Pre-terminated cabling components with MPO connectors are becoming more and more common in fiber optic networks. They can be found in data centres, server rooms, equipment rooms of telecommunication service providers and, increasingly, in customer premises. The individ-ual components are pre-terminated and only need to be plugged together, which significantly

Whitepaper

MPO

reduces installation time. In addition, cabling with MPO connectors allows simple migration to 40 and 100 Gigabit Ethernet over multimode fibers.This whitepaper describes the different compo-nents used and looks in detail at the different connectivity methods for maintaining the polar-ity in cabling with MPO connectors.

1 Introduction

Installers, network designers and end-users are increasingly opting for plug and play solutions for fiber optic links. Where traditional fiber optic instal-lations require expert knowledge, special tools and sophisticated equipment such as splicing and test equipment, the individual components of ready-to-connect solutions only need to be plugged together. Simple, clean, fast. Compact connectors such as the MPO connect several fibers in a single mating pro-cess, saving time and space compared to convention-al cabling with individual fiber connectors. However, MPO connectors are not only used for con-

necting fiber optic distribution panels and modules. In the meantime they are also used to connect active network components such as switches and servers. The internationally oriented Institute of Electrical and Electronics Engineers (IEEE) has specified the MPO for Ethernet variants that simultaneously trans-mit data at 40 Gigabits per second or above over multiple multimode fibers.Years ago, the MPO was almost only found in data centres, but nowadays it is increasingly used in office and industrial building cabling.

© Telegärtner 12 2019

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The optical fibers inside the MPO connector are aligned next to each other in a plastic block ("fer-rule"). Depending on the number of fibers, the ferrule may contain several parallel rows of fibers. 12 fibers per row is the most commonly used variant. Occasionally, connectors with 24 fibers aligned in two parallel rows of twelve fibers are used. Other fib-er counts are rare (see section 5 "Cabling with MPO connectors with other fiber counts").A key on one side of the connector ensures proper orientation of the MPO connector.

When two MPO connectors are plugged together they are aligned by pins in the connector ferrule and not by a sleeve in the adapter, as is the case with SC or LC connectors. One MPO connector has two guide pins, the other one has two holes which the pins slide into when plugged together. Connectors with pins are referred to as "male" or "pinned” connec-tors, and those with holes as "female" or "unpinned” connectors.For multimode fibers, flat polished MPO connec-tors are used (i.e. polish angle of 90° to the fiber’s longitudinal axis); for singlemode fibers, the connec-tors almost always have an angled physical contact (APC). The ends of angled physical connectors are usually ground at an angle of 8° to the fiber’s longi-tudinal axis.

EN 50174-1 recommends that connectors with pins should only be used where the risk of damage to the pins is minimal. Cables that are frequently plugged and unplugged should have with connec-tors without pins. In practice, this (usually) means:

• Active components ports: with pins (male)• Distribution panel ports: with pins (male)• Patch cords with MPO connectors: without pins (female)• Installation cables:

- with pins (male), if patch panels and MPO adapters are being connected together

- without pins (female) if fanout modules (mod-ules in distribution panels with adaptors at the front for single fiber connectors such as LC, SC or ST, and an MPO adapter at the back) are being connected.

An easy way to remember this is: connectors with

pins are used on the "network side" or "jack side”, and connectors without pins are used for patch cords. However, this is not a strict rule, it’s only com-mon practice.

MPO stands for "Multifiber Push-On” which is a self-locking multi-fiber connector. MPO is the name assigned to the connector by IEC 61754-7, and TIA/EIA 604-5. MTP® is a registered trademark of the US-based company US Conec. MPO and MTP® connec-tors are compatible with each other. MTP® connectors offer numerous advantages over conventional MPO connectors. During the mating process, simple guide pins with chamfered ends can scrape off fine plastic particles from the edge of the holes they are being inserted into. If these particles move to the front of a glass fiber, they can interfere with the transmission of the optical signals. MTP® connectors have guide pins with rounded ends to prevent plastic being chipped off the ferrule when they are inserted. The ferrules of MTP® connectors are floating to ensure the smooth-est possible mating process and exact positioning of the ferrules of two connectors within a connection. MTP® connectors also have an optimized internal fiber guidance. Many companies use the term "MPO/MTP® connector" to emphasize that their products use high quality MTP® connectors. Telegärtner also uses MPO/MTP® connectors to meet its own high quality standards.

