SEMICONDUCTOR OPTICAL AMPLIFIER WITH BRAGG GRATING
In one embodiment, a light source is 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 the emitted optical signal. The SOA includes an optical waveguide extending along a longitudinal direction from an input end of the SOA to an output end of the SOA. The optical waveguide is configured to guide and provide optical gain to the seed optical signal while the seed optical signal propagates in the longitudinal direction along the optical waveguide from the input end to the output end. The SOA also includes a Bragg grating disposed parallel to the optical waveguide, where the Bragg grating includes a region of the SOA having a refractive index that varies along the longitudinal direction.
1 . A light source configured to emit an optical signal, the light source comprising:
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 optical signal, wherein the SOA comprises:
an optical waveguide extending along a longitudinal direction from an input end of the SOA to an output end of the SOA, wherein the optical waveguide is configured to guide and provide optical gain to the seed optical signal while the seed optical signal propagates in the longitudinal direction along the optical waveguide from the input end to the output end; and
a Bragg grating disposed parallel to the optical waveguide, wherein the Bragg grating comprises a region of the SOA having a refractive index that varies along the longitudinal direction.
2 . The light source of claim 1 , wherein the refractive index varies periodically along the longitudinal direction.
3 . The light source of claim 1 , wherein the Bragg grating is configured to provide a distributed reflection of light within a particular wavelength range.
4 . The light source of claim 1 , wherein the Bragg grating is configured so that light within a particular wavelength range propagating along the optical waveguide receives greater optical gain from the optical waveguide than light outside of the particular wavelength range.
5 . The light source of claim 4 , wherein the particular wavelength range is centered at a wavelength of the seed optical signal and has a spectral width of less than 2 GHz.
6 . The light source of claim 4 , wherein:
the emitted optical signal comprises pulses of light; and
the particular wavelength range that receives greater optical gain from the optical waveguide corresponds to a spectral linewidth of the emitted pulses of light.
7 . The light source of claim 1 , wherein the light source is part of a lidar system, the lidar system comprising:
a scanner configured to direct the emitted optical signal into a field of regard of the lidar system;
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 on a round-trip time for the portion of the emitted optical signal to travel from the lidar system to the target and back to the lidar system.
8 . The light source of claim 7 , wherein the Bragg grating is configured so that light within a particular wavelength range propagating along the optical waveguide receives greater optical gain from the optical waveguide than light outside of the particular wavelength range, wherein a spectral width of the particular wavelength range corresponds to an electrical bandwidth of the receiver.
9 . The light source of claim 8 , wherein the spectral width of the particular wavelength range is less than 2 GHz and is approximately equal to the electrical bandwidth of the receiver.
10 . The light source of claim 8 , wherein the spectral width of the particular wavelength range is approximately 300 MHz, and the electrical bandwidth of the receiver is approximately 300 MHz.
11 . The light source of claim 7 , wherein:
the Bragg grating is configured so that light within a particular wavelength range propagating along the optical waveguide receives greater optical gain from the optical waveguide than light outside of the particular wavelength range;
the emitted optical signal comprises pulses of light; and
a spectral linewidth of the pulses of light corresponds to an electrical bandwidth of the receiver.
12 . The light source of claim 11 , wherein the spectral linewidth of the pulses of light is less than 2 GHz and is approximately equal to the electrical bandwidth of the receiver.
13 . The light source of claim 11 , wherein the spectral linewidth of the pulses of light is approximately 300 MHz, and the electrical bandwidth of the receiver is approximately 300 MHz.
14 . The light source of claim 1 , wherein the optical waveguide is a tapered optical waveguide, wherein a width of the tapered optical waveguide increases from the input end to the output end.
15 . The light source of claim 1 , wherein the light source further comprises an electronic driver configured to:
supply a substantially constant electrical current to the seed laser diode so that the seed optical signal comprises light having a substantially constant optical power; and
supply pulses of electrical current to the SOA so that the emitted optical signal comprises pulses of light, wherein each pulse of current causes the SOA to amplify a temporal portion of the seed optical signal to produce one of the emitted pulses of light.
16 . The light source of claim 1 , further comprising a fiber-optic amplifier configured to receive the emitted optical signal from the SOA and further amplify the emitted optical signal.
17 . The lidar system of claim 1 , wherein the light source is configured as a three-terminal device, wherein (i) the light source comprises a common anode, wherein an anode of the seed laser diode is electrically connected to an anode of the SOA or (ii) the light source comprises a common cathode, wherein a cathode of the seed laser diode is electrically connected to a cathode of the SOA.
18 . The lidar system of claim 1 , wherein the light source is configured as a four-terminal device comprising:
a seed laser anode and a SOA anode, wherein the seed laser anode and the SOA anode are electrically isolated from one another; and
a seed laser cathode and a SOA cathode, wherein the seed laser cathode and the SOA cathode are electrically isolated from one another.
19 . 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; and
a semiconductor optical amplifier (SOA) configured to amplify the seed optical signal to produce the emitted optical signal, wherein the SOA comprises:
an optical waveguide extending along a longitudinal direction from an input end of the SOA to an output end of the SOA, wherein the optical waveguide is configured to guide and provide optical gain to the seed optical signal while the seed optical signal propagates in the longitudinal direction along the optical waveguide from the input end to the output end; and
a Bragg grating disposed parallel to the optical waveguide, wherein the Bragg grating comprises a region of the SOA having a refractive index that varies along the longitudinal direction;
a scanner configured to direct the emitted optical signal into a field of regard of the lidar system;
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 on a round-trip time for the portion of the emitted optical signal to travel from the lidar system to the target and back to the lidar system.
20 . A lidar system comprising:
a light source configured to emit (i) local-oscillator light and (ii) pulses of light, wherein each emitted pulse of light is coherent with a corresponding portion of the local-oscillator light, and wherein the light source comprises:
a seed laser diode configured to produce a seed optical signal and the local-oscillator light; and
a semiconductor optical amplifier (SOA) configured to amplify temporal portions of the seed optical signal to produce the emitted pulses of light, wherein each amplified temporal portion of the seed optical signal corresponds to one of the emitted pulses of light, and wherein the SOA comprises:
an optical waveguide extending along a longitudinal direction from an input end to an output end of the SOA, wherein the optical waveguide is configured to guide and provide optical gain to the temporal portions of the seed optical signal while the temporal portions of the seed optical signal propagate in the longitudinal direction along the optical waveguide from the input end to the output end; and
a Bragg grating disposed parallel to the optical waveguide, wherein the Bragg grating comprises a region of the SOA having a refractive index that varies along the longitudinal direction;
a receiver configured to detect the local-oscillator light and a received pulse of light, the received pulse of light comprising light from one of the emitted pulses of light that is scattered by a target located a distance from the lidar system, wherein the local-oscillator light and the received pulse of light are coherently mixed together at the receiver; and
a processor configured to determine the distance from the lidar system to the target based at least in part on a time-of-arrival for the received pulse of light.