External cavity laser with reduced optical mode-hopping

A system, comprising:

• a processor;
• memory, coupled to the processor, configured to store a program module;
• and
• an optical source, wherein the optical source includes:
• a semiconductor optical amplifier defined in a semiconductor other than silicon and having a first edge and a second edge, wherein the semiconductor optical amplifier includes a reflective coating on the first edge, and wherein the semiconductor optical amplifier is configured to provide an optical signal at the second edge;
• and
• a photonic chip optically coupled to the semiconductor optical amplifier, wherein the photonic chip includes:
• an optical waveguide configured to convey the optical signal;
• a ring resonator, optically coupled to the optical waveguide and having a resonance wavelength, configured to reflect at least the resonance wavelength in the optical signal, wherein the reflective coating and the ring resonator define an optical cavity;
• a thermal-tuning mechanism, thermally coupled to the ring resonator, configured to adjust the resonance wavelength;
• a photo-detector, optically coupled to an output of the ring resonator, configured to measure optical power output by the ring resonator;
• and
• control logic, electrically coupled to the thermal-tuning mechanism and the photo-detector, configured to adjust the temperature of the ring resonator based on the measured optical power to lock a cavity mode of the optical cavity to a carrier wavelength
• wherein the optical source further includes a temperature-compensation element, optically coupled to the optical waveguide, configured to compensate for a temperature dependence of indexes of refraction of the optical waveguide.

A method for locking a cavity mode for an external cavity laser, the method comprising:

• generating an optical signal in a semiconductor optical amplifier defined in a semiconductor other than silicon, wherein the semiconductor optical amplifier includes a reflective coating on a first edge, and wherein the semiconductor optical amplifier provides the optical signal at a second edge;
• conveying the optical signal in an optical waveguide on a photonic chip;
• reflecting at least a resonance wavelength in the optical signal using a ring resonator having the resonance wavelength, wherein the reflective coating and the ring resonator define an optical cavity;
• measuring an optical power output by the ring resonator using a photo-detector;
• and
• modifying a temperature of the ring resonator using a thermal-tuning mechanism, thermally coupled to the ring resonator, to adjust the resonance wavelength based on the measured optical power to lock the cavity mode of the optical cavity
• using a temperature-compensation element, optically coupled to the optical waveguide, to compensate for a temperature dependence of indexes of refraction of the optical waveguide.