Single Lightpath Research Articles

One-shot measurement of birefringence by radial analysis

Due to complexity and bulky configuration of conventionally mechanical rotation approaches, a more convenient approach is to measure the birefringence effect (phase retardation and fast axis) by nano-fabricated spatial devices. Previous literature introduced radially-polarized illumination and eliminated the need for rotation mechanics in the illumination optics but still required rotation devices in the analyzer part. This work aims to achieve a compact and one-shot birefringence measurement by introducing spatial concepts in both the modulator and analyzer. By proposing a novel birefringence measurement by the combination of radial illumination and radial analyzer, this work is the first time to integrate no-mechanical motion and one-shot birefringence measurement in a single light path. What’s more, we are the first to introduce Fourier analysis in birefringence measurement, replacing the previous average intensity calculation, which is easily influenced by light source fluctuations. Based on our one-shot & non-mechanical measurement design and Fourier analysis algorithm, our birefringence measurement achieved very stable phase retardation measurement (standard deviation < 0.3°) and high accuracy fast axis measurement (average absolute error < 0.04°).

Detection and Classification of Citrus Fruit Infestation by Bactrocera dorsalis (Hendel) Using a Multi-Path Vis/NIR Spectroscopy System

In this study, a multi-path Vis/NIR spectroscopy system was developed to detect the presence of Bactrocera dorsalis (Hendel) infestations of citrus fruit. Spectra were acquired for 252 citrus fruit, 126 of which were infested. Two hundred and fifty-two spectra were acquired for modeling in their un-infested stage, slightly infested stage, and seriously infested stage. The location of the infestation is unclear, and considering the impact of the light path on the location of the infestation, each citrus fruit was tested in three orientations (i.e., fruit stalks facing upward (A), fruit stalks facing horizontally (B), and fruit stalks facing downward (C)). Classification models based on joint X-Y distance, multiple transmittance calibration, competitive adaptive reweighted sampling, and partial least squares discriminant analysis (SPXY-MSC-CARS-PLS-DA) were developed on the spectra of each light path, and the average spectra of the four light paths was calculated, to compare their performance in infestation classification. The results show the classification result changed with the light path and fruit orientation. The average spectra for each fruit orientation consistently gave better classification results, with overall accuracies of 92.9%, 89.3%, and 90.5% for orientations A, B, and C, respectively. Moreover, the best model had a Kappa value of 0.89, and gave 95.2%, 80.1%, and 100.0% accuracy for un-infested, slightly infested, and seriously infested citrus fruit. Furthermore, the classification results for infested citrus fruits were better when using the average spectra than using the spectrum of each single light path. Therefore, the multi-path Vis/NIR spectroscopy system is conducive to the detection of B. dorsalis infestation in citrus fruits.

A survivable VON embedding algorithm based on resource awareness of correlation lightpaths in elastic optical networks

To address the problems of low spectrum utilization and high bandwidth blocking probability of virtual optical network embedding in elastic optical networks, we propose a Survivable virtual optical network Embedding algorithm based on resource awareness of correlation lightpaths (SE-RACL), which can further optimize network resource allocation compared to traditional single lightpath resource allocation algorithms. Firstly, according to the multi-dimensional attributes of nodes, the importance sorting formulas of virtual nodes and physical nodes are designed to increase the cooperation between virtual node embedding and link embedding and reduce the bandwidth consumption of link embedding. Secondly, in the spectrum allocation process of the working lightpath, the spectrum block matching degree formula is designed by combining the spectrum fragmentation degree changes and resource reductions of correlation lightpaths, which is used to optimize the network spectrum resource allocation. Finally, in order to improve the sharing degree of protection resources and the success probability of spectrum allocation under single link failure, a correlation lightpaths spectrum allocation method based on the minimum free frequency slot consumption is proposed. Simulation results show that the SE-RACL algorithm can effectively reduce the bandwidth blocking probability and enhance the spectrum utilization.

Impact of the refractive index on coupling structures for silicon solar cells

Structured surfaces are used to reduce reflection and enhance light-trapping in silicon solar cells. In this simulation study, we investigated the relationship between the refractive index of front-side coupling structures on top of planar wafer-based crystalline silicon solar cells and the light-trapping performance of the structures. A crossed diffraction grating with a period of 1 μm and random pyramid structures with varying refractive indices were considered. Simulations were carried out both at the cell level and at the complete module stack level. It is shown that the single pass light path enhancement factor (LPEF) only provides a rough estimate of the light-trapping properties. The light-trapping behavior can only be reliably assessed in the complete system level and these results deviate from the estimated single pass LPEF. It can also be shown that the refractive index of the structure strongly influences the light-trapping behavior.

