Thin-Film Lithium Niobate (TFLN)-based multimode interference power splitter for multi-band operation

This article leverages thin-film lithium niobate (TFLN) with low dispersion material properties and the order selection in self-imaging effect by critical dimension optimization to reduce the wavelength sensitivity of multimode interference (MMI) power splitters. We experimentally demonstrated two types of multi-band 3 dB 1 × 2 MMI power splitters: the dual-band device achieving synchronous operation in both O-band (1260–1360 nm) and U-band (1620–1650 nm), and the ultra-broadband device covering the entire communication band from 1260 nm to 1675 nm. The fabrication processing of the devices is compatible with wafer-level mass production technology. The dual-band MMI achieves excess loss (EL) ≤ 1.8 dB and imbalance (IM) ≤ 0.33 dB in the O-band, while demonstrating EL ≤ 0.42 dB and IM ≤ 0.24 dB in the U-band. The ultra-broadband one maintains EL below 0.38 dB across 1240–1650 nm, achieving a bandwidth coverage of 410 nm. This research successfully addresses the longstanding challenge of combined multi-band operation, low-loss, and manufacturing compatibility in traditional material platform, while providing critical technological underpinnings for next-generation high-capacity optical communications and coordinated multi-band transmission architectures.