Showing papers on "Bend radius published in 2008"

Transformation-optical design of adaptive beam bends and beam expanders

Abstract: We describe the design of adaptive beam bends and beam splitters with arbitrary bend and split angles by use of finite embedded coordinate transformations. The devices do not exhibit reflection at the entrance or exit surfaces. It is shown that moderate and practically achievable values of the relative permittivity and permeability can be obtained for beam bends and splitters with both small and large bend radius. The devices are also discussed in the context of reconfigurable metamaterials, in which the bend and split angles can be dynamically tuned. The performance of adaptive beam bends and splitters is demonstrated in full wave simulations based on a finite-element method. Furthermore, the design of an adaptively adjustable transformation-optical beam expander/compressor is presented. It is observed that a pure transformation-optical design cannot result in a reflectionless beam expander/compressor.

Theoretical modelling of a bi-dimensional U-shaped surface plasmon resonance based fibre optic sensor for sensitivity enhancement

Abstract: Theoretical analysis of a surface plasmon resonance based fibre optic sensor with a uniform semi-metal coated U-shaped probe is carried out using a bi-dimensional model. All the rays of the p-polarized light launched in the fibre and their electric vectors are assumed to be confined in the plane of bending of the U-shaped probe. The effect of the bending radius of the probe on the sensitivity of the sensor is studied. The study shows that as the bending radius of the probe decreases the sensitivity of the sensor increases. For the light launching conditions used, the maximum sensitivity achieved is several times more than that reported for a fibre optic tapered probe. In addition to high sensitivity, the most advantageous feature of a U-shaped probe is that it can be used as a point sensor.

Optical fiber fanout devices and methods for forming the same

Abstract: Optical fiber fanout devices include a housing having a fiber telescoping cavity therein. An optical fiber tubing receiving opening in the housing extends to the fiber telescoping cavity. The optical fiber tubing receiving opening is configured to secure a plurality of optical fiber tubes therein. An optical fiber receiving opening in the housing also extends to the cavity. The optical fiber receiving opening is displaced from the optical fiber tubing receiving opening by a distance selected to define an arc for an optical fiber extending from the optical fiber receiving opening to the optical fiber tubing receiving opening that exceeds a minimum bend radius for the optical fiber.

Dependence of the critical current of YBa2Cu3O7−δ coated conductors on in-plane bending

Abstract: A new method to measure the effect of in-plane bending on the critical current of YBa2Cu3O7−δ coated conductors is presented. Such a bending mode can be important in transmission cables, saddleback magnets, and double-pancake windings. A linear strain distribution over the width of the conductor develops in this bending mode, where one half of the conductor is under axial compressive strain and the other half is under axial tensile strain. A reversible reduction in critical current of up to 5% is measured in 4 mm wide conductors at a critical bending radius of 0.25–0.28 m. The critical current degrades irreversibly for bending radii less than this because the strain at the edge of the conductor that is under tension irreversibly damages the conductor. The results are described by use of a model that calculates the critical current as a function of in-plane bending radius by taking into account the strain gradient over the width of the sample and the measured dependence of the critical current on axial strain. A similar approach can be used to calculate the degradation of the critical current n of other deformation modes, such as torsion, or other more complex geometries.

Volume reflection dependence of 400 GeV/c protons on the bent crystal curvature.

Abstract: The trend of volume reflection parameters (deflection angle and efficiency) in a bent (110) silicon crystal has been investigated as a function of the crystal curvature with 400 GeV/c protons on the H8 beam line at the CERN Super Proton Synchrotron. This Letter describes the analysis performed at six different curvatures showing that the optimal radius for volume reflection is approximately 10 times greater than the critical radius for channeling. A strong scattering of the beam by the planar potential is also observed for a bend radius close to the critical one.

