is an interworking standard developed in the late 1980s and early 1990s to define data rates, optical characteristics, and operations protocols over a data communications channel for support of multivendor optical transmission. This technology is explored in Chapter 3, "Traditional SONET Architecture," but common data rates are shown in Table 2-7. WDM is a multiplexing technology. Optical multiplexers aggregate mul- tiple lambdas onto a single waveguide (in this case, the fiber). Demulti- plexers separate the combined signal into individual lambdas and output ports/fibers. Three basic categories of multiplexers are star couplers, thin- film filters, and phased array (see Figure 2-31). A star coupler is an all-fiber technology that is inexpensive and robust, but suffers from high signal loss. Typically, it is used for low-count systems. Thin-film filters are manufac- tured according to well-known semiconductor processes. They are a robust and proven technology that enables the network designer to pay as one scales. This technology can be used up to about 40 lambdas. A planar array waveguide is a silicon semiconductor technology that is robust and proven. This technology can be used for midrange systems (16 to 40 lambdas); it is cheaper on a per-channel basis than thin-film filters, but users must pay for the entire capability (the wafer) up front. Other technologies used in WDM include bulk gratings, fiber Bragg gratings (FBGs), Mach-Zehnder struc- tures, and a combination of Mach-Zehnder structures and FBGs. (Thin-film filters, FBGs, and array waveguides are discussed in greater detail in the following section.) Table 2-7 Siglum Data Rate (Mbps) Common Data Rates OC-1/STS-1 51.84 OC-3/STS-3/STM-1 155.52 OC-12/STS-12/STM-4 622.08 OC-48/STS-48/STM-16 2,488.32 OC-192/STS-192/STM-64 9,953.28 OC-768/STS-768/STM-256 39,813.12 Chapter 2 Multiplexer Demultiplexer Figure 2-31 Multiplexing 1 x n technologies. Top: Coupler Fiber Coupler Star coupler. Center: Thin film. Bottom: Arrayed waveguide. Multiplexer Demultiplexer 4.