Optical coupling between coated fibers in a compact fiber ribbon

Optical coupling between coated optical fibers in a fiber ribbon for use in compact and high-density optical cable is described. By means of a measurement system having a sensitivity of -70 dB. optical coupling of -40 dB due to a small radius fiber bend is measured for an actual fiber ribbon coated with UV-curable resin. The optical coupling mechanism is discussed using analysis models of a coated optical fiber bend. Theoretical analyses and experimental results confirm that optical coupling occurs only when the refractive indices of coating materials satisfy the condition of radiating light traveling from a fiber core to a ribbon coat.