A CONTROL LOOP WHICH ENSURES HIGH SIDE-MODE-SUPPRESSION RATIO IN A TUNABLE DBR LASER

We present a control loop which ensures single-mode operation of a tunable distributed-Bragg-reflector (DBR) laser. This control loop uses no external optics. The error signal is derived from an integrated detector which measures the light transmitted through the Bragg section. Using this signal to control the current to the Bragg section, the laser is tuned to where the side-mode-suppression ratio is high. This guarantees that the laser will remain single-mode, even when modulated. This servo will find application in wavelength-division-multiplexed (WDM) systems.