Figure 6-11.Expanded-beam connector operation.
can combine the optical signal from two or more fibers
into a single fiber.
Fiber-optic couplers can be either active or passive
devices. The difference between active and passive
couplers is that a passive coupler redistributes the
optical signal without optical-to-electrical conversion.
Active couplers are electronic devices that split or
combine the signal electrically and use fiber-optic
detectors and sources for input and output.
Figure 6-12 shows the design of a basic fiber-optic
coupler. A basic fiber-optic coupler has N input ports
and M output ports. N and M ports typically range from
1 to 64. The number of input ports and output ports
varies, depending on the intended application for the
coupler. Types of fiber-optic couplers include optical
splitters, optical combiners, X couplers, star couplers,
and tree couplers.
AREA LIGHTING SYSTEMS
This section covers streetlighting, floodlighting,
and security lighting systems. When properly
constructed and installed, these original basewide
lighting systems will provide years of trouble-free
operation with a minimum of minor maintenance and
bulb changing required to keep the system fully
Several factors can change the base requirements
for area lighting. These factors include such changes as
facility usage, updating of systems, changes in the base
mission, or expanding existing systems.
With the cost of energy rising daily, any system that
can provide a higher level of efficiency for the energy
used must be considered. The use of the newer high-
pressure discharge systems for lighting seems to offer
savings both in the lifespan of the bulbs and in the
lumens per watt of energy used These systems are
replacing the older incandescent systems in an ever-
increasing pace. The higher initial cost of these systems
is being offset by the efficiency of the energy used and
savings of energy dollars.
You will need an understanding of lighting
techniques and effects to understand the physical
concepts and terminology involved in lighting systems.
We will use both the American Standard (AS) and the
metric system (SI) when discussing lighting concepts.
The AS standards will be without brackets, whereas the
SI terms will be noted in square brackets [ ].
The candlepower [candela], abbreviated cp [cd], is
the unit of luminous intensity. It is comparable to the
voltage in an electrical circuit and represents the force
that generates the light you can see. An ordinary wax
candle has a luminous intensity of approximately one
Figure 6-12.Basic passive fiber-optic coupler design.