Dispersion Fluctuations Research Articles

Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers

The effect of dispersion fluctuations on the conversion efficiency of large frequency shift parametric sidebands is studied by numerical simulation and experiment. Numerical results based on periodic and random dispersion models are used to fit the experimental results. The fitting parameters provide a measure of the uniformity of the photonic crystal fiber used in the experiment. This allows us to place limits on the required uniformity of a photonic crystal fiber for strong frequency conversion.

Zero-dispersion wavelength mapping in short single-mode optical fibers using parametric amplification

We demonstrate a novel convenient nondestructive method based on optical parametric amplification that allows retrieval of the zero-dispersion wavelength map along a short optical fiber span with a high-spatial resolution. The improved resolution relies on the high sensitivity to the local longitudinal dispersion fluctuations of the parametric high-gain spectrum.

The effect of phase mismatch on two-pump fiber optical parametrical amplifier

In the paper, the effect of phase mismatch on two-pump fiber optical parametric amplifier is investigate based on analytic solutions of parametric gain. The phase mismatch is mainly induced by the fiber losses, the fourth-order dispersion and zero-dispersion wavelength fluctuations. The fiber losses reduce the pump powers resulting in a fall of the parametric gain, and make the phase mismatch vary with propagation distance leading to an obvious gain ripple. When the fiber losses are taken into account, the fourth-order dispersion produces a deeper ripple on the parametric gain and deteriorates the gain flatness. Zero-dispersion wavelength fluctuations result in variations of gain spectrum, and the long-scale fluctuations are more devastating than the short-scale ones.

Effective solute transport in temporally fluctuating flow through heterogeneous media

We investigate the effective spreading of a passive solute evolving from a finite source in temporally fluctuating flow through a heterogeneous porous medium. To this end, we distinguish between two stochastic processes: one to represent the spatial variability of hydraulic conductivity (K) and one to model the temporal fluctuations of the hydraulic gradient (J). In a second‐order perturbation approach we systematically investigate the time evolution of “effective” dispersion coefficients, which quantify solute spreading in response to longitudinal and transverse fluctuations of the hydraulic gradient, spatial heterogeneity, and local dispersion. The effective dispersion coefficients consist of three contributions that reflect (1) local dispersion, (2) the interaction between local dispersion and spatial heterogeneity, and (3) the interaction of local dispersion, spatial heterogeneity, and temporal fluctuations (i.e., time fluctuations enhance spreading only as a consequence of the interplay with spatial heterogeneity). Furthermore, longitudinal and transverse temporal fluctuations of the hydraulic gradient induce macroscopic contributions to the longitudinal as well as the transverse effective dispersion coefficients, which can both be comparable to the contributions to longitudinal dispersion due to steady flow, i.e., large. An application to a field‐scale tracer experiment gives evidence that temporal fluctuations help in explaining observed macroscopic transverse solute spreading. Furthermore, aquifer remediation techniques that rely on the mixing of injected reactants with resident contaminants, or simply on dissolving these, can benefit from forcing velocity fluctuations. The presented results provide a quantitative basis for the design of such hydraulic manipulation techniques.

Optimal Design of Dual-Pump Fibre-Optical ParametricAmplifiers with Dispersion Fluctuations Based on Hybrid GeneticAlgorithm

Solutions of dual-pump fibre-optical parametric amplifiers (DP-FOPAs)with dispersion fluctuations are derived by using a matrix operator.Based on these solutions and a hybrid genetic algorithm, we haveoptimized three-section DP-FOPAs to increase the signal band andimprove the gain uniformity. The optimizations demonstrate that whendispersion fluctuations are taken into account, the 44-nm signal bandwith the 0.37-dB ripple and over 14.8-dB gain can be obtained from thethree-section DP-FOPA, instead of the lowest gain of ~13 dB withthe ripple of more than 15 dB from the single-section DP-FOPA.

Soliton broadening under random dispersion fluctuations: Importance sampling based on low-dimensional reductions

We demonstrate that dispersion-managed solitons are less likely to experience critical broadening under the influence of random dispersion fluctuations than are solitons of the integrable nonlinear Schrödinger equation, and that this robustness increases with map strength from the constant-dispersion (integrable) limit to the large-map-strength limit. To achieve this, we exploit a separation of scales in dispersion-managed soliton dynamics to implement an importance-sampled Monte Carlo approach that determines the probability of rare broadening events. This approach reconstructs the tails (i.e., the regions of practical importance) of probability distribution functions with an efficiency that is several orders of magnitude greater than conventional Monte Carlo simulations. We further show that the variational approach with an appropriately scaled ansatz is surprisingly good at capturing the effect of random dispersion on pulse broadening; where it fails, it can still be used to guide very efficient simulation of the original equation.

