Coplanar Waveguide Electro-optic Modulator

The electro-optic modulator is one of the key components in the optical fiber communication system. In recent years, the research on the electro-optic modulator has been widely concerned. But there still have been many factors in developing wide bandwidth of electro-optic modulator. The main factors affecting bandwidth are the velocity matching and impedance matching. The important aspect of meeting velocity matching and impedance matching is to design of traveling wave electrodes. Therefore, the research in this paper are mainly about the design of the traveling wave electrode and the analysis of factors of bit error rate in microwave fiber-optic transmission system.Firstly,the optical waveguide has been designed and simulated. the single-mode transmission conditions and the mode field distribution of the ridge waveguide structure are achieved by effective index method. and the the effect of cladding layer and core layer thickness on the metal associated optical loss is calculated. Secondly, the microwave loss of both the microstrip line and coplanar waveguide electrode is compared and analyzed. The simulation results show that the conductor loss of the coplanar waveguide electrode was smaller. Therefore, the coplanar waveguide structure is used in our paper. The electric field distribution of the coplanar waveguide electrode in the optical waveguide is analyzed by the theory of electromagnetic. The best position of the electric field amplitude is achieved through simulation. Thirdly, three different transition structures of electrode are designed and compared. Fourthly, we propose a co-simulate method to co-simulate the coplanar waveguide electrode. Accordingly, we divide the electrode into some modules, while each module is simulated respectively by the CAD tools, and then we combined each module together to analyze the whole electrode system. We can conclude that the co-simulate method can greatly reduce the computing time and be easy to optimize the design with the mentioned method. From the simulated results, this method is feasible. Finally, the electro-optical modulator with a new coplanar waveguide electrode structure is optimized by the method of co-simulation. And we obtained a bandwidth of 140GHz and the half-wave voltage of 7.2V electro-optic modulator which Operated wavelength of the modulator is 1550nm. The results present that velocity matching, impendent matching and lower microwave propagating loss are realized in modulators with thick electrodes. The modeling procedure has been validated by comparison with experimental results presented in other literature.