LIDAR SYSTEM WITH DETECTOR ARRAY
In one embodiment, a lidar system includes a light source configured to emit pulses of light and a scanner configured to scan the emitted pulses of light across a field of regard of the lidar system. The scanner includes (i) a beam deflector configured to direct each emitted pulse of light along a first scan axis and (ii) a scan mirror configured to scan the emitted pulses of light along a second scan axis different from the first scan axis. The lidar system also includes a receiver that includes a one-dimensional detector array that includes multiple detector elements arranged along a direction corresponding to the first scan axis. The receiver is configured to (i) detect a received pulse of light that includes a portion of one of the emitted pulses of light scattered by a target and (ii) determine a time of arrival of the received pulse of light.
1 . A lidar system comprising:
a light source configured to emit pulses of light;
a scanner configured to scan the emitted pulses of light across a field of regard of the lidar system, the scanner comprising:
a beam deflector configured to direct each emitted pulse of light along a first scan axis; and
a scan mirror configured to scan the emitted pulses of light along a second scan axis different from the first scan axis;
a receiver comprising a one-dimensional detector array comprising a plurality of detector elements arranged along a direction corresponding to the first scan axis, wherein the receiver is configured to:
detect a received pulse of light, the received pulse of light comprising a portion of one of the emitted pulses of light scattered by a target located a distance from the lidar system; and
determine a time of arrival of the received pulse of light; and
a processor configured to determine the distance from the lidar system to the target based on the time of arrival of the received pulse of light.
2 . The lidar system of claim 1 , wherein the received pulse of light is part of an input beam of light, the input beam comprising a plurality of received pulses of light, wherein the input beam, prior to being detected by the receiver, is reflected by the scan mirror and bypasses the beam deflector.
3 . The lidar system of claim 2 , wherein the received pulse of light is directed to a portion of the detector array corresponding to a direction along the first scan axis at which the emitted pulse of light was directed by the beam deflector.
4 . The lidar system of claim 2 , wherein:
the emitted pulses of light are part of an output beam of light, the output beam of light having a beam diameter of d 1 ;
the input beam of light has a beam diameter of d 2 , wherein d 2 is greater than d 1 ;
an aperture of the beam deflector has a length or diameter of s 1 ; and
an aperture of the scan mirror has a length or diameter of s 2 , wherein:
s 2 is greater than s 1 ,
s 2 is greater than or equal to d 2 ,
s 1 is greater than or equal to d 1 , and
s 1 is less than d 2 .
5 . The lidar system of claim 1 , wherein a scanning speed of the beam deflector is greater than or equal to four times a scanning speed of the scan mirror.
6 . The lidar system of claim 1 , wherein the scan mirror comprises a polygon mirror configured to rotate to scan the emitted pulses of light along the second scan axis, wherein the polygon mirror comprises a plurality of reflective surfaces angularly offset from one another along a periphery of the polygon mirror, each reflective surface configured to reflect, in sequence as the polygon mirror rotates, a portion of the emitted pulses of light.
7 . The lidar system of claim 6 , wherein:
the polygon mirror comprises S reflective surfaces, wherein S is an integer greater than or equal to 2;
the polygon mirror is configured to rotate at a rotation speed of R revolutions per second;
the portion of the emitted pulses of light reflected from each of the reflective surfaces of the polygon mirror are associated with a single scan across at least a portion of the field of regard of the lidar system; and
the lidar system is configured to produce point clouds at a frame rate of F frames per second according to an expression F=S×R.
8 . The lidar system of claim 6 , wherein:
the polygon mirror is configured to rotate about a rotation axis; and
one or more of the reflective surfaces of the polygon mirror have non-zero angles with respect to the rotation axis of the polygon mirror.
9 . The lidar system of claim 8 , wherein:
each of the reflective surfaces has one of r different angles with respect to the rotation axis, wherein r is an integer greater than or equal to 2 and less than or equal to a number of reflective surfaces of the polygon mirror;
the field of regard of the lidar system is subdivided into r regions; and
each reflective surface of the polygon mirror is configured to scan one of the portions of the emitted pulses of light along the second scan axis within one of the r regions of the field of regard.
10 . The lidar system of claim 9 , wherein:
the beam deflector is configured to direct the emitted pulses of light over an angular range of α along the first scan axis; and
the field of regard has an angular extent along the first scan axis of greater than or equal to 80% of r×α and less than or equal to r×α.
11 . The lidar system of claim 9 , wherein two or more of the reflective surfaces have equal angles with respect to the rotation axis of the polygon mirror, wherein the two or more reflective surfaces are each configured to scan one of the portions of the emitted pulses of light along the second scan axis within a same one of the r regions of the field of regard.
12 . The lidar system of claim 9 , wherein:
the polygon mirror comprises S reflective surfaces, wherein S is greater than or equal to r;
the polygon mirror is configured to rotate at a rotation speed of R revolutions per second; and
the lidar system is configured to produce point clouds at a frame rate of R frames per second, wherein each point cloud comprises pixels corresponding to pulses of light reflected from each of the S reflective surfaces.
13 . The lidar system of claim 1 , wherein the scan mirror comprises a galvanometer scanner.
