Direct Photochemical Patterning of Lithium Niobate Structures for Scalable Nonlinear Optical Metasurfaces.

Lithium niobate (LN) is one of the most sought-after materials for nanophotonic devices, including frequency converters, modulators, and quantum light sources. Integration of LN into optical devices, however, is hampered by significant top-down fabrication challenges due to its exceptional chemical resistance. Scalable fabrication methods that preserve material quality while reducing fabrication complexity and cost are, therefore, crucial to advancing LN devices. A photochemical metal-organic decomposition technique is presented for the scalable patterning of LN at ambient conditions, eliminating the need for harsh etching conditions and cleanroom protocols. The method utilizes a solution of a custom-prepared photosensitive organometallic precursor as a negative photoresist. The ultraviolet (UV) light exposure of the thin films of the precursor through a photomask, followed by rinsing with ethanol, yields amorphous patterns, which transform into crystalline LN after a calcination step. This method enables a scalable fabrication of a range of complex geometric shapes with a feature resolution down to 30 μm. The patterned LN metasurfaces exhibit a tunable second harmonic generation activity with an isotropic optical response. This approach offers a scalable and low-cost pathway for manufacturing LN photonics and the potential to fabricate other materials (e.g., barium titanate and lithium tantalate).