Index

Fiber optics communication page

    Fiber optic communication general info

    Optical Fibres are fibres of glass, usually about 120 micrometres in diameter, which are used to carry signals in the form of pulses of light over distances up to 50 km without the need for repeaters. These signals may be coded voice communications or computer data. Fiber has extremely low RF attenuation (less than 1dB/km), very high bandwidth, immunity to EMI, no signal egress, flat broadband delay characteristics plus a cable design that is light weight and small size.

    The actual speed of light in a vacuum is 300 000 kilometers per second, or 186,000 miles per second. The light in the fiber optic cable travels slower than that. The index of refraction (IOR) is a way of measuring the speed of light in a material. Index of Refraction is calculated by dividing the speed of light in a vacuum by the speed of light in some other medium. The Index of Refraction of a vacuum by definition has a value of 1. The typical value for the cladding of an optical fiber is 1.46. The core value is 1.48. With those values the speed of the light in fiber optic is typically around 200 000 kilometers per second.

    In the early days of fiber-optic transmission (in the 1970s and early 1980s)telecommunication network developers were attracted by the single-mode optical fiber's low loss, low weight and inherent protectionagainst tapping (no one then had been able to tap an optical fiber, nowadays it can be done but it is not easy). Optical fiber allowed developers to bridge long distances with a small number of repeater stations and run high speed data rates at the same time. Depending on the fiber optic cable and the equipments on the ends you can transmit you data over fiber optic cable form tens of meters up to even hundreds of kilometers. The data rates can be extremely high, easily many gigabits per second.

    Fiber optic cable is very low loss medium. Attenuation in highly purified glass is on the order of 0.15 dB/km at 1550 nm compared with something closer to 1 dB/cm for window glass or, perhaps more directly useful, 10 dB/km for copper coax at 50 MHz. Unfortunately, attenuation is not the cable's only cumulatively degrading effect on a data stream. Dispersion terms (properties of the physical media and of the transmitted light spectra) spread the pulse widths, blurring the pulse stream and limiting maximum spans and signaling rates. This is not a problem in low speeds, but will be significant when speeds come to gigabits per second.

    There are two major basic fiberoptic types: singlemode and multimode. The concepts of singlemode and multimode are really straightforward, is is primarily a question of how large the core diameter is.

    • In multimode fiber the core diameter ranges from 50 to 100 microns (typical cable types for this are 62.5/125 micrometer and 50/125 micrometer models).
    • In singlemode fiber, the core diameter is a in order of 7 to 9 microns.
    Both of those cable types are made of pure glass and work best with infrared signals. In addition to those glass fiber cables, there exist also fiber optic cable made of plastic. Those plastic cables are considerably different compared to the ones made of fiber. The greatest differences are that plastic fiber optic cables are typically quite thick (1 mm core is commonly used), work typically best with visible light (red) and have very high loss (in order of 0.3 dB per meter for normal 1 mm cables). Plastic fiber optic cables work in multimode. Because of high loss, the maximum communications distance is very limited (up to 10-20 meters typical). Plastic fiber optic cables are commonly used for lighting applications (most often 1 mm or 2 mm thick fibers carry light from halogen bulb to location), slow speed industrial communications (1 mm fiber optic) and consumer digital audio interconnections (1 mm fiber).

    If you are dealing with an average building or campus, you don't have to worry about singlemode versus multimode. You can easily use either for almost any application, present or future.If, on the other hand you're dealing with wiring up long distances, then singlemode vs. multimode is of concern. You use singlemode fiber cables for long distances (typically 30-50km between repeaters) and very high data rate capacities(gigabit per second).

    Multimode fiber is qualified at two primary wavelengths: 850nm (short wavelength) and 1300nm (long wavelength). The de-facto bandwidth standard for 50/125?m optical fiber is 500 MHz?km @ 850nm and 500 MHz?km @ 1300nm. Fiber provides its lowest attenuation in the second optical window as 1310 nm, so that wavelenghts most commonly used. 850 nm is used for some short-haul transmission due availability of very low cost components for this wavelength.

    The power levels sent fiber opti cable depend on application. Typically the power levels used are form 50 nW up to 10 mW (-45 dBm to +10 dBm). Typical telecommunication applications use 1300 and 1550 nm wavelengthsat power range of +3 to -45 dBm (50 nW to 2mW). But on very long distance applications the applied power can be even higher (even up to 50-100 mW).

    Typical fiber data communication applications use wavelengths of 665, 850, 1300 or 1550 nm at -10 to -30 dBm signal levels (1 to 100uW). CATV systems typically use 1300 and 1550 nm wavelengthsat +10 to -6 dBm signl level (250 uW to 10mW).

