Widely-tunable mid-infrared fiber-feedback optical parametric oscillator

We devise and implement two variants of mid-infrared optical parametric oscillators (OPOs) based on a polarization-maintaining fiber-feedback cavity, which allow to robustly deliver sub-picosecond MIR pulses without the need of active stabilization. The first one integrates an erbium-doped fiber into the OPO cavity as the additional gain medium. The synergistic dual-gain operation significantly reduces the pump threshold to launch a stable MIR pulse formation. The other OPO configuration adopts a chirped-poling nonlinear crystal in a passive-fiber cavity to achieve a broader operational spectral range. The wide phase-matching bandwidth facilitates easy wavelength tuning by simply adjusting the cavity length through the dispersion filtering effect. Therefore, the presented mid-infrared OPO source is featured with high compactness, robust operation, and wide tunability, which would be attractive for subsequent applications, such as infrared photonics, biomedical examination, and molecular spectroscopy.