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Regular perturbation on the group-velocity dispersion parameter for nonlinear fibre-optical communications
摘要： Communication using the optical fibre channel can be challenging due to nonlinear effects that arise in the optical propagation. These effects represent physical processes that originate from light propagation in optical fibres. To obtain fundamental understandings of these processes, mathematical models are typically used. These models are based on approximations of the nonlinear Schr?dinger equation, the differential equation that governs the propagation in an optical fibre. All available models in the literature are restricted to certain regimes of operation. Here, we present an approximate model for the nonlinear optical fibre channel in the weak-dispersion regime, in a noiseless scenario. The approximation is obtained by applying regular perturbation theory on the group-velocity dispersion parameter of the nonlinear Schr?dinger equation. The proposed model is compared with three other models using the normalized square deviation metric and shown to be significantly more accurate for links with high nonlinearities and weak dispersion.
关键词： group-velocity dispersion,nonlinear fibre-optical communications,regular perturbation theory,nonlinear Schr?dinger equation
更新于2025-09-23 15:19:57
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Dispersion properties of uniform trapezoidal optical waveguides
摘要： A method for calculation of the propagation constant of guided modes in the optical waveguides with trapezoidal cross-sections is proposed. The method enables to calculate a propagation constant correction factor that arises due to perturbations of the cross-section of a reference rectangular waveguide. The correction factor is analytically calculated within the framework of the coupled-mode theory. A re?ned form of the coupling coe?cient is obtained owing to the application of a concept of e?ective excitation sources and accurate account of boundary conditions. An impact of the waveguide cross-section shape on its dispersion properties is analysed. The necessity to take into account the proposed form of the coupling coe?cient is demonstrated by comparison of the simulation results with other methods of dispersion calculation.
关键词： coupled-mode theory,optical waveguides,trapezoidal cross-sections,dispersion properties,propagation constant
更新于2025-09-23 15:19:57
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Behavior of waveguide scattering matrices in a neighborhood of thresholds
摘要： A waveguide occupies a d+1-dimensional domain with several cylindrical outlets to in?nity. The waveguide is described by a general elliptic boundary value problem with spectral parameter μ, selfadjoint with respect to the Green formula. At in?nity, the coe?cients of the problem stabilize at an exponential rate to functions independent of the axial variable in the corresponding cylinder. On every interval of the continuous spectrum between neighboring “thresholds”, a unitary scattering matrix S(μ) is de?ned; the size of S(μ) is ?nite for any μ, remains to be constant on any such interval, and varies from an interval to an interval. The basic result claims the existence of ?nite one-sided limits of the scattering matrix S(μ) at every threshold.
关键词： stable basis of waves,Elliptic problems,dispersion relations,one-sided limits at thresholds,analytic continuation
更新于2025-09-23 15:19:57
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Dispersion Measurement of Electro-Optic Coefficient ?322 of Lithium Niobate Based on Photoelastic Modulation
摘要： A novel method for determining the electro-optic (EO) coe?cient γ22 of lithium niobate and its dispersion using photoelastic modulation is presented. A spectroscopic polarimetry was constructed with the photoelastic modulator (PEM), and a monochromator was selected to automatically scan the wavelength of a light source. Phase retardation induced by an EO sample was loaded into the modulation signals to demodulate the EO coe?cients. The PEM and data processing were controlled in the same ?eld programmable gate array (FPGA), and the DC and harmonic terms were extracted simultaneously by employing digital phase-locked technology. An experimental system was built to analyze the principle of this scheme in detail. After the modulation phase retardation amplitude of the PEM was precisely calibrated, the EO coe?cient γ22 of a Y-cut lithium niobate crystal plate was measured in the spectral range from 0.42 to 0.8 μm. The experimental results demonstrated that the measurement sensitivity of the system was 1.1 × 10?14 m/V for a sampling time of 198.9 ms. Plotting the measured results against the light wavelength, the dispersion of the EO coe?cients was obtained similar to the Cauchy dispersion formula γ22 = 5.31 × 10?12 + 4.071 × 10?13/λ2 + 7.184 × 10?14/λ4 in the visible light range. This method is suitable for studying dispersion of the EO coe?cients of crystals as well as of thin ?lms and two-dimensional materials.
关键词： electro-optic (EO) coe?cient,digital phase-locked technology,polarization modulation,dispersion measurement
更新于2025-09-23 15:19:57
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Complex Bianisotropy Effect on the Propagation Constant of a Shielded Multilayered Coplanar Waveguide Using Improved Full Generalized Exponential Matrix Technique
摘要： A theoretical study of the electromagnetic propagation in a complex medium suspended multilayer coplanar waveguide (CPW) is presented. The study is based on the generalized exponential matrix technique (GEMT) combined with Galerkin’s spectral method of moments applied to a CPW printed on a bianisotropic medium. The analytical formulation is based on a Full-GEMT, a method that avoids usual procedures of heavy and tedious mathematical expressions in the development of calculations and uses matrix-based mathematical expressions instead. These particularities are exploited to develop a mathematical model for the characterization of wave propagation in a three-layer shielded suspended CPW structure. This study is based on the development of mathematical formulations in full compact matrix-based expressions resulting in Green’s functions in a matrix form. The implemented method incorporates a new accelerating procedure developed in the GEMT which provides an initial value used to speed up searching for the exact solution in the principal computation code. This helped us to obtain accurate solutions with tolerable computing time. Good agreements have been achieved with the literature in terms of accuracy and rapid convergence. The results for di?erent cases of bianisotropy have been investigated, and particularly, the e?ect on the dispersion characteristics is presented and compared with the isotropic case.
