Optical transmission system

DETAILED DESCRIPTION Referring to FIG.
1, there is illustrated a typical lightwave system.
Normally several low rate (tributary-rate) electrical digital signals are multiplexed together in multiplexer 10 to generate a high capacity linerate electrical signal at the output port.
The tributary rate signals can be multiplexed together by bit interleaving or block interleaving to generate the high capacity line rate signal.
The multiplexed digital electrical signal is transmitted over line 12 to an input port which modulates a laser beam by turning the output signal of laser 14 "on" or "off" according to the data.
The modulated output of the laser is coupled into a fiber optic transmission line 16 (usually a single mode fiber) for transmission to a remote location.
At the remote location, the optical data, in digital form, is detected by an optical receiver 18 and converted to an electrical signal.
The electrical signal is amplified, retimed and reshaped.
Thereafter, the signal is fed to demultiplexer 20 where it is demultiplexed into its tributary rate components to recover the original tributary rate digital signals.
The laser 14, the optical receiver 18 and the multiplexing electronics are referred to, collectively, as the line terminating equipment.
To be cost effective, lightwave transmission systems are normally designed to transmit the maximum signal bit rate along the maximum distance possible before requiring a signal regeneration equipment.
With no signal regeneration, the capacity and the length of a fiber transmission path is limited by two factors: system loss and dispersion.
The system loss is governed by the power of the signal from the transmitter, the sensitivity of the receiver, and the losses in the fiber and in the various components such as connectors, etc.
that are part of the transmission path.
Dispersion characteristics of optical fiber also limits the length of a fiber transmission path.
If a light source does not have a single frequency, the dispersion causes the light pulse to broaden as it travels down the fiber, and this broadening of the light pulse will reduce the maximum bit rate that can be transmitted