Researches On Silicon Subwavelength Structure Optical Devices

With the proliferation of voice services and the emergence of various new data and graphics services,especially the continuous development of FTTH and IP network technologies,the information capacity and processing speed of communication systems have shown explosive growth.The electrical conduction technology based on metal conduction is facing serious heat dissipation and insurmountable electronic bottlenecks,and it has become increasingly unsuited to the high-speed and high-bandwidth requirements of information storage,information transmission,and information processing.Taking photon as information carrier and waveguide as transmission medium,optical interconnections can be realized with optical interconnections within the chips to achieve high-density,high-rate data transmission.This is a powerful method to break the performance bottleneck of electrical interconnects.The development of planar optics and their mutual integration are prerequisites for the realization of on-chip optical interconnections.Silicon-based photonics,which uses silicon as its main material,is believed to be the most promising optical interconnection platform due to the advancement of the microelectronics industry,the deepening of researchers'awareness of silicon materials and the maturation of silicon-based compatible technologies.In this thesis,the passive components based on free-form subwavelength structures in silicon-based optical interconnect chips and their inverse design methods are taken as research objectives.First,we introduce the classification and main numerical simulation methods of silicon-based waveguides,and use the finite-difference time-domain method to analyze the mode field distribution characteristics of strip waveguides.Then,this thesis introduces the definition of the device's reverse design,and introduces the free-form sub-wavelength structure and several reverse design methods based on this structure.In addition,this thesis also briefly introduces the fabrication and testing of silicon-based waveguides,including key equipment,main process flow,and test methods.Based on the study of existing free-form subwavelength structures,this thesis proposes a new sub-wavelength structure,the photonic-crystal-like subwavelength structure.This structure is insensitive to the inevitable hysteresis effect of process error,and can greatly improve the processing of the resulting devices.Actual performance.This article combines this structure with the reverse design algorithm to design a variety of passive devices,including a large bandwidth 3 dB power splitter,a star optical cross-connector,and an optical differentiator.This thesis designs,fabricates,and tests the 3 dB power splitter based on the traditional square-wavelength pixel sub-wavelength structure and the photonic-crystal-like sub-wavelength structure.Through the comparison of the experimental results,the photonic-crystal-like sub-wavelength structure is proved to have higher tolerance.The resulting 3 dB power splitter based on a photonic crystal-like subwavelength structure results in a more consistent test structure and better performance.With the increase of on-chip devices,the number of waveguides connected between devices increases,and the number of nodes between each two crossing waveguides also increases parabolically.The continued use of traditional cross-type optical cross-connections will make the intercross connection between waveguides consume a lot of on-chip space and reduce the density of on-chip devices.In order to solve this problem,this dissertation proposes an optical star-crossing based on the photonic-crystal-like subwavelength structure.By achieving single-point crossing of multiple waveguides,the distribution density of on-chip interconnection devices is greatly improved.This thesis finally achieved4×4,5×5,6×6 star-crossings with port density of 7.1?m~2/port,5.83?m~2/port and 7.3?m~2/port respectively.Compared to the traditional crossings,the composed star-crossings have improved the degree of port density by nearly one order of magnitude.The on-chip optical differentiator is an important part of an on-chip optical arithmetic chip.The device size of the existing on-chip optical differentiator is relatively large,and generally reaches 100?m or more.In this dissertation,the traditional multimode interferometer structure and photonic-crystal-like subwavelength structure are combined to design an on-chip differentiator with a footprint of only 6.62?m×4.02?m.