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Articles 1201 - 1221 of 1221
Full-Text Articles in Engineering
Observation And Investigation Of The Ferrielectric Subphase With Qt>1/2, Yuri Panarin, O. Kalinovskaya, J. K. Vij
Observation And Investigation Of The Ferrielectric Subphase With Qt>1/2, Yuri Panarin, O. Kalinovskaya, J. K. Vij
Articles
The high-temperature femelectric phase with qT > 1/2 has been found to exist in a antiferroelectric liquid crystal. This phase has been identified using dielectric spectroscopy and conoscopy.
Theoretical Investigations Of Electro-Optical Synchonisation Of Self-Pulsating Laser Diodes, A. Egan, P. Rees, J. O'Gorman, M. Harley-Stead, Gerald Farrell, Joe Hegarty, P. Phelan
Theoretical Investigations Of Electro-Optical Synchonisation Of Self-Pulsating Laser Diodes, A. Egan, P. Rees, J. O'Gorman, M. Harley-Stead, Gerald Farrell, Joe Hegarty, P. Phelan
Articles
The synchronisation mechanism of selfpulsating laser diodes is determined and it is shown how this results in a frequency-dependent phase difference between the electrical input and optical output. The time-to-lock of the electrical input to the optical output is examined, particularly with regard to the importance of the initial phase difference between the signals. The effect of synchronisation on timing jitter in self pulsating lasers is also investigated.
The Control Of A Process With Time Delay By Using A Modified Smith Predictor Compensator, Aidan O'Dwyer, John Ringwood
The Control Of A Process With Time Delay By Using A Modified Smith Predictor Compensator, Aidan O'Dwyer, John Ringwood
Conference papers
A modification is proposed to the Smith predictor compensator structure for the control of a process with time delay. The modification facilitates the achievement of an improved closed loop system regulator response, with little degradation in the corresponding servo response. The compensator design procedure is discussed, and simulation results are provided to demonstrate the applicability of the method.
Model Parameter And Time Delay Estimation In The Frequency Domain, Aidan O'Dwyer, John Ringwood
Model Parameter And Time Delay Estimation In The Frequency Domain, Aidan O'Dwyer, John Ringwood
Conference papers
This paper discusses the estimation of the parameters (including the time delay) of single input, single output (SISO) process models from an appropriate number of arbitrarily specified points on the process frequency response. The method involves combining an analytical approach with a least squares approach using a gradient algorithm, to provide accurate and robust estimates of the parameters.
Instability In Self-Pulsation In Laser Diodes And Its Effect On All-Optical Synchonization, Jonathan Hyland, Gerald Farrell
Instability In Self-Pulsation In Laser Diodes And Its Effect On All-Optical Synchonization, Jonathan Hyland, Gerald Farrell
Articles
The effect of short- and long-term frequency instability in self pulsation on all-optical synchronization using a twin-section laser diode is experimentally investigated. Short-term frequency instability broadens the unlocked full width at half maximum (FWHM) of the fundamental of the rf spectrum of the self-pulsating laser diode. We show experimentally that the value of the unlocked FWHM, and thus the level of short-term instability, has a direct effect on the optical power required to maintain synchronization. A novel means of reducing the FWHM is presented based on a reflective transmission line stub connected to the absorber of the twin-section self-pulsating laser …
Comparison Of Self Pulsation In Multisection Lasers With Distributed Feedback And Intracavity Satuarable Absorbers, P. Phelan, D. Mcdonald, A. Egan, Joe Hegarty, R. O'Dowd, Gerald Farrell, S. Lingren
Comparison Of Self Pulsation In Multisection Lasers With Distributed Feedback And Intracavity Satuarable Absorbers, P. Phelan, D. Mcdonald, A. Egan, Joe Hegarty, R. O'Dowd, Gerald Farrell, S. Lingren
Articles
The authors report a comparison of the self-pulsing characteristics of two types of semiconductor laser. They show that the self-pulsing frequency of the DFB laser is decoupled from the resonance frequency. They discuss the various characteristics, their significance in relation to optical synchronisation, and use the results to suggest a possible explanation for the mechanism for self-pulsation in the DFB laser.
