Researches On Optical Properties Of Metallic Nanoscale Cavity-coupled Waveguides And Their Applications To Photonic Devices

With the development of information technology, the high speed, miniaturization,and high integration have become the inevitable trendency for current components.The photonic components has an unequalable advantage of broad transmissionbandwidth over electronic components, but the traditional optical components can’treach the miniaturization of current electronic components due to the diffractive limitof light. Thus, the two kinds of components can not be integrated with each other.Recently, researchers have found an effective pathway to solve above problems,which is known as surface plasmon polaritons (SPPs). SPPs are electromagneticwaves trapped on the surface of metal and propagating along the metal owing to thecoupling interaction between the external incident light field and free electrons inmetal. The optical field power attenuates exponentially in the direction perpendicularto the surface of metal, and is concentrated near the metal dielectric interface with asubwavelength size. SPPs have the advantage of overcoming the traditional diffractivelimit, which provides the potential for the miniaturization and integration of photonicdevices. In this dissertation, we mainly study the optical properties of metallicnanoscale cavity coupled waveguides, and design various new kinds of promisinghigh efficiency nanophotonic devices by means of the novel optical properties.The main novel researches included in this dissertation are as follows:1. The optical filtering properties in several kinds of metallic nanoscalecavity coupled waveguides have been systematically investigated. We have proposeda series of high efficiency plasmonic devices, such as nanoscale band pass/stop filtersand wavelength division demultiplexers (WDDMs). By using finite differencetime domain (FDTD) method, we numerically simulate transmission responses andfield distributions in the metallic nanoscale cavity coupled waveguides, andsystematically analyze the relative characteristics of transmission spectrum bycombining with temporal coupled mode theory (CMT). It is worth mentioning that a dual cavity interference destructive method has been proposed to effectively solve theproblem about low efficiency of plasmonic waveguide based WDDMs, and thetransmission efficiency has been improved by more than50%. The proposed methodand relative results may find important applications in ultra high optical integrationand optical computing.2. A small dimension Bragg reflector has been proposed in the metallicnanowaveguide. By introducing the Kerr nonlinear defect layer into the Braggwaveguide, we realize the nonlinear transmission properties and observe an obviousoptical bistability effect. Transmission features of the structure can be applied for therealization of nanoscale optical switching function. Moreover, we also firstlyintroduce the Kerr nonlinear material into the low loss nanodisk resonator, and obtainthe nonlinear features of signal optical transmission with the change of the intensity ofpump light. Meanwhile, a novel tooth shaped waveguide is employed to efficientlyreflect the pump light, which effectively avoids the interference of pump light to thesignal light. We have successfully designed a novel ultrafast nanoplasmonicall optical switch with a response time of100fs.3. By temporal CMT, we have analyzed the transmission characteristics in themetallic nanowaveguide directly coupled with Fabry Perot (F P) cavities. FDTDsimulations have shown that the transmission spectrum possesses typicalelectromagnetically induced transparency (EIT) like line shape when resonantwaveguide satisfies the certain phase matching condition. We have derived thecoupled mode equations of the metallic nanowaveguide coupled with multiplecavities. Based on the equivalent model of multi cavity coupled waveguide, we haverationally explained the multi peak EIT like effect and its characteristics in theplasmonic multi cavity coupled waveguide system. By using the theoreticalcalculation and numerical simulation, the influence of the physical parameters onEIT like response has been investigated. We have also observed the obvious opticaldelay in the transparency windows, which provides promising pathway for therealization of nanoscale multi wavelength slow light effect. Especially, the EIT likeeffect generated in metallic nanowaveguides coupled with multiple resonators has been used to design a novel type of tunable multi channel band pass plasmonic filters.4. The transmission properties have been investigated in metallicnanowaveguide side coupled with a pair of cavities. We observe that the transmissionspectrum exhibits an asymmetric Fano resonance line shape. Through analyzing withthe CMT, it is found that the Fano resonance can be equivalent to the coherentsuperposition of two reconstructed resonant modes. We have also studied thedependence of Fano resonant spectrum on the coupling separation between the twocavities. The theoretical derivation and analysis is verified by the FDTD simulations.By employing the sensitivity of asymmetric Fano resonance to the change ofsurrounding refractive index, we have proposed a novel plasmonic nanosensor with ahigh sensitivity of900nm/RIU.