Evgeni A. Bezus

Design of diffractive lenses for focusing surface plasmons

We present a method of designing diffractive optical elements for transforming and focusing surface plasmons. The method is based on a phase modulation of the surface plasmon provided by the dielectric block with varying geometric parameters located on the interface. The problem of SP diffraction by a dielectric block is solved using the rigorous coupled wave analysis. We demonstrate that the modulation can be implemented not only by changing the length of the dielectric block at fixed height, but also by changing the height at fixed length as well as by simultaneous changing of both parameters. The height modulation and combined height–length modulation are believed to be considered for the first time. As an example, the design of diffractive elements for focusing surface plasmons is considered. It is demonstrated that combining the height and length modulations allows us to increase the diffraction efficiency by more than 10%.

Scattering suppression in plasmonic optics using a simple two-layer dielectric structure

We demonstrate that a planar structure consisting of two isotropic dielectric layers can be used to minimize parasitic scattering in plasmonic elements. It is shown using rigorous electromagnetic simulations that the utilization of the proposed structure allows reducing the scattering losses by an order-of-magnitude (1%–2%). The proposed approach can be used for the design of various plasmonic elements such as lenses, reflectors, and plasmonic crystals.

Low-scattering surface plasmon refraction with isotropic materials

We show theoretically and numerically that a planar structure consisting of two isotropic dielectric layers can be used to minimize parasitic scattering of surface plasmon polaritons for arbitrary incidence angle. The average scattering losses are reduced by an order-of-magnitude down to 1-3%. The surface plasmon refraction with the scattering suppression can be accurately described by an analytical model based on the Fresnel equations. The proposed approach can be used for the design of plasmonic lenses, reflectors, plasmonic crystals and plasmonic laser cavities.

Scattering in elements of plasmon optics suppressed by two-layer dielectric structures

Based on the results of simulations in the framework of a rigorous electromagnetic theory of diffraction, it is shown that a structure comprising two isotropic dielectric layers on a metal surface can be used to suppress parasitic scattering in elements of plasmon optics. The proposed dielectric structure makes possible a tenfold decrease (to 1–3%) in the level of scattering losses. This approach can also be applied in creating various elements of plasmon optics, in particular, lenses and Bragg reflection gratings.

Spatial differentiation of optical beams using phase-shifted Bragg grating

We present a theoretical study of a new application of the phase-shifted Bragg grating (PSBG) as an optical spatial differentiator operating in reflection. We demonstrate that the PSBG allows to calculate the first-order spatial derivative at oblique incidence and the second-order derivative at normal incidence. As an example, the differentiator is numerically shown to be able to convert an input 2D Gaussian beam into a 2D Hermite-Gaussian mode. We expect the proposed application to be useful for all-optical data processing.

Design of an optical element forming an axial line segment for efficient LED lighting systems.

An LED optical element is proposed as an alternative to cold-cathode fluorescent lamps. The optical element generates two symmetric uniformly illuminated line segments on the diffuse reflector. The illuminated segments then act as secondary linear light sources. The calculation of the optical element is reduced to the integration of the system of two explicit ordinary differential equations. The results of the simulation of an illumination system module consisting of a set of optical elements generating a set of line segments on the surface of the diffuse reflector are presented. The elements are located directly on the surface of the reflector. The simulation results demonstrate the uniform illumination of a rectangular area at a distance of 30-40 mm from the light source plane. The lighting efficiency of the designed system exceeds 83%.

Suppression of the spectral selectivity of two-layer phase-relief diffraction structures

The method and results of studying the effect of relief depth on the attainable degree of reducing the spectral selectivity of two-layer diffraction structures based on plastics and glass. The possibilities of suppressing the spectral selectivity of double- and single-relief structures are compared.

Diffraction gratings for generating varying-period interference patterns of surface plasmons

The generation of surface plasmon interference patterns using a dielectric diffraction grating with a metal film applied in the substrate region is studied. It is shown by way of numerical simulation within the rigorous electromagnetic theory that high contrast interference patterns with a period several times smaller than that of the diffraction grating can be produced. At the interference maxima, the field intensity is ten times that of the incident wave. Techniques to control the interference pattern period by varying the wavelength and the incidence angle are discussed.

Optical computation of the Laplace operator using phase-shifted Bragg grating

Diffraction of a 3D optical beam on a multilayer phase-shifted Bragg grating (PSBG) is considered. It is shown that the PSBG enables optical computation of the spatial Laplace operator of the electromagnetic field components of the incident beam. The computation of the Laplacian is performed in reflection at normal incidence. As a special case, the parameters of the PSBG transforming the incident Gaussian beam into a Laguerre-Gaussian mode of order (1,0) are obtained. Presented numerical results demonstrate high quality of the Laplace operator computation and confirm the possibility of the formation of Laguerre-Gaussian mode. We expect the proposed applications to be useful for all-optical data processing.

Analytical design of freeform optical elements generating an arbitrary-shape curve

A method is proposed for designing refractive optical elements focusing a collimated incident beam into a curve with specified shape. A general relationship for the freeform surface of the optical element is derived as an envelope of a parametric family of hyperboloids of revolution that focuses the incident beam into the points on the curve. Using the thin optical element approximation, the calculation of the hyperboloid parameters providing required irradiance distribution along the curve is reduced to the solution of an explicit first order differential equation. Optical elements generating line segment focus and circular arc focus are designed. The simulation results demonstrate generation of high-quality curves.