C: Abbreviation for Celsius. Measure of temperature where pure water freezes at 0° and boils at 100°.

Cable: One or more optical fibers enclosed, with strength members, in a protective covering.

Cable Assembly: A cable that is connector terminated and ready for installation.

Cable Plant: The cable plant consists of all the optical elements including fiber, connectors, splices, etc. between a transmitter and a receiver.

Cable Television: Communications system that distributes broadcast and non-broadcast signals as well as a multiplicity of satellite signals, original programming and other signals by means of a coaxial cable and/or optical fiber.

Carrier-to-Noise Ratio (CNR): The ratio, in decibels, of the level of the carrier to that of the noise in a receiver’s IF bandwidth before any nonlinear process such as amplitude limiting and detection takes place.

CATV: Originally an abbreviation for community antenna television; the term now typically refers to cable television.

C-Band: The wavelength range between 1530 nm and 1562 nm used in some CWDM and DWDM applications.

CCIR: Abbreviation for Consultative Committee on Radio. Replaced by ITU-R.

CCITT: Abbreviation for Consultative Committee on Telephony and Telegraphy. Replaced by ITU-T.

CCTV: Abbreviation for closed-circuit television. An arrangement in which programs are directly transmitted to specific users and not broadcast to the general public.

CD: Abbreviation for compact disk. Often used to describe high-quality audio, CD-quality audio, or short-wavelength lasers; CD Laser.

CDMA: Abbreviation for code-division multiple access. A coding scheme in which multiple channels are independently coded for transmission over a single wideband channel using an individual modulation scheme for each channel.

Center Wavelength: In a laser, the nominal value central operating wavelength. It is the wavelength defined by a peak mode measurement where the effective optical power resides (see illustration). In an LED, the average of the two wavelengths measured at the half amplitude points of the power spectrum.

Central Office (CO): A common carrier switching office in which users’ lines terminate. The nerve center of a communications system.

CGA: Abbreviation for color graphics adapter. A low-resolution color standard for computer monitors.

Channel: A communications path or the signal sent over that path. Through multiplexing several channels, voice channels can be transmitted over an optical channel.

Channel Capacity: Maximum number of channels that a cable system can carry simultaneously.

Channel Coding: Data encoding and error correction techniques used to protect the integrity of data. Typically used in channels with high bit error rates such as terrestrial and satellite broadcast and videotape recording.

Circulator: Passive three-port devices that couple light from Port 1 to 2 and Port 2 to 3 and have high isolation in other directions.

Cladding: Material that surrounds the core of an optical fiber. Its lower index of refraction, compared to that of the core, causes the transmitted light to travel down the core.

Cladding Mode: A mode confined to the cladding; a light ray that propagates in the cladding.

Cleave: The process of separating an optical fiber by a controlled fracture of the glass, for the purpose of obtaining a fiber end, which is flat, smooth, and perpendicular to the fiber axis.

cm: Abbreviation for centimeter. Approximately 0.3937 inches.

CMOS: Abbreviation for complementary metal oxide semiconductor. A family of IC’s. Particularly useful for low-speed or low-power applications.

CMTS: Abbreviation for cable modem termination system.

Coarse Wavelength-Division Multiplexing (CWDM): CWDM allows eight or more channels to be stacked in the 1550 nm region of optical fiber, the C-Band. Extended CWDM can include as many as 18 channelsranging from 1270 nm to 1610 nm.

Coating: The material surrounding the cladding of a fiber. Generally a soft plastic material that protects the fiber from damage.

Coherent Communications: In fiber optics, a communication system where the output of a local laser oscillator is mixed optically with a received signal, and the difference frequency is detected and amplified. Essentially using an optical signal as an FM signal, i.e. modulating the wavelength (color) of the light.

Color Subcarrier: The 3.58 MHz signal which carries color information in a TV signal.

Composite Second Order (CSO): An important distortion measure of analog CATV systems. It is mainly caused by second-order distortion in the transmission system.

