Tunable semiconductor laser having cavity with ring resonator mirror and mach-zehnder interferometer

Abstract

A semiconductor laser is provided having a cavity including a gain chip, a Mach-Zehnder wide tuning port, and a ring resonator mirror. Optical signals generated by the gain chip propagate through the Mach-Zehnder wide tuning port and into the ring resonator mirror where the optical signals are reflected back through the Mach-Zehnder wide tuning port to the gain chip. The ring resonator is configured to reflect only those optical signals back into the laser cavity having wavelengths within a set of sharp peaks and the laser cavity therefore can resonate only within one of the sharp peaks. The ring resonator mirror is heated to adjust its dimensions so as to maintain one of the sharp peaks at a selected emission wavelength. As optical signals reflected from the ring resonator pass through the Mach-Zehnder wide tuning port, the signals are split between two channels of differing lengths resulting in optical interference. The optical interference limits the ability of the laser cavity to resonate at wavelengths other than near the center of a single broad peak determined by the relative lengths of the two channels. The Mach-Zehnder wide tuning port is heated to vary the relative lengths of the two channels so as to maintain the single broad peak at the selected transmission wavelength. In this manner, the laser cavity is controlled to resonate substantially only at the selected wavelength. Resonance at the other sharp resonance peaks permitted by the ring resonator is significantly reduced, thereby significantly reducing transmission sidebands generated by the laser.