Simultaneous measurement of refractive-index and temperature with high sensitivity by combined use of long-period grating and defect cavity in photonic crystal fibers

A dual-parameter sensor for measuring refractive-index and temperature is designed based on a magnetic fluids infiltrated photonic crystal fiber. By inserting a defective cavity in the cladding layer and inscribing a long-period grating on the fiber core, the proposed sensing mechanism can be achieved directly. The mode coupling and the confinement loss of cladding modes are investigated, and a dual-parameter matrix method is utilized to solve the cross-sensitivity problem. In addition, the relationship between resonant wavelength and external magnetic-field has been studied, which can be used for measuring the magnetic field.