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• Fiber Optic Overview

  Feb 6, 2016 by Articles / 674 Views

  Fiber Optic Communication - The Future Of Networking & Data Transmission

  Fiber optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information.

  First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks. Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers have reached internet speeds of over 100 petabits per second using fiber-optic communication.

  Fiber's advantages has led to its use as the backbone of all of today's communications, telecom, Internet, CATV, etc. - even wireless, where towers are connected on fiber and antennas are using fiber up the towers.

  

   

  Optical Fiber - The Better Solution

  

  This photo from the infancy of fiber optics (to the right) was used to illustrate that one tiny optical fiber could carry more communications signals than a giant copper cable. Today one single mode fiber could carry the same amount of communications as 1000 of those old copper cables!

  Fiber offers thousands of times more bandwidth than copper cables and can go more than 1000 times further before needing repeaters - both of which contribute to the immense economic advantage of fiber optics over copper. You can do a similar analysis for using wireless transmission also, but wireless is limited by the available wireless spectrum which is overcrowded because of everyone's desire to use more mobile devices.

  Why Convert From Copper Cable To Fiber Optic Cable?

  If you need some convincing before you make your first fiber optic cable purchase keep the following facts in mind.

  Optical Fiber - Much More Efficient & Secure

  Fiber optic cable operates much more efficiently and is more secure than traditional copper cabling. Fiber can transmit far more information over greater distance and with a higher clarity while offering a more secure connection. Fiber optic cable is resistant to electromagnetic interference and generates no radiation of its own. This point is important in locations where high levels of security must be maintained. Copper wire radiates energy that can be monitored. In contrast, taps in  Fiber optic cable  Fiber  are easily detected. Copper cable, is also subject to problems with attenuation, capacitance, and crosstalk.

  Optical Fiber - Does Not Require Grounding

  Since fiber is made of glass, which is a bad electrical conductor, it does not require grounding and shields itself from other electrical interference. Fiber cables can be run near electrical cables without fear that it will weaken or interrupt the signal.

  Optical Fiber - Corrosion Resistant

  Fiber optic cable does not corrode and is not as sensitive to water or chemicals. This means you can safely run fiber cable in direct contact with dirt or in close proximity to chemicals (with the proper outer jacket materials).

  Optical Fiber - The Safer Choice

  Since fiber is not a good conductor of electricity, an installer or user will be safe from electrocution if there is a break in the outer jacket and the fiber is exposed.

   

  How Fiber Optic Communication Works

  The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal.

  Fiber (or fibre) consists of a strand of pure glass a little larger than a human hair. Fiber optic cable employs photons and pulsing laser light for the transmission of digital signals. Photons pass through the glass with negligible resistance. As light passes through the cable, its rays bounce off the cladding in different ways as shown below. The optic core of fiber optic cable is pure silicon dioxide. The electronic 1s and 0s of computers are converted to optically coded 1s and 0s. A light-emitting diode on one end of the cable then flashes those signals down the cable. At the other end, a simple photodetector collects the light and converts it back to electrical signals for transmission over copper cable networks.

  

  Step index multimode was the first fiber design but is too slow for most uses, due to the dispersion caused by the different path lengths of the various modes. Step index fiber is rare - only POF uses a step index design today.

  Graded index multimode fiber uses variations in the composition of the glass in the core to compensate for the different path lengths of the modes. It offers hundreds of times more bandwidth than step index fiber - up to about 2 gigahertz.

  Singlemode fiber shrinks the core down so small that the light can only travel in one ray. This increases the bandwidth to almost infinity - but it's practically limited to about 100,000 gigahertz - that's still a lot!

   

  Optic Fiber Cable Construction

  

   

  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 (or fibers formed into ribbons or bundles) 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 ("dark") 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.

  A “dopant” is added to the core to actually make it less pure than the cladding. This changes the way the core transmits light. Because the cladding has different light properties than the core, it tends to keep the light within the core. Because of these properties, fiber optic cable can be bent around corners and can be extended over distances of up to 100 miles.
  
  A typical laser transmitter can be pulsed billions of times per second. In addition, a single strand of glass can carry light in a number of wavelengths (colors), meaning that the data-carrying capacity of fiber optic cable is potentially thousands of times greater than copper cable.

   

  Types Of Fiber Optic Cable

  • Plastic cable, which works only over a few meters, is inexpensive and works with inexpensive components.
  • Plastic-coated silica cable offers better performance than plastic cable at a little more cost.
  • Single-index monomode fiber cable is used to span extremely long distances. The core is small and provides high bandwidth at long distances. Lasers are used to generate the light signal for single-mode cable. This cable is the most expensive and hardest to handle, but it has the highest bandwidths and distance ratings.
  • Step-Index multimode cable has a relatively large diameter core with high dispersion characteristics. The cable is designed for the LAN environment and light is typically generated with a LED (light-emitting diode).
  • Graded-index multimode cable has multiple layers of glass that contain dispersions enough to provide increases in cable distances.

