PDF of this tutorialPhotonic networks are based upon a combination of electrical and optical components and transmission media that allow the delivery of multiple channels of data over any given fiber in the core or backbone network. Channel multiplexing is achieved either by means of time division multiplexing (TDM) or by sending multiple channels (at different wavelengths, or colors) of light over each fiber. This latter approach is known as DWDM. By adopting either multiplexing approach, operators can cost-effectively add capacity.
But these new approaches come at a price. While multiple-wavelength all-optical systems actually make networks simpler operationally, they become extremely complex technologically. The thousands of components that make up multiple wavelength systems must perform in a very precise and exacting manner, while operating in conjunction with many other components. And the entire assemblage must be adjusted and tuned for optimal network performance.
As a consequence, test and measurement technology plays a key role in both the development and the deployment of photonic networks. Laser wavelengths, for example, now need to be measured with better than 0.01 nm accuracy. Aging studies of semiconductor lasers require wavelength resolutions of 0.001 nm. High dynamic range measurements are required to verify that the wavelength demultiplexer at the receiver is accurately separating the desired signal from adjacent channels, and that any cross-talk between channels (introduced through fiber nonlinearities) is not causing power from one channel to be transferred into another.
The simple power measurements used to find fault conditions in single wavelength systems are not sufficient for using in measuring parameters of multiple wavelength systems. Spectral monitors are now necessary to evaluate the performance (wavelength, channel power, signal-to-noise ratio, etc.) of each channel in DWDM systems.
In short, equipment manufacturers need the most advanced test and measurement tools available to accurately characterize every component and network element during product development, manufacturing, and system test; and network operators need those same advanced tools to verify system performance (and standards conformance) before deployment.
Finally, as the number of competitive carriers increases, the issue of interoperability becomes a more and more important concern. Photonic networks of the future will need to carry traffic from many different sources. Conformance with telecommunications standards will be essential.
In such a challenging environment, advanced test and measurement capabilities serve as enabling technologies, not just functions performed after a network has been deployed.
