Guide to Bend-insensitive Multimode Fiber

četvrtak , 07.07.2016.

A common problem facing cabling installers during installation or other fiber handling is the light losses or weaker optical signal, which is cause by the fact that when a fiber bend radius exceeds the specified figure, the angle at which the light hits the cladding changes and some light will escape and result in power loss. It’s known that light losses is the commonplace found in fibers, like LC-SC multimode fiber patch cord. In 2009, bend-insensitive multi-mode fiber (BIMMF) has been introduced, which can withstand tight bends, or even kinks, or other withstand tough treatment without suffering significant light losses in many cases. It seems to be an ideal product. How much do you know about it? Have some ideas about its working principle, its compatibility, its testing issues? Follow this article and find answers.

BIMMF Working Principle
An introduction to the working principle helps you to understand how BIMMF reduces signal losses with its bend-insensitivity and becomes the preferred choice in data center applications.

BIMMF technology prevents light from escaping. BIMMF has an innovative core design that incorporates a graded-index core profile combined with a specially engineered optical trench. A specially engineered optical trench (image below) is used to trap the light in the many modes which propagate within the fiber core. The trench, or also called moat, with low refractive index, surrounds the core in BIMMF to reflect lost light back into the core. It acts like a barrier for propagating light. Keeping the light in the core, even in the most challenging bending scenarios, significantly reduces the bend-induced. The trench is just an annular ring of lower index glass surrounding the core with very carefully designed geometry to maximize the effect.

BIMMF Compatibility Issues
One question with BIMMF is whether it’s compatible with conventional fibers. Can they be spliced or connected to other conventional (non-BI) fibers without problems? How does the inclusion of higher order modes affect bandwidth?

Measurement of core size, NA, differential mode delay (DMD) and bandwidth were developed prior to the introduction of BI MMF designs. These measurements are in the process of being evaluated and updated, so measurement results may depend on the manufacturer of the BIMMF. For the most part, it appears that BIMMF can be made to be compatible to other non-BI fibers by modifying the core design slightly or careful engineering of the trench surrounding the core, but at this point it is left to the manufacturers to show their product will perform equivalently to the installed base of fiber.

When short lengths of BIMMFs are measured, they may have a larger effective NA and core size than conventional MMFs since they propagate "leaky modes" that are attenuated in conventional fiber designs. This may affect splice or connector loss when mating BIMMF with conventional MMF but usually only in one direction, from BIMMF to conventional MMF, in a manner similar to the losses from mismatched fibers.

BIMMF Testing
Testing BIMMFs or using them for reference cables for testing is another matter. For testing, link set ups included both all BIMMF channels and mixed links using a combination of BIMMF assemblies and standard nonBIMMF assemblies. 10G and 40G testing used full duplex traffic with two transceivers (e.g. E10GSFPLR or QFX-QSFP-40G-SR4), and this approach is necessary, since the trunk cables contain only 12 fibers and per the standard, and full duplex traffic at 100G requires 20 fibers. The channel configurations for the various active tests are shown below.


BIMMF Advantages & Design Challenges
This kind of cable has obvious advantages. In patch panels, it should not suffer from bending losses where the cables are tightly bent around the racks. In buildings, it allows fiber to be run inside molding around the ceiling or floor and around doors or windows without inducing high losses. It's also insurance against problems caused by careless installation.

However, BIMMF profiles pose a complex design challenge. Profile parameters must be carefully selected to ensure all key attributes satisfy all relevant industry standards. Bandwidth is a key parameter for MMFs and the graded-index profile remains a key driver to achieve high bandwidth. Any deviation from the optimum profile results in reduction of bandwidth of the MMFs. Inappropriate trench location can result in delay errors of the higher-order modes, and this can significantly impair bandwidth performance. Locating the trench too far from the fiber core can result in failure to comply with fundamental industry standards. The fiber's trench location must be carefully engineered to ensure superior bandwidth and macrobend response while maintaining industry standard requirements for core diameter, numerical aperture and chromatic dispersion.

Conclusion
BIMMF is fully compliant with the OM3 and OM4 standards for laser-optimized fibers, and is also backward compatible with the installed base of 50-Ľm MMFs. With its improved bend -sensitivity, BIMMF allows for less light losses in the stressed section of the fiber, reducing the challenges encountered in installations in local area network (LAN) data centers.

