Multimode optical fibers

Multimode optical fibers (MOF) can be used for multiservice applications, and offer considerable potential for local networks (business, private home, etc.). The majority of intra-building local networks are based on multimode glass optical fibers for high-speed digital applications (10 Gbps) covering distances of just a few hundred meters (< 300 m). What's more, the demand for transmission bandwidth within a local network is constantly increasing, largely due to the explosion generated by the exchange of high-capacity digital data streams (music, video, data files) and the ever-increasing transmission rate. The deployment of the "multiple play" concept through "Fiber To The Home (FTTH)" (data, telephony, TV, video-on-demand, etc.) proposed by the majority of ISPs demonstrates the need for adequate propagation media, i.e. capable of meeting bandwidth and multiservice requirements.

Multimode glass and plastic fibers seem to meet these different needs because, on the one hand, they offer interesting bandwidth capacities at several wavelengths compatible with the optical telecom components (passive or active) available on the shelf. On the other hand, they are easier to handle, and connectivity is less critical than for single-mode optical fibers, whose field of application is more dedicated to long-distance transmissions than to intra-building communications. The great handling flexibility of these multimode fibers makes them an ideal candidate for the development of the "Do It Yourself (DIY)" concept, where each FTTH subscriber would be able to build his or her own fiber network.

The various manufacturing processes for these multimode glass and plastic optical fibers will be presented, with particular emphasis on the performance achieved in terms of linear attenuation and optical bandwidth. Indeed, new multimode glass optical fibers with optimized bandwidth have been created by several manufacturers to meet the demand generated by the transmission of high-speed digital signals (10 Gbps) over distances of less than a kilometer. – Bandwidth Length products (BL) in excess of 6 GHz.km have been obtained for these glass FOMs, and manufacturing processes are now known and mastered to obtain high-purity glass with optimized refractive index profiles. These FOMs offer a good compromise between manufacturing costs and performance. Nevertheless, a new generation of plastic FOMs has emerged with the aim of significantly reducing the cost of fiber optic network connectivity. They use materials that are more flexible and less brittle than glass, at the expense of lower purity. Plexiglas PMMA (PolyMethylMethAcrylate) and CYTOP ^TM (CYclic Transparent Optical Polymer) are the most commonly used materials in the plastic FOM community....