ayers for a 100-GHz filter design used in DWDM systems, whereas there are approximately 50 layers in a 20-nm CWDM filter. The result is higher manufacturing yields for CWDM filters (see Figure 6-6). The CWDM filter costs about 50 percent less than the DWDM filter, and the cost is projected to drop by a factor of three in the next two to three years as automated manufacturing takes hold. The adoption of new filter and multiplexing/ demultiplexing technologies is expected to decrease costs even further. 6.2.2 Lower-Power Requirements The operating costs of optical transport systems depend on maintenance and power. Although maintenance costs are assumed to be comparable for both CWDM and DWDM systems, the power requirements for DWDM are significantly higher. For example, DWDM lasers are temperature-stabilized with Peltier coolers integrated into their module package. The cooler along Chapter 6 Figure 6-6 CWDM filter designs. Three-port device Dual Fiber Input Port GRIN Lens GRIN Lens Pass Port Reflected Port Single Fiber Thin Film Filter Coarse WDM (CWDM) filter designs use fewer layers, and the alignment tolerances are relaxed relative to those for DWDM devices, which significantly lowers the manufacturing costs of the CWDM devices. with the associated monitor and control circuitry consumes around 4 watts per wavelength. Meanwhile, an uncooled CWDM laser transmitter uses about 0.5 watts of power. The transmitters in an 8-channel CWDM system consume approximately 4 watts of power, while the same functionality in a DWDM system can consume up to 30 watts. As the number of wavelengths in DWDM systems and transmission speeds increases, power and the ther- mal management associated with them become a critical issue for board designers. The lower-power requirement resulting from the use of uncooled lasers in CWDM systems has positive financial implications for system operators. For example, the cost of battery backup is a major consideration in the operation of transport equipment. Minimizing operating power and the costs