Showing papers on "Coupled mode theory published in 2009"
TL;DR: High quality factor microdisk resonators are demonstrated in a Si(3)N(4) on SiO(2) platform at 652-660 nm with integrated in-plane coupling waveguides with critical coupling to several radial modes.
Abstract: High quality factor (Q approximately 3.4 x 10(6)) microdisk resonators are demonstrated in a Si(3)N(4) on SiO(2) platform at 652-660 nm with integrated in-plane coupling waveguides. Critical coupling to several radial modes is demonstrated using a rib-like structure with a thin Si(3)N(4) layer at the air-substrate interface to improve the coupling.
167 citations
TL;DR: In this paper, the authors proposed an efficient weakly radiative wireless energy transfer scheme between two identical classical resonant objects, strongly coupled to an intermediate resonant object of substantially different properties, but with the same resonance frequency.
119 citations
TL;DR: A cladding-modulated Bragg grating implemented using periodic placements of silicon cylinders in the cladding along a silicon waveguide is proposed, demonstrating coupling strengths differing by an order of magnitude.
Abstract: A cladding-modulated Bragg grating implemented using periodic placements of cylinders along a waveguide is proposed in a silicon-on-insulator platform. The coupling strength is varied by changing the distance between the cylinders and the waveguide. This implementation enables precise control and a wide dynamic range of coupling strengths and bandwidths that can be practically achieved for applications with specific bandwidth requirements. Modeling results are verified experimentally, and we demonstrate coupling strengths differing by 1 order of magnitude (43 and 921 per cm) with bandwidths of 8 and 16 nm, respectively. This method scheme enables weakly coupled devices with high fabrication tolerance to be realized.
113 citations
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TL;DR: In this article, a theory for Fano interference in light scattering by individual obstacles based on a temporal coupled-mode formalism is presented. But this theory is applicable for obstacles that are much smaller than the incident wavelength, or for systems with two-dimensional cylindrical or three-dimensional spherical symmetry.
Abstract: We present a theory for Fano interference in light scattering by individual obstacle, based on a temporal coupled-mode formalism. This theory is applicable for obstacles that are much smaller than the incident wavelength, or for systems with two-dimensional cylindrical or three-dimensional spherical symmetry. We show that for each angle momentum channel, the Fano interference effect can be modeled by a simple temporal coupled-mode equation, which provides a line shape formula for scattering and absorption cross-section. We validate the analysis with numerical simulations. As an application of the theory, we design a structure that exhibits strong absorption and weak scattering properties at the same frequency.
109 citations
TL;DR: In this paper, the authors proposed a coupled mode theory for optical isolation in waveguides, which can provide a broadband (>0.8 GHz), high contrast ratio (>20 dB) optical isolation at telecommunication wavelength.
Abstract: Photonic transitions in waveguides can create nonreciprocal phase response for counterpropagating modes. Such effect can be used in Mach–Zehnder interferometers to form optical isolators and circulators. Performance of such device is analyzed using coupled mode theory given the experimentally available modulation in silicon. The proposed scheme can provide a broadband (>0.8 THz), high contrast ratio (>20 dB) optical isolation at telecommunication wavelength.
77 citations
TL;DR: A guided-wave chemical sensor for the detection of environmental pollutants or biochemical substances has been designed based on an asymmetric directional coupler employing slot optical waveguides, having the minimum detectable refractive index change as low as 10-5.
Abstract: A guided-wave chemical sensor for the detection of environmental pollutants or biochemical substances has been designed. The sensor is based on an asymmetric directional coupler employing slot optical waveguides. The use of a nanometer guiding structure where optical mode is confined in a low-index region permits a very compact sensor (device area about 1200 μm2) to be realized, having the minimum detectable refractive index change as low as 10-5. Silicon-on-Insulator technology has been assumed in sensor design and a very accurate modelling procedure based on Finite Element Method and Coupled Mode Theory has been pointed out. Sensor design and optimization have allowed a very good trade-off between device length and sensitivity. Expected device sensitivity to glucose concentration change in an aqueous solution is of the order of 0.1 g/L.
76 citations
TL;DR: It is for the first time that guided and radiation field is treated in a unified and straightforward fashion without having to resort to cumbersome radiation modes.
