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Showing papers on "Coupled mode theory published in 2008"


Journal ArticleDOI
TL;DR: In this article, a single weakly coupled quantum dot can control the transmission of photons through a photonic crystal cavity that is coupled to waveguides on the chip and demonstrated dipole induced transparency.
Abstract: We demonstrate dipole induced transparency in an integrated photonic crystal device. We show that a single weakly coupled quantum dot can control the transmission of photons through a photonic crystal cavity that is coupled to waveguides on the chip. Control over the quantum dot and cavity resonance via local temperature tuning, as well as efficient out-coupling with an integrated grating structure is demonstrated.

127 citations


Journal ArticleDOI
TL;DR: Resonance-splitting and enhanced notch depth are experimentally demonstrated in micro-ring resonators on SOI platform as a result of the mutual mode coupling.
Abstract: Resonance-splitting and enhanced notch depth are experimentally demonstrated in micro-ring resonators on SOI platform as a result of the mutual mode coupling. This coupling can be generated either by the nanometer-scaled gratings along the ring sidewalls or by evanescent directional coupling between two concentric rings. The transmission spectra are fitted using the time-domain coupled mode analysis. Split-wavelength separation of 0.68 nm for the 5-microm-radius ring, notch depth of 40 dB for the 10-microm-radius ring, and intrinsic Q factor of 2.6 x 10(5) for the 20-microm-radius ring are demonstrated. Notch depth improvement larger than 25 dB has been reached in the 40-39-microm-radius double-ring structure. The enhanced notch depth and increased modal area for the concentric rings might be promising advantages for bio-sensing applications.

118 citations


Journal ArticleDOI
TL;DR: It is observed that both thermal and optical Kerr effects can be utilized to improve the sensitivity of the coupled optical microcavities as refractive index sensors.
Abstract: We theoretically investigate the application of coupled optical microcavities as refractive index sensors. Coupled microcavities support a very sharp asymmetrical Fano resonance, which gives rise to faster changes in output transmission than the changes from a single cavity. With the output transmission at a fixed wavelength that varies much faster than it does in a single-cavity resonance, the result is enhanced sensitivity of the device to the changes in refractive index. In addition, it is observed that both thermal and optical Kerr effects can be utilized to improve the sensitivity.

90 citations


Journal ArticleDOI
TL;DR: A strongly coupled, chirped Bragg grating made by sinusoidally modulating the sidewalls of a silicon waveguide is designed, fabricated, and experimentally characterized.
Abstract: A strongly coupled, chirped Bragg grating made by sinusoidally modulating the sidewalls of a silicon waveguide is designed, fabricated, and experimentally characterized. By varying the device parameters, the operating wavelength, device bandwidth, sign (normal or anomalous), and magnitude of group-velocity dispersion may be engineered for specific photonic applications. Asymmetric Blackman apodization is best suited for maximizing the useable bandwidth while providing good ripple suppression. Dispersion values up to 7.0 x 10(5) ps/nm/km are demonstrated at 1.55 microm.

87 citations


Journal ArticleDOI
TL;DR: Fitting the positions, widths and heights of resonances in the experimental spectra to the characteristic equation for microsphere modes and to universal coupled microresonator theory establishes sphere radius and index, identify mode numbers, and determine losses.
Abstract: Evanescent coupling of light from glass channel waveguides into the whispering gallery modes of glass microspheres of radius 15µm and 100µm is studied experimentally at wavelengths near 1550nm. Fitting the positions, widths and heights of resonances in the experimental spectra to the characteristic equation for microsphere modes and to universal coupled microresonator theory, we establish sphere radius and index, identify mode numbers, and determine losses. The results provide detailed information for the design of optical devices incorporating microsphere resonators in planar lightwave circuits.

77 citations


Journal ArticleDOI
TL;DR: A new type of optical resonator that consists of embedded ring resonators (ERRs) that exhibit unique amplitude and phase characteristics and allow designing compact filters, modulators, and delay elements is proposed.
Abstract: We propose a new type of optical resonator that consists of embedded ring resonators (ERRs). The resonators exhibit unique amplitude and phase characteristics and allow designing compact filters, modulators, and delay elements. A basic configuration of the ERRs with two rings coupled in a point-to-point manner is discussed under two operating conditions. An ERR-based microring modulator shows a high operation speed up to 30 GHz. ERRs with distributed coupling are briefly described as well.

