- 标题
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- 实验方案
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Intelligent 2-dimensional soft decision enabled by k-means clustering for VCSEL-based 112-Gbps PAM-4 and PAM-8 optical interconnection
摘要： In this work, we proposed an intelligent 2-dimensional soft decision (2D SD) enabled by k-means clustering, for vertical-cavity surface-emitting laser (VCSEL) based 112-Gbps PAM-4 and PAM-8 optical interconnection. At high modulation speed, VCSEL based link suffers from severe level nonlinearity, level-dependent noise and inter-symbol interference (ISI). For characterizing the above-mentioned three distortions, 2D signaling is performed through time-slotted mapping of PAM. Without extra requirement of Monte Carlo approach, channel conditional probability density function (PDF) can be intelligently estimated using inline data, thanks to 2D k-means machine learning. Thus, improved precision of log likelihood ratio (LLR) can be realized by additional consideration of nonlinearity, level-dependent noise and ISI. Both simulations and experiments have been carried out for proof-of-concept investigations on VCSEL and multimode fiber (MMF) links. 112-Gbps PAM-4 and PAM-8 signaling have been experimentally realized using a commercial-product-level VCSEL with 100-m MMF transmission. The results indicate significant improvement of the proposed k-means 2D SD without training using prior-known sequences.
关键词： multidimensional signal processing,optical fiber communication,Decision support systems,machine learning
更新于2025-09-12 10:27:22
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Dark sub-gap states in metal-halide perovskites revealed by coherent multidimensional spectroscopy
摘要： Metal-halide perovskites show excellent properties for photovoltaic and optoelectronic applications, with power conversion efficiencies of solar cell and LEDs exceeding 20%. Being solution processed, these polycrystalline materials likely contain a large density of defects compared to melt-grown semiconductors. Surprisingly, typical effects from defects (absorption below the bandgap, low fill factor and open circuit voltage in devices, strong non-radiative recombination) are not observed. In this work, we study thin films of metal-halide perovskites CH3NH3PbX3 (X = Br,I) with ultrafast multidimensional optical spectroscopy to resolve the dynamics of band and defect states. We observe a shared ground state between the band-edge transitions and a continuum of sub-bandgap states, which extends at least 350 meV below the band edge). We explain the comparatively large bleaching of the dark sub-bandgap states with oscillator strength borrowing from the band-edge transition. Our results show that upon valence to conduction band excitation such sub-gap states are instantaneously bleached for large parts of the carrier lifetime and conversely, that almost dark sub-bandgap states can be populated by light excitation. This observation helps unraveling the photophysical origin of the unexpected optoelectronic properties of these materials.
关键词： photovoltaic,defect states,metal-halide perovskites,optoelectronic,ultrafast multidimensional optical spectroscopy
更新于2025-09-12 10:27:22
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Coherence Change Detection For Sentinel-1 Sar: Methods And Applications
摘要： We propose a full Space and Time Coherent Change Detection (ST-CCD) that takes advantage of Sentinel-1 (S1) short interferometric revisit to enhance sensitivity in detecting changes at a fine space resolution. It extends the Generalized Likelihood Ratio Test (GLRT) used for change detection by single baseline images, to the multi-pass, multi-polarimetric stacks of S1 data. Applications are shown for damage mapping after hazards and for agriculture. A preliminary validation is performed by processing data referred to central Italy earthquake in 2016.
关键词： interferometry,damage mapping,Synthetic aperture radar,multidimensional signal detection
更新于2025-09-10 09:29:36
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Non-Iterative MDS Method for Collaborative Network Localization with Sparse Range and Pointing Measurements
摘要： Multi-agent localization is a basic requirement for many networked applications. The particular application to swarming Unmanned Aerial Vehicles (UAV’s) or munitions requires spatial coordination of agents, including the ability to assume and maintain a prescribed ?ight formation. An in-?ight awareness of network morphology and node location is therefore needed. While global navigation satellite systems (GNSS) offer an attractive solution, signal occlusion, spoo?ng, and jamming present unacceptable vulnerabilities- particularly for mission-critical operations. Alternative network localization methods using inter-agent radio frequency (RF) ranging and Angle of Arrival have been well studied over the past 15 years, but existing algorithms are not well suited to fast-moving networks. Iterative methods such as SMACOF tend to converge slowly. Faster non-iterative multi-dimensional scaling (MDS) methods for range, bearing, or vector measurements have also been formulated. However, these MDS methods generally require the full pairwise inter-agent measurement matrix - placing a severe requirement on swarm connectivity and leading to low tolerance for missing or badly estimated measurements. Even vector-based MDS, which incorporates both range and direction constraints, is shown here to require 4-vertex connectivity to achieve perfect localization. Results from rigidity theory, however, suggest that a lower connectivity threshold should be suf?cient to guarantee a unique con?guration (up to translation and rotation). In contrast, our proposed “vertex resequencing” and “edge resequencing” techniques further lower the vertex-connectivity threshold to 3 and 2, respectively. These localization techniques, which extend vector-based MDS with Nystr¨om approximation, prescribe a graph-based kernel sampling scheme and weighted coordinate reconstruction which suppress the effect of missing measurements.