Abstract: A coupled-mode formulation is described in which the radiation fields are represented in terms of discrete complex modes. The complex modes are obtained from a waveguide model facilitated by the combination of perfectly matched boundary (PML) and perfectly reflecting boundary (PRB) condition. By proper choice of the PML parameters, the guided modes of the structure remain unchanged, whereas the continuous radiation modes are discretized into orthogonal and normalizable complex quasi-leaky and PML modes. The complex coupled-mode formulation is identical to that for waveguides with loss and/or gain and can be solved by similar analytical and numerical techniques. By identifying the phase-matching conditions between the complex modes, the coupled mode formulation may be further simplified to yield analytical solutions. The complex coupled-mode theory is applied to Bragg grating in slab waveguides and validated by rigorous mode-matching method. It is for the first time that we can treat guided and radiation field in a unified and straightforward fashion without having to resort to cumbersome radiation modes. Highly accurate and insightful results are obtained with consideration of only the nearly phase-matched modes.
74 citations
TL;DR: In this paper, a new approach for estimating resonant characteristics of near-field coupled small antennas is proposed based on the equivalent circuit representation of the interaction of two antennas using the addition theorem of spherical modes.
Abstract: This letter proposes a new approach for estimating resonant characteristics of near-field coupled small antennas. It is based on the equivalent circuit representation of the interaction of two antennas using the addition theorem of spherical modes. Using the proposed method, the splitting of the resonant frequency and the resonant impedance of the near-field coupled small antennas can be obtained by the impedance characteristics of the isolated antenna. The results are shown to be in good agreement with the full electromagnetic (EM) simulation.
60 citations
TL;DR: Strong mutual-coupling induced by the grating inside the ring leads to split resonances and accompanying large anomalous dispersion, thus providing a new approach to realizing fast light in the over-Coupled region of the ring resonator.
Abstract: We report experimental demonstration of fast light in an over-coupled ultra-compact silicon ring resonator with resonance-splitting. Strong mutual-coupling induced by the grating inside the ring le ...
58 citations
TL;DR: A metallic slot waveguide, with a dielectric strip embedded within, is investigated for the purpose of enhancing the optics-to-THz conversion efficiency using the difference-frequency generation (DFG) process, and a fully-vectorial coupled-mode theory is developed.
Abstract: A metallic slot waveguide, with a dielectric strip embedded within, is investigated for the purpose of enhancing the optics-to-THz conversion efficiency using the difference-frequency generation (DFG) process. To describe the frequency conversion process in such lossy waveguides, a fully-vectorial coupled-mode theory is developed. Using the coupled-mode theory, we outline the basic theoretical requirements for efficient frequency conversion, which include the needs to achieve large coupling coefficients, phase matching, and low propagation loss for both the optical and THz waves. Following these requirements, a metallic waveguide is designed by considering the trade-off between modal confinement and propagation loss. Our numerical calculation shows that the conversion efficiency in these waveguide structures can be more than one order of magnitude larger than what has been achieved using dielectric waveguides. Based on the distinct impact of the slot width on the optical and THz modal dispersion, we propose a two-step method to realize the phase matching for general pump wavelengths.
58 citations
TL;DR: A rigorous numerical analysis on tunable characteristics of guided-mode resonances (GMRs) in coupled gratings shows that this characteristic will provide a useful means to realize a tunable filter in conjunction with micro/nano-electromechanical system technologies.
Abstract: We present a rigorous numerical analysis on tunable characteristics of guided-mode resonances (GMRs) in coupled gratings. Two schemes of strong and negligible evanescent coupling of guided modes are treated. Both show wide range tunability. In the case of strong evanescent coupling, independent control of the center wavelength and the linwidth of the resonance is obtained via variations of a gap size between the gratings and lateral alignment conditions. We believe that this characteristic will provide a useful means to realize a tunable filter in conjunction with micro/nano-electromechanical system technologies. We also present a generalized theoretical analysis on the tunable characteristics of the GMRs in coupled gratings, which is qualitatively in good agreement with the numerical analysis.
TL;DR: In this article, a long period grating (LPG) formed by introducing periodic grooves along one side of a photonic crystal fiber (PCF) with a focused CO2 laser beam was used for structural shape sensing in harsh environments.
Abstract: In this paper, we present a directional bend sensor based on a long period grating (LPG) formed by introducing periodic grooves along one side of a photonic crystal fiber (PCF) with a focused CO2 laser beam. A bend sensitivity of 2.26 nm/m-1 within a range of - 5 ~ + 5 m-1 is experimentally demonstrated. Numerical simulation suggests that the directional response is the result of asymmetric cladding geometry resulted from collapse and/or deformation of air holes and asymmetric material-index modulation caused by one-sided illumination of the CO2 laser beam. The sensitivity could be further enhanced by increasing the area of the air-silica photonic crystal cladding and optimizing the size of individual air holes. The easy fabrication process and good linear response of the proposed sensor make it a suitable candidate for structural shape sensing in harsh environments.
