Comb laser

A method for generating radiation, the method comprising:

• providing a reflective semiconductor optical amplifier (RSOA), comprising a gain medium configured to amplify laser radiation within a given gain band and a first reflector disposed at a first end of the gain medium;
• optically coupling the RSOA to an external laser cavity, which is disposed on an optical substrate and comprises a second reflector, a comb filter disposed between the second reflector and the RSOA and configured to pass a set of distinct wavelength sub-bands within the gain band, the set of distinct wavelength sub-bands defining a comb, and a bandpass filter, disposed between the second reflector and the RSOA in series with the comb filter, the bandpass filter having a passband encompassing a subset of the wavelength sub-bands in the comb;
• and
• applying an electrical drive to the RSOA, whereby the laser radiation in subset of the wavelength sub-bands in the comb is emitted through the second reflector.

An integrated optical device, comprising:

• an optical substrate;
• and
• multiple optical ring resonators, which are disposed on the optical substrate and interconnected in series by waveguides, and which comprise:
• a first optical ring resonator, configured to pass a set of distinct wavelength sub-bands, the set of distinct wavelength sub-bands defining a comb;
• and
• one or more second optical ring resonators, each second optical ring resonator among the one or more second optical ring resonators configured to filter out a selected group of the wavelength sub-bands in the comb.