Multi-channel add-drop filter using superimposed gratings in hybrid SiN-TFLN platform

We propose a novel grating-assisted contra-directional coupler for sparse wavelength division multiplexing (WDM) systems, utilizing a hybrid silicon nitride (SiN) and thin-film lithium niobate (TFLN) platform. The innovative design of this device is achieved by superimposing two grating structures with different periodicities, enabling simultaneous extraction of four distinct wavelengths. The four wavelengths with a channel spacing of 16 nm are collected using two output ports, each handling a pair of wavelengths. The integration of SiN on LN ensures efficient mode confinement and simplified fabrication. Numerical simulations of this structure demonstrate minimal insertion loss (∼1 dB), low crosstalk and robust performance to fabrication imperfections. Our results show that this unique device can offer a compact and scalable solution for sparse WDM applications.