N.J. Smith

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.

Modulational instabilities in fibers with periodic dispersion management

We analytically and numerically analyze the occurrence of modulational instability in fibers with periodic changes in the group-velocity dispersion. For small variations, a set of resonances occurs in the gain spectrum. However, large dispersion variations eliminate these resonances and restrict the bandwidth of the fundamental gain spectrum. This research has been motivated by the adoption of dispersion management techniques in long-haul optical communications.

Picosecond soliton transmission using concatenated nonlinear optical loop-mirror intensity filters

We investigate the use of nonlinear optical loop mirrors as saturable absorbers in picosecond soliton transmission systems. It is found that they allow short (1–5-ps) pulses to be propagated through chains of optical amplifiers spaced at intervals of typically 10 km. The loop mirror removes dispersive waves and stabilizes the peak amplitude of the soliton. An additional advantage is that the self-frequency shift of the soliton may be suppressed by bandwidth filtering without causing growth of dispersive waves at the center of the passband. The timing jitter and soliton interactions present in the scheme are also described.

DISPERSION MANAGEMENT FOR WAVELENGTH-DIVISION-MULTIPLEXED SOLITON TRANSMISSION

Residual frequency shifts that are due to two-soliton collisions in stepwise exponentially dispersion-tapered fiber are calculated. Two-step dispersion profiles to minimize the frequency shifts and associated timing jitter are specifically identified. These profiles will improve the performance of wavelength-division-multiplexed soliton systems and permit operation with longer amplifier spans over an increased bandwidth.

Dark soliton sideband formation and stability in periodically amplified systems

We investigate the stability of dark solitons with respect to periodic amplification by studying sideband generation. It is shown that these sidebands grow exponentially as a result of a four-wave mixing process with the cw background. We derive expressions for the positions of the sidebands and present numerical simulations that are in excellent agreement with the theoretical description. A comparison is made with bright solitons, showing that dark soliton propagation is less perturbed only over very short amplifier chains. We also relate our results to laser cavities and discuss the prospects for dark soliton lasers.

Stable propagation of solitons with increased energy through the combined action of dispersion management and periodic saturable absorption

It is shown, through numerical simulations, that by using a combination of dispersion management and periodic saturable absorption it is possible to transmit solitonlike pulses with greatly increased energy near to the zero net dispersion wavelength. This system is shown to support the stable propagation of solitons over transoceanic distances for a wide range of input powers.

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.

Gordon-Haus jitter reduction in enhanced power soliton systems

We have shown that the Gordon-Haus timing jitter in an enhanced power soliton transmission system is substantially lower than in a conventional soliton transmission line with equal path-average dispersion. The ability to simultaneously increase receiver SNR and reduce timing jitter will allow significant increases in amplifier spacing for given combinations of bit rate and system length. Examples of the possibilities allowed by this technique are presented.

Gordon-Haus jitter suppression using an intra-span phase modulator and post transmission dispersion compensator

We analyze the reduction of Gordon-Haus jitter using a mid-span phase modulator and post transmission dispersion compensator. The timing jitter variance at the the receiver may in principle be reduced by a factor of 20, however pulse broadening considerations may reduce this. We also examine how the phase modulator may cause nonGaussian statistics at the receiver.