Techniques for enhancing LO and RX overlap in FMCW lidars using birefringent crystals

A frequency modulated continuous-wave (FMCW) light detection and ranging (LiDAR) system, comprising:

• an optical source to emit an optical beam;
• an optical window to reflect a first portion of the optical beam to generate a local oscillator (LO) signal;
• an optical scanner to transmit a second portion of the optical beam to a target to scan the target to generate a target return signal;
• a birefringent crystal plate to transmit the LO signal and the target return signal to a photodetector (PD) and shift the LO signal and the target return signal by different displacements to increase a percentage of an overlap of the LO signal and the target return signal on a detection plane of the PD, wherein an optical axis of the birefringent crystal plate is disposed to create a first angle with respect to a front surface of the birefringent crystal plate on a cross-section, and wherein the first angle is determined based on a distance of the target;
• and
• the PD to mix the target return signal with the LO signal on the detection plane of the PD to extract range and velocity information of the target.

A frequency modulated continuous-wave (FMCW) light detection and ranging (LiDAR) system, comprising:

• an optical source to emit an optical beam;
• an optical window to reflect a first portion of the optical beam to generate a local oscillator (LO) signal;
• an optical scanner to transmit a second portion of the optical beam to a target to scan the target to generate a target return signal;
• a birefringent crystal plate to transmit the LO signal and the target return signal to a photodetector (PD) and shift the LO signal and the target return signal by different displacements to increase a percentage of an overlap of the LO signal and the target return signal on a detection plane of the PD, wherein the LO signal is to incident on a front surface of the birefringent crystal plate with an angle of 90 degrees, and to exit a back surface of the birefringent crystal plate with a first lateral displacement relative to a path of the incident LO signal;
• and
• the PD to mix the target return signal with the LO signal on the detection plane of the PD to extract range and velocity information of the target.

A method of frequency modulated continuous-wave (FMCW) light detection and ranging (LiDAR), comprising:

• emitting an optical beam by an optical source;
• reflecting a first portion of the optical beam to generate a local oscillator (LO) signal;
• transmitting, by an optical scanner, a second portion of the optical beam to a target to scan the target to generate a target return signal;
• transmitting the LO signal and the target return signal to a photodetector (PD) and shifting the LO signal and the target return signal by different displacements by a birefringent crystal plate to increase a percentage of an overlap of the LO signal and the target return signal on a detection plane of the PD, wherein an optical axis of the birefringent crystal plate is disposed to create a first angle with respect to a front surface of the birefringent crystal plate on a cross-section, and wherein the first angle is determined based on a scan speed of the optical scanner;
• and
• mixing, by the PD, the target return signal with the LO signal to extract range and velocity information of the target.

A method of frequency modulated continuous-wave (FMCW) light detection and ranging (LiDAR), comprising:

• emitting an optical beam by an optical source;
• reflecting a first portion of the optical beam to generate a local oscillator (LO) signal;
• transmitting, by an optical scanner, a second portion of the optical beam to a target to scan the target to generate a target return signal;
• transmitting the LO signal and the target return signal to a photodetector (PD) and shifting the LO signal and the target return signal by different displacements by a birefringent crystal plate to increase a percentage of an overlap of the LO signal and the target return signal on a detection plane of the PD, wherein an optical axis of the birefringent crystal plate is disposed to create a first angle with respect to a front surface of the birefringent crystal plate on a cross-section, and wherein the first angle is determined based on a distance of the target;
• and
• mixing, by the PD, the target return signal with the LO signal to extract range and velocity information of the target.

A method of frequency modulated continuous-wave (FMCW) light detection and ranging (LiDAR), comprising:

• emitting an optical beam by an optical source;
• reflecting a first portion of the optical beam to generate a local oscillator (LO) signal;
• transmitting, by an optical scanner, a second portion of the optical beam to a target to scan the target to generate a target return signal;
• transmitting the LO signal and the target return signal to a photodetector (PD) and shifting the LO signal and the target return signal by different displacements by a birefringent crystal plate to increase a percentage of an overlap of the LO signal and the target return signal on a detection plane of the PD, wherein the LO signal is to incident on the front surface of the birefringent crystal plate with an angle of 90 degrees, and to exit a back surface of the birefringent crystal plate with a first lateral displacement relative to a path of the incident LO signal;
• and
• mixing, by the PD, the target return signal with the LO signal to extract range and velocity information of the target.