Study On Silicon Modulators Based On Anti-symmetric Bragg Waveguide Gratings

With the advent of information age,requirements for high-performance computing and datacenters increase rapidly.Recently,optical fiber communication has shown great advantages and aroused wide concern due to its large transmission capacity and high speed.As a key device for electro-optical convresion in optical fiber communication,modulators become one of the most important research field.Compared with other silicon photonic modulators such as Mach-Zehnder modulators and microring modulators,Bragg grating modulators have advantages of small footprint and single-mode resonance.Furthermore,there is no crosstalk between channels.However,Bragg grating modulators also have disadvantages.The residual reflected light remains in nature for traditional Bragg gratings,which are detrimental to the input port.The usually used solution is using an isolator,which increases the cost and complexity of package structure.Aiming at the reflected light in Bragg grating modulators,this paper mainly focuses on silicon modulators based on antisymmetric Bragg waveguide gratings.The light is resonant in ASBWG along with mode conversion between the fundamental transverse electric（TE₀）and the first-order transverse electric（TE₁）mode,which is called hybrid mode resonance.According to this,this paper proposes two kinds of silicon modulators:directly-coupled ASBWG modulators and side-coupled ASBWG resonator modulators.In directly-coupled ASBWG modulator,when the incident light is in the TE₀mode,the reflected light of the ASBWG is in the TE₁mode.Therefore,the reflected TE₁mode is radiated in a tapered waveguide that connect a multi mode and single mode waveguide.In side-coupled ASBWG resonator modulator,the TE₀mode in the bus waveguide will be coupled to the resonator waveguide and becomes forward TE₁mode.However,the backward TE₀mode in the resonator cannot be guided to the bus waveguide due to the large difference in effective index.As a result,no TE₀mode is reflected.In this paper,based on the coupled mode theory,a time domain dynamic-state simulation model that can study the dynamic optical and electrical characteristics of ASBWG modulators is proposed.Using this model,we analyze the working performance of different modulator parameters and design modulators.The side-coupled ASBWG modulators can achieve operating voltage of 0.24 V,3d B bandwidth of 39 GHz,extinction ratio of 3.36 d B in eye diagrams at 100 Gb/s,and the attenuation of 19.3 d B.In this paper,a time-domain dynamic-state simulation model that can study electro-optical modulation is proposed and two silicon modulators based on ASBWG are designed.The design of the two modulators can reduce reflection and avoid bad effect on the input port while keeping the original advantages of traditional Bragg grating modulators.This paper provides a theoretical basis and promotes the application of Bragg grating modulators.