2 Cabling with MPO connectors

With few exceptions, Ethernet variants for data rates up to and including 10 Gigabit use two fibers per channel: one fiber for transmitting and one for receiving data. The fibers are typically terminated with individual fiber connectors, such as LC, SC or ST connectors.

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If many ports have to be connected, MPO harness ca-bles with single fiber connectors such as LC, SC or ST at one end and an MPO connector at the other end might come in handy. Instead of a conventional fiber optic cable, a plug and play trunk cable is installed between the patch panels. Compared to conven-tional cabling where there are multiple single fiber connectors at both ends, cabling with MPO connec-tors saves time and space. There is no need to assem-ble connectors or test the installed fiber optic link.

Fiber optic cables with MPO connectors only have to be plugged together. There is no need for time-consuming on-site plug assembly. With harness ca-bles, active network components such as switches or servers can be connect-ed in the usual manner using LC, SC or other connectors.

If users prefer traditional patch cords with two fibers, instead of harness cables they can use fanout modules instead of harness cables. These modules have adaptors at the front for single fiber connectors and MPO adapters at the back.

If fanout modules are used instead of harness cables, conventional two-fiber patch cords can be used with single fiber connectors such as LC, SC or almost any other connec-tor. Fanout modules have adaptors at the front for single fiber connec-tors and adapters at the back for MPO connectors.

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Examples of universal cables with one or more MPO connectors

3 Components in cabling with MPO connectors

Normally, only a small variety of components are used in cabling with MPO connectors.

Cables with MPO connectors are normally used to connect distribution panels or fanout modules. These cables are also known as trunk cables or array cables.They are available as robust universal cables for both indoor and outdoor installation or as outdoor cables for outdoor installation. The cables typically contain 12, 24 or 48 fibers.

Thin, flexible cables can also be used in particularly protected areas such as data centres and large server rooms. They are similar to MPO patch cords and, like them, only have a single MPO connector at each end. Round cables are easier to install around curves and bends than flat cables, which only permit limited bending.

Example of an MPO patch cord. Thin trunk cables are

similar but longerThe cable jacket and the plug are often colour-coded to indicate the fiber type in the cable. However, not all colours are standardised and, in practice, different manufacturers use different colours. For example, a cable with an aqua-colored jacket may well contain OM3 or OM4 multimode fibers. Likewise, the tradi-tional colour of orange for fiber optic cables might be used without regard to the type of fiber in the cable.

If the end-user subsequently migrates to 40 or 100 Gigabit Ethernet, which specifies the MPO connector for mul-timode fibers, the MPO trunk cables can still be used. Only the patch cords and fanout module need to be replaced by MPO patch cords and distribution panels with MPO adapters at the front. This avoids the expense of reinstalling cable, opening/closing fire stops and the general disruption that any installation work causes.

Cabling for 40 and 100 Gigabit Ethernet with MPO connectors.

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Typical colours of cable sheathing and connector housing. Other colours are also used.

MPO connectors for singlemode fibers almost al-ways have an angled ferrule (typical angle of 8°); it is extremely rare for them to have a flat one.MPO cabling with OM1 and OM2 multimode fibers is almost only found in legacy networks.MPO adapters are usually black or grey, regardless of the fiber category.

Harness cables allow ports with single fiber connec-tors such as LC, SC or ST to be connected to cabling with MPO connectors in the easiest possible manner. A harness cable is also known as a fanout cable. Cable splitters are used to separate the multi-fiber cable into multiple single-fiber cables. In technical terms, these single-fiber cables are also known as “legs”. Harness cables are rare these days. They were mainly used with active network components with multiple ports such as mainframes and switches.

The connection between the single fiber connec-tors and the MPO connectors is usually made using fanout modules. There are adaptors at the front of the compact metal or plastic module housings for single-fiber connectors and MPO adapters at the

Example of an MPO harness cable (also known as a fanout cable).

Examples of fanout modules: module with a particularly robust metal hous-ing (side panel removed for demon-stration purposes) (left) and module with a particularly high port density (right).

back. The two are connected via optical fibers.MPO connectors can be directly connected to one an-other using MPO distribution panels. Like the patch panels for single fiber connectors, these are availa-ble in 19" design with one height unit as well as in modular design. In the case of modular design, single fiber connector modules, fanout modules and front panels with MPO adapters can be integrated into the same patch panel.

