Poynting Vector Distribution Research Articles

Dipole and quadrupole surface plasmon resonance contributions in formation of near-field images of a gold nanosphere

AbstractMultipolar plasmon optical excitations at spherical gold nanoparticles and their manifestations in the particle images formatted in the particle surface proximity are studied. The multipolar plasmon size characteristic: plasmon resonance frequencies and plasmon damping rates were obtained within rigorous size dependent modelling. The realistic, frequency dependent dielectric function of a metal was used. The distribution of light intensity and of electric field radial component at the flat square scanning plane scattered by a gold sphere of radius 95 nm was acquired. The images resulted from the spatial distribution of the full mean Poynting vector including near-field radial components of the scattered electromagnetic field. Monochromatic images at frequencies close to and equal to the plasmon dipole and quadrupole resonance frequencies are discussed. The changes in images and radial components of the scattered electromagnetic field distribution at the scanning plane moved away from the particle surface from near-field to far-field region are discussed.

An Estimation Method of Poynting Vector with Near-Magnetic-Field Measurement

A new technique to estimate the Poynting vector distribution from near-magnetic-field measurement is proposed. To calculate the Poynting vector, both electric and magnetic field should be known. In the proposed method, only magnetic-field measurement of three orthogonal axes is required. Electric field is estimated from the measured magnetic field by using the Maxwell's equation. The modified Yee cell is employed to estimate electric field from the measured magnetic field. Finally, the Poynting vector is calculated from the measured magnetic field and the estimated electric field. Since the proposed method enables us to understand propagation direction of electro-magnetic energy, it can be utilized to locate an emission source and to investigate a mechanism of undesired emission. Experiments are carried out to discuss the accuracy and to validate practical usefulness.

Power splitter based on cascaded multimode photonic crystal waveguides with triangular lattice of air holes

We propose a power splitter based on two-dimensional photonic crystals with triangular lattice of air holes. The structure can be divided into three sections consisting of the input waveguide, area-defect regions, and output waveguides. The operational principle of the splitter is that an incident field in the frequency range of interest is split into a twofold mode pattern with small distance in the first area-defect and then one of which is shifted by the secondary area-defect regions to output port. We optimize the size of area-defects for the mode-splitting and the shifting from the numerical analysis of distribution of time-averaged Poynting vectors by a finite-difference time domain method. And the transmittance over 45% per each output with a bandwidth about 0.06 a/ λ is achieved.

Measurement of Transport Current Losses in HTS Conductors With Large Current Capacity by Using HTS Current Transformer

In order to evaluate the transport current loss characteristics in HTS conductors with large current capacity, we developed a new compact measurement system. This system enables us to measure the transport current losses electrically in the straight HTS conductors with the current capacity of 1 kA class by using the small capacity AC power supply of about 50 A. In this system, an HTS current transformer is used to feed current to the sample conductor for the measurement. The secondary current of this current transformer can be induced at about 1 kA at 77 K when the primary current is 40 A. The current transformer is made very compactly, and the externals size is 70 mm in diameter, and 110 mm in length. The sample conductor is connected with the secondary coil of this current transformer. The loss measurement is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both a potential lead and a pickup coil. To confirm the validity of this measurement system, we measured the transport current losses in an HTS conductor. As a sample conductor, we used a parallel conductor composed of 16 Ag-sheathed Bi-2223 multifilamentary tapes. The obtained results showed that this compact system was useful for measuring AC loss characteristics of large scale HTS conductors.

A Quench Monitoring System of Superconducting Coils by Using the Poynting Vector Method

A new quench monitoring system by using the Poynting vector method was proposed. This new system can indirectly detect normal transitions which are suddenly induced during an operation of superconducting coils. In this system, the superconducting coil is surrounded by the thin metallic cylinder composed of several pieces, where the cylinder is electrically insulated from the coil; potential leads to measure local electric fields are directly attached to this cylinder surface and pickup coils to measure local magnetic fields are put on the surface. The Poynting vector distribution around the coil can be obtained by using many sets of both the potential lead and the pickup coil. Since sudden changes of energy flow profiles around the superconducting coil are induced in the event of local normal transitions of the coil winding, such an event of coils can be detected by the change of the Poynting vector. This system has no risk of the destructive voltage breakdown which may happen in case of the existing balance voltage method, because there is no need of direct contacts on the coil windings. In addition, this method is expected to be higher reliability and sensitivity than the acoustic emission method. A demonstration test was carried out of monitoring the quench for the Bi-2223 coil partially immersed in liquid nitrogen, and a sign of normal transitions before the quench was successfully detected by this method.

