- What is "Fiber Optics"?
Fiber
optics refers to the technology of transmitting light down thin strands
of highly transparent material, usually glass but sometimes plastic.
Fiber optics is used in communications, lighting, medicine, optical
inspections and to make sensors. The FOA is primarily interested in
communications fiber optics, so this book will focus on that
application.- Fiber Optics in communications works by sending light signals down hair thin strands of glass
fiber (and sometimes plastic fiber.) It began about 40 years
ago in the R&D labs (Corning, Bell Labs, ITT UK, etc.) and
was first installed commercially in Dorset, England by STC and Chicago, IL, USA in 1976 by AT&T. By the early
1980s, fiber telecommunications networks connected the major cities on each coast.
- By
the mid-80s, fiber was replacing all the telco copper, microwave and
satellite links. In the 90s, transoceanic fiber optic cables replaced satellites between most continents. Now fiber has become cost effective for
direct connection to the home.
- CATV discovered fiber in the mid-1990s and used it first to
enhance the reliability of their networks, a big problem. Along the
way, they discovered they could offer phone and Internet service on that
same fiber and greatly enlarged their markets. As cell phones took hold
in the market, their backbones were built on fiber.
- Computer
networks (LANs) started using fiber about the same time as the telcos.
Industrial links were among the first applications as the noise
immunity of fiber and its distance capability make it ideal for the
factory floor. Connecting graphics displays and mainframe storage
links, the predecessors of today's fiber SANs (storage area networks)
in data centers came next. Today fiber is used in most corporate LANs as backbones, connections to desktops for engineering or graphic workstations and many wireless access points.
- Other
applications developed too: cell phone network antenna connections,
aircraft, ship and automobile data busses, CCTV for security, even
links for consumer digital stereo! Big users of fiber optics today are
municipalities who use it for connecting schools, departments, smart
traffic lights and CCTV surveillance systems. Some even offer direct
fiber connections to their citizens or businesses.
- Today
fiber optics is either the dominant medium or a logical choice for
every communication system. Costs have been reduced so much that fiber
to the home is now cost effective, especially since it can offer
services (entertainment as well as communications) that no other medium
offers.
Which Fiber Optics?
Whenever
you read an article or talk to someone about fiber optics, you need to
know the point of view. We're mainly concerned with communications
fiber optics, but it's also used in medical or nondestructive testing
inspection and lighting. Fiber optics, you see, is not all the
same. Even
in communications, we have "outside plant" fiber optics as used in
telephone networks, CATV, metropolitan networks, utilities, etc. or
"premises" fiber optics as found in buildings and campuses.Just like "wire" which can mean lots of different things
- power, security, HVAC, CCTV, LAN or telephone - fiber optics
is not all the same. And this can be a big source of confusion
to the novice. Lets define our terms.
Outside Plant (OSP)
Telephone companies, CATV and the Internet all use lots of fiber
optics, virtually all of which is singlemode fiber and most of which is outside buildings. It hangs from poles,
is buried underground, pulled through conduit or is even submerged
underwater. Most of it goes relatively long distances, from a
few hundred feet to hundreds of miles.
Outside plant cables often have very high fiber
counts, up to 288 fibers or more. Cable designs are optimized for the
application: cables in conduit for pulling tension and resisting
moisture, buried cables for resisting moisture and rodent damage,
aerial for continuous tension and extreme weather and undersea for
resisting moisture penetration. Installation requires special equipment
like pullers or plows, and even trailers to carry giant spools of cable.
Long distances mean cables are spliced together, since cables
are not manufactured in lengths longer than about 4-5 km (2.5-3 miles), and most splices
are by fusion splicing. Connectors (generally SC or LC styles) on factory
made pigtails are spliced onto the end of the cable. After installation,
every fiber and every splice is tested with an OTDR.
If this sounds expensive, you are right! The installer usually
has a temperature controlled van or trailer for splicing and/or
a bucket truck. Investments in fusion splicers, OTDRs and other equipment can be quite expensive.
