Wavelength division multiplexing: ultra high speed fiber optics

The global telecommunications and networking backbone contains millions of kilometers of fiber-optic cabling, but we use only one ten-thousandth of the potential bandwidth of those cables. One reason is that a single converter from electrical to optical signals can only make use of a small amount of the optical spectrum, limiting the achievable bandwidth to about 2.5 Gbit/s. Wavelength division multiplexing (WDM) helps to resolve this disparity. WDM takes advantage of the fact that multiple wavelengths (or frequencies) of IR light can be transmitted simultaneously down a single optical fiber, and each of those frequency channels can carry independent information. With the use of WDM, the capacity of a single strand of fiber, 250 microns in diameter, can carry between 10 and 80 Gbps; a typical cable of 18 mm in diameter contains up to 200 fibers