General Cable Fiber Optics Catalog
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Fiber Optic Technical Information Glossary Macrobending: Macroscopic axial deviations of a fiber from a straight line. MegaHertz: One million Hertz. Microbending: Curvatures of the fiber which involve axial displacements a few micrometers and spatial wavelengths of a few millimeters. Microbends cause loss of light and consequently increase the attenuation of the fiber. Micrometer (µm): One millionth of a meter or a micron. Conventional unit of measurement for optical fibers. Micron: See Micrometer. Modal Dispersion: Pulse spreading due to multiple light rays traveling different distances and speeds through an optical fiber. Mode: A term used to describe an independent light path through a fiber, as in multimode or singlemode. Mode Field Diameter (MFD): The diameter of optical energy in a singlemode fiber. Because the MFD is greater than the core diameter, MFD replaces core diameter as a practical parameter. Monochromatic: Consisting of a single wavelength. In practice, radiation is never perfectly monochromatic but, at best, displays a narrow band of wavelengths. Multimode Fiber: An optical waveguide in which light travels in several modes. Typical core and cladding sizes are 50 µm/125 µm and 62.5 µm/125 µm. Multiplex: Combining two or more signals into a single bit stream that can be individually recovered. Nanometer: One billionth of a meter (nm). National Electric Code (NEC): Defines building flammability requirements for indoor cables. Numerical Aperture (NA): Measure of the range of angles of incident light transmitted through a fiber. Depends on the differences in index of refraction between the core and the cladding. (The number that expresses the light-gathering ability of a fiber.) Optical Return Loss (ORL): The ratio, expressed in decibels, of optical power reflected by a component or an assembly to the optical power incident on a component or assembly that is induced into a link or system. Optical Time Domain Reflectometer (OTDR): An instrument used to measure the transmission performance of optical fibers. Optical Transmitter: See Transmitter. Optical Waveguide: Dielectric waveguide with a core consisting of optically transparent material of low attenuation (usually silica glass) and with cladding consisting of optically transparent material of lower refractive index than that of the core. It is used for the transmission of signals with lightwaves and is frequently referred to as a fiber. In addition, there are some optical components, such as laser diodes, which are referred to as optical waveguides. PE: Abbreviation used for polyethylene. Polyethylene is a type of plastic, commonly used as a jacketing material for outside plant cables, that possesses good mechanical properties including good moisture resistance. However, it is very flammable and not suitable for indoor jacketing applications. PVC: Abbreviation used for polyvinyl chloride. Polyvinyl chloride is a plastic material that is widely used as a jacketing material in indoor cables. PVDF: Abbreviation denoting polyvinylidene fluoride, a fluoropolymer plastic material often used as a jacket in plenum cables, especially in larger fiber count cables. Pigtail: A fiber optic connector that is terminated to one end of an optical fiber cable. A short length of optical fiber, permanently fixed to a component, used to couple power between the component and a transmission fiber. Plenum: The air handling space such as that found above drop-ceiling tiles or in raised floors. It is also the most stringent fire code rating for indoor cables. Plenum Cable: A cable that meets the most stringent flammability and smoke-generating test and is suitable for installation in a plenum area without a conduit. Power: The rate at which energy is transferred. Preform: A glass structure from which an optical fiber waveguide can be drawn. Primary Coating: The plastic coating applied directly to the cladding surface of the fiber during manufacture to preserve the integrity of the surface. Receiver: A detector and electronic circuitry to change optical signals into electrical signals. Reflection: The abrupt change in direction of a light beam at an interface between two dissimilar media so that the light beam returns into the media from which it originated. Refraction: The bending of a beam of light at an interface between two dissimilar media or in a medium whose refractive index is a continuous function of position (graded index medium). Refractive Index: The ratio of the velocity of light in a vacuum to that in an optically dense medium. Repeater: In an optical-fiber communication system, an optoelectronic device or module that receives an optical signal, converts it to electrical form, amplifies it (or in the case of a digital signal, reshapes, retimes or otherwise reconstructs it) and retransmits it in optical form. Riser: Pathways for indoor cables that pass between floors. It is normally a vertical shaft or space. A riser cable rating indicates good flammability characteristics, but not necessarily low smoke as in a plenum type. 53