Couplers In Terms Research Articles

Evaluation of narrowband coupling techniques against frequency variation

This article presents the design of two couplers using a simple stub, one in series and one in parallel, and a coupler design using a quarter lambda section. The aim is to compare the behavior of the frequency variation for a passing bandwidth through the transmission line, considering their respective variation in the lengths in which the couplers are located and the distances of the stubs. In such a way, that each design can be compared and analyzed to determine which of all three is the best coupler in terms of low impacts due to a passing bandwidth. For this, each design is made with the help of the software Amanogawa (Amanogawa.com, s. f.) and by means of the Smith chart. Similarly, the simulation of each one is carried out and through a physical experiment, stub in parallel, the results obtained are corroborated. Observing that the parallel stub method proves to be the most optimal, in terms of implementation and acceptance of a higher bandwidth pass-through variation.

Efficient adiabatic-coupler-based silicon nitride waveguide crossings for photonic quantum computing.

Optical integrated quantum computing protocols, in particular using the dual-rail encoding, require that waveguides cross each other to realize, e.g., SWAP or Toffoli gate operations. We demonstrate efficient adiabatic crossings. The working principle is explained using simulations, and several test circuits are fabricated in silicon nitride (SiN) to characterize the coupling performance and insertion loss. Well-working crossings are found by experimentally varying the coupler parameters. The adiabatic waveguide crossing (WgX) outperforms a normal directional coupler in terms of spectral working range and fabrication variance stability. The insertion loss is determined using two different methods: using the transmission and by incorporating crossings in microring resonators. We show that the latter method is very efficient for low-loss photonic components. The lowest insertion loss is 0.18 dB (4.06%) enabling high-fidelity NOT operations. The presented WgX represents a high-fidelity (96.2%) quantum NOT operation.

Symmetrical and asymmetrical microstripline‐based transmit/receive switches for 7‐Tesla magnetic resonance imaging

SummaryThe transmit/receive (T/R) switch is an important device in magnetic resonance imaging scanners whenever T/R radio frequency coils are intended to be used. It is placed between transmit amplifiers and T/R radio frequency coils. The T/R switch adds loss to the radio frequency (RF) transmit chain, reducing the delivered power to the coil and increasing the noise figure of the receive chain. Therefore, T/R switches should be designed for as low insertion loss as possible. In addition, they need to handle high power in transmit. In this article, three T/R switches for 7‐Tesla magnetic resonance imaging scanners are designed using Eagle, and validated by simulation (HFSS & ANSYS) and measurement. Low reflection coefficients (< −20 dB), low insertion loss (≃0.3 dB), and high isolation (>40 dB) were demonstrated for the designed couplers. The fabricated microstripline‐based switches were more robust than a design utilizing commercial couplers in terms of heat dissipation, high power capabilities, and lower insertion loss.

Efficient Grating Couplers for Space Division Multiplexing Applications

Grating couplers are developed as one of the building blocks in silicon photonics to couple light between on-chip devices and optical fibers. For emerging high-capacity datacom and telecom systems enabled by space division multiplexing, it is essential to couple light together with mode conversion functions. In this work, we show the feasibility of combining conventional grating couplers and mode converters, both with a high efficiency. The proposed devices are very compact, built on standard silicon-on-insulator wafers, with no extra fabrication efforts required. It is shown that the LP01, LP11a, LP11b, and LP21b modes in a few-mode optical fiber can be successfully excited directly from the proposed grating couplers, which have the fundamental mode as an input from an integrated waveguide. The overall coupling efficiency, including mode conversion efficiency, can be as high as 50%. We also analyze the performance of the grating couplers in terms of bandwidth, efficiency, and tolerance to device fabrication errors.

Scrambling-Type Three-Mode PLC Multiplexer Based on Cascaded Y-Branch Waveguide With Integrated Mode Rotator

A novel scrambling-type mode multiplexer (MUX) is proposed for future mode-division multiplexing with large number of modes. The proposed MUX does not aim at high modal extinction ratio as in a conventional-mode MUX, rather, all the modes are moderately mixed assuming that an MIMO-based receiver is used. The proposed configuration is superior to the conventional-mode MUX based on asymmetric directional couplers in terms of the fabrication tolerance of the waveguide width and scalability to a large number of modes. The wavelength dependence is also small since no coherent coupling devices are used, except for mode rotators. A three-mode multiplexer design based on a cascaded Y-branch waveguide and an integrated mode rotator on a silica planar lightwave circuit shows that low-loss and small wavelength dependence multiplexing is possible and a proof-of-concept device is fabricated.

