MODEL FOR BIDIRECTIONAL TRANSMISSION IN AN OPEN CASCADE OF OPTICAL AMPLIFIERS

derive a model for signal propagation and the generation and propagati on of amplified spontaneous emission (ASE) in a completely open bidire ctional cascade of optical amplifiers, The effect of single Rayleigh s cattering of both signal and ASE is included, Our model predicts and o ur experiments substantially verify that the dominant gain saturating mechanism is the Rayleigh backscattered ASE centered around the 1535 n m peak in the ASE spectrum and that the spectral shape of the output A SE becomes much more sharply peaked around the 1535 nm gain peak, In a n experimental open cascade of three EDFA's the ASE spectral density a t the 1535 nm gain peak is increased by as much as 8-9 dB, resulting i n gain compression ranging from 1-2 dB near 1550 nm to as much as 3-5 dB nearer 1538 nm, This combined with multiple Rayleigh scattering of the ASE around our 1538 and 1540 nm signal wavelengths results in Rayl eigh scattering induced reductions of the optical signal to ASE ratio of 1-2 dB at the output of the first amplifier increasing to 3-5 dB at the output of the third amplifier each signal traverses.