Passive nonlinear pulse shaping in normally dispersive fiber

We propose a simple method for passive nonlinear optical pulse shaping that utilizes pulse prechirping and nonlinear propagation in a normally dispersive nonlinear fiber to generate various temporal waveforms of practical interest from conventional laser pulses.

A study of the effect of harmonics in the system on the performance of residual current-operated circuit-breakers and electromechanical overcurrent relays

Residual current-operated circuit-breakers (RCCBs) have proved useful devices for the protection of both human beings against ventricular fibrillation and installations against fire. Although they work well with sinusoidal waveforms, there is little published information on their characteristics. Due to shunt connected non-linear devices, not the least of which is the use of power electronic equipment, the supply is distorted. Consequently, RCCBs as well as other protection relays are subject to non-sinusoidal current waveforms. Recent studies showed that RCCBs are greatly affected by harmonics, however the reasons for this are not clear. A literature search has also shown that there are inconsistencies in the analysis of the effect of harmonics on protection relays. In this work, the way RCCBs operate is examined, then a model is built with the aim of assessing the effect of non-sinusoidal current on RCCBs. Tests are then carried out on a number of RCCBs and these, when compared with the results from the model showed good correlation. In addition, the model also enables us to explain the RCCBs characteristics for pure sinusoidal current. In the model developed, various parameters are evaluated but special attention is paid to the instantaneous value of the current and the tripping mechanism movement. A similar assessment method is then used to assess the effect of harmonics on two types of protection relay, the electromechanical instantaneous relay and time overcurrent relay. A model is built for each of them which is then simulated on the computer. Tests results compare well with the simulation results, and thus the model developed can be used to explain the relays behaviour in a harmonics environment. The author's models, analysis and tests show that RCCBs and protection relays are affected by harmonics in a way determined by the waveform and the relay constants. The method developed provides a useful tool and the basic methodology to analyse the behaviour of RCCBs and protection relays in a harmonics environment. These results have many implications, especially the way RCCBs and relays should be tested if harmonics are taken into account.

Normative MEG data to flash and pattern reversal stimuli

We have attempted to establish normative values of components of the magnetic evoked field to flash and pattern reversal stimuli prior to clinical use of the MEG. Full visual field, binocular evoked magnetic fields were recorded from 100 subjects 16 to 86 years of age with a single channel dc Squid (BTI) second-order gradiometer at a point 5-6cm above the inion. The majority of subjects showed a large positive component (out going magnetic field) of mean latency 115 ms (SD range 2.5 -11.8 in different decades of life) to the pattern reversal stimulus. In many subjects, this P100M was preceeded and succeeded by negative deflections (in going field). About 6% of subjects showed an inverted response i.e. a PNP wave. Waveforms to flash were more variable in shape with several positive components; the most consistent having a mean latency of 110ms (SD range 6.4-23.2). Responses to both stimuli were consistent when measured on the same subject on six different occasions (SD range 4.8 to 7.3). The data suggest that norms can be established for evoked magnetic field components, in particular for the pattern reversal P100M, which could be used in the diagnosis of neuro-opthalmological disease.

Passive nonlinear pulse shaping in normally dispersive fiber systems

We propose a novel approach to characterize the parabolically-shaped pulses that can be generated from more conventional pulses via nonlinear propagation in cascaded sections of commercially available normally dispersive (ND) fibers. The impact of the initial pulse chirp on the passive pulse reshaping is examined. We furthermore demonstrate that the combination of pulse pre-chirping and propagation in a single ND fiber yields a simple, passive method for generating various temporal waveforms of practical interest.