Model Parameter And Time Delay Estimation Using Gradient Methods, Aidan O'Dwyer, John Ringwood
Model Parameter And Time Delay Estimation Using Gradient Methods, Aidan O'Dwyer, John Ringwood
Conference papers
A number of approaches have been proposed for parameter and time delay estimation of process models in single input, single output (SISO) control systems using gradient descent algorithms; some of these approaches involve the selection of a rational polynomial that is used to approximate time delay variations. This paper takes a generalised approach to the investigation of the most appropriate choice of the rational polynomial, and the gradient descent algorithm, to be used.
A Frequency Domain Based Self-Tuning Pid Controller, John Ringwood, Aidan O'Dwyer
A Frequency Domain Based Self-Tuning Pid Controller, John Ringwood, Aidan O'Dwyer
Conference papers
Traditionally, both explicit and implicit self-tuning controllers have employed time domain techniques for the identification and tracking of plant and controller parameters. The use of the frequency domain provides concise information on the dynamics of the process which has led to its wide acceptance as a domain for controller design. This paper demonstrates a method employing recursive, on-line measurement of the process frequency response, with a straightforward calculation of PID controller parameters. The computational effort involved is comparable with that of a time domain technique.
All Optical Timing Extraction With Frequency Division Using A Twin Section Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty, J. A. Shields
All Optical Timing Extraction With Frequency Division Using A Twin Section Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty, J. A. Shields
Articles
All-optical timing extraction from a coded line signal with division of the extracted clock frequency is demonstrated using a single twin-section self-pulsating laser diode. Either the bit-rate clock or a submultiple of the bit-rate clock can be extracted, depending only on the dc biases applied to the self-pulsating laser diode. Timing extraction is carried out for the first time without optical injection locking of the self-pulsating laser diode by the optical data source.
The Influence Of The Unlocked Characteristics Of A Self-Pulsating Laser Diode On Synchronisation, Gerald Farrell, P. Phelan, Joe Hegarty
The Influence Of The Unlocked Characteristics Of A Self-Pulsating Laser Diode On Synchronisation, Gerald Farrell, P. Phelan, Joe Hegarty
Articles
All-optical synchronization and timing extraction based on self-pulsating twin section lasers has been demonstrated. We investigate the variation of the unlocked full-width at- half-maximum of the fundamental of the RF spectrum of a self-pulsating laser diode. We show for the first time that the value of the unlocked FWHM has a direct influence on the power required to maintain synchronization. We also show that the variation of the FWHM with frequency is dependent on the slope of the absorber bias versus self-pulsation frequency characteristic. The results have important implications for the design and selection of self-pulsating laser diodes for synchronization …
All-Optical Timing Extraction With Frequency Division Using A Twin-Section Laser Diode, Gerald Farrell, Paul Phelan, Joe Hegarty, J. Shields
All-Optical Timing Extraction With Frequency Division Using A Twin-Section Laser Diode, Gerald Farrell, Paul Phelan, Joe Hegarty, J. Shields
Articles
All-optical timing extraction from a coded line signal with division of the extracted clock frequency is demonstrated using a single twin-section self-pulsating laser diode. Either the bit-rate clock or a submultiple of the bit-rate clock can be extracted, depending only on the DC biases applied to the self-pulsating laser diode. Timing extraction is carried out for the first time without optical injection locking of the self-pulsating laser diode by the optical data source
A Comparison Of Techniques For Time Delay Estimation, Aidan O'Dwyer
A Comparison Of Techniques For Time Delay Estimation, Aidan O'Dwyer
Conference papers
This paper reviews some of the techniques used for the identification of unknown lumped time delays in single input, single output (SISO) control systems and evaluates a number of these techniques in simulation and in implementation. Both off line and on line identification techniques are considered.
All Optical Clock Distribution With Synchronous Frequency Division And Multiplication, Gerald Farrell, P. Phelan, Joe Hegarty
All Optical Clock Distribution With Synchronous Frequency Division And Multiplication, Gerald Farrell, P. Phelan, Joe Hegarty
Articles
A master optical clock from a mode locked laser is distributed to two slave twin section lasers. One slave laser divides the optical modulation frequency by 2, the other slave laser multiplies the frequency by 2. It is also possible to vary the multiplication4ivision ratio in a slave laser using only DC control of the absorber of the twin section laser.
