Network-Passive

Why not use Bend Insensitive (BI) Fiber Cables for enterprise applications?

With Fiber To The Home (FTTH/x) becoming a popular method to access high speed broadband connections, Bend Insensitive (BI) Fibers are being commonly used for the FTTH/x access networks. Basically, Bend Insensitive Fiber Cables can perform well even if they are bent beyond their recommended bend-radius, during the installation/ maintenance. But why not use Bend Insensitive fiber cables for enterprise applications as well?

Bend Radius and Normal Fiber Bending/ Stapling Issues:

Fiber Cable Manufacturers generally specify a certain bend radius (30 mm, for example) for their Fiber Optic cables. You can take a geometrical compass and draw an arc with radius of 30 mm. When you install fiber cables, you are not supposed to bend them beyond the curve visible in the arc. If you do, there may be fiber optic losses (when optical signals are transmitted through it) as some light near the outer part of the fiber core might get coupled from the core into the cladding (Core is the innermost part of fiber cable where light travels while cladding is the protective layer that surrounds the core).

If you staple the thin indoor fiber cable(s) tightly around a rack/patch panel, that might lead to long term performance degradation (data loss) / fiber damage.

What are Bend Insensitive (BI) Fiber Cables?

Bend Insensitive (BI)/ Bend Tolerant fibers introduce certain optimizations in the fiber manufacturing processes that make them transmit light with minimum loss even if they are bent beyond the bend-radius (like 90 Degrees or wound around an iron rod, for example).

In these fibers, an optical trench (a protective coating) is built using a lower refractive index material around the core so that the light that tries to go out of the core (due to heavy bends) can be reflected back in, thereby minimizing data loss. Other factors like core diameter, right wavelengths (longer wavelengths being more sensitive to stress/bending), Single Mode (or) Multi Mode, etc are optimized to minimize the losses due to excessive fiber cable bends during installation/ maintenance.

Advantages of Bend Insensitive Fiber Cables:

* Fiber Cable installation errors due to steep cable bends (inside patch panels, racks, entrance/ exit points, etc) can be avoided.

* Patch Cords could benefit greatly due to bend insensitive fiber because the chances of heavily bending patch cords during installation/ maintenance is very high.

* Higher bandwidth applications can be confidently deployed using bend insensitive fibers as accidental excessive bending of fibers does not cause much of performance degradation.

* Bend Insensitive fiber cables are very useful for indoor fiber cable installations as they can now be taken around walls, pillars, ceilings, ducts, and other uneven surfaces within the buildings without worrying about excessive fiber bends.

* Bend Insensitive fiber cables can be spliced using the same methods used for normal cables and their splice performance could be measured using OTDR (Optical Time Domain Reflectometers), just like normal fiber cables.

* The normal fiber connectors and accessories are compatible to be used with bend insensitive fibers (Mostly).

* Bend Insensitive fibers also show a great deal of resilience in situations where fibers are fixed to surfaces using clamping, tie-wrapping or stapling.

* The cost of manufacturing bend insensitive fibers are not very high when compared to the cost of manufacturing normal fiber cables.

There are some disadvantages of Bend Insensitive fibers like incompatibility with regular fibers (especially in the case of multi-mode fibers), higher sensitivity to bends at higher wavelengths (like 1625 nm) which are being increasingly used, lack of application in outdoor fiber cables that have long straight runs, etc.

You can also read a nice article on Bend Insensitive fibers by the Fiber Optic Association.

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