Showing papers in "Journal of Optics in 2013"

Goos-Hanchen and Imbert-Fedorov beam shifts: an overview

Abstract: We consider reflection and transmission of polarized paraxial light beams at a plane dielectric interface. The field transformations taking into account a finite beam width are described based on the plane-wave representation and geometric rotations. Using geometrical-optics coordinate frames accompanying the beams, we construct an effective Jones matrix characterizing spatial-dispersion properties of the interface. This results in a unified self-consistent description of the Goos–Hanchen and Imbert–Fedorov shifts (the latter being also known as the spin Hall effect of light). Our description reveals the intimate relation of the transverse Imbert–Fedorov shift to the geometric phases between constituent waves in the beam spectrum and to the angular momentum conservation for the whole beam. Both spatial and angular shifts are considered as well as their analogues for higher-order vortex beams carrying intrinsic orbital angular momentum. We also give a brief overview of various extensions and generalizations of the basic beam-shift phenomena and related effects.

Chiral metamaterials: from optical activity and negative refractive index to asymmetric transmission

Abstract: We summarize the progress in the development and application of chiral metamaterials. After a brief review of the salient features of chiral metamaterials, such as giant optical activity, circular dichroism, and negative refractive index, the common method for the retrieval of effective parameters for chiral metamaterials is surveyed. Then, we introduce some typical chiral structures, e.g., chiral metamaterial consisting of split ring resonators, complementary chiral metamaterial, and composite chiral metamaterial, on the basis of the studies of the authors’ group. The coupling effect during the construction of bulk chiral metamaterials is mentioned and discussed. We introduce the application of bianisotropic chiral structures in the field of asymmetric transmission. Finally, we mention a few directions for future research on chiral metamaterials.

Optical super-oscillations: sub-wavelength light focusing and super-resolution imaging

Abstract: Optical super-oscillations, first predicted in 1952 and observed in 2007, offer a promising route to optical super-resolution imaging and show potential for manufacturing with light and data-storage applications such as direct optical recording and heat assisted magnetic recording. We review the history and basic physics behind the phenomenon of super-oscillation and its application in optics. We overview recent results in creating optical super-oscillations using binary masks, spatial light modulators and planar metamaterial masks. We also investigate the limits and competitiveness of super-oscillatory imaging.

Design of multi-band metamaterial perfect absorbers with stacked metal?dielectric disks

Abstract: Simple periodic structures of stacked metal and dielectric microdisks can display very high absorbance over multiple bands at infrared frequencies (3–10 μm wavelengths). The stack can be envisaged as intersecting tri-layers, each tri-layer composed of metal–dielectric–metal disks that form independent impedance matched resonators, and give rise to large absorbance at different frequencies. Numerical simulations show that dual-band and multi-band absorbers with near unity absorbance on all their bands can be flexibly designed whereby the dielectric materials determine the absorption band of the metamaterial. The multi-band absorber is reasonably polarization insensitive and the absorbance remains large even with large angles of incidence. This approach of multi-layered stacked metamaterials is compared and shown to be superior to another approach to multiple-band metamaterial perfect absorbers having closely packed resonators within a unit cell.

Optical properties of Ag nanoparticle layers deposited on silicon substrates

Abstract: Silver nanoparticles of various sizes, shapes and modified distances between them were prepared on silicon substrates using thermally evaporated metal thin films of varying thicknesses followed by annealing. The ∼4 nm silver thin film annealed around ∼300 °C showed considerable reflectance reduction from the silicon substrate in the entire polychromatic spectrum. The effects of dipolar and quadrupolar resonances of silver nanoparticles on the reflectance reduction from the silicon substrate are discussed. The quadrupolar resonances of silver nanoparticles lead to reduced reflectance from the silicon substrate in the near UV–visible region (∼350–600 nm) due to the enhanced forward scattering. The reflectance reduction in the Vis and NIR regions (∼600–1300 nm range) is explained by the interaction of the surface plasmons of the metal nanoparticles, which is very sensitive to the size and shape of the particles, and the distances between them. Some of the waveguide modes existing at the interface between the silicon and the metal nanoparticles also couple the excited surface plasmons, which helps in trapping the light near the NIR region. With proper tuning of the metal particle sizes, shapes and distances between the particles in the layers, one can reduce the total reflectance from the silicon substrate in the entire polychromatic solar spectrum.

