Optical Lightpaths Research Articles

Distinguishing motion artifacts during optical fiber-based in-vivo hemodynamics recordings from brain regions of freely moving rodents.

Motion artifacts in the signals recorded during optical fiber-based measurements can lead to misinterpretation of data. In this work, we address this problem during in-vivo rodent experiments and develop a motion artifacts correction (MAC) algorithm for single-fiber system (SFS) hemodynamics measurements from the brains of rodents. (i)To distinguish the effect of motion artifacts in the SFS signals. (ii)Develop a MAC algorithm by combining information from the experiments and simulations and validate it. Monte-Carlo (MC) simulations were performed across 450 to 790nm to identify wavelengths where the reflectance is least sensitive to blood absorption-based changes. This wavelength region is then used to develop a quantitative metric to measure motion artifacts, termed the dissimilarity metric (DM). We used MC simulations to mimic artifacts seen during experiments. Further, we developed a mathematical model describing light intensity at various optical interfaces. Finally, an MAC algorithm was formulated and validated using simulation and experimental data. We found that the 670 to 680nm wavelength region is relatively less sensitive to blood absorption. The standard deviation of DM () can measure the relative magnitude of motion artifacts in the SFS signals. The artifacts cause rapid shifts in the reflectance data that can be modeled as transmission changes in the optical lightpath. The changes observed during the experiment were found to be in agreement to those obtained from MC simulations. The mathematical model developed to model transmission changes to represent motion artifacts was extended to an MAC algorithm. The MAC algorithm was validated using simulations and experimental data. We distinguished motion artifacts from SFS signals during in vivo hemodynamic monitoring experiments. From simulation and experimental data, we showed that motion artifacts can be modeled as transmission changes. The developed MAC algorithm was shown to minimize artifactual variations in both simulation and experimental data.

Microscope calibration protocol for single-molecule microscopy

Single-molecule microscopy allows for the investigation of the dynamics of individual molecules and the visualization of subcellular structures at high spatial resolution. For single-molecule imaging experiments, and particularly those that entail the acquisition of multicolor data, calibration of the microscope and its optical components therefore needs to be carried out at a high level of accuracy. We propose here a method for calibrating a microscope at the nanometer scale, in the sense of determining optical aberrations as revealed by point source localization errors on the order of nanometers. The method is based on the imaging of a standard sample to detect and evaluate the amount of geometric aberration introduced in the optical light path. To provide support for multicolor imaging, it also includes procedures for evaluating the geometric aberration caused by a dichroic filter and the axial chromatic aberration introduced by an objective lens.

On the benefits of domain adaptation techniques for quality of transmission estimation in optical networks

Machine learning (ML) is increasingly applied in optical network management, especially in cross-layer frameworks where physical layer characteristics may trigger changes at the network layer due to transmission performance measurements (quality of transmission, QoT) monitored by optical equipment. Leveraging ML-based QoT estimation approaches has proven to be a promising alternative to exploiting classical mathematical methods or transmission simulation tools. However, supervised ML models rely on large representative training sets, which are often unavailable, due to the lack of the necessary telemetry equipment or of historical data. In such cases, it can be useful to use training data collected from a different network. Unfortunately, the resulting models may be uneffective when applied to the current network, if the training data (the source domain) is not well representative of the network under study (the target domain). Domain adaptation (DA) techniques aim at tackling this issue, to make possible the transfer of knowledge among different networks. This paper compares several DA approaches applied to the problem of estimating the QoT of an optical lightpath using a supervised ML approach. Results show that, when the number of samples from the target domain is limited to a few dozen, DA approaches consistently outperform standard supervised ML techniques.

Shared Risk Link Group disjointness and geodiverse routing: A trade‐off between benefit and practical effort

AbstractThe resilience to disasters is a very relevant problem in telecommunication networks. This work addresses the problem of 1 + 1 optical lightpath protection considering maximally shared risk link group (SRLG)‐disjoint geodiverse paths, applied in the context of an optical network. The resilience to geographically correlated disasters is accomplished by guaranteeing geodiversity of the paths. This work focuses on estimating the increase of the path lengths and the increase in cost of the required transponders, compared to simple link‐disjointness (i.e., when no constraints on SRLG‐disjointness or geodiversity are considered). Results in different networks allow to evaluate the effect of SRLG‐disjointness to ensure some geodiversity.

