Zero dispersion single mode optical fiber with center core and side core in the 1.5 .mu.m wavelength region

A zero dispersion single mode optical fiber for transmission in the 1.5 .mu.m wavelength region, comprising:

• a center core having a radius a.sub.1 and a maximum refractive index n.sub.1 ;
• a side core disposed on an outer side of said center core, said side core having a radius a.sub.2 and a maximum refractive index n.sub.3 which is lower than the maximum refractive index n.sub.1 of said center core;
• and
• a cladding portion disposed on an outer side of said core having a refractive index n.sub.2 ;
• each of the refractive indices of said center core and said side core having a step-like profile in the direction of the radius of said optical fiber;
• and wherein the radii a.sub.1 and a.sub.2, the relative refractive index difference .DELTA..sub.1 =(n.sub.1.sup.2 -n.sub.2.sup.2)/2n.sub.1.sup.2 and the relative refractive index difference .DELTA..sub.2 =(n.sub.3.sup.2 -n.sub.2.sup.2)2n.sub.3.sup.2 are determined by all of the following factors:
• (1) 0.1.ltoreq.R.DELTA..ltoreq.0.3 , where R.DELTA.=.sup..DELTA.2 /.DELTA..sub.1 ;
• (2) .DELTA..sub.1 .gtoreq.0.005;
• (3) 0<R.sub.a <1, where R.sub.a =a.sub.1 ;/a.sub.2
• (4) the chromatic dispersion .sigma.=(k/c.lambda.)d.sup.2 .alpha./dk.sup.2) of said single mode optical fiber showing zero dispersion in said 1.5 .mu.m wavelength region, where c is the velocity of light in a vacuum, .lambda. is the wavelength of light, k=2.pi./.lambda. is the wavenumber and .beta. is the propagation constant of the HE.sub.11 mode;
• and
• (5) the predetermined mode field diameter.