Upgrading existing optical fibre plants to higher bit-rates

To upgrade existing conventional fibre lines to very high data rates, effective methods of coping with the chromatic dispersion problem are therefore needed. Several techniques for the compensation of chromatic dispersion have been suggested so far. They include the use of externally modulated chirp-free transmitters, pre-chirping techniques of the transmitter laser, dispersion supported transmission, midpoint spectral inversion, dispersion compensating fibres, chirped fibre gratings, nonlinear optical techniques, etc. In this paper those of the above mentioned dispersion compensation techniques which seem to be the more mature are discussed and compared. In particular, attention is focused on the use of dispersion compensating fibres, soliton propagation and midpoint spectral inversion. Their practical implementation and effectiveness is also demonstrated describing transmission experiments both on laboratory and field test beds