Subwavelength Imaging With Layered Metamaterials

The amplification of a broad spectrum of evanescent waves (produced by e.g. a point source) by a single layer of noble metal can lead to a subwavelength resolution. Thus a practical multilayered structure named as a superlens is suggested to improve the subwavelength image in the near-field zone. In the past few years, subwavelength imaging has become a new widely researched field due to many important potential applications. In this thesis, we study not only the near-field subwavelength focusing with multilayered structure, but also the far-field amplification of the subwavelength object with cylindrical multilayered structure.In Chapter 2, a device with a simple configuration, a dielectric layer and a silver layer with certain thicknesses are sandwiched between the photomask and the film of photoresis, is proposed to enhance the resolution of conventional optical lithography significantly and several contrast experiments are also carried out. Those experiments confirm the imaging capability of silver layer.In Chapter 3, The Fabry-Perot resonance effect is studied in order to achieve subwavelength imaging at a far distance from the source at optical frequencies. Two different structures (with matched and mismatched impedances) of alternative metal and dielectric layers are considered in lossless cases first at a relatively short distance (e.g., about one wavelength) from the source. It is found that the impedance match is not necessary for subwavelength focusing since the Fabry-Perot resonance effect is utilized here. An appropriate period is chosen so that the Fabry-Perot resonance occurs in an evanescent regime, and consequently the evanescent waves near the Fabry-Perot resonance peak are amplified. With such a mechanism, a structure with a good resolution, acceptable sidelobes and a larger displacement range (when the thickness of the period is within such a displacement range, subwavelength focusing with acceptable sidelobes can be achieved) is designed.In Chapter 4, appropriate surface termination is used to improve dramatically the subwavelength imaging resolution of a multilayered positive-negative permittivity structure operating in the infrared or optical frequencies. The imaging resolution of the improved multilayered structure resists practical material loss well, and it is not sensible to the thickness of the interface layers, the total thickness and the period of the multilayered structure. Based on the improved multilayered structures, an optimized structure (i.e., the effective impedance is chosen between 0 and 1) is designed to obtain a higher resolution.In Chapter 5, layered structures are proposed by using two special materials to achieve some tunable properties. Composite metal-dielectric layer with an appropriate metal filling factor instead of negative permittivity layer is utilized first to help to operate at practically any desired wavelength and achieve good resolution as appropriate surface termination is also utilized. A three-level ladder-type atomic (or molecular) EIT system is utilized to realize negative permeability at microwave frequency. Such permeability can be controllably manipulated by external coupling fields and used as the negative permeability material to construct certain layered structures to achieve subwavelength image(similarly, EIT system can also realize negative permittivity and can be used in layered structure).A far-field hyperlens with cylindrical layered structure is studied in Chapter 6. It is found that structure with finite but long dispersion curve can be utilized for far-field imaging beyond the diffraction limit. Appropriate parameters are chosen for the hyperlens to achieve good performance.