Air-gap-coupled MEMS-tunable Littrow SiN wavelength-division multiplexer

We present the design and simulation of a novel, to our knowledge, three-channel Littrow configuration wavelength-division multiplexer (WDM) operating in the 1518–1582 nm range, based on silicon nitride (SiN) waveguides integrated with an enhanced concave diffraction grating. The device employs an air-gap-coupled system, enabling wavelength tuning with reduced actuation force and improved mechanical efficiency. The SiN core with SiO 2 cladding provides low-loss guidance, while wavelength selectivity is achieved through controlled mechanical displacement. In the absence of actuation, the output channels are centered at 1562, 1550, and 1538 nm, yielding a total tuning range of 64 nm across the three channels. Numerical simulations in COMSOL Multiphysics confirm the coupling efficiency and validate the feasibility of this configuration for practical wavelength-division multiplexer applications in telecommunications and optical sensing.