Liquid crystal-based tunable coupler and filter for CWDM using parallel long-period waveguide gratings

We present a design of a three-port tunable coupler on a silicon-on-insulator (SOI) platform. The device has three parallel Si strip waveguides separated by liquid crystal (LC) cladding regions containing long-period waveguide gratings. Light launched into the central waveguide can be switched to one of the sidearm waveguides by applying an electric field across the LC layer using split ITO electrodes at a particular wavelength. The switching can be tuned across the wavelength range of 1535.2–1574.8 nm. Correspondingly, the transmission spectrum of the central waveguide shows a rejection band. The proposed structure can be used as an integrated-optic voltage-controlled tunable wavelength coupler/filter for CWDM applications.