Singlemode or multimode glass fiber?

Compared to alternative cabling systems, fiber optic cables offer numerous advantages - regardless of whether a single fiber type is used or different fiber types are combined. Fiber optic cables, for example, are insensitive to electromagnetic interference and do not themselves cause any electromagnetic interference. While the information on copper wires is transmitted by electrical signals and wandering electrons, on a fiber optic cable light particles (so-called photons) take over this function. Thus, a fiber optic cable allows the bridging of long distances and supports high bandwidths at the same time. At first glance, the different types of optical fiber (singlemode or multimode) differ primarily in the diameter of the core and sheath. But what advantages do singlemode and multimode fiber optic cables actually offer in practice and how can performance and costs be meaningfully evaluated against each other?

Multimode or Singlemode: A comprehensive need analysis is the key to success

The biggest challenge in selecting the right fiber type is to carry out a comprehensive analysis of current and future customer requirements. Fact is: a sustainable and meaningful infrastructure can only be built on a broad understanding of the purposes of a data center. For most data center operators, aspects such as high bandwidth, low or adjusted latencies and various aspects of power management play a decisive role in their decision. Of course, the costs for optical transceivers as well as system and installation costs must also be kept in mind. As data transfer speeds and technologies continue to evolve, structured cabling should always support network infrastructures with data rates beyond the current data rates.

Singlemode: Prices will fall

Until now, parallel optical data transmission in data center cabling was a clear domain of multimode fiber. However, since the length limitations for the common protocols on multimode fibers quickly lead to limitations in the cabling structure, depending on the protocol, with a maximum of 150 meters (IEEE 802.3), the trend - also driven by mega data centers such as Facebook, Google and Amazon and many others - is clearly moving in the direction of singlemode. Singlemode fibers support any future data rate and range, but are still well above multimode cabling in the current cost comparison. However, experts assume that the price difference between singlemode and multimode transceivers will converge in the coming years. The reason for this, in addition to the high demand of mega data centers, is silicon photonics technology, which offers software-configurable access with high bandwidth to computing and mass storage resources and enables the decoupling of hardware and software resources for modularly structured data centers in a software-defined infrastructure (SDI).

Various categories and optical classes have been defined for fiber optic cables to classify performance and maximum bandwidth. Classes OS1 and OS2 exist for singlemode optical fibers and classes OM1, OM2, OM3, OM4 and OM5 for multimode optical fibers. The categories are internationally standardized according to ISO/IEC 11801 and 24702. Single- and multimode cables are not compatible with each other. Within a complete network installation, however, different fiber optic types can of course be used.

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