Experimental teaching of light wave–particle duality for Optics course

The paper presents an innovative experimental setup that can show the wave–particle duality of light. A new experimental class for teaching light wave–particle duality concept based on the presented setup is also designed for undergraduates who major in Optics. Based on optical radiation pressure theory, the three-dimensional space trapping, localization, and movement of the particles reveal the particle property of light. Based on the beam interferometry technology, the recording and detection of the dual beam interference signal verify the wave property of light. The presented setup employs fiber optical light path, enabling the setup to be resistant to external interference, easy to assemble and move, and low in cost. The presented experimental practice can give students more opportunities to broaden and deepen their understanding of the taught subject content, while using modern experimental instruments and working on problems. During the class, students can know how to use optical instruments in a proper way, understand light wave–particle duality and related concepts, and increase awareness and curiosity of related cutting-edge scientific research. According to the class questionnaire survey, students were satisfied with the practical experimental class.

Optical absorption enhancement of P3HT:PCBM films through nanocavities using polystyrene as a template

A relatively simple and inexpensive method to enhance the optical absorption of P3HT:PCBM films is hereby presented. By evaporating different concentrations of polystyrene in the mixtures, nanocavities were obtained. An increase in the optical light path due to the internal reflection between the cavities and the P3HT:PCBM media, enhances the optical absorption. Theoretical density photocurrents were calculated for these films, and considerable increases were obtained compared to films without cavities. The methodology proposed may have promising applications in active materials for organic solar cells.

Recent research progress on spectrum management approaches in software-defined elastic optical networks

The flex-grid technology or elastic optical network (EON) is accepted to be a propitious solution for the future transport network due to its unique properties, which are bandwidth aggregation that creates super wavelength channels, different data rate accommodation, bandwidth segmentation that creates sub-wavelength channels, and elastic variation of assigned bandwidth. The software-defined network (SDN) is incorporated with the emerging technology of EON for enhancing its performance by enabling dynamic provisioning and releasing of optical lightpaths. This reduces the required time for lightpath control, which leads to improve the network performances. This paper exploits the software-defined elastic optical network (SD-EON) by identifying its architectures, existing literature, resource management approaches, and future challenges. In addition, the performance of EONs related to the SDN technology is compared in terms of blocking probability. Numerical results indicate that the SD-EON accommodates 25% more admissible traffic than the EON without considering SDN, when the acceptable blocking probability is considered 0.01.

µCube: A Framework for 3D Printable Optomechanics

Scientific instruments often require the integration of mechanics, electronics and optics. While the use of 3D printing techniques and commodity electronics has lowered the cost of instrumentation, the design and prototyping of optical components and light paths can be challenging and expensive. In recent years, attempts have been made to make optical devices more affordable using 3D printing as a method for production of optomechanical components. In this paper we present an assembly standard for the production of 3D printed optical devices. We describe a framework for parametric design of modular mounts, present two modules built using the framework, and demonstrate the potential for generalised design of modular optical devices following the μCube standard.

Optical Pipelined Multi-bus Interconnection Network Intrinsic Topologies

Digital all-optical parallel computing is an important research direction and spans conventional devices and convergent nano-optics deployments. Optical bus-based interconnects provide interesting aspects such as relative information communication speed-up or slow-down between optical signals. This aspect is harnessed in the newly proposed All-Optical Linear Array with a Reconfigurable Pipelined Bus System (OLARPBS) model. However, the physical realization of such communication interconnects needs to be considered. This paper considers spatial layouts of processing elements along with the optical bus light paths that are necessary to realize the corresponding interconnection requirements. A metric in terms of the degree of required physical constraint is developed to characterize the variety of possible solutions. Simple algorithms that determine spatial layouts are given. It is shown that certain communication interconnection structures have associated intrinsic topologies.

A protocol for registration and correction of multicolour STED superresolution images.

Multicolour fluorescence imaging by STimulated Emission Depletion (STED) superresolution microscopy with doughnut-shaped STED laser beams based on different wavelengths for each colour channel requires precise image registration. This is especially important when STED imaging is used for co-localisation studies of two or more native proteins in biological specimens to analyse nanometric subcellular spatial arrangements. We developed a robust postprocessing image registration protocol, with the aim to verify and ultimately optimise multicolour STED image quality. Importantly, this protocol will support any subsequent quantitative localisation analysis at nanometric scales. Henceforth, using an approach that registers each colour channel present during STED imaging individually, this protocol reliably corrects for optical aberrations and inadvertent sample drift. To achieve the latter goal, the protocol combines the experimental sample information, from corresponding STED and confocal images using the same optical beam path and setup, with that of an independent calibration sample. As a result, image registration is based on a strategy that maximises the cross-correlation between sequentially acquired images of the experimental sample, which are strategically combined by the protocol. We demonstrate the general applicability of the image registration protocol by co-staining of the ryanodine receptor calcium release channel in primary mouse cardiomyocytes. To validate this new approach, we identify user-friendly criteria, which - if fulfilled - support optimal image registration. In summary, we introduce a new method for image registration and rationally based postprocessing steps through a highly standardised protocol for multicolour STED imaging, which directly supports the reproducibility of protein co-localisation analyses. Although the reference protocol is discussed exemplarily for two-colour STED imaging, it can be readily expanded to three or more colours and STED channels.