Bending loss analyses of photonic crystal fibers based on the finite-difference time-domain method

Abstract: This is a report on an effective simulation method for the bending loss analyses of photonic crystal fibers. This method is based on the two-dimensional finite-difference time-domain algorithm and a conformal transformation of the refractive index profile. We observed the temporal dynamics of light waves in a bent fiber in a simulation and obtained the bending loss as a function of bend radius and optical wavelength for the commercial photonic crystal fibers. The accuracy of this method was verified by good agreement between the simulation and experimental data.

Large-mode-area optical fibers with reduced bend distortion

Abstract: In a LMA optical fiber the index of the core region is graded (i.e., as viewed in a radial cross-section) and has a grading depth of Δn g , as measured from a central maximum at or near the axis to a lower level that is not greater than the central maximum and not less than the index of the cladding region. When the fiber is to be bent at a bend radius, the grading depth, the radius of the core region, and the difference between the central maximum index and the cladding region index are configured to reduce bend distortion. They may also advantageously be configured to maximize the effective mode-field area of the fundamental mode, suppress higher order modes, and reduce bend loss. In a preferred embodiment, the core region includes a centralized gain region, which in turn includes a dark region that is no more than 30% of the area of the gain region. Also described is a method of making such LMA fibers.

Cable manager including nestable radius limiter

Abstract: A cable radius limiter having a radius limiting surface that prevents damage to cables due to excessive bending. The cable radius limiter includes mounting structure and cable retaining structure arranged such that the limiter can be operably oriented and mounted to a mounting bracket in both a first mounting orientation and a second mounting orientation. Two radius limiters can be mounted together to form a cable spool.

Micro-structured fiber profiles for mitigation of bend-loss and/or mode distortion in LMA fiber amplifiers, including dual-core embodiments

Abstract: An apparatus and method for compensating for mode-profile distortions caused by bending optical fibers having large mode areas. In various embodiments, the invention micro-structures the index of refraction in the core and surrounding areas of the inner cladding from the inner bend radius to the outer bend radius in a manner that compensates for the index changes that are otherwise induced in the index profile by the geometry and/or stresses to the fiber caused by the bending.

Bend performance of leakage channel fibers.

Abstract: Bend loss of the first three modes of leakage channel fibers with various designs are studied using finite element method. It is found that very low bend loss at small bend radius can be achieved with large d/Λ. It is also found that best differential mode loss is achieved at large bend radius. It is further found that 2nd order mode loss becomes 9.1 times of fundamental mode loss at small bend radius for the bend orientation where the bending plane crosses centers of two holes and independent of d/Λ. Bend loss dependence of bend orientations are also studied. Excellent agreement between experiment and simulation is obtained.

Suppression of higher-order modes by resonant coupling in bend-compensated optical fibers

Abstract: The effect of bending is anticipated in an optical fiber design, so that resonant coupling remains an effective strategy for suppressing HOMs. The index profile of the fiber and its bend radius are configured so that there is selective resonant coupling of at least one HOM, but not the fundamental mode, in the bent segment of the fiber. In an illustrative embodiment, the core and cladding regions are configured to support the propagation of signal light in a fundamental transverse mode and at least one higher-order transverse mode in the core region. The cladding region includes an outer cladding region and an annular trench region. The trench region includes at least one axially extending, raised-index pedestal (waveguide) region having a refractive index higher than that of the outer cladding region.

Single-mode optical fiber design with wide-band ultra low bending-loss for FTTH application

Abstract: We propose a new design of a single-mode optical fiber (SMF) which exhibits ultra low bend sensitivity over a wide communication band (1.3 µm to 1.65 µm). A five-cladding fiber structure has been proposed to minimize the bending loss, estimated to be as low as 4.4×10-10 dB/turn for the bend radius of 10 mm.

