| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical fiber having a higher fluorine concentration in cladding than in core at the time of synthesizing the core and the clad together.SOLUTION: An optical fiber comprises an inside glass part at the center, and a first outside glass layer and a second outside glass layer sequentially enclosing the inside glass part. The inside glass part has an external diameter of 7.5 to 11.5 μm, and the external diameter of the first outside glass layer is 2 to 4.5 times as long as the external diameter of the inside glass part. The relative refractive index difference of the inside glass part to the first outside glass layer is 0.25 to 0.5%, and the relative refractive index difference of the first outside glass layer to pure silica glass is -0.5 to -0.25%. No manufacturing interface is between the inside glass part and the first outside glass layer. The quantity of addition of fluorine of the inner glass part is 0 g/cmto the quantity of addition of fluorine of the first outer glass part. An alkali metal element is added to the optical fiber so that the transmission loss of a wavelength of 1383 nm is 1.0 dB/km or less whereas the transmission loss of a wavelength of 1550 nm is 0.181 dB/km or less. |
