The authors analyze the signal-to-noise ratio (SNR) at the photodetector output for a single-mode fiber optic digital transmission system including online optical amplifiers and an optical preamplifier. The effect of timing error on the performance of a direct detection PIN receiver is also studied. This allows an accurate design of the optical link in terms of the bit error rate desired (10-9 is required for optical communications). It is suggested that for a system with no timing error the signal-to-noise ratio at the photodetector output must be 21.6 dB. With timing uncertainty a higher SNR is necessary and, for a given value of ns, this allows the design of the link in terms of the gain or the optical amplifiers and their number in a more realistic way.

Peer Reviewed