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The research begins with an investigation of wavelength drift in Coarse Wavelength Division Multiplexing (CWDM) systems, especially in the context of temperature dependent wavelength drift. A simple model was proposed using a typical ‘application’ from ITU-T G.695. OptiSystem was chosen as the simulation platform due to its ease of use, the variety and flexibility of its inbuilt components and similar models simulated on the platform in the past. The research then investigates the measurement of wavelength drift focusing on how to determine an acceptable wavelength accuracy for a CWDM wavelength monitor. The chosen approach arose from observations of the results from a model of how wavelength drift impacts the most important system parameter in CWDM systems, which is error performance. The statistical confidence levels of Bit Error Ratio (BER) measurements taken by typical industry test and measurement equipment was considered and their statistical worst case BER results were calculated. An argument is made equating wavelength drift to an equivalent degradation of a links BER. Using the model developed a minimum wavelength accuracy of 0.1365 nm for the CWDM wavelength monitor was calculated. Following a survey of instruments marketed to the CWDM industry, a set of attributes that are representative of the different types of instruments available was made. These attributes were categorised into parameters and features. Each parameter and feature was considered in the context of a wavelength monitor for use in CWDM systems with a subsequent reclassification of the attributes into ‘essential features’ and ‘key parameters’, hence the attributes of a CWDM wavelength monitor were specified. An in-depth investigation of wavelength measurement operating principles was carried out with the aim of identifying a suitable technology to implement a CWDM wavelength monitor. The ratiometric wavelength measurement operating principle was chosen to implement a proof of principle CWDM wavelength monitor as it offers the best potential to meet the required specification with a least complex solution. The ratiometric wavelength measurement operating principle was discussed in more detail followed by an investigation of the maximum discrimination of the optical filter used in this technique. The limits on the maximum discrimination of the optical filter due to an optical sources wideband noise were then modelled with a proof of principle experiment carried out to validate the model.
Freir, T. (2017) Wavelength drift in CWDM systems: Impact and Measurement. Masters thesis, DIT, 2017.