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Guide to Fibre Optics

Fibre Optic Cable
Fibre Optic Patch Panels
Fibre Optic Wall Mount Patch Boxes
Fibre Optic Patch Leads
Fibre Optic Pigtails
Fibre Optic Adapters
Fibre Optic Fusion Splicing
Fibre Optic Cleaning Products
Fibre Optic Products for Harsh Environments
Fibre Optic Broadcast Products
Fibre Optic High Density Solutions

Is your fibre clean or not

 

  1. What is "Fibre Optics"?

It's the communications technology that works by sending signals down hair thin strands of glass fibre. By the mid-80s, fibre was replacing all the telco copper, microwave and satellite links. Computers and LANs started using fibre about the same time as the telcos. Industrial links were among the first as the noise immunity of fibre and its distance capability make it ideal for the factory floor. Mainframe storage networks came next, the predecessors of today's fibre SANs (storage area networks.) Other applications developed too: aircraft, ship and automobile data busses, CCTV for security, even links for consumer digital stereo. Today fibre optics is either the dominant medium or a logical choice for every communication system.

  1. Which Fibre Optics?

Outside Plant (OSP): Telephone companies, CATV and the Internet all use lots of fibre optics, most of which is outside buildings. It hangs from poles, is buried underground, pulled through conduit or is even submerged underwater. Most of it goes relatively long distances, from a few thousand feet to hundreds of miles.

Outside plant installations are all singlemode fibre and cables often have very high fibre counts, up to 288 fibres. Cable designs are optimized for resisting moisture and rodent damage. Installation requires special pullers, and even trailers to carry giant spools of cable.

Long distances mean cables are spliced together, since cables are not longer than about 4 km (2.5 miles), and most splices are by fusion splicing. Connectors (SC, ST or FC styles) on factory made pigtails are spliced onto the end of the cable. After installation, every fibre and every splice is tested with an OTDR.

Contractors doing outside plant work are few and far between. Most outside plant telephone installs are done by the telco themselves, while a small number of large, specialized installers do sub contract work.

Premises Cabling: By contrast, premises cabling- cabling installed in a building or campus - involves short lengths, rarely longer than a few hundred feet, with 2 to 48 fibres per cable typically. The fibre is mostly multimode, With singlemode fibres coming more to the forefront

Cables between buildings can be bought with double jackets, PE for outside plant protection LSZH for building applications requiring flame retardant cable jackets, so cables can be run continuously between buildings. Splicing cables together is very rare as connectors have low loss, and patch panels give more flexibility for moves, adds and changes.

Most connectors are SC style with LCs coming to the fore ST is still used but is becoming rarer. Termination is by installing connectors directly on the ends of the fibres, either by using glue and polish or more commonly by splicing of ready made pigtails to the fibre – another method which offers significant benefits is to use a mechanically spliced connector as  termination method. Testing is done by a Light source and meter, but every installer should have a flashlight type tracer to check fibre continuity and connection. There are thousands of cabling installers who do fibre optic work. They've found out it isn't "rocket science," and their small initial investment in training, tools and test equipment is rapidly paid back.

  1. The Installers
    Few installers do both outside plant and premises cabling. The companies that do are usually very large and often have separate divisions doing each with different personnel. Most contractors do nothing but premises cabling.

  2. The Ferrule
    The Fibre is mounted in a long, thin cylinder, the ferrule, which acts as a Fibre alignment mechanism. The ferrule is bored through the centre at a diameter that is slightly larger than the diameter of the fibre cladding. The end of the Fibre is located at the end of the ferrule. Ferrules are typically made of ceramic, but they may also be constructed of metal or plastic. The most distinct differentiations between connector types are the diameter of the ferrule, 2.5mm or 1.25mm, and the type of polish.

  3. Fibre Optic Connector Performance Definitions

Insertion Loss (IL): is the amount of optical power lost as a result of a connection. Expressed in decibels, it is the ratio of measured optical power before and after the connector. It always is tested because it is the most important connector parameter.

Return Loss (RL) : is a term applied to the light reflection in the connector’s interface that return to the source. The greater the absolute value, the better. Such as –60dB return loss is better than –35dB return loss.

Back Reflection: represents the total accumulated light reflected back to the source along a link. This return of the light is due to different physical phenomena such as multiple connector back-reflections, bad splicing, etc. High back reflection can cause bad or harmful consequences such as light source wavelength fluctuations, output power fluctuations, or even damage the light source permanently. 

Fibre Connector Coupling Loss: Connector loss is caused by a number of factors. Loss is minimized when the two Fibre cores are identical and perfectly aligned, the connectors are properly finished and no dirt is present. Only the light that is coupled into the receiving Fibre’s core will propagate, so all the rest of the light becomes the connector loss.

