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FIBRE OPTIC CABLING
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With high density panels and ODF ’ s comes the necessity for HD connectors . One of the most popular fibre optic connectors used today is the LC connector . It offers double the density ( being half the size ) of previous connectors ( SC being the main predecessor ). The latest range of LC variants offer features such as uniboot ’ and pull-tabs . The uniboot type of connector uses a single jacketed round duplex cable of approximately 2mm diameter . This type of cable is very compact and very easy to manage in high-density situations . The pull tab LC has an extended tab which allows the operator to connect and disconnect the connector easily ( in high density panels , it is often difficult to gain finger access to the connector body itself ).
channel . The more connections and splices in the channel , the greater the loss will be .
The ideal connection will be a duplex fibre connected directly from one transceiver to another . This will provide no connection losses . However , this is simply not possible in most situations and doesn ’ t provide any flexibility to allow connections to be changed . As ever , the channel design is an area which must allow for flexibility in the connection options ( patching ) and minimum number of connections . The lowest loss and flexible systems will utilise low loss , directly terminated and machine polished connectors . The connector interface is critical to provide good continuity for the optical signal , with minimum losses and reflections . The geometry of this interface must be controlled and is
" Factory pre-terminated fibres not only offer the best performance , but they also decrease the installation time "
Another recent and beneficial feature of some optical fibres is the development of bend-insensitive fibres . Bend insensitivity is available for all fibres discussed here , and is becoming increasingly popular in high-density patching applications , as well as other applications . These fibres tolerate relatively tight bends without causing loss of the transmitted light , resulting in a lower loss channel . This is also a useful feature for the fibres within splice cassettes ( pigtails ). As the cassettes get smaller , the fibre bend radius gets tighter . Over the full channel , which might consist of several cassettes , splices , patch lead connections etc , these losses accumulate .
Working with connections As data rates increase , the allowable loss within each channel becomes more critical , and the limits are being squeezed . This necessitates the use the low loss connectors and fibres , best termination techniques , and generally a design that minimises the number of connections within the only reliably achievable when polished on a good quality PC ( physical contact ) polishing machine and verified using an interferometer . If the fibre cores of the mating connectors do not make full contact due to a poor quality polish , there will be an air gap that will cause a large reflection . Most undesirable , especially in high data rate systems .
Factory pre-terminated fibres not only offer the best performance , but they also decrease the installation time as no splicing or termination is required on site , only final testing . One of the drawbacks of pre-terminated links is the fact that the lengths must be known prior to the installation . This is a problem with some installations , especially those in old buildings where the exact routes are unknown , but in data centres , the routes are well defined . Overlength management is easy to design into the containment to accommodate slack cable as required .
Finally , we mustn ’ t forget that the best performance and reliability is achieved through good design to achieve the lowest losses possible across the channel . This would all be pointless if the connectors are dirty however . The vast majority of problems that affect the performance of the channel are caused by dirt at the connector interface . Dirt will either block the signal completely , or partially , causing high loss and high reflections . Both will interrupt the signal and result in an unreliable connection . Connector cleaning practices are well documented and must be followed . n
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