Optimal {mathscr{P}}{mathscr{T}} -symmetric switch features exceptional point

We consider the optimization problem of least energy-cost path in open systems that are described by non-Hermitian Hamiltonians. We apply it to find the optimal gain-loss profile for a non-uniform PT-symmetric coupler performing a binary transfer function. We bring evidence that the gain-loss profile fulfilling this requirement corresponds to a non-conventional situation where light intensity is conserved at every point along the PT-symmetric system. Besides, we find that the optimal profile corresponds to a practically important case of optical switching operation achieved with minimal amount of aggregate amplification level. We show that switching architectures using such type of gain-loss profiles are much more advantageous than conventional uniform PT-symmetric couplers in terms of gain and energy. Furthermore, this type of optimal profile turns out to be robust against fabrication imperfections. This opens new prospects for functional applications of PT-symmetric devices in photonics.

Quantum Statistical Properties of the Codirectional Kerr Nonlinear Coupler in Terms of suleft (2right ) Lie Group in Interaction with a Two-level Atom

The problem of the codirectional Kerr coupler has been considered several times from different point of view. In the present paper we introduce the interaction between a two-level atom and the codirectional Kerr nonlinear coupler in terms of suleft (2right ) Lie algebra. Under certain conditions we have adjusted the Kerr coupler and consequently we have managed to handle the problem. The wave function is obtained by using the evolution operator where the Heisnberg equation of motion is invoked to get the constants of the motion. We note that the Kerr parameter χ as well as the quantum number j plays the role of controlling the atomic inversion behavior. Also the maximum entanglement occurs after a short period of time when χ = 0. On the other hand for the entropy and the variance squeezing we observe that there is exchange between the quadrature variances. Furthermore, the variation in the quantum number j as well as in the parameter χ leads to increase or decrease in the number of fluctuations. Finally we examined the second order correlation function where classical and nonclassical phenomena are observed.

Analytical model for the coupling constant of a directional coupler in terms of slab waveguides

We present an analytical model for a generic two-wave directional coupler, in the conceptual frame of coupled single-mode planar (slab) waveguides. The modal relation of dispersion is expressed exactly under a matrix form. In the simplest symmetric configuration, the lift of degeneracy between the propagation constants of the even (slow) and odd (fast) supermodes is the exact image of the coupling constant.

Empirical Analysis of Widely Tunable Fused Fiber Coupler Assisted by External Medium of High Thermo-Optic Coefficient

This article reports the fused fiber coupler whose transmission spectrum is widely tuned or switched with temperature. With a proper choice of the external medium applied on the fused region of the coupler, the tuning range could be expanded up to the free spectral range of the coupler itself. A polymer with a matched refractive index and high thermo-optic coefficient was used as the external medium, and a micro-coil heater was installed to tune or switch the coupler. As the elongation length of the coupler increased in the fabrication process, the tuning range increased also. With the polymer having a thermo-optic coefficient of −1.8 × 10−4/°C and a 1.440 room temperature refractive index, wavelength tuning as wide as 210 nm was experimentally obtained. The fabrication process of the tunable fused coupler and the temperature-dependent spectral properties of the implemented couplers in terms of the elongation length and the polymer index are presented in detail. The feasibility of the proposed device as a tunable filter, optical switch, and variable optical attenuator are also presented.

Compact dual‐band rat‐race couplers

AbstractIn this letter, a design of a compact, dual‐band, rat‐race coupler is presented. The dual‐band characteristics are obtained by using two shunt open‐stubs with the conventional coupler. The proposed design can cover a wide range of frequency ratio of the dual bands within the fabrication limit of a low and high impedance microstrip line. Frequency variations of the bandwidths of this coupler in terms of isolation, matching, amplitude, and phase imbalance are also discussed. Theoretical prediction has been verified in the microstrip line by fabricating a dual‐band coupler at the 900/1900‐MHz mobile bands. Experimental results agree well with the theoretical predictions. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 277–281, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23063

Composition methods for four-port couplers in photonic integrated circuitry

Planar photonic integrated circuits based on four-port couplers offer enhanced sophistication and functionality. Each four-port coupler is characterized by sixteen signal coupling coefficients governed by ten energy constraints. The ability to generate the constrained sixteen coupling coefficients is needed in the analysis of the four-port coupler. However, the energy constraint equations are nonlinear and cumbersome to solve directly. We introduce two techniques to reduce these signal coupling coefficients to a set of six free parameters. Hence we can characterize all possible couplers in terms of their sixteen constrained coupling coefficients, or either of two sets of six free parameters. This reduction in parameters has significant ramifications for the design, specification, and empirical characterization of these useful building blocks.