All-optical nonlinear fibre signal processing

All-optical technologies for data processing and signal manipulation are expected to play a major role in future optical communications. Nonlinear phenomena occurring in optical fibre have many attractive features and great, but not yet fully exploited potential in optical signal processing. Here, we overview our recent results and advances in developing novel photonic techniques and approaches to all-optical processing based on fibre nonlinearities. Amongst other topics, we will discuss phase-preserving optical 2R regeneration, the possibility of using parabolic/flat-top pulses for optical signal processing and regeneration, and nonlinear optical pulse shaping. A method for passive nonlinear pulse shaping based on pulse pre-chirping and propagation in a normally dispersive fibre will be presented. The approach provides a simple way of generating various temporal waveforms of fundamental and practical interest. Particular emphasis will be given to the formation and characterization of pulses with a triangular intensity profile. A new technique of doubling/copying optical pulses in both the frequency and time domains using triangular-shaped pulses will be also introduced.

Passive nonlinear pulse shaping in normally dispersive fiber

We propose a simple method for passive nonlinear optical pulse shaping that utilizes pulse prechirping and nonlinear propagation in a normally dispersive nonlinear fiber to generate various temporal waveforms of practical interest from conventional laser pulses.

All-optical nonlinear fibre signal processing

All-optical technologies for data processing and signal manipulation are expected to play a major role in future optical communications. Nonlinear phenomena occurring in optical fibre have many attractive features and great, but not yet fully exploited potential in optical signal processing. Here, we overview our recent results and advances in developing novel photonic techniques and approaches to all-optical processing based on fibre nonlinearities. Amongst other topics, we will discuss phase-preserving optical 2R regeneration, the possibility of using parabolic/flat-top pulses for optical signal processing and regeneration, and nonlinear optical pulse shaping. A method for passive nonlinear pulse shaping based on pulse pre-chirping and propagation in a normally dispersive fibre will be presented. The approach provides a simple way of generating various temporal waveforms of fundamental and practical interest. Particular emphasis will be given to the formation and characterization of pulses with a triangular intensity profile. A new technique of doubling/copying optical pulses in both the frequency and time domains using triangular-shaped pulses will be also introduced.

Tailored waveform generation in mode-locked fiber lasers by in-cavity pulse shaper

We numerically show the possibility of pulse shaping in a mode-locked fiber laser by inclusion of an amplitude-phase spectral filter into the laser cavity. Various advanced temporal waveforms are generated, including parabolic, flat-top and triangular pulses. © 2014 OSA.

Subject identification via ECG fiducial-based systems:influence of the type of QT interval correction

Electrocardiography (ECG) has been recently proposed as biometric trait for identification purposes. Intra-individual variations of ECG might affect identification performance. These variations are mainly due to Heart Rate Variability (HRV). In particular, HRV causes changes in the QT intervals along the ECG waveforms. This work is aimed at analysing the influence of seven QT interval correction methods (based on population models) on the performance of ECG-fiducial-based identification systems. In addition, we have also considered the influence of training set size, classifier, classifier ensemble as well as the number of consecutive heartbeats in a majority voting scheme. The ECG signals used in this study were collected from thirty-nine subjects within the Physionet open access database. Public domain software was used for fiducial points detection. Results suggested that QT correction is indeed required to improve the performance. However, there is no clear choice among the seven explored approaches for QT correction (identification rate between 0.97 and 0.99). MultiLayer Perceptron and Support Vector Machine seemed to have better generalization capabilities, in terms of classification performance, with respect to Decision Tree-based classifiers. No such strong influence of the training-set size and the number of consecutive heartbeats has been observed on the majority voting scheme.

Temporal and spectral nonlinear pulse shaping methods in optical fibers

The combination of the third-order optical nonlinearity with chromatic dispersion in optical fibers offers an extremely rich variety of possibilities for tailoring the temporal and spectral content of a light signal, depending on the regime of dispersion that is used. Here, we review recent progress on the use of third-order nonlinear processes in optical fibers for pulse shaping in the temporal and spectral domains. Various examples of practical significance will be discussed, spanning fields from the generation of specialized temporal waveforms to the generation of ultrashort pulses, and to stable continuum generation.

