Strain sensitivity of long period gratings in hollow-core photonic bandgap fibers

We investigate the strain sensitivity of long period gratings (LPGs) fabricated in hollow-core photonic bandgap fibers (HC-PBFs). The LPGs are fabricated by periodically deforming the air-holes along the PBFs by use of a CO 2 laser. Resonant couplings between the LP 01 and LP 11 core modes results in two highly polarization-dependant loss dips in the transmission spectrum. The sensitivity of the resonant wavelength to strain was found to vary from -1.48 to -2.4 pm/μe when the grating pitch was changed from 225 to 175 μm. Theoretical investigation suggests that the size and shape of the core can have significant influence on the strain sensitivity.