Research On Propagation Properties Of Surface Plasmons In Metallic Artificial Structures And Its Applications

Surface plasmon is a coupled electromagnetic mode formed by the interaction between light and the surface free electrons of metal. Surface plasmons have unique physical properties such as surface propagation and near-field localization. They can confine light energy in a small scale far beyond the diffraction limit. Based on the propagation properties of surface plasmons in the artificial metallic structures, a wide range of applications can be explored. Under the background of surface plasmon subwavelength optics, theoretical designs and numerical simulations are carried out in the following three aspects.Firstly, researches on enhancing the optical coupling of quantum well infrared photodetectors by using metallic compound structures are carried out. We design metallic compound structures that consist of an overlaying gold film and periodic gold stripes or gold disk arrays on the top of a quantum well photodetector with a thick active region which operates at 4.3μm. Numerical simulations show that surface plasmon resonance can occur at the operating wavelength of the quantum well photodetector if the structural parameters of the metallic compound structures are optimized. Electric field component parallel to the growth direction of quantum wells can be enhanced so that the intersubband transition can be realized and optical coupling efficiency of quantum well photodetector can be improved. Compared with one-dimensional periodic structures, two-dimensional periodic structures can achieve higher coupling efficiency and the coupling is insensitive to the polarization of the incident light. Additionally, we show that the optical coupling can also be enhanced based on the air-dielectric-metal waveguide resonance when the substrate is removed. When this kind of coupling method is adopted, the thickness of top contact doesn’t need to be reduced and the active region doesn’t need to be placed right below the metallic grating, which can overcome the difficulty in the fabrication of device that is brought by the near-field effect of surface plasmons.Secondly, silver-air-silver waveguide is used to split light of different wavelengths. We design a splitter consisting of an input and two output channels for the two wavelengths 1310 nm and 1550 nm in the optical commucations. By adopting side-coupled cavities to the output channels, light of one wavelength is forbidden to propagate and light of another wavelength can pass with a high transmittance. The forbidden wavelength is only determined by the size of the cavity that is connected to the output channel. When T-shaped cavity is used, the transmittance at the passing wavelength can approach 90%. Compared with those previously reported spliiters with periodic metallic gratings, the splitter we design is smaller in size and low in energy loss.Finally, metallic artificial structure is designed to achieve the directional beaming of light from broad angle incidence. In order to avoid the great decay of transmitted beam energy after light at a large incident angle passes through the structured metal, light is incident from the back-side of a GaAs substrate. The high refractive index of the substrate decreases the incident angle. A gold thin film with a slit is deposited on the substrate. Finite numbers of grooves are arranged on the both sides of the exit. Enhanced optical transmission can occur at the desired working wavelength 1.55μm by optimizing the width of the slit and the depth of gold film. The wave vector of surface plasmon polariton and reciprocal lattice vector can match when the structural parameters of the grooves are carefully chosen. Then the surface plasmon can be deactivated into photon and the energy of the transmitted beam can be focused in the collimated direction. The energy doesn’t decay much at large incident angle and the directional beaming of light from broad angle incidence can be achieved.The results obtained in the above three aspects of work can provide theoretical basis for the successive design and fabrication of the related devices.