Abstract

Performance degradation due to Fresnel reflections (for connectors, splicers, and passive components) and Rayleigh backscattering, is an important consideration in optical fiber telecommunication systems incorporation erbium-doped fiber amplifiers (EDFAs). It is generally accepted that, to eliminate the possibility of laser action and interferometric interference due to Fresnel reflectors on either side of the EDFA, an optical isolator (OI) should be located at either the input or the output of every EDFA.^1-5 Furthermore, in receiver preamplifier applications, an OI at the input to the EDFA can yield substantial improvement in receiver sensitivity by preventing backward propagating ASE (B-ASE) from entering the transmission fiber and thus contributing to the forward propagating ASE (F-ASE) through reamplification of the backscattered component.⁴ In this paper, we experimentally examine the influence of reflections on EDFA gain and the F-ASE spectrum, and thus determine the relative advantages that may be gained by locating an OI at either the input or the output of an EDFA. Our results indicate that, when optical reflections are of the order the amplifier gain, locating an OI at the input yields at least 3 dB more improvement in the noise figure than locating one at the output.

© 1992 Optical Society of America