Patent ID: 7509010

Claim:
An end surface closely arranged multicore optical fiber, comprising: at least two core/clad single-mode optical fibers, including a clad surrounding a core and at one end individual single-mode optical fibers closely arranged in parallel to each other and bound together, with a core diameter being maintained and an outer diameter of the clad being reduced, wherein when at least one end of the end surface closely arranged multicore optical fiber where the single-mode optical fibers are molded, with the clad diameter being reduced, and are converged is to be optically connected with a multimode optical fiber, a distance L between centers of adjacent single-mode optical fibers at the end where the clad diameter is reduced is as follows: a lower limit distance L is twice the core diameter of the single-mode optical fiber or greater; and D represents the core diameter of the multimode optical fiber, where D is 80 μm or less, d represents the core diameter of the single-mode optical fiber, and n is a number (2, 3, 4, or 7) of the single-mode optical fibers that are bound together, an upper limit L is as follows: L≦D−d , when n= 2; L≦√ 3( D−d )/2, when n= 3; L≦√ 2( D−d )/2, when n= 4; and L ≦( D−d )/2, when n =7, and at the other end of the optical fibers, the individual single-mode optical fibers are individually independent from each other.