Second-order Bragg gratings in single-mode chalcogenide fibres

Bragg gratings with a second-order resonance wavelength in the near-IR spectral region have been inscribed into single-mode chalcogenide (As₂S₃) glass fibre by a He — Ne laser beam using a configuration typical of Bragg grating fabrication in germanosilicate fibre, with the use of a phase mask that ensures effective diffraction of the writing light into the +1 and -1 orders. The spectra of the inscribed gratings show no resonances due to cladding mode excitation because the cladding material is photosensitive.