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Electrical Fiber Optics in Sensors and Contr ol Systems 157
Light Pulse
Light Pulse
Electrical
Pulse Pulse
In Out
Electrical Light
To To
Light Electrical
Conversion Conversion
LED Photo
Light Source Detector

Electrical Pulse Out
Equals Electrical Pulse In
FIGURE 3.32 Fiber-optic communication system.

3.11 Fiber-Optic Information Link
A fiber-optic communication system (Fig. 3.32) consists of:

• A light source (LED or laser diode) pulsed by interface cir-
cuitry and capable of handling data rates and voltage levels
of a given magnitude.
• A detector (photodiode) that converts light signals to electri-
cal signals and feeds interface circuitry to re-create the origi-
nal electrical signal.
• Fiber-optic cables between the light source and the detector
(called the transmitter and the receiver, respectively).
It is usual practice for two-way communication to build a trans-
mitter and receiver into one module and use a duplex cable to com-
municate to an identical module at the end of the link. The 820- to
850-nm range is the most frequent for low-data-rate communication,
but other wavelengths (1300 and 1550 nm) are used in long-distance
systems. Fiber selection must always take transmission wavelength
into consideration.

3.12 Configurations of Fiber Optics
The selection of optical fiber plays a significant part in sensor perfor-
mance and information flow. Increased fiber diameter results in
higher delivered power, but supports a lower bandwidth. A fiber
with a 200-μm core diameter (glass core, silicone plastic cladding), by
virtue of its larger diameter and acceptance angle, can transmit five to
seven times more light than a 100-μm core fiber, or up to 30 times