An Ultracompact Directional Coupler Based on GaAs Cross-Slot Waveguide

We experimentally realize a cross-slot waveguide based on GaAs-AlGaAs-GaAs substrate carrying both of transverse-electric slot mode and transverse-magnetic slot mode. A low refractive index AlO
_x
layer is formed between two high index GaAs layers by thermal oxidation method. A polarization splitter is obtained through a 25-μm-long ultracompact directional coupler based on the waveguide. The measured result fits well with calculation using the beam-propagation method.