Resonance-temperature-insensitive phase-shifted long-period fiber gratings induced by surface deformation with anomalous strain characteristics

We report the fabrication of phase-shifted long-period fiber gratings by use of a CO2laser with a surface deformation technique and a point-by-point method. Due to periodicities that are structurally induced by a heat source and refractive-index modulation caused by a perturbational photoelastic effect, the results of thermal testing show a grating temperature coefficient of 28 pm/°C at a range from 22 to 180°C, indicating that the band rejections of the grating that is formed remain unchanged in their resonant strengths even at temperatures up to the fictive point of fiberglass. It is found for what is believed to be the first time that such a grating possesses an anomalous strain behavior of resonance with -1.52 × 10-4dB / με for the right notch and 7.05 × 10-5dB / με for the left notch.