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Principal Sponsors:
 | Dense Wavelength Division Multiplexing (DWDM) Testing |
1. The Need for New Testing Tools
Although both designing and implementing DWDM systems calls for considerably more care than has been needed for conventional systems, by and large, the skill and capability necessary has increased to a degree: existing knowledge bases and facilities, with some additional training and upgraded instrumentation, will meet the challenges that the new technology presents. However, the same cannot be said for field testing. New parameters must be measured, and component characteristics once of interest only before installation must now be verified regularly. In addition, accuracy and stability requirements reach new levels, and an entirely new dimension—wavelength—must be considered. Field test equipment suitable for troubleshooting in single-wavelength systems cannot cope with these needs. New instrumentation is urgently required.
Testing and troubleshooting single-wavelength systems in the field can be accomplished by monitoring a few well-defined parameters. For example, optical power loss, or attenuation, has always been a key factor in the performance of fiber-optic links, and portable optical loss test sets have been developed to measure this loss in the field. Instruments with optical time domain reflectometric capabilities have been developed to locate faulty elements in a link. As system sophistication has grown, so has the significance of optical return loss, especially in the CATV field, where source-laser instability caused by reflected energy can have serious effects on signal quality. Field instrumentation has been developed to monitor this parameter as well. All this test equipment is still required in the dense WDM environment—but with characteristics adapted to the much more stringent needs of wavelength division systems.
In the fiber itself, both chromatic and polarization mode dispersion spread signal pulses and set limits on the transmission capacity, and their effects may be severe on the transmission signal integrity. New instrumentation capabilities may be needed to identify the sources of these disturbing influences and ensure that they do not adversely affect performance.
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