What Is Fiber Optic Cable Bend Radius and Why Does It Matter?

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Fiber optic technology allows us to take calls and send instant messages around the world in a fraction of a second. As the backbone of our global internet infrastructure, fiber optic cables rely on light beams rather than electric transmission as a faster and more reliable alternative to copper-based wiring systems. But fiber optic cabling is also known for being fragile. So, what happens when fiber cables bend or become damaged?

How are fiber optic cables made? 

Let’s start by discussing exactly how fiber optic cables are made. The core of this cable type is made from pure glass fibers which will vary in quantity depending on the quality of cable you’ve chosen. Cladding surrounds the core, with a lower refractive index than the core itself. This difference in refractive index allows light to travel down the fiber optic cable without escaping.

To protect the glass core and cladding, fiber optic cables are typically surrounded by a buffer coating made from either acrylate or UV-cured urethane. The buffer helps to protect the fragile inner components of the cable from damage. It also makes the cable more flexible and easier to handle.

Why do fiber cables need to bend?

The nature of any cable installation project means you’ll often want to bend the cables into position during routing. Perhaps you’ll need to weave them behind furniture, or lay them between a router in your building and a conduit beneath the ground. It’s unlikely that your fiber optic cables will be laid in straight lines during installation and often you may need to bend them as part of your cable management. 

But as we know, fiber optic cables are constructed from glass and are fragile. So, what are the implications of bending them into place during cable assembly?

Can fiber cable be bent? 

fiber optic cabling

Yes, you can bend fiber optic cables during the installation process. This is particularly useful if you’re pulling the cables into place rather than blowing them. But you can’t bend your cables indefinitely and you’ll need to know the maximum pulling tension before damage occurs. The extent you can bend your cables by is known as the fiber optic bend radius.

Fiber optic 90-degree bend 

A common measurement you may come across is the fiber optic 90-degree bend radius. This refers to the angle at which the cable can be bent before becoming damaged.

If you imagine a garden hose, if you kink it too much, the water flow will be reduced or stopped completely. The same goes for fiber optics; if you bend or swivel it too sharply, the light flow will be reduced. There are a few ways to reduce this.

  • Optical fiber loopback – this device allows for signals to be sent and received in the same direction without any data or signal loss due to bending.
  • Optical fiber tap – this helps to monitor the light passing through the fiber without interrupting the data flow.

Why is fiber optic cable bend radius a concern? 

Light can leak out of micro cracks in the cladding of the fiber if it’s bent too sharply, causing data loss, and attenuation. In some cases, this can lead to complete failure which is why it’s critical to be aware of the bend radius when you’re installing fiber optic cables.

But while bend radius is important to consider, it’s also important to keep in mind other factors affecting data loss.

  • Temperature can cause the fiber to expand or contract which can lead to microbending. This is when the fiber is bent so slightly that it’s not visible to the naked eye but it can still cause data loss.
  • Humidity can also affect how light travels through the fiber. When water droplets are present, they can act as a lens and refract the light. This can cause data loss too.

Bend radius is just one of many factors to consider in fiber optics. But it’s an important one to keep in mind, especially if you’re working with long lengths of fiber optic cable.

What is the maximum bend radius of fiber optic cable? 

Bend radius is the measurement of how much a cable can be bent before it becomes damaged. Your cable will usually have different specifications for how much it can be bent depending on the tension and load applied to the cable. These measurements will vary but the larger the bend radius, the better. This is because it gives you more flexibility when it comes to installation and it also reduces the risk of damage.

What is the critical bending radius of optical fiber? 

The critical bending radius is the point at which light starts to leak out of the fiber. This is usually around eight times the diameter of the cable but it can vary depending on the type of fiber and the cladding.

Single-mode fiber bend radius 

Single-mode fiber has a higher critical bending radius than multimode fiber. This is because single-mode fiber has a smaller core and is made from pure glass. This makes it more resistant to bending.

The minimum bend radius for single-mode fiber is around 20mm but it’s recommended you check with your cable manufacturer to find the exact bend radius for your single-mode fiber cable. 

Multimode fiber bend radius 

Multimode fiber has a larger core than single-mode fiber and is made from a glass-clad material, making it less resistant to bending. The minimum proper bend radius for multimode fiber is around 30mm but, as with single-mode fiber, always check with your manufacturer first. 

Fiber optic bend radius calculator 

fiber optic cabling

The precise bend radius as defined by ANSI (American National Standards Institute) will depend on factors including: 

  • the pulling tension
  • the tensile load
  • the cladding material
  • type of fiber
  • the cable’s outside diameter.

Often the bend radius will be provided by your cable manufacturer. If not, you can use a simple formula like this as a rule of thumb to calculate the minimum acceptable bend radius.

Bend Radius = Cable Outer Diameter x Cable Multiplier. 

This will give you the recommended bend radius for the fiber cable without damage occurring. 

Fiber optic cable repair 

Unfortunately, though, fiber optic cables can become damaged and may not always be under warranty. If this is something you’re experiencing, The Network Installers are experts in the speedy repair of your cables. 

Get in touch and we’ll conduct a survey to analyze the extent of the damage to your fiber network. You can expect us to use tools such as an Optical Time Domain Reflectometer, fiber optic cutters, strippers, and fusion splice equipment to fully restore connectivity in rapid time.

Contact The Network Installers 

Whether you need us to install a patch cable for your fiber optic network, or splice your cables together, The Network Installers will provide the best solution for your business. 

Contact us today if you have any queries about fiber optic cable bend radius or need assistance with installation or repair work. 

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The Network Installers is a low voltage electrical contractor that provides data cabling, network installation, fiberoptic installation, and WIFI installation. We've been serving commercial customers since 2008 with exceptional quality, consistency, and professionalism.


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