Characterizing diode laser coherence using photonic integrated circuits

During this summer REU at Clemson University, I implemented two interferometer-based photonic circuits to characterize diode lasers fabricated in Prof. Lin Zhu's lab. The first circuit measures a laser's linewith by splitting the beam, shifting the frequency of one of the split beams, then recombining the beams. This method provides a rapid measurement of the laser's frequency noise spread.

The second photonic circuit I constructed measured phase noise in lasers by splitting the beam, and, using a closed PID control loop, maintaining a quarter-wave phase difference upon recombination. This method converts phase noise to intensity noise that can be characterized using a spectrum analyzer.