Research On The Key Application Technologies Of Silicon Photonic Crystal Nanobeam Cavity

The unique advantages and rapid development of integrated photonic technology have led to further development and breakthroughs in the research and application fields of modern optics,such as optical communication and all-optical information processing,optical computing and photonic neural networks,optical quantum computing and key distribution,microwave photonics and spectral analysis and sensing,which have gradually moved toward integration.These optical research and applications have in turn put forward the requirements of lower energy consumption,smaller size,higher efficiency and lower cost to the basic devices of integrated photonic technology.As a resonant device with both very small size and high modulation efficiency,the photonic crystal nanobeam cavity has the potential to be a new type of basic unit structure for integrated photonic devices to meet the development requirements of integrated photonic technology.However,nanobeam cavities currently lack wider application,mainly because they face the core problem of low transmission efficiency when used as a multi-port unit structure,which limits their access to more complex combinatorial functions and scalable integration.In addition to this core problem,there are a series of key issues: such as the lack of high extinction ratio structural design of nanobeam resonant cavity design;nanobeam resonant cavities usually have only one high quality factor Q value resonant mode,which does not meet the demand of multiple nonlinear effects on multi-frequency optical field interaction;when using nanobeam resonant cavities for the application of large-scale arrays,it is necessary to overcome the process error problem of numerous cell structures,etc.Based on the above development needs and the various problems faced by nanobeam resonant cavities,this thesis is oriented to the practical applications of four types of nanobeam resonant cavities,namely,integrated optical switches,high extinction ratio filters,four-wave mixing resonant cavities,and miniaturized spectrometers,and the key technologies are studied and verified by theoretical analysis and actual device fabrication,and the main contributions and results can be summarized as follows.(1)Firstly,from the theory and design method of photonic crystals,this study proposes a design optimization method to construct a slowly changing photonic crystal structure by calculating the energy band structural properties through the plane wave expansion method first,and then optimize the optical field through the time-domain finite difference method to realize a high-Q small mode-volume nanobeam cavity.(2)To address the core problem of low transmission efficiency of nanobeam cavity,a universal semi-symmetric Fano resonant theoretical model is proposed to theoretically derive the high transmission efficiency condition,and a nanobeam cavity optical switch with high transmission efficiency is actually fabricated based on the theoretical design,which significantly reduces the insertion loss of the operating wavelength from 8.5 d B to1.5 d B.The structure feature is the four semi-symmetrical air holes on the double-bending waveguide coupled with the nanobeam cavity,and the core size is only 3 μm × 5 μm,which is much smaller than that of conventional optical switch devices.(3)To address the key problem of the lack of high extinction ratio structure of the nanobeam cavity,a Fano-enhanced high-order nanobeam cavity filter with a structure of multiple identical nanobeam cavities arranged in close coupling is proposed,which achieves a high extinction ratio of 70 d B and a low insertion loss of 1 d B with a size of only 20 μm× 10 μm.It also eliminates the need for active tuning calibration compared to conventional high-order resonator filtering schemes.(4)To address the key problem of a single operating resonant frequency of the nanobeam cavity,a special energy band engineering-based photonic crystal nanobeam cavity structure is proposed to have only three equally spaced high-Q resonant frequency modes to meet the optical field frequency requirements of four-wave mixing applications.The structure is a single nanobeam multi-mode cavity with inverse taper of the central hole parameters and a core size of only 20 μm × 1 μm.Fano coupling can be used to further enhance the nonlinear efficiency.(5)To address the problem of process errors in the application of nanobeam cavity arrays in spectrometer applications,a small-size designable photonic crystal nanobeam is combined with a computational spectral reconstruction algorithm to improve the process tolerance of nanobeam cavity arrays by the algorithm,and the advantages are complemented to obtain a nanobeam spectrometer with small size,easy scalability,and easy transplantability.The structure is a dense arrangement of nanobeam cavity cells with tapering width,the core length of which is only 6 μm and the cell spacing is 3 μm.The theory shows that the nanobeam spectrometer operating in the 1550 nm band can be easily transplanted to the 1310 nm and 2400 nm bands.