Fibre Optic Cable - Bend Radius.

A Fibre Optic Cable Bend radius is the maximum level of bending that a cable can take before it is permanently damaged or the bandwidth performance is limited.

If you bend a fibre cable too much, the optical signal within can refract and leak through the cladding.

Besides, bending also causes permanent damage like micro cracks.

The decrease in performance is also known as bend loss, a loss of signal strength.

Bend Radius exceeded


Minimum Bend Radius of Fibre Cable

The smallest possible radius for a fibre cable to be bent around is also its minimum bend radius.

ANSI/TIA/EIA-568B.3 sets performance specifications, which is also the new standard, allowing maximum pulling tensions for 50/125-micron and 62.5/125-micron fibre cables.

 How to Calculate the Minimum Bend Radius of Fibre Optic Cable?

The allowable bend radius varies depending on:

- type of optic cable

- Tensile load - the condition of the cable under stress during installation 

- the condition of the cable once reset (no-load) after installation,

- the outside diameter or OD.

Allowable Bend Radius = Cable Multiplier x Cable Outer Diameter

The cable multiplier entirely depends on the cable type and industry standards and are typically referred to as short-term and long-term bend radius.

- Short-term bend radius – This is the maximum bend whilst installing. It is the larger of the two bend radii.

- Long-term bend radius – This is the tightest recommended bend after installation and is the smaller of the two.


What is Bend Insensitive Fibre Optic Cable?

A Bend insensitive fibre patch cable is designed to transmit light with as little loss as possible when bent beyond the standard bend radius of a cable.

BIF (Bend Insensitive Fibre) uses a ring of lower index of refraction material which is basically an optical trench to reflect the lost light back into the core.

Data centres and other establishments with space constraints primarily make use of this technology.

In comparison to traditional fibre optic cables, bend-insensitive fibre is suitable for demanding environments by offering greater flexibility.

BIFs come in 50/125 MMF (OM3 and OM4) and 9/125 SMF versions.

Different Types of Bend Insensitive Fibre Optic Cables

Bend Insensitive Single-mode Fibre Optic Cable (BISMF)

Bend-insensitive single-mode fibre optic cable was first introduced in 2007.

It can sustain more stress like stretching, bending, and twisting without much degradation in performance.

According to ITU recommendation G.657, there are two types of bend-insensitive fibre optic cables: G.657 A and G.657 B.

Whilst the glass is exactly the same between A and B, it is only the cable construction that makes it A or B.

* A is Tight Buffered (Indoor typically)

* B is Loose Tube (Outdoor typically).

They are much more flexible than their traditional counterparts.

This makes it possible to install BISMF cables in today’s increasingly data-oriented centres with different installation methods.

Bend Insensitive Multimode Fibre Optic Cable (BIMMF)

BIMMF is popular in both intra-building backbones and data centres.

It meets the demand for increased quality, connectivity, and performance.

The new series of BIMMFs offer minimum bend-induced attenuation, which comes in handy for minimizing system downtime while increasing reliability.

Bend insensitive multimode fibre optic cables come on all laser-optimized grades: OM2, OM3, OM4 and OM5.

They also feature 10 times less signal loss even when bent.


One word of advice is to always make sure you do not exceed the bend radius of any optic cable. Adhere to this plan and you are well on your way to a very successful fibre optic installation.