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Principal Sponsors:
 | Dense Wavelength Division Multiplexing (DWDM) Testing |
9. Field Testing DWDM Systems
As previously indicated, the implementation of DWDM transmission systems in the field on a large scale will have a major impact on each level of installation and system verification. New skills must be developed to face these new challenges, and existing test instrumentation will require adaptation. Nevertheless, one instrument emerges as the apparent reference DWDM system characterization tool: the optical spectrum analyzer.
The optical spectrum analyzer is eminently suited to almost all of the field testing needed in DWDM systems: measurements of signal levels, signal-to-noise ratio, and crosstalk as well as channel spacing and stability. The graphic presentation of modern OSA instruments, clearly showing how the parameter of interest varies with wavelength, gives an excellent overview of many of the phenomena crucial to the proper operation of DWDM networks and valuable clues for the subsequent investigation of any problems that the measurement might reveal. Nevertheless, in many contexts it offers too much information and often not the specific information the field maintainer or troubleshooter needs. Operating and readout procedures and tools must be greatly simplified from those appropriate to laboratory OSAs if the instrument is to be cost-effective in the field (see Figure 13).
However, to complement OSA testing in the field, center wavelengths must be accurately measured. This parameter can be important, especially if the system under study is part of a larger one with standards that must be respected. Other instrumentation offering more accurate wavelength calibration—a wavelength meter, most likely—is also needed for such operations as the measurement of DFB characteristics.
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