| On-chip electro-optic modulator(EOM),a vital bridge connecting the electric and optical fields on the same chip,is an indispensable component for the on-chip optical communication based on photonic integrated circuits(PICs).Facing with the rapid increase in the on-chip transmission capacity and bandwidth,high-performance PICs need to be developed,where the EOM gradually becomes a performance bottleneck since the low-speed and narrow-bandwidth modulation strongly limits and even stops the transmission performance enhancement of PICs.Therefore,high-performance EOM becomes our pursuit goal.At the same time,LN is a widely used material for the EOM in the industry field since LN has wide transparent window(from400 nm to 5μm),large EO,piezoelectric,photoelastic,and nonlinear coefficients together with quite stable physical and chemical properties.Based on the above situations,this thesis proposes three kinds of Mach Zehnder Interferometer(MZI)electro-optic modulators based on Lithium Niobate on Insulator(LNOI)platform.Through the simulation software(COMSOL Multiphysics)based on finite element analysis,it is proved that these structures can have excellent performance.The main research content of the thesis is as follows:(1)An LNOI electro-optical modulator based on the heterogeneous waveguide structure of ridged lithium niobate and silicon is proposed.The existing ridge waveguide is analyzed,and its advantages combined with silicon produce a good constraint on light,which is conducive to ensuring low optical loss when reducing the electrode spacing.In this structure,when the electrode gap is 4μm,the absorption loss of light of the electrode is only 15 dB/m,and low optical loss is the prerequisite for the good performance of electro-optical modulators.After parameter optimization,the half-wave voltage length product(V_πL)is 1.63 V·cm and the 3 dB modulation bandwidth is 47 GHz when the modulation region length is 10 mm and the optical wavelength is 1550 nm.(2)A LNOI electro-optic modulator based on a slot waveguide structure is proposed.A layer of ultra-thin silicon is deposited on the slot waveguide.This structure can not only improve the electro-optical overlap factor by relying on the characteristics of the slit waveguide,but also rely on ultra-thin silicon to compress more light into lithium niobate,which is very important for reducing V_πL.efficient.This structure can also play a good confinement effect on light,and for different electrode gaps,waveguide geometric parameters that meet the requirements of low optical loss(<20 dB/m)can be found.After parameter optimization,when the modulation length is 4 mm and the optical wavelength is 1550 nm,V_πL can achieve high performance of 1.45 V cm and a 3 dB modulation bandwidth of 119 GHz.(3)A LNOI electro-optic modulator with a narrow slot waveguide structure is proposed,and an improved scheme of etching slots near the electrodes is proposed based on this basic structure.This improved scheme can be further effective on the basis of the original scheme.The optical loss is reduced to 1/40 of the original solution(the optical loss of the original solution is only about 15 dB/m).After parameter optimization,the modulation length is 4 mm,and the original structure can achieve the excellent performance of V_πL=1.39 V cm and 3 dB modulation bandwidth of 109 GHz when the optical wavelength is 1550 nm.After reducing the optical loss,V_πL and 3 dB Although the modulation bandwidth is slightly affected,it can still reach 1.49 V cm and 96 GHz.In summary,three new structures are proposed,focusing on how to maximize modulation performance and ensure device compactness.The results show that the electro-optical modulators of these three structures have good performance and advantages,and it is hoped that the design scheme proposed in this thesis can promote the rapid development of high-performance compact thin-film lithium niobate electro-optical modulators. |
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