Theoretical Analysis and Experimental Evaluation of SiO2-CBN-MgO Rib Waveguide Structure

This letter reports the design, simulation, optimization, and optical characterization of an electro-optical SiO₂-calcium barium niobate (CBN)-MgO rib waveguide structure. To achieve the single mode and low loss operation, the proposed rib waveguide structure is simulated and optimized with respect to CBN thin film thickness, etching depth, and rib width. Propagating optical mode profile of the waveguide is simulated using a beam propagation method solver. To verify the design and simulation, CBN thin film is coated on MgO substrate using a pulsed laser deposition technique, and SiO₂-CBN-MgO is fabricated with various CBN thicknesses and rib widths. A smooth and nearly vertical etching of rib side wall enables the fabrication of high quality rib waveguides. The waveguides are characterized and measured wave profiles are compared with simulated results. It is found that the guided modes are well confined within the rib and extended through the core. An excellent agreement between simulations and measurements is observed, thereby validating the design method.