# Recent Development of Mid-Infrared Supercontinuum Generation in Fluoroindate Glass Fibers
## 8 Summary and Outlook
For instance, optical parametric oscillators and amplifiers can generate high peak power pulses with the possibility of output wavelength tuning; however, they can only be used for low average power SC generation, mainly in laboratory rooms. Single-pump oscillators, for instance, the Q-switched and mode-locked fiber lasers [122], can support watt-level SC generation, providing the SC system simplicity and cost reduction, but in this case, the pump pulse structure has high amplitude fluctuations affecting the stability of the output SC power. MOPAs seeded with \(\sim\)1.55 or \(\sim\)2 \(\upmu\)m nanosecond and sub-nanosecond optical pulses [59, 60, 61, 77, 114], especially the all-fiber ones, can offer pump beams with high average power, being perfectly suited for high-power SC systems. Furthermore, they can generate optical pulses with adjustable durations and repetition frequencies independently. It allows changing the peak power of pumping pulses (time-averaged pump power) in the same laser configuration. They are much more complex compared to single oscillators, mainly due to the number of fiber amplifiers needed to provide the optical pump beam with the required power level. On the other hand, they can be fusion spliced with a nonlinear fluoride fiber, making the whole SC system all fiber, which is favorable in the context of practical applications where output parameters stability over a longer operation term is required. Furthermore, this approach enables scaling up the average output SC power linearly while maintaining a relatively constant spectral width of the output spectrum. Although significant progress has been realized, higher output powers, improved spectral characteristics (higher bandwidth and enhanced flatness), and higher reliability of the entire SC system can be achieved further. However, some issues still need to be considered to achieve this aim. First, the development of the first SC sources utilizing InF3 fibers was hindered by the poor quality of the nonlinear medium that hindered the generation of high output SC powers. Thermal effects and the optical damage threshold, defined by a low transition temperature, were the main factors limiting the output power. Over the last few years, the quality of InF3 fibers has significantly improved, and it can be assumed that further improvements pertaining to enhanced optical and mechanical properties are expected. In particular, fibers without absorbing centers are required. Second, further advances in pump laser systems and techniques for launching pump radiation into a nonlinear fiber are required. Further investigation remains to be conducted to achieve robust and compact high-power mid-IR SC sources for practical use. Ensuring the wall plug efficiency of the entire SC laser system is problematic. It was shown that for the scaling up of power, pulsed fiber-based multi-stage MOPA systems are usually utilized, and the more complex the system, the lower is its total power conversion efficiency. In this context, pulsed laser systems developed as single oscillators or MOPAs with a reduced and optimized number of amplifiers should be used. Furthermore, to improve SC system reliability and ruggedness, it should be developed in an all-fiber format that is feasible. The recent reports show that attenuation at the splice point of silica and fluoroindate single-mode fibers can be as low as 0.03 dB (measured at a wavelength of 2 \(\upmu\)m [42]). Another approach to avoid system failure is to protect an InF3 fiber end facet from photodegradation, and the power intensity at the output end is to splice a multimode AlF3 fiber endcap [42; 126]. These modifications should improve the performance of high-power SC sources and decrease the system complexity. Third, the output power stability of SC sources is also an important parameter that defines true potential toward real-world practical applications. Unfortunately, this issue was not investigated in most of the reviewed papers. Nevertheless, some conclusions seem to be obvious.