Parameters Of Coupler Research Articles

All-optical devices using nonlinear fiber couplers

The coupler parameters for various all-optical devices using weakly-coupled nonlinear fibers are anticipated from a graphical method of representing extrema of core power called the power flow portrait. These devices are then analyzed in detail both analytically and numerically. Devices considered include a bandpass power filter, various schemes for logic gates, and a novel power-dependent switch utilizing saturation. By anticipating the mode portrait required to obtain the desired output characteristics, the required device and material parameters needed to achieve these portraits are determined, in the case of the bandpass power filter, from a catalog of nonlinear directional coupler mode portrait types, and by extrapolation in the case of the power-dependent switch.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis and design of slot-coupled directional couplers between double-sided substrate microstrip lines

The characteristics of a slot-coupled directional coupler between two microstrip lines coupled through a rectangular slot in the common ground plane are studied. Conformal mapping techniques are used to obtain analytic closed-form expressions for the coupler's even and odd-mode impedance and propagation constants for any coupler configuration. Using the spectral domain approach, a full-wave analysis is performed to determine the dispersion properties of coupler parameters. Theoretical and experimental results for a 10-dB coupler at 10 GHz are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-performance integrated-optical chip for a broad range of fiber-optic gyro applications

A high-performance integrated-optical device for a broad range of fiber-optic gyro applications is reported. The circuit contains four directional couplers and six phase modulators that form the fiber-loop coupler, the bias and serrodyne phase modulators, and an on-chip interferometric serrodyne phase detector. The chip was fabricated by the annealed-proton-exchange method in X-cut LiNbO(3), which yielded a highly polarizing guided circuit with a polarization extinction ratio of at least 60 dB. Other performance parameters include low half-wave voltages (3.5-5.5 V) at 1.3 microm and splitting and tapping directional coupler parameters well within the design needs required by application.

Theoretical investigation of light coupling phenomena in wavelength-flattened couplers

A study of light coupling phenomena in wavelength-flattened couplers by normal mode analysis is discussed. The effective index method and step approximation of the taper are used to analyze the mode coupling in the fused-taper region. It is shown that coupler parameters such as the dissimilarity of the two fibers, the degree of fusion, the minimum taper waist and the taper length should be optimized to get flat coupling characteristics. The optimum relationship among these coupler parameters is determined for fused-taper couplers employing standard telecommunication fibers. >

Improvement of the power spectral response in the three-guided coupler demultiplexer

To improve the power spectral response of directional coupler type demultiplexers, the three-guide coupler with varying coupling coefficients along the light propagation direction is theoretically examined. A new configuration of the three-guide coupler is presented, which gives 0.16- and 0.13-microm rejection bandwidths of -20 dB in the 1.3- and 1.55-microm wavelength regions, respectively. These are 5 times wider than the conventional two-guide coupler demultiplexer. Furthermore, a simple design method for obtaining the coupler parameters is presented.

The design of a mode selective directional coupler for a high power gyroklystron†

The design method of mode selective directional couplers from a transverse electric mode in a circular waveguide to the fundamental mode in a rectangular wave guide is presented in this paper. The design results for a TE01 circular mode coupler intended for use in the output power measurement of a high power gyroklystron are reported; these results indicate that more than 50-80dB directivity and sufficient suppression of unwanted modes can be obtained with a coupler less than 07m in length. The effects of frequency and rectangular wave guide size on coupler parameters are also discussed in this paper

Steady-State Curving Performance of Railway Freight Truck with Damper-Coupled Wheelsets

SUMMARY The focus of this paper is on the steady-state curving behaviour of a freight car system with Damper Coupled Wheelset (DCW), where the wheels of conventional shape within an axle are coupled through a damper element. A freight truck model with two DCW and pseudo-car body on curved track is developed to study the influence of wheelset coupler parameter on the curving response and performance. The response is primarily evaluated in terms of wheelset tracking error and yaw misalignment in response to track curvature and cant deficiency. The curving performance is evaluated in terms of slip and flange boundaries. The results in general, indicate that when the value of coupler parameter is reduced, the wheelset response to track curvature increases, and results in flanging and wheel slip on a less tighter curve than those corresponding to conventional rigid axled wheelsets.

