A tunable laser comprised of a gain section for creating a light beam by spontaneous emission over a bandwidth, a phase section for controlling the light beam around a center frequency of the bandwidth, a cavity for guiding and reflecting the light beam, a front mirror bounding an end of the cavity, and a back mirror bounding an opposite end of the cavity. The back mirror has a &kgr;effB approximately equal to &agr;Tune, where &kgr;effB is an effective coupling constant and &agr;Tune is the maximum amount of propagation loss anticipated for an amount of peak tuning required, and a length of the back mirror is made to produce greater than approximately 80% reflectivity.