Fanout Assemblies in 40G Interconnection

40G transmission is very common in the backbone network now. However, not all the devices and network are upgraded to 40G. To adapting the network between devices and network of different data rate. It is necessary to connection 40G devices to 10G devices for network interconnection. To solve this problem, fanout technology is be accepted and widely used in data center. Fanout products for interconnection is easy to understand. It’s kind of like the water pipeline in our building: water is transferred from the trunk pipeline in a building. Then trunk pipeline fans out into several pipelines that have smaller diameters to bring the water to every house. This post will introduce several Fanout products that are commonly used for 40G data center interconnection.

40G MPO Fanout Cables

The first fanout component is 40G MPO fanout cable, also called breakout cable or harness cable. MPO fanout cable is a multi-fiber optical cable with one end terminated with a male/female MPO connector and the other end attached with several LC connectors. Actually, there are various types of MPO fanout cables, according to connector type, cable length and cable type. But they all have the similar structure. Here will introduce three most popular MPO fanout cables according to the package type.

The first one to be introduced is also what most customer need. This cable is fan out into 12 fibers or 24 fibers. The above picture shows a typical 12-fiber MPO harness cable. The MPO connector of this fanout cable is linked to 6 duplex LC connectors, which is really useful for backbone cabling from 40G devices to 10G devices. The second one is a little bit smaller version of the former. The fibers are fanout directly from the MPO connectors. With small size, this kind of mini MPO harness cable can be easily put into patch panel and increase the cabling density largely and effectively.

The third to be introduced is a special one—MPO cassette. Literally, it looks like a cassette and looks very different from other MPO fanout cables. However, when you look inside the cassette, it has not much difference from other MPO fanout cables. MPO Cassette actually contains one or several mini MPO fanout cables in side the cassette, which is designed for those who want have everything in clean and tidy status. As it can be installed in a standard rack and the cables are all well protected. A 12-fiber MPO cassette usually has a 12-fiber mini MPO fanout cable in side the cassette, with a MPO connector on the backside and 12 LC connector in the front. For a 24-fiber MPO cassette, there could be a 24-fiber fanout cable or two 12-fiber cables inside. The following picture is a MPO cassette with two 12-fiber MPO fanout cable inside it, thus there are two MPO connector on its backside.

40G Fanout Direct Attach Cables

To decrease the 40G interconnection cost, Direct attach cable (DAC) is being widely used. There are also fanout versions of 40G DAC which support 40G to 10G cabling. These kind of 40G DAC usually have one QSFP+ connector on one end and four SFP+/XFP connectors or several LC connectors at the other end. For example, the following is 40G QSFP+ to 8 LC DAC. The QSFP+ connector of it can be used to plug in the 40G device which has QSFP+ port. On the other end, the four duplex LC connectors are used to separately connect four SFP+ transceivers , which are used to plug in 10G devices with SFP+ switched (shown in the following picture). If you used a 40G QSFP+ to 4 SFP+ DAC, this process would be easier, cause the SFP+ connector can be plugged into the SFP+ switch directly.

Conclusion

All in all, fanout technology plays an important role in the 40G data center for both connecting devices supporting different data rate and distribution. Most fanout products are factory pre-terminated. The installation and maintenance doesn’t need many skills. In Fiberstore, a variety of fanout products of high quality and reliability can be customized according to your application. If you are seeking for solutions for fanout product, please feel free to contact sales@fs.com for more details.

Source： http://www.fiber-optic-tutorial.com/fanout-assemblies-in-40g-interconnection.html

Cabling With High Density Push-Pull Tab Patch Cords

It is inevitable to plug fiber patch cables from the patch panels, switches or cassettes in today’s data center cabling. However, this simple movement becomes harder and harder nowadays. Why? Both the data rate of every optical fiber and the fiber counts being used are increased to support high data rate up to 40/100G or more. Thus, the cabling density increased largely with the deployment of 40/100G Ethernet network. Finger access to every patch cable that is loaded on the patch panel, switches or cassettes becomes difficult. Especially for these patch cables in the middle of the space.

