Stabilization of a Birefringence-Free Electro-Optic Etalon

Fabry-Perot interferometers, or etalons, can be used as optical telecommunication devices to decode information encoded in the phase of light waves. This is a common practice in telecommunications technologies around the world. The etalon in our experiment was designed to be birefringence-free and controlled using the electro-optic effect. We characterized the etalon's optical properties and stabilized its operating point with real-time feedback, with the goal of building a practical, robust device capable of decoding phase-shift keyed (PSK) signals and operating in field conditions. We found the etalon's birefringence level was around 2.826 parts per million. We stabilized the etalon such that it returns to its stabilization set point quickly after being perturbed, proving the etalon can be used as a demodulator for PSK signals.