IMPROVEMENTS IN OR RELATING TO SIGNAL TRANSMISSION IN AN OPTICAL SYSTEM

摘要

A method of reducing Raman tilt in a transmission apparatus capable of transmitting a plurality of signals, occupying contiguous channels in a transmission band, through a length of optical transmission cable which exhibits the Raman effect of transferring energy from the shorter wavelength sinals at one end of the transmission band towards the longer wavelength signals at the other end of the transmission band, including the transmissio n of half the maximum number of signals at twice the normal channel frequency spacing at a higher-than-normal level and the transmission signals in select ed ones, fewer than all, of the available channels at the normal channel spacin g at a normal power level. As new channels are added at the lower frequency channel spacing, the powers of both neighbouring channels are reduced to the normal power level.