Oznake: MMFs, BIMMF, LC-SC multimode fiber patch cord, BIMMF testing, transceivers, E10GSFPLR

10GbE Interconnect Solutions Overview

četvrtak , 31.03.2016.

New sophisticated networking services, coupled with the increase of Internet users push the Internet traffic to an even higher point, driving the need for increased bandwidth consequently. One Ethernet technology—10 Gigabit Ethernet (GbE) is adequate for such bandwidth demand, and has become widely available due to the competitive price and performance, as well as its simplified cabling structure.

Several cable and interconnect solutions are available for 10GbE, the choice of which depends on the maximum interconnect distance, power budget and heat consumption, signal latency, network reliability, component adaptability to future requirements, cost. Here cost includes more than what we call the equipment interface and cable cost, but more often the labor cost. Thus, choosing a 10GbE interconnect solution requires careful evaluation of each option against the specific applications. This text aims to introduce two main 10GbE interconnect solutions: fiber optics and copper.

Fiber Optics Solution
Fiber optic cables include single-mode fiber (SMF) and multi-mode fiber (MMF). MMF is larger in diameter than that of single-mode, thus portions of the light beam follow different paths as they bounce back and forth between the walls of the fiber, leading to the possible distorted signal when reach the other end of the cable. The amount of distortion increases with the length of the cable. The light beam follows a single path through thinner single-mode cable, so the amount of distortion is much lower.

The typical 10GBASE port type that uses MMF is 10GBASE-SR which uses 850nm lasers. When used with OM3 MMF, 10GBASE-SR can support 300m-connection distances, and when with OM4 MMF, 400m link length is possible through 10GBASE-SR SFP+ transceiver.

10GBASE-LR (eg. E10GSFPLR), 10GBASE-ER and 10GBASE-ZR are all specified to work via SMF. SMF can carry signals up to 80km, so it is more often used in wide-area networks. But since SMF requires a more expensive laser light source than MMF does, SMF is replaced by MMF when the required connection distance is not so long.

Copper Solution
10GBASE-CX4, SFP+ Direct Attach (DAC) and 10GBASE-T are all specified to operate through copper medium.

10GBASE-CX4
Being the first 10GbE copper solution standardized by the IEEE as 802.3ak in 2002, 10GBase-CX4 uses four cables, each carrying 2.5gigabits of data. It is specified to work up to a distance of 15m. Although 10GBase-CX4 provides an extremely cost-effective method to connect equipment within that 15m-distance, its bulky weight and big size of the CX4 connector prohibited higher switch densities required for large scale deployment. Besides, large diameter cables are purchased in fixed lengths, causing problems in managing cable slack. What’s more, the space isn’t sufficient enough to handle these large cables.

SFP+ DAC
SFP+ Direct Attach Cable (DAC), or called 10GSFP+Cu, is a copper 10GBASE twin-axial cable, connected directly into an SFP+ housing. It comes in either an active or passive twin-axial cable assembly. This solution provides a low-cost and low energy-consuming interconnect with a flexible cabling length, typically 1 to 7m (passive versions) or up to 15m (active versions) in length. Below is the SFP+ to SFP+ passive copper cable assembly with 1m length, 487655-B21, a HP compatible 10GbE cabling product.


10GBASE-T
10GBASE-T, known as IEEE 802.3an-2006, utilizes twisted pair cables and RJ-45 connectors over distances up to 100m. Cat 6 and Cat 6a are recommended, with the former reaching the full length at 100m, and the latter at 55m. In a word, 10GBASE-T permits operations over 4-connector structured 4-pair twisted-pair copper cabling for all supported distances within 100m. Besides, 10GBASE-T cabling solution is backward-compatible with 1000BASE-T switch infrastructures, keeping costs down while offering an easy migration path from 1GbE to 10GbE.

Conclusion
In summary, two main media options are available for 10GbE interconnect: copper and fiber optics, including 10GBASE-CX4, SFP+ DAC, 10GBASE-T, 10GBASE-SR, 10GBASE-LR, 10GBASE-ER, 10GBASE-ZR, and so on. Fiberstore offers all these 10GBASE SFP+ modules and cables for your 10GbE deployment, which are quality-assured and cost-effective, like E10GSFPLR and 487655-B21 mentioned above. For more information about 10GbE interconnect solutions, you can visit Fiberstore.

Oznake: SMF, MMF, 10GBASE-LR, E10GSFPLR, SFP+ DAC, 487655-B21, 10Gbase-T