Cascaded Mach-Zehnder interferometers in crystallized sapphire-derived fiber for temperature-insensitive filters

We have demonstrated a novel approach to construct a cascaded Mach-Zehnder interferometer (MZI) based on local crystallization of sapphire-derived fiber (SDF). When the SDF is spliced to standard single mode fibers, the crystallization of SDF occurs near the spliced points. Such crystallized points in SDF could excite and recombine two core modes, which leads to an in-fiber MZI. Moreover, by applying an arc discharge to the SDF, the crystallization could create a cascaded MZI with a temperature-insensitive feature, showing great potential in industrial sensing applications where the required sensors can endure high temperature as well as exhibit low cross-sensitivity from temperature.