Cladding-Mode Resonance in Polarization-Maintaining Photonic-Crystal-Fiber-Based Sagnac Interferometer and Its Application for Fiber Sensor

A novel cladding-mode-resonance-based polarization-maintaining photonic-crystal-fiber Sagnac interferometer (PMPCF-SI) and its application for fiber sensor are demonstrated. By introducing a mode field diameter mismatch at a splicing joint of an inbuilt single-mode fiber (SMF)-PMPCF-SMF structure connected in an SI, an intermodal interference is constructed by the excited cladding modes and the polarization modes of the PMPCF. With such a PMPCF-SI, simultaneous strain and temperature measurements are demonstrated. The SI behaves as a sensor and a filter simultaneously. By measuring the wavelength variation and transmissivity difference between two almost symmetrical resonance peaks in the spectral response of the SI, simultaneous strain and temperature measurements are achieved.