Research On The Novel Devices Based On Metal-dielectric Thin Film

Metal thin film is a very important part of optical thin films. It possesses the properties of high reflectivity, low polarized effect, good electric conductivity, and can exite surface plasmon wave. It has a wide application in broad-band reflectors, beam splitters, absorbers, sensors and blocking electromagnetic wave devices. In this dissertation, the work is focused on the novel devices based on the metal thin film which is fabricated by coating technology, including the numerical computational methods and the fabrication of the metal-dielectric thin film devices, such as, one-dimensional (1D) omnidirectional passband filter, negative refraction and complete band gap in 1D metal-dielectric periodic structure, and the subwavelength imaging with a planar metallic lens. The main contents in this paper are as follows:1. Design a novel metal-dielectric Fabry-Perot (F-P) filter that can exhibit an omnidirectional transmission for TM-polarized light. The omnidirectional pass band occurs when the sum of the reflection phase shift at the metal-spacer interface and the propagation shift in the spacer region is almost 2Ï€for every incidence angle. We numerically and experimentally demonstrate such an omnidirectional narrow bandpass filter in an Air/Ag/ZnS/Ag/Glass structure. Moreover, we introduce an anti-reflection coating in both sides of the metal-dielectric F-P structure to increase the transmittance. According to the low angle effect of high index dielectric layer and metallic layer, a filter which almost maintains filter characteristics when used in the case of oblique incidence or large cone angle incidence is proposed. And we prove the low angle dependence effect of the novel filter by theory and experiment. Study on the projected band diagram of a 1D metal-dielectric periodic structure, find it can possess an omnidirectional band for a TM-polarized light, owing to the compensation effect of power flow in the parallel direction in the metal. An experiment has been done to verify the design by using an Ag/Zns stack. Such an omnidirectional pass band can be realized in different wavelength region with proper design.2. Near -1 effective index is achieved using 1D metal-dielectric periodic structure with a proper choice of parameters. Considering realistic material parameters, we present a study of the complex band structure and show that the absorption losses in metallic layers not only decrease the transmittance, but also change the negative refraction angle in the metamaterial (and thus its effective optical index). Then, another 1D metal-dielectric periodic structure which is less sensitive to the losses is proposed. The negative refraction of TM mode and positive refraction of TE mode make the 1DMD structure to be a novel polarization beam splitter. The transfer matrix method (TMM) is used to simulate as the Gaussian beam incident in the finite one-dimensional metal-dielectric structure for both polarizations. The influence of different incident angles and the dissipation of the metal layer on the beam splitter is discussed.3. It is widely believed that a 1D periodic layered structure with ordinary materials can only have a band gap for certain propagation directions. However, we reveal that a 1D metal-dielectric periodic structure can trap transverse magnetic waves for any angle of propagation in a plane, owing to the existence of a two-dimensional (2D) complete band gap. The complete gap comes from Bragg scattering together with the cut-off effect of the metal-dielectric-metal waveguide. A criteria for the geometric and material parameters to realize a 2D complete gap is introduced and the complete band-gap effect with real structures is illustrated using finite difference time domain (FDTD) method.4. Research on the near-field subwavelength imaging with a planar silver lens. The metallic thin film structure is modeled by a Drude model in FDTD method. In practice a Cr grating mask with 1μm period is imaged onto a photosensitive material through a silver thin film structure by utilizing optical near-field lithography techniques. Analyze the self-collimation phenomena in 1D metal-dielectric periodic structure from the equal frequency surface, and find that a silver/HfO₂ stack with suitable parameters can have aλ/5 resolution at a visible wavelength.