Widely tunable narrow-linewidth ZGP optical parametric oscillator with injection of single frequency seed

In the absence of wavelength selection elements, the output spectrum of a ZnGeP₂ (ZGP) optical parametric oscillator (OPO) is typically much broader than the pump spectrum due to the large parametric spectral gain bandwidth of the ZGP crystal. In this paper, we construct a narrow-linewidth ring cavity ZGP-OPO with an injection of 3.8 μm single-frequency MgO:PPLN laser. This setting achieved effective compression of the linewidth of signal and idler light, and the corresponding maximum output power of signal and idler light were 9.6 W and 6.85 W with a repetition rate of 15 kHz. With seed injection, the full width half maximum (FWHM) of linewidth of the signal light was compressed from 21.84 nm to 0.42 nm at 3816.89 nm, and the linewidth of idler light was compressed from 28.62 nm to 0.74 nm at 4622.06 nm. Furthermore, we investigated the spectral tuning characteristics, achieving a tuning range of 3696.08––3827.14 nm for signal light, corresponding to a tuning bandwidth of 131.06 nm. And the tuning range for the idler light was from 4604.48 to 4808.66 nm, corresponding to a tuning bandwidth of 204.18 nm. Our work proved that the spectrum linewidth of ZGP-OPO can be effectively compressed by seed injection technology.