  Cable specifications list the core and cladding diameters as fractional numbers. For example, the minimum recommended cable type for FDDI (Fiber Distributed Data Interface) is 62.5/125 micron multimode fiber optic cable.That means the core is 62.5 microns and the core with surrounding cladding is a total of 125 microns.

  • The core specifications for step-index and graded-index multimode cables range from 50 to 1,000 microns.
  • The cladding diameter for step mode cables ranges from 125 to 1,050 microns.
  • The core diameter for single-mode step cable is 4 to 10 microns, and the cladding diameter is from 75 to 125 microns.

  

   

  Indoor Vs. Outdoor Optic Fiber Cable Applications

  For  indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid (e.g. Twaron or Kevlar), 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 outdoor applications or 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 (normally a glass rod epoxy), 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.

  To purchase your fiber cables, please click link below:

  Fiber Patch Cables

   

   

   

   

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• The Composition and Classification of Fiber Optic Cables

  Feb 6, 2016 by Articles / 518 Views

  To satisfy optical, mechanical and environmental performances and specifications, fiber optic cable was born. The fiber optic cable uses one or more fibers that placed in the sheath as the transmission medium. Accompanied by the continuous advancement of network technology, fiber optic cable constantly participates in the construction of telecommunications networks, the construction of the national information highway, Fiber To The Home (FTTH) and other occasions for large-scale use. Although fiber optic cable is still more expensive than other types of cable, it's favored for today's high-speed data communications because it eliminates the problems of twisted-pair cable and so fiber optic cable is still a good choice for people. But how to really get a good performance, state-of-the-art products, we need to understand some basics to identify the types of fiber optic cables.

  Composition

  Fiber optic cable consists of the core, the cladding and the coating. The core is a cylindrical rod of dielectric material. Dielectric material conducts no electricity. Light propagates mainly along the core of the fiber. The core is generally made of glass. The core is described as having a radius of (a) and an index of refraction n1. The core is surrounded by a layer of material called the cladding. Even though light will propagate along the fiber core without the layer of cladding material, the cladding does perform some necessary functions. (The basic structure of an optical fiber is shown in the following figure.)

   

  Structure: Core: This central section, made of silica, is the light transmitting region of the fiber.Cladding: It is the first layer around the core. It is also made of silica, but not with the same composition as the core. This creates an optical wave guide which confines the light in the core by total reflection at the core-cladding interface.Coating: It is the first non-optical layer around the cladding. The coating typically consists of one or more layers of a polymer that protect the silica structure against physical or environmental damage.Strengthening Fibers: These components help protect the core against crushing forces and excessive tension during installation. The materials can range from Kevlar to wire strands to gel-filled sleeves.Cable Jacket: This is the outer layer of any cable. Most fiber optic cables have an orange jacket, although some may be black or yellow. The jacket material is application specific. The cable jacket material determines the mechanical robustness, aging due to UV radiation, oil resistance, etc.

   

  Jacket Material: PolyEthylene (PE): PE (black color) is the standard jacket material for outdoor fiber optic cables. PE has excellent moisture- and weather-resistance properties. It has very stable dielectric properties over a wide temperature range. It is also abrasion-resistant.PolyVinyl Chloride (PVC): PVC is the most common material for indoor cables, however it can also be used for outdoor cables. It is flexible and fire-retardant. PVC is more expensive than PE.PolyVinyl DiFluoride (PVDF): PVDF is used for plenum cables because it has better fire-retardant properties than PE and produces little smoke.Low Smoke Zero Halogen (LSZH) Plastics: LSZH plastics are used for a special kind of cable called LSZH cables. They produce little smoke and no toxic halogen compounds. But they are the most expensive jacket material. 

   

  Fiber Size

  The size of the optical fiber is commonly referred to by the outer diameter of its core, cladding and coating. Example: 50/125/250 indicates a fiber with a core of 50 microns, cladding of 125 microns, and a coating of 250 microns. The coating is always removed when joining or connecting fibers. A micron (µm) is equal to one-millionth of a meter. 25 microns are equal to 0.0025 cm. (A sheet of paper is approximately 25 microns thick).

   

  Classification

  Besides the basics, Fiber optic cables can be classified by other ways.

