Mid-infrared (mid-IR) fiber lasers in the 2.5-5 µm wavelength range have great potential to play a pivotal role in spectroscopy and medicine . However, at present the non-existence of fiber-coupled optical components for these wavelengths severely limits the ability to build highly efficient alignment-free, low loss all-fiber lasers. This relates to the fact that fabricating various in-fiber components in fluoride fiber is a challenging problem, due to the difference in glass properties and handling requirements compared to standard silica fibers. Here, we address this problem by reporting the direct femtosecond (fs) laser inscription of high reflectivity (99.98%), low loss (<0.5 dB), Type-I fiber Bragg gratings (FBGs) into the core of soft-glass ZBLAN fibers for mid-IR applications.
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