Fiber Optics

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• Splice 22 is a gainer from the hut, shoot it from the cabinet and average it before anybody reburns it.

  TranslationThe OTDR shows an apparent gain at splice 22 from one direction; test from the other end and average both readings to get the real loss before redoing the splice.

• Green into green, there's a blue jumper in the splitter cabinet and the ORL is in the toilet.

  TranslationAPC connectors must mate only with APC; someone used a UPC jumper in the PON cabinet and the link's optical return loss is far too poor.

• Event at 3.4 klicks is way worse at 1550, check the slack in that handhole for a macrobend.

  TranslationAn OTDR event 3.4 km out shows much more loss at 1550 nm than at 1310 nm, which points to a tight bend in the cable stored in the handhole.

• Both ends see light out and nothing in, roll the pair at the panel.

  TranslationTransmitters at both ends are working but neither receiver gets light, so the duplex fibers are crossed wrong; swap them at the patch panel.

• Open the can on pole 41, strip, clean, cleave and burn the blue tube first, that's the hospital.

  TranslationRe-enter the splice closure on pole 41 and fusion splice the fibers in the blue buffer tube first, because they carry the hospital's service.

• Put the launch box on, your first connector is buried in the dead zone and I can't read its loss.

  TranslationAdd the launch cable between the OTDR and the link, because without it the first connector falls inside the instrument's dead zone and cannot be measured.

• Light levels are minus 24 on a minus 23 optic, we have zero margin, go scope and clean every connector in the path.

  TranslationReceived power is below the transceiver's sensitivity rating, so the link has no margin; inspect and clean all connectors to recover the lost power.

The glass itself: singlemode and multimode, core and cladding, fiber grades, wavelengths and dispersion.

• Bend-insensitive fiberalso BIF, bend-optimized fiber
  Fiber designed to lose very little light when bent tightly, used in drops, apartment wiring and dense patching.
• Chromatic dispersionalso CD
  Pulse spreading caused by different wavelengths in a light source traveling at slightly different speeds in fiber.
• Cladding
  The layer of slightly lower-index glass around the core that keeps light trapped inside it.
• Corealso fiber core
  The central glass region of an optical fiber where the light actually travels.
• Glass
  Installer shorthand for optical fiber itself, or for the fiber plant as a whole. Shop talk
• Lambdaalso wavelength, wave
  A single wavelength channel on a fiber, named after the Greek letter used for wavelength. Shop talk
• Mode field diameteralso MFD
  The effective width of the light spot traveling in a singlemode fiber, slightly larger than the physical core.
• Multimode fiberalso MM, MMF
  Fiber with a 50 or 62.5 µm core that carries many light paths at once, used for short links inside buildings and data centers.
• Numerical aperturealso NA
  A measure of how wide a cone of light a fiber can accept and guide, written as a number such as 0.20.
• OM grades
  The OM1 to OM5 performance classes for multimode fiber, each rated for bandwidth and reach at a given data rate.
• OS2
  Optical Singlemode 2: the low-water-peak cabled singlemode grade used for most indoor and outdoor singlemode installs.
• Singlemode fiberalso SM, SMF
  Optical fiber with a core so small that light travels in a single path, used for long-haul, metro, FTTH and campus backbones.
• Two-fiftyalso 250 micron
  Splicer slang for fiber that has only its 250 µm acrylate coating, with no tight buffer over it. Shop talk
• Windowalso transmission window
  A wavelength region where fiber loss is low enough to run links, such as 850, 1310 or 1550 nm.

Cable construction, buffers and jackets, pathways, and the gear and slang of pulling cable into place.

