Abstract: Fused biconical tapered couplers formed from the pulling of heated optical fibers have controllable coupling ratios by dynamically adjusting the heat intensity and pull speed during fabrication. Fiber coupler fabrication begins by arranging two optical fibers, heating the optical fibers using a heat source a predetermined distance from the optical fibers, and pulling the optical fibers at an initial pulling velocity as the heated optical fibers soften. The heat source is moved away from the optical fibers and the pulling velocity is selectively reduced in response to a substantial change in the detected coupling ratio. Changes in the coupling ratio are controlled by selectively reducing the pulling speed and the heat intensity to a point where the pulling of the optical fibers may be halted, and the heat removed, without a substantial change in the detected coupling ratio. The coupling ratio may be monitored at different wavelengths for fabrication of wideband couplers and wavelength division multiplexers.