An asymmetric nonlinear directional coupler, where the switching of a signal controlled by a strong pump, is investigated, in order to reduce the necessary switching power. It is shown that the switching power is reduced by 67% when the control wavelength is located in the vicinity of the signal wavelength.

A recently proposed method for soliton compression by propagation of solitons through a fiber junction has been investigated both experimentally and theoretically. The consequences of fiber loss and its remedy by lumped amplification have been considered. By inserting an intermediate fiber section between two fibers of different dispersions, a one-soliton in the first fiber can be transformed into a compressed soliton containing most of the energy of the original soliton with minor subsequent oscillations in the pulse width. A soliton with 11 ps initial pulse width has been compressed by a factor of 2.4 while conserving its soliton character. Numerical simulations using the Zakharov-Shabat eigenvalue problem reveal that the resulting output pulse consists of only one soliton and a small amount of radiation.

The influence of detuning and loss have been investigated for a fiber laser modelocked by cross phase modulation from an external pulsed signal. It is shown, that a simplified model based on path averaging of the modulation signal can be used to predict the influence of detuning and loss on the laser behaviour accurately.

A fast and accurate method for numerical modelling of a cross-phase-modulated (XPM) fibre laser is introduced. The method can handle variations in the laser parameters and deal with detuning and loss in the laser, and is suitable for optimizing the performance of XPM lasers. For a given modulation pulse width, it is shown in numerical examples that the quality of signal pulses depends on the repetition rate of the external modulation and the length of the modulation path.

A pump controlled nonlinear directional coupler is investigated in order to minimize the necessary switching power, and it is shown that a reduction by up to 80% in the switching power in a nonlinear directional coupler may be obtained by reducing the linear coupling of the pump.

A theoretical method is presented for investigation of modelocking in a fiber laser, where the modulation is performed by the cross phase modulation (XPM) from synchronous pumping using an external signal. Using this method, modelocking in a cross phase modulated fiber laser has been investigated.

A new theoretical method is presented for investigation of the modelocking performance of a synchronous pumped cross phase modulated fiber laser. By using this method, the modelocking performance of a non detuned modulated fiber laser has been investigated for a constant sech shaped modulation as a function of the modulation power and duty cycle, and as a function of the filter bandwidth, modulation path length and dispersion.

In nonlinear long distance transmission, the distributed erbium doped fiber (d-EDF) is a promising component due to very low signal power excursions [1]. This allows a spacing between two pump power stations in the order of 100 km [1], when the pump wavelength is 1.48 μm. Thus having a signal wavelength near 1.55 μm, the background loss is canceled out by stimulated emission from both Raman scattering and erbium ions. Using a very small erbium concentration the noise figure may be minimized and transparency may be obtained for a total bidirectional pump power of around 100 mW giving noise figures near 10 dB [1],[2].

Initial overlap between solitons propagating at different carrier frequencies gives rise to a change in the frequencies of the solitons. The frequency change can have a severe effect on the transmission system because it will result in a time displacement of the solitons that is due to the fiber dispersion. The frequency change caused by initial overlap between two solitons at different carrier frequencies is calculated for a transmission system with periodic gain and loss.