Research On Design And Application Of Metal/Alternative Plasmonic Material-Based Micro/Nano-photonic Devices

Plasmonics is one of the most active frontier research fields in optics since the new century,which is also an important part of nanophotonics.Surface plasmon polaritons(SPP)has novel optical properties,such as beyond the classical optical diffraction limit,sub-wavelength electro-magnetic field localization,and near-field enhancement.With the unceasing progress and updating of micro-nano processing technology and electro-magnetic/waveguide theory,the design and application of SPP-based optical structures has been rapidly developed and brought new solutions to photonic integration technology.Based on the demand of micro-/nano-photonic devices in the future photonic integrated system,the research of this paper is based on a couple of electromagnetic wave carriers,such as surface plasmon polaritons(SPP)waveguides,silicon-on-insulator(SOI)optical waveguides,hyperbolic metamaterial(HMM),and metallic diffraction grating.Based on the metals and alternative plasmonic materials,high-performance surface plasmon resonance(SPR)sensors,polarization switches,polarizers,and nanocouplers in whispering-gallery mode biosensors are demonstrated.Finite-element method-based electro-magnetic numerical simulations are performed to study the electric field distributions,reflection/transmission efficiency,and device performance of the above-mentioned micro-/nano-photonic structures(sensitivity,quality factor,modulation depth,polarization extinction ratio,insertion loss,etc.).The main research contents and innovations of this thesis are as follows:1.Numerical investigations of near-infrared SPR refractive index sensors.Two types of structures are proposed:metal/insulator/metal slot SPP waveguide-fillet cavity coupled system,and metal/insulator/semicon-ductor hybrid SPP waveguide-rectangular cavity coupled system.The sensing principle is the linear relationship between the transmission resonance wavelength and the refractive index of the sensing material.Numerical simulation results show that the designed first-type SPR sensor has spectral sensitivity of 1496 nm/RIU,spectral resoluation of 12 nm,quality factor of 124.6,and transmission efficiency of 95%.The second-type SPR sensor has spectral sensitivity of 1817.5 nm/RIU,spectral resolution of 7.4 nm,quality factor of 224.3,and transmission efficiency of 9 7.6%.The design can meet the needs of the future photonic integrated systems for SPR sensing structures.2.Numerical investigations of SOI strip optical waveguides based polarization control elements.Two types of polarization switches and one TE-pass polarizer are proposed.The switches are based on SOI waveguide-horizontal HMM and SOI waveguide-vertical HMM coupeld systems,where the two HMM are made of Si/vanadium dioxide(VO2)and Si/indium tin oxide(ITO),respectively.The tunable optical properties of VO2 and ITO can change the effective index of the HMM in the wave propagation direction.Therefore,the HMM is designed to provide(cause)mode matching(mismatching)between the SOI waveguide and the HMM for the TE mode propagation.Numerical simulation results show that the Si/VO2 HMM based polarization switch has device size of 0.0176 ?m3,modulation depth of 5.6 dB,insertion loss of 1.25 dB,and operating bandwidth of 215 nm.The Si/ITO HMM based polarization switch has device size of 0.037 ?m3,modulation depth of 27.8 dB,insertion loss of 0.004 dB,and wide operating bandwidth of 300 nm.In addition,a TE-pass polarizer based on a SOI strip waveguide and an HMM cladding layer is proposed,where the HMM is made of Cu and silicon nitride.The working principle is to convert the TM mode into SPP confined in the HMM cladding layer,while maintain the TE mode propagation in the SOI waveguide.The designed TE-pass polarizer has ultracompact device length of 2?m,polarization extinction ratio of 52.34 dB,insertion loss of 0.35 dB,and operating bandwidth of 61nm.The above-mentioned polarization switches and polarizer can meet the high-density integration requirement of the SOI waveguide-based polarization control elements in the future photonic integrated system.3.Numerical investigations of SPP nanocoupler in the WGM biosensors.A novel nanocoupler for robust far-field coupling to ultrahigh-Q WGM microtoroid optical resonators is proposed.The coupling mechanism is based on the diffraction effect of the gold nanorod array(GNA)and its near-field coupling with the WGM inside the microtoroid.Furthermore,a new three-dimensional numerical simualtion method based on electromagnetic finite-element beam-envelope method-Floquet periodic boundary condition is proposed(called 3D FloWBEM).Using this method,eigenfrequency and frequency-domain analysis of the GNA-microtoroid coupled system are carried out to obtain the electric field distributions,the spectra of the build-up energy inside the microtoroid,and the Fano resonances in the reflection spectra,the Q-factors of the coupled WGM,the amplitude ratio of the clockwise WGM to the counter-clockwise WGM,and the signal-to-background ratio(SBR)of the Fano resonances.Numerical simulation results show that the coupled WGM has ultrahigh Q of 2.1 × 107,which can meet the requirement of the label-free single molecule biosensor for high sensitivity and resolution.Furthermore,the Fano lineshaped reflected light signal shows good SBR of 3.86%,which is greater than the noise level of many commercial detectors.This design is an alternative to the traditional fiber taper-based evanescent coupling method,which can meet the needs of stable and robust nanocouplers in WGM biosensors,optical filtering systems,and even future portable optical devices.Also,the proposed modelling approach can provide new ideas and methods for the numerical investigation of the nanostructured WGM optical resonators with large size and high Q.