Optical Amplification and Signal Processing in Highly Nonlinear Optical Fiber

Fundamentals of parametric processing in highly nonlinear optical fiber are reviewed. Experimental procedures necessary for construction of one- and two-pump parametric amplifier architectures are described. Pump phase broadening, dispersion fluctuation and birefringence form basic impairment mechanisms in fiber parametric devices and are analyzed in two-pump parametric devices. Parametric signal processing is introduced with specific applications in all-optical regeneration, band conjugation, multicasting, packet switching and signal distortion reversal.

Soliton broadening under random dispersion fluctuations: Importance sampling based on low-dimensional reductions

Soliton broadening under random dispersion fluctuations: Importance sampling based on low-dimensional reductions

Chromatic dispersion fluctuations in optical fibers due to temperature and its effects in high-speed optical communication systems

Several research groups have been proposing different dispersion compensation schemes, for very high-speed (⩾40Gbit/s) long-haul systems operating in the C-band window (1530–1563nm) over standard single mode fibers, known as ITU-T G.652 fibers. The focus on these high chromatic dispersion fibers is due to the large amount of standard single mode fibers already installed in the field. Although several dispersion compensation techniques have proved to be successful, the long term stability of this kind of systems remains to be seen. In fact, when in the field, these high speed systems present a very unstable behavior, which is translated in large variations of the bit error rate. In order to stabilize the systems strong forward error correction codes have been used. In this work, we prove quantitatively that this inherent instability is mainly due to chromatic dispersion variations induced by temperature swings. Two models for the chromatic dispersion and chromatic dispersion slope variations with temperature are developed and validated using laboratory measurements previously published. After the effect of temperature change is analyzed in terms of eye opening penalty, it is shown that for systems operating at 40Gbit/s and above temperature effects have to be considered in system design.

Impact of Dispersion Fluctuations on Dual-Pump Fiber-Optic Parametric Amplifiers

Effects of zero-dispersion wavelength (ZDWL) fluctuations on dual-pump fiber-optic parametric amplifiers are investigated analytically and numerically. It is found that the signal gain varies considerably from fiber to fiber even though each fiber may have the same ZDWL on average. Moreover, the gain spectrum becomes highly nonuniform for a given fiber because of such dispersion fluctuations. Numerical simulations show that this problem can be solved to a large extent by reducing wavelength separation between the two pumps, but only at the expense of a reduced amplifier bandwidth.

Comparison of Nonlinear Pulse Interactions in 160-Gb/s Quasi-Linear and Dispersion Managed Soliton Systems

The understanding and development of 160-Gb/s transmission systems requires the study of the impact of different dispersion compensation schemes on pulse propagation in nonlinear fiber. In this paper, we present an investigation of 160-Gb/s optical transmission systems, focusing on optimal propagation regimes, and in particular, we analyze different transmission limitations and dominant nonlinear effects by comparing quasi-linear and dispersion managed soliton systems. Two quasi-linear systems, one using nonzero dispersion-shifted fiber (NZDSF) and the other single-mode fiber (SMF), and one short-period (1 km) dispersion managed soliton (DMS) system are studied, both for single-channel and wavelength-division-multiplexed (WDM) transmission. First, the performance of the two quasi-linear systems in single-channel transmission are compared and it is shown that the NZDSF and SMF systems allow similar error-free transmission distances with only small differences in the intrachannel four-wave mixing (IFWM) induced amplitude jitter. The effect of pulsewidth on transmission performance in this regime was investigated and the use of shorter pulses was found to result in lower amplitude jitter. We analyzed the behavior of the DMS system and showed that the reduced pulse broadening during transmission allowed a significantly longer single-channel transmission distance with a smaller impact of nonlinearities compared to quasi-linear propagation. The sensitivity of the DMS system performance to statistical fluctuations in the fiber dispersion was studied and the results show the level of accuracy in the dispersion management map which must be ensured in these systems. Finally, the performance of the DMS in WDM transmission was investigated and it was found that it was subject to very large penalties increasing the minimum channel spacing possible because of the strong impact of interchannel cross-phase modulation (XPM).

160 Gbit/s adaptive dispersion equaliser using asynchronous chirp monitor with balanced dispersion configuration

Adaptive dispersion equalisation operating at 160 Gbit/s using an asynchronous chirp monitor with a balanced dispersion configuration is demonstrated for the first time. The dispersion fluctuation of an 80 km DSF was successfully eliminated over a temperature range of 40°C (from 5 to 45°C).

