Practical Applications of Graded Index Multimode Fiber

Posted by Jonathan Benfield on Tue, Aug 3, 2021 @ 09:08 AM

Communications engineers face many complicated decisions when selecting the most appropriate type of fiber optic cabling for their specific needs. Should the fiber be single mode or multimode? If it is multimode, should it be step index fiber or graded index? Those are just two of the multitude of questions that need to be answered when selecting the best fiber solution.

In many cases, the best approach is to understand the specific use-case or application that the fiber will be used for, then determine the cable that best meets that use case.  How much distance is needed? How important is speed, latency, etc?  Knowing the answers to these questions can help guide the decision process.

When to Choose Graded Index Fiber

Graded index fiber is a type of optical fiber where the core’s refractive index decreases as the radial distance (distance to the core center) increases. This fiber is most often classified as G.651.1 under International Telecommunication Union (ITU) standards.

Graded index fiber offers an optimal solution in a broad number of use cases. Like most other multimode fibers, graded index is also most applicable for short distance applications. 

Compared to step index multimode fiber, graded index delivers lower modal dispersion, allowing it to handle higher transmission bandwidths.

Reducing Modal Dispersion with Graded Index Fiber

Modal dispersion is the result of having multiple modes traveling through different paths in the same fiber. When light travels via multiple modes, some signals are received faster than others. This results in a broadened signal and less bandwidth. Modal dispersion limits the bandwidth of the signal to tens of, meaning that when the fiber is 1km long, the signal bandwidth cannot exceed tens of MHz without confusion.

As mentioned above, multimode fiber can be either graded index or step index. Graded index offers numerous advantages compared to step index multimode fiber, including the significant decrease in modal dispersion. Modal dispersion is further decreased by using fiber with a smaller core size, such as 50um commonly seen in today’s OM3 and OM4 fibers, which are used to transmit 10G and beyond across hundreds of meters.

Ideal Applications for Graded Index Fiber

With the ability to deliver high levels of bandwidth across short to medium distances, graded index fiber can be the best choice for a variety of use cases.

  • Residential and Commercial Buildings: With graded index fiber enabling higher bandwidths, it is deployed in a variety of buildings such as offices, apartments, or similar larger structures.
  • Data Centers:  While data centers today also utilize single mode fibers, graded index multimode fibers especially OM3 and OM4 are utilized across data centers for a significant number of high bandwidth applications.  
  • Large Vessels: With communications networks being important everywhere, even at sea, ships are an excellent opportunity for graded index fiber as it provides solid bandwidth and the graded index fiber helps the signal travel further.
  • Local Area Networks & Small Campuses: In buildings or on campuses that have their own local networks, this fiber can deliver better bandwidth and distance especially across and between larger buildings around the campus.

Graded Index Multimode Fibers from M2 Optics

Graded index multimode fiber is just one of the many types of optical fibers that M2 Optics offers, typically packaged in an efficient Fiber Lab solution for testing and networking applications.

If you require multimode fiber for a project and require more information and pricing, contact us and a member of the M2 team will help you to start customizing your perfect solution today.

Topics: optical fiber, multimode fiber