F.M. Knox

Energy-scaling characteristics of solitons in strongly dispersion-managed fibers.

We present an empirical scaling law that models the increased energy required for launching a soliton into an optical system with sections of both normal and anomalous dispersion fiber. It is shown that the inclusion of periodic attenuation and amplification can be handled as separate problems, provided that the interval between optical amplifiers is substantially different from the period of the dispersion map. These concepts are illustrated by reference to an example system comprising dispersion-shifted fiber combined with anomalous standard fiber.

Soliton transmission using periodic dispersion compensation

We examine the behavior of solitons in optical fibers where the dispersion is alternated between the normal and anomalous regimes. The periodic nature of the system strongly modifies the shape of the stable soliton (solitary wave) pulses, and increases their energy when compared with solitons in equivalent uniform fibers. Power enhancement factors of up to 70 are numerically observed. This leads to both an increased signal-to-noise ratio (SNR) at the receiver and reduced Gordon-Haus timing jitter. The interaction between pairs of isolated pulses is examined. We also examine implementations including periodic amplification, and show that the energy scalings introduced by the amplification and the dispersion management are independent provided that the periods of the two processes are dissimilar. We show that there is an optimum dispersion compensation ratio which minimizes the received Gordon-Haus jitter. A diagrammatic technique is presented for estimating the performance of dispersion compensated soliton transmission systems.

10-Gbt/s soliton communication systems over standard fiber at 1.55 /spl mu/m and the use of dispersion compensation

The limits to soliton propagation at 10 Gbt/s in standard fiber systems at 1.55 /spl mu/m are assessed. We show that propagation for up to 200 km is possible using 36-km amplifier spacings and 30-ps solitons. In order to extend this distance and increase the range of usable pulse widths, the use of dispersion compensating fiber, as part of each amplifier, is evaluated. In addition this scheme significantly reduces the average power requirements. >

Average soliton propagation in periodically amplified systems with stepwise dispersion-profiled fiber

Average soliton propagation in periodically amplified soliton systems with stepwise varying fiber dispersion is studied. Optimal dispersion profiles are obtained by minimization of a simple and intuitively appealing perturbation function. At a given data rate, n-fold profiling is shown to permit n-fold extension of amplifier spacing. Equivalently, at a given amplifier spacing, it permits n-fold increase of data rate. Hence, we demonstrate the feasibility of 40-Gbit/s operation over several hundred kilometers, using 5-ps solitons and 50-km amplifier spans.

Average soliton dynamics in strongly perturbed systems

Abstract We advance the average soliton concept to include averaging of the pulse shape in addition to the pulse energy. A simple prescription is presented for the optimum launch position of a bandwidth-limited sech( t ) pulse, relative to the periodic cycle. We identify how this result can also be obtained from the Lie algebra approach by Hasegawa and Kodama (Optics Lett. 15 (1990) 1443). Improved stability and reduced pulse distortion is demonstrated in a numerical example. Application of this result will enhance the performance of some strongly perturbed, soliton-based, amplified optical communication systems.

Dispersion as Control Parameter in Soliton Transmission Systems

A review is presented of the role of dispersion in managing solitons in high data rate transmission. It is shown that piecewise intra-amplifier dispersion profiling may be used to minimise the effect of periodic amplification. Jitter may be controlled by multistage dispersion compensation. Finally an investigation of periodic dispersion compensation in a generalised NLS system is presented showing the suppression of modulational instability and the existence of a new stable soliton like pulse.

Fabrication of highly efficient grating band-pass filters and their applications in soliton propagation system

We report here fabrication of highly efficient in-fiber grating bandpass filters using the established UV-side- exposure technique. Various combinations of passband/stopband and transmission/rejection of single- and multi-channel filters have been produced in hydrogenated standard telecom, high Ge-doped and B/Ge-codoped fibers. Up to > 60 dB rejection stopbands ranging from -2 nm to 55 nm, and passbands with 0.02 nm - 3 nm linewidths and transmissivity up to > 90% have been achieved with these devices. By concatenating several structures, a bandpass filter has been demonstrated with a combination of a 0.16 nm passband centered in a approximately 35 nm stopband, representing the highest reported finesse of 220 for any multi-nanometer stopband filter. We also report the first application of a grating bandpass filter for suppressing timing jitter in soliton propagation system, enabling transmission of 10 ps solitons over a distance of 2700 km.

Optimising transmission capacity: long distance and terrestrial applications

This paper identifies the important limiting processes in transmission capacity for amplified soliton systems. Some novel control techniques are described for optimizing this capacity. In particular, dispersion compensation and phase conjugation are identified as offering good control of jitter without the need for many new components in the system. An advanced average soliton model is described and demonstrated to permit large amplifier spacing. The potential for solitons in high-dispersion land-based systems is discussed and results are presented showing 10 Gbit s-1 transmission over 1000 km with significant amplifier spacing.

Design of soliton systems for optimum capacity

This paper identifies some novel approaches to soliton control which may give simple remedies to the limitations imposed by jitter and soliton interaction. Specifically, post-transmission dispersion compensation is shown to reduce significantly the main limitation on long distance transmission. The principle is that the timing jitter can be reduced substantially by employing a dispersive element, post-transmission, with a dispersion of opposite sign equal to one half the system dispersion. The need for filters may be obviated in many cases by this technique, however, compensation combined with fixed frequency filtering will reduce still further these limitations allowing transmission of 10 Gbit s-1 or more over many thousands of km. Similarly phase conjugation either within the system or post-transmission is shown to offer excellent soliton control not only over jitter effects but also soliton-soliton interaction. Potential for solitons in standard fibre systems including dark solitons and very high data rate intermediate length systems are identified.