Parallel Optics Technology Overview

The number of network connections in data centers is on the rise. Data centers have to achieve ultra-high density in cabling. Multimode fiber optics is the medium of the future for satisfying the growing need for transmission speed and data volume over short distances. Parallel optics technology is what you get if you combine both trends—cabling density and the use of fiber optics. It is a suitable solution for high-performance data networks in data centers. This passage provides introductory information on parallel optics technology.

What Is Parallel Optics?

Parallel optics is a term used to represent both a type of optical communication and the devices on either end of the link that transmit and receive information. It differs from traditional fiber optic communication in that data is simultaneously transmitted and received over multiple optical fibers. In parallel optical communication, the devices on either end of the link contain multiple transmitters and receivers. For example, four transmitters on End A communicate with four receivers on End B, spreading a single stream of data over four optical fibers. With this configuration, a parallel optics transceiver can use four 2.5Gb/s transmitters to send one 10Gb/s signal from A to B.

Parallel optical devices are fundamentally different in construction from serial optical devices. Two complementary technologies have enabled the development and deployment of parallel optics devices: vertical cavity surface emission lasers (VCSELs) and the MPO connector. Parallel optic transmission technology spatially multiplexes or divides a high-data-rate signal among several fibers that are simultaneously transmitted and received. At the receiver, the signals are de-multiplexed to the original high-data-rate signal. MPO connectivity is used throughout the parallel optic link and interfaces into the transceiver module. An MPO connector and its connectivity method is showed in the picture below (Tx stands for transmit, Rx stands for receive).

Applications of Parallel Optics Technology

Parallel optic interfaces (POIs) are a fiber optic technology primarily targeted for short-reach multimode fiber systems (less than 300 meters) that operate at high data rates. Duplex fiber serial transmission with a directly modulated 850 nm VCSEL has been used to date for data rates up to 10G. Current and future protocols expected to use parallel optics include 40G and 100G Ethernet, InfiniBand and Fibre Channel speeds of 32G and higher. IEEE has already included physical layer specifications and management parameters for 40Gbps and 100Gbps operation over fiber optic cable. The uses of parallel optics technology continues to evolve and takes shape as higher-speed fiber optic transmission. 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.

Why Choose Parallel Optics?

Parallel optical communication uses multiple paths to transmit a signal at a greater data rate than the individual electronics can support. Parallel transmission can either lower the cost of a given data rate (by using slower, less expensive optoelectronics) or enable data rates that are unattainable with traditional serial transmission. Moreover, POIs offer an economical solution that utilizes multimode fiber, which is optimized with VSCEL sources. This means that for speeds faster then 16G, parallel optics, is the most practical, cost-effective solution.

Parallel optics is one technology currently on the market for high data rates networking solutions. Fiberstore is a professional manufacturer and supplier, which offers a large amount of cables and transceivers for your parallel optics applications, such as QSFP+ transceiver and QSFP+ cable. Parallel optical transceivers used for 40GBASE-SR4 and 40GBASE-CSR4 have 10-Gbps electrical lanes that are mirrored in the optical outputs.

40 GbE and 100 GbE over Multimode Fiber

To support the changing and fast-growing bandwidth demands of data centers, the IEEE ratified standards for supporting 40 GbE (Gigabit Ethernet) and 100 GbE (Gigabit Ethernet), known as IEEE 802.3ba. Both 40 and 100 GbE can be deployed using the same cabling systems in use today. Multimode will employ parallel optics using MPO interconnects and require additional cable infrastructure depending on the system deployed while single mode fiber will employ serial transmission and use LC or SC connectors. Each has its own advantages and disadvantages. In this post, 40 GbE and 100 GbE over multimode fiber will be introduced.

40 GbE and 100 GbE Standard

IEEE published the IEEE 802.3ba standard for 40 Gigabit and 100 Gigabit Ethernet in June 2010. multimode optical fiber OM1, OM2, OM3 and OM4 have different capabilities of supporting different Ethernet applications. Only the laser optimized multimode fiber (grades OM3 and OM4) are capable of supporting 40G and 100G Ethernet. The next part will focus on the cabling requirements of 40 GbE and 100 GbE over multimode fiber. The table below shows 40GE and 100GE specifications.

Implementing Parallel Optics

Traditionally, the Ethernet standard has relied upon duplex fiber cabling with each channel using one fiber to transmit and the other to receive. However, the 802.3ab standard requires multiple lanes of traffic per channel. To do this, the 40/100GbE standard uses parallel optics. The 802.3ba standard defines the parallel operation of four OM3/OM4 fibers for 40 GbE in 40GBASE-SR4 and the parallel operation of ten OM3/OM4 fibers for 100 GbE in 100GBASESR10. Two fibers have to be used per link because this arrangement is full duplex operation, i.e. simultaneous transmission in both directions. Therefore the number of fibers increases to eight for 40GBASE-SR4 and to 20 for 100GBASE-SR10. In the parallel optical link, the signal is split, transmitted over separate fibers and then joined again. That means the individual signals have to arrive at the receiver at the same time. Any skew in signal components has to be kept within tight tolerances. Trunk cables preterminated with MPO/MTP connectors are therefore the best choice for reliable transmission.

