Glossary – C


A container that may enclose connection devices, terminations, and equipment.

Cable assembly
A fixed length of cable with connectors installed on both ends. Sometimes called a patchcord, patch cable, or jumper.

Cable jacket
The protective outer covering of wire or optical cable. Common materials include polyethylene (PE), polyurethane (PU), polyvinyl chloride (PVC) and Teflon (plenum).

Cable rack
Vertical or horizontal open support attached to a ceiling or wall.

Cable tray
A ladder, trough, solid bottom, or channel raceway intended for, but not limited to, the support of telecommunications cable.

Carrier frequency
The electromagnetic wave frequency selected to transmit information. Optical carrier frequency is from the infrared, visible, or ultraviolet spectrum areas (1012Hz and above).

Carrier-to-noise ratio (CNR)
A quantification of analog system noise. The ratio, expressed in decibels, of the level of the carrier to that of the noise in the receiver bandwidth before any nonlinear process such as amplitude limiting and detection takes place.

The C-band is the “conventional” DWDM transmission band, occupying the 1530 to 1565 nm wavelength range, as specified by the ITU-T G.692. Most EDFAs operate in the C-band.

Center wavelength (CW)
The nominal value operating wavelength in a laser; thereby, the wavelength defined by a peak mode measurement where the effective optical power resides. Also, the average of the two wavelengths measured at half amplitude points of the power spectrum in lasers and LEDs.

Central office (CO)
The building in which telephone companies, etc., locate their switching equipment and terminate their circuits. Sometimes called an “exchange.”

Central strength member (CSM)
A semi-rigid, fibered glass or metallic rod located in the center of a multifiber cable assembly. Usually referred to as dielectric, it provides a directional form for wrapping and stability. This inhibits the buffers from being damaged (stressing the fibers) during the bending of the cable.

Central tube cable
See Unitube cable. This type of cable has a large central tube in which the fibers are grouped using color-coded binder thread. Unitube cables
are physically smaller than stranded-type cables. Also known as central tube or LXE cable.

Centralized cabling
Provides connections from the work areas to the centralized cross connect by allowing the use of pull-through cables, an interconnect, or splice in the telecommunications closet.

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

Chromatic dispersion (CD)
The variation in the velocity of light (group velocity) as a function of wavelength. It causes pulses of a modulated laser source to broaden when traveling within the fiber, up to a point where pulses overlap and bit error rate increases. CD is a limiting factor in high-speed transmission and must be properly compensated, which implies proper testing. A combination of material and waveguide dispersion.

The low refractive index material, usually glass, that surrounds and protects the core and provides the optical refractive barrier.

A technique where an optical fiber is scratched to produce flat end surfaces that are perpendicular to the longitudinal axis
of the fiber. See scribe.

Cleave and crimp
A connector installation technique, also known as a no-polish connector. The plug is installed onto the cable with the optic protruding from the end. The cable is crimped to the connector and the optic is cleaved as close to the connector endface as possible.

Cleave tool
A device consisting of a scribing blade, usually made from either diamond or tungsten carbide, used to score a fiber in order to break it without causing a fracture, hackles or angular irregularities. Also known as a cleaver or scribe tool.

In data communications, a device that generates preciselyspaced timing pulses used for synchronizing transmissions and recording elapsed times.

Closed circuit television (CCTV)
Video transmissions not provided for public access.

Short for splice closure. A cable and fiber management product that environmentally protects and houses optical splices. Available as in-line
or butt style, the closure is usually in a dome or clamshell configuration. Splice closures can also hold connectors and optical splitters. Telcordia GR-771 specifies mechanical requirements and environmental specifications and tests

Coarse wavelength division multiplexing (CWDM)
Applies to greater separation of wavelengths than DWDM. In single-mode applications, CWDM defines a 20-nm separation from 1471 nm to 1611 nm. With multimode fibers, the wavelengths are 778, 800, 825, and 850 nm.

A plastic or acrylate coating, normally up to 245-250 microns, that is placed over the cladding during the manufacturing process. After this process, the fiber can be colored or upper coated to 900 microns for use in tight buffered cables. See buffer coating.

Coaxial cable
A type of cable with a central conductor, an insulator, and a solid or braided shield inside a tough jacket. The inner insulation maintains a constant distance between the central conductor and the shielding, providing a superior quality signal over longer distances.

COder/DECoder. A device or software that allows converts analog to digital and digital to analog in order to transmit data over digital lines.

Coefficient of expansion
The rate that a material or composite object expands or contracts due to temperature changes

Lasers and LEDs emit coherent light waves that are in phase with one another. Coherence describes properties of the correlation between a single wave, or between several waves or wave packets. When interfering, two waves can add together to create a wave of greater amplitude than either one
(constructive interference) or subtract from one another to create a wave of lesser amplitude than either one (destructive interference).

A process in which a divergent or convergent beam of radiation is converted into a beam with the minimum divergence as possible, preferably parallel.

Color code
A color system for circuit identification by use of solid colors, contrasting stripes, tracers, braids, surface markings, etc., as determined by the TIA-598 standard.

