1. Field of the Invention
The present invention relates to the field of fusion splicing optical fibers, and more specifically, to the fusion splicing of thermally dissimilar glass fibers, that is glass fibers with substantially different softening temperatures.
2. Description of the Related Art
In the field of fiber optics, fiber splicing is a well-known and widely practiced technique. Typically, the fibers are brought close to each other and aligned so that their cores are coaxial with each other. Heat is transferred to both fiber ends by a filament around the end of the fiber or an electric arc between two electrodes that are positioned on either side of the axis of the two optical fibers. The heat is sufficient to soften the glass at the end of each of the two fibers. The optical fibers are then brought in contact and the hardening of the softened glass occurs as the temperature is lowered below the softening and glass transition temperatures to form a permanent bond between the fibers. See, for instance, D. L. Bisbee, “Splicing Silica Fibers with an Electric Arc”, Applied Optics, Vol. 15, No. 3, March 1976, pp. 796-798. These techniques have been designed for and used to fuse fibers that have the same or very similar material compositions, e.g. two standard silica fibers.
In many applications, two fibers having different glass compositions and substantially different softening temperatures must be fusion spliced. Typically, a specialty fiber of some sort is being fusion spliced to a standard silica fiber. The standard fusion splicing process must be modified to accommodate the difference in softening temperatures and provide a low loss (<0.3 dB), low back reflection (<−50 dB) and mechanically reliable fusion splice. See, for instance, A. Barnes et al., “Sapphire fibers: optical attenuation and splicing techniques,” Vol. 34, No. 30 Applied Optics, 20 Oct. 1995 pp. 6855-6858 discloses a capillary-tube splice technique for splicing sapphire fiber to silica fiber, Y. Kuroiwa et al., “Fusion Spliceable and High Efficiency Bi2O3-based EDF for Short-length and Broadband Application Pumped at 1480 nm,” Optical Fiber Communication, Optical Society of America, February, 2001, discloses a method of fusion splicing a bismuth oxide (Bi2O3) based Er doped fiber (Bi-EDF) to a silica telecom fiber, U.S. patent application Publication No. US 2001/0047668 A1 published on Dec. 6, 2001 discloses a method of fusion splicing Bismuth based glass fibers with standard silica fibers in which the fibers are aligned with their cleaved ends in contact and then asymmetrically heated, and U.S. patent application Publication No. US 2002/0164132 A1 published on Nov. 7, 2002 discloses heating the end of the fiber of lower melting point by conduction from the pre-heated end of the fiber of higher melting point.
Formation of a mechanically sound joint between thermally dissimilar fibers without degrading optical performance remains an elusive problem. Present techniques focus on optimizing the fusion splicing parameters, e.g. temperature and time, and post-treatment of the joint to improve mechanical strength. These techniques are limited and often ineffective and may degrade optical performance.