Numerical Investigation of Over One Octave High‐Coherence Supercontinuum Generation in Mid‐Infrared Based on As2Se3 Tapered Photonic Crystal Fiber.

The generation of high‐coherence mid‐infrared (MIR) supercontinuum (SC) spanning over one octave in As2Se3 tapered photonic crystal fiber (As2Se3‐TPCF) is investigated through numerical simulations. Combined with the photonic crystal fiber and tapered fiber's structural characteristics, six As2Se3‐TPCFs with different tapered structures are designed. The tapered regions are the power function and cosine tapered structures, respectively, while the taper waist and the untapered region have the same structure. Moreover, the nonlinear coefficient of the taper waist is 2.23825 W−1m−1 calculated by the finite element method (FEM), and the zero‐dispersion wavelength (ZDW) in the down‐taper moves with the increase of transmission distance, shifted from 5.2 to 2.4 μm. The temporal and spectral features of the MIR SC generated in As2Se3‐TPCFs are numerically simulated by solving the generalized nonlinear Schrödinger equation (GNLSE), and the spectral broadening of As2Se3‐TPCFs is mainly caused by self‐phase modulation, Raman soliton self‐frequency shift, and dispersive wave generation. Finally, six As2Se3‐TPCFs with lengths of 0.1 m are pumped by short pulses with a center wavelength of 4.0 μm, pulse width of 40 fs, and pulse energy of 250 pJ, the results show that the linear tapered As2Se3‐TPCF and the cosine tapered As2Se3‐TPCF can achieve high‐coherence MIR spectra spanning 1.6 octaves, with spectral widths from 2.1 to 6.4 μm. [ABSTRACT FROM AUTHOR]