RF-wave generation using external cavity laser diodes frequency-stabilized to single optical cavity by using orthogonal polarized modes

We propose a novel stabilization technique for two 1550-nm band external cavity laser diodes (ECLDs) used in optical generation of microwave and millimeter wave signals. Using FM sideband technique, those two ECLDs are simultaneously locked to two resonant modes of a single Fabry-Perot cavity. In the scheme, a new gamma-type optical configuration is used for simultaneous phase modulation of orthogonally polarized two wavelengths transmitted through slow and fast axis of polarization maintaining fiber. The gamma-type optical configuration, which consists of a phase modulator and a Faraday rotator mirror combined with an optical circulator, is a simple and compact apparatus to achieve double-pass phase modulation with the same modulation index. In this paper, we show the results of frequency stabilization of two ECLDs using gamma-type configuration, and compare with the results obtained in conventional non-gamma-type configuration. Short-term stability of 200 kHz at an averaging of 10 ms is achieved in the simple gamma-type configuration.