Showing papers on "Coupled mode theory published in 2010"
TL;DR: Transmission characteristics of two coupled identical cavities, of either standing-wave (SW) or traveling- wave (TW) type, are analyzed, based on temporal coupled mode theory, and it is interesting to notice that a side-coupled SW cavity system performs similarly to an under-couple TW cavity.
Abstract: We analyze transmission characteristics of two coupled identical cavities, of either standing-wave (SW) or traveling-wave (TW) type, based on temporal coupled mode theory. Mode splitting is observe ...
311 citations
TL;DR: It is found that the resonance wavelengths can be easily manipulated by adjusting the radius and refractive index of the nanocavity, which is in good agreement with the results obtained by finite-difference time-domain (FDTD) simulations.
Abstract: A novel and simple plasmonic filter based on metal-insulator-metal plasmonic waveguides with a nanodisk resonator is proposed and investigated numerically. By the resonant theory of disk-shaped nanocavity, we find that the resonance wavelengths can be easily manipulated by adjusting the radius and refractive index of the nanocavity, which is in good agreement with the results obtained by finite-difference time-domain (FDTD) simulations. In addition, the bandwidths of resonance spectra are tunable by changing the coupling distance between the nanocavity and waveguides. This result achieved by FDTD simulations can be accurately analyzed by temporal coupled mode theory. Our filters have important potential applications in high-density plasmonic integration circuits.
250 citations
07 Jun 2010
TL;DR: In this article, a light-trapping theory was developed to reveal that the conventional limit 4n2 can be substantially surpassed in nanophotonic regimes, opening new avenues for highly efficient solar cells.
Abstract: We use a rigorous electromagnetic approach to develop a light-trapping theory, which reveals that the conventional limit 4n2can be substantially surpassed in nanophotonic regimes, opening new avenues for highly efficient solar cells.
179 citations
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.
126 citations
TL;DR: A new, efficient adiabatic in-plane fiber-to-chip coupler design that allows to reduce the coupler length multiple times in comparison with pure inverse taper-based couplers of similar efficiency is proposed.
Abstract: A new, efficient adiabatic in-plane fiber-to-chip coupler design is proposed. In this design, the light from the fiber is coupled into a low-index waveguide with matching mode size. The mode is first adiabatically reduced in size with a rib taper, and then transferred into a high-index (e.g. silicon) waveguide with an inverse taper. The two-stage design allows to reduce the coupler length multiple times in comparison with pure inverse taper-based couplers of similar efficiency. The magnitude of length reduction increases with the refractive index of the low-index waveguide and the fiber mode size.
111 citations
TL;DR: It has been demonstrated using Finite Element Methods (FEM) that the high performance SIMS waveguide can be used to fabricate deep sub-wavelength integrated plasmonic devices such as directional couplers with the ultra short coupling lengths, sharply bent waveguides, and ring resonators having a functional size of ≈1 µm and with low insertion losses and nearly zero radiation losses.
Abstract: We report the first study of nanoscale integrated photonic devices constructed with semiconductor-insulator-metal strip (SIMS) waveguides for use at telecom wavelengths. These waveguides support hybrid plasmonic modes transmitting through a 5-nm thick insulating region with a normalized intensity of 200-300 μm−2. Their fundamental mode, unique transmission and dispersion properties are consistent with photonic devices for guiding and routing of signals in communication applications. It has been demonstrated using Finite Element Methods (FEM) that the high performance SIMS waveguide can be used to fabricate deep sub-wavelength integrated plasmonic devices such as directional couplers with the ultra short coupling lengths, sharply bent waveguides, and ring resonators having a functional size of ≈1 µm and with low insertion losses and nearly zero radiation losses.
83 citations
TL;DR: In this article, the maximum transmission and absorption cross sections for subwavelength resonant apertures are only related to the wavelength of the incident light and the directivity of the aperture's radiation pattern.
