ABSTRACT
References ...........................................................................................................90
With the need for greater capacity of optical communication systems, wavelength division multiplexing (WDM) technology was developed. WDM basically puts multiple signals on a single fiber, each one represented by a different wavelength. While early systems utilized two or three wavelengths with relatively wide separation, we would today characterize those as wide wavelength division multiplexing (WWDM) systems, and primarily they employed dual window (Fused Biconic Taper) FBT couplers. These devices typically operated in the range of 810/870/1310 nm or 1310/1550 nm, with light sources such as Fabry Perot (FP) lasers or light emitting diodes (LEDs) operating at those wavelengths. Those early systems [1] eventually evolved in what we today know as coarse wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM) systems. While DWDM is the technology of choice for long-haul or ultra long-haul (ULH) applications across the network backbones, in metro applications CWDM rapidly filled the gap between DWDM and WWDM systems, yet less expensive and complex than DWDM. Today, CWDM is becoming more widely accepted as an important transport architecture, where up to 18 wavelengths are available for transmitting information over a fiber link in metro or access networks.