Analytical Optimization of Optical Fiber Curvature Gauges

Abstract: `The ldquocurvature gaugerdquo sensor monitors deflection of structures under mechanical loading in applications in which strain gauges have traditionally been used. Structural deflection-curvature is measured rather than material strain. The sensitive zone of the curvature gage is precision machined into the plastic optical fiber on grinding or milling machines. The cutout produced removes a part of the fiber core and introduces light loss that is related to the bend-radius of the fiber. This modulation mechanism is described analytically in this paper. Results relate the relative light loss to the fiber curvature for different parameters of the sensitive zone (depth, length, number of cuts, bend radius, and pitch of cuts). This allows a quantitative optimization of the gauge without having to produce thousands of sensors with slightly different combination of parameters in order to accomplish a similar objective experimentally.

All-fibre temperature sensor based on macro-bend singlemode fibre loop

Abstract: An all-fibre temperature sensor is proposed based on a macro-bend singlemode fibre loop using a ratiometric power measurement scheme. The sensor has a linear characteristic with temperature at a fixed wavelength and bend radius. A direct linear relationship between the bend loss of the singlemode fibre and temperature is reported for the first time. By measuring the change in bend loss of the system a change in temperature can be measured assuming the system is calibrated. The proposed sensor has a higher temperature resolution than other conventional fibre-optic sensors and also benefits from simplicity.

Design of a trenched bend insensitive single mode optical fiber using spot size definitions.

Abstract: We have designed a bend insensitive single mode optical fiber with a low-index trench using spot-size definitions and their optimization technique. The bending loss at a 5 mm of bending radius was negligible, while single mode properties were intact.

Apparatus and method for compensating for and using mode-profile distortions caused by bending optical fibers

Abstract: An apparatus and method for compensating for mode-profile distortions caused by bending optical fibers having large mode areas. In various embodiments, the invention micro-structures the index of refraction in the core and surrounding areas of the inner cladding from the inner bend radius to the outer bend radius in a manner that compensates for the index changes that are otherwise induced in the index profile by the geometry and/or stresses to the fiber caused by the bending. Some embodiments of an apparatus and method include a fiber having a plurality of substantially parallel cores, the fiber including a straight section and a curved section; guiding signal light primarily in a second core in the straight section; guiding the signal light from the second core into a first core between the straight section and the curved section; and guiding the signal light primarily in the first core in the curved section.

Mechanical stability of poly-Si TFT on metal foil

Abstract: We have studied the mechanical stability of poly-Si thin-film transistor on 50 μm-thick flexible metal foil with a field-effect mobility of 81.2 cm 2 /V s, a threshold voltage of −2.4 V, and an on/off current ratio of 10 6 . We have measured the electrical properties under various compressive and tensile strains by changing the bending radius of the base metal foil. We have found that the TFT is stable until the bending radius of 50 mm which corresponds to the strain of ∼1.4%.

Focused-Ion-Beam Fabrication of Slots in Silicon Waveguides and Ring Resonators

Abstract: We present the focused-ion-beam fabrication of slots in existing silicon waveguides and racetrack resonators. The etch process was conducted with iodine enhancement and an alumina hard mask. We demonstrate a propagation loss of 100 dB/cm for slot waveguides and a Q value of 850 for slot racetrack resonators with bend radius of 6 mum.

Numerical Modeling of S-Band EDFA Based on Distributed Fiber Loss

Abstract: A numerical model for the analysis and design of S-band erbium-doped fiber amplifiers has been developed. The model is able to accurately predict the amplifier performances by taking into account the amplified spontaneous emission suppression due to the bending, as well as leakage losses of the fiber used as active medium. The model has been validated by comparing numerical and experimental data of bending loss, amplifier gain, and noise figure of an S-band optical amplifier based on a depressed-cladding erbium-doped fiber. A good agreement has been verified by varying fiber bending radius, input signal power, and wavelength. The model has been then applied to the optimization of the amplifier performances for wavelength-division multiplexer applications. The numerical results show that 20-25 dB gain can be achieved over a 25-30 nm range centered in a different part of the S-band from 1460 to 1525 nm, just by changing the bending radius and the length of a depressed-cladding fiber.

