Fabrication and optical optimization of spot-size converters with strong cladding layers

A silicon-on-insulator (SOI) optical fiber-to-waveguide spot-size converter (SSC) overlaid with specially treated silica is investigated for integrated optical circuits. Unlike the conventional process of simply depositing the hot silica on silicon waveguides, two successive layers of silicon dioxide were grown on etched SSC structures by PECVD (plasma-enhanced chemical vapor deposition). The two layers have 0.8% index contrast and supply stronger cladding for an incident light beam. Additionally, this process is able to reduce the effective refractive index of the input mode to less than 1.47 (extremely close to that of the fiber), substantially weakening the unwanted back reflection. Exploiting this technology, it was demonstrated that the SSC showed a theoretical low mode mismatch loss of 1.23 dB for a TE-like mode and has an experimental coupling efficiency of 66%.

State Key Development Program 2006CB302803 2007CB613405 State High Technology Research and Development Program of China 2006AA03Z424 National Natural Science Foundation of China 60577044 This work is supported by the State Key Development Program for Basic Research of China (grant Nos 2006CB302803 and 2007CB613405) the State High Technology Research and Development Program of China (grant No. 2006AA03Z424) and the National Natural Science Foundation of China (grant No. 60577044).