Design considerations for fibre optic connectors

Fibre optic cables are used in favour of copper cables because they have higher bandwidth and a larger capacity for carrying data. Furthermore, data can be transmitted over longer distances using fibre optic cables and these are immune to electromagnetic interference.

Challenges arise when you need to connect your cables together or to other electronic devices. Yes, fibre optic connectors make reconfiguring systems a lot easier, but they can also introduce losses, or attenuation, at each connection point if the fibre is misaligned.

Losing light signal power

Attenuation is the reduction in light signal power caused by reflections in the fibre core density and is most common when the signal is transmitted through connector surfaces. To reduce attenuation, manufacturers need to carefully consider every part of the connector design, including the materials of the connector components.

Most modern fibre optic connectors use pre-radiused, polished ceramic ferrules because manufacturers can create a closer fit and a smoother transmission of signals. The polish can also prevent dust and debris build up at the terminal. This, coupled with fibres being closely aligned, means less light is lost and attenuation at the connection point is reduced.

However, there’s no escaping dust and debris in some environments. This is why many fibre optic connectors for use in military and industrial applications, like the Amphenol FSI MIL-83526 expanded beam, are designed to expand and collimate the optical signal through the connector. Larger beam diameters will improve insertion loss performance in the presence of dust and debris.

Connector material isn’t the only design consideration at play here. Manufacturers and connector suppliers must also consider the quality of termination and whether the connector is single or multimode.

Singlemode or multimode?

Singlemode systems, because of their narrow fibre cores, offer a much higher bandwidth and lower attenuation compared to multimode systems. Typically, singlemode cores are between eight and ten micrometres in diameter and the core is made to tighter tolerances. This eliminates intermodal dispersion and, as a result, greatly increases bandwidth. Singlemode fibre is also often more affordable because less material is used in the core.

Installation costs for singlemode fibre can mount up however because the laser light sources are more expensive than LEDs and VCSELs used for multimode systems. Higher precision connector termination techniques are also needed for singlemode fibre due to the narrower cores.

Choosing a trusted connector supplier is crucial to guaranteeing high-quality, high-speed fibre optic cables and connectors. Available for both single and multimode systems, the Sure-Seal fibre optic patch cord and pigtail range supplied by PEI-Genesis undergoes three levels of factory testing to optimise light signal transmission. These include insertion loss and return loss measurement, to minimise attenuation. Ferrule geometry is also measured to check that connector termination has been carried out correctly.

Maintaining fibre integrity at termination

To terminate a connector, the outer jacket of the cable is stripped back to expose some of the Kevlar for strain relief in the termination. Most ferrules will have a stripping template to ensure correct lengths are maintained. It’s important that a small amount of fibre can protrude from the end so light signals can be transmitted.

If termination isn’t carried out correctly, too much light will be lost, and a reliable network connection won’t be maintained. Manufacturers must also be mindful of micro and macro bending, which both increase the chances of attenuation and are common when a connector has been poorly terminated.

PEI-Genesis can support customers in customising and configuring the connector and cable assemblies to support high-speed network communications across a variety of critical industries. Both Sure-Seal and Amphenol connectors are built for longevity, meaning customers are guaranteed long-term, future-proofed performance.