Fiber Optic :: Glossary :: M

Macro bend - A large fiber bend that can be seen with the unaided eye.

Macrobendiing - Macroscopic axial deviations of a fiber optic cable from a straight line, in contrast to microbending.

MAN - Metropolitan Area Network. This is a network linking LANs and other networks at many sites within a city area. Dimensions are usually of the order to 10's of km.

Manchester - Balanced signaling code, used at lower data rates.

Material dispersion - Light pulse broadening caused by various wavelengths of light traveling at different velocities down a fiber optic cable. Material dispersion increases with the increasing spectral width of the source. It is attributable to the wavelength dependence of the refractive index of the material used to form the fiber optic cable. It is characterized by the material dispersion parameter, M (l).

Material scattering - In an optical waveguide it is that part of the total scattering attributable to the properties of the materials used for waveguide fabrication.

MAU- Medium Attachment Unit. This is an active component of an Ethernet LAN connecting peripheral devices with the electrical bus cable.

MBPS - Mega Bits Per Second - 1 million BPS.

MDPE- Medium density polyethylene jacketing.

Mechanical splice - A splice in which fiber optic cables are joined mechanically for example by being glued or crimped in place. However, they are not fused together.

MFD - Mode field diameter.

MHz. - Mega Hertz, 1 million Hz.

Microbend Loss - The loss attributed to microscopic bends in fiber optic cable.

Microbending - Curvatures of the fiber optic cable which involves axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Micro bends cause loss of light and consequently increase attenuation of the fiber optic cable.

Micrometer - 1 millionth of a meter, abbreviated mm. Also referred to a micron.

Micron - See micrometer.

Misalignment loss - The loss of power resulting from angular misalignment, lateral displacement and end - separation.

MM - Millimeter, 1 thousandth of a meter.

MMF - Multi-mode fiber optic cable.

Modal bandwidth - A bandwidth limiting mechanism in multi-mode fiber optic cables. It is also used in single-mode fiber optic cables when operated at wavelengths below cutoff. Modal bandwidth arises because of the different arrival times of the various modes. It is a synonym for intermodal dispersion.

Modal dispersion - The dispersion resulting from difference in the time it takes for different rays to traverse a fiber optic cable.

Modal noise - The fluctuation in optical power due to the interaction of the power traveling in more than 1 mode.

Mode coupling - The transfer of energy between modes. In a fiber optic cable, mode coupling occurs until the EMD is reached.

Mode field diameter - The diameter of optical energy in a single-mode fiber optic cable. Because the MFD is greater than the core diameter, MFD replaces the core diameter as a practical parameter.

Mode filter - A device used to remove high-order modes from a fiber optic cable and thereby simulate EMD.

Mode mixing - The numerous modes of a multi-mode fiber optic cable differ in their propagating velocities. As long as they propagate independently of each other, the fiber optic cable bandwidth varies inversely with the fiber optic cable length due to multi-mode distortion. As a result of inhomogeneities of the fiber optic cable geometry and the index profile, a gradual energy exchange occurs between modes with different velocities. Due to this mode mixing, the bandwidth of long multi-mode fiber optic cables is greater than the value obtained by linear extrapolation from measurements on short fiber optic cables.

Mode scrambler - A device composed of one or more fiber optic cables in which strong mode coupling occurs. Frequently used to provide a mode distribution that is independent of source characteristics.

Modem - An acronym for Modulator-Demodulator. This is a device that carries out both modulation and demodulation. With the modulation function the modem takes information, which is in digital form - usually, 0's and 1's, and represents it by signals, which can be sent (transmitted) over a transmission medium. With the demodulation function the modem takes signals out of the transmission medium (received) and determines which digits then represent, what sequence of 0's and 1's.

Modes - In guided wave propagation, such as that through fiber optic cable, it is the distribution of electromagnetic energy that satisfy Maxwell's equations and boundary conditions. Specifically, applied to optics and transmission down a fiber optic cable a mode is loosely equivalent to a light ray of classic ray optic theory. Sometimes used to denote a light path through a fiber optic cable.

Modulation - The process by which the characteristic of one wave (the carrier) is modified by another wave (the information signal). Examples include amplitude modulation (AM), and frequency modulation (FM).

Monochromatic - Consisting of a single wavelength. In practice, radiation is never perfectly monochromatic but, at best, displays a narrow band of wavelengths.

Multi-mode fiber optic cable - Type of fiber optic cable that support more than 1 propagation mode.

Multiplexing - The process by which 2 or more signals are transmitted over a single transmission medium. Examples include Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM).