Geiger-mode LiDAR system having improved signal-to-noise ratio
A GmAPD-based LiDAR system and methods for developing a point-cloud image of a detection region are disclosed. The methods include scanning the detection region during a plurality of detection frames that defines an image frame. In each detection frame, the detection region is interrogated with a different one of a series of optical pulses and reflections of the optical pulse are detected at a GmAPD-based receiver that is gated such that a different sampling region within the detection region is selectively sampled in each detection frame. The sampling regions are defined such that longer-range areas of the detection region are sampled more times in the image frame than shorter-range areas of the detection region. As a result, objects throughout the entire detection region can be detected with high SNR.
1. A method for generating a point-cloud image of a detection region that extends from a minimum range, Lmin, to a maximum range, Lmax, the method comprising:
transmitting a first optical signal toward the detection region, wherein the first optical signal comprises an optical pulse train having a first periodicity;
providing a receiver including at least one single-photon detector;
establishing a sequence of detection frames having substantially uniform duration, each detection frame having a start time based on the transmission of a different optical pulse of the optical pulse train and a stop time based on Lmax, wherein the sequence of detection frames defines a first image frame; and
establishing a gating period within each detection frame of the sequence thereof such that each detection frame of the sequence thereof includes only one gating period, wherein the receiver is enabled to detect a single photon received from the detection region only during the gating period;
wherein each detection frame of the sequence thereof is characterized by a gate delay between its respective start time and its respective gating period; and
wherein the gate delays of the plurality thereof are non-uniform.
2. The method of claim 1 wherein the magnitude of the gate delays of the plurality thereof changes monotonically through the sequence of detection frames.
3. The method of claim 1 wherein the magnitude of the gate delays of the plurality thereof changes linearly through the sequence of detection frames.
4. The method of claim 1 wherein the magnitude of the gate delays of the plurality thereof changes exponentially through the sequence of detection frames.
5. The method of claim 1 wherein the magnitude of the gate delays of the plurality thereof changes according to a first function through the sequence of detection frames, wherein the first function is selected from the group consisting of a power-law function, a polynomial function, a random-number-generating function, and a quasi-random-number-generating function.
6. The method of claim 1 wherein the at least two gate delays of the plurality thereof have the same magnitude.
7. The method of claim 1 wherein the receiver is provided such that it comprises an imager including a two-dimensional arrangement of single-photon detectors that includes the at least one single-photon detector.
8. The method of claim 1 wherein the system is characterized by a signal-to-noise ratio that exceeds a minimum signal-to-noise ratio over a distance range from the receiver that extends from approximately zero to the maximum range, Lmax.
9. A method for generating a point-cloud image of a detection region that extends from a minimum range, Lmin, to a maximum range, Lmax, the method comprising:
providing a light detection and ranging (LiDAR) system such that the LiDAR system comprises a transmitter and a receiver comprising at least one single-photon detector, wherein the transmitter is operative for transmitting a first optical signal comprising an optical-pulse train having a first periodicity;
transmitting the first optical signal toward the detection region;
establishing a sequence of detection frames having substantially uniform duration, the sequence including N detection frames and each detection frame having a start time that is based on the transmission of a different optical pulse of the optical-pulse train thereof and a stop time based on Lmax, wherein the sequence of detection frames defines a first image frame;
establishing a plurality of sample regions having non-uniform scan range, wherein the plurality of sample regions includes N sample regions, and wherein the detection region includes each of the plurality of sample regions; and
for each detection frame of the sequence thereof, enabling the receiver to selectively detect a second optical signal received from a different sample region of the plurality thereof.
10. The method of claim 9 wherein each sample region of the plurality thereof ends at Lmax.
11. The method of claim 10 wherein Lmin changes monotonically through the sequence of detection frames.
12. The method of claim 10 wherein Lmin changes according to a linear function through the sequence of detection frames.
13. The method of claim 10 wherein Lmin changes according to a first function through the sequence of detection frames, wherein the first function is selected from the group consisting of a power-law function, a polynomial function, a random-number-generating function, and a quasi-random-number-generating function.
14. The method of claim 9 wherein the plurality of sample regions are defined by operations comprising:
for each detection frame;
establishing a gate delay and a gating period within each detection frame of the sequence thereof, wherein the gating period begins at the end of the gate delay; and
enabling the receiver to detect a single photon received from the detection region only during the gating period; and
wherein the plurality of gate delays is established such that their magnitudes are non-uniform through the sequence of detection frames.
15. The method of claim 14 wherein the plurality of gate delays is established such that their magnitudes change through the sequence of detection frames according to a first function, and wherein the first function is selected from the group consisting of a linear function, a power-law function, a polynomial function, a random-number-generating function, and a quasi-random-number-generating function.
16. The method of claim 9 wherein LiDAR system is provided such that the receiver includes an imager including a two-dimensional arrangement of single-photon detectors that includes the at least one single-photon detector, the two-dimensional arrangement defining a focal-plane array.
17. A light detection and ranging (LiDAR) system for estimating a point-cloud image of a detection region that extends from a minimum range, Lmin, to a maximum range, Lmax, the system comprising:
a transmitter that is operative for transmitting a first optical signal comprising an optical-pulse train having a first periodicity, the optical-pulse train comprising a plurality of optical pulses;
a receiver comprising at least one single-photon detector; and
a processor operative for providing a gating signal to the receiver, the gating signal including a sequence of detection frames having substantially uniform duration, wherein each detection frame of the plurality thereof has a start time based on the transmission of a different optical pulse of the optical-pulse train thereof and a stop time based on Lmax, and wherein each detection frame of the plurality thereof includes a gate delay and a single gating period, and further wherein the plurality of gate delays is non-uniform;
wherein the receiver is enabled to detect a single photon only during the plurality of gating periods.
18. The system of claim 17 wherein the magnitude of the gate delays of the plurality thereof changes linearly through the sequence of detection frames.
19. The system of claim 17 wherein the magnitude of the gate delays of the plurality thereof changes exponentially through the sequence of detection frames.
20. The system of claim 17 wherein the magnitude of the gate delays of the plurality thereof changes through the sequence of detection frames according to a first function that is selected from the group consisting of a power-law function, a polynomial function, and random-number-generating function, and a quasi-random-number-generating function.
21. The system of claim 17 wherein the receiver comprises an imager including a two-dimensional arrangement of single-photon detectors that includes the at least one single-photon detector.