Core-on-clad method for fabricating mid-infrared optical fibers

Abstract We introduce a core-on-clad (COC) method for the fabrication of mid-IR fibers using a single crucible, which is different from a conventional double crucible process. The COC method involves stacking a core rod on a cladding rod in the single crucible and drawing it into the optical fiber directly. With this method, we developed a mid-IR fiber having a core–clad diameter ratio of 90%. By inserting a steel ring between the core and clad rods, the core–clad ratio was further reduced by about 82% and 52%, which depended on the inner hole sizes of the ring. After purification of raw materials, the transmission loss was measured at 1.2 dB/m for the wavelength of 3 μm and 0.26 dB/m for 5 μm. These large core mid-IR fibers can be applied for the beam delivery of medical lasers such as Er–YAG.