All Optical Synchronisation With Frequency Division Using A Self Pulsating Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty
All Optical Synchronisation With Frequency Division Using A Self Pulsating Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty
Articles
A master optical clock from a mode locked laser is distributed to two slave twin section lasers. One slave laser divides the optical modulation frequency by 2, the other slave laser multiplies the frequency by 2. It is also possible to vary the multiplication4ivision ratio in a slave laser using only DC control of the absorber of the twin section laser.
All-Optical Synchronisation And Multiplication Of The Frequency Of Mode-Locked Signals, P. Phelan, Gerald Farrell, Joe Hegarty
All-Optical Synchronisation And Multiplication Of The Frequency Of Mode-Locked Signals, P. Phelan, Gerald Farrell, Joe Hegarty
Articles
We report all-optical synchronized multiplication by rational fractions of the modulation frequency of optical signals in self-pulsing two-section semiconductor laser diodes. The effect is based on the overlap of harmonics of the input signal with harmonics of the self-pulsation. We illustrate this new generic function with modelocked inputs rich in harmonics were fractions of 1,2, and 3 / 2 are generated, and we identify a number of applications for this effect.
Self-Pulsation Operating Regime For The Absorber Of A Twin Section Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty
Self-Pulsation Operating Regime For The Absorber Of A Twin Section Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty
Articles
The voltage-current characteristic of the absorber of a twin section laser diode is investigated as a function of the gain section current. For self pulsation to occur the absorber must be operated within a specific region of the voltage-current characteristics. This region only exists for absorber voltage current characteristics which contain an S-shaped negative resistance.
Standardised Control Techniques For Induction Generators In Both Grid-Connected And Isolated Applications, John Brazil, Aidan O'Dwyer, M. Murphy
Standardised Control Techniques For Induction Generators In Both Grid-Connected And Isolated Applications, John Brazil, Aidan O'Dwyer, M. Murphy
Conference papers
Induction generators are particularly suitable for small hydro applications and are widely used at present. However, with conventional grid-connected techniques, it is not always possible to use them in regions with weak grids because of excessive connection transients. Consequently, their many advantages cannot be fully exploited in these regions. Standardised control systems have been developed by ECS for isolated applications of induction generators and these will now be further developed to permit reduced-transient grid connections.
Fast Discharges In Thin Liquid Layers, Charles J. Frei, Aidan O'Dwyer
Fast Discharges In Thin Liquid Layers, Charles J. Frei, Aidan O'Dwyer
Conference papers
Several mechanisms can be at work when electrical discharges occur across a thin layer of an insulating liquid. The evidence is derived from the time-lag distributions of series of consecutive discharges when the measurements are performed with a sequence of constant voltage pulses.
Bistabiity By Induced Waveguiding In Coupled Semiconductor Lasers, Daniel Heffernan, J. Mcinerney, L. Reekie, D. Bradley
Bistabiity By Induced Waveguiding In Coupled Semiconductor Lasers, Daniel Heffernan, J. Mcinerney, L. Reekie, D. Bradley
Articles
Recently, McInerney, Reekie, and Bradley observed bistability in twin diode GaAs/GaAlAs injection lasers in an external cavity when both diodes were above threshold. We show that this bistability may be explained by a form of self-focusing which is produced by induced waveguiding in the wide stripe lasers. A detailed analysis is performed on a standard model of these diodes in an external cavity. We have found very good agreement between theory and experiment.
Proposal For A Digital Pseudorandom Number Generator, C. Downey
Proposal For A Digital Pseudorandom Number Generator, C. Downey
Articles
A digital hardware implementation of a linear congruential sequence generator using shift and add techniques of multiplication is described. The sequence is of long period, low serial correlation and is rectangularly distributed. The method has certain advantages over conventional feedback shift register techniques.
Algorithms For The Solution Of Systems Of Coupled Second-Order Ordinary Differential Equations, Brendan O'Shea
Algorithms For The Solution Of Systems Of Coupled Second-Order Ordinary Differential Equations, Brendan O'Shea
Articles
Several step-by-step methods for the computer solution systems of coupled second-order ordinary differential equations, are examined from the point of view of efficiency “time-wise” and “storage-wise”. Particular reference is made to a system arising in the close-coupling approximation of the Schroedinger equation. The stability of the solution is also considered.