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abstract: We demonstrate and characterize polarization division multiplexed (PDM) DWDM data transmission for the first time in a range of systems incorporating a net gain polarization insensitive fiber optical parametric amplifier (PI FOPA) for loss compensation. The PI FOPA comprises a modified diversity loop architecture to achieve 15dB net gain, and up to 2.3THz ~18nm) bandwidth. Three representative systems are characterized using a 100Gb/s PDM QPSK signal in conjunction with emulated DWDM neighbouring channels: (a) a 4x75km in line fiber transmission system incorporating multiple EDFAs and a single PI FOPA (b) N cascaded PI FOPA amplification stages in an unlevelled Nx25km recirculating loop arrangement, with no EDFAs used within the loop signal path, and (c) M cascaded PI FOPA amplification stages as part of an Mx75.6km gain flattened recirculating loop system with the FOPA compensating for the transmission fiber loss, and EDFA compensation for loop switching and levelling loss. For the 4x75km in line system (a) we transmit 45x50GHz spaced signals 'equivalent' data rate of 4.5Tb/s) with average OSNR penalty of 1.3dB over the band at 10 BER. For the unlevelled 'FOPA only' 25.2km cascaded system (b) we report a maximum of eight recirculations for all 10x100GHz spaced signals, and five recirculations for 20x50GHz spaced signals. For the 75.6km levelled system (c) we achieve eight recirculations for all 20x50GHz signals resulting in a total transmission distance of 604.8km. (c) 2017 Optical Society of America OCIS codes: (060.2320) Fiber optics amplifiers and oscillators; (060.2330) Fiber optics communications; (190.4410) Nonlinear optics, parametric processes. References and links 1. M. Islam, "Raman amplifiers for telecommunications," IEEE J. Sel. Topics Quantum Electron. 8(3) 548 559 (2002) 2. C. Headley and G. P. Agrawal, Raman amplification in fiber optical communication systems (Academic, 2005) 3. R. Kashyap, "The fiber fuse from a curious effect to a critical issue: A 25th year retrospective," Opt. express 21(5) 6422 6441 (2013) 4. M. J. O' Mahony, "Semiconductor laser optical amplifiers for use in future fiber systems," IEEE J. Lightw. Technol. 6(4) 531 544 (1988) 5. M. F. C. Stephens, D. Nesset, R. V. Penty, I. H. White, and M. J. Fice, "Wavelength conversion at 40 Gbit/s via four wave mixing in semiconductor optical amplifier with integrated pump laser," Electronics Letters 35(5) 420421, (1999) 6. Z. Li, A. M. Heidt, J. M. O. Daniel, Y. Jung, S. U. Alam, and D. J. Richardson, "Thulium doped fiber amplifier for optical communications at 2 mm," Opt. Express 21(8) 9289 9297 (2013) 7. N. Simakov, Z. Li, Y. Jung, J. M. O. Daniel, P. Barua, P. C. Shardlow, S. Liang, J. K. Sahu, A. Hemming, W. A. Clarkson, S. U. Alam, and D. J. Richardson, "High gain holmium doped fibre amplifier," Opt. Express 24(13) 13946 13956 (2016) 8. F. Poletti, N. V. Wheeler, M. N. Petrovich, N. K. Baddela, E. Numkam Fokoua, J. R. Hayes, D. R. Gray, Z. Li, R. Slavik, and D. J. Richardson, "Towards high capacity fibre optic communications at the speed of light in vacuum," Nat. Photonics 7(4) 279 284 (2013) 9. V. Gordienko, M. F. C. Stephens, A. E. El Taher, and N. J. Doran, "Ultra flat wideband single pump Ramanenhanced parametric amplification," Opt. Express 25(5) 4810 4818 (2017) 10. Z. Tong, C. Lundstrom, P. A. Andrekson, M. Karlsson, and A. Bogris, "Ultralow noise, broadband phasesensitive optical amplifiers, and their applications," IEEE IEEE J. Sel. Topics Quantum Electron. 18(2) 10161032 (2012) 11. M. F. C. Stephens, M. Tan, I.D. Phillips, S. Sygletos, P. Harper, and N.J. Doran, "1.14 Tb/s DP QPSK WDM polarization diverse optical phase conjugation," Opt. Express 22(10) 11840 11848 (2014) 12. A. D Ellis, M. Tan, M. A. Iqbal, M. A. Z. Al Khateeb, V. Gordienko, G. S. Mondaca, S. Fabbri, M. F. C. Stephens, M. E. McCarthy, A. Perentos, I. D. Phillips, D. Lavery, G. Liga, R. Maher, P. Harper, N. Doran, S. K. Turitsyn, S. Sygletos, and P. Bayvel, "4 Tb/s transmission reach enhancement using 10x 400 Gb/s superchannels and polarization insensitive dual band optical phase conjugation," IEEE J. Lightw. Technol. 