Multi-component-intermodal-interference mechanism and characteristics of a long period grating assistant fluid-filled...

A compact in-line modal interferometer based on a long period grating (LPG) inscribed in water-filled photonic crystal fiber (PCF) is proposed and demonstrated. The interferometer works from the interference between fundamental core mode and different vector components of LP(11) core mode. The LPG is especially inscribed to realize the energy exchange between the fundamental core mode and different vector components of LP(11) core mode in the PCF. We build a complete theoretical model and systematically analyze the multi-component-intermodal-interference mechanism of the interferometer based on coupled-mode theory. Due to the asymmetric index distribution over the cross section of the PCF caused by CO(2)-laser side illumination, the dispersion curves and temperature sensitivities referring to different vector components of LP(11) core mode are quite different. Thus the interferometer is polarization-dependent and the adjacent interference fringes according to different components of LP(11) mode show greatly discrimination in sensitivities of temperature and strain, making it a good candidate for multiple physics parameters measurements.