Digital Transmission
Most fibre optic systems are digital transmission systems where the light is being turned off or on
to represent zeros and ones. The actual quantity of light getting through is not critical (provided
there is enough to see it). The system will nearly always consist of the following items:
Transmitter
A transmitter converts the input electrical signal to a serial bit stream of zeros and ones. This
stream is converted into an optical signal, made up of pulses of light, by a suitable light source
usually a laser for telecommunications systems or an LED (light emitting diode) for datacoms or
short range systems.
Optical Waveguide Fibre
Optical fibre can be identified by the type of paths that the lightwave rays, or modes, travel within
the fibre core. There are two types of fibre: Multimode and Singlemode.
An optical fibre acts as the transmission medium, guiding the light from the transmitter to the receiver.
Receiver
The receiver will have a photo-diode which converts the optical signal back into an electrical
signal and then some electronics to convert the signal back to the same form that was fed into the
transmitter.
Cable
The fibre will need protection from the harsh environment where it is to be installed. This
protection is provided by an appropriate cable construction to suit each situation.
Connectors
At each end of the system the fibre end face must line up with the active equipment (light source or the detector). A connector like the ST style is used for this application. The fibre is installed and polished inside the connector.
Splices
Splices are used to join together sections of fibre cable that are installed in the environment, eg. overhead and underground. Splices are usually submersible for all outdoor applications. Patrick Boshell is V.P. Engineering and Outside Plant at e>connect in Toronto, Ontario.