Refractive index dispersion of chalcogenide glasses for ultra-high numerical-aperture fiber for mid-infrared supercontinuum generation

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

“…(1) assumed that the material band gap, where a resonance in refractive index occurs, is at zero frequency and the model is thus not correct if bandgaps or vibrational absorption bands fall within or close to the frequency range of interest as is the case with chalcogenide glasses (Dantanarayana 2012;Dantanarayana et al 2014). In order to extend the Swanepoel method to chalcogenide glasses operating transparently in the MIR spectral region, another refractive index model is needed to replace the Cauchy model as the dispersive equation.…”

“…In order to extend the Swanepoel method to chalcogenide glasses operating transparently in the MIR spectral region, another refractive index model is needed to replace the Cauchy model as the dispersive equation. Dantanarayana et al (2014) demonstrated that a two-term Sellmeier model is sufficient to describe the refractive index dispersion of chalcogenide glasses in the transparent region (where k 2 ( n 2 ). Following Dantanarayana et al (2014), the transparent region of As 40 Se 60 and GeAsSe was taken to be where the extinction coefficient k was smaller than 0.0005, which for the two glasses studied in that The second overtone of the fundamental stretching band Fig.…”

“…Dantanarayana et al (2014) demonstrated that a two-term Sellmeier model is sufficient to describe the refractive index dispersion of chalcogenide glasses in the transparent region (where k 2 ( n 2 ). Following Dantanarayana et al (2014), the transparent region of As 40 Se 60 and GeAsSe was taken to be where the extinction coefficient k was smaller than 0.0005, which for the two glasses studied in that The second overtone of the fundamental stretching band Fig. 2 Transmission spectra for: a a 20 lm target thick pressed Ge 16 As 24 Se 15.5 Te 44.5 sample at normal incidence (solid curve, blue online) and at an incident angle of 30°(dotted curve, red online) and b a 25 lm target thick pressed As 40 Se 60 sample at normal incidence (solid curve, blue online) and at an incident angle of 30°(dotted curve, red online).…”

“…The properties of mid-infrared (MIR) transparency, high refractive index, low phonon energy, high optical non-linearity (Zakery and Elliott 2003), and an ability to doped them with rare-earth element ions (Sanghera and Aggarwal 1999;Sanghera et al 2009;Tang et al 2015;Falconi et al 2016), make chalcogenide glasses attractive for use in planar photonic integrated circuits (Seddon et al 2006Abdel-Moneim et al 2015), and narrow-and broad-band fibre-based laser sources (Petersen et al 2014) and amplifiers (Hu et al 2015;Falconi et al 2017) for the MIR. Although much research effort has been paid to the development and characterisation of chalcogenide glasses for photonics, relatively little refractive index dispersion data are presently available at MIR wavelengths, see for example: Orava et al (2009), Qiao et al (2011), Dantanarayana et al (2014), Gleason et al (2016), Wang et al (2017) and references therein.…”

“…This illustrates the importance of the thermal history of the glass on its physical structure, and hence on its physical properties such as density and refractive index. In Dantanarayana et al (2014) we reported the continuous linear refractive index dispersion at ambient temperature of two bulk chalcogenide glasses, AsSe and GeAsSe, over the 0.4-33 lm wavelength range obtained by means of spectroscopic ellipsometry. A two-term Sellmeier equation, with one resonant visible-region absorption and one resonant far-infrared absorption, was determined as sufficient and appropriate for fitting the refractive index dispersion over the wavelength range for which the extinction coefficient was less than 0.0005.…”