When designing a fiber optic network, the first decision installers need to make is whether to use a singlemode fiber or multimode fiber. This article makes that choice easier by explaining the differences between the two, and when installers should pick one over the other.
Comparing Singlemode Fiber vs. Multimode Fiber
Let’s compare a singlemode fiber and multimode fiber to get a better understanding.
A singlemode fiber has a very small core size that is less than 10 µm (10 micro-inches). The core permits only one ray of light, also referred to as mode, to be transmitted usually at 1310 nm and 1550 nm nanometers. These parameters are what make less light reflection to be produced when light passes through the core of a singlemode fiber. The result is lower attenuation or the rate measured at which the signal light decreases in intensity. Also, it allows the signal to travel further. Therefore, installers prefer to use a singlemode fiber for long distance, high bandwidth applications.
Multimode fiber has a larger core size that is 62.5 µm (62 micro-inches) or 50 µm (50 micro-inches). It directs many modes at the same time, allowing additional data to pass through the multimode fiber core. The following parameters will generate more light reflections, disperse light more, and increase the attenuation. As a result, the quality of the signal reduces over long distances. Therefore, installers prefer to use multimode fibers for short distances in local area networks (LANs).
What’s the difference between singlemode fiber and multimode fiber?
Since the cores of a singlemode and multimode fiber are different, the way in which an electromagnetic wave transfers its energy from one point to another is also different.
Light propagation between singlemode and multimode fibers differs. Multimode fiber obtains two types — step index and grade index. Singlemode fiber has one type — step index. The light propagation during signal transmission in a singlemode fiber reduces less than that of multimode fibers.
Laser diode-based fiber optic transmission equipment is required for singlemode fiber. The equipment has to be precisely calibrated to transmit light into the fiber optic cable. LED-based fiber optic equipment is typically used with multimode fiber for short distance transmissions. Also, the alignment requirements for singlemode connectors used with singlemode fiber are more rigorous than that of multimode fiber connectors.
Even though the cost of a singlemode fiber cable is cheaper than that of a multimode fiber cable, singlemode fiber cable systems are typically more expensive. The reason being singlemode fiber requires a transceiver that has a laser with a smaller spot-size and narrower spectral width, allowing it to function at a longer wavelength. In addition, the alignment between two fibers and the tolerances between two connectors has to be more precise. The end result is a higher cost for singlemode fiber interconnects.
VCSEL-based transceivers that are designed for use with multimode fibers are manufactured more easily into array devices. Therefore, they have a lower cost than equivalent singlemode transceivers. Even with the use of multiple fiber lanes and multi-transceiver arrays, there are substantial cost savings over singlemode technology using single or multichannel operations over simplex-duplex connectivity. Multimode fiber systems present the lowest cost and upgrade path to 100 Gigabit Ethernet (100GbE) for standards-based applications using parallel-optic based interconnects.
Which one to choose? Singlemode Fiber vs. Multimode Fiber
Distance is the most important thing to consider when deciding to use singlemode or multimode fiber. It’s typical to install multimode fibers from 300 meters to 400 meters within a data center. Singlemode fiber can run from 10 kilometers (10km) to 80 kilometers (80km), and even farther. Installers must use the proper optics for the distance required.
The illustration below shows common features between singlemode fiber and multimode fiber. Both are incompatible and cannot be mixed between two endpoints. The optics are also incompatible.
Multimode is a better choice for transmission distances up to 550 meters in data center applications and less expensive. For distances above 550 meters, singlemode fiber is best. Besides the distance, the total cost of ownership (TCO) should also be taken into consideration. Most importantly, choosing the right fiber for the network is the intelligent choice.
Learn more about ICC’s singlemode and multimode fiber optic systems.
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