Showing papers on "Coupled mode theory published in 2011"
TL;DR: The relationship between maximum efficiency air gap is analyzed using equivalent circuits and the Neumann formula and proposed equations for the conditions required to achieve maximum efficiency for a given air gap are proposed.
Abstract: The progress in the field of wireless power transfer in the last few years is remarkable. With recent research, transferring power across large air gaps has been achieved. Both small and large electric equipment have been proposed, e.g., wireless power transfer for small equipment (mobile phones and laptops) and for large equipment (electric vehicles). Furthermore, replacing every cord with wireless power transfer is proposed. The coupled mode theory was proposed in 2006 and proven in 2007. Magnetic and electric resonant couplings allow power to traverse large air gaps with high efficiency. This technology is closely related to electromagnetic induction and has been applied to antennas and resonators used for filters in communication technology. We have studied these phenomena and technologies using equivalent circuits, which is a more familiar format for electrical engineers than the coupled mode theory. In this paper, we analyzed the relationship between maximum efficiency air gap using equivalent circuits and the Neumann formula and proposed equations for the conditions required to achieve maximum efficiency for a given air gap. The results of these equations match well with the results of electromagnetic field analysis and experiments.
543 citations
TL;DR: The tunable multi-channel wavelength demultiplexer based on metal-insulator-metal plasmonic nanodisk resonators is designed and numerically investigated by utilizing Finite-Difference Time-Domain (FDTD) simulations and it is found that the channel wavelength of WDM is easily tuned.
Abstract: The tunable multi-channel wavelength demultiplexer (WDM) based on metal-insulator-metal plasmonic nanodisk resonators is designed and numerically investigated by utilizing Finite-Difference Time-Domain (FDTD) simulations. It is found that the channel wavelength of WDM is easily tuned by changing the geometrical parameters of the structure and the material filled in the nanodisk resonator. The multi-channel WDM structure consisting of a plasmonic waveguide and several nanodisk resonators increases the transmission up to 70% at telecommunication regime, which is two times higher than the results reported in a recent literature [Opt. Express 18, 11111 (2010)]. Our WDM can find important potential applications in highly integrated optical circuits.
218 citations
TL;DR: Using the coupled-mode and coupled-power theories, impacts of random phase-offsets and correlation lengths on crosstalk in multi-core fibers are investigated for the first time.
Abstract: Coupled-mode and coupled-power theories are described for multi-core fiber design and analysis. First, in order to satisfy the law of power conservation, mode-coupling coefficients are redefined and then, closed-form power-coupling coefficients are derived based on exponential, Gaussian, and triangular autocorrelation functions. Using the coupled-mode and coupled-power theories, impacts of random phase-offsets and correlation lengths on crosstalk in multi-core fibers are investigated for the first time. The simulation results are in good agreement with the measurement results. Furthermore, from the simulation results obtained by both theories, it is confirmed that the reciprocity is satisfied in multi-core fibers.
216 citations
TL;DR: The hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.
Abstract: We demonstrate that in a hybrid plasmonic system the optical force exerted on a dielectric waveguide by a metallic substrateisenhancedbymorethan1orderofmagnitudecompared to the force between a photonic waveguide and a dielectric subs- trate. A nanoscale gap between the dielectric waveguide and the metallic substrate leads to deep subwavelength optical energy con- finement with ultralow mode propagation loss and hence results in the enhanced optical forces at low input optical power, as numeri- cally demonstrated by both Maxwell's stress tensor formalism and the coupled mode theory analysis. Moreover, the hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.
210 citations
TL;DR: An optical effect analogous to electromagnetically induced transparency (EIT) is observed in nanoscale plasmonic resonator systems that consists of a slot cavity as well as plAsmonic bus and resonant waveguides.
