A MEMS-based swept laser source is formed from two coupled cavities. The first cavity includes a first mirror and a fully reflective moveable mirror and operates to tune the output wavelength of the laser. The second cavity is optically coupled to the first cavity and includes an active gain medium, the first mirror and a second mirror. The second cavity further has a length substantially greater than the first cavity such that there are multiple longitudinal modes of the second cavity within a transmission bandwidth of the first cavity output.