Lidar system with semiconductor optical amplifier

Abstract

In one embodiment, a lidar system includes a light source configured to emit an optical signal. The light source includes 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 an amplified seed optical signal, where the emitted optical signal includes the amplified seed optical signal. The light source further includes an electronic driver configured to supply electrical current to the seed laser diode and electrical current to the SOA. The lidar system also includes a receiver configured to detect a portion of the emitted optical signal scattered by a target located a distance from the lidar system. The lidar system further includes a processor configured to determine the distance from the lidar system to the target.

What is claimed is: 
     
         1 . A lidar system comprising:
 a light source configured to emit an optical signal, the light source comprising:
 a seed laser diode configured to produce a seed optical signal; 
 a semiconductor optical amplifier (SOA) configured to amplify the seed optical signal to produce an amplified seed optical signal, wherein the emitted optical signal comprises the amplified seed optical signal; and 
 an electronic driver configured to supply electrical current to the seed laser diode and electrical current to the SOA; 
   a receiver configured to detect a portion of the emitted optical signal scattered by a target located a distance from the lidar system; and   a processor configured to determine the distance from the lidar system to the target based at least in part on a round-trip time for at least a portion of the emitted optical signal to travel from the lidar system to the target and back to the lidar system.   
     
     
         2 . The lidar system of  claim 1 , wherein the electronic driver is directly bump-bonded to an anode or a cathode of the SOA via one or more solder bumps. 
     
     
         3 . The lidar system of  claim 1 , wherein the electronic driver is configured to supply electrical current to the SOA via (i) a first low-inductance electrical connection between the electronic driver and an anode of the SOA and (ii) a second low-inductance electrical connection between the electronic driver and a cathode of the SOA, wherein:
 the first and second electrical connections each has an inductance of less than 10 nanohenries; and   the first and second electrical connections each has a length of less than 10 millimeters.   
     
     
         4 . The lidar system of  claim 3 , wherein the first and second electrical connections each comprises one or more bump bonds and/or one or more vias. 
     
     
         5 . The lidar system of  claim 1 , wherein the seed laser diode and the SOA are configured as a three-terminal device comprising a common anode or a common cathode. 
     
     
         6 . The lidar system of  claim 1 , wherein the seed laser diode and the SOA are configured as a four-terminal device comprising a seed laser anode, a seed laser cathode, a SOA anode, and a SOA cathode. 
     
     
         7 . The lidar system of  claim 1 , wherein:
 the electrical current supplied to the SOA comprises pulses of current, each pulse of current corresponding to an optical pulse emitted by the SOA; and   the SOA is further configured to optically absorb seed-laser light during a period of time between two successive pulses of current.   
     
     
         8 . The lidar system of  claim 7 , wherein the SOA being configured to optically absorb seed-laser light during the period of time between two successive pulses of current corresponds to the optical pulses emitted by the SOA having a temporal extinction ratio (TER) greater than 40 dB. 
     
     
         9 . The lidar system of  claim 1 , wherein the SOA comprises an input end, an output end, and a tapered waveguide disposed between the input end and the output end, wherein:
 a width of the tapered waveguide increases from the input end towards the output end;   the input end is configured to receive the seed optical signal;   the tapered waveguide is configured to amplify the seed optical signal as the seed optical signal propagates along the tapered waveguide from the input end to the output end; and   the output end is configured to emit the amplified seed optical signal.   
     
     
         10 . The lidar system of  claim 9 , wherein the SOA further comprises an anti-reflection coating on the output end configured to reduce a reflectivity of the output end at a wavelength of the amplified seed optical signal. 
     
     
         11 . The lidar system of  claim 9 , wherein the SOA waveguide is angled with respect to the input and output ends. 
     
     
         12 . The lidar system of  claim 1 , further comprising an enclosure, wherein the seed laser diode, the SOA, and the electronic driver are disposed within the enclosure. 
     
     
         13 . The lidar system of  claim 12 , further comprising a thermoelectric cooler (TEC) disposed within the enclosure, wherein the TEC is configured to perform one or more of: (i) stabilize a temperature associated with the seed laser diode or the SOA, (ii) remove heat produced by the seed laser diode, (iii) remove heat produced by the SOA, and (iv) remove heat produced by the electronic driver. 
     
     
         14 . The lidar system of  claim 12 , further comprising one or more lenses disposed within the enclosure, wherein the one or more lenses are configured to collimate or focus the amplified seed optical signal. 
     
     
         15 . The lidar system of  claim 12 , wherein the enclosure comprises a thermally conductive material. 
     
     
         16 . The lidar system of  claim 12 , wherein the enclosure is configured to prevent water vapor, liquid water, dirt, or dust from entering the enclosure. 
     
     
         17 . The lidar system of  claim 1 , wherein the light source further comprises one or more lenses configured to collect the amplified seed optical signal and produce the emitted optical signal as a collimated free-space optical beam. 
     
