Method and system for time separated quadrature detection of doppler effects in optical range measurements
In some implementations, a light detection and ranging (LIDAR) system includes a transmitter configured to transmit an optical signal that is output from a laser and modulated based on a modulating signal, a receiver configured to receive a returned optical signal in response to transmitting the optical signal, and a processor. The processor is configured to produce a first optical signal based on the returned optical signal and a first version of the modulating signal, produce a second optical signal based on the returned optical signal and a second version of the modulating signal, generate a digital signal based on the first optical signal and the second optical signal, determine a Doppler frequency shift of the returned optical signal based, at least in part, on the digital signal, and provide data indicative of the Doppler frequency shift to a vehicle.
1. A light detection and ranging (LIDAR) system comprising:
a transmitter configured to transmit an optical signal that is output from a laser and modulated based on a modulating signal;
a receiver configured to receive a returned optical signal in response to transmitting the optical signal;
a processor configured to:
produce a first optical signal based on the returned optical signal and a first version of the modulating signal;
produce a second optical signal based on the returned optical signal and a second version of the modulating signal;
generate a digital signal based on the first optical signal and the second optical signal; determine a Doppler frequency shift of the returned optical signal based, at least in part, on the digital signal;
based on the Doppler frequency shift, determine a distinction between a first object and a second object; and
segment the first object and the second object based on the distinction between the first and second objects such that a vehicle is controlled based on the Doppler frequency shift.
2. The LIDAR system according to claim 1 , wherein the processor is further configured to operate the vehicle based on the Doppler frequency shift.
3. The LIDAR system according to claim 1 , further comprising an optical or optical hybrid mixer configured to:
mix, during a first time interval, the returned optical signal with a first reference optical signal that is modulated based on the first version of the modulating signal, to produce the first optical signal; and
mix, during a second time interval, the returned optical signal with a second reference optical signal that is modulated based the second version of the modulating signal, to produce the second optical signal.
4. The LIDAR system according to claim 3 , wherein the second time interval is non-overlapping with the first time interval.
5. The LIDAR system according to claim 4 , wherein the first time interval and the second time interval occur an equal number of times randomly during a processing time interval.
6. The LIDAR system according to claim 3 , wherein the first time interval and the second time interval alternate an equal number of times during a processing time interval.
7. The LIDAR system according to claim 3 , wherein the processor is configured to:
detect the first optical signal during the first time interval to produce a first electrical signal; and
detect the second optical signal during the second time interval to produce a second electrical signal.
8. The LIDAR system according to claim 7 , wherein in generating the digital signal, the processor is configured to generate the digital signal by using a digitized sample of one of the first electrical signal and the second electrical signal as a real part of the digital signal and a digitized sample of a different one of the first electrical signal and the second electrical signal as an imaginary part of the digital signal.
9. The LIDAR system according to claim 1 , wherein the modulating signal is a digital signal.
10. The LIDAR system according to claim 1 , wherein the transmitted optical signal is a phase-encoded optical signal.
11. The LIDAR system according to claim 1 , wherein the transmitted optical signal is an up and down chirped optical signal.
12. The LIDAR system according to claim 1 , wherein the processor is configured to determine the Doppler frequency shift of the returned optical signal based on a Fourier transform of the digital signal.
13. The LIDAR system according to claim 1 , wherein
the first version of the modulating signal is an in-phase version of the modulating signal, and
the second version of the modulating signal is a quadrature version of the modulating signal representing a quadrature local oscillator signal.
14. An autonomous vehicle control system comprising one or more processors, wherein the one or more processors are configured to:
cause a transmitter to transmit an optical signal that is output from a laser and modulated based on a modulating signal;
cause a receiver to receive a returned optical signal in response to transmitting the optical signal;
produce a first optical signal based on the returned optical signal and a first version of the modulating signal;
produce a second optical signal based on the returned optical signal and a second version of the modulating signal;
generate a digital signal based on the first optical signal and the second optical signal;
determine a Doppler frequency shift of the returned optical signal based, at least in part, on the digital signal;
based on the Doppler frequency shift, determine a distinction between a first object and a second object; and
control a vehicle based on the Doppler frequency shift to segment the first and second objects based on the distinction between the first and second objects.
15. The autonomous vehicle control system according to claim 14 , wherein the processor is further configured to cause an optical or optical hybrid mixer to:
mix, during a first time interval, the returned optical signal with a first reference optical signal that is modulated based on the first version of the modulating signal, to produce the first optical signal; and
mix, during a second time interval, the returned optical signal with a second reference optical signal that is modulated based the second version of the modulating signal, to produce the second optical signal.
16. The autonomous vehicle control system according to claim 14 , wherein the modulating signal is a digital signal.
17. The autonomous vehicle control system according to claim 14 , wherein the transmitted optical signal is a phase-encoded optical signal.
18. The autonomous vehicle control system according to claim 14 , wherein the transmitted optical signal is an up and down chirped optical signal.
19. The autonomous vehicle control system according to claim 14 , wherein
the first version of the modulating signal is an in-phase version of the modulating signal, and
the second version of the modulating signal is a quadrature version of the modulating signal representing a quadrature local oscillator signal.
20. An autonomous vehicle, comprising:
a light detection and ranging (LIDAR) system including:
a transmitter configured to transmit an optical signal that is output from a laser and modulated based on a modulating signal;
a receiver configured to receive a returned optical signal in response to transmitting the optical signal;
a processor configured to
produce a first optical signal based on the returned optical signal and a first version of the modulating signal,
produce a second optical signal based on the returned optical signal and a second version of the modulating signal,
generate a digital signal based on the first optical signal and the second optical signal, and
determine a Doppler frequency shift of the returned optical signal based, at least in part, on the digital signal;
at least one of a steering system or a braking system; and
a vehicle controller comprising one or more processors configured to control operation of the at least one of the steering system or the braking system based on the Doppler frequency shift.