Microwave Instantaneous Frequency Measurement Based on Single Lightpath Polarization Multiplexing

Microwave Instantaneous Frequency Measurement Based on Single Lightpath Polarization Multiplexing

Generation of arbitrary cylindrical vector vortex beams with cross-polarized modulation

Cylindrical vector vortex beams (CVVBs), possessing both spatially nonuniform phase and polarization distribution, have attracted research interests in many applications due to their unique optical properties. Although various methods have been previously demonstrated, the generation of CVVBs with arbitrary topological charge and polarization order remains elusive. We introduce cross-polarized modulation method to construct CVVBs via changing the phases of the orthogonal polarization components of light beams. Two cross-polarized modulation approaches are demonstrated for conjugate and consistent phase orthogonal circular polarization beams. The phases of the orthogonal circular polarization components of light beams can be flexibly manipulated by exploiting the polarization-sensitivity of spatial light modulators, which leads to changed topological charges and polarization orders, and a group of CVVBs with different topological charges and polarization orders are successfully generated. Because of the adjustable orders and the single light path, the CVVBs generation method possess not only flexibility but also high stability.

Quality of Transmission Estimation and Short-Term Performance Forecast of Lightpaths

With ever-increasing traffic, the need of more dynamic, flexible, and autonomous optical networks is more important than ever. The availability of performance monitoring data makes it possible to leverage machine learning (ML) for fast quality of transmission (QoT) estimation and performance prediction of lightpaths in complex optical networks. In this article, we will explore classifiers based on support vector machine (SVM) and artificial neural network (ANN) for QoT estimation of unestablished lightpaths. Using a synthetic knowledge base (KB), the classification accuracy of the ANN and SVM models decreased from 99%, with a complete feature set, to 85.03% and 88.52%, respectively, with a reduced feature set. We also propose a Long Short-Term Memory (LSTM), an Encoder-Decoder LSTM and a Gated Recurrent Unit (GRU) models, trained with 13-months field performance data, for lightpath signal-to-noise (SNR) prediction over forecast horizons up to four days. Positive R2 values combined with low (<0.285 dB) root mean square error (RMSE) indicated that the GRU model achieved slightly better predictions than the naive method for forecast horizons ranging from 1 to 96 hours, whereas the LSTM performed better over 24 to 96-hour forecast horizons. The Encoder-Decoder LSTM model achieved the lowest R2 and the highest RMSE values (0.296 dB). Additional input data will be needed to improve the prediction accuracy of the LSTM and GRU models trained with single lightpath data.

A survivable VON embedding algorithm based on resource mean and spectrum coherence-aware in elastic optical networks

Abstract To address the problems of severe spectrum fragmentation and high bandwidth blocking probability of virtual optical network embedding in elastic optical networks, we propose a survivable virtual optical network embedding algorithm based on resource mean and spectrum coherence-aware (SVONE-RMSC). Firstly, according to the lightpath spectrum resources state of candidate substrate nodes to the correlative substrate nodes that have been embedded, we design the spectrum resource mean formula to enhance the correlation between virtual node embedding and virtual optical link embedding. Secondly, the algorithm optimizes the spectrum allocation methods. Specifically, to weaken the disruption of spectrum allocation to the spectrum continuity of the working lightpaths, the formula of spectrum coherence is designed. When allocating the spectrum resources for the protection lightpaths, we propose a spectrum allocation method based on spectrum coherence-aware, so as to maximize the spectrum coherence while minimizing the free frequency slots consumption. Finally, when the lack of spectrum resources on the single lightpath leads to the failure of virtual optical link embedding, different path splitting methods are designed to re-embed the virtual optical link. Simulation results show that the SVONE-RMSC algorithm can effectively reduce the bandwidth blocking probability and enhance the spectrum utilization.

一种环形结构单光路检测型光纤电流传感器

一种环形结构单光路检测型光纤电流传感器

A magneto-optical microscope for quantitative measurement of magnetic microstructures.

An optical system is presented to quantitatively map the stray magnetic fields of microscale magnetic structures, with field resolution down to 50 μT and spatial resolution down to 4 μm. The system uses a magneto-optical indicator film (MOIF) in conjunction with an upright reflective polarizing light microscope to generate optical images of the magnetic field perpendicular to the image plane. A novel single light path construction and discrete multi-image polarimetry processing method are used to extract quantitative areal field measurements from the optical images. The integrated system including the equipment, image analysis software, and experimental methods are described. MOIFs with three different magnetic field ranges are calibrated, and the entire system is validated by measurement of the field patterns from two calibration samples.

