Optimization of DFB fiber laser performance based on a superimposed cavities structure

A simple technique based on superimposed cavities structure for direct real-time assessment of a DFB fiber laser mode condition during operation is demonstrated and used to provide a cavity mode conditioning feedback mechanism to optimize output performance. Significant improvements to the output performance and robustness are achieved over the entire pump power range without ambient isolation.

Supermode-noise suppression using a nonlinear Fabry–Pérot filter in a harmonically mode-locked fiber ring laser

A simple efficient method for stabilizing a harmonically mode-locked fiber ring laser is proposed. In this method, a linear optical filter and a nonlinear Fabry–Pérot filter in which the refractive index is optical intensity dependent are located in the laser cavity. The linear filter is used to select a fixed lasing wavelength, and the Fabry–Pérot filter introduces a negative all-optical feedback mechanism that is able to suppress pulse-to-pulse amplitude fluctuations in the laser cavity. The scheme was experimentally demonstrated using a fiber Bragg grating as the linear filter and a laser diode biased below threshold as the nonlinear Fabry–Pérot, and stable harmonically mode-locked pulses with a supermode noise suppression ratio >55 dB were obtained.

Time resolved bit error rate analysis of a fast switching tunable laser for use in optically switched networks

We investigate the use of different direct detection modulation formats in a wavelength switched optical network. We find the minimum time it takes a tunable sampled grating distributed Bragg reflector laser to recover after switching from one wavelength channel to another for different modulation formats. The recovery time is investigated utilizing a field programmable gate array which operates as a time resolved bit error rate detector. The detector offers 93 ps resolution operating at 10.7 Gb/s and allows for all the data received to contribute to the measurement, allowing low bit error rates to be measured at high speed. The recovery times for 10.7 Gb/s non-return-to-zero on–off keyed modulation, 10.7 Gb/s differentially phase shift keyed signal and 21.4 Gb/s differentially quadrature phase shift keyed formats can be as low as 4 ns, 7 ns and 40 ns, respectively. The time resolved phase noise associated with laser settling is simultaneously measured for 21.4 Gb/s differentially quadrature phase shift keyed data and it shows that the phase noise coupled with frequency error is the primary limitation on transmitting immediately after a laser switching event.

Directed phase separation of PFO:PS blends during spin-coating using feedback controlled in situ stroboscopic fluorescence microscopy

Uniform thin-films of polymer blends can be produced through spin-coating, which is used on an industrial scale for the production of light emitting diodes, and more recently organic photovoltaic devices. Here, we present the results of the direct observation, and control, over the phase separation of polystyrene and poly(9,9′-dioctylfluorene) during spin-coating using high speed stroboscopic fluorescence microscopy. This new approach, imaging the fluorescence, from a blend of fluorescent + non-fluorescent polymers allows for intensity to be directly mapped to composition, providing a direct determination of composition fluctuations during the spin-coating process. We have studied the compositional development and corresponding structural development for a range of compositions, which produce a range of different phase separated morphologies. We initially observe domains formed by spinodal decomposition, coarsening via Ostwald Ripening until an interfacial instability causes break-up of the bicontinuous morphology. Ostwald ripening continues, and depending upon composition a bicontinuous morphology is re-established. By observing compositional and morphological development in real-time, we are able to direct and control morphological structure development through control of the spin coating parameters via in situ feedback. © 2013 The Royal Society of Chemistry.

A comparison of two distributed large-volume measurement systems:the mobile spatial co-ordinate measuring system and the indoor global positioning system

Advances in the area of industrial metrology have generated new technologies that are capable of measuring components with complex geometry and large dimensions. However, no standard or best-practice guides are available for the majority of such systems. Therefore, these new systems require appropriate testing and verification in order for the users to understand their full potential prior to their deployment in a real manufacturing environment. This is a crucial stage, especially when more than one system can be used for a specific measurement task. In this paper, two relatively new large-volume measurement systems, the mobile spatial co-ordinate measuring system (MScMS) and the indoor global positioning system (iGPS), are reviewed. These two systems utilize different technologies: the MScMS is based on ultrasound and radiofrequency signal transmission and the iGPS uses laser technology. Both systems have components with small dimensions that are distributed around the measuring area to form a network of sensors allowing rapid dimensional measurements to be performed in relation to large-size objects, with typical dimensions of several decametres. The portability, reconfigurability, and ease of installation make these systems attractive for many industries that manufacture large-scale products. In this paper, the major technical aspects of the two systems are briefly described and compared. Initial results of the tests performed to establish the repeatability and reproducibility of these systems are also presented. © IMechE 2009.

