Experimental investigation of backreflection at air-core photonic bandgap fiber terminations

Backreflection from the termination of air-core photonic bandgap fibers (PBFs) is experimentally investigated based on a range-extended Mach-Zehnder and Michelson hybrid (M2) interferometer. For primary waves generated by the fundamental modes, the reflectivity is about −90 dB; for secondary waves caused by other modes, the reflectivity is less than −80 dB when compared to the intensity of the primary wave and −20 to −50 dB when compared to their own incident intensity. To suppress the reflection, ~3-centimeter PBF at the end is filled with alcohol through the capillary effect, and this proposed method is shown to be much more convenient and effective than the conventional angle cleaving method.