Integrated photonic crystal beam splitters based on thin film lithium niobate

We propose and demonstrate integrated photonic crystal (PhC) beam splitters based on X-cut thin film lithium niobate (TFLN). Its working principle is based on bandgap guidance and total reflection in the PhC slab. We designed two structures: one features a triangular lattice, while the other exhibits a tetragonal lattice. These structures have compact footprint, with size of 14.857×4.982 and 15.275×5.295 µm² for triangular and tetragonal lattices, respectively. We fabricate these devices by directly etching the TFLN. The measured insertion losses are 3.482 (triangular lattice) and 2.181 (tetragonal lattice) dB. Our proposed PhC beam splitter provides a novel approach for the realization of compact photonic devices on TFLN.