2ND-ORDER DISTORTION IMPROVEMENTS OR DEGRADATIONS BROUGHT BY ERBIUM-DOPED FIBER AMPLIFIERS IN ANALOG LINKS USING DIRECTLY MODULATED LASERS

Within lightwave analog amplitude-modulated (AM) CATV systems using directly modulated lasers, erbium-doped fiber amplifiers (EDFA's) act upon the signal distortion because of the interaction between the laser chirp and the EDFA wave-length-dependent gain. This interaction is theoretically investigated in order to predict the EDFA-induced distortion. The relevant gain tilt characteristic for analog applications and the way to measure it are described. Expected and measured distortions at the EDFA output are in excellent agreement. Fiber amplifiers are found to decrease the signal distortion level when the gain tilt is negative, i.e., for wavelength above the gain maximum.