Abstract: We develop the coupled-mode theory for nanoscale resonant apertures. We show that the maximum transmission and absorption cross sections for subwavelength resonant apertures are only related to the wavelength of the incident light and the directivity of the aperture’s radiation pattern. A general relation between the transmission cross section and the directivity is proven from the coupled-mode theory. As a specific example, we apply the theory to a nanoslit aperture in a metallic film and obtain excellent agreement with direct numerical simulations.
72 citations
TL;DR: In this paper, the authors describe the strong optomechanical dynamical interactions in ultrahigh-Q/V slot-type photonic crystal cavities with light localization in an air mode with 0.02(λ/n)3 modal volumes.
Abstract: We describe the strong optomechanical dynamical interactions in ultrahigh-Q/V slot-type photonic crystal cavities. The dispersive coupling is based on mode-gap photonic crystal cavities with light localization in an air mode with 0.02(λ/n)3 modal volumes while preserving optical cavity Q up to 5 × 106. The mechanical mode is modeled to have fundamental resonance Ωm/2π of 460 MHz and a quality factor Qm estimated at 12,000. For this slot-type optomechanical cavity, the dispersive coupling gom is numerically computed at up to 940 GHz/nm (Lom of 202 nm) for the fundamental optomechanical mode. Dynamical parametric oscillations for both cooling and amplification, in the resolved and unresolved sideband limit, are examined numerically, along with the displacement spectral density and cooling rates for various operating parameters.
70 citations
TL;DR: Numerical results of the tilted fiber Bragg gratings with outer-cladding index equal, lower and higher than that of the inner-Cladding indicate that the complex coupled mode approach is highly effective in the simulation of couplings to cladding and radiation modes in tilted fiber gratings.
Abstract: A full vector complex coupled mode theory (CMT) for the analysis of tilted fiber gratings is presented. With the combination of the perfectly matched layer (PML) and the perfectly reflecting boundary (PRB), the continuous radiation modes are well represented by a set of discrete complex modes. Simulation of coupling to radiation modes is greatly simplified and may be treated in the same fashion as guided modes. Numerical results of the tilted fiber Bragg gratings (TFBGs) with outer-cladding index equal, lower and higher than that of the inner-cladding indicate that the complex coupled mode approach is highly effective in the simulation of couplings to cladding and radiation modes in tilted fiber gratings. The reflective TFBGs are investigated by the proposed approach in detail.
70 citations
TL;DR: It is shown that total absorption is obtainable in a multiple-port system by properly configuring multiple coherent lightwaves at the condition of critical coupling and analytic expressions for the partial absorbance at each port, the total absorbance, and their sum rule provide a non-perturbing method to probe coupling characteristics of highly localized optical modes.
Abstract: We theoretically investigate resonant absorption in a multiple-port surface-plasmon polaritons (SPP) resonator near the condition of critical coupling at which internal loss is comparable to radiation coupling. We show that total absorption is obtainable in a multiple-port system by properly configuring multiple coherent lightwaves at the condition of critical coupling. We further derive analytic expressions for the partial absorbance at each port, the total absorbance, and their sum rule, which provide a non-perturbing method to probe coupling characteristics of highly localized optical modes. Rigorous simulation results modeling a surface-plasmon resonance grating in the multiple-order diffraction regime show excellent agreements with the analytic expressions.
68 citations
TL;DR: This paper investigates the scaling issues of silicon traveling-wave microresonators down to ultimate miniaturization levels in SOI platforms and demonstrates Q's as high as ~10(5) for resonators as small as 1.5 μm radius.