Perfect absorption in graphene multilayers

Abstract: We demonstrate that 100% light absorption can be achieved in a graphene-based hyperbolic metamaterial, consisting of periodically arranged graphene layers which are tilted with respect to the interface. The geometrical parameters of the multilayered structure and the chemical potential of graphene are chosen in such a way that the in-plane relative effective permittivity is close to 1. Under this condition, the graphene multilayer exhibits asymmetry which appears as a very large difference between waves propagating upward and downward with respect to multilayer boundaries. One of them has a very high attenuation constant and neither of the waves undergo reflection at slab interfaces, resulting in total absorption even for an optically ultra-thin slab.

Metal?insulator?metal light absorber: a continuous structure

Abstract: A type of light absorber made of continuous layers of metal and dielectric films is studied. The metal films can have thicknesses close to their skin depths in the wavelength range concerned, which allows for both light transmission and reflection. Resonances induced by multiple reflections in the structure, when combined with the inherent lossy nature of metals, result in strong absorption spectral features. An eigen-mode analysis is carried out for the plasmonic multilayer nanostructures which provides a generic understanding of the absorption features. Experimentally, the calculation is verified by a reflection measurement with a representative structure. Such an absorber is simple to fabricate. The highly efficient absorption characteristics can be potentially deployed for optical filter designs, sensors, accurate photothermal temperature control in a micro-environment and even for backscattering reduction of small particles, etc.

Polarized light imaging of birefringence and diattenuation at high resolution and high sensitivity.

Abstract: Polarized light microscopy provides unique opportunities for analyzing the molecular order in man-made and natural materials, including biological structures inside living cells, tissues, and whole organisms. 20 years ago, the LC-PolScope was introduced as a modern version of the traditional polarizing microscope enhanced by liquid crystal devices for the control of polarization, and by electronic imaging and digital image processing for fast and comprehensive image acquisition and analysis. The LCPolScope is commonly used for birefringence imaging, analyzing the spatial and temporal variations of the differential phase delay in ordered and transparent materials. Here we describe an alternative use of the LC-PolScope for imaging the polarization dependent transmittance of dichroic materials. We explain the minor changes needed to convert the instrument between the two imaging modes, discuss the relationship between the quantities measured with either instrument, and touch on the physical connection between refractive index, birefringence, transmittance, diattenuation, and dichroism.

Electronic analogy of the Goos–Hänchen effect: a review*

Abstract: The analogies between optical and electronic Goos–Hanchen effects are established based on electron wave optics in semiconductor or graphene-based nanostructures. In this paper, we give a brief overview of the progress achieved so far in the field of electronic Goos–Hanchen shifts, and show the relevant optical analogies. In particular, we present several theoretical results on the giant positive and negative Goos–Hanchen shifts in various semiconductor or graphene-based nanostructures, their controllability, and potential applications in electronic devices, e.g. spin (or valley) beam splitters.

Unusual reflection of electromagnetic radiation from a stack of graphene layers at oblique incidence

Abstract: We study the interaction of electromagnetic (EM) radiation with single-layer graphene and a stack of parallel graphene sheets at arbitrary angles of incidence. It is found that the behavior is qualitatively different for transverse magnetic (or p-polarized) and transverse electric (or s-polarized) waves. In particular, the absorbance of single-layer graphene attains a minimum (maximum) for the p (s)-polarization at the angle of total internal reflection when the light comes from a medium with a higher dielectric constant. In the case of equal dielectric constants of the media above and beneath graphene, for grazing incidence graphene is almost 100% transparent to p-polarized waves and acts as a tunable mirror for the s-polarization. These effects are enhanced for a stack of graphene sheets, so the system can work as a broad band polarizer. It is shown further that a periodic stack of graphene layers has the properties of a one-dimensional photonic crystal, with gaps (or stop bands) at certain frequencies. When an incident EM wave is reflected from this photonic crystal, the tunability of the graphene conductivity renders the possibility of controlling the gaps, and the structure can operate as a tunable spectral-selective mirror.

Channel-drop filter based on a photonic crystal ring resonator

Abstract: In this paper combining a square lattice photonic crystal with a 12-fold quasicrystal, we proposed a new design for an optical channel-drop filter. Our proposed structure has a transmission efficiency very close to 1 and the band width and quality factor values for this structure are 4.5 nm and 344. After designing the channel-drop filter we investigated the effect of different parameters on the output wavelength of the filter. It has been shown that by changing the dielectric rods' refractive index, radius of initial structure rods and the radius of the 12-fold quasicrystal rods we can obtain different output wavelengths of the filter.

