Using an ultracompact groove-slit-groove (GSG) structure, a refractive index sensor with a broadband response is proposed and experimentally demonstrated. Due to the interference of surface plasmon polaritons (SPPs), the transmission spectra in the GSG structure exhibit oscillation behaviors in a broad bandwidth, and they are quite sensitive to the refractive index of the surroundings. Based on the principle, the characteristics of its refractive index sensing are demonstrated experimentally. In the experiment, the structure is illuminated with a bulk light source (not a tightly focused light source) from the back side. This decreases the difficulty of the experimental measurement and can protect strong light sources from damaging the detection samples. Meanwhile, the whole structure of the sensor can be made more ultracompact without considering the influence of the incident waves.
The intensity distribution of light scattered by a capillary tube filled with a liquid is studied using geometrical optics or ray tracing. Several intensity step points are found in the scattering pattern due to contributions from different geometrical rays. The scattering angles of these intensity step points vary with the capillary parameters, i.e., with the inner and outer radii of the capillary wall and the refractive indices of the liquid and the wall material. The relations between the scattering angles of the step points and the capillary parameters are analyzed using the reflection law and Snell's law. A method is developed to determine the capillary parameters from measurements of the scattering angles of the step points. An experiment is designed to provide measured data from which the capillary parameters can be obtained by the proposed method. It is shown that this method provides capillary parameters of high precision. (c) 2012 Optical Society of America
Based on the strongly coupled-resonator effects, a high wavelength-resolution plasmonic Y-splitter, consisting of a Y-branch metal-insulator-metal waveguide with a baffle in each channel, is numerically investigated using the finite element method. Due to the coupling of different resonators (with nearly equal bandwidths) in the Y-splitter, sharp and asymmetric transmission spectra occur. This greatly increases the wavelength resolution of the Y-splitter to be Delta lambda a parts per thousand aEuro parts per thousand 15 nm, which is significantly narrower than the bandwidth of the single resonator (Delta lambda (FWHM) a parts per thousand aEuro parts per thousand 110 nm). An analytic model based on the scattering matrix theory is provided to describe and explain this phenomenon.
A metal-insulator-metal vertical nanocavity is proposed to be integrated at the center of a plasmonic lens. Utilizing cavity resonance effect, the light intensity at the center of the integrated plasmonic lens gets enhancement up to 5500 times compared to that without the cavity, and the light field is tightly confined into a spot as small as 6.0 x 10(-3)lambda(2)(0). The Purcell factor of the cavity reaches up to 1400, ensuring greatly enhanced light-matter interaction inside the cavity. Moreover, the proposed structure takes advantage of linearly polarized light excitation and easy fabrication. (C) 2012 Optical Society of America
Highly efficient plasmonic nanofocusing is proposed and demonstrated in a T-shape micro-slit surrounded by multi-slits. The nanofocusing phenomenon is achieved based on the multimode interference in the micro-slit, the constructive interference in the T-shape slit, and also the multiple-beam interference of the light radiated from the multi-slits and the transmitted light from the T-shape micro-slit. Because of the large illumination areas of the incident light on the wide slit aperture in the proposed structure, a large amount of light can pass through the wide slit. This leads to a highly efficient nanofocusing. Meanwhile, the wide slit means easy fabrication. In the experiment, the focusing phenomenon in the proposed structure was successfully demonstrated with a scanning near-field optical microscopy (SNOM) technology. (C) 2012 Optical Society of America
By utilizing a dielectric-film-coated asymmetric T-shape single slit, comprising two grooves of slightly detuned widths immediately contacting with a single nanoslit, the plasmon-induced transparency was experimentally demonstrated. Because of the symmetry breaking in the unit-cell structure, the scattered lights from the two grooves with slightly detuned widths interfere destructively, leading to the plasmon-induced transparency. As a result, a response spectrum with nearly the same interference contrast but a much narrower bandwidth emerges in the unit-cell structure with the footprint of only about 0.9 mu m(2), compared with that in the symmetric T-shape single slit. These pronounced features in the structure, such as the increased quality factor, ultracompact size, easy fabrication, and experimental observation, have significant applications in ultracompact plasmonic devices.
Multiple plasmon-induced transparencies are numerically predicted in an ultracompact plasmonic structure, comprising series of stub resonators side-coupled with a metal-isolator-metal waveguide. Because of the phase-coupled effect, electromagnetically induced transparency (EIT)-like spectral response occurs between two adjacent stub resonators with detuned resonant wavelengths. In this approach, multiple EIT-like spectral responses, with bandwidths of the order of several nanometers, are obtained in the plasmonic structure with a small footprint of about 0.6 mu m(2). An analytic model and the relative phase analysis based on the scattering matrix theory are used to explain this phenomenon. (C) 2012 Optical Society of America