<title>Strong Bragg gratings in nonsensitized low-loss planar waveguides as building blocks for WDM network components</title>

Abstract

The performance of WDM networks is highly dependent on the wavelength selective components within the network. When using Bragg gratings as wavelength selective elements they have to fulfill a number of criteria such as low loss, high reflectivity, nearly square filter function and high background rejection. Highly photosensitive germanium doped silica-on-silicon planar waveguides have been produced by plasma enhanced chemical vapor deposition (PECVD). Total insertion losses (including fiber to waveguide coupling losses) down to 1 dB for a 5.1 cm long waveguide have been measured at 1541 nm. A germanium content of 8.6 mol% in the core combined with the PECVD process insures high photosensitivity towards 193 nm. Twenty mm long Bragg gratings have been induced by illuminating the waveguides with 193 nm light through a phase mask. The induced gratings show up to 99.98 percent reflectivity and a background rejection better than 22 dB at plus or minus 1 nm from the Bragg wavelength. No hydrogen loading or any other kind of sensitization was necessary to produce these gratings. The spectral flatness (3 dB reflection bandwidth: 0.55 nm and 1 dB reflection bandwidth: 0.47 nm) around the Bragg wavelength and the high background rejection make these gratings well suited building blocks for multi-wavelength network components.