34(8) 1717 1723 (2016) 13. S. Takasaka, and R. Sugizaki, "Polarization Insensitive Fiber Optical Parametric Amplifier Using a SBS Suppressed Diversity Loop," in Optical Fiber Communication Conference (Optical Society of America, 2016) paper M3D.4. 14. M. F. C. Stephens, V. Gordienko, and N.J. Doran, "20 dB net gain polarization insensitive fiber optical parametric amplifier with> 2 THz bandwidth," Opt. Express 25(9) 10597 10609 (2017) 15. L. Gruner Nielsen, D. Jakobsen, S. Herstrom, B. Palsdottir, S. Dasgupta, D. Richardson, C. Lundstrom, S. Olsson, and P. Andrekson, "Brillouin Suppressed Highly Nonlinear Fibers," in European Conference on Optical Communication (ECOC 2012) paper We.1.F.1. 16. M. F. C. Stephens, I. D. Phillips, P. Rosa, P. Harper, and N. J. Doran, "Improved WDM performance of a fiber optical parametric amplifier using Raman assisted pumping," Opt. Express 23(2) 902 911 (2015) 17. A. Redyuk, M. F. C. Stephens, and N. J. Doran, "Suppression of WDM four wave mixing crosstalk in fibre optic parametric amplifier using Raman assisted pumping," Opt. Express 23(21) 27240 27249 (2015) 18. J. D. Marconi, M. C. Fugihara, F. A. Callegari, and H. L. Fragnito, "In line one pump parametric amplifier with independent polarization gain: a field trial demonstration," Microwave and Optical Tech. Lett. 55(5) 1104 1107 (2013) 19. Z. Lali Dastjerdi, O. Ozolins, Y. An, V. Cristofori, F. Da Ros, N. Kang, H. Hu, H. C. H. Mulvad, K. Rottwitt, M. Galili, and C. Peucheret, "Demonstration of cascaded in line single pump fiber optical parametric amplifiers in recirculating loop transmission," in European Conference on Optical Communication (ECOC 2012) paper Mo.2.C.5. 20. N. El Dahdah, D. S. Govan, M. Jamshidifar, N. J. Doran, and M. E. Marhic, "Fiber Optical Parametric Amplifier Performance in a 1 Tb/s DWDM Communication System" IEEE IEEE J. Sel. Topics Quantum Electron. 18(2) 950 957 (2012) 21. D. Elson, G. Saavedra, K. Shi, D. Semrau, L. Galdino, R. Killey, B. Thomsen, and P. Bayvel, "Investigation of bandwidth loading in optical fibre transmission using amplified spontaneous emission noise," Opt. Express 25(16) 19529 19537 (2017) 22. M. McCarthy, N. Mac Suibhne, S. T. Le, P. Harper, and A. D. Ellis, "High spectral efficiency transmission emulation for non linear transmission performance estimation for high order modulation formats," in European Conference on Optical Communication (ECOC 2014) paper P.5.7. 23. J. Hansryd, P. A. Andrekson, M. Westlund, J. Li, and P. O. Hedekvist, "Fiber based optical parametric amplifiers and their applications," IEEE J. Sel. Top. Quantum Electron. 8(3) 506 520 (2002) 24. M. F. C. Stephens, A. Redyuk, S, Sygletos, I. D. Phillips, P. Harper, K. J. Blow, and N. J. Doran, "The Impact of Pump Phase Modulation and Filtering on WDM Signals in a Fiber Optical Parametric Amplifier," in Optical Fiber Communication Conference (Optical Society of America, 2016) paper W2A.43. 25. J. M. Chavez Boggio, A. Guimaraes, F. A. Callegari, J. D. Marconi, and H. L. Fragnito, "Q penalties due to pump phase modulation and pump RIN in fiber optic parametric amplifiers with non uniform dispersion," Opt. Commun. 249(4) 451 472 (2005) 26. A. Mussot, A. Durecu Legrand, E. Lantz, C. Simonneau, D. Bayart, H. Maillotte, and T. Sylvestre, "Impact of pump phase modulation on the gain of fiber optical parametric amplifier," IEEE Photon. Technol. Lett. 16(5) 1289 1291 (2004) 27. J. M. Chavez Boggio, J. D. Marconi, and H. L. Fragnito, "Experimental and numerical investigation of the SBSthreshold increase in an optical fiber by applying strain distributions," J. Lightw. Technol. 23(11) 3808 3814 (2005) 28. Z. Lali Dastjerdi, T. Lund Hansen, N. Kang, K. Rottwitt, M. Galili, and C. Peucheret, "High frequency RIN transfer in fiber optic parametric amplifiers," in Conference on Lasers and Electro Optics Europe (CLEOEurope 2011) paper CI2.5. 29. F. Zhang, Y. Luo, Y.Wang, L. Li, L. Zhu, Z. Chen, and C. Wu, "Experimental Comparison of Different BER Estimation Methods for Coherent Optical QPSK Transmission Systems," IEEE Photon. Technol. Lett. 23(18) 1343 1345 (2011)
author_names: Steiner Mfc

