Research On Plasmonic Hyperbolic Metamaterials And Their Sensing Applications

In modern society,there is an ever-pressing need for the highly sensitive,rapid and economical detection methods for biomolecular that deal with public health crises,disease diagnosis and drug analysis.Surface plasmon optical biosensors have the advantages of label-free,high sensitivity,and real-time detection,which is a research hotspot in the field of nanophotonics and biological detection.The performance of conventional surface plasmon sensor has reached a bottleneck.Plasmonic hyperbolic metamaterial sensors have excellent performance such as high sensitivity and high factor of merit,which is an important direction for the research of novel surface plasmon sensors.At present,the research based on hyperbolic metamaterial sensors has made significant progress,but still faces the following problems:the theoretical problem of how to effectively excite the high-sensitivity sensing guided modes in hyperbolic metamaterials,the problem of efficient design of hyperbolic metamaterials,and the process problem of high-quality preparation of hyperbolic metamaterials,which will largely restrict the performance of hyperbolic metamaterial sensors.Focusing on the above problems,through the combination of theory and experiment,this paper deeply explored the sensing mechanism,intelligent design method and high-quality preparation process of hyperbolic metamaterials.The main research contents and achievements are shown as follows:（1）The highly sensitive sensing theory of hyperbolic metamaterials was studied.For the prism-coupled hyperbolic metamaterial sensing model of nanorods,the wavelength sensitivity expression of bulk plasmon polariton mode was derived by effective medium theory and wave-vector matching,and it was found that the refractive index sensitivity of the low-order mode was higher,and the sensitivity increased with the increase of the filling factor and height of the nanorod.By adjusting the modal index,a way to realize multi-layer hyperbolic metamaterial highly sensitive sensing under prism coupling was opened.The sensing mode of directly excitation of multi-layer hyperbolic metamaterials without external coupling was verified theoretically,and the high sensitivity of 27500 nm/RIU was realized.Finally,the physical mechanism of slow-light enhanced plasmon sensing in hyperbolic metamaterials was theoretically revealed,and the bulk plasmon polariton mode with low group velocities in hyperbolic metamaterials has higher sensitivity.（2）Efficiently designing hyperbolic metamaterials by intelligent algorithms were studied.1)An innovative algorithm framework combining particle swarm optimization algorithm and fully connected neural network was proposed for the rapid optimization and design of highly sensitive ridged hyperbolic metamaterial sensor.The neural network prediction replaced the time-consuming electromagnetic calculations and improved the efficiency of particle swarm optimization algorithm by 4 orders of magnitude.2)Aiming at the difficult problem of modeling long spectral sequences,the gated recurrent neural network that is good at processing sequence data was used to realize the inverse design and spectral prediction of nanorod hyperbolic metamaterials.The inverse design model can accurately design the data of testset and user-defined various types of Gaussian spectra.The average relative error of the spectral prediction model is only 0.32%,and the various spectral line can be accurately predicted by the model whether it is flat,rising or inflection.3)The application of self-attention model with global information perception capability to the inverse design of nanorod hyperbolic metamaterials was explored.（3）The process preparation of gold nanorod hyperbolic metamaterial sensor was studied,and the ultra-sensitive bulk sensitivity and label-free biomolecule detection were demonstrated experimentally.Aiming at the problem of poor periodicity and irregular arrangement of nanorod array prepared based on anodic aluminum oxide template,the hyperbolic metamaterials with good periodicity,consistent pore size and high neatness were prepared by combining electron beam lithography and electrochemical growth process.In the glycerol refractive index sensitivity test,the sensor made has a sensitivity of up to 41600nm/RIU and a quality factor of 416 RIU^-1.By biotin-streptavidin specific binding experiments,the lower detection limit of the sensor for streptavidin was estimated to be 2.4n M.On the whole,the prepared nanorod hyperbolic metamaterial sensor shows excellent sensing performance.