Inverse Design Of Silicon Based Mode Division Multiplexing Photonic Devices

With the rapid development of the information society,people not only focus on the increasement of the capacity and speed of the communications Internet,but also have the ultimate pursuit of optical communication device integration density.It's crucial to develop the on-chip optical interconnection technology.Nowadays,the research of the Integrated silicon-based photonic devices on chip with its unique materials characteristics and technical advantages has become attractive for academic research and industrial applications.On the other hand,with the increasing in the integration scale and capacity of the communication,mode division multiplexing is recognized as an effective capacity expansion technology.Silicon-based optical waveguides can manipulate high-order waveguide modes effectively and minimize inter-mode crosstalk and improve mode selectivity.Therefore,multimode silicon photonics has gained more and more attention.But the problems still exist in silicon-based multimode multiplexed photonic devices,such as the big insertion loss and large size of the devices,which limit its applications.In this article,we mainly employ the topological optimization algorithm to inversely design all kinds of compact silicon-based multimode multiplexed photonic devices to reduce devices size and insertion loss significantly.The main research work is summarized as follows:(1)The development of multi-mode silicon-based integrated photonics has summarized through analysising related literature researches.For the mode filters and multi-mode interferometers,the directional coupler model was selected as the initial structure of the inversely design.Through the direct binary search algorithm,we optimized design some target-optimized devices.(2)According to the performance parameters of silicon-based multimode photonic devices,we set the target factors reasonably,and the finite-time-domain difference method is used to simulate the operation.We can achieve the structure of photonic devices,with random engraved holes of the best quality factor by iterativing optimization the different variables,which has the advantages of ultra-small size,low loss,and high performance.(3)In this dissertation,the direct binary search algorithm was used to inversely design silicon-based high-order mode filter,dual-polarization higher order mode filter,dual-mode interferometers,and four-mode interferometers.The simulation results show that the higher order mode filter,the TE₁mode loss is less than 0.2 dB,and isolation is more than 25 dB in the wavelength range of 1500 nm to 1580 nm.For the dual-polarization type higher order mode filter,TE₁mode loss is less than 1.5 dB,isolation is more than 25 dB;TM₁mode loss is less than 1.6 dB,and isolation is more than 20 dB.At the center wavelength of 1550 nm,the total transmittance of each mode of the dual-mode interferometer and the four-mode interferometer is greater than 87%and 80%,respectively,and the imbalance of each mode of the device is lower than 0.1%and 5%.(4)The silicon-based micro-nano device manufacturing process has been used to prepare the devices,which required performance testing.It is obtained that the TE₁mode loss less than 0.1 dB and the isolation more than15 dB of the higher order mode filter at the wavelength of 1550 nm,the working bandwidth is 60 nm.For the dual-mode interferometer,the operating wavelength is slightly shifted,the loss is less than 2.5 dB at 1542 nm,and the imbalance in transmittance between each mode is less than 0.2 dB.At last,the experimental errors and process tolerance of the devices have been summarized and analyzed.