Frequency stabilization of two orthogonally polarized external cavity laser diodes using a novel γ-type optical configuration consist of a phase modulator and a Faraday rotator mirror

We propose a novel method to stabilize two external cavity lasers for optical generation of microwave and millimeter wave signals. In our method, two 1550-nm, servo-locked external cavity laser diodes (ECLDs) are simultaneously locked to two resonance frequencies of a single Fabry-Perot optical cavity. The stabilization of two lasers are realized by introducing classical FM sideband technique. In .-type optical configuration, two wavelengths from the ECLDs with orthogonal polarization are simultaneously phase modulated by a phase modulator with a Faraday rotator mirror. The .-type optical configuration is designed as a compact, stable and double-pass phase modulation apparatus with same modulation index for two orthogonally polarized signals transmitted through a polarization maintaining fiber. We obtain short-term stability of 200 kHz at an averaging of 10ms, which is measured with the square root of the Allan variance from the beat note between frequency stabilized lasers.