Multichannel amplification characteristics of saturated erbium-doped fiber amplifiers

Erbium-doped fiber amplifiers (EDFAs) are attractive for various optical fiber transmission systems and networks owing to their several advantages such as high gain and low noise. A EDFA with its high output saturation power and wide gain profile is specially suitable for wavelength-division multiplexing (WDM) applications such as multichannel CATV distribution systems [1]. In these applications, the EDFA is normally used as a post (or a booster) amplifier and operates at a saturated region. Although it has been demonstrated that the EDFA is immune to patterning effects and interchannel interference, and has low gain saturation induced crosstalk [2], [3], there is little information about effects of wavelength spacing and fiber length in a saturated EDFA for multichannel applications. In this paper, we report the experimental results on wavelength and fiber length dependence of gain for saturated EDFAs in a two-channel amplification system. The experimental results show that when an EDFA operates at the saturated region in a multichannel system, a shorter fiber length than that in single-channel should be selected to get a flat gain profile, and that the Ge/Al/Er-doped silica fiber is desirable for multichannel amplification use since a gain hole-burning is observed for the Ge/Er-doped silica fiber.