Optical Networking Best Practices Handbook

3.1. LONG-WAVELENGTH VCSELS

Vertical cavity surface-emitting lasers emitting in the 850-nm wavelength regime are now key optical sources in optical communications. Presently, their main commercial applications are in local area networks (LANs) and storage area networks (SANs) using multimode optical fibers. The key VCSEL attributes that attracted applications are wafer-scale manufacturability and array fabrication. Given that fiber coupling is the bottleneck, there is very little prospect at the moment for two-dimensional (2-D) arrays. In spite of this, the advantages of one-dimensional (1-D) VCSEL arrays are still reasonably profound [2].

While the development of 850-nm VCSELs was very rapid, with major progress made from 1990 to 1995, applications took off after the establishment of Gigabit ethernet (GbE) standards in 1996. Being topologically compatible to LEDs, multimode 850-nm VCSELs became the most cost-effective upgrade in speed and power. This is a good example of an enabling application, as opposed to a replacement application [2].

A typical 850-nm VCSEL consists of two oppositely doped distributed Bragg reflectors (DBRs) with a cavity layer in between, as shown in Figure 3.4 [2]. There is an active region in the center of the cavity layer, consisting of multiple quantum wells (QWs). Current is injected into the active region via a current-guiding structure provided by either an oxide aperture or proton-implanted surroundings. Since the entire cavity can be grown with ...