Index matching material
A material, usually a liquid, gel or paste or film whose index of refraction matches the fibre optic glass. It is used at the end face of the fibre to reduce Fresnel reflections.

Index of refraction
The ratio between the speed of light in a vacuum and lights speed in a referenced medium.

Index profile
Curve of the refractive index over the cross section of an optical waveguide.

Insertion loss
Attenuation between the inlet and the outlet port. Loss in an optical fibre due to the methods of coupling the fibre to the power, as well as absorption, dispersion, scattering, micro-bending, diffusion. Usually measured in dB per incident, for instance a coupler, a connector, a splice or in fibre, dB per km. Most commonly used to describe the power lost at the entrance to a waveguide, (a fibre is a waveguide) due to axial misalignment, lateral displacement, Fresnel reflection etc. that is most applicable to connectors.

Intrinsic joint loss
This is the theoretical minimum loss that a given joint or device will have as a function of its nature.

IP-DSLAM
Ethernet-interface Digital Subscriber Line Access Multiplexer; DSLAM with Ethernet interface and
Ethernet management and protocol interface

IR: Infrared
This is the band of electromagnetic radiation beyond the red wave length, whose wavelength is between 750 and 1,000 nanometers.

Isolator
These are usually installed to protect the source from interference by unacceptable noise to signal ratios caused by reflectance, mostly caused by EDFA systems, and/or the cumulative effect of the passive plant.