Propagation characteristics of photonic crystal fibers selectively filled with ionic liquid

We present a numerical and experimental study of the propagation characteristics of photonic crystal fibers (PCFs) selectively filled with ionic liquid (IL; 1-butyl-3-methylimidazolium iodine). Three types of IL-filled PCF are investigated: one with all air holes filled, one with an IL-filled air hole in the second ring, and one with an IL-filled air hole in the third ring. The results show that the third type of IL-filled PCF is the most sensitive to temperature; the sensitivity of resonant dips between the LP01 and LP21 modes is ∼−2.9 nm/°C. Moreover, the intensity of the resonant dips changes with the polarization angle of the light source; the sensitivity is ∼−0.79 dB per unit polarization angle. Based on this property, IL-filled PCFs with different utilities can be realized by changing the filling position flexibly. Consequently, IL-filled PCFs can be used under flexible conditions and controllable temperatures to create a compact polarization-angle sensor.