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Black Box Explains...Multimode vs. single-mode Fiber.

Multimode vs. single-mode. Multimode cable has a large-diameter core and multiple pathways of light. It can be used for most general data and voice applications, such as adding segments to an... more/see it nowexisting network.

Multimode comes in two core sizes and four varieties: 62.5-micron OM1, 50-micron OM2, 50-micron OM3, and 50-micron OM4. (OM stands for optical mode.) All have the same cladding diameter of 125 microns, but 50-micron fiber cable has a smaller core (the light-carrying portion of the fiber). Although all can be used in the same way, 50-micron cable, particularly laser-optimized OM3 and OM4 50-micron cable, provides longer link lengths and/or higher speeds and is recommended for premise applications (backbone, horizontal, and intrabuilding links) and should be considered for new installations. OM3 and OM4 can also be used with LED and laser light sources.

Single-mode cable (OS1, OS2) has a small (8–10-micron) glass core and only one pathway of light. (OS stands for optical single-mode.) With only a single wavelength of light passing through its core, single-mode realigns the light toward the core center instead of simply bouncing it off the edge of the core as multimode does. OS1 is applied to inside-plant tight-buffered cable. OS2 is applied to loose-tube cables.

Single-mode provides far greater distances than multimode cable and can go as far as 40 km so it’s typically used in long-haul network links spread out over extended areas, including CATV and campus backbone applications. Single-mode cable also provides higher bandwidth than multimode fiber.

Specification comparison

OM1 62.5-/125-Miron Multimode Fiber

850-nm Wavelength:
Bandwidth: 160 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 220 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 500 m

OM2 50-/125-Micron Multimode Fiber
850-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m
OM3 50-/125-Micron Multimode Fiber

850-nm Wavelength:
Bandwidth: 1500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m

OM4 50-/125-Micron Multimode Fiber
850-nm Wavelength:
Bandwidth: 3500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m

OS2 8–10-Micron Single-Mode Fiber
Premise Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 1.0 dB/km;

Outside Plant Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 0.1 dB/km

Black Box Explains…OM1, OM2, OM3, and OM4

The demand for increased network bandwidth is driving the migration towards 40- and 100-GbE networks. This demand is being fueled by multiple factors, including ever-growing global IP traffic; greater switching,... more/see it nowrouting, virtualization, and data center connections; higher bandwidth applications; video-on-demand; convergence; and more.

When planning your 40-/100-GbE migration, consider your cabling infrastructure and how it will meet your current and future data requirements. What you install today needs to give you the scalability to accommodate the need for higher bandwidth for the next 15 to 20 years. The cables of choice for data center connectivity and what is recommended by the TIA are OM3 and OM4 laser-optimized multimode fiber.

There are different categories of graded-index multimode fiber optic cable. The ISO/IEC 11801 Ed 2.1:2009 standard specifies categories OM1, OM2, and OM3. The TIA/EIA recognizes OM1, OM2, OM3, and OM4. The TIA/EIA ratified OM4 in August 2009 (TIA/EIA 492-AAAD). The IEEE ratified OM4 (802.ba) in June 2010.

OM1 and OM2
OM1 specifies 62.5-micron cable and OM2 specifies 50-micron cable. These are commonly used in premises applications supporting Ethernet rates of 10 Mbps to 1 Gbps. They are also typically used with LED transmitters. OM1 and OM2 cable are not suitable though for today's higher-speed networks.

OM3 and OM4
OM3 is specified in ISO 11801. OM4 was ratified by the TIA in August 2009 (TIA/EIA 492-AAAD). The IEEE ratified OM4 (802.3ba 40G/100G Ethernet) in June 2010. It was amended in 2012 to IEEE 802.3-2012. The 802.3-bm Task Force is currently working on updates. The standard provides detailed guidelines for 40-/100-GbE transmission over OM3 and OM4 multimode cable and single-mode fiber optic cable. OM1, OM2, and copper are not included.

Laser optimized
OM3 and OM4 are both 50-micron laser-optimized multimode fiber (LOMMF) and were developed to accommodate faster networks such as 10-, 40-, and 100-GbE. They also support existing networks. Laser-optimized multimode fiber cable differs from standard multimode cable because it has graded refractive index profile fiber optic cable in each assembly. This means that the refractive index of the core glass decreases toward the outer cladding, so the paths of light towards the outer edge of the fiber travel more quickly than the other paths. This increase in speed equalizes the travel time for both short and long light paths, ensuring accurate information transmission and receipt over much greater distances, up to 300 meters at 10 Gbps. Laser-optimized cable is aqua colored.

