Single-mode fiber is a common type of optical fiber that is used to transmit over longer distances. It is one of the two optical fiber types, the other being multi-mode fiber. A single-mode fiber is a single glass fiber strand used to transmit a single mode or ray of light.
Single-mode fiber features only one transmission mode. Compared with multi-mode fiber, it can carry higher bandwidths; however, it needs to have a light source having a narrow spectral width.
Single-mode fiber is also known as a single-mode optical fiber, uni-mode fiber, mono-mode optical fiber and single-mode optical waveguide.
Techopedia explains Single-Mode Fiber
Single-mode fiber provides users with a greater transmission rate in addition to nearly 50 times longer distance as opposed to multi-mode fiber. However, single-mode fiber is more expensive than multi-mode fiber. Among all the differences between single-mode and multi-mode fibers, the most basic is the size difference in the fibers’ core as well as the associated loss or attenuation and fiber bandwidth.
The optical fiber itself includes three fundamental parts: the core, the cladding and the coating or buffer. The most central part of the optical fiber is the core. This is the place through which the light travels. The core of single-mode fiber is much smaller than that of multi-mode fiber. There are three fundamental diameter sizes for fiber cores.
Single-mode fiber features a core diameter of nominally 9 µm, whereas multi-mode fiber often features a 62.5-µm or 50-µm core diameter. The small core, coupled with a single light wave, eradicates any distortion caused by overlapping light pulses, offering a minimal signal attenuation plus the highest transmission speed.
In contrast, multi-mode fiber provides users with high bandwidth at high speeds across moderate distances.
It is not advisable to mix and match fibers. If you try to connect a single-mode fiber with a multi-mode fiber, it may result in a 20-dB loss, which is 99% of the total power.