Effect of fiber-far-end reflections on the bit error rate in optical communication with single-frequency semiconductor lasers.

For a semiconductor laser oscillating in a single longitudinal mode, the reflection feedback from the far end of an optical fiber generates closely spaced side modes corresponding to the external-cavity longitudinal modes. Using a simple model, it is shown that power fluctuations associated with these feedback- induced side modes significantly decrease the receiver sensitivity over its shot-noise-limited value for a given bit error rate. A typical value of the penalty in receiver sensitivity is estimated to be 2 dB although higher values are not ruled out.