Generation of two colliding pulses with tunable THz-range frequency difference in high-nonlinear photonic crystal fiber

Abstract

Two-wavelength light sources are of interest for THz-range oscillators based on difference frequency generation [1–5], and also for the oscillators, based on the optical rectification [6]. Easy way to produce pulses with frequency difference is the use of dispersion oscillating fiber [7]. We discuss the possibility to use a highly nonlinear photonic crystal fiber for generation the overlapping pulse pairs with the difference of carrier frequencies in THz range from femtosecond pulses train from only one laser. First, each pulse from the laser should be duplicated using beamsplitter. Then the pulses should be launched sequently into photonic crystal fiber. The pulse frequency is to be in anomalous dispersion regions, and pulses are to be high-order solitons. Due to Raman effect these solitons split to fundamental soliton with red shift and other smaller pulses with nonshifted frequency. Due to group velocity dispersion (GVD) the Raman-shifted pulse propagate slower depending on pulse parameters. Thus there exist some definite length in the fiber where Raman-shifted pulse collides with unshifted pulse. This distance and the value of the shift can be controlled by pulse parameters and depend on the fiber parameters. The results of numerical modeling of the nonlinear propagation of multi-soliton pairs of pulses in photonic crystal fiber are presented below.