Abbreviation for Institute of Electrical and Electronic Engineers. A technical professional association that contributes to voluntary standards in technical areas ranging from computer engineering, biomedical technology and telecommunications, to electric power, aerospace and consumer electronics, among others.



Abbreviation for Intermediate Frequency. A frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception.



The total passive opposition offered to the flow of electric current. Determined by the particular combination of resistance, inductive reactance, and capacitive reactance in a given circuit. A function of frequency, except when in a purely resistive network.


Impedance Matching

The connection of an additional impedance to an existing one in order to achieve a specific effect, such as to balance a circuit or to reduce reflection in a transmission line.


In-line Amplifier

An EDFA or other type of amplifier placed in a transmission line to strengthen the attenuated signal for transmission onto the next, distant site. In-line amplifiers are all-optical devices.

In-line Amplifier

Index of Refraction

The ratio of the velocity of light in free space to the velocity of light in a fiber material. Always greater than or equal to one. Also called refractive index.

n = C/V

C = The speed of light in a vacuum.
V = The speed of the same wavelength in the fiber material.


Index-matching Fluid

A fluid whose index of refraction nearly equals that of the fibers core. Used to reduce Fresnel reflection loss at fiber ends. Also known as index-matching gel.


Infrared (IR)

The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (about 0.7 μm) and the shortest microwaves (about 0.1 μm).


Infrared Emitting Diode

LEDs that emit infrared energy (830 nm or longer).


Infrared Fiber

Colloquially, optical fibers with best transmission at wavelengths of 2 mm or longer, made of materials other than silica glass. See also fluoride glasses.


Infrared Fiber

Colloquially, optical fibers with best transmission at wavelengths of 2 mm or longer, made of materials other than silica glass. See also fluoride glasses.



Abbreviation for indium gallium arsenide. Generally used to make high-performance long-wavelength detectors.



Abbreviation for indium gallium arsenide phosphide. Generally used for long-wavelength light emitters.



Indium Phosphide. A semiconductor material used to make optical amplifiers and HBTs.


Insertion Loss

The loss of power that results from inserting a component, such as a connector, coupler (illustrated), or splice, into a previously continuous path.


Insertion Loss

The loss of power that results from inserting a component, such as a connector, coupler (illustrated), or splice, into a previously continuous path.

Insertion Loss

Integrated Detector/Preamplifier (IDP)

A detector package containing a PIN photodiode and transimpedance amplifier.


Integrated Systems Digital Network (ISDN)

An integrated digital network in which the same time-division switches and digital transmission paths are used to establish connections for services such as telephone, data, electronic mail and facsimile. How a connection is accomplished is often specified as a switched connection, non-switched connection, exchange connection, ISDN connection, etc.



The square of the electric field strength of an electromagnetic wave. Intensity is proportional to irradiance and may get used in place of the term “irradiance” when only relative values are important.


Intensity Modulation

In optical communications, a form of modulation in which the optical power output of a source varies in accordance with some characteristic of the modulating signal.



1. Between local access and transport areas (LATAs). 2. Services, revenues, and functions related to telecommunications that begin in one LATA and that terminate in another or that terminate outside of the LATA.


Interchannel Isolation

The ability to prevent undesired optical energy from appearing in one signal path as a result of coupling from another signal path. Also called crosstalk.



Any extraneous energy, from natural or manmade sources, that impedes the reception of desired signals. The interference may be constructive or destructive, resulting in increased or decreased amplitude, respectively.



An instrument that uses the principle of interference of electromagnetic waves for purposes of measurement. Used to measure a variety of physical variables, such as displacement (distance), temperature, pressure, and strain.


Interferometric Intensity Noise (IIN)

Noise generated in optical fiber caused by the distributed back reflection that all fiber generates mainly due to Rayleigh scattering. OTDRs make use of this scattering power to deduce the fiber loss over distance.


Interferometric Sensors

Fiber optic sensors that rely on interferometric detection.


Intermodulation (Mixing)

A fiber nonlinearity mechanism caused by the power dependant refractive index of glass. Causes signals to beat together and generate interfering components at different frequencies. Very similar to four wave mixing.


International Telecommunications Union (ITU)

A civil international organization, headquartered in Geneva, Switzerland, established to promote standardized telecommunications on a worldwide basis. The ITU-R and the ITU-T are committees under the ITU, which is recognized by the United Nations as the specialized agency for telecommunications.



A worldwide collection of millions of computers that consists mainly of the world wide web and e-mail.


Intersymbol Interference

1) In a digital transmission system, distortion of the received signal, manifested in the temporal spreading and consequent overlap of individual pulses to the degree that the receiver cannot reliably distinguish between changes of state, i.e., between individual signal elements. At a certain threshold, intersymbol interference will compromise the integrity of the received data. Intersymbol interference may be measured by eye patterns.


Intrinsic Losses

Splice losses arising from differences in the fibers being spliced.



Abbreviation for Internet protocol. A standard protocol, developed by the DOD, for use in interconnected systems of packet-switched computer communications networks.



Abbreviation for intelligent peripheral interface as defined by ANSI X3T9.3 document.



IRE Unit

An arbitrary unit created by the Institute of Radio Engineers to describe the amplitude characteristic of a video signal, where pure white is defined as 100 IRE with a corresponding voltage of 0.714 Volts and the blanking level is 0 IRE with a corresponding voltage of 0.286 Volts.

IRE Unit


Power per unit area.



Abbreviation for Instrumentation, Systems, and Automation Society. An international, non-profit, technical organization. The society fosters advancement of the use of sensors, instruments, computers, and systems for measurement and control in variety of applications



Abbreviation for International Standards Organization. Established in 1947, ISO is a worldwide federation of national standards committees from 140 countries. The organization promotes the development of standardization throughout the world with a focus on facilitating the international exchange of goods and services, and developing the cooperation of intellectual, scientific, technological, and economical activities.



Abbreviation for Internet service provider. A company or organization that provides Internet connections to individuals or companies via dial-up, ISDN, T1, or some other connection.