Surface-wave mechanism of subwavelength imaging by a flat left-handed superlens

We develop a theory describing the dynamics and interaction of electromagnetic surface waves (ESWs) resonantly excited by an external source in a slab of left-handed material (LHM) with identical negative (equal to −1) values of dielectric permittivity and magnetic permeability that makes up a so-called perfect lens, or a superlens. We show that subwavelength imaging by a superlens is associated with the degeneracy of the spectrum of eigen electromagnetic surface modes at the interfaces of the metamaterial slab, whereas the dynamic response of the superlens is completely determined by the dynamics of these modes and the dispersion properties of the metamaterial. We obtain conditions that enable one to find out when a superlens produces subwavelength images of an external source. We consider the cases of a stationary and a pulse source, as well as of a source that moves with constant velocity or oscillates in space.     

Coupling effect in a near-field object–superlens system

The coupling effect in a near-field object–superlens system has been studied, where the object is a silver cylinder and the superlens is a silver slab. A semi-analytical formulation has been established to study the system with and without the coupling effect. The analysis shows that the coupling effect significantly changes the field distributions of both the object and the image, leading to the conclusion that such a system must be designed and analyzed as a whole. Our study also suggests that it is possible to design a superlens system with mismatched permittivities.     

周期性和孤立的纳米结构的超透镜亚波长成像

超透镜光刻技术是一种很有前景的纳米结构成像技术,由于其具有可以克服衍射极限的能力,直到2005年,张翔和他的同事在365 nm紫外线波长下成功的对一排纳米线和刻在高分子膜上的四个字母NANO实现了超分辨成像,分辨率高达1/6入射波长。通过传递矩阵方法优化出超透镜结构,并通过选择适当的材料和设计在超透镜结构中的每个层的厚度以及合理的优化实验等方法制备一个新的超透镜结构,利用这种超透镜结构实现了周期性纳米结构及孤立纳米结构的亚波长成像。实验结果表明,对于周期性的纳米结构,其图像分辨率达到100 nm,而孤立结构的分辨率低于50 nm,小于入射波长的1/7。     

突破衍射极限的超级透镜技术及其应用研究

基于超材料的超级透镜能让携带物体高频信息的倏逝波分量参与成像,从而实现对小于半个工作波长的超精细结构的分辨。分析了几种典型的超透镜,如近场、远场和双曲超透镜的工作原理和研究进展,并对超透镜技术在实时生物成像、高密度光存贮、光刻等方面的应用前景进行了分析和总结。     

Disorders influences on the focusing effect of all-dielectric photonic crystal slab superlens

The influences of structure disorders on the subwavelength focusing properties of an all-dielectric photonic crystal slab superlens are theoretically studied. The structure disorders are considered as randomly perturbing the position or diameter of air holes of the photonic crystal slab. The results show that the photonic crystal slab superlens can tolerate within 10% degree of positional disorder or 15% degree of diameter disorder without destroying the focusing function.     

并矢格林函数下的球形超透镜

应用并矢量格林函数法完成了球形超透镜的数值模拟,证明了球形超镜的亚波长成像能力.并矢格林函数法是处理电磁场问题的一种系统理论和有效方法,它弥补了坐标变换法的不足.与平板透镜相比,球形超透镜有几个优点,包括有限的横截面,能成放大或者缩小的像,很高的分辨率,进行二维成像等. 关键词： 球形超透镜 并矢量格林函数法 表面模 高分辨率     

The reconstruction of finite extent objects with the superlens

The imaging of three-dimensional source objects with the Veselago–Pendry superlens has not been extensively researched. In this paper, we attempt to answer two fundamental questions. Firstly, can the superlens image an object with non-zero dimension normal to the lens surfaces—at least in principle? Secondly, if the answer is yes, would it be possible to realize such a system, and what are the conditions that it would have to satisfy? To answer these questions, we develop an image reconstruction algorithm based on a spatial Fourier decomposition of the field functions and an optimal sampling technique employing Deslauriers–Dubuc interpolation wavelets. We conclude that it is theoretically possible to image 3-D objects with the superlens, but that real-world limitations impose stringent restrictions on the system.     

银层超透镜光学传递函数的研究

银层超透镜对基于表面等离子体激元的超分辨光刻、 成像和生物传感有着重要作用.利用银层超透镜的光学传递函数详 细研究了银板的表面等离子体激元共振和成像特性, 并利用时域有限差分法计算模拟了银层超透镜的成像过程, 得到与理论推导公式相符合的结果, 证明了光学传递函数的可靠性, 为基于表面等离子体激元的传感器件、 超分辨成像以及辅助增强干涉光刻提供了快速参数优化方法.     

A new near-field phase-correction method for superlens

A new phase-correction method in a realistic loss superlens imaging system is theoretically predicted.The image resolution is enhanced using the near-field active phase-correction method.Resolvable separation between two slits has been significantly improved toλ/20 for the symmetrical superlens system andλ/12 for unsymmetrical system.     

Study on the imaging characteristics of far-field superlens

The optical transfer function of the far-field superlens imaging system is established in this thesis to make it easy to describe the corresponding relation between the far-field angular spectrum and the near-field object superresolution information. We utilized the established optical transfer function to make detailed research on the imaging characteristics of the far-field superresolution, also reconstruct the near-field nano-information through the far-field angular spectrum, which proves that the resolution of the far-field superlens with structure coupled with metal grating can reach 50 nm, and provides a helpful reference for the study of the new optical microscope imaging of superresolution.     

