Search

Slit arrays based on noble metals have been widely proposed as planar transverse-magnetic (TM)-lenses, illuminated by a linearly polarized light with the polarization perpendicular to slits and implementing the focusing capability beyond the diffraction limit. However, due to intrinsic plasmonic losses, these TM-lenses cannot work efficiently in the ultraviolet wavelengths. In this Letter, taking advantage of the unique transmission through metallic slits not involving plasmonic losses, a metallic slit array with transverse-electric (TE)-polarized design is proposed, showing for the first time, to the best of our knowledge, the realization of sub-diffraction-limit focusing for ultraviolet light. Additionally, in contrast to the situations of TM-lenses, a wider slit leads to a greater phase delay and much larger slits can be arranged to construct the TE-lenses, which is quite beneficial for practical fabrication. Furthermore, deep-subwavelength focusing can be achieved by utilizing the immersing technology.

We present a conceptual demonstration of a metallic planar lens composed of double-turn waveguides for sub-diffraction-limit focusing. The phase delay of a single double-turn waveguide dependent on its structural parameters is investigated by employing the finite-difference time-domain (FDTD) numerical method. The design utilizes the surface plasmon polaritons (SPPs) that propagate along the metal-insulator-metal (MIM) waveguides to achieve the desired spatial phase modulation in the transmitted field. The simulated focal length achieved is in positive agreement with the design and the full-width at half-maximum (FWHM) is 0.446λ, well beyond the diffraction limit. This superfocusing performance can be maintained very well under the slight change of film thickness and slit width, showing the robustness of the design. The maximum aspect ratio of nanoslits constructing the proposed lens is 3.33, which is far less than the previous reports, alleviating the later fabrication. The metallic planar lens as demonstrated will find its applications in such fields as lithography, integrated optics, and super-resolution imaging.

Many discovery methods for geographic information services have been proposed. There are approaches for finding and matching geographic information services, methods for constructing geographic information service classification schemes, and automatic geographic information discovery. Overall, the efficiency of the geographic information discovery keeps improving., There are however, still two problems in Web Map Service (WMS) discovery that must be solved. Mismatches between the graphic contents of a WMS and the semantic descriptions in the metadata make discovery difficult for human users. End-users and computers comprehend WMSs differently creating semantic gaps in human-computer interactions. To address these problems, we propose an improved query process for WMSs based on the graphic contents of WMS layers, combining Support Vector Machine (SVM) and user relevance feedback. Our experiments demonstrate that the proposed method can improve the accuracy and efficiency of WMS discovery., Competing Interests: The authors have declared that no competing interests exist.