Fabrication of long period fiber gratings of subnanometric bandwidth.

Abstract

This Letter reports on the fabrication of long period fiber gratings having subnanometric bandwidths in the 1500nm spectral region. Large gratings have been photo inscribed in a high NA fiber; the grating pitch and the order of the HE cladding mode are optimized to produce gratings with a large number of periods and prevent the coupling to TE, TM, or EH modes. Resonances with a FWHM of 0.83 and 0.68nm have been achieved for gratings 15 and 20cm long, respectively; the free spectral range between the transmission notches is 125nm. The polarization effects and the sensitivity of the gratings to temperature and to strain variations are presented as well.