| 摘要 |
PURPOSE:To reduce bending loss and to enable use over a wide wavelength range by decreasing gradually the refractive index of the part of the innermost layer which contacts the 2nd layer in the direction where the radius increases and then connecting it to the 2nd layer, and specifying the difference between the largest refractive index of the innermost layer and the refractive index of the outermost layer, etc. CONSTITUTION:The part of the innermost layer 1 which contacts the 2nd layer 2 decreases gradually in the direction where the radius increases to connect with the 2nd layer 2, and the refractive indexes n2-n4 of the 2nd layer 2, the 3rd layer 3, and the outermost layer 4 are made constant in radial directions. Then, the difference DELTA1 between the maximum refractive index n1 of the innermost layer 1 and the refractive index n4 of the outermost layer 4 is 1.0-1.1%, the difference DELTA2 between the refractive index n2 of the 2nd layer 2 and the refractive index n4 of the outermost layer 4 is -0.3--0.2%, and the difference DELTA3 between the refractive index n3 of the 3rd layer 3 and the refractive index n4 of the outermost layer 4 is 0.2+ or -0.02%; and the radius r1 of the innermost layer 1 is 3+ or -0.3mum, the ratio of the radius r1 of the innermost layer 1 and the radius r2 of the 2nd layer 2 is 2.3, and the ratio of the radius r1 of the innermost layer 1 and the radius r3 of the 3rd layer is 3. |