65 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical and numerical analysis of low-loss right angle waveguide bends and T-junctions based on ultra-compact photonic crystal ring resonators (PCRR) is presented.

64 citations


Journal ArticleDOI
TL;DR: A femtosecond fiber laser was applied to fabricate broadband directional couplers inside bulk glass for general power splitting application in the 1250 to 1650-nm wavelength telecom spectrum, permitting simple design and implementation of broadband coupler for bulk 3D optical circuit integration.
Abstract: A femtosecond fiber laser was applied to fabricate broadband directional couplers inside bulk glass for general power splitting application in the 1250 to 1650-nm wavelength telecom spectrum. The broadband response was optimized over the 400-nm bandwidth by tailoring the coupling strength and the waveguide interaction length to balance the differing wavelength dependence of the straight interaction and bent transition regions. High spatial finesse of the femtosecond-laser writing technique enabled close placement (~6 μm) of adjacent waveguides that underpinned the wavelength-flattened broadband response at any coupling ratio in the 0% to 100% range. The spectral responses were well-represented by coupled mode theory, permitting simple design and implementation of broadband couplers for bulk 3D optical circuit integration.

61 citations


Journal ArticleDOI
TL;DR: In this paper, a submicrometer integrated optical sensor based on Bragg gratings in silicon-on-insulator technology is theoretically proposed, and the grating analysis is performed using a mixed numerical approach based on the finite-element method and coupled mode theory.
Abstract: A submicrometer integrated optical sensor based on Bragg gratings in silicon-on-insulator technology is theoretically proposed in this paper. The grating analysis is performed using a mixed numerical approach based on the finite-element method and coupled mode theory. The possibility to use third-order instead of first-order grating is discussed and performances compared, thus overcoming fabrication problems associated to submicrometer scale features. A detection limit of approximately 10-4 refractive index unit has been calculated for a 173-mum-long grating. Strategies to further improve this value have been discussed too. Finally, fabrication tolerances influence on optimized gratings has been investigated.

42 citations


Journal ArticleDOI
TL;DR: In this article, an exact analytical solution for the inverse scattering problem formulated by using the coupled-mode theory in the microwave range, assuming single-mode operation, is presented, where the solution is a series that gives the required coupling coefficient for the microwave device as a function of the target frequency response.
Abstract: In this paper, we present an exact analytical solution for the inverse scattering problem formulated by using the coupled-mode theory in the microwave range, assuming single-mode operation. The solution is a series that gives the required coupling coefficient for the microwave device as a function of the target frequency response. A clear physical meaning for the terms of the series is discussed, and several useful properties for the synthesis are given, thus providing a deep understanding of the synthesis mechanics. The method allows for the design of microwave devices with arbitrary frequency response only constrained by principles of causality, passivity, and stability. The resulting device is, in general, a nonuniform waveguide that features a continuously varying profile, e.g., a nonuniform microstrip line with continuously varying strip width. As an example of the potential of the synthesis method, a matched filter for ultra-wideband applications is finally designed in microstrip technology and successfully tested.

40 citations


Journal ArticleDOI
TL;DR: In this article, the authors numerically studied a taper-microsphere coupling system with coupled-mode theory by introducing a mode-coupling mechanism and obtained transmission and reflection coefficients directly through numerical calculation for a spherical silica microcavity.
Abstract: We have numerically studied a taper-microsphere coupling system with coupled-mode theory by introducing a mode-coupling mechanism. Transmission and reflection coefficients have been obtained directly through numerical calculation for a spherical silica microcavity. In the presence of the modal coupling mechanism, the optimal condition for transferring the light energy into the microsphere is no longer the critical coupling point. Instead, it should be in the under-coupling regime and can be reached by optimizing the size of the fiber taper and the taper-microsphere gap.

Journal ArticleDOI
Chuantao Zheng1, Chun-Sheng Ma1, Xin Yan1, Xian-Yin Wang1, Da-Ming Zhang1 
TL;DR: In this article, the authors used coupled mode theory, electro-optic modulation theory, conformal transforming method, image method, and the proposed transfer matrix technique for analyzing the transmission powers, rise time, fall time, switching time and switching frequency of the polymer directional coupler electrooptic switches.

