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On the Complexity Reduction of the 2nd-order Volterra Nonlinear Equalizer for IM/DD systems
摘要： To cope with the various nonlinear signal distortions in IM/DD transmission systems, a theoretical analysis on the Volterra nonlinear equalizer (VNLE) is provided, focusing on computational complexity aspects. The analysis yields a simple reduced-complexity scheme for the 2nd-order VNLE (R2-VNLE) based on a performance-complexity trade-off. An experimental verification is performed with single-sideband 28-GBaud PAM-4 electro-absorption modulated signals, generated by a distributed-feedback laser, over transmission distances of up to 80-km of standard single-mode fiber in the C-band. A comparison of the results for different equalization schemes, including a signal-signal beat interference mitigation technique, shows superior performance for the R2-VNLE.
关键词： PAM-4,Volterra filter,direct detection,Nonlinear equalization,optical interconnects,intensity modulation
更新于2025-09-23 15:22:29
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Four-Wave Mixing in Metamaterials
摘要： Interaction of four counterpropagating waves in a cubic medium being “left” for the signal wave is considered in the constant-intensity approximation. Analytical expression for the signal wave intensity is derived for the general case of four-wave interaction in a metamaterial. The influence of different parameters on the signal wave amplification coefficient, efficiency of conversion into the signal wave, and the reflection coefficient of the mirror whose role is played by the metamaterial is analyzed. It has been obtained for the first time that the determining role in the backward signal wave amplification is played by the total length of the metamaterial and the intensities of all three forward waves. An analysis has shown that the optimal thickness of the metamaterial depends not only on the phase mismatch and the strong coherent pump field intensity, as in the constant-field approximation, but also on the intensity of the weak wave at the frequency ω2. It has been demonstrated for the first time that the efficiency of frequency conversion in metamaterials depends on the total metamaterial length, input intensities of all four interacting waves, phase mismatch, and losses in the medium. It is established that the maxima of the reflection coefficient of the metamaterial depend on the total metamaterial length and the intensities of all three forward waves.
关键词： metamaterial,negative refraction,four-wave interaction,constant-intensity approximation
更新于2025-09-23 15:22:29
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Investigation of energy transfer in Pr3+, Yb3+ co-doped phosphate phosphor: the role of 3P0 and 1D2
摘要： The synthesis, crystal structure and photoluminescence and decay kinetics properties have been carried out for the Pr3+-Yb3+ co-doped YPO4 phosphors. Upon excitation with 447 nm, the intense emissions from 3P0, 1D2 and 1G4 excited states are all observed in the Pr3+ singly doped phosphors. The population of 1D2 state is attributed to cross-relaxation 3P0 +3H4 → 1D2+3H6 and/or non-radiative multiphonon relaxation from 3P0 because of the larger maximum phonon energy of YPO4 host (1080 cm-1),which needs only 3-4 phonons to balance the energy gap between 3P0 and 1D2 excited states. For the Pr3+-Yb3+ codoped samples, the effect of Yb3+ concentration on the luminescence and decay kinetics of Pr3+ are investigated for the interpretation of observed experimental results. The observations and discussions manifest that the efficient energy transfer from Pr3+ to Yb3+ occurs, involving mainly 1D2 and 1G4 levels of Pr3+ ions instead of 3P0 level, which is not in accordance with many reported results. It is hoped that our results may give a new insights into the energy transfer mechanism in Pr3+-Yb3+ codoped system.
关键词： YPO4,luminescence decay,emission intensity,energy transfer
更新于2025-09-23 15:22:29
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The CMS Beam Halo Monitor electronics
摘要： The CMS Beam Halo Monitor has been successfully installed in the CMS cavern in LHC Long Shutdown 1 for measuring the machine induced background for LHC Run II. The system is based on 40 detector units composed of synthetic quartz Cherenkov radiators coupled to fast photomultiplier tubes (PMTs). The readout electronics chain uses many components developed for the Phase 1 upgrade to the CMS Hadronic Calorimeter electronics, with dedicated firmware and readout adapted to the beam monitoring requirements. The PMT signal is digitized by a charge integrating ASIC (QIE10), providing both the signal rise time, with few nanosecond resolution, and the charge integrated over one bunch crossing. The backend electronics uses microTCA technology and receives data via a high-speed 5 Gbps asynchronous link. It records histograms with sub-bunch crossing timing resolution and is read out via IPbus using the newly designed CMS data acquisition for non-event based data. The data is processed in real time and published to CMS and the LHC, providing online feedback on the beam quality. A dedicated calibration monitoring system has been designed to generate short triggered pulses of light to monitor the efficiency of the system. The electronics has been in operation since the first LHC beams of Run II and has served as the first demonstration of the new QIE10, Microsemi Igloo2 FPGA and high-speed 5 Gbps link with LHC data.
