Channel monitoring for optical WDM networks

Abstract

As in any other transmission systems, signals transported in optical WDM networks suffer from various kinds of distortions and impairments. Optical amplifiers give rise to amplified spontaneous emission (ASE) noise. Network components such as optical cross-connects (OXCs) and optical add-drop multiplexers (OADM) introduce both interband and intraband crosstalk. Different kinds of dispersion including chromatic dispersion, polarization mode dispersion (PDM) are limiting factors in today's longhaul transmission networks. In addition, fiber nonlinearities including self-phase modulation (SPM), cross-phase modulation (XPM) and four wave mixing (FWM) are harmful to the desired optical signals, since the signal transmission power is highly increased in today's high-speed optical transmission networks. In order to efficiently operate, manage and maintain optical networks, efficient optical monitoring techniques are highly desired. Bit error rate (BER) is a fundamental performance parameter for digital transmission systems. The conventional method uses error codes that are appended to the data frame to facilitate the measurement of BER. However, this method requires prior knowledge of the bit rate and coding format of the signal and it is not suitable for transparent optical networks because transparent optical network is capable to carry arbitrary data rates and protocols simultaneously. One promising solution for BER estimation in optical networks is to make use of optical signal's amplitude histograms.