Single mode optical fibers with Brillouin frequency-shift management

A method of making a single-mode optical fiber comprising a fiber longitudinal direction and a Brillouin frequency shift Δf, the method comprising:

• a) forming a preform comprising a core section surrounded by a cladding section, wherein at least one of the core section and the cladding section comprises a width that varies with a preform longitudinal direction;
• b) drawing the preform to form the optical fiber to define a core region from the core section and a cladding region from the cladding section;
• and
• wherein:
• iv. the core region comprises an inner core region immediately surrounded by an outer core region, the inner core region comprising a delta value of Δ1 and radius of r1, and the outer core region comprising a delta value Δ2<Δ1 and a radius r2>r1 and an annular width δr=r2−r1, wherein r2 is in the range from 3 μm to 10 μm and δr is in the range from 1 μm to 9 μm, and wherein Δ1−Δ2 is in the range from 0.3% to 2%;
• v. the cladding region immediately surrounding the outer core region and comprising a delta value of Δ3<Δ2 and a radius r3>r2, wherein r3 is in the range from 100 to 150 μm;
• and
• vi. at least one of r1, r2, δr and r3 changes with a period p in the longitudinal direction between first and second values each comprising a level distance dF, and wherein the change occurs over a transition distance dT such that 0<dT/dF<0.1 and wherein the Brillouin frequency shift Δf changes over each period by an amount δ[Δf] that is at least 10 MHz.

A method of making a single-mode optical fiber comprising a fiber longitudinal direction and a Brillouin frequency shift Δf, the method comprising:

• a) forming a preform comprising a core section surrounded by a cladding section;
• b) drawing the preform by changing the fiber diameter with a period p along the fiber longitudinal direction to form the optical fiber to define a core region from the core section and a cladding region from the cladding section;
• and
• wherein:
• iii. the core region comprises an inner core region immediately surrounded by an outer core region, the inner core region comprising a delta value of Δ1and radius of r1, and the outer core region comprising a delta value Δ2<Δ1 and a radius r2>r1 and an annular width δr=r2−r1, wherein r2 is in the range from 3 μm to 10 μm and δr is in the range from 1 μm to 9 μm, and wherein Δ1−Δ2 is in the range from 0.3% to 2%;
• iv. the cladding region immediately surroundings the outer core region and comprises a delta value of Δ3<Δ2 and a radius r3>r2, wherein r3 is in the range from 100 to 150 μm;
• and
• wherein at least one of r1, r2, δr and r3 changes with a period p in the longitudinal direction between first and second values each comprising level distance dF, and wherein the change occurs over a transition distance dT such that 0<dT/dF<0.1 and wherein the Brillouin frequency shift Δf changes over each period by an amount δ[Δf] that is at least 10 MHz.