| Silicon photonics has been widely considered to be the best choice to realize highly-integrated photonic chips,due to its miniaturization and ability to be integrated with nano electronic devices.Thanks to the development of high precision nano manufacturing technology,the inverse-design methods have been developed.This design idea greatly increases the possibility of device structure design.Theoretically,the device structure can have arbitrary size and shape,which has potentiality for devices with novel functions.Therefore,inverse design is a very valuable research topic.This dissertation focuses on the realization of the inverse design and the function extension of the device.The main research contents are as follows:(1)The realization of the inverse design method is analyzed in detail.The simulation platform of the inverse design is mainly composed of MATLAB programming,which is to solve the problem definition module and device structure optimization module,and the python programming which is used as electromagnetic field solver module.The functions of each module and data transmission process are introduced.The simulation processes of inverse design contains:1)Generation process,which is used to define the initial structure parameters and the target performance of the device;2)Optimization process,including global optimization,local optimization and level-set optimization;3)Solving process of electromagnetic field based on FDFD algorithm;4)Verification process,to verify device performance by using commercial software as Lumerical.(2)The optimization technology is studied,the function of the device is expanded.Firstly,the optimization of the device design area is discussed,including the modification of the design area shape and multi-area optimization.The shape of the design area is changed to circle or rectangle,in order to study the influence of different design area shapes on optimization results.The simulation results show that the transformation efficiency of rectangular area(95.44%)are better than those of circular area(89.78%)when using inverse design method to design mode converter.Although the multi-area optimization can improve the computation time,the conversion efficiency(85.95%)is affected slightly by the multi-region.(3)A 2.8?m × 2.8?m T-junction polarization splitter on SOI is first proposed by inverse design method.The TE and TM fundamental modes at 1550nm are split from the lower output and the upper outputs respectively,with conversion efficiencies of 78.83%and 83.08%,respectively.The insertion loss and extinction ratio variations of the device in a wavelength range from 1520nm to 1580nm are analyzed,from which we can see that the insertion losses of two output ports of TE and TM at 1558nm are 1.93dB and 1.84dB respectively,while the extinction ratios are 19.3dB and 13.99dB respectively.The effect different locations of output waveguides on the device performance are investigated.The results show that better polarization splitting performance is obtained with output waveguides locating at the center of edges of the design area.(4)The inverse design method is used to design a vertical coupler between optical fiber and silicon waveguide,and a mode converter from optical fiber to silicon waveguide.Firstly,the vertical coupling of a single-mode fiber and a silicon waveguide is achieved with calculated coupling efficiency of 33.83%,which indicates the feasibility of realizing vertical coupling of optical fiber and waveguide by inverse design.Secondly,the coupled mode LP01 and LP11 in few mode fibers are vertically coupled and converted into TE fundamental mode into the waveguide,with coupling efficiencies of 30.47%and 21.2%,respectively.It also indicates the feasibility of the inverse design algorithm to realize the vertical coupling of the few mode optical fibers and silicon waveguide. |
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