Fiber type Typical colour of cable sheathing Typical colour of MPO connector

Multimode OM1 orange beige

Multimode OM2 orange beige

Multimode OM3 aqua aqua

Multimode OM4 violet violet or black

Multimode OM5 lime green lime green

Singlemode OS1, OS1a and OS2 yellow blue

Singlemode OS1, OS1a and OS2 with angled connector (APC)

yellow green

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Example of an MPO distribution panel (left) and an MPO module for a plug and play fiber optic link with four MPO connectors (right).

4 Infrastructures with 12-fiber MPO connectors

“IEC 61754-7-1 type MPO connector family – One fiber row” is an international standard that specifies MPO connectors with 12 fibers. Apart from the con-nector dimensions, it also defines the positions of the fibers in the connector ferrule. If the 12-fiber MPO connector is oriented so that the key points upwards, then, when viewed from the front, fiber position 1 is on the far left, position 12 on the far right. This is the position of the fibers in the connector and not a certain order of the fiber colours, as defined in ANSI/TIA-568.3-D and EN 50174-1. The fiber positions are the same regardless of whether the connector has guide pins (male) or not (female). Depending on the manufacturer, there might be a white dot on the connector housing indicating fiber position 1. Hence, the location of fiber 1 is known, even if the connector is plugged in. If two connectors are plugged together and their dots are on the same side, the connectors are connected according to con-nectivity method A or C (key up to key down - see sec-tions 4.1 and 4.3); if the dots are on different sides, the connectors are connected according to connec-tivity method B (key up to key up - see section 4.2). The American ANSI/TIA-568.3-D standard speci-fies three ways to assign the fibers in a cable to the twelve positions in a connector: connectivity meth-ods A, B and C. To make it easier to distinguish between the cables, they are named after the connectivity method and

the number of fiber rows in the connectors at both ends. For example, a 12-fiber cable in connectivity method A is known as a type A:1-1 cable (connec- tivity method A, single-row connector at one end of the cable, single-row connector at the other).

12-fiber MPO connector with marked fiber positions.

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4.1 Connectivity method A

In connectivity method A the same fiber positions are always connected, i.e. position 1 with position 1, posi-tion 2 with position 2, etc. This means one connector is inserted with its key pointing up, the other with its key pointing down into the correspondingly designed adapter. This connectivity method is therefore also known as "key up to key down".

Connector 1Key up

Connector 2Key down

Pos. 1 Pos. 1

Pos. 2 Pos. 2

Pos. 3 Pos. 3

Pos. 4 Pos. 4

Pos. 5 Pos. 5

Pos. 6 Pos. 6

Pos. 7 Pos. 7

Pos. 8 Pos. 8

Pos. 9 Pos. 9

Pos. 10 Pos. 10

Pos. 11 Pos. 11

Pos. 12 Pos. 12"Key up to key down" orientation in the adapter; the table on the right shows the assignment of the fiber positions when two type A cables are connected.

Pre-assembled type A cables also have a connector at one end with the key pointing up ("key up") and a connector at the other end with the key pointing down ("key down").

Type A:1-1 cable

For data rates up to and including 10 Gbit/s, Ethernet requires two fibers per link: one for trans-mitting and one for receiving data. So-called fanout modules have one or more MPO adapters at the back and adaptors at the front for single fiber connec-tors such as LC or SC. Viewed from the front, fanout modules look like conventional fiber optic patch panels.To maintain the integrity of the transmit and receive

Viewed from above: a type A polarity cable link. A fiber optic patch cord where connector A is connected to con-nector A and connector B to connector B is used at one end of the link.

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Viewed from above: a type A polarity cable link. A type B polarity fiber optic patch cord is used at one end (key up to key up).

signal paths, the two fibers in a link must be flipped. In connectivity method A, this is done by simply using a two fiber patch cord where connector A is connected to connector A and connector B to connector B on one side of the link.

40GBASE-SR4 40G Ethernet and 100GBASE-SR10 100G Ethernet transmit data simultaneously over eight and 20 fibers respectively. If 12-fiber cabling with MPO connectors is used, this can be imple-mented with one or two cable links. According to EN 50174-1:2018-10, connectors with guide pins shall be used where there is least risk of damage. Here, this means the connectors on the trunk cable have pins because they are plugged into the patch panel on the side facing away from the user ("network side"). The patch cords have connectors without pins.To maintain the integrity of the transmit and receive signal paths, the fiber groups in a link must be cross-connected. In connectivity method A, this is easily implemented: a 12-fiber MPO patch cord with identically oriented connectors on both sides (key up to key up = type B patch cord) is used on one side of the link.

