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Fiber Optics
Fiber Optics Training & Terms
| Question | Answer |
|---|---|
| OFP | Optical Fiber Plenum |
| What are three primary advantages of fiber optics over metallic wires or wireless data links? | Fiber can transport more information longer distances in less time. It is also immune to electromagnetic interference, and can be used for special applications that require transmitting light (such as medical imaging.) |
| Why are repeaters used? | Long-Distance data links need repeaters to regenerate signals that have been attenuated. |
| What are three elements in a fiber optic data link? | Transmitter, cable and receiver. |
| What are the core and cladding diameters of singlemode fiber? | Core is 8-9 microns, cladding is 125 microns. |
| What is attenuation? | Attenuation is signal loss, measured in dB (decibels). |
| What is dispersion? | Dispersion is the spreading out of a narrow light pulse as it travels through a cable. Dispersion reduces bandwidth. |
| Modal dispersion: | The temporal spreading of a pulse in an optical waveguide caused by modal effects. |
| Multimode fiber: | A fiber with core diameter much larger than the wavelength of light transmitted that allows many modes of light to propagate. Commonly used with LED sources for lower speed, short distance links. |
| Optical loss test set (OLTS) | A measurement instrument for optical loss that includes both a meter and source. |
| Scattering | The change of direction of light after striking small particles that causes loss in optical fibers. |
| Visual fault locator | A device that couples visible light into the fiber to allow visual tracing and testing of continuity. Some are bright enough to allow finding breaks in fiber through the cable jacket. |
| Singlemode fiber | A fiber with a small core, only a few times the wavelength of light transmitted, that only allows one mode of light to propagate. Commonly used with laser sources for high speed, long distance links. |
| Repeater, regenerator | A device that receives a fiber optic signal and regenerates it for retransmission, used in very long fiber optic links. |
| Fusion splicer | An instrument that splices fibers by fusing or welding them, typically by electrical arc. |
| dBm | Optical power referenced to 1 milliwatt. |
| Decibel (dB) | A unit of measurement of optical power which indicates relative power on a logarithmic scale, sometimes called dBr. dB=10 log ( power ratio) |
| Backscattering | The scattering of light in a fiber back toward the source, used to make OTDR measurements. Bandwidth: The range of signal frequencies or bit rate within which a fiber optic component, link or network will operate. |
| Absorption | That portion of fiber optic attenuation resulting of conversion of optical power to heat. |
| Cleaver | A tool that precisely "breaks" the fiber to produce a flat end for polishing or splicing. |
| Fiber Stripper | Used to remove the buffer coating of the fiber itself for termination. There at three types in common use, called by their trade names: "Miller Stripper", "No-Nik" and "Micro Strip." |
| Three elements of Fiber Data Link. | Light Source at one end, Fiber at point to point & the light detector. |
| Visual Fault Locator | A device that allows visual tracing and testing of continuity. |
| Two Types of Fiber. | Single-Mode & Multi-Mode |
| What does MCVD stand for? | Modified Chemical Vapor Deposition |
| OFNR | Optical Fiber Nonconductive Riser |
| What is Optical Fiber Nonconductive Riser? | Optical fiber cable used in vertical shafts, or in runs between floors, must have fire-resistant characteristics capable of preventing the spread of fire from floor-to-floor. OFNR refers to the fiber rating of the cable jacketing. |
| OFNG | Optical Fiber Nonconductive General Purpose |
| What is Optical Fiber Nonconductive General Purpose? | Type OFNG cable must be resistant to the spread of fire and suitable for general-purpose use, with the exception of risers and plenums. |
| OVD | outside vapor deposition |
| VAD | vapor axial deposition |
| OFNP | Optical Fiber Nonconductive Plenum |
| Optical Fiber Nonconductive Plenum | Cable installed in ducts, plenums, and other spaces used for environmental air must be listed as having adequate fire-resistant and low-smoke producing characteristics. |
| EMD | Equilibrium modal distribution |
| Equilibrium modal distribution | Steady state modal distribution in multimode fiber, achieved some distance from the source, where the relative power in the modes becomes stable with increasing distance. |
| What are the core and cladding diameters of singlemode fiber? | Core is 8-9 microns, cladding is 125 microns |
| What is numerical aperture? | Numerical Aperture measures the largest angle of light that can be accepted into the core |
| How fast is singlemode optical fiber? | Very fast! So fast, the electronic testers can't measure it accurately. The speed is approximately 100 THz-km. |
| What units are used to measure optical fiber bandwidth? | The bandwidth-distance product in units of MHz×km is used because the longer a cable gets, the lower its bandwidth. |
