 8 VoT1 DSL SONET Opt MM Opt SM cost of producing less-precise components (such as lasers, filters, and so on) has fallen as yields have improved. This topic is covered in more detail in Chapter 6, "Coarse Wavelength Division Multiplexing (CWDM) Technology." Vertical Cavity Surface-Emitting Laser (VCSEL) With current technology, lasers used in networking systems emit the signal from the edge of the diode. A substantial amount of research is currently under way to develop lasers that emit the signal from the surface of the diode. VCSELs have been around for quite a number of years, but engineering and cost improvements are still being sought. The main feature of VCSELs that makes them potentially cheaper than edge-emitting lasers is that an entire wafer can be tested without dicing it into individual diodes. Currently, edge-emitting lasers for communication applications are expensive, around $1,000 each. In addition, the packaging process with VCSELs is less complicated and therefore less costly. VCSELs have the potential to cost much less, provided that they can be produced at the appropriate communication wavelengths. Currently, most VCSELs operate at 840- and 980-nm wavelengths. The cost of the individual 840-nm VCSEL is in the $2 to $20 range. These VCSELs are used in data communication applications for intracomputer and intercomputer communication systems that have distances in the 10-m range. VCSELs in the 980-nm range are not currently used because their emission straggles several wavelengths, making transmission problematic. Dense Wavelength Division Multiplexing (DWDM) Systems The key issue VCSEL developers are grappling with is the output power that a VCSEL emits at a single wavelength, the so-called single- mode VCSEL. The output power of these VCSELs is in the 1- to 4-milliwatt range, which is far below that of edge-emitting lasers (edge- emitting lasers currently provide power in the hundreds of milliwatts). Clearly, the gap between VCSEL and edge-emitting products is large, but the power requirements