Numerical investigation on W-type index chalcogenide fiber based MIR supercontinuum generation

Abstract

This work presents a numerical study of a W-type index chalcogenide fiber design for Mid-Infrared (MIR) supercontinuum (SC) generation beyond 10µm. Our fiber design consists of a Ge15Sb15Se70 glass core, a Ge20Se80 glass inner cladding and a Ge20Sb5Se75 glass outer cladding. These chalcogenide materials have the advantages to broaden the spectrum to 12µm, due to their low material absorption. The optical mode distribution of the chalcogenide fiber is simulated by a finite element method based on edge elements. With a 6 µm core diameter and a 12 µm inner cladding diameter, the proposed fiber design exhibits flat anomalous dispersion in the wavelength range (4.3-6.5µm), with a peak of about 7ps/(nm.km). The position of the second zero-dispersion wavelength (ZDW) can be easily and precisely controlled by the inner cladding size and should be shifted to around 7µm for a 18 µm inner cladding diameter. This design is more suitable for a pump wavelength at 6.3µm which is in the anomalous dispersion regime between two ZDWs and can broaden the spectrum due to the soliton dynamics. Our fiber design modelling shows that the nonlinear parameter at 6.3µm is 0.1225W −1 m −1 , when using a nonlinear refractive index nNL=3.44 ×10 −18 m 2 W −1 , and the chromatic dispersion is D = 3.24ps/(nm.km). Compared to previously reported step-index fibers, the proposed W-type index chalcogenide structure ensures single mode propagation, which improves the nonlinearity, flattened dispersion profile and reduces the losses, due to a tight confinement of the mode within the core.

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

“…The chromatic dispersion D(λ) is calculated from the effective index neff values versus wavelength λ by the following formula [22]      …”

“…The V-parameter for the W-type index chalcogenide fiber can be written as [8]: 22 This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.…”

“…Typically, the Ge15Sb15Se70 glass offers a high nonlinear refractive index of about 10.34m 2 W −1 at the wavelength of 1.55 µm [25]. We assume that the nonlinear refractive index nNL at 6.3 µm to be about 30% of that value at 1.55 µm as suggested in [22] resulting in a nonlinear parameter of about 0.12 W -1 m -1 . This nonlinear parameter is two times higher than previously reported step-index fiber [8].…”

“…Content may change prior to final publication. addition, edge elements lead to an easy implementation of boundary conditions at material interfaces [21,22]. However, the required number of floating point operations per conjugate gradient operation and the storage requirements in linear edge elements are more than twice as expensive to linear nodal elements [23].…”