Journal ArticleDOI
TL;DR: In this paper, a ring resonator composed of a plasmonic waveguide is presented, where an array of silver nanorods is used to determine the modes of ring resonators, the generalized multipole technique (GMT) is used.
Abstract: A ring resonator composed of a plasmonic waveguide is presented. For the plasmonic waveguide, an array of silver nanorods is assumed. To determine the modes of this ring resonator, the generalized multipole technique (GMT) is used. Using this analysis, we obtain various modes of the proposed ring resonator. The mode field and the corresponding quality factor of each mode of the ring resonator is computed. The results are compared with those obtained using the finite-element method (FEM) and the finite-difference time domain (FDTD) method.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional photonic crystal power splitter based on directional coupling was proposed and the effects of changing coupling length and distance between parallel waveguides on output transmissions were investigated.
Abstract: In this paper, first by applying a theoretical approach (coupled-mode theory and one-dimensional scattering theory model) as well as a numerical approach, the transmission properties of different right angle bend geometries are investigated. Then using optimized bends, a two-dimensional photonic crystal power splitter based on directional coupling is analyzed. Effects of changing coupling length and distance between parallel waveguides on output transmissions are investigated. By further splitting the power in each branch a power splitter with four output branches is proposed. Our numerical simulation with a finite-difference time-domain (FDTD) technique shows that total transmission up to 96% and 92% is obtained for power splitters with two and four output branches, respectively, throughout the calculated coupling lengths. As another application a compact size wavelength multi/demultiplexer composed of optimized 90° bent waveguides and directional couplers is designed.

Journal ArticleDOI
TL;DR: In this article, the surface relief guided-mode resonant gratings with specified central wavelength and FWHM in the visible wavelength range can be designed by analyzing the complex poles of Reflectance and transmission coefficient matrix algorithm (RTCM), a variant of S-matrix propagation algorithm proposed for calculation of multilayer gratings.

Journal ArticleDOI
TL;DR: The effect of symmetry breaking in a system with two coupled Fano resonators is described and it is shown that one achieves the effect at very low input powers.
Abstract: We describe the effect of symmetry breaking in a system with two coupled Fano resonators. A general criterion is derived and optimal parameter regions for switching are identified. By extending the single resonator behavior we show that one achieves the effect at very low input powers.

Journal ArticleDOI
TL;DR: In this paper, the system of coupled discrete equations describing a two-component superlattice with interlaced linear and nonlinear constituents is studied as a basis for investigating binary waveguide arrays, such as ribbed AlGaAs structures.
Abstract: The system of coupled discrete equations describing a two-component superlattice with interlaced linear and nonlinear constituents is studied as a basis for investigating binary waveguide arrays, such as ribbed AlGaAs structures, among others. Compared to the single nonlinear lattice, the interlaced system exhibits an extra band-gap controlled by the, suitably chosen by design, relative detuning. In more general physics settings, this system represents a discretization scheme for the single-equation-based continuous models in media with transversely modulated linear and nonlinear properties. Continuous wave solutions and the associated modulational instability are fully analytically investigated and numerically tested for focusing and defocusing nonlinearity. The propagation dynamics and the stability of periodic modes are also analytically investigated for the case of zero Bloch momentum. In the band-gaps a variety of stable discrete solitary modes, dipole or otherwise, in-phase or of staggered type are found and discussed.

Journal ArticleDOI
TL;DR: In this article, large and periodically corrugated optical waveguide structures are shown to possess specific modal regimes of slow-light propagation that are easily attainable by employing coupled-mode theory and the plane-wave expansion method.
Abstract: Large and periodically corrugated optical waveguide structures are shown to possess specific modal regimes of slow-light propagation that are easily attainable. The very multimode nature of the coupling is studied by employing coupled-mode theory and the plane-wave expansion method. Given a large enough light cone, associated with a surrounding medium with low enough refractive index, we notably identify a critical slowdown regime with an interesting bandwidth-slowdown product. Essential features of these original systems are further explored: the nature of the coupled modes, the role of gain, symmetry effects, polarization, and relation with photonic-crystal systems. Practical systems are introduced using finite-difference time-domain methods, which provides first-order rules for the use of the above phenomena and their implementation in devices. © 2008 Optical Society of America OCIS codes: 230.7370, 050.5298, 050.2770, 050.1940, 130.5296, 130.2790.