Modeling impact of ROADM intra-node Add/Drop contention on a single node lightpath blocking performance

We propose an analytical model to evaluate the lightpath blocking performance for a single ROADM node with intra-node add/drop contention, in which the number of lightpaths that can be added/dropped with the same wavelength is limited by the add/ drop contention factor. Different models of traffic load per nodal degree are considered to validate the effectiveness of the analytical model. The simulation results show that the proposed analytical model is effective in predicting the performance for different values of add/drop contention factor C and for variable offered loads at the node. The add/drop contention factor shows an important impact on the lightpath blocking performance and properly raising the contention factor can significantly improve the lightpath blocking performance. When the add/drop contention factor C exceeds a certain level, the performance of a ROADM with intra-node contention is close to that of a contentionless ROADM.

Self-mixing interferometry based on all phase FFT for high-precision displacement measurement

Self-mixing interferometry is an extreme simple and compact laser technique to develop non-contact displacement sensors. In order to enhance the precision of this type of sensor, an improved FFT algorithm, based on all phase FFT instead of conventional FFT, has been proposed to provide a phase reference for self-mixing displacement measurement system which has only single light path and lacks reference. The principle and the experimental realization of the proposed algorithm have been presented. The operation mechanism utilizes all phase FFT, which can estimate the phase from signal accurately, to achieve phase reference when the external target is held stationary and then compensate this reference to the phase when the target starts to move. Resultant displacement value reflects the actual position of the target. Reconstruction errors are on the order of nanometers in the displacements ranging from 100nm to 1μm. Therefore, the proposed method can find application in displacement measurement in industrial and scientific environments.

Imaging in scattering media using correlation image sensors and sparse convolutional coding.

Correlation image sensors have recently become popular low-cost devices for time-of-flight, or range cameras. They usually operate under the assumption of a single light path contributing to each pixel. We show that a more thorough analysis of the sensor data from correlation sensors can be used can be used to analyze the light transport in much more complex environments, including applications for imaging through scattering and turbid media. The key of our method is a new convolutional sparse coding approach for recovering transient (light-in-flight) images from correlation image sensors. This approach is enabled by an analysis of sparsity in complex transient images, and the derivation of a new physically-motivated model for transient images with drastically improved sparsity.

Integrated design of fault localization and survivable mapping in IP over transparent WDM networks

Lightpaths play multiple critical roles in cross-layer fault management of IP over transparent optical networks. While the roles of lightpaths have been discussed specifically in fault localization as well as fault recovery phases, these existing works only take a sporadic, piecemeal view of these roles by studying each of them individually as a separate lightpath routing problem. In this paper, we instead take an integrated, systematic view by considering these multiple roles jointly as one single lightpath routing problem. In particular, we propose a new design model to fulfill the lightpath layout requirements in both identifying fiber link failures for fault localization and ensuring IP topology connectivity for fault recovery. With a much smaller formulation size, our new model significantly outperforms the existing counterpart in computational efficiency, scalability, and solution quality.

Integrated Packet/Circuit Hybrid Network Field Trial With Production Traffic [Invited

We report the first field trials of an integrated packet/circuit hybrid optical network. In a long-haul field trial with production traffic, the mean capacity utilization of an Ethernet wavelength is doubled. The transport shares a single lightpath between the circuit and packet layers. Router bypassing is demonstrated at sub-wavelength granularity in a metro network field trial. In both trials the circuit quality of service is shown to be independent of the load of the network. The vacant resources in the circuit are utilized by the packet layer's statistical multiplexing in an interleaved manner without affecting the timing of the circuit. Inaddition, an analytical model that provides an upper bound on the maximum achievable utilization is presented.

Unlinking absorption and haze in thin film silicon solar cells front electrodes

AbstractWe study the respective influence of haze and free carrier absorption (FCA) of transparent front electrodes on the photogenerated current of micromorph thin film silicon solar cells. To decouple the haze and FCA we develop bi‐layer front electrodes: a flat indium tin oxide layer assures conduction and allows us to tune FCA while the haze is adjusted by varying the thickness of a highly transparent rough ZnO layer. We show how a minimum amount of FCA leads only to a few percents absorption for a single light path but to a strong reduction of the cell current in the infrared part of the spectrum. Conversely, a current enhancement is shown with increasing front electrode haze up to a saturation of the current gain. This saturation correlates remarkably well with the haze of the front electrode calculated in silicon. This allows us to clarify the requirements for the front electrodes of micromorph cells. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Wavelength-Routed Networks With Lightpath Data Interchanges

We observe that tunable wavelength converters (TWCs) that are traditionally installed in wavelength-routed (WR) networks for wavelength contention resolution can be further utilized to provide fast data switching between lightpaths. This allows us to route a data unit through a sequence of lightpaths from source to destination if a direct single lightpath connection is not available or if we want to minimize the overhead of setting up new lightpaths. Since TWCs have a tuning time of picoseconds, it may be possible to use the installed TWCs as lightpath data interchanges (LPIs) to improve the performance of WR networks without significant optical hardware upgrade. Compared with the multihop electronic grooming approach of lightpath networks, the LPI approach has a simpler WR node architecture, does not need expensive high-speed electrical multiplexers/routers, and does not sacrifice the bit-rate/format transparency of data between the source and destination. Our simulation results show that WR networks with LPIs can have much lower blocking probability than WR networks without LPIs if the traffic duration is short. We show that LPIs can also be used to provide new data transportation services such as optical time division multiplexing access (OTDMA) time-slotted service in WR networks.

