ClearCurve
From Wikipedia, the free encyclopedia
ClearCurve is Corning's brand name for a new optical fiber that can be bent around short-radius curves without losing its signal. It is constructed with a conventional fiber on the inside, surrounded by a cladding containing a new nanostructured reflector. ClearCurve is hundreds of times more flexible than conventional optical cable, transmitting high-quality signals even when wrapped around small objects like a pen, where a conventional cable would lose the signal completely.
Although originally introduced to serve the needs of pulling fiber in apartment buildings and other high-density units where conventional fiber is too inflexible, in 2009 Intel announced their intention to use it as the basis of a new computer interconnect system code-named Light Peak. ClearCurve's small size and high bandwidth capabilities offer great improvements over existing copper wiring in this role, and Intel is positioning Light Peak as a truly universal bus that can carry any existing traffic over a single cable.
Conventional fiber
Conventional optical fiber consists of a thin inner cylindrical core of glass or plastic with a similar material layered in a thin coating around it. Slight differences in the index of refraction between the two layers causes total internal reflection, trapping a light beam inside the inner core. This process is limited to a critical angle; when the light beam approaches the interface at a shallow angle most of it will be reflected, but as it gets closer to the critical angle more and more will travel through the interface and be lost.[1]
The critical angle depends on the relative difference in index of refraction, larger differences will increase the critical angle and trap more light. However, changing the index of refraction in most materials generally changes its mechanical properties too, which means that different types of cables are used for different purposes. Cables intended to be highly efficient over long runs are generally less flexible, while those that require higher flexibility are generally only useful for shorter distances. Even cables designed to be flexible, like TOSLINK, are less flexible than a similar sized braided copper cable.
To keep the fibers as straight as possible, most high-performance optical cables use a form of armour that resists tight bending. This is normally a helical winding, similar to BX cable, or a series of straight fibers running parallel to the core.[2] Since the armour is fairly large, the cables normally carry a number of fibers inside. The resulting armoured bundle is then surrounded in an environmental cladding, typically plastic. The bundle is about the size of a conventional power cable found on an electrical appliance, but much less flexible.
Fiber to the home
Optical cabling has long formed the backbone of major terrestrial networks, delivering signals over long distances. The signals are then converted into other forms at the company end offices, and distributed from there in some other form, typically telephone wiring or coax cable in the case of cable television. The multi-fiber armoured cable is well suited to this role.
Since the 1990s there has been an ongoing effort to supply fiber to the home (FTTH). Using fiber to deliver signals all the way to the home provides the same advantages as it does on the longer hauls, namely much higher bandwidth, lower costs, and less interference with other sources. However, given the deliberate lack of flexibility of the cable, these installations generally end in a utility room where they are converted to copper for distribution within the home.[3]
While this sort of installation is useful for individual dwellings, it is less useful in large multi-unit dwellings. Corning estimates that an apartment installation would require an average of twelve right angle turns between the distribution point and the units. Conventional fiber would lose the signal after one or two such bends, making it useless in this role.[4] As is the case for individual homes, the fiber can be converted to copper for the last section of delivery, but the longer runs demand much higher performance, larger cable. Finding room to run these cables in an existing structure may not be possible.