For fiber patch cords attached with connectors like LC, things become more complex. Because this type of connectors are usually locked in the port with a latch on the connector body. If you want to plug out a patch cord with LC connectors, you should firstly unlock the connector from the port by clicking the latch with is with small size (shown in the following picture). Usually an external tool is used to unplug the specific connector in a high density cabling. It seems a problem doesn’t matter much in the whole cabling. However, during practical cabling, network engineer could be headache about this annoying problem. To find an easy and elegant way to solve this finger access problem, a new type of patch cords was invented, which is designed for high density cabling and is known as push-pull tab patch cords.

What Is High Density Push-pull Tab Fiber Patch cable?

Compare with the traditional patch cords. This new type patch cord is attached with a connector with a push-pull tab, which can perfectly solve the fiber access problem in high density cabling. Except the additional tab for pushing and pull, these connectors don’t change much from the traditional ones that attached to patch cords. But this little change makes a great difference. The following is offering you the details about this novel product.

High density push-pull tab fiber patch cords are usually attached with LC or MPO connectors, as these two types of connector are currently the most popular in high density cabling like 40G, 100G, 120G or more. The following pictures shows the details of these two types of connectors with push-pull tab.

The one in the left of the following picture is an LC connector attached on push-pull tab patch cable. It’s of standard LC size. When the tab is pulled the LC connector would be unlocked from the port easily, cause the tab is linked to the latch of the LC connector. Once the LC connector is unlocked, the patch cords would be smoothly plugged out from the port and other patch cords around it by pulling the tab slightly. As for MPO connector with push-pull tab shown in the following picture on the right side. Finger access becomes easier. The tab can greatly simplify the use of MPO connectivity when manual access to the release slider and rear portion of the connector is restricted. In this way, easy insertion and extraction of MPO patch cords can be achieved.

Get More From Push-pull Tab Patch Cable

Is finger access the only advantage of push-pull tab patch cords. Definitely NO. The following illustrating will surely make you exciting about push-pull tab patch cable.

• Flexibility and adjustability: it has been proved that push-pull tab can increase the cabling density by 30% to 50%, which can satisfy the future high density cabling requirements for 120G or more.
• Reliability: To reach the specific connector you want, you might loosen or remove other connectors around it, which can highly increase the reliability of the network.
• Cost-save and time-save: it is clear that with push-pull tab patch cords, cabling becomes easy and elegant with higher ROI.

Fiberstore Push-Pull Tab Fiber Patch Cable Solutions

If you are looking for a simple and easy high density patch cabling solution, push-pull tab patch cords provided by Fiberstore can satisfy your requirements. The following chart is the most common applications of push-pull tab patch cords for your references.

Application	Patch Cords	Cable Type	Connectors on Both Ends
10G to 10G Cabling	Duplex LC Push-pull Tab Patch Cord	OM3/OM4/Single-mode	Duplex LC	Duplex LC
40G to 40G Cabling	12-fiber MPO Push-pull Tab Trunk Cable	OM3/OM4/Single-mode	MPO (male/female)	MPO (male/female)
40G to 10G Cabling	12-fiber MPO to 8 LC Push-pull Tab Break out Cable	OM3/OM4/Single-mode	MPO (male/female)	4 Duplex LC
100G to 100G Cabling	24-fiber MPO Push-pull Tab Trunk Cable	OM3/OM4/Single-mode	MPO (male/female)	MPO (male/female)

For more details and customized solution of push-pull tab patch cords, you can always access Fiberstore by FS.COM or emailing us at sales@fs.com

Source: http://www.fiber-optic-tutorial.com/cabling-with-high-density-push-pull-tab-patch-cords.html

Understanding Loss in Fiber Optic

Fiber optic transmission has various advantages over other transmission methods like copper or radio transmission. Fiber optic which is lighter, smaller and more flexible than copper can transmit signals with faster speed over longer distance. However, many factors can influence the performance of fiber optic. To ensure the nice and stable performance of the fiber optic, many issues are to be considered. Fiber optic loss is a negligible issue among them, and it has been a top priority for many engineers to consider during selecting and handling fiber optic. This article will offer detailed information of fiber optic loss.

