Optical fiber paved the way for fast data transmission over long distances. The connectivity performance of fiber optic cables must be maximized to meet this demand. This requires extreme attention to detail, as connectivity issues can depend on very slight differences.
Ferrules come in different bore sizes depending on the size of the fiber it will carry. One reason for the variance is that the diameter is intentionally slightly larger than normal for "standard" fiber diameters to allow for differences in cladding. Cladding is defined as a layer of glass or plastic surrounding the core with a lower index of refraction. By reflection, it confines light to the core to improve light transmission.
Ferrules are manufactured using injection molded ceramic. After the initial forming step, the ferrules are precision drilled and then polished to remove any machining marks, nicks or scratches. The bore diameter of the ferrule is then measured and sorted into different "grades". Matching the grade of the ferrule to the application and desired performance level is a critical step in preparation, while specifying fibers with less variation in cladding diameter.
Singlemode ferrules require the highest bore tolerances due to the high tolerances required to ensure proper alignment of the fiber, dictated by the small size of the optical core, typically 9 microns in diameter. Even a small mismatch between two single-mode fibers can cause huge losses in optical transmission. With larger core sizes (50 microns, 62.5 microns or up to 100 microns), multimode ferrule terminations can be more forgiving and less sensitive to mismatch.
Hole size is the first step in a quality termination. Unwanted changes in aperture due to placement changes will prevent the fiber from being fixed along the central axis. This change will cause a core alignment mismatch, potentially increasing connection loss.
Pore size depends on extremely precise and minute factors. Fiber optics is a technology that requires extreme accuracy and attention to detail. If this factor is deficient to even a small extent, loss of light and data will occur. The greater the difference, the lower the connection performance.