Scanning lidar with optical switching
A scanning LiDAR with no moving parts includes a laser transmitter with a first magneto-optic switch delivering pulses to a first linear fiber array to a field of view (FOV), a receiver with optics directing reflected light to a second, orthogonal linear fiber array coupled to a second magneto-optic switch to deliver the light to a detector, and a controller to process detector signals and generate FOV data. A scanning method for improving resolution includes scanning along a first direction, directing light reflected from an object along a second direction orthogonal to the first direction to form a received beam provided to a detector, processing detector signals to generate a pixel array, and varying an intensity profile within a pixel to move peak intensity in a continuous manner within the pixel by synchronously varying polarization of the transmitted and received light using associated Faraday rotators and phase masks.
1 . A method comprising:
generating laser pulses;
optically switching the laser pulses to each of a first plurality of fibers arranged in a first linear array to illuminate a field of view;
shaping the laser pulses output from the first plurality of fibers to form pulsed beams having elliptical cross-sections with an angular divergence along a first axis at least 20 times greater than an angular divergence along a second axis perpendicular to the first axis;
directing light reflected from an object illuminated by the laser pulses within the field of view to a second plurality of fibers arranged in a second linear array, wherein the second linear array of fibers is positioned orthogonally to the first linear array of fibers;
optically switching light from the second plurality of fibers to direct the light to at least one detector; and
processing signals from the detector to generate data representing the field of view, the data corresponding to pixels with each pixel corresponding to an intersection of the elliptically shaped cross sections of the transmitted and received pulsed beams.
2 . The method of claim 1 wherein generating laser pulses comprises generating laser pulses using a fiber laser having an output wavelength of between 900 nm and 1700 nm.
3 . The method of claim 1 wherein at least one of optically switching the laser pulses and optically switching the light from the second plurality of fibers comprises controlling a magneto-optical switch.
4 . The method of claim 1 wherein the at least one detector is only one detector and wherein optically switching the light from the second plurality of fibers comprises optically switching the light to a single fiber coupled to the detector.
5 . The method of claim 1 wherein the at least one detector includes a plurality of detectors and wherein optically switching the light from the second plurality of fibers comprises optically switching light from different groups of fibers to different detectors operating in parallel.
6 . The method of claim 1 further comprising:
polarizing the laser pulses that illuminate the field of view;
detecting polarization of the light reflected from the object illuminated by the laser pulses; and
generating polarization data representing the field of view based on detecting the polarization of the light reflected from the object.
7 . The method of claim 6 further comprising varying polarization of the laser pulses to increase light intensity detected from a selected one of the second plurality of fibers relative to light intensity from fibers adjacent to the selected fiber.
8 . A scanning lidar system comprising:
a transmitter including a laser and a first optical switch configured to receive laser pulses from the laser;
a first plurality of fibers each coupled to a different one of a plurality of outputs of the first optical switch, wherein outputs of the first plurality of fibers are positioned in a first linear array;
a first at least one optical element configured to receive the laser pulses from at least one of the first plurality of fibers and to redirect the laser pulses to illuminate at least a portion of a field of view, wherein the first at least one optical element comprises an aspherical lens configured to form an output beam having an elliptical cross section;
a receiver including a second optical switch and at least one detector;
a second plurality of fibers each coupled to a different input of the second optical switch, an output of the second optical switch coupled to the at least one detector, wherein outputs of the second plurality of fibers are positioned in a second linear array orthogonal to the first linear array;
a second at least one optical element configured to receive the laser pulses reflected from the field of view and to redirect received reflected pulses to at least one of the second plurality of fibers, wherein the second at least one optical element comprises collection optics positioned upstream of beam shaping optics, the beam shaping optics configured to form beams having an elliptical cross section; and
at least one controller configured to control the first optical switch to direct the laser pulses from an input of the first optical switch to each of the plurality of outputs in turn, to control the second optical switch to direct light from each of the second plurality of fibers in turn to the output of the second optical switch, and to process signals from the at least one detector to generate data representing the field of view, wherein the data correspond to pixels with each pixel corresponding to an intersection of the elliptically shaped cross sections of the transmitted and received pulsed beams.
9 . The system of claim 8 wherein the first optical switch and the second optical switch have no moving parts associated with switching light from the input to one of the plurality of outputs, or from the plurality of outputs to the input, respectively.
10 . The system of claim 8 wherein at least one of the first and second optical switches comprises a Faraday rotator.
11 . The system of claim 8 wherein at least one of the first and second optical switches comprises a magneto-optic switch.
12 . The system of claim 8 wherein the at least one controller comprises a first microprocessor-based controller configured to control the first optical switch and a second microprocessor-based controller in communication with the first controller and configured to control the second optical switch.
13 . The system of claim 8 wherein the laser comprises a fiber laser configured to generate pulses having a wavelength between 900 nanometers (nm) and 1700 nanometers (nm).
14 . The system of claim 8 wherein the laser is configured to generate pulses having a nominal wavelength of 1550 nanometers (nm).
15 . The system of claim 8 wherein the at least one first optical element is shaped to form an output beam having an angular divergence along a first axis of at least 20 times the angular divergence along a second axis perpendicular to the first axis.
16 . The system of claim 8 wherein the at least one first optical element comprises a plurality of optical elements, each of the plurality of optical elements associated with one of the first plurality of fibers.
17 . The system of claim 8 wherein the beams having an elliptical cross section have an angular divergence along a second axis at least 20 times the angular divergence along a first axis perpendicular to the second axis.
18 . The system of claim 8 wherein the at least one detector comprises an avalanche photodiode.
19 . The system of claim 8 wherein the at least one detector comprises a plurality of detectors configured to operate in parallel.
20 . The system of claim 8 wherein the laser is configured to transmit polarized pulses and wherein the detector comprises a plurality of detectors each configured to detect received light having a different angle of polarization.
21 . The system of claim 20 wherein the at least one controller processes signals from the plurality of detectors to generate degree of polarization or angle of polarization data representing the field of view.
22 . The system of claim 20 wherein the first at least one optical element and the second at least one optical element each comprises a polarization rotator controlled by the at least one controller and a polarization phase mask.
23 . The system of claim 20 wherein the first at least one optical element and the second at least one optical element each comprise a first linear polarizer, a Faraday rotator, a half-wave retarder phase mask, and a second linear polarizer.
24 . The system of claim 8 wherein the at least one controller is further configured to operate the laser and the first and second optical switches to refresh the data at 100 Hz.
25 . The system of claim 8 further comprising a housing containing the transmitter, the receiver, and the at least one controller and at least one optical head located outside of the housing and containing the first at least one optical element and the second at least one optical element, wherein the first plurality of fibers and the second plurality of fibers extends between the housing and the optical head.
26 . The system of claim 25 wherein the housing contains a transmitter and a receiver associated with each of a plurality of remotely located optical heads each coupled by an associated fiber bundle.
27 . A vehicle comprising a lidar system according to claim 1 .
28 . The vehicle of claim 27 further comprising an actuator configured to rotate at least one of the optical heads.