When a beam of light which carrying signals travels through the core of fiber optic, the strength of the light will become lower. Thus, the signal strength becomes weaker. This loss of light power is generally called fiber optic loss or attenuation. This decrease in power level is described in dB. During the transmission, something be happened and causes the fiber optic loss. To transmit optical signals smoothly and safely, fiber optic loss must be decreased. The cause of fiber optic loss located on two aspects: internal reasons and external causes of fiber optic, which are also known as intrinsic fiber core attenuation and extrinsic fiber attenuation.

Intrinsic Fiber Core Attenuation

Internal reasons of fiber optic loss caused by the fiber optic itself, which is also usually called intrinsic attenuation. There are two main causes of intrinsic attenuation. One is light absorption and the other one is scattering.

Light absorption is a major cause of fiber optic loss during optical transmission. The light is absorbed in the fiber by the materials of fiber optic. Thus light absorption is also known as material absorption. Actually the light power is absorbed and transferred into other forms of energy like heat, due to molecular resonance and wavelength impurities. Atomic structure is in any pure material and they absorb selective wavelengths of radiation. It is impossible to manufacture materials that are total pure. Thus, fiber optic manufacturers choose to dope germanium and other materials with pure silica to optimize the fiber optic core performance.

Scattering is another major cause for fiber optic loss. It refers to the scattering of light caused by molecular level irregularities in the glass structure. When the scattering happens, the light energy is scattered in all direction. Some of them is keeping traveling in the forward direction. And the light not scattered in the forward direction will be lost in the fiber optic link as shown in the following picture. Thus, to reduce fiber optic loss caused by scattering, the imperfections of the fiber optic core should be removed, and the fiber optic coating and extrusion should be carefully controlled.

Extrinsic Fiber Attenuation

Intrinsic fiber core attenuation including light absorption and scattering is just one aspect of the cause in fiber optic loss. Extrinsic fiber attenuation is also very important, which are usually caused by improper handling of fiber optic. There are two main types of extrinsic fiber attenuation: bend loss and splicing loss.

Bend loss is the common problems that can cause fiber optic loss generated by improper fiber optic handling. Literally, it is caused by fiber optic bend. There are two basic types. One is micro bending, and the other one is macro bending (shown in the above picture). Macro bending refers to a large bend in the fiber (with more than a 2 mm radius). To reduce fiber optic loss, the following causes of bend loss should be noted:

• Fiber core deviate from the axis;
• Defects of manufacturing;
• Mechanical constraints during the fiber laying process;
• Environmental variations like the change of temperature, humidity or pressure.

fiber optic splicing is another main causes of extrinsic fiber attenuation. It is inevitable to connect one fiber optic to another in fiber optic network. The fiber optic loss caused by splicing cannot be avoided, but it can be reduced to minimum with proper handling. Using fiber optic connectors of high quality and fusion splicing can help to reduce the fiber optic loss effectively.

The above picture shows the main causes of loss in fiber optic, which come in different types. To reduce the intrinsic fiber core attenuation, selecting the proper fiber optic and optical components is necessary. To decrease extrinsic fiber attenuation to minimum, the proper handling and skills should be applied.

Source：http://www.fiber-optic-tutorial.com/understanding-loss-in-fiber-optic.html

Basic of Optical Distribution Frame (ODF)

Driven by requirements for high-speed data rate, the deployment of fiber optic has been growing. As the growth of installed fiber optic, the management of optical transmission networks becomes more difficult. Many factors should be considered during fiber optic cabling, like flexibility, future viability, cost of the deployment and management, etc. To handle large amounts of fiber optic with lower cost and higher flexibility, various optical distribution frames (ODF) are being widely used to connector and schedule optical fiber. Choosing right fiber optic distribution frames is the key to successful cable management.

What Is ODF?

An optical distribution frame (ODF) is a frame used to provide cable interconnections between communication facilities, which can integrate fiber splicing, fiber termination, fiber optic adapters & connectors and cable connections together in a single unit. It can also work as a protective device to protect fiber optic connections from damage. The basic functions of ODFs provided by today's vendors are almost the same. However, they come into different shapes and specifications. To choose the right ODF is not an easy thing.

