The demand for faster data-transmission rates has led to considerable interest in developing high-capacity optical data links for short-haul local-area network and fiber-to-the-desktop applications. Most of the work done so far has focused on one-dimensional parallel optical data links that utilize multimode fiber ribbons with the one-data-channel-per-fiber arrangement. Even with a very complicated system configuration this results in a maximum aggregate data-transmission rate of only 2-3 gigabytes per second (Gb/s). The transmission capacity can be significantly expanded by using a wavelength-division multiplexing (WDM) configuration, which allows multiple data channels in each fiber. For this system to be commercially viable the corresponding transmitter and receiver modules must be low cost.

The new WDM structure and packaging system offers the following benefits:

• Multiple-channel VCSEL/RCPD links can be packaged in the same manner as a single-channel data link without resorting to complicated waveguide-coupling optics. This substantially reduces manufacturing costs;
  
• The overall system capacity can be multiplied by combining several of the direct-coupled WDM links in parallel into a fiber ribbon cable.
  

These WDM data links are ideal for high-capacity (a few Gb/s to 100 Gb/s) local-area network and fiber-to-the-desktop applications. The availability of such multiple-wavelength emitter and detector arrays is also a key issue for the realization of ultra-high-density multiple-layer digital versatile disk (DVD) technology.

Scientists at the University of California have developed a novel device structure and simple packaging scheme for low-cost high-performance multimode WDM optical data links. These links consist of monolithically integrated multiple-channel vertical-cavity surface-emitting laser (VCSEL) and narrow-band resonant-cavity photodetector (RCPD) arrays with their emitting or photon-collecting elements closely packed within a small 60-micrometer-diameter area.