TL;DR: It is demonstrated through coupled-mode theory that complete depletion of the pump frequency - i.e., quantum-limited conversion - is possible and the output power at the point of optimal total conversion efficiency is adjustable by varying the mode quality (Q) factors.
Abstract: We propose a scheme for efficient cavity-enhanced nonlinear THz generation via difference-frequency generation (DFG) processes using a triply resonant system based on photonic crystal cavities. We show that high nonlinear overlap can be achieved by coupling a THz cavity to a doubly-resonant, dual-polarization near-infrared (e.g. telecom band) photonic-crystal nanobeam cavity, allowing the mixing of three mutually orthogonal fundamental cavity modes through a chi((2)) nonlinearity. We demonstrate through coupled-mode theory that complete depletion of the pump frequency - i.e., quantum-limited conversion - is possible. We show that the output power at the point of optimal total conversion efficiency is adjustable by varying the mode quality (Q) factors.
TL;DR: In this paper, a planar microdisk optical resonators fabricated from Ge23Sb7S70 chalcogenide glass on a silicon substrate are applied for cavity-enhanced spectroscopic measurement of chemical molecular absorption fingerprint.
Abstract: Planar microdisk optical resonators fabricated from Ge23Sb7S70 chalcogenide glass on a silicon substrate are applied for cavity-enhanced spectroscopic measurement of chemical molecular absorption fingerprint. A 0.02 cm- 1 detection limit for these devices is demonstrated. This detection limit represents a threefold improvement as compared to a straight waveguide sensor, while the physical device length is reduced by 40-fold. The reduction in device footprint with enhanced sensitivity makes the structure attractive for ldquosensor-on-a-chiprdquo device applications. We also present a design optimization approach for cavity-enhanced IR absorption spectroscopy using traveling-wave resonators, which indicates that further performance improvement can be achieved in optimally coupled, low-loss resonant cavities.
TL;DR: The finite-difference time-domain (FDTD) simulation results of proposed CDF which is implemented in two dimensional photonic crystals (2D-PC), show that the analysis is valid.
Abstract: We have proposed a three-port high efficient channel-drop filter (CDF) with a coupled cavity-based wavelength-selective reflector, which can be used in wavelength division multiplexing (WDM) optical communication systems. The coupling mode theory (CMT) is employed to drive the necessary conditions for achieving 100% drop efficiency. The finite-difference time-domain (FDTD) simulation results of proposed CDF which is implemented in two dimensional photonic crystals (2D-PC), show that the analysis is valid. In the designed CDF, the drop efficiency larger than 0.95% and the spectral line-width 0.78 nm at the center wavelength 1550 nm have been achieved.
TL;DR: By introducing deformed airhole structures, a single-mode PC-PBS is proposed, which significantly enhance the performance of the circuit with the extinction ratios remaining above 20 dB for both transverse-electric (TE) andTransverse-magnetic (TM) polarizations.
Abstract: In this work, we present the design of an integrated photonic-crystal polarization beam splitter (PC-PBS) and a low-loss photonic-crystal 60 waveguide bend. Firstly, the modal properties of the PC-PBS and the mechanism of the low-loss waveguide bend are investigated by the two-dimensional finite-difference time-domain (FDTD) method, and then the integration of the two devices is studied. It shows that, although the individual devices perform well separately, the performance of the integrated circuit is poor due to the multi-mode property of the PC-PBS. By introducing deformed airhole structures, a single-mode PC-PBS is proposed, which significantly enhance the performance of the circuit with the extinction ratios remaining above 20dB for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. Both the specific result and the general idea of integration design are promising in the photonic crystal integrated circuits in the future. (C) 2009 Optical Society of America
TL;DR: In this article, the coupled mode theory is used to analyze apodized fiber Bragg gratings (FBGs), and two discretization techniques of PUA are presented to analyze the apodization profile of gratings.
Abstract: In this paper, the coupled mode theory is used to analyze apodized fiber Bragg gratings (FBGs). Since the profile of gratings varies with the propagation distance, the coupled mode equations (CMEs) of apodized FBGs are solved by the fourth-order Runge-Kutta method (RKM) and piecewise-uniform approach (PUA). We present two discretization techniques of PUA to analyze the apodization profile of gratings. A uniform profile FBG can be expressed as a system Corresponding author: H.-W. Chang (hchang@faculty.nsysu.edu.tw).
TL;DR: A general recipe for tailoring flat dispersion curves in photonic crystal waveguides is presented, based on the critical coupling criterion, to circumvent most of the common trial-and-error procedures for flatband engineering.
