Design And Application Of Silicon-based Multimode Interference Coupler

With the rapid development of modern communication technology,the development bottleneck of traditional microelectronics industry becoming more and more prominent.People hope to break through the traditional "Moore's Law" through the realization of integrated optical circuits.Silicon photonics has been more and more attracted because of the excellent material properties of silicon and the compatibility with traditional microelectronic CMOS processes.In silicon photonics,as an important silicon passive device,the silicon coupler is the key to achieving on-chip beam combination and splitting.Compared with the common directional coupler(DC)and Y splitter,multimode interference(MMI)couplers have the advantages of low loss,high process tolerance,large bandwidth,polarization insensitivity and many other advantages,has been widely used.However,the size of traditional MMI devices is relatively large,and reports on miniaturized silicon MMI have only appeared in recent years.In order to meet the needs of silicon integration,this article will focus on the design of a compact,low-loss,good uniformity silicon MMI,with an overall device size on the order of several micrometers.In different types of silicon MMI designs,a universal theoretical design model is needed to determine the design parameters.In this paper,based on the principle of self-imaging imaging of MMI,the mode distribution of MMI is analyzed by guided mode transmission analysis(G-MPA),and the general imaging law of three types of interference MMI is obtained.Based on the theoretical basis,this paper makes a detailed analysis of the phase relationships in different types of MMI.The paper based on the theoretical design model to determine the theoretical parameters.For symmetric interference type 1 x2 MMI and paired interferometric 2x2 MMI,a linear,parabolic wedge-shaped waveguide(Taper)method is proposed to reduce the loss of the device.By analyzing the principle of MMI imaging,a parabolic multimode waveguide coupling region is proposed to optimize the loss and imbalance of 2×2 MMI.The additional loss of 1×2 MMI obtained by simulation is less than 0.05dB,the additional loss of 2x2 MMI is less than 0.25dB,and the 3dB imbalance is less than 0.2dB.However,in the actual application of optical switches and optical phased arrays,the phase in the MMI is an important parameter that affects the performance of the entire device.The phase relationship between the 1×2 and 2×2 MMIs obtained by simulation in this paper has little difference with the theory.The main performance of the MMI obtained through optimization has reached a very high level,fully meeting the needs of on-chip integration.Then based on the simulation results,the paper processes and tests the preliminary designed devices.For the case where the loss of the MMI device is very low,the paper adopted multiple MMI cascade methods to design the appropriate L-edit layout.Then build the platform according to the existing experimental conditions.The additional loss of 1×2 MMI is 0.3dB,the additional loss of 2×2 MMI is about 0.7dB,and the imbalance of spectroscopy is about 0.3dB by testing.The test results show that the preliminary design of MMI has met the demand for on-chip optical coupling of silicon devices.Finally,for the practical application of MMI in silicon devices,a 1×2 thermo-optical switch based on MMI and DC was proposed using the designed 1 x2 MMI.Based on the existing silicon active test platform,the performance of the thermo-optical switch were tested and analyzed.The extinction ratio of the device was about 20dB,the heating power was 16.5mW,and the rise time and fall time were aboutl7?s and 3?s.The experimental results show that the performance of the designed silicon MMI satisfies the practical requirements for application in thermo-optical switch.The design of the silicon-based MMI has a huge impact on the silicon-based integration.Further optimize the performances of silicon MMI,study its polarization correlation,and conduct experimental design of the phase relationship in silicon-based MMI.More applications will be implemented in silicon-based phased arrays,polarization beam splitters,and phase shifters.