    Signal is transmitter to the optical fiber using a LED (in low power short distance applications) or using semicondictor laser. There are two main types of semiconductor lasers in use for fiber optics communications: Fabrey-Perot lasers and VCSELs (vertical-cavity surface-emitting lasers). Fabrey-Perot lasers have been tradidionally the most commonly used ones. VCSELs (vertical-cavity surface-emitting lasers) are commercially available infrared semiconductor lasers with wavelength of around 850 nm.

    The optical signal on the cable is detected on the receiver end of the cable using a suitable photodetector (usually PIN photodiode). Silicon photodiodes are typically sensitive to light in the range of 400 to 1000 nm and germanium and indium-gallium-arsenide photodiodes are typically sensitive to light in the range of 800 to 1600 nm.

    Fiber optic communications is typically implemented using a wire pair, where one wire is for transmitting data to other ent and other for receiving data from other end. This is the most typical setup. There are some special systems that allow bidirectional communications over one fiber.

    There is a large number of different fiber optic connectors designed for different applicatons. Most connectors are designed to terminate a single cable, but there are also duplex models that can terminate one wire pair. For duplex connectors there is no single standard that says which of the fiber should be transmit and which is receive. Typically the electronics has the transmit on the left, with the key way "up".

    Optical fibres carry signals with much less energy loss than copper cable and with a much higher bandwidth. This means that fibres can carry more information over longer distances and with fewer repeaters required that can be done with copper cables. Optical fibre cables are much lighter and thinner than copper cables with the same bandwidth. Optical fibres are much more difficult to tap information from undetected.Fiber optic cables are immune to Electromagnetic interference from radio signals, car ignition systems, lightning etc.In spite of the fact that the raw material for making optical fibres, sand, is abundant and cheap, optical fibres are still more expensive per metre than copper. Optical fibres cannot be joined (spliced) together as a easily as copper cable and requires additional training of personnel and expensive precision splicing and measurement equipment.

    Fiber information

    The optical fiber made of glass is used for high speed data communication.

    There are two main types of fiber optic cable:

    • Single Mode cable is a single stand of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission. Single Mode Fiber with a relatively narrow diameter, through which only one mode will propagate typically 1310 or 1550nm. Carries higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width. Synonyms mono-mode optical fiber, single-mode fiber, single-mode optical waveguide, uni-mode fiber. Single-mode fiber allows you to have high transmission rate and long cables, because small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fiber cable type.
    • Multimode cable is made of of glass fibers, with a common diameters in the 50-to-100 micron range for the light carry component (the most common size is 62.5). Multimode fiber gives you high bandwidth at high speeds over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable's core typically 850 or 1300nm. Typical multimode fiber core diameters are 50, 62.5, and 100 micrometers. In long cable run multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission.

    There are several different kinds of of fiber optic cables:

    • STEP-INDEX MULTIMODE FIBER has a large core, up to 100 microns in diameter. As a result, some of the light rays that make up the digital pulse may travel a direct route, whereas others zigzag as they bounce off the cladding. Consequently, this type of fiber is best suited for transmission over short distances, in an endoscope, for instance.
    • GRADED-INDEX MULTIMODE FIBER contains a core in which the refractive index diminishes gradually from the center axis out toward the cladding. The higher refractive index at the center makes the light rays moving down the axis advance more slowly than those near the cladding. Also, rather than zigzagging off the cladding, light in the core curves helically. Graded index multimode glass fibers are generally used for LAN data networks.
    • SINGLE-MODE FIBER has a narrow core (eight microns or less), and the index of refraction between the core and the cladding changes less than it does for multimode fibers. Light thus travels parallel to the axis, creating little pulse dispersion. Telephone and cable television networks install millions of kilometers of this fiber every year. Single mode fiber optic cables are generally used for long distance high speed telecommunication networks.
    • Plastic Optical Fiber (POF) is generally used for illumination and low speed short data. Plastic Optical Fibers are typically step-index fibers. Plastic fiber opti cables have very high loss compared to other fiber types made of glass, and are thus only suitable for short distances. Normally, a 650nm (red) LED is used as the light source for POF optical transceiver modules. POF typically uses PMMA (acrylic), a general-purpose resin as the core material, and fluorinated polymers for the clad material. Most POF being used has a fiber diameter of 1000um, with a core diameter of 980um. Due to this large diameter, transmission is possible even if the ends of the fiber are slightly soiled or damaged, or if the light axis is slightly off center. Therefore, parts such as optical connectors can be made inexpensively and installation work is simplified. POF is strong and very difficult to bend. There is only a small loss even when bent to a 25mm radius. Nrmally, a 650nm (red) LED is used as the light source for POF optical transceiver modules. Since POF transmits very little infrared light, it can be used for cold lighting (lighting that do not produce heat), for semiconductor manufacturing equipment and the lighting displays of artwork. From an optical standpoint, conventional POF is much lower in performance than glass fiber. It has a loss of 0.15-0.2 dB per meter at 650 nm and its bandwidth is limited by its large NA and step-index profile. However, it is adequate for running short links, such as inside of instruments or within a room for desktop connections up to 50 meters. And of course in automobiles, where it has gained a foothold with the new MOST and Flexray networks. But recent developments in POF technology have led to low NA POF that offers higher bandwidth and graded-index POF (GI-POF) that combines the higher bandwidth of graded-index fiber with the low cost of POF.

