Bandwidth-Maintaining Multimode Optical Fibers

Abstract

The specification describes multimode optical fibers with specific design parameters, i.e., controlled refractive index design ratios and dimensions, which render the optical fibers largely immune to moderately severe bends. The modal structure in the optical fibers is also largely unaffected by bending, thus leaving the optical fiber bandwidth essentially unimpaired. Bend performance results were established by DMD measurements of fibers wound on mandrels vs. measurements of fibers with no severe bends.

1 . A bend resistant multimode optical fiber comprising a core region with a first radius a1 and a profile alpha, wherein alpha is a core shape profile parameter and defines a shape of a graded refractive index profile of the multimode optical fiber, an inner cladding extending radially from first radius a1 to second radius a2 wherein there is substantially a constant refractive index from first radius a1 to second radius a2, a trench extending radially from second radius a2 to a third radius a3, and an outer cladding extending to a fourth radius a4, wherein a maximum refractive index of the core region is d1, a refractive index of the inner cladding is d2, a refractive index of the trench is d3, and a refractive index of the outer cladding is d4, wherein:
 a1 is 7-50 microns;   alpha is 1.6 to 2.2;   (a2−a1)/a1 is 0.4 to 0.7;   (a3−a2)/a1 is 0.086 to 0.7;   a4 is 30-250 microns;   d1-d4 is −0.019 to 0.032;   d2-d4 is −0.01 to 0.01;   d3-d4 is −0.05 to −0.0025; and   d4 is 1.397 to 1.511,   
       wherein the multimode optical fiber that exhibits a change in differential mode delay measured as bend mode performance of less than 0.07 picoseconds per meter from an unbent state to bent state, given a reference state of 2 turns around a 10 mm diameter. 
     
     
         2 . (canceled) 
     
     
         3 . The optical fiber of  claim 1  wherein:
 a1 is 22-29 micrometers; and 
 a3-a2 is at least 2.5 microns. 
 
     
     
         4 . The optical fiber of  claim 3  wherein a3-a2 is in the range 10-13 microns. 
     
     
         5 . The optical fiber of  claim 1  wherein the trench has a cross-sectional area in the range 500-3500 micrometers 2 . 
     
     
         6 . The optical fiber of  claim 1  wherein the trench has a cross-sectional area in the range 2000-2900 micrometers 2 . 
     
     
         7 . The optical fiber of  claim 5  wherein d2-d3 is at least 0.0025. 
     
     
         8 . The optical fiber of  claim 5  wherein d3 is no greater than 1.452. 
     
     
         9 .- 15 . (canceled) 
     
     
         16 . The optical fiber of  claim 1  wherein the fiber is made using a method selected from the group consisting of CVD, OVD, MCVD, PCVD, VAD, and any combinations thereof. 
     
     
         17 . The optical fiber of  claim 1  wherein change in differential mode delay exhibited by the fiber is measured in accordance with a TIA/EIA-455-220 test procedure.