Coupled-mode Analysis Research Articles

A coupled-mode theory analysis of intermixing in semiconductor distributed Bragg reflectors

On the basis of the coupled-mode theory, we have been able to successfully model and analyse the effect of intermixing on important optical properties of semiconductor distributed Bragg reflectors (DBRs). An expression for the coupling coefficient $$\kappa $$ as a function of diffusion length $$L_D$$ for intermixed DBRs has been derived. The derived expression for the intermixed DBRs allows the reflectivity, stop-band width, and penetration depth, to be calculated analytically. A 25 period GaAs/AlAS DBR centred at 980 nm was used to validate and test the model. It has been shown that the obtained results agree with those reported earlier using the transfer matrix method. As so, the presented model may provide a simple yet versatile rapid technique for the analysis of intermixed DBRs composed of any material system in which the diffusion process is Fickian and its corresponding refractive index is known.

Light Scattering Spectroscopy of Orthoterphenyl: Idealized and Extended Mode Coupling Analysis

Light Scattering Spectroscopy of Orthoterphenyl: Idealized and Extended Mode Coupling Analysis

Coupled mode analysis for simplified gain calculations in erbium-doped coaxial fibers

We have developed a coupled mode analysis for an erbium-doped coaxial fiber (EDCF) with doping only in the inner rod. With this analysis, the gain characteristics of the EDCF can be obtained in terms of the gain characteristics of a conventional single-core erbium-doped fiber. We have illustrated the use of this method in studying an EDCF and shown its application for inherent gain flattening.

Sound absorption and transmission through flexible micro-perforated structures

This work presents a theoretical and experimental study on sound absorption and transmission through structures made up of single and multiple-layer micro-perforated panels (MPPs). As they contribute to improve acoustical comfort, speech intelligibility and comply with lightweight, transparency and fiberless requirements, increasing applications are found in architectural acoustics or in the aeronautic and surface transport industries. A fully coupled modal approach is proposed to calculate the absorption coefficient and the transmission loss of finite-sized layouts made up of multiple flexible MPPs separated by air gaps. Validation results are obtained for single and double-layer thin MPPs against the transfer matrix approach and against measurements performed in a standing wave tube and in an anechoic chamber. Analytical approximations are derived from coupled-mode analysis for the Helmholtz-type and structural resonance frequencies of a single layer MPP structure together with relationships on the air-frame relative velocity over the MPP surface at these resonances. Principled guidelines are provided for enhancing both the sound absorption and transmission properties of multiple-layer MPP structures through suitable setting of the design parameters.

Non-monotonic size dependence of diffusion and levitation effect: A mode-coupling theory analysis

We present a study of diffusion of small tagged particles in a solvent, using mode coupling theory (MCT) analysis and computer simulations. The study is carried out for various interaction potentials. For the first time, using MCT, it is shown that only for strongly attractive interaction potential with allowing interpenetration between the solute-solvent pair the diffusion exhibits a non-monotonic solute size dependence which has earlier been reported in simulation studies [P. K. Ghorai and S. Yashonath, J. Phys. Chem. B 109, 5824-5835 (2005)]. For weak attractive and repulsive potential the solute size dependence of diffusion shows monotonic behaviour. It is also found that for systems where the interaction potential does not allow solute-solvent interpenetration, the solute cannot explore the neck of the solvent cage. Thus these systems even with strong attractive interaction will never show any non-monotonic size dependence of diffusion. This non-monotonic size dependence of diffusion has earlier been connected to levitation effect [S. Yashonath and P. Santikary, J. Phys. Chem. 98, 6368 (1994)]. We also show that although levitation is a dynamic phenomena, the effect of levitation can be obtained in the static radial distribution function.

Analysis of Mode Coupling and Threshold Gain Control for Nanocircular Resonators Confined by Isolation and Metallic Layers

Mode coupling and the control of mode <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor and threshold gain are analyzed for nanocircular resonators confined by isolation and metallic layers based on solving eigenvalue equation for multiple-layer structure circular resonators. For nanocircular resonators only confined by a metallic layer, the metallic layer can enhance the mode confinement for transverse magnetic (TM) whispering-gallery modes (WGMs) and result in high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> TM WGMs. But transverse electric (TE) WGMs can form hybrid modes of surface plasmon polaritons and dielectric modes, with the mode <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factors limited by the metallic layer absorption. By introducing a low index isolation layer between the resonator and the metallic layer, we can greatly enhance the mode <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factors for TE WGMs. However, the mode coupling between different radial modes and the variation of the optical confinement factor in the active layer can result in the oscillation of the mode <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor and threshold gain versus the isolation layer thickness. The optimization of the isolation layer thickness is important to enhance the mode <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor and the optical confinement factor for realizing low threshold gain.

