Patent ID: 6879764

Claim:
Dispersion shifted fiber having low dispersion slope of about ≦0.05 ps/nm 2 .km comprising a centre core, two claddings, a ring core and an outer glass region, wherein a first cladding of said two claddings is provided onto said outer periphery of said centre core, a second cladding of said two claddings is provided onto an outer periphery of said first cladding and said ring core is provided onto an outer periphery of said second cladding, and said outer glass region surrounds said ring core characterized in that said centre core and said ring core have higher refractive indices, and said claddings have lower refractive indices than said outer glass region; and the refractive indices are constrained by the following equation: n 1 >n 4 >n 5 >n 2 >n 3 , and values of their refractive indices are constrained by the following equations: 0.008>( n 1 −n 5 )>0.0075 0.0015>( n 4 −n 5 )>0.0012 −0.001<( n 2 −n 5 )<−0.0006 −0.0015<( n 3 −n 5 )<−0.0008 wherein n 1 , n 2 n 3 , n 4 and n 5 represent the refractive index of said centre core, said first cladding, said second cladding, said ring core and said outer glass region respectively; and the radius of said members of the fibre are restricted by the following equations: a 1 =about 2.8 μm a 2 =about 4.3 μm a 3 =about 6.3 μm a 4 =about 9.2 μm wherein a 1 , a 2 , a 3 , and a 4 represents radius of said centre core, said first cladding, said second cladding and said ring core respectively.