    There are two main mechanical fiber optic cable constructions:

    • Loose-Tube Cable: In a loose-tube cable design, color-coded plastic buffer tubes house and protect optical fibers. A gel filling compound impedes water penetration. Excess fiber length (relative to buffer tube length) insulates fibers from stresses of installation and environmental loading. Buffer tubes are stranded around a dielectric or steel central member, which serves as an anti-buckling element. Loose-tube cables typically are used for outside-plant installation in aerial, duct and direct-buried applications. Loose-tube cable is used in the majority of outside-plant installations in North America.
    • Tight-Buffered Cable: With tight-buffered cable designs, the buffering material is in direct contact with the fiber. This design is suited for "jumper cables" which connect outside plant cables to terminal equipment, and also for linking various devices in a premises network. The tight-buffered design provides a rugged cable structure to protect individual fibers during handling, routing and connectorization. Yarn strength members keep the tensile load away from the fiber. Multi-fiber, tight-buffered cables often are used for intra-building, risers, general building and plenum applications.

    The history of actively using fiber optics is not very long. The use of fiber-optics was generally not available until 1970 when Corning Glass Works was able to produce a fiber with a loss of 20 dB/km. It was recognized that optical fiber would be feasible for telecommunication transmission only if glass could be developed so pure that attenuation would be 20dB/km or less. Today's optical fiber attenuation ranges from 0.5dB/km to 1000dB/km depending on the optical fiber used. Attenuation limits are based on intended application. The use of different cable types depends on the application.

    Connector information

    Fiber optic connectors have traditionally been the biggest concern in using fiber optic systems. While connectors were once unwieldy and difficult to use, connector manufacturers have standardized and simplified connectors greatly. This increasing user-friendliness has contributed to the increase in the use of fiber optic systems; it has also taken the emphasis off the proper care and handling of optical connectors. But still there are many different kind of optical fiber connectors.

    The ideal interconnection of one fiber to another would have two fibers that are optically and physically identical held by a connector or splice that squarely aligns them on their center axes. However, in the real world, system loss due to fiber interconnection is a factor. Insertion loss is the primary consideration for connector performance. There are three types of insertion loss: fiber-related loss, connector-related loss, and system factors that contribute to loss. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters.

    Fiber-to-fiber interconnection can consist of a splice, a permanent connection, or a connector, which differs from the splice in its ability to be disconnected and reconnected. Simply put, fiber optic splicing involves joining two fiber optic cables together. The other, more common, method of joining fibers is called termination or connectorization. Fiber splicing typically results in lower light loss and back reflection than termination making it the preferred method when the cable runs are too long for a single length of fiber or when joining two different types of cable together. Splicing is also used to restore fiber optic cables when a buried cable is accidentally severed. Splices are "permanent" connections between two fibers.

    Fiber optic connectors are used in applications where cable interconnections needs to be changed sometimes (for example fier cross connection, equipment connection cables etc.). There are many different kind of fiber connectors in use. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters. But all connectors have the same four basic components.

    • The Ferrule: The fiber is mounted in a long, thin cylinder, the ferrule, which acts as a fiber alignment mechanism.
    • The Connector Body: The connector body holds the ferrule. It is usually constructed of metal or plastic.
    • The Cable: The cable is attached to the connector body.
    • The Coupling Device: Most fiber optic connectors use a coupling device such as an alignment sleeve to mate the ferrules from two different fiber connectors precisely directly to each other.

