Patent ID: 8824848

Claim:
A multimode optical fiber comprising: a core extending along a predetermined axis and having a maximum refractive index n 1 and an outer diameter 2 a , and a cladding provided on an outer peripheral surface of the core and having a refractive index n 0 (<n 1 ) at an interface to the core, wherein in a cross section of the multimode optical fiber perpendicular to the predetermined axis, the core has a refractive-index profile n(r) a shape of which is defined by an exponent α(r) that varies with a distance r (0≦r≦a) in a radial direction from a center of the core, wherein the refractive-index profile n(r) of the core is defined by Expression (1) below: n ⁡ ( r ) = n 1 ⁡ ( 1 - 2 ⁢ Δ core ⁡ ( r a ) α ⁡ ( r ) ) 1 2 ⁢ ⁢ where ⁢ ⁢ Δ core = ( n 1 2 - n 0 2 ) 2 ⁢ n 1 2 , ( 1 ) wherein when Δ core represents a maximum relative refractive-index difference of the core and when Δ(r) represents a relative refractive-index difference of the core at a position distant by the distance r from the center of the core, the exponent α(r) is defined by Expression (2) below: α ⁡ ( r ) = r ⁡ ( - ⅆ ⅆ r ⁢ Δ ⁡ ( r ) ) Δ core - Δ ⁡ ( r ) ⁢ ⁢ where ⁢ ⁢ Δ core = ( n 1 2 - n 0 2 ) 2 ⁢ n 1 2 ⁢ ⁢ and ⁢ ⁢ Δ ⁡ ( r ) = ( n ⁡ ( r ) 2 - n 0 2 ) 2 ⁢ n ⁡ ( r ) 2 , and ⁢ ( 2 ) wherein an average of variation d(α(r))/dr of the exponent along the radial direction satisfies Expression (3) below in a standard range in which the distance r is not less than 0.4 a and not more than 0.6 a ⅆ ⅆ r ⁢ α ⁡ ( r ) _ > 0. ( 3 )