Birefringent photonic crystal fiber coils and their application to transverse displacement sensing.

We have experimentally investigated the birefringent properties of photonic crystal fiber (PCF) coils in cooperation with a Sagnac loop interferometer. By reducing the bending radius of the PCF coils, very clear interference patterns can be observed for the bending-induced stress effect. Increasing the fiber turns can result in more obvious interference patterns with smaller fringe spacing but has no contribution to the increment of the birefringence value.