Singlemode means that the fiber allows one type of light mode to be spread at a time. On the other hand, multimode means that the fiber can spread more light modes at a time. The differences between singlemode and multimode are mainly in the fiber core diameter, wavelength and light source, bandwidth, color and distance.
Core diameter
Singlemode fiber cables have a much smaller core diameter than multimode. The typical core diameter is 9 µm for single mode and usually 50 µm and 62.5 µm for multimode. This means that it can have higher “light collections” and simplify connections. The dressing diameter for single mode and multimode is 125 μm.
The attenuation of multimode is higher than singlemode due to the larger core diameter. The fiber core of the singlemode cable is very narrow, so the light that passes through these fiber optic cables is not reflected as many times, which keeps the attenuation to a minimum.
Wavelength and light source
Due to the larger core diameter of multimode fiber cables, some affordable light sources such as LEDs (light-emitting diodes) and VCSELs (vertical cavity surface-emitting lasers) operating at 850 nm and 1300 nm wavelength are used. Singlemode fiber cables often use a laser or laser diodes to produce light injected into the cable. And the usual fiber wavelengths are 1310 nm and 1550 nm.
Bandwidth
Multimode fiber bandwidth is limited by light mode, and maximum bandwidth is currently 28000MHz * km for OM5 fiber cables. While fiber bandwidth in a single mode is unlimited theoretically because it only lets one light mode pass at a time.
Color outer coat
According to the standard definition TIA-598C, for non-military applications, single mode cable is coated with yellow outer sheath, and multimode fiber cables are coated with orange, lime, magenta or aqua color.
Distance
It is known that singlemode fiber is suitable for long distance applications, while multimode optical fiber is designed for short distances. When it comes to single mode vs. multimode fiber spacing, what are the quantifiable differences?
Single mode fiber distance is much longer than for multimode fiber cables at data rates from 1G to 10G, while OM3 / OM4 / OM5 multimode fibers support a higher data rate. Because multimode optical fiber has a large core diameter and supports more than one light mode, the fiber spacing is limited by modal scattering which is a common phenomenon in multimode step index fiber. While singlemode fiber is not. That is the essential difference between them. In addition, OS2 single mode fiber can support longer distances in 40G and 100G links.
FAQ: Frequently Asked Questions
As mentioned above, singlemode and multimode fiber optic cable have their advantages in terms of cost and installation. It is not the case that single mode optical fibers are better than multi mode, or vice versa. It is important to choose the one that best suits the installation in terms of distance, speed and core diameter.
The answer to this question is no. Multimode fiber and single mode fiber have different core diameters, and the number of light modes they send is also different. If you mix the two fibers, or connect them directly together, this leads to a large optical loss, which results in a link fluttering or being down.
In general, the answer is no. Large optical loss will occur if a multimode transceiver is connected to single mode fiber. However, the opposite will work. For example, 1000BASE-LX single mode SFP can operate on multimode fiber cable by using mode conditioning fiber cable. Sometimes fiber mediaconverters can also be used to solve such problems between single mode receivers and multimode transceivers.
When making a decision between single mode and multimode fiber cables, the first factor you should consider is the fiber distance you actually need. For example, in a data center, multimode fiber cables are enough for a distance of 300-400 meters. While there are applications that require distances of up to several thousand meters, single mode fiber is the best choice. And in applications that can use single mode and multimode fiber, other factors such as cost and future upgrade requirements should be considered before choosing.
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