The Inverse Design And Realization Of Multimode Waveguide Bends Based On Digitized Meta-structure

Recent years,information generated in internet has increased in an explosive way,which starts to make the conventional information processing technology little helpful when it comes to this situation.With the development of integrated photonics circuits,however,on-chip Mode Division and Multiplexing?MDM?as a promising solution to handle the problem exists.Bends play a vitally important role in MDM systems and have been widely included in many silicon photonics design suits.Because of the deployment of bends,the integrated photonics system could be designed with flexible routes,which will lead to reducing occupied layout area and increasing the integration density on chip.Therefore,my thesis,according to this research background,has proposed a method based on inverse design to design a kind of special bend which could support more than one mode light transmitting with low loss and demonstrated with experiment.In the design process,we choose Silicon-on-Insulator?SOI?as material platform and Lumerical FDTD Solution software as optimization platform which could compile and run the optimization algorithm script.First of all,we initially digitalize the intact silicon waveguide bend into a number of pixels whose materials properties could be changed in order to cause influence on modes light transmittance in bent segment.Then,the optimization algorithm will find the materials property of each pixel:silicon or air until the whole optimized structure could support modes light transmitting with high efficiency.In this paper,we design three kinds of bends which could support two modes?TE₀,TE₁?,three modes?TE₀,TE₁,TE₂?and four modes?TE₀,TE₁,TE₂,TE₃?transmitting with low loss,and the operating wavelength ranging from 1535 nm to 1565 nm.The simulated results suggest that the transmittance loss and mode crosstalk of all three bends are around1 dB and below-15 dB,respectfully,which meets the requirement of design specification.In the meantime,we also elaborate the whole fabrication process of silicon photonics in general cleaning room laboratory,which includes slicing,cleaning,coating,electron beam exposure,developing and fixing,RIE etching,removing resistance and microscope check.After a series of fabrication tests,we finally obtain sample with high quality and characterize its optical performance.We also give the details on building method of measurement system and the points needing attention.Scanning the wavelength and recording and normalized the data,we get the measured results.Through sophisticated analysis,we think the experiment results are in accordance with that of simulation when considering the tolerated fabrication error,and it also means that the device we design could be used in on-chip system.Compared with other waveguide bends already reported in paper,our devices have many advantages such as compact size,low transmittance loss,more supportable modes,easy fabrication and so on.We believe that these bends are promising to be deployed in future integrated photonics system and make the occupied area reduced and integration density increased.