Lateral Stability Behavior of Railway Freight Car System With Elasto-Damper Coupled Wheelset: Part 1—Wheelset Model

A general model of single rail vehicle wheelset with elasto-damper coupling between the wheels, has been developed as a first step in developing a railway freight truck model with elasto-damper coupled wheelset (EDCW). By choosing different coupler parameters, various stiffness-damper combinations, as well as rigid axle (conventional wheelset) could be simulated. The mathematical model of EDCW has been validated by comparing the model under limiting cases with those of published results for conventional system. In this paper, the results of linearized stability analysis of EDCW model on tangent track are presented and discussed. The investigation showed that wheelset coupler parameters have significant influence on the stability behavior of the wheelset, and there is an optimal coupler parameter which can improve the wheelset critical speed over the conventional system.

Lateral Stability Behavior of Railway Freight Car System With Elasto-Damper Coupled Wheelset: Part 2—Truck Model

To investigate the effect of elasto-damper coupled wheelset (EDCW), on the lateral stability behavior of freight cars, a railway freight truck model with two EDCW and pseudo-car body has been developed. The results of linearized stability analysis showed, that for small values of wheelset coupler stiffness, damping has significant influence on the stability behavior of wheelset relative spin as well as wheelset and truck lateral modes. The results further showed that, by utilizing an optimal EDCW coupler parameter, the critical speeds corresponding to truck hunting and wheelset lateral mode can be made equal. In doing so, the truck hunting critical speed on tangent track can be improved by over 100 percent in comparison to truck model with conventional rigid axle wheelsets.

Analysis of the microwave phase shifter with a non-ideal 3 dB coupler

The paper presents a general analysis of the binary phase shifter with the 3 dB, 90° coupler described by scattering matrix with known coefficients values. The inequalities found permit one to determine the effect of the coupler parameters on the phase shifter parameters, such as phase shift error, coefficient of parasitic amplitude modulation, reflection and insertion loss. The results of the analysis were applied to design phase shifters which have about 6% relative phase error in almost two-octave frequency band.

Analysis of tunable single-mode fiber directional couplers using simple and accurate relations

We present simple and accurate relations for the study of parallel and curved tunable single-mode fiber directional couplers employing step-index or graded-index fibers. Analytical results for the various coupler parameters such as coupling coefficient, effective interaction length, tunability, and channel wavelength separation in directional coupler wavelength filters are presented. These results must prove very useful for an easy, quick, and accurate prediction or design of tunable single-mode fiber directional couplers.

Microstrip-Slot Coupler Design-Part I: S-Parameters of Uncompensated and Compensated Couplers

Using the even-odd mode analysis of four-port networks with double symmetry, the scattering parameters of the microstrip-slot coupler are derived from the even- and odd-mode parameters of the coupler cross section. The uncompensated coupler and the coupler compensated by extending the slot fines are treated and design specifications are given covering the compensation slot lines. A comparison with experimental data will be given in Part II.

All-single-mode fiber resonator

An all-fiber-ring resonator has been constructed using a single strand of single-mode optical fiber and a directional coupler. Derivation of the resonator finesse in terms of fiber and directional coupler parameters is given. A finesse of 80 has been achieved experimentally. Applications of such a fiber-ring resonator are discussed.

Holographic Coupler For Fiber Optics

The analysis and demonstration of a holographic coupler for single-mode optical fibers and cables is discussed. The holographic coupler is composed of two holographic windows. The holographic window is rigidly attached to the cable end. The coupling between windows proceeds by means of plane waves. The tolerances for some of the critical coupler parameters are relaxed, namely transverse alignment. Precision work is restricted to the factory produc-tion, but of simple implementation. The result is a coupler with relatively undemanding assembly operations in the field.

