Laser transmitter for reduced SBS

A laser transmitter comprising

• a tunable laser source for delivering to an optical fiber an optical output signal in any one of N different longitudinal modes, said source including
• a gain section including an MQW active region, a DFB region optically coupled to said active region for selecting the nominal wavelength of the longitudinal mode which lases, and a first waveguide optically coupled to said active region to permit egress of the laser output signal,
• a composite reflector optically coupled to one end of said first waveguide so as to form a cavity resonator with said DFB region, said composite reflector including an MQW second region optically coupled to said MQW active region, a second waveguide having one end optically coupled to said first waveguide, and a relatively high reflectivity dielectric layer disposed at the other end of said second waveguide,
• first tuner means for applying a tuning voltage to said MQW second region to induce therein changes in refractive index, thereby to alter the center wavelength of said output signal, and driver means for applying drive current to said active region, and
• the current applied to said active region and the shape of said first waveguide being mutually adapted so that said N longitudinal modes have essentially the same threshold gain and so that a portion of said DFB region spanned by said first waveguide is segmented into N zones, each zone providing optical feedback at a different wavelength corresponding to a different one of said longitudinal modes, and
• a dither source for applying to said MQW second region a dither signal effective to broaden the spectrum of said output signal, thereby to reduce SBS in said fiber.