Wavelength shift and split of cladding mode resonances in microbend long-period fiber gratings under torsion

摘要

The spectrum behavior of microbend long-period fiber gratings under torsional load is investigated. The coupling coefficients between the core and cladding modes grow nonlinear with increasing displacement of deformer plates. A resonance wavelength shift proportional to the square of the twist angle has been observed for various cladding modes. For large values of the twist rate applied to the gratings, each resonance splits into two peaks. When the resonance peaks reach a certain wavelength limit with increasing twist rate, they reduce their amplitudes and finally vanish.