STABILIZATION AND TUNING OF A DOUBLY RESONANT OPTICAL PARAMETRIC OSCILLATOR

We present experimental results of frequency tuning and stabilization of a type-II phase-matched potassium titanyl phosphate (KTP) doubly resonant optical parametric oscillator. Four tuning elements were employed to control the stability and tuning of the parametric oscillator. Discrete frequency tuning of a nearly degenerate optical parametric oscillator over a range of approximately 3 THz was obtained by crystal angle tuning and cavity-length scanning. We achieved continuous frequency tuning over a 0.5-GHz range through the use of temperature and electro-optic tuning of the KTP crystal. Using these frequency-control techniques, we phase locked the signal-idler beat frequency to an external microwave frequency source, thus demonstrating tunable optical frequency division. The power spectral density of the residual phase noise of the phase-locked signal-idler beat note was measured to be 0.3 mrad/square-root Hz. Characteristics of two different cavity designs, their operations, tuning behavior, and stability issues are examined.