Cross-phase-modulation-induced instabilities and frequency shifts of ultrashort laser pulses in a photonic-crystal fiber

This work shows that a second input laser field spectrally separated from the first laser pulse can serve as a convenient control knob for spectral transformations of ultrashort laser pulses in photonic crystal fibers (PCFs). This study also explores the potential of cross-phase modulation (XPM) and XPM-induced instability as physical mechanisms behind this control. Results show that the capability of PCFs to radically enhance nonlinear-optical processes, suggests the ways to extend XPM-based short-pulse control techniques to lower energy pulses and substantially shorter fibers, allowing, in particular, efficient frequency tuning of femtosecond probe pulses within a broad spectral range by using a low-energy pump field, launched into a PCF with a variable delay time. Group delay between the pump and probe pulses leads to an XPM-induced frequency shift of the probe field, allowing its frequency to be smoothly tuned by varying the delay time between the pulses at the input of the fiber.