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1、Absorption The loss of light as it passes through a material, generally due to its conversion to other energy forms (typically heat). Absorption coefficient An indicator of a materials internal absorptance. If the unit transmission of the material is t, the absorption coefficient (a) is: a= -log e t
2、 Acceptance Angle The angle over which the core of an optical fiber accepts incoming light; usually measured from the fiber axis. Related to numerical aperture (NA). ACWDM advanced custom WDM. Adhesive An intermolecular substance that serves to hold materials together. Two types are used in the opti
3、cal industry: one, which must be transparent and colorless, to cement lenses together; and a general-purpose adhesive for bonding prisms and other glass parts to their metallic supports ADM add/drop multiplexer (capitalize only when indicating a product name). Adapter A device for connecting two par
4、ts (as of different diameters) of an apparatus; an attachment for adapting devices for uses not originally intended. AH-Dielectric Cable Cable made entirely of dielectric (insulating) materials without any metal conductors, armor, or strength members. AM amplitude modulation. A modulation scheme in
5、which the amplitude of a carrier wave is changed by information signals. Analog A signal that varies continuously (e.g., sound waves). Analog signals have frequency and bandwidth measured in hertz. Angle of incidence The angle formed between a ray of light striking a surface and the normal to that s
6、urface at the point of incidence Angle of reflection The angle formed between the normal to a surface and the reflected ray. This angle lies in a common plane with the angle of incidence and is equal to it. Angle of refraction The angle formed between a refracted ray and the normal to the surface. T
7、his angle lies in a common plane with the angle of incidence. Angstrom (? A unit of length, 0.1 nm or 10-10 m, often used to measure wavelength but not part of the Sl system of units. Often written Angstrom because the special symbol is not available. APC angled physical contact APD avalanche photod
8、iode. A device that uses avalanche multiplication of photocurrent via hole-electrons created by absorbed photons. When the reverse-bias voltage of a device nears breakdown level, the hole-electron pairs collide with ions, create more hole-electron pairs, and achieve a signal gain. APON ATM based pas
9、sive optical network. APS automatic protection switching. AR antireflection. AR coating antireflective coating. A thin layer of material applied to optical parts to reduce reflections. ASE amplified spontaneous emission. Armor A protective layer, usually metal, wrapped around a cable. ATM (Asynchron
10、ous Transfer Mode) A digital transmission switching format, with cells containing 5 bytes of header information followed by 48 data bytes. Part of the B-ISDN standard. Attenuation Reduction of signal magnitude, or loss, normally measured in decibels. Fiber attenuation is normally measured per unit l
11、ength in decibels per kilometer. Attenuation coefficient the rate of optical power loss with respect to distance along the fiber, usually measured in dB/km at a specific wavelength. The lower the number, the better the fiber 抯 attenuation will be. Attenuator An optical element that reduces the inten
12、sity of light passing through it (i.e., attenuates it). Avalanche Photodiode (APD) A semiconductor photodetector with integral detection and amplification stages. Electrons generated at a p/n junction are accelerated in a region where they free an avalanche of other electrons. APDs can detect faint
13、signals but require higher voltages than other semiconductor electronics. Average Power The average level of power in a signal that varies with time. AWG array waveguide filter. Axis The center of an optical fiber. Backbone System A transmission network that carries high-speed telecommunications bet
14、ween regions (e.g., a nationwide long-distance telephone system). Sometimes used to describe the part of a local area network that carries signals between branching points. Back Reflection ( or Backreflection) Back reflection refers to the reflected light as a portion of the input power and is the i
15、nverse of return loss, so that high return loss equals loss back reflection. Backscattering Scattering of light in the direction opposite to that in which it was originally traveling. Band pass The range of frequencies that will pass through a filter or other device. Synonymous with passband Bandwid
16、th The highest frequency that can be transmitted in analog operation. Also (especially for digital systems), the information-carrying capacity of a system. Baud Strictly speaking, the number of signal-level transitions per second in digital data. For some common coding schemes, this equals bits per second, but this is not true for more complex coding, where it is often misused. Telecommunication specialists prefer bits per second, which is less ambiguous. Beams
