Fiber-Amplifier Cascades with Equalization Employing Mach-Zehnder Optical Filters in Multiwavelength Systems

Recent rapid advances in Erbium-Doped Fiber Amplifier (EDFA) technology make the WDM option particularly attractive for increased capacity and multiple access optical networking [1-2], In these applications, cascaded EDFAs may be deployed on a large scale in future lightwave systems. However, the nonflat gain spectra of the EDFAs impose a difficulty in optical networks using WDM technology since each optical channel experiences a different optical gain. Although each individual amplifier exhibits only modest gain variations over a spectral interval of roughly 20 nm, these variations accumulate through successive amplifiers, resulting in exponentially increasing interchannel power differences [3]. Various proposals for equalizers have been discussed.