Coupled-mode theory analysis of optical forces between longitudinally shifted periodic waveguides

This work was supported by the Australian Research Council programs (including Future Fellowship FT100100160 and Discovery Project DP130100086) and the supercomputing infrastructure of the Australian NCI National Facility.

Contactless electron effective mass determination in GaInNAs/GaAs quantum wells

The electron effective masses in n-type modulation doped Ga0.7In0.3NyAs1−y/GaAs quantum wells with nitrogen mole fractions of y = 0.004 and 0.010 were investigated experimentally. Two experimental techniques: magnetic field dependent photoluminescence measurements and phonon-plasmon coupled-mode line-shape analysis of vibrational spectroscopy measurements, were employed in the investigations. In the first technique, the effective masses of the electrons have been determined from the diamagnetic energy shift dependencies up to 11 T. The vibrational properties of the samples were studied using Raman scattering spectroscopy at room temperature. The effective masses obtained from both two techniques are in good agreement with the current results in the literature.

Characteristic analysis of coupled transmission lines in stripline-type beam position monitor

Signal transmission characteristics in stripline electrodes of a stripline-type beam position monitor (BPM) are discussed on the basis of a coupled-mode analysis in electromagnetically coupled transmission lines. The physical prospect in the calibration procedure of stripline electrodes is improved in terms of signal transmission characteristics in the frequency domain. It is demonstrated that in the signal transmission with electromagnetic coupling between the stripline electrodes, the magnetic- and electric-coupling parameters play an important role depending upon the spatial configuration and mechanical structure of the stripline electrodes. In this report, a theoretical analysis, and experimental investigation into signal transmission characteristics and performance in a standard stripline-type BPM are described in detail on the basis of a coupled-mode analysis in uniform transmission lines.

Theory analysis of mode coupling in tilted long period fiber grating based on the full vector complex coupled mode theory

The mode coupling in the tilted long period fiber grating (TLPG) is analyzed by using the full vector complex coupled mode theory (FV-CCMT). Compared with the non-tilted LPG, new resonance bands corresponding to the LP1m cladding modes are observed in the transmission spectrum of the TLPG. The coupling to LP1m cladding modes is the combination of the coupling to degenerate vector modes TE0m, TM0m and HE2m with different propagation constants. The maximum coupling between LP01 and LP1m modes occurs at a tilt angle of ∼87°. Numerical results show that the state of polarization (SOP) of the input light would induce the shift of the new resonance wavelength. Also, the RI sensitivity of the new resonance wavelength is much higher than that of the normal resonance wavelength corresponding to the LP0m cladding modes. Such TLPG would find application in chemical and biological sensing fields.

All-Optical Switches Based on Multiple Cascaded Resonators With Reduced Switching Intensity-Response Time Products

The general nonlinear behavior of multiple cascaded resonators is analyzed by using the coupled-mode theory in time and then compared to a single resonator from the viewpoint of optical bistable operation. Our analysis reveals that from the perspective of switching intensity, the multiple resonator structure is more advantageous than the single resonator with an equivalently increasing quality factor. It is also shown that a switching intensity-response time product, suggested as a performance metric for optical bistable devices, decreases linearly as the number of cascaded resonators increases. The effect of coupling n resonators is equivalent to a single resonator device with n-time increased quality factor in terms of the performance metric. The coupled-mode theory analysis is confirmed by a numerical study of the bistable operation of one-dimensional photonic crystal resonator structures using the finite-difference time-domain method.

