Toward an optical synthesizer: a single-frequency parametric oscillator using periodically poled LiNbO_3

We demonstrate single-frequency operation of a cw quasi-phase-matched singly resonant optical parametric oscillator (SRO). We obtained widely tunable output from 1.66 to 1.99 $\mathit{\mu }\mathrm{m}$ (signal) and from 2.29 to 2.96 $\mathit{\mu }\mathrm{m}$ (idler) by employing a periodically poled lithium niobate multigrating chip. Using a single-frequency miniature Nd:YAG ring laser as a pump source results in SRO output with high spectral purity and frequency stability ($<10 \mathrm{MHz}/min$), which can be continuously tuned over 2 GHz without mode hops. We obtain a minimum SRO threshold of 260 mW by resonating the pump wave in the SRO cavity.