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Reflections and multiple Rayleigh backscattering in WDM single-fiber loopback access networks

: Arellano, C.; Langer, K.D.; Prat, J.


Journal of Lightwave Technology 27 (2009), Nr.1, S.12-18
ISSN: 0733-8724
Fraunhofer HHI ()
optical crosstalk; optical fibre losses; optical fibre subscriber loops; optical noise; rayleigh scattering; semiconductor optical amplifier; superradiance; wavelength division multiplexing

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.