Optical System Performance Evaluation Based on Required OSNR 615 5.8.3 Measurement of R-OSNR Due to Optical Filter Misalignment The complex transfer functions of optical devices such as optical filters, add/ drop multiplexers, and narrowband dispersion compensators are important parameters that have significant impact in system performance. Techniques to measure individual optical components were discussed in the previous chapters. However, their impact in the transmission performance depends on system con- figurations, modulation formats, and the combination with other system build- ing blocks. Therefore a relevent measurement of optical device performance and its impact on an optical system is to place the device into the system. The change of R-OSNR introduced by this particular device can be measured as an indica- tion of the device quality. Figure 5.8.11 shows the schematic diagram of an experimental setup to char- acterize the impact of a wavelength-selective switch (WSS) in an optical transmis- sion system. Noise loading technique is used to evaluate the R-OSNR degradation due to the optical device under test. In this measurement, a tunable transmitter is used whose optical wavelength can be continuously tuned. The WSS is placed in a recirculating loop, in which 80 km of standard single-mode fiber is used with two optical amplifiers to compensate for the loss and a disper- sion compensator reduces the accumulated dispersion. An optical recirculating