# Recent Development of Mid-Infrared Supercontinuum Generation in Fluoroindate Glass Fibers
## 8 Summary and Outlook  
Mid-infrared supercontinuum sources have developed rapidly in the last 15 years. The emergence of specialty glass fibers, such as fluoroindate fibers, as well as the advances in fiber-based pulsed oscillators and amplifiers, have accelerated the development of high-power SC systems operating in the spectral range of 2-5 \(\upmu\)m. In addition to the output power, the spectral width and flatness of the continuum are important parameters that determine the SC source performance and its usefulness. The first demonstration of SC generation in a fluoroindate fiber was reported by [PERSON] in 2013 [101]. Since then, much effort has been devoted to improving all the key output parameters of such sources. In less than a decade, the output SC power has been scaled up by more than three orders of magnitude (from less than 10 mW to more than 11 W). Furthermore, interesting pump schemes that enable watt-level SC generation have been proposed. The main achievements in this field are summarized in the chart shown in Figure 14, which illustrates the average SC output power increase over the past nine years. Additionally, Table 1 presents a summary of the most important results on SC generation using InP\({}_{3}\) fibers, as well as the basic information about the parameters of pump radiation and pump laser system configurations. As can be seen in Figure 14, remarkable progress has been made in scaling up the output SC power (illustrated by the increased number of reports as well as increasingly higher output powers), particularly during the last four years. A record time-averaged output power of 11.8 W with a spectrum spanning from \(\sim\)1.9 to 4.9 \(\upmu\)m has been demonstrated, which is certainly not the power limit of this technology. This can be scaled up further if improved thermal management and heat dissipation techniques are implemented. Another vital parameter of mid-IR SC generation is the power distribution toward the red wavelengths. Using optimized nonlinear InP\({}_{3}\) fibers and applying suitable pump sources, it was possible to demonstrate an LWE of 5.42 \(\upmu\)m for low-power systems (an output power of  
Figure 14: Summary of the most important reports on SC generation (with an LWE of output spectrum beyond 4 \(\upmu\)m) in fluoroindate fibers published in the last decade. The bandwidth in the diagram represents the full spectral range (* average output power not revealed; it is supposed to be <100 mW). 8 mW) and 5.1 \(\upmu\)m for high-power operation (an output power of 4.06 W). Furthermore, an excellent spectral flatness (5 dB@ 2.0-5.0 \(\upmu\)m and 10 dB@ 1.96-4.97 \(\upmu\)m) was also achieved. This progress cannot occur without suitable pump sources, particularly those allowing output SC power scaling up. In addition to conventional femtosecond ML laser systems, including optical parametric generation techniques, a spectrum of interesting laser system solutions that provide picosecond and nanosecond pulses has been proposed. It includes fiber-based MOPA systems seeded with semiconductor lasers operating at wavelengths of 1.55 and 2 \(\upmu\)m, Q-switched and ML fiber single oscillators, 2-\(\upmu\)m fast gain-switched and simultaneous ML fiber lasers and amplifiers, and fiber amplifiers directly seeded with picosecond ML lasers. Regarding nonlinear InF3 fibers, most reports have focused on fibers with a length of 8-15 m and a core diameter of 7-10 \(\upmu\)m. The fibers with the lowest attenuation and an appropriate profile of the dispersion curve supported the most efficient red-shifting of the generated SC with an LWE of up to 5.42 \(\upmu\)m. There is scope for further spectrum extension, but it would be rather difficult because of the high absorption losses over 5 \(\upmu\)m resulting from the multiphonon absorption edge of fluoroindate glasses. All the pump laser systems summarized in Table 1 have their advantages and disadvantages.