Optical fiber comprising a refractive index trench

An optical fiber, adapted for single mode operation at an operating wavelength .lambda..sub.op, that comprises

• (a) a core having a refractive index n.sub.1 (a), and a radius a.sub.1, where a is the radial fiber coordinate;
• (b) a cladding that contactingly surrounds the core and extends outward from a.sub.1, at least the part of the cladding between a.sub.1 and a radius a.sub.d consists of relatively low optical loss first cladding material having a refractive index that nowhere exceeds the maximum value of n.sub.1 (a);
• associated with the fiber are fiber characteristics comprising:
• (i) a curve of chromatic dispersion vs wavelength, the curve having a slope and a zero at least at one zero dispersion wavelength .lambda..sub.o ;
• (ii) a dependence of .lambda..sub.o on a.sub.1 ;
• (iii) a spectral range in which the absolute value of the curve of chromatic dispersion vs. wavelength is less than a predetermined value;
• (iv) a curve of integrated mode power vs. radius;
• (v) a bending loss at a given bend radius;
• and
• (vi) a maximum core doping level and, associated therewith, a Rayleigh scattering loss;
• (c) the cladding comprises a first cladding region that extends from a.sub.1 to radius a.sub.2 and has a refractive index n.sub.2 (a), an index trench that extends from a.sub.2 to a radius a.sub.3 and has a refractive index n.sub.3 (a), and a second cladding region that extends outward from a.sub.3 and has a refractive index n.sub.4 (a), with a.sub.1 <a.sub.2 <a.sub.3 .ltoreq.a.sub.d, and with the maximum value of n.sub.3 (a) being less than the minimum value of n.sub.2 (a) and also less than n.sub.4 (a=a.sub.3), the refractive index of the second cladding at a.sub.3.