ECL: Abbreviation for emitter-coupled logic. A high-speed logic family capable of GHz rates.

EDFA: See Erbium-doped fiber amplifier.

Edge-emitting Diode: An LED that emits light from its edge, producing more directional output than surface-emitting LED's that emit from their top surface.

Effective Area: Light is not distributed in the fiber core uniformly. Rather, it follows a distribution that typically peaks in the center of the core and then tails off near the core-cladding interface. It usually extends some short distance into the cladding as well. (See evanescent wave.) Note: For a Gaussian power distribution in a single-mode optical fiber, the mode field diameter (MFD) is that at which the light intensity is reduced to 1/e of its maximum value. The effective area is the area defined by the MFD.

EGA: Abbreviation for enhanced graphics adapter. A medium-resolution color standard for computer monitors.

EIA: Abbreviation for Electronic Industries Association. An organization that sets video and audio standards.

EMI (Electromagnetic Interference): Any electrical or electromagnetic interference that causes undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.

EMP (Electromagnetic Pulse): A burst of electromagnetic radiation that creates electric and magnetic fields that may couple with electrical/electronic systems to produce damaging current and voltage surges.

EMR (Electromagnetic Radiation): Radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible, and infrared radiation, and radar and radio waves.

Electromagnetic Spectrum: The range of frequencies of electromagnetic radiation from zero to infinity.

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ELED: See edge-emitting diode.

Ellipticity: Describes the fact that the core or cladding may be elliptical rather than circular.

EM: Abbreviation for electromagnetic.

Endoscope: A fiber optic bundle used for imaging and viewing inside the human body.

E/O: Abbreviation for electrical-to-optical converter. A device that converts electrical signals to optical signals, such as a laser diode.

Equilibrium Mode Distribution (EMD): The steady modal state of a multimode fiber in which the relative power distribution among modes is independent of fiber length.

Erbium-doped Fiber Amplifier (EDFA): Optical fibers doped with the rare earth element, erbium, which can amplify light in the 1550 nm region when pumped by an external light source.

ESCON: Abbreviation for enterprise systems connection. A duplex optical connector used for computer-to-computer data exchange.

Evanescent Wave: Light guided in the inner part of an optical fiber's cladding rather than in the core, i.e., the portion of the light wave in the core that penetrates into the cladding.

Excess Loss: In a fiber optic coupler, the optical loss from that portion of light that does not emerge from the nominal operation ports of the device.

External Modulation: Modulation of a light source by an external device that acts like an electronic shutter.

Extinction Ratio: The ratio of the low, or OFF optical power level (P_L) to the high, or ON optical power level (P_H):

Extrinsic Loss: In a fiber interconnection, that portion of loss not intrinsic to the fiber but related to imperfect joining of a connector or splice.

Eye Diagram: A diagram that shows the proper function of a digital system. The "openness" of the eye relates to the BER that can be achieved.