Fiber In Communications
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has become the communications medium of choice for telephones, cell
phones, CATV, LAN backbones, security cameras, industrial networks,
just about everything.
Why use fiber?
biggest advantage of optical fiber is the fact it is the most cost
effective means of transporting information. FIber can transport more
information longer distances in less time than any other
communications medium, as the photo on the left from the late 1970s
illustrates so well. The bandwidth and distance capability of fiber
means that fewer cables are needed, fewer repeaters, less power and
less maintenance. In addition, fiber is unaffected by the interference
of electromagnetic radiation which makes it possible to transmit
information and data with less noise and less error. Fiber is lighter
than copper wires which makes it popular for aircraft and automotive
applications. These advantages open up the doors for many other
advantages that make the use of optical fiber the most logical choice
in data transmission.
advantages have led to fiber becoming the transport medium of choice
for practically all data, voice and video communications.
telcos and CATV operators use fiber for economic reasons, but their
cost justification requires adopting new network architectures to take
advantage of fiber's strengths. LAN and premises network designers and
installers now realize that they must also adopt new network
architectures too. A properly designed premises cabling network can
also be less expensive when done in fiber instead of copper. Conversion
from copper networks is easy with media converters, gadgets that
convert most types of systems to fiber optics. Even adding the cost of
the media converters, the fiber optic network will usually be less than
copper when the proper architecture is used.
Fiber Optic Communication Networks
Outside Plant Networks
networks were the first major users of fiber optics. Fiber optic links
were used to replace copper or digital radio links between telephone
switches, beginning with long distance links, called long lines, where
fiber's distance and bandwidth capabilities made fiber significantly
more cost effective. Telcos use fiber to connect all their central
offices and long distance switches because it has thousands of times
the bandwidth of copper wire and can carry signals hundreds of times
further before needing a repeater - making the cost of a phone
connection over fiber only a few percent of the cost of the same
connection on copper.
long distance links were converted to fiber, telcos began replacing
shorter links between switches with fiber, for example between switches
in the same metropolitan area. Today, with the exception of some rugged
or remote locations, the entire telephone backbone is fiber optics.
Cables on the land are run underground, direct buried or aerially,
depending on the geography and local regulations. Connections around
the world are run primarily on undersea cables which now link every
continent and most island nations with the exception of Antarctica.
long distance links were converted to fiber, telcos began replacing
shorter links between switches with fiber, for example between switches
in the same metropolitan area. Today, practically all the telephone
networks have been converted to fiber. Telcos and other groups are now
running fiber right to the home, (FTTH) using low cost passive optical
network (PON) systems that use splitters to share the cost of some
fiber optic components among as many as 32 subscribers. More on FTTH, FTTH PON types and FTTH network architecture.
cell phone networks have fiber
backbones. It's more efficient and less expensive than using precious
wireless bandwidth for backbone connections. Cell phone towers with
many antennas will have large cable trays or pedestals where fiber
cables connect to the antenna electronics. More on wireless.
Internet has always been based on a fiber optic backbone. It started as
part of the telephone network when it was primarily voice and data
traffic was mixed into the total traffic. But data has
become the largest communications network as data traffic has outgrown
voice traffic. The Internet now transmits user communications, e.g.
requesting and downloading web pages or email, peer-to-peer
transmissions, streaming video and massive data transfers between data
centers. Large Internet providers are moving toward dedicated Internet
networks that do not have the high overhead of telco networks which are
burdened with transporting dozens of different types of communications
services still being supported by the telco system providers. Now the
telcos are moving their voice communications to
Internet protocol (IP) for lower costs.
The Internet architecture looks like the telecom network shown above. The major difference is the traffic and switching. Internet traffic is mainly IP/Ethernet not the dozens of digital telecom protocols still being used. Switching is replaced by routing which uses switches called routers which learn many possible routes for traffic and can bypass switches which are out of service.
