Broad bandwidth graded index multimode optical fiber for distributed temperature sensing in the 1550 nm region

Abstract

Disclosed herein is a method for measuring temperature via distributed temperature sensing comprising transmitting light through a fiber optic cable; detecting backscattered light in the fiber optic cable, wherein the backscattered light comprises an anti-Stokes band and a Stokes band; calculating a ratio between an intensity of the anti-Stokes band and an intensity of the Stokes band; and using the calculated ratio to determine a temperature being sensed in the fiber optic cable; wherein the fiber optic cable comprises, from the center to the periphery; a central core having a refractive index that decreases progressively from a center of the central core to an edge of the core, wherein the refractive index follows an alpha profile; wherein a bandwidth-length product of the multimode optical fiber has a value greater than 2000 MHz-km at 1550 nm.

What is claimed is: 
     
         1 . A method for measuring temperature via distributed temperature sensing comprising:
 transmitting light through a fiber optic cable;   detecting backscattered light in the fiber optic cable, wherein the backscattered light comprises an anti-Stokes band and a Stokes band in the fiber optic cable;   calculating a ratio between an intensity of the anti-Stokes band and an intensity of the Stokes band; and   using the calculated ratio to determine a temperature being sensed in the fiber optic cable; wherein:
 the fiber optic cable comprises a multimode optical fiber including, from the center to the periphery: 
 a central core having a refractive index that decreases progressively from a center of the central core to an edge of the core, wherein the refractive index follows an alpha profile such that the central core has a value of alpha in the range of 1.70 to 1.98; 
   a cladding having refractive index smaller than a minimum refractive index of the central core; wherein a bandwidth-length product of the fiber optic cable has a value greater than 2000 MHz-km at 1550 nm and the bandwidth-length product is highest within a region from 1450 nm to 1650 nm.   
     
     
         2 . The method of  claim 1 , wherein the central core comprises a silica doped with germanium, fluorine, phosphorus pentoxide, boron trioxide, alumina or a combination thereof. 
     
     
         3 . The method of  claim 2 , wherein the cladding comprises a silica with no dopant. 
     
     
         4 . The method of  claim 1 , wherein the cladding comprises a silica doped with fluorine. 
     
     
         5 . The method of  claim 1 , wherein the optical fiber is optimized to maximize a bandwidth in the wavelengths of 1400 nm to 1700 nm. 
     
     
         6 . The method of  claim 1 , wherein the multimode fiber further comprises:
 a trench region at a periphery of the cladding; wherein:   the trench region has a refractive index smaller than the refractive index of the cladding; and   the trench region comprises a comprising a silica doped with fluorine to impart bend-insensitivity.