Abstract: An optical effect analogous to electromagnetically induced transparency (EIT) is observed in nanoscale plasmonic resonator systems. The system consists of a slot cavity as well as plasmonic bus and resonant waveguides, where the phase-matching condition of the resonant waveguide is tunable for the generation of an obvious EIT-like coupled resonator-induced transparency effect. A dynamic theory is utilized to exactly analyze the influence of physical parameters on transmission characteristics. The transparency effect induced by coupled resonance may have potential applications for nanoscale optical switching, nanolaser, and slow-light devices in highly integrated optical circuits.
168 citations
TL;DR: It is experimentally demonstrated for the first time a very compact plasmonic hetero-oligomer structure where the multiple radiant and subradiant modes can be tailored independently and lead to directional double Fano resonances.
Abstract: We experimentally demonstrate for the first time a very compact plasmonic hetero-oligomer structure where the multiple radiant and subradiant modes can be tailored independently. Unlike previous approaches based on collective excitations in complex plasmonic systems, we show precise engineering of resonances leading to simultaneous spectral overlap of multiple plasmonic modes with opposite radiative character. This asymmetric behavior combined with inherent spatial features of the structure leads to directional double Fano resonances as shown with numerical analysis. A model based on temporal coupled mode theory is also provided to describe the double Fano behavior.
146 citations
TL;DR: The authors' simulations show that, for an exemplary four-level gain model, the excitation of dark Fano resonances featuring arbitrarily large quality factors can lead to a significant reduction of the lasing threshold of PCSELs with respect to conventional vertical-cavity surface-emitting lasers.
Abstract: We present a theoretical analysis of lasing action in photonic crystal surface-emitting lasers (PCSELs). The semiclassical laser equations for such structures are simulated with three different theoretical techniques: exact finite-difference time-domain calculations, an steady-state ab-initio laser theory and a semi-analytical coupled-mode formalism. Our simulations show that, for an exemplary four-level gain model, the excitation of dark Fano resonances featuring arbitrarily large quality factors can lead to a significant reduction of the lasing threshold of PCSELs with respect to conventional vertical-cavity surface-emitting lasers. Our calculations also suggest that at the onset of lasing action, most of the laser power generated by finite-size PCSELs is emitted in the photonic crystal plane rather than the vertical direction. In addition to their fundamental interest, these findings may affect further engineering of active devices based on photonic crystal slabs.
99 citations
TL;DR: Based on the asymmetry factor derived from the CMT analysis, methods to control transmittance asymmetry are demonstrated and interpreted as Fano-type interference between the quasi-continuum T-junction-resonator local-modes and discrete stub eigenmodes.
Abstract: We use coupled mode theory (CMT) to analyze a metal-insulator-metal (MIM) plasmonic stub structure, to reveal the existence of asymmetry in its transmittance spectra. Including the effect of the near field contribution for the stub structure, the observed asymmetry is interpreted as Fano-type interference between the quasi-continuum T-junction-resonator local-modes and discrete stub eigenmodes. Based on the asymmetry factor derived from the CMT analysis, methods to control transmittance asymmetry are also demonstrated.
93 citations
TL;DR: A filter design formalism is presented for the synthesis of coupled-resonator optical waveguide (CROW) filters and a method is described for the conversion of the coupling coefficients to the parameters based on ring resonators and grating defect resonators.
Abstract: We present a filter design formalism for the synthesis of coupled-resonator optical waveguide (CROW) filters. This formalism leads to expressions and a methodology for deriving the coupling coefficients of CROWs for the desired filter responses and is based on coupled-mode theory as well as the recursive properties of the coupling matrix. The coupling coefficients are universal and can be applied to various types of resonators. We describe a method for the conversion of the coupling coefficients to the parameters based on ring resonators and grating defect resonators. The designs of Butterworth and Bessel CROW filters are demonstrated as examples.
78 citations
TL;DR: It is demonstrated that the broad band antenna response of a pair of NWs can be tuned significantly by engineering their optical coupling and an intuitive coupled-mode theory is developed to explain the observations.
