POWER PENALTIES DUE TO BRILLOUIN AND RAYLEIGH-SCATTERING IN A BIDIRECTIONAL COHERENT TRANSMISSION-SYSTEM

In case of a large number of channels and a limited available optical bandwidth (limited laser tuning range) it may be necessary to chose a channel spacing near 0 or 11 GHz, where Rayleigh-and Brillouin backsca ttering introduce crosstalk in a bidirectional system. Although there is much literature on stimulated Brillouin scattering, that occurs at high powers, there is hardly any attention paid to what happens at rel atively low input powers. Furthermore there are no system measurements which thoroughly investigate these effects. We performed extensive bi directional system experiments to investigate the crosstalk from Brill ouin scattering in more detail, including its polarization properties. We found, that, while for high powers most of the energy is backscatt ered to a 11 GHz lower frequency, for low powers there is no differenc e for the crosstalks at 11 GHz higher or 11 GHz lower than the signal frequency. The power budget is limited to 40 dB for both cases. The pr edicted 33.3% degree of polarization of low-power Brillouin scattering is experimentally confirmed for the first time.