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Enhanced optical Kerr nonlinearity of graphene/Si hybrid waveguide
摘要： In this work, we experimentally study the optical Kerr nonlinearities of graphene/Si hybrid waveguides with enhanced self-phase modulation. In the case of CMOS compatible materials for nonlinear optical signal processing, Si and silicon nitride waveguides have been extensively investigated over the past decade. However, Si waveguides exhibit strong two-photon absorption (TPA) at telecommunication wavelengths, which leads to a signi?cant reduction of the nonlinear ?gure-of-merit (FOM). In contrast, a silicon nitride based material system usually suppresses the TPA but simultaneously leads to the reduction of Kerr nonlinearity by one order of magnitude. Here, we introduce a graphene/Si hybrid waveguide, which maintains the optical properties and CMOS compatibility of Si waveguides, while enhancing the Kerr nonlinearity, by transferring over to the top of the waveguides. The graphene/Si waveguides are measured to have an enhanced nonlinear parameter of 510 W(cid:2)1 m(cid:2)1, compared with that of the Si waveguide of 150 W(cid:2)1 m(cid:2)1. An enhanced nonlinear FOM of 2.48 6 0.25 has been achieved, which is four times larger than that of the Si waveguide of 0.6 6 0.1. This work reveals the potential application of graphene/Si hybrid waveguides with high Kerr nonlinearity and FOM for nonlinear all-optical signal processing.
关键词： nonlinear all-optical signal processing,graphene/Si hybrid waveguide,optical Kerr nonlinearity,CMOS compatible,self-phase modulation
更新于2025-11-28 14:23:57
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Soliton slow light for closed loop quantum systems
摘要： This paper describes the dynamics of solitonic pulse propagation in a closed loop quantum system comprised of five atomic energy levels. Although the propagation of an intense probe pulse suffers losses and broadening in linear regime, there exist specific conditions where the probe pulse is found to become robust during its propagation. We attribute this regime to the formation of an optical soliton with a slow group velocity because of the balance between the dispersion and Kerr optical nonlinearity. Results obtained are based on the theoretical model using the coupled Maxwell-Bloch equations for the nonlinear propagation.
关键词： Optical solitons,Kerr nonlinearity,Nonlinear pulse propagation,Closed-loop quantum system
更新于2025-09-23 15:23:52
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Bright optical solitons for Lakshmanan–Porsezian–Daniel model with spatio-temporal dispersion by improved Adomian decomposition method
摘要： This paper conducts numerical studies of optical solitons with Lakshmanan–Porsezian–Daniel model having spatio-temporal dispersion. A newly proposed version of the well-known Adomian's decomposition method is applied to secure numerical simulations of the recently reported analytical soliton solutions. The focus of this paper stays with bright soliton solutions to the model.
关键词： improved Adomian decomposition method,Lakshmanan–Porsezian–Daniel model,Optical Soliton,Kerr law nonlinearity
更新于2025-09-23 15:23:52
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Enhanced performance of odd order square geometrical shaping QAM constellation in underwater and free space VLC system
摘要： Visible light communication(VLC) employing light-emitting diodes(LED) as light source has become a promising field for underwater wireless communication. However, due to the complex underwater environment and scattering, absorption and diffusion effects during optical transmission in water, the underwater VLC system will suffer from poor SNR and highly nonlinear distortion. In this paper, we proposed and experimentally demonstrated a novel Square Geometrical Shaping(SGS) odd order QAM discrete multitone(DMT) and carrier-less amplitude phase(CAP) modulation based VLC system. Unlike to traditional odd order QAM constellation aiming at the minimum Euclidean distance but without Gray coding at edge constellation points, the new SGS constellation boasts acceptable Euclidean distance and thoroughly Gray coding for every constellation point. Therefore, the system performance can be effectively enhanced by SGS constellation for low SNR and high nonlinearity cases. Both numerical and experimental results verify that SGS 32QAM and 128QAM constellations can outperform traditional QAM constellation by mitigating nonlinearity in a blue LED based underwater and free space VLC system using DMT modulation or CAP modulation. By employing SGS 128QAM, we successfully demonstrate 2.534Gb/s 1.2meter underwater transmission at the driving voltage of 1.1Vpp.
关键词： SGS constellation,nonlinearity,CAP,VLC underwater system,QAM-DMT
更新于2025-09-23 15:23:52
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PAPR reduction in all-optical OFDM based on time interleaving odd and even subcarriers
摘要： In this paper, a new all-optical approach for reducing peak-to-average power ratio (PAPR) in all-optical orthogonal frequency division multiplexing (AO-OFDM) system based on time interleaving odd and even subcarriers (TIOES) is proposed and analytically modeled. In this approach, all subcarriers are initially modulated with higher modulation format such as m-array quadrature amplitude modulation (mQAM) and encoded by return-to-zero (RZ) coder. Then, odd and even subcarriers are temporally interleaved. An analytical model for estimating the impact of the interleaved time on PAPR reduction and induced nonlinear phase noise (NPN) is developed. The effect of reducing PAPR on performance of AO-OFDM system is also numerically investigated using VPItransmissionMaker? commercial software. This system utilizes an optical coupler-based inverse fast Fourier transform/fast Fourier transform. The results reveal that minimum PAPR is occurred when interleaved time between odd and even subcarriers equal to half symbol duration where the PAPR has been reduced by 3 dB. In addition, by employing proposed technique, the signal to noise ratio (SNR) is improved by about 2.5 dB at transmission distance of 800 km as compared with 4QAM AO-OFDM without PAPR technique.