Surface plasmons in layered structures with semiconductor and metallic films

The complete spectrum of eigenwaves including surface plasmon polaritons (SPP), dynamic (bulk) and complex waves in the layered structures containing semiconductor and metallic films has been explored. The effects of loss, geometry and the parameters of dielectric layers on the eigenmode spectrum and, particularly, on the SPP modes have been analysed using both the asymptotic and rigorous numerical solutions of the full-wave dispersion equation. The field and Poynting vector distributions have been examined to identify the modes and elucidate their properties. It has been shown that losses and dispersion of permittivity qualitatively alter the spectral content and the eigenwave properties. The SPP counter-directional power fluxes in the film and surrounding dielectrics have been attributed to vortices of power flow, which are responsible for the distinctive features of SPP modes. It has been demonstrated for the first time that the maximal attainable slow-wave factor of the SPP modes guided by thin Au films at optical frequencies is capped not by losses but the frequency dispersion of the actual Au permittivity.

Optical and polarization phase manipulation of diffraction from grating nanostructure at excited waveguide resonance

Resonant grating-waveguide structures can exhibit far field intensity spectra with narrow bandwidth around predefined wavelengths. In this paper we studied the spatial electromagnetic field distribution along with the Poynting vector distribution in the various layers of a resonant grating-waveguide structure, when it is subjected to polarization phase and polar and azimuth angle manipulation. It was found that there exists correlation of the confinement properties including the guided modes available and the evanescent field profile with the reflection and transmission efficiencies, as well as the polarization. A zero waveguide mode (TE 0 like) exists at (nearly) normal incidence. However, for incidence in conical mounting the confinement is similar to that of first waveguide mode (TE 1 like), and its confinement is not efficient which is correlated to the bandwidth. The refractive index of grating lines also essentially affects the resonance properties. Numerical dependence of the peak wavelength on the index is parabolic like.

Structure of image fields in an aplanatic optical system with coherent point source illumination

Using the vector Fourier transform and stationary phase method, an integral representation of the structure of image field in an aplanatic system with polarized point source located at arbitrary position on the optical axis is obtained. Effects of wide aperture angle in object space on the structure of image field are examined numerically for the case of linearly polarized illumination. Simulation calculations show that, in a plane perpendicular to the optical axis, if the object space aperture angle is wide, the distribution of magnetic field will not be identical to that of electric field after they are rotated 90° around the optical axis with respect to each other, the contours of distribution of the electric and magnetic energy densities and the Poynting vector are approximately elliptical, and the object space aperture angle is the dominant factor that makes the distribution of Poynting vector lose circular symmetry. At the same time, the major axis of the contour of distribution of the electric energy density is perpendicular to the direction of the electric vector in the object space when using small image aperture angle, and will turn graduately to the same direction as the electric vector in the object space with the increase of image aperture angle. These conclusions are completely different from the predications of the previous theory.

Application of the fast-Fourier-transform-based volume integral equation method to model volume diffraction in shift-multiplexed holographic data storage

Numerical simulation of diffraction on thick holographic gratings in shift-multiplexed optical data storage application is presented. The grating is generated by the interference of a spherical reference wave and a plane signal wave corresponding to a single pixel of the input data page. To describe diffraction on this weak-index-modulated grating, we use the volume integral equation in the first Born approximation. This description yields a convolution integral that can be efficiently evaluated by a 3D fast Fourier transform (FFT) technique. For a 51.2 microm recording layer thickness, a serial-divided single personal computer code was built based on parallel FFT coding principles. Diffracted electric field and Poynting-vector distributions are calculated for probe beams spatially shifted with respect to the reference beams. The shift selectivity curves show significant differences from previous analytical calculations based on paraxial propagation and infinite gratings, as they have monotonic decrease in all three directions instead of sinclike functions with Bragg nulls. With the chosen numerical aperture of 0.6 and linear polarization, both the scalar and vector calculations provided similar results within 5%.

Three-Dimensional Finite-Difference Time-Domain Simulation of Optical Absorption Properties of Al–N Films with Mesoscopic Surface Roughness

Incompletely nitrided sputtered aluminum (Al–N) films with mesoscopic surface roughness have a promising function of high solar absorptance [T. Ishiguro et al.: Jpn. J. Appl. Phys. 41 (2002) 292]. In this paper, we present an application by three-dimensional finite-difference time-domain (FDTD) method to the simulation of the optical properties of Al–N films. From the observed data, the optical and structural parameters of the specimen are determined. The simulation reproduces the systematic changes in the surface roughness dependences of absorptance and reflectance. The evaluated distribution of the local Poynting vector shows the refraction effect at the slope of protuberances on a rough surface. Additionally, energy absorption mainly takes place at the surface skin depth. As a result, it is confirmed that the FDTD method is useful for understanding local optical behavior in specimens with mesoscopic surface roughness.