14 . The lidar system of claim 1 , wherein the beam deflector comprises a microelectromechanical systems (MEMS) device comprising a reflective surface configured to pivot to direct the emitted pulses of light along the first scan axis.
15 . The lidar system of claim 1 , wherein the beam deflector comprises a polygon mirror configured to rotate to direct the emitted pulses of light along the first scan axis, wherein the polygon mirror comprises a plurality of reflective surfaces angularly offset from one another along a periphery of the polygon mirror, each reflective surface configured to reflect, in sequence as the polygon mirror rotates, a portion of the emitted pulses of light.
16 . The lidar system of claim 1 , wherein the beam deflector comprises an electro-optic device, an acousto-optic device, a liquid-crystal device, a vibrating optical fiber, a resonant-mirror scanner, or an optical phased array.
17 . The lidar system of claim 1 , wherein:
the received pulse of light is part of an input beam of light comprising a plurality of received pulses of light; and
the receiver further comprises a lens configured to focus the input beam of light onto the detector array, wherein each received pulse of light is directed to a portion of the detector array corresponding to a direction along the first scan axis at which a corresponding emitted pulse of light was directed by the beam deflector.
18 . The lidar system of claim 1 , wherein the second scan axis is substantially orthogonal to the first scan axis.
19 . The lidar system of claim 1 , wherein each detector element is configured to detect received pulses of light originating from a particular direction with respect to the first scan axis.
20 . The lidar system of claim 1 , wherein the detector array comprises silicon (Si) detector elements, silicon-germanium (SiGe) detector elements, silicon-germanium-tin (SiGeSn) detector elements, or indium-gallium-arsenide (InGaAs) detector elements.
21 . The lidar system of claim 1 , wherein each detector element is an avalanche photodiode (APD), a PN photodiode, a PIN photodiode, or a quantum dot photodetector.
22 . The lidar system of claim 1 , wherein the detector array further comprises an optical filter configured to transmit particular wavelengths of light to the detector elements.
23 . The method of claim 1 , wherein each detector element of the one-dimensional detector array comprises an anode and a cathode wherein the anodes of the one-dimensional detector array are electrically isolated from one another, and the cathodes of the one-dimensional detector array are electrically isolated from one another.
24 . The lidar system of claim 1 , wherein:
the received pulse of light is incident on one or more detector elements of the detector array;
the one or more detector elements are configured to produce one or more respective photocurrent signals corresponding to the received pulse of light; and
the receiver further comprises an electronic amplifier configured to amplify the one or more photocurrent signals to produce one or more voltage signals, each voltage signal corresponding to one of the photocurrent signals.
25 . The lidar system of claim 24 , wherein the receiver further comprises a pulse-detection circuit comprising a plurality of comparators coupled to a respective plurality of time-to-digital converters (TDCs), wherein:
each comparator is configured to receive one of the voltage signals and provide an electrical-edge signal to a corresponding TDC when the received voltage signal rises above or falls below a particular threshold voltage; and
the corresponding TDC is configured to produce a time value corresponding to a time when the electrical-edge signal was received, wherein the time of arrival of the received pulse of light is determined based on one or more time values produced by one or more of the TDCs.
26 . The lidar system of claim 24 , wherein the receiver further comprises a N×n electronic multiplexer disposed between the detector array and the electronic amplifier, wherein:
N is a number of inputs of the multiplexer, and n is a number of outputs of the multiplexer;
the one-dimensional detector array comprises N detector elements, and each input of the multiplexer is coupled to one of the detector elements;
the electronic amplifier comprises n inputs, and each output of the multiplexer is coupled to one of the inputs of the electronic amplifier, wherein n is an integer greater than or equal to 1; and
the multiplexer is configured to couple the one or more photocurrent signals from the one or more detector elements to one or more respective inputs of the electronic amplifier.
27 . The lidar system of claim 1 , wherein the light source comprises:
a seed laser diode configured to produce seed light; and
an optical amplifier configured to amplify the seed light to produce the emitted pulses of light, wherein the optical amplifier comprises a semiconductor optical amplifier (SOA), a fiber-optic amplifier, or a SOA followed by a fiber-optic amplifier.
28 . The lidar system of claim 27 , wherein the seed laser diode is a sampled-grating distributed Bragg reflector (SG-DBR) laser configured to produce the seed light at a plurality of different wavelengths, wherein each of the emitted pulses of light has a particular wavelength of the plurality of different wavelengths.
29 . The lidar system of claim 28 , wherein the beam deflector is configured to direct each emitted pulse of light along the first scan axis by angularly deflecting each emitted pulse of light along the first scan axis according to the particular wavelength of the emitted pulse of light.
30 . The lidar system of claim 1 , wherein:
the time of arrival of the received pulse of light corresponds to a round-trip time (T) for the portion of the one of the emitted pulses of light to travel to the target and back to the lidar system; and
the distance (D) to the target is determined from an expression D=c·T/2, wherein c is a speed of light.
31 . The lidar system of claim 1 , wherein the emitted pulses of light have optical characteristics comprising:
one or more wavelengths between 1400 nanometers (nm) and 1600 nm;
a pulse energy between 0.01 μJ and 100 μJ;
a pulse repetition frequency between 80 kHz and 10 MHz; and
a pulse duration between 1 ns and 100 ns.