Polarisation effects in long span systems

The potential for long span optical unregenerated systems has been greatly enhanced by the development to maturity of erbium fibre amplifiers. The transmission of optical signals over many amplified sections has revealed a class of problems induced by polarisation fluctuations. This paper describes the origin and system implications of polarisation dependent loss, polarisation dependent gain and polarisation mode dispersion and interactions between them. The influence of polarisation scrambling is also discussed and a rationale for including these effects into system power budgets is presented.