Abstract: High Q traveling-wave resonators (TWR)s are one of the key building block components for VLSI Photonics and photonic integrated circuits (PIC). However, dense VLSI integration requires small footprint resonators. While photonic crystal resonators have shown the record in simultaneous high Q (~105-106) and very small mode volumes; the structural simplicity of TWRs has motivated many ongoing researches on miniaturization of these resonators with maintaining Q in the same range. In this paper, we investigate the scaling issues of silicon traveling-wave microresonators down to ultimate miniaturization levels in SOI platforms. Two main constraints that are considered during this down scaling are: 1) Preservation of the intrinsic Q of the resonator at high values, and 2) Compatibility of resonator with passive (active) integration by preserving the SiO2 BOX layer (plus a thin Si slab layer for P-N junction fabrication). Microdisk and microdonut (an intermediate design between disk and ring shape) are considered for high Q, miniaturization, and single-mode operation over a wide wavelength range (as high as the free-spectral range). Theoretical and experimental results for miniaturized resonators are demonstrated and Q's as high as ~105 for resonators as small as 1.5 μm radius are achieved.
TL;DR: In this article, a detailed investigation of resonance-continuum coupling is carried out both experimentally and theoretically in metamaterials based on high-permittivity dielectric subwavelength resonators.
Abstract: A detailed investigation of resonance-continuum coupling is carried out both experimentally and theoretically in metamaterials based on high-permittivity dielectric subwavelength resonators. An original experimental scheme is designed at microwave frequencies, which mimics a periodic array of resonators. Fano resonances are discussed in the framework of temporal coupled mode theory for the cases where one or two resonator modes couples to the continuum. Fano lineshapes are unambiguously demonstrated experimentally for the single-mode case in agreement with theoretical modeling. Numerical evidence of resonance trapping is shown in the two-mode case when modes with the same symmetry coincide in frequency.
21 Mar 2010
TL;DR: In this article, the advantages of using holey fibers as well as effective ways with solid fibers were confirmed for large Aeff Multi-Core Fibers (MCFs), and the solid MCFs with Aeff >100μm2 and suppressed micro bending loss were actually fabricated.
Abstract: For large Aeff Multi-Core Fibers (MCFs), advantages of using holey fibers as well as effective ways with solid fibers were confirmed. The solid MCFs with Aeff >100μm2 and suppressed micro bending loss were actually fabricated.
TL;DR: By fine-tuning the lattice modulation, this work demonstrates coherent destruction of tunneling (CDT) in optically induced three-dimensional photonic lattices and shows unusual behavior of beam propagation, including light tunneling inhibition, anomalous diffraction, and negative refraction mediated by zero or negative coupling in the waveguide arrays.
Abstract: We demonstrate coherent destruction of tunneling (CDT) in optically induced three-dimensional photonic lattices. By fine-tuning the lattice modulation, we show unusual behavior of beam propagation, including light tunneling inhibition, anomalous diffraction, and negative refraction mediated by zero or negative coupling in the waveguide arrays. Image transmission based on CDT is also proposed and demonstrated. Our experimental results are in good agreement with our theoretical analyses.
TL;DR: In this article, the modal properties of hybrid plasmonic waveguides were investigated using coupled-mode theory and finite element method, and it was shown that the coupling between the nanowire fundamental HE11 mode and surface plasmor mode results in three different supermodes.
Abstract: We investigate the modal properties of nanowire-metal hybrid plasmonic waveguides by use of the coupled-mode theory and finite-element method. We show that the coupling between the nanowire fundamental HE11 mode and surface plasmon mode results in three different supermodes. We numerically calculate the dispersion relations, normalized mode areas, and confinement factors of these different modes for plasmonic nanolaser applications and show that the lowest threshold mode is determined by the waveguide geometry.
TL;DR: In this paper, a cross-sectional eigenmode orthogonality relation is derived for a one-dimensional 1D -periodic system, which allows to significantly simplify the coupled mode theory in the fixed eigen mode basis.