• Aramid yarnalso Kevlar, yarn
  The yellow strength yarn inside fiber cables that takes the pulling load so the glass does not.
• Bend radiusalso minimum bend radius, MBR
  The tightest curve a fiber or cable can take without extra loss or damage, stated separately for pulling and at rest.
• Blown fiberalso air-blown fiber, ABF
  Fiber or microcable pushed through small ducts by high-speed compressed air instead of being pulled with a line.
• Buffer
  The protective plastic layer or tube around coated fiber, either a tight 900 µm jacket or a loose gel-filled tube.
• Fiber color codealso TIA-598 color code
  The fixed sequence of twelve colors that identifies each fiber and buffer tube in a cable.
• Figure-eightalso figure-8
  To lay pulled cable on the ground in a figure 8 pattern so it can be fed onward without twisting or kinking. Shop talk
• Icky pickalso icky-pic, gel
  Slang for the sticky petroleum gel that fills loose buffer tubes and some cable cores to keep water out. Shop talk
• Innerductalso subduct, inner duct
  Smaller plastic tubing placed inside a larger conduit to divide it into separate protected paths for fiber cables.
• Jacketalso sheath, outer jacket
  The outer plastic sheath of a fiber cable, chosen for fire rating indoors and for UV and moisture resistance outdoors.
• Loose-tube cablealso loose buffer cable
  Outside plant cable whose fibers float inside gel-filled or dry tubes, protecting them from strain and temperature changes.
• Lubealso pulling lube, pulling lubricant
  Cable pulling lubricant applied to fiber cable and duct to cut friction and keep pulling tension down. Shop talk
• Mule tapealso pull tape
  Flat, low-stretch polyester pull tape with printed footage marks, left in conduit to pull cable later. Shop talk
• Pullalso cable pull
  A cable pulling operation, from setup at the feed end to the cable arriving at the far vault. Shop talk
• Ribbon cablealso ribbon fiber
  High-count cable in which fibers are bonded side by side into flat ribbons, usually 12 across, for mass splicing.
• Rodalso snake
  To push a stiff fiberglass duct rodder through a conduit to prove the path or to carry a pull line through. Shop talk
• Service loopalso slack loop, maintenance loop
  Extra cable coiled and stored at a vault, pole or panel so the fiber can be re-spliced or moved later.
• Snowshoealso slack storage bracket
  An oval aerial bracket, shaped like a snowshoe, used to store slack loops of fiber cable on the strand. Shop talk
• Sockalso pulling grip, basket grip
  A woven wire mesh pulling grip that slips over a cable end and tightens as it is pulled. Shop talk
• Tight-buffered cablealso tight-buffer cable
  Indoor fiber cable in which each fiber has its own 900 µm plastic buffer, ready to terminate directly.
• Zipcordalso zip cord, duplex cord
  Duplex fiber cable made of two simplex cords joined side by side, like lamp cord, used mainly for patch cords. Shop talk

Connector types, polishes, panels, polarity and the habits that keep end faces clean.

