Vladimir Kochergin

Surface-plasmon-assisted resonant tunneling of light through a periodically corrugated thin metal film

We present experimental results and a numerical model confirming that surface plasmons can resonantly enhance light transmission through a corrugated metal film. A new interpretation in terms of plasmon-assisted light tunneling is given to recent experiments on light penetration through periodic subwavelength holes in a thin metal film. We designed a narrow-band filter suitable for applications in optical communication by optimizing the film and the grating parameters.

Aluminum plasmonic nanostructures for improved absorption in organic photovoltaic devices

We model the absorption enhancement in organic photovoltaic devices induced by incorporating Al, Ag, and Au nanoparticles in the active layer. We find that Al nanoparticles should yield significantly greater enhancement than Ag or Au. This is because the much higher plasma frequency of Al ensures a better overlap between plasmon resonance and absorption band of organic semiconductors. Our predictions are verified experimentally by demonstrating enhanced absorbance in a poly(3-hexylthiophene-2,5-diyl): [6,6]-phenyl C61 butyric acid methyl ester layer with embedded functionalized Al nanoparticles.

Improved effective medium approach: Application to metal nanocomposites

An improved effective medium approximation (EMA) is presented that accounts for higher order interactions between metal nanoparticles in metal-dielectric composite materials and compared to experimental results. The theoretical results of this formalism are applied to a composite material consisting of spherical gold nanoparticles randomly distributed in a dielectric matrix, which has been extensively characterized with respect to its structural and optical properties. The experimental results and theoretical predictions are compared and the results are discussed. It is shown that the modified theory expands the range to which EMA can be applied to a metal filling fraction of ∼20% at very little additional computational expenses. The improved theory also allows extracting more information from the optical characterization of the composite material such as the distribution of the interparticle distances in a composite.

Adjustable optical anisotropy in porous GaAs

We report a theoretical investigation of the optical properties of porous (100) GaAs having crystallographic pores. An effective medium approach is used for the calculations. A biaxial anisotropy of the material is predicted for most of the material parameters. The parameter windows for different kinds of uniaxial anisotropy are predicted as well. It is shown that the type and value of the optical anisotropy, and even the direction of the optical axes, can be controlled by GaAs etching parameters, and this letter gives the theoretical blueprint for the overall pore morphology required for that.

Optical filtering by leaky guided modes in macroporous silicon

We propose an optical filtering mechanism in a porous material based on wavelength-dependent losses for leaky modes in pore waveguides. The spectral transmission characteristics of such filters can be controlled by applying thin-film coatings to the pore walls. Such filters will find application in the deep UV spectral range where traditional approaches to filter design fail due to lack of suitable materials.

Porous silicon filters for mid- to far-IR range

We present in this paper the development of novel mid-to-far IR filters that are based on porous silicon structures. The diameters of the pores in such filters are by orders of magnitude less than the central wavelength of the transmission band, leading to effective averaging of the porous structure by the light waves. Such filters have a number of important advantages over multilayer interference filters. Since the filters are made from a single material by means of an electrochemical etching process (rather than through deposition), these filters do not exhibit delamination problems and are well suited for operation at extreme temperatures (for example, in the environment of space). Our fabrication technique permits the fabrication of filters up to 200 mm (8 inches) in diameter, suitable for any wavelength from below 1.1 μm to more than 45 μm. The results of experimental testing of such filters are shown to prove the main predictions.

Optical demultiplexing in a planar waveguide with colloidal crystal

We report the first experimental demonstration of demultiplexing capabilities of a 2-D waveguide grating consisting of a monolayer colloidal crystal deposited on a top of a planar waveguide. Self-assembled periodical structure with hexagonal symmetry is formed by crystallization of polystyrene colloidal particles. The experiments are performed in the 1550-nm wavelength region.

A Fiber Bragg Grating Temperature Sensor for 2–400 K

We demonstrate fiber optic, multiplexible temperature sensing using a fiber Bragg grating (FBG) with an operational range of 2-400 K, and a temperature resolution better than 10 mK for temperatures <;12 K. This represents a significant reduction in the lowest usable temperature as well as a significant increase in sensitivity at cryogenic temperatures compared with previously reported multiplexible solutions. This is accomplished by mounting the section of the fiber with a FBG on a polytetrafluoroethylene coupon, which has a non-negligible coefficient of thermal expansion down to <;4 K. The sensors exhibit a good stability over multiple temperature cycles and acceptable sensor-to-sensor repeatability. Possible applications for this sensor include distributed temperature sensing across superconducting elements and cryogenic temperature measurements in environments where electrical measurements are impractical or unsafe.

Macroporous silicon-based polarization components

Currently used transmission-type polarizers exhibit strong limitations in the deep UV and shorter wavelength. We propose an entirely different type of polarizer to solve many of the problems caused by the absence of adequate materials in this spectral range. The new polarizers consist of three-dimensionally ordered Macroporous Silicon (MPSi), with the pores used as waveguide cores separated by the reflective silicon host. Ordered pores serve as a two-dimensional array of optical waveguides. Multilayer coating of the pore walls, together with the rectangular shape of the pores (with the length along one axis being several times greater than that of the second axis) results in polarized transmission. Calculations demonstrate potentially very high extinction. In addition, the extinction achieved by such polarization components does not exhibit degradation with the angle of incidence, permitting operation in tilted and divergent light beams to simplify optical system design and fabrication. The fabrication process is different from that used in the fabrication of multilayer interference filters. It permits the fabrication of deep UV polarizers up to 200mm in diameter, suitable for wavelengths from above 600nm to less than 50nm. Far-UV polarizers can be manufactured as simply and economically as the near UV ones. The theory of light propagation through such MPSi layers is developed, the main predictions of the theory are experimentally validated, and the fabrication procedure for MPSi UV polarizers is described.

Macroporous silicon UV filters for space and terrestrial environments

Currently used optical filters exhibit strong limitations in the deep UV and shorter wavelength ranges. We propose an entirely different type of UV filter to solve many of the problems due to inadequate materials and fabrication techniques. These filters consist of three-dimensionally ordered Macroporous Silicon (MPSi), with the pores used as waveguide cores separated by the reflective silicon host. Ordered pores serve as a two-dimensional array of optical waveguides. Multilayer coating of the pore walls results in the band-pass, short-pass, or band-blocking transmittance spectra of MPSi filters. Such filters have a number of advantages. They do not exhibit spectral shifts of the passed or blocked spectral bands with the angle of incidence, permitting operation in tilted and divergent light beams to simplify optical system design and fabrication. Due to their structures (fewer and thinner layers on the pore walls required to gain the same level of rejection), the filters do not exhibit delamination problems and are well suited for operation at extreme temperatures (for space as well as for terrestrial environments). The fabrication process is different from that used for multilayer interference filters. This process permits the fabrication of filters up to 200mm in diameter that are suitable for wavelengths from longer than 400 nm to shorter than 100 nm. Far-UV filters can be manufactured as simply and economically as the near UV ones. The theory of light propagation through the MPSi layers is developed, the main predictions of the theory are experimentally validated, and the fabrication procedure for MPSi UV filters is reported.