Amplification schemes and multi-channel DBP for unrepeatered transmission

The performance of unrepeatered transmission of a seven Nyquist-spaced 10 GBd PDM-16QAM superchannel using full signal band coherent detection and multi-channel digital back propagation (MC-DBP) to mitigate nonlinear effects is analysed. For the first time in unrepeatered transmission, the performance of two amplification systems is investigated and directly compared in terms of achievable information rates (AIRs): 1) erbium-doped fibre amplifier (EDFA) and 2) second-order bidirectional Raman pumped amplification. The experiment is performed over different span lengths, demonstrating that, for an AIR of 6.8 bit/s/Hz, the Raman system enables an increase of 93 km (36 %) in span length. Further, at these distances, MC-DBP gives an improvement in AIR of 1 bit/s/Hz (to 7.8 bit/s/Hz) for both amplification schemes. The theoretical AIR gains for Raman and MC-DBP are shown to be preserved when considering low-density parity-check codes. Additionally, MC-DBP algorithms for both amplification schemes are compared in terms of performance and computational complexity. It is shown that to achieve the maximum MC-DBP gain, the Raman system requires approximately four times the computational complexity due to the distributed impact of fibre nonlinearity.

Orthogonally polarized bright–dark pulse pair generation in mode-locked fiber laser with a large-angle tilted fiber grating

We report on the generation of orthogonally polarized bright–dark pulse pair in a passively mode-locked fiber laser with a large-angle tilted fiber grating (LA-TFG). The unique polarization properties of the LA-TFG, i.e., polarization-dependent loss and polarization-mode splitting, enable dual-wavelength mode-locking operation. Besides dual-wavelength bright pulses with uniform polarization at two different wavelengths, the bright–dark pulse pair has also been achieved. It is found that the bright–dark pulse pair is formed due to the nonlinear couplings between lights with two orthogonal polarizations and two different wavelengths. Furthermore, harmonic mode-locking of bright–dark pulse pair has been observed. The obtained bright–dark pulse pair could find potential use in secure communication system. It also paves the way to manipulate the generation of dark pulse in terms of wavelength and polarization, using specially designed fiber grating for mode-locking.

In-cavity pulse shaping and dissipative parametric instability mode-locking in fibre lasers

At the level of fundamental research, fibre lasers provide convenient and reproducible experimental settings for the study of a variety of nonlinear dynamical processes, while at the applied research level, pulses with different and optimised features – e.g., in terms of pulse duration, temporal and/or spectral shape, energy, repetition rate and emission bandwidth – are sought with the general constraint of developing efficient cavity architectures. In this work, we review our recent progress on the realisation of pulse shaping in passively- mode-locked fibre lasers by inclusion of an amplitude and phase spectral filter into the laser cavity. We present a fibre laser design in which pulse shaping occurs through filtering of a spectrally nonlinearly broadened pulse in the cavity. This strategy of pulse shaping is illustrated through the numerical demonstration of the laser operation in different pulse-generation regimes, including parabolic, flattop and triangular waveform generations, depending on the amplitude profile of the in-cavity spectral filter [1]. As an application of this general approach, we show that the use of an in-cavity flat-top spectral filter makes it possible to directly generate sinc-shaped Nyquist pulses of high quality and of a widely tunable bandwidth from the laser [2]. We also report on a recently-developed versatile erbium-doped fibre laser, in which conventional soliton, dispersion-managed soliton (stretched-pulse) and dissipative soliton mode-locking regimes can be selectively and reliably targeted by programming different group-velocity dispersion profiles and bandwidths on an in-cavity programmable filter [3]. Further, we report on our recent results on the passive mode locking of a Raman fibre laser by a recently predicted new type of parametric instability – the dissipative Faraday instability [4], where spatially periodic zig-zag modulation of spectrally dependent losses can lead to pattern formation in the temporal domain. High-order harmonic mode locking is achieved in a very simple experimental configuration, with the laser cavity including an optical fibre and two chirped fibre Bragg gratings, and no additional mode-locking elements. The results not only open up new possibilities for the design of mode-locked lasers, but extend beyond fibre optics to other fields of physics and engineering. References [1] S. Boscolo, C. Finot, H. Karakuzu, P. Petropoulos, “Pulse shaping in mode-locked fiber laser by in-cavity spectral filter,” Opt. Lett., vol. 39, pp. 438–441, 2014. [2] S. Boscolo, C. Finot, S. K. Turitsyn, “Bandwidth programmable optical Nyquist pulse generation in passively mode-locked fiber laser,” IEEE Photon. J., vol. 7, 7802008(8), 2015. [3] J. Peng, S. Boscolo, “Filter-based dispersion-managed versatile ultrafast fibre laser,” Sci. Rep., 2016, In press. [4] A. M. Perego, N. Tarasov, D. V. Churkin, S. K. Turitsyn, K. Staliunas, “Pattern generation by dissipative parametric instability,” Phys. Rev. Lett., vol. 116, 028701, 2016.