4.2 Connectivity method B

In connectivity method B, the lowest fiber position of one connector is connected to the highest fiber position of the other connector, the second lowest is connected to the second highest, i.e., position 1 with position 12, position 2 with position 11, etc. This means both connectors are inserted with their keys pointing up into the correspondingly designed adaptor. This connectivity method is therefore also known as "key up to key up".

Pre-assembled type B cables also have connectors at both ends with the key pointing up ("key up"). Of course, the adapter can also be installed "upside down", in which case both keys point down ("key down to key down").

The different orientation of the MPO connectors at the cable ends and in the adapter means the sig-nal path in connectivity method B is different to the signal path in connectivity method A. A two-fiber A-A

patch cord at one end of the channel, unlike with connectivity method A, is not required. Instead the fanout module must be either rotated 180° at one end (i.e. "upside down"), or a fanout module must be used with either differently oriented adaptors for the single fiber connectors or with the pigtails arranged in reverse order inside. This is all allowed and works.EN 50174-1:2018-10 specifies in detail a type B polarity link with modules rotated 180° relative to each other. It also expressly permits other connectiv-ity methods.

Type B:1-1 cable

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Connector 1Key up

Connector 2Key up

Pos. 1 Pos. 12

Pos. 2 Pos. 11

Pos. 3 Pos. 10

Pos. 4 Pos. 9

Pos. 5 Pos. 8

Pos. 6 Pos. 7

Pos. 7 Pos. 6

Pos. 8 Pos. 5

Pos. 9 Pos. 4

Pos. 10 Pos. 3

Pos. 11 Pos. 2

Pos. 12 Pos. 1

"Key up to key up" orientation in the adapter;the table below shows the assignment of the fiber posi-tions when two type B cables are connected.

Viewed from above: a type B polarity cable link. The two fanout modules are rotated 180° relative to each other (one module is installed “upside down”).

40GBASE-SR4 40G Ethernet and 100GBASE-SR10 100G Ethernet transmit data simultaneously over eight and 20 fibers respectively. If 12-fiber cabling with MPO connectors is used, this can be imple-mented with one or two cable links. According to EN 50174-1:2018-10, connectors with guide pins shall be used where there is least risk of damage. This is on the side facing away from the user ("network side") in the patch panel. Hence, with this connectivity method, connectors on the trunk cable have pins and connectors and the patch cords do not.To maintain the integrity of the transmit and receive signal paths, the fiber groups in a link must be cross-connected. In connectivity method B, this happens automatically as the fiber sequence is reversed in a type B MPO adapter (fiber 1 is connected to fiber 12, fiber 2 is connected to 11, etc.). This means that in networks with parallel fib-ers in a channel, type B polarity cables can be used throughout.

Viewed from above: a type B polarity cable link.

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Type C:1-1 cable

4.3 Connectivity method C

Like in connectivity method A, the same fiber posi-tions of two connectors are always connected in con-nectivity method C, i.e. position 1 with position 1, position 2 with position 2, etc. This means one con-nector is inserted with its key pointing up, the other is inserted into the adapter with its key pointing down into the correspondingly designed adapter. Since the orientation of the connectors in the adapter is identi-cal to that of connectivity method A, the same name has been used, i.e. "key up to key down".

Like in connectivity method A, type C polarity cables have a connector at one end with the key pointing up ("key up") and a connector at the other end with the key pointing down ("key down"). However, in connectivity method C, fibers are pairwise flipped in the cable. Thus, in 40GBASE-SR4 40G Ethernet and 100GBASE-SR10 100G Ethernet where data is trans-mitted over parallel fibers, type C polarity cabling is not the best choice.

In connectivity method C, the pairwise flip in the cable rules out the possibility of an extension cable because the crossed fiber pairs in such a cable would cancel out the pairwise flip in the installed cable. This is why type A extension cables are used instead in connectivity method C. These extension cables should be clearly marked to distinguish them from cables with flipped pairs.

The fanout modules of connectivity method C are identical to those of connectivity method A. In contrast to connectivity method A, no special two-fiber patch cords are required in connectiv-ity method C because the fiber pairs are flipped in the MPO cable which maintains the integrity of the transmit and receive signal paths.

Type C polarity cable links were not originally intended for applications that use multiple fibers

Connector 1Key up

Connector 2Key up

Pos. 1 Pos. 2

Pos. 2 Pos. 1

Pos. 3 Pos. 4

Pos. 4 Pos. 3

Pos. 5 Pos. 6

Pos. 6 Pos. 5

Pos. 7 Pos. 8

Pos. 8 Pos. 7

Pos. 9 Pos.10

Pos. 10 Pos. 9

Pos. 11 Pos. 12

Pos. 12 Pos. 11

Viewed from above: a type C polarity cable link. Stand-ard patch cords are used at both ends.

