Measurements of Noise-seeded Dynamics in Nonlinear Fiber Optics

Nonlinear physical systems are ubiquitous in nature - formation of sand dunes, currents occuring in a rapidly flowing river or a simple double rod pedulum are just a few examples from everyday life. Studying and understanding these systems has interested scientists for decades. Because these nonlinear systems might be chaotic, measurements of such systems need to be performed on a real-time basis and by statistical analysis methods.The propagation of short and intense pulses in optical fibers are another well-known example of nonlinear systems. However, the rapid fluctuations of optical fields has prohibited studying these systems on a real-time basis, until recent years. This thesis demonstrates the use of state-of-the-art real-time measurement techniques to capture the stochastic dynamics of noise-seeded nonlinear processes in optical fibers allowing for novel insights and interpretation within analytical frameworks.In particular, we characterize noisy picosecond pulse train emerging from spontaneous modulation instability using a time lens system. The experimental results are compared with analytical Akhmediev breather solutions showing remarkable agreement, allowing to understand the complex dynamics from an analytical viewpoint. An experimental demonstration of a high dynamic range real-time spectral measurement system for spontaneous modulation instability is also introduced to study the random breather structures in the spectral domain, paving the way for possible indirect optical rogue wave detection schemes.By combining real-time temporal and spectral measurements unforeseen details of transition dynamics of a mode-locking of a fiber laser are also reported. The simultaneous spectro-temporal acquisition allows for complete electric field reconstruction with numerical algorithms, which has not been possible before at megahertz repetition rates with sub-picosecond and sub-nanometer resolutions demonstrated here.Supercontinuum generation is one of the most well-known examples of nonlinear fiber optics that is also becoming widely spread in applications. The details of the complex and noise driven dynamics are now well-known, but the connection of the stability of such light sources with traditional coherence theory was only derived recently. Experimental measurement of supercontinuum stability in the framework of second-order coherence theory is demonstrated, filling a gap in characterization of non-stationary light sources.Finally, an application of supercontinuum generation is proposed in terms of all-optical signal amplification. This is based on the inherently sensitive nature of the nonlinear process to any input fluctuations. The potential of such a highly nonlinear system for a practical application is demonstrated and the underlying dynamics leading to this sensitivity are explained

Kohti täydellistä superkontinuumin koherenssin määritystä

Experimental characterization of supercontinuum second order coherence properties is performed for the fi rst time. The experimental method is based on an approximation separating the supercontinuum second order coherence functions into coherent and quasi-stationary parts. The approximation was discovered recently in light of numerical studies and the objective of the work in the thesis is to verify these numerical results experimentally. In the theory section the mathematical formulation of the coherence functions is given accompanied with discussion of the physical meaning of the functions. Furthermore the physical processes and experimental parameters aff ecting supercontinuum coherence properties are adressed to further understand the behavior of the results. The possibility for using approximations of the second order coherence functions for modeling supercontinuum behavior in optical systems is also considered. Finally emphasis is put also on describing the various experimental methods used to ensure reliable retrieval of the coherence functions. Experiments are performed for three distinct cases: coherent, partially coherent and incoherent supercontinuum generated in a photonic crystal fi ber by a Ti:Sapphire femtosecond laser with an adjustable peak power for the input pulse. Obtained results are compared to simulated results generated with parameters corresponding to the experiment. Good agreement between the experimental and numerical results is observed, further justifying the approximation made and laying groundwork for future studies made in the fi eld

Amplifier similariton generation from a Yb-doped all-normal-dispersion fiber laser employing a hybrid-mode-locking technique

Apart from the classical nonlinear polarization rotation (NPR) mechanism, we incorporate an additional stabilization mechanism of frequency shifting in a Yb-doped all-normal-dispersion fiber laser oscillator. The similariton pulse with a pulse duration of 7.8 ps and a spectrum width of 20.5 nm is generated. By using a grating pair, the pulse duration can be compressed to be 140 fs. By employing time-stretch dispersion Fourier transform (TS-DFT) technique, the mode-locking pulse buildup process is investigated. The use of frequency shifting as a stabilization technique opens a new route towards reliable laser oscillator fabrication for the industrial-grade system.acceptedVersionPeer reviewe

Exploring pre-service special needs teachers’ assessment conceptions and assessment self-efficacy

This survey study (N = 148) investigates the interrelationships between assessment conceptions, assessment self-efficacy, prior education, and teaching experience amongst Finnish pre-service special educational needs teachers (pre-service SENs). The results showed that assessment conceptions and assessment self-efficacy are intertwined. Assessment conceptions, prior studies, and teaching experience were clustered into three different pre-service SEN types: Assessment Positives, Assessment Cautious, and Assessment Criticals. Pre-service SENs with assessment-positive or assessment-cautious conceptions reported higher assessment self-efficacy than students with assessment-critical conceptions. Practical implications are discussed.</p

Assessment conception patterns of Finnish pre-service special needs teachers: the contribution of prior studies and teaching experience

