Optoelectronic oscillator stabilized to an intra-loop Fabry-Perot cavity by a dual servo system

We report construction and characterization of an optoelectronic oscillator (OEO), which is stabilized to an intra-loop Fabry-Perot cavity by a dual servo system. In addition to providing strong mode selection and increasing the Q factor by adding significant loop length, the cavity serves as a stable frequency reference. In order to fully exploit the stability we employ a dual servo system. Carrier frequency is locked to the cavity mode by using Pound-Drever-Hall technique. The OEO loop length is adjusted by comparing the phase difference between the carrier-sideband beat signals at upstream and downstream sides of the cavity so that the OEO mode spacing is commensurate with the free spectral range of the cavity. This dual servo system and additional stabilizations of the seed laser frequency to a cesium transition and the laser power result in an order of magnitude improvement in OEO frequency stability over a previous work using a free-running Fabry-Perot cavity. Long term Allan deviation of the OEO is 6 x 10(-8). It represents 4 x 10(-4) of the cavity resonance linewidth. We also discuss possibility of relating the OEO frequency to an atomic transition as an absolute frequency reference. (C) 2010 Optical Society of America