Linear Taper Research Articles

Nanofocusing in a metal–insulator–metal gap plasmon waveguide with a three-dimensional linear taper

The development of techniques for efficiently confining photons on the deep sub-wavelength spatial scale will revolutionize scientific research and engineering practices. The efficient coupling of light into extremely small nanofocusing devices has been a major challenge in on-chip nanophotonics because of the need to overcome various loss mechanisms and the on-chip nanofabrication challenges. Here, we demonstrate experimentally the achievement of highly efficient nanofocusing in an Au–SiO_2–Au gap plasmon waveguide using a carefully engineered three-dimensional taper. The dimensions of the SiO_2 layer, perpendicular to the direction of wave propagation, taper linearly below 100 nm. Our simulations suggest that the three-dimensional linear-tapering approach could focus 830 nm light into a 2 × 5 nm^2 area with ≤3 dB loss and an intensity enhancement of 3.0 × 10^4. In a two-photon luminescence measurement, our device achieved an intensity enhancement of 400 within a 14 × 80 nm2 area, and a transmittance of 74%.

Influence of Gravity and Taper on the Vibration of a Standing Column

AbstractThe stability and natural vibration of a standing tapered vertical column under its own weight are studied. Exact stability criteria are found for the pointy column and numerical stability boundaries are determined for the blunt tipped column. For vibrations we use an accurate, efficient initial value numerical method for the first three frequencies. Four kinds of columns with linear taper are considered. Both the taper and the cross section shape of the column have large influences on the vibration frequencies. It is found that gravity decreases the frequency while the degree of taper may increase or decrease frequency. Vibrations may occur in two different planes.

Seismic response of fractures by numerical simulation

SUMMARY Fractures occur on a wide range of scales and are important in the study of hydrocarbon reservoirs. Seismic simulation by finite-difference modelling using an equivalent medium method can devise the elastic parameters of a cell intersected by a fracture as those of a medium with an equivalent seismic response. Numerical experiments confirm that diffractions from the fracture tips are a strong component of the total wavefield. However, a comparison of boxcar, linear, angular and elliptic tapering suggests that there is little dependence on shape because the energy involved in a single diffraction is much lower than the incident energy. An open, fluid filled fracture has stronger effect on the wavefield than the wet and dry, multiple crack models, because an open fracture would have a stronger dissimilarity to the background rock. The density of microcracks within a fracture also has strong effect on the seismic response, however the properties of those cracks are not significant to the overall seismic response. Considering a distribution of a large number of fractures, even when the overall density of fractures is held constant, longer fractures attenuate seismic energy more than smaller ones. For the orientation effect, fractures oriented in the direction of propagation seem to affect the wavefield more than those perpendicular because of the incident wave striking the fracture at an angle greater than the critical angle. Experiments on clustering of the fractures indicate that although clusters which are large compared to the wavelength may attenuate and ‘shield’ more than for a uniform distribution, smaller ones in fact attenuate less, because of the ‘healing’ effect. These are important results when trying to characterize the fracture properties including density, clustering, size and orientation of a fractured reservoir from field seismic data.

Design of the Grand Touring sports car wing: geometric and aerodynamic twist

Wing twist gives the Grand Touring sports car an eye-catching ‘aerodynamic shape’. From the functional viewpoint, wing twist may improve downforce, provide stall control and enhance aerodynamic efficiency if the twist is optimised. This study aims, first, to explore the influence of linear geometric and aerodynamic twist upon spanwise upwash velocity, downforce and induced drag distributions and, second, to evaluate the use of optimum twist in achieving minimum induced drag while preserving high downforce, in wings with linear taper for the Grand Touring car. Baseline wing prototypes were designed and fitted, subsequently, with a Gurney flap and endplates to obtain complete wings. Aerodynamics for straight wings and wings with geometric, aerodynamic and optimised twist were computed using modified versions of the Prandtl’s Lifting-line Theory. Straight and geometrically-twisted wings with constituent NACA 651-412 airfoils present superior aerodynamic efficiency at angles of attack ≤ 1° and may be used as stabilisers on high-speed circuits. Geometric twisting elicits a partial, rather than complete, wing stall that contributes to safety in motor racing. A geometrically-twisted wing constructed with a NASA LS(1)-0413 airfoil yields high downforce at the expense of large induced drag via a double-peaked induced drag distribution, and it is suitable for high-downforce racing circuits. Nonetheless, the analysis suggests that a twist-optimised wing for the Grand Touring car very nearly duplicates the ideal aerodynamic performance of an elliptic wing and yields high downforce and minimum possible induced drag. The findings support the implementation of optimum wing twist at the conceptual stages of Grand Touring sports car design.