Abstract: We present a general recipe for tailoring flat dispersion curves in photonic crystal waveguides. Our approach is based on the critical coupling criterion that equates the coupling strength of guided modes with their frequency spacing and results in a significant number of the modes lying collectively in the slow-light regime. We first describe the critical coupling scheme in photonic crystal waveguides using a simple coupled mode theory model. We also determine that canonical photonic crystal waveguides natively correspond to strongly coupled modes. Based on these analyses, our design recipe is as follows: Tune the profile of the first Fourier component of the waveguide periodic dielectric boundary to lower the coupling strength of the guided modes down to its critical value. We check that this generalized tuning may be accomplished by adjusting any desired optogeometric parameter such as hole size, position, index etc. We explore the validity of this general approach down to the narrow two-missing rows waveguides. The interest of this method is to circumvent most of the common trial-and-error procedures for flatband engineering.
TL;DR: It is shown that whereas supermode theory provides a good approximation of the mode profiles, next-to-nearest-neighbor coupling becomes significant at small separation distances between arrayed waveguides.
Abstract: We investigate coupled-mode theory in designing high index contrast silicon-on-insulator waveguide couplers and arrayed waveguides. We develop and demonstrate a method of solution to the inverse problem of reconstructing the coupling matrix from the modal profiles obtained, in this case, from finite-difference frequency-domain field calculations. We show that whereas supermode theory provides a good approximation of the mode profiles, next-to-nearest-neighbor coupling becomes significant at small separation distances between arrayed waveguides. These distances are quantified for three different silicon-on-insulator material platforms. We also point out the phenomenon of field skewing and deformation at small separations.
TL;DR: A compact modulator based on a photonic crystal nanocavity whose resonance is electrically controlled through an integrated p-i-n junction whose sub-micron size promises very low capacitance, high bandwidth, and efficient on-chip integration in optical interconnects.
Abstract: We describe a compact modulator based on a photonic crystal nanocavity whose resonance is electrically controlled through an integrated p-i-n junction. The sub-micron size of the nanocavity promises very low capacitance, high bandwidth, and efficient on-chip integration in optical interconnects.
31 May 2009
TL;DR: In this article, the authors demonstrate all-optical modulation via ultrafast optical carrier injection in a GaAs photonic crystal cavity using a degenerate pump-probe technique.
Abstract: We demonstrate all-optical modulation via ultrafast optical carrier injection in a GaAs photonic crystal cavity using a degenerate pump-probe technique. The low switching(absorption) energy∼120fJ(10fJ), and fast response(∼15ps), limited only by carrier lifetime, suggest practical all-optical switching applications.
TL;DR: An on-chip tunable long-period grating device by integrating a liquid crystal photonic bandgap fiber on silicon structures that results in a stable grating and permits this device to be more easily applied in practical systems.
Abstract: We design and fabricate an on-chip tunable long-period grating device by integrating a liquid crystal photonic bandgap fiber on silicon structures. The transmission axis of the device can be electrically rotated in steps of 45° as well as switched on and off with the response time in the millisecond range. The strength of the loss peak is controlled electrically, and the spectral position of the loss peak is thermally tunable. This compact design results in a stable grating and permits this device to be more easily applied in practical systems.
TL;DR: In this article, a new design of multicore photonic crystal fibers (PCFs) is proposed and investigated through full-vectorial finite element method and finite-element beam propagation method.
Abstract: A new design of multicore photonic crystal fibers (PCFs) is proposed and investigated through full-vectorial finite-element method and finite-element beam propagation method. The fiber design comprises four identical cores surrounding a central core. The optical power launched into the central core is equally divided into other neighboring four cores with a 25% of coupling ratio. The coupled-mode analysis is also carried out to understand the supermode patterns and the coupling characteristics. Through numerical simulations, it is demonstrated that the optical power can be divided equally in a 5.8-mm-long multicore PCF. The power coupling characteristics obtained through coupled-mode analysis are in very good agreement with those calculated from beam propagation method solver.
TL;DR: In this article, a model based on Fick's law of diffusion and coupled mode theory is proposed to describe single-beam surface relief grating formation in azopolymers thin films.
Abstract: A model based on Fick's law of diffusion as a phenomenological description of the molecular motion, and on the coupled mode theory, is developped to describe single-beam surface relief grating formation in azopolymers thin films. It allows to explain the mechanism of spontaneous patterning, and self-organization. It allows also to compute the surface relief profile and its evolution in time with good agreement with experiments.