  Transmission Mode:

  • Multi-Mode Fiber (MMF) Cable: Center glass core is coarse (50 or 62.5 µm). It can transmit a variety of patterns of light. However, because its dispersion is large, which limits the frequency of the transmitted digital signal, and with increasing distance, the situation will be more serious. For example, 600Mb/km of 2km fibers provide the bandwidth of only 300 Mbps. Therefore, MMF cable's transmission distance is relatively short, generally only a few kilometers. General MMF patch cables are in orange, also some are gray, joints and protection are beige or black. 
  • Single-Mode Fiber SMF Cable: Center glass core is relatively fine (core diameter is generally 9 or 10 µm), only one mode of light transmission. Therefore, the dispersion is very small, suitable for remote communication, but it plays a major role in the chromatic dispersion, so that SMF cable has a higher stability requirement to the spectral width of the light source, just as narrower spectrum width, better stability. General SMF patch cables are in yellow, with joints and cases in blue.

   

  Transmission Way:

  • Simplex Cable: Single strand of fiber surrounded by a 900µm buffer then a layer of Kevlar and finally the outer jacket. Available in 2 mm or 3 mm and plenum or riser jacket. Plenum is stronger and made to share in fire versus riser is made to melt in fire. Riser cable is more flexible.
  • Duplex Cable: Two single strands of fiber optic cable attached at the center. Surrounded by a 900µm buffer then a layer of Kevlar and finally the outer jacket. In data communications, the simultaneous operation of a circuit in both directions is known as full duplex; if only one transmitter can send at a time, the system is called half duplex.

   

  Cable Core Structure:

  • Central Tube Cable: Fiber, optical fiber bundles or fiber optic cable with no stranding directly into the center position.
  • Stranded Tube Cable: A few dozens or more root fiber or fiber tape unit helically stranded around the central strength member (S twist or SZ twisted) into one or more layers of fiber optic cable.
  • Skeleton After Tube Cable: Fiber or fiber after spiral twisted placed into the plastic skeleton cable slot.

   

  Fiber Road Laying:

  • Aerial Cable: Aerial cables are for outside installation on poles. They can be lashed to a messenger or another cable (common in CATV) or have metal or aramid strength members to make them self supporting. The cable shown has a steel messenger for support. It must be grounded properly. A widely used aerial cable is optical power ground wire which is a high voltage distribution cable with fiber in the center. The fiber is not affected by the electrical fields and the utility installing it gets fibers for grid management and communications. This cable is usually installed on the top of high voltage towers but brought to ground level for splicing or termination. 
  • Direct-Buried Cables:
    • Armored Cable: Armored cable is used in direct-buried outside plant applications where a rugged cable is needed and/or rodent resistance. Armored cable withstands crush loads well, needed for direct burial applications. Cable installed by direct burial in areas where rodents are a problem usually have metal armoring between two jackets to prevent rodent penetration. Another application for armored cable is in data centers, where cables are installed underfloor and one worries about the fiber cable being crushed. Armored cable is conductive, so it must be grounded properly. 
    • Breakout Cable: Breakout cable is a favorite where rugged cables are desirable or direct termination without junction boxes, patch panels or other hardware is needed. It is made of several simplex cables bundled together inside a common jacket. It has a strong, rugged design, but is larger and more expensive than the distribution cables. It is suitable for conduit runs, riser and plenum applications. It's perfect for industrial applications where ruggedness is needed. Because each fiber is individually reinforced, this design allows for quick termination to connectors and does not require patch panels or boxes. Breakout cable can be more economic where fiber count is not too large and distances are not too long, because it requires so much less labor to terminate.
  • Submarine Cable: Submarine cable is the cable wrapped with insulating materials, laying at the bottom of the sea, to set up a telecom transmission between countries.

   

  Cable State. Based on 900µm tight buffered fiber and 250µm coated fiber there are two basic types of fiber optic cable constructions:

  • Tight Buffered Cable: Multiple color coded 900µm tight buffered fibers can be packed tightly together in a compact cable structure, an approach widely used indoors, these cables are called tight buffered cables. Tight buffered cables are used to connect outside plant cables to terminal equipment, and also for linking various devices in a premises network. Multi-fiber tight buffered cables often are used for intra-building, risers, general building and plenum applications. Tight buffered cables are mostly built for indoor applications, although some tight buffered cables have been built for outdoor applications too.
  • Loose Tube Cable: On the other hand multiple (up to 12) 250µm coated fibers (bare fibers) can be put inside a color coded, flexible plastic tube, which usually is filled with a gel compound that prevents moisture from seeping through the hollow tube. Buffer tubes are stranded around a dielectric or steel central member. Aramid yarn are used as primary strength member. Then an outer polyethylene jacket is extruded over the core. These cables are called loose tube cables. Loose tube structure isolates the fibers from the cable structure. This is a big advantage in handling thermal and other stresses encountered outdoors, which is why most loose tube fiber optic cables are built for outdoor applications. Loose-tube cables typically are used for outside-plant installation in aerial, duct and direct-buried applications. 

