Abstract

We study the information capacity and the spectral efficiency of communication systems with optical amplifiers, in the direct detection intensity modulation case. We show that with typical values of OSNR of the order of 20dB, multilevel signaling can increase the spectral efficiency by no more than a factor of 3.5 relative to binary modulated systems. The highest spectral efficiency is obtained with a symmetric optical spectrum, and it cannot be improved by removing one sideband as in the single sideband modulation case.

© 2001 Optical Society of America