Modal Excitations in Fully and Partially Ethanol-Filled Photonic Bandgap Fibers and Their Applications as Fiber Sensors

The light guidance characteristics of the fully and partially ethanol-filled photonic bandgap fibers (PBFs) are investigated and their applications as modal interferometers (MIs) for temperature sensing are demonstrated. Different from the ethanol-filled solid core photonic crystal fibers (PCFs), the ethanol-filled PBFs are much easier to excite more high order cladding modes, and the effective refractive index difference between the interference modes can reach 26.6 times bigger than that of the ethanol-filled solid core PCF. Without using special splicing techniques, just splicing a short section of the fully or partially ethanol-filled PBF between the single mode fibers, a PBG-based MI can be constructed with a high thermal sensitivity. Moreover, the thermal sensitivity can be adjusted within a large range by selectively filling the air core and/or air claddings of the PBF with ethanol. Experimental results show that the fully ethanol-filled PBF-based MI has the thermal sensitivity up to -292 pm/°C while that of the partially ethanol-filled PBF-based MI is changed to -120 pm/°C. They are 43.8 and 18 times bigger than that of the unfilled PBF-based MI.