TE/TM-mode pass polarizers and splitter based on an asymmetric twin waveguide and resonant coupling

A new passive TE/TM-mode polarization filter for an InGaAsP/InP material system based on an asymmetric twin waveguide (ATG) and resonant coupling is investigated. Linear taper sections with different taper angles are introduced to couple between the two vertically separated waveguides. At a wavelength of 1.55 μm extinction ratios (ER) of 20 dB for the TE- and more than 10 dB for the TM-mode are reported for devices shorter than 400 μm. Furthermore we show, this concept can be expanded to a polarization splitter.

Fast and Accurate Array Calibration Using a Synthetic Array Approach

A new method for the calibration of arrays is presented that allows the simultaneous calibration of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> array elements. It comprises the measurement of the array output signal at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> phase settings applied to the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> elements involved in the calibration. These <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> phase settings correspond to a linear phase taper that is unique for each of the involved elements and reveals therefore <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> different phase tapers. The complex <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> measurements of the array signal are thought to be the excitation coefficients of a synthetic <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -element linear phased array. The array factor of this synthetic <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -element array comprises a superposition of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> +1 array factors all pointing with their main beam into different directions. By converting this superposition of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> +1 array factors into a set of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> +1 simultaneous linear equations, the signals of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> individual elements to be calibrated including the combined signal contribution of the static elements, can be solved by standard matrix inversion techniques. Computer simulations are presented to demonstrate the capabilities of the new calibration method.

Power aware channel width tapering of serially connected MOSFETs

In this paper a new transistor channel width tapering scheme called Hill tapering for FET chains is proposed with specific emphasis on power dissipation and layout area of the tapered chains. This tapering scheme results in the lowest power dissipation and physical area compared to any of the existing tapering schemes like linear, exponential or optimal tapering. It also offers high speed operation. The proposed scheme is general and can be used in all domino logic circuit designs. SPICE simulation results have shown that up to 81% power dissipation reduction could be achieved by using the proposed tapering scheme.

Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy

The two-way insertion loss of a 1 m length of waveguide was reduced by nearly 5 dB over a 4% bandwidth at W-band (94 GHz) for an electron paramagnetic resonance (EPR) spectrometer relative to WR10 waveguide. The waveguide has an oversize section of commercially available rectangular WR28 and a novel pair of tapers that vary in cross section with axial position according to a hyperbolic-cosine (HC) function. The tapers connect conventional rectangular WR10 waveguide to the WR28. For minimum loss, the main mode electric field is parallel to the long side of the WR28. Using mode coupling theory, the position of maximum flare (inflection point) in the taper was optimized with respect to the coupling to higher order modes and the reflection of the main mode. The optimum inflection point position is about one-tenth of the taper length from the small end of the taper. Reflection and coupling were reduced by about 20 dB relative to a pyramidal (linear) taper of the same length. Comb-like dips in the transmission coefficient produced by resonances of the higher order modes in the oversize section were about 0.03 dB. Specially designed high-precision, adjustable WR28 flanges with alignment to about 5 μm were required to keep higher order mode amplitudes arising from the flanges comparable to those from the HC tapers. Minimum return loss was about 30 dB. This paper provides a foundation for further optimization, if needed. Methods are not specific to EPR or the microwave frequency band.

Study on inverse taper based mode transformer for low loss coupling between silicon wire waveguide and lensed fiber

We have simulated the coupling loss of three types of Inverse Taper and taper-lensed fiber using three dimensional (3D) semi-vectorial beam propagation methods (BPM) respectively. Our results showed that the performances of exponential inverse taper and quadratic inverse taper were better than the commonly used linear inverse taper. Especially, for TM mode the improvement in the reduction of devices size is 53% and 136% for exponential and quadratic inverse taper compared with the linear inverse taper.

Compact Single-Mode Silicon Hybrid Rib/Strip Waveguide With Adiabatic Bends

We report a low-loss, hybrid silicon waveguide geometry that consists of straight rib sections with a propagation loss of 0.27 ± 0.012 dB/cm and compact photonic wire bends. The rib and wire waveguides are both single mode and connected through a short double-etched linear taper section. To reduce bend losses, circular bends were combined with variable adiabatic seminatural spline shapes with only a limited footprint penalty.

