Finally, the functionality offered by the structure of Figure 17.23, and more, can be
implemented in principle using cascaded integrated-optics variable delay lines [92].
In summary, while recent year s have seen major progress in the generation/
emulation of PMD, with fairly low values of insertion loss (1 dB) and PDL
(0.5 dB), a fully satisfying solution has not yet emerged. Multisection emulators
have a single built-in mean DGD and are not repeatable; PMD sources stably
emulate only a few low orders of PMD and thus do not faithfully represent higher
orders of real fibers, and variable DGD implementations, while very flexible, need
increases in scale (number of sections), stability, and repeatability, before becom-
ing universal emulators. For