This glossary defines technical terms that are specifically used in the fiber optics industry. Although an attempt is made to explain the most important terms in the industry, this is not a complete dictionary. If you have any questions or would like us to add a term to the glossary, please contact us.

Attenuation - The phenomenon of the loss of average optical power in an optical fiber or medium.

Bend Loss - Loss of power in an optical fiber due to bending of the fiber. Usually caused by exceeding the critical angle required for total internal reflection by internal light paths.

Core - The light conducting portion of an optical fiber. It has a higher refractive index than the cladding.

Cladding - Low refractive index material that surrounds the core of an optical fiber. It contains the core light while protecting against surface scattering. The cladding can be silica, plastic or specialty materials.

Critical Angle - The angle at which total internal reflection begins to take place.

Fiber Bundle - A rigid or flexible, concentrated assembly of glass or plastic fibers used to transmit light.

Fiber Optics - The branch of optical technology concerned with the transmission of radiant power through fibers made of transparent materials such as glass, fused silica or plastic.

Fresnel reflection loss - Reflection losses incurred at input and output of optical elements because of the difference in refractive index between glass and the immersion medium.

Fused quartz - Crystal quartz that is melted at a white heat and cooled to form an amorphous glass. It is not birefringent and the refractive index is much lower than that of crystal quartz. Fused quartz of optical quality can be prepared by suitable techniques.

Fused silica - Glass consisting of almost pure silicon dioxide (SiO2). Also called vitreous silica. It is also called fused synthetic silica. Frequently used in optical fibers and windows.

Incoherent bundle - A bundle of filaments of optical glass or other transparent materials that transmit only light, not optical images. The arrangement of the individual fibers in the bundle is not sufficiently regular to transmit optical images.

Index of Refraction - The ratio of the speed of light in a vacuum to the speed of light in a refractive material at a given wavelength.

Multimode distortion - In an optical waveguide, the distortion resulting from differential mode delay. Axial rays, with the shortest path length, will have the shortest transmission time, while rays entering the fiber at its maximum acceptance angle will travel further and require the maximum time.

Multimode fiber - An optical fiber that will allow more than one mode to propagate.

Numerical aperture - The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index ri of the medium in which the vertex of the cone is located. Alternatively, the square root of the difference between the square of the core ri less the square of the
clad (ri).

Optical fiber - A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote internal reflection.

Total Internal Reflection - The phenomenon involving the total
reflection of all incident light off the core/clad boundary.

Transmission - In optics, the conduction of radiant energy through a medium. Often denotes the percentage of energy passing through an element or system relative to the amount that entered.

Ultraviolet - That invisible region of the spectrum just beyond the violet end of the visible region. Wavelengths range from 1 to 400 nm.

Visible spectrum - That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to 700 nm in wavelength.