OPTICAL NETWORK

摘要

An optical network comprises an erbium-doped silica-based optical fibre (30) hav ing a D-shaped cross-section. The wave-guide carries information signals at 1.53 .mu.m from a signal source (38) a nd provides amplification to the information signals when pumped by an optical pump source operating at 0.994 .mu.m (36). Optical signals are tapped from the waveguide (30) by means of evanescent couplers (32 and 34). The waveguide (30) provides amplification to at least partially restore tapping loss to the information signal due to the optical taps. The core of the optical waveguide (3 0) is chosen to substantially minimise the spot size of signals ata the wavelength of the pump source (36) so as to provide preferential extraction of the information signal in order to leave the pump source substantially undisturbed to be able to pump regions of th e amplifying waveguide (30) beyond the optical tap.