High-performance Bragg gratings in chalcogenide rib waveguides written with a modified Sagnac interferometer

We demonstrate the highest-quality Bragg gratings reported to date in chalcogenide glass rib waveguides, both in strength and apodization. A modified Sagnac interferometer is employed to write gratings in As2S3-based rib waveguides, achieving an induced refractive index modulation of the order of 10−2 and a grating transmission rejection of more than 30 dB. We obtain good agreement between experimental and theoretical results based on a transfer-matrix formulation for multilayer optical structures. In addition, we report fabrication of phase-shifted Bragg gratings, as well as an investigation of the role of birefringence, higher-order modes, and aging. Finally, grating growth dynamics are investigated by in situ monitoring during writing.