Electro-optically tunable Barium Strontium Titanate Filter for the 2 μm range

We demonstrate a novel tunable optical notch filter with maximum transmittance of 67% based on a thin film Ba0.5Sr0.5TiO3 (BST) layer integrated into a Fabry–Pérot cavity, designed for operation at 2μm. The filter structure consists of a 450nm BST film sandwiched between two Distributed Bragg Reflector mirrors composed of alternating TiO2 and SiO2 layers. Electrodes patterned directly onto the BST layer enabled the application of an in-plane electric field, inducing a blue shift at the notch wavelength via the quadratic electro-optic effect. Optical characterization 18 reveals a maximum spectral change of 3.8nm under a 210V DC bias. Our results highlight both the feasibility and design trade-offs of using paraelectric BST for tunable integrated photonic filters, which can be a potential candidate for high-speed optical communication.