Most CATV systems are using fiber backbones too. CATV
companies use fiber because it give them greater reliability
and the opportunity to offer new services, like phone service and
used to have a terrible reputation for reliability, not really a
problem with service but with network topology. CATV uses very high
frequency analog signals, up to 1 GHz, which has high attenuation over
coax cable. For a city-wide system, CATV needed many amplifiers
(repeaters) to reach the users at the end of the system; 15 or more we
common. Amplifiers failed often, meaning that subscriber downstream of
the failed amp lost signal. Finding and fixing failed amps was
difficult and time consuming, causing subscriber complaints.
development of highly linear distributed feedback (DFB) lasers allowed
CATV systems to be converted to analog optical systems.
CATV companies "overbuild" with fiber. They connect their headends with
fiber and then take fiber into the neighborhood. They lash the fiber
cable onto the aerial "hardline" coax used for the rest of the network
or pull it in the same conduit underground. The fiber allows them to
break their network into smaller service areas, typically fewer than 4 amplifiers deep, that prevent large
numbers of customers from being affected in an outage, making their network more
reliable and easier to troubleshoot, providing better service and
The fiber also gives CATV operators a return path which they
use for Internet and telephone connections, increasing their revenue
potential. Most current CATV systems still use AM (analog) systems which
simply convert the electrical TV signals into optical signals. Look for
them to convert to more digital transmission in the future.
is even developing its own version of fiber to the home called RF over
glass (RFOG.) This uses a interface at the home that is like a cable
modem but with an optical input that accepts the same analog radio
frequency (RF) signals that are used throughout the HFC network.
systems can have a wider reach and are more secure on fiber.
Practically any system today has a fiber optic option. CCTV cameras
used for surveillance often use fiber for it's distance capability and
security, especially in large buildings like airports and around cities
with metropolitan networks. Fiber also has much more bandwidth than
coax so several cameras can be multiplexed onto one fiber.
Bidirectional links allow controlling pan, zoom and tilt (PZT) cameras.
Other security devices like intrusion alarms or perimeter alarms can
utilize fiber and some even use fiber optic sensors.
cities have incorporated fiber optics into their communications
networks. Metropolitan networks use fiber for many other applications
besides CCTV surveillance cameras, including connecting public service
agencies such as fire, police and other emergency services, hospitals,
schools, as well as connecting municipal WiFi and traffic management
systems as shown in the photo. Cities can install cables to strategic
locations so various services can share the fibers in the cables,
saving installation costs. Cities are also learning to bury extra
conduits every time a roadway is dug up so when cables need installing,
no further construction is needed.
use fiber for communications, CCTV surveillance and network management.
Electrical utilities have used fiber optics for decades for
communications and managing their distribution systems. They realized
quickly that fiber’s immunity to electromagnetic interference would
allow them to operate communications and control networks in close
proximity to electrical circuits without problems. Electrical utilities
take full advantage of fiber's immunity to noise also, even running
fiber inside high voltage power distribution cables. Some utilities
install fibers inside their high voltage distribution networks using
optical power ground wire (OPGW) and lease fibers to other
telecommunications companies. Utilities use fiber in one
non-communications application; fiber optic sensors allow monitoring
high voltage and current in their distribution systems. The interest in
"smart grid" management of power distribution to enhance efficiency is
based on using fiber optics for network management.
networks, mostly computer LANs (local area networks) use fiber optics
primarily in the backbone but increasingly to the desk and to connect
wireless access points. The LAN backbone often needs longer distances
than copper cable (Cat 5/5e/6/6A) can provide and of course, the fiber
offers higher bandwidth for future expansion. Fiber's ability to handle
network upgrades meant that one fiber type outlived nine generations of
copper cables in LANs. A new fiber type (OM3) offers future potential
for upgrades while copper continues to struggle with network speed
recently large corporate LANs use fiber backbones with copper wire to
the desktop. LAN switches and hubs are usually available with fiber
optic ports but PCs have interfaces to Ethernet on copper. Inexpensive
media converters allow connecting PCs to fiber. Fiber to the desk can
be cost effective if properly
designed using centralized fiber architecture without local switching
in the telecom closet, but many users no longer want to be "tethered"
to a network cable. Desktop computer sales are declining and laptops
are the PC of choice for most users, with wireless connections to the
network. Generally only high data users like engineers and graphics
designers use desktop workstations; everybody else gets a
More on premises networks and fiber in premises networks.
