Frequency stabilization of a hybrid-integrated InP-Si₃N₄ diode laser

Diode lasers in the visible and the infrared based on hybrid integration of a semiconductor optical amplifier with a long and low-loss Si₃N₄ frequency-selective circuit have the advantage of generating narrow intrinsic linewidths in the kHz range and even down to 40 Hz. This high level of frequency stability on short timescales benefits short-term measurements, such as for interferometry and coherent data communication. However, as with all lasers, technical noise and long-term drifts are present, increasing the linewidth on longer timescales.
We present our investigation into stabilization schemes by locking an InP-Si3N4 hybrid-integrated laser to an absolute frequency reference, e.g., to absorption lines of acetylene (C₂H₂) in the laser’s infrared emission range. The laser is frequency controlled via the diode current and by thermal tuning of integrated microring resonators and a cavity phase section. We discuss the optimal way to stabilize the laser frequency through feedback on these controls. Experimental results on the frequency stability over longer terms will be presented.