Composite Sync: A signal consisting of horizontal sync pulses, vertical sync pulses, and equalizing pulses only, with a no-signal reference level.

Composite Triple Beat (CTB): An important distortion measure of analog CATV systems. It is mainly caused by third-order distortion in the transmission system.

Composite Video: A signal which consists of the luminance (black and white), chrominance (color), blanking pulses, sync pulses, and color burst.

Concentrator: 1) A functional unit that permits a common path to handle more data sources than there are channels currently available within the path. Usually provides communication capability between many low-speed, asynchronous channels and one or more high-speed, synchronous channels. 2) A device that connects a number of circuits, which are not all used at once, to a smaller group of circuits for economy.

Concentricity: The measurement of how well-centered the core is within the cladding.

Connector: A mechanical or optical device that provides a demountable connection between two fibers or a fiber and a source or detector.

Connector Plug: A device used to terminate an electrical cable (illustrated) or an optical cable.

Connector Receptacle: The fixed or stationary half of a connection that is mounted on a panel/bulkhead. Receptacles mate with plugs.

Connector Variation: The maximum value in dB of the difference in insertion loss between mating optical connectors (e.g., with remating, temperature cycling, etc.). Also called optical connector variation.

Converter: Device that is attached between the television set and the cable system that can increase the number of channels available on the TV set, enabling it to accommodate the multiplicity of channels offered by cable TV.  Converter boxes are becoming obsolete as old model televisions requiring a converter are replaced by modern televisions, which incorporate a converter into the television directly. Also called a set-top box.

Core: The light-conducting central portion of an optical fiber, composed of material with a higher index of refraction than the cladding. The portion of the fiber that transmits light.

Counter-Rotating: An arrangement whereby two signal paths, one in each direction, exist in a ring topology.

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Coupler: An optical device that combines or splits power from optical fibers.

Coupling Ratio/Loss (C_R, C_L): The ratio/loss of optical power from one output port to the total output power, expressed as a percent or as decibels. For a 1 x 2 coupler with output powers O₁ and O₂, and O_i representing both output powers:

Critical Angle: In geometric optics, at a refractive boundary, the smallest angle of incidence at which total internal reflection occurs.

Cross-Connect: Connections between terminal blocks on the two sides of a distribution frame or between terminals on a terminal block (also called straps). Also called cross-connection or jumper.

Cross-Gain Modulation (XGM): A technique used in wavelength converters where gain saturation effects in an active optical device, such as a semiconductor optical amplifier (SOA), allow the conversion of the optical wavelength. Better at shorter wavelengths (e.g. 780 nm or 850 nm).

Cross-Phase Modulation (XPM): A fiber nonlinearity caused by the nonlinear index of refraction of glass. The index of refraction varies with optical power level which causes different optical signals to interact.

Crosstalk (XT): 1) Undesired coupling from one circuit, part of a circuit, or channel to another. 2) Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates and undesired effect in another circuit or channel.

CSMA/CD: Abbreviation for carrier sense multiple access with collision detection. A network control protocol in which (a) a carrier sensing is used and (b) while a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, waits for a jam signal, and then waits for a random time interval before trying to send that frame again.

CTS: Abbreviation for clear to send. In a communications network, a signal from a remote receiver to a transmitter that it is ready to receive a transmission.

Customer Premises Equipment (CPE): Terminal, associated equipment, and inside wiring located at a subscriber’s premises and connected with a carrier’s communication channel(s) at the demarcation point (demarc), a point established in a building or complex to separate customer equipment from telephone company equipment.

Cutback Method: A technique of measuring optical fiber attenuation by measuring the optical power at two points at different distances from the test source.

Cutoff Wavelength: In single-mode fiber, the wavelength below which the fiber ceases to be single-mode.

CW: Abbreviation for continuous wave. Usually refers to the constant optical output from an optical source when it is biased (i.e., turned on) but not modulated with a signal.