Abstract: We analytically study roughness-induced scattering loss in a photonic crystal waveguide PCW . A crosssectional eigenmode orthogonality relation is derived for a one-dimensional 1D -periodic system, which allows us to significantly simplify the coupled mode theory in the fixed eigenmode basis. Assisted by this simplification, analytic loss formulas can be obtained with reasonable assumptions despite the complexity of PCW mode fields. We introduce the radiation and backscattering loss factors 1 and 2 such that the loss coefficient can be written as = 1ng+ 2ng 2 ng is the group index . By finding analytic formulas for 1 and 2, and examining their ratio, we show why the backscattering loss generally dominates the radiation loss for ng 10. The interplay between certain mode-field characteristics, such as the spatial phase, and structure roughness is found crucial in the loss-generation process. The loss contribution from each row of holes is analyzed. The theoretical loss results agree well with experiments. Combined with systematic simulations of loss dependences on key structure parameters, the insight gained in this analytic study helps identify promising pathways to reducing the slow light loss. The cross-sectional eigenmode orthogonality may be applicable to other 1D-periodic systems such as electrons in a polymer chain or a nanowire.
TL;DR: In this paper, all the necessary parameters to describe optical racetrack micro resonators fabricated with silicon on insulator (SOI) technology are discussed, including dispersion law, effective index mismatch, and mode mismatch between bend and straight waveguides.
Abstract: We discuss all the necessary parameters to describe optical racetrack micro resonators fabricated with silicon on insulator (SOI) technology. We focus on some fundamental aspects crucial for a comprehensive and realistic modelling of racetrack resonators as building blocks of complex add-drop filters, like SCISSOR (Side-Coupled Integrated Spaced-Sequences of Resonators) or CROW (Coupled Resonator Optical Waveguides). When the radius of curvature is lower than 5 μm, and/or the separation gaps between waveguide and resonator is small, dispersion law, effective index mismatch, and mode mismatch between bend and straight waveguides are relevant for modelling. A new mode solver, specifically suited for high index contrast small mode area waveguides, is used whose results are compared with the measurement of the optical response of some resonant devices.
TL;DR: This paper reports on the first theoretical demonstration of fast light generation in an ultra-compact double vertical stacked ring resonator coupled to a bus waveguide and proves how this physical effect can be exploited to design fast light resonant devices.
Abstract: Speed manipulation of optical pulses is a very attractive research challenge enabling next-generation high-capacity all-optical communication networks. Pulses can be effectively slowed by using different integrated optical structures such as coupled-resonator waveguiding structures or photonic crystal cavities. Fast light generation by means of integrated photonic devices is currently a quite unexplored research field in spite of its crucial importance for all-optical pulse processing. In this paper, we report on the first theoretical demonstration of fast light generation in an ultra-compact double vertical stacked ring resonator coupled to a bus waveguide. Periodic coupling between the two rings leads to splitting and recombining of symmetric and anti-symmetric resonant modes. Re-established degenerate modes can form when a symmetric and an anti-symmetric mode having different resonance order exhibit the same resonance wavelength. Under degenerate mode conditions, wide wavelength ranges where the group velocity is negative or larger than the speed of light in vacuum are generated. The paper proves how this physical effect can be exploited to design fast light resonant devices. Moreover, conditions are also derived to obtain slow light operation regime.
TL;DR: In this article, two different types of coaxial hybrid plasmonic nanowire waveguides were investigated and their modal properties were analyzed by using the mode hybridization concept and calculated the dispersion relations, normalized mode areas, and confinement factors.
Abstract: We investigate two different types of coaxial hybrid plasmonic nanowire waveguides. The first type consists of a metal cladding, a sandwiched low index dielectric layer, and a high index dielectric core. The second type is the reverse version of the first type. We analyze their modal properties by the use of the mode hybridization concept and calculate the dispersion relations, normalized mode areas, and confinement factors. For the first kind of hybrid waveguide, we can obtain less loss with similar confinement and slightly less overlap between optical modes and the core region. For the second kind of hybrid waveguide, we can obtain strong confinement and enhanced optical fields in a low refractive index region.
TL;DR: A coupled-mode theory describing light propagation in an array of nonlinear plasmonic waveguides predicts a two-band dependence of the propagation constant versus transverse quasi-momentum and existence of discrete and gap plAsmon solitons.
