## 4 Supercontinuum Generation in Chalcogenide MOFs  
As one of the promising applications of chalcogenide fibers, Mid-IR supercontinuum generation has been investigated extensively with both step-index and microstructured chalcogenide fibers [41; 42; 43; 44]. The first generation of supercontinuum was demonstrated in 2006 for chalcogenide MOFs [36]. One meter of a selenide-based chalcogenide MOF was pumped by a Ti:sapphire laser, with an output wavelength at 2.5 \(\upmu\)m and pulse duration and pulse energy of 100 fs and 100 pJ, respectively. The experimental results displayed in Figure 4 show that effective wavelength broadening can be achieved through pumping around the ZDW or the anomalous region [1] of the fiber. Figure 4: Output spectrum of supercontinuum generated in chalcogenide microstructured optical fibers made by the stack and draw technique. Reproduced with permission from [36], copyright INOE, 2006. Later in 2010, [PERSON] et al. reported the fabrication of the first As\({}_{2}\)S\({}_{3}\) chalcogenide MOFs with a suspended core. Instead of the \"stack-and-draw\" method, mechanical drilling was used to prepare the fiber preform. By pumping a 45-m-long section of MOF with an 8-ps mode-locked laser at around 1.55 \(\upmu\)m, a continuum covering more than 200 nm from 1450 to over 1700 nm was obtained [11]. Several other pumping schemes have been investigated to generate Mid-IR supercontinua. In 2016, [PERSON] et al. used a two-cascading configuration, based on a 1.55-\(\upmu\)m laser-diode-pumped thulium-doped silica fiber and a Zr-Ba-La-Al-Na fluoride (ZBLAN) fiber, to pump a chalcogenide MOF, which generated a Mid-IR supercontinuum up to 4.4 \(\upmu\)m [45]. By comparing the output spectra of ZBLAN fibers with different chromatic dispersions, it was concluded that solitons located in the long-wavelength part of the pump are essential for the effective generation of the supercontinuum. This was corroborated by a series of simulations. The spectrum of the supercontinuum was extended to 7 \(\upmu\)m with a total output power of 6.5 mW. Then, in 2017, [PERSON] et al. demonstrated a Mid-IR SC generation from a tapered large-mode-area chalcogenide MOF [22]. The tunable Mid-IR pump light utilized in the experiment was achieved by combining a tunable seed laser and a 1.04-\(\upmu\)m mode-locked Yb:KYW (ytterbium-doped potassium yttrium tungstate crystal) solid-state laser into periodically-poled MgO:LiNbO\({}_{3}\) crystals to obtain quasi-phase-matched parametric anti-Stokes generation from 3.7 to 4.5 \(\upmu\)m. In order to increase the spectral broadening and reduce the confinement losses, tapered fibers with a diameter of 15.1 \(\upmu\)m and shorter lengths before and after the taper, with length before taper (L\({}_{\text{bt}}\)) of 7.5 cm and length after taper (L\({}_{\text{at}}\)) of 4.5 cm, was utilized in the experiment. At the end, an output spectrum from 1 to 11.5 \(\upmu\)m with an average output power of 35.4 mW was obtained, as shown in Figure 5.  
Besides, hybrid chalcogenide MOFs were fabricated by [PERSON] et al. to generate a Mid-IR supercontinuum [46]. The hybrid MOF has been made with four AsSe\({}_{2}\) capillaries and inserted into an As\({}_{2}\)S\({}_{5}\) glass tube (Figure 6a). The high refractive index difference (around 0.61) between the core and the cladding would improve light confinement in the fiber, which was the original intent of the fiber designing. As for the pump light, a tunable optical parametric oscillator (OPO) emitting 200-fs pulses at a repetition of 80 MHz was employed. For the purpose of extending the output spectra, different pump wavelengths: 3062 nm, 3241 nm, and 3389 nm, located at positions far from the ZDW in the normal dispersion range, close to the ZDW in the normal dispersion range, and close to ZDW in the anomalous dispersion range, respectively, were used to pump the 2-cm-long hybrid MOF.