Showing papers by "Graham Town published in 2001"
TL;DR: This work has found zero-velocity, moving and exploding pulsating localized structures, period doubling of pulsations and the sequence of PD bifurcations, and found chaotic pulsating solitons of the Ginzburg-Landau equation.
Abstract: The complex Ginzburg-Landau equation (CGLE) is a standard model for pulse generation in mode-locked lasers with fast saturable absorbers. We have found complicated pulsating behavior of solitons of the CGLE and regions of their existence in the five-dimensional parameter space. We have found zero-velocity, moving and exploding pulsating localized structures, period doubling (PD) of pulsations and the sequence of PD bifurcations. We have also found chaotic pulsating solitons. We have plotted regions of parameters of the CGLE where pulsating solutions exist. We also demonstrate the coexistence (bi- and multistability) of different types of pulsating solutions in certain regions of the parameter space of the CGLE.
396 citations
TL;DR: Finite-difference time-domain calculations of downtapered holey fiber are presented, showing that large spot-size conversion factors are obtainable with minimal loss by use of short, optimally shaped tapers.
Abstract: Adiabatically tapered holey fibers are shown to be potentially useful for guided-wave spot-size and numerical-aperture conversion. Conditions for adiabaticity and design guidelines are provided in terms of the effective-index model. We also present finite-difference time-domain calculations of downtapered holey fiber, showing that large spot-size conversion factors are obtainable with minimal loss by use of short, optimally shaped tapers.
66 citations
TL;DR: In this paper, the optimal Holey fiber parameters for minimum splice loss were determined using finite-difference time-domain simulations, and it was found that the optimal parameters could also be predicted using analytical approximations incorporating the effective index model.
Abstract: Splice losses between standard step-index fiber and holey optical fibers were calculated for a range of fiber parameters and wavelengths using finite-difference time-domain simulations. The optimal holey fiber parameters for minimum splice loss were determined. It was found that the optimal parameters could also be predicted using analytical approximations incorporating the effective index model.
65 citations
TL;DR: In this paper, it was shown that the complex cubic-quintic Ginzburg-Landau equation has a multiplicity of soliton solutions for the same set of equation parameters.
36 citations
11 May 2001
TL;DR: In this article, the authors derived general guidelines for adiabatic taper design, and calculated the mode-field distributions at both ends of an optimally shaped taper, and used them to design a waveguide with low loss.
Abstract: Summary form only given. A major problem with standard step index fibers is their inefficiency in coupling to integrated optical devices and waveguides, semiconductor devices such as laser diodes, other fiber waveguides with different properties, etc. Coupling losses are mainly caused by mismatch of the modal field distributions, and partly by changes in wave impedance. It is known that holey fiber may be designed to remain single mode over an extremely wide range of wavelengths. It follows that a fixed wavelength the size of the waveguide may be scaled by an appreciable factor and remain single mode. Consequently, adiabatically tapered holey fibers may be used to perform significant scaling of guided mode-field distributions with low loss. The effective index of the guided mode may also vary significantly. We have derived general guidelines for adiabatic taper design, and calculated the mode-field distributions at both ends of an optimally shaped taper.
35 citations
TL;DR: In this article, it was shown that three stable pulses of different shapes can exist in systems described by the complex Ginzburg-Landau equation, such as passively mode-locked lasers with a fast saturable absorber.
33 citations
Journal Article•
28 citations
26 Mar 2001
TL;DR: In this paper, the authors have found complicated pulsating behavior of solitons of the CGLE and regions of their existence, and they have also found period doubling (PD) of pulsations and the sequence of PD-bifurcations leading to chaotic pulsating solITons.
Abstract: We have found complicated pulsating behavior of solitons of the CGLE and regions of their existence. We have also found period doubling (PD) of pulsations and the sequence of PD-bifurcations leading to chaotic pulsating solitons.
