| The minimum line width of microelectronic chips is approaching the physical limit at present.It's difficult to improve the performance of microelectronic chip by improving the integration of chips.Integrating the microelectronic system and optoelectronic system into a monolithic chip is the key technology to improve the performance in the post-Moore law period.Due to the process compatibility with micro electric processing technology,silicon-based optoelectronic integration technology is an important research field.With the development of processing technology of optoelectronics,the devices and systems of optoelectronics have been improved tremendously that can be used in practical applications.The current key research fields are at the optimization of the optoelectronic devices and at the improvement of the performance.Compared with the rapid development of devices,there's little research on the simulation method.The mainstream simulation methods for silicon photonics are finite-difference time-domain(FDTD)method,finite-element method(FEM),beam propagation method(BPM)and the mode analysis method.The former three methods are the universal simulation method,the high acquirement and long simulation time limit the practical application on the large structure silicon photonic devices and systems.The mode simulation methods are the most suitable methods for silicon devices due to the clear physical concept,low computation memory requirement and high computation efficiency.However,there're still some problems need to research,for example,the low simulation accuracy.To address the above problems,we analyze the silicon photonic devices with complex mode analysis method in this thesis,and propose a high efficiency method to simulate the devices and systems.Grating coupler,Bragg grating reflector,high performance Y branch splitter and asymmetrical transmission directional coupler have been analyzed with high efficiency simulation model of integrated devices,which are based on the complex mode analysis method in frequency domain of electromagnetic field.The reasons that affect the precision of the complex mode analysis method are deeply analyzed.And high precision method is proposed.The main work and innovation of this thesis are as follows:(1)To solve problem of low accuracy of complex mode analysis method,we propose that the orthogonality of complex modes is the main reason that affect the precision of complex mode simulation method.The way where the orthogonality and the number of employed modes affect the simulation accuracy is comprehensively studied by applying high accuracy one-dimensional complex modes.Furthermore,the computational accuracy and efficiency of high precision complex mode matching method has been compared with FDTD method by utilizing the two-dimensional grating coupler model.(2)The two-dimensional effective model of the devices with grating structure has been proposed,and new simulation model of grating devices has been established based on high precision complex mode matching method.The Bragg grating reflector,which is usually utilized in silicon laser,and grating coupler have been simulated for testing of the computational accuracy and efficiency of the new model.Compared with the FDTD method,the new model has higher efficiency as the computational accuracy is same.In addition,the PSO(Particle swarm optimization)optimization method has been used to optimize the new grating coupler model.And the coupling efficiency of the optimized model is as good as the best results as we know.Compared with the FDTD optimizing process,the new model is more efficiency.(3)To solve the problems in the fabrication of Y junction beam splitter due to the small structure,based on the principle of mode matching theory,the broadband and high uniformity Y junction beam splitter has been proposed and fabricated.With the tapered output branch,the bandwidth of the splitter is improved tremendously.Furthermore,the widened splitting angle reduce the sensitivity to the fabrication technology and improve the power uniformity of two output port.The simulation and experimental results show that the bandwidth of the splitter is larger than 100nm,the process stability is improved with 4dB compared with the normal output waveguide splitter.(4)The integrated device with gain/loss material has been analyzed systematically by complex mode analysis method.The simulation model adopted here is asymmetrical transmission directional coupler which is based on the parity-time symmetry theory.The asymmetrical transmission condition has been derived by complex coupled theory.And the problem of the gain/loss system simulation by using of normal orthogonal mode has been investigated.(5)To solve the low accuracy of the three-dimensional waveguide mode calculation method,the high precision semi-analytical two-dimensional mode calculation method has been proposed based on high precision one-dimensional complex mode and complex mode matching method.The reason that affect the accuracy in finite-difference mode solver has been investigated comprehensively.The numerical error is reduced in the new method by applying high precision one-dimensional complex mode and high precision complex mode matching method.Compared with the finite-difference method,the new method proposed in this thesis is less sensitive to the mesh size and simulation window size.Therefore,the high precision complex mode would be obtained with small simulation window due to the less sensitivity to the simulation window size.In conclusion,the accuracy and the efficiency of complex mode analysis method in the simulation of integrated optoelectronic devices have been investigated comprehensively.The complex mode analysis method is not only suitable for analyzing the active/passive devices with high precision,but also suitable for the simulation of integrated optical communication system.The research of this thesis provides a powerful simulation tool for the rapid development of integrated optoelectronics. |
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