Fused Biconical Taper (FBT) Process & Packaging

   Gould's fiber optic components are manufactured using the fused biconical taper process on fully software controlled automatic fabrication stations. The process consists of placing two or more fibers adjacent to each other, then fusing and stretching them to create a central coupling region. A fused coupler is a structure formed by two independent optical fibers. The FBT based devices work as a result of an energy transfer by coupling proximity between optical fiber cores. Consider two parallel single-mode optical fiber in close proximity. If the evanescent tails of each waveguide have considerable overlap, it can be shown that there are two possible solutions for mode propagation in the two waveguide structures. These are the Supermodes or Eigenmodes. The two solutions have symmetric and anti-symmetric energy distributions and differing propagation constant values. As the relative phases of the modes change, the energy is shared between the two fibers and at the matching and mismatched phase, the energy is alternately maximized in each fiber cores, i.e. the energy beats back and forth between the waveguides.
The energy transfer is dependent on the core separation (d) and the interaction length (L).
 Fused Biconical Taper (FBT) Process

FBT Coupler Packaging

Using two separate fibers for the fusion process the result will be always a 2x2 Coupler. To obtain a 1x2 Coupler (or Splitter) one of the input fibers will be cut and terminated to avoid back-reflections from that end, The fused fibers are then mounted on a Quartz substrate (glued or glass-soldered) and put into a metal tube of typically 3mm diameter.
FBT Coupler Packaging
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