In this work, we present a new design of a tunable nanofocusing lens using a circular grating of linear-variant depths and nonlinear-variant widths. Constructive interference of cylindrical surface plasmon launched by the sub-wavelength metallic structure forms a sub-diffraction-limited focus, the focal length can be adjusted by varying the geometry of each groove in the circular grating. According to the numerical calculation, the range of focusing points shift is much more than other plasmonic lens, and the relative phase of emitting light scattered by surface plasmon coupling circular grating can be modulated by the nonlinear-variant width and linear-variant depth. The simulation result indicates that the different relative phase of emitting light lead to variant focal length. We firstly show a unique phenomenon for the linear-variant depths and nonlinear-variant widths of the circular grating that the positive change and negative change of the depths and widths of grooves can result in different of variation trend between relative phases and focal lengths. These results paved the road for utilizing the plasmonic lens in high-density optical storage, nanolithography, super-resolution optical microscopic imaging, optical trapping, and sensing.
2. Cao, , P. F., , X. P. Zhang, L. Cheng, and Q. Q. Meng, "Far field imaging research based on multilayer positive- and negative-refractive-index media under off-axis illumination," Progress In Electromagnetics Research, Vol. 98, 283-298, 2009.
3. Cao, , P. F., , L. Cheng, Y. E. Li, X. P. Zhang, Q. Q. Meng, and W. J. Kong, "Reflectivity and phase control research for superresolution enhancement via the thin flms mismatch," Progress In Electromagnetics Research, Vol. 107, 365-378, 2010.
4. Monti, , G., L. Tarricone, and , "Negative group velocity in a split ring resonator-coupled microstrip line," Progress In Electromagnetics Research, Vol. 94, 33-47, 2009.
5. Cao, , P., , X. Zhang, W.-J. Kong, L. Cheng, and H. Zhang, "Superresolution enhancement for the superlens with anti-re°ection and phase control coatings via surface plasmons modes of asymmetric structure," Progress In Electromagnetics Research , Vol. 119, 191-206, 2011.
6. Barnes, , W. L. and Surface plasmon, "Surface plasmon subwavelength optics," Nature, Vol. 424, 824-830, 2003.
7. Lezec, , H. J., , A. Degiron, E. Devaux, R. A. Linke, F. Martin, Moreno, L. J. Garcia-Vidal, and T. W. Ebbesen, "Beaming light from a subwavelength aperture," Science, Vol. 297, 820, 2002.
8. Luo, , Z., , T. Suyama, X. Xu, and Y. Okuno, "A grating based plasmon biosensor with high resolution," Progress In Electromagnetics Research, Vol. 118, 527-539, 2011.
9. Liu, X., J. Lin, T. F. Jiang, Z. F. Zhu, Q. Q. Zhan, J. Qian, and S. He, "Surface plasmon properties of hollow AuAg alloyed triangular nanoboxes and its applications in SERS imaging and potential drug delivery," Progress In Electromagnetics Research, Vol. 128, 35-53, 2012.
10. Ebbesen, , T. W., , H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, "Extraordinary optical transmission through sub-wavelength hole arrays," Nature, Vol. 391, 667-669, 1998.
11. Kumar, , S., , G. Sharma, and V. Singh, "Sensitivity modulation of surface plasmon resonance sensor configurations in optical fiber waveguide," Progress In Electromagnetics Research Letters, Vol. 37, 167-176, 2013.
12. Fang, , N. and X. Zhang, "Imaging properties of a metamaterial superlens," Appl. Phys. Lett., Vol. 82, 161-163, 2003.
13. Shi, , H., C. Wang, C. Du, X. Luo, X. Dong, and H. Gao, "Beam manipulating by metallic nano-slits with variant widths," Optics Express, Vol. 13, No. 18, 6815-6820, 2005.
14. Jia, , B., H. Shi, J. Li, Y. Fu, C. Du, and M. Gu, "Near-field visualization of focal depth modulation by step corrugated plasmonic slits," Appl. Phys. Lett., Vol. 94, 151912, 2009.
15. Shi, , H., C. Du, and X. Luo, "Focal length modulation based on a metallic slit surrounded with grooves in curved depths," Appl. Phys. Lett., Vol. 91, 093111, 2007.
