Fiber Optic Glossary: W, X, Y, Z

W: Abbreviation for Watt. A linear measurement of optical power, usually expressed in milliwatts, microwatts, and nanowatts.
WAN: See Wide Area Network.
Waveguide: A material medium that confines and guides a propagating electromagnetic wave. In the microwave regime, a waveguide normally consists of a hollow metallic conductor, generally rectangular, elliptical, or circular in cross-section. This type of waveguide may, under certain conditions, contain a solid or gaseous dielectric material. In the optical regime, a waveguide used as a long transmission line consists of a solid dielectric filament (fiber), usually circular in cross-section. In integrated optical circuits an optical waveguide may consist of a thin dielectric film. In the RF regime, ionized layers of the stratosphere and the refractive surfaces of the troposphere may also serve as a waveguide.
Waveguide Coupler: A coupler in which light gets transferred between planar waveguides.
Waveguide Dispersion: The part of chromatic dispersion arising from the different speeds light travels in the core and cladding of a single-mode fiber (i.e., from the fiber’s waveguide structure).
Wavelength: The distance between points of corresponding phase of two consecutive cycles of a wave. The wavelength relates to the propagation velocity, and the frequency, by:	Wavelength = Propagation Velocity / Frequency
Wavelength Converter: A device which receives one wavelength and outputs a second wavelength, usually to take a standard signal and convert it to an ITU wavelength.
Wavelength-division Multiplexing (WDM): Sending several signals through one fiber with different wavelengths of light.
Wavelength Isolation: A WDM’s isolation of a light signal in the desired optical channel from the unwanted optical channels. Also called far-end crosstalk.
Wavelength Routing Switch (WRS): A switch, used in optical networks, that routes wavelengths as required to specific terminals in the network.
Wavelength Selective Coupler: A device which couples the pump laser wavelength to the optical fiber while filtering out all other unwanted wavelengths. Used in erbium-doped fiber amplifiers.
Wavelength Stability: The maximum deviation of the peak wavelength of an optical source from its average wavelength.
WDM: See wavelength-division multiplexing.
Weather Fade: In satellite systems, the loss of a satellite signal due to extremely heavy (and generally very localized) rain, snow, or other extreme weather.
Wide Area Network (WAN): A physical or logical network that provides capabilities for a number of independent devices to communicate with each other over a common transmission-interconnected topology in geographic areas larger than those served by local area networks or metropolitan area networks.
Wideband: Possessing large bandwidth.
Wireless: A network or terminal that uses electromagnetic waves, such as RF, infrared, laser, visible light, and acoustic energy, not wires, for telecommunications.
WWW (World Wide Web) : The collection of millions of graphical pages that heavily utilize HTML to provide access to information. One of the key components of the Internet.

X-Band: The frequency range between 8.0 and 8.4 GHz.
XC: See cross-connect.
XGM: See cross-gain modulation.
XPM: See cross-phase modulation.
X-Series Recommendations: Sets of data telecommunications protocols and interfaces defined by the ITU.
XT: See crosstalk.
Y Coupler: A variation on the tee coupler in which input light is split between two channels (typically planar waveguide) that branch out like a Y from the input.

Zero-dispersion Slope: In single-mode fiber, the rate of change of dispersion with respect to wavelength, at the fiber’s zero-dispersion wavelength.
Zero-dispersion Wavelength (l₀): In a single-mode optical fiber, the wavelength at which material dispersion and waveguide dispersion cancel each other out. The wavelength of maximum bandwidth in the fiber. Also called zero-dispersion point.
Zipcord: A two-fiber cable consisting of two single fiber cables having conjoined jackets. A zipcord cable can be easily divided by slitting and pulling the conjoined jackets apart.