关键词： Cherenkov and transition radiation,Front-end electronics for detector readout,Beam-line instrumentation (beam position and profile monitors; beam-intensity monitors; bunch length monitors)
更新于2025-09-23 15:22:29
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Millimeter-wave home area network prospect with cost-effective RoF links
摘要： The growth towards the millimeter-wave band in the home area networks (HAN) leads to high data rate transmission to satisfy the new user services. Unfortunately, the transmission coverage in this band is limited to short distances because of the strong air absorption and obstacles such as walls. The effort is then focused on the extension of the network coverage of the wireless link in this band. Solutions based on multiple connected access points to optical fibers are useful methods to ensure wireless connectivity to the entire home. For HAN applications, radio-over-fiber (RoF) using intensity modulation and direct detection technique is the mostly favorite technology for the transmission of a broadband wireless signal because dealing with a cost-effective solution. We investigate in this paper the performance of such RoF-wireless architecture with low-cost optoelectronic modules through the error vector magnitude (EVM) metric. The RoF links investigated are a directly modulated VCSEL with integrated photoreceiver module, an electroabsorption-modulated laser with PIN photodiode and a Mach–Zehnder Modulator with PIN photodiode. A simulation approach based on equivalent electrical circuit models of photonic components is developed in ADS (Advanced Design System) by using a co-simulation technique that combines both analog and digital signals. The downlink channel of the complete transmission system including wireless channel and frequency conversion circuits to millimeter-wave (mm-wave) band is studied by simulation. The obtained results of EVM show good performances of cost-effective links with QPSK and 16-QAM modulation over a dynamic range of 15 dB.
关键词： Radio over fiber,Intensity modulation–direct detection,Home area network,Wireless channel
更新于2025-09-23 15:22:29
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A regularized approach evaluating origin intensity factor of singular boundary method for Helmholtz equation with high wavenumbers
摘要： Evaluation of the origin intensity factor of the singular boundary method for Helmholtz equation with high wavenumbers has been a difficult task for a long time. In this study, a regularized approach is provided to bypass this limitation. The core idea of the subtraction and adding-back technique is to substitute an artificially constructed general solution of the Helmholtz equation into the boundary integral equation or the hyper boundary integral equation to evaluate the non-singular expressions of the fundamental solutions at origin. The core difficulty is to derive the appropriate artificially constructed general solution. The regularized approach avoids the unstable inverse interpolation and has strict mathematical derivation process. Therefore, it is easy-to-program and free of mesh dependency. Numerical experiments show that the proposed technique can be used successfully to avoid singularity and hyper singularity difficulties encountered in the boundary element method and the singular boundary method.
关键词： Three-dimensional Helmholtz equation,Singularity and hyper singularity,Boundary element method,Origin intensity factor,Singular boundary method
更新于2025-09-23 15:22:29
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Investigation on Near-Infrared Quantitative Detection based on Heteromorphic Sample Pool
摘要： To enhance the detection precision of samples with scattering characteristics by near infrared spectroscopy (NIRS), this study developed a heteromorphic sample pool and established the related 2D light intensity acquisition system, which can simultaneously acquire multi-path exit light adsorption and scattering information of the samples under test. The Intralipid-20% phantom solutions in 34 samples with different concentrations were detected, while one-dimensional (1D) exit light intensity distributions and two-dimensional (2D) exit light intensity distributions on the surface of the samples were analyzed and modeled using partial least squares. In contrast with the prediction results based on the modeling method of 1D exit light intensity distribution, the modeling method of 2D exit light intensity distribution exhibits more favorable results; specifically, correlation coefficient enhanced by 2.48%, while root mean square error reduced by 6.89%. The experimental results demonstrate that using heteromorphic sample pool can effectively achieve NIRS-based detection precision and speed of chemical components in the solutions with scattering characteristics, which can provide important references for high-throughput and high-precision detection of turbid media in analytical chemistry.