| What are the two newer, faster types of multimode fiber? How fast are they? | Laser-rated 50/125 micron fiber carries 500 Mhz-km at both 850 nm and 1310 nm. Laser-optimized 50/125 micron fiber carries 2000 Mhz-km at 850 nm and 500 MHz-km at 1310 nm. |
| What is the attenuation of graded-index multimode fiber? | 3 dB/km at 850 nm; 1 dB/km at 1300 nm |
| What is bandwidth? | Bandwidth is the number of bits per second that can be sent through a data link. |
| What are the core and cladding diameters of multimode step-index fiber? | Core is 200 microns, cladding is 240 microns. This old fiber is not as common as the graded-index 62.5 micron and 50 micron types. |
| What are the three elements in a fiber optic data link? | Transmitter, cable, and receiver. |
| What are the core and cladding diameters of multimode graded-index fiber? | Core is 50 or 62.5 microns, cladding is 125 microns. There are two rare, larger sizes: 85/125 and 100/140 |
| What is the difference between step-index and graded-index multimode fiber? | Step-index suffers from modal dispersion, which makes its bandwidth low. Graded-index fiber has far less modal dispersion and much higher bandwidth. |
| What are the two most common types of fiber optic cable that have already been installed? | 8/125 micron singlemode and 62.5/125 micron multimode. (The numbers are diameters core/cladding) |
| What sources and wavelengths are used with singlemode fiber? | Singlemode fiber is used with laser sources at 1300 and 1550 nm |
| What are the three primary advantages of fiber optics over metallic wires or wireless data links? | Fiber can transport more information longer distances in less time. It is also immune to electromagnetic interference, and it can be used for special applications that require transmitting light (such as medical imaging). |
| What is a VCSEL? | A Vertical Cavity Surface Emitting Laser (VCSEL) is an inexpensive light source that replaces LEDs, and is used in Gigabit Ethernet. |
| Can you mix fiber types in the same network link? | No. You will lose 20 dB connecting singlemode to multimode fiber, and you will lose 3 dB connecting 50 micron to 62.5 micron multimode. Both are unacceptable for most networks. |
| What is a ribbon cable? | Dozens of fibers packed together, with buffer, strength member, and jacket outside. |
| When are distribution cables used? | Used for riser and office cabling |
| When are breakout kits used? | To terminate fibers in loose-tube cables |
| What type of cable is mass spliced or mass terminated? | Ribbon cable can be mass fusion spliced or mass terminated. |
| How are distribution cables terminated? | They must be terminated inside a patch panel or junction box |
| Do Breakout Cables require Breakout Kits? | No. Each fiber can be broken out and individually connectorized. |
| How are loose-tube cables terminated? | With breakout kits, or fusion splicing to pre-connectorized pigtails |
| How do loose-tube cables protect the fiber from water? | With gel or tape to block water, and armor to protect the cable from rodents |
| What is a Distribution cable? | Several tight-buffer fibers bundled together with kevlar reinforcement and one jacket. |
| How do breakout cables compare with distribution cables? | Breakout cables are stronger, larger and more expensive than distribution cables |
| Can loose-buffer cables be used outdoors? | Yes, they are commonly used outdoors. |
| What is a Breakout Cable? | Several tight-buffer fibers bundled together, each with its own with Kevlar reinforcement and jacket. |
| Can tight-buffer cables be used outdoors? | No, because the buffer strains the fiber as temperature fluctuates, increasing attenuation |
| What cable is rugged and used for patch cords? | Tight buffer, simplex or duplex |
| What cable prevents rodent damage? | Armored cable |
| What are the components of a simplex cable? | Tight-buffered fiber, strength member, and jacket, as shown. |
| What are simplex and zipcord cables used for? | Patch cables, short-run office cabling, test equipment. |
| What do the ratings OFNG and OFCG mean? | Optical Fiber Nonconductive General purpose, and Optical Fiber Conductive General purpose |
| Can outside plant cable be used indoors? | No, because of fire safety only 50 feet of outsude cable can be used indoors. |
| What kind of cable has the highest fiber count in the smallest diameter? | Ribbon cable |
| What does the rating OFN-LS mean? | Optical Fiber Nonconductive Low Smoke density |
| What is a Figure-8 cable? | A cable with an attached wire for aerial installation |
| What do the ratings OFN and OFC mean? | Optical Fiber Nonconductive, and Optical Fiber Conductive. |
| What is the difference between hybrid and composite cable? | Composite cable contains copper wires and fiber optics, and hybrid cable contains singlemode and multimode fibers |
| What do the ratings OFNR and OFCR mean? | Optical Fiber Nonconductive Riser-rated, and Optical Fiber Conductive Riser-rated. Riser cables can be used to go vertically between floors in a building. |
| What bend radius is allowable while the cable is under tension? | 20 times the diameter |
| What type of cable has many fibers, but can still be terminated with no breakout kit? | Breakout cable. |
| What is zipcord? | Zipcord is duplex cable |
