Dispersion-shifted monomode optical fiber

A monomode optical fibers with substantially zero chromatic dispersion in the vicinity of 1.55 .mu.m, comprising an optical core having:

• a central portion of index varying with distance from the axis of said optical fiber between a minimum index n.sub.s +h.alpha.n, with -1<h<0 and with .DELTA.n strictly positive, and a maximum index n.sub.s ;
• a layer surrounding said central portion, of index that varies with distance from the axis of said fiber over the range n.sub.s to n.sub.s +.DELTA.n;
• and optical cladding surrounding said layer and having an index substantially equal to n.sub.s, said profile being defined by the following geometrical parameters:
• a:
• total radius of the core measured at said layer;
• y:
• ratio of the radius of said central portion to a, where 0<y<1;
• said fiber being characterized in that a and .DELTA.n are determined so that the chromatic dispersion of said fiber is substantially zero at 1.55 .mu.m and the cutoff wavelength .lambda..sub.c of said fiber is such that 1.4 .mu.m<.lambda..sub.c <1.55 .mu.m, y being an arbitrary value in the range 0 to 1, and h being selected so that the following relationships are satisfied:
• ##EQU7##