Long-term stable operation and absolute frequency stabilization of a doubly resonant parametric oscillator

We demonstrate a doubly resonant optical parametric oscillator that operated on a single mode pair for 18 h without mode hops, and whose output frequencies can be tuned by almost 10 GHz without mode hops by the tuning of the pump laser frequency. The tuning range is limited by the available pump tuning range. Active stabilization is used that minimizes the detuning of the parametrically generated waves with respect to the DRO cavity resonances. Absolute frequency stabilization of the idler wave is achieved by locking its frequency to an ultra-stable cryogenic reference resonator, using the pump laser frequency as control parameter. The frequency instability reached is below the 1-kHz level.