| Silicon integrated nanophotonic devices are receiving overwhelming attention in the past few decades due to various advantages over integrated electronic circuits including absence of Joule effect,huge bandwidth,low power consumption,high transmit efficiency,small footprint,as well as the compatibility with complementary metal-oxide-semiconductor(CMOS)fabrication process.As the development of fabrication technology in last decade,it becomes easy for us to design and fabricate silicon photonics devices in sub-wavelength scale.However,the traditional way to design devices is to acquire an initial structure through analytical theory with following complicated and heavy workload of optimization,which would lead to large device size or difficulty in complicated device design.Recently,the inverse design method is proposed by researchers to boost the integration density.The inverse design method is a way that combines the mathematics optimization algorithm with electromagnetic computational theory to search the structure satisfies the objective function among infinite structure space.Technically,devices of arbitrarily size or shape could be achieved by inverse design meth,which means devices with more complicated function in smaller size could be realized.Due to those advantages of inverse design method,silicon integrated nanophotonic device obtains great feasibility and possibility in integration,which makes it an ideal solution for photonics integrated circuit.In this dissertation,it is focused on inverse design method to enhance the integration density of silicon integrated nanophotonic devices for practical applications.Firstly,we investigate the development of the inverse design method,analyze and summarize about the mathematical optimization algorithm and electromagnetic computation.Then,a new inverse design platform combined with particle swarm optimization(PSO)and finite-difference-time-domain(FDTD)is achieved through our study.The main research efforts are summarized as follow:(1)We have designed an ultra-compact polarization beam splitter on silicon-on-insulator(SOI).The device is designed by a Particle swarm optimized(PSO)inverse-design method with a rather small footprint of 2×?m2.Simulation results shows that the transmission is greater 50%at designed wavelength 1550 nm.The extinction ratio of our device is greater than 10 dB within a bandwidth of 40 nm.Benefiting jfrom the global optimization of our inverse-design method,the transmission and extinction ratio can be kept functional for both polarizations when the designed pixel side length varies from 100 to 130 nm and the width of input waveguide varies from 300 to 350 nm.(2)An all-optical diode based on mode converting with footprint 2×2?m2 is designed through our inverse design method based on PSO.The device could convert TE00 mode to TE01 mode through the forward transport and block the TE00 mode from backward at the same time.The diode has an operation bandwidth of 100 nm,from 1500 to 1600 nm,and an extinction ratio of 15 dB at 1550 nm.Also,we have proved the that the best condition of diode based on TE00/TE01 mode converting is that the the waveguide has a width between 580 and 680 nm and a thickness less than 210 nm.(3)Some structures of logic gates are realized.An all-optical NOT gate with footpri1t of 1.2×1.2?m2 is designed and could reach a high respond of 0.2 ps.After that,due to the shortage of PSO in the design,a new method based on MOPSO is proposed.All-optical AND and NOT gates are realized in the same area 1.2×1.2 ?m2,and the device robustness of the changes of phase difference and pixel side length is analysized.(4)A module-inverse-design method is proposed.Firstly,the half-adder unit is deconstructed to 5 modules:2 beam splitters,1 hub,1 XOR gate and 1 AND gate.Then those modules are realized in a same design area of 2×2?m2.The whole unit has size smaller than 10×5?m2 which leads to a high operating speed of 1.4 THz.And the extinction ratios of the Sum and Carry are 7 dB and 15 dB,repectively. |
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