(INVITED) Methods for determining the refractive indices and thermo-optic coefficients of chalcogenide glasses at MIR wavelengths

Chalcogenide glasses have attracted much attention for the realization of photonic components owing to their outstanding optical properties in the mid-infrared (MIR) region. However, relatively few refractive index dispersion data are presently available for these glasses at MIR wavelengths. This paper presents a mini review of methods we have both used and developed to determine the refractive indices and thermo-optic coefficients of chalcogenide glasses at MIR wavelengths, and is supported by new results. The mini review should be useful to both new and established researchers in the chalcogenide glass field and fields of MIR optics, fiber-optics and waveguides. Three groups of methods are distinguished: (1) spectroscopic ellipsometry, (2) prism-based methods, and (3) methods using Fourier transform infrared (FTIR) transmission data. The mini review is supported by a brief discussion of refractive index models

Determining the refractive index dispersion and thickness of hot-pressed chalcogenide thin films from an improved Swanepoel method

The well-known method presented by Swanepoel can be used to determine the refractive index dispersion of thin films in the near-infrared region from wavelength values at maxima and minima, only, of the transmission interference fringes. In order to extend this method into the mid-infrared (MIR) spectral region (our measurements are over the wavelength range from 2 to 25 μm), the method is improved by using a two-term Sellmeier model instead of the Cauchy model as the dispersive equation. Chalcogenide thin films of nominal batch composition As40Se60 (atomic %) and Ge16As24Se15.5Te44.5 (atomic %) are prepared by a hot-pressing technique. The refractive index dispersion of the chalcogenide thin films is determined by the improved method with a standard deviation of less than 0.0027. The accuracy of the method is shown to be better than 0.4% at a wavelength of 3.1 μm by comparison with a benchmark refractive index value obtained from prism measurements on Ge16As24Se15.5Te44.5 material taken from the same batch

Broadband, mid-infrared emission from Pr3+ doped GeAsGaSe chalcogenide fiber, optically clad

We present a study of mid-infrared photoluminescence in the wavelength range 3.5–5.5lm emitted from Pr3+: GeAsGaSe core/GeAsGaSe cladding chalcogenide fiber. The Pr3+doped fiber optic preform is fabricated using extrusion and is successfully drawn to low optical loss, step-index fiber. Broadband mid-infrared photoluminescence is observed from the fiber, both under 1.55microns or 1.94 microns wavelength excitation. Absorption, and emission, spectra of bulk glass and fiber are presented. Luminescent lifetimesare measured for the fiber and the Judd–Ofelt parameters are calculated. The radiative transition rates calculated from Judd–Ofelt theory are compared with experimental lifetimes. The observed strong broad-band emission suggests that this type of fiber is a good candidate for further development to realize both fiber lasers and amplified spontaneous emission fiber sources in the mid-infrared region

Determining small refractive index contrast in chalcogenide-glass pairs at mid-infrared wavelengths

A two-composition thin film (Ge20Sb10Se70/Ge20Sb10Se67S3 atomic%core/cladding glasses) was fabricated using a hot-fibre-pressing technique in which both glasses follow the same post-fibre processing. A simple approach is proposed that uses normal incidence transmission spectra to determine their refractive index contrast over the wavelength range from 2 to 25 μm with an error of less than _ 0.002. Using an improved Swanepoel method, the calculated numerical aperture of these two compositions was within _ 0.011 of that obtained from prism minimum deviation measurements. Results show that introducing 3 atomic % S into the Ge-Sb-Se glass system lowered the refractive index and blue-shifted the visible optical bandgap, the far-infrared fundamental vibrational absorption bands and the zero-dispersion wavelength