Types of ODF

According to the structure, ODFs can mainly be divided into three types, namely wall mount ODF, floor mount ODF and rack mount ODF.

Wall mount ODF (shown in the following picture) usually uses design like a small box which can be installed on the wall and is suitable for fiber distribution with small counts. Floor mount ODF adopts closed structure. It is usually designed with relatively fixed fiber capacity and nice appearance.

Rack mount ODF (shown in the following picture) is usually modularity in design with firm structure. It can be installed on the rack with more flexibility according to the fiber optic cable counts and specifications. This kind of optical distribution system is more convenient and can provide more possibilities to the future variations. Most of the rack mount ODF is 19'', which ensures that they can be perfectly installed on to the commonly used standard transmission rack.

ODF Selection Guide

The selection of the ODF is not limited to the structure, many factors like applications should be considered. Some of the most important are introduced as following.

Fiber Counts: with the number of fiber connections in places like data center increase, the need for high density ODF become the trend. And it is very common to find ODF with 24 ports, 48 ports or even 144 ports for fiber optic cables in the market now. Meanwhile, many vendors can provide the customized ODFs according to the customers' requirement.

Manageability: High-density is the good but management is not easy. ODF should provide an easy management environment for technicians. The basic requirement is ODF should allow for easy access to the connectors on the front and rear of those ports for insertion and removal. This requires that ODF should reserve enough space. In addition, the color of adapters installed on the ODF should be remain consistent with the color code of fiber optic connectors to avoid wrong connections.

Flexibility: as mentioned rack mount ODF is relatively flexible during applications with the modular design. However, anther aspect which can increase the ODF’s flexibility effectively is the port size for adapters on the ODF. For example, an ODF with ports of duplex LC adapter size can be installed with duplex LC, SC or MRTJ adapters. An ODF with ports of ST adapter size can be installed with both ST adapters and FC adapters.

Protection: optical distribution frames integrate fiber connections in it. The fiber connections like splicing joint, fiber optic connectors are actually really sensitive in the whole transmission network and is directly related to the stability and reliability of the network. Thus, a good ODF should have protection device to prevent fiber optic connections from damages produced by dust or stress.

Conclusion

The ODF is the most popular and comprehensive fiber optic distribution frame which can reduce the cost and increase the reliability and flexibility of fiber optic network during both deployment and maintenance. The high density ODF is the trend in telecommunication industry. Selecting an ODF is important and complex which requires full consideration including applications and management. The factors like structure, fiber counts and protection are just the basic elements. The ODF which can meet the current requirements and the challenge of future growing and easing of expansion without sacrificing cable management or density can only be selected with repeated comparison and full consideration.

Source: http://www.fiber-optic-tutorial.com/basic-of-optical-distribution-frame-odf.html

Fiber Patch Cable Management

Deploying more fiber optic cable is just the first step to meet the high-bandwidth requirements, strong management over the fiber optic cable is a basic requirement for a successful fiber optic network infrastructure. Fiber patch cable might be the weakest link in optical network infrastructures. To deliver and guarantee and optimal network performance, patch cable management is critical. In addition, well management of fiber patch cable can lower operation cost & time and increases the reliability and flexibility of network operation and maintenance. This post will offer the critical elements that should be noted during patch cable management, as well as tips for fiber patch cable management.

Elements That Affects Patch Cable Management

To get a flexible and well organized patch cable management, the factors that affect the performance of the fiber optic patch cable should be introduced first. Here are four key elements that should be considered during patch cable management.

Bend Radius

Unlike copper, fiber optic made of glass is much fragile and need more protection and attention during the operation and management. Thus, the fiber’s bend radius will impact its reliability and performance. If a fiber cable is bent excessively, the optical signal within the cable may refract and escape through the fiber cladding which will cause a loss of signal strength and is known as bend loss. What’s more, bending, especially during the installation and pulling of fiber optic patch cable might also cause micro cracks and damage the fiber permanently. Generally, there are two basic types of bends in fiber, which are microbends and macrobends as shown in the following picture. The macrobends are larger than microbends.