Journal ArticleDOI
TL;DR: Characteristics of the propagating modes of the waveguide amplifier are analyzed theoretically using the transfer matrix method, indicating robust single-transverse-mode operation with large modal gain.
Abstract: A new optically pumped waveguide amplifier with ultra-large mode area is proposed. This amplifier is based on gain guiding in a transverse grating waveguide in which the pump is confined by the photonic bandgap while the signal is guided by optical gain. Characteristics of the propagating modes of the waveguide amplifier are analyzed theoretically using the transfer matrix method, indicating robust single-transverse-mode operation with large modal gain.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the properties of a surface-corrugated long-period grating fiber taper fabricated using contact optical lithography and wet etching techniques.
Abstract: We describe the properties of a surface-corrugated long-period-grating fiber taper fabricated using contact optical lithography and wet etching techniques. The preservation of cylindrical symmetry in this device facilitates investigation of the modal behavior. Comparison of the measured and calculated transmission spectra reveals that the widely used coupled-mode theory is not applicable. Instead, a mode-projection model, in which modal propagation and coupling are treated separately within the grating, explains the experiments very well.

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional photonic crystal add-drop filter based on ring resonators was proposed, which can be applicable to photonic integrated circuits. And the simulation results of this filter obtained from the finite-difference time-domain method are consistent with those from the coupled-mode theory.
Abstract: We propose coupled-mode analysis of a two-dimensional photonic crystal add-drop filter based on ring resonators, which can be applicable to photonic integrated circuits. Mechanism of this proposed add-drop filter is analogous to that of ring resonators resonance, which involves interaction of waveguides and resonators. Simulation results of this filter obtained from the finite-difference time-domain method are consistent with those from the coupled-mode theory. Total transmission up to 99% is verified by both methods.

Journal ArticleDOI
TL;DR: The integration of a 30% efficient grating coupler with a compact photonic crystal wavelength demultiplexer (DeMUX) aimed at coarse WDM applications is demonstrated.
Abstract: We demonstrate the integration of a 30% efficient grating coupler with a compact photonic crystal wavelength demultiplexer (DeMUX). The DeMUX has seven output channels that are spaced 10 nm apart and is aimed at coarse WDM applications. The integrated devices are realized on a high-index-contrast InP membrane using a simple benzocyclobutene wafer bonding technique. Cross talks of −10 to −12 dB for four channels 20 nm apart are obtained without optimization.

Journal ArticleDOI
TL;DR: In this article, a channel drop filter using mirror cavities is proposed to achieve a three output port filter in two-dimensional (2D) photonic crystals. And the theoretical mechanism behind these structures is explained by coupling mode theory.
Abstract: In this paper, a heterostructure channel drop filter in two-dimensional photonic crystals based on mirror cavities is investigated. First a channel drop filter using mirror cavities is presented. Then in order to achieve a three output port filter, we present a heterostructure built on a hybrid two-dimensional (2D) photonic crystal that includes two different refractive indices. Our numeric simulation with the finite-difference time-domain (FDTD) technique shows that the heterostructure has acceptable output efficiency over 80%. Finally, by applying a theoretical approach (coupled mode theory), the physical mechanism behind these structures is explained.

Journal ArticleDOI
TL;DR: In this paper, the authors used coupled mode theory to design a method for determining how to tune the microcavity resonant frequencies and showed that pulses can be captured almost completely, with arbitrarily small reflected power.
Abstract: We describe a dynamically tuned system capable of capturing light pulses incident from a waveguide in a pair of microcavities. We use coupled mode theory to design a method for determining how to tune the microcavity resonant frequencies. The results show that pulses can be captured almost completely, with arbitrarily small reflected power. We optimize the pulse capture bandwidth by varying the cavity coupling constants and show that the maximum bandwidth is comparable to the resonant-frequency tuning range. Our system may be implemented using refractive-index tuning in a 2-D silicon photonic crystal slab. Current technology would allow for capture of pulses with widths as low as ~100 ps, with a holding time limited only by cavity loss rates.

Journal ArticleDOI
TL;DR: A coupled mode theory (CMT) model of the behavior of a polarization source in a general photonic structure is developed, and an analytical expression for the resulting generated electric field is obtained; loss, gain and/or nonlinearities can also be modeled.
Abstract: We develop a coupled mode theory (CMT) model of the behavior of a polarization source in a general photonic structure, and obtain an analytical expression for the resulting generated electric field; loss, gain and/or nonlinearities can also be modeled. Based on this treatment, we investigate the criteria needed to achieve an enhancement in various nonlinear effects, and to produce efficient sources of terahertz radiation, in particular. Our results agree well with exact finite-difference time-domain (FDTD) results. Therefore, this approach can also in certain circumstances be used as a potential substitute for the more numerically intensive FDTD method.

