Communications theory analysis of multichannel carrier density intermodulation distortion effects in a semiconductor optical amplifier

It is shown that, for worst-case conditions, four-wave mixing effects in a traveling-wave semiconductor optical amplifier can result in the individual carriers experiencing different gains depending on channel separation, multiplex size, and channel position. It is also shown that the highest-frequency carrier experiences the lowest gain and that the position of the minimum gain never exceeds Delta omega tau /sub e/>1. For worst-case multichannel system design, it is anticipated that four-wave mixing effects will be negligible if normalized channel separations >or=10 Delta omega tau /sub e/ (of order >or=3 GHz) are used, and it is envisaged that, for practical gigabit/second frequency multiplexed coherent systems, this will be automatically satisfied.<>