Photonic crystal fiber-based broadly tunable femtosecond laser sources and applications

Abstract

Photonic crystal fiber (PCF) is considered as a special type of 2-dimensional photonic crystal structure. As the result of its large design flexibility, there are numerous different types of PCFs exhibiting vastly different optical properties. Among them, the small-core PCFs have extremely high effective nonlinearity, which makes them an ideal nonlinear medium for new frequency generation. However significant nonlinear process in fiber only occurs when the phase matching condition is satisfied. Therefore, the dispersion properties of PCFs are also critical. In this paperr, three different approaches are taken to extend the tunability of an Yb-fiber-based femtosecond source. All of the schemes are enabled by the unique dispersion and nonlinear properties of photonic-crystal-fibers (PCFs). In the first approach, by adopting the newly available PCF into an optical parametric oscillator (FOPO) and combining it with our newly-developed mode-locked Yb-fiber laser [1], we extend the tunability of this fiber-based system to over 200-nm around 1 μm [2]. The second scheme uses Raman soliton self-frequency shifting effect in PCFs. Femtosecond soliton pulses tunable from 1100 nm to 1300 nm are generated. In the third approach, by taking advantage of broadly variable phase matching point for the Cherenkov radiation in PCFs, broadly tunable femtosecond visible pulses from 450 nm to 630 nm are achieved [3].