Theoretical analysis of feedback mechanisms of two-dimensional finite-sized photonic-crystal lasers

Theoretical investigations are carried out for close-to-lasing two-dimensional finite-sized photonic crystals with active (gain) lattice points. First, laser oscillations with lower thresholds are found to occur near the photonic band edges where optical gain is enormously intensified. For several modes isolated around the band edge, the field-intensity spectra in reciprocal space and the Poynting-vector distributions in real space are investigated in detail in close-to-lasing photonic crystals. By comparing the phenomena that occur in photonic crystals with a symmetric or an asymmetric outward form, this paper clarifies the differences in the feedback mechanisms of these crystals. In a symmetric photonic crystal, laser oscillation occurs through the waves propagating along the straight passages. This feedback is basically the same as that of ordinary one-dimensional lasers, although it exhibits a complicated behavior that light waves propagating in a variety of directions interfere with each other. In an asymmetric photonic crystal, laser oscillation occurs through the waves circulating within the crystal, which could be called recurrent-photon feedback. This feedback, however, can be construed as an extension of the feedback in ordinary one-dimensional distributed-feedback lasers.

Electromagnetic distributions demonstrating asymmetry using a spectral-domain dyadic Green's function for ferrite microstrip guided-wave structures

An anisotropic dyadic Green's function is used in a theoretical formulation for finding the behavior of the surface currents and electromagnetic fields of nonreciprocal structures. Dispersion diagrams, surface current, magnetic- and electric-field distributions, and Poynting-vector distributions are then found for microstrip structures containing a multilayered medium including a ferrite material layer. Such structures can variously be used as isolators, magnetostatic wave generators, or other devices relying upon nonreciprocal action. Calculations are done using a fast solver anisotropic Green's function spectral-domain computer code. Asymmetry in the surface current, electric and magnetic fields, and Poynting-vector distributions is found, demonstrating explicitly the effect of the nonreciprocity of the ferrite layer.

The near-field power density distribution characteristics for different types of optical fiber probes

When the mechanism of near-field photolithography is analyzed, the most important work is the near-zone field analysis of the optical fiber probe. In this paper, the electromagnetic theory for near-field radiation using the magnetic current and electric current as sources is adopted as the model of the near-field optics. By applying this theorem, the near-field distribution characteristics of the uncoated probe and metal-coated probe are explored. Furthermore, the simulations of the near-field for different light source, such as parallel beam of light (plane wave) and Gaussian-distributed light passing through the optical fiber probe are also discussed. Based upon the model of this research, the time-average Poynting vector distribution of the radiation field, and the relationship between the power density and near-field distance for the optical fiber probe can be estimated. According to the results, when the near-field distance between the metal-coated probe and sampling is maintained at 0.3ρ0≤Z≤0.6ρ0, the process is proved to be more adequate for the near-field photolithography. Meanwhile, from the analysis of the near-field power density distribution, it provides an evaluation of concentration of photo active compound (PAC) in the photoresist after exposure and contour after development. The relationship between the power density and near-field distance can be used as a rule of tip-sampling distance modulation when controlling the magnitude of exposure energy. This near-field photolithography engineering perplexity encountered can therefore be solved.

An optical vortex as a rotating body: mechanical features of a singular light beam

With an example of the Laguerre–Gaussian LG01 mode we show that the free-space evolution of a vortex light beam can be interpreted as the mechanical motion of a 'body' whose density is determined by the mass equivalent of the beam energy. As mechanical attributes, this 'body' possesses angular velocity and moment of inertia, in addition to the common orbital angular momentum. The beam 'body' is not rigid and its radial layers glide with respect to each other analogous to the motion occurring in fluid vortices. Absolute values of the layer velocities agree with the energy transfer rates following from the consideration of the Poynting vector distribution.

