Abstract: This paper proposes a germanium-core silicon-cladding photonic crystal fiber with a hexagonal lattice structure. An improved Grey Wolf optimization algorithm is employed for the inverse design of the fiber's structure parameters, yielding a narrow anomalous dispersion band (5.196-7.544 µm) bounded by two zero-dispersion wavelengths in the mid-infrared region. Numerical simulations demonstrate that under femtosecond pulse pumping with a peak power of 2 kW, a pulse width of 100 fs at the wavelength of 5.5 µm, the fiber can generate a broadband mid-infrared supercontinuum covering 3 µm to 10 µm. Under the mixed noise model incorporating 1% amplitude fluctuation, anti-correlated pulse duration jitter, and quantum noise, the average first-order complex degree of coherence for the generated mid-infrared supercontinuum can be maintained at 98.27%. This study confirms the feasibility of generating broadband, highly coherent mid-infrared supercontinuum by pumping ultrashort pulses within the narrow anomalous dispersion band of silicon-germanium fibers, providing a promising light source solution for applications in mid-infrared optical frequency combs and precision spectroscopy.

Key words: mid-infrared supercontinuum, photonic crystal fiber, anomalous dispersion band, coherence