Tips to minimise insertion loss in optical fibre connections

Unlike copper wire, optical fibre rarely requires amplifiers. The light signal is transmitted down the central core, which is wrapped in a reflective layer to create what is known as total internal reflection. However, whether installing optical fibre networks to the home, to the antenna, to the server room or any other application, network engineers can face the challenge of various types of insertion loss, or weakening of the optical signal, which is measured in decibels.

For high quality single mode fibre, loss should be as low as 0.1 dB/km. However, it’s impossible not to incur some degradation of signal over the full length of the network connection. Here are some of the ways you can limit insertion loss when using fibre optic connectors:

1.Polish and clean the ends
A rough cut can result in a scattered signal and may also trap dirt particles around the edges. As the fibre is hair-thin, even airborne dust particles can scatter and absorb light signals. After cutting with a cleaving tool, polish the ends with a professional polishing kit and wipe with a lint-free isopropyl alcohol wipe, ensuring that your skin never touches the end of the ferrule.

2. Minimise end gaps
In an optical fibre connection, if there is any gap between the two fibres this can cause the emerging cone of light to be refracted by the air, thereby causing losses in the signal. Ensure that the fibres are not cleaved at an angle, and that the connecting fibres are lined up perfectly without any gaps.

3.Connect the same size fibres
As there are several different types of optical fibre available on the market, it is possible that you may need to connect two different types together in a network at some point. If you connect a small fibre to a larger one, the losses resulting from this will be minimal, but a large fibre should never be connected to a smaller one, as this will result in substantial losses due to the difference in core size and the numerical aperture of most small core fibres.

4.Avoid unnecessary bending
Bending of fibre optic cables is a major cause of insertion loss due to light refracting through the cladding. Optical fibre cables can quite easily become coiled or kinked during installation, and each small bend or coil can cost a loss of up to 0.2dB. Minimise tight bends and if the cable must be coiled, keep the radius as large as possible.

5.Protect the connection
If your connection is going to be in any way exposed to dirt, water, salt spray high/low temperatures, or any type of shock, it’s essential to consider the best way to protect the safety of the optical fibre connection. This could be done with a purpose-built box to protect the connection, or with a high-quality rugged connector housing with a secure locking mechanism that will protect the interface from ingress. Bulgin’s 4000 series fibre range of rugged LC connectors are specially engineered to keep fibre connections protected from any kind of environment. Featuring a secure quick-twist bayonet connection, the 4000 Series is IP68 rated and offers an average insertion loss of <0.1dB.

Courtesy of Bulgin.