G V

H P

Dowie Nj
title: In line and cascaded DWDM transmission using a 15 dB net gain polarization insensitive fiber optical parametric amplifier
year: 2017

abstract: Optical fibres have been developed as an ideal medium for the delivery of optical pulses ever since their inception (Kao Hockham, 1966) Much of that development has been focused on the transmission of low energy pulses for communication purposes and thus fibres have been optimised for singlemode guidance with minimum propagation losses only limited by the intrinsic material absorption of silica glass of about 0.2dB/km in the near infrared part of the spectrum (Miya et al. 1979) The corresponding increase in accessible transmission length simultaneously started the interest in nonlinear fibre optics, for example with early work on the stimulated Raman effect (Stolen et al. 1972) and on optical solitons (Hasegawa Tappert, 1973) Since the advent of fibre amplifiers (Mears et al. 1987) available fibre coupled laser powers have been increasing dramatically and, in particular, fibre lasers now exceed kW levels in continuous wave (cw) operation (Jeong et al. 2004) and MW peak powers for pulses (Galvanauskas et al. 2007) in all fibre systems. These developments are pushing the limits of current fibre technology, demanding fibres with larger mode areas and higher damage threshold. However, it is increasingly difficult to meet these requirements with fibres supporting one single optical mode and therefore often multiple modes are guided. Non fibre based laser systems are capable of delivering even larger peak powers, for example commercial Ti:sapphire fs lasers now reach the GW regime. Such extreme powers cannot be transmitted in conventional glass fibres at all without destroying them (Gaeta, 2000) but there is a range of applications for such pulses coupled into hollow core capillaries, such as pulse compression (Sartania et al. 1997) and high harmonic generation (Rundquist et al. 1998) For typical experimental parameters, these capillaries act as optical waveguides for a large number of spatial modes and modal interactions contribute significantly to the system dynamics. In order to design ever more efficient fibre lasers, to optimise pulse delivery and to control nonlinear applications in the high power regime, a thorough understanding of pulse propagation and nonlinear interactions in multimode fibres and waveguides is required. The conventional tools for modelling and investigating such systems are based on beam propagation methods (Okamoto, 2006) However, these are numerically expensive and provide little insight into the dependence of fundamental nonlinear processes on specific fibre properties, e.g. on transverse mode functions, dispersion and nonlinear mode coupling. For such an interpretation a multimode equivalent of the nonlinear Schrodinger equation, the standard and highly accurate method for describing singlemode nonlinear pulse propagation (Agrawal, 2001; Blow Wood, 1989) is desirable. In this chapter, we discuss the basics of such a multimode generalised nonlinear Schrodinger equation (Poletti Horak, 2008) its simplification to experimentally relevant situations and a few select applications. We start by introducing and discussing the theoretical framework for fibres with chi(3) nonlinearity in Sec. 2. The following sections are devoted to multimode nonlinear applications, presented in the order of increasing laser peak powers. A sample application in the multi kW regime is supercontinuum generation, discussed in Sec. 3. Here we demonstrate how fibre mode symmetries and launching conditions affect intermodal power transfer and spectral broadening. For peak powers in the MW regime, self focusing effects become significant and lead to strong mode coupling. The spatio temporal evolution of pulses in this limit is the topic of Sec. 4. Finally, at GW peak power levels, optical pulses can only be delivered by propagation in gases. Still, intensities become so high that nonlinear effects related to ionisation must be taken into account. An extension of the multimode theory to include these extreme high power effects is presented in Sec. 5 and the significance of mode interaction is demonstrated by numerical examples pertaining to a recent experiment. Finally, we end this chapter with conclusions in Sec. 6
author_names: Peter Horak

