Fabry Perot

Generally refers to any device, such as a type of laser diode, that uses mirrors in an internal cavity to produce multiple reflections.



Measure of temperature where pure water freezes at 32° and boils at 212°


Failure Rate

See FIT Rate.


Fall Time

Also called turn-off time. The time required for the trailing edge of a pulse to fall from 90% to 10% of its amplitude; the time required for a component to produce such a result. Typically measured between the 90% and 10% points or alternately the 80% and 20% points.

Fall Time


Abbreviation for federal acquisition regulation. The guidelines by which the U.S. government purchases goods and services. Also the criteria that must be met by the vendor in order to be considered as a source for goods and services purchased by the U.S. government.


Far-End Crosstalk

See wavelength isolation.


Faraday Effect

A phenomenon that causes some materials to rotate the polarization of light in the presence of a magnetic field parallel to the direction of propagation. Also called magneto-optic effect.



Abbreviation for fiber Bragg gratings. See Bragg grating.



A threaded optical connector that uses a special curved polish on the connector for very low backreflection. Good for single-mode or multimode fiber.



Abbreviation for Federal Communications Commission. The U.S. Government board of five presidential appointees that has the authority to regulate all non-Federal Government interstate telecommunications as well as all international communications that originate or terminate in the United States.



Abbreviation for frame check sequence. An error-detection scheme that (a) uses parity bits generated by polynomial encoding of digital signals, (b) appends those parity bits to a digital signal, and (c) uses decoding algorithms that detect errors in the received digital signal.



Abbreviation for Food and Drug Administration. Organization responsible for, among other things, laser safety.



Abbreviation for fiber distributed data interface. 1) A dual counter-rotating ring local area network. 2) A connector used in a dual counter-rotating ring local area network (illustrated).



See frequency-division multiplexing.



see Frequency-division Multiplexing (FDM)



See forward error correcting.



1) Supplies the input of a system, subsystem, or equipment, such as a transmission line or antennae. 2) A coupling device between an antennae and its transmission line. 3) A transmission facility between either the point of origin of the signal or at the head-end of a distribution facility.



A rigid tube that confines or holds a fiber as part of a connector assembly.



Abbreviation for field-effect transistor. A semiconductor so named because a weak electrical signal coming in through one electrode creates an electrical field through the rest of the transistor. This field flips from positive to negative when the incoming signal does, and controls a second current traveling through the rest of the transistor. The field modulates the second current to mimic the first one, but it can be substantially larger.


Fiber Fuse

A mechanism whereby the core of a single-mode fiber can be destroyed at high optical power levels.

(Photo courtesy of Dr. D.D.Davis.)

Fiber Fuse

Fiber Grating

An optical fiber in which the refractive index of the core varies periodically along its length, scattering light in a way similar to a diffraction grating, and transmitting or reflecting certain wavelengths selectively.

Fiber Grating

Fiber Optic Attenuator

A component installed in a fiber optic transmission system that reduces the power in the optical signal. It is often used to limit the optical power received by the photodetector to within the limits of the optical receiver. A fiber optic attenuator may be an external device, separate from the receiver, or incorporated into the receiver design as illustrated (far left).

Fiber Optic Attenuator

Fiber Optic Cable

A cable containing one or more optical fibers.


Fiber Optic Communication System

The transfer of modulated or unmodulated optical energy through optical fiber media which terminates in the same or different media.


Fiber Optic Link

A transmitter, receiver, and cable assembly that can transmit information between two points.

Fiber Optic Link

Fiber Optic Span

An optical fiber/cable terminated at both ends which may include devices that add, subtract, or attenuate optical signals.


Fiber Optic Subsystem

A functional entity with defined bounds and interfaces which is part of a system. It contains solid state and/or other components and is specified as a subsystem for the purpose of trade and commerce.

Fiber Optic Subsystem

Fiber-in-the-loop (FITL)

Fiber optic service to a node that is located in a neighborhood.


Fiber-to-the-Curb (FTTC)

Fiber optic service to a node connected by wires to several nearby homes, typically on a block.

Fiber-to-the-Curb (FTTC)

Fiber-to-the-Home (FTTH)

Fiber optic service to a node located inside an individual home.

Fiber-to-the-Home (FTTH)

Fibre Channel

An industry-standard specification that originated in Great Britain which details computer channel communications over fiber optics at transmission speeds from 132 Mb/s to 1062.5 Mb/s at distances of up to 10 kilometers.



A device which transmits only part of the incident energy and may thereby change the spectral distribution of energy.


FIT Rate

Number of device failures in one billion device hours.


Fluoride Glasses

Materials that have the amorphous structure of glass but are made of fluoride compounds (e.g., zirconium fluoride) rather than oxide compounds (e.g., silica). Suitable for very long wavelength transmission. This material tends to be destroyed by water, limiting its use.



see Frequency Modulation


Forward Error Correcting (FEC)

A communication technique used to compensate for a noisy transmission channel. Extra information is sent along with the primary data payload to correct for errors that occur in transmission.

Forward Error Correcting (FEC)

FOTP (Fiber Optic Test Procedure

Standards developed and published by the Electronic Industries Association (EIA) under the EIA-RS-455 series of standards.


Four Wave Mixing (FWM)

A nonlinearity common in DWDM systems where multiple wavelengths mix together to form new wavelengths, called interfering products. Interfering products that fall on the original signal wavelength become mixed with the signal, mudding the signal, and causing attenuation. Interfering products on either side of the original wavelength can be filtered out. FWM is most prevalent near the zero-dispersion wavelength and at close wavelength spacings.

Four Wave Mixing (FWM)


see Fabry Perot


Free-Space Optics

Also called free-space photonics. The transmission of modulated visible or infrared (IR) beams through the atmosphere via lasers,  LEDs, or IR-emitting diodes (IREDs) to obtain broadband communications.


Frequency Modulation

A method of transmission in which the carrier frequency varies in accordance with the signal.

Frequency Modulation

Frequency Stacking

The process that allows two identical frequency bands to be sent over a single cable by up converting one of the frequencies and “stacking” it with the other.


Frequency-division Multiplexing (FDM)

A method of deriving two or more simultaneous, continuous channels from a transmission medium by assigning separate portions of the available frequency spectrum to each of the individual channels.


Frequency-shift Keying (FSK)

Frequency modulation in which the modulating signal shifts the output frequency between predetermined values. Also called frequency-shift modulation, frequency-shift signaling.


Fresnel Reflection Loss

Reflection losses at the ends of fibers caused by differences in the refractive index between glass and air. The maximum reflection caused by a perpendicular air-glass interface is about 4% or about -14 dB.



Abbreviation for full service access network. A forum for the world’s largest telecommunications services providers and equipment suppliers to work define broadband access networks based primarily on the ATM passive optical network structure.



see Fiber-to-the-Curb



see Fiber-to-the-Home


Full-duplex Transmission

Simultaneous bidirectional transfer of data.

Full-duplex  Transmission

Fused Coupler

A method of making a multimode or single-mode coupler by wrapping fibers together, heating them, and pulling them to form a central unified mass so that light on any input fiber is coupled to all output fibers.

Fused Coupler

Fused Fiber

A bundle of fibers fused together so they maintain a fixed alignment with respect to each other in a rigid rod.


Fusion Splicer

An instrument that permanently bonds two fibers together by heating and fusing them.

Fusion Splicer


Abbreviation for fiber under test. Refers to the fiber being measured by some type of test equipment.



Abbreviation for full width half maximum. Used to describe the width of a spectral emission at the 50% amplitude points. Also known as FWHP (full width half power).