Multipass Hollow Core-PCF Microcell Using a Tapered Micromirror

We demonstrate the insertion of a micromirror into the core of a hollow core photonic crystal fiber (HC-PCF). The micromirror is formed from a single mode fiber that has been tapered to fit into the hollow core and fixed in place using a fusion splicer. A large range of reflectivities higher than 4% was also achieved by silver-coating the silica tapered-fiber end-face using thermal evaporation. The current micromirror provides two key advantages over using a full-sized fiber splice to create a reflective interface. First, the tapered fiber tip can be coated to increase the reflectivity without degradation due to heating during the splicing process. Second, increased efficiency of input and output coupling is possible because of improved mode-field overlap with the fundamental mode of the HC-PCF. We show potential applications of micromirrors for the formation of microcavities in hollow-core fibers and for gas saturated absorption spectroscopy.