   

  Environment & Situation:

  • Indoor Cable: Such as distribution cables. Distribution cable is the most popular indoor cable, as it is small in size and light in weight. They contain several tight-buffered fibers bundled under the same jacket with Kevlar strength members and sometimes fiberglass rod reinforcement to stiffen the cable and prevent kinking. These cables are small in size, and used for short, dry conduit runs, riser and plenum applications. The fibers are double buffered and can be directly terminated, but because their fibers are not individually reinforced, these cables need to be broken out with a "breakout box" or terminated inside a patch panel or junction box to protect individual fibers.
  • Outdoor Cable: Outdoor fiber cable delivers outstanding audio, video, telephony and data signal performance for educational, corporate and government campus applications. With a low bending radius and lightweight feature, this cable is suitable for both indoor and outdoor installations. These are available in a variety of configurations and jacket types to cover riser and plenum requirements for indoor cables and the ability to be run in duct, direct buried, or aerial/lashed in the outside plant.

  To purchase your fiber cables, please click link below:

  Fiber Patch Cables

   

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• Mode Conditioning Patch Cable Tutorial

  Feb 6, 2016 by Articles / 432 Views

  There are bandwidth limitations of multimode fiber. Most current LAN networks are composed of about 90% multimode fiber. As the fiber cable plant is upgraded to single mode fiber cables, we must also provide a migration path that continues to reuse the installed multimode cable plant for as long as possible. However, there are some technical issues involved when using single mode equipment on existing multimode cable plant. The biggest problem is caused by Differential Mode Delay (DMD). It refers when a fast rise-time laser pulse is applied to multimode fiber, significant pulse broadening occurs due to the difference in propagation times of different modes within the fiber.

  To solve the problem, mode conditioning patch cable was developed as a solution for network applications where Gigabit Ethernet hubs with laser based transmitters are deployed. Mode conditioning patch cable is the mean to achieve the drive distance of installed fiber plant beyond its original intended applications. It allows customer upgrading their hardware technology without the cost of upgrading fiber plant. In addition, mode conditioning patch cable significantly improves data signal quality while increasing the transmission distance.

   

  What is Mode Conditioning Patch Cable?

  

   

  Mode Conditioning Patch Cable, or Mode Conditioning Patchcord (MCP), is a duplex multimode patch cable that has a small length of single mode fiber at the start of the transmission length. Designed to "condition" the laser launch and obtain an effective bandwidth closer to that measured by the overfilled launch method, the MCP allows for laser transmitters to operate at gigabit rates over multimode fiber without being limited by DMD. The point is to excite a large number of modes in the fiber, weighted in the mode groups that are highly excited by overfill launch conditions, and to avoid exciting widely separated mode groups with similar power levels. This is achieved by launching the laser light into a single mode fiber, then coupling it into a multimode fiber that is off-center relative to the single mode fiber core. This is shown beside.

  Tips: Different offsets are required for 50µm and 62.5µm multimode fibers. Engineers have found that an offset of 17~23 µm can achieve an effective modal bandwidth equivalent to the overfill launch method for 62.5µm multimode fibers. And an offset of 10~16 µm is good for 50µm multimode fibers.

  The basic principle behind the cable is to launch laser into the small section of single mode fiber. The other end of single mode fiber is coupled to the multimode section of the cable with the offset from the center of the multimode fiber. This patch cable is required with transceivers (e.g.1000BASE-LX/LH, 10GBASE-LX4 and 10GBASE-LRM) that use both single mode and multimode fibers. When launching into multimode fiber, the transceiver can generate multiple signals that causes DMD which can severly limit transmission distances. The MCP removes these multiple signals, eliminating problems at the receiver end. Here is a figure that shows an MCP and how it is typically connected to a transceiver module. When required, it is inserted between a transceiver module and the multimode cable plant.

  

   

  Requirements for Using MCPs in Laser-Based Transmissions

  Gigabit Ethernet

  The requirement for MCP is specified only for 1000BASE-LX/LH transceivers transmitting in the 1300nm window and in applications over multimode fiber. MCP should never be used in 1000BASE-SX links in the 850nm window. MCP is required for 1000BASE-LX/LH applications over FDDI-grade, OM1, and OM2 fiber types. MCP should never be used for applications over OM3, also known as "laser-optimized fiber".

  Note:

   

  1. In some cases, customers might experience that a link would be operating properly over FDDI-grade, OM1 or OM2 fiber types without MCP. However please note there is no guarantee link will be operating properly over time, and the recommendation remains to use the MCP.