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.

A diagnostic framework for demand amplification problems in supply chains

This dissertation delivers a framework to diagnose the Bull-Whip Effect (BWE) in supply chains and then identify methods to minimize it. Such a framework is needed because in spite of the significant amount of literature discussing the bull-whip effect, many companies continue to experience the wide variations in demand that are indicative of the bull-whip effect. While the theory and knowledge of the bull-whip effect is well established, there still is the lack of an engineering framework and method to systematically identify the problem, diagnose its causes, and identify remedies. ^ The present work seeks to fill this gap by providing a holistic, systems perspective to bull-whip identification and diagnosis. The framework employs the SCOR reference model to examine the supply chain processes with a baseline measure of demand amplification. Then, research of the supply chain structural and behavioral features is conducted by means of the system dynamics modeling method. ^ The contribution of the diagnostic framework, is called Demand Amplification Protocol (DAMP), relies not only on the improvement of existent methods but also contributes with original developments introduced to accomplish successful diagnosis. DAMP contributes a comprehensive methodology that captures the dynamic complexities of supply chain processes. The method also contributes a BWE measurement method that is suitable for actual supply chains because of its low data requirements, and introduces a BWE scorecard for relating established causes to a central BWE metric. In addition, the dissertation makes a methodological contribution to the analysis of system dynamic models with a technique for statistical screening called SS-Opt, which determines the inputs with the greatest impact on the bull-whip effect by means of perturbation analysis and subsequent multivariate optimization. The dissertation describes the implementation of the DAMP framework in an actual case study that exposes the approach, analysis, results and conclusions. The case study suggests a balanced solution between costs and demand amplification can better serve both firms and supply chain interests. Insights pinpoint to supplier network redesign, postponement in manufacturing operations and collaborative forecasting agreements with main distributors.^

Temporal scaling of optical rogue waves in unidirectional ring fiber laser

A fiber mode-lock laser allows generation of the optical rogue wave (ORW) at different time scales. The criteria for distinguishing between them is a comparison of the event lifetime with the main characteristic time of the system. The characteristic time can be estimated from the decay of an autocorrelation function (AF). Thus, in comparison with AF characteristic time, fast optical rogue wave (FORW) events have duration less than the AF decay time and it appeared due to pulse-pulse interaction and nonlinear pulses dynamics. While slow optical rogue wave (SORW) have a duration much more longer than the decay time of the AF which it papered due to hopping between different attractors. Switching between regimes can be managed by change the artificial birefringence that induced in a laser cavity. For understanding the role playing by the periodical amplification and the resonator, we have performed an unidirectional fiber laser experiments without a saturable absorber. This laser experiment allowed to generate of most of the RW patterns which were either observed experimentally or predicted theoretically. In this way, we have observed the generation of an FORW along with SORW under similar conditions. Most of the patterns were found to be mutually exclusive which means that only one RW mechanism was realized in each regime of generation.

Mode-locked laser pulse sources for wavelength division multiplexing

Recent theoretical investigations have demonstrated that the stability of mode-locked solution of multiple frequency channels depends on the degree of inhomogeneity in gain saturation. In this paper, these results are generalized to determine conditions on each of the system parameters necessary for both the stability and existence of mode-locked pulse solutions for an arbitrary number of frequency channels. In particular, we find that the parameters governing saturable intensity discrimination and gain inhomogeneity in the laser cavity also determine the position of bifurcations of solution types. These bifurcations are completely characterized in terms of these parameters. In addition to influencing the stability of mode-locked solutions, we determine a balance between cubic gain and quintic loss, which is necessary for existence of solutions as well. Furthermore, we determine the critical degree of inhomogeneous gain broadening required to support pulses in multiple frequency channels. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Relative intensity noise transfer in higher-order distributed amplification through ultra-long fiber cavities

