GaAs directional-coupler switch with stepped Δβ reversal

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Abstract
A GaAs electro‐optic waveguide switch in which the power isolation in both switch states can be electrically optimized has been demonstrated. The devices exhibit up to 25‐dB power isolation in both states, with total power output constant to within ⩽0.3 dB. The device is formed on one chip and consists of two equal‐length directional‐coupler switches in series separated by a 25‐μm gap. This structure permits the sign of Δβ, the electro‐optically induced propagation constant difference between the guides, to be reversed midway along the device length. The loss associated with propagation across the waveguide gap is small (⩽0.2 dB), suggesting that similar gaps could be used to electrically isolate waveguide devices on a common substrate in future GaAs‐based integrated optical circuits.