Subwavelength particles in an inhomogeneous light field: optical forces associated with the spin and orbital energy flows

Abstract: We analyse the ponderomotive action experienced by a small spherical particle immersed in an optical field, in relation to the internal energy flows (optical currents) and their spin and orbital constituents. The problem is studied analytically, on the basis of the dipole model, and numerically. The three sources of the field mechanical action—the energy density gradient and the orbital and spin parts of the energy flow—differ in their ponderomotive mechanisms, and their physical nature manifests itself in the dependence of the optical force on the particle radius a. If a ≪ λ (the radiation wavelength), the optical force behaves as aν, and integer ν can be used to classify the sources of the mechanical action. This classification correlates with the multipole representation of the field–particle interaction: the gradient force and the orbital momentum force appear due to the electric or magnetic dipole moments per se; the spin momentum force emerges due to interaction between the electric and magnetic dipoles or between the dipole and quadrupole moments (if the particle is polarizable electrically but not magnetically or vice versa). In principle, the spin and orbital currents can be measured separately through the probe particle motion, employing a special choice of particles with the necessary magnetic and/or electric properties.

Fano resonances and topological optics: an interplay of far- and near-field interference phenomena*

Abstract: Fano resonances and optical vortices originate from two types of interference phenomena. Usually, these effects are considered to be completely independent, and in many cases Fano resonances are observed without any link to vortices, as well as vortices with a singular phase structure that are not accompanied by Fano resonances. However, this situation changes dramatically when we study light scattering at the nanoscale. In this paper, we demonstrate that Fano resonances observed for light scattering by nanoparticles are accompanied by the singular phase effects usually associated with singular optics, and we introduce and describe optical vortices with characteristic core sizes well below the diffraction limit.

Overcoming the diffraction limit induced by microsphere optical nanoscopy

Abstract: The microsphere optical nanoscopy (MONS) technique recently demonstrated the capability to break the optical diffraction limit with a microsphere size of 2–9 μm fused silica. We report that larger polystyrene microspheres of 30, 50 and 100 μm diameters can overcome the diffraction limit in optical imaging. The sub-diffraction features of a Blu-ray Disc and gold nano-patterned quartz were experimentally observed in air by coupling the microspheres with a standard optical microscope in the reflected light illumination mode. About six to eight times magnification was achieved using the MONS. The mechanism of the MONS was theoretically explained by considering the transformation of near-field evanescent waves into far-field propagating waves. The super-resolution imaging was demonstrated by experiments and theoretical simulations.

Electromagnetic multi-Gaussian Schell-model beams

Abstract: A recently introduced class of scalar multi-Gaussian Schell-model (MGSM) beams is extended to the electromagnetic domain. The realizability conditions and the beam conditions for the parameters of the new source are established. The behavior of the polarization properties of the beam on propagation in free space and in first-order imaging systems is investigated. The formation of the uniform polarization state in the central part of the transverse beam cross-section is explored in detail.

Aliasing-reduced Fresnel diffraction with scale and shift operations

Abstract: Numerical simulation of Fresnel diffraction with fast Fourier transform (FFT) is widely used in optics, especially computer holography. Fresnel diffraction with FFT cannot set different sampling rates between source and destination planes, while shifted-Fresnel diffraction can set different rates. However, an aliasing error may be incurred in shifted-Fresnel diffraction in a short propagation distance, and the aliasing conditions have not been investigated. In this paper, we investigate the aliasing conditions of shifted-Fresnel diffraction and improve its properties based on the conditions.

Design of a tunable terahertz narrowband metamaterial absorber based on an electrostatically actuated MEMS cantilever and split ring resonator array

Abstract: A dynamically tunable terahertz (THz) narrowband metamaterial absorber is presented. The absorber is based on an electrostatically actuated micro-electro-mechanical systems (MEMS) cantilever and split ring resonator (SRR) array. An equivalent LC circuit model for a transverse electric (TE) polarization wave is introduced to analyze the mechanism of frequency tuning. A finite element method is applied to simulate the mechanical characteristics of the cantilever, and a finite integration technique is used to study the frequency tuning properties of the absorber. The results show that, for a TE polarization wave, there is only one absorption peak in the frequency range from 0.6 to 1.6 THz. The absorption peak frequency can be continuously tuned from 1.32 to 1.28 THz, and then abruptly to 1.12 THz. The maximum tunable frequency is 0.20 THz, which is about 15% of the initial resonance frequency. For a transverse magnetic (TM) polarization wave, there are two tunable absorption peaks in this frequency range. Moreover, for a TE wave, some geometric dimensions affecting the initial resonance frequency are investigated.

