Research On High Speed Silicon Based Electrooptic Modulators

In recent years,with the development of new applications such as short video,higher requirements have been put forward for the communication capacity of the global communication network.Optoelectronic integration technology is the key technology to support large-capacity communication network.The increase of network bandwidth puts forward higher requirements for the performance of optoelectronic units.In this paper,based on the equivalent circuit model of the carrier-depleted silicon modulator,the influence of its physical structure parameters on the performance of the modulator is studied,and the equivalent model of the traveling wave electrode is established.On this basis,the structure of the ridge waveguide is optimized to improve the operating bandwidth.The concrete research content is as follows:1.In this paper,the two-dimensional depletion region of the PN junction in the phase shift region of the modulator is characterized,and the equivalent model of the two-dimensional circuit is established by the partition capacitance and conformal transformation,and the calculation method of the capacitance of each part is given.In order to ensure the modulation depth,the T-track electrode was designed in this paper.The parameters of the electrode equivalent circuit are extracted by using the transmission matrix method,and the equivalent model of the traveling wave electrode bandwidth is established by combining the concept of average voltage.The correctness of the model is proved by comparing with the simulation results.The relationship of each physical quantity in this equivalent model is clear,which clearly shows how each structural parameter affects the performance of the modulator,and lays a foundation for the bandwidth optimization of the modulator below.2.In order to improve the working bandwidth of the modulator,the single-mode ridge waveguide structure is designed in this paper.The effects of different doping concentration and doping region on insertion loss and phase shift efficiency are studied.In order to obtain better phase shift efficiency and lower insertion loss,the doping concentration of holes is slightly higher than that of electrons and the position is biased to the N-region to obtain higher modulation efficiency and smaller insertion loss.3.In this paper,a large bandwidth modulator is proposed based on hetero-doped slot waveguide structure.In order to solve the problem of large junction capacitance and high microwave loss in conventional ridge waveguide,it is proposed to reduce junction capacitance by etching slit in the middle of ridge waveguide.The interaction area between the optical field and carrier depletion region is increased by heteromorphic doping,and the phase shift efficiency is guaranteed.At the same phase shift efficiency,the junction capacitance is reduced by 24%compared with the conventional doping mode.The matching of impedance and refractive index is realized by using T-shaped electrode structure.Compared with the traditional ridge waveguide,the bandwidth of the modulator designed in this paper is increased by 32%and reaches 42GHz at 4V DC bias voltage.The proposed silicon carrier depletion modulator is compatible with CMOS technology,improves the performance of the modulator,expands the bandwidth,and satisfies the application in high-speed communication links.