Thin Film Lithium Niobate Electro-optic Modulator Based On Slot Waveguide

With the development of optical communication technology,optoelectronic devices begin to pursue high performance,low power consumption,low cost and miniaturized integrated devices.Electro-optic modulator(EOM)has become a key in modern optical fiber communication,microwave photonic systems,quantum photonics and data center applications.At the same time,lithium niobate has become the most popular modulation material in photoelectric research field and industrial products because of its wide band(from 350 nm to 5μm),large electro-optic,piezoelectric and elasto-optic coefficients,stable physical and chemical properties.In this work,Mach-Zehnder Interferometer(MZI)electro-optic modulator based on the Lithium Niobate on insulator(LNOI)platform was proposed.The design is unique in that the main modulated waveguide structure is a slot waveguide with optical field enhancement by embedding silicon nanowires in thin film lithium niobate,rather than the lithium niobate ridge waveguide or unetched lithium niobate waveguide previously reported.It is proved that this structure can effectively reduce the half-wave voltage product(V_πL)of EOM and maintain a good bandwidth condition by COMSOL Multiphysics and FDTD Solutions.The applicability design and performance verification of various couplers connected with the designed modulator were carried out.What’s more,two optimization methods of modulation electrodes were established to further improve the performance of the modulator.The main content and results are as follows:Firstly,A heterogeneous integrated EOM based on LNOI platform was proposed.Through the analysis of a variety of existing electro-optic modulators,it is found that not only the thin film lithium niobate perfectly inherits the excellent performance of the massive lithium niobate in its own material properties,but also its processing has been greatly improved in recent years.This allows us to consider the use of a thin film lithium niobate modulator with a slot structure that requires fine etching to the nanometer level.Because of the strong optical binding capability of the slot waveguide,the electro-optic overlap integral of the modulator is increased,and the half-wave voltage product of the device is reduced.The proposed thin-film lithium niobate MZI electro-optic modulator based on slot waveguide has good performance(V_πL=1.78 V·cm and 3 d B bandwidth of 40 GHz at wavelength of1550 nm and electrode spacing of 6μm).Secondly,the pattern coupling structure matching this EOM was verified and optimized on a new heterogeneous integration platform of lithium niobate and silicon.In the thin-film lithium niobate modulator,the mode light is incident through the horizontal silicon waveguide,transmitted to the lithium niobate in the slot waveguide through the coupler.This transmission mode is quite different from that applied in the ridge waveguide and diffusion waveguide before.Therefore,in this chapter,the Strip-to-Slot mode couplers and 1×2 MMI beam splitters of the original silicon-on-insulator platform(SOI)are used for performance verification On the LNOI platform of deposited Silicon(at1550 nm wavelength:The transmission losses of the devices are～0.1 d B and～0.04 d B respectively.The two devices are integrated and upgraded and a new mode transmission structure is proposed.Compared with the two discrete structures analyzed previously,it has the characteristics of high integration,small device size and high transmission efficiency.Finally,two optimized methods of changing electrode spacing and optimizing electrode structure are provided to further improve the performance of the EOM.The electrode design parameters of electro-optic modulator were optimized according to the characteristics of slit waveguide with strong optical field constraint and narrow optical mode field area.The optimized V_πL is 1.51 V·cm and 1.35V·cm respectively),which is far superior to other LNOI electro-optic modulators at present.To sum up,a new kind of thin film based on slot waveguide lithium niobate MZI electro-optic modulator was designed.The modulation structure,modulation performance,machining mode,process error and applicability of related devices were considered comprehensively.The results show that it has certain feasibility.It is hoped that the device design scheme can promote the rapid development of high performance and small size EOM。...