The main aim of this study was to investigate how Finnish pre-service special needs teachers’ (N = 134) assessment conceptions, prior academic studies in special education and teaching experience together cluster into different patterns representing different student types. Their assessment conceptions formed three main factors: 1) assessment measures learning, 2) assessment supports teaching and learning, and 3) assessment as a harmful action. All three factors were emphasised differently in each pattern. Assessment conceptions, prior studies, and teaching experience were clustered together in three different patterns: Assessment Criticals, Assessment Positives, and Assessment Cautious. The Assessment Criticals emphasised assessment as a harmful action, and they had fewer prior studies and less teaching experience. The Assessment Positives emphasised assessment for teaching and learning, and they had more prior studies and less teaching experience. Finally, the Assessment Cautious emphasised assessment of learning, and assessment as a harmful action, and they had more studies and more teaching experience. This study shows that relative to national guidelines, students have very different starting points for professional growth during studies. Additionally, this study will discuss the implications for special needs teacher education.</p

SOX9 has distinct roles in the formation and progression of different non-small cell lung cancer histotypes

The transcription factor SOX9 is a key regulator of multiple developmental processes and is frequently re-expressed in non-small cell lung cancer (NSCLC). Its precise role in the progression of NSCLC histotypes has, however, remained elusive. We show that SOX9 expression relates to poor overall survival and invasive histopathology in human non-mucinous adenocarcinoma and is absent in murine early minimally invasive and low in human in situ adenocarcinoma. Interestingly, despite wide SOX9 expression across advanced NSCLC histotypes, its genetic deletion in the murine Kras(G12D);Lkb1(fl/fl) model selectively disrupted only the growth of papillary NSCLC, without affecting the initiation of precursor lesions or growth of mucinous or squamous tissue. Spatial tissue phenotyping indicated a requirement of SOX9 expression for the progression of surfactant protein C-expressing progenitor cells, which gave rise to papillary tumours. Intriguingly, while SOX9 expression was dispensable for squamous tissue formation, its loss in fact led to enhanced squamous tumour metastasis, which was associated with altered collagen IV deposition in the basement membrane. Our work therefore demonstrates histopathology-selective roles for SOX9 in NSCLC progression, namely as a promoter for papillary adenocarcinoma progression, but an opposing metastasis-suppressing role in squamous histotype tissue. This attests to a pleiotropic SOX9 function, linked to the cell of origin and microenvironmental tissue contexts. (c) 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.Peer reviewe

Real-time measurements of spontaneous breathers and rogue wave events in optical fibre modulation instability

Modulation instability is a fundamental process of nonlinear science, leading to the unstable breakup of a constant amplitude solution of a physical system. There has been particular interest in studying modulation instability in the cubic nonlinear Schrödinger equation, a generic model for a host of nonlinear systems including superfluids, fibre optics, plasmas and Bose–Einstein condensates. Modulation instability is also a significant area of study in the context of understanding the emergence of high amplitude events that satisfy rogue wave statistical criteria. Here, exploiting advances in ultrafast optical metrology, we perform real-time measurements in an optical fibre system of the unstable breakup of a continuous wave field, simultaneously characterizing emergent modulation instability breather pulses and their associated statistics. Our results allow quantitative comparison between experiment, modelling and theory, and are expected to open new perspectives on studies of instability dynamics in physics

Role of oral pathogens in the pathogenesis of intracranial aneurysm : review of existing evidence and potential mechanisms

Degeneration of intracranial aneurysm wall is under active research and recent studies indicate an increased risk of rupture of intracranial aneurysm among patients with periodontal diseases. In addition, oral bacterial DNA has been identified from wall samples of ruptured and unruptured aneurysms. These novel findings led us to evaluate if oral diseases could predispose to pathological changes seen on intracranial aneurysm walls eventually leading to subarachnoid hemorrhage. The aim of this review is to consider mechanisms on the relationship between periodontitis and aneurysm rupture, focusing on recent evidence.Peer reviewe

Advanced multimodal laser imaging tool for urothelial carcinoma diagnosis (AMPLITUDE)

Bladder cancer (BC) is the eleventh most diagnosed cancer worldwide. The age-standardized incidence rate (per 100 000 person/years) is 9.0 for men and 2.2 for women [1]. Urothelial carcinoma (UC) represents about 90% of all bladder tumors, thus carrying an enormous social and economic burden [2]. UCs are classified in different stages and grades, depending on their invasiveness and on their degree of cytological abnormalities. The key aspect for a positive prognosis is the early and accurate diagnosis of the lesion stage, in order to identify the most aggressive disease forms and treat them promptly. It is well known that tissue metabolism constitutes a basic mechanism, which is at the base of many pathologies, especially BC. Being able to detect and characterize tissue metabolism and molecular fingerprints at the cellular level could be a key aspect in characterizing the pathology and enabling both early detection and therapy monitoring. The new European Union Horizon 2020 project called AMPLITUDE, the ‘Advanced Multimodal Photonics Laser Imaging Tool for Urothelial Diagnosis in Endoscopy’, starting in January 2020, proposes the development of an advanced multi-modal imaging tool exploiting new laser technologies in an approach combining confocal and non-linear imaging to fulfil unmet clinical needs in terms of the specificity and accuracy of urothelial cancer diagnosis and therapy monitoring. The project is coordinated by Tampere University (Finland) and carried out in cooperation with leading European research organizations including Aston Insitute of Photonic Technologies—AIPT (UK), Consiglio Nazionale delle Ricerche—CNR (Italy), Institute of Photonic Sciences—ICFO (Spain), University of Milan-Bicocca, Modus Research and Innovation Ltd. (UK) and University of Florence (Italy), as well as industrial partners: Ampliconyx Oy (Finland), Femtonics Ltd. (Hungary), HC Photonics (Taiwan), and LEONI Fiber Optics GmbH (Germany)