Multimode lidar receiver for coherent distance and velocity measurements
The subject matter of this specification can be implemented in, among other things, systems and methods that enable lidar devices capable of detecting and processing multiple optical modes present in a beam reflected from a target object. Different received optical modes can be spatially separated and electronic signals can be generated that are representative of a coherence information contained in various optical modes. Multiple generated electronic signals can be amplified, phase-shifted, mixed, etc., to identify signals, individually or in a combination, that can be used for identification of a range and velocity of the target object with the highest accuracy.
1. A system comprising:
an optical subsystem configured to;
receive a beam reflected from an object, the beam comprising a plurality of modes, and
use a diffractive optical element to spatially separate the plurality of modes;
a plurality of light detectors, each of the plurality of light detectors configured to receive, from the optical subsystem:
a respective mode of the plurality of modes, and
a local oscillator (LO) copy of a beam transmitted towards the object, and to output:
one or more electronic signals representative of a difference between the respective mode of the plurality of modes and the LO copy; and
one or more circuits to determine, based on at least a subset of the one or more electronic signals, at least one of a velocity of the object or a distance to the object.
2. The system of claim 1 , further comprising an RF circuit configured to impart an angle modulation to the beam transmitted towards the object, wherein the angle modulation comprises at least one of a phase modulation or a frequency modulation.
3. The system of claim 1 , wherein the optical subsystem is further configured deliver each of the plurality of modes to a respective light detector of the plurality of light detectors.
4. The system of claim 3 , wherein the diffractive optical element comprises a holographic optical element.
5. The system of claim 1 , wherein each of the plurality of light detectors comprises one or more balanced photodetectors.
6. The system of claim 1 , wherein the difference between the respective mode and the LO copy comprises a phase difference between the respective mode and the LO copy.
7. The system of claim 1 , wherein the one or more circuits comprise:
a combiner, operatively coupled with the plurality of light detectors, to produce a combined electronic signal based on the one or more electronic signals outputted by each of the plurality of light detectors, and wherein the at least one of the velocity of the object or the distance to the object is determined based on the combined electronic signal, a phase of a first electronic signal of the one or more electronic signals is adjusted.
8. The system of claim 7 , wherein to produce the combined electronic signal, the combiner is to adjust at least one of (i) an amplitude of a first electronic signal of the one or more electronic signals, (ii) a phase of at least one of the first electronic signal or a second electronic signal of the one or more electronic signals.
9. The system of claim 1 , wherein the optical subsystem comprises a photonic integrated circuit (PIC) having an array of waveguides to deliver each of the plurality of modes to a respective light detector of the plurality of light detectors.
10. The system of claim 1 , wherein the one or more circuits are further configured to determine, based on the at least the subset of the one or more electronic signals, a distance to the object.
11. A sensing system comprising:
an optical subsystem to:
transmit a first beam towards an object, wherein the first beam is a single-mode beam; and
receive a second beam generated upon interaction of the first beam with the object, wherein the second beam comprises a plurality of optical modes;
a light detection subsystem, operatively coupled with the optical subsystem, to
generate a plurality of electronic signals, wherein each of the plurality of electronic signals is obtained using a respective one of the plurality of optical modes; and
one or more circuits, operatively coupled with the light detection subsystem, to:
identify one or more electronic signals of the plurality of electronic signals based at least on signal-to-noise (SNR) ratios of the one or more electronic signals, and
determine, using the one or more identified electronic signals, a characteristic of the object, wherein the characteristic of the object comprises at least one of a velocity of the object or a distance to the object.
12. The sensing system of claim 11 , wherein each of the plurality of electronic signals is further obtained using a local copy of the first beam and is representative of a phase difference between a respective one of the plurality of optical modes and the local copy of the first beam.
13. The sensing system of claim 11 , wherein each of the plurality of electronic signals is a radio frequency signal.
14. The sensing system of claim 11 , wherein the one or more electronic signals have highest SNR ratios of the plurality of electronic signals.
15. The sensing system of claim 11 , wherein the one or more circuits are configured to:
produce a combined electronic signal comprising two or more electronic signals of the plurality of electronic signals, wherein at least one of the two or more electronic signals has an adjusted phase or an adjusted amplitude; and
determine the characteristic of the object using the combined electronic signal.
16. A method comprising:
transmitting a first beam towards an object, wherein the first beam is a single-mode beam;
receiving a second beam generated upon interaction of the first beam with the object, wherein the second beam comprises a plurality of optical modes;
generating a plurality of electronic signals, wherein each of the plurality of electronic signals is obtained using a respective one of the plurality of optical modes;
identifying one or more electronic signals of the plurality of electronic signals based at least on signal-to-noise (SNR) ratios of the one or more electronic signals; and
determining, using the one or more identified electronic signals, a characteristic of the object, wherein the characteristic of the object comprises at least one of a velocity of the object or a distance to the object.
17. The method of claim 16 , wherein each of the plurality of electronic signals is further obtained using a local copy of the first beam and is representative of a phase difference between a respective one of the plurality of optical modes and the local copy of the first beam.
18. The method of claim 16 , wherein the first beam comprises a radio frequency (RF) modulation, the method further comprising:
comparing one or more electronic signals to the RF modulation of the first beam.
19. The method of claim 16 , wherein the one or more electronic signals have highest SNR ratios of the plurality of electronic signals.
20. The method of claim 16 , wherein determining the characteristic of the object comprises:
producing a combined electronic signal comprising two or more electronic signals of the plurality of electronic signals, wherein at least one of the two or more electronic signals has an adjusted phase or an adjusted amplitude; and
determining the characteristic of the object using the combined electronic signal.