Comprehensive numerical analysis of mode coupling in few mode fibers for mode multiplexed transmission

Mode multiplexed transmission is a novel idea to increase the transmission capacity in a multiplicative order for optical fiber communication links. Mode coupling is one of the fundamental issues in this mode of transmission which limits the length of the span. In this paper we established the theoretical background of mode coupling in step index few mode fibers followed by a numerical analysis of a limited case of four spatial modes. We observed the relationship of coupling coefficients with physical parameters of optical fiber and impact of difference of propagation constants of coupling modes. In the end we suggested about reasonable selection of normalized frequency value of fiber by including the effects of group delay dispersion of coupling modes. Keyword Few Mode Fibers; Mode Coupling; Coupling Coefficients Abid munir, xiangjun xin, bo liu, Ashiq Hussain,Shahab ahmad Niazi, Abdul latif,Aftab hussain, Comprehensive numerical analysis of mode coupling in few mode fibers for mode multiplexed transmission, RNIS: Research Notes in Information Science, Volume 10, pp. 63 ~ 72, 2012

Collocation analysis of higher mode coupling in waveguides with discontinuous cross-section

Standard techniques for analyzing transmission and reflection at discontinuities in a waveguide use weighted residuals to match modal series on each side of the junction. Convergence of the model equations generally is slow, which led Homenticovschi and Miles [JASA, 128 (2010) 628-638] to introduce a renormalization technique. Such a formulation does not lend itself well to implementation of a general computational algorithm. Slow convergence of the standard approach a consequence of using weighted residuals, which is a smoothing process, to interrogate a discontinuity. Evidence of this may be found in the analysis of scattering from cylinders having a discontinuous surface impedance [Ginsberg, JASA, 92 (1992) 1721-1728]. That work showed that a weighted residual formulation converges slowly, whereas a proper description of the field, including the singular nature of the velocity at the discontinity, is obtained from a collocation solution that satisfies the surface boundary condition at a discrete set of points. The present work uses standard modal series to represent the signal in each side of the discontinuity. The junction conditions of the waveguide are satisfied at a dscrete number of points. The rate of convergence will be assessed for a variety of schemes for selecting the collocation points, and the implementation of the formulation as part of a computational algorithm of networks will be discussed.

Vibroacoustic properties of thin micro-perforated panel absorbers

This paper presents theoretical and experimental results on the influence of panel vibrations on the sound absorption properties of thin micro-perforated panel absorbers (MPPA). Measurements show that the absorption performance of thin MPPAs generates extra absorption peaks or dips that cannot be understood assuming a rigid MPPA. A theoretical model is established that accounts for structural-acoustic interaction between the micro-perforated panel and the backing cavity, assuming uniform conservative boundary conditions for the panel and separable coordinates for the cavity cross-section. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed panel response. It is shown analytically and experimentally that the air-frame relative velocity is a key factor that alters the input acoustic impedance of thin MPPAs. Coupled mode analysis reveals that the two first resonances of an elastic MPPA are either panel-cavity, hole-cavity, or panel-controlled resonances, depending on whether the effective air mass of the perforations is greater or lower than the first panel modal mass. A critical value of the perforation ratio is found through which the MPPA resonances experience a frequency "jump" and that determines two absorption mechanisms operating out of the transitional region.

Magnetically tunable silicon-ferrite photonic crystals for terahertz circulator

The gyromagnetic properties of ferrite materials and the nonreciprocal property of a silicon-ferrite photonic crystal cavity are investigated in the terahertz region. Through the structure optimization and analysis of defect mode coupling, we design a magnetically tunable circulator, of which central operating frequency can be tuned from 180 to 205GHz and the maximum isolation is 65.2dB. Moreover, the further study shows that the gyrotropy, dispersion, and ferromagnetic loss of ferrite materials under the different external magnetic fields greatly affect the transmission and isolation property of this device. This circulator is flexible to realize functions of controllable splitting, routing, filtering and isolation by changing the external magnetic field for the THz applications.