    The method for attaching fiber optic connectors to optical fibers varies among connector types. Here are some general advice:

    • Cut the cable one inch longer than the required finished length
    • Carefully strip the outer jacket of the fiber with ?no nick? fiber strippers.
    • Cut the exposed strength members
    • Remove the fiber coating with a suitable chemical (soaking the fiber for two minutes in paint thinner and wiping the fiber clean with a soft, lint-free cloth) or with a fiber stripper (be sure to use strippers made specifically for use with fiber).
    • Clean the bared fiber with isopropyl alcohol (industrial grade 99% pure isopropyl alcohol) poured onto a soft, lint-free cloth that is folded twice (Kimwipes? or any lens-grade, lint-free tissue, type sold for eyeglasses should work quite well)
    • Attach the connector (the connector may be connected by applying epoxy or by crimping)
    • Anchor the cable strength members to the connector body
    • Prepare the fiber face to achieve a good optical finish by cleaving and polishing the fiber end (fiber must have a smooth finish that is free of defects such as hackles, lips, and fractures)
    • Clean the fiber connector with isopropyl alcohol (industrial grade 99% pure isopropyl alcohol) poured onto a soft, lint-free cloth that is folded twice (Kimwipes? or any lens-grade, lint-free tissue, type sold for eyeglasses should work quite well). Chean both the sides of the connector ferrule and the connector fiber end.
    • Use the microscope (30X microscope) to verify the quality of the fiber termination and the cleaning
    • Mate the connector immediately or protect it with a dist cap.

    Several different types of terminations are available for multimode and single mode fibers. Each version has its advantages and disadvantages, so learning more about how each works helps decide which one to use. Choose the style that suits the particular situation best and be prepared to work with both technologies.

    Whatever you do, follow the manufacturer's termination instructions closely. Multimode connectors are usually installed in the field on the cables after pulling, while singlemode connectors are usually installed by splicing a factory-made "pigtail" onto the fiber. That is because the tolerances on singlemode terminations are much tighter and the polishing processes are more critical. Singlemode fiber requires different connectors and polishing techniques than multimode. Most SM fiber is terminated by splicing on a preterminated pigtail, but you can put SM connectors on in the field if you know what you are doing.You can install singlemode connectors in the field for low speed data networks, but you may not be able to get losses lower than 1 dB! And you easily get also high back reflections, so don't try it for anything but data networks (not for telco or CATV).

    Several different types of terminations are available for multimode fibers. Each version has its advantages and disadvantages, so learning more about how each works helps decide which one to use.

    • Epoxy/Polish: Most connectors are the simple "epoxy/polish" type where the fiber is glued into the connector with epoxy and the end polished with special polishing film. These provide the most reliable connection, lowest losses (less than 0.5 dB) and lowest costs, especially if you are doing a lot of connectors. The epoxy can be allowed to set overnight or cured in an inexpensive oven. A "heat gun" should never be used to try to cure the epoxy faster as the uneven heat may not cure all the epoxy or may overheat some of it which will prevent it ever curing!
    • "Hot Melt": This is a 3M trade name for a connector that already has the epoxy (actually a heat set glue) inside the connector. You strip the cable, insert it in the connector, crimp it, and put it in a special oven. In a few minutes, the glue is melted, so you remove the connector, let it cool and it is ready to polish. Fast and easy, low loss, but not as cheap as the epoxy type, it has become the favorite of lots of contractors who install relatively small quantities of connectors.
    • Anaerobic Adhesives: These connectors use a quick setting adhesive to replace the epoxy. They work well if your technique is good, but often they do not have the wide temperature range of epoxies, so only use them indoors. A lot of installers are using Loctite 648, with or without the accellerator solution, that is neat and easy to use.
    • Crimp/Polish: Rather than glue the fiber in the connector, these connectors use a crimp on the fiber to hold it in. Early types offered "iffy" performance, but today they are pretty good, if you practice a lot. Expect to trade higher losses for the faster termination speed. And they are more costly than epoxy polish types. A good choice if you only install small quantities and your customer will accept them.
    • Prepolished/splice: Some manufacturers offer connectors that have a short stub fiber already epoxied into the ferrule and polished perfectly, so you just cleave a fiber and insert it like a splice. While it sound like a great idea, it has several downsides. First it is very costly, five to ten times as much as an epoxy polish type. Second, you have to make a very good cleave to make them low loss. Third, even if you do everything correctly, you loss will be higher, because you have a connector loss plus two splice losses at every connection! Monitor the loss with a visual fault locator and "tweak" the connection to best results.

    Choose the connector carefully and clear it with the customer if it is anything other than an epoxy/polish type. Some customers have strong opinions on the types or brands of connectors used in their job. Find out first, not later! Never, never, NEVER take a new connector in the field until you have installed enough of them in the office. The field is no place to experiment or learn!

    Have the right tools for the job. Make sure you have the proper tools and they are in good shape before you head out for the job. This includes all the termination tools, cable tools and test equipment. More and more installers are owning their own tools like auto mechanics, saying that is the only way to make sure the tools are properly cared for.