What should be noted is that bend radius might not be seen during the initial installation of fiber patch cable. This is because the number of patch cables routed to the optical distribution ODF is usually small. However, when more patch cords are added on the top of installed patch cables in the future the problems will come across (shown in the following picture). A fiber patch cable that working fine for years might suddenly have an increased level of attenuation, as well as a potentially shorter service life.

Path of Patch Cable

Patch cable path is an aspect closely related to bend radius that can affect the performance and maintenance of the patch cable. The path of the patch cable should be clearly defined and easy to follow. Improper cable routing can cause increased congestion in the termination panel, increasing the possibility of bend radius violations and long-term failure. However, the well managed patch cable path ensures that bend radius requirements are maintained at all points and makes accessing individual patch cable easier, quicker and safer. What should be mentioned is that the well organized fiber patch cords can help to decrease operating costs and the time required to turn-up or restore service.

Accessibility of Patch Cable

The third aspect is accessibility of the installed patch cable. If the installed patch cable is easy to be accessed, the maintenance and operation would be quick without inducing a macrobend on an adjacent fiber, and it can also offer proper bend radius protection. Accessibility is critical during network reconfiguration operations and directly impacts operation costs and network reliability.

Physical Protection

Patch cables routed between pieces of equipment can largely affect network reliability. Without proper protection, they would be easy to be damaged by technicians and equipment accidentally. Thus, physical protection of the installed patch cords is very important.

Tips for Fiber Patch Cable Management

According to the mentioned aspects that can affect the performance and maintenance of the fiber optic patch cable, here offers several tips that can help to increase the performance of patch cords, as well as the reliability and flexibility of patch cable management.

Tip 1: Pay attention to the bend radius of the patch cable. Generally, for 1.6mm and 3.0mm cords the minimum un-loaded bend radius is 3.5 cm, and the minimum bend radius of MPO patch cable is ten times the cord diameter.

Tip 2: Never pull or stress the patch cords (shown in the following figure). During the patching process, excessive force can stress fiber patch cables and connectors attached to them, thus reducing their performance. There might be something wrong if you need to use force in pulling a cord.

Tip 3: Routing cords through cable pathways. If the existing cord is the right length, it may be possible to re-use it. If this is the case, remove the cord completely and re-run it in through the cable pathways. This is the only sure way to ensure there are no tangles, kinks or strains in the cord. For efficient routing, find the best path between the ports to be connected. Avoid routing cords through troughs and guides that are already congested.

Tip 4: Bundling and tying cords gives the panel a neat appearance but tight bundling increases the risk of pinching (shown in the following figure). Do not tighten cable ties beyond the point where individual cords can rotate freely.

Tip 5: Labeling is necessary. Labeling is the most important part of a System Administrator’s responsibilities. At any administration point in a cabling infrastructure, including patching panels, accurate labels are essential. These will identify pair modularity and tell technicians where the other end of the cable is terminated.

Tip 6: Inspect fiber cords for physical damage including stress marks from sharp bends on the sheath, or damage to connectors as shown in the following figure.

Conclusion

A strong and successful patch cable management which can increase the reliability and flexibility and decrease the cost of network operation and maintenance should provide bend radius protection, reasonable patch cable path, easy accessibility of patch cable and physical protection. When the four mentioned aspects are satisfied, there is already half the success to strong patch cable management.

Source: http://www.fiber-optic-tutorial.com/fiber-patch-cable-management.html

Causes of Mechanical Splice Termination Failures

FTTH (fiber to the home) has become increasingly popular in optical communication industry. Fiber optic termination, as one of the topics which have never been out of fashion in this field, has naturally become a focus of FTTH network deployment, especially the indoor termination. In FTTH network, mechanical splice connectors are usually used in FTTH indoor termination with the advantages of flexibility, fast-installation and cost-effective. Currently manufactures can provide various types of mechanical splice connectors of high quality which have low insertion loss and high performance. However, no matter how excellent the mechanical splicing technology is, there are still fiber optic termination failures and bad fiber optic termination due to improper operation. To avoid it, this post is to offer the causes of mechanical splice termination failures.

