Numerical investigation on frequency-shifting-induced spectral compression of femtosecond solitons in highly nonlinear fiber

We present a numerical investigation on nonlinear propagation of femtosecond pulses in anomalously dispersive highly nonlinear fiber (HNLF) with positive third-order dispersion (TOD). Soliton self-frequency shift (SSFS) in the HNLF is shown to enable efficient spectral compression of ultrashort pulse whose parameters satisfy 0.8 ≤ N ≤ 1.3 for the soliton order N. A spectral-compression factor up to 2.5 can be achieved for 60-fs, 1550-nm fundamental solitons red-shifted to 1609 nm in the HNLF. We show that the fiber TOD has significant influence on the SSFS-induced spectral-compression performance. Using HNLF with larger TOD parameter, greater spectral-compression factor can be obtained. We also find that the impact of initial pulse chirp on output spectral width is negligible, indicating SSFS-based spectral-compression method is efficient for both chirped pulses and transform-limited pulses.