Periodic spectral filter with integrated optical directional coupler

The direction of light propagation in integrated optical circuits can be inverted at the substrate edges by halved directional couplers with mirror planes at the substrate end facets. Thus the output and input of a directional coupler can be fed back on to the substrate forming a periodic spectral filter with extremely high frequency sensitivity. The filter characteristic is analysed with respect to frequency, feedback efficiency, parameters of the directional coupler and temperature. The filter pass and stop bands can be controlled electrically.

Analysis of optical channel waveguides and directional couplers with graded-index profile

A theoretical analysis of graded-index optical channel waveguides and directional couplers fabricated by the beam-writing technique is presented. The analysis is based on a combination of the effective-index-of-refraction method and the WKB method, which is shown to apply for directional couplers as well as for channel waveguides, when special care is taken in connecting the field at the gap region. The mode dispersion characteristics and the field profile of a channel waveguide were derived. The conversion length of a directional coupler was also determined as a function of the coupler parameters and the mode order. The guided mode field has long evanescent tails outside the guide, and the positions of the turning points are located further away from the guide center for higher-order modes. Accordingly, the conversion length of a coupler increases slowly with the waveguide spacing and exhibits a strong dependence on the transverse mode order. The results are summarized in a few practically useful design charts by employing the normalizations of the device parameters. Some design examples are given and the fabrication tolerances are discussed.

Sensitivity Analysis of Coupled Microstrip Directional Couplers

Sensitivities of the parameters (coupling, bandwith and impedance) of a coupled-line directional coupler with respect to even- and odd-mode impedances have been evaluated. These are used to determine the accuracy required from the closed-form expressions for even- and odd-mode impedances of microstriplines. Closed-form expressions satisfactory for a coupling coefficient greater than 0.3 are proposed and used for evaluating the effect of dimensional tolerances on the performance of microstrip directional couplers. This effect is significant when compared with effects of unequal phase velocities and dispersion.

Design of wideband codirectional couplers and their realisation at microwave frequencies using coupled comblines

The combline directional coupler (c.d.c.) is a recently described planar device suitable for m.i.c. applications which couples power in a forward direction through controlled phase matching of the coupled waves. As a result high coupling levels (up to almost 0 dB) may be achieved at high frequencies (up to 20 GHz) without the need for close conductor spacings. The bandwidth of a basic c.d.c. is approximately 30%. We describe here two methods of broadbanding the c.d.c. which retain the advantages just mentioned and which enable operation over almost a decade to be achieved. Results for a 1.9–19 GHz, 3 dB power dividing coupler are presented. Both methods involve a spatial variation of the coupler parameters, and one of them, using the theory of warped modes, makes possible directional couplers which have a combination of frequency range and coupling level flexibility not at present obtainable by any other means. Particular attention is paid to practical details; design tables and methods are given which enable experimental couplers to be produced with any desired coupling level. We present experimental examples illustrating the various types of coupler design discussed and compare their performances. An indication is also given of the way in which the broadband design methods used for the c.d.c. may be applied to other types of planar forward directional coupler.

Radiation control in thin-film waveguides by modulation of prism coupler parameters

An investigation was made of the possibility of modulation and scanning of radiation at the exit from a thin-film waveguide by varying the coupling parameters and by utilizing the electro-optic and photoelastic properties of light-extraction devices.

THEORY OF COUPLED WAVEGUIDES

In this paper, the author endeavors to study the diffraction of electromagnetic wave by a long slot with conducting environment on opposite sides (i.e., a slot-coupled system of arbitrary shapes) from the viewpoint of coupled waves. A novel theory, which is justified by clear physical reasoning, is presented for a practical solution of the relevant boundary-value problem. In the light of this theory, problems of coupled waveguides, like problems of a single waveguide structure, are attacked by the same mathematical approach, namely, the theories of development in the orthogonal functions. Thus, two types of problems heretofore treated diferently are brought under a unified and coherent point of view. To illustrate the applicability of the present theory, the author solves the problem of a long slot directional coupler, whose usefulness in the development of long-distance waveguide transmission is well-known, and derives a set of original formulas for computing the coupler parameters. As concluding remarks, some further appliations of the theory are freely discussed.