Femtosecond Laser Inscribed Long-Period Gratings in All-Solid Photonic Bandgap Fibers

Long-period fiber gratings are inscribed in all-solid photonic bandgap fibers by use of a femtosecond laser with the line-scanning method. The coupling from the fundamental core mode to LP₁₁ core mode can be readily obtained and the resonant wavelength of the grating is found to be highly sensitive to tensile strain while being nearly insensitive or only slightly sensitive to temperature, curvature, and external refractive index. Such gratings can be effectively used in stable spectral filters and optical fiber sensors with largely reduced cross-sensitivity.