  1. Types of Connection Polishing

    The polish on a Fibre connector determines the amount of back reflection. Back reflection is a measure of the light reflected off the polished end of a Fibre connector measured in negative db. The Physical Contact (PC) polish is a flat finish of the connecting area and is the most common. The Angled Physical Contact (APC) is at an 8° angle. An APC greatly reduces back reflections caused by the physical interface.

  2. Fibre Optic Connector Termination Types

Anaerobic Adhesive: use a quick setting adhesive, that cures at room temperature, and the end polished with polishing film. They work well if your technique is repeatable, but often they do not have the wide temperature range of epoxies, so they are only used indoors. Thus, generally used for factory terminations only.

Epoxy/Polish : These connectors are the simple "epoxy/polish” type where the Fibre is glued into the connector with epoxy and cured in a heated  oven, and the end polished with special polishing film. These provide a very reliable connection with low losses. They can be factory or field installed.

Crimp/Polish: Rather than glue the Fibre in the connector, these connectors use a crimp on the Fibre 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.

Pre-Polished: Many manufacturers offer connectors that have a short stub Fibre already epoxied into the ferrule and polished perfectly, so you just cleave a Fibre and insert it like a splice. These are more expensive – but fast termination times, losses comparable to pigtail splicing, and minimal outlay on equipment make them a very attractive option

  1. FIBRE OPTIC CONNECTOR TYPES

    ST Connector (FOCIS 2): ST stands for Straight Tip – a quick release bayonet style connector  ST’s were the predominant connector in the late 80s and early 90s. ST connectors are among the most commonly used fibre optic connectors in networking applications. They are cylindrical with twist lock coupling, 2.5mm keyed ferrule.

SC Connector (FOCIS 3): The SC (Subscriber Connector) was developed specifically as a telecom connector and has almost superseded the ST. It features push-pull coupling which eliminates rotation which can damage Fibre end-faces. This design also allows higher packaging density. An important element of the design is an isolated ferrule, which protects the ferrule and fibre from cable stresses. The SC is available in the usual simple configuration and with duplex adapters as well.

FC Connector (FOCIS 4): FC stands for Ferrule Connector or Fixed Connection. The FC connector was developed by NTT as a single mode telecom connector. It uses a combination of thread (screw-on) and keyed design to provide high repeatability and good Fibre end-face protection.

MTP/MPO Connector (FOCIS 5): The MPO connector family is defined by two different standards. International the MPO is defined by IEC-61754-7. In the USA, the MPO is defined by TIA-604-5 (FOCIS 5). The MTP multi-Fibre connector is US Conec’s trademarked name for their MPO connector. The MTP connector is fully compliant with both FOCIS 5 and IEC-61754-7; therefore it is an MPO connector. The MTP connector design is distinctly different than the MPO. The MTP connector is a high performance MPO. The MTP/MPO is a connector manufactured specifically for a multi-Fibre ribbon Fibre. MPO = Multi-Fibre Push On. 

LC Connector (FOCIS 10): LC is a small form factor (SFF) Fibre optic connector. The LC connector uses a 1.25mm ferrule, half the size of the ST. Otherwise; it is a standard ceramic ferrule connector. The LC Duplex uses the same footprint coupler size as the SC Simplex and the LC Quad the same as the SC Duplex coupler – giving double the density as SC in the same footprint. The LC has good performance and is highly favoured for single mode and OM3 multimode and has been gaining the preference of equipment manufacturers because of its compact size and performance.

MTRJ Connector (FOCIS 12): MTRJ stands for Mechanical Transfer Registered Jack. MTRJ connector is a small form factor (SFF) duplex connector with both Fibres in a single polymer ferrule.MTRJ Connector uses pins for alignment and has male and female versions. MTJR connector is multimode only. The MTRJ connector resembles the RJ-45 connector used in Ethernet networks. The MTRJ was designed by AMP, but was later standardized as FOCIS 12 (Fibre Optic Connector Intermateability Standards) in EIA/TIA-604-12. Almost obsolete.

  1. Fibre Optic Connector Applications

    Private Networks (Enterprise)
    Small to medium networks:ST, SC are predominant
  • Large Networks: ST, SC with LC growing rapidly
  • Data Centres: LC and MTP dominate

    Public Networks (Service Providers)
  •     Telco’s: SC with LC growing due to density
  •     CATV: FC, SC 

    10. Fibre Optic Cable Transmission Distances


    These are the maximum recommended distances achieved with each fibre type: