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Splicing & Polishing


  • Basics of Fiber Optic Splicing

    Fiber Optics Splicing is becoming  more and more a common skill requirement for cabling technicians. A fiber optic splice is defined by the fact that it gives a permanent or relatively permanent connection between two fiber optic cables. Fiber optic cables might have to be spliced together for a number of reasons—for example, to create a link of a particular length, or to repair a broken cable or connection. As fiber optic cables are generally only manufactured in lengths up to about 5 km, when lengths of 10 km are required, for example, then it is necessary to splice two lengths together to make a permanent connection.

    Classification of Techniques Used for Optical Fiber Splicing

    Mechanical splices
    The mechanical splices are normally used when splices need to be made quickly and easily. Mechanical fiber optic splices can take as little as five minutes to make, although the level of light loss is around ten percent. However this level of better than that which can be obtained using a connector. Some of the sleeves for mechanical fibre optic splices are advertised as allowing connection and disconnection. In this way a mechanical splice may be used in applications where the splice may be less permanent.

     

    Fusion splices
    This type of connection is made by fusing or melting the two ends together. This type of splice uses an electric arc to weld two fiber optic cables together and it requires specialised equipment to perform the splice. Fusion splices offer a lower level of loss and a high degree of permanence. However they require the use of the expensive fusion splicing equipment.

    Mechanisms of Light Loss at Optical Fiber Joint

    When joining optical fibers, the opposed cores must be properly aligned. Optical fiber splice loss occurs mostly in the following manner.

    Poor concentricity
    Poor concentricity of joined optical fibers causes a splice loss. In the case of general purpose single-mode fibers, the value of splice loss is calculated roughly as the square of the amount of misalignment multiplied by 0.2. (For example, if the light source wavelength is 1310 nm, misalignment by 1 µm results in approximately 0.2 dB of loss.)

    Poor concentricity
    Axial run-out
    A splice loss occurs due to an axial run-out between the light axes of optical fibers to be joined. For example, it is necessary to avoid an increased angle at fiber cut end when using an optical fiber cleaver before fusion splicing, since such an angle can result in splicing of optical fibers with run-out.

    Axial run-out
    Gap
    An end gap between optical fibers causes a splice loss. For example, if optical fiber end faces are not correctly butt-joined in mechanical splicing, a splice loss.
     
    An end gap between optical fibers
    Reflection
    An end gap between optical fibers results in 0.6 dB of return loss at the maximum due to the change in refractive index from the optical fiber to the air. In addition, the whole optical fiber ends should be cleaned because loss can also occur due to dirt between optical fiber ends.

    Classification and Principles of Fusion Splices

    Fusion splicing is classified into the two methods, as follows:

    Core alignment

    Optical fiber cores observed with a microscope are positioned with the help of image processing so that they are concentrically aligned. Then, an electric arc is applied to the fiber cores. The fusion splicer used has cameras for observation and positioning in two directions.

    Fs core_alignment.jpg

    Stationary V-groove alignment

    This fusion splicing method uses V-grooves produced with high precision to position and orient optical fibers and utilizes the surface tension of melted optical fibers for alignment effects (cladding alignment). Splices made by this method achieve low loss thanks to the recent advancement of optical fiber production technology, which has improved the dimensional accuracy regarding the placement of core. This method is primarily used for splicing a multi-fiber cable in a single action.

    Fs V-groove.jpg
     

    Tips for Better Splices:

    1. Thoroughly and frequently clean your splicing tools. When working with fiber, keep in mind that particles not visible to the naked eye could cause tremendous problems when working with fiber optics. "Excessive" cleaning of your fiber and tools will save you time and money down the road.
     
    2. Properly maintain and operate your cleaver. The cleaver is your most valuable tool in fiber splicing. Within mechanical splicing you need the proper angle to insure proper end faces or too much light escaping into the air gaps between the two fibers will occur. The index matching gel will eliminate most of the light escape but cannot overcome a low quality cleave. You should expect to spend around $200 to $1,000 for a good quality cleaver suitable for mechanical splicing.
     
    For Fusion splicing, you need an even more precise cleaver to achieve the exceptional low loss (0.05 dB and less). If you have a poor cleave the fiber ends might not melt together properly causing light loss and high reflection problems. Expect to pay $1,000 to $4,000 for a good cleaver to handle the precision required for fusion splicing. Maintaining your cleaver by following manufacturer instructions for cleaning as well as using the tool properly will provide you with a long lasting piece of equipment and ensuring the job is done right the first time.
     
    3. Fusion parameters must be adjusted minimally and methodically (fusion splicing only). If you start changing the fusion parameters on the splicer as soon as there is a hint of a problem you might lose your desired setting. Dirty equipment should be your first check and them continue with the parameters. Fusion time and fusion current are the two key factors for splicing. Different variables of these two factors can produce the same splice results. High time and low current result in the same outcome as high current and low time. Make sure to change one variable at a time and keep checking until you have found the right fusion parameters for your fiber type.
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