Towards Ultimate Pulse Propagation in Optical Fibres

Abstract

Optical fibres are being employed in telecommunications systems because of their significant advantages over other transmission media. Data has been transmitted at rates up to 2 Gbits/sec¹ and over distances in excess of 100 km without repeaters². Although impressive, these figures are far from the ultimate obtainable. Present day systems transmit data in the form of an encoded train of optical noise bursts. In concept this is as primitive as radio engineering was in the days of Hertz and Marconi. It is only within the last 2–3 years that serious effort has been directed to exploit the coherence properties of lasers for optical communications. In the laboratory, narrowband single-frequency lasers and coherent detection are being used to increase both transmission range and data rate. An alternative is to harness the nonlinear properties of fibres by using high peak power (>1 W), short duration (~1ps), transform limited pulses. In low loss fibres, high intensities can be maintained within the small diameter core (~6 μm) over long interaction lengths (10–100 km), and thus nonlinearity can manifest itself at relatively low power levels. Nonlinear effects are now of major relevance to future systems because they can either limit performance or be exploited to improve it.