Continuous-Wave 3.1–3.6 μm Difference-Frequency Generation of Dual Wavelength-Tunable Fiber Sources in PPMgLN-Based Rapid-Tuning Design

We report on a single-frequency continuous wave (CW) difference-frequency generation (DFG) source based on single-frequency wavelength-tunable polarization-maintaining ytterbium- and erbium-doped fiber master oscillator–power amplifiers (MOPAs), acting as the pump and signal source, respectively, and a 40-mm long periodically poled MgO-doped LiNbO 3 (PPMgLN) crystal. Owing to the dual wavelength-tuning of the MOPAs, the generated idler light reaches a wavelength-tuning range of close to 500 nm, from ∼3117.2 to ∼3598.8 nm, only by tuning the launched pump and signal wavelengths from 1040 to 1084.6 nm and from 1545.2 to 1561.4 nm, respectively, without any change of temperature or grating period of the PPMgLN. Compared to temperature-based idler-wavelength-tuning, this method is potentially faster in speed. The maximum idler power exceeds 60 mW, which is the highest reported power for a wavelength-tunable single-frequency CW DFG source. A rapidly wideband-tunable DFG source with tens of milliwatts of output power in a narrow line can be a practical tool for mid-infrared molecular spectroscopy, detection, and sensing at high measurement rates.