The Basic of Mechanical splicing

Before finding the cause of mechanical splice failure, the basic of mechanical splicing should be introduced. To finish a mechanical splice, the buffer coatings of fiber optic should be removed mechanically with sharp blades or calibrated stripping tools. In any type of mechanical stripping, the key is to avoid nicking the fiber. Then the fibers will be cleaved. Two fiber ends are then held closely in retaining and aligning a mechanical splice connector with some index matching gel between them. The gel are used to form a continuous optical path between fibers and reduce reflecting losses.

Causes of Mechanical Splice Termination Failures

Mechanical splice connector is sensitive to many factors. There are also a large number of factors to cause failures. However, most of the factors are located at the end face of fiber optic. The following is to describe them in details.

Contamination

When facing mechanical splice failures, there would be no argument that contamination is the first thing to think about. There are many ways that contamination can be carried into the fiber termination splices. Generally, there are the following possible causes of splice contamination:

• Using a dirty cleave tool: as the fiber should be cleave before inserted in the connector, a fiber optic cleaves would be used. If a dirty cleave is used, the contamination would be attached on the end face of the fiber optic and be embedded in the connector. Thus, do remember to clean the surfaces thoroughly with alcohol wipes;
• Wiping the fiber after cleaving;
• Setting the connector or fiber down on a dusty surface;
• Heavy airborne dust environment;
• Glass fragments from insertion broken fibers, or applying excessive force;
• Polluted index matching gel.

Please note that once the contamination is carried inside the mechanical splice connector, especially with the index matching gel, there would be little possibility to clean them out, which means the connector may be scrapped.

Glass Fragmentation

Improper operation like overexertion when inserting the fiber optic into the mechanical splice connector might break the fiber optic and produce glass fragmentation which will cause air gap and optical failure. Or if a broken fiber if inserted, there will also be optical failure. If the glass fragments are embedded in the connector, they cannot be cleaned out and the connector would be scrapped. Thus, be gentle and carefully when splicing the fiber ends.

Bad Cleave

Cleaving the fiber optic is an important step during fiber optic mechanical splicing. The quality of the cleave can decide the quality of the optical splice transmission to some degree. It is not easy to inspect the cleave quality in the field. There are several possibilities there might cause the bad cleaves:

• Dull or chipped cleave tool blade
• The bent tongue on the cleave tool concentrated too much bend stress on the fiber
• Bending the fiber too much or too tight of a radius
• Applying no tension or insufficient tension to the fiber while cleaving.

Excessive Fiber Gap

Fiber gap is another factor that might cause the fiber optic termination failure. The fiber optic transmission is very sensitive to the gap between two fiber ends in the mechanical splice connector. Improper operations that might cause the excessive fiber gap are listed as following:

• Cleaving the fiber without enough lengths;
• The fiber is not fully inserted, or pulled back during termination;
• The fiber was not held steady during termination and was pushed back into the fan-out tubing when terminating outdoor cable.

These faults can be corrected one time.

Excessive Cleave Angle

During fiber cleaving, cleave angle can be produced easily and is difficult to be inspected in field. These angles are typically ranging from 1 to 3 degree. Even with precision tool, there might still be cleave angle ranging from 0.5 to 1 degree. The angle is generally produced by bent tongue, fiber bending or insufficient fiber tension.

However the cleave angles can be corrected by fine tuning with a VFL (visual fault locator). Rotating the fiber while using a VFL and terminate the connector at the position (as shown in the following picture).

Conclusion

Fiber optic mechanical splicing gives quick and high quality result at a low price for fiber optic termination. Choosing the right fiber optic mechanical splice connector and fiber optic cleaver of high quality is not enough. Acknowledge the possible causes to fiber optic termination failures and use the right tools with skills can reduce the risk of termination failure effectively.

Source: http://www.fiber-optic-tutorial.com/causes-of-mechanical-splice-termination-failures.html

Understand Polarity in MPO System

MPO/MTP technology, which is of high density, flexibility and reliability with scalable, upgradeable properties, is one of the contributors that lead the migration to 40/100GbE. However, the network designers face another challenge which is how to assure the proper polarity of these array connections using multi-fiber MPO/MTP components from end-to-end. Maintain the correct polarity across a fiber network ensures that a transmit signal from any type of active equipment will be directed to receive port of a second piece of active equipment – and vice versa. To ensure the MPO/MTP systems work with correct polarity, the TIA 568 standard provided three methods, which will be introduced in this article.

