Patent ID: 7406235

Claim:
A graded-index multimode fiber comprising: a silica glass core comprising a central region and an outer peripheral region; and a cladding provided at an outer periphery of the core, wherein the central region of the core contains one of germanium and phosphorus, and the outer peripheral region of the core contains fluorine, and the graded-index multimode fiber has a refractive index profile which satisfies the following: n ⁡ ( r ) = { n 1 ⁡ [ 1 - F ⁡ ( r ) ] 1 / 2 ⁢ ( 0 ≤ r ≤ a ) n 1 ⁡ [ 1 - F ⁡ ( a ) ] 1 / 2 ⁢ ( r > a ) ⁢ ⁢ F ⁡ ( r ) = { 2 ⁢ Δ 1 ⁡ ( r a 0 ) α 1 ⁢ r < a 0 2 ⁢ Δ 2 ⁡ ( r a ) α 2 ⁢ a 0 ≤ r ≤ a ⁢ ⁢ n 1 2 ⁡ [ 1 - 2 ⁢ Δ 2 ⁡ ( a 0 a ) α 2 ] = n 0 2 ⁢ ⁢ n 1 2 ⁡ [ 1 - 2 ⁢ Δ 1 ] = n 0 2 wherein n(r) is a refractive index of the fiber at a distance “r” from the center of the core, n 1 is a refractive index at the center of the core, Δ 1 is a maximum relative refractive index difference of one of germanium and phosphorus contained in the central region of the core with respect to the cladding, Δ 2 is a maximum relative refractive index difference of fluorine contained in the central region of the core with respect to the cladding, “a” is a core radius, and α 1 is a refractive index profile exponential parameter of the one of germanium and phosphorus contained in the central region of the core, α 2 is a refractive index profile exponential parameter of fluorine contained in the outer peripheral region of the core, a 0 is a distance between the central and outer peripheral regions of the core, and n 0 is a refractive index of pure silica.