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