Abstract: The present relates to the protective structure for an optical fiber coupler made from bare fiber parts of a plurality of optical fibers therein, the bare fiber parts being formed by removing the coating of the plurality of optical fibers and comprises a case made of material having a coefficient of thermal expansion equivalent to optical fibers and having space for enclosing the optical fiber coupler, and fiber supporting portions, being arranged inside of the space of the case and being fused with the bare fiber parts.