Optical Networking Best Practices Handbook

Chapter 9. Wave Division Multiplexing

Wave division multiplexing (WDM) describes the concept of combining several streams of data onto the same physical fiber-optic cabling. This capacity increase is achieved by relying on one of the fundamental principles of physics. Different wavelengths of light do not interfere. The main idea is to use several different wavelengths (or frequencies) of light, with each carrying a different stream of data [1].

This feat is accomplished via several components. First, the transmitted data must be sent on a particular carrier wavelength. Typical fiber-optic systems use three distinct wavelengths: 850, 1310, and 1550 nm. If the signal is already optical, at one of these wavelengths, it must be converted into a wavelength within the WDM spectrum. Typically, several independent signals will each be converted into a separate carrier wavelength within the spectrum. These signals then are combined via an optical combiner (basically, a carefully constructed piece of glass) such that most of the power of all the signals is transferred onto a single fiber. On the other end, the light is split into many channels using a splitter (another carefully constructed piece of glass). Each of these channels is passed through a filter to select only the particular wavelength of interest. Finally, each filtered wavelength is sent to a separate receiver, sometimes located on different devices, where it is converted back into the original format (either copper, or some ...