• APCalso angled polish, green connector
  Angled Physical Contact: a singlemode connector polish with an 8 degree angle that sends reflections into the cladding.
• Barrelalso adapter, bulkhead
  Installer slang for a fiber adapter, the double-ended bulkhead part that joins two connectors. Shop talk
• Click cleaneralso one-click cleaner, pen cleaner
  A pen-shaped one-click connector cleaner that wipes a fresh strip of cleaning tape across the end face. Shop talk
• Connectoralso plug
  A removable termination that aligns the end of one fiber with another so light passes between them.
• End facealso endface, ferrule end face
  The polished tip of a connector ferrule and fiber, where light leaves one fiber and enters the next.
• Epoxy and polishalso epoxy polish, field polish
  The field termination method of gluing fiber into a connector and polishing the end face by hand.
• Ferrule
  The precision ceramic or metal cylinder in a connector that holds the fiber and lines it up with its mate.
• Hockey puckalso polishing puck, polishing fixture
  The round polishing fixture that holds a connector square to the lapping film during hand polishing. Shop talk
• Inspect before you connectalso IBYC
  The fiber tech's rule that every connector end face gets scoped, and cleaned if needed, before it is mated. Shop talk
• Jumperalso patch cord, patch cable
  A short fiber cable with connectors on both ends, used to patch equipment to panels or panels to each other.
• LCalso little connector
  Lucent Connector: the small latching connector with a 1.25 mm ferrule used on most transceivers and data center panels.
• MPOalso MTP, array connector
  Multi-fiber Push-On: a single connector that terminates 8, 12, 16 or 24 fibers in one rectangular ferrule.
• Patch
  To connect two ports, usually equipment to panel or panel to panel, with a jumper. Shop talk
• Patch panelalso LIU, fiber distribution panel
  A rack-mounted enclosure of adapters where permanent cable fibers end and jumpers connect them to equipment.
• Pigtailalso pig tail, tail
  A short fiber with a factory connector on one end and bare fiber on the other, spliced onto a cable to terminate it.
• Polarity
  The arrangement that ensures each transmitter in a fiber link connects to the receiver at the far end.
• Pre-termalso pre-terminated cable
  Short for pre-terminated cable: factory-made assemblies with connectors already on, pulled in and plugged in. Shop talk
• Rollalso flip, swap the pair
  To swap the two fibers of a duplex pair so transmit and receive line up with the far end. Shop talk
• SCalso square connector, stick and click
  Subscriber Connector: a square push-pull connector with a 2.5 mm ferrule, common in telecom and FTTH.
• Spaghettialso rat's nest
  A messy tangle of patch cords hanging in front of a rack, with no cable management or labeling. Shop talk
• Splice-on connectoralso SOC, fusion splice-on connector
  A connector with a factory-polished fiber stub that is fusion spliced directly onto the field fiber.
• UPCalso ultra polish, blue connector
  Ultra Physical Contact: a domed singlemode connector polish with no angle, color-coded blue.

Fusion and mechanical splicing, fiber preparation, cleaving and the closures that protect the joints.

• Burnalso fuse
  Splicer slang for making fusion splices, from the electric arc that welds the glass. Shop talk
• Canalso closure, splice case
  Outside plant slang for a splice closure, especially a cylindrical dome closure on a pole or in a vault. Shop talk
• Cleave
  To break a stripped fiber in a controlled way so its end is flat, mirror-smooth and square to the axis.
• Cleave angle
  How far a cleaved fiber end deviates from a perfect right angle to the fiber axis, in degrees.
• Fusion splicealso fusion
  A permanent joint made by melting two cleaved fiber ends together with an electric arc.
• Fusion spliceralso splicer
  The instrument that aligns two fiber ends, welds them with an electric arc and estimates the splice loss.
• Index-matching gelalso index-matching fluid, index gel
  A clear gel with nearly the same refractive index as fiber, used to fill gaps between fiber ends.
• Mechanical splicealso mech splice
  A joint that holds two cleaved fiber ends together in an alignment device with index-matching gel, no arc needed.
• Splice closurealso splice case, can
  A sealed, re-enterable housing that protects fiber splices in outside plant, on poles, in vaults or buried.
• Splice protectoralso heat-shrink sleeve, sleeve
  A heat-shrink sleeve with a steel rod that is shrunk over a fusion splice to protect the bare glass.
• Strip, clean, cleavealso fiber prep, prep
  The three-step fiber prep routine done before every splice or splice-on connector. Shop talk

Loss, reflection and power units, OTDR traces and their artifacts, and certification test methods.

