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

Upgrade to High Data Rate Transmission With Parallel Optics

Parallel optics represent a type of optical communication technology as well as the devices on either end of the link that transmit and receive information which are also known as parallel optical transceivers. Compared with traditional optical communication, parallel optical communication employs a different cabling structure for signal transmitting aiming at high-data transmission for short reach multimode fibers that are less than 300 meters. Traditional fiber optic transceivers cannot satisfy the increasing demand for high speed transmission, like 40GbE, while parallel optics technology can be a cost effective solution for 40/100GbE transmission.

Comparison between parallel optics technology and the traditional serial optical communication would better explain what parallel optics is and the reason why it is a cost effective solution to high data rate transmission. The following of this article will offer the comparison between the two optical communication technology from two aspects: connectivity method and key components.

Connectivity Method

Literally, parallel optics and serial optics transmit signals in different ways. In traditional serial optical communication, on each end of the link, there are one transmitter and one receiver. For example, the transmitter on End A communicates to the receiver on End B, sending a single stream of data over a single optical fiber. And a separate fiber is connected between the transmitter on End B and the receiver on End A. In this way, a duplex channel is achieved by two fibers.

While in parallel optical communication, duplex transmission is achieved in a different way. A signal is transmitted and received through multiple paths, thus, the parallel optical communication can support higher data rate than the traditional optical communication. This is because, the devices for parallel optic communication on either end of the link contain multiple transmitters and receivers. For instance, in 2010 IEEE 802.3ba approved the 40GBASE-SR4 physical-medium-dependent multimode parallel optical solution, which uses eight fibers to transmit four duplex channels each at 10 Gigabit Ethernet. In this case, four 10Gbps transmitters on End A communicate with four 10Gbps receivers on End B, spreading a single stream of data over four optical fibers at a total data rate of 40Gbps.

Key Components

The parallel optical communication transmitting signals over multiple fibers, which has great advantages over traditional serial optical communication. It also means that it requires different components to support its high data rate transmission.

Connector: As previously mentioned, duplex transmission in serial optical communication uses 2-fiber duplex connectors, like duplex LC connectors to link the optics with other devices, while in parallel optical communication, multi-fibers are used to reach a higher data rate. Thus, multi-fiber connectors, like 12-fiber MPO connectors are used to connect with other devices. MPO connector is one key technology support parallel optical communication. This connectivity method is showed in the following picture?(Tx stands for transmit; Rx stands for receive).

Optical transceiver light source: Another complementary technology for parallel transmission is the light source of parallel optics—VCSELs (Vertical Cavity Surface Emission Lasers). Comparing with the edge-emitting semiconductor lasers in the traditional optics, VCSELs have better formed optical output which enables them to couple that energy into optical fibers more efficiently. In addition, VCSELs emit from the top surface, they may be tested while they are part of a large production batch (wafer), before they are cut into individual devices, which dramatically lowers the cost of the lasers. The following chart is about the comparison between VCSELs and edge-emitting semiconductor lasers. Cheaper to manufacture, easier to test, less electrical current required, supporting higher data rate, parallel optics using VCSELs could be a better choice to reach 40/100GbE transmission compared with traditional serial optics.

VCSEL vs Edge-Emitting Laser

Feature	VCSEL	Edge-Emitting Laser
Power consumption	2-3 mW	20 mW
Beam quality/ease of coupling	Better, round low divergence	Fine, asymmetric
Speed	10 Gbps	1 Gbps
Temperature stability	0.06 nm/oC	0.25 nm/oC
Specral width	1 nm	1-2 nm
Speckle	Low in an array	High

 

Parallel Optics for 40/100GbE Transmission

IEEE has already included physical layer specifications and management parameters for 40Gbps and 100Gbps operation over fiber optic cable. Two popular parallel optics solutions for 40Gbps and 100Gbps over multimode fibers are introduced here. For 40G, 40GBASE-SR4 transceiver is usually used, which requires a minimum of eight OM3/OM4 fibers for a transmit and receive link (4 fibers for Tx and 4 fibers for Rx). 100GBASE-SR10 transceiver is for 100Gbps transmission, which requires a minimum of 20 OM3/OM4 fibers for a Tx/Rx link, 10 fibers are used for Tx and the other 10 are for Rx.

Conclusion

The capabilities and uses of parallel optics and MPO technology continue to evolve and take shape as higher-speed fiber optic transmission, including 40/100GbE. It is uncertain that parallel optical communication would be the trend in the future. However, many cabling and network experts have pointed out that parallel optical communication supported with MPO technology is currently a way to equip an environment well prepared for the 40/100GbE transmission.

Source: http://www.fiber-optic-tutorial.com/upgrade-to-high-data-rate-transmission-with-parallel-optics.html

Migrating to 40/100G With OM3/OM4 Fiber

To meet the continuously increased requirements, data center 40/100G migration is underway. The infrastructure of data centers for the 40G/100G should meet the requirements like high speed, reliability, manageability and flexibility. To meet these requirements, product solutions and the infrastructure topology including cabling must be considered in unison. Cable deployment in the data center plays an important part. The cable used in data center must be selected to provide support for data rate applications not only of today but also the future. Today, two types of multimode fiber—OM3 and OM4 fibers (usually with aqua color)—have gradually become the media choice of data center during 40/100G migration. This article illustrates OM3/OM4 multimode fibers in 40/100G migration in details.

