Mach-Zehnder interferometer in no-core fiber based on femtosecond laser inscribed waveguides

We demonstrated a fiber in-line Mach-Zehnder interferometer constructed by femtosecond laser written waveguides in no-core fiber. Such an interferometer device consists of a section of no-core fiber, fusion spliced with single mode fiber at its two ends. One of the interferometer arms is formed by the waveguide inscribed and the other follows the diverging light path inside the no-core fiber before arriving at the end of single mode fiber core. Such a device based on internal structure can be used not only for temperature and strain, but also for external refractive index measurement.