Continuous wavelength tuning of nondegenerate femtosecond doubly resonant optical parametric oscillators

We report an approach for continuous tuning of the central wavelengths of a femtosecond nondegenerate doubly resonant optical parametric oscillator (DRO). Key in this scheme is the insertion of a wavelength-selective element into the DRO cavity-length-locking system, which allows selected narrow-band emission from a DRO to be detected and enables the DRO cavity length to be locked away from the peak of its cavity resonances. In a preliminary experiment, we demonstrated a femtosecond nondegenerate DRO with its central-wavelength continuously-tunable over each of its cavity resonances and achieved a wavelength-tuning range of 1910–2070 nm for the signal wave and 2140–2340 nm for the idler wave. This is, to the best of our knowledge, the first demonstration of the continuous-wavelength-tuning capability of DRO systems.