Slot-grating flat lens for telecom wavelengths.

We present a stand-alone beam-focusing flat lens for use in the telecommunications wavelength range. Light incident on the back surface of the lens propagates through a subwavelength aperture and is heavily diffracted on exit and partially couples into a surface plasmon polariton and a surface wave propagating along the surface of the lens. Interference between the diffracted wave and re-emission from a grating patterned on the surface produces a highly collimated beam. We show for the first time a geometry at which a lens of this type can be used at telecommunication wavelengths (λ=1.55 µm) and identify the light coupling and re-emission mechanisms involved. Measured beam profile results at varying incident wavelengths show excellent agreement with Lumerical FDTD simulation results.

Extraordinary optical transmission through multi-layered systems of corrugated metallic thin films.

Optical transmission through multi-layered systems of corrugated metallic thin films is investigated by rigorous electromagnetic simulations based on an exact Green tensor method. Compared to a single metal slab of equivalent thickness and volume, it was found that the multi-layered system can significantly impede the field decay, often leading to transmission greater than that expected from the Fabry-Perot resonance-like behavior exhibited by subwavelength slits in a single slab. Extraordinary optical transmission is also observable for systems of layers whose combined thicknesses are much greater than the skin depth of the metal. Structures consisting of up to five layers with a net thickness of 500 nm for the metal films were considered in our study. These findings demonstrate that an appreciable fraction of the optical power that is incident on the thin metal films can be transmitted over distances greater than their skin depth using plasmonic resonances.

Directional, nonpropagating, and polychromatic excitations in one-dimensional wave systems.

It has been demonstrated that, in a one-dimensional wave system, monochromatic waves may be generated which are completely localized to the region of excitation or which propagate in only one direction. We further the discussion of such nonpropagating and directional excitations and demonstrate that they can be extended to excitations of an arbitrary finite number of frequencies. Two techniques for mathematically constructing these excitations are discussed. Furthermore, the relation between nonpropagating excitations and nonscattering scatterers is discussed. The results presented here may be useful in the development of devices for one-dimensional and quasi-one-dimensional wave systems.

Diffraction of evanescent waves and nanomechanical displacement detection.

Sensitive displacement detection has emerged as a significant technological challenge in mechanical resonators with nanometer-scale dimensions. A novel nanomechanical displacement detection scheme based upon the scattering of focused evanescent fields is proposed. The sensitivity of the proposed approach is studied using diffraction theory of evanescent waves. Diffraction theory results are compared with numerical simulations.

Surface plasmons modulate the spatial coherence of light in Young's interference experiment.

It is shown how surface plasmons that travel between the slits in Young's interference experiment can change the state of spatial coherence of the field that is radiated by the two apertures. Surprisingly, the coherence can both be increased and decreased, depending on the slit separation distance. This results in a modulation of the visibility of the interference fringes. Since many properties of a light field-such as its spectrum, polarization, and directionality - may change on propagation and are dependent on the spatial coherence of the source, our results suggest that the use of surface plasmons provides a new way to alter or even tailor the statistical properties of a light field.

Strategies for employing surface plasmons in near-field optical readout systems.

The enhanced transmission of light through subwavelength-size holes in a metal plate is well-known to be associated with surface plasmons. We have undertaken a systematic theoretical study of several strategies for applying these plasmon effects in a near-field optical readout system using an exact Green's tensor formulation. Based on the results of our simulations with light of wavelength lambda = 500 nm, data structures separated by 120 nm could be clearly resolved, and asymmetries of about +/-10 nm in the optical readout system could be tolerated without serious degradation of the performance. Advantages and disadvantages of each strategy are discussed.