    Dust and dirt are your enemies. It's very hard to terminate or splice in a dusty place. Try to work in the cleanest possible location away from heating vents and such. Use lint-free wipes to clean every connector before connecting or testing it.

    Most connectors use epoxies or other adhesives to hold the fiber in the connector. Use only the specified epoxy, as the fiber to ferrule bond is critical for low loss and long term reliability! If you use hardware store epoxies (Crazy Glue etc.) you will regretted doing it later.

    Don't overpolish. Contrary to common sense, too much polishing is just as bad as too little. The ceramic ferrule in most of today's connector is much harder than the glass fiber. Polish too much and you create a concave fiber surface, increasing the loss. A few swipes is all it takes. Remember singlemode fiber requires different connectors and polishing techniques. Change polishing film regularly. Polishing builds up residue and dirt on the film.

    Inspect and test, then document. Keep good records. Smart users require it and expect to pay extra for good records. Put covers on connectors and patch panels when not in use. Keep them covered to keep them clean.

    With polished connectors (hot melts or regular epoxy or any other type of glue, does not matter) your fiber is glued into the ferrule very strongly. Most connectors use epoxies or other adhesives to hold the fiber in the connector. Use only the specified epoxy, as the fiber to ferrule bond is critical for low loss and long term reliability. Most connectors are the simple "epoxy/polish" type where the fiber is glued into the connector with epoxy and the end polished with special polishing film. These provide the most reliable connection, lowest losses (less than 0.5 dB) and lowest costs, especially if you are doing a lot of connectors. The epoxy can be allowed to set overnight or cured in an inexpensive oven. There are also connectors that use hot glue (3M makes those) or anaerobic adhesives (Loctite 648 glue is quite often used). Whatever you do, follow the manufacturer's termination instructions closely . Good epoxy polish connectors will have losses less than 0.5 dB (0.2-0.3 dB being quite normal for well installed connectors). Tolerances on singlemode terminations are very tight and the polishing processes are very critical. You can install singlemode connectors in the field for low speed data networks, but you may not be able to get losses lower than 1 dB. Instead of field installation singlemode connectors are usually installed by splicing a factory-made "pigtail" onto the fiber.

    Crimp/Polish is another method to install fiber to the connector. Rather than glue the fiber in the connector, these connectors use a crimp on the fiber to hold it in. Early types offered "iffy" performance, but today they are pretty good, if you practice a lot. Expect to trade higher losses for the faster termination speed. And they are more costly than epoxy polish types. A good choice if you only install small quantities and your customer will accept them.

    Some manufacturers offer connectors that have a short stub fiber already epoxied into the ferrule and polished perfectly, so you just cleave a fiber and insert it like a splice. While it sound like a great idea, it has several downsides. First it is very costly, five to ten times as much as an epoxy polish type. Second, you have to make a good cleave to make them low loss, and that is not as easy as you might think. Third, even if you do everything correctly, you loss will be higher, because you have a connector loss plus two splice losses at every connection! The best way to terminate them is to monitor the loss with a visual fault locator and "tweak" them.

    Crimp-style connectors like AMP's LightCrimp and UniCam by Corning, as well as the clones (these guys OEM manufacture for everyone and their brother) are best suited for repair work, not the new installs. The reality of the thing is: you are inserting two additional mechanical splices on every fiber, and that may be especially bad on singlemode cables. Reliability of the crimp-style connectors also leaves to desire more. Some crimp-style are notorious for not allowing ANY touching after the install is done, some allow light pull. In crimp style connector the fiber is hold in place with a well crimped (or just rotated) plastic part that holds the whole thing together. Any light pull on the fiber may potentially separate the fiber from the connector, which destroys the link. Sometimes accidental pulls on fiber are unavoidable, especially if you are working in a densely populated shelf, and dressing your fibers in. Cleaving stage is very important in no polish fiber terminations. If you need to work on environement where there is dust in the air, the crimp style no polish connectors will do much better (because the dust in the air may not allow you to do good polishing). The no polish crimp connectors can be pricey compared to other systems, but the reduction in labor can go a long ways toward evening the cost. You should be able to do one end of a 24 strand fiber in about 45 minutes including setup time and have all the fibers test out to less than a half dB insertion loss. AMP and other manufacturers have already stated the future in premise fiber is the mechanical connector. Also, even though there are extra splices within the connector, youd have to be commander data to notice a fe dbs of extra loss.