Enhanced absorption of graphene in the visible region by use of plasmonic nanostructures

Abstract: Low absorption of graphene in the visible range of the spectrum makes it difficult to uniquely benefit from this material in ultra-fast optoelectronic applications. We numerically propose to utilize patterned metallic nanostructures to increase light absorption in single-layer graphene. Simulation results show that excitation of surface plasmon resonances in the metallic nanostructures significantly enhances the local electromagnetic field near the graphene layer, therefore leading to a dramatic enhancement of the absorption in the graphene layer itself. Broadband high optical absorption can be realized by engineering the metal nanostructures, while maintaining insensitivity to the incident angle. Our results pave a new and promising way to enhance visible-light absorption in the graphene layer, which is potentially interesting for graphene-based photovoltaics.

Instabilities, solitons and rogue waves in -coupled nonlinear waveguides

Abstract: We considered the modulational instability of continuous-wave backgrounds, and the related generation and evolution of deterministic rogue waves in the recently introduced parity?time (𝒫𝒯)-symmetric system of linearly coupled nonlinear Schr?dinger equations, which describes a Kerr-nonlinear optical coupler with mutually balanced gain and loss in its cores. Besides the linear coupling, the overlapping cores are coupled through the cross-phase-modulation term too. While the rogue waves, built according to the pattern of the Peregrine soliton, are (quite naturally) unstable, we demonstrate that the focusing cross-phase-modulation interaction results in their partial stabilization. For 𝒫𝒯-symmetric and antisymmetric bright solitons, the stability region is found too, in an exact analytical form, and verified by means of direct simulations.

Improved decryption quality and security of a joint transform correlator-based encryption system

Abstract: Some image encryption systems based on modified double random phase encoding and joint transform correlator architecture produce low quality decrypted images and are vulnerable to a variety of attacks. In this work, we analyse the algorithm of some reported methods that optically implement the double random phase encryption in a joint transform correlator. We show that it is possible to significantly improve the quality of the decrypted image by introducing a simple nonlinear operation in the encrypted function that contains the joint power spectrum. This nonlinearity also makes the system more resistant to chosen-plaintext attacks. We additionally explore the system resistance against this type of attack when a variety of probability density functions are used to generate the two random phase masks of the encryption–decryption process. Numerical results are presented and discussed.

Superweak momentum transfer near optical vortices

Abstract: Near a vortex in a monochromatic light beam, the length of the local wavevector (phase gradient) can exceed the wavenumber in any of the plane waves in the superposition representing the beam. One way to detect these ‘superweak’ momenta could be by ‘superkicks’ imparted to a small particle located near the vortex, by absorbing individual large-momentum photons from the beam. A model for this process is a two-level atom with a transition resonant with the light beam. A semiclassical analysis shows that the momentum distribution of the atom is shifted by interaction with the vortex beam, by amounts that can almost reach the target superkicks and are usually greater than the momenta in the plane waves comprising the beam.

Optical proximity correction using a multilayer perceptron neural network

Abstract: Optical proximity correction (OPC) is one of the resolution enhancement techniques (RETs) in optical lithography, where the mask pattern is modified to improve the output pattern fidelity. Algorithms are needed to generate the modified mask pattern automatically and efficiently. In this paper, a multilayer perceptron (MLP) neural network (NN) is used to synthesize the mask pattern. We employ the pixel-based approach in this work. The MLP takes the pixel values of the desired output wafer pattern as input, and outputs the optimal mask pixel values. The MLP is trained with the backpropagation algorithm, with a training set retrieved from the desired output pattern, and the optimal mask pattern obtained by the model-based method. After training, the MLP is able to generate the optimal mask pattern non-iteratively with good pattern fidelity.

Optical rogue waves in the generalized inhomogeneous higher-order nonlinear Schrodinger equation with modulating coefficients

Abstract: Higher-order dispersive and nonlinear effects (alias the perturbation terms) such as third-order dispersion, self-steepening, and the self-frequency shift play important roles in the study of ultra-short optical pulse propagation. We consider optical rogue wave solutions and interactions for the generalized higher-order nonlinear Schrodinger (NLS) equation with space- and time-modulated parameters. An appropriate transformation is presented to reduce the generalized higher-order NLS equation to an integrable Hirota equation with constant coefficients. This transformation allows us to relate a certain class of exact solutions of the generalized higher-order NLS equation to the variety of solutions of the integrable Hirota equation. In particular, we illustrate the approach in terms of the two lowest-order rational solutions of the Hirota equation as seeding functions, to generate rogue wave solutions localized in time that have complicated evolution in space, with or without the differential gain or loss term. We simply analyze the physical mechanisms of the obtained optical rogue waves on the basis of these constraints. Finally, the stability of the obtained rogue wave solutions is addressed numerically. The obtained rogue wave solutions may raise the possibility of related experiments and potential applications in nonlinear optics and other fields of nonlinear science, such as Bose–Einstein condensates and ocean waves.

