Abbreviation for gallium aluminum arsenide. Generally used for short wavelength light emitters.



Abbreviation for gallium arsenide. Used in light emitters.



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.



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.

Gap Loss


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

Gaussian Beam


One billion bits of data per second or 109 bits. Equivalent to 1 for binary signals.



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.



Generally used in detectors. Good for most fiber optic wavelengths (e.g., 800-1600 nm). Performance is inferior to InGaAs



Abbreviation for gigahertz. One billion Hertz (cycles per second) or 109 Hertz.



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.

Graded-index Fiber


Abbreviation for gradient index. Generally refers to the SELFOC lens often used in fiber optics.


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.