CHARACTERISTICS OF A CW MONOLITHIC KTIOPO4 OPTICAL PARAMETRIC OSCILLATOR

We developed a doubly resonant, cw monolithic optical parametric oscil lator (OPO) characterized by a low threshold and stable long-term oper ation for use as a light source for optical frequency measurement. We used KTiOPO4 as a nonlinear crystal and obtained a pump threshold of 7 mW and an output power of 6 mW for a pump power of 40 mW. The OPO ope rated in a single longitudinal mode pair of a signal and an idler, ove r 1 h without mode hopping in the free-running condition. The signal a nd the idler wavelengths were tunable by 1 nm by changing the crystal temperature by 20 degrees C. The continuous tuning of the beat frequen cy between the signal and the idler was achieved by temperature tuning (slow control, 80 MHz/K) and E-field tuning (fast control, 0.75 MHz/V ). We demonstrated the feasibility of frequency control by phase locki ng the beat frequency. The beat frequency could be successfully phase locked to a signal generated by a synthesizer through the electrooptic effect of the crystal. The phase locking could be maintained over 1 h .