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Choosing the right fibre type for your application can be a daunting task. Although multimode and single-mode fibres are nowadays commonly used, their differences still can be confusing. So, what are their respective characteristics, advantages, and disadvantages?
Multiode and single-mode are two types of fibre optical cable with different uses. Single-mode fibre is designed to propagate a single light wave (mode), whereas multimode fibre is capable of supporting multiple -simultaneous- modes. This is achieved by using an optical core with a larger diameter (ø 50 or 62.5 µm for MMF and 9 µm for SMF).
The smaller core diameter in single-mode fibres (SMF) results in a lower attenuation and thus, longer transmission distances and higher bandwidths. It’s simple physics: a smaller pipe means less reflection.
When it comes to bandwidth, single-mode is the clear champion: SMF supports more powerful laser light sources with lower attenuation, commonly working on 1310 and 1550 nm wavelengths. A single light mode provides virtually unlimited bandwidth.
MMF, on the other side, relies on the transmission of multiple light waves (modes) with less powerful LED and VCSEL light sources but higher attenuation, most commonly using 850 and 1310 nm wavelengths. This means, that the five grades of MMF sport different distance capabilities and have limited bandwidth.
Due to the larger core diameter of a multimode fibre, the light modes will get reflected on the core-cladding interface many times, which results in a much higher attenuation than in a single-mode fibre, where a single light mode passes through the fibre core without too many reflections.
The transmission distance depends mainly on the electronics and their output capabilities. In practice though, single-mode will always outperform multimode. SMF supports both, short- and long-distance links, regardless of bandwidth, while MMF will only work for short-distance transmission.
With all the advantages of single-mode fibre described here above, one would expect SMF to be more expensive than MMF, while the opposite is the case. Single-mode fibre is more efficient in the manufacturing process and will be 30% cheaper than multimode fibre on average. On the other hand, single-mode transceivers will have to be equipped with stronger light sources and more complicated optical processors than multimode transceivers which translates to higher costs for the initial set-up (5x higher on average).
Now we know the differences between MMF and SMF, which fibre type should have our preference? It all depends: single-mode patch cables are less expensive and supports higher bandwidths and link distances. Yet, we’ll spend more on transceivers.
In practice this means, that we will choose single-mode over multimode fibre for building prewires, networking, AV distribution, security, broadcast, and all other long-reach data transmission applications in carrier networks, MANs and PONs. Multimode, with it’s shorter reach, is more commonly used in enterprise, data centres and LANs.
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