Extending differential optical absorption spectroscopy for limb measurements in the UV

Abstract. Methods of UV/VIS absorption spectroscopy to determine the constituents in the Earth's atmosphere from measurements of scattered light are often based on the Beer-Lambert law, like e.g. Differential Optical Absorption Spectroscopy (DOAS). While the Beer-Lambert law is strictly valid for a single light path only, the relation between the optical depth and the concentration of any absorber can be approximated as linear also for scattered light observations at a single wavelength if the absorption is weak. If the light path distribution is approximated not to vary with wavelength, also linearity between the optical depth and the product of the cross-section and the concentration of an absorber can be assumed. These assumptions are widely made for DOAS applications for scattered light observations. For medium and strong absorption of scattered light (e.g. along very long light-paths like in limb geometry) the relation between the optical depth and the concentration of an absorber is no longer linear. In addition, for broad wavelength intervals the differences in the travelled light-paths at different wavelengths become important, especially in the UV, where the probability for scattering increases strongly with decreasing wavelength. However, the DOAS method can be extended to cases with medium to strong absorptions and for broader wavelength intervals by the so called air mass factor modified (or extended) DOAS and the weighting function modified DOAS. These approaches take into account the wavelength dependency of the slant column densities (SCDs), but also require a priori knowledge for the air mass factor or the weighting function from radiative transfer modelling. We describe an approach that considers the fitting results obtained from DOAS, the SCDs, as a function of wavelength and vertical optical depth and expands this function into a Taylor series of both quantities. The Taylor coefficients are then applied as additional fitting parameters in the DOAS analysis. Thus the variability of the SCD in the fit window is determined by the retrieval itself. This new approach provides a description of the SCD the exactness of which depends on the order of the Taylor expansion, and is independent from any assumptions or a priori knowledge of the considered absorbers. In case studies of simulated and measured spectra in the UV range (332–357 nm), we demonstrate the improvement by this approach for the retrieval of vertical profiles of BrO from the SCIAMACHY limb observations. The results for BrO obtained from the simulated spectra are closer to the true profiles, when applying the new method for the SCDs of ozone, than when the standard DOAS approach is used. For the measured spectra the agreement with validation measurements is also improved significantly, especially for cases with strong ozone absorption. While the focus of this article is on the improvement of the BrO profile retrieval from the SCIAMACHY limb measurements, the novel approach may be applied to a wide range of DOAS retrievals.

Impairment-aware traff ic grooming in WDM optical networks

A novel heuristic algorithm that considers transmission impairment (especially amplified spontaneous emission (ASE) noise) is developed for traffic grooming in wavelength division multiplexing (WDM) optical networks. Span constraints, which are determined by the impairment, are added to constrain the maximal transparent reach limit of a lightpath. Under span constraints, a series of short lightpaths will be built up explicitly to relay traffic when a single lightpath cannot meet the requirement of transmission quality. Both problem formulations and heuristic algorithms are given for impairment-aware traffic grooming. Numerical results show that the successful routing of each low-speed traffic stream is guaranteed and the efficiency of wavelength channels and lightpath usage are both improved by considering transmission impairment.

QoS aware traffic grooming and integrated routing on IP over WDM networks

In this article, we consider traffic grooming and integrated routing in IP over WDM networks. The challenges of this problem come from jointly considering traffic grooming, IP routing, and lightpath routing and wavelength assignment (RWA). Due to the high bandwidth of optical fiber, there exists a mismatch between the capacity needed by an IP flow and that provided by a single lightpath. Traffic grooming is therefore used to increase the network utilization by aggregating multiple IP flows in a single lightpath. However, traffic grooming incurs additional delays that might violate Quality-of-Service (QoS) requirements of IP users. In this work, the tradeoff between traffic grooming and IP QoS routing is well-formulated as a mixed integer and linear optimization problem, in which the revenue from successfully provisioning IP paths is to be maximized. Problem constraints include IP QoS, routing, optical RWA, and the WDM network capacity. We propose a novel Lagrangean relaxation (LGR) algorithm to perform constraint relaxation and derive a set of subproblems. The Lagrangean multipliers are used in the proposed algorithm to obtain a solution in consideration of grooming advantage and resource constraints simultaneously. Through numerical experiments and comparisons between the proposed algorithm and a two-phase approach, LGR outperforms the two-phase approach under all experimental cases. In particular, the improvement ratio becomes even more significant when the ratio of IP flow to the wavelength capacity is smaller.