| 摘要 |
An optical amplifier for amplifying an optical signal having a signal wavelength lambda s, comprises an optical fibre (20) having an erbium doped core (34) surrounded by cladding (42, 32, 30), a pump (22) for pumping the fibre with pump light at a pump wavelength lambda p coupled to the fibre, said erbium doped optical fibre having a NA higher than 0.2, the difference in the coefficient of thermal expansion of the core adjacent the core/cladding interface and the coefficient of thermal expansion of the cladding at at least one radius less than 2 mu m from said interface being lower than a predetermined value, corresponding to a ratio of erbium loss to background loss, at said pump wavelength, greater than a minimum ratio calculated by a given increasing function of the ratio erbium loss/background loss versus erbium loss, in which said minimum ratio is about 20 when erbium loss is 0.15 dB/m and about 120 when erbium loss is 3.5 dB/m. <IMAGE> |