01 Jan 2009
TL;DR: In this article, the authors used coupled inductance model in circuit theory to analyze the power transfer efficiency of this technology, instead of using coupled mode theory (CMT), and verified the analysis result by some simulations and experiments.
Abstract: Wireless energy transfer by coupled magnetic resonances is a popular technology in which energy can be transferred via coupled magnetic resonances in the non-radiative near-field. In this paper, we use coupled inductance model in circuit theory to analyze the power transfer efficiency of this technology, instead of using coupled mode theory (CMT). The analysis result is verified by some simulations and experiments.
TL;DR: In this article, the authors experimentally demonstrate continuously tunable pulse propagation in SOI microring resonators with mutual mode coupling, which is induced by nanosized gratings along the ring sidewalls.
Abstract: In this paper, we experimentally demonstrate continuously tunable pulse propagation in SOI microring resonators with mutual mode coupling, which is induced by nanosized gratings along the ring sidewalls. In the presence of the mutual mode coupling, dispersion-induced group delay is investigated in single-waveguide and double-waveguide coupled single-ring resonators, respectively. In particular, pulse propagation in the drop channel of a double-waveguide coupled resonator is observed and exhibits continuously tunable delay and advancement features in the experiment. Delayed pulses are also obtained at the reflection port of a single-waveguide coupled resonator due to the existence of backward whispering gallery mode (WGM).
TL;DR: In this article, an analytical method to estimate the scattering of RF power into multiple modes inside a non-uniform waveguide using perturbation techniques is presented, which may be applied to a wide variety of non-unicast waveguides.
Abstract: An analytical method to estimate the scattering of RF power into multiple modes inside a nonuniform waveguide using perturbation techniques is presented. This method is quite general, much faster than numerical methods, and may be applied to a wide variety of nonuniform waveguides. We have used this method to design and analyze a three-section mode transformer that converts a TE01 circular waveguide mode to a TE20 rectangular waveguide mode. This mode converter is specially suitable for use in ultra-high-power applications. Due to the complexity of the problem, we have used the symbolic solver Mathematica to produce most of our analytical results. The results match within reasonable accuracy with High Frequency Structure Simulator field solver simulations. We also present the application of this mode converter to variety of ultra-high-power microwave components and experimentally show the performance of these devices.
TL;DR: Coupled mode theory is a reliable yet very simple and practical tool to design and explore new structures of patterned coupling constant and confinement of light in designated areas of one-dimensional semi-conductor waveguide arrays is demonstrated.
Abstract: Structuring the coupling constant in coupled waveguide arrays opens up a new route towards molding and controlling the flow of light in discrete structures We show coupled mode theory is a reliable yet very simple and practical tool to design and explore new structures of patterned coupling constant We validate our simulation and technological choices by successful fabrication of appropriate III-V semiconductor patterned waveguide arrays We demonstrate confinement of light in designated areas of one-dimensional semi-conductor waveguide arrays
TL;DR: In this article, a highly efficient quasi-optical mode converter with a bandwidth of 38 GHz was designed and tested using a dimpled-wall waveguide antenna (launcher), one quasi-elliptical mirror, and two toroidal mirrors.
Abstract: A highly efficient quasi-optical mode converter with a bandwidth of 38 GHz has been designed and tested. The mode converter combines low-diffraction losses and a Gaussian mode content up to 97% for a set of nine modes in the range of 105 to 143 GHz for a 1-MW CW gyrotron. This was achieved using a dimpled-wall waveguide antenna (launcher), one quasi-elliptical mirror, and two toroidal mirrors. The optimization of the launcher was done using coupled-mode theory. The simulation results show a well-focused Gaussian beam for all nine operating modes. The curvature radii of the toroidal mirrors were determined by Gaussian mode transformation (ABCD-law) and subsequently optimized for a multimode operation. The simulations of the quasi-optical mode converter are based on the electric field integral equation and, thus, are 3-D. Experimental low-power measurements show close agreement with predictions.
TL;DR: A new mode adapter is proposed which allows more efficient launching of the optical power selectively in the fundamental mode of a multimode waveguide and increases the performances in terms of coupling efficiency, coupling tolerances and transmitted power with respect to previously proposed solutions.
Abstract: We propose a new mode adapter which allows more efficient launching of the optical power selectively in the fundamental mode of a multimode waveguide Theoretical and experimental results confirm that such a mode adapter increases the performances in terms of coupling efficiency, coupling tolerances and transmitted power with respect to previously proposed solutions Proof of principle of device operation is obtained with a simple Coupled Mode Theory model Experimental results are obtained at a wavelength of 840 nm in Lithium Niobate Soft Proton Exchanged waveguides and agree very well with theoretical predictions