WCA July 2013

From optical cable to optical wire – an evolutionary approach By Wayne Kachmar, Fellow, Electro-Optical Engineering, TE Connectivity, North Bennington, Vermont, USA Abstract

This article will introduce a new design in optical fibre cable that allows small form factor cables to have handling characteristics that are as good or better than copper wire. Currently, most light guides are housed in cable designs that follow an orthodox design protocol based on one of three basic cable types: loose tube, ribbon or tight buffer. All require very specific handling techniques that require special care and simply cannot be handled the same by installers who are accustomed to handling copper. Yet, the need for a fibre to act more like copper is becoming more and more apparent as cable sizes decrease and applications, such as central offices, data centres, enterprise, and fibre-to-the home/desk (FTTH/D), demand more fibre density. A fibre cable with the behavioural characteristics of a copper cable will improve installations in terms of time, flexibility and cost. 1 Introduction Many new optical fibre cable developments have occurred in the recent past, such as reduced bend radius fibre (RBRF), nano-composite material fillers, new materials for strength, connector technology, new regulatory compliance issues (RoHS, REACH), and size/ cost constraints. During this time, cable design solutions assumed fibre-optic cable to be a composite product where separate elements (tight buffered fibre, aramid yarn polymer jacket) were not bonded. Therefore, different handling and installation requirements were mandated based on a non-coupled core structure. In many cases, installation stresses were overcome by sheer bulk or material strength. Many analogue comparisons to copper have been made in the cable world. Other than speciality products, such as guided torpedo fibres, no true optical analogues to wire have been developed. Typically, cables contain one or more insulated conductors and additional structural elements to achieve mechanical, environmental or other performance criteria. To date, most optical fibre designs use a “loose core” to achieve engineered performance in an optical cable – even single fibre cables that require minimal protection. The result is that many designs require installation handling different from traditional copper cable installations. Many failures are a direct result of installer unfamiliarity with the special handling required by traditional indoor simplex or duplex fibre cables. Thus, the need for a fibre to act more like copper in terms of handling is important as fibre

Conventional 1.6mm optical patch cord with Aramid yarns

1.2mm optical ‘wire’ Aramid tape strength member

❍ ❍ Figure 1 : 1.2mm vs conventional 1.6mm

adapts to use in applications where copper once was king. There is a perception by many installers that fibre can be handled and installed using the same methods as its copper predecessor. However, glass is still glass, and the performance of traditional fibre cable can still be affected by improper handling and installation. So, why does this perception matter? In today’s environment, optical system solutions are being provided to a much broader selection of customers. Many of these installation professionals have significant experience with copper installation practices. Yet they are, for the most part, unfamiliar with the installation practices of the fibre cables they are now being asked to install. Thus, it is incumbent on fibre cable manufacturers to educate them on acceptable handling practices. More importantly, to improve the acceptance of optical fibre systems in new applications, we must provide products that will succeed under new criteria. In terms of optical fibre cable, we must design products that behave closer to copper insulated wire in fibre cable handling, placement and management. New optical waveguides have made this option viable, but we as cablers need to continue the evolution and design installable “cables” (wires) that meet customer needs and define a new class of optical waveguide product. The design presented here is a geometric core design whereby the optical fibre is located in the centre of the core and loose yarns have been removed in place of geometric strength members. These strength members provide multiple functions, such as outer jacket adhesion (to assist with hand pulling), fibre buffering (against impact and crush loads) and reliable access to the optical fibre for fusion splicing or field connectorisation.

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