Optical beat noise suppression and power equalization in subcarrier multiple access passive optical networks by downstream feedback

This paper describes a cost-effective method of suppressing optical beat noise in subcarrier multiple access passive optical networks. The method is based on initial power equalization followed by automatic fine tuning of laser wavelengths, via downstream feedback control of their mean powers, so that the receiver noise floor level is continuously minimized. Application and performance of the method is demonstrated for a low-cost 16-channel system with uncooled Fabry-Perot lasers, utilizing narrow-band QPSK modulated subcarrier frequencies over more than one octave. In static and dynamic temperature worst-case situations a considerable reduction in the number of transmission errors caused by optical beat noise is observed, depending on the temperature change rate.