"Key up to key down" orientation in the adapter; the table below shows the assignment of the positions when two type C cables are connected.

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simultaneously. Nevertheless, with the appropriate modifications, 12-fiber type C links can also be used for 40GBASE-SR4 40G Ethernet and 100GBASE-SR10 100G Ethernet, where data is transmitted simultaneously over eight and 20 fibers respectively. According to EN 50174-1:2018-10, connectors with guide pins shall be used where there is least risk of damage. Here, this means the connectors on the trunk cable have pins because they are plugged into the patch panel on the side facing away from the user ("network side"). The patch cords have connectors without pins.To maintain the integrity of the transmit and receive signal paths, the pairwise flip in the trunk cable must be undone at one end of the channel. This is done using a type C polarity MPO patch cord, i.e. one in which fibers are pairwise flipped, too. At the other end is a standard type B polarity MPO patch cord (key up to key up).

4.4 Connectivity method "D" and others

The ANSI/TIA-568.3-D standard does not specify a connectivity method “D”, nor a connectivity method with letters other than A, B or C. Methods with other letters are vendor-specific.Method "D" is the term often used to indicate a vendor- or customer-specific solution. This allows special requests to be implemented or existing verndor- specific cabling to be extended even when they are not standard compliant.

Viewed from above: a type C polarity cable link. A type B polarity fiber optic patch cord is used at one end (key up to key up) and a type C polarity one with cross-connected fiber pairs at the other end.

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4.5 Comparison of connectivity methods A, B and C

The three methods use different MPO adapters, fiber assignments, fanout modules and patch cords at the ends of the channel.

Because of the clear network structure and sim-ple management, many users prefer connectivity method A, in which the fibers are arranged in the same position throughout, regardless of the number of connections in the channel. It is recommended ei-ther colour marking the two-fiber A-A patch cords, attaching permanent stickers to them or marking them in some other way to distinguish them from the standard patch cords. If A-A patch cords are used where they shouldn’t be, data transmission will not work. When migrating to networks such as 40GBASE-SR4 or 100GBASE-SR10 where parallel fibers are used, a type B MPO patch cord (key up to key up) must be used at one end of the channel to ensure that the transmit and receive fibers are assigned to the correct positions. This patch cord should also be marked ac-cordingly in order to distinguish it from type A patch cords. The type A trunk cable can still be used in net-works with parallel fibers.

Connectivitymethod

MPO adapter Fiber assignment in a connection

Fanout module Two fiber patch cords

A Type A Key up to key down

Same throughout, fiber 1 to fiber 1,fiber 2 to fiber 2,...

Same module type at both ends of link, mod-ules installed in same orientation

Patch cord with A-A assignment at one end of channel

B Type BKey up to key up

In reverse order,fiber 1 to fiber 12,fiber 2 to fiber 11,...

Module at one end of the link rotated by 180°, or different module types with differently oriented couplers for the single fiber connectors

Standard patch cord at both ends of channel

C Type A Key up to key down

Pairwise flip, fiber 1 to fiber 2,fiber 2 to fiber 1,...

Same module type at both ends of link, mod-ules installed in same orientation; identical to method A

Standard patch cord at both ends of channel

Connectivity method B requires different or, at least, differently installed fanout modules. As a result, the designing, material ordering, installation, documenta-tion and management are all more time-intensive. In particular, if multiple patch panels are connected, care must be taken to ensure the correct orientation and/or module type is used in each patch panel. The migration to 40GBASE-SR4 and 100GBASE-SR10 is very straight-forward: the trunk cable can still be used, and type B MPO patch cords (key up to key up) are used at both ends of the channel.

In type C polarity trunk cables, fibers are pairwise flipped. This might make the migration to networks such as 40GBASE-SR4 and 100GBASE-SR10 more time-intensive, as these networks use parallel fibers. A type B polarity MPO patch cord must be used at one end of a type C trunk cable; at the other end, a type C patch cord is needed to undo the pairwise flip. This is why connectivity method C is normally only found in legacy networks.

If vendor-specific connectivity methods are used, the manufacturer’s instructions must be observed. The migration to 40GBASE-SR4 and 100GBASE-SR100 might therefore be more of a problem or, at least, more time-intensive.