Francesco Poletti
title: Multimode Nonlinear Fibre Optics: Theory and Applications
year: 2012

abstract: Metal based additive manufacturing enables the production of even complex shaped parts that cannot be produced with conventional processes (e.g. milling) Taking advantage of the geometrical freedom in part production, an increasing number of industrial applications nowadays resort to these techniques. Hence, the additive manufacturing technology has currently passed the threshold from prototyping to mass production. This requires short processing times which are potentially reached by the adoption of multiple lasers with increasing output power. Typically, single mode lasers are used to reach customer demands, e.g. surface smoothness. An optical setup of fibre beam delivery, collimation, focusing, and beam deflection is utilized to allow laser scan velocities of up to 1000 mm/s. For future applications of laser powers in the range of several kilowatts a critical level of absorbed power in these optical elements is likely to occur. The resulting thermally induced focal shift can lead to an undesirable beam defocussing and the corresponding increase of beam diameter will then lead to a loss of intensity in the powder bed interaction zone. To encounter this challenge for a future utilization of even higher laser powers, measures can be taken to reduce thermally induced focal shift. One possible approach comprises the insertion of additional optical glasses which compensate the focal shift by means of a converse thermal behaviour, i.e. negative refraction index gradient. Related to this topic, the measurement of absorption in optical components and the power dependent focal position are presented within this work. Laboratory measurements are complemented by the application of the corresponding results on an appropriate manufacturing system configuration. The investigations demonstrate that the desired reduction of thermally induced focal shift can be reached.
title: Lasers in Manufacturing Conference 2015 Reliable Beam Positioning for Metal based Additive Manufacturing by Means of Focal Shift Reduction
year: 2015

