Tomasz Szoplik

Asymmetric transmission of terahertz radiation through a double grating

We report on experimental evidence of unidirectional transmission of terahertz waves through a pair of metallic gratings with different periods. The gratings are optimized for a broadband transmission in one direction, accompanied with a high extinction rate in the opposite direction. In contrast to previous studies, we show that the zero-order nonreciprocity cannot be achieved. Nonetheless, we confirm that the structure can be used successfully as an asymmetric filter.

Corrugated metal-coated tapered tip for scanning near-field optical microscope.

This paper addresses an important issue of light throughput of a metal-coated tapered tip for scanning near-field microscope (SNOM). Corrugations of the interface between the fiber core and metal coating in the form of parallel grooves of different profiles etched in the core considerably increase the energy throughput. In 2D FDTD simulations in the Cartesian coordinates we calculate near-field light emitted from such tips. For a certain wavelength range total intensity of forward emission from the corrugated tip is 10 times stronger than that from a classical tapered tip. When realized in practice the idea of corrugated tip may lead up to twice better resolution of SNOM.

Photonic crystals : physics and technology

Basics.- to Photonic Crystals and Photonic Band-Gaps.- Physics of Slow Bloch Modes and Their Applications.- Nonlinear Optics in Photonic Crystals.- Quasi Phase Matching in Two-Dimensional Quadratic Nonlinear Photonic Crystals.- Harmonic Generation in Nanostructures: Metal Nanoparticles and Photonic Crystals.- Ultra-fast Optical Reconfiguration via Nonlinear Effects in Semiconductor Photonic Crystals.- Nonlinear Optics with Photonic-Crystal Fibres.- Technology, Integration an Active Photonic Crystals.- Photonic Crystal and Photonic Band-Gap Structures for Light Extraction and Emission Control.- Silicon-Based Photonic Crystals and Nanowires.- Characterisation and Measurements of Nanostructures.- Near Infrared Optical Characterization Techniques for Photonic Crystals.- Characterization Techniques for Planar Optical Microresonators.- On SNOM Resolution Improvement.- Simulation Techniques.- Photonic Crystals: Simulation Successes and some Remaining Challenges.- Plane-Wave Admittance Method and its Applications to Modelling Photonic Crystal Structures.

Nonsymmetric Fourier transforming with an anamorphic system

The idea of obtaining a nonsymmetric Fourier transform with crossed cylindrical lenses of different focal lengths is presented. The anamorphic rotation-variant system produces a scaled Fourier transform F(u,mv) of an object f(x,y), where m is a scaling constant. The system performs controlled angular magnification of an object spectrum. It is shown that the super resolution in one direction is gained by reducing the number of degrees of freedom of the optical message in the other. Experimental results are shown where the scaling constant m of up to 10 has been obtained.

Performance of Scanning Near-Field Optical Microscope Probes with Single Groove and Various Metal Coatings

We investigate the performance of a simple corrugated aperture scanning near-field optical microscope (SNOM) probe with various cladding metals. The probes have only one corrugation, however, they offer increased transmission over both uncorrugated probes and those with many grooves. Enhancement of light throughput results from excitation of surface plasmons at the corrugation at the core–cladding interface. We show how the choice of metal influences radiation properties of grooved probes.

Nanofocusing of radially polarized light with dielectric-metal-dielectric probe

Nanofocusing properties of a tip in the form of a dielectric tapered fiber with metal apertureless coating and dielectric nanocladding can be tuned within a wide spectral range by choice of cladding permittivity. The silica core of diameter decreasing from 2 mum to 5 nm in apex is covered with a silver layer and has a 5 nm dielectric cladding. Internal illumination with a radially polarized Laguerre-Gauss beam guided in fiber is used. In body-of-revolution finite-difference time-domain simulations we find that with an increase of the refractive index of nanocladdings the maximum enhancement occurs for increasingly longer wavelengths.

Description of near– and far–field light emitted from a metal–coated tapered fiber tip

We present an analytical calculation of near- and far-field radiation emitted from a metal-coated tapered fiber probe. From FDTD simulations made in Cartesian coordinates we find that charge distribution on a tip is rim localized and its density is a bipolar periodic and continuous function. Similar angular charge density distributions may result from random irregularities of tip surfaces created in the fabrication process. Thus forward emission from a tip can be described as emission of quasi-dipoles and multi-quasi-dipoles. Analytically calculated characteristics are in agreement with our FDTD simulations and previous measurements of Obermüller and Karrai.

Ge wetting layer increases ohmic plasmon losses in Ag film due to segregation.

We have investigated the influence of the Ge wetting layer on both ohmic and scattering losses of a surface plasmon-polariton (SPP) wave in Ag film deposited on SiO2 substrate with an e-beam evaporator. Samples were examined by means of atomic force microscopy (AFM), spectroscopic ellipsometry (SE), two-dimensional X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and microscopic four-point probe (M4PP) sheet resistance measurements. Ag films of 100 nm thickness were deposited at 180 and 295 K directly onto the substrates with or without a Ge interlayer. In AFM scans, we confirm the fact that the commonly used Ge adhesion layer smooths the surface of Ag film and therefore reduces scattering losses of the SPP wave on surface roughness. However, our ellipsometric measurements indicate for the first time that segregation of Ge leads to a considerable increase in ohmic losses connected with a boost of the imaginary part of Ag permittivity in the 500-800 nm spectral range. Moreover, the trend develops over time, as confirmed in a series of measurements performed over an interval of three months. XPS analysis confirms the Ge segregation to the Ag free surface and most probably to grain boundaries. M4PP measurements show that the specific resistivity in Ag films evaporated on a Ge interlayer at 295 K is nearly twice as high as in layers deposited directly on a SiO2 substrate. The use of an amorphous Al2O3 overlayer prevents Ge segregation to free surface.

Ultrasmooth metal nanolayers for plasmonic applications: surface roughness and specific resistivity

The future of plasmonic devices depends on effective reduction of losses of surface plasmon-polariton waves propagating along metal-dielectric interfaces. Energy dissipation is caused by resistive heating at the skin-deep-thick outer layer of metal and scattering of surface waves on rough metal-dielectric interfaces. Fabrication of noble metal nanolayers with a smooth surface still remains a challenge. In this paper, Ag layers of 10, 30, and 50 nm thickness deposited directly on fused-silica substrates and with a 1 nm wetting layer of Ge, Ti, and Ni are examined using an atomic-force microscope and four-probe resistivity measurements. In the case of all three wetting layers, the specific resistivity of silver film decreases as the thickness increases. The smallest, equal 0.4 nm root mean squared roughness of Ag surface of 10 nm thickness is achieved for Ge interlayer; however, due to Ge segregation the specific resistivity of silver film in Ag/Ge/SiO₂ structures is about twice higher than that in Ag/Ti/SiO₂ and Ag/Ni/SiO₂ sandwiches.

Energy transport in plasmon waveguides on chains of metal nanoplates

An interest in energy transport in 3D chains of metal nanoparticles is oriented towards future applications in nanoscale optical devices. We consider plasmonic waveguides composed of silver nanoplates arranged in several geometries to find the one with the lowest attenuation. We investigate light propagation of 500-nm wavelength along different chains of silver nanoplates of subwavelength length and width and wavelength-size height. Energy transmission of the waveguides is analysed in the range of 400–2000 nm. We find that chain of short parallel nanoplates guides energy better than two electromagnetically coupled continuous stripes and all other considered nonparallel structures. In a wavelength range of 500–600 nm, this 2-μm long 3D waveguide transmits 39% of incident energy in a channel of λ × λ/2 cross section area.