For an optical fiber, a refractive index profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface.
Note 1: The step-index profile corresponds to a power-law index profile with the profile parameter approaching infinity.
Note 2: The step-index profile is used in most single-mode fibers and some multimode fibers.

The metric unit of solid angle. See International System of Units.

An undesired signal occurring in the main channel from modulation of the stereophonic channel or that occurring in the stereophonic channel from modulation of the main channel. [47CFR]

A subcarrier within the FM broadcast baseband used for transmitting signals for stereophonic sound reception of the main broadcast program service. [47CFR]

Abbreviation for standard time and frequency signal. See standard time and frequency signal service.

Nonmoving visual information, i.e., fixed images, such as graphs, drawings, and pictures.

Video imagery that is not intended to convey the appearance of movement.

In a quantum mechanical system, the radiation emitted when the internal energy of the system drops from an excited level (induced by the presence of radiant energy at the same frequency) to a lower level.
Note: An example of stimulated emission is the radiation from an injection laser diode operated above the lasing threshold.

Abbreviation for standard telegraph level, studio-to-transmitter link, Satellite Time and Location.

See stop signal.