Data Center and Multimode Fibers

Multimode fiber is being widely used in data centers. You might ask why not single-mode fiber? The answer is cost. As is known to all, the price of single-mode fiber is generally more expensive than multimode fiber. In addition multimode fibers provide a significant value proposition when compared to single-mode fiber, as multimode fiber utilizes low cost 850 nm transceivers for serial and parallel transmission. If you had all money you wanted and you’d just run single-mode fiber which has all the bandwidth you need, then you can go plenty of distance. However, this perfect situation would cost a lot of money. Thus, most data center would choose multimode fiber. OM1, OM2, OM3 and OM4 are the most popular multimode fiber. But OM3 and OM4 are gradually taking place of OM1 and OM2 in data centers.

OM stands for optical multimode. OM3 and OM4 are both laser-optimized multimode fibers with 50/125 core, which are designed for use with 850nm VCSELS (vertical-cavity surface-emitting laser) and are developed to accommodate faster networks such as 10, 40 and 100 Gbps. Compared with OM1 (62.5/125 core) and OM2 (50/125 core), OM3 and OM4 can transport data at higher rate and longer distance. The following statistics (850 nm Ethernet Distance) shows the main differences between these four types multimode fibers, which can explain why OM3 and OM4 is more popular in data center now in some extent.

850 nm Ethernet Distance

Fiber Type	1G	10G	40/100G
OM1	300 m	36 m	N/A
OM2	500 m	86 m	N/A
OM3	1 km	300 m	100 m
OM4	1 km	550 m	150 m

 

Why Use OM3 and OM4 in 40/100G Migration

The Institute of Electrical and Electronics Engineers (IEEE) 802.3ba 40/100G Ethernet Standard was ratified in June 2010. The standard provides specific guidance for 40/100G transmission with multimode and single-mode fibers. OM3 and OM4 are the only multimode fibers included in the standard. The reason why OM3 and OM4 are applied in 40/100G migration is that they can meet the requirements for the migration cabling performance.

Bandwidth, total connector insertion loss and transmission distance are two three main factors should be considered when evaluation the performance needed for cabling infrastructure to meet the requirements for 40/100G. These factors can impact the cabling infrastructure’s ability to meet the standard’s distance of at least 100 meters over OM3 fiber and 150 meters over OM4 fiber. The following explains why OM3/OM4 are the chosen ones for 40/100G migration.

Get Higher Bandwidth With OM3/OM4

Bandwidth is the first reason why OM3 and OM4 are used for 40/100G migration. OM3 and OM4 are optimized for 850nm transmission and have a minimum 2000 MHz?km and 4700 MHz?km effective modal bandwidth (EMB). Comparing the OM1 and OM2 with a maximum 500 MHz?km, advantages of OM3 and OM4 are obvious. With a connectivity solution using OM3 and OM4 fibers that have been measured using the minimum Effective Modal Bandwidth calculate technique, the optical infrastructure deployed in the data center will meet the performance criteria set forth by IEEE for bandwidth.

Get Longer Transmission Distance With OM3/OM4

The transmission distance of fiber optic cables will influence the data center cabling. The manageability and flexibility will be increased with fiber optic cables with longer transmission distance. OM3 fiber and OM4 fiber can support longer transmission distance compare with other traditional multimode fibers. Generally OM3 fibers can run 40/100 Gigabit at 100 meters and OM4 fibers can run 40/100 Gigabit at 150 meters. This high data rate and longer distance cannot be achieved by other traditional multimode fiber like OM1 and OM2. Employing OM3 fiber and OM4 in 40/100G migration is required.

Get Lower Insertion Loss With OM3/OM4

Insertion loss has always been an import factor that technically should consider during the data center cabling. This is because the total connector loss within a system channel impacts the ability to operate over the maximum supportable distance for a given data rate. As total connector loss increased, the supportable distance at that data rate decreases. According to the 40/100G standard, OM3 fiber is specified to a 100m distance with a maximum channel loss of 1.9dB, which includes a 1.5dB total connector loss budget. And OM4 fiber is specified to a 150m distance with a maximum channel loss of 1.5 dB, including a total connector loss budget of 1.0 dB. With low-loss OM3 and OM4 fiber, maximum flexibility can be achieved with the ability to introduce multiple connector mating into the connectivity link and longer supportable transmission distance can be reached.

OM3 or OM4?

Choosing OM3/OM4 is a wise and required choice for data center 40/100G migration. However, OM3 and OM4, which is better? Numerous factors can affect the choice. However, the applications and the total costs are always the main factors to consider to figure out whether OM3 or OM4 is needed.

First, the connectors and the termination of the connectors for OM3 and OM4 fibers are the same. OM3 is fully compatible with OM4. The difference is just in the construction of fiber cable, which makes OM4 cable has better attenuation and can operate higher bandwidth at a longer distance than OM3. Thus, the cost for OM4 fiber is higher than OM3. As 90 percent of all data centers have their runs under 100 meters, choosing OM3 comes down to a costing issue. However, looking in the future, as the demand increases, the cost will come down. Thus, OM4 might be the most viable product at some point soon.

No matter choosing OM3 or OM4, the migration is underway. With good performance like high data rate, long transmission distance and lower inserting loss, OM3/OM4 fiber is a must in data center migration to 40/100G.

Source: http://www.fiber-optic-tutorial.com/migrating-to-40100g-with-om3om4-fiber.html