Avner Yanai

Demonstration of Nanofocusing by the use of Plasmonic Lens Illuminated with Radially Polarized Light

We experimentally demonstrate the focusing of surface plasmon polaritons by a plasmonic lens illuminated with radially polarized light. The field distribution is characterized by near-field scanning optical microscope. A sharp focal spot corresponding to a zero-order Bessel function is observed. For comparison, the plasmonic lens is also measured with linearly polarized light illumination, resulting in two separated lobes. Finally, we verify that the focal spot maintains its width along the optical axis of the plasmonic lens. The results demonstrate the advantage of using radially polarized light for nanofocusing applications involving surface plasmon polaritons.

Plasmonic focusing with a coaxial structure illuminated by radially polarized light

We propose and analyze a plasmonic lens that is illuminated by a radially polarized light. The lens is made of a coax-like geometry consisting of an annular dielectric slit surrounded by metal. Focusing efficiency is enhanced by the use of a circular grating assisting the coupling of light into surface plasmons. Further enhancement is obtained by introducing a circular Bragg grating on top of the structure, reflecting the surface plasmon modes that are propagating in the counter-focus direction. Using the Finite-Difference Time-Domain approach we investigate the transmission and the focusing mechanisms, and study the effect of structural parameters on the performance of the plasmonic lens.

Efficient coupling and field enhancement for the nano-scale: plasmonic needle.

Theoretical demonstration of efficient coupling and power concentration of radially-polarized light on a conical tip of plasmonic needle is presented. The metallic needle is grown at the center of radial plasmonic grating, engraved in a metal surface. The electromagnetic field distribution was evaluated by Finite Elements and Finite-Difference-Time-Domain methods. The results show that the field on the tip of the needle is significantly enhanced compared to the field impinging on the grating. The power enhancement exhibited a resonant behavior as a function of needle length and reached values of approximately 10(4). Test samples for few types of characterization schemes were fabricated.

Enhanced efficiency of thin film solar cells using a shifted dual grating plasmonic structure

We propose an ultrathin solar cell architecture design which incorporates two periodic layers of metallic and dielectric gratings. Both layers couple the incident light to photonic and plasmonic modes, thus increasing absorption within the cell. The relative position between the two gratings is examined, and is shown to have significant impact on absorption. A lateral shift between the two layers introduces structural asymmetry, and enables coupling of the incident field to optically dark photonic modes. Furthermore, the lateral shift influences mode interactions. Current density enhancement is calculated under AM1.5 G solar illumination, and is found to reach a value of 1.86. The structure proposed is optimized and compared to solar cells with a single layer of metallic or dielectric nanostructures.

Light transmission through a circular metallic grating under broadband radial and azimuthal polarization illumination

We study light transmission through circular metallic grating under radial/azimuthal polarization illumination and observe strong polarization selectivity and a resonance behavior making it attractive for applications relying on radial polarization.

Near- and far-field properties of plasmonic oligomers under radially and azimuthally polarized light excitation.

We present a comprehensive experimental and theoretical study on the near- and far-field properties of plasmonic oligomers using radially and azimuthally polarized excitation. These unconventional polarization states are perfectly matched to the high spatial symmetry of the oligomers and thus allow for the excitation of some of the highly symmetric eigenmodes of the structures, which cannot be excited by linearly polarized light. In particular, we study hexamer and heptamer structures and strikingly find very similar optical responses, as well as the absence of a Fano resonance. Furthermore, we investigate the near-field distributions of the oligomers using near-field scanning optical microscopy (NSOM). We observe significantly enhanced near-fields, which arise from efficient excitation of the highly symmetric eigenmodes by the radially and azimuthally polarized light fields. Our study opens up possibilities for tailored light-matter interaction, combining the design freedom of complex plasmonic structures with the remarkable properties of radially and azimuthally polarized light fields.

The role of short and long range surface plasmons for plasmonic focusing applications

We propose and analyze a new plasmonic lens allowing the simultaneous focusing of both short and long range surface plasmons polaritons. The considered geometry is circularly symmetric and the SPP excitation is radially polarized. The long range and the short range modes are compared and found to have very different focusing properties. The trade-offs between the modes are discussed. The interplay between these two modes is used to demonstrate a practical focusing scenario providing a smaller spot size compared with previous version of plasmonic lenses, and a large depth of focus simultaneously.

Subwavelength plasmonics for graded-index optics on a chip

Planar plasmonic devices are becoming attractive for myriad applications, owing to their potential compatibility with standard microelectronics technology and the capability for densely integrating a large variety of plasmonic devices on a chip. Mitigating the challenges of using plasmonics in on-chip configurations requires precise control over the properties of plasmonic modes, in particular their shape and size. Here we achieve this goal by demonstrating a planar plasmonic graded-index lens focusing surface plasmons propagating along the device. The plasmonic mode is manipulated by carving subwavelength features into a dielectric layer positioned on top of a uniform metal film, allowing the local effective index of the plasmonic mode to be controlled using a single binary lithographic step. Focusing and divergence of surface plasmons is demonstrated experimentally. The demonstrated approach can be used for manipulating the propagation of surface plasmons, e.g., for beam steering, splitting, cloaking, mode matching, and beam shaping applications.

Tunability of reflection and transmission spectra of two periodically corrugated metallic plates, obtained by control of the interactions between plasmonic and photonic modes

We theoretically study the interactions between plasmonic and photonic modes within a structure that is composed of two thin corrugated metallic plates, embedded in air. We show that the interactions depend on the symmetry of the interacting modes. This observation is explained by the phase difference between the Fourier components of the two gratings. The phase can be controlled by laterally shifting one grating with respect to the other. Therefore, this relative shift provides an efficient “knob” that allows one to control the interaction between the various modes, resulting in an efficient modulation of light transmission and reflection in the proposed structure. Based on this concept we show that the investigated structure can be used as a tunable plasmonic filter.

Giant resonance absorption in ultra-thin metamaterial periodic structures

We study the interaction of an incident plane wave with a metamaterial periodic structure consisting of alternating layers of positive and negative refractive index with average zero refractive index. We show that the existence of very narrow resonance peaks for which giant absorption - 50% at layer thickness of 1% of the incident wavelength - is exhibited. Maximum absorption is obtained at a specific layer thickness satisfying the critical coupling condition. This phenomenon is explained by the Rayleigh anomaly and by the excitation of Fabry Perot modes in the periodic layer. In addition, we investigate the modes supported by the structures for several limiting cases, and show that zero phase accumulation in the periodic metamaterial is obtained at resonance.