Abstract: Systems of coupled resonators manifest a myriad of exciting fundamental physical phenomena. Analogous to the synthesis of molecules from single atoms, the construction of photonic molecules from stand-alone optical resonators represents a powerful strategy to realize novel functionalities. The coupling of high quality factor (Q) dielectric and semiconductor microresonators is by now well-understood and chipscale applications are abound. The coupling behavior of low-Q nanometallic structures has also been exploited to realize high-performance plasmonic devices and metamaterials. Although dense arrays of semiconductor nanoparticles and nanowires (NWs) find increasing use in optoelectronic devices, their photonic coupling has remained largely unexplored. These high refractive index nano-objects can serve as low-Q optical antennas that can effectively receive and broadcast light. We demonstrate that the broad band antenna response of a pair of NWs can be tuned significantly by engineering their optical coupli...
73 citations
TL;DR: A concept for the design of nonlinear optical diodes is proposed that uses the multistability of coupled nonlinear microcavities and the dependence of switching thresholds on the direction of incidence to describe the dynamical properties of such systems.
Abstract: A concept for the design of nonlinear optical diodes is proposed that uses the multistability of coupled nonlinear microcavities and the dependence of switching thresholds on the direction of incidence. A typical example of such a diode can be created by combining two mirror-symmetric microcavities where modes of the opposite parity dominate. It is shown that a strong nonreciprocal behavior can be achieved together with a negligible insertion loss. To describe the dynamical properties of such systems, a model based on the coupled-mode theory is developed, and a possible implementation in the form of multilayered structures is considered.
TL;DR: In this article, a kind of multi-channel plasmonic filters based on metal-insulator-metal waveguides with disk-shaped nanocavities is proposed and numerically investigated.
TL;DR: In this article, an integrated GaAs disk/waveguide system is presented, where a millimeter-long waveguide is suspended and tapered on the chip over a length of 25 µm to evanescently couple to high Q optical whispering gallery modes of a GaAs disks.
Abstract: We report on an integrated GaAs disk/waveguide system. A millimeter-long waveguide is suspended and tapered on the chip over a length of 25 μm to evanescently couple to high Q optical whispering gallery modes of a GaAs disk. The critical coupling regime is obtained both by varying the disk/guide gap distance and the width of the suspended nanoscale taper. Experimental results are in good agreement with predictions from coupled mode theory.
TL;DR: In this article, the numerical results based on the finite-difference time-domain method can be accurately explained by the resonant theory, and the transmission characteristics of the drop waveguide are influenced by the coupling distance between the resonator and drop/bus waveguides.
Abstract: Nanoplasmonic wavelength demultiplexing (WDM) structures based on metal-insulator-metal waveguides are designed and investigated numerically. The WDM structures possess a series of resonator-based channel drop filters near a bus waveguide. The demultiplexing wavelength of each channel can be tuned by adjusting the geometrical parameters and refractive index of the resonator. The numerical results based on the finite-difference time-domain method can be accurately explained by the resonant theory. Meanwhile, the transmission characteristics of the drop waveguide are influenced by the coupling distance between the resonator and drop/bus waveguides, which can be exactly analyzed by the temporal coupled-mode theory. Additionally, it is found that the drop efficiencies can be improved by a factor of more than 1.8 when a reflection feedback is introduced in the bus waveguide.
TL;DR: In this paper, a ring-bus-ring (RBR) resonator system is proposed to generate a spectrum resembling electromagnetically induced transparency (EIT), which is qualitatively different compared to other existing EIT schemes.
Abstract: This paper presents theoretical studies on the ring-bus-ring (RBR) resonator system, which consist of two resonators indirectly coupled through a center waveguide between them. By controlling the intercavity interaction and engineering the phase response through incorporation of RBR with Mach-Zehnder interferometer, we show that it is possible to generate a spectrum resembling electromagnetically induced transparency (EIT), which is qualitatively different compared to other existing EIT schemes. The transparency becomes sharper as the coupling strength between resonators is increased, with the background spectrum significantly reduced as a result of additional phase shift from indirect coupling. In addition, the EIT-like spectrum is generated out of low-finesse resonators, in contrast with existing EIT schemes where the resonator's finesse is required to be high. Comparisons with finite-difference-time-domain simulation show fairly a good agreement with analytical formulations.