关键词： Muller’s method,dispersion characteristics,chiral,acceleration procedure,complex propagation constant,full-GEMT,multilayer CPW structure,Tellegen
更新于2025-09-23 15:19:57
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Estimation of power loss spectra in slightly flattened distorted Bragg fiber waveguide
摘要： Dispersion characteristic and fiber loss spectra of a Bragg fiber waveguide having slightly flattened distortion are estimated for sensing applications. The characteristic and optical power loss equations of waveguide are obtained by matching the fields at various boundaries under quarter wave stack conditions. It is found that the optimum power loss is inversely proportional to the ninth power of distortion coefficient. The obtained results show that optimum fiber loss decreases with decrease of refractive index of cladding layer ′ ′b (low refractive index layer) and increase of refractive index of cladding layer ′ ′a (high refractive index layer). Also, fiber losses are estimated with increase of the high and low refractive index cladding layer losses. This loss spectrum of fiber can be considered as sensing signal. Since obtained fiber losses in distorted Bragg fiber are higher than standard Bragg fiber therefore, the sensitivity of proposed structure is higher than the standard Bragg fiber. Also, the sensitivity increases with the increase of refractive index of core medium. These results would be helpful to design a novel highly sensitive sensor based on hollow core distorted Bragg fiber.
关键词： Power losses,Distorted Bragg fiber,Dispersion curve,Sensitivity
更新于2025-09-23 15:19:57
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Low-Loss and Dispersion-Flattened Octagonal Porous Core PCF for Terahertz Transmission Applications
摘要： In order to make the direct transmission more effective, we have intended an octagonal shape cladding design in this paper. The minimum resultant effective material loss obtained from our proposed photonic crystal fiber is 0.007 cm-1 at 0.5 THz is very effective. The proposed design gives an ultra-high birefringence of 0.06 with an effective area of about 4 9 10-6 m2, a core power fraction of 70% for 290 lm core diameter with a core porosity of 80% at 1.6 THz frequency and closely zero flattened dispersion of variation of 0.3 ± 0.1 ps/THz/cm at a wide frequency range of 0.7–2.1 THz.
关键词： Terahertz,Core porosity,Effective material loss,Octagonal core,Confinement loss,Dispersion
更新于2025-09-23 15:19:57
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Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study
摘要： Interdot coherent excitonic dynamics in nanometric colloidal CdSe quantum dots (QD) dimers lead to interdot charge migration and energy transfer. We show by electronic quantum dynamical simulations that the interdot coherent response to ultrashort fs laser pulses can be characterized by pump-probe transient absorption spectroscopy in spite of the inevitable inherent size dispersion of colloidal QDs. The latter, leading to a broadening of the excitonic bands, induce accidental resonances that actually increase the efficiency of the interdot coupling. The optical electronic response is computed by solving the time-dependent Schrodinger equation including the interaction with the oscillating electric field of the pulses for an ensemble of dimers that differ by their size. The excitonic Hamiltonian of each dimer is parameterized by the QD size and interdot distance, using an effective mass approximation. Local and charge transfer excitons are included in the dimer basis set. By tailoring the QD size, the excitonic bands can be tuned to overlap and thus favor interdot coupling. Computed pump-probe transient absorption maps averaged over the ensemble show that the coherence of excitons in QD dimers that lead to interdot charge migration can survive size disorder and could be observed in fs pump-probe, four-wave mixing, or covariance spectroscopy.
关键词： coherent electronic dynamics,pump-probe transient absorption spectroscopy,CdSe quantum dots dimers,exciton dynamics,size dispersion effects
更新于2025-09-23 15:19:57
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Applicability of small-signal laser and fiber models for passive optical networks operating at the 1550??nm window
摘要： Small-signal techniques are a useful engineering tool to estimate system performance, though small-signal models need to be tested against the large-signal from which they are derived. We show that combined small-signal models for lasers and optical fiber are valid for passive optical networks employing directly modulated semiconductor lasers, provided that the modulation extinction ratios are < 4 dB and the transmission distances < 25 km. For larger extinction ratios and longer transmission distances, large-signal approaches are needed in order to investigate system capabilities. The small-signal models break down due to the increasing adiabatic chirp in semiconductor lasers with increasing modulation current. We estimate how the small-signal models can estimate for the performance of 10 Gbit/s signal from directly modulated lasers. We verify the equivalence of the small-signal and large-signal regimes and we develop a quality metric to identify the range of fiber lengths and signal extinction ratios over which the small-regime remains valid.
关键词： Frequency,Modulation,Passive Optical Networks,Semiconductor lasers,Phase,Fiber dispersion,Numerical modelling
更新于2025-09-23 15:19:57
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Methanol-Filled Hybrid Photonic Crystal Fiber with High Birefringent and Negative Dispersion
摘要： A unique hexagonal lattice structure of silica-based solid core photonic crystal fiber (PCF) surrounded by array of air holes is proposed. The cladding portion of the structure consists of five rings where core is made up of 11 small rings filled with methanol. Three different-shaped structures are used to analyze the effect on PCF parameters where the first structure uses circular air holes in cladding and core, the second structure consists of circular air holes in cladding and elliptical air holes in core, and the last structure was designed by using elliptical air holes in both cladding and core. Optical properties birefringence, confinement loss, and negative dispersion have been found theoretically and compared. A novel and relatively simple approach depicts the results that attain high birefringence, low confinement loss, and negative dispersion. It is found that the presence of elliptic air holes instead of circular air holes in the core region and the cladding brings higher birefringence, low confinement loss, and highly negative dispersion.
关键词： Photonic crystal fiber,Effective refractive index,Dispersion,Birefringence,Confinement loss
更新于2025-09-23 15:19:57