Ultrasensitive photonic crystal fiber refractive index sensor

TLDR: A refractive index sensing geometry exploiting modes beyond cutoff in a selectively infiltrated PCF demonstrates a detection limit of 4.6×10−7 RIU and sensitivity of 30,100nm/RIU, a one-order-of-magnitude improvement over previous PCF sensors.

Abstract: We introduce a microfluidic refractive index sensor based on a directional coupler architecture using solid-core photonic crystal fibers. The sensor achieves very high sensitivity by coupling the core mode to a mode in the adjacent fluid-filled waveguide that is beyond modal cutoff, and with strong field overlap. We demonstrate the device through the selective infiltration of a single hole with fluid along a microstructured optical fiber. A detection limit of 4.6x10(-7) refractive index units has been derived from measurements with a sensitivity of 30,100 nm per refractive index unit, which is the highest for a fiber device to date.