Investigation For The Optimal Design And Fabrication Technology Of BaTiO₃ Crystal Thin-film Waveguides

The vigorous development of the optical communication industry is inextricably linked to the continuously upgrading of the key devices,driving the research and development of the central technologies-optical waveguides and integrated devices.At present,the commonly used optical waveguide materials are polymers,lithium niobate?LiNbO₃?crystal and semiconductors etc.LiNbO3 electro-optic?EO?modulation devices are the most stable and fastest EO devices in applications,but due to the limitation of the EO properties of the material itself,it is hard to have a higher modulation rate.Therefore,it is found that barium titanate?BaTiO₃?crystal thin-film material has the higher electro-optic effect,good stability and easy being fabricated for waveguides,implying the important research value.This project investigates the single-mode conditions of the rib waveguides based on the properties of the thin film waveguides of BaTiO3 crystals and the theory of forming guided-mode,and further design two types of BaTiO3 thin-film based rib waveguides:?1?on BaTiO3 film the Si3N4 film is deposited and etch to form the rib waveguides;?2?direct engraving BaTiO3 film to form the full BaTiO3 rib waveguides.With a software tool,the optical propagation losses of the two kinds of rib waveguides based on BaTiO₃ crystal thin films are simulated,then the waveguides are optimized,and finally the experimental samples are successfully fabricated.The simulations for the optical propagation loss performances of the two types of rib waveguides show the advantages of full BaTiO3 rib waveguide over BaTiO₃/Si₃N₄ ones.The fabrication of waveguides is executed through the growth of BaTiO₃thin films with the pulsed laser deposition?PLD?technology,deposition of Si3N4 thin films with chemical vapor deposition?PECVD?technology,the fabrication processes of two types of waveguide structures with the inductively coupled plasma?ICP?etching technology.Simulations show:on 0.5?m thick BaTiO₃ film,the rib height from 0.1 to 0.5?m and the rib width from 2.0 to 5.0?m,the linear BaTiO3/Si3N4 rib waveguide and full BaTiO3 rib waveguide can run the TE/single-mode and the optical propagation loss rates are about0.05dB/m,which is almost independent of the rib dimensions.However,for the curved waveguides,BaTiO₃/Si₃N₄ rib structure having R=10mm can reach its lowest optical propagation loss rate of about 0.3dB/mm,which is 5 times of its linear waveguide,while full BaTiO3 rib waveguide having R=2mm can reach its lowest optical propagation loss rate of0.2dB/mm,which is 4 times of its linear waveguide.With the fabricated chips of 8mm long waveguides,the linear BaTiO₃/Si₃N₄ rib waveguides have an average propagation loss higher than the full BaTiO3 ones by 3dB,while for the curved waveguides with R=5mm,a full BaTiO3 has a propagation loss higher than its linear one by 3dB,and BaTiO3/Si3N4 has the optical propagation loss doubling its linear one,which testifies the software simulations.