Theoretical And Experimental Investigation Of Several Key Micro-Nanophotonic Components

Micro-nanophotonics focuses on the interaction between light and matter at micro- and nano-scale and its applications in the generation, transportation, modulation, detection and sensing of light. Optoelectronic material can exhibit diverse fantastic effects by introducing micro-and nano-structures with dimensions close to or less than wavelength. Micro-nanophotonic components including lasers, interconnectors, sensors and optical delayers have potential applications in information optpelectronics, biology, medicine and defense, and have drawn wide attention of researchers all over the world. This dissertation focuses on theoretical and experimental investigation of several key micro-nanophotonic components. The main innovative contributions are as followings:1. Micro-nanophotonic components based on microstructured fibers(1) A design of a surface plasmon resonance sensor based on Ag nanolayer in a microstructured optical fiber was proposed. This sensor has a simple structure, its outer six big holes can enhance the microfluidics of analyte and coupling between the guided mode and surface plasmons. The calculation results showed that, the sensitivity of this sensor were 1500 nm/RIU corresponding to a resolution of 6.67×10-5 RIU. Compared to the sensor with Au nanolayer under the same structure, the sensitivity and Q factor of the sensor with Ag nanolayer are better.(2) Tunable slow light based on stimulated Brillouin scattering was experimentally realized using a highly nonlinear microstructured fiber designed and drawn by Fiberhome Telecommunications Technologies Co. Ltd. The microstructured fiber is comprised of one layer of pomelo-like air holes around the core and outer five layers of circular air holes. It achieves a high nonlinearity coefficient of 136 (W·km)-1@1550 nm. The experiment setup was a structure composed of single pump and a single-stage delay. The pulse width of the signal was 100 ns. When the pump power was 162.6 mW, a maximum delay of 76 ns, equaled to 0.76 pulse width, was achieved in the highly nonlinear microstructured fiber with length of 120 meters. In addition, by adjusting the pump power, tunable slow light was realized.(3) A dispersion compensator based on a structure of coupled asymmetric subwavelength-diameter wires to realize a high negative dispersion was proposed. The waveguide consists of an optical nanofiber and a GaAs nanowire. Modal index and dispersion as functions of diameter and space of nanowires were calculated using finite elements method. The calculation results showed that the symmetric supermode in the coupled structure exhibited a giant negative dispersion up to -4.5×106 ps/nm/km.2. Micro-nanophotonic components based on surface plasmons(1) The surface plasmons existing in the gap between two adjacent silver nanowires form a gap plasmonic mode supporting long-distance transmission under strong confinement. Theoretical investigation showed that when two adjacent silver nanowires were placed on a silica substrate, there was a critical gap distance Dp between two silver nanowires which approximately equaled to the radius of the nanowires. When the gap distance was less than Dp, the influence of the substrate on the gap plasmon mode could be neglected. Moreover, plasmonic waveguiding properties of the gap plasmon mode were not sensitive to roughness of substrate surface.(2) By introducing an asymmetry into a symmetric hybrid plasmonic waveguide, an asymmetric hybrid plasmonic waveguide was proposed. This waveguide combines advantages of hybrid and symmetric plasmonic modes. Theoretical analysis showed that when this waveguide was placed on a silica substrate, it could eliminate the influence of substrate on its guiding properties, restore its broken symmetric mode and realize a long propagation length of 2.49×103 μm under subwavelength confiment.(3) Based on the asymmetric hybrid plasmonic waveguide, an asymmetric hybrid plasmonic waveguide, which realized cm-level propagation length, was proposed by embedding a silver nanowire in the waveguide. Theoretical investigation showed that the waveguide realized quite long propagation length of 2.69 cm with subwavelength confinement and extremely large figure of merit of 139037 was achieved. The proposed waveguide can be used as a directional coupler. It achieved coupling length of only 1.01 μm at S= 0.1 μm with negligible loss. Strong dependence of coupling length on the operating wavelength makes the proposed waveguide promising to be employed as wavelength-selective components in WDM systems.(4) A low-threshold-gain nanolaser with all three dimensions smaller than its lasing wavelength was proposed and investigated, which was constructed based on an asymmetric hybrid plasmonic waveguide with Ag-coated end facets. Theoretical investigation showed that minimum threshold gain of 260 cm-1 was achieved for a Fabry-Perot cavity length of 1 μm. The corresponding quality factor and Purcell factor were 219 and 172, respectively. By moderately sacrificing the threshold gain and quality factor (increased up to 1261 cm-1 and decreased to 45), the cavity length could be further reduced down to 200 nm.(5) Using metal-insulator-metal structure, a micro plasmonic sensor with all three dimensions less than 1 μm based on a circular resonator was proposed. Theoretical incestigation showed that its sensitivity was 1010 nm/RIU corresponding to a resolution of 9.9×10-5 RIU. And its sensing properties are not sensitive to changes of structure parameters, which means that technique errors in fabrication process have little influence on its sensing properties. In addition, with transmittance of 5% at the resonant wavelength, this sensor can realize wavelength-selective characteristic in a specific wide band.3. GaAs/AlGaAs nanowire lasers(1) Evanescent-wave pumped GaAs/AlGaAs core-shell nanowire laser was first demonstrated at room temperature. The GaAs core was passivated by an AlGaAs layer of 10 nm thickness to strongly enhance its optical emission efficiency. The nanowire with one-dimension geometry was employed both gain medium and Fabry-Perot cavity supporting coherent optical feedback. The nanowires were adhered on the surface of microfiber and axially excited by the evanescent wave outside the microfiber surface. When pump energy was beyond 1.5 μJ, the GaAs/AlGaAs nanowire realized single-mode lasing emission at room temperature. The lasing wavelength and linewidth were 868.6 nm and ～1.8 nm, respectively. By varying the length of the nanowire, seven different lasing wavelengths were observed in the range from 852.5 nm to 882.5 nm.(2) Enhanced spontaneous and stimulated emission from GaAs/AlGaAs nanowire via the Purcell effect were first demonstrated. By integrating the nanowire and SiO2-Au substrate, the hybridization of the dielectric modes in the nanowire with surface plasmons on the surface of Au formed hybrid plasmonic modes. Taking advantage of the nanolocalized electromagnetic field of hybrid plasmonic modes, intensities of spontaneous and stimulated emission were enhanced via the Purcell effect by factors of four and ten, respectively. And the Purcell effect made the GaAs/AlGaAs nanowire behave the full plasmonic lasing action under the pump power of 40 mW.