What are the Differences Between Fiber Optic Speed and Distance?

ICC White Papers

With the demand for greener data centers that can support higher bandwidth at long distances steadily growing, fiber patch cables are being used for installations more frequently. In order to establish which fiber optic cable is most appropriate for the job, two primary layers must be understood first: the core and cladding.

Basic fiber cable structure: core, cladding, and insulation

The Core

At the core of an optic cable is a cylinder made of either glass or plastic. Cladding, which is what surrounds the core, is also made of glass or plastic.

The amount of light that is able to transmit through the fiber is dependent on the diameter of the outer core: The larger the core, the more light is able to pass through. Finding the diameter of the outer core is done by finding the average of the diameters of the smallest circles restricted to the core-cladding boundary. The mode field diameter is another measurement that defines the maximum intensity of light. Singlemode fiber has a larger diameter due to light entering the cladding.

There are three common core sizes: 62.5/125 (62.5 µm), 50/125 (50 µm) and 9/125 (9 µm) and they are measured in microns, which equates to one-millionth of a meter. Singlemode fiber has a narrow diameter at 8.3 to 10 microns and the diameter ratio of the core to cladding is 9 to 125 microns. Multimode fiber can come with a wide diameter of 50 to 100 microns, but the most common size is 50/125. The diameter ratio of the core to cladding for multimode fiber is 50 to 125 microns.

Fiber cable core sizing diagram: OM1 Multimode - 62.5 µm, OM2/OM3/OM4 - 50 µm, OS1 Singlemode 9 µm

The Cladding

Cladding is made of reflective material that surrounds the core. This not only helps keep light within the core, but also helps move it through the length of the fiber. Light can sometimes saturate the core as well as the cladding, so it is important that the cladding supports various refractive indexes as well as modes. Modern fibers are built with a higher refractive index than that of the cladding to ensure the quick dissipation of light.

More data is able to be transmitted through a multimode fiber optic cable because the light wave disperses into numerous paths within the core. However, the signal loses strength over long distances. Singlemode fiber optic cable, on the other hand, has a narrow sized core which decreases the amount of light reflections and increases the strength of the signal to travel over longer distances. However, less data is able to be transmitted compared to multimode fiber optic cable.

Fiber cable cores: multimode fiber signal - shortwave lasers, singlemode fiber signal - longwave lasers

The Coatings

The multiple layers of plastic that surround the fiber are called coatings. These coatings act as a buffer to preserve strength, absorb shock, and add an additional layer of protection. They come in a variety of microns, from 250 to 900.

Core-cladding Concentricity

There are a number of factors that can affect the loss of connection between two optical fibers. The most notable is core-cladding concentricity; this affects the quality of light transmission. Other factors include fiber core to fiber cladding as well as ferrule edge to ferrule bore. Having the diameter of the fiber mirror the diameter of the bore can also affect the concentricity.

ICC’s fiber patch cables are individually inspected to not exceed 1.5 microns, which helps keep the core as close as possible to the center. This inspection helps remove the possibility of misalignment and decreases optical loss within the core-cladding offset.

Bad Concentricity vs. Good Concentricity

Bandwidth versus Distance

The chart below shows the comparison between fiber optic bandwidth and distance. As the data rate in bandwidth increases, the distance decreases.

Data Rate Fast Ethernet
1Gb Ethernet
1Gb Ethernet
1000BA SE-LX
10Gb Base SE-SR 40Gb Base SR4 100Gb Base SR10
Category Type Core Distance
OS1 Singlemode 9/125 200 meters 5K meters 5K meters 10K meters Not Supported Not Supported
OM1 Multimode 62.5/125 200 meters 275 meters Not Supported 33 meters Not Supported Not Supported
OM2 Multimode 50/125 200 meters 550 meters Not Supported 82 meters Not Supported Not Supported
Laser Optimized
Multimode 50/125 200 meters 550 meters Not Supported 300 meters 100 meters 100 meters
Laser Optimized
Multimode 50/125 200 meters 550 meters Not Supported 400 meters 150 meters 150 meters

This chart displays the differences between Singlemode and Multimode fiber optic cables. Singlemode OS1, covers up to 10,000 meters, which is 50 times more than what multimode can cover. Multimode comes in four different categories: OM1, OM2, OM3, and OM4. The most commonly used are the OM1 and OM2. These fibers are used to support 1Gb Ethernet applications and are supported themselves with 10 Gigabit Ethernet (10GbE) at a length of 33 meters and 82 meters, respectively. OM3 and OM4 cables, which are laser-optimized, are also supported by 10GbE but can run distances of 300m and 550m.

Visit ICC’s Fiber Optic System solution page to learn more.