Scattering caused by fluctuations in density
(inhomogeneities) in a fiber which are smaller than
the wavelength of the light. Rayleigh scattering is
largely responsible for the attenuation in a fiber and it
decreases with the fourth power of the wavelength.

A component (part of a terminal device) in optical
communications for converting optical signals into
electrical signals. It comprises a receiver diode (PIN
photodiode or avalanche photodiode) that can be
coupled to an optical fiber, a low-noise amplifier and
electronic circuits for processing the signal.

The minimum optical power required by the receiver
for low-noise signal transmission. With digital signal
transmission, the mean optical power in mW or dBm
is specified, with which a particular bit error rate,
e.g. 10^–9, is achieved.

Connecting element of the active optical component
and the fiber connector. The component is accommodated
in a rotationally symmetrical guide. The optical
path can be guided by an optical system. The ferrule
in the connector is centred by a sleeve which is aligned
with the optically active surface area of the component.
The housing is formed by the connector’s locking
mechanism.

Reciprocal value of return loss. Expressed as a negative
value in decibels.

Return of rays (waves) at a boundary between
two media having different refractive indices,
the angle of incidence being equal to the angle
of reflection.

Ratio of incident optical power to reflected optical
power; usually given in decibels (positive values).

Method for the space-resolved measurement of power
return loss (➔ Optical time domain reflectometer).

Ratio of the velocity of light in a vacuum to the
propagation velocity in the respective medium. The
refractive index is a function of the material and the
wavelength.

Difference between the maximum refractive index
occurring in the core of a fiber and the refractive index
in the cladding. The refractive index difference defines
the size of the numerical aperture of the optical fiber.

Characteristic of the refractive index over the crosssectional
area of the fiber core.

Proportion of the light in relation to the total scattered
light that is in the reverse direction within the acceptance
range and is guided in the fiber.

Spacing between two events at which the optical time
domain reflectometer is still able to recognise the second
event precisely and measure its attenuation.

The ability of an OSA to plot two closely adjacent
wavelengths separately. The resolution bandwidth
is usually determined by the spectral properties of the
optical filter in the OSA.

Ratio of the incident optical power to the returned
optical power (reflected and scattered light), which
is caused by a specific length of a fiber section (usually
expressed in decibels: positive values). Sometimes
the returned optical power means just the reflected
light.

Method for modulating amplitudes in which
the on and off levels are not maintained for an entire
bit interval.

Design in which the optical fibers are arranged
in the form of ribbons. The fibers in a ribbon cable can
all be spliced together at the same time.

Interconnection of several fibers with a primary coating
which are held together by means of an additional
shared jacket (similar to a flat cable).