High-Speed Δβ-Reversal Directional Coupler Switch

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Abstract
Waveguide electro-optic directional coupler crosspoints find use in many applications including modulators and switches for optical fiber communication.[1] Recently there has been significant progress in titanium-diffused lithium niobate (Ti:LiNbO3) devices in both of these areas.[2],[3] To date, however, the emphasis of the device performance for modulation has been speed, drive voltage, and insertion loss; whereas, for switching it has been level of integration crosstalk, and insertion loss. Presently, for example, the switch arrays can be reconfigured only relatively slowly (0.1-1 GHz) and are appropriate for space division switching applications. However, optical switches capable of low crosstalk at reconfiguration rates above 1 GHz are important for time-division switching applications such as optical time-division multiplexing (OTDM).[4] The requirements for use in modulation and switching are, in fact, not necessarily conflicting. In this paper we describe a directional coupler crosspoint structure designed specifically for switching at multi-gigahertz reconfiguration rates with low ( < -20 dB ) crosstalk in both switch states.