| What do the ratings OFNP and OFCP mean? | Optical Fiber Nonconductive Plenum-rated, and Optical Fiber Conductive Plenum-rated. The Plenum is the area above the ceiling that carries ventilation. |
| What is an OGW cable? | Optical Ground Wire cables carry both electric power and fiber optic signals. |
| What are the components of a duplex cable? | Two simplex cables, each containing tight-buffered fiber, strength member, and jacket, as shown. |
| What are intrinsic loss factors at a join? | Problems the splicer cannot fix: Core diameter mismatch, Concentricity of fiber core or connector ferrules, Core ellipticity, Numerical Aperture mismatch |
| What does a reflectance value of 20 dB mean? | A reflectance of 20 dB means that 1% of the light is reflected |
| What are the acceptable loss and reflectance values for a singlemode splice? | Loss 0.15 dB, reflectance 50 dB. |
| What are the acceptable loss and reflectance values for a multimode splice? | Loss 0.25 dB, reflectance 50 dB. |
| What are the acceptable loss and reflectance values for a multimode connector pair? | Loss 0.75 dB, reflectance 25 dB. |
| What is FOCIS? | Fiber Optic Connector Intermateability Standard: A document produced by a connector manufacturer so others can mate to their connector |
| When is fusion splicing recommended? | Fusion splicing makes the strongest and best join for singlemode fiber, but it may lower bandwidth of multimode fiber. |
| What are the three mounting methods for connectors? | Adhesives, Crimping to hold the fiber, and Splicing to preconnectorized pigtails |
| How does the epoxy-polish method compare to other connectorization methods? | Takes longer, but costs less and has lowest loss and reflectance |
| What is the Main Cross-Connect? | The start of a bulding's internal backbone; it should be near the data center or PBX |
| What is innerduct? | Small pipes that sit inside conduit |
| What is the Telecom closet? | Transition from backbone to horizontal cable plant |
| What is a Splice Panel? | Hardware that holds and protects splices in one or more splice trays. |
| What is MCS Road Cable? | Cable designed to be inserted directly into a slit cut into pavement |
| What is the Intermediate Cross-Connect? | Connects interbuilding cable plant to intrabuilding cable plant |
| How long can a backbone be in Premises cabling? | 2000 meters max. |
| What is homerun cabling in a building? | Cables go from the Main Cross-Connect directly to the outlets, with only a single patch panel or splitter in between. |
| What is a splice tray? | Hardware that holds and protects splices, usually 12 or 24. |
| What are the two main types of hardware? | Premises Hardware – indoor, and Outside plant Hardware – outdoor |
| What are Plug and Play assemblies? | Preterminated cable with SC or other connectors in a special sock for pulling, or MTP ribbon cable connectors (12 fibers in a single SC-size plug) that plugs into a preconnectorized patch panel |
| What is an MTP connector? | A MTP ribbon cable connector connects 12 fibers in a single SC-size plug. |
| What is conduit? | Pipes that protect cable |
| What is a Patch Panel? | Provides a centralized location for connecting fibers, testing, monitoring, and restoring riser or trunk cables |
| What are splice closures? | Outside plant hardware to protect splices from water and the elements. |
| What are typical ranges of optical power used in fiber optics? | Usually in the range +10 dBm to -40 dBm, up to +30 dBm for analog CATV (cable TV) or DWDM (Dense Wavelength Division Multiplexing) systems |
| What Is EMD and how do you achieve it? | Equilibrium Modal Distribution is the mixture of modes that is found in a long multimode cable. To achieve it in the lab, use a mandrel wrap. |
| What is an attenuator, and when is it used? | Attenuators simulate the loss of a long fiber run. Variable attenuators allow testing a network to see how much loss it can withstand, and fixed attenuators can be used to prevent a detector from being saturated by too much optical power. |
| What are OTDR Ghosts? | Extra spikes seen at twice the distance to an actual reflective event, caused by secondary reflections. |
| What causes errors in OTDR distance measurements? | Errors in the index of refraction of the fiber, and the uncertainty in the amount of slack in the cable. |
| What device measures optical power, and what are the usual items measured? | A power meter, typically used to measure source output or receiver signal level |
| What is an optical splitter? | A device that splits light from one fiber into two fibers, or from any number M fibers to any other number N fibers. Also called a coupler. |
| How should you choose reference cables for testing? | Use cables with low loss, keep them clean, and use high quality mating adapters-- ceramic or metal, not plastic. |
| What devices measures fault location? | OTDR (Optical Time-Domain Reflectometer) or VFL (Visual Fault Locator) |
| What is a "gainer splice"? | An illusion caused by joining different fiber types and measuring them with an OTDR, in which the fiber appears to have more light on the other side of a splice. |
| What three wavelengths are power meters calibrated at? | 850 nm, 1300 nm, 1550 nm |
Created by:
stjohn45
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