A broadband Fabry–Pérot cavity antenna designed using an improved resonance prediction method

AbstractWe have proposed a wideband Fabry–Pérot cavity (FPC) base station antenna for wireless broadband Internet (WiBro) service in Korea. To widen the radiation bandwidth of our antenna, unit cells printed on a superstrate have been gradually tapered according to a proposed linear tapering equation. Also, all openings in the lateral directions have been enclosed using four metallic sidewalls to enhance the overall performance of the antenna by reducing unnecessary wave leakage. Furthermore, the radiation aperture has been designed in a rectangular shape to create sharp and sectoral beam shapes in the elevational and azimuthal directions, respectively. For a more accurate determination of the FPC resonance, an improved prediction formula has been used. We have demonstrated the basic principle of bandwidth widening using higher mode behavior, which appears at a higher frequency region by means of tapered cells on the superstrate. In addition, to show the effectiveness of simple tapering of unit cells, we have compared the performance of two antennas covered with the tapered and uniform (nontapered) superstrate. Tapering the unit cells has expanded the fractional radiation bandwidth about four times wider than that of the antenna using uniform unit cells. The measured behaviors of our antenna are in good agreement with the simulated data, which confirms the validity of our design and analysis approach. The measured behaviors of our antenna are in good agreement with the simulated data, which confirms the validity of our design and analysis approach. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1065–1069, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25898

A Loaded Wideband Linearly Tapered Slot Antenna With Broad Beamwidth

A novel wideband linearly tapered slot antenna (LTSA) with broad beamwidth is presented. In the proposed design, the basic microstrip-fed LTSA is loaded with a joint action structure (JAS) comprising tapered slots and patches. Compared to the basic unloaded version, the loaded LTSA (LLTSA) exhibits improved impedance characteristic in the lower band. Additionally, broad beams in principal planes, moderately high front-to-back (F/B) ratio, and improved gain are also obtained. Simulation and measurement results reveal that the proposed LLTSA can provide an impedance bandwidth of 66%, while a pattern bandwidth of 35% and more than 117° 3-dB beamwidths of E-plane and H-plane patterns in that band are also achieved.

Method for improving the spectral flatness of the supercontinuum at 1.55μm in tapered microstructured optical fibers

We propose a method for enhancing the flatness of a supercontinuum centered at 1.55 $\ensuremath{\mu}$m by the use of specially designed tapered microstructured optical fibers (MOFs). Based on the procedure presented one can determine the linear taper profile parameters and the optimum launching conditions needed to achieve the broadest supercontinuum spectra (SC) and the best spectra flatness. We quantify the maximally broad and flat SC using the calculated standard deviation of the spectra at the required wavelength range and show that it is possible to obtain significantly better results than those obtained by using an untapered fiber.

Broadband coupler between silicon waveguide and hybrid plasmonic waveguide

Efficient broadband coupling of light between a dielectric waveguide and a hybrid plasmonic waveguide is investigated theoretically. A plasmonic linear taper is used as a coupler which connects the two types of waveguides. Broadband coupling is realized by such a compact plasmonic taper with a length of only 0.4 microm, which achieves a coupling efficiency of 70% (1.5 dB) at the 1.55 microm telecommunication wavelength.

Tapered plasma channels to phase-lock accelerating and focusing forces in laser-plasma accelerators

Tapered plasma channels are considered for controlling dephasing of a beam with respect to a plasma wave driven by a weakly relativistic, short-pulse laser. Tapering allows for enhanced energy gain in a single laser-plasma accelerator stage. Expressions are derived for the taper, or longitudinal plasma density variation, required to maintain a beam at a constant phase in the longitudinal and/or transverse fields of the plasma wave. In a plasma channel, the phase velocities of the longitudinal and transverse fields differ and, hence, the required tapering differs. The length over which the tapered plasma density becomes singular is calculated. Linear plasma tapering as well as discontinuous plasma tapering, which moves beams to adjacent plasma wave buckets, is also considered. The energy gain of an accelerated electron in a tapered laser-plasma accelerator is calculated and the laser pulse length to optimize the energy gain is determined.

Enhanced Transmission in a Fiber-Coupled Au Stripe Waveguide System

We experimentally demonstrated the enhanced transmission in a fiber-coupled Au stripe waveguide system using a linearly tapered (LT) structure at a telecommunication wavelength of 1.55 ?m. The LT structure consists of two 100- ?m-long tapered regions connecting various widths of input and output waveguides with a waist region. The lowest insertion loss of the 1-cm-long LT-Au stripe waveguide is ~ 4.3 dB, when it has 6-?m -wide input and output waveguides and a 4- ?m-wide waist waveguide. The insertion loss is reduced by ~ 2 dB compared to the 4-?m-wide and 1-cm-long straight Au stripe waveguide, which is achieved by decreasing the coupling loss. The losses of the LT region, which has a tapered angle of less than 0.3° between the input-output waveguides and the waist waveguide, are smaller than 0.4 dB. We showed that the insertion loss of the Au stripe waveguide can be reduced by introducing the LT structure, which can also provide efficient mode conversion.