    There is a third way to install connectors to fibers. This method uses ready made pigtails, that are short piece of fiber opti cable terminated to connector on the factory. This piece of fiber is then spliced to the ends of the cable you have. Fusion splicing with factory-made pigtails is the way to go in installations where there is a high performance concern as well as the dust from the construction. Multimode connectors are usually installed in the field on the cables after pulling, while singlemode connectors are usually installed by splicing a factory-made "pigtail" onto the fiber. That is because the tolerances on singlemode terminations are much tighter and the polishing processes are more critical. As for single mode, I'd fusion splice pigtails if I didn't want to puck-n-polish.

    Tips for fiber connector installation: Never, never, NEVER take a new connector in the field until you have installed enough of them in the office that you can put them on in your sleep. The field is no place to experiment or learn! It'll cost you big time! Make sure you have the proper tools and they are in good shape before you head out for the job. This includes all the termination tools, cable tools and test equipment. Dust and dirt are your enemies. It's very hard to terminate or splice in a dusty place. Try to work in the cleanest possible location. Use lint-free wipes. Don't overpolish, because too much polishing is just as bad as too little (can create a concave fiber surface, increasing the loss). A few swipes is all it takes. Change polishing film regularly. Polishing builds up residue and dirt on the film. Remember singlemode fiber requires different connectors and polishing techniques. Most SM fiber is terminated by splicing on a preterminated pigtail, but you can put SM connectors on in the field if you know what you are doing. Expect much higher loss, approaching 1 dB and high back reflections, so don't try it for anything but data networks, not telco or CATV.

    Cables can be pulled with connectors already on them if, and a big if, you can deal with these two problems: First, the length must be precise. Too short and you have to pull another longer one (its not cost effective to splice), too long and you waste money and have to store the extra cable length. Secondly, the connectors must be protected. Some cable and connector manufacturers offer protective sleeves to cover the connectors, but you must still be much more careful in pulling cables. You might consider terminating one end and pulling the unterminated end to not risk the connectors. There is a growing movement to install preterminated systems (both single/dual fiber per normal connector and many fibers on one special connector).

    Tips for cleaning fiber connection: Clean the fiber connector with isopropyl alcohol (industrial grade 99% pure isopropyl alcohol) poured onto a soft, lint-free cloth that is folded twice (Kimwipes? or any lens-grade, lint-free tissue, type sold for eyeglasses should work quite well). Chean both the sides of the connector ferrule and the connector fiber end. Air can be used to remove lint or loose dust from the port of a transmitter or receiver to be mated with the connector. Never insert any liquid into the ports.

    The fiber end face and ferrule must be absolutely clean before it is inserted into a transmitter or receiver. Dust, lint, oil (from touching the fiber end face), or other foreign particles obscure the end face, compromising the integrity of the optical signal being sent over the fiber. Single-mode fibers have cores that are only 8-9 ?m in diameter. A 1 ?m dust particle landing on the core of a single-mode fiber can cause up to 1 dB of loss. Larger dust particles (9 ?m or larger) can completely obscure the core of a single-mode fiber. As a point of reference, a typical human hair is 50-75 ?m in diameter, approximately 6-9 times larger! Dust particles can be 20 ?m or larger in diameter.

    Fiber optic connectors need to be cleaned every time they are mated and unmated (at least on networks built using single mode fiber). Connectors not in use should be covered over the ferrule by a plastic dust cap. Unprotected connector ends are most often damaged by impact, such as hitting the floor. Most connector manufacturers provide some sort of protection boot. Fiber optic connectors need to be cleaned every time they are removed from the cap (there can be residue that will remain on the ferrule end after the cap is removed). Never touch the fiber end face of the connector.

    One should never clean an optical connector attached to a fiber that is carrying light. Optical power levels as low as +15 dBm, or 32 milliwatts, may cause an explosive ignition of the cleaning material when it contacts the end of the optical connector, destroying the connector. Typical cleaning materials, such as tissues saturated with alcohol, will combust almost instantaneously when exposed to optical power levels of +15 dBm or higher. The micro-explosions at the tip of the connector can leave pits in the end of the connector and crack the connector?s surface, destroying its ability to carry light with low loss. It is also a safety issue not to work with fibers connected to opticla power source. A few milliwatts at 850 nm can do permanent damage to a retina and optical amplifiers can generate optical powers of 0.1-1 Watt of more into a single-mode fiber.

    The use of index-matching gel, a gelatinous substance that has a refractive index close to that of the optical fiber, is a point of contention between connector manufacturers. Glycerin, available in any drug store, is a low-cost, effective index-matching gel. Using glycerin will reduce connector loss and backreflection, often dramatically. However, the index-matching gel may collect dust or abrasives that can damage the fiber end faces. It may also leak out over time, causing backreflections to increase.

