Dual-Resonance-Coupling and Sensing Characteristics in an All-Solid Photonic Bandgap Fiber Interferometer Based on LP01 Cladding Supermodes

A dual-resonance-coupling phenomenon and the sensing characteristics of an in-fiber modal interferometer based on cascaded long period gratings inscribed in an all-solid photonic bandgap fiber are demonstrated. Theoretical and experimental investigations reveal that the dual-resonance dips result from the coupling between fundamental core mode and two different kinds of LP
₀₁
cladding supermodes. Due to the deep grooves and asymmetric index distribution along the long period grating caused by side illumination, this dual-resonance interferometer is sensitive to polarization and twist, and the dual-resonance dips according to different LP
₀₁
cladding supermodes exhibit different responses to twist. Furthermore, the transmission loss and the resonance wavelength of each interference dip show discrimination in sensitivities of temperature and twist, making it a good candidate for multiple physics parameters measurements.