Highly accurate etching of ridge-waveguide directional couplers using <i>in</i> <i>situ</i> reflectance monitoring and periodic multilayers

Abstract

A novel periodic multilayer structure has been used in conjunction with in situ reflectance monitoring to give ±10 nm endpoint detection during reactive-ion-beam etching. The method has been used to fabricate ridge-waveguide directional couplers in GaAs/AlGaAs having coupling lengths within 100 μm of the desired 650 μm value. The added loss due to coupling length error was only 0.3 dB per guide. The method is directly applicable to photonic integrated circuits employing complex optical routing of waveguides, directional couplers and y-junctions where total height of the waveguide plays a key role in performance of the circuit.