   

  2. There is a risk associated to this type of nonstandard deployment without MCP, especially when the jumper cable is an FDDI-grade or OM1 type. In such case the power coupled directly into a 62.5µm fiber could be as high as a few dBm and the adjacent receiver will be saturated. This can cause high bit error rate, link flaps, link down status and eventually irreversible damaged to the device.

   

  3. In the event customers remain reluctant to deploy MCP cables, and for customers using OM3 cables, please measure the power level before plugging the fiber into the adjacent receiver. When the received power is measured above -3dBm, a 5dB attenuator for 1300nm should be used and plugged at the transmitter source of the optical module on each side of the link.

   

  4. Another alternative for short reaches within the same location is to use a single-mode patch cable. There will be no saturation over single-mode fiber.

   

  10-Gigabit Ethernet

  The requirement for MCP is specified only for 10GBASE-LX4 and 10GBASE-LRM transceivers transmitting in the 1300nm window and in applications over multimode fiber. MCP should never be used in 10GBASE-SR links in the 850nm window. MCP is required for 10GBASE-LX4 and 10GBASE-LRM applications over FDDI-grade, OM1, and OM2 fiber types. MCP should never be used for applications over OM3, also known as "laser-optimized fiber."

  Notes for 10GBASE-LX4:

   

  1. In some cases, customers might experience that a link would be operating properly over OM2 fiber type without MCP. However chances of experiencing a properly operating link over FDDI-grade or OM1 fiber types without MCP are very low.

   

  2. In the event customers remain reluctant to deploy MCP cables over OM2, and for customers using OM3 cables, it is required to a plug a 5dB attenuator for 1300nm at the transmitter source of the optical module on each side of the link in order to avoid saturation, and potential subsequent link flaps and damage to the device.

   

  3. Another alternative for short reaches within the same location is to use a single-mode patch cable. There will be no saturation over single-mode fiber. Please note the 10GBASE-LX4 devices can reach up to 10 km over single-mode fiber as per compliance to IEEE.

   

  Notes for 10GBASE-LRM:

   

  1. For customers using OM3 fiber type, MCP should not be used. It is highly recommended to measure the power level before plugging the fiber into the adjacent receiver. When the received power is measured to be above 0.5dBm, a 5dB attenuator for 1300nm should be used and plugged at the transmitter source of the optical module on each side of the link.

   

  2. Another alternative for short reaches within the same location is to use a single-mode patch cable. There will be no saturation over single-mode fiber. Please note the 10GBASE-LRM devices can reach up to 300 meters over single-mode fiber.

   

  Notes for the Installation of MCPs

  When using 1000BASE-LX/LH, 10GBASE-LX4 and 10GBASE-LRM transceivers with legacy 62.5µm or 50µm multimode fiber, you must install MCP between the transceiver and the multimode fiber cable on both ends of the link. The MCP is required for all links over FDDI-grade, OM1 and OM2 fiber types, and should never be used for applications over OM3 and more recent fiber types.

  Note: It is not recommended using 1000BASE-LX/LH, 10GBASE-LX4 and 10GBASE-LRM transceivers with multimode fiber and no patch cable for very short link distances (tens of meters). The result could be an elevated Bit Error Rate (BER) and receiver damage.

  The MCP is installed between the transceiver and the patch panel. Two MCPs are required per installation. To install the patch cable, follow these steps:

   

  Step 1 - Plug the single mode fiber connector into the transmit bore of the transceiver.

  Step 2 - Plug the other half of the duplex connector into the receive bore of the transceiver.

  Step 3 - At the other end of the patch cable, plug both multimode connectors into the patch panel.

  Step 4 - Repeat Step 1 through Step 3 for the second transceiver located at the other end of the network link.

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• What is Fiber Optic Loopback?

  Feb 6, 2016 by Articles / 435 Views

  Fiber optic loopback cable and fiber optic loopback module, are collectively known as Fiber Optic Loopback. Fiber optic loopback is designed to provide a media of return patch for a fiber optic signal, offer a generous yet manageable fiber loop virtually eliminating bend loss, and commonly used for fiber optic testing applications or network restorations. It is used to diagnose the problems of optical networking equipment. Sending a loopback test to network equipment, one at a time, is a technique for isolating a problem. Fiber optic loopbacks can be compliant with Fast Ethernet, Fibre Channel, ATM and Gigabit Ethernet etc.

   

  Types of Fiber Optic Loopbacks

  Fiber optic loopbacks can be with various jacket types, cable diameters, connector terminations and cable lengths. Traditional fiber optic loopbacks, i.e.  Fiber Optic Loopback Cables, can be regarded to be two fiber optic connectors on the same piece of simplex fiber optic patch cable put together, thus it forms a loop. Classified by the connector types, two most commonly used fiber optic loopback cables are SC and LC type, while there are also FC, MTRJ, and MTP etc types.

