OADM Chapter 2 Figure 2-51 OADM. Optical Add/Drop Module 1 1, 2, 3, X 1 1, 2, 3, y. Circulator Circulator Drop 1x Add 1y between two end terminals along any route can replace an optical amplifier. Commercially available modules enable carriers to drop or add up to four STM-16/OC-48 channels between DWDM terminals. OADMs enable cer- tain wavelengths to pass through the node uninterrupted and also have broadcast capabilities for dropping information on several channels (typi- cally four) to become express channels. Optical add/drop is well suited for meshed or branched network configurations as well as for ring architec- tures used to enhance survivability. OADMs are reasonably inexpensive and, in particular, are cheaper than electronic ADMs. Fixed-lambda systems are mature and widely deployed; configurable-lambda systems are maturing rapidly. Configurable-lambda systems are tapped for use in the IONs discussed in Chapter 7. 2.9.6 Optical Crossconnects (OXCs) Many current-generation optical networks use OXCs. Figure 2-52 depicts OXC system functionality. OXCs are capable of interconnecting multiple DWDM systems (for example, Terminals A, B, and C in Figure 2-53) and switching optical channels in and out of DWDMs without having to convert the signal into a lower-speed electrical signal. OXCs also facilitate inter- connections between the DWDM systems and Internet Protocol (IP) routers, SONET/SDH multiplexers, and Asynchronous Transfer Mode (ATM) switches. Their deployment is critical to all-optical networks, not just because they support higher bandwidth, but because they also support more sophisticated network designs. For example, OXCs can perform tra- ditional SONET/SDH functions (such as restoration, signaling, perfor- Optics Primer Figure 2-52 OXC function. Micro-electrical systems (2D and 3D MEMs) Thermo-optic Opto-mechanical Bubble jet Figure 2-53 Optical Cross Connect OXC example. Terminal A Input Input Input Terminal C Terminal B SONET Switch mance monitoring, fault management, and multiplexing). Putting th