Abstract

The Er⁺³-doped fiber amplifier (EDFA) is widely recognized as an ideal optical repeater for long-distance lightwave transmission systems. However, the gain spectrum of an EDFA is not uniform; it exhibits a sharp peak ~1.53 μm and a broadband with smaller gains for longer wavelengths. For undersea WDM systems containing several hundred cascaded amplifiers, even a fraction of a dB in the gain spectrum of each individual amplifier would lead to differences of several tens of dB among the WDM signal levels after propagation through long amplifier chains. Gain equalizers are required in these systems to compensate for the wavelength variation of the amplifier gain spectrum. This is particularly important for soliton systems where the optical power levels must be carefully controlled to effectively maintain soliton propagation. Recently, Inoue et al.¹ have reported gain equalization using a Mach-Zehnder optical fiber. Here we propose to use the acoustooptic tunable filter (AOTF)² as a gain equalizer in WDM lightwave systems because it is capable of controlling the signal levels of the multiple wavelengths simultaneously and independently.

© 1992 Optical Society of America