TL;DR: A new hybrid plasmonic waveguide is introduced and it is demonstrated that the resultant hybrid modes possess small mode areas and long propagation distances, as well as high excitation efficiency from the conventional dielectric modes.
Abstract: A new hybrid plasmonic waveguide is introduced and characterized in the paper. By coupling the photonic modes of a Si waveguide with the higher-order plasmonic modes of a silver nanowire, we demonstrate that the resultant hybrid modes possess small mode areas and long propagation distances, as well as high excitation efficiency (~90%) from the conventional dielectric modes. Such hybrid waveguides may find applications in the high-dense photonic integrations.
TL;DR: In this paper, the authors considered light transmission in a 2D photonic crystal waveguide coupled with two identical nonlinear defects positioned symmetrically aside the waveguide, and they showed three scenarios for the transmission.
Abstract: We consider light transmission in a two-dimensional (2D) photonic crystal waveguide coupled with two identical nonlinear defects positioned symmetrically aside the waveguide. With the coupled mode theory, we show three scenarios for the transmission. The first one inherits the linear case and preserves the symmetry. In the second scenario, the symmetry is broken because of different light intensities at the defects. In the third scenario, the intensities at the defects are equal but phases of complex amplitudes are different. That results in a vortical power flow between the defects similar to the dc Josephson effect if the input power over the waveguide is applied and the defects are coupled. All of these phenomena agree well with computations based on an expansion of the electromagnetic field into optimally adapted photonic Wannier functions in a 2D photonic crystal.
TL;DR: In this article, a simple yet rigorous theoretical model capable of analytical estimation of plasmonic field enhancement in complex metal structures is presented, where the complex structures are treated as coupled multipole modes with highest enhancements obtained due to superposition of high-order modes in small particles.
Abstract: We describe a simple yet rigorous theoretical model capable of analytical estimation of plasmonic field enhancement in complex metal structures. We show that one can treat the complex structures as coupled multipole modes with highest enhancements obtained due to superposition of high-order modes in small particles. The model allows one to optimize the structures for the largest possible field enhancements, which depends on the quality factor $Q$ of the metal and can be as high as ${Q}^{2}$ for two spherical particles. The hot spot can occur either in the nanogaps between the particles or near the smaller particles. We trace the optimum field enhancement mechanism to the fact that the extended dipole modes of larger particles act as efficient antennas, while the modes in the gaps or near the smaller particles act as the compact subwavelength cavities. The present analytical approach can be conveniently extended to incorporate large numbers of particles in various intricate arrangements.
TL;DR: A field propagation model where a global optical filter, characterized by its optical transfer function, embraces all the intermediate optical components in a linear link to provide the most general and versatile description of complex analog photonic systems.
Abstract: The concept of filtered Microwave Photonic Links is proposed in order to provide the most general and versatile description of complex analog photonic systems. We develop a field propagation model where a global optical filter, characterized by its optical transfer function, embraces all the intermediate optical components in a linear link. We assume a non-monochromatic light source characterized by an arbitrary spectral distribution which has a finite linewidth spectrum and consider both intensity modulation and phase modulation with balanced and single detection. Expressions leading to the computation of the main figures of merit concerning the link gain, noise and intermodulation distortion are provided which, to our knowledge, are not available in the literature. The usefulness of this derivation resides in the capability to directly provide performance criteria results for complex links just by substituting in the overall closed-form formulas the numerical or measured optical transfer function characterizing the link. This theory is presented thus as a potential tool for a wide range of relevant microwave photonic application cases which is extendable to multiport radio over fiber systems.
TL;DR: A compact structure to concentrate optical waves from a silicon-on-insulator waveguide to a deep sub-wavelength and high intensity surface plasmon focal spot at the tip of a metallic strip taper is numerically designed.