MPO Connector

To understand the polarity in 40/100 GbE Transmission, the key of MPO technology—MPO connector should be first introduced. MPO connector usually has 12 fibers. 24 fibers, 36 fibers and 72 fibers are also available. Each MTP connector has a key on one of the flat side added by the body. When the key sits on the bottom, this is called key down. When the key sits on top, this is referred to as the key up position. In this orientation, each of the fiber holes in the connector is numbered in sequence from left to right and is referred as fiber position, or P1, P2, etc. A white dot is additionally marked on one side of the connector to denote where the position 1 is. (shown in the following picture) The orientation of this key also determines the MPO cable's polarity.

Three Cables for Three Polarization Methods

The three methods for proper polarity defined by TIA 568 standard are named as Method A, Method B and Method C. To match these standards, three type of MPO truck cables with different structures named Type A, Type B and Type C are being used for the three different connectivity methods respectively. In this part, the three different cables will be introduced firstly and then the three connectivity methods.

MPO Trunk Cable Type A: Type A cable also known as straight cable, is a straight through cable with a key up MPO connector on one end and a key down MPO connector on the opposite end. This makes the fibers at each end of the cable have the same fiber position. For example, the fiber located at position 1 (P1) of the connector on one side will arrive at P1 at the other connector. The fiber sequence of a 12 fiber MPO Type A cable is showed as the following:

MPO Trunk Cable Type B: Type B cable (reversed cable) uses key up connector on both ends of the cable. This type of array mating results in an inversion, which means the fiber positions are reversed at each end. The fiber at P1 at one end is mated with fiber at P12 at the opposing end. The following picture shows the fiber sequences of a 12 fiber Type B cable.

MPO Trunk Cable Type C: Type C cable (pairs flipped cable) looks like Type A cable with one key up connector and one key down connector on each side. However, in Type C each adjacent pair of fibers at one end are flipped at the other end. For example, the fiber at position 1 on one end is shifted to position 2 at the other end of the cable. The fiber at position 2 at one end is shifted to position 1 at the opposite end etc. The fiber sequence of Type C cable is demonstrated in the following picture.

Three Connectivity Methods

Different polarity methods use different types of MTP trunk cables. However, all the methods should use duplex patch cable to achieve the fiber circuit. The TIA standard also defines two types of duplex fiber patch cables terminated with LC or SC connectors to complete an end-to-end fiber duplex connection: A-to-A type patch cable—a cross version and A-to-B type patch cable—a straight-through version.

The following part illustrates how the components in MPO system are used together to maintain the proper polarization connectivity, which are defined by TIA standards.

Method A: the connectivity Method A is shown in the following picture. A type-A trunk cable connects a MPO module on each side of the link. In Method A, two types of patch cords are used to correct the polarity. The patch cable on the left is standard duplex A-to-B type, while on the right a duplex A-to-A type patch cable is employed.

Method B: in Connectivity Method B, a Type B truck cable is used to connect the two modules on each side of the link. As mentioned, the fiber positions of Type B cable are reversed at each end. Therefore standard A-to-B type duplex patch cables are used on both sided.

Method C: the pair-reversed trunk cable is used in Method C connectivity to connect the MPO modules one each side of the link. Patch cords at both ends are the standard duplex A-to-B type.

Conclusion

Network designer using MPO/MTP components to satisfy the increasing requirement for higher transmission speed, during which one of the big problems—polarity, can be solved by selecting the right types of MPO cables, MPO connectors, MPO cassette and patch cables. The three different polarization methods can be applied according to the satisfy requirements in different situations. For more information about polarity in MPO systems and 40/100GbE transmission polarity solutions, please visit Fiberstore tutorial at "Polarity and MPO Technology in 40/100GbE Transmission".

Source: http://www.fiber-optic-tutorial.com/understanding-polarity-in-mpo-system.html