stems evolving to 800 Gbps. Near-term projections are in the terabit per second range. You can also observe DWDM channel growth. Although the current upper range is OC-192 (10 Gbps), the near-term pro- jected upper range is OC-768 (40 Gbps). The availability of mature sup- porting technologies, such as precise demultiplexers and erbium-doped fiber amplifiers (EDFAs), has enabled DWDM with 8, 16, and even higher channel counts to be commercially delivered. DWDM systems have been used extensively in the long-haul space and typically cost from $100,000 to $1 million or more. There are active and passive elements in a DWDM system. Figure 1-20 illustrates the active and passive components that comprise a DWDM sys- tem. Active components create the optical signals (wavelengths of light) that travel throughout the fiber-optic network. Passive components manip- ulate and guide light along the fiber. Transmitter modules (TxM) are responsible for sending input signals, whereas receiver modules (RxM) are responsible for receiving output sig- nals. Each wavelength enters and leaves the DWDM system separately through TxM and RxM. As indicated in Figure 1-21, TxM and RxM consist of passive and active components. The passive components (isolators, cou- plers, attenuators, detectors, and DWDM mux and demux components) are used to route and guide the wavelengths through the network. The active components (modulators, transmission lasers, and wavelength lockers) are used to create, modulate, or amplify the wavelengths. TxMs and RxMs can Figure 1-20 Dense Wave Division Multiplexing Active and passive components of a Multiplexer Demultiplexer DWDM system. 1,2,3,X 1,2,3,Y. Optical Optical Amplifier Amplifier Optical Add/Drop Transmitters Receivers Chapter 1 Figure 1-21 Transmitters and Receivers Transmitter and receiver components Components Components of a DWDM system. Attenuator Attenuator DWDM Mux Detector Coupler Coupler Isolator DWDM Demux Modulator Transmission Laser Wavelength Locker Transmitters Receivers Figure 1-22 Multiple