ly upward from the surface of the semiconductor; hence the name vertical-cavity laser. Vertical-cavity surface-emitting lasers (VCSELs) date to laboratory efforts during the mid-1980s. However, it wasn't until 1996 that Honey- well introduced a commercial VCSEL. The VCSEL emits light from the top surface of a semiconductor and can be mounted on top of a silicon photodiode integrated circuit, which reduces packaging cost. In compari- son, this level of packaging was not possible with the use of commonly available edge-emitting lasers. The first generation of VCSELs operate at 850 nm and are commonly used for gigabit transmission over multimode fiber at distances of a few hundred meters. Because transmission at longer distances is accomplished over single-mode fiber using 1310- or 1550-nm lasers operating in a trans- verse mode, which are several times more expensive than VCSELs, a sig- nificant amount of research is oriented toward the latter. More recent advances in VCSEL technology make it possible to manufacture this type of cost-effective laser in the 1300-nm operating range, and it is quite possi- ble that 1500-nm VCSEL lasers may be available in the future. VCSELs have several advantages over older semiconductor lasers, which emit light via their edges and are referred to as edge-emitting devices. Chapter Four Advantages of VCSELs include lower production cost, lower packaging cost, increased reliability, lower power requirements, and simplified fiber coupling. The lower production cost results in the ability of VCSELs to be processed in batches of thousands of units at the same time. In com- parison, edge-emitting lasers are created via a crystal-cleaving process that occurs either on an individual basis or on a row of devices. Although part of the production cost, packaging must also be consid- ered. Edge-emitting lasers are hermetically sealed, which adds to their production cost. In VCSELs, however, the active regions are buried sever- al micrometers beneath the VCSEL surface. This means that VCSELs have