A Femtosecond-Laser-Induced Fiber Bragg Grating with Supermode Resonances for Sensing Applications

A Bragg grating is inscribed into the cladding of an all-solid photonic bandgap fiber by use of side femtosecond illumination.Multimode resonances are observed,with calculations resulting from guided supermodes in the cladding by the phase matching condition.All supermode resonances show nearly the same sensitivity to strain and temperature,about 0.98pm/με and 12.78pm/℃,respectively,while their resonant wavelengths are insensitive to bend.An annealing test shows that this grating can endure temperatures higher than 1100℃ where it can still keep high reflectivity and good repeatability.Such a Bragg grating could have potential applications in fiber sensors for strain and temperature measurements,with low cross-sensitivity to bend or an external refractive index,especially in harsh environments.