Siemens SIMATIC NET PROFIBUS Owner's Manual page 79

Receiver
The receiver of a digital optical transmission system consists of an optoelectric
converter (a photodiode), that converts the optical signals to electrical signals and
a signal converter that converts the electrical pulses received from the diode into
signals compatible with the connected electronics.
Attenuation
The attenuation of the transmission path is determined by the following factors:
S The choice of optical fiber
S The wavelength of the transmit diodes
S The type of connector
S With glass optical fibers, the number of splices (including repair splices)
S The length of the optical fiber (cable length)
S The link power margin on the link (for example for aging and temperature
dependency of the LEDs and photodiodes).
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Configuring Networks
3-13