Lidar system with dynamic scan speed
In one embodiment, a lidar system includes a light source configured to emit a first set of optical signals that include a first optical signal. The lidar system also includes a scanner that includes a polygon mirror configured to: rotate around an axis of rotation at a rotation rate, and direct the first set of emitted optical signals into a field of regard of the lidar system with the polygon mirror rotating at a first rotation rate. The lidar system further includes a receiver configured to detect a first received optical signal that includes a portion of the first optical signal that is scattered by a target located a distance from the lidar system. The lidar system also includes a controller configured to adjust the rotation rate of the polygon mirror for a second set of optical signals emitted by the light source.
1 . A lidar system comprising:
a light source configured to emit a first set of optical signals comprising a first optical signal;
a scanner comprising a polygon mirror configured to:
rotate around an axis of rotation at a rotation rate; and
direct the first set of emitted optical signals into a field of regard of the lidar system with the polygon mirror rotating at a first rotation rate;
a receiver configured to detect a first received optical signal comprising a portion of the first optical signal that is scattered by a target located a distance from the lidar system; and
a controller configured to adjust the rotation rate of the polygon mirror for a second set of optical signals emitted by the light source subsequent to the first set of optical signals, wherein the controller is configured to adjust the rotation rate at least in part to calibrate the receiver.
2 . The lidar system of claim 1 , wherein the polygon mirror includes a plurality of reflective surfaces angularly offset from one another along a periphery of the polygon mirror.
3 . The lidar system of claim 1 , wherein the receiver is further configured to detect a second received optical signal comprising a portion of the second optical signal scattered by the target, and wherein the second received optical signal impinges on the receiver at a different location than the first received optical signal.
4 . The lidar system of claim 1 , wherein:
the receiver comprises a detector configured to detect the first received optical signal and produce an electrical signal corresponding to the first received optical signal;
the target is a calibration target located a fixed distance from the lidar system;
the controller is configured to adjust the rotation rate of the polygon mirror for the second set of optical signals to a second rotation rate different from the first rotation rate;
the second set of optical signals is emitted by the light source subsequent to the controller adjusting the rotation rate of the polygon mirror to the second rotation rate;
the second set of optical signals comprises a second optical signal; and
the receiver is further configured to detect a second received optical signal comprising a portion of the second optical signal scattered by the calibration target.
5 . The lidar system of claim 4 , wherein the second received optical signal impinges on the detector at a different location than the first received optical signal.
6 . The lidar system of claim 5 , wherein:
the second rotation rate is greater than the first rotation rate; and
the second received optical signal impinges on the detector farther along in a direction of spot movement, thereby simulating a virtual target farther from the lidar system than the calibration target located the fixed distance from the lidar system.
7 . The lidar system of claim 1 , wherein:
the receiver comprises a detector configured to detect the first received optical signal and produce an electrical signal corresponding to the first received optical signal;
the light source is further configured to emit the first set of optical signals with an amount of power;
the target is a calibration target having a known reflectivity value;
the receiver is further configured to determine an actual amplitude of the first received optical signal based at least in part on the electrical signal produced by the detector; and
the controller is further configured to:
determine an expected amplitude of the first received optical signal based at least in part on the amount of power, the known reflectivity value, and the distance to the target; and
determine a correction factor for the detector based at least in part on a disparity between the expected amplitude and the actual amplitude.
8 . The lidar system of claim 7 , wherein the controller is further configured to adjust the rotation rate of the polygon mirror to obtain a plurality of correction factors for the detector.
9 . The lidar system of claim 7 , wherein:
the detector is a first detector;
the receiver further comprises one or more additional detectors; and
the controller is further configured to obtain a correction factor for one or more of the first detector and additional detectors.
10 . The lidar system of claim 1 , wherein:
increasing the rotation rate decreases an operating range of the lidar system; and decreasing the rotation rate increases the operating range of the lidar system.
11 . The lidar system of claim 10 , wherein:
the rotation rate of the polygon mirror for the second set of optical signals is a second rotation rate that is greater than the first rotation rate; and
an operating range of the lidar system for the first set of optical signals is greater than an operating range of the lidar system for the second set of optical signals.
12 . The lidar system of claim 11 , wherein the controller is further configured to adjust a pulse repetition frequency of the optical signals emitted by the light source based at least in part on the rotation rate of the polygon mirror, wherein a pulse repetition frequency of the second set of optical signals is greater than a pulse repetition frequency of the first set of optical signals.
13 . The lidar system of claim 10 , wherein:
the receiver comprises a detector configured to detect the first received optical signal and produce an electrical signal corresponding to the first received optical signal;
less than 20% of the first received optical signal impinges on the detector; and
the distance to the target is greater than or equal to an operating range of the lidar system for the first set of optical signals.
14 . The lidar system of claim 10 , wherein:
the lidar system is a pulsed lidar system;
the optical signals comprise pulses of light wherein the pulses of light are emitted with a particular pulse repetition frequency; and
the controller is further configured to decrease the pulse repetition frequency of the light source based at least in part on a decreased rotation rate of the polygon mirror.
15 . The lidar system of claim 1 , wherein the receiver comprises a first detector and a second detector, each detector configured to detect the first received optical signal and produce an electrical signal corresponding to the first received optical signal.
16 . The lidar system of claim 15 , wherein the controller is further configured to provide a control signal to the polygon mirror to adjust the rotation rate at least in part to identify a rotation rate at which electrical signals from the first and second detectors in response to a subsequent received optical signal are approximately equal.
17 . The lidar system of claim 15 , wherein:
the target is a calibration target located a fixed distance from the lidar system; and
the controller is further configured to provide a control signal to increase the rotation rate of the polygon mirror to simulate a virtual target at a farther distance from the lidar system than the fixed distance of the calibration target in order to calibrate a portion of the second detector.
18 . The lidar system of claim 1 , wherein:
the polygon mirror is configured to scan the first set of emitted optical signals along a first direction; and
the scanner further comprises a second mirror configured to scan the first set of optical signals along a second direction different from the first direction.
19 . The lidar system of claim 1 , wherein the light source comprises:
a seed laser diode configured to produce a seed optical signal; and
a semiconductor optical amplifier (SOA) configured to amplify the seed optical signal to produce the emitted first optical signal.
20 . A method comprising:
emitting, by a light source of a lidar system, a first set of optical signals comprising a first optical signal;
rotating a polygon mirror around an axis of rotation at a rotation rate;
directing, by the polygon mirror, the first set of emitted optical signals into a field of regard of the lidar system with the polygon rotating at a first rotation rate;
detecting, by a receiver, a first received optical signal comprising a portion of the first optical signal that is scattered by a target located a distance from the lidar system; and
adjusting, by a controller, the rotation rate of the polygon mirror for a second set of optical signals emitted by the light source subsequent to the first set of optical signals, wherein the adjusting the rotation rate is performed at least in part to calibrate the receiver.