Polarisation phenomena in mode locked fibre lasers and fibre Raman amplifiers griffon tutorial

For a fibre Raman amplifier with randomly varying birefringence, we provide insight on the validity of previously explored multi-scale techniques leading to polarisation pulling of the signal state of polarisation to the pump state of polarisation. Unlike previous study, we demonstrate that in addition to polarisation pulling a new random birefringence-mediated phenomenon that goes beyond existing multi-scale techniques can boost resonance-like gain fluctuations similar to the Stochastic Anti-Resonance. For mode locked fibre lasers we report on fast and slow polarisation dynamics of fundamental, bound state, and multipulsing vector solitons along with stretched pulses. We demonstrate that tuning cavity anisotropy and birefringence along with parameters of an injected signal with randomly varying state of polarisation provides access to the variety of vector waveforms previously unexplored.

Deconvolution of magnetic acoustic change complex (mACC)

Objective: The aim of this study was to design a novel experimental approach to investigate the morphological characteristics of auditory cortical responses elicited by rapidly changing synthesized speech sounds. Methods: Six sound-evoked magnetoencephalographic (MEG) responses were measured to a synthesized train of speech sounds using the vowels /e/ and /u/ in 17 normal hearing young adults. Responses were measured to: (i) the onset of the speech train, (ii) an F0 increment; (iii) an F0 decrement; (iv) an F2 decrement; (v) an F2 increment; and (vi) the offset of the speech train using short (jittered around 135. ms) and long (1500. ms) stimulus onset asynchronies (SOAs). The least squares (LS) deconvolution technique was used to disentangle the overlapping MEG responses in the short SOA condition only. Results: Comparison between the morphology of the recovered cortical responses in the short and long SOAs conditions showed high similarity, suggesting that the LS deconvolution technique was successful in disentangling the MEG waveforms. Waveform latencies and amplitudes were different for the two SOAs conditions and were influenced by the spectro-temporal properties of the sound sequence. The magnetic acoustic change complex (mACC) for the short SOA condition showed significantly lower amplitudes and shorter latencies compared to the long SOA condition. The F0 transition showed a larger reduction in amplitude from long to short SOA compared to the F2 transition. Lateralization of the cortical responses were observed under some stimulus conditions and appeared to be associated with the spectro-temporal properties of the acoustic stimulus. Conclusions: The LS deconvolution technique provides a new tool to study the properties of the auditory cortical response to rapidly changing sound stimuli. The presence of the cortical auditory evoked responses for rapid transition of synthesized speech stimuli suggests that the temporal code is preserved at the level of the auditory cortex. Further, the reduced amplitudes and shorter latencies might reflect intrinsic properties of the cortical neurons to rapidly presented sounds. Significance: This is the first demonstration of the separation of overlapping cortical responses to rapidly changing speech sounds and offers a potential new biomarker of discrimination of rapid transition of sound.

Endocrine regulation of dynamic communication signals in gymnotiform fish

Communication signals are shaped by the opposing selection pressures imposed by predators and mates. A dynamic signal might serve as an adaptive compromise between an inconspicuous signal that evades predators and an extravagant signal preferred by females. Such a signal has been described in the gymnotiform electric fish, Brachyhypopomus gauderio, which produces a sexually dimorphic electric organ discharge (EOD). The EOD varies on a circadian rhythm and in response to social cues. This signal plasticity is mediated by the slow action of androgens and rapid action of melanocortins. My dissertation research tested the hypotheses that (1) signal plasticity is related to sociality levels in gymnotiform species, and (2) differences in signal plasticity are regulated by differential sensitivity to androgen and melanocortin hormones. To assess the breadth of dynamic signaling within the order Gymnotiformes, I sampled 13 species from the five gymnotiform families. I recorded EODs to observe spontaneous signal oscillations after which I injected melanocortin hormones, saline control, or presented the fish with a conspecific. I showed that through the co-option of the ancient melanocortin pathway, gymnotiforms dynamically regulate EOD amplitude, spectral frequency, both, or neither. To investigate whether observed EOD plasticities are related to species-specific sociality I tested four species; two territorial, highly aggressive species, Gymnotus carapo and Apteronotus leptorhynchus, a highly gregarious species, Eigenmannia cf. virescens , and an intermediate short-lived species with a fluid social system, Brachyhypopomus gauderio. I examined the relationship between the androgens testosterone and 11-ketotestosterone, the melanocortin α-MSH, and their roles in regulating EOD waveform. I implanted all fish with androgen and blank silicone implants, and injected with α-MSH before and at the peak of implant effect. I found that waveforms of the most territorial and aggressive species were insensitive to hormone treatments; maintaining a static, stereotyped signal that preserves encoding of individual identity. Species with a fluid social system were most responsive to hormone treatments, exhibiting signals that reflect immediate condition and reproductive state. In conclusion, variation in gymnotiform signal plasticity is hormonally regulated and seems to reflect species-specific sociality.