关键词： two-dimensional (2D) light intensity distribution,heteromorphic sample pool,near-infrared spectrum
更新于2025-09-23 15:22:29
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Assessment of tooth wear based on autofluorescence properties measured using the QLF technology in vitro
摘要： Background: The difference in autofluorescence between enamel and dentine layer has prompted recommendations to use the quantitative light-induced fluorescence (QLF) method for quantifying tooth wear (TW). This study investigated the potential of QLF for distinguishing the severity of occlusal TW based on differences in the autofluorescence intensity. Methods: In total, 106 extracted permanent molars and premolars having suspected wear without pulp exposure were used. The severity of wear was determined by visually examining all teeth using the tooth wear index (TWI) of Smith and Knight. QLF images were captured and converted into 8-bit grayscale images. The difference in the fluorescence intensity (ΔG) was calculated by comparing mean grayscale levels between sound and worn areas. Finally, histological examination was conducted by stereomicroscope to confirm the presence of dentine exposure. Results: 100 teeth were included in the final analysis without six teeth having enamel cracks around worn area. The ΔG values increased with the severity of TW as quantified using conventional TWI codes, and differed significantly between the sound and enamel- and dentine-wear teeth (P<0.001). The histology indicated that enamel remained on 57 teeth, while 43 teeth had dentine-exposed wear and showed significant differences in ΔG compared with enamel-remained teeth. Conclusions: The fluorescence intensity differed significantly depending on the presence of dentine exposure. ΔG could be used to distinguish between sound and enamel- and dentine-wear teeth with a significant correlation. These findings indicate that QLF could be useful for determining the severity of TW of occlusal surfaces noninvasively.
关键词： tooth wear index (TWI),fluorescence intensity,tooth wear,quantitative light-induced fluorescence (QLF),occlusal wear
更新于2025-09-23 15:22:29
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Propagation properties of a partially coherent anomalous hollow vortex beam in underwater oceanic turbulence
摘要： Based on the extended Huygens–Fresnel principle, the cross-spectral density function of a partially coherent anomalous hollow vortex beam (AHVB) propagating in underwater oceanic turbulence has been derived, and the influences of the beam parameters and underwater oceanic turbulence on the average intensity and coherence properties are investigated by using numerical examples. Our results show that the partially coherent AHVB with smaller coherence length and smaller M will evolve into the flat-topped faster as the propagation distance increases, and the partially coherent AHVB propagating in stronger underwater oceanic turbulence (the larger χT and ? or the smaller ε) will lose the initial dark hollow center and evolve into the Gaussian beam more rapidly. In the influences of oceanic turbulence on the spreading of partially coherent AHVB, it is found that the parameters χT and ? will cause the larger spreading than the parameter ε at the same propagation distance. This research is useful to the practical application of the partially coherent AHVB beam in underwater oceanic turbulence.
关键词： Laser propagation,Vortex beam,Dark hollow beam,Average intensity
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - High Intensity Focused Ultrasound (HIFU) Combines Optical Coherence Tomography(OCT) for Biological Tissue Treatment and Evaluation
摘要： Light intensity focused ultrasound (LIFU) is an early stage medical technology that is in various stages of development to treat a range of disorders including super?cial diseases. Optical coherence tomography (OCT) is a rapid development imaging technique in recent ten years, which is a good way to monitor the tissue structure of super?cial diseases. In this study, OCT system is used to monitor the tissue structure of super?cial diseases during LIFU treatment. During the treatment, LIFU was performed on the lesion area of the sample with different energy levels for different times: 5s, 10s, 15s, 20s, 25s, 30s, respectively. During the treatment, the OCT system was working to monitor the tissue structure. The results showed that the light intensity of the lesion area increased with the treatment time, and the structure of the tissue changed. This study provides a new method for monitoring the treatment of super?cial diseases with LIFU.
关键词： Monitoring,Optical coherence tomography,Tissue structure,Super?cial diseases,Light intensity focused ultrasound
更新于2025-09-23 15:22:29