Design Of Micro/Nano Photonic Devices Based On Surface Plasmon Polaritons (SPPs)

Surface Plasmon Polaritons (SPPs) are electromagnetic surface waves propagating at the interfaces of metals and dielectrics, excitation of which is attributed to high density of free electrons in metals. The free electrons in metals oscillate collectively with the electric field forces of incident light. The SPPs exhibit high near-field concentration, sub-wavelength mode confinement and high sensitivity to dielectric environment. SPPs are fascinating in nano-photonic devices because of their specialty quite different from custom photonic modes. In this work, we combined SPPs with different solar cell structures and nonlinear waveguides, and investigated the mechanisms and performances of new devices.The main work and conclusions of this paper are:1. We exhibited the numerical methods and key steps of the Finite Element Methods (FEM), and investigated the solving of harmonic propagation of electromagnetic waves and eigenmodes of waveguides with FEM. These are the bases of the following numerical designing work.2. Using VO2/Ag and ZnO/VO2/ZnS multilayer films as smart windows, simultaneous enhancements of both the luminous transmittance and modulation of solar transmittance were achieved via structural design. The extinction ratio of VO2films as optical switches was enhanced from50:1to550:1with an embedded metallic grating.3. We introduced a metallic nanograting structure at the bottom of a-Si/μc-Si thin-film tandem solar cells, and carried out an investigation into the light absorption in the top and bottom cells via electromagnetic simulation. Tuning effects of structural parameters are investigated. Three mechanisms, the Fabry-Perot resonance, planar waveguide mode and surface plasmon resonance, are involved in different wavelength regions. It indicated that broadband and polarization-insensitive light absorption enhancement was obtained in the bottom cell while the light absorption in the top cell remained unchanged by the influence of this metallic nanograting. It caused that total carrier generation enhancement can be achieved as much as60%for both polarization.4. A metallic hole-array structure was inserted into a tandem solar cell structure as an intermediate electrode, which allows a further fabrication of a novel tandem solar cell. The hole-array layer reflects the higher-energy photons back to the top cell, and transmits lower-energy photons to the bottom cell via the extraordinary optical transmission (EOT) effect. In this case light absorption in both top and bottom cells can be simultaneously enhanced. Importantly, this new design could remove the constraints of lattice-matching and current-matching between the commonly used two cascaded cells in a tandem structure, and therefore, the tunnel junction will be no longer required. A PCBM/CIGS tandem cell was designed and investigated as an example of different material combinations. A systematic study was made on the structural tuning effects, with period values from hundreds nanometers to micrometers. Surface plasmon polaritons, magnetic plasmon polaritons, localized surface plasmons, and waveguide modes participate in the EOT and absorption enhancement. More than40%integrated power enhancement can be achieved in a broad structural parameter range.5. A novel scheme of surface plasmon amplifier in3D hybrid waveguide structure was proposed. The plasmon amplifier was based on a nonlinear difference-frequency process between the hybrid plasmonic mode and the low-loss photonic waveguide mode in a periodically poled LiNbO3(PPLN) waveguide. Threshold and efficiency of the nonlinear amplifying process and the propagating properties of the hybrid waveguide were analyzed. The propagation length of the hybrid plasmonic waveguide at1550nm wavelength was enhanced to the millimeter order, while the compact plasmonic mode confinement was preserved.Highlights of our work are as following:1. Using multilayered films, simultaneous enhancements of both the luminous transmittance and modulation of solar transmittance were achieved via structural design. The extinction ratio of VO2films as optical switches was enhanced from50:1to550:1with an embedded metallic grating.2. A metallic nanograting structure was introduced at the bottom of a-Si/μc-Si thin-film tandem solar cells. It indicated that broadband and polarization-insensitive light absorption enhancement was obtained in the bottom cell, and the total carrier generation enhancement can be achieved as much as60%for both polarizations.3. A metallic hole-array structure was inserted into a tandem solar cell structure as an intermediate electrode, which allows a further fabrication of a novel tandem solar cell. In this case light absorption in both top and bottom cells can be simultaneously enhanced via structural and material optimizations. Importantly, this new design could remove the constraints of lattice-matching and current-matching between the commonly used two cascaded cells in a tandem structure, and therefore, the tunnel junction will be no longer required. More than40%integrated power enhancement can be achieved in a broad structural parameter range in PCBM/CIGS tandem solar cells, and the structure can be flexibly applied to different combinations of photovoltaic materials.4. A novel scheme of surface plasmon amplifier in3D hybrid waveguide structure was proposed. The plasmon amplifier was based on a nonlinear difference-frequency process between the hybrid plasmonic mode and the low-loss photonic waveguide mode in a periodically poled LiNbO3(PPLN) waveguide. The propagation length of the hybrid plasmonic waveguide at1550nm wavelength was enhanced to the millimeter order, while the compact plasmonic mode confinement was preserved.