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Loss of light radiation when passing through matter as the result of conversion into other forms of energy, e.g. heat energy. With photodiodes, the absorption is the process that destroys a photon as it arrives and through its energy elevates an electron from the valence band to the conduction band.

Acceptance angle

The largest possible angle within which light in
the area of the fiber core can impinge on the end face,
thus enabling it to be guided along the fiber core.


Functional module that makes it possible to add
and drop partial signals to/from a multiplex signal.

Amplified spontaneous emission

Component for checking the state of polarisation
of the light. Differs from a polariser only with regard
to its function in the selected optical design. The analyser
is located on the observer side.


Kurzes Stück eines Lichtwellenleiters mit einem Stecker
zur Kopplung optischer Bauelemente (z. B. einer
Laserdiode). Es ist meist fest mit dem Bauelement

APC connector
Arrayed waveguide grating

Integrated, optical component that functions as a multiplexer/
demultiplexer. Different input wavelengths
cause differences in phase, permitting a channel
separation similar to the classic diffraction grating.


Reduction in the optical signal power in a fiber due
to scattering, absorption, mode conversion or at a coupling
point (connector, splice). Attenuation is a dimensionless
variable and is usually given in decibels.

Attenuation coefficient

Is the attenuation based on the length of the fiber.
The attenuation coefficient is expressed in dB/km
and is an important parameter for characterising a fiber.

Attenuation dead zone

Minimum spacing from a reflecting event in order
to be able to measure the attenuation of a following
event (OTDR measurement).

Attenuation-limited operation

Limitation of the achievable transmission link due
to the effects of attenuation.

Avalanche photodiode

Receiver component that is based on the avalanche
effect: the photoelectric current is amplified through
carrier multiplication.