What Are the Limitations of Multimode Fiber?

If you have watched the History Channel, you are probably familiar with The Men Who Built America and The Food That Built America. While J.D. Rockefeller, Andrew Carnegie, McDonald’s, and KFC are quintessential to America’s history, it is surprising that Data Systems That Changed the World hasn’t been aired–a series that would have no choice but to place great emphasis on fiber. 

This, of course, is due to the fascinating contribution and history of fiber. Invented in 1965, patented in 1966, and used in NASA television cameras sent to the moon in 1968 (apologies to the conspiracy theorists), fiber got off to a great start. Then, in the 1970s, the world was introduced to multimode fibers with single-mode fibers following a decade later. 

But then something happened–the use of fiber quickly dwindled and didn’t pick back up until the early 2000s. It was around 2005 that the interest in multimode fiber resurfaced. How could it not with its advanced data transfer methods in today’s fast-paced world?

This article is specifically about multimode fiber, which, despite its benefits, has its limitations. Distance, bandwidth, attenuation, and dispersion affect its overall performance. And this article will provide valuable insights and information on multimode fiber.

Types of Multimode Fiber

To better understand multimode fiber, it’s essential to know how it differs from its single-mode counterpart. The difference is simple: single mode fiber is used for longer distances, and multimode is used for shorter distances–such as within a building or on campus. 

There are five types of multimode fiber (OM1, OM2, OM3, OM4, and OM5), and they each come with different qualities. We understand that this terminology can be quite intimidating, but that’s why we’re here. We will break these down in simple, easy-to-understand ways. 

OM1 Fiber

The first of the two early forms of multimode fiber, OM1, entered the stage in 1989. It comes in an orange jacket, utilizes an LED light source, and supports a data rate of 1GB at 850 nanometers (nm). It is capable of distances up to 33m and, with a bandwidth of 200 MHz/km, OM1 fiber is generally used in Ethernet applications such as short-haul networks, Local Area Networks (LANs), and small, private networks. 

OM2 Fiber

As with OM1, OM2 is the second of the early forms of fiber, debuting in 1998. Similar to OM1, OM2 also comes with an orange jacket and LED light source; however, it differs by being applied in 1G Ethernet applications and reaching a distance of up to 82m. It is mainly used in LANs and private networks and offers a bandwidth of 500 MHz/km.

OM3 Fiber

Coming in an aqua-colored jacket, OM3 fiber is laser optimized and supports a data rate of 10 Gbps. OM3 fiber has a distance of up to 300m and is generally used in more extensive private networks like college campuses. With a bandwidth of 2,000 MHz/km, it is a little faster than the first two.

OM4 Fiber

OM4 fiber was launched in 2009 and features an aqua-colored jacket, laser optimization, and a bandwidth of 4,700 MHz/km. Compared to OM3 fiber, the OM4 cable reaches a longer distance at the same data rate, reaching up to 400m. However, it can go beyond this by reaching distances up to 150m at 40G, respectively. The OM4 fiber cable is often seen in high-speed networks like data centers, financial institutions, and corporate offices. 

OM5 Fiber

The latest and greatest fiber cable, OM5, is similar to OM4. It differs, however, by being designed to include extra bandwidth beyond 850nm. The OM5 cable can also transmit multiple signals using a single fiber, saving fiber in the process.

Distance Limitations of Multimode Fiber

The greatest limitation of multimode fiber is its short distances–reaching a maximum distance of around 550 meters–to be able to maintain its speed and reliability. However, many factors contribute to this. We will discuss them below. 

Attenuation

Attenuation is one of those intimidating terms we briefly discussed earlier–as most words over four syllables generally are. But the good news is it has a straightforward dictionary definition: it is the reduction in power of the light signal as it is transmitted. So how does attenuation affect multimode fiber distance?

Well, the functioning of the optical data link depends on the light reaching the receiver with enough power. And as stated, attenuation is the reduction of power caused by components such as cables, cable splices, and connectors. 

All fiber is light-based–it relies on light to function properly. When attenuation comes into the picture, causing the light to lose its power, the distance of your fiber cable can decrease significantly. 

Dispersion

Dispersion–yet another terrifying word but has another simple explanation–is the spreading of a signal over time. Unlike attenuation, dispersion limits the bit rate and link length. A functioning data link must contain enough light to exceed the minimum power that the receiver requires.

Bandwidth Limitations of Multimode Fiber

On the other side of multimode fiber limitations, we have bandwidth. As with the distance issue, the bandwidth limitation is the product of many factors. 

Modal Dispersion

Multimode fibers have different modes with varying velocities. Modal dispersion occurs when light rays travel along multiple paths that have multiple path lengths. These rays will arrive at the end of the fiber since they do not travel the same distance. 

In most cases, modal dispersion is the dominant trait that reduces bandwidth. This dispersion occurs due to the optical path length varying with each mode. 

Connectors

Connectors link cables with a secure connection, permitting light pulses to travel through the cable easily. Many types of connectors accommodate different applications. Choosing the right fiber connector ensures the ideal performance you want. 

Naturally, the wrong connector can facilitate attenuation and bandwidth limitations. This is simply due to the light being restricted from traveling as freely as it needs. 

Splices

Joining two fiber cables together is known as fiber splicing, and there are two forms: mechanical and fusion. Splicing is used to restore fiber cables when one has been damaged. Given the two options, you probably want to know which is better in terms of performance.

Fusion splicing is the way to go–it is more expensive but lasts longer than mechanical splicing. It also reduces attenuation because the cables are fused or welded together. Unlike mechanical splicing, where the fibers are not permanently joined, they are just held together so light can pass from one to the other. 

Bends

A fiber cable is composed of a core and a cladding–both are made from glass and designed to capture the light within the core and send it to the opposite end of the fiber. The light follows many paths along this journey, bouncing back and forth. Thus, bends can be your fiber cable’s worst nightmare. 

When a fiber is bent, it changes the angle at which the light bounces, resulting in a loss of power. This is known as bend sensitivity, which happens to all fiber cables. Some, however, have a higher degree of bend sensitivity.

Addressing the Limitations of Multimode Fiber

With multimode fiber, you will undoubtedly be subjected to some limitations. But that doesn’t mean you can’t do anything to lessen them. Here are a couple of strategies for addressing your multimode fiber limitations.



Upgrade to High-Performance Fiber

If you’re using OM1 or OM2 fiber cables, you can always upgrade to the higher-performance band types (OM3, OM4, and OM5). This is just like upgrading your router or iPhone–sometimes, it’s necessary. 

Ensure Proper Installation and Maintenance

Like copper telephone wires, fiber is installed underground. And it’s pretty costly, so you want to be sure it’s installed properly. Proper fiber installation can address the limitations of attenuation, dispersion, connectors, splices, and bends–which, in turn, makes your experience all the better. 

The Bottom Line

Understanding the limitations of multimode fiber is the first step to grasping how they affect performance. Deciding to go with fiber is a big deal, so you want to be aware of how attenuation, dispersion, splices, and bends can negatively impact it. 

Those same limitations are what you should consider when planning, designing and deploying fiber optic infrastructure. But with the best strategies–proper installation and using high-performance fibers–you should be able to navigate it with ease.