| Metamaterials are artificial composite materials constructed from subwavelength building blocks that are densely packed into an effective material. They exhibit many dramatic optical properties which are not observed in natural materials, such as negative refractive index. Due to their unusual physical properties, metamaterials also show various interesting potential applications, such as subdiffraction imaging and invisibility cloaks etc.. In this dissertation, based on a robust holographic lithography and the relationship between the magnetic response wavelength of the metal plate pairs and their sizes, we design and fabricate a tunable magnetic metamaterial and an optical magnetic metamaterial working at multiple frequencies simultaneously. In addition, to achieve negative refractive index, we also design and fabricate a low-loss X-shaped hole metamaterial by using holographic lithography and electron-beam evaporation and lift-off. The work of this dissertation is divided in to the following parts:1. A tunable magnetic metamaterialThe electromagnetic properties of metamaterials are very closely related to the size of their cell structures. In the near infrared region, the LC circuit model of elliptical plate pairs reveals that the magnetic response wavelength can be adjusted by the length of axis of elliptical plate pairs, the thickness and permittivity of the dielectric in the middle layer. However, the magnetic response wavelength is limited toward a short wavelength by modulating the parameters of the dielectric, and the strength of the magnetic response becomes weak as increasing the thickness of the dielectric layer. Owing to the linear relationship between the length of axis of elliptical plate pairs and the magnetic response wavelength, the response wavelength can be simply and effectively adjusted. Experimentally, the magnetic response wavelength adjusted in a range of from 1260 nm to 2100 nm is achieved by varying the length of axis of the elliptical plate pairs. In addition, the measurements show that, by rotating the polarization direction between the major and minor axes of elliptical plate pairs, two fixed magnetic responses are observed, and the wavelengths of them are closely related to the lengths of the major and minor axes, respectively. 2. A magnetic metamaterial working at multiple frequencies simultaneouslyIn our experiment, due to the deposition and lift-off processes, the samples exhibit a sidewall angle approximately 20 degree. By alternately depositing metal and dielectric layers on a template with elliptical hole arrays and then lift-off, a multilayer elliptical plates structure is obtained with a size variation of the functional layers. Measurements and simulations reveal that the metamaterial exhibits multiple resonance peaks in the near infrared region. Due to the large sidewall angle, each functional layer with different size is relatively independent, and produces magnetic response at different wavelength. Furthermore, the retrieved effective permeability also confirms that the metamaterial exhibits multiple magnetic responses, and the effective permeability is even negative at short response wavelengths. In addition, the impact of sidewall angle on the magnetic response is also studied. The results show that as the sidewall angle becomes smaller, the interaction between the functional layers becomes stronger and the magnetic responses are produced by the collective effect of multiple functional layers.3. A low-loss X-shaped hole metamaterial with negative refractive indexBased on a robust holographic lithography, an X-shaped hole metamaterial is designed and fabricated. In the experiment, to achieve a low-loss metamaterial, a preferable proportion between the width of metal wires and the size of plate pairs is realized by controlling the exposure dose. Measurements and simulations reveal that the X-shaped hole metamaterial exhibits a strong electromagnetic response at 2000 nm. The retrieved electromagnetic parameters show that the X-shaped hole metamaterial exhibits a negative refractive index in a large range of from 1860 nm to 2220 nm. The figure of merit (FOM) is larger than 1 in the range of from 1860 nm to 2120 nm where the electric permittivity and the magnetic permeability are negative simultaneously. And the FOM reaches the maximum about 2.74 with the transmittance of 62% at 2040 nm. |
