Integrated optical components produced in GaAs and InP epitaxial layers using the photo-elastic effect
Studies have been made of optical waveguides produced in GaAs and InP epitaxial layers. Of the possible waveguiding mechanisms present in these devices the contribution from the photo-elastic effect (strain-induced refractive index changes) dominates. Stresses in evaporated metal films and their control have been investigated. Strain-induced waveguides have been used to produce a novel directional-coupler structure with a short coupling length (~2mm). In GaAs bias has been applied to control the amount of light at the output of each of the two waveguides forming these couplers and it has been possible to isolate the light in either the excited or the coupled waveguide. A new theoretical model, based on finite difference techniques, has been developed and used to analyse strain-induced, slab and rib waveguide structures. Results obtained have been compared with those from other methods. Theoretical predictions of guiding properties in GaAs strain-induced waveguides give good agreement with experimental results in all cases. Optical waveguiding in InP layers using the same photoelastic mechanisms, assessed experimentally, indicates that the refractive index changes are similar to those in GaAs but slightly larger. One of the first measurements of the nonzero electro-optic coefficient, r41, of InP is described. Guiding properties vary little with time in both InP and GaAs. The reflection of light guided in a single-mode photoelastic waveguide into a second perpendicular guide using a vertical etched facet running at 450 to the direction of propagation is proposed for providing bending with negligible loss and some experimental results are reported.