herent natural properties of the optical devices and eliminates the need to artificially control the component characteristics. The following paragraphs identify typical CWDM optical elements: CWDM uncooled coaxial lasers. Distributed-feedback multiquantum well (DFB/MQW) lasers are often used in CWDM systems. These lasers typically come in 8 wavelengths and feature a 13-nm bandwidth. Wavelength drift is typically only 5 nm under normal office conditions (say, with a 50°C total temperature delta), making temperature compensation unnecessary. For additional cost savings, the lasers do not require external gratings or other filters to achieve CDWM operation. They are available with or without an integral isolator. CWDM transmitters/receivers. OC-48 CWDM transmitters typically use an uncooled DFB laser diode (LD) and are pigtailed devices in a standard 24-pin dual inline package (DIP). Six to 8 channels are supported Coarse Wavelength Division Multiplexing (CWDM) Technology (6 channels are located at 1,510 to 1,610 nm, and 2 additional channels are located at 1,470 and at 1,490 nm). The OC-48 receiver typically uses an avalanche photodetector diode (APD) photodetector, has a built-in DC-DC converter, and employs a phase-locked loop (PLL) for clock recovery. Transmission distances of up to 50 km are achievable with these modules. CWDM wavelength division multiplexers/demultiplexers. In four- or eight-channel modules, you would typically use thin-film filters optimized for CWDM applications, with filtering bands matched to the CWDM wavelengths. Filters need to feature low insertion loss and high isolation between adjacent channels. CWDM optical add/drop modules (OADMs). These are available in various configurations with one, two, or four add/drop channels using the same thin-film filters as the CWDM mux and demux modules. 6.2 CWDM Systems CWDM³ technology was first commercially deployed in the early 1980s for transporting digital video signals over multimode fiber. Quante Corporation marketed a 4-wavelength system that