New high-directivity coupler design with coupled spurlines

A new high-directivity coupler using coupled spurlines is proposed. The effective capacitances of coupled spurlines generate an isolation zero at any desired frequency due to their equalization effect on the odd-mode and even-mode phase velocities. The measurement results demonstrate an improved performance over the conventional parallel-line coupler in terms of the isolation and the coupling flatness.

Temporal soliton switching in a rectangular nonlinear directional coupler

We address the theory of temporal soliton switching in a planar geometry directional coupler constructed from silica and doped silica glass and operating at the central wavelength of 1.55 microm, significant for erbium-doped amplification. We formulate the field in the coupler in terms of the supermodes of the total structure and take account of the two transverse dimensions of the rectangular channels. In the case of the weak coupling between channels consistent with elimination of pulse breakup, the effect of the fields in the outer corner regions of the channels results in a switching intensity that differs significantly from that derived from coupled-mode theory on the basis of a slab model of the coupler.

Simplified design technique for high-performance microstrip multisection couplers

A new design technique has been developed which improves the design of a microstrip multisection coupler by a simplified version of the nonuniform coupler method. The technique achieves the performance of a smooth, discontinuity free, nonuniform coupler with a sectional breakdown of the coupling along the structure that can be simply and quickly optimized in a commercial simulator such as Libra. The design is further improved by the use of the saw-tooth odd- and even-mode equalization technique, and the effectiveness of this is verified experimentally. The measured results demonstrate an improved performance over the multisection coupler in terms of coupling performance and bandwidth, while the size and the fabrication tolerance are better than the nonuniform line coupler.

Modeling of symmetric 2 × 2 fused-fiber couplers

A complete analysis of symmetric 2 × 2 fused-fiber couplers in terms of supermode beating is made. The tranverse and longitudinal geometry of the couplers has been carefully modeled to take into account the fabrication parameters. The first two scalar supermodes and their polarization corrections have then been calculated for each degree of fusion and taper ratio, resulting in powerful tools for the design of particular couplers. The good agreement between the observed and the predicted responses for slightly and strongly fused couplers confirms the validity of each step of this analysis.

Finline multiport couplers

The propagation characteristics of asymmetric and multiple coupled slots in uni- and bilateral finlines are evaluated by using a hybrid mode formulation. All the normal mode parameters of the coupled slot structures required for the design of the multiport circuits are computed. Numerical results include the propagation constants including conductor and dielectric losses, modal characteristic impedances, and the equivalent voltage eigenvector matrices of typical finline structures. These parameters are then used to derive equivalent circuits of the coupled dispersive lines and the expression for the immitance and scattering parameters of the multiports. The applications of the coupled finlines in the design of power dividers and couplers in terms of the normal mode parameters are demonstrated with typical design examples of four and six port structures. Experimental results for an X-band six port are included to ascertain the validity of the theoretical results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A uniformly coupled asymmetric TEM-mode transmission-line directional coupler

An analysis of an asymmetric coupled four-port transmission-line coupler in terms of a two-port transmission line corresponding to two normal modes is presented. This method permits the use of a transmission matrix approach which simplifies considerably the derivation of an expression for coupling and also establishes the mathematical equivalence of such couplers to transmission-line stepped impedance filters. The coupling as well as the terminating impedances required for an impedance match and infinite directivity have been determined in terms of self and mutual immittance parameters, expressions for which have been determined as explicit functions of the line parameters. The method of design of a coupler for specified values of coupling and terminating impedances is also presented.

Shielding Effects in Thin-Film Integrated Circuits

The shielding effect of a thin (or thick) film ground plane on two film conductors has been theoretically investigated by viewing the problem as that of determining the scattering matrix coefficients of a microstrip directional coupler in terms of various transmission-line parameters. The effect of resistive losses in the film conductors and ground plane are considered and methods of systematically determining all transmission parameters have been evolved. Recently published equations for the design of coupled microstrips are used to determine pertinent transmission-line parameters. These results can serve as a guide to designers of thin-film integrated circuits, wherein undesired coupling levels can be predicted and optimum circuit layouts can be determined.