Abstract: We present a coupled-mode theory describing light propagation in an array of nonlinear plasmonic waveguides. Our model predicts a two-band dependence of the propagation constant versus transverse quasi-momentum and existence of discrete and gap plasmon solitons.
TL;DR: Experimental results indicated that these two resonant spectra shifts were linearly dependent on the variation of the RI in the range of 1.3333 approximately 1.4118 and on the temperature in therange of -10 degrees C approximately + 80 degrees C.
Abstract: A fiber-optic sensor for simultaneous measurement of refractive index (RI) and temperature was proposed and demonstrated. It was fabricated by cascading two sections of specialty double cladding (DC) fibers which presented a pair of well-separated resonant spectra dips. The sensing properties of temperature and ambient RI were investigated theoretically based on the coupled mode theory. Experimental results indicated that these two resonant spectra shifts were linearly dependent on the variation of the RI in the range of 1.3333~1.4118 and on the temperature in the range of −10°C~ + 80°C. Such a fiber-optic sensor is simple and easy for mass production and has potential applications for biosensors or chemical sensors.
Proceedings Article•
01 Dec 2010TL;DR: In this article, the authors presented the characteristics of wireless energy transfer to multiple devices using the coupled mode theory (CMT), by assuming that resonant coils between devices are independent.
Abstract: In this paper, characteristics of wireless energy transfer to multiple devices is presented. Using the coupled mode theory (CMT), coupling behavior of resonant coils is analyzed, by assuming that resonant coils between devices are independent. Maximum efficiency of energy transfer to resonant coils of devices and time for the maximum energy transfer are obtained. It is shown that the energy transfer to each device is divided with the rate of the square of the coupling coefficient. It is also shown that the number of devices should be decided carefully to design the wireless energy transfer system since total efficiency is likely to be saturated despite devices increasing. For verification, an equivalent circuit model is derived and using the model, reflection and transmission are simulated. Theoretical results are compared with simulated ones.
TL;DR: In this paper, a method for modeling the mode-coupling process in strongly modulated long period gratings (LPGs) is reported, which is based on calculating the variations of local-mode profiles and propagation constants over the perturbed regions and solving the coupled localmode equations to obtain a quantitative description of the energy exchange.
Abstract: A method for modeling the mode-coupling process in strongly modulated long period gratings (LPGs) is reported. The method is based on calculating the variations of local-mode profiles and propagation constants over the perturbed regions and solving the coupled local-mode equations to obtain a quantitative description of the intermodal energy exchange. The mode-coupling process and the spectral characteristics of a CO2 laser-inscribed LPG in a photonic crystal fiber are numerically modeled and found in good agreement with the experimentally measured results. Compared with the methods based on the conventional coupled-mode and the mode-projection theories, the current method provides a more accurate description of the mode coupling process for LPGs with strong but slow-varying perturbations.
TL;DR: A versatile and easy-to-realize configuration for a guided-wave voltage-tunable distributed feedback grating based on reorientation in nematic liquid crystal and coplanar comb electrodes is proposed and numerically investigated.
Abstract: We propose and numerically investigate a versatile and easy-to-realize configuration for a guided-wave voltage-tunable distributed feedback grating based on reorientation in nematic liquid crystal and coplanar comb electrodes. The device has a wide tuning range exceeding 100 nm and covers C and L bands for wavelength division multiplexing.
TL;DR: In this article, the propagation of ultrashort pulses in a nonlinear two-core photonic crystal fiber (PCF) was analyzed by solving a pair of coupled-mode equations that include all the significant linear and nonlinear terms.
Abstract: We analyze the propagation of ultrashort pulses in a nonlinear two-core photonic crystal fiber (PCF) by solving a pair of coupled-mode equations that include all the significant linear and nonlinear terms. In particular, we highlight the fact that the coupling coefficient dispersion can cause significant pulse distortion over a short length of a two-core PCF. We also study all-optical switching and multi-frequency generation and obtain a reasonable agreement with recent experimental data.
