Optical couplers in which fibers are directly bonded to each other show potential for stable optical performance, therefor numerous proposals have been made in this area, particularly regarding glass fiber.
In this report, an attempt was made to bond plastic optical fibers and typical optical characteristics were compared with various other techniques. A prototype optical coupler employing plastic optical fiber with a diameter of 1mm was fabricated. For the techniques such as “bonding using an optical adhesive” and “thermal fusion via partial heating” which require stripping of the clad layer or other forms of pretreatment, conflicting relationships were found between the joined length, the distribution ratio and the excess loss. But with ultrasonic bonding employing instantaneous fusion for one second or less, stable results were obtained in the range where the excess loss is approximately 1 dB or less and the output ratio approximately 1:1.4. In particular, the permanent bonding technique employing ultrasonic energy minimizes the difference in refractive index at the bond surface, and thus is optically satisfactory.
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