| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical fiber preform capable of forming a low loss optical fiber by wire drawing.SOLUTION: The optical fiber preform comprises: a core part which includes a K addition area having a diameter d1 and a K concentration of 50 atomic ppm or more and has an outer diameter d2 of 4×d1 or more and 8×d1 or less; and a clad part surrounding the core part and having a refractive index smaller than that of the core part. The average K concentration of the entire core part is preferably 5 atomic ppm or more and 50 atomic ppm or less. In the core part, the Cl concentration of the K addition area is 1000 atomic ppm or less, and the Cl concentration of an area except the K addition area is preferably 3000 atomic ppm or more. When the outer diameter of an area having a K concentration of 50 atomic ppm or less and a Cl concentration of 1000 atomic ppm or less is d3, a value of d3/d1 is preferably 1.2-2. |