  Besides the traditional fiber optic loopbacks, there are also molded fiber optic loopbacks (or fiber optic loopback plugs), i.e. Fiber Optic Loopback Modules, with compact design. Unlike the traditional fiber optic loopback cables with visible cable parts, fiber optic loopback module has its cables and fibers well protected inside the housing. It integrates every part into one single body, which help save space and make it easier to operate as well as offer better protection to the whole product. By incorporating a rigid connector shell for fiber protection with an easy to use, ergonomic package, the fiber optic loopback module is designed for durability and performance. Molded fiber optic loopbacks are also mainly available in SC and LC types, which are easy to use for fiber optic test purpose in the lab experiments or manufacturing environment.

  Just like fiber optic patch cables, fiber optic loopbacks can also be classified by fiber types:  singlemode and multimode. The fiber types can be 9/125µm single mode fiber, 50/125µm multimode fiber, or 62.5/125µm multimode fiber. Typically single mode SC and LC loopbacks are blue, and typical multimode LC and SC loopbacks are beige. The color also goes with the practice of fiber optic patch cables.

   

  Applications of Fiber Optic Loopback

  A tipical application of fiber optic loopback is to check fiber optic transceiver by loopback test. Loopback test means a hardware or software method, a loopback test, feeds a received signal or data back to the sender. It is utilized as an aid in debugging physical connection problems.

  Loopback test is the easiest way to ensure the transceiver is working faultlessly. On fiber optic transceiver manufacturing floors and in R&D labs, a fiber optic loopback is used to verify the transceiver whether it is working perfectly as designed. Basically what the loopback does is directly routing the laser signal from the transmitter port back to the receiver port. Then the transmitted pattern is compared with the received pattern to make sure they are identical and have no error.

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• Fiber Optic Connector Tutorial

  Feb 6, 2016 by Articles / 414 Views

  The using of fiber optic connectors has traditionally been the biggest concern in fiber optic systems. While connectors were once unwieldy and difficult to use, connector manufacturers have standardized and simplified connectors greatly. This increases the user use convenient connectors during the use of optical fiber systems; It is also emphasizing taken proper care of and deal with the fiber optic connectors. To learn more about the fiber optic connectors, you should read this tutorial.

  What is Fiber Optic Connector?

  Fiber Optic Connector, or optical fiber connector, is removable activities between optical fiber and optical fiber connection device. It is to put the fiber of two surface precision docking, so that the optical output of optical energy to maximize the fiber optic coupler in receiving optical fiber, and optical link due to the intervention and to minimize the effects on the system, this is the basic requirement of fiber optic connector. To a certain extent, fiber optic connector also affects the fiber optic transmission reliability and the performance of the system.

   

  Key Features of Fiber Optic Connectors

  The key features of fiber connector include optical properties, interchangeability, repeatability, tensile strength, temperature, insertion times, etc.

  • 1. Optical Properties: The optical performance requirements of fiber optic connectors, mainly are the two basic parameters of Insertion Loss and Return Loss.
  • Insertion Loss is a connection loss of the link effective optical power loss because of the insertion of the connector. Insertion Loss is smaller the better, general requirements should not be more than 0.5 dB.
  • Return Loss (or Reflection Loss) refers to the suppression of link connector optical power of reflection, its typical value should not be less than 25 dB. In actual application of the connector, the pin surface after the special polishing process can make the return loss larger, generally not less than 45dB.
  • 2. Interchangeability and Repeatability: Fiber optic connectors are universal passive devices, the fiber connector of the same type, can be used in any combination and can be used repeatedly, thereby additional imported losses are generally in the range of less than 0.2dB.
  • 3. Tensile Strength: To the done fiber optic connectors, the general requirements of the tensile strength shall be not less than 90N.
  • 4. Temperature: Generally, fiber optical connector must be used at a temperature of -40C to +70C.
  • 5. Insertion Times: Currently fiber optic connectors can generally be pluged more than l000 times.

   

  Structure of Fiber Optic Connectores

  Optical fiber to fiber optic interconnection can be made by a joint, a permanent connection, or a connector, and is different from the plug in it can be to disconnect and reconnect. Fiber optic connector types are as various as the applications for which they were developed. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters. But all connectors have the same four basic components.

  

  Ferrule: The fiber is installed in a long, thin cylinder, the ferrule, which act as a fiber alignment mechanism. The ferrule is bored through the center at a diameter that is slightly larger than the diameter of the fiber cladding. The end of the fiber is located at the end of the ferrule. Ferrules are typically made of metal or ceramic, but they may also be constructed of plastic.

