An optical fiber cable is a cable containing one or more optical fibers that are used to
carry light. The optical fiber elements are typically individually coated with plastic
layers and contained in a protective tube suitable for the environment where the cable
will be deployed. Different types of cable are used for different applications, for example
long distance telecommunication, or providing a high-speed data connection between different
parts of a building.
Design
Optical fiber consists of a core and a cladding layer, selected for total internal reflection
due to the difference in the refractive index between the two. In practical fibers, the
cladding is usually coated with a layer of acrylate polymer or polyimide. This coating
protects the fiber from damage but does not contribute to its optical waveguide properties.
Individual coated fibers then have a tough resin buffer layer and/or core tube(s) extruded
around them to form the cable core. Several layers of protective sheathing, depending
on the application, are added to form the cable. Rigid fiber assemblies sometimes put
light-absorbing glass between the fibers, to prevent light that leaks out of one fiber
from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber
bundle imaging applications.
For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible
fibrous polymer strength members like aramid, in a lightweight plastic cover to form a simple
cable. Each end of the cable may be terminated with a specialized optical fiber connector
to allow it to be easily connected and disconnected from transmitting and receiving equipment.
For use in more strenuous environments, a much more robust cable construction is required.
In loose-tube construction the fiber is laid helically into semi-rigid tubes, allowing
the cable to stretch without stretching the fiber itself. This protects the fiber from
tension during laying and due to temperature changes. Loose-tube fiber may be "dry block"
or gel-filled. Dry block offers less protection to the fibers than gel-filled, but costs considerably
less. Instead of a loose tube, the fiber may be embedded in a heavy polymer jacket, commonly
called "tight buffer" construction. Tight buffer cables are offered for a variety of
applications, but the two most common are "Breakout" and "Distribution". Breakout cables
normally contain a ripcord, two non-conductive dielectric strengthening members, an aramid
yarn, and 3 mm buffer tubing with an additional layer of Kevlar surrounding each fiber. The
ripcord is a parallel cord of strong yarn that is situated under the jacket(s) of the
cable for jacket removal. Distribution cables have an overall Kevlar wrapping, a ripcord,
and a 900 micrometer buffer coating surrounding each fiber. These fiber units are commonly
bundled with additional steel strength members, again with a helical twist to allow for stretching.
A critical concern in outdoor cabling is to protect the fiber from contamination by water.
This is accomplished by use of solid barriers such as copper tubes, and water-repellent
jelly or water-absorbing powder surrounding the fiber.
Finally, the cable may be armored to protect it from environmental hazards, such as construction
work or gnawing animals. Undersea cables are more heavily armored in their near-shore portions
to protect them from boat anchors, fishing gear, and even sharks, which may be attracted
to the electrical power that is carried to power amplifiers or repeaters in the cable.
Modern cables come in a wide variety of sheathings and armor, designed for applications such
as direct burial in trenches, dual use as power lines, installation in conduit, lashing
to aerial telephone poles, submarine installation, and insertion in paved streets.
Capacity and market In September 2012, NTT Japan demonstrated
a single fiber cable that was able to transfer 1 petabit per second over a distance of 50
kilometers. Modern fiber cables can contain up to a thousand
fibers in a single cable, with potential bandwidth in the terabytes per second. In some cases,
only a small fraction of the fibers in a cable may be actually "lit". Companies can lease
or sell the unused fiber to other providers who are looking for service in or through
an area. Companies may "overbuild" their networks for the specific purpose of having a large
network of dark fiber for sale, reducing the overall need for trenching and municipal permitting.
Reliability and quality Optical fibers are very strong, but the strength
is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing
process. The initial fiber strength, as well as its change with time, must be considered
relative to the stress imposed on the fiber during handling, cabling, and installation
for a given set of environmental conditions. There are three basic scenarios that can lead
to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigues,
and zero-stress aging. Telcordia GR-20, Generic Requirements for
Optical Fiber and Optical Fiber Cable, contains reliability and quality criteria to protect
optical fiber in all operating conditions. The criteria concentrate on conditions in
an outside plant environment. For the indoor plant, similar criteria are in Telcordia GR-409,
Generic Requirements for Indoor Fiber Optic Cable.
