Bandwidth (of a signal or a transmission path):
A measure of the maximum frequency by which a signal be modulated. It is a measure of information-carrying capacity; the greater the bandwidth, the greater the information carrying capacity.

Bandwidth (of a WDM-channel):
The range of optical wavelengths which can be transmitted through a component. It is the wavelength range, which defines the spectral width of one WDM channel.

Center Wavelength:
Wavelength of an optical source (e.g. laser) at peak power.

Center Wavelength (of a WDM channel):
Middle position of an optical bandpass.

Channel:
A communication path or the signal sent over that path. See also: Optical Channel.

Channel Spacing:
The wavelength separation of the center wavelengths between adjacent WDM channels.

Coupler:
An optical device containing one or several input and output ports to distribute an optical signal.

Coupling Ratio:
The ratio of optical power from one output port to the total output power, expressed as a percentage.

CWDM:
Coarse wavelength division multiplexing. Very cost-effective WDM transmission technology due to larger channel spacing and the possibility of using uncooled laser transmitters.

dB Decibel:
Standard logarithmic unit for the ratio of two quantities. In optical fibers, the ratio is power and represents loss or gain.

Demux:
Demultiplexer. The process that separates two or more signals from a single communications line.

Directivity:
Fraction of optical power transferred from one input port to any other input port.

DWDM:
Dense Wavelength Division Multiplexing involving high channel counts.

Excess Loss:
Lost optical power in an optical component i.e. light that does not emerge from any optical output port.

Fiber Coating:
Material immediately around the optical fiber to preserve the integrity of the fiber.

Insertion Loss:
Loss of optical power resulting from the insertion of a component or device into the optical path.

Interference Filter:
Optical element consisting of multiple layers of dielectric thin films coated on a glass substrate transmitting a certain wavelength range and reflecting the residual light.

Isolation:
Ability to prevent undesired optical energy from appearing in a signal path.

Isolator:
An optical component used to block out reflected light.

LAN Local Area Network:
A high speed transmission network (Mb/s) in which all segments of the transmission are situated in an office, building or campus environment. The network is owned by the user organization.

Laser:
Light Amplification by Stimulated Emission of Radiation. Light source producing coherent light through stimulated emission.

Link Loss:
Insertion loss for the combined WDM mux and demux components.

Loose tube:
Thin plastic tube around the optical fiber – providing protection and better handling of the fiber.

Multiplexing:
The process by which two or more signals are transmitted over a single communications line.

Mux, Multiplexer:
A device that puts two or more signals into a single channel.

nm Nanometer:
A unit of measurement equal to one billionth of a meter. Commonly used to define optical wavelengths.

Optical Bandpass:
See Bandwidth (of a WDM-channel).

Optical Channel:
An optical wavelength band for WDM optical communications.

Optical Fiber:
Fiber made of dielectric material and consisting of the core, light- carrying medium, and the cladding, protective layer allowing total internal reflection of the light for propagation purposes.

PDL, Polarization Dependent Loss:
The difference in dB between the maximum and the minimum values of loss (attenuation) due to the variation of the polarization states of light propagating through a device.

Pigtail:
Fiber attached to a connector, source, detector, coupler or any other optical com-ponent.

Polarization:
Characteristic of electromagnetic radiation where the electric-field vector of the wave energy is perpendicular to the main direction, or vector, of the electromagnetic beam.

Port:
Opening for light or fiber to and from a component.

Return Loss:
Fraction of power transferred from an input port back to the same input port.

Switch:
Device that switches light between one or multiple input ports to one or multiple output ports on coupler products.

Tap:
Branching component that removes and/or inserts a small fraction of optical power onto the fiber.

Uniformity:
The difference between the maximum insertion loss and the minimum insertion loss for each input port and all output ports. For WDM devices this is measured at
23°C .

WDM Wavelength Division Multiplexing:
Optical transmission technique using two or more optical channels over a common optical fiber. The channels are differentiated by their wavelengths and frequencies.

WWDM:
Wide WDM – Transmission technology using only two optical channels. WWDM mux/demux components combine/split the optical spectrum into a short wavelength and a long wavelength region.