Both OM3 and OM4 are designed for use with 850-nm vertical-cavity surface-emitting lasers (VCSELS) and have aqua sheaths.

OM3 specifies an 850-nm laser-optimized 50-micron cable with an effective modal bandwidth (EMB) of 2000 MHz/km. It can support 100-Gbps link distances up to 100 meters.

OM4 specifies a high-bandwidth 850-nm laser-optimized 50-micron cable with an EMB of 4700 MHz/km. It can support 100-Gbps link distances of 150 meters.

OM3 allows for 1.5 dB of connector loss at 100 meters at all speeds; OM4 allows for 1.0 dB of loss at 150 meters for 40-100-GbE. Both OM3 and OM4 rival single-mode fiber in performance while being significantly less expensive to implement. In addition, single-mode electronics are also expensive.

Manufacturing process
Laser-optimized OM3 and OM4 cable are made with a different process than OM1 and OM2, which are made with a small defect in the core called an index depression. These cables are used with LED light sources. OM3 and OM4 are manufactured without the center defect.

As networks migrated to higher speeds, VCSELs became more commonly used rather than LEDs, which have a maximum modulation rate of 622 Mbps and can’t be turned on and off fast enough to support higher-speed applications. Thus manufacturers changed the production process to eliminate the center defect and enable OM3 and OM4 cables to be used directly with the VCSELS.

Parallel transmission
40- and 100-GbE over OM3 and OM4 uses parallel optics where data is simultaneously transmitted and received over multiple fibers. 40-GbE consists of (4) 10-Gbps fiber channels each way, for a total of 8 fibers. 100-GbE consists of 10 fiber channels each way, for a total of 20 fibers. The signals are then aggregated at each end in an arrayed transceiver (connector) containing 4 or 10 VCSELs and detectors. For multimode fiber, the Media Dependent Interface (MDI) is the MPO adapter (IEC 61754-7). OM3/OM4 Comparison
850 nm High Performance EMB (MHz/km)

OM3: 2000

OM4: 4700

850-nm Ethernet Distance
OM3: 1000 m

OM4: 1000 m

OM3: 300 m

OM4: 550 m

OM3: 100 m

OM4: 150 m

OM3: 100 m

OM4: 150 m


Black Box Explains...Loose-tube vs. tight-buffered fiber optic cable.

There are two styles of fiber optic cable construction: loose tube and tight buffered. Both contain some type of strengthening member, such as aramid yarn, stainless steel wire strands, or... more/see it noweven gel-filled sleeves. But each is designed for very different environments.

Loose tube cables, the older of the two cable types, are specifically designed for harsh outdoor environments. They protect the fiber core, cladding, and coating by enclosing everything within semi-rigid protective sleeves or tubes. In loose-tube cables that hold more than one optical fiber, each individually sleeved core is bundled loosely within an all-encompassing outer jacket.

Many loose-tube cables also have a water-resistant gel that surrounds the fibers. This gel helps protect them from moisture, so the cables are great for harsh, high-humidity environments where water or condensation can be a problem. The gel-filled tubes can expand and contract with temperature changes, too.

But gel-filled loose-tube cables are not the best choice when cable needs to be submerged or where it’s routed around multiple bends. Excess cable strain can force fibers to emerge from the gel.

Tight-buffered cables, in contrast, are optimized for indoor applications. Because they’re sturdier than loose-tube cables, they’re best suited for moderate-length LAN/WAN connections, long indoor runs, and even direct burial. Tight-buffered cables are also recommended for underwater applications.

Instead of a gel layer or sleeve to protect the fiber core, tight-buffered cables use a two-layer coating. One is plastic; the other is waterproof acrylate. The acrylate coating keeps moisture away from the cable, like the gel-filled sleeves do for loose-tube cables. But this acrylate layer is bound tightly to the plastic fiber layer, so the core is never exposed (as it can be with gel-filled cables) when the cable is bent or compressed underwater.

Tight-buffered cables are also easier to install because there’s no messy gel to clean up and they don’t require a fan-out kit for splicing or termination. You can crimp connectors directly to each fiber.

Want the best of both worlds? Try a hybrid, breakout-style fiber optic cable, which combines tight-buffered cables within a loose-tube housing. collapse

Black Box Explains...50-µm vs. 62.5-µm fiber optic cable.

