Ultrafast all optical switching based on pulse trapping in photonic crystal fibers

We present a theoretical investigation of the ultrafast all optical switching based on pulse trapping in photonic crystal fibers. We numerically solve the coupled nonlinear Schrodinger equations for two independent ultrashort pulses propagation in photonic crystal fiber using a standard split-step Fourier algorithm to analyze the phenomenon of pulse trapping across the zero-dispersion wavelength. It is shown that one pulse (for example the second one) of the signal pulse train propagating in the normal dispersion region can be trapped by an ultrashort soliton pulse propagating in the anomalous dispersion region. The soliton and trapped pulse co-propagate along the fiber. The soliton pulse is red-shifted due to soliton self-frequency shift and the trapped pulse is blue-shifted to satisfy the group velocity matching. Only the second pulse among the signal pulse train is trapped by the soliton pulse and the optical spectrum of the trapped pulse is distinctly blue-shift through the cross phase modulation and is separated from the untrapped ones, thus it can be picked out easily by use of a wavelength filter such as a fiber Bragg gating. The ultrafast all optical switching with a 1THz repetition frequency is confirmed directly. As the input peak power of the pump pulse increases, the red-shift of the soliton is considerably enhanced with the simultaneous further blue-shift of the trapped pulse to satisfy the condition of group velocity matching.