| 摘要 |
An erbium doped fibre amplifier has a gain medium with a characteristic such that, if the gain changes at one wavelength, the gain at another wavelength changes by substantially the same amount. The characteristic may be achieved by using a gain medium with this property or by the construction of the amplifier. The gain medium can be an erbium-doped fibre with a wavelength independent gain swing over a range of wavelengths (especially a low Al 3+ -content aluminogermanosilicate EDF). As an alternative, the gain medium can consist of at least two pieces of EDF's, so that changes of the shape of the gain spectra (induced by changes of the operating conditions) in the different types of EDFs effectively offset each other. The gain spectrum can also be modified by means of optical filter(s) 3 placed before and/or after, between two sections of, and/or distributed along the gain medium, or by means of a "filtering EDF", specially selected in a constant population inversion region of the EDFA. The gain spectrum thus obtained is both flat and independent of operating conditions so that a dynamic gain flatness which is independent of input signal power, operating gain, and population inversion is realised. |