Pairing an epsilon-negative slab with a mu-negative slab: Resonance, tunneling and transparency

Here, we analyze the transverse-magnetic (TM) wave interaction with a pair of slabs, one being an epsilon-negative (ENG) layer in which the real part of permittivity is assumed to be negative while its permeability has positive real part, and the other being a mu-negative (MNG) layer that has the real part of its permeability negative but its permittivity has positive real part. Although the wave interaction with each slab by itself has predictable features, we show that the juxtaposition and pairing of such ENG and MNG slabs may, under certain conditions, lead to some unusual features, such as resonance, complete tunneling, zero reflection and transparency. The field distributions inside and outside such paired slabs are analyzed, and the Poynting vector distributions in such structures are studied. Using equivalent transmission-line models, we obtain the conditions for the resonance, complete tunneling and transparency, and we justify and explain the field behavior in these resonant paired structures. Salient features of the tunneling conditions, such as the roles of material parameters, slab thicknesses, dissipation, and angle of incidence are discussed. The analogy and correspondence between the ENG-MNG pair and the pair of a slab of conventional material juxtaposed with a "double-negative" medium is also discussed. Finally, a conceptual idea for a potential application of such a "matched" lossless ENG-MNG pair in "ideal" image displacement and image reconstruction is proposed.

A cavity-backed rectangular aperture antenna with application to a tilted fan beam array antenna

A rectangular aperture of A/sub x//spl times/A/sub y/, cut in the top conducting plate of a triplate transmission line and backed by a cavity, radiates a tilted beam off the direction normal to the aperture. The mechanism of the radiation is explained using the Poynting vector distribution above the aperture and the phase distribution of the electric field over the aperture. The tilt angle is calculated as a function of side length A/sub x/ for a representative value of A/sub y/=18 mm=0.747/spl lambda//sub 12.45/, where /spl lambda//sub 12.45/ is the wavelength at a test frequency of 12.45 GHz. A tilted beam of approximately 27/spl deg/ is realized at A/sub x//A/sub y/=8/9 with a gain of approximately 8 dB. Using this value of A/sub x//A/sub y/, an array antenna composed of rectangular cavity-backed aperture elements is investigated. The array forms a tilted fan beam without phase shifters. The frequency responses of the gain and input impedance are discussed.

On the physical meaning of nonactive powers in three-phase systems

This letter presents three-dimensional graphs of the Poynting vector distribution surrounding a three-phase line. Such displays help engineering students understand the physical mechanism of electric energy transmission and its separation in active and nonactive components.

FDTD analysis and measurement of aperture antennas based on the triplate transmission-line structure

First, two aperture antennas designated as P-type and C-type antennas are analyzed using the finite-difference time-domain (FDTD) method. Each antenna is made of a triplate transmission line (TTL). A square aperture is cut out of the top plate of the TTL for both antennas to allow radiation. The bottom of the TTL is a planar plate for the P-type antenna and a plate with a hollow cavity for the C-type antenna. The power flow is expressed using Poynting vectors. It is revealed that parallel-plate mode power in the TTL is lower in the C-type antenna, compared with that in the P-type antenna. Second, an array antenna composed of two C-type elements is analyzed. The Poynting vector distribution in the aperture is found to remain almost unchanged when the element spacing is varied. The input impedance of the array antenna converges at an element spacing of approximately 0.9 wavelength. The theoretical radiation patterns are in good agreement with measured data.

Zero infrared reflectance anomaly in doped silicon lamellar gratings. III. Electric field phase and energy flux distributions across the grating profile

Spatial (in-depth by lateral) electric field phase and Poynting vector distributions inside zero-reflectance binary lamellar gratings in variously doped n-Si irradiated by a normally incident TE polarized plane electromagnetic wave of wavelength 10.6 μm are studied. The electric field phase distribution surfaces for such gratings in dielectric-like Si up to the uppermost lossy case appear to have a channel with abrupt vertical walls formed by π to −π jumps of the electric field phase. For the gratings in metallic-like Si it is shown that the normal component of the Poynting vector vanishing in the grating line achieves a relatively large (as compared to a grating with the same doping but a high reflectance) negative value in the grating groove center. Such a flux confinement supports the idea of a cavity-resonance nature of the total absorption.

Numerical Analysis of the Near-field Diffraction Pattern of a Small Aperture

Abstract We show the three-dimensional (3-D) distribution of the time-averaged Poynting vector in the near-field of a small aperture (radius < λ) using Bethe's diffraction theory. Our numerical calculation shows that the characteristic of the near-field diffraction depends on the incident angle of the beam on the aperture. Specifically, the near-field diffraction corresponding to the normal incident has a quite different character than that of the oblique incident. We also discuss the variation of the propagation of the time-averaged Poynting vector with the aperture size, the wavelength and the distance from the aperture.