Cable types OFC: Optical fiber, conductive
OFN: Optical fiber, nonconductive OFCG: Optical fiber, conductive, general use
OFNG: Optical fiber, nonconductive, general use
OFCP: Optical fiber, conductive, plenum OFNP: Optical fiber, nonconductive, plenum
OFCR: Optical fiber, conductive, riser OFNR: Optical fiber, nonconductive, riser
OPGW: Optical fiber composite overhead ground wire
ADSS: All-Dielectric Self-Supporting Jacket material
The jacket material is application specific. The material determines the mechanical robustness,
aging due to UV radiation, oil resistance, etc. Nowadays PVC is being replaced by halogen
free alternatives, mainly driven by more stringent regulations.
Fiber material There are two main types of material used
for optical fibres. These are glass and plastic. They offer widely different characteristics
and therefore fibres made from the two different substances find uses in very different applications.
Color coding Patch cords
The buffer or jacket on patchcords is often color-coded to indicate the type of fiber
used. The strain relief "boot" that protects the fiber from bending at a connector is color-coded
to indicate the type of connection. Connectors with a plastic shell typically use a color-coded
shell. Standard color codings for jackets and boots are shown below:
Remark: It is also possible that a small part of a connector is additionally colour-coded,
e.g. the leaver of an E-2000 connector or a frame of an adapter. This additional colour
coding indicates the correct port for a patchcord, if many patchcords are installed at one point.
Multi-fiber cables Individual fibers in a multi-fiber cable are
often distinguished from one another by color-coded jackets or buffers on each fiber. The identification
scheme used by Corning Cable Systems is based on EIA/TIA-598, "Optical Fiber Cable Color
Coding." EIA/TIA-598 defines identification schemes for fibers, buffered fibers, fiber
units, and groups of fiber units within outside plant and premises optical fiber cables. This
standard allows for fiber units to be identified by means of a printed legend. This method
can be used for identification of fiber ribbons and fiber subunits. The legend will contain
a corresponding printed numerical position number and/or color for use in identification.
Propagation speed and delay Optical cables transfer data at the speed
of light in glass. This is typically around 180,000 to 200,000 km/s, resulting in 5.0
to 5.5 microseconds of latency per km. Thus the round-trip delay time for 1000 km is
around 11 milliseconds. Losses
Typical modern multimode graded-index fibers have 3 dB/km of attenuation loss at 850 nm
and 1 dB/km at 1300 nm. 9/125 singlemode loses 0.4/0.25 dB/km at 1310/1550 nm. POF
loses much more: 1 dB/m at 650 nm. Plastic optical fiber is large core fiber suitable
only for short, low speed networks such as within cars.
Each connection made adds about 0.6 dB of average loss, and each joint adds about 0.1
dB. Depending on the transmitter power and the sensitivity of the receiver, if the total
loss is too large the link will not function reliably.
Invisible IR light is used in commercial glass fiber communications because it has lower
attenuation in such materials than visible light. However, the glass fibers will transmit
visible light somewhat, which is convenient for simple testing of the fibers without requiring
expensive equipment. Splices can be inspected visually, and adjusted for minimal light leakage
at the joint, which maximizes light transmission between the ends of the fibers being joined.
The charts at "Understanding wavelengths In fiber optics" and "Optical power loss in fiber"
illustrate the relationship of visible light to the IR frequencies used, and show the absorption
water bands between 850, 1300 and 1550 nm. Safety
Because the infrared light used in communications can not be seen, there is a potential laser
safety hazard to technicians. In some cases the power levels are high enough to damage
eyes, particularly when lenses or microscopes are used to inspect fibers which are inadvertently
emitting invisible IR. Inspection microscopes with optical safety filters are available
to guard against this. Small glass fragments can also be a problem
if they get under someone's skin, so care is needed to ensure that fragments produced
when cleaving fiber are properly collected and disposed of appropriately.