Electromagnetic rogue waves in beam–plasma interactions

Abstract: The occurrence of rogue waves (freak waves) associated with electromagnetic pulse propagation interacting with a plasma is investigated, from first principles. A multiscale technique is employed to solve the fluid Maxwell equations describing weakly nonlinear circularly polarized electromagnetic pulses in magnetized plasmas. A nonlinear Schr?dinger (NLS) type equation is shown to govern the amplitude of the vector potential. A set of non-stationary envelope solutions of the NLS equation are considered as potential candidates for the modeling of rogue waves (freak waves) in beam?plasma interactions, namely in the form of the Peregrine soliton, the Akhmediev breather and the Kuznetsov?Ma breather. The variation of the structural properties of the latter structures with relevant plasma parameters is investigated, in particular focusing on the ratio between the (magnetic field dependent) cyclotron (gyro-)frequency and the plasma frequency.

Elements of image processing in localization microscopy

Abstract: Localization microscopy software generally contains three elements: a localization algorithm to determine fluorophore positions on a specimen, a quality control method to exclude imprecise localizations, and a visualization technique to reconstruct an image of the specimen. Such algorithms may be designed for either sparse or partially overlapping (dense) fluorescence image data, and making a suitable choice of software depends on whether an experiment calls for simplicity and resolution (favouring sparse methods), or for rapid data acquisition and time resolution (requiring dense methods). We discuss the factors involved in this choice. We provide a full set of MATLAB routines as a guide to localization image processing, and demonstrate the usefulness of image simulations as a guide to the potential artefacts that can arise when processing over-dense experimental fluorescence images with a sparse localization algorithm.

Generation and interferometric analysis of high charge optical vortices

Abstract: We report on the generation of optical vortex beams using spatial phase modulation with spiral phase mirrors. The spiral phase mirrors are manufactured by direct machining with an ultra-precision single point diamond turning lathe. The imperfection of the machined phase mirrors and its impact on the generated vortex beams are analyzed with interferometric measurements. Our phase mirror has a surface roughness of 3 nm and a maximum peak–valley deviation of λ/30. The vortex charges of our light beams are directly verified by counting the fringes of their corresponding interferograms. We directly observed the successful generation of an optical vortex beam with a charge as high as 5050. We study the Fourier images of the vortex beams to characterize the quality of the beams. We obtained a conversion efficiency of 92.8% from a TEM00 beam to a vortex beam with charge 1020. This technique of generating optical singularities can potentially be used to produce more complex optical wavefronts, such as optical knots.

Experimental demonstration of the generation of the longitudinal E-field component on the optical axis with high-numerical-aperture binary axicons illuminated by linearly and circularly polarized beams

Abstract: We analytically and numerically show that by introducing asymmetry into axicon design it becomes possible to generate the longitudinal E-field component on the optical axis for linearly and circularly polarized incident beams. Binary axicons with high numerical aperture (NA) are fabricated in three configurations?axisymmetric and spiral, and bi-axicon?by electron beam lithography. Experimental measurements for the near-field diffraction of the most common and easy to implement incident beams?linearly and circularly polarized?are conducted. The experimental results agree with the theoretical analysis.

Single molecule localization microscopy for superresolution

Abstract: In recent years there has been a rash of developments in light microscopies circumventing traditional resolution limits associated with the diffraction of light occurring between the sample and the detector. Collectively, these techniques are referred to as 'superresolution' microscopies. One major family of superresolution techniques, variably referred to as PALM, FPALM and STORM, uses temporal control of the excited state of fluorophores to sequentially identify single non-overlapping emitters in time and space. Conventional images of single point emitters are fitted to sub-diffraction-limited areas, and a composite image is reconstructed from position data collected over many thousands of individual imaging frames. This paper provides a brief overview of superresolution microscopy, followed by a detailed discussion of STORM, including practical guidelines for sample preparation designed to help to make the technique more accessible to the non-specialist.