FIBER OPTICS AND LIGHTING SYSTEMS
This chapter will expand on the information you
learned in the CE Basic TRAMAN on fiber optics and
area lighting and also introduce you to airfield lighting
The CE Basic TRAMAN taught you that a fiber-
optic data link had three basic functions:
To convert an electrical input signal to an optical
To send the optical signal over an optical fiber
To convert the optical signal back to an electrical
The fiber-optic data link converts an electrical
signal into an optical signal, permitting the transfer of
data along an optical fiber. The fiber-optic device
responsible for that signal conversion is a fiber-optic
transmitter.A fiber-optic transmitter is a hybrid
device. The transmitter converts electrical signals into
optical signals and launches the optical signals into an
optical fiber. A fiber-optic transmitter consists of an
interface circuit, a source drive circuit, and an
The interface circuit accepts the incoming
electrical signal and processes it to make it compatible
with the source drive circuit. The source drive circuit
intensity modulates the optical source by varying the
current through the source. An optical source converts
electrical energy (current) into optical energy (light).
Light emitted by an optical source is launched, or
coupled, into an optical fiber for transmission.
Fiber-optic data link performance depends on the
amount of optical power (light) launched into the
optical fiber. This chapter provides an overview of
optical sources and fiber optic transmitters.
OPTICAL SOURCE PROPERTIES
The development of efficient semiconductor
optical sources, along with low-loss optical fibers, has
led to substantial improvements in fiber-optic
communications. Semiconductor optical sources have
the physical characteristics and performance
properties necessary for successful implementations
of fiber-optic systems. Optical sources should do the
Be compatible in size to low-loss optical fibers
by having a small light-emitting area capable of
launching light into fiber.
Launch sufficient optical power into the optical
fiber to overcome fiber attenuation and connection
losses, allowing for signal detection at the receiver.
Emit light at wavelengths that minimize optical
fiber loss and dispersion. Optical sources should have a
narrow spectral width to minimize dispersion.
Allow for direct modulation of optical output
Maintain stable operation in changing
environmental conditions (such as temperature).
Cost less and be more reliable than electrical
devices, thereby permitting fiber-optic communication
systems to compete with conventional systems.
Semiconductor optical sources suitable for fiber-
optic systems range from inexpensive light-emitting
diodes (LEDs) to more expensive semiconductor
lasers. Semiconductor LEDs and laser diodes (LDs)
are the principal light sources used in fiber optics.
DIODES AND LASER DIODES
Semiconductor LEDs emit incoherent light.
Spontaneous emission of light in semiconductor LEDs
produces light waves that lack a fixed-phase
relationship. Light waves that lack a fixed-phase
relationship are referred to as incoherent light. LEDs
are the preferred optical source for multimode systems
because they can launch sufficient power at a lower
cost than semiconductor laser diodes (LDs).
Semiconductor LDs emit coherent light. Light
waves having a fixed-phase relationship are referred to
as coherent light. Since semiconductor LDs emit more
focused light than LEDs, they are able to launch optical