The effect of male -male competition and its underlying regulatory mechanisms on the electric signal of the gymnotiform fish Brachyhypopomus gauderio

Sexually-selected communication signals can be used by competing males to settle contests without incurring the costs of fighting. The ability to dynamically regulate the signal in a context-dependent manner can further minimize the costs of male aggressive interactions. Such is the case in the gymnotiform fish Brachyhypopomus gauderio, which, by coupling its electric organ discharge (EOD) waveform to endocrine systems with circadian, seasonal, and behavioral drivers, can regulate its signal to derive the greatest reproductive benefit. My dissertation research examined the functional role of the EOD plasticity observed in male B. gauderio and the physiological mechanisms that regulate the enhanced male EOD. To evaluate whether social competition drives the EOD changes observed during male-male interactions, I manipulated the number of males in breeding groups to create conditions that exemplified low and high competition and measured their EOD and steroid hormone levels. My results showed that social competition drives the enhancement of the EOD amplitude of male B. gauderio. In addition, changes in the EOD of males due to changes in their social environment were paralleled by changes in the levels of androgens and cortisol. I also examined the relationship between body size asymmetry, EOD waveform parameters, and aggressive physical behaviors during male-male interactions in B. gauderio, in order to understand more fully the role of EOD waveforms as reliable signals. While body size was the best determinant of dominance in male B. gauderio, EOD amplitude reliably predicted body condition, a composite of length and weight, for fish in good body condition. To further characterize the mechanisms underlying the relationship between male-male interactions and EOD plasticity, I identified the expression of the serotonin receptor 1A, a key player in the regulation of aggressive behavior, in the brains of B. gauderio. I also identified putative regulatory regions in this receptor in B. gauderio and other teleost fish, highlighting the presence of additional plasticity. In conclusion, male-male competition seems to be a strong selective driver in the evolution of the male EOD plasticity in B. gauderio via the regulatory control of steroid hormones and the serotonergic system.

Digital signal processing implementation for near real-time wavelet transformation system for binary images

Communication has become an essential function in our civilization. With the increasing demand for communication channels, it is now necessary to find ways to optimize the use of their bandwidth. One way to achieve this is by transforming the information before it is transmitted. This transformation can be performed by several techniques. One of the newest of these techniques is the use of wavelets. Wavelet transformation refers to the act of breaking down a signal into components called details and trends by using small waveforms that have a zero average in the time domain. After this transformation the data can be compressed by discarding the details, transmitting the trends. In the receiving end, the trends are used to reconstruct the image. In this work, the wavelet used for the transformation of an image will be selected from a library of available bases. The accuracy of the reconstruction, after the details are discarded, is dependent on the wavelets chosen from the wavelet basis library. The system developed in this thesis takes a 2-D image and decomposes it using a wavelet bank. A digital signal processor is used to achieve near real-time performance in this transformation task. A contribution of this thesis project is the development of DSP-based test bed for the future development of new real-time wavelet transformation algorithms.