Dual-Wavelength Add-Drop filters with aperiodic gratings on a Hybrid SiN-TFLN Platform

We demonstrate a compact dual-wavelength optical filter based on a contra-directional coupler with superimposed Bragg gratings on a hybrid SiN-TFLN (Silicon Nitride on thin-film lithium niobate) platform. The device supports add-drop functionality at 1533 nm and 1563 nm through an aperiodic grating formed by the superposition of two distinct Bragg grating periods. This structure eliminates the need for cascaded designs while achieving low insertion losses of -0.70 dB and -1.39 dB. Three-dimensional Finite Difference Time Domain (3D-FDTD) simulations demonstrate effective spectral separation with a 30 nm channel spacing, making the design suitable for sparse WDM applications.