Most outside plant telephone installs are done by the telco themselves,
while a small number of large, specialized installers do CATV, utility and municipal
work.
Premises Cabling
By contrast, premises cabling- cabling installed in a building
or campus - involves shorter lengths, rarely longer than a few
hundred feet, typically with fewer fibers per cable. The fiber
is mostly multimode, except for the enlightened user who installs
hybrid cable with both multimode and singlemode fibers for future high bandwidth applications.
Splicing is practically unknown in premises applications. Cables
between buildings can be bought with double jackets, PE for outside
plant protection over PVC for building applications requiring
flame retardant cable jackets, so cables can be run continuously
between buildings. Today's connectors often have lower loss than
splices, and patch panels give more flexibility for moves, adds
and changes.
Most connectors are SC or ST style with LCs becoming more popular. Termination
is by installing connectors directly on the ends of the fibers,
primarily using adhesive or sometimes prepolished splice techniques. Testing is done by a source and
meter, but every installer should have a flashlight type tracer
to check fiber continuity and connection.
Unlike the outside plant technician, the premises cable installer (who
is often also installing the power cable and Cat 5/6 for LANs too!)
probably has an investment of less than $2,000 in tools and test
equipment.
There are thousands of cabling installers who do fiber optic
work. They've found out it isn't "rocket science,"
and their small initial investment in training, tools and test
equipment is rapidly paid back. The Installers
Few installers do both outside plant and premises cabling. The
companies that do are usually very large and often have separate
divisions doing each with different personnel. Most contractors
do nothing but premises cabling.
Fiber vs Copper
- The
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.
Wireless
was used as a long distance medium until fiber became available, but
wireless is limited by available transmission frequencies so it was
dropped as a long distance medium. While local wireless has grown
exponentially, it uses fiber as a backbone and connection to the
international phone system. - These advantages makes the use of optical fiber the most logical choice
in data transmission.
- Twenty
five years ago, fiber was just being introduced. It was expensive and
required PhD's from Bell Labs to install it while copper wire was easy
to install. Today most communications installers do fiber and wireless as well as copper.
Because fiber is so
powerful, at today's network speeds fiber still has plenty of headroom
and users can look to the future of ten to one hundred gigabit speeds with confidence.
Telcos use DSL over copper today but it's very limited in bandwidth
over typical subscriber connection lengths and many older copper wires
will not support DSL speeds, leading to the adoption of fiber to the home. Copper gigabit Ethernet can work over short cables
in LANs or but only if it is carefully installed and tested. - But isn't fiber more expensive?
Telcos and CATV operators use fiber because it's actually much cheaper.
They optimize the architecture of their network to take advantage of
fiber's speed and distance advantages. In LANs, you need to follow
the EIA/TIA 568 standard for "centralized fiber" to optimize the
fiber usage, and then it can be cheaper than copper. Installing the proper fiber
today in a LAN will give you good chance of being able to handle new
network speeds for years to come. One fiber, FDDI grade 62.5/125, outlasted 9 generations
of copper! See Networks for more information on how to use fiber.
- The Secret To Success In Fiber
Optics Is Training!
You wouldn't try to drive a truck or fly a plane without taking
lessons. Likewise for improving your golf or tennis game. Well,
the secret to fiber optics is training too. With some basic knowledge
and hands-on practice gained in a training course, fiber is pretty
easy to install.
Where to Get Training?
Well, you can start right here at the FOA, of course! This reference guide is
designed to get you started and you should have "hands-on" training
leading to a recognized certification program like the FOA CFOT to be
qualified to install fiber. Check the website
of the Fiber Optic Association at http://www.TheFOA.org.
for the leading fiber optic certification program in the industry.
Finally, take advantage of the training offered by manufacturers
and distributors whenever you can, often this training is free
or cheap! (but limited to the manufacturer's equipment
of course.) - How about Certification?
- That's what the FOA is all about. We have hundreds of FOA-approved schools offering FOA certifications.
About 25,000 students have been certified by FOA schools
(10/2008.)Around the world, FOA is recognized as the leader in fiber
optic education and certification.
