G: Abbreviation for giga. One billion
or 109. |
| GaAlAs: Abbreviation for
gallium aluminum arsenide. Generally used for
short wavelength light emitters. |
| GaAs: Abbreviation for gallium
arsenide. Used in light emitters. |
| Gain: The ratio of output current, voltage, or power to
input current, voltage, or power, respectively.
Gain is usually expressed in dB. If the ratio is less
than unity, the gain, expressed in dB, will
be negative, in which case there is a loss between input and output. |
| GaInAsP: Abbreviation
for gallium indium arsenide phosphide. Generally
used for long wavelength light emitters. |
| Gap
Loss: Loss resulting from the end
separation of two axially aligned fibers. |
|
| Gate: 1) A device having one output channel
and one or more input channels, such that the
output channel state is completely determined
by the input channel states, except during switching
transients. 2) One of the many types of combinational
logic elements having at least two inputs. |
Gaussian Beam: A beam pattern used to approximate
the distribution of energy in a fiber core.
It can also be used to describe emission patterns
from surface-emitting
LEDs. Most people would recognize it as
the bell curve (illustrated). The Gaussian beam
is defined by the equation:
E(x) = E(0)e-x2/w02 |
|
| GBaud: One billion bits
of data per second or 109 bits. Equivalent
to 1 for binary signals. |
| Ge: Abbreviation for germanium. Generally
used in detectors. Good for most
fiber optic wavelengths (e.g., 800-1600 nm).
Performance is inferior to InGaAs |
| Genlock: A process of
sync generator locking. This is usually performed
by introducing a composite video signal from
a master source to the subject sync generator.
The generator to be locked has circuits to isolate
vertical drive, horizontal drive and subcarrier.
The process then involves locking the subject
generator to the master subcarrier, horizontal,
and vertical drives so that the result is that
both sync generators are running at the same
frequency and phase. |
| GHz: Abbreviation for gigahertz. One billion
Hertz (cycles per second) or 109 Hertz. |
| Graded-index
Fiber: Optical fiber in
which the refractive
index of the core is in the form of a parabolic
curve, decreasing toward the cladding. |
 |
| GRIN: Abbreviation for gradient
index. Generally refers to the SELFOC lens often
used in fiber optics. |
| Ground
Loop Noise: Noise that results
when equipment is grounded at points having
different potentials thereby creating an unintended
current path. The dielectric properties
of optical fiber provide
electrical isolation that eliminates ground
loops. |
| Group
Index: Also called group refractive
index. In fiber optics, for a given mode propagating
in a medium of refractive index (n), the group
index (N), is the velocity of light in a vacuum
(c), divided by the group velocity of the mode. |
| Group
Velocity: 1) The velocity of propagation
of an envelope produced when an electromagnetic
wave is modulated by, or mixed with, other waves
of different frequencies. 2) For a particular
mode, the reciprocal of the rate of change of
the phase constant with respect to angular frequency.
3) The velocity of the modulated optical power. |