Optical switching based small-world data center network

Redesigning data center networks, particularly taking advantages of optical switching technologies to reduce cost-per-bandwidth and energy consumption, has spawned interests of researchers worldwide in recent years. In this paper, we introduce and analysis our recently proposed optical switching technology powered data center network architecture, which is inspired from the small world data center network topology yet has additional flexibility brought by optical lightpath's reconfigurability. Specifically, logically full-meshed optical burst switching rings are employed to compose a lattice substrate, which provide dense connectivity for small groups of ToR switches to accommodate highly clustered and dynamic regional data traffic, while a reconfigurable wavelength circuit switching plane offers direct connections among the racks to effectively reduce overall network diameter. A centralized control plane is employed to realize traffic-adaptive optical lightpath scheduling mechanisms. We thoroughly study the throughput and latency performance of the proposed architecture through numerical simulations, and particularly reveal the impact of traffic patterns. It turns out that, the proposed network architecture can achieve high throughput with significantly reduced cost, and exploiting its traffic-adaptive reconfiguration capability can effectively improve throughput and reduce latency under varying traffic distributions.

Quality of Service Provisioning and Energy Minimized Scheduling in Software Defined Flexible Optical Networks

The over-provisioning of capacities in optical networks is not a sustainable approach in the long run. In this paper, we propose a software defined networking scheme for quality of service provisioning through energy efficient assignment of optical transponders, employing bandwidth variable distance adaptive modulation and coding. Our scheme enables avoiding over-provisioning of transponder capacity as well as short-term major changes in equipment allocation for networks with dynamic traffic. We make use of the seasonal auto-regressive integrated moving average model to forecast the statistics of network traffic for an arbitrary time span based on the requirements and the constraints of the service provider. The quality of service measure is defined as the probability of congestion at the core router ports. A stochastic linear programming approach is used to provide a solution for energy efficient assignment of optical transponders and electronic switching capacity while ensuring a certain level of quality of service to core routers. The scheduling of optical lightpath capacities is performed for the entire duration of time under consideration, whereas the scheduling of electronic switching capacities is performed based on the short-term dynamics of the traffic. Numerical results show up to 48% improvement in the energy efficiency of optical networks and 45% reduction in the number of optical lightpaths through the implementation of the proposed technique, compared to a design based on employing conventional fixed optical transponders and no traffic rerouting, where both schemes satisfy the congestion probability requirements.

Crystalline Silicon Solar Cells with Enhanced Light Trapping via Rear Side Diffraction Grating

Effective light trapping concepts are increasingly relevant for thinner crystalline silicon solar cells. Diffractive rear side structures can be designed to enhance optical light path lengths in the weakly absorbed infrared wavelength range. However, because of the rather difficult passivation of these nano-scale structures and possible plasma induced damages, the optical gain has so far not been shown on final device level for wafer-based crystalline silicon solar cells in combination with a high open circuit voltage.In this work, we fabricated and characterized silicon solar cells with an optically active layer at the rear side which is electrically decoupled from the silicon bulk by a thin, planar passivation layer. A binary diffraction grating was realized on the rear side via Nanoimprint Lithography (NIL) and plasma etching. For the rear side metallization a laser based foil process and photolithographically opened point contacts with evaporated aluminum were used as two alternative process routes. The best cell shows an EQE increase of up to 29 % absolute at 1100 nm compared to planar reference cells. This corresponds to a total Jsc gain of 1.2 mA/cm2 and a best cell efficiency of 19.4 % (Voc: 683.1 mV, Jsc: 35.4 mA/cm2, FF: 81.0 %) with planar front side and SiO2 antireflection coating.Optical simulations, which fit well to the experimental data, show that cell efficiencies of 20.8 % and 21.3 % can be reached with a planar front by using an optimized single layer (SiNxOy) or double layer (MgF, SiNx) ARC, respectively. By calculating Jsc for different cell thicknesses it is shown that a 100 μm thick solar cell incorporating the fabricated diffractive grating is expected to exhibit a higher Jsc than a planar cell with 250 μm thickness.