16. Wang, , J., W. Zhou, and , "Nearfield beam shaping through tuning diffraction coupling angles," Journal of Computational and Theoretical Nanoscience, Vol. 7, No. 6, 1021-1024, 2010.
17. Fu, , Y. and X. Zhou, "Plasmonic lenses: A review," Plasmonics, Vol. 5, No. 3, 287-310, 2010.
18. Liu, , Z., , J. M. Steele, W. Srituravanich, Y. Pikus, C. Sun, and X. Zhang, "Focusing surface plasmons with a plasmonic lens," Nano Lett., Vol. 5, No. 9, 1726-1729, 2005.
19. Yin, , L., , V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett.,, Vol. 5, 1399-1402, 2005.
20. Fu, , Y. Q. and X. G. Luo, "Plasmonic microzone plate: Superfocusing at visible regime," Appl. Phys. Lett., Vol. 91, No. 6, 061124, 2007.
21. Fu, , Y., C. Du, W. Zhou, and L. E. N. Lim, "Nanopinholes-based optical superlens," Research Letters in Physics, Vol. 2008, 148505, 2008.
22. Zou, D. Q., "Beam adjustment with double subwavelength metal its surrounded by tapered dielectric gratings," Chin. Phys. Lett., Vol. 27, No. 1, 17801, 2010.
23. Zhang, M., , J. Du, H. Shi, S. Yin, L. Xia, B. Jia, M. Gu, and C. Du, "Three-dimensional nanoscale far-field focusing of radially polarized light by scattering the SPPs with an annular groove," Optics Express, Vol. 18, No. 14, 14664-14670, 2010.
24. Cheng, , L., P. Cao, Y. Li, W. Kong, X. Zhao, and X. Zhang, "High e±cient far-¯eld nanofocusing with tunable focus under radial polarization illumination," Plasmonics,, Vol. 7, No. 1, 175-184, 2012.
25. Lopez-Tejeira, F., , F. Garcia-Vidal, and L. Martin-Moreno, "Scattering of surface plasmons by one-dimensional periodic nanoindented surfaces," Phys. Rev. B,, Vol. 72, No. 16, 161405, 2005.
26. Nikitin, , A., F. Lopez-Tejeira, and L. Martin-Moreno, "Scattering of surface plasmon polaritons by one dimensional in homogeneities," Phys. Rev. B, Vol. 75, No. 3, 35129, 2007.
27. Yu, L., , D. Lin, Y. Chen, Y. Chang, K. Huang, J. Liaw, J. Yeh,J. Liu, C. Yeh, and C. Lee, "Physical origin of directional beaming emitted from a subwavelength slit," Phys. Rev. B, Vol. 71, No. 4, 41405, 2005.
28. Lockyear, , M. J., A. P. Hibbins, and J. R. Sambles, "Surfacetopography-induced enhanced transmission and directivity of microwave radiation through a subwavelength circular metal aperture," Appl. Phys. Lett., Vol. 84, 2040-2042, 2004.
29. Fu, , Y., , W. Zhou, and L. E. N. Lim, "Near-field behavior of zone-plate-like plasmonic nanostructures," JOSA A,, Vol. 25, No. 1, 238-249, 2008.
30. Fu, , Y. and W. Zhou, "Hybrid Au-Ag subwavelength metallic structures with variant periods for superfocusing," J. Nanophoton., Vol. 3, No. 1, 033504, 2009.
31. Fox, M., Optical Properties of Solids, Oxford Univerity Press, 2001.
32. Lee, , K. H., I. Ahmed, R. S. M. Goh, E. H. Khoo, E. P. Li, and T. G. G. Hung, "Implementation of the FDTD method based on Lorentz-Drude dispersive model on GPU for plasmonics applications," Progress In Electromagnetics Research, Vol. 116, 441-456, 2011.
33. Youngworth, , K. and T. Brown, "Focusing of high numerical aperture cylindrical-vector beams," Optics Express, Vol. 7, No. 2, 77-87, 2000.
34. Liu, , Y., , D. F. P. Pile, Z. Liu, D. Wu, C. Sun, and X. Zhang, "Negative group velocity of surface plasmons on thin metallic films," Proc. SPIE, Vol. 6323, 63231M, 2006.
35. Monti, , G. and L. Tarricone, "Negative group velocity in a split ring resonator-coupled microstrip line," Progress In Electromagnetics Research, Vol. 94, 33-47, 2009.