What is Fiber Optic Bend Radius: A Beginner’s Guide

Perhaps you have heard much about the bend radius when attending mathematics courses. This article will emphasize fiber optic bend radius to ensure the longevity and efficiency of optic cables during their installations.

What Is Fiber Bend Radius?

You may know how physical objects, including poles used for sports competitions, bend in our daily lives. When athletes make their jumps against the poles, the poles bend slightly or sharply. The curvature is the very parameter measuring how sharp the poles bend. The same holds for the optical cables.

Bend radius, which measures the inside curvature of the cable, is the minimum radius installers can bend optical fibers without damaging their performance. It is a vital parameter that enables installers to guarantee that fiber optic cables are efficient and durable.

Bend Radius vs Diameter vs Minimum Bend Radius

Another two terms we urgently need to understand are the diameter and minimum bend radius. Because the bending of fiber optic cables might cause certain damage, the curvature should not be too slight. The minimum bend radius under pulling tension should typically be 20 times the diameter of fiber optic cables. However, it had better be 10 times the cable diameter. We can see the above terms more vividly in Figure 1 and Figure 2.

  Diameter = 2 X Radius

The diameter defines the circle’s width, and the radius is the distance from the center to the edge of the circle.

Critical Bending Radius

In terms of optic cables, we should carefully consider one crucial factor: the critical bending radius. This term refers to the extent to which light leaks out of the optical fiber. The critical bending radius is usually nearly 8 times the diameter of the optic cable. Depending on different fiber types, fiber lengths, and the cladding, the critical bending radius should change accordingly.

Singlemode Fiber Bend Radius

Singlemode fiber has a relatively higher critical bending radius than multimode fiber. The reason is that singlemode fiber possesses a smaller core, and pure glass constitutes its primary material. In consideration of this attribute, singlemode fiber has a higher bending resistance.

Although the minimum bend radius for singlemode fiber is approximately 20mm, we suggest that you make some inquiries with fiber optic manufacturers so that the appropriate bend radius can be found for your singlemode bend-insensitive fiber.

Multimode Fiber Bend Radius

Since multimode fiber has a much larger core than singlemode fiber and glass-clad materials are utilized for its manufacturing process, this kind of fiber shows less bending tolerance. Ideally, the minimum bend radius for multimode fiber should be about 30mm.

Calculation of Fiber Optic Bend Radius

You may wonder how we can calculate fiber optic bend radius, and precisely, this is also a significant concern for us. Most fiber cable providers tend to offer you the exact bend radius, and sometimes, if they do not provide one, you must grasp the calculation method. Now, some explanations will be intended for you.

According to ANSI (American National Standards Institute), many factors can influence the precise bend radius, including pulling tension, tensile loads, fiber types, cladding materials, and outside cable diameter.

The exact bend radius of fiber optic cables can be determined much more easily with the specific calculation formula:

  Bend Radius = Cable Outer Diameter x Cable Multiplier.

If you still have some difficulty in handling this calculation process, we will cite one example to help you better understand.

For example, when the fiber optic cable has a 3mm outer jacket, the bend radius is 3mm X 10 = 30mm. This is because the bending radius is ten times the equivalent of the cable’s outer jacket diameter.

Why Fiber Optic Bend Radius Counts

Apart from temperature and humidity, the minimum bend radius is a paramount factor in traditional fiber optics installations. These three factors play an essential role in lessening data bend loss and attenuation.

The following four aspects will give you a clear understanding of why fiber optic bend radius matters.

Protect Optic Fiber Integrity

The critical component of a fiber optic cable is widely thought to be the optical fiber core, which is usually just roughly 125 microns in diameter. If the bend radius is minimal, the fiber core may not withstand high stress and tends to become deformed. The optical fiber can even potentially be broken, which undermines the optical properties in turn.

Avoid Optical Singal Transmission Loss

When installers bend fiber optic cables during their installations, their cables more or less suffer from bending loss, thereby decreasing the optical signal power. Provided that the bend radius is excessively small, there comes a more significant increase in bending loss. If this happens, it may severely influence the signal transmission quality.

Guarantee Reliability and Long-term Stability

The fatigue process of optical fiber tends to gain acceleration due to excessive bending. In the meantime, higher bending always amounts to the shorter lifespan of fiber optic cables. So, adherence to proper or recommended bending radius is helpful in the improvement of the cable’s reliability and long-term stability.

Conform with International Standards

A variety of international standards apply to the bending radius of fiber cables. Consequently, conformity with these standards can ensure that the cables are safe and compatible.

Advice on Fiber Optic Cable Protection

If the optical cable bends exceed the minimum bend radius, light signals might leak out, drastically increasing insertion loss (i.e., attenuation) and degrading transmission performance. Exceeding the minimum bend radius can also break the fiber’s glass. Here, we provide some valuable tips for protecting fiber optic cables.

• Never try to twist the fiber optic cables
• Less repetitive reflexing of the cables
• Lower the pulling tension of fiber optic cables
• Adhere to international cabling standards and requirements
• Ensure that the minimum bend radius is 20 times the cable diameter when pulling the fiber cable

Conclusion

This article can serve as a beginner’s guide on how to interpret the fiber optic bend radius. It can also teach you how to choose the proper bend radius when installing your cables. In addition, the importance of fiber optic bend radius is explained in detail. In order to guarantee the durability, stability, and efficiency of fiber optic cables, some valuable advice is also intended for your reference.

References

• https://en.wikipedia.org/wiki/Bend_radius
• https://www.essentracomponents.com/en-us/news/solutions/wire-cable/fiber-optics-faqs-the-advantages-bend-radius-explained-and-more