abstract: Organisms are under strong selection to respond adaptively to environmental stress, even when different stresses occur simultaneously or in rapid succession, as they often do in natural environments. However, at a molecular level, stress responses are often studied in isolation and under controlled growth conditions. This leaves us with an ever finer picture of single stress responses but little understanding of how additional stressors modify those responses. Without companion studies of more complex systems of interacting stresses, we do not know how phenotypes are shaped under natural conditions. Based on whole organism studies in largely agricultural settings, we do know that stresses interact profoundly to shape phenotypes. We also have examples of cross talk among signalling pathways associated with specific abiotic and biotic stress responses which hint at the existence of mechanisms that may integrate global plant stress responses. To move plant stress biology forward in transformative ways, we need greater collaboration among plant biologists studying different stresses in order to address the complexity of plant stress responses under natural conditions. In 2015, the University of Missouri Interdisciplinary Plant Group (IPG) organized its annual symposium around the topic of Plants Between a Rock and a Hard Place: The Interface between Plant Abiotic and Biotic Stress Responses. A primary goal of the meeting was to promote and enhance multi stress collaboration within the plant stress biology community by bringing together world renowned experts in different aspects of plant stress biology who have already begun to study the interactions between different stresses. In this special issue of the Journal of Experimental Botany, we present some of the topics and research that were covered at the symposium. Foyer et al. (2016) set the stage with a detailed look at how an abiotic stress can shape a plant's response to attack by phloem feeding aphids. They present a strong case to challenge the oft held notion that abiotic stress events result in an increased susceptibility to biotic stress factors. The complex signalling pathways that direct plant responses to abiotic and biotic stressors overlap in many ways that lead to cross tolerance phenomena. The plant's response to aphid infestation involves interactions between hormone, redox, nitric oxide, kinase, and calcium signalling pathways that mirror aspects of the plant's response to abiotic factors. The preponderance of evidence suggests that abiotic stressors do not predispose a plant to aphid attack and, in fact, may provide some measure of protection and that this may hold true for other abiotic biotic stressor interactions. Viruses depend on vectors such as plant associated insects to move from plant to plant. To spread throughout an infected plant successfully and to facilitate vector transmission to another, viruses must manipulate the cellular processes of the host with a very limited set of proteins encoded in their small genomes. Studying these proteins from viruses and other plant associated pathogens can provide novel insights into the processes involved in abiotic and biotic stress responses. Schoelz et al. (2016) provide an intriguing overview of the multifunctional P6 protein of Cauliflower Mosaic Virus, a novel function of which is to direct large protein assemblies devoted to virus replication into plasmodesmata for cell to cell movement. In contrast to viruses, most microbial pathogens of plants do not enter the host cytoplasm. A first line of defence, therefore, occurs at the plant plasma membrane where receptors detect conserved non self molecules collectively called microbe or pathogen associated molecular patterns (M/PAMPs) to initiate a broad defence response termed PAMP triggered immunity (PTI) (Macho and Zipfel, 2014) While PAMPs and the corresponding plant receptors have been identified for a variety of microbial pathogens, a notable exception has been PAMPs derived from plant parasitic nematodes. The review by Holbein et al. (2016) provides a fascinating update on progress in identifying elements of plant PTI responses to nematodes, thus broadening the arsenal for breeding resistance into crop plants. Biotic and abiotic stressors often elicit systemic responses which depend on signalling from local sites of exposure to other areas of the plant. At the cellular or tissue level, the possible interplay between the various signalling pathways can be complex, especially when two or more stressors are combined as is often the case in the field. Huber and Bauerle (2016) describe the hydraulic, chemical, and electrical components that are part of the long distance communication array of all plants. They provide a comprehensive assessment of what is known about how they operate and interact to co ordinate a systemic response in the plant. The authors highlight the large gaps in knowledge that need to be addressed and make clear that combinations of stressors often elicit novel responses that differ from responses to single stressors. Plant responses to abiotic and biotic stressors can lead to changes that appear to be 'memorized' and influence the stress tolerance of the next generation. The review by Bilichak and Kovalchuk (2016) explores possible epigenetic mechanisms associated with this phenomenon, highlighting the evidence that certain stress induced epigenetic factors escape full scale reprogramming of the epigenome during gametogenesis. The authors speculate that a better understanding of these epigenetic factors would enable the engineering of epigenetic modifications to cross stress tolerance for crop improvement strategies in plant breeding. The symposium was also an opportunity to showcase new and focused unpublished data. The research paper by MacQueen and Bergelson (2016) focuses on plant innate immunity to microbial pathogens. They show that abiotic factors such as temperature and humidity, which are known to influence pathogen aggressiveness, impact expression levels of plant resistance genes. These resistance genes provide a second line of defence against microbial pathogens, but their continued high expression reduces plant fitness. Therefore, modulation of resistance gene expression levels by abiotic factors probably reflects an adaptive advantage by balancing plant defence readiness and fitness in the absence of pathogens. Finally, the research paper by Zhang et al. (2016) identifies an intriguing connection between the auxin and jasmonic acid (JA) signalling pathways via hormone metabolism. Even though auxin and JA regulate quite distinct developmental and stress response pathways, it was found that some of the indole 3 acetic acid (IAA) hydrolases (IAH) also metabolize JA isoleucine, a bioactive derivative of JA. Manipulation of IAH expression levels led to surprising perturbations of these hormone signalling modules, highlighting the degree to which these two signalling pathways are interconnected via metabolic cross talk. Worldwide, humans rely on plants for food, fibre, and fuel, and face the daunting task of growing food for nine billion people by 2050 while reducing the carbon, fertilizer, and water footprint of agriculture. In addition, the consensus prediction is that global climate change will destabilize plant growth conditions in terms of higher CO2 levels and increased risks of severe fluctuations in temperature and precipitation (Schroeder et al. 2013) These adverse abiotic conditions will most likely favour the spread of plant pathogens and pests into new geographic areas. Such a scenario increases the need to develop abiotic stress and pathogen and pest resistant crop plants at a speed that cannot be met by breeding alone (Dangl et al. 2013) The combination of abiotic and biotic stresses not only threatens agriculture but also plants in natural environments that fulfil important ecosystem services. Addressing these major challenges will require an interdisciplinary and concerted approach. We hope that our readers will find, as we did, that the reviews and research articles in this special issue provide a useful and stimulating contribution towards addressing these challenges. We are grateful to the sponsors of our symposium, in particular the National Science Foundation, the USDA National Institute of Food and Agriculture, and the Journal of Experimental Botany for their support.
author_names: Walter Gassmann

