Interchannel power equalization and ASE noise rejection in multistage EDFA amplified WDM systems employing fibre gratings

We investigate the use of fibre gratings to provide simultaneous ASE noise rejection and the interchannel power equalization. The basic structure employs one fibre grating per channel in a cascade arrangement using a single circulator or 3 dB coupler. This optical filter provides a bandpass characteristic at each channel location, rejecting the accumulated ASE noise, not only out of the WDM total band, but also between channels inside the WDM band. This structure can be easily fabricated with uniform gratings, providing flexible wavelength location and channel bandwidths for different WDM system spectral distributions. Furthermore, this structure allows for the individual control of the channel power, by simply varying the grating reflectivity.