Hybrid cables There are hybrid optical and electrical cables
that are used in wireless outdoor Fiber To The Antenna applications. In these cables,
the optical fibers carry information, and the electrical conductors are used to transmit
power. These cables can be placed in several environments to serve antennas mounted on
poles, towers, and other structures. According to Telcordia GR-3173, Generic Requirements
for Hybrid Optical and Electrical Cables for Use in Wireless Outdoor Fiber To The Antenna
Applications, these hybrid cables have optical fibers, twisted pair/quad elements, coaxial
cables and/or current-carrying electrical conductors under a common outer jacket. The
power conductors used in these hybrid cables are for directly powering an antenna or for
powering tower-mounted electronics exclusively serving an antenna. They have a nominal voltage
normally less than 60 VDC or 108/120 VAC. Other voltages may be present depending on
the application and the relevant National Electrical Code.
These types of hybrid cables may also be useful in other environments such as Distributed
Antenna System plants where they will serve antennas in indoor, outdoor, and roof-top
locations. Considerations such as fire resistance, Nationally Recognized Testing Laboratory Listings,
placement in vertical shafts, and other performance-related issues need to be fully addressed for these
environments. Since the voltage levels and power levels
used within these hybrid cables vary, electrical safety codes consider the hybrid cable to
be a power cable, which needs to comply with rules on clearance, separation, etc.
See also Fiber optic coupler
Fusion splicing ISO/IEC 11801
Optical communication Optical interconnect
Optical power meter Optical time-domain reflectometer
Parallel optical interface Power-over-fiber
Submarine communications cable TIA/EIA-568-B Color coding for electrical
cable Notes and references
^ "Light collection and propagation". National Instruments' Developer Zone. Retrieved 2007-03-19. Hecht,
Jeff. Understanding Fiber Optics. Prentice Hall. ISBN 0-13-027828-9.
^ "Definition: rip cord". Its.bldrdoc.gov. Retrieved 2011-12-10.
^ Chirgwin, Richard. "NTT demos petabit transmission on single fibre". The Register. Retrieved
2014-02-16. ^ "GR-20, Generic Requirements for Optical
Fiber and Optical Fiber Cable". Telcordia. ^ "GR-409, Generic Requirements for Indoor
Fiber Optic Cable". Telcordia. ^ "Polymethylmethacrylate - online catalogue
source, sources, small quantity and quantities from". Goodfellow. Retrieved 2011-12-10.
^ "Polyvinylchloride - Unplasticised - online catalogue source, sources, small quantity
and quantities from". Goodfellow. Retrieved 2011-12-10.
^ "Polyethylene - High density". GoodFellow. Retrieved 2014-01-13.
^ "Polyethylene - Low Density". GoodFellow. Retrieved 2014-01-13.
^ "Polyethylene - U.H.M.W. - online catalogue source, sources, small quantity and quantities
from". Goodfellow. Retrieved 2011-12-10. ^ "Polyethylene terephthalate". GoodFellow.
Retrieved 2014-01-13. ^ "Polyamide-nylon 12–30% glass fibre reinforced".
GoodFellow. Retrieved 2014-01-13. ^ "Polyamide-nylon 6". GoodFellow. Retrieved
2014-01-13. ^ "Single-Mode VS. Multimode Fiber Cable".
Retrieved 2013-09-24. ^ Crawford, Dwayne. "Who is Erika Violet and
what is she doing in my data center?". Tech Topics. Belden. Retrieved Feb 12, 2014.
^ a b c Leroy Davis. "Fiber wire color coding". Retrieved 2007-12-01.
^ Latency and Jitter Retrieved 2011-05-29. ^ Optical Fiber Retrieved 2010-08-20.
^ Calculating the Maximum Attenuation for Optical Fiber Links. Cisco document 27042.
Retrieved 2010-08-20. ^ Hayes, Jim. "Understanding Wavelengths In
Fiber Optics". The Fiber Optic Association. Retrieved 2014-01-13.
^ "Optical power loss in fiber". Ad-net.com.tw. Retrieved 2014-01-13.
^ GR-3173-CORE, Generic Requirements for Hybrid Optical and Electrical Cables for Use in Wireless
Outdoor Fiber To The Antenna Applications, Telcordia.
External links Fiber Optic Association The FOA Reference
Guide To Fiber Optics Accurately Testing Fiber Optic Cables