Parametric amplification in presence of dispersion fluctuations

Parametric amplification in fibers with dispersion fluctuations is analyzed. The fluctuations are modelled as a stochastic process, with their size at a given position modelled as a Gaussian, and the autocorrelation decreasing exponentially. Two models are studied: in one the dispersion is piecewise constant, while in the other it is continuous. We find that the amplification does not depend on the models' details and that only fluctuations with long correlation lengths affect the amplification significantly.

Far-infrared probe of size dispersion and population fluctuations in doped self-assembled quantum dots

We investigate the FIR magneto-optical transitions in doped self-assembled InAs quantum dots with an average filling ranging from 0.6 to 6 electrons per dot. Significant changes in the magnetic field dispersion, the line-width and the amplitude of the transitions are observed as the doping level is varied, in agreement with our theoretical calculations. We show that our technique is an effective tool to obtain informations regarding the dot size homogeneity and the electron filling uniformity.

Impact of dispersion fluctuations on 40-Gb/s dispersion-managed lightwave systems

We study numerically the impact of random dispersion fluctuations on the performance of 40-Gb/s dispersion-managed lightwave systems designed using either the chirped return-to-zero or the soliton format and employing backward-pumped distributed Raman amplification. We consider two-section dispersion maps with β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> =±4 and ±8 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /km and show that the Q parameter decreases rapidly in both cases as the nonlinear effects become stronger. The impact of dispersion fluctuations can be reduced by lowering the average input power, but the system length is then limited by amplifier noise.

Far-infrared probe of size dispersion and population fluctuations in doped self-assembled quantum dots

We investigate the FIR magneto-optical transitions in doped self-assembled InAs quantum dots with a filling ranging from 1 to 6 electrons per dot. Significant changes in the line width and the dispersion of the transitions are observed as the doping level is varied, in agreement with our theoretical calculations. We show that our technique is a very effective tool to obtain informations regarding the dot size dispersion and the electron filling fluctuations.

Dispersion-managed soliton propagation in optic fibers with random dispersion

Propagation of dispersion-managed solitons in optic fibers with randomly distributed dispersion is studied. It is shown that the effect of the dispersion fluctuations can be described within the framework of a modified nonlinear Schrodinger equation with a frequency-dependent damping term (∼ω4). The presence of randomly modulated dispersion leads to the damping of optical pulses. The condition for stable pulse propagation is determined based on the corresponding variational equations.

Influence of dispersion fluctuations on four‐wave mixing efficiency in optical fibers

AbstractThe four‐wave mixing (FWM) used in optical fibers is expected to be a simple wavelength conversion technique for ultrafast optical signals. Highly efficient generation of stable FWM light is desired. FWM efficiency depends on the zero‐dispersion wavelength of the fiber, the wavelength of the pump light, and the wavelength of the signal light, and reaches its maximum efficiency when the pump wavelength and zero‐dispersion wavelength match in degenerate FWM. However, the zero‐dispersion wavelength fluctuates in the longitudinal direction in actual optical fibers, and these changes affect the FWM generation characteristics. In this paper, we analyze FWM generation that accounts for the zero‐dispersion wavelength fluctuations in the longitudinal direction of the optical fibers and explain the theory of the dependence of the FWM efficiency on the pump wavelength. In addition, by conducting FWM generation experiments, we demonstrate the differences in the characteristics of the optical fibers and clearly show the relationship between the FWM generation characteristics and zero‐dispersion wavelength distribution. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(8): 16–24, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10032

Stabilization of dispersion-managed solitons in random optical fibers by strong dispersion management

The propagation of dispersion-managed solitons in optical fibers with randomly perturbed dispersion maps is considered. The interplay between the periodic dispersion management and the random dispersive fluctuations is precisely analyzed. Analytic expressions are derived for the moments of the pulse widths as well as for the probability density functions. It is shown that a strong dispersion management stabilizes the soliton, while a small anomalous residual dispersion is necessary for preventing from a stochastic resonance phenomenon. Analytical results are confirmed by direct numerical simulations.

Pulse broadening induced by dispersion fluctuations in optical fibers

A general theory is presented to describe the effects of dispersion fluctuations on optical pulses propagating inside single-mode fibers modeled as a linear dispersive medium. It is shown that the pulse broadening induced by dispersion fluctuations can be quite large in dispersion-managed lightwave systems, especially at high bit rates, and can exceed that induced by third-order dispersion and polarization mode dispersion.