# A Review of Mid-Infrared Supercontinuum Generation in Chalcogenide Glass Fibers
## 3 MIR SC Generation in ChG Fibers
### SC Generation in ChG MOF Fibers
When the pump wavelength was shifted from 3.5 to 4.7 \(\upmu\)m, the solitonic long wavelength edge moved to longer wavelengths in the simulated spectra, and accordingly, the dispersive waves were shifted to shorter wavelengths. Consequently, the broadest numerical spectrum, spanning from 1.65 to 7.7 \(\upmu\)m, and the largest experimental output power of 15.6 mW were obtained in this work. In SCFs, dispersion profile optimization can be accomplished by changing the structural parameters, such as the fiber core diameter (\(d\)) and the bridge width (\(w\)) [90; 134; 135; 91]. As can be seen from Figure 7, the calculated ZDWs of SCFs can be shifted to shorter wavelengths by reducing \(d\) and \(w\) to match the pump wavelength. For example, the SCF fiber geometry was carefully designed by Mouawad et al. [86] in 2014 to allow efficient pumping by an OPO delivering 200 fs pulses at 2.5 \(\upmu\)m, which was close to the ZDW in the anomalous dispersion regime. The As\({}_{2}\)S\({}_{3}\) SCF fiber had an outer diameter of 130 \(\upmu\)m and three holes centered on a central solid core with a diameter of 3.4 \(\upmu\)m, exhibiting a ZDW close to 2.4 \(\upmu\)m and a \(\gamma\) of 1150 W\({}^{-1}\)km\({}^{-1}\). At a peak pump power of 4.86 kW, this fiber was clearly pumped in the anomalous dispersion regime and was characterized by a strong, rapid SPM process followed by soliton fission. The resulting spectrum extended from 600 to 4100 nm in the \(-\)40 dB range. Figure 6: Calculated waveguide dispersion as a function of the wavelength for MOFs with three different \(d/\Lambda\) ratios for \(n=1.444\) and \(n=2.5\), where n is the linear refractive index of the glass matrix (reproduced with permission from [131], copyright Taylor & Francis, 2009). Several researchers have reported wide SC generation in ChG-silica waveguides [136; 137; 138]. To more precisely engineer the dispersion profile, hybrid MOFs fabricated by two materials for the core and cladding glasses were proposed and studied theoretically and experimentally [139; 140; 141], and the adjustability of these can greatly facilitate effective SC generation. Recently, Cheng et al. [80] fabricated a hybrid four-hole AsSe\({}_{2}\)-As\({}_{2}\)S\({}_{5}\) MOF with a large refractive index difference with a ZDW of 3380 nm and \(\gamma\) of 4.9 \(\times\) 10\({}^{4}\) W\({}^{-1}\)km\({}^{-1}\), and they obtained a 1.25-5.4 \(\upmu\)m SC source pumped at 3389 nm. The introduced As\({}_{2}\)S\({}_{5}\) cladding exhibits better transmission properties compared with those of As\({}_{2}\)S\({}_{3}\) glass in the visible and IR range. Subsequently, Cheng et al. [142] designed a hybrid MOF made of a ChG core and a tellurite cladding, and the ZDW of this fiber was downshifted to 2370 nm. By pumping at 2600 nm in the anomalous dispersion regime, flattened SC generation spanning from \(\sim\)950 to 3350 nm was experimentally realized. Besides tellurite glasses, borosilicate glasses have also been used as cladding materials of MOFs. Salem et al. [143] numerically reported MIR SC generation from 1 to 5 \(\upmu\)m in an As\({}_{2}\)S\({}_{5}\)-borosilicate MOF. It has been shown that fiber loss increases due to microdeformations when the core size of MOF is decreased [72]. The output SC spectrum bandwidth is critically correlated with MOF attenuation, especially regarding dramatic absorption peaks. Savelii et al. [144] experimentally demonstrated SC generation spanning from 1.2 to 3.2 \(\upmu\)m in a 45-mm-long As\({}_{2}\)S\({}_{3}\) SCF with a core diameter of 3.2 \(\upmu\)m when pumped at 2.3 \(\upmu\)m with a peak power of 4.6 kW. However, the SC generation could be extended to 5.5 \(\upmu\)m when the extra losses of absorption peaks were neglected in the numerical simulation. The extra losses induced by OH- and SH- groups confirmed the dramatic limitation of the SC broadening process. Additionally, the design of MOFs with air holes implies that the fiber core can be in contact with the ambient atmosphere.