Watt-level single-frequency optical parametric oscillator around 2 µm

A single-frequency optical parametric oscillator (OPO) operating in the wavelength range around 2 µm is reported. The OPO comprises a periodically poled LiNbO₃ (PPLN) crystal for quasi-phase matching and a four-mirror ring-cavity resonant to the signal. The OPO signal and idler are tuned from 1.89 to 2.05 µm and from 2.21 to 2.42 µm, respectively, by changing the crystal temperature. Output powers in excess of 2 W are demonstrated at a pump power of 9 W for both the signal and idler over all of the respective tuning ranges. A detailed characterization of the intensity and frequency noise is presented. The OPO exhibits an integrated intensity noise below 0.1% and a linewidth of ∼58 kHz for an observation time of 1 ms. The reported performance makes this source an ideal candidate for the generation of squeezed light around 2 µm via cascaded second-harmonic generation (SHG) and parametric downconversion (PDC).