Chunlei Du

A polarization bifocal lens based on the polarization effect caused by asymmetrical hole arrays had been designed, fabricated, and characterized experimentally. By considering the fact that the skin depth of an infrared electromagnetic field inside metal is much shorter than the incident wavelength, a polarization bifocal lens composed of high deep-width ratio metallic holes was realized by using a gold-coated silicon structure to replace the one directly formed on a thick metal film. An infrared optical experiment setup is built based on the secondary imagery method for characterizing the focal length of the designed bifocal lens. The measured focal lengths of the fabricated bifocal lens coincide well with the designed values, which proves the validity for realizing the polarization elements with the proposed structure and the feasibility of the fabrication process.

A general conformal transformation method (CTM) is proposed to construct the conformal mapping between two irregular geometries. In order to find the material parameters corresponding to the conformal transformation between two irregular geometries, two polygons are utilized to approximate the two irregular geometries, and an intermediate geometry is used to connect the mapping relations between the two polygons. Based on these manipulations, the approximate material parameters for TE and TM waves are finally obtained by calculating the Schwarz-Christoffel (SC) mappings. To demonstrate the validity of the method, a phase modulator and a plane focal surface Luneburg lens are designed and simulated by the finite element method. The results show that the conformal transformation can be expanded to the cases that the transformed objects are with irregular geometries.

In this letter, a surface wave antenna based on the excitation of spoof surface plasmon mode at microwave frequency is proposed and demonstrated experimentally to effectively modulate the far field radiation, by integrating with one‐dimensional subwavelength periodic corrugated grooves. Compared with the traditional surface wave antenna, the far field divergence of this spoof surface plasmon antenna exhibits a remarkable red shift. The numerical simulation and experimental data well accord with the predicted results given by grating scattering theory. Consequently, the surface wave antenna can be achieved with unique function and minimized in size by introducing spoof surface plasmon. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2179–2183, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25462

A type of metamaterial composing of stacked cut-wire plasmonic structures has been designed, fabricated, and characterized. The excitation of electric resonance caused by the surface plasmons effect dominates the electric field states, so that the effective refractive index can behave as a dramatic increase at visible frequencies, which is intimately associated with the resonance strength and can be modulated by reasonably changing the structure geometries. The phenomenon has been demonstrated with the measured transmittances being in agreement with simulation results. And the effective parameters judged by Kramers–Kronig relations have been uniquely retrieved from the simulated transmission and reflection data.

The effective plasma frequency f_p of periodic metallic wires whose characteristic dimensions are comparable to their skin depth has been analyzed. And a relevant analytic model is constructed by considering the skin effect and making a reasonable shape approximation, which is suitable for the case that the cross section of the wire is noncircular. To verify this model, a wires array with rectangle cross section is designed and the corresponding stacked Au-SiO₂ nanostrips are fabricated. The experimental and simulational transmittances of the metamaterial have been evaluated with a good agreement, although the presence of quartz substrate and structural imperfections in experiment will have an impact, which validates that the multilayer Au-SiO₂ nanostrips could function similarly to a natural bulk metal with discrepancies of f_p values less than 8%. It could be confirmed that the theoretic formula is trustworthy in predicting f_p for designing and realizing a controllable artificial metal in optical region.

Three-dimensional (3D) nanoscale focusing of radially polarized light in far field by a simple plasmonic lens composed of an annular slit and a single concentric groove is reported. The numerical calculations reveal that the incident light is coupled to surface plasmon polaritons (SPP) by the annular slit and a focal spot with a size less than a half of the illumination wavelength is formed in the far field due to the constructive interference of the scattered light by the groove. More importantly, the focal length can be modulated by changing the groove diameter. This structure provides an admirable choice for the nano-optical devices.