What makes a fibre optic cable? The big impact of tiny variables

Contributed Article

by UCL Swift

Fiber optics have paved the way for rapid data transmission across longer distances. The connection performance of fiber optic cables must be at its maximum in order to meet this demand. This requires extreme attention to detail, as connectivity issues can depend on very minute variances.

In this article, we will discuss bore diameter, core concentricity and circularity, including what they are and how they affect fiber optic power.

Bore Diameter

Ferrules come with varying bore diameters depending on the size of the optical fiber it will host. One reason for variance is that the diameter is purposefully slightly larger than normal from a “standard” fiber diameter to allow for differences in cladding. Cladding is defined as a layer of either glass or plastic that surrounds the inner core with a lower index of refraction. Through reflection, it confines light to the core to improve light transmission.

Ferrules are manufactured using injection-molded ceramic. After the initial molding step, the ferrules are put through a precision boring process and then polished to remove any machining marks, nicks or scratches.The ferrules then have the bore diameter measured and sorted into different “grades.” Matching the grade of the ferrule to the application and desired performance level is a key step in preparation, along with specifying a fiber with low variation of the cladding diameter.

Singlemode ferrules require the highest tolerance on bore diameter due to the high tolerances necessary to guarantee correct alignment of the fibers (dictated by the small size of the optical core, typically 9 microns in diameter). Even a tiny mismatch between two singlemode optical fibers can produce large losses in light transmission. Multimode ferrule terminations can be more forgiving due to larger core size (50 microns, 62.5 microns, or up to 100 microns) and are not as sensitive to mismatch.

Bore diameter is the first step in a quality termination. Unwanted variation in bore diameters will prevent the optical fibers from being fixed along the center axis due to variation in placement. This variation will contribute to a mismatch in core alignment, possibly increasing the connection loss.

The bore diameter depends on extremely precise and minute factors. Fiber optics is a technology that requires extreme accuracy and attention to detail. If this factor falls short to a tiny degree, then loss of light and data occurs. The greater the discrepancy, the lower the connectivity performance.


Click here to read the full article, including a detailed explanation of core concentricity and circularity

UCL Swift manufactures ferrules used to make splice-on-connectors and to make connectors for cable assemblies. After creating the ferrules and machining the various features, each ferrule is subjected to multiple measurements to ensure compliance to internal standards (Ilsintech typically uses a higher internal standard than what can be found in general specifications). Each ferrule is graded according to dimensional performance (including bore diameter) and identified for where it will be used, or potentially discarded if it does not meet UCL Swift standards for performance. We use the best of the best to make connectors. Contact UCL Swift today at 972-556-0916 for ordering information

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