at least one of a sequence of frequency shifts or a sequence of phase shifts;   an optical interface subsystem configured to:
 receive a third beam caused by interaction of the second beam with an object, the third beam comprising the plurality of chirped portions that are time-delayed; and 
   one or more circuits configured to:
 determine, based on a phase difference of the third beam and the LO beam, a velocity of the object and a distance to the object. 
   
     
     
         19 . The system of  claim 18 , wherein the sequence of shifts is characterized by a correlation function that is a peaked function of a time delay. 
     
     
         20 . The system of  claim 18 , further comprising:
 a beam splitter configured to produce a local oscillator (LO) copy of the first beam; and   a coherent photodetector configured to:
 input the third beam and the LO beam; and 
 generate one or more electrical signals representative of a phase difference between the third beam and the LO beam; and 
   a signal processing stage configured to determine the velocity of the object and the distance to the object using the one or more electrical signals.