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Principal Sponsors:
 | Dense Wavelength Division Multiplexing (DWDM) Testing |
3. Parameters to Be Measured in the Field
The core measurement capabilities needed in the spectral domain include the following:
- channel power—One must be able to measure the optical power in each channel to verify the equal distribution of power over the bandwidth of the optical amplifiers (EDFAs) that are used in the link (i.e., to measure the spectral uniformity of the optical power).
- channel center wavelength and spacing—The precise value of the center wavelength of each channel must be measured in order to detect unacceptable drifts in DFB laser sources.
- signal-to-noise ratio—This is one of the most important parameters to be measured for each channel in a DWDM system, as it is the best indicator of the overall performance of the channel. The noise measurement it incorporates must be based on measurements of the noise floor between channels.
- crosstalk—This parameter reveals the level of unwanted signal (noise plus contribution from other channels) in the passband of the tested channel. It is awkward to incorporate its measurement into field tests because it is a two-step operation, but it can be critical.
- total optical power—Because adverse effects of nonlinear phenomena in the optical fiber depend on the total power carried, the parameter must be measured or calculated by summing the individual channel powers.
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