Energy‐aware traffic allocation to optical lightpaths in multilayer core networks

SummaryThe amount of traffic that is generated by users and high‐demanding services is expected to rise dramatically in the forthcoming years. This will unavoidably deteriorate the performance and increase the consumed energy of core networks, thus constraining the growth of Internet. To this effect, multilayer traffic engineering schemes in IP/multiprotocol label switching over dense wavelength division multiplexing networks have been proposed for achieving improved performance and increased energy savings by flexibly allocating traffic to optical lightpaths. In particular, the consumed energy in a router can be minimized if the lightpaths are established so as to traverse a router without electronic processing and conversion of their signal between optical and electrical layer. Accordingly, this paper aims at providing an energy‐aware solution to the problem of traffic allocation to optical lightpaths in multilayer core networks. The problem is first formulated and then a solution based on a heuristic algorithm, called energy‐aware traffic allocation to optical lightpaths (ETAL) is proposed. The efficiency and worthiness of ETAL is validated through numerous scenarios and simulations. The derived results indicate that the proposed algorithm is an efficient traffic engineering solution that exhibits better performance in terms of consumed energy (up to 44%), when compared to other similar traffic allocation schemes. Copyright © 2015 John Wiley & Sons, Ltd.

First field demonstration of cloud datacenter workflow automation employing dynamic optical transport network resources under OpenStack and OpenFlow orchestration

For the first time, we demonstrate the orchestration of elastic datacenter and inter-datacenter transport network resources using a combination of OpenStack and OpenFlow. Programmatic control allows a datacenter operator to dynamically request optical lightpaths from a transport network operator to accommodate rapid changes of inter-datacenter workflows.

Establishment of Dynamic Lightpaths in Filterless Optical Networks

In this paper, we study the performance of dynamic routing and wavelength assignment (RWA) in filterless optical networks. These types of broadcast and select networks benefit from breakthroughs in advanced transmission technologies for replacing optical filters and active photonic switching devices, such as wavelength selective switches, with passive optical interconnections between nodes, creating passive optical light trees. We introduce an RWA scheme for establishing passive optical lightpaths in a filterless context and managing unfiltered channels at intermediate egress nodes, which, by propagating downstream of the terminating nodes, participate in wavelength usage and increase the risk of wavelength exhaustion. Simulation results are presented for six network topologies, along with the performance evaluation of active photonic and filterless optical network solutions with static and dynamic RWA schemes. We show that the performance of the proposed scheme depends on the average degree of node connectivity.

The influence of blood glucose level upon the transport of light in diabetic and non-diabetic subjects

The present paper describes the influence of blood glucose concentrations up on the light transport pattern and to detect the feasibility of this principle for noninvasive blood glucose measurement. The characteristics of the blood glucose molecules to influence the optical signal transportation have been investigated and calculated by utilizing the mathematical parameters on the resultant output signal. Investigational studies on non-diabetic and diabetic subjects reveal that blood glucose concentrations have empirical relationship over light transport phenomenon in the biological tissues. When blood glucose levels increases, the optical property of the biological tissue changes, causing lower distribution patterns, accordingly the optical light path is reduced. Furthermore, variation in the optical light path relating to blood glucose concentrations is very weak in nature. To overcome this difficulty, in our pilot study, amplitude modulated ultrasound and infrared techniques have been utilized. The output signal results of this hybrid noninvasive technology for the measurement of blood glucose levels are promising in nature. It can be employed for the design and development of the noninvasive blood glucometer.

Modified Surface Texturing of Aluminium-Doped Zinc Oxide (AZO) Transparent Conductive Oxides for Thin-Film Silicon Solar Cells

For thin-film solar cells, the properties of the front transparent conductive oxide (TCO) electrode is an important factor in determining the overall performance of the solar cells. An efficient light trapping scheme is required to increase the optical light path and thus enhance the photon absorption within the solar cells. Improved photon absorption is necessary to increase the short-circuit current density (Jsc) and thus the efficiency of cells. In this paper we report the results of the texturing of aluminium-doped zinc oxide (ZnO:Al or AZO) thin films for enhanced light scattering. AZO films were deposited onto soda-lime glass sheets by in-line DC magnetron sputtering. An effective AZO texturing method was developed using diluted hydrogen chloride (HCl) and hydrogen fluoride (HF) acids through either a two-step etching or a mixed etching process, which significantly improves the uniformity of the textured surface. Texturing based on HCl and HF combines the advantages of the large craters created by HCl etching and smaller jagged but uniform features resulting from HF etching. In this work, we demonstrate that by adopting the two-step or the mixed texturing method, it is possible to achieve high haze values of above 40% with very low surface roughness values. The combination of low surface roughness and high haze is beneficial to prevent shunting issues, and is thus very attractive for the fabrication of thin-film silicon solar cells.