Abstract: We have numerically designed a compact structure to concentrate optical waves from a silicon-on-insulator waveguide to a deep sub-wavelength and high intensity surface plasmon focal spot at the tip of a metallic strip taper. A systematic design approach is developed to obtain an optimal photon-surface plasmon side coupling efficiency of up to 50% at 1.55 μm wavelength, and an over 50 times increase in electric field intensity in a focal region of around 20nm × 20nm × 7nm in size. The length of the whole device is 2.2 μm. We expect fabrication of the proposed device to be simpler than devices in previous work.
TL;DR: In this article, a wide-band photonic crystal Y-splitter for TE modes is proposed, where a triangular lattice of air holes etched in a GaAs slab is used as the platform.
Abstract: In this study, a wide-band photonic crystal Y-splitter for TE modes is proposed. A triangular lattice of air holes etched in a GaAs slab is used as the platform. In order to numerically analyze the structures, plane wave expansion (PWE) and finite difference time domain (FDTD) methods are used. In comparison with the structures reported in the literature, the proposed topology has a less complexity while it provides more than 100nm bandwidth. The simplicity of the design, its high transmission ratio and its wide bandwidth makes it a suitable choice for the implementation of photonic crystal integrated circuits.
TL;DR: It is demonstrated that the group delay in an on-chip photonic-crystal device with two resonators side coupled to a waveguide can be controlled by tuning either the propagation phase of the waveguide or the frequency of the resonators.
Abstract: We measure the group delay in an on-chip photonic-crystal device with two resonators side coupled to a waveguide. We demonstrate that such a group delay can be controlled by tuning either the propagation phase of the waveguide or the frequency of the resonators.
TL;DR: In this paper, the authors investigated the wavelength dependence of the pump absorption along Yb3+-doped fibers, for cladding-pumped single as well as coupled multimode (GTWaveTM) fibers.
Abstract: We investigate experimentally and theoretically the wavelength dependence of the pump absorption along Yb3+-doped fibers, for cladding-pumped single as well as coupled multimode (GTWaveTM) fibers. We show that significant spectral absorption distortions occur along the length with the 976nm absorption peak affected the most. We have developed a novel theoretical approach, based on coupled mode theory, to explain the observed effects. We have also investigated the mode mixing requirements in order to improve the absorption spectral distribution along the increase the overall absorption efficiency and discuss the implications on fiber laser performance.
TL;DR: In this paper, surface relief Bragg gratings integrated with aluminum oxide ridge waveguides were used to achieve monolithic distributed Bragg reflector cavities with finesse up to 147 and quality factors of more than 1E6.
Abstract: >The design, fabrication, and characterization of surface relief Bragg gratings integrated with aluminum oxide ridge waveguides are reported. After patterning a photoresist layer by laser interference lithography, uniform gratings with a depth of 120 nm and a period of 507 nm were etched into the SiO$_2$ top cladding. The grating length varied between 1.25 mm and 4.75 mm. The grating-induced loss was 0.08 ± 0.01 dB/cm, while the maximum grating reflectivity exceeded 99%. These values enabled the realization of monolithic distributed Bragg reflector cavities with finesse up to 147 and quality factors of more than 1E6. The measured performance agrees very well with predictions based on coupled mode theory.
TL;DR: Numerically, it is shown that the lossy side-coupled plasmonic resonators can be used as bistable switches without compensation and the nonlinear transmission formula of the resonators is correct to adapt the lost condition.
Abstract: We show numerically that the lossy side-coupled plasmonic resonators can be used as bistable switches without compensation. While the internal loss imposes on the bistable characteristics by reducing the transmission contrast and raising the input power requirement, it makes the switching more available by enlarging the width of the hysteresis loop. We also correct the nonlinear transmission formula of the resonators to adapt the lossy condition. Both the theoretical and simulation results are in good agreement.
TL;DR: In this article, the authors demonstrate evanescent coupling between a series of single mode dielectric waveguides and adjacent plasmonic waveguide with relatively large cross section (200 nm×300 nm).