As today’s networks expand, the demand for more bandwidth and greater distances increases. Gigabit Ethernet and the emerging 10 Gigabit Ethernet are becoming the applications of choice for current and... more/see it nowfuture networking needs. Thus, there is a renewed interest in 50-micron fiber optic cable.

First used in 1976, 50-micron cable has not experienced the widespread use in North America that 62.5-micron cable has.

To support campus backbones and horizontal runs over 10-Mbps Ethernet, 62.5-micron fiber, introduced in 1986, was and still is the pre-dominant fiber optic cable because it offers high bandwidth and long distance.

One reason 50-micron cable did not gain widespread use was because of the light source. Both 62.5- and 50-micron fiber cable can use either LED or laser light sources. But in the 1980s and 1990s, LED light sources were common. Because 50-micron cable has a smaller aperture, the lower power of the LED light source caused a reduction in the power budget compared to 62.5-micron cable—thus, the migration to 62.5-micron cable. At that time, laser light sources were not highly developed and were rarely used with 50-micron cable — and, when they were, it was mostly in research and technological applications.

The cables share many characteristics. Although 50-micron fiber cable features a smaller core (the light-carrying portion of the fiber), both 50- and 62.5-micron cable use the same cladding diameter of 125 microns. Because they have the same outer diameter, they’re equally strong and are handled in the same way. In addition, both types of cable are included in the TIA/EIA 568-B.3 standards for structured cabling and connectivity.
As with 62.5-micron cable, you can use 50-micron fiber in all types of applications: Ethernet, FDDI, 155-Mbps ATM, Token Ring, Fast Ethernet, and Gigabit Ethernet. It is recommended for all premise applications: backbone, horizontal, and intrabuilding connections. And it should be considered especially for any new construction and installations. IT managers looking at the possibility of 10 Gigabit Ethernet and future scalability will get what they need with 50-micron cable. collapse

Black Box Explains...How fiber is insulated for use in harsh environments.

Fiber optic cable not only gives you immunity to interference and greater signal security, but it’s also constructed to insulate the fiber’s core from the stress associated with use in... more/see it nowharsh environments.

The core is a very delicate channel that’s used to transport data signals from an optical transmitter to an optical receiver. To help reinforce the core, absorb shock, and provide extra protection against cable bends, fiber cable contains a coating of acrylate plastic.

In an environment free from the stress of external forces such as temperature, bends, and splices, fiber optic cable can transmit light pulses with minimal attenuation. And although there will always be some attenuation from external forces and other conditions, there are two methods of cable construction to help isolate the core: loose-tube and tight-buffer construction.

In a loose-tube construction, the fiber core literally floats within a plastic gel-filled sleeve. Surrounded by this protective layer, the core is insulated from temperature extremes, as well as from damaging external forces such as cutting and crushing.

In a tight-core construction, the plastic extrusion method is used to apply a protective coating directly over the fiber coating. This helps the cable withstand even greater crushing forces. But while the tight-buffer design offers greater protection from core breakage, it’s more susceptible to stress from temperature variations. Conversely, while it’s more flexible than loose-tube cable, the tight-buffer design offers less protection from sharp bends or twists. collapse

Black Box Explains...Fiber optic cable construction.

Fiber optic cable consists of a core, cladding, coating, strengthening fibers, and cable jacket.

This is the physical medium that transports optical data signals from an attached light source to... more/see it nowa receiving device. The core is a single continuous strand of glass or plastic that’s measured (in microns) by the size of its outer diameter. The larger the core, the more light the cable can carry.

All fiber optic cable is sized according to its core’s outer diameter.

The three multimode sizes most commonly available are 50, 62.5, and 100 microns. Single-mode cores are generally less than 9 microns.

This is a thin layer that surrounds the fiber core and serves as a boundary that contains the light waves and causes the refraction, enabling data to travel throughout the length of the fiber segment.

This is a layer of plastic that surrounds the core and cladding to reinforce the fiber core, help absorb shocks, and provide extra protection against excessive cable bends. These buffer coatings are measured in microns (µ) and can range from 250 to 900 microns.

Strengthening fibers
These components help protect the core against crushing forces and excessive tension during installation.

The materials can range from Kevlar® to wire strands to gel-filled sleeves.

Cable jacket
This is the outer layer of any cable. Most fiber optic cables have an orange jacket, although some types can have black or yellow jackets. collapse

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