Abstract
We select a chalcogenide core glass, AsSe, and cladding glass, GeAsSe, for their disparate refractive indices yet sufficient thermal-compatibility for fabricating step index fiber (SIF) for mid-infrared supercontinuum generation (MIR-SCG). The refractive index dispersion of both bulk glasses is measured over the 0.4 µm–33 µm wavelength-range, probing the electronic and vibrational behavior of these glasses. We verify that a two-term Sellmeier model is unique and sufficient to describe the refractive index dispersion over the wavelength range for which the experimentally determined extinction coefficient is insignificant. A SIF composed of the glasses is fabricated and calculated to exhibit an ultra-high numerical aperture >0.97 over the entire wavelength range 0.4-33 µm suggesting that the SIF glass pair is a promising candidate for MIR-SCG. Material dispersion characteristics and the zero dispersion wavelength, both critical design parameters for SIF for MIR-SCG, are derived.
Highlights
The chalcogenide glasses [1] are based on Group 16 elements of the Periodic Table: S, Se and Te, usually formulated with additions of Group 14 and Group 15, such as the germanium and arsenic elements, respectively, to increase glass stability and robustness
The AsSe core and GeAsSe cladding bulk glass samples, were analyzed by means of spectroscopic ellipsometry at ambient temperature (298K) at incident angles 55° to 75°, in 10° intervals; the incident angle range was close to the Brewster angle, in order to collect the data in the angular region with most sensitivity to the reflection differences between p- and s- polarized light
step index fiber (SIF) constructed from this AsSe/GeAsSe glass pair had a calculated numerical aperture (NA) greater than 0.97 over the entire wavelength range of refractive index measurement by means of ellipsometry: 0.4-33 μm. This ultra-high NA allows the core modes to be strongly confined in the fiber core and theoretically a MIR-SC to be unhindered across the wavelength range, making this glass pair a promising candidate for SIF mid-infrared supercontinuum generation (MIR-supercontinuum generation (SCG))
Summary
The chalcogenide glasses [1] are based on Group 16 elements of the Periodic Table: S, Se and Te, usually formulated with additions of Group 14 and Group 15, such as the germanium and arsenic elements, respectively, to increase glass stability and robustness. The chalcogenide glasses are amorphous semiconductors, exhibiting an optical band-gap They combine low phonon energy and high optical nonlinearity [2]; chalcogenide-glass optical fibers are suitable as mid-infrared (MIR, 3-25 microns) supercontinuum generation (SCG) sources. The AsSe core and GeAsSe cladding glass pair was chosen to give ultra-disparate refractive indices for ultra-high numerical aperture (NA) SIF, and to have sufficient thermal-compatibility above and below the glass transition (Tg) in order to enable fiber fabrication [5]. We have measured refractive index dispersion of the AsSe core and GeAsSe cladding glasses from the visible region (VIS: 0.4-0.7 μm), through the near-infrared (NIR: 0.7-3 μm), MIR (3-25 μm) and into the FIR (limited here up to 33 μm by the ellipsometer employed). Material dispersion of the glasses and the zero dispersion wavelengths are derived and the variation of numerical aperture (NA) with wavelength is calculated for SIF, comprised of the AsSe core and GeAsSe cladding glasses
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