Simulation of guiding-centre soliton transmission system stability in the presence of polarisation mode dispersion

Results of full numerical simulations of a guiding-centre soliton system with randomly birefringent SMF fibre are shown and analysed. It emerges that the soliton system becomes unstable even for small amounts of PMD.

Soliton generation from randomly modulated return-to-zero pulses

We consider return-to-zero (RZ) pulses with random phase modulation propagating in a nonlinear channel (modelled by the integrable nonlinear Schrödinger equation, NLSE). We suggest two different models for the phase fluctuations of the optical field: (i) Gaussian short-correlated fluctuations and (ii) generalized telegraph process. Using the rectangular-shaped pulse form we demonstrate that the presence of phase fluctuations of both types strongly influences the number of solitons generated in the channel. It is also shown that increasing the correlation time for the random phase fluctuations affects the coherent content of a pulse in a non-trivial way. The result obtained has potential consequences for all-optical processing and design of optical decision elements.

Soliton transmission at 10 Gbit/s over 2022 km of standard fibre with dispersion compensation

We present experimental results of 10 Gbit/s, 20 ps soliton data transmission over standard fibre, dispersion compensated to 0.5 ps/nm/km. Acceptable Q values were measured to a distance of 2022 km.

Environmentally stable high-power soliton fiber lasers that use chirped fiber Bragg gratings

Environmentally stable high-power erbium fiber soliton lasers are constructed by Kerr or carrier-type mode locking. We obtain high-energy pulses by using relatively short fiber lengths and providing large amounts of negative dispersion with chirped fiber Bragg gratings. The pulse energies and widths generated with both types of soliton laser are found to scale with the square root of the cavity dispersion. Kerr mode locking requires pulses with an approximately three times higher nonlinear phase shift in the cavity than carrier mode locking, which leads to the generation of slightly shorter pulses with as much as seven times higher pulse energies at the mode-locking threshold.

Soliton switching using cascaded nonlinear-optical loop mirrors

We demonstrate multiple-peaked switching in a nonlinear-optical loop mirror and present an experimental investigation of device cascading in the soliton regime based on a sequence of two independent nonlinear-optical loop mirrors. Cascading leads to an enhanced switching response with sharper switching edges, flattened peaks, and increased interpeak extinction ratios. We observe that pulses emerging from the cascade retain the sech2 temporal profile of a soliton with minimal degradation in the spectral characteristics.

Analysis of power jitter induced by interchannel interactions in dispersion-managed optical soliton transmission systems

Collision-induced power jitter is theoretically and numerically examined in dispersion-managed wavelength-division-multiplexed optical soliton transmission systems. The variational method is mainly used to develop a time efficient jitter calculation approach. The power jitter causes a serious problem for a singly periodic dispersion managed line having almost zero average dispersion, which can be reduced by applying doubly periodic dispersion management.

Evaluating the capacity of long haul soliton transmission

We review recent developments in the use of optical solitons for communication systems spanning transoceanic distances. The implementation of "soliton control" to alleviate the detrimental impact of effects such as amplifier noise is shown to be critical for obtaining advantages over competing technologies. The potential performance of two control strategies, namely straight line filtering and synchronous phase modulation, is examined in detail. Design diagrams are used to determine the maximum permissible amplifier spacing, which is a key determinant of system economics. To focus the enquiry, two example system spans are taken, representing transatlantic and transpacific distances. It is concluded that straight line filtering provides very little improvement over a basic design without control. However synchronous phase modulation, which may be implemented using a handful of actively driven components, provides very substantial benefits. These may be used either to extend the overall bit-rate-distance product of the system or to increase the amplifier spacing at more moderate capacities.

Dispersion managed soliton systems

Dispersion managed solitons have been discovered to have some remarkable properties which indicate an outstanding opportunity for exploitation in transmission systems. This paper will review and interpret these discoveries and discuss the potential for WDM of these solitons for both long distance systems and for the upgrade of the installed fibre base.

Picosecond soliton propagation using nonlinear optical loop mirrors as intensity filters

The authors show that by inserting nonlinear optical loop mirrors into an optical fibre transmission line, 1.5 ps solitons may be transmitted over at least 750 km, with amplifiers spaced at 15 km intervals.

Picosecond soliton control using nonlinear optical loop mirrors

We show that by inserting nonlinear optical loop mirrors into an optical fibre transmission line, that 1.5 ps solitons may be transmitted over at least 750 km, with amplifiers spaced at 15 km intervals.

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.

Soliton transmission through a disordered system

An exact formula for the transmission time in a disordered nonlinear soliton-bearing classical one-dimensional system is obtained.

Beyond the formal/informal economy binary hierarchy

Purpose – This paper aims to evaluate critically the conventional binary hierarchical representation of the formal/informal economy dualism which reads informal employment as a residual and marginal sphere that has largely negative consequences for economic development and needs to be deterred. Design/methodology/approach – To contest this depiction, the results of 600 household interviews conducted in Ukraine during 2005/2006 on the extent and nature of their informal employment are reported. Findings – Informal employment is revealed to be an extensively used form of work and, through a richer and more textured understanding of the multiple roles that different forms of informal employment play, a form of work that positively contributes to economic and social development, acting both as an important seedbed for enterprise creation and development and as a primary vehicle through which community self-help is delivered in contemporary Ukraine. Research limitations/implications – This survey reveals that depicting informal employment as a hindrance to development and deterring engagement in this sphere results in state authorities destroying the entrepreneurial endeavour and active citizenship that other public policies are seeking to nurture. The paper concludes by addressing how this public policy paradox might start to be resolved. Originality/value – This paper is one of the first to document the role of informal employment in nurturing enterprise creation and development as well as community exchange.