Low-loss controlled-birefringence waveguides fabricated by electron-beam irradiation of germanium doped FHD silica.

Abstract

Silica-on-silicon planar waveguides have proved to be a key technology for integrated optics, mainly due to their high transparency, chemical stability, ease of coupling with optical fibers and their compatibility with already developed silicon manufacturing techniques. The main techniques used to deposit the glass layers are flame hydrolysis deposition (FHD) and chemical vapor deposition [1,2] Nevertheless, this technology presents several drawbacks that have been largely addressed in the literature: due to the different thermal expansion between the silicon and the glass layers, the deposited layers present high level of stress, which translates into significant birefringence [3]. Also, the main technique for the fabrication of optical devices in planar silica is by dry-etch patterning of the core layer. This process introduces significant roughness on the walls of the waveguides, leading to losses and polarization-dependent behavior due to the different degree of smoothness of the different sides of the core of the waveguide [4]. The birefringence and loss of the waveguides are key parameters in the design of integrated optical devices.