Heidi M Appel

Melvin J Oliver
title: The interface between abiotic and biotic stress responses
venue: Journal of experimental botany
year: 2016

abstract: The measured bending field of the CERN Proton Synchrotron (PS) is received in real time by the longitudinal beam control system and converted into the revolution frequency used as set point for beam phase and radial loops. With the renovation of the bending field measurement system the transmission technique is changed from a differential sequence of pulses, the so called B train, to a stream of Ethernet frames based on the White Rabbit protocol. The packets contain field, its derivative and auxiliary information. A new frequency program for the conversion of the bending field into the revolution frequency, depending also on parameters like radius of the accelerator and the particle type, has been developed. Instead of storing large conversion tables from field to frequency for fixed parameters, the frequencies are directly calculated in programmable logic (FPGA) In order to reduce development time and keep flexibility, the conversion is processed in real time in the FPGA using Xilinx floating point primitives mapped by a higher level tool Simulink System Generator. Commissioning with beam of the new frequency program in the PS is progressing.
author_names: Damien Perrelet

Ylenia Brischetto

Heiko Damerau

Daniel Oberson

Magnus Sundal

A Villanueva
title: White Rabbit Based Revolution Frequency Program for the Longitudinal Beam Control of the CERN PS
year: 2015

abstract: This book provides an excellent introduction to the topic of smart structures and materials. It is easy to read, being only 200 pages long. It begins with a layman's view of the topic, placing smart structures in terms of simple concepts before moving on to a step by step approach to the specifics. The style of the book is meant to be at the awareness level more than the detailed analysis level and the author achieves this successfully. The use of comparative tables in almost every chapter is particularly good for quickly disseminating information. All the important topics are covered, albeit somewhat briefly in some sections. The eight chapters span aspects such as materials, sensing and actuation and signal processing. Several case studies are included and the book concludes by contemplating where the future may be with regard to smart structures and materials. The most detailed chapter of the book deals with the author's principal research field, namely sensing technologies and optical fibres. It is somewhat unfortunate that this is the only chapter which offers a good list of references; this is the only real weakness of the book. Overall, this is a worthwhile purchase for undergraduates, researchers and industrialists who want to be exposed to the important developing area of smart materials and structures and who want an easy text to read on the subject. The author has done a splendid job of producing a book that should stimulate further interest in a technology which is clearly part of the future.
author_names: Geoffrey R Tomlinson
title: Smart Structures and Materials
year: 1996

