1625/1650 nm optical time-domain reflectometers (OTDRs) are commercially available and are used for on-line monitoring of fibers carrying signals in the 1550-nm window. Because OTDRs operate with high peak powers stimulated Raman scattering (SRS) will deplete the signal in the 1550-nm window. We have considered OTDR pulses that are copropagating with the signal. If the OTDR pulses are counter-propagating the system degradation is reduced significantly. However, this solution restricts the use ofan OTDR in a network node to monitoring fibers with incoming traffic. The OTDR-introduced penalty can alternatively be reduced by choosing a wavelength closer to the signal window or by decreasing the peak power or duty cycle of the OTDR pulses.

Recently 1625/1650 nm optical time domain reflectometers (OTDRs) have become commercially available. One application of these OTDRs is the monitoring of fibres with live traffic at 1550 nm. The authors present experimental results which show that stimulated Raman scattering (SRS) gives rise to a depletion of the signal.

We demonstrate experimentally a versatile fibre ring laser. When all-optically mode-locked by a data signal the fibre laser can generate either a copy of a repetitive data signal, a recovered optical clock, or a recovered frame synchronization signal. We propose to use the recovered frame synchronization signal in a novel true all-optical demultiplexer.

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.

We have developed a computer model of a novel fibre ring laser, optically mode-locked by cross phase modulation. We have analysed the modulation process in detail, showing that, in the context of the earlier experiment, the nonlinear birefringence induced by cross-phase modulation gives rise to a loss modulation component. Numerical results suggest that this feature is essential if efficient mode-locking is to occur. The importance of attenuation and group delay dispersion in the modulator fibre has been demonstrated.

All-optical frame synchronisation recovery is demonstrated experimentally. A frame encoded input data signal forces a fibre laser to modelock. The fixed header is copied onto the laser output, whereas in the payload area the clock is recovered. The authors propose to use this frame synchronisation signal in an all-optical demultiplexer that unambiguously identifies each individual channel.

We demonstrate an optically mode-locked laser that generates a repetitive pattern of ultrashort pulses when driven by a repetitive pattern of optical pulses from an external source. Two modes of operation are described: in one mode of operation the generated pattern is determined directly by the driving pulse train; in the other mode it represents the result of logic operations between elements of the driving pulse train.

The waveguide parameters for a Nd-doped fluoride fiber amplifier have been optimized for small-signal and booster operation using an accurate numerical model. The optimum cutoff wavelength is shown to be 800 nm and the numerical aperture should be made as large as possible. Around 80% booster quantum conversion efficiency can be reached for an input power of 10 dBm and a pump power of 100 mW by the use of one filter.

A general procedure for determining the optimum placement of filters in Nd3+-doped ZBLANP fibres is presented. Extra gain of 5 dB per filter is predicted for the first four filters, yielding 20 dB of gain with 125 mW of pump power using three filters.

The viability of using mode coupling notch filters to suppress the amplified spontaneous emission around 1050 nm in Nd3+ doped ZBLAN fibres was demonstrated. A gain value of 9.2 dB was observed at 1328 nm using one pump at 795 nm and one mode coupling filter.

A model for Nd3+-doped ZBLANP fibres is verified. The model predicts high gain improvements by suppressing the 1050 nm amplified spontaneous emission. The gain in dB can be more than tripled and a gain to pump power ratio of 0.16 dB/mW is obtained independently of the pump power.