基于宽带立体超透镜的远场超分辨率成像

为突破传统衍射极限实现远场超分辨率成像,提出了一种微波频段宽带立体超透镜用于目标远场超分辨率成像.该透镜可将携带着目标超分辨率信息的凋落波分量转换为传播波分量辐射到远场,进而可在远场接收这些信息并用于超分辨率成像.分别从频域和时域两方面对该透镜的超分辨率特性进行验证.在频域,利用多重信号分类算法对借助于该结构的扩展目标实现了λ/12的远场超分辨率成像,大幅度提升了成像效果.在时域,结合时间反演技术,验证了带宽提升对空间超分辨率聚焦特性带来的明显优势.

Far-field super-resolution imaging based on wideband stereo-metalens

The resolution of traditional far-field imaging system is generally restricted by half of wavelength of incident light due to the diffraction limit. The reason is that evanescent waves carrying subwavelength information cannot propagate in the far-field and make no contribution to the imaging. To realize the far-field super-resolution imaging, the imaging system should be able to collect both propagation and evanescent waves. Many ideas were presented to provide feasible alternatives but with narrow frequency band. In this paper, a wideband metalens is proposed to realize far-field super-resolution based on stereometamaterials. A typical model of stereometamaterials is studied, which consist of a stack of two identical spiral resonators in each cell, with various twist angles. For each case, there are two observable resonances (ω-and ω +), obviously. The phenomenon can be explained as the plasmon hybridization between the two resonators due to their close proximity. The case with a twist angle of 90° is chosen as the basic cell to constitute the stereo-metalens (S-ML). The last S-ML can work in a frequency range from 1.06 to 1.53 GHz, which is much wider than the planar-metalens. Simulations of near-and far-field spectra are conducted to validate the conversion between evanescent waves and propagation waves. Then with the help of antennas in the far-field to receive the information, sub-wavelength image can be reconstructed. The simulations in frequency-and time-domain are performed to verify the super-resolution characteristics of the S-ML. In frequency-domain, an imaging simulation of L-shaped extended target is combined with multiple signal classification imaging method. The resolution defined by full width at half maximum is 19 mm, corresponding to λ/12. For comparison, a similar simulation without the S-ML is performed, indicating a resolution of 1.5λ. It shows the ability of the S-ML to enhance the imaging resolution. In time-domain, by using time reversal technique, the spatial super-resolution characteristic of the S-ML is validated. Compared with the planar-metalens, the S-ML has good spatial super-resolution characteristic. All results show that the S-ML has a good potential application in imaging.