Among the different possible amplification solutions offered by Raman scattering in optical fibers, ultra-long Raman lasers are particularly promising as they can provide quasi-losless second order amplification with reduced complexity, displaying excellent potential in the design of low-noise long-distance communication systems. Still, some of their advantages can be partially offset by the transfer of relative intensity noise from the pump sources and cavity-generated Stokes to the transmitted signal. In this paper we study the effect of ultra-long cavity design (length, pumping, grating reflectivity) on the transfer of RIN to the signal, demonstrating how the impact of noise can be greatly reduced by carefully choosing appropriate cavity parameters depending on the intended application of the system. © 2010 Copyright SPIE - The International Society for Optical Engineering.

High spatial and temporal resolution interrogation of fully distributed chirped fiber Bragg grating sensors

A novel interrogation technique for fully distributed linearly chirped fiber Bragg grating (LCFBG) strain sensors with simultaneous high temporal and spatial resolution based on optical time-stretch frequency-domain reflectometry (OTS-FDR) is proposed and experimentally demonstrated. LCFBGs is a promising candidate for fully distributed sensors thanks to its longer grating length and broader reflection bandwidth compared to normal uniform FBGs. In the proposed system, two identical LCFBGs are employed in a Michelson interferometer setup with one grating serving as the reference grating whereas the other serving as the sensing element. Broadband spectral interferogram is formed and the strain information is encoded into the wavelength-dependent free spectral range (FSR). Ultrafast interrogation is achieved based on dispersion-induced time stretch such that the target spectral interferogram is mapped to a temporal interference waveform that can be captured in real-Time using a single-pixel photodector. The distributed strain along the sensing grating can be reconstructed from the instantaneous RF frequency of the captured waveform. High-spatial resolution is also obtained due to high-speed data acquisition. In a proof-of-concept experiment, ultrafast real-Time interrogation of fully-distributed grating sensors with various strain distributions is experimentally demonstrated. An ultrarapid measurement speed of 50 MHz with a high spatial resolution of 31.5 μm over a gauge length of 25 mm and a strain resolution of 9.1 μϵ have been achieved.

In-situ formation of solidified hydrogen thin-membrane targets using a pulse tube cryocooler

An account is given of the Central Laser Facility's work to produce a cryogenic hydrogen targetry system using a pulse tube cryocooler. Due to the increasing demand for low Z thin laser targets, CLF (in collaboration with TUD) have been developing a system which allows the production of solid hydrogen membranes by engineering a design which can achieve this remotely; enabling the gas injection, condensation and solidification of hydrogen without compromising the vacuum of the target chamber. A dynamic sealing mechanism was integrated which allows targets to be grown and then remotely exposed to open vacuum for laser interaction. Further research was conducted on the survivability of the cryogenic targets which concluded that a warm gas effect causes temperature spiking when exposing the solidified hydrogen to the outer vacuum. This effect was shown to be mitigated by improving the pumping capacity of the environment and reducing the minimum temperature obtainable on the target mount. This was achieved by developing a two-stage radiation shield encased with superinsulating blanketing; reducing the base temperature from 14 0.5 K to 7.2 0.2 K about the coldhead as well as improving temperature control stability following the installation of a high-performance temperature controller and sensor apparatus. The system was delivered experimentally and in July 2014 the first laser shots were taken upon hydrogen targets in the Vulcan TAP facility.

A bistable reaction-diffusion system in a stretching flow

We examine the evolution of a bistable reaction in a one-dimensional stretching flow, as a model for chaotic advection. We derive two reduced systems of ordinary differential equations (ODEs) for the dynamics of the governing advection-reaction-diffusion partial differential equations (PDE), for pulse-like and for plateau-like solutions, based on a non-perturbative approach. This reduction allows us to study the dynamics in two cases: first, close to a saddle-node bifurcation at which a pair of nontrivial steady states are born as the dimensionless reaction rate (Damkoehler number) is increased, and, second, for large Damkoehler number, far away from the bifurcation. The main aim is to investigate the initial-value problem and to determine when an initial condition subject to chaotic stirring will decay to zero and when it will give rise to a nonzero final state. Comparisons with full PDE simulations show that the reduced pulse model accurately predicts the threshold amplitude for a pulse initial condition to give rise to a nontrivial final steady state, and that the reduced plateau model gives an accurate picture of the dynamics of the system at large Damkoehler number. Published in Physica D (2006)