- Standards
- The
adoption of any technology depends on having workable standards
to insure product compatibility. Most of what we call standards are
voluntary standards created by industry groups. Standards are not
"codes" or actual laws that you must follow to be in compliance with
local ordinances but sensible guidelines to ensure proper operation of
communications systems. Standards are often developed by groups within
each country, like EIA/TIA or IEEE in the US, but are increasingly
becoming international under the auspices of ISO and IEC.
Standards
like EIA/TIA 568 ( from the Electronic Industries Alliance/
Telecommunications Industry Association in the US) which covers all of
the things you need to know to install a standard premises cabling
network are good guidelines for designs and should be followed to
ensure interoperability.
Primary measurement standards like for
optical power measurements are set by standards organizations in each
country like NIST (the US National Institute of Standards and
Technology) and coordinated worldwide.
The only common "mandatory standard" in the US - we call them codes - is the NEC 770 (National Electrical
Code). The NEC specifies fire prevention
standards for fiber optic cables. Other countries have similar codes for building safety. If an indoor cable doesn't have
a NEC rating - don't install it - it won't pass inspection! - A listing of the EIA/TIA
standards is on the website
of The Fiber Optic Association. Information on the EIA/TIA standards
can be found on the website of most of the suppliers of structured
cabling hardware.
More on standards.
Before we get started - Safety
First!
You
might think that eye damage from working with lasers would be the big
concern in fiber optic installations. The reality is that high power
lasers burning holes in metal or burning off warts mostly have little
relevance to your typical fiber optic installation. Optical sources
used in fiber optics are generally of much lower power levels (The
exception is high power DWDM or CATV systems). Of course, you should
always be careful with your eyes, especially when using a fiber optic
microscope which can concentrate all the light from the fiber into your
eye. NEVER look into a fiber unless you know no light is present - use
a power meter to check it - and anyway, the light is in the infrared
and you can't see anything anyway!
The real safety lecture will
always be about small scraps of glass cleaved off the ends of
the fibers being terminated or spliced. These scraps are very
dangerous! The cleaved ends are extremely sharp and can easily
penetrate your skin. If they get into your eyes, they are very
hard to flush out. Don't even think about what happens if you
eat one. Always wear safety glasses whenever working with fiber and always carefully dispose of all fiber scraps!
Always follow these rules when
working with fiber.
1. Always wear safety glasses to protect your eyes from fiber scraps.
2. Dispose of all scraps properly. Always use a properly marked container to dispose of later
and work on a black pad which makes the slivers of glass easier
to spot.
3. Do not drop them on the floor where they will stick in carpets
or shoes and be carried elsewhere.
4. Do not eat or drink anywhere near the work area.
Fiber
optic splicing and termination use various chemical adhesives and
cleaners as part of the processes. Follow the instructions for use
(detailed on the chemical's MSDS - material safety data sheet)
carefully. Remember, even simple isopropyl alcohol, used as a cleaner,
is flammable. Read more about fiber optic safety.
Zero Tolerance for Dirt
With fiber optics, our tolerance
to dirt is near zero. Airborne particles are about the size of
the core of SM fiber- they absorb lots of light and may scratch
connectors if not removed! Dirt on connectors is the biggest
cause of scratches on polished connectors and high loss measurements!
1. Try to work in a clean area.
Avoid working around heating outlets, as they blow dust all over
you
2. Always keep dust caps on connectors, bulkhead splices, patch
panels or anything else that is going to have a connection made
with it.
3. Use special fiber optic cleaners or lint free pads and isopropyl alcohol to clean the connectors.
4. Ferrules on the connectors/cables used for testing will get
dirty by scraping off the material of the alignment sleeve in
the splice bushing - creating an attenuator. You can see
the front edge of the connector ferrule getting black! Use the
metal or ceramic alignment sleeve bulkheads only for testing. Read more about cleaning fiber optic components.
Test Your Comprehension
Table of Contents: The FOA Reference Guide To Fiber Optics
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