12 citations
Journal Article•
TL;DR: In this paper, the authors have found complicated pulsating behavior of solitons of the CGLE and regions of their existence, and they have also found period doubling (PD) of pulsations and the sequence of PD-bifurcations leading to chaotic pulsating solITons.
Abstract: We have found complicated pulsating behavior of solitons of the CGLE and regions of their existence. We have also found period doubling (PD) of pulsations and the sequence of PD-bifurcations leading to chaotic pulsating solitons.
7 citations
TL;DR: In this paper, a simple three-species charge-carrier transport model was proposed to describe the dynamics during thermal poling of a germanosilicate optical fiber, and the authors numerically solved the equations and reported one-dimensional space-time solutions for the electrooptic (EO) coefficient.
Abstract: We formulate a simple quantitative three-species charge-carrier transport model, consisting of two distinct positive ions and a single negative ion, to describe the dynamics during thermal poling of a germanosilicate optical fiber. We numerically solved the equations and report one-dimensional space-time solutions for the electrooptic (EO) coefficient. In the two-cation model, our findings show the EO coefficient initially dips near the anode and then monotonically rises to a steady-state value, higher than that produced by the initial applied poling field. However, at the cathode, the electric field quickly dropped to zero where it remained zero for the poling duration. The introduction of a moving negative ion clearly shows the existence of a dead time characteristic appearing at the cathode, resulting in a gain in the initial EO coefficient. This model also reveals that the resulting EO evolution in a thermally poled germanium-boron codoped fiber can he attributed to the movement of just two ions of opposite polarity. To explain the increase in the EO coefficient in boron codoped germanosilicate fiber, we found it necessary to allow for an increase in the third-order susceptibility by a factor of /spl sim/3.4.
5 citations
TL;DR: In this article, an efficient numerical procedure for the equilibrium solution of the internal electric field distribution resulting from poling of photo-refractive materials is described. But this method is not suitable for modeling semiconductor devices that are intended for low bias.
Abstract: We describe an efficient numerical procedure for the equilibrium solution of the internal electric field distribution resulting from poling of photo-refractive materials. This technique has been developed to model the equilibrium state in poled bulk devices requiring bulk charge neutrality to facilitate the modelling of blocking boundaries for a high externally applied voltage (bias) in the kV range for a small number of points. This technique is an improvement on existing conventional numerical techniques employed for modelling semiconductor devices that are intended for low bias. This method can also accommodate the modelling of planar insulators and organic optical materials. We develop an algorithm incorporating the existing Newton–Raphson method for solving Kukhtarev's equations that enforces conservation of charge within the modelled system. We apply this technique to model one-dimensional charge separation in ultraviolet (UV) excited poling of glass and, report numerical equilibrium electric field distribution for a 2 kV bias. The convergence behaviour of the algorithm is investigated and compared against the Newton–Raphson method. Copyright © 2001 John Wiley & Sons, Ltd.
15 Jul 2001
TL;DR: In this article, it was shown that pulsations in mode-locked fiber lasers can have a multi-frequency behavior and can take the form of period doubling, period tripling and contain even two or several non-commensurate frequencies.
Abstract: We show that pulsations in mode-locked fiber lasers can have a multi-frequency behaviour. Pulsations can take the form of period doubling, period tripling and contain even two or several non-commensurate frequencies.
TL;DR: In this article, the effects of thermal and ultraviolet light pretreatments of a variety of optical fibers with different core dopants were investigated and a negative correlation was found between the onset of optical damage to the fibers and the formation of seeded second-harmonic generation (SHG).
Abstract: In this article we report the effects of thermal and ultraviolet light pretreatments of a variety of optical fibers with different core dopants. Except for fibers codoped with phosphorus, a negative correlation was found between the onset of optical damage to the fibers and the formation of seeded second-harmonic generation (SHG). From our results and from those of other workers, we conclude that there is a link between susceptibility to optical damage and the formation of seeded SHG in germanosilicate optical fibers.