  Connector Body: Also known as the connector housing, the body holds the ferrule. It is usually constructed of metal or plastic and includes one or more assembled pieces which hold the fiber in place. The details of these connector body assemblies vary among connectors, but the welding and/or crimping is commonly used to attach strength members and cable jackets to the connector body. The ferrule extends past the connector body to slip into the couping device.

  Cable: The cable is attached to the connector body. It acts as the point of entry for the fiber. Often, a strain relief boot is added over the junction between the cable and the connector body, providing extra stength to the junction.

  Coupling Device: Most fiber optic connectors do not use the male-female configuration common to electronic connectors. Instead, a coupling device such as an alignment sleeve is used to mate the connectors. Similar devices may be installed in fiber optic transmitters and receivers to allow these devices to be mated via a connector. These devices are also known as feed-through bulkhead adapters.

   

  Types of Fiber Optic Connectors

  According to the different classification methods, fiber optic connectors can be divided into different types. According to the different transmission media, fiber connectors can be divided into single-mode and multimode fiber optic connectors. According to the different structures, fiber connectors can be divided into various types like ST, SC, FC, LC, MT-RJ, MPO/MTP, MU, DIN, E2000, SMA, BICONIC, D4, etc. According to the pin end surface of the connector, they can be divided into PC, UPC and APC. According to the number of fiber cores, fiber connectors can be divided into single-core and multi-core fiber optic connectors. In all, about 100 fiber optic connectors have been introduced to the marketplace, but only a few represent the majority of the market. Here is a rundown of the connectors that have been the leaders of the industry.

  ST Connector: ST is probably still the most popular connector for multimode networks, widely used in the optical distribution frame (ODF), like most buildings and campuses. It has a bayonet mount and a long cylindrical 2.5 mm ceramic (usually) or polymer ferrule to hold the fiber. Most ferrules are ceramic, but some are metal or plastic. ST connectors are constructed with a metal housing and are nickel-plated, can be inserted into and removed from a fiber-optic cable both quickly and easily. They have ceramic ferrules and are rated for 500 mating cycles. From a design perspective, it is recommended to use a loss margin of 0.5 dB or the vendor recommendation for ST connectors.

  SC Connector: This is a kind optical fiber connector developed by Japan's NTT. SC is a snap-in connector with a 2.5 mm ferrule that is widely used for it's excellent performance. Its shell is rectangular, adopted by the pin type and the structure of the coupling sleeve size. The end face of the pin is used more PC or APC model grinding method, fastening way is to use the plug pin bolt type, do not need to rotate. SC connector latches with a simple push-pull motion. SC connectors provide for accurate alignment via their ceramic ferrules. Typical matched SC connectors are rated for 1000 mating cycles. SC connector features with low price, involve loss small ripple, high compressive strength and high density installation.

  FC Connector: FC connector was originally developed by NTT, Japan. FC is short for FERRULE CONNECTOR. It also uses a 2.5 mm ferrule, its external strengthening way is to use metal sleeve, fastening way as the turnbuckle. FC connectors offer extremely precise positioning of the fiber-optic cable with respect to the transmitter's optical source emitter and the receiver's optical detector. FC connectors feature a position locatable notch and a threaded receptacle. FC connectors are constructed with a metal housing and are nickel-plated. They have ceramic ferrules and are rated for 500 mating cycles. This kind of connector is simple in structure, convenient operation.

  LC Connector: LC type connector is a famous BELL developed by the institute of research, using convenient operation modular jack (RJ) latch mechanism is made. The pin and the size of the sleeve is adopted by the general SC, FC, half size is 1.25 mm. It can improve the density of optical fiber connector in the optical fiber distribution frame. Otherwise, it's a standard ceramic ferrule connector, easily terminated with any adhesive. LC connector features with good performance and is highly favored for single mode.

  MT-RJ Connector: MT-RJ is a duplex connector used with single-mode and multimode fiber optic cables. It uses pins for alignment and has male and female versions. MT-RJ connectors are constructed with a plastic housing and provide for accurate alignment via their metal guide pins and plastic ferrules. MT-RJ connectors are rated for 1000 mating cycles. The typical insertion loss for matched MT-RJ connectors is 0.25 dB for SMF and 0.35 dB for MMF.

  MPO/MTP Connector The MPO Connector is the industry acronym for "Multi-fiber Push On", with push-on insertion release mechanism, provides consistent and repeatable interconnections and available with 4, 8, 12, or 24 fibers. MTP® is a trademark of US Conec for MPO connector. The MTP/MPO is a connector manufactured specifically for a multifiber ribbon cable. The MTP/MPO single-mode connectors have an angled ferrule allowing for minimal back reflection, whereas the multimode connector ferrule is commonly flat. The ribbon cable is flat and appropriately named due to its flat ribbon-like structure, which houses fibers side by side in a jacket.

