Frequency detuning effects in a loop-back WDM-PON employing gain-saturated RSOAs

We report that, in a loop-back wavelength-division-multiplexed passive optical network link with gain-saturated reflective semiconductor optical amplifiers, the upstream performance is strongly affected not only by the gain saturation but also by the selective spectral filtering caused by the frequency difference between the optical downstream signal and the cascaded filter's passband. We experimentally investigate these effects and propose to use an additional negatively detuned optical filter at an optical network terminal to improve the upstream transmission performance.