# New Candidate Multicomponent Chalcogenide Glasses for Supercontinuum Generation
## 1 Introduction
Most studies to date on this topic have been dedicated to measurement of the optical nonlinearity of fibers made of single ChG material [2; 8; 9; 10], while other special geometries, such as micro-structured optical fibers [11; 12; 13] and refractive index-graded fibers [14; 15], have been investigated more recently. Extensively studied are simple binary ChGs, such as As\({}_{2}\)S\({}_{3}\) and As\({}_{2}\)Se\({}_{3}\) fibers, reported to show high nonlinear refractive indices as characterized in the near-IR and MWIR spectral region [16; 17; 18; 19]. These materials have potential to enable broad spectral emission suitable for use as a source; however, detailed optical material property data have largely not extended past the MWIR, where most labs routinely characterize such properties. While an optimal material would need to be transmissive over a broad spectral range and have tailorable linear and nonlinear refractive indices as well as composition-tailorable dispersion behavior, the extension of any generated SC to wavelengths needs to be close to the material's band-edge, or more importantly, into the deep sub-bandgap region. This region is especially important for potential photo-induced material modification, as both linear and nonlinear absorption increases near the band edge. This, as reported for As\({}_{2}\)S\({}_{3}\) and other glass systems [52; 53], can lead to deleterious effects such as photo-structural modification where light is sufficiently energetic to cause bond re-arrangement thereby modifying or significantly altering desirable optical properties. As the mechanism of SC requires high pump intensities coupled with high host optical nonlinearity, broad spectral window, and suitable laser damage resistance at the high(er) powers needed to induce the optical nonlinearity, intensity-dependent performance combined with knowledge of fabrication flexibility and thermal stability is key to defining suitable SC candidate materials [2; 20]. In addition to the optical property merits of ChG glasses, their high viscoelasticity enables easy shaping to reduced dimensions such as fiber and thin film geometries that can be integrated into photonic devices [14; 20]. Ideally, these devices require a high nonlinear figure of merit (FOM = \(n_{2}/\langle\lambda I^{n-2}\alpha_{\text{nPA}}\rangle\), where \(n_{2}\) is the nonlinear refractive index, \(\lambda\) is the wavelength, \(I\) is the laser pump power, and \(\alpha_{\text{nPA}}\) is the multiphoton absorption coefficient, respectively) [26]. This FOM trades off wavelength-specific nonlinearities with undesirable nonlinear loss, providing a guide for expected material performance. As noted, this is often hard to calculate, as data is often only measured at a single wavelength, not across the spectrum enabled by the broadband material. Compositional tuning is one way to engineer the optical properties of ChGs; however, such engineering does not always include consideration of other physical properties important for manufacturability, and ultimately, the usage environment. In this paper, we review prior efforts to engineer optical properties via compositional tuning (only) in homogeneous glasses; we further extend these findings to present the potential for SC property enhancement through microstructural modification (i.e., selective conversion of a glass to a glass ceramic). Formation of such an optical composite offers parallel opportunities for both optical property-tailoring (linear and nonlinear refractive indices and optical dispersion) combined with improvements to thermal, mechanical [54; 55], and chemical stability critical for optimizing in-use performance [56; 57]. To illustrate the potential to leverage optical and physical property engineering where multi-spectral data is being compiled, we examined the property tailoring enabled in a model glass system recently investigated for the creation of optical nanocomposites, specifically multiple compositions within the multicomponent GeSe\({}_{2}\)-As\({}_{2}\)Se\({}_{3}\)-PbSe (GAP-Se) system.