The optical gain of reflective optical network units (ONUs) may produce a critical amplifying feedback on the single-fiber transmission impairments. In this paper, its influence on the passive optical networks transmission with reflective-ONU is theoretically analyzed and experimentally confirmed. Analytical expressions for the optical crosstalk-to-signal ratio and the $Q$-parameter in presence of Rayleigh backscattering, reflection interferences and ASE noise are given. As a resulting design guideline, the ONU gain should be adjusted to about 3 dB below the total link loss; in addition, component return loss at the drop section must be higher than 30 dB. Experimental results with two basic types of reflective-ONUs, namely a loop structure formed by a Mach–Zehnder modulator and an optical amplifier, and another one employing a reflective-SOA, are in agreement with the theoretical approach.
© 2009 IEEE
Cristina Arellano, Klau-Dieter Langer, and Josep Prat, "Reflections and Multiple Rayleigh Backscattering in WDM Single-Fiber Loopback Access Networks," J. Lightwave Technol. 27, 12-18 (2009)