Targeted gene modification in Fragaria vesca mediated by CRISPR/Cas9 system

Genome editing is becoming an important biotechnological tool for gene function analysis and crop improvement, being the CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeat-CRISPR associated protein 9) system the most widely used. The natural CRISPR/Cas9 system has been reduced to two components: a single-guide RNA (sgRNA) for target recognition via RNA-DNA base pairing, which is commonly expressed using a promoter for small-RNAs (U6 promoter), and the Cas9 endonuclease for DNA cleavage (1). To validate the CRISPR/Cas9 system in strawberry plants, we designed two sgRNAs directed against the floral homeotic gene APETALA3 (sgRNA-AP3#1 and sgRNA-AP3#2). This gene was selected because ap3 mutations induce clear developmental phenotypes in which petals and stamens are missing or partially converted to sepals and carpels respectively (2). In this work, we used two different U6 promoters to drive the sgRNA-AP3s expression: AtU6-26 from Arabidopsis (4), and a U6 promoter from Fragaria vesca (FvU6) (this work). We also tested two different coding sequences of Cas9: a human- (hSpCas9) (3) and a plant-codon optimized (pSpCas9) (this work). Transient expression experiments using both CRISPR/Cas9 systems (AtU6-26:sgRNA-AP3#1_35S:hSpCas9_AtU6-26:sgRNA-AP3#2 and FvU6:sgRNA-AP3#1_35S:pSpCas9_FvU6:sgRNA-AP3#2) were performed infiltrating Agrobacterium tumefaciens into F. vesca fruits. PCR amplification and sequencing analyses across the target sites showed a deletion of 188-189 bp corresponding to the region comprised between the two cutting sites of Cas9, confirming that the CRISPR/Cas9 system is functional in F. vesca. Remarkably, the two systems showed different mutagenic efficiency that could be related to differences in expression of the U6 promoters as well as differences in the Cas9 transcripts stability and translation. Stable transformants for both F. vesca (2n) and Fragaria X anannassa (8n) are currently being established to test whether is possible to obtain heritable homozygous mutants derived from CRISPR/Cas9 strategies in strawberry. Thus, our work offers a promising tool for genome editing and gene functional analysis in strawberry. This tool might represent a more efficient alternative to the sometimes inefficient RNAi silencing methods commonly used in this species.

The development of an algorithm to track blood pressure accurately based on the pulse transit time method

Oscillometric blood pressure (BP) monitors are currently used to diagnose hypertension both in home and clinical settings. These monitors take BP measurements once every 15 minutes over a 24 hour period and provide a reliable and accurate system that is minimally invasive. Although intermittent cuff measurements have proven to be a good indicator of BP, a continuous BP monitor is highly desirable for the diagnosis of hypertension and other cardiac diseases. However, no such devices currently exist. A novel algorithm has been developed based on the Pulse Transit Time (PTT) method, which would allow non-invasive and continuous BP measurement. PTT is defined as the time it takes the BP wave to propagate from the heart to a specified point on the body. After an initial BP measurement, PTT algorithms can track BP over short periods of time, known as calibration intervals. After this time has elapsed, a new BP measurement is required to recalibrate the algorithm. Using the PhysioNet database as a basis, the new algorithm was developed and tested using 15 patients, each tested 3 times over a period of 30 minutes. The predicted BP of the algorithm was compared to the arterial BP of each patient. It has been established that this new algorithm is capable of tracking BP over 12 minutes without the need for recalibration, using the BHS standard, a 100% improvement over what has been previously identified. The algorithm was incorporated into a new system based on its requirements and was tested using three volunteers. The results mirrored those previously observed, providing accurate BP measurements when a 12 minute calibration interval was used. This new system provides a significant improvement to the existing method allowing BP to be monitored continuously and non-invasively, on a beat-to-beat basis over 24 hours, adding major clinical and diagnostic value.

