Cable
A package or assembly for an optical fibre or fibres that may include buffering, strength members and/or an outer jacket.

Central member
The center component of a cable. It serves as an antibuckling element to resist temperature-induced stresses. Sometimes serves as a strength element. The central member material is steel, fiberglass, or glass-reinforced plastic.

Chromatic dispersion
The separation of a beam into ist various wavelength components. In an optical fibre, dispersion occors because of the differing wavelengths propagating at different speeds.

Cladding
The material, normally a glass or plastic with a slightly mismatched index or refraction that protects the core and provides optical insulation to the light signal carried in the core. The low refractive index optical material surrounds the core of an optical fibre. It is used to cause reflection of the core light while preventing surface contact from scattering or the generation of frustrated internal reflection. In all-glass fibres, the cladding is glass. In plastic-clad silica fibres, e.g. HCS-fibres, the plastic cladding also may serve as the coating

Cladding mode
Light contained within the cladding by the buffer boundary.

Composite cable
A cable containing both fiber and copper media or containing two different fiber types simultaneously.

Concentricity error
The tolerance errors describing the lack of concentricity between the core in position to its cladding, as well as the distribution of concentricity errors between the distribution of the fibre cladding and the ID of the ferrule capillary diameter. Also the concentricity between the ID capillary diameter and the OD of the ferrule.

Connector
A device mounted on the end of a fibre optic cable for mating to a similar mateable device.

Core
The central part of the fibre having a higher index of refraction than the cladding, which guides the light.
Usually made of Ge-doped synthetic silica, but can be doped with additional materials to provide special fiber characteristics.

Core eccentricity
A measure of the displacement of the center of the core relative to the cladding center.

Core ellipticity (non-circularity)
A measure of the departure of the core from roundness.

Coupler
A device that connects three or more fibre ends. Most often made by the fused biconic taper process wherein the fibre is stretched, the mode fields of the two fibres are brought into intimate contact allowing or causing the light in one core to be shared with the core in the neighbouring fibre. The split ratio is determined by the degree of intimacy, for instance 50/50 in a 1 by two. The key characteristics of the coupler are the split ratio tolerance, the excess loss, the wavelength dependence and the total insertion loss.

Coupling
Transferring light into or out of an optical fibre. (Does not mean a coupler was used; for instance splicing and connecting result in coupling.)

Coupling ratio (CR)
Percentage division ratio of the optical performance at the outlets of an optical coupler or splitter.

Crimp and Cleave (C&C)
A process of finishing an end of fiber, allowing it to be terminated.

Critical angle (of total reflection)
The smallest angle that will completely reflect a ray within a fibre. The issue of the critical angle relates to why angled physical contact connectors create a coupling with lower reflectance.

Crosstalk
In fibre optics, crosstalk is the assimilation of transient unwanted signals or noise from another fibre or device.

Cutback
A method for measuring the attenuation or bandwidth in a fibre by measuring from the end, and then from a shorter length and comparing the difference.

Cutback measurement
Measurement of optical loss made by measuring the loss of both a long and shorter unit of a fibre.

Cutoff wavelength
The wavelength where the second order mode experiences 19.3 dB greater attenuation than the fundamental mode. The cutoff wavelength is a function of both the number of bends and length of the fibre.

CWDM
Coarse Wave Division Multiplexing is an optical multiplexing technique used to increase the carrying capacity of a fiber network.