Design of W-Type Index Chalcogenide Fiber for Highly Coherent Mid-IR Supercontinuum Generation

This paper presents the design of a W-type index chalcogenide fiber for mid-infrared beyond 10 μm. The main advantages of the W-type index fiber are the possibility to control the chromatic dispersion with a larger possible core area for single-mode operation compared to a common step-index fiber and to enhance the fiber nonlinearity. Our fiber design consists of Ge
₁₅
Sb
₁₅
Se
₇₀
glass core, Ge
₂₀
Se
₈₀
glass inner cladding, and Ge
₂₀
Sb
₅
Se
₇₅
glass outer cladding. The optical mode distribution of the chalcogenide fiber is numerically calculated by a finite element method based on edge element analysis. With 6-μm core diameter and 12-μm inner cladding diameter, the proposed fiber design exhibits flat anomalous dispersion in the wavelength range (4.3-6.5 μm) with a peak of about 7 ps/(nm·km). Also, it offers a high nonlinear coefficient of 0.12 W
^-1
m
^-1
at a pump wavelength of 6.3 μm. The simulation results show that our proposed fiber design provides a highly coherent Mid-IR SC extending from 3.7 to 12 μm pumped at low peak pump power of 1 kW.