TL;DR: In this paper, the Mach-Zehnder directional coupler made of a 12'μm thick silicon-on-insulator waveguide was theoretically verified by using the beam propagation method, thereby significantly improving the polarization dependence and coupling loss with a conventional fiber.
Abstract: The length of a directional coupler, including the straight and curved parts, is strongly polarization dependent, especially for use in waveguide tap monitoring applications. Three types of curved structure in the coupled regions are presented to demonstrate the different phase contributions in a directional coupler. A 12 μm thick silicon-on-insulator waveguide single-mode region was theoretically verified by using the beam propagation method, thereby significantly improving the polarization dependence and coupling loss with a conventional fiber. The Mach–Zehnder directional coupler made of a 12 μm thick silicon-on-insulator waveguide could minimize the severe polarization dependence on the optical tap port and achieve a flattened wavelength response by implementing the coupled phase effect from the directional coupler’s curved structures. The results demonstrated that the optical waveguide tap port, carrying a portion of the light signal, showed a 0.024 coupling ratio and 0.3 dB for the polarization-dependent loss at a 1550 nm wavelength. The wavelength variation in the tap splitting ratio and polarization was less than 1% and 0.6 dB, respectively, across the entire C-band. A 0.26 dB per interface coupling loss was also achieved between the 12 μm thick silicon-on-insulator waveguide and SMF-28 fiber.
TL;DR: In this paper, a new modal technique is proposed for dynamic analysis of concrete arch dam-reservoir systems in frequency domain, which relies on the new mode shapes that are entitled "ideal-coupled modes".
TL;DR: This is the first demonstration of the tuning of resonance-spacing in an integrated traveling-wave-resonator and it is numerically shown that these modes exhibit high field-enhancements which makes this device extremely useful for nonlinear optics and sensing applications.
Abstract: In this work a traveling-wave resonator device is proposed and experimentally demonstrated in silicon-on-insulator platform in which the spacing between its adjacent resonance modes can be tuned. This is achieved through the tuning of mutual coupling of two strongly coupled resonators. By incorporating metallic microheaters, tuning of the resonance-spacing in a range of 20% of the free-spectral-range (0.4nm) is experimentally demonstrated with 27mW power dissipation in the microheater. To the best of our knowledge this is the first demonstration of the tuning of resonance-spacing in an integrated traveling-wave-resonator. It is also numerically shown that these modes exhibit high field-enhancements which makes this device extremely useful for nonlinear optics and sensing applications.
TL;DR: In this article, the authors proposed a mode converter/splitter based on optical analogy of multistate stimulated Raman adiabatic passage in multimode waveguides.
Abstract: We propose and describe mode converter/splitter based on optical analogy of multistate stimulated Raman adiabatic passage in multimode waveguides. Computer-generated planar holograms are used to implement the coupling coefficients that mimic the optical pulses used in the transfer among quantum states of atoms and molecules. The mode coupling properties in multimode waveguides are analyzed using the coupled-mode theory and shown to resemble the multistate stimulated Raman adiabatic passage process. Key features of multistate systems are illustrated with theoretical calculations and numerical examples. Mode converter and splitter are designed based on the theoretical analysis and verified using beam propagation simulations.
TL;DR: In this article, a photonic-crystal demultiplexer is implemented on a silicon-on-insulator (SoI) platform, which operates on the principle of mini-stopbands of broader waveguides.
Abstract: In this paper, we implement on a silicon-on-insulator (SoI) platform a photonic-crystal demultiplexer that operates on the principle of mini-stopbands of broader waveguides. Previous InP-based membrane versions showed modest crosstalk at 10 nm spacing. Here, we implement a second cavity in the form of a second parallel waveguide almost identical to the core one. Simulations employing three-modes coupled-mode theory and finite-difference time-domain help optimizing the coupling. The experimental realization with deep ultraviolet exposure and grating couplers is the first of this demux strategy on SoI. It successfully shows crosstalk in the 15-20 dB range on a very small footprint.