Photonic Crystal Fiber-Based Modal Interferometer for Refractive Index Sensing

A core-cladding-mode interferometer is fabricated by splicing a single-mode fiber to an endlessly single-mode photonic crystal fiber (ESM-PCF). The optimum collapsed length of ESM-PCF is investigated to ensure a higher order cladding mode of ESM-PCF to be excited, serving as a sensing beam. At the end of ESM-PCF, a spherical end-facet with big radius is proposed to ensure from where the higher order cladding mode is to be reflected and then it interferes with the core mode serving as a reference beam. Such a device has an enhanced refractive index sensitivity of ~ 199 nm/RIU, offering potentials in biological and chemical applications.