Design And Characterization Of Traveling-wave Electrodes For Inp-Based Rectangular Mach-zehnder High Speed Electro-optical Modulators

With optical interconnection gradually replacing the traditional electrical interconnection,optical devices used in optical communications have the trend of possessing these features of high density integration,low power consumption,and miniaturization.As one of the indispensable basic components in photonic integrated circuits,due to the limitation of the larger traditional waveguide coupler size and the longer modulation arm for the low light-matter interaction efficiency,electro-optic modulator is challenging to scale down the chip area of based devices and improve its integration density.Thus,based on trench couplers and 90 °waveguide bends configuration,we design a Mach-Zehnder(MZ)electro-optic modulator in an InP substrate,and propose a T type of microstrip travelling-wave(TW)electrode structure.This TW electrode can reduce the high frequency signal transmission loss,improve the bandwidth,which shows the convenient way for online testing of the device on a wafer level.Using deep etched waveguide light can be confined in the active quantum well area,thus gaining a greater overlapping factor of electric and light field interaction.This can further scale down the chip area.In this work,we first introduce the modulator device structure and epitaxial growth of each layer material,and design T type microstrip TW electrodes including the structures of transmission,input/output,and transition regions of the TW electrodes.We utilize scattering parameter S,transmission line theory to analysis and calculate the microwave properties of travelling-wave electrodes,such as impedance match,return loss,and bandwidth,which are the key performance parameters.Using the equivalent circuit of the TW electrode,we calculate the modulator bandwidth,which is limited to 70 GHz by material itself modulation capacity.The finite element simulation method is used to optimize the structural parameters of transmission,the input and output and the transition area.The simulation results show that the overall travelling-wave electrodes have high performance,whose matching impedance is greater than the 42?,return loss is less than 15 dB,and the bandwidth is up to 65 GHz.Experimentally we fabricate travelling-wave electrodes on a InP substrate,and use the network analyzer to measure its S parameters.Due to the bandwidth limitation of this instrument,the optimal performance with return loss-12 dB and bandwidth at least 20 GHz were achieved.These results verify a valid simulation method.The G-S-G microstrip line electrode designed in this thesis can meet the requirement of device testing on a wafer level.This high speed modulator exhibits a small chip area of 40 ?m × 40 ?m which meets a highly integrated,low energy consumption,and high speed modulation requirement at the same time,meanwhile such device layout can be configured and extended in the direction of two-dimensional.And it can be potentially applied to large-scale InP based photonic integrated circuits and on-chip optical interconnect systems.