    • What is Fiber Optic Splicing - Knowledge of fiber optic splicing methods is vital to any company or fiber optic technician involved in Telecommunications or LAN and networking projects.    Rate this link
    • Fiber Optic Connectors - Fiber optic connectors have traditionally been the biggest concern in using fiber optic systems. While connectors were once unwieldy and difficult to use, connector manufacturers have standardized and simplified connectors greatly.    Rate this link
    • Connector Loss Test Measurements    Rate this link
    • Fiber Optic Termination - a good tutorial    Rate this link
    • Fiber Connector Termination Methods    Rate this link
    • MT-RJ Information Page - a new small form factor two-fiber connector designed to meet the optical fiber industry's request for a new interface technology that is significantly lower in cost and smaller than the duplex SC interface    Rate this link
    • Fiber Optic Termination - We terminate fiber optic cable two ways - with connectors that can mate two fibers to create a temporary joint and/or connect the fiber to a piece of network gear or with splices which create a permanent joint between the two fibers. These terminations must be of the right style, installed in a manner that makes them have little light loss and protected against dirt or damage in use. No area of fiber optics has been given greater attention than termination. Manufacturers have come up with over 80 styles of connectors and and about a dozen ways to install them. There are two types of splices and many ways of implementing the splice. Fortunately for me and you, only a few types are used most applications. Different connectors and splice termination procedures are used for singlemode and multimode connectors, so make sure you know what the fiber will be before you specify connectors or splices!    Rate this link
    • Fiber Optic Termination - We terminate fiber optic cable two ways - with connectors that can mate two fibers to create a temporary joint and/or connect the fiber to a piece of network gear or with splices which create a permanent joint between the two fibers. These terminations must be of the right style, installed in a manner that makes them have little light loss and protected against dirt or damage in use.    Rate this link
    • Fiber Optic Termination    Rate this link

    Splicing fibers

    Fiber-to-fiber interconnection can consist of a splice, a permanent connection, or a connector, which differs from the splice in its ability to be disconnected and reconnected. Simply put, fiber optic splicing involves joining two fiber optic cables together. The other, more common, method of joining fibers is called termination or connectorization. Fiber splicing typically results in lower light loss and back reflection than termination making it the preferred method when the cable runs are too long for a single length of fiber or when joining two different types of cable together. Splicing is also used to restore fiber optic cables when a buried cable is accidentally severed. Splices are "permanent" connections between two fibers.

    There are two methods of fiber optic splicing, fusion splicing & mechanical splicing. The choice is usually based on cost or location. Most splicing is on long haul outside plant SM cables, not multimode LANs. Mechanical splices are simply alignment devices, designed to hold the two fiber ends in a precisely aligned position thus enabling light to pass from one fiber into the other. (Typical loss: 0.3 dB) In fusion splicing a machine is used to precisely align the two fiber ends then the glass ends are "fused" or "welded" together using some type of heat or electric arc. This produces a continuous connection between the fibers enabling very low loss light transmission. (Typical loss: 0.1 dB) Mechanical splicing has a low initial investment ($1,000 - $2,000) but costs more per splice ($12-$40 each). The initial investment for fusion splicing is much higher ($15,000 - $50,000) but the cost per splice for fusion splicing is lower ($0.50 - $1.50 each) and connection performance is better. Fusion is expensive equipment and cheap splices, while mechanical is cheap equipment and expensive splices. Fusion splicing produces lower loss and less back reflection than mechanical splicing because the resulting fusion splice points are almost seamless. Fusion splices are used primarily with single mode fiber where as Mechanical splices work with both single and multi mode fiber.

    Four basic steps to completing a proper fusion splice:

    • 1. Preparing the fiber: Strip the protective coatings, jackets, tubes, strength members, etc. leaving only the bare fiber showing.
    • 2. Cleave the fiber: The cleaved end must be mirror-smooth and perpendicular to the fiber axis to obtain a proper splice.
    • 3. Fuse the fiber: There are two steps within this step, alignment and heating. Alignment can be manual or automatic depending on what equipment you have. Once properly aligned the fusion splicer unit then uses an electrical arc to melt the fibers, permanently welding the two fiber ends together.
    • 4. Protect the fiber: Protecting the fiber from bending and tensile forces will ensure the splice not break during normal handling. A typical fusion splice has a tensile strength between 0.5 and 1.5 lbs and will not break during normal handling but it still requires protection from excessive bending and pulling forces. Using heat shrink tubing, silicone gel and/or mechanical crimp protectors will keep the splice protected from outside elements and breakage.

