Design of deep-etched, AlGaAs/GaAs optical waveguides with reduced fabrication tolerance sensitivity

Deep-etched GaAs/AlGaAs optical waveguides for use in integrated electrooptic devices were designed and simulated using the beam propagation method (BPM). Waveguides with a low fundamental mode loss (<0.1 dB/cm) but high second horizontal mode loss (>20 dB/cm) were achieved. This design is less susceptible to inaccuracies in the aluminium fraction in AlGaAs than other deep-etched waveguide designs. In practice it is difficult to accurately control the proportion of aluminium (value of x) in Al/sub x/Ga/sub 1-x/As for low percentages of aluminium, hence this design will be easier to implement. Very small radius low-loss bends are simulated by BPM and low-loss multimode interference (MMI) structures are designed by the same method.