abstract: The detailed knowledge of the temporal behaviour of astrophysical objects is one of the main sources of information about physical processes occurring in several classes of objects. In this PhD thesis we investigated two different astrophysical topics, both of them linked to timing. We present the scientific analysis of the data collected from the Crab pulsar by means of the novel optical extremely fast photon counters Aqueye and Iqueye, that have the best temporal resolution ever achieved in the optical domain (hundreds of picoseconds) Aqueye (Barbieri et al. 2008, 2009) was designed to be mounted at the Copernico telescope in Asiago. Iqueye (Naletto et al. 2009, 2010) is an improvedversion for the NTT telescope. Here we also discuss some ideas on modelling the millisecond variability observed in the X ray flux from Low Mass X ray Binaries with either a neutron star or a black hole. The timing analysis of the optical emission from the Crab pulsar requires to time tag with extreme precision the photons as collected by an inertial observer. Therefore we must refer the time of arrival of photons (TOAs) to a reference frame that approximates an inertial frame to the level of precision needed. One usually refers TOAs to a reference system located at the solar system barycenter. Tempo2 (Hobbs et al. 2006, Edwards et al. 2006) is a software meant to model with extreme precision (up to 1 ns) TOAs as collected by an inertial observer. After baricentering TOAs a numerical code making use of a standard template was used to determine the phase of the mean peak of the Crab pulsar profile. By studying the phase behaviour it is possible to extract information about both the rotational period of the fast rotating neutron star and its derivatives. Moreover, the analysis of the phase residuals left out after subtracting the standard pulsar timing model may reveal interesting features of the pulsar and its surroundings. With the anlysis of the residuals one can also check for possible discrepancies on the modelling. If some systematic residuals show up, then it is interesting to investigate the physical origin. Just to quote a few noticeable examples, we mention the discovery of the first extrasolar planetary system around the pulsar PSR B1257+12, obtained from the analysis of pulsar phase residuals (Wolszczan Frail 1992; Wolszczan 1994; Konacki Wolszczan 2003) Other foundamental results deal with tests of General Relativity theory (Helfand et al. 1980; Kramer et al. 2006) Moreover, pulsar timing is now being planned as a tool to reveal gravitational wave (Stappers et al. 2006; Manchester 2010) The analysis of the optical phase residuals of the Crab pulsar we performed has revealed poor corrections in the Roemer delay due to the Tempo2 configuration files. After correcting for them we can conclude that the rotational periods of the Crab pulsar measured by Aqueye/Iqueye agree with those quoted in the Jodrell Bank radio archive up to a few picoseconds. The TOAs from a photon counter usually are affected by noise that obeys the Poisson statistics. We noticed possible discrepancies between the radio and optical rotational periods larger than the estimated Poissonian error, but a more extensive analysis of the pulsar timing noise and related errors is needed before any definitive conclusion can be drawn. We were able to measure the spin down of the neutron star already over a baseline of a few days. Discrepancies with that reported in the Jodrell Bank radio archive are underlined. By comparing the time of arrival of the optical peak at the solar system barycenter with that quoted in the Jodrell Bank radio ephemerides archive we find a radio optical delay in agreement with that reported in the literature (Shearer et al. 2003; Oosterbroek et al. 2008) that is, an optical peak leading the radio one by about 120 microsec. We also noticed same radio optical phase drift with time, which may be related to the radio optical rotational period discrepancies mentioned above. A further investigation on the possible origin of these discrepancies led to the preliminary conclusion that the signal from the Crab pulsar may be affected by an extra noise component, known as timing noise, not suitable described by the Poissonian statistics. Non Poissonian noise in the signal from neutron stars has been reported by other authors (Boynton et al. 1972; Lyne et al. 1993; Scott et al. 2003; Hobbs et al. 2006b; Patruno et al. 2009) but using integration times of months or years. Further observations to confirm the existence of non Poissonian noise in the Crab pulsar are needed. In this PhD thesis we also present some ideas on the origin of the millisecond X ray timing variability in the X ray flux from Low Mass X ray Binaries (LMXBs) with either a black hole or a neutron star (e.g. van der Klis et al. 2004) These quasi periodic oscillations (QPOs) at frequencies up to 1200 Hz, were discovered by means of the X ray photon counters on board of the Rossi X ray Timing Explorer satellite (RXTE; Bradt et al. 1993) Millisecond time scales are typical for matter orbiting close to the compact object. Therefore, timing studies of these sources could provide a way to investigate the motion of matter in a strongly curved space time, thus probing General Relativity in the strong field limit. We describe some ideas on fitting relativistic frequencies in the Kerr metric to observed QPO frequencies in LMXBs. Using a grid of masses and specific angular momenta for the neutron star we show that numerical fits have a low kh2/dof for masses of the neutron star above 2 M. Such masses are bigger than the canonical value 1.4M measured in double radio pulsars. However, in accreting bynary systems a mass of the neutron star larger than the canonical value has been measured (Casares et al. 2006, 2010) We note that precise measurements of neutron star masses by means of millisecond QPOs are uncertain because of the yet poorly understood phenomenology. If high frequency QPOs in the X ray flux of LMXBs are produced by orbiting blobs of matter close to the compact object then a full consistent modelling should also account for the interaction of the shape of the blob with the curved geometry of the space time. In collaboration with the Department of Mathematics and Physics of the University of Ljubljana we ran simulations of light curves and power spectra produced by clumps of free particles orbiting a Schwarzschild black hole, that are deformed by tidal interaction. The numerical code was developed by (Cadez et al. 2008, Kostic et al. 2009) The numerical simulations reproduce the high frequency part of the power spectrum observed in the black hole LMXB XTE J1550 564 (Germana et al. 2009)
author_names: Claudio Germana
title: Timing studies of compact objects
year: 2011