    Four steps to performing a mechanical splice:

    • 1. Preparing the fiber: Strip the protective coatings, jackets, tubes, strength members, etc. leaving only the bare fiber showing
    • 2. Cleave the fiber: The process is identical to the cleaving for fusion splicing but the cleave precision is not as critical.
    • 3. Mechanically join the fibers: Simply position the fiber ends together inside the mechanical splice unit. The index matching gel (or epoxy) inside the mechanical splice apparatus will help couple the light from one fiber end to the other.
    • 4. Protect the fiber: The completed mechanical splice provides its own protection for the splice.

    Cleaving involves cutting the fiber end flush with the end of the ferrule. Cleaving, also called the scribe-and-break method of fiber end face preparation, takes some skill to achieve optimum results. Properly done, the cleave produces a perpendicular, mirror-like finish. NOTE: The cleaver does not cut the fiber! It merely nicks the fiber and then pulls or flexes it to cause a clean break. The goal is to produce a cleaved end that is as perfectly perpendicular as possible. A good cleaver for fusion splicing can often cost $1,000 to $3,000. These cleavers can consistently produce a cleave angle of 0.5 degree or less.

    Passive Optical Networks

    For the last two decades, it has been a dream for telecommunication carriers to develop a new era wherein a variety of services are provided over an optical access platform instead of existing Plain Old Telephone Service (POTS)-oriented metallic networks. Passive optical network (PON) is a promising technology for building optical access networks.

    • Ethernet Passive Optical Networks (EPON) - Should there be an IEEE standard ? - slide set in pdf format    Rate this link
    • FIBER FIGHT: Ethernet Duels ATM for Home Access - With the price of fiber decreasing, many are pointing to PONs as the ideal solution for bridging the last-mile gap. The trick is choosing the right PON technology to deploy.    Rate this link
    • FSAN - forum to develop broadband access networks    Rate this link
    • Last Mile Lexicon    Rate this link
    • Asynchronous Transfer Mode (ATM) Passive Optical Networks (PONs) - This tutorial discusses the economics, operator and customer benefits, and technological development of optical distribution networks with asynchronous transfer mode passive optical networks (ATM PONs). ATM?PON infrastructure is widely cited by telecommunications carriers and equipment vendors as potentially the most effective broadband access platform for provisioning advanced multimedia services as well as legacy services such as tier 1 (T1). Since 1995, an influential group of worldwide carriers and equipment vendors has been developing requirement specifications for a full-service access network with ATM PON as the core technology.    Rate this link
    • Ethernet Passive Optical Networks - Ethernet passive optical networks (EPON) are an emerging access network technology that provides a low-cost method of deploying optical access lines between a carrier's central office (CO) and a customer site. EPONs build on the International Telecommunications Union (ITU) standard G.983 for asynchronous transfer mode PONs (APON) and seek to bring to life the dream of a full-services access network (FSAN) that delivers converged data, video, and voice over a single optical access system.    Rate this link

    Fibre Channel

    Fibre Channel (FC) is the most common choice for transport instorage area network (SAN) implementations.Fibre Channel is a data management system, a unified approach tostorage, network and control. It provides accessible supervision,scalable performance and versatile connectivity, via simplepoint-to-point topologies with dedicated bandwidth or loops withshared bandwidth.The promise of Fibre Channel storage is, that by using a high-speednetworking technology, you can easily connect a wide variety of storagedevices to your server and you can share content stored on thesestorage devices. Much of this promise has been delivered, but there arestill some issues to be resolved.

    Resilient Packet Ring

    Resilient Packet Ring is a new data link layer optimized for data traffic for optical networks used in LANs, MANs or WANs. RPR is an alternative layer 2 (link layer) technology that is better optimized to address the multi-service transport requirements over ring topologies that prevail in metropolitan area networks (for example Ethernet and SDH). The IEEE 802.17 standard will define a Resilient Packet Ring (RPR) Media Access Control (MAC) that is physical layer independent. RPR is focused on providing a new MAC layer optimized for the MAN and WAN while leveraging Ethernet's physical layer which has had significant enhancements and widespread adoption.

    • IEEE 802.17 Resilient Packet Ring Working Group - The IEEE 802.17 Resilient Packet Ring Working Group (RPRWG) will define a Resilient Packet Ring Access Protocol for use in Local, Metropolitan and Wide Area Networks for transfer of data packets at rates scalable to many gigabits per second. The new standard will use existing Physical Layer specifications and will develop new PHYs where appropriate.    Rate this link

<[email protected]>

Back to ePanorama main page ??
 
| Submit site | Info | Advertise | Feedback | Disclaimer | Privacy | Ad. FAQ | Legal Notice |
Copyright © 1994-2011