Optical parametric division

A novel concept of optical frequency division based on an efficient, one-step parametric downconversion process is described. An input optical frequency is halved by phase locking the beat frequency of the two subharmonic outputs of an optical parametric oscillator to a microwave frequency source. The approach was demonstrated in a tunable KTP optical parametric oscillator whose phase-locked beat-note linewidth was at the Hz level. A wideband phase modulator that matched the optical and microwave phase velocities was fabricated to facilitate difference frequency measurements. A modulation index of 0.36 with a microwave power of 0.5 W was obtained at 12.4 GHz. When the modulator was enclosed in an optical cavity to enhance the modulation, it generated a fifth order sideband at 62 GHz with 0.1 % sideband power. A new method for measuring optical frequencies from the UV to the near-IR relative to the cesium clock is also described