Abstract: Heat assisted magnetic recording (HAMR) is a possible solution to further increase hard drive recording density. In a HAMR system, an external light source is employed to locally heat up magnetic media. To achieve a realistic HAMR system, a near-field transducer (NFT) is necessary to focus optical fields down to 10-20 nm in size. Different approaches to excite NFTs have been investigated, including focusing of external light sources and coupling from dielectric waveguides. Here we demonstrate evanescent coupling between a series of single mode dielectric waveguides and adjacent plasmonic waveguides with relatively large cross section (200 nm×300 nm). We envision for these large plasmonic guides could then be used, in turn, to efficiently drive NFT's with smaller cross sectional area. A series of samples with various overlap length of the dielectric c and plasmonic waveguides demonstrates that coupling in these waveguides can be designed and understood using mode indices calculated from the eigenmodes of the waveguide cross sections. Coupling strength which oscillates with the length of the overlap section of the waveguides is shown according to standard coupled mode theory.
TL;DR: In this paper, a variety of multipole plasmonic lattice solitons, including dipoles, quadrupoles, and necklaces, were theoretically demonstrated in two-dimensional metallic nanowire arrays with Kerr-type nonlinearities.
Abstract: We theoretically demonstrate a variety of multipole plasmonic lattice solitons, including dipoles, quadrupoles, and necklaces, in two-dimensional metallic nanowire arrays with Kerr-type nonlinearities. Such solitons feature complex internal structures with an ultracompact mode size approaching or smaller than one wavelength. Their mode sizes and the stability characteristics are studied in detail within the framework of coupled mode theory. The conditions to form and stabilize these highly confined solitons are within the experimentally achievable range.
TL;DR: In this paper, the symmetrical input wave with the antibonding bound state in a straight waveguide coupled with two cavities positioned perpendicular to the waveguide was shown to give rise to nonsymmetrical outputs in the T-shape waveguide.
Abstract: erot interferometer architecture. Similarly, the second mechanism of the symmetry breaking is the result of mixing the symmetrical input wave with the antibonding bound state in a straight waveguide coupled with two cavities positioned perpendicular to the waveguide. In both cases the mixing is due to nonlinearity. In turn, the symmetry-breaking solutions give rise to nonsymmetrical outputs in the T-shape waveguide. These effects are directly demonstrated by the electromagnetic field solutions which are complimented by coupled mode theory for the light transmission.
TL;DR: This work considers a system consisting of a photonic crystal cavity coupled to two input and two output waveguides and investigates the demultiplexing of an optical time division multiplexed signal, based on a coupled mode theory.
Abstract: The performance of all-optical switches is a compromise between the achievable bandwidth of the switched signal and the energy requirement of the switching operation. In this work we consider a system consisting of a photonic crystal cavity coupled to two input and two output waveguides. As a specific example of a switching application, we investigate the demultiplexing of an optical time division multiplexed signal. To quantify the energy-bandwidth trade-off, we introduce a figure of merit for the detection of the demultiplexed signal. In such investigations it is crucial to consider patterning effects, which occur on time scales that are longer than the bit period. Our analysis is based on a coupled mode theory, which allows for an extensive investigation of the influence of the system parameters on the switching dynamics. The analysis is shown to provide new insights into the ultrafast dynamics of the switching operation, and the results show optimum parameter ranges that may serve as design guidelines in device fabrication.
TL;DR: An optical coupling system, which consists of waveguide, cavity and waveguide resonator, is presented to investigate coupled-resonator-induced transparency effect and the effect is numerically demonstrated by simulating the propagation of electromagnetic waves in photonic crystals by finite-difference time-domain method.
Abstract: We present an optical coupling system, which consists of waveguide, cavity and waveguide resonator, to investigate coupled-resonator-induced transparency effect The transmission properties are analyzed theoretically by using coupled-mode theory in time domain We also numerically demonstrate the effect by simulating the propagation of electromagnetic waves in photonic crystals by finite-difference time-domain method