Observation of equivalent Rayleigh scattering mirrors in lightwave systems with optical amplifiers

Experimental and theoretical studies that indicate that Rayleigh scattering acts as an equivalent mirror which can generate high levels of multiple reflection noise in lightwave systems employing optical amplifiers are discussed. The relative intensity noise can be calculated as a simple function of the amplifier gain and the ratio of total backscattered to incident power in the fibers. In high-speed digital systems, this noise limits the maximum usable repeater gain to less than 20 dB, unless optical isolators are employed.<>