HSdataline are specialists in the design and installation of Fibre Optical network cabling systems.
Optical Fibre Choices
Glass
Optical fibres are comprised of a core and cladding of differing refractive indices. A core of high refractive index is surrounded by a cladding layer of lower refractive index. This difference forms a boundary, which constrains most of the light within the core by the phenomena of total internal reflection. In general there are two types of optical fibre, Singlemode and Multimode.
Singlemode Fibre Optic
This typically has a core diameter of approximately 8um. Above its cut off wavelength, a single mode is transmitted down the fibre. This approach effectively eliminated intermodal dispersion, but with 'bandwidth' is none the less limited by second-order effects such as intramodal dispersion. The combination of huge bandwidth and low attenuation makes singlemode fibre the preferred option for telecommunications systems world-wide. However, singlemode fibres require lasers, producing low numerical aperture light, in order to achieve an effective launch into the fibre. It is the high cost of these devices that has, until now, limited the use of singlemode fibre within LAN's.
Multimode Fibre Optic
Multimode fibres on the other hand, have much larger core diameters, typically 50 or 62.5 um. This effectively permits many modes to be transmitted along different paths down the fibre. Modern graded index multimode fibres have a complex optical core manufactured so that the refractive index varies in a controlled manner, from a high central axis to a lower refractive index material at the outside of the core. Careful design of this profile optimises the transmission characteristics of the fibre. As a result, it is the most commonly used fibre in LANs and premises cabling because the larger core diameter makes if simple to terminate and ideally suited to LED (light Emitting Diodes) sources with their high numerical aperture launch conditions.
Plastic Fibre Optic
Plastic fibre has long held the promise of very low cost and easy termination. To date, however, nobody has been able to demonstrate a plastic fibre, at an affordable price, with the distance and bandwidth performance of Category 5 copper cable, let alone any silica glass fibre.
There is a wide range in performance of optical fibres available on the market today ranging from the low cost, low bandwidth so-called 'data grade' fibre up to the high quality, well proven product such as the MillenniuM brand. There is a significant risk that lower grade products will not be capable of providing the performance envelope demanded by the latest standards.
