High-performance amplified optical links without isolators or bandpass filters

Using a simple analysis of saturated amplifier cascades, the authors examine the consequences of removing optical bandpass filters and/or isolators, while still relying on saturation effects to provide automatic power control. The authors find that optical bandpass filters can be removed at only a modest cost in system performance. Moreover, isolators can also be removed or reduced in number, so long as reflection-induced degradations permit. When isolators are removed or reduced in number, backward-traveling spontaneous emission plays a significant role, via saturation effects, in the regulation of optical signal power.<>