abstract: Digital Signal Transmission: C. C. BISSELL and D. A. CHAPMAN (Cambridge University Press, 1992,321 pp. PS15.95, $34.95paperback, PS45, $79.95hardback) The subject of digital transmission is large and complex and a thorough treatment of the topic requires considerable detailed discussion and involves significant mathematical theory. However most students at undergraduate level require an easily readable text with the mathematical content kept to the bare essentials. This book is aimed at second and third year undergraduate students and practising engineers that require updating in modern techniques. The mathematical theory has been kept to a minimum and the standard mathematical results are presented in appendices. A large portion of the text has been derived from the authors' contributions to the Open University course on Digital Telecommunications and perhaps as a consequence the text is written in a style which makes it very suitable for self study. The book only considers a limited number of topics in depth and places the emphasis on the engineering aspects of digital transmission and interpretation of mathematical models. The chapters are grouped into three parts. Part I considers models and discusses continuous and discrete time signals and systems as well as random signals and noise. Part 2 describes processes and explains details of the pulses that are used for digital transmission, and it also discusses line codes and channel codes, including scrambling, block codes and convolution coding. The final part of the book is devoted to digital transmission over the public switched telephone network. The topics considered in this part are relevant analogue and digital signal sources, coding techniques, digital transmission hierarchies and the features of an optical fibre link. I found this an interesting and useful book which has been written with the undergraduate student very much in mind. It is very appropriate for use in universities as a student text for the typical telecommunication undergraduate course. ROBERT J. SIMPSON, Professor of Electronic Engineering, University of CentralLancashire
author_names: Robert J Simpson
title: Book Review: Digital Signal Transmission
year: 1993

abstract: Digital Signal Transmission: C. C. BISSELL and D. A. CHAPMAN (Cambridge University Press, 1992,321 pp. PS15.95, $34.95paperback, PS45, $79.95hardback) The subject of digital transmission is large and complex and a thorough treatment of the topic requires considerable detailed discussion and involves significant mathematical theory. However most students at undergraduate level require an easily readable text with the mathematical content kept to the bare essentials. This book is aimed at second and third year undergraduate students and practising engineers that require updating in modern techniques. The mathematical theory has been kept to a minimum and the standard mathematical results are presented in appendices. A large portion of the text has been derived from the authors' contributions to the Open University course on Digital Telecommunications and perhaps as a consequence the text is written in a style which makes it very suitable for self study. The book only considers a limited number of topics in depth and places the emphasis on the engineering aspects of digital transmission and interpretation of mathematical models. The chapters are grouped into three parts. Part I considers models and discusses continuous and discrete time signals and systems as well as random signals and noise. Part 2 describes processes and explains details of the pulses that are used for digital transmission, and it also discusses line codes and channel codes, including scrambling, block codes and convolution coding. The final part of the book is devoted to digital transmission over the public switched telephone network. The topics considered in this part are relevant analogue and digital signal sources, coding techniques, digital transmission hierarchies and the features of an optical fibre link. I found this an interesting and useful book which has been written with the undergraduate student very much in mind. It is very appropriate for use in universities as a student text for the typical telecommunication undergraduate course. ROBERT J. SIMPSON, Professor of Electronic Engineering, University of CentralLancashire
author_names: Malcolm S Woolfson
title: Book Review: Modern Electronic Communication
year: 1993

abstract: Digital Signal Transmission: C. C. BISSELL and D. A. CHAPMAN (Cambridge University Press, 1992,321 pp. PS15.95, $34.95paperback, PS45, $79.95hardback) The subject of digital transmission is large and complex and a thorough treatment of the topic requires considerable detailed discussion and involves significant mathematical theory. However most students at undergraduate level require an easily readable text with the mathematical content kept to the bare essentials. This book is aimed at second and third year undergraduate students and practising engineers that require updating in modern techniques. The mathematical theory has been kept to a minimum and the standard mathematical results are presented in appendices. A large portion of the text has been derived from the authors' contributions to the Open University course on Digital Telecommunications and perhaps as a consequence the text is written in a style which makes it very suitable for self study. The book only considers a limited number of topics in depth and places the emphasis on the engineering aspects of digital transmission and interpretation of mathematical models. The chapters are grouped into three parts. Part I considers models and discusses continuous and discrete time signals and systems as well as random signals and noise. Part 2 describes processes and explains details of the pulses that are used for digital transmission, and it also discusses line codes and channel codes, including scrambling, block codes and convolution coding. The final part of the book is devoted to digital transmission over the public switched telephone network. The topics considered in this part are relevant analogue and digital signal sources, coding techniques, digital transmission hierarchies and the features of an optical fibre link. I found this an interesting and useful book which has been written with the undergraduate student very much in mind. It is very appropriate for use in universities as a student text for the typical telecommunication undergraduate course. ROBERT J. SIMPSON, Professor of Electronic Engineering, University of CentralLancashire
author_names: Trevor M Benson
title: Book Review: Fiber Optic Communication Systems
year: 1993