The relationship between the optical density of cataract and its influence on retinal nerve fibre layer thickness measured with spectral domain optical coherence tomography

The purpose of this study was to model the influence of cataract on Spectral Domain Optical Coherence Tomography (SDOCT) image quality and Retinal Nerve Fibre Layer (RNFL) thickness measurements. SDOCT images, made with two different devices (3DOCT-1000, Topcon and Cirrus HD-OCT), before and after cataract surgery were compared and judged against measurements from normal subjects using artificial filters simulating the effects of cataract. Optical density of the images was calculated based on a mathematical model described previously. In total, forty-eight eyes were included for pre- and postoperative cataract extraction measurements. OCT image quality significantly (p < 0.001) improved postoperative and postoperative RNFL thickness was significantly (p < 0.001) thicker in both groups of patients. The measurements using artificial filters showed a rather precise linear relation between change in filter induced optical density and change in RNFL thickness (R = 0.941, p < 0.001 for 3DOCT-1000 and R = 0.785, p < 0.001 for Cirrus HD-OCT). For the patient groups, the relation was less marked, 3DOCT-1000 Rs = 0.697, p < 0.03 and Cirrus HD-OCT Rs = 0.444, p < 0.03. The predictive potential based on the found linear relationship between OCT-effective optical density of cataract and the cataract-induced underestimation was however limited, and mean difference ± SD between predicted and measured RNFL thickness were 1.68 ± 7.55 (3DOCT-1000) and 3.71 ± 2.97 (Cirrus HD-OCT) micron. A linear relationship exists between OCT-effective optical density of cataract and underestimation of RNFL thickness measured with OCT. This finding holds promise to correct for cataract-induced changes in RNFL measurements, but will differ for each type of OCT device.

Ship emissions of SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;: DOAS measurements from airborne platforms

Abstract. A unique methodology to measure gas fluxes of SO2 and NO2 from ships using optical remote sensing is described and demonstrated in a feasibility study. The measurement system is based on Differential Optical Absorption Spectroscopy using reflected skylight from the water surface as light source. A grating spectrometer records spectra around 311 nm and 440 nm, respectively, with the telescope pointed downward at a 30° angle from the horizon. The mass column values of SO2 and NO2 are retrieved from each spectrum and integrated across the plume. A simple geometric approximation is used to calculate the optical path. To obtain the total emission in kg h−1 the resulting total mass across the plume is multiplied with the apparent wind, i.e. a dilution factor corresponding to the vector between the wind and the ship speed. The system was tested in two feasibility studies in the Baltic Sea and Kattegat, from a CASA-212 airplane in 2008 and in the North Sea outside Rotterdam from a Dauphin helicopter in an EU campaign in 2009. In the Baltic Sea the average SO2 emission out of 22 ships was (54 ± 13) kg h−1, and the average NO2 emission was (33 ± 8) kg h−1, out of 13 ships. In the North Sea the average SO2 emission out of 21 ships was (42 ± 11) kg h−1, NO2 was not measured here. The detection limit of the system made it possible to detect SO2 in the ship plumes in 60% of the measurements when the described method was used. A comparison exercise was carried out by conducting airborne optical measurements on a passenger ferry in parallel with onboard measurements. The comparison shows agreement of (−30 ± 14)% and (−41 ± 11)%, respectively, for two days, with equal measurement precision of about 20%. This gives an idea of the measurement uncertainty caused by errors in the simple geometric approximation for the optical light path neglecting scattering of the light in ocean waves and direct and multiple scattering in the exhaust plume under various conditions. A tentative error budget indicates uncertainties within 30–45% but for a reliable error analysis the optical light path needs to be modelled. A ship emission model, FMI-STEAM, has been compared to the optical measurements showing an 18% overestimation and a correlation coefficient (R2) of 0.6. It is shown that a combination of the optical method with modelled power consumption can estimate the sulphur fuel content within 40%, which would be sufficient to detect the difference between ships running at 1% and at 0.1%, limits applicable within the IMO regulated areas.