Top 11 Fiber Questions_Bend_FiberThe Top Fiber Questions blog series is dedicated to answering the most asked questions in the industry. From now until the end of the year, we hope to provide great answers. Most importantly, we’d love for you to ask your fiber questions in the comments below. 

Question:

Can I bend fiber around a sharp corner? 

Answer:

I am a big proponent of bend insensitive fiber (BIF), although I like to call it RBR fiber, or reduced bend radius fiber. Why is that? 

  • It gives great flexibility in the construction of panels and frames, assisting in better cable management.
  • There are clear specifications for the bend radius.
  • With proper testing and use, the RBR fiber provides a more reliable network.

CLICK TO TWEET: A fiber question for you: can you bend fiber around a sharp corner

In the past, we were limited to where and how we placed slack storage. We devised spools up in the overhead tray to keep a large bend radius. Sometimes we’d run patches through different frames to keep the bends out and take up all the slack needed. Now that RBR fiber is rated to a particular standard, there are panels, frames, wall boxes, etc. that can spool the slack right in the unit.  

But does this mean you no longer worry about how to handle slack coils? Does bend-induced loss go away? Do you even bother testing for it? There are still fiber optic glass bend radius standards.  ITU-T G.657.A1 has a minimum bend radius of 10 mm, G.657.A2/B2 at 7.5 mm and G.657.B3 down to 5 mm. With specified bend radii, you need to maintain clean systems with the proper RBR.  There may still be bend loss, but maybe not in the same way as the past. Historically, you would trace the fiber to physically see the bend. With today’s fiber, the bend loss might indicate more of an improper seating of a connector or a routing issue in a splice tray.  

What about testing? One might argue that testing at one wavelength is fine. I believe it is beneficial to test at both 1550 nm and 1310 nm, and compare results. Remember that if 1550 nm loss is higher than the 1310 nm loss, then there is a bend in the system under test. Because of the characteristics of RBR fiber, the bend will be extreme and may help find the bend. There is also a possibility that the bend is occurring within the connector and not visible. Hence, discovering if the loss is bend induced or some other attenuation is critical.  

RBR fiber is a great step in fiber technology that will expand to all parts of the network – even the outside plant. Keep in mind, with proper use and cable management, we should be able to eliminate bend loss through the entire network.

Speaking of OSP: our next topic is how RBR impacts optical time-domain reflectometer (OTDR) readings and splice machine operations. In the meantime, tell us your bendable fiber stories.

About the Author

Mark Winick

Mark Winick has 20 years of experience in the telecommunications field, currently as a principal field application engineer. Before that, Winick spent time on the sales engineer and project systems engineer teams. Specialties include project management, technical training and quality assurance. He graduated from the U.S. Naval Academy with a B.S. in electrical engineering.

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