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Transmit (Tx) and receive (Rx) lane assignments in active network component ports (in switch, server, etc.) for 40GBASE-SR4 (above) and 100GBASE-SR10 (below, "Rec-ommended Option A" as recommended by IEEE 802.3).

5 Cabling with MPO connectors with other fiber counts

The 40 Gigabit Ethernet variant 40GBASE-SR4 transmits 10 Gigabits per second over each multi-mode fiber. To achieve the full 40 Gigabit per second data rate, four fibers are used to transmit and four to receive data, i.e. a total of eight fibers are used simultaneously. In 12-fiber MPO ports, fiber positions 1 to 4 are used to transmit and 9 to 12 to receive data. The fibers in the middle positions, i.e. positions 5 to 8 are not used.

The 100 Gigabit Ethernet variant 100GBASE-SR10 also transmits 10 Gigabits per second over each multimode fiber. It mostly uses a 24-fiber MPO connector to do so. This connector has the same dimensions as the 12-fiber one, but has two rows of 12 fibers. In 100GBASE-SR10 the upper row of fibers receives data and the lower transmits it. The first and the last fiber in each row are not used.

100GBASE-SR10 does not have to use a 24-fiber MPO connector. IEEE 802.3 also recognizes the use of 12-fiber MPO connectors. In "Alternative Option B" the 12-fiber MPO ports are beside each other, in "Alternative Option C" they are on top of each other. These B and C alternatives - like the "Recommen- ded Option A" - have nothing to do with connectivity methods A, B and C of MPO cabling; they only use the same three letters.

As far as transmission is concerned, the unused fiber positions in the MPO connectors could be left as they are. However, there is a risk of dust and dirt particles collecting in the holes which might move to the front of the fibers during the mating process and affect transmission. For this reason, many manufacturers

Transmit (Tx) and receive (Rx) lane assignments in active network component ports for 100GBASE-SR10 with 12-fiber MPO connectors; "Alternative Option B" with ports beside each other (left), "Alternative Option C" with ports above each other (right). However, the 24-fiber MPO for 100GBASE-SR10 is recommended by IEEE 802.3.

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tend to use all the fiber positions in an MPO connec-tor. For example, in the case of eight-fiber harness cables with MPO connectors, a 12-fiber cable is used between the connector and cable splitter with fibers 5 to 8 terminating in the cable splitter and only the fibers 1 to 4 and 9 to 12 being fed out of the cable splitter and fitted with single fiber connectors.

Some manufacturers provide MPO splitter modules which allow all fibers in 12- and 24-fiber cables to be used. At the back, these modules either have two ports for 12-fiber MPO connectors or one for a 24-fiber MPO connector, and three ports at the front for 12-fiber connectors, of which only eight fibers are used. Here, it would be worthwhile performing a viability study to compare the cost of a 24-fiber cable and a 2x12 to 3x8 or 1x24 to 3x8 splitter module with the cost of three 12-fiber cables without a splitter module. If splitter modules and eight-fiber MPO connectors are used, these components must be clearly marked to distinguish them from the exter-nally identical 12-fiber variants.

MPO connectors with 8, 16 and 32 fiber positions in the ferrule are also available. These connec-tors usually have a laterally offset key and are not compatible with 12- and 24-fiber connectors. They are very rare in practice.

6 Cabling with MPO connectors in locations with stricter environmental requirements

The use of MPO connections is no longer restricted to data centre and office cabling. In industrial environ-ments and outdoors, users also benefit from being able to simultaneously connect multiple fibers quickly and easily.

However, harsh ambient conditions often prevail in industrial locations. Dust, humidity, vibrations and temperature fluctuations impair the functionality of connections. The international standard IEC 60529 specifies the different classes of protection against the intrusion of solid foreign bodies and water (ingress protection code, IP code for short).

Fiber optic connections usually meet just IP20. This means they are protected against solid foreign bod-ies with a diameter of 12.5 mm or more, such as fingers, but not against the penetration of water. IP67 level of protection is usually required for use in industrial locations. An additional housing protects the connections against dust and the effects of short-term immersion in water.The requirements for outdoor use are even more stringent. In most cases, protection class IP68 is required. This means an additional housing must not only be dust-proof, but also provide protection against long-term immersion in water. Moreover, the housing must be protected against ultraviolet radiation (technical term: UV-stable) and reliably pro-tect the connection over a wide temperature range, e.g. from -25 °C to +55 °C.

