Glossary I-Z

INDEX OF REFRACTION (Or Refractive Index)

The relationship between the speed of light in vacuum or isolation, and the speed of light in a specific material or substance.  The refractive index of a material is a dimensionless quantity that quantifies the decrease in propagation speed of the electromagnetic radiation, when it passes through a material.



The signal loss of power following the insertion of a component in an optical circuit (for example, the loss due to the presence of a coupling in an optical network).



A network protocol which belongs to the Internet protocol suite TCP / IP port on which the operation of the Internet is based. IP is a protocol in which information is sectioned into small packets, which travel separately across the network, and then are reunified by the information receiving device.



International Telecommunications Union: the UN agency that assists in the development and coordination of worldwide technical standards for telecommunications).



Light Amplification by Stimulated Emission of Radiation:  A device capable of emitting a beam of coherent monochromatic and concentrated light in a highly collimated beam straight, through the process of stimulated emission. The laser brightness is very high compared to traditional light sources. The use of laser in optical fibers is due to the peculiarity of emitting a large optical power in a few square microns.


LED (Light Emitting Diode)

A device used in a transmitter for converting optical information into electrical information. The LEDs have large spectrum widths.


LSZH (Low Smoke Zero Halogen)

An abbreviation used in cables that do not contain halogens, and that, in the event of fire, guarantee a very limited production of opaque smoke and toxic gasses which are harmful and corrosive.



The last mile refers to the final leg of the access network, i.e. the network that extends between the data center or provider and the end user. Also called the local loop, can experience limitations when composed of copper wire.



The method used in telecommunications wherein multiple analog or digital signals are combined into a single transmission medium. Many different signals can be sent within the same wire, with different wavelengths.


OLT (Optical Line Termination)

An apparatus present in data centers that has the dual purpose of converting the signal from electrical to optical of the various systems of the service provider (Telecom Italy, Vodafone etc), and coordinating the multiplexing.



Multimode fiber New definition:

OM1: 62.5 fibers / 125

OM2: 50/125

OM3: 50/125 of high quality that can carry 10 Gb Ethernet data rates up to a maximum length of 300m.

OM4: 50/125 multimode fibers of the highest quality suitable to carry up to 10 Gb Ethernet at a maximum distance of 550m.


OTDR (Optical Time Domain Reflectometer)

An instrument that assesses the performance over time of the reflected component of the signal by sending a short pulse of light into the fiber and observing the backscattered light. Analysis by optical reflectometer allows the user to evaluate the length and overall attenuation of the fiber, including the presence of joints, couplings, and mitigations that they introduce. One can also find a complete break of the optical transmission line and estimate the distance from the point of analysis.



Transducer device that converts an optical signal at a given wavelength into an electrical signal.



A type of network architecture in optical fiber, characterized by the presence of a fiber coming from the central platform that is split along the path into more fibers, through the use of splitters. It is an optical network in a tree structure, in which each user receives a portion of the signal, according to the number of splitters present along the network (the lower the number of splitters, the less signal).

This is distinguished from the “point to point” network, in which each user has a dedicated network derived from the central platform (with obvious advantages in terms of available bandwidth).



Type of fiber optic network architecture in which each user has a fiber connection dedicated to them, derived from the Central platform. This architecture is more expensive than the PON but allows greater bandwidth capacity and is customizable for each user.



In computing and telecommunications, POP (Point of Presence) is a network access point (router), provided by an Internet Service Provider (ISP), that can route traffic to the end users connected to it (individuals and small organizations).



Internet Service Provider or  ISP  (or simply ‘provider’ when used in computer context), is a commercial structure or organization that offers users (residential or business) internet services by contract, principally access to Internet and e-mail.



Return loss is the loss of signal power resulting from imperfections generated at the discontinuities in a line of optical fiber transmission. It is measured in dB at specific wavelengths.



A router is an electronic device which, in a packet switched computer network, is responsible for routing data, subdivided into packets between different networks.



VDSL is a DSL technology that achieves high transmission speeds using DSL technology. It is, therefore, an enhancement of classical ADSL, whose data travel through copper. For very short distances, less than 300 meters, it is possible to have a connection at 26 Mbit / s symmetric or 52 Mbit / s downstream or download and 12 Mbit / s in the transmission or upload.

A variant of VDSL, called VDSL2, is currently used by Telecom Italy in FTTC (Fiber to the cabinet).



The wavelength measures the distance between any point of a wave to the corresponding point on the next wave, from crest to crest for example.  The wavelength determines the nature of the various forms of radiant energy that comprise the electromagnetic spectrum (the color of light).
Wavelengths used in optical fiber communications are measured in nanometers (nm) and are related to frequencies of infrared rays: 850 nm (the first window), 1300 nm (second window) and 1550 nm (third window).