     
         18 . The lidar system of  claim 17 , wherein the one or more lenses comprise:
 a fast-axis collimating lens configured to collimate the amplified seed optical signal along a first axis; and   a slow-axis collimating lens configured to collimate the amplified seed optical signal along a second axis different from the first axis.   
     
     
         19 . The lidar system of  claim 1 , wherein the light source further comprises one or more lenses configured to couple the amplified seed optical signal into an optical fiber. 
     
     
         20 . The lidar system of  claim 19 , wherein the one or more lenses comprise:
 a fast-axis collimating lens configured to collimate the amplified seed optical signal along a first axis;   a slow-axis collimating lens configured to collimate the amplified seed optical signal along a second axis different from the first axis; and   a focusing lens configured to focus the amplified seed optical signal into the optical fiber.   
     
     
         21 . The lidar system of  claim 1 , wherein the light source further comprises one or more coupling lenses disposed between the seed laser diode and the SOA, wherein the seed laser diode and the SOA are separate devices and the seed optical signal is a free-space optical beam that is coupled into a waveguide of the SOA by the one or more coupling lenses. 
     
     
         22 . The lidar system of  claim 1 , wherein the light source further comprises a fiber-optic amplifier, the fiber-optic amplifier comprising:
 one or more pump laser diodes configured to produce pump-laser light; and   an optical gain fiber configured to absorb, by a gain material of the optical gain fiber, at least a portion of the pump-laser light and further amplify, by the gain material, the amplified seed optical signal as the amplified seed optical signal propagates along the optical gain fiber.   
     
     
         23 . The lidar system of  claim 22 , wherein the gain fiber is a multi-clad gain fiber comprising a core, an inner cladding, and one or more additional cladding layers, wherein the core is configured to guide the amplified seed optical signal and the inner cladding is configured to guide the pump-laser light. 
     
     
         24 . The lidar system of  claim 1 , wherein the light source further comprises an optical filter configured to transmit the amplified seed optical signal and block amplified spontaneous emission (ASE) light produced by the SOA. 
     
     
         25 . The lidar system of  claim 1 , wherein the emitted optical signal has a wavelength between 1500 nm and 1510 nm. 
     
     
         26 . The lidar system of  claim 1 , wherein the light source further comprises a grating located at or near an output end of the SOA, wherein the grating is configured to:
 transmit a fundamental optical mode of the amplified seed optical signal; and   angularly deflect one or more higher-order transverse optical modes of the amplified seed optical signal.   
     
     
         27 . The lidar system of  claim 1 , wherein:
 the seed laser diode is a first seed laser diode, and the seed optical signal is a first seed optical signal;   the SOA is a first SOA, and the amplified seed optical signal is a first amplified seed optical signal;   the first amplified seed optical signal comprises light having a first polarization; and   the light source further comprises:
 a second seed laser diode configured to produce a second seed optical signal; 
 a second SOA configured to amplify the second seed optical signal to produce a second amplified seed optical signal having a second polarization orthogonal to the first polarization; and 
 a polarization combiner configured to combine the first and second amplified seed optical signals to produce a combined optical signal comprising light having the first polarization and the second polarization, wherein the emitted optical signal comprises the combined optical signal. 
   
     
     
         28 . The lidar system of  claim 1 , wherein the lidar system further comprises a scanner configured to scan the emitted optical signal across a field of regard of the lidar system, the scanner comprising one or more mirrors, wherein each mirror is mechanically driven by a galvanometer scanner, a resonant scanner, a microelectromechanical systems (MEMS) device, a voice coil motor, or a synchronous electric motor. 
     
     
         29 . The lidar system of  claim 1 , wherein the lidar system further comprises a scanner configured to scan the emitted optical signal across a field of regard of the lidar system, wherein the scanner comprises:
 a polygon mirror configured to scan the emitted pulses of light along a first direction within the field of regard; and   a scan mirror configured to scan the emitted pulses of light along a second direction within the field of regard, the second direction different from the first direction.   
     
     
         30 . The lidar system of  claim 1 , wherein the lidar system further comprises a scanner configured to scan the emitted optical signal across a field of regard of the lidar system, wherein the scanner comprises a solid-state scanning device configured to scan the emitted optical signal without use of moving parts. 
     
     
         31 . The lidar system of  claim 1 , wherein the lidar system is part of a vehicle comprising an advanced driver assistance system (ADAS) configured to assist a driver of the vehicle in operating the vehicle, wherein the lidar system is configured to provide information about a surrounding environment of the vehicle to the ADAS. 
     
     
         32 . The lidar system of  claim 1 , wherein the lidar system is part of an autonomous vehicle comprising an autonomous-vehicle driving system configured to guide the autonomous vehicle through a surrounding environment toward a destination, wherein the lidar system is configured to provide information about the surrounding environment to the autonomous-vehicle driving system.