Coupler Surface Research Articles

Comparative study of Yb:KYW planar waveguide lasers Q-switched by direct- and evanescent-field interaction with carbon nanotubes.

Both direct- and evanescent-field interactions with carbon nanotubes (CNTs) are applied to achieve stable Q-switched operation of Yb:KYW planar waveguide lasers. The performance characteristics were investigated in a same cavity configuration and analyzed in detail in the following three cases, CNTs deposited onto end mirror (M-coating), output coupler (OC-coating) and top surface of the planar waveguide (WG-coating). Maximum output powers, repetition rates, and minimum pulse durations are 61 mW, 1103 kHz and 215 ns for OC-coating, 39 mW, 1052 kHz and 275 ns for WG-coating, and 26 mW, 1119 kHz and 217 ns for M-coating, respectively. From the calculation of the configuration-dependent stability range, the beam size and the electric field distribution in the Yb:KYW planar waveguide, it is confirmed that the evanescent-field interaction scheme makes stable Q-switching possible with much lower intensities at saturable absorber compared to the direct-field interaction scheme in the presented waveguide laser operation.

High-efficiency chirality-modulated spoof surface plasmon meta-coupler

Efficiently exciting surface plasmon polaritons (SPP) is highly desired in many photonic applications, but most approaches (such as prism and grating couplers) cannot control flexibly their SPP excitation directions. While Pancharatnam-Berry (PB) metasurfaces were recently proposed to achieve direction-controllable SPP excitations, such scheme suffers from low-efficiency issue due to both direct reflections at the coupler surface and the mode mismatch between the coupler and the guiding-out plasmonic structure. In this article, we solve these issues via imposing two criterions to guide design both the metasurface and the plasmonic metal, based on which a direction-controllable SPP excitation with very high efficiency can be realized. As a proof of concept, we designed/fabricated a realistic device working in the microwave regime, and performed both near-field and far-field measurements to demonstrate that it can achieve an spoof SPP conversion efficiency ~78%, much higher than previous devices. Full-wave simulations are in good agreement with experiments, showing that the efficiency can be further pushed to 92% with optimized designs. Our findings can stimulate spoof SPP-related applications, particularly can help enhance the spin-dependent light-matter interactions in low frequency regime.

Optical fiber–Ta2O5 waveguide coupler covered with hydrophobic zeolite film for vapor sensing

Coupler comprising side-polished optical fiber and tantalum pentoxide (Ta2O5) waveguide coated with 330nm hydrophobic MFI-type zeolite films was utilized as chemical sensor for acetone vapors. The thickness of the zeolite films was selected through theoretical modeling of the resonant wavelength shift in order to achieve the highest possible sensitivity. The spectral positions of the resonances were determined through solving of the characteristics equations for the coupled waveguides and finding their mode effective refractive indices. The optical quality of the coupler surface, that is responsible for the proper operation of the device, was controlled through 3D optical imaging prior to and after deposition of the zeolite films. The application of side-polished optical fiber–Ta2O5 waveguide coupler covered with hydrophobic zeolite film for acetone vapor sensing was demonstrated and discussed.

The Coupler Surface of the RSRS Mechanism

Two degree-of-freedom (2-DOF) closed spatial linkages can be useful in the design of robotic devices for spatial rigid-body guidance or manipulation. One of the simplest linkages of this type, without any passive DOF on its links, is the revolute-spherical-revolute-spherical (RSRS) four-bar spatial linkage. Although the RSRS topology has been used in some robotics applications, the kinematics study of this basic linkage has unexpectedly received little attention in the literature over the years. Counteracting this historical tendency, this work presents the derivation of the general implicit equation of the surface generated by a point on the coupler link of the general RSRS spatial mechanism. Since the derived surface equation expresses the Cartesian coordinates of the coupler point as a function only of known geometric parameters of the linkage, the equation can be useful, for instance, in the process of synthesizing new devices. The steps for generating the coupler surface, which is computed from a distance-based parametrization of the mechanism and is algebraic of order twelve, are detailed and a web link where the interested reader can download the full equation for further study is provided. It is also shown how the celebrated sextic curve of the planar four-bar linkage is obtained from this RSRS dodecic.

How Coupler-Knuckle’s Surface S Angle Impact on Coupler Operation Performances

The rail wagon coupler is casting part. Some of foreign products’ error dispersion is significantly greater than domestics’. What influence generated by the results acting on the actual use of performance is still not clear. To this end, this article studied the influence generated by the angle of surface S tangent of coupler-knuckle on coupling connection contour and starting bearing line (referred to as surface S angle) to traction reliability, coupling feasibility and acting force in tangent line, systematically. And authors explored the value ranges of surface S angle in order to ensure the operation performance of coupler-knuckle. Firstly, find the major factors which are associated to surface S angle by studying the movement mechanism of coupling and traction. For example, the maximum level angle of coupler-knuckles, the ability for vehicle to pass the curves, etc. And then, get analytical expression of coupler surface S angle and related factors by means of theoretical derivation. After that, obtain value ranges of surface S angle. Finally, carry on experiments with multi-body dynamics simulation software RecurDyn. On the one hand, eliminate unreasonable value ranges obtained by theoretical derive, on the other hand, analyze the changing rule of the acting force on coupler-knuckle contour. The results prove that, when coupler surface S angle is , the traction performance of coupler is relatively stable, the coupling performance is relatively reliable, the contact force on coupler-knuckle contour is smaller. The conclusion is consistent with surface S angle parameter required by the standard system of Association of American Railroads. The research results above provided the theoretical basis for improving coupler’s manufacturability.

