Modern Optical Networks - Optical Signal Processing by Silicon Photonics - page 20

3.1 Evolution of Optical Fiber Communication Systems

The principles of fiber-optical communication systems are covered in many text-
books, for example, [ 7 , 8 ]. This section describes the basic principle of optical net-
work. Optical communication link is shown in Fig. 3.1 . Four key elements make up
nearly every optical communication link. The transmitter at the input of link consists
of a light source, typically a semiconductor laser diode (SLD) since the SLD gives
longer transmission distances than other light sources. The light is modulated either
directly by varying the laser driving current, or by an external modulator. At the out-
put of the link a photodetector converts the optical data signal into an electronic sig-
nal [ 9 ]. The transmission medium for the optical data signal is a fiber-optic cable.
The fourth element of link is the regenerator. For a long transmission distances,
regenerators can be used between the transmitter and the receiver to remove the
noise and recover the signal distorted along the fiber. The regenerators used for
single channel system are generally OEO regenerator, in which the optical signal
is received (optical signal is converted to electrical signal), regenerated, and re-
transmitted by a transmitter (electrical signal is converted back to optical signal).
OEO converters are also format-dependent, and their speed is limited by available
electronics. Nevertheless, OEO converters are so far one of the most mature tech-
nologies, due to its straight forward approach.

Pre- Amp

Decision
Circuit

PD

Tx

Transmission Fiber

λ 1

λ 1

Rx

SLD

Pre- Amp

Decision
Circuit

PC

MZ-IM

Rx Tx

O/E/O Regenerator

Fig. 3.1 A typical optical communication link [ 8 ]