• Attenuationalso fiber loss
  The gradual loss of optical power as light travels along a fiber, expressed in decibels.
• Attenuation coefficientalso attenuation rate
  Fiber loss per unit length, in dB/km, which sets how much a given length of glass will lose.
• Backscatteralso Rayleigh backscatter, backscattering
  The small fraction of light scattered in the fiber that travels back toward the source, which OTDRs measure.
• Bidirectional averagingalso two-way averaging
  Testing a fiber with an OTDR from both ends and averaging the results to get true splice losses.
• dBmalso decibel-milliwatt
  Optical power in decibels relative to one milliwatt, the unit of power meters and transceiver specs.
• Event
  Any point on an OTDR trace where the signal departs from the smooth fiber slope, such as a splice, connector or break.
• Event dead zonealso EDZ
  The distance after a reflective event during which an OTDR cannot detect a second, separate event.
• Fiber identifieralso live fiber identifier, LFI
  A clip-on tester that detects light in a fiber through a gentle bend, without cutting it or interrupting traffic.
• Gainer
  A splice that shows an apparent gain of light on an OTDR trace, an artifact of mismatched backscatter. Shop talk
• Ghostalso echo, ghost event
  A false event on an OTDR trace caused by a strong reflection bouncing back and forth in the fiber.
• Insertion lossalso IL
  The optical power lost when a component or a whole link is placed in the light path, measured in dB.
• Launch cablealso launch box, pulse suppressor
  A long reference fiber placed between the OTDR and the cable under test so the first connector can be measured.
• Light levelsalso levels
  The transmit and receive optical power readings on a transceiver, read from a meter or the switch's optic diagnostics. Shop talk
• Loss budgetalso link loss budget, cable plant loss budget
  The calculated total loss a fiber link should have, built from fiber length, connectors and splices.
• Macrobendalso macrobending
  A bend in a fiber tight enough to see, which lets light escape the core and causes loss.
• Mandrel wrapalso mandrel
  Multimode test jumper wound around a smooth rod to strip out high-order modes and stabilize loss readings.
• Marginalso system margin, power margin
  The spare optical power left after link loss is subtracted from what the transmitter and receiver can tolerate.
• Microbendalso microbending
  A tiny, invisible deformation of the fiber axis caused by pressure, which scatters light out of the core.
• OLTSalso light source and power meter, LSPM
  Optical Loss Test Set: a light source and power meter used together to measure end-to-end link loss.
• One-jumper referencealso one-cord reference, Method B
  A loss-test reference set with a single launch jumper between source and meter, so both link end connectors are counted.
• OTDR
  Optical Time Domain Reflectometer: a tester that maps a fiber's loss and events by timing light reflected back along it.
• Receive cablealso tail cord, tail cable
  A reference fiber attached at the far end of a link so an OTDR can measure the loss of the last connector.
• Red lightalso VFL
  Installer slang for a visual fault locator and the red laser it puts into the fiber. Shop talk
• Reflectancealso back reflection
  The fraction of light reflected by a single event such as a connector, in dB, where more negative is better.
• Return lossalso ORL, optical return loss
  How much weaker reflected light is than the light sent in, in dB, where bigger numbers mean less reflection.
• Shoot
  To test a fiber with an OTDR, as in shoot the fiber or shoot it from both ends. Shop talk
• Tracealso signature, OTDR trace
  The graph an OTDR produces, plotting returned power in dB against distance along the fiber.
• VFLalso visual fault locator, red light
  Visual Fault Locator: a bright red laser pen that shows breaks, bends and bad connectors as visible glowing points.

How fiber is used in the field: dark and lit fiber, FTTH and PON, WDM and the aerial and buried plant.

• Backhoe fadealso dig-in
  Joking term for a fiber outage caused by an excavator digging through buried cable. Shop talk
• Cable plantalso fiber plant
  All the passive fiber infrastructure of a network: cable, splices, connectors, panels and closures.
• Dark fiberalso dark, unlit fiber
  Installed fiber with no transmission equipment attached, either spare or leased bare to a customer who lights it.
• Dropalso drop cable, service drop
  The final fiber cable run from a distribution terminal on the street to a single customer building.
• FTTH
  Fiber to the Home: access networks that run fiber all the way into each residence.
• Home runalso home-run
  A dedicated fiber run straight from the central point to one end location, with no splitter or shared path in between. Shop talk
• Litalso live, hot
  Describes a fiber that is carrying live traffic from active equipment, as opposed to dark. Shop talk
• PON
  Passive Optical Network: a point-to-multipoint fiber network where unpowered splitters share one fiber among many users.
• Splitteralso optical splitter, coupler
  A passive optical device that divides the light from one fiber among several output fibers.
• Strandalso messenger, messenger strand
  The galvanized steel messenger wire strung between poles that supports aerial fiber cable.
• WDMalso wave division
  Wavelength Division Multiplexing: sending several signals on different wavelengths over the same fiber.

Frequently asked questions

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