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Verwertbare Ergebnisse
Summary : The bit-error probability (BEP) is the most relevant signal-performance criterion of digital transmission systems. In transparent (i.e. no regeneration on bit level) optical networks not all optical nodes will contain the resources for bit-error counting of high-speed signals, e.g. at 10Gbit/s or more.
A possible approach to estimate the bit-error probability of an optical signal utilizes the information contained in the amplitude histogram of the signal to be investigated. Such a histogram may be obtained using an oscilloscope operating in either synchronous mode (triggered) or asynchronous mode (not triggered by the data bits).
Summary : The optical signal-to-noise ratio (OSNR) is an important quality characteristic in optically amplified transmission systems. In optically amplified wavelength division multiplex (WDM) point-to-point links, the measurement of the noise level in the optical regime (caused by amplified spontaneous emission (ASE)) is usually performed at some frequency offset at both sides off the carrier using, e.g., an optical spectrum analyzer. The determination of the noise level at the carrier frequency is then done by linear interpolation.
In WDM networks, however, a channel signal may pass many WDM filters. The above mentioned method is no longer applicable in WDM end-to-end links because of the filter action on the ASE spectrum. Our method to determine the noise level uses polarization extinction. It thus becomes compatible with WDM networks. Measurement setups based on this technique could be used in every optically transparent optical network node for the purpose of optical signal supervision.
Summary : The result obtained is a measurement technique suitable for an Optical Signal Supervision System of an All-Optical Network. The measurable effect is the Coherent Homowavelength Cross-talk (C-HOC).
Two different methods to monitor and measure C-HOC by means of an Electrical Spectrum Analyzer have been devised during MOON project duration. The measured parameters are cross-talk level and the relative time delay of the interfering path with respect to the main one. The measurement of the time delay allows for the identification of the interfering path. This methodology poses one condition to the optical node architecture which is that every path between input and output must have different lengths.
The first method uses non-modulated lasers (usually local equipment) as a source signal to perform such measurement. The maximum of the detected Power Spectral Density without the dc term gives information of the cross-talk level whereas the first relative minimum gives information about the relative delay of the interferent path. This measuring method of C-HOC is suitable for the implementation stage of a network node or during its maintenance procedures. Using this methodology it is possible to measure very low cross-talk levels with the only limitation of the Analyzer sensitivity.
The second method studies the detected Power Spectral Density (psd) for real traffic signals. When there exist a coherent cross-talk component, the detected psd is modified from where cross-talk parameters can be deduced. When the cross-talk level is high it is possible to deduce its parameters directly from the psd. When it is low, then some signal processing to the detected psd trace must be applied in order to deduce cross-talk parameters. This is a non-intrusive measurement and therefore it is suitable to be performed during in-service stage. It can assess the Manager about degradation of optical signals due to components malfunction of an optical node.
In both methods, analytical, simulation and experimental studies have been carried out.
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