Textile composites with integrated optical fibres : quantification of the influence of single and multiple fibre bends on the light transmission using a Monte Carlo ray-tracing method

Abstract: Monte Carlo ray-tracing simulations of the propagation of light rays along bent multimode optical fibres indicate that, for optical fibres integrated into composite components, the influence of macroscale bends induced by the component shape on the light transmission is relatively small. Mesoscale bends caused by integration of the fibres into the reinforcement fabric structure applying textile processes may cause significant transmission losses, which decrease exponentially with increasing ratio of bending radius and fibre radius and increase with increasing bending angles. Based on geometrical models of optical fibres integrated in woven fabric structures, which show multiple mesoscale bends, simulations prove that the lowest bending losses occur for fabrics with a low degree of crimp.

Ultrahigh Relative Refractive Index Contrast GaAs Nanowire Waveguides

Abstract: An effective and practical fabrication procedure toward compound semiconductor nanowire waveguide on insulator is developed. GaAs nanowire waveguides with a cross-section of 400×400 nm2, bend radius of 10 µm, and a high relative refractive index contrast, Δ, of 40% were successfully fabricated for the first time. The propagation loss at 1.55 µm was measured to be approximately 4.5 dB/mm, and the bend loss was less than 0.8 dB per 90° bend. The losses were considered to be dominated by light scattering at the rough sidewalls.

Flexible and Extendable Hose for Holding Tank Drainage

Abstract: A flexible collapsible corrugated sewer hose has a collapsible and expandable corrugated section providing durability, a tight bend radius and a relatively small collapse ratio. An expansion of the corrugations permits convenient manipulation and installation of the sewer hose having a self supporting structure and crush resistance without helical reinforcement.

Sheet Metal Forming Limit Under Stretch-Bending

Abstract: The Forming Limit Diagram (FLD) as developed by Keeler etc. has been widely used to assess sheet metal failure during a variety of forming operations. Its theoretical and empirical foundation is based on localized necking under biaxial loading for the sheet metal. While the in-plane deformation is generally the dominant mode for most forming operations, sheet metal bending is inevitably coupled to the deformation process, and the traditional Forming Limit Diagram has to be modified to take into account the bending effect, especially when the bending radius becomes smaller. This paper presents a theoretical formulation for the Bending-Enhanced Forming Limit model. The deformation theory of plasticity is employed for the instability analysis, and the bending is assumed only in the direction along one principal loading. The obtained results show that the forming limit is enhanced by the bending effect, consistent with experimental observations.Copyright © 2008 by ASME

A Small Polymeric Ridge Waveguide With a High Index Contrast

Abstract: In this paper, an optimal design of a small polymeric ridge waveguide with a high index contrast is presented. In order to reduce the leakage to the substrate and pure bending losses, the buffer layer of the present waveguide is etched partially. The single-mode condition, the bending characteristics, and the birefringence of the present small polymeric ridge waveguide are also studied. By adjusting the core width and the core height, it is possible to obtain a polarization-insensitive small polymer ridge waveguide. For the bending loss, the numerical results show that the dominant part is the transition loss between the straight and bending sections (other than the pure bending loss) and the transition loss could be reduced greatly by introducing a lateral offset. However, the transition loss is still too large to obtain a very small bending radius (e.g., 10 mum). When only the pure bending loss is necessary to consider in some special case (e.g., microrings without any transitions), one can have a bending radius less than 10 mum due to the possibility of low pure bending loss.

Bend performance-enhanced photonic crystal fibers with anisotropic numerical aperture

Abstract: An error was made in converting the units of bend radius within the computer program used to obtain the reported results. This caused the calculated values of the bending induced stress to be significantly smaller than their true value. Corrected results for stress within the fiber and bend losses are reported. Since bending-induced stresses cause a relatively small correction to the refractive index profile, these corrections result in no changes in the main conclusions of this work.