What Is 40 GbE and 100GbE over Multimode Fiber?

40G Ethernet and 100G Ethernet over multimode fiber uses parallel optics at 10 Gb/s per lane. One lane uses 1 fiber for each direction of transmission. 40G Ethernet requires 8 fibers. 100G Ethernet requires 20 fibers. The minimum performance that is needed to support 40 GbE and 100 GbE over multimode fiber is OM3 fiber for a distance of 100 meters. Cabling with OM4 fiber provides the capability to extend the reach up to 150 meters. Parallel optical channels with multi-fiber multimode optical fibers of the categories OM3 and OM4 are used for implementing 40 GbE and 100 GbE. The small diameter of the optical fibers poses no problems in laying the lines, and 802.3ba standard incorporated the MPO multi-fiber connector for 40GBASE-SR4 and 100GBASE-SR10, which can contact 12 or 24 fibers in the tiniest of spaces.

Conclusion

Optical fiber cabling is commonly deployed for backbone cabling in data centers for switch to switch connections and also for horizontal cabling for switch to server and storage area network connections. The use of pre-terminated optical fiber cabling can facilitate the migration path to 40G and 100G Ethernet in the future. Fiberstore can supply you with top-quality components for your 40 GbE and 100 GbE network, like 40G QSFP transceivers, and all kinds of QSFP+ cable choices, it also assists you competently with all questions involving planning, installation and maintenance.

Are You Ready for 40G and 100G?

Data centers regularly undertake their own great migration, to ever higher speed networks. 10G, unimaginable a decade ago, is now common in larger enterprises. And now many enterprises have to adopt 40 Gigabit Ethernet or even 100G in the aggregation and core layers of data center networks in order to meet the overall bandwidth demands of top-of-rack servers. The need is clear: a 40/100G Ethernet migration plan is quickly becoming a matter of survival. Is your network cabling optimized for this inevitable growth? Are you ready for 40G and 100G?

Fiber Transmissions at Higher Speeds

When moving to 40/100GbE, the most important difference in backbone and horizontal multimode applications is the number of fiber strands. 40GBASE-SR4 uses 8 strands in total, 4 strands to transmit and 4 to receive. 100GBASE-SR10 uses 10 lanes to transmit and another 10 lanes to receive for a total of 20 strands. In data centers and backbones, it may be possible to have 8 or 20 individual strands of fiber. However, those strands may take disparate paths from one end to the other and this can cause delay skew (known as bit skew) resulting in bit errors. For this reason, the 40/100GbE standards are written around fiber optic trunk assemblies that utilize a MPO/MTP multi-fiber array connector. Data is transmitted and received simultaneously on MTP interfaces through 10G simplex transmission over each individual strand of the array cable. In these assemblies, all strands are the same length. Also referred to as "parallel optics", this construction minimizes bit/delay skew, allowing the receive modules to receive each fibers information at virtually the same time.

Copper Transmissions at Higher Speeds

The first 10GbE capable copper interface was developed for the 10GBASE-CX4 application. The physical requirements for this shielded four-lane copper connector is standardized under SFF-8470. As a passive assembly, the SFF-8470/CX4 cables have a reach of 15m. This assembly supports 10GbE, InfiniBand, FibreChannel and FCoE. These assemblies use twinax cable, constructed of two inner conductors with an overall foil covered by a braid shield. Due to their low latency, these cables are popular in supercomputing clusters, High Performance Computing and storage. As part of the 802.3ba 40/100GbE standard, multi-lane 40GBASE-CR4 and 100GBASE-CR10 was defined. This standard specifies the use of 4 and 10-lane twinax assemblies to achieve 40 and 100GbE speeds for distances up to 7m.

40/100G MPO/MTP System

MPO/MTP is available in both 12 and 24 strand termination configurations used at the end of a trunk assembly. A modular laser optimized multimode MPO/MTP system that supports 40G and 100G fiber optic networks includes trunks, harnesses, array cords, modules, and adapter plates. For 40GbE, a 12-fiber cabling solution with each channel featuring four dedicated transmit fibers and four dedicated receiver fibers is used. In general, the middle four fiber remain unused. Parallel transmission is also used for 100GbE with a 24-fiber solution or two 12-fiber solution.

At present, 40GbE is taking over from 10GbE as the new high-growth market segment. Meanwhile, the 40GbE optics are universal in data center and the market of 100GbE is accelerating. Being prepared for 40/100G is essential: within a few short years higher-speed Ethernet will be common in data centers across all types of organizations. Fiberstore is ready. Fiberstore offers various optical communication products to meet diverse demands. For example, we provide 40GBASE-SR4 QSFP+ transceivers, like Finisar FTL410QE2C 40GBASE-SR4 QSFP+ transceiver and Mellanox MC2210411-SR4 40GBASE-SR4 QSFP+ transceiver, which are branded by famous companies and quality guaranteed.