Community antenna television (CATV)
Assumed to be cable television, CATV uses fiber and coaxial media to provide voice, video, or data services.

Competitive local exchange carrier (CLEC)
A company that provides its own network and switching in competition with the already-established ILEC. A newlyformed exchange company in direct competition with the ILEC for the telecom transport market in a specific area. Also known as competitive access provider (CAP).

Composite cable
A cable with a combination of optical fibers and copper (coaxial, twisted pair, or power). Often confused with hybrid cables.

Composite second order (CSO)
An analog signal distortion that can result in a visual impairment in picture quality, e.g., a rolling or intermittent diagonal line across the TV screen.

Composite triple beat (CTB)
Combination of distortions caused by nonlinearities generated by amplifiers and other components in a cable TV network handling many RF signals.

Any technique for reducing a transmission bandwidth requirement by reduction of the data stream needed to convey the information. Compression standards are identified by MPEG.

A pipe made of metal, plastic, or clay used for the installation of communications or power cables between two or more locations.

Cone of acceptance
See critical angle.

Most fiber optic connectors consist of two plugs and one adapter. Connectors can be push/pull types (SC, LC, MPO etc.), bayonet (ST), or threaded (FC). Most use a 2.5-mm ferrule but small form factor types use the smaller 1.25-mm ferrule. Other features include a key and keyway that provide critical alignment for repeatability and for strain relief internally and at the rear boot. Bonding techniques include thermal cure, anaerobic adhesive, and UV adhesive. Splice-on plugs use a prepolished fiber stub and then are mechanically or fusion spliced. Military, industrial, and heavy-duty specialized connectors may use expanded beam lenses and termini contacts (instead of ferrules) based on standard Mil/Aero
dimensions. Key specifications for all connectors include attenuation, reflectance, and repeatability.

A step during the optical fiber manufacturing process during which the bait rod is removed and the remaining silica is heated at high temperatures (sintering) to drive out impurities and water and leave only a pure glass rod.
Continuity testing

A test that shows that the optical path is continuous with no breaks.

Continuous wave (CW)Energy is emitted from a module continuously, rather than in short pulses. CW applications require the laser to be on at all
times. Constant output from an optical source that is active but not modulated by a signal.

Controlled environment vault (CEV)
A reinforced vault designed to provide an environmentallystable underground area to house fiber optic transmission equipment and electronics for switching, monitoring, back-up power, remote terminals, etc.

Tight buffered breakout cables used to build patch cords (jumpers). Internally, the fibers are normally one or two 900-micron coated fibers. The term “zipcord” describes a two-fiber cordage to allow two separate plugs to have their own strain relief.

The light guiding part of the fiber with a refractive index higher than that of the cladding.

Core concentricity
A measure of the relationship between the geometric center of the core of an optical fiber and the geometric center of the cladding, or how centered the core is.

Core ovality
A ratio of the minimum to maximum diameters of the core within an optical fiber, or how round the core is.

See splitter.

Coupling loss
The optical attenuation of a connection or passive device, expressed as a value in dB.

Coupling ratio
A measure of how a device distributes light from its inputs to its outputs. Expressed as either a percentage or in dB.

A 100-Gb/s C form factor pluggable optical transceiver from Cisco.

Crimp sleeve
A sleeve of lightweight metal is deformed by compression to encapsulate material and provide strain relief at the rear of a fiber optic plug.

Critical angle
The minimum angle at which light can be propagated within a fiber. Sine critical angle equals the ratio of the numerical aperture to the index of refraction of the fiber core.

See patch panel.

Cross-phase modulation (XPM)
A nonlinear optical effect where one wavelength of light affects the phase of a similar wavelength of light.

Crush resistance
A test that determines the ability of a fiber optic cable to mechanically and optically withstand the effects of a compressive force. Testing specifies the changes in optical transmittance or attenuation during compressive loading. Specified in the TIA/EIA 455-41 “Compressive Loading
Resistance of Fiber Optic Cables” fiber optic test procedure.

Carrier suppressed return-to-zero differential quadrature phase shift keying, a technology that makes it possible to generate DWDM signals with bit rates of 100 Gb/s and beyond per channel and transmit them over long distances.

Curing oven
An oven specifically manufactured to use thermal curing to harden the epoxy injected into a fiber-optic ferrules.

Customer premises equipment (CPE)
The telecommunications terminal equipment located on the customer’s premises, including telephones, private branch exchanges, and data terminals.

Cutback method
A technique for measuring fiber attenuation by performing two transmission measurements. One is done at the output end of the full length of the fiber. The other is usually done within 1-3 meters of the input end and accessed by “cutting back” the test fiber and measuring the change in the pre- and post-cutback measurements.

Cutoff wavelength
That wavelength greater than which a particular waveguide mode ceases to be a bound mode. When transmitting lower than a single-mode fiber’s cutoff wavelength, the fiber transmits multimode. For G.652 single-mode fibers the cutoff wavelength is 1260 nm. For G.655 fibers, it can range from 1260 nm to 1450 nm.