Establishing reference values for central blood pressure and its amplification in a general healthy population and according to cardiovascular risk factors

AIMS: Estimated central systolic blood pressure (cSBP) and amplification (Brachial SBP-cSBP) are non-invasive measures potentially prognostic of cardiovascular (CV) disease. No worldwide, multiple-device reference values are available. We aimed to establish reference values for a worldwide general population standardizing between the different available methods of measurement. How these values were significantly altered by cardiovascular risk factors (CVRFs) was then investigated. METHODS AND RESULTS: Existing data from population surveys and clinical trials were combined, whether published or not. Reference values of cSBP and amplification were calculated as percentiles for 'Normal' (no CVRFs) and 'Reference' (any CVRFs) populations. We included 45,436 subjects out of 82,930 that were gathered from 77 studies of 53 centres. Included subjects were apparently healthy, not treated for hypertension or dyslipidaemia, and free from overt CV disease and diabetes. Values of cSBP and amplification were stratified by brachial blood pressure categories and age decade in turn, both being stratified by sex. Amplification decreased with age and more so in males than in females. Sex was the most powerful factor associated with amplification with 6.6 mmHg (5.8-7.4) higher amplification in males than in females. Amplification was marginally but significantly influenced by CVRFs, with smoking and dyslipidaemia decreasing amplification, but increased with increasing levels of blood glucose. CONCLUSION: Typical values of cSBP and amplification in a healthy population and a population free of traditional CVRFs are now available according to age, sex, and brachial BP, providing values included from different devices with a wide geographical representation. Amplification is significantly influenced by CVRFs, but differently in men and women.

Kohärente transiente und effiziente Endzustandskontrolle in Atomen und Molekülen

Es ist ein lang gehegter Traum in der Chemie, den Ablauf einer chemischen Reaktion zu kontrollieren und das Aufbrechen und Bilden chemischer Bindungen zu steuern. Diesem Ziel verschreibt sich auch das Forschungsgebiet der Femtochemie. Hier werden Femtosekunden Laserpulse eingesetzt um auf dem Quantenlevel molekulare Dynamiken auf ihren intrinsischen Zeitskalen zu kontrollieren und das System selektiv und effizient von einem Anfangs- in einen Zielzustand zu überführen. Der Wunsch, mit geformten Femtosekunden Laserpulsen Kontrolle über transiente Dynamiken und finale Populationen auszuüben, zu beobachten und zu verstehen, bildet auch die Motivation für diese Arbeit. Hierzu wurden mit Hilfe der Photoelektronenspektroskopie Untersuchungen zur Wechselwirkung atomarer und molekularer Prototypsysteme mit intensiven, geformten Femtosekunden Laserpulsen durchgeführt. Die Verwendung von Modelsystemen ermöglicht es, grundlegende Mechanismen der kohärenten Kontrolle in intensiven Laserfeldern zu analysieren, ohne dass sie durch komplexe Wechselwirkungen verschleiert werden. Zunächst wurde die Wechselwirkung von Kaliumatomen mit gechirpten Femtosekunden Laserpulsen untersucht. In den Experimenten wurden sowohl transiente Dynamiken als auch die Endbesetzungen der elektronischen Zustände abgebildet. In den folgenden Experimenten wurde das Quantenkontrollszenario SPODS auf die gekoppelte Elektronen-Kern-Dynamik in Molekülen übertragen. Die Kontrolle basiert auf der Erzeugung und Manipulation von Ladungsoszillationen durch Pulssequenzen. Der letzte Teil widmet sich der Entwicklung adiabatischer Kontrollmechanismen in Molekülen. Bei den Experimenten wurden gechirpte Airypulse eingesetzt um robuste Starkfeldanregung in molekularen Systemen zu induzieren. In Zukunft wird die Erforschung immer komplexerer Moleküle im Rahmen der transienten Kontrolle im Fokus stehen. Dabei werden nicht nur die effiziente Besetzung gebundener Zustände von Interesse sein, sondern auch die gezielte Dissoziation in spezifische Fragmente, photoinduzierte Isomerisierungsreaktionen oder die Kontrolle über transiente Dynamiken, die Einfluss auf andere molekulare Eigenschaften haben. Vor dem Hintergrund dieses übergeordneten Wunsches, photochemische Reaktionen immer komplexerer Moleküle, bis hin zu großen, biologisch relevanten Molekülen, zu kontrollieren, ist es umso wichtiger, die zugrundeliegenden Anregungsmechanismen in einfachen Systemen nachzuvollziehen. In den hier präsentierten Experimenten wurde gezeigt, wie die simultane Beobachtung der bekleideten und der stationären Zustände in atomaren Systemen zu einem umfassenden Bild der lichtinduzierte Dynamiken führen kann. Die gewonnenen Erkenntnisse können auf die Steuerung gekoppelter Dynamiken übertragen werden, durch die Kontrolle auch in molekularen Systemen möglich wird.