Microfiber coupler based label-free immunosensor

Optical microfibers and related structures which incorporate large evanescent field and minimal size offer new opportunities for biosensing applications. In this paper we report the development of an immunosensor based on a tapered microfiber coupler embedded in a low refractive index polymer. Biomolecules adsorbed on the microfiber coupler surface modify the surrounding refractive index. By immobilizing antigens on the surface of the sensing area, the microfiber coupler was able to operate as a label-free immunosensor to detect specific antibodies. We experimentally demonstrated for the first time the sensing ability of this sensor using a fibrinogen antigen-antibody pair. By monitoring the spectral shift in the wavelength domain, the sensor was shown to be capable of detecting the specific binding between fibrinogen and anti-fibrinogen. The detected signal was found to be proportional to the anti-fibrinogen present.

Fiber-optic coupler based refractive index sensor and its application to biosensing

A simple and highly sensitive biosensor based on a fiber-optic coupler is developed. The change of refractive index due to biomolecular interaction on the surface of the coupler can be detected as the change of the transmission power. The sensitivity of the sensor is evaluated to be a noise level equivalent to a refractive index variation of 4×10−6. The binding of streptavidin is detected to be concentration dependent over a range of 0.5–2μg∕ml, by immobilizing biotin on the coupler surface via aminosilan treatment. This sensor allows the construction of a low-cost, portable, and label-free biosensing system.

Interactive Visualization of the Coupler Surfaces of the Spatial 4C Mechanism

This paper presents a methodology for generating and displaying the coupler surfaces of the spatial 4C mechanism. The 4C mechanism is a two-degree-of-freedom spatial four-bar linkage. The path traced by a point attached to the coupler or floating link defines a surface in space. It is shown that the coupler surface of the spatial 4C mechanism is a ruled surface with 16thdegree directrices. An interactive graphical user interface has been created and integrated with kinematic analysis routines to generate and interactively display these coupler surfaces. The result is a user-friendly and efficient means of generating and visualizing the coupler surfaces of the spatial 4C four-bar mechanism.

Chemical Properties of Fused Fiber Coupler Surface

The fused fiber coupler is examined for its glass properties. The process of fusion by an H2 flame causes not only an increase of H2O combined with SiO2 but also a loose SiO2 structure and a rough surface near the center of the coupler. Such a change in glass properties is inevitable for commonly produced fiber couplers, although its effect on the long-term stability of the couplers is not known at this time.

Enhanced coupling to microsphere resonances with optical fibers

Morphology-dependent resonances (MDR's) of polystyrene microspheres were excited by an optical fiber coupler. For optical elimination of the air–cladding interface at the optical fiber coupler surface, the microsphere was immersed in an index-matching oil. MDR's were observed, even though the relative refractive index between the microsphere and the oil was only 1.09. The observed MDR spectra are in good agreement with the generalized Lorenz–Mie theory and the localization principle. The scattering efficiency into each MDR is estimated as a function of the impact parameter by means of generalized Lorenz–Mie theory.

Real-time measurement of nucleic-acid hybridization using evanescent-wave sensors: steps towards the genosensor

Nucleic acids are used as receptors in biosensing for the determination of complementary nucleic-acid strands. This may be useful in clinical diagnostics, e.g., searching for DNA from viruses, or in other fields of hygiene or environmental monitoring. In this study we demonstrate the reversible binding of DNA oligonucleotides to immobilized DNA targets. Using both a grating coupler detector and surface plasmon resonance, the evanescent field is employed to distinguish between bound and unbound species. As a bridge for the immobilization of the DNA, streptavidin (or avidin) is coupled to the sensor surface. Three different targets have been investigated: (1) randomly biotinylated poly(dA); (2) 5′-biotinylated 24-mer consisting of balanced amounts of purines and pyrimidines; and (3) 5′-biotinylated 13-mer. The binding kinetics of poly (dT) have been investigated, demonstrating this fast process as multibinding complex formation, since no sequence specificity is involved. The binding of a variety of 13-mers to 24-mer and 13-mer templates has been observed and the binding kinetics analysed. In a 13-mer point mutations can be resolved by analysis of association and dissociation rate constants.

Specific binding of photosynthetic reaction centres to herbicide-modified grating couplers

The photosynthetic reaction centre (RC) of Rhodobacter sphaeroides binds not only ubiquinones, but also most of the photosystem II herbicides. This binding has been observed by several means, usually using free herbicides capable of moving into the quinone binding site. It is shown that the binding process can be observed directly, i.e., in real time, if a herbicide derivative is immobilized on a grating coupler surface and the RC is solubilized with the aid of a stabilizing detergent; it also binds if incorporated in an artificial membrane forming liposomes. The specificity of the binding is demonstrated by binding inhibition by an overdose of free quinones and photosystem II herbicides. First quantitative analyses are reported, showing the direction for a new kind of sensing device.