RIN transfer in 2nd-order distributed amplification with ultralong fiber lasers

We investigate numerically the effect of ultralong Raman laser fiber amplifier design parameters, such as span length, pumping distribution and grating reflectivity, on the RIN transfer from the pump to the transmitted signal. Comparison is provided to the performance of traditional second-order Raman amplified schemes, showing a relative performance penalty for ultralong laser systems that gets smaller as span length increases. We show that careful choice of system parameters can be used to partially offset such penalty. © 2010 Optical Society of America.

Fluorescence Characteristics of Size-Fractionated Dissolved Organic Matter: Implications for a Molecular Assembly Based Structure?

Surface freshwater samples from Everglades National Park, Florida, were used to investigate the size distributions of natural dissolved organic matter (DOM) and associated fluorescence characteristics along the molecular weight continuum. Samples were fractionated using size exclusion chromatography (SEC) and characterized by spectroscopic means, in particular Excitation-Emission Matrix fluorescence modeled with parallel factor analysis (EEM-PARAFAC). Most of the eight components obtained from PARAFAC modeling were broadly distributed across the DOM molecular weight range, and the optical properties of the eight size fractions for all samples studied were quite consistent among each other. Humic-like components presented a similar distribution in all the samples, with enrichment in the middle molecular weight range. Some variability in the relative distribution of the different humic-like components was observed among the different size fractions and among samples. The protein like fluorescence, although also generally present in all fractions, was more variable but generally enriched in the highest and lowest molecular weight fractions. These observations are in agreement with the hypothesis of a supramolecular structure for DOM, and suggest that DOM fluorescence characteristics may be controlled by molecular assemblies with similar optical properties, distributed along the molecular weight continuum. This study highlights the importance of studying the molecular structure of DOM on a molecular size distribution perspective, which may have important implications in understanding the environmental dynamics such materials.

Seawater carbonate chemistry and particulate organic particles during a semicontinuous batch culture experiment with Trichodesmium IMS101, 2007

Diazotrophic (N2-fixing) cyanobacteria provide the biological source of new nitrogen for large parts of the ocean. However, little is known about their sensitivity to global change. Here we show that the single most important nitrogen fixer in today's ocean, Trichodesmium, is strongly affected by changes in CO2 concentrations. Cell division rate doubled with rising CO2 (glacial to projected year 2100 levels) prompting lower carbon, nitrogen and phosphorus cellular contents, and reduced cell dimensions. N2 fixation rates per unit of phosphorus utilization as well as C:P and N:P ratios more than doubled at high CO2, with no change in C:N ratios. This could enhance the productivity of N-limited oligotrophic oceans, drive some of these areas into P limitation, and increase biological carbon sequestration in the ocean. The observed CO2 sensitivity of Trichodesmium could thereby provide a strong negative feedback to atmospheric CO2 increase.

Geochemical data and radiocarbon ages of organic matter fractions and bacteriohopanepolyol data of sediment core GeoB6518-1 from the Congo River basin

The age of organic material discharged by rivers provides information about its sources and carbon cycling processes within watersheds. While elevated ages in fluvially-transported organic matter are usually explained by erosion of soils and sediments, it is commonly assumed that mainly young organic material is discharged from flat tropical watersheds due to their extensive plant cover and high carbon turnover. Here we present compound-specific radiocarbon data of terrigenous organic fractions from a sedimentary archive offshore the Congo River in conjunction with molecular markers for methane-producing land cover reflecting wetland extent in the watershed. We find that the Congo River has been discharging aged organic matter for several thousand years with increasing ages from the mid- to the Late Holocene. This suggests that aged organic matter in modern samples is concealed by radiocarbon from nuclear weapons testing. By comparison to indicators for past rainfall changes we detect a systematic control of organic matter sequestration and release by continental hydrology mediating temporary carbon storage in wetlands. As aridification also leads to exposure and rapid remineralization of large amounts of previously stored labile organic matter we infer that this process may cause a profound direct climate feedback currently underestimated in carbon cycle assessments.

Data compilation on the biological response to ocean acidification: environmental and experimental context of data sets and related literature

The exponential growth of studies on the biological response to ocean acidification over the last few decades has generated a large amount of data. To facilitate data comparison, a data compilation hosted at the data publisher PANGAEA was initiated in 2008 and is updated on a regular basis (doi:10.1594/PANGAEA.149999). By January 2015, a total of 581 data sets (over 4 000 000 data points) from 539 papers had been archived. Here we present the developments of this data compilation five years since its first description by Nisumaa et al. (2010). Most of study sites from which data archived are still in the Northern Hemisphere and the number of archived data from studies from the Southern Hemisphere and polar oceans are still relatively low. Data from 60 studies that investigated the response of a mix of organisms or natural communities were all added after 2010, indicating a welcomed shift from the study of individual organisms to communities and ecosystems. The initial imbalance of considerably more data archived on calcification and primary production than on other processes has improved. There is also a clear tendency towards more data archived from multifactorial studies after 2010. For easier and more effective access to ocean acidification data, the ocean acidification community is strongly encouraged to contribute to the data archiving effort, and help develop standard vocabularies describing the variables and define best practices for archiving ocean acidification data.