关键词： Nystr¨om Method,multidimensional scaling,swarming munitions,collaborative localization
更新于2025-09-09 09:28:46
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An improved multidimensional reconciliation algorithm for continuous-variable quantum key distribution
摘要： Reconciliation is a crucial procedure for continuous-variable quantum key distribution (CV-QKD) systems since it directly affects the performance of practical system including processing speed, secret key rate, and maximal transmission distance. In this paper, we proposed a novel initial decoding message computation method for multidimensional reconciliation with low density parity check code, which does not need the norm information from the encoder. Both theoretical analysis and simulation results demonstrate that the improved scheme can greatly decrease the communication traffic and storage resource consumption of the reconciliation procedure almost without degradation in the reconciliation efficiency. What is more, the improved scheme can decrease the secure key consumption for classical channel authentication, then increase the secure key rate, and also be conducive to the realization of high-speed CV-QKD systems.
关键词： Continuous-variable quantum key distribution,Quantization,Multidimensional reconciliation,Low density parity check code,Reconciliation efficiency
更新于2025-09-09 09:28:46
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[Topics in Current Chemistry Collections] Multidimensional Time-Resolved Spectroscopy || Multidimensional Vibrational Coherence Spectroscopy
摘要： Multidimensional vibrational coherence spectroscopy has been part of laser spec-troscopy since the 1990s and its role in several areas of science has continuously been increasing. In this contribution, after introducing the principals of vibrational coherence spectroscopy (VCS), we review the three most widespread experimen-tal methods for multidimensional VCS (multi-VCS), namely femtosecond stimu-lated Raman spectroscopy, pump-impulsive vibrational spectroscopy, and pump-degenerate four wave-mixing. Focus is given to the generation and typical analysis of the respective signals in the time and spectral domains. Critical aspects of all multidimensional techniques are the challenges in the data interpretation due to the existence of several possible contributions to the observed signals or to opti-cal interferences and how to overcome the corresponding difficulties by exploiting experimental parameters including higher-order nonlinear effects. We overview how multidimensional vibrational coherence spectroscopy can assist a chemist in under-standing how molecular structural changes and eventually photochemical reactions take place. In order to illustrate the application of the techniques described in this chapter, two molecular systems are discussed in more detail in regard to the vibra-tional dynamics in the electronic excited states: (1) carotenoids as a non-reactive system and (2) stilbene derivatives as a reactive system.
关键词： Excited states,Photoisomerization,Multidimensional spectroscopy,Coherence spectroscopy,Vibronic coupling,Ultrafast laser spectroscopy,Raman,Vibrational spectroscopy
更新于2025-09-04 15:30:14
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[Topics in Current Chemistry Collections] Multidimensional Time-Resolved Spectroscopy || Two-Dimensional Resonance Raman Signatures of Vibronic Coherence Transfer in Chemical Reactions
摘要： Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in condensed phase systems. 2DRR spectroscopy is motivated by knowledge of non-equilibrium effects that cannot be detected with traditional resonance Raman spectroscopy. For example, 2DRR spectra may reveal correlated distributions of reactant and product geometries in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this chapter, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide. We show that signatures of "vibronic coherence transfer" in the photodissociation process can be targeted with particular 2DRR pulse sequences. Key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopy techniques are also addressed. Overall, recent experimental developments and applications of the 2DRR method suggest that it will be a valuable tool for elucidating ultrafast chemical reaction mechanisms.
关键词： Coherence transfer,Raman spectroscopy,Multidimensional spectroscopy,Ultrafast spectroscopy,Photodissociation
更新于2025-09-04 15:30:14