PDF of this tutorialThe optimal placement of a PMDC in a network is directly prior to the receiver function of a transmission system. In long-haul and ultra long-haul multichannel optical systems, the receiver is usually located within the DWDM optical transmission equipment at the central office or point-of-presence (POP) site. There are two general types of DWDM transmission systems. Systems where the receiver function is within the DWDM network element are known as “open” DWDM systems (see Figure 12). In this example, the PMDC subsystem is located after the optical demultiplexing but before the receive transponders. Since the adaptive optic PMDC is an all-optical device, locating within the DWDM system is easy and straightforward.
Figure 12. PMDC Location in an "Open" DWDM System
Some older multichannel optical systems do not utilize transponders for the DWDM function; these systems are known as “closed” systems (see Figure 13).
Figure 13. PMDC Location in a "Closed" DWDM System
In these types of systems, the receiver function is located not within the DWDM network element but in a synchronous optical network (SONET) or synchronous digital hierarchy (SDH) network element, whose receiver mates up with the transmitter’s wavelength. In order to mate exactly, the DWDM network element and the SONET/SDH network elements must be manufactured by the same vendor, hence the term “closed.” In this example, the PMDC subsystem is located between the optical demultiplex stage of the DWDM system and the SONET/SDH element; again, since an adaptive optic PMDC is all-optical, it can also operate within a “closed” system.
