| High demand on larger capacity of data transmission through optical network has drawn the extensive development and studies on optical modulators for past half century. Optical modulator is one of the crucial elements in fiber communication systems since it transforms the electrical signal to the light signal. This process is required to transmit the information such as data or voice through fiber medium which has very low loss at communication band and enormous bandwidth. In recent years there has been a widespread concern about the high-speed polymer electro-optic modulator.Among the various kinds of optical modulators, Mach-Zehnder (MZ) intensity modulator based on electro-optic (EO) effect has served as one of the fundamental and important elements in optical fiber data transmission system. The advantages of polymer materials are as follows:(1)It is very easy to get highμβchromophores and large macroscopic E-O activity in the chromophore-incorporated polymers.(2)We have a lot of methods to maintenance the long-term temporal stability toward the environment.(3)Optical loss can be minimized from design and processing of materials to fabrication and integration of devices.The MZ polymer EO modulator consists of waveguide and microwave electrode. When the waveguide has been fabricated, the performances of a EO modulator is decided by its microwave electrode system.Performances of microwave electrode system can be considered from the following aspects:(1) Achieve the maximum electric field with the applied voltage.(2) The electric field should be applied along the direction of maximum material nonlinearity.(3) Wide operation bandwidth.(4) Achieve a close speed match with the lightwave.(5) Easy fabrication process and tolerance.(6) Impedance matches to the external microwave driving source.(7) Feasible microwave packaging with standard interface.To design the electrode system, We need to calculate the parameters such as the width,thickness and electrodes gap of electrode and waveguide, from these parameters we can modeling and design the features of impedance, microwave loss, band width, extinction ratio,half-wave voltage about the MZ optical modulators,all the calculations are the fundamental of electrode design.In order to achieve a good performance, detailed studies of the microwave electrode system have been done. This paper mainly covers the following aspects: (1) Study and analyze the modulation characteristics of the conventional microstrip line (MSL) electrode,coplanar waveguide (CPW) traveling wave electrode and In-plane CPW electrode.(2) Calculated the structure of PMMA:DR1/PMMA:PMMA, and get the best structural parameters, and the absorption loss of the metal are also analyzed.(3) Simulated the characteristic impedance, microwave loss, skin depth,3dB bandwidth, half-wave voltage, and high frequency of MSL and CPW electrode system by using the software of Matlab, Ansys, BPM and others.(4) The curve of Zo,αc, ad, Neff,δ, f of MSL and CPW electrode has been drawn.(5) Optimization results for the CPW electrode:t= 3μm, W= 33μm, h= 12μm, Vπ= 45V, f= 62.7GHz, and for the CPW electrode:t= 3μm, W= 26μm, h=10μm, Vπ= 23V, f=44.3GHz. These theory results basically can be able to meet the requirements of practical 20GHz electro-optic modulator.(6) The S curve of the samples of electrode measured by Vector network analyzer, and for S21 curve characteristics of 0-20GHz,we have made a deeply analysis.(7) Research and analysis the key processes, such as spin coating, etching (including RIE etching, ICP etching, wet etching). |
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