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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 (-and +), 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 /12. For comparison, a similar simulation without the S-ML is performed, indicating a resolution of 1.5. 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.
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Keywords:
- far-field /
- super-resolution imaging /
- wideband /
- stereo-metalens
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[25] Gruber F K, Marengo E A, Devaney A J 2004 J. Acoust. Soc. Am. 115 3042
[26] Fink M 1992 IEEE Trans. Ultrason. Ferroeletr. Freq. Control 39 555
[27] Lerosey G, de Rosny J, Tourin A, Derode A, Montaldo G, Fink M 2004 Phys. Rev. Lett. 92 193904
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[1] Merlin R 2007 Science 317 927
[2] Grbic A, Jiang L, Merlin R 2008 Science 320 511
[3] Grbic A, Merlin R 2008 IEEE Trans. Antennas Propag. 56 3159
[4] Zhu S X 2000 Opt. Instrum. 22 34 (in Chinese) [祝生祥 2000 光学仪器 22 34]
[5] Pohl D W, Denk W, Lanz M 1984 Appl. Phys. Lett. 44 651
[6] Pendry J B 2000 Phys. Rev. Lett. 85 3966
[7] Pendry J B, Ramakrishna S A 2003 J. Phys.: Condens. Matter 15 6345
[8] Nicholas F, Lee H, Sun C, Zhang X 2005 Science 308 534
[9] Yang C, Zhang H X, Wang H X, Xu N, Xu Y Y, Huang L Y, Zhang K X 2012 Acta Phys. Sin. 61 164101 (in Chinese) [杨晨, 张洪欣, 王海侠, 徐楠, 许媛媛, 黄丽玉, 张可欣 2012 61 164101]
[10] Liu Z W, Durant S, Lee H, Pikus Y, Fang N, Xiong Y, Sun C, Zhang X 2007 Nano Lett. 7 403
[11] Liu Z W, Lee H, Xiong Y 2007 Science 315 1686
[12] L C, Li W, Jiang X Y, Cao J C 2014 Europhys. Lett. 105 28003
[13] Lemoult F, Lerosey G, de Rosny J, Fink M 2010 Phys. Rev. Lett. 104 203901
[14] Lemoult F, Fink M, Lerosey G 2011 Waves Random and Complex Media 21 614
[15] Ourir A, Lerosey G, Lemoult F, Fink M, de Rosny J 2012 Appl. Phys. Lett. 101 111102
[16] Jouvaud C, Ourir A, de Rosny J 2014 Appl. Phys. Lett. 104 243507
[17] Wang R, Wang B Z, Gong Z S, Ding X 2015 Sci. Rep. 5 11131
[18] Gao Q, Wang B Z, Wang X H 2015 IEEE Trans. Antennas Propag. 63 5586
[19] Zheng B, Zhang R R, Zhou M, Zhang W B, Lin S S, Ni Z H, Wang H P, Yu F X, Chen H S 2014 Appl. Phys. Lett. 104 073502
[20] Liu N, Liu H, Zhu S, Giessen H 2009 Nat. Photon. 3 157
[21] Prodan E, Radloff C, Halas N J, Nordlander P 2003 Science 302 419
[22] Wang H, Brandl D W, Le F, Nordlander P, Halas N J 2006 Nano Lett. 6 827
[23] Nordlander P, Oubre C, Prodan E, Li K, Stockman M I 2004 Nano Lett. 4 899
[24] Cheney M 2001 Inverse Prob. 17 591
[25] Gruber F K, Marengo E A, Devaney A J 2004 J. Acoust. Soc. Am. 115 3042
[26] Fink M 1992 IEEE Trans. Ultrason. Ferroeletr. Freq. Control 39 555
[27] Lerosey G, de Rosny J, Tourin A, Derode A, Montaldo G, Fink M 2004 Phys. Rev. Lett. 92 193904
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