Mid‐infrared supercontinuum (mid‐IR SC) sources in the 2–20 µm molecular fingerprint region are in high demand for a wide range of applications including optical coherence tomography, remote sensing, molecular spectroscopy, and hyperspectral imaging. Herein, mid‐IR SC generation is investigated in a cascaded silica‐ZBLAN‐chalcogenide fiber system directly pumped with a commercially available pulsed fiber laser operating in the telecommunications window at 1.55 µm. This fiber‐based system is shown to generate a flat broadband mid‐IR SC covering the entire range from 2 to 10 µm with several tens of mW of output power. This technique paves the way for low cost, practical, and robust broadband SC sources in the mid‐IR without the requirement of mid‐infrared pump sources or Thulium‐doped fiber amplifiers. A fully realistic numerical model used to simulate the nonlinear pulse propagation through the cascaded fiber system is also described and the numerical results are used to discuss the physical processes underlying the spectral broadening in the cascaded system. Finally, recommendations are provided for optimizing the current cascaded system based on the simulation results.

In this paper, we report the design and fabrication of a highly birefringent polarization-maintaining photonic crystal fiber made from chalcogenide glass, and its application to linearly-polarized supercontinuum generation in the mid-infrared region. The fiber was drawn using the casting method from As 38 Se 62 glass which features a transmission window from 2 to 10 μm and a high nonlinear index of 1.13×10 -17 m 2 W −1 . It has a zero-dispersion wavelength (ZDW) at 4.56 μm for the fast axis and 4.68 μm for the slow axis and, at average ZDW, a large birefringence of 6.5×10 -4 and consequently strong polarization maintaining properties are expected. Using this fiber, we experimentally demonstrate supercontinuum generation spanning from 3.1 to 6.02 μm and 3.33-5.78 μm using femtosecond pumping at 4 μm and 4.53 μm, respectively. We further investigate the supercontinuum bandwidth versus the input pump polarization angle and we show very good agreement with numerical simulations of the two-polarization model based on two coupled generalized nonlinear Schrödinger equations.

No abstract