Cloaking an acoustic sensor with single-negative materials

In this review, a brief introduction is given to the development of acoustic superlens cloaks that allow the cloaked object to receive signals while its presence is not sensed by the surrounding, which can be regarded as “cloaking an acoustic sensor”. Remarkably, the designed cloak consists of single-negative materials with parameters independent of the background medium or the sensor system, which is proven to be a magnifying superlens. This has facilitated significantly the design and fabrication of acoustic cloaks that generally require double-negative materials with customized parameters. Such innovative design has then been simplified further as a multi-layered structure comprising of two alternately arranged complementary media with homogeneous isotropic single-negative materials. Based on this, a scattering analyses method is developed for the numerical simulation of such multi-layered cloak structures, which may serve as an efficient approach for the investigation on such devices.     

Novel optical lithography using silver superlens

This work has demonstrated that with silver superlens,the resolution of conventional optical lithography can be improved significantly.Experimental and simulative results are given to verify the facts that the resolution and the pattern fidelity are sensitive to the contact tightness between layers.     

Dynamic study and applications of metamaterial systems

We investigate the dynamic characteristics of metamaterial systems, such as the temporal coherence gain of the superlens, the causality limitation on the ideal cloaking systems, the relaxation process and essential elements in the dispersive cloaking systems, and the extending of the working frequency range of cloaking systems. The key point of our study is the physical dispersive properties of metamaterials, which are well-known to be intrinsically strongly dispersive. With physical dispersion, new physical pictures can be obtained for the waves propagating inside metamaterial, such as the “group retarded time” for waves inside the superlens and cloak, the causality limitation on real metamaterial systems, and the essential elements for design optimization. Therefore, we believe the dynamic study of metamaterials will be an important direction for further research. All theoretical derivations and conclusions are demonstrated by powerful finite-difference time-domain simulations.     

Loss and back-coupling effects on subwavelength imaging of three-dimensional superlens

The loss and back-coupling effects on the subwavelength imaging of three-dimensional superlens are reported in this paper. The loss is added in the image region of a superlens. The back-coupling effects are considered by adding a shielded layer above the object region. (1) By adding loss in the image region, the long range plasmon mode is drastically suppressed. (2) The back-coupling shield above the objects has the effects of amplifying the higher spatial frequency components while suppressing the long range plasmon mode. Because of (1) and (2), the transfer function becomes flatter. Subsequently, the finer resolution of images is obtained. This is confirmed by the field and intensity distribution generated by the horizontal magnetic dipoles and vertical electric dipoles located in the object region and the image intensity distributions of the patterned mask structures in the lithography.     

Image quality deterioration due to phase fluctuation in layered superlens

Optical transfer function (OTF) and image spectrums of the layered metal (M)-dielectric (D) superlenses (MD)n (where n is the number of cycles) are analyzed via transfer matrix method and effective-medium model. It is shown that the magnitude of OTF (MTF) with a high cutoff wave vector does not guarantee high resolution; the fluctuation of phase of OTF (PTF) is also a prime factor causing superlens imaging distortion. When the layered metal-dielectric superlenses have a small number of cycles, we find that the different types of superlenses (such as (MD)nM, (MD)n, and (DM)nD) with the same effective permittivity have totally different performances; the superlens with (DM)nD arrangement has the best performance; this will be valuable for designing layered metal-dielectric superlenses with less cycles.     

Far-field superlens for nanolithography

A far-field optical lithography is developed in this paper. By designing the structure of a far-field optical superlens, lithographical resolution can be improved by using a conventional UV light source. The finite different time domain numerical studies indicate that the lithographic resolution at 50~nm line width is achievable with the structure shown in this paper by using 365~nm wavelength light, and the light can be transferred to a far distance in the photoresist.     

十二重准晶光子结构中的负折射与成像

最近实验证明周期性的光子晶体中存在电磁波的负折射现象，并且观测到亚波长成像．然而，这些研究主要集中在剧期性结构中，对非周期结构的研究还没有相关的报道。文章报道了一种新的理论和实验结果：非周期性十二重准晶光子结构同样存在负折射，并且可以实现超透镜的远场成像。具有这些特性的光子准晶可以广泛的应用于光集成器件中。     

Overcoming the diffraction limit using multiple light scattering in a highly disordered medium

We report that disordered media made of randomly distributed nanoparticles can be used to overcome the diffraction limit of a conventional imaging system. By developing a method to extract the original image information from the multiple scattering induced by the turbid media, we dramatically increase a numerical aperture of the imaging system. As a result, the resolution is enhanced by more than 5 times over the diffraction limit, and the field of view is extended over the physical area of the camera. Our technique lays the foundation to use a turbid medium as a far-field superlens.     

Sub-diffraction-limited far-field imaging in infrared

We investigated a far-field superlens operating at mid-infrared wavelength that allows resolving subwavelength features in the far-field. By utilizing evanescent enhancement provided by surface plasmon excitation of silver nanorods and Moiré effect, we numerically demonstrated that subwavelength information of an object can be converted to propagating information. This information can then be captured by conventional optical components. A simple image reconstruction algorithm can restore the subwavelength object. A sub-diffraction-limited resolution of 2.5 μm at 6-μm wavelength is demonstrated.     

Near-Field Optical Transfer Function for Far-Field Super-Resolution Imaging

The far-field superlens based on surface plasmon polaritons （SPP） has shown great application potential, but it is difficult and time-consuming to reconstruct the far-field image. We derive a near-field optical transfer function （NOTF） of a silver slab and analyse its validity so that accurate information of nano-seale object in the near-field can be computed rapidly. The NOTF is helpful not only for analysing the super-resolution imaging process in far-field, but also for providing a track to describe the transmission of optical information from near-field to far-field by using the optical transfer functions theorv only.