Tunable laser and method for tuning a lasing mode

A tunable laser for tuning a lasing mode based on light beams travelling through at least one block of channel waveguides with at least two tunable combs, the tunable laser comprising:

• a frequency selective optical multiplexer comprising a first terminal for receiving and/or transmitting light, at least one block of channel waveguides, each channel waveguide having a reflectively coated first tail and a second tail, and an optical coupling element optically coupling the first terminal with the second tails of the channel waveguides of the at least one block of channel waveguides, each of the channel waveguides having a different length;
• a gain element, configured to generate a broad spectrum of light, the gain element coupling the first terminal of the frequency selective optical multiplexer with a reflective element;
• a phase element coupled to the gain element, wherein the phase element is configured to fine-tune the lasing mode and to offset a phase drift of the tunable laser;
• and
• a plurality of optical tuners, each optical tuner coupled to a respective plurality of branches of the at least one block of channel waveguides, wherein the plurality of optical tuners are configured to tune a lasing mode based on light beams travelling through the at least one block of channel waveguides.