Variable Branching of Any Single-Mode Fiber Installed in Optical Access Networks

We propose a side-polished fiber coupler in which part of the core of one fiber is removed to branch the target fibers. With this coupler, we demonstrate variable branching ratio of any single-mode fiber that complies with G.652.D and G.657.A1 commonly used in optical access networks. We also present design and fabrication methodologies of the proposed fiber coupler to achieve a stable branching ratio regardless of the effective refractive indices of target fibers. Simulation and experimental results reveal that the proposed coupler greatly expands the range in which high branching ratios can be obtained compared with the conventional directional coupler; it achieves high branching ratios of more than 50% over the target range of the effective refractive index that covers G.652.D and G.657.A1 fibers. Experiments also show that the proposed coupler ensures a variable branching ratio independent of the effective refractive indices of the target fibers while keeping the excess loss as low as that of the conventional coupler.