Modelling and characteristics of photoelastic waveguides in Si1-xGex/Si heterostructures

The modelling of the strain, refractive index and optical mode intensity pr ofiles of photoelastic waveguide structures in Si1-xGex/Si heterojunctions are presented. Strain profiles due to the difference in the thermal expansi on of Si1-xGex and SiNy are produced by depositing SiNy stripes on the hete rostructure surface. The corresponding strain-induced refractive index chan ges are modelled by finite element analysis. The photoelastic constants are calculated and are used to find the strain-induced refractive index profil es in the waveguides. It is shown that these photoelastic waveguides exhibi t a low degree of birefringence because they are oriented along the [100] c rystal axis. Optical mode profiles are generated from finite difference cal culations which show that there are three distinct guiding regions under ea ch SiNy stressor stripe; these vary with stripe width. Experimental results show good agreement with the model, and both show that the modal character istics of the photoelastic waveguides are determined by the SiNy stripe wid th.