  MU Connector: MU connector looks like a miniature SC with a 1.25 mm ferrule, with a simple push-pull design and compact miniature body. It is used for for compact multiple optical connectors and self-retentive mechanism for backplane applications. The connectors are composed of plastic housing. MU connectors are the optical connectors which miniaturized and were advanced the density application and performance. The table below illustrates some types of above connectors and lists some specifications. Each connector type has strong points.

  Connector Type	Coupling Type	Fiber Type	Insertion Loss	Polish	No. of Fibers	Typical Applications
  ST	Twist on	SM, MM	0.40 dB(SM) 0.50dB(MM)	PC, UPC	1	LANs
  FC	Screw on	SM, MM	0.5 - 1.0 dB	PC, UPC, APC	1	Datacom, Telecommunications
  SC	Snap on	SM, MM	0.2 - 0.45 dB	PC, UPC, APC	1	CATV, Test Equipment
  LC	Snap on RJ45 style	SM, MM	0.15 dB (SM) 0.10 dB (MM)	PC, UPC, APC	1	Gigabit Ethernet, Video Multimedia
  MU	Push / Pull	SM, MM	0.30 dB	PC, UPC, APC	1	Data Communications, Voice Networks, Telecommunications, DWDM
  MT-RJ	Snap on RJ45 style	SM, MM	0.30 dB	N/A	2	Gigabit Ethernet, Asynchronous Transmission Mode (ATM)
  MPO / MTP	Push / Pull	SM, MM	0.30 dB	N/A	4, 8, 12, 16	Active Device Transceiver, Interconnections for O/E Modules

  DIN Connector: DIN is an abbreviation for Deutsches Institut für Normung or German Institute for Standardization, which is a German manufacturing industry standards group. DIN connector encompasses several types of cables that plug into an interface to connect devices. It is round, with pins arranged in a circular pattern. Typically, a full-sized DIN connector has three to 14 pins with a diameter of 13.2 millimeters. This type of connector was used widely for PC keyboards, MIDI instruments, and other specialized equipment.

  E2000 Connector: E2000 fiber optic connector has a push-pull coupling mechanism, with an automatic metal shutter in the connector as dust and laser beam protection. One-piece design for easy and quick termination, used for high safety and high power applications. E2000 connector available for Singlemode PC, APC and Multimode PC. The E2000 Connector is one of the few fiber optic connectors featuring a spring-loaded shutter which fully protects the ferrule from dust and scratches. The shutter closes automatically when the connector is disengaged, locking out impurities which could later lead to network failure, and locking in potentially harmful laser beams.

   

  Obsolete Connectors

  SMA Connector: Amphenol developed the SMA from the "Subminiature A" hence SMA, microwave connector. The model 905 had a machined ferrule exactly 1/8 inch in diameter that mated in a machined adapter. When the adapters were not precise enough for better fibers, a necked-down ferrule that mated with a Delrin adapter for better insertion loss performance. These connectors are still in use on some military and industrial systems.

  BICONIC Connector: This is the Biconic, the yellow body indicating a SM version (MMs were usually black). Developed by a team led by Jack Cook at Bell Labs in Murray Hill, NJ, the Biconic was molded from a glass-filled plastic that was almost as hard as ceramic. It started with the fiber being molded into the ferrule. This lasted until the company could get a 125 micron/5mil pin insert into the plastic mold, at which point the fiber was glued into the ferule with epoxy. When singlemode versions first appeared, the ferrules were ground to center the fiber core in the ferrule to reduce loss. Since it was not keyed and could rotate in the mating adapters, it had an airgap between the ferrules when mated, meaning loss was never less than 0.3 dB due to fresnel reflection. Usually MM Biconics had losses of 0.5-1 dB and SM 0.7 dB or higher.

  D4 Connector: D4 connector was probably the first connector to use ceramic or hybrid ceramic/stainless steel ferrules. It's keyed and spring loaded, the ferrule has a 2.0mm diameter ferrule. D4 connectors have a high-performance threading mounting system and a keyed body for repeatability and intermateability.

   

  Color Codes

  Since the earliest days of fiber optics, orange, black or gray are multimode and yellow is singlemode. However, the advent of metallic connectors like the FC and ST made color coding difficult, so colored boots were often used. The TIA 568 color code for connector bodies and/or boots is Beige for multimode fiber, Blue for singlemode fiber, and Green for APC (angled) connectors.

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