Mobile applications such as radio and television broadcasting, events or trade fairs require solutions with flexible yet extremely robust cables which can be quickly assembled and disassembled, maybe several times a day, depending on the application. Compact connector protective houings which can be attached and removed quicky and reliably play an important role here.

A range of locking types that include

- push-pull with self-locking mechanism for frequent and quick mating and unmating

- hand screw with knurled union nut for easy installation and protection against unintentional loosening and

- screw with hexagon nut for particularly secure connections and use in extreme climatic conditions from -40 °C to +70 °C

allow users to select the connector best suited to their needs. Care should be taken here to ensure that all the different connector locking types fit onto the protective housing of the same jack.

15

Example of an MPO/MTP® connector with a weatherproof housing (IP68 MPO TOC plug set ).

MPO/MTP® connector in a 4.3-10 connector housing. The connector housings with different locking mech-anisms all fit on the same jack.

Screw type- for particularly secure

connections- for use under extreme

climatic conditions

Handscrew type- for easy installation - with device against

unintentional release

Push-Pull type- for fast an very easy

connections- for frequent insertion /

removal

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300

0 ±6

0

250

0 ±6

0

1 2 ... 4

Connector 12 MPO female MM black with dustcab

Cable MM 8×G50/125µ OM4 violet

8× 2.1mm tubes with colored fibers

4× connector LC Duplex MM violet

FanOut-Box

tubes distinguished with numbers

B A

Fibers configuration MPO1 2 3 4 5 6 7 8 9 10 11 12o o o o x x x x o o o o

RD GN BU YE TQ BK OG PK

Fibers configuration MPO - LC Duplex

Fiber pos. LC-D 1 2 3 4B A B A B A B A

Fiber pos. MPO 12 1 11 2 10 3 9 4 Colored fibers PK RD OG GN BK BU TQ YE

ca./approx.ca./approx.ca./approx.

with 4×LC-D MM; MPOfm+LC-D violet

Volumen/volume[mm³]

untolerierte Form- und Lagetoleranzen /geometrical tolerances without tolerances

Tol. A + Tol. B(Tol. A + Tol. B)/2

DIN

ISO

110

1

Tol. A + Tol. B

Gewicht/weight

[g]

Oberfläche/surface[mm²]

LT20.10.2017

Maße/ dimensions: mm

11Blatt/ sheet von/ ofOriginal : DIN A4

Änd./rev.

IndexDatum/

dateName/ name

Änderungs-Nr. /revision code

Benennung/ titleMaßstab/ scale

Datum/ date Name/ name

gez./ drawn

gepr./ appr.

Werkstoff/material

Oberfläche/finish

Ersatz für/replaces

untolerierte Maße nach/dimensions without

tolerances according to

Zeichnungsnr./ drawing no.Unterl./doc. type

MPO Harness 8×2.1mm OM4 3.0m1:2

KR20.10.2017

L00832A0046DIN ISO 2768-m KAlle

Rec

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vorb

ehal

ten

/ al

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ved

©

Tele

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er G

erät

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7 Application-specific solutions

As the use of MPO connectors grows, so does the number of application-specific solutions.

Eight-fiber harness cable40 Gigabit Ethernet QSFP+ modules with MPO port use eight fibers, i.e. four to transmit and four to receive data. 10 Gbit/s are transmitted over each fib-er. Depending on manufacturer and type, it might be possible to configure these QSFP+ modules to provide four independent 10 Gbit/s transmission channels. They can then be connected to SFP+ modules which transmit 10 Gbit/s and have an LC duplex port. The connection is made using eight-fiber harness cables with an MPO connector at one end and four LC duplex connectors at the other. Fibers 1 to 4 and 9 to 12 are used in the MPO connector. To

Example of an eight-fiber harness cable.

allow users to change the fiber assignments on site, some manufacturers only fit simplex LC connectors to the harness cable but ship it with clips so that the user can make duplex connectors as required. Like with single fiber connectors, there are also mechanically- and colour-coded MPO connectors and adapters on the market to ensure that cable and adapter match. This means users can operate different networks beside each other without the risk of a faulty connection due to attaching the wrong patch cord. However, coded MPO connectors are very rare in practice.

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8 Migration to parallel optical networks with MPO connectors

The migration from networks with two fibers per port to networks such as 40GBASE-SR4 and 100GBASE-SR10 with parallel fibers can be relatively straightfor-ward and cost-effective if the already existing cabling consists of MPO trunk cables and fanout modules. The trunk cable installed in the telecommunications room or building can still be used. Only the fanout modules need to be replaced by front panels with MPO adapters, and the two-fiber patch cords by MPO patch cords.