Surface characteristics generated in CNC chip breaking tool paths

One method for creating broken chips in turning processes involves oscillating the cutting tool in the feed direction utilizing the CNC machine axes. Using computer simulations it is possible to combine the motion of the axes with the geometry of the cutting tool to predict the surface characteristics, mapping surface parameters for a wide range of chip breaking situations. These data allow the selection of chip breaking cutting parameters to simultaneously ensure broken chips, and acceptable surface characteristics. This paper describes the computational method, and presents results of comparison for cutting tests using single axis, linear taper and outer contouring motions.

Computer Simulations Assessing the Potential Performance Benefit of a Final Increase in Training During Pre-Event Taper

A nonlinear model of training responses was utilized to test whether a 2-phase taper could be more effective than a traditional linear taper. Simulations were conducted using model parameters previously determined in 6 nonathletes trained on a cycle ergometer (non-ATH) and 7 elite swimmers trained in sport-specific conditions (ATH). Linear and 2-phase tapers were compared after a 28-day overload period at 120% of normal training. The 2-phase taper was assumed to be identical to the optimal linear taper, except for the final 3 days during which the training load was varied to maximize the final performance. The optimal linear taper was characterized by a mean training reduction by 32 +/- 6% during 35 +/- 6 days in non-ATH and by 49 +/- 18% during 33 +/- 16 days in ATH. The last 3 days of the 2-phase taper were characterized by a significant increase in training load by 23 +/- 18% in non-ATH and 29 +/- 42% in ATH (p < 0.005). The optimal taper characteristics were not statistically different between non-ATH and ATH. The maximal performance reached with the 2-phase taper was higher by 0.04 +/- 0.02% in non-ATH and 0.01 +/- 0.01% in ATH than with the optimal linear taper (p < 0.001). Positive and negative influences of training on performance were estimated as indicators of adaptation and fatigue, respectively. The negative influence was completely removed during both tapers, whereas the positive influence was slightly further enhanced during the 2-phase pattern. In conclusion, simulations showed that a 20 to 30% increase in training at the end of the taper, as compared to a prolonged reduction in training, allowed additional adaptations without compromising the removal of fatigue.

Fabrication and performance-analysis of a planar silica-based cascaded symmetric Y-branch 1 × 8 optical power splitter

Fabrication of a planar silica-based cascaded symmetric Y-branch 1 × 8 optical power splitter is described in this study. Post-fabrication, thorough analysis of device-performance is presented in terms of insertion loss, non-uniformity and polarization-dependent loss. The fabricated device is designed based on cascaded Y-branching waveguide, comprising of a linear taper and symmetric S-bend arc branching waveguides. The simulated values of the average insertion loss, non-uniformity and polarization-dependent loss at the wavelength of 1550 nm are found to be 9.37 dB, 0.35 dB and 0.04 dB respectively. However, the above parameters have been measured to be around 17.5 dB, 1.5 dB and 1.8 dB respectively, for the fabricated device at that wavelength. Measured parameters are compared with the simulated results over a wavelength region of C & L band range. Some preventive points to minimize the deviation of the measured values of the parameters from those of the simulated results are also discussed.

Geometric strategies for attainment of identical outflows through all of the exit ports of a distribution manifold in a manifold system

The focus of this investigation is to identify strategies whose application is capable of perfecting manifold design to achieve the same rate of mass outflow through each of the exit ports of a distribution manifold. A quantitative systematic study based on numerical simulation is performed in which each of eight proposed strategies is evaluated with regard to its capability for producing the same per-exit-port mass outflow. Each of the strategies is geometric in nature and is characterized by geometrical parameters which can be varied systematically in order to attain outflow uniformity. A quantitative metric, the standard deviation from uniformity of the individual outflows through the exits of the distribution manifold, was used to identify the degree of mass outflow uniformity that was achieved by the use of the various parameter values which characterize each strategy. The end result of the study is the identification of the certain strategies that are most effective for the attainment of the goal of outflow uniformity. These are: (a) enlargement of the cross-sectional area of the distribution manifold (Section 4.1), (b) variation of the cross-sectional areas of the outflow channels (Section 4.5), (c) linear tapering of the cross-sectional area of the distribution manifold, and (d) non-linear tapering of the cross-sectional area of the manifold by means of quarter-elliptical contouring of the manifold wall (Section 4.3).