Tunable fiber polarizing filter based on a single-hole-infiltrated polarization maintaining photonic crystal fiber.

A tunable fiber polarizing filter based on selectively filling a single hole of a solid-core polarization maintaining photonic crystal fiber with high index liquid are proposed and demonstrated. Two groups of polarization-dependent resonance dips in the transmission spectrum of the single-hole-infiltrated photonic crystal fiber are observed. Theoretical and experimental investigations reveal that these resonant dips result from the couplings between the silica core fundamental mode at x or y polarization and high order modes (TM(01), TE(01) and HE(11)) in the liquid core. Especially, a distinctive characteristic near the strongest resonant point (SRP) is demonstrated and revealed. The transmission loss and spectral shape at the SRP wavelength are extremely sensitive to the filling length and temperature (or Refractive Index, RI), which permits a fiber bandpass or bandstop polarizing filter with a good performance on tunability and controllability. Furthermore, the narrowband dips on both sides of the SRP wavelength have wavelength-dependent tuning velocities, providing a method to achieve flexible and controllable filters as well as two- or multi-parameter sensors with a compact structure.