Research On Inverse-designed Silicon Based Passive Devices And Multilayer Integrated Photonic Platforms

The wave of information revolution with information technology as the main body has promoted the word into the information age in the 21 st century.Traditional integrated circuits limited by parasitic capacitance and parasitic resistance cannot meet the needs of the current rapidly growing communication capacity.Large bandwidth,high speed,low power consumption,low delay,and compact integrated optical circuit has attracted much more attention from researchers.As the integration density of optical chips increases,the number of the devices and the complexity of the lines on the chip will increase exponentially.To further increase the integration density,this paper proposes two feasible ideas: reducing the size of the devices and increasing the integration dimension,that is,inverse-designed ultra-compact silicon-based devices and three-dimensional integrated chips.The main work is summarized as follows:(1)The current status and significance of silicon photonics,inverse-designed nanophotonic devices and three-dimensional integrated chips are introduced.The coupling mode theory and theoretical models of several optimization algorithms are analyzed to establish the base for subsequent inverse design of silicon-based passive devices and the design of three-dimensional optical cross-connector.(2)The particle swarm optimization algorithm,the function of fmincon and the direct binary search algorithm are used to inversely design the arbitrary-ratio power splitter,the polarization-insensitive power splitter and the high-order mode filter to achieve highperformance silicon-based passive devices with low loss and large bandwidth in an ultracompact size.The loss of the designed arbitrary-ratio splitter is less than 0.29 dB at the center wavelength of 1550 nm and the power distribution ratio error is less than 0.05.For the polarization-insensitive splitter,its loss at 1550 nm is less than 0.35 dB and the transmittance imbalance of the splitter is less than 0.06%.The loss of TE1 mode filter is only about 0.18 dB at 1550 nm and the crosstalk is less than-27 dB.In addition,the direct binary search algorithm and the function of fmincon are combined to design the mode hybridizer.Combining the advantages of these two algorithms,the loss of the designed device is less than 0.49 dB at 1550 nm and the transmittance imbalance of the device is less than 0.6%.(3)Based on the SiN-on-SOI platform,a three-dimensional optical cross-connector is designed,including an inverse taper vertical coupler and a sub-wavelength grating waveguide crossover.By optimizing the structural parameters,the theoretical loss is less than 0.14 dB in the wavelength range of 1500-1600 nm.(4)The process flow for preparing silicon-based two-dimensional planar devices and three-dimensional devices is discussed in detail,and directional coupling mode filters,three-dimensional optical cross-connector are experimentally fabricated.The measurement results show that the loss of the TE1 mode filter is about 0.7 dB at 1550 nm and the crosstalk is less than-16 dB.The vertical coupling loss of the three-dimensional optical crossconnector is less than 0.76 dB in the wavelength range of 1550-1600 nm and the crosstalk at the waveguide crossing is less than-30 dB.