Sound absorption and transmission through flexible micro-perforated panels backed by an air layer and a thin plate

This paper describes theoretical and experimental investigations into the sound absorption and transmission properties of micro-perforated panels (MPP) backed by an air cavity and a thin plate. A fully coupled modal approach is proposed to calculate the absorption coefficient and the transmission loss of finite-sized micro-perforated panels-cavity-panel (MPPCP) partitions with conservative boundary conditions. It is validated against infinite partition models and experimental data. A practical methodology is proposed using collocated pressure-velocity sensors to evaluate in an anechoic environment the transmission and absorption properties of conventional MPPCPs. Results show under which conditions edge scattering effects should be accounted for at low frequencies. Coupled mode analysis is also performed and analytical approximations are derived from the resonance frequencies and mode shapes of a flexible MPPCP. It is found that the Helmholtz-type resonance frequency is deduced from the one associated to the rigidly backed MPPCP absorber shifted up by the mass-air mass resonance of the flexible non-perforated double-panel. Moreover, it is shown analytically and experimentally that the absorption mechanisms at the resonances are governed by a large air-frame relative velocity over the MPP surface, with either in-phase or out-of-phase relationships, depending on the MPPCP parameters.

Coupled mode analysis of thin micro-perforated panel absorbers

The prediction of the isolating properties of lightweight Micro Perforated Panels (MPP) is a subject that has been intensively studied due to their important applications in a wide range of areas such as building acoustics and the aeronautic, astronautic and automotive industries. MPPs have been mostly considered as rigid structures, accounting only for inertia and neglecting any vibrating effects. However, simulation and experimental studies on thin MPPs have found that the absorbing performance can experience variations in the low frequency range from the results expected assuming a rigid structure. The work presented here is a theoretical and experimental study on the influence of panel vibrations on the sound absorption properties of thin MPP absorbers. Measurements show that the absorption performance generates extra absorption peaks or dips that cannot be understood assuming a rigid MPP. A theoretical model is established that exactly accounts for structural-acoustic interaction between the micro-perforated panel and the backing cavity without restriction on the absorber cross-sectional shape or on the panel boundary conditions. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed panel response. The effect of micro-perforations on panel-cavity or hole-cavity resonances is revealed through coupled mode analysis.

2004 2点吊り振子の3つのmode間非線形相互作用の解析と線形振動実験(G05-1 振動・騒音の解析と制御,G05 機械力学部門)

2004 2点吊り振子の3つのmode間非線形相互作用の解析と線形振動実験(G05-1 振動・騒音の解析と制御,G05 機械力学部門)

A rigorous full-wave analysis of mode coupling in rectangular waveguide bends

From Maxwell's equations in an orthogonal curvilinear coordinate system, a rigorous full-wave analysis of mode coupling in rectangular waveguide bends is performed, obtaining the general and explicit formulas of coupling coefficients for any modes in rectangular waveguides. This full-wave analysis turns out to be necessary for analysing mode conversion in microwave devices involving waveguide bends. To validate the theory calculation, some miter-joint mode converters, which are composed of several miter-joint waveguides, are proposed and studied. It shows that, in some instances, miter-joint mode converters and bend converters have similar conversion characteristics if they have equal bend angles and equivalent axial lengths. The excellent behaviour of our results enables engineers to design these types of waveguide bends quickly.

Coupled-Mode Analysis for Chiral Fiber Long-Period Gratings Using Local Mode Approach

Starting from the conventional coupled-mode theory and using the mode transformation method, a unified local mode approach is presented to analyze the chiral fiber long-period gratings (CLPGs) formed by twisting a high-birefringence fiber as an example of a chiral fiber with double-helix symmetry. Similarly, a helical-core fiber, as an example of single-helix CLPGs, is analyzed by using the ideal mode approach. The coupled-mode equations for both the cases are transformed and reduced to two-mode equations. The derivation is simple, and the results are explicit in concept. These results reveal the scheme of polarization selectivity of mode coupling, and for the first time, the necessary condition for achieving the polarization selection is given. The analysis indicates that conventional coupled-mode theory is efficient for studying chiral fiber grating, and more importantly, it is better to be understood. A numerical simulation has been done on a twisted conventional Panda fiber with a beat length of 2.5 mm. It has been shown that in a right-handed twisted structure, a total power transfer of a right-handed circular polarization light is obtained with a grating pitch of 0.382 mm and a grating length of 64.9 mm at the wavelength of 1.55 μm . On the other hand, through the simulation on single-helix CLPG with an eccentric core, it has been shown that a total power transfer of the core mode to LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode is obtained with a grating pitch of 0.723 mm and a grating length of 10.46 mm at the wavelength of 1.55 μm.