Journal ArticleDOI
TL;DR: It is shown that coupled mode theory formulated in the curvilinear coordinates associated with a bend can describe correctly both the bending induced loss and beam degradation and is on par with such "exact" numerical approaches as finite element and finite difference methods for prediction of macro-bending induced losses.
Abstract: In the hollow core photonic bandgap fibers, modal losses are strongly differentiated, potentially enabling effectively single mode guidance. However, in the presence of macro-bending, due to mode coupling, power in the low-loss mode launched into a bend is partially transferred into the modes with higher losses, thus resulting in increased propagation loss, and degradation of the beam quality. We show that coupled mode theory formulated in the curvilinear coordinates associated with a bend can describe correctly both the bending induced loss and beam degradation. Suggested approach works both in absorption dominated regime in which fiber modes are square integrable over the fiber crossection, as well as in radiation dominated regime in which leaky modes are not square integrable. It is important to stress that for multimode fibers, full-vectorial coupled mode theory developed in this work is not a simple approximation, but it is on par with such “exact” numerical approaches as finite element and finite difference methods for prediction of macro-bending induced losses.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a new scheme for an efficient photonic crystal 90° bend and power splitter and used coupled mode theory to analytically investigate the structures and finite difference time domain to simulate and optimize the structures performances.
Abstract: We propose a new scheme for an efficient photonic crystal 90° bend and power splitter. First we design a 90° bend by placing a super defect at the junction of two orthogonal photonic crystal waveguides. We changed the parameters of the super defect to optimize the transmission coefficient of the bent structure. Our two-dimensional (2D) simulations show more than 85% efficiency over a wide range of wavelengths. Then using this new scheme and adding another waveguide we design a new power splitter and optimize it with the same procedure. We used the coupled mode theory to analytically investigate the structures and finite difference time domain to simulate and optimize the structures performances.

Journal ArticleDOI
TL;DR: In this paper, photonic crystal planar waveguides for use as wavelength-selective applications via the mini-stopband extraction mechanism are discussed and experimental data for the core of a compact demux system is presented.
Abstract: We discuss devices based on photonic crystal planar waveguides for use as wavelength-selective applications via the mini-stopband extraction mechanism. We present experimental data for the core of a compact demux system. We show that spatial and spectral behaviours are as intended from coupled-mode theory, as well as from the finite-difference time-domain approach. Finally, we propose architectures with large crosstalk and some inherent fabrication-related advantages achieved by duplicating the basic multimode waveguide and using it as a spectral filter.

Journal ArticleDOI
TL;DR: In this paper, the authors present analytical and numerical studies of a photonic lattice with short and long-range harmonic modulations of the refractive index, which can be prepared experimentally with holographic photolithography.
Abstract: We present analytical and numerical studies of a photonic lattice with short- and long-range harmonic modulations of the refractive index. Such structures can be prepared experimentally with holographic photolithography. In the spectral region of the photonic bandgap of the underlying single-periodic crystal, we observe a series of bands with anomalously small dispersion. The related slow-light effect is attributed to the long-range modulation of the photonic lattice that leads to formation of an array of evanescently coupled high-Q cavities. The band structure of the lattice is studied with several techniques: (i) transfer matrix approach; (ii) an analysis of resonant coupling in the process of band folding; (iii) effective-medium approach based on coupled-mode theory; and (iv) the Bogolyubov-Mitropolsky approach. The latter method, commonly used in the studies of nonlinear oscillators, was employed to investigate the behavior of eigenfunction envelopes and the band structure of the dual-periodic photonic lattice. We show that reliable results can be obtained even in the case of large refractive index modulation.

Journal ArticleDOI
TL;DR: In this paper, the authors extended Coupled Mode Theory (CMT) to the case of infinite 2D photonic arrays, made of periodically repeated identical groups of different waveguides (supercells).
Abstract: Coupled-mode theory (CMT) is extended to the case of infinite 2-D photonic arrays, made of periodically repeated identical groups of different waveguides (supercells). Born-Karman boundary conditions, applied to the CMT equations for this system, are used to compute the photonic band structure. This method was found to be more efficient and much less resource-consuming than the existing approaches, for the analysis of finite large-sized arrays.