Novel large cross-section single-mode AlGaAs/GaAs asymmetric optical switch based on carrier injection effect

A novel AlGaAs/GaAs asymmetric Y-junction optical switch, with 1.7um-thick core layer for single-mode operation at 1.55um, has been designed and fabricated. The switch is based on total internal reflection (TIR) from a carrier-induced index barrier. At the TIR interface inside the Y-junction, a small tapered gap is introduced to obtain a sharp carrier gradient profile for improved switching efficiency. A double masking technique, suitable for monolithic circuit integration, is used to achieve a nearly perfect gap vertex. The switch's strip-loaded waveguide design has a five-layer-heterostructure with a W-shaped index profile, and can provide high coupling efficiency to a single-mode fiber. We have obtained a low optical loss of 1.0dB/cm on 5um-wide waveguides. The asymmetric Y-junction design is carried out by simulating two-dimensional carrier-induced index change based on the calculated carrier concentration and self-heating temperature profile using finite element method (FEM). Preliminary experimental results indicate that optical switches with small size, low loss, fast switching speed and high extinction ratio can be obtained. Switching times of a few nanoseconds have been obtained.

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