- Centralized Fiber LANs
When most contractors and end users look at fiber optics versus Category-rated UTP cabling for a LAN, they compare the same old copper LAN with fiber directly replacing the copper links. The installed cost of a fiber optic cable plant comparable to the cost of Cat 5/6/6A, but fiber often requires medial conversion electronics which add cost to the link for fiber.
- However, the real difference comes if you use a centralized fiber optic network - shown on the right of the diagram above. Since fiber does not have the 90 meter distance limitation of UTP cable, you can place all electronics in one location in or near the computer room. The telecom room is only used for passive connection of backbone fiber optic cables, so no power, UPS, ground or air conditioning is needed. These auxiliary services, necessary with Cat 5 hubs, cost a tremendous amount of money in each telecom room.
If designing a new building, you do not even need the cost of the telecom room itself.
- In addition, having all the fiber optic hubs in one location means better utilization of the hardware, with fewer unused ports. Since ports in modular hubs must be added in modules of 8 or 16, it's not uncommon with a hub in a telecom closet to have many of the ports in a module empty . With a centralized fiber system, you can add modules more efficiently as you are supporting many more desktop locations but need never have more than a one module with open ports.
- More on fiber in premises networks and fiber versus copper, generally and in LANs
Industrial plants use fiber for it's ruggedness, distance and noise immunity.
In an industrial environment, electromagnetic interference (EMI) is
often a big problem. Motors, relays, welders and other industrial
equipment generate a tremendous amount of electrical noise that can
cause major problems with copper cabling, especially unshielded cable
like UTP. In order to run copper cable in an industrial environment, it
is often necessary to pull it through conduit to provide adequate
shielding. Fiber is also very flexible, so many industrial robots use
fiber for controls, often plastic fiber.
Fiber optics has complete immunity to EMI. You only need to choose a cable type that is rugged enough for the installation, with breakout cable being a good choice for it's heavy-duty construction. The fiber optic cable can be installed easily from point to point, passing right next to major sources of EMI with no effect. Conversion from copper networks is easy with media converters, gadgets that convert most types of systems to fiber optics. Even with the cost of the media converters, the fiber optic network will be less than copper run in conduit.
- Military and Platforms
military uses fiber everywhere, on bases, platforms (ships and planes),
and on the battlefield because it's hard to damage, tap or jam.
Airplanes use fiber for its reliability and noise immunity, but also
like the lighter weight of fiber. Even millions of cars have fiber
networks connecting all the electronics because fiber is immune to
noise and saves weight.
Fiber Optic Links
optic links work by sending optical signals over fiber. Fiber optic
transmission systems all use data links that work similar to the
diagram shown above. Each fiber link consists of a transmitter on one
end of a fiber and a receiver on the other end. Most systems operate by
transmitting in one direction on one fiber and in the reverse direction
on another fiber for full duplex operation. Transmitters are
semiconductor LEDs or lasers and receivers are semiconductor
For more information on fiber optic links, see the next section on Transmission Systems.
Designing Fiber Optic Networks
is a big topic so we have a complete section
on the subject of Design. Fiber's extra bandwidth and distance capability makes it possible to do things not possible with copper wire or wireless.
First and foremost, it's necessary to understand thoroughly what
signals are to
be transmitted over the fiber and the specifications of the
transmission equipment. Then map and visit the work site to understand
where the fiber optic cable plant needs to be installed. Know
the standards but use common sense in designing the
installation. Consider what are the possible problems and work around or
prevent them. Don't cut corners which may affect performance or
reliability. Document everything completely. Plan for future expansion
and restoration in case of problems. There is no substitute for
experience and common sense here!
Test Your Comprehension
The FOA Reference Guide to Outside Plant Fiber Optics
The FOA Online Reference Guide to Fiber Optics
You can buy the printed version of the The FOA Reference Guide to Outside Plant Fiber Optics from the FOA eStore or Amazon.