Difference between Single mode & Multimode Fiber Cables
Fiber optics are essential for building the most capable networks, but when making design choices, there are plenty of options that serve fiber optics in general. One of the primary choices available to any network engineer exists between single-mode fiber and multimode fiber.
These are physically different approaches to fiber optics communication, and as such, they offer different strengths and weaknesses. To effectively choose the right design for your network, it helps to have a better understanding of what separates these types of cables.
Single Mode Fiber
Single-mode fiber is aptly named. It’s a fiber optics design that only allows a single light mode to transmit through the cable at a given time. This provides a few trade-offs in performance. Single-mode fiber has less attenuation, and that allows the cables to span longer distances without suffering significant losses. Attenuation is measures the ammount of light lost between input and output of the fiber.
Meanwhile, single-mode fiber is often more expensive than multimode for equipment and installation costs. It also doesn’t serve the highest data rates that can be reached by multimode fiber.
To better understand what makes single-mode fiber special, we can look at the design essentials and common use cases for this type of fiber optic cabling.
There are two defining attributes to single mode fiber that largely determine how and why it does what it does. Those two attributes are the small core and the single light mode. The small core is usually 9 micrometers wide. Because of this, most single-mode fiber designs require laser diodes to create the light signals within the fiber system.The typical wavelengths used are 1310nm and 1550nm. These signals are housed inside a fiber cable that is sheathed in yellow as a standard. The signals can maintain multi-Gigabit speeds, and single-mode networks can run up to 10km in distance.
Because only one mode is used in the cables, there is very low attenuation. This is what makes them so effective at long ranges, and with no theoretical limit to bandwidth, single-mode fiber will stay in use for the foreseeable future.
Ultimately, single-mode fiber is all about long-distance networks. Since it can handle transmissions across multiple kilometers, single-mode is ideal for uses that need to span such distances.
You will see it deployed for campus-wide networking. It’s essential to metro access networks and submarine networks. As single-mode components can cost quite a bit more than multimode components, distance is usually the justification for using the more expensive equipment.
As the name implies, multimode fiber supports multiple light modes for simultaneous transmission. This allows it to pack more information in a single cable, giving it higher maximum data transmission rates. But, the multimode design allows for more attenuation, and that prevents it from spanning the same distances as single-mode fiber.
Multimode fiber components typically cost as much as or less than single-mode counterparts. This makes multimode fiber preferable when all other considerations are equal.
Multimode fiber is much wider than single-mode. Typically, the entire fiber is 50 micrometers or 62.5 micrometers. Because of this width, it’s common to use LEDs or VCSELs for the light source, and that is a large part of what makes multimode equipment less expensive.
Additionally, multimode fiber runs at 850nm or 1300nm with a maximum bandwidth of 28GHz. The standard sheath colors are aqua and orange.
Ultimately, multimode fiber is capable of higher data transmission rates than single-mode, but the cable runs can’t handle extreme distances. Most multimode fiber networks have a maximum run that is less than 500 meters (although exceptions do exist).
When It’s Used
The average cost of multimode fiber is less than single-mode fiber, so it shows up in more applications. More importantly, the higher maximum data rates make multimode fiber ideal for networks that serve the highest demands.
Multimode is common in data centers and other large-data systems. It serves high-capacity buildings that don’t require multi-kilometer runs. Smaller campuses would constitute additional common use cases for multimode fiber.
One more note on using single mode vs multimode, the type of fiber you are using, single or multi, will determine the type of fiber transceiver you will need to use. The same transceiver type cannot be used for both modes.
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