From Optical Networking Best Practices Handbook

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 other non-WDM wavelength) [1].

There are two types of WDM systems in common use, providing coarse (CWDM) and dense (DWDM) granularity of wavelengths. CWDM systems typically provide up to 8 or 16 wavelengths, separated by 20 nm, from 1310 to 1630 nm. Some DWDM systems provide up to 144 wavelengths, typically with 2-nm spacing, roughly over the same range of wavelengths [1].

Products & Services
Fiber Optic Cables
Fiber optic cables are composed of one or more transparent optical fibers enclosed in protective coverings and strength members. Fiber optic cables are used to transmit "light" data.
Wavelength Division Multiplexers (WDM)
Wavelength division multiplexers (WDM) are devices that combine light signals with different wavelengths, coming from different fibers, onto a single fiber. They include dense wavelength division multiplexers (DWDM), devices that use optical (analog) multiplexing techniques to increase the carrying capacity of fiber networks beyond levels that can be accomplished via time division multiplexing (TDM).
Optical Add/Drop Multiplexers
Optical Add/Drop Multiplexers (OADMs) are used in wavelength-division multiplexing systems for multiplexing and routing fiber optic signals.
Optical Spectrum Analyzers
Optical spectrum analyzers (OSA) can divide a lightwave signal into its constituent wavelengths. This means that it is possible to see the spectral profile of the signal over a certain wavelength range.
Diode Lasers
Diode lasers use light-emitting diodes to produce stimulated emissions in the form of coherent light output. They are also known as laser diodes.

Topics of Interest

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Fiber systems usually carry multiple channels of data and multiple frequencies. Tunable laser diodes are used to create this wavelength division multiplexing (WDM) combination. The concept behind...

2.1 Wavelength Division Multiplexing: Basic Principles Telecommunications makes wide use of optical techniques in which the carrier wave belongs to the classical optical domain. The wave modulation...

Overview A powerful aspect of an optical communication link is that many different wavelengths selected from the spectral regions ranging from the O-band through the L-band can be sent along a single...

4.3 DWDM SYSTEMS AND NETWORK LAYERS DWDM systems are applicable to many network types and network layers. They are applicable to long-haul optical transport networks (OTN), backbone networks, large...

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