关键词： PAPR reduction,mQAM modulation,Nonlinear phase noise,Fiber nonlinearity,AO-OFDM systems
更新于2025-09-23 15:23:52
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Matter wave soliton solutions for driven Gross–Pitaevskii equation with distributed coefficients
摘要： We have obtained the matter wave soliton solution for the driven nonautonomous GP equation with quadratic-cubic nonlinearities. We have revealed their interesting dynamical features for the experimentally realizable form of nonlinear interactions. Additionally, we have described that by suitably choosing some system parameters, we can control their characteristics such as amplitude and width etc. We have found that our results/solutions are stable and can be applied for future applications.
关键词： Bose-Einstein condensates,GP equation,Matter wave solitons,Quadratic-cubic nonlinearity
更新于2025-09-23 15:23:52
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Dynamic spectrum nonlinear modeling of VIS & NIR band based on RBF neural network for noninvasive blood component analysis to consider the effects of scattering
摘要： Dynamic spectrum (DS) is expected to achieve non-invasive analysis of blood components by extracting the absorbance of arterial blood at multiple wavelengths. However, the nonlinearity caused by scattering of blood components is still a factor that limits the detection accuracy. According to the idea of “overlay modeling” in the “M + N” theory, theoretically, the consideration of nonlinear factor in modeling analysis can further improve the prediction accuracy of calibration model. But there is currently no recognized formula to describe this nonlinear relationship. In this paper, the ability of RBF neural network to approximate arbitrary nonlinear functions with arbitrary precision is used to approximate the nonlinear relationship between the spectrum and the component concentration from the perspective of ?tting. The calibration sets and prediction sets were randomly selected from the VIS & NIR band DS data of 231 volunteers, and 10 groups of modeling experiments were carried out. The results showed that compared with the conventional partial least squares (PLS) modeling method, the modeling indicators (correlation coe?cient (R) and root mean square error(RMSE)) of prediction set using radial basis function (RBF) neural network modeling have been signi?cantly improved. The modeling experiments suggest that the nonlinearity caused by scattering should not be ignored in DS non-invasive blood component analysis. By ?tting the nonlinear relationship, RBF neural network can better re?ect the actual mapping relationship between the spectrum and the component concentration, because it can not only consider the general part (Linear factor) in DS, but also the details (Nonlinear factor), which can e?ectively improve the accuracy of the non-invasive blood component analysis based on DS.
关键词： Scattering,Nonlinearity,RBF neural network,Dynamic spectrum (DS),Non-invasive detection
更新于2025-09-23 15:23:52
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A nonlinear photonic crystal fiber for liquid sensing application with high birefringence and low confinement loss
摘要： This paper presents a nonlinear Photonic Crystal Fiber (PCF) based sensor to detect liquid analytes. An extensive analysis has been presented at wide range of wavelength (0.6 μm?1.6 μm) in order to investigate the impact of some design parameters. The numerical investigation has been done using the full vector Finite Element Method (FEM). The proposed model provides an outstanding nonlinear coefficient value with high birefringence, high sensitivity, and low confinement loss. The designed model can be used in sensing and bio-sensing research and their applications.
关键词： Effective Area,Sensitivity,Nonlinearity,Confinement loss,Photonic Crystal Fiber,Birefringence
更新于2025-09-23 15:23:52
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Prediction of First Higher Order Modal Field for Graded Index Fiber in Presence of Kerr Nonlinearity
摘要： We report evaluation of first higher order modal field for dual mode optical fiber having step and parabolic index profiles. The study is carried out both in absence as well as in presence of Kerr nonlinearity. The analysis is based on a simple iterative method involving Chebyshev formalism. Taking some typical step- and parabolic-index fibers as examples, we show that our results agree excellently with the exact results which can be obtained by applying rigorous methods. Thus, our simple formalism stands the merit of being considered as an accurate alternative to the existing cumbersome methods. The prescribed formalism provides scope for accurate estimation of different propagation parameters associated with first higher order mode in such kinds of fibers in presence of Kerr nonlinearity. The execution of formalism being user friendly, it will be beneficial to the system engineers working in the field of optical technology.
关键词： first higher order modal field,dual mode graded-index fiber,Kerr nonlinearity,Chebyshev technique
更新于2025-09-23 15:23:52
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An efficient blind calibration method for nonlinearity mis-matches in <i>M</i>-channel TIADCs
摘要： As gain, offset, and timing mismatches, nonlinearity mismatches also contribute to spurious components which deteriorate TIADC’s performance. This paper proposes an efficient blind calibration method for nonlinearity mismatches in M-channel TIADCs. A modified model for nonlinearity mismatches is established by exploiting binary Hadamard transform (BHT) and differentiator. The calibration is composed of two stages—mismatches compensation and coefficients identification. The principle of mismatches compensation is to reconstruct estimations of the mismatches-induced spurious components and subtract them from the original TIADC’s output. The coefficients identification is performed based on filtered-x least mean square (FxLMS) algorithm. By using improved model and calibration algorithm, the proposed method consumes less computational resource according to the complexity comparison. To tackle the 4-order nonlinearity mismatches in an 16-channel TIADC, the proposed method consumes 23% fewer multipliers than the previous work. Simulation results reveal that both effective resolution and dynamic range improve a lot after calibration.
关键词： frequency-dependent nonlinearity mismatches,TIADC,filtered-x least mean square,binary Hadamard transform,differentiator
更新于2025-09-23 15:23:52