Bragg section effects on linewidth and lineshape in 1.55-μm DBR tunable laser diodes

We report linewidth and lineshape measurements on 1.55-μm distributed Bragg reflector tunable laser diodes using the heterodyne method. We measure Lorentzian linewidths ranging from 3.5 to 25 MHz without any passive section injection. Biasing the Bragg section enhances the residual linewidth up to 6.2 MHz, changes the linewidth-power product, and brings an additional Gaussian lineshape. The feedback sensitivity of the overall setup is also demonstrated.