An optical fiber structure includes a first fiber array and a second fiber array, which are placed one on the other. For example, the first fiber array includes a substrate having four V-shaped grooves and four first optical fibers, the output ends of which are linearly arranged and fixed to the grooves. The second fiber array includes a substrate having four V-shaped grooves and four second optical fibers, the output ends of which are linearly arranged and fixed to the grooves. The first optical fiber has a taper portion, in which the core diameter decreases along an optical axis, and the core diameter and the outer diameter of the first optical fiber at the tip of the taper portion thereof are 60 μm and 80 μm, respectively. The core diameter and the outer diameter of the second optical fiber are 105 μm and 125 μm, respectively.