Fabry-Perot based multi resonant cavity tunable laser

A laser comprising:

• a ring resonator structure;
• and
• a Fabry-Perot filter connected in cascade to the ring resonator structure by a coupling waveguide,
• wherein the coupling waveguide is configured to propagate light having a frequency corresponding to any of the resonant frequencies of the ring resonator structure to the Fabry-Perot filter, and the Fabry-Perot filter is configured to select one or more frequencies and return light having a frequency matching any of the selected frequencies to the ring resonator structure via the coupling waveguide,
• wherein the ring resonator structure comprises a plurality of ring resonators, each connected to one another in cascade, wherein each pair of adjacent ring resonators is connected by a respective connecting waveguide,
• wherein one or more of the connecting waveguides is a straight waveguide,
• wherein the coupling waveguide is a first coupling waveguide, and a first ring resonator amongst the plurality of ring resonators is connected to a gain medium of the laser by a second coupling waveguide,
• wherein a last ring resonator amongst the plurality of ring resonators is coupled to the first coupling waveguide, and
• wherein the first ring resonator is coupled to the second coupling waveguide by evanescent coupling.