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Photonic crystal fiber based modal interferometer for refractive index sensing

A core-cladding-mode interferometer (CCMI) is fabricated by splicing a single-mode fiber (SMF) to an endlessly singlemode photonic crystal fiber (ESM-PCF). The optimum collapsed length of ESM-PCF is investigated to ensure a higherorder cladding mode of ESM-PCF to be excited, serving as a sensing beam. At the end of ESM-PCF, a spherical endfacet with big radius is proposed to ensure from where the higher-order cladding mode 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.