When cabling with MPO connectors, connectors with pins are normally used on the "network side" or "jack side", and connectors without pins are used for patch cords. This means trunk cables connecting fanout modules usually have connectors without pins because the fanout modules have connectors with pins. If a fanout module is replaced by a panel with MPO adapters, the patch cord on this side must have a connector with pins. Depending on the manufac-turer, it might be possible to modify the MPO con-nectors fitted to the trunk cable. However, this should always be done by a qualified specialist.

In type A polarity parallel optical networks, a type B MPO patch cord (key up to key up) must be used at one end of the channel to ensure that the trans-mit and receive fibers are assigned to the correct positions. This patch cord should also be marked accordingly to distinguish it from type A patch cords.

In parallel optical applications with type B polarity, type B polarity MPO patch cords (key up to key up) are used at both ends of the channel.

In type C polarity trunk cables, fibers are pairwise flipped. This might make the migration to networks such as 40GBASE-SR4 and 100GBASE-SR10 more time-intensive, as these networks use parallel fibers. A type B polarity MPO patch cord must be used at one end of a type C trunk cable; at the other end, a type C patch cord is needed to undo the pairwise flip of the fibers. Connectivity method C is normally only found in legacy networks.

If a vendor-specific connectivity method is used, the manufacturer’s instructions for each component must be observed. The migration to 40GBASE-SR4 and 100GBASE-SR100 might therefore be more of a problem or, at least, more time-intensive.

9 Practical tips

Depending on the manufacturer and type, an MPO connector with guide pins can be converted to one without, and vice versa. However, this should always be done by a qualified specialist. For example, when removing the pins in a connector, a bridge without pins must be inserted into the connector as a replace-ment for the bridge connecting the two pins in the connector. This ensures the ferrule stays firmly seated in the connector housing. Under no circumstances should the pins be pulled out by force.If connectors have to be frequently changed from male to female or vice versa, there are specially designed ones available. The same applies to modi-fying the connectivity method. There are connectors on the market whose key orientation (top or bottom) can be changed without tools.

There are also special tools available for cleaning MPO/MTP® connectors. The tools for connectors with and without guide pins as well as for freely accessible connectors and connectors in an adapter can vary considerably. Hence, care should be taken to ensure the used tool always cleans the connector properly and does not damage it.

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10 Quality aspects of MPO/MTP® connectors

In cabling with MPO/MTP® connectors, it’s not just the connectors themselves that are important, but also the workmanship with which they have been made.

The ferrule of an MPO/MTP® connector is made of plastic. It must therefore be ground and polished more gently than the ceramic ferrule in an LC or SC connector. In particular, care must be taken at the corners and edges of the plastic ferrule to ensure the outer fiber positions are not ground more than those at the centre of the ferrule, otherwise the fibers in the outer positions will have poor or no contact with each other. This is one of the reasons why the

field assembly of MPO connectors has proved to be a problem. On the other hand, connectors which are factory assembled, ground and polished, guarantee high quality with excellent transmission performance. As part of Telegärtner’s comprehensive certified quality management, all connectors undergo full testing and inspection.

Testing an MPO/MTP® connector. Precise measurements to strict facto-ry specifications guarantee reliable connections.

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11 Standards and further information

MPO connectors are specified in numerous standards:

International standards (English):ISO/IEC 11801-1 (12- and 24-fiber connectors)ISO/IEC 14763-2 (connectivity methods)IEC 61754-7-1 (12-fiber MPO connectors)IEC 61754-7-2 (24-fiber MPO connectors)

European standards (national language):EN 50173-1 (12- and 24-fiber connectors)EN 50174-1 (connectivity methods)

US-American standards:ANSI/TIA-568.3 (12- and 24-fiber connectors, connectivity methods)

TelegärtnerKarl Gärtner GmbH

Lerchenstr. 35D-71144 Steinenbronn

e-mail: info@telegaertner.comWeb: www.telegaertner.com

© Telegärtner 12 2019

Author:Dirk Traeger

Technical Solutions Manager DataVoice

Telegärtner Karl Gärtner GmbH

Telephone: +49(0) 7157/1 25 - 0Fax: +49(0) 7157/1 25 - 5120

Further literature:

Data/Network Technology Basic Knowledge; Special Topic, Telegärtner Karl Gärtner GmbH, Steinenbronn