The effects of audio cueing and an instructions, feedback and praise package on the distribution of teacher praise to students of differing on-task levels

In an audio cueing system, a teacher is presented with randomly spaced auditory signals via tape recorder or intercom. The teacher is instructed to praise a child who is on-task each time the cue is presented. In this study, a baseline was obtained on the teacher's praise rate and the children's on-task behaviour in a Grade 5 class of 37 students. Children were then divided into high, medium and low on-task groups. Followinq baseline, the teacher's praise rate and the children's on-task behaviour were observed under the following successively implemented conditions: (l) Audio Cueing 1: Audio cueing at a rate of 30 cues per hour was introduced into the classroom and remained in effect during subsequent conditions. A group of consistently low on-task children were delineated. (2) Audio Cueing Plus 'focus praise package': Instructions to direct two-thirds o£ the praise to children identified by the experimenter (consistently low on-task children), feedback and experimenter praise for meeting or surpassing the criterion distribution of praise ('focus praise package') were introduced. (3) Audio Cueing 2: The 'focus praise package' was removed. (4) Audio Cueing Plus 'increase praise package': Instructions to increase the rate of praise, feedback and experimenter praise for improved praise rates ('increase praise package') were introduced. The primary aims of the study were to determine the distribution of praise among hi~h, medium and low on-task children when audio cueinq was first introduced and to investigate the effect of the 'focus praise package' on the distribution of teacher praise. The teacher distributed her praise evenly among the hiqh, medium and low on-task groups during audio cueing 1. The effect of the 'focus praise package' was to increase the percentage of praise received by the consistently low on-task children. Other findings tended to suggest that audio cueing increased the teacher's praise rate. However, the teacher's praise rate unexpectedly decreased to a level considerably below the cued rate during audio cueing 2. The 'increase praise package' appeared to increase the teacher's praise rate above the audio cueing 2 level. The effect of an increased praise rate and two distributions of praise on on-task behaviour were considered. Significant increases in on-task behaviour were found in audio cueing 1 for the low on-task group, in the audio cueing plus 'focus praise package' condition for the entire class and the consistently low on-task group and in audio cueing 2 for the medium on-task group. Except for the high on-task children who did not change, the effects of the experimental manipulations on on-task behaviour were e quivocal. However, there were some indications that directing 67% of the praise to the consistently low on-task children was more effective for increasing this group's on-task behaviour than distributing praise equally among on-task groups.

Carbon Inputs from Miscanthus Displace Older Soil Organic Carbon Without Inducing Priming Soil Carbon Sequestration Below Miscanthus

Peer reviewed

Data feedback and behavioural change intervention to improve primary care prescribing safety (EFIPPS) : multicentre, three arm, cluster-randomised controlled trial

Funding and trial registration: Scottish Government Chief Scientist Office grant CZH/3/17. ClinicalTrials.gov registration NCT01602705.

An Audit and Feedback Intervention for Reducing Antibiotic Prescribing in General Dental Practice : The RAPiD Cluster Randomised Controlled Trial

Funding: This study was conducted as part of the TRiaDS programme of implementation research which is funded by NHS Education for Scotland (NES). The Health Services Research Unit which is funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorates supported the study. The funder had no influence over the design, conduct, analysis and write up of the study.

Dynamics of vector rogue waves in a fiber laser with a ring cavity

A pulse–pulse interaction that leads to rogue wave (RW) generation in lasers was previously attributed either to soliton–soliton or soliton–dispersive-wave interaction. The beating between polarization modes in the absence of a saturable absorber causes similar effects. Accounting for these polarization modes in a laser resonator is the purpose of the distributed vector model of laser resonators. Furthermore, high pump power, high amplitude, and short pulse duration are not necessary conditions to observe pulse attraction, repulsion, and collisions and the resonance exchange of energy between among them. The regimes of interest can be tuned just by changing the birefringence in the cavity with the pump power slightly higher than the laser threshold. This allows the observation of a wide range of RW patterns in the same experiment, as well as to classify them. The dynamics of the interaction between pulses leads us to the conclusion that all of these effects occur due to nonlinearity induced by the inverse population in the active fiber as well as an intrinsic nonlinearity in the passive part of the cavity. Most of the mechanisms of pulse–pulse interaction were found to be mutually exclusive. This means that all the observed RW patterns, namely, the “lonely,” “twins,” “three sisters,” and “cross,” are probably different cases of the same process.