Fused fiber couplers Fused fiber coupler is one of the lowest-priced but with high performance fiber optical devices widely used in optical communication systems. It is also called biconical tapering coupler. The single mode fiber confines most of optical energy in the fiber core. When the fiber is tapered, its core diameter is reduced. Then the optical energy spreads more and more into the cladding region of the fiber waveguide. If there i..