Ultrasensitive Properties of a Long-Period Grating Inscribed in a Dual-Mode Photonic Crystal Fiber

Sensitivity properties of a long-period grating inscribed in Ge-core, dual-mode photonic crystal fiber (PCF) have been studied numerically. While the fundamental mode of the PCF shows similar characteristics to conventional fibers, its higher order mode exhibits nonmonotonicity in phase matching curve that leads to dual resonance peaks. The dual peaks shift in opposite directions with any changes in strain or temperature and exploiting the separation between the peaks can result in an ultrasensitive device. Our analysis shows that the dual peaks separate by 180 nm when 2-mε strain is applied and 170 nm with a 275 °C rise in temperature, which are much higher than the shift in single resonance peaks. Numerical investigations on simultaneous measurement of strain and temperature are also made for the dual resonance case. Furthermore, due to a relatively small cladding radius, the fundamental mode shows a peak shift of 1848 nm per refractive index units when the ambient refractive index changes from 1.325 to 1.35. We infer that our proposed device can be used as a high-performance sensor for single or multiparameter sensing.