Soliton self-frequency shift in a short tapered air–silica microstructure fiber

We report a soliton self-frequency shift of more than 20% of the optical frequency in a tapered air–silica microstructure fiber that exhibits a widely flattened large anomalous dispersion in the near infrared. Remarkably, the large frequency shift was realized in a fiber of length as short as 15 cm, 2 orders of magnitude shorter than those reported previously with similar input pulse duration and pulse energies, owing to the small mode size and the large and uniform dispersion in the tapered fiber. By varying the power of the input pulses, we generated compressed sub-100-fs soliton pulses of $\sim 1‐\mathrm{nJ}$ pulse energy tunable from 1.3 to $1.65 \mu \mathrm{m}$ with greater than 60% conversion efficiency.