| 摘要 |
PROBLEM TO BE SOLVED: To make the island shape approximately uniform over the entire part, to obviate the receipt of damage during handling, to provide interchangeability with conventional glass fibercord as well and to obtain high performance by providing the outer peripheral part of a sea-and-island structure with a protective layer satisfying prescribed conditions. SOLUTION: The optical fiber has a sea-and-island structure integrated with plural island parts 1, 4, 5 in the state where these parts are separated from each other by a sea part 2 and a protective layer 3 integrated with the outer peripheral part of the sea-and-island structure. The island parts 4, 5 are composed of plural layers having core parts 1 as central layers. The refractive indices of the respective layers of the island parts 4, 5 decrease successively toward the outer peripheral from the center and the refractive index of the sea part 2 is below the refractive index of the outermost peripheral layers of the island parts 4, 5. The refractive index of the protective layer 3 is below the refractive index of the sea part 2 and is lower by 0.002 to 0.2 than the refractive index of the core parts 1. In addition, the refractive index difference between the respective layers is preferably 0.002 to 0.1. When the refractive index difference is smaller than 0.002, the quantity of the light captured into the fibers decreases and the difficulty in the detection of the light on the exist is difficult. |
