Work on transatlantic communications systems has already shown [1] that the maximum bit-rate/distance product for any system length is always obtained by transmitting well spaced transform limited pulses (solitons), e.g. 20 ps pulses for 10 Gbit/s transmission over 5000 km [2]. In a 40 Gbit/s network similar techniques would allow transmission over 1-2000 km using 3-5 ps pulses [3]. The principal barrier to development of such systems has always been the lack of a suitable pulse transmitter, which must produce high power, transform limited ps pulses at GHz rates, and must also be portable and stable for long periods (years). Recently it has been shown that suitable pulses can be generated by optically amplified semiconductor laser sources [4-6], similar to those used in current lightwave transmission systems. Two techniques have been used; gain switching and filtering [4],which is simple to implement but produces substantial pulse to pulse jitter, and mode-locking [5,6], which produces better pulses but is subject to stability problems. In this paper we show for the first time that the mechanical problems associated with external cavity mode-locked lasers can be overcome, without compromising on output pulse quality, by building a packaged cavity, and that the important operating parameters are amenable to external control for long term stability.

In a recent paper [1] we demonstrated an all-optical demultiplexer using a nonlinear optical loop mirror (NOLM) in which a signal at one wavelength is used to switch a signal at a different wavelength [2], [3]. The switching signal in that case was generated from a modelocked Nd-YAG laser at 1.32um operating at 76 MHz and the switched signal was a gain switched DFB laser operating at 1.56um at 1 GHz. The purpose of this present work is to extend the optical switching into the gigabit regime while, at the same time, avoiding high power laser systems.

The switching of a 20 Gbit/s pulse train at 2.5 Gbit/s in an all-fibre NOLM is demonstrated. An entirely semiconductor case powered configuration was used with a long loop (6.4 km) ensuring low power (10 mW) for the switching pulses.<>

The transmission of a 10 GHz repetition rate optical pulse train over a 28.5 km long distributed erbium-doped fibre amplifier is reported. In the linear dispersion regime, the pulses broaden so that the tails of adjacent pulses overlap. However, given sufficiently high signal powers, the optical Kerr effect causes pulse narrowing back to the original 18 ps pulsewidth.<>

Miniature, fibre tailed and packaged, wavelength tunable actively mode locked semiconductor lasers have been developed for use as sources of approximately 20 ps transform limited pulses. Continuous stable operation with >40 nm tuning ranges centred either at 1.3 mu m or 1.55 mu m have been demonstrated. The package has an adjustable cavity length enabling the repetition frequency to be selected be...

A simple packaged laser preamplifier receiver with 50 Ohm electronics and no optical filter, has been constructed. The receiver has a bandwidth of 3 GHz, a dynamic range >25 dB and a sensitivity (for 10-9 BER) of -38.5 dBm at 565 Mbit/s

The first demonstration of two packaged 1.5 μm semiconductor laser amplifiers in an optical system is reported. Total coupling losses for the fibre-tailed packages were 10dB and 13 dB, respectively. In a 140 Mbit/s intensity-modulated system experiment, using the amplifiers as linear repeaters, a total repeater again of 26 dB was achieved.