Optical fiber article for handling higher power and method of fabricating or using

Abstract

An optical fiber preform, and method for fabricating, having a first core, a second core spaced from the first core and first and second regions, the first region having an outer perimeter having a first substantially straight length and the second region having an outer perimeter having a second substantially straight length facing the first straight length. One of the regions can comprise the first core and the other comprises the second core. The preform can be drawn with rotation to provide a fiber wherein a first core of the fiber is multimode at a selected wavelength of operation and a second core of the fiber is spaced from and winds around the first core and has a selected longitudinal pitch. The second core of the fiber can couple to a higher order mode of the first core and increase the attenuation thereof relative to the fundamental mode of the first core.

1 . An optical fiber preform extending in a longitudinal direction for drawing an optical fiber therefrom having a first core, and a second core winding about the first core, comprising:
 a first core;   a second core spaced from the first core;   first and second regions, said first region when viewed in cross section having an outer perimeter having a first substantially straight length and the second region having an outer perimeter having a second substantially straight length facing said first substantially straight length;   one of said first and second regions comprising said first core and a cladding disposed about said first core and the other of said first and second regions comprising said second core and a cladding disposed about said second core;   said preform being constructed and arranged such that the preform can be drawn with rotation about an axis passing through the first core to provide the fiber wherein a first core of the fiber is multimode at a selected wavelength of operation and a second core of the fiber is spaced from and winds around the first core of the fiber and has a selected longitudinal pitch and wherein at said wavelength of operation the second core of the fiber couples to a higher order mode of the first core of the fiber and increases the attenuation thereof relative to the fundamental mode of the first core of the fiber; and   wherein the term “cross section” means cross section taken perpendicular to the longitudinal direction.   
   
   
       2 . The optical fiber preform of  claim 1  wherein said optical fiber preform comprises an outer perimeter bounding the cross section of the optical fiber preform and defining the geometrical center of the preform and wherein said first core comprises a cross sectional area within which the geometrical center lies. 
   
   
       3 . The optical fiber preform of  claim 1  wherein said first and second substantially straight lengths are contiguous and substantially parallel. 
   
   
       4 . The optical fiber preform of  claim 1  wherein the outer perimeter of said first region includes a first curved length characterized by a first radius of curvature and the outer perimeter of said second region comprises a second curved length that is characterized by a second radius of curvature that is substantially the same as said first radius of curvature and wherein said first radius of curvature originates within the cross sectional area of said first core and said second radius of curvature does not originate from within the cross sectional area of said second core. 
   
   
       5 . The optical fiber preform of  claim 1  wherein the outer perimeter of said first region includes a first curved length characterized by a first radius of curvature and the outer perimeter of said second region comprises a second curved length that is characterized by a second radius of curvature that is different than said first radius of curvature and wherein said first radius of curvature originates within the cross sectional area of said first core and said second radius of curvature originates from within the cross sectional area of said second core. 
   
   
       6 . The optical fiber preform of  claim 1  wherein said first and second regions are fused together. 
   
   
       7 . The optical fiber preform of  claim 1  wherein the outer perimeter of said second region comprises only substantially straight lengths. 
   
   
       8 . The optical fiber preform of  claim 1  comprising a stress-inducing region for providing a fiber drawn from the preform with a selected birefringence. 
   
   
       9 . An optical fiber preform extending in a longitudinal direction for drawing an optical fiber therefrom having a first core, and a second core winding about the first core, comprising:
 a unitary core rod comprising a first core and a cladding disposed about said core;   an arrangement of elongate members forming a ring disposed about said core rod;   a second core comprising at least one of the elongate members of the arrangement forming a said ring;   a tube disposed about the arrangement of elongate members;   said preform being constructed and arranged such that the preform can be drawn with rotation about an axis passing through the first core to provide the fiber wherein the first core of the fiber is multimode at a selected wavelength of operation and a second core of the fiber is spaced from and winds around the first core of the fiber and has a selected longitudinal pitch and wherein at said wavelength of operation the second core of the fiber couples to a higher order mode of the first core of the fiber and increases the attenuation thereof relative to the fundamental mode of the first core of the fiber; and   wherein the term “cross section” means cross section taken perpendicular to the longitudinal direction.   
   
   
       10 . The optical fiber preform of  claim 9  wherein the optical fiber preform comprises an outer perimeter bounding the cross section of the optical fiber preform and defining the geometrical center of the preform and wherein said first core comprises a cross sectional area within which the geometrical center lies. 
   
   
       11 . The optical fiber preform of  claim 9  wherein said core comprises a diameter and wherein the thickness of the cladding of the core rod is no greater than 15% of the diameter of the core rod. 
   
   
       12 . The optical fiber preform of  claim 9  comprising another tube interposed between said arrangement of elongate members and said core rod. 
   
   
       13 . The optical fiber preform of  claim 9  wherein at least one of said elongate members comprises a stress-inducing region for providing a fiber drawn from the preform with a selected birefringence. 
   
   
       14 . A method of fabricating an optical fiber preform extending in a longitudinal direction for drawing an optical fiber therefrom having a first core, and a second core winding about the first core, comprising;
 providing a first elongate member having when viewed in cross section an outer perimeter having a first curved length and a first substantially straight length, the first elongate member further including, within the outer perimeter of the first elongate member, a core and a cladding disposed about the core;   providing a second elongate member having when viewed in cross section an outer perimeter having a second substantially straight length and a curved length and a second core within the outer perimeter of the second elongate member;   arranging the preform such that the first substantially straight length faces the second substantially straight length;   the preform being further constructed and arranged such that the preform can be drawn with rotation about a longitudinal axis passing through the first core to provide the fiber wherein the first core of the fiber is multimode at a selected wavelength of operation and the second core of the fiber is spaced from and winds around the first core of the fiber and has a selected longitudinal pitch and wherein at the wavelength of operation the second core of the fiber couples to a higher order mode of the first core of the fiber and increases the attenuation thereof relative to the fundamental mode of the first core of the fiber; and   wherein the term “cross section” means cross section taken perpendicular to the longitudinal direction.   
   
   
       15 . The method of  claim 14  wherein arranging the preform comprises arranging the preform such that the outer perimeter of the cross section of the preform defines a geometrical center and the geometrical center lies within the cross sectional area of the first core. 
   
   
       16 . The method of  claim 14  wherein arranging the preform comprises arranging the preform such that the first and second substantially straight lengths are contiguous and substantially parallel. 
   
   
       17 . The method of  claim 14  wherein arranging the preform comprises fusing said first and second elongate members together. 
   
   
       18 . The method of  claim 14  wherein arranging the preform comprises disposing a tube about said first and second elongate members. 
   
   
       19 . The method of  claim 14  wherein said first curved length is characterized by a first radius of curvature and said second curved length is characterized by a second radius of curvature, the first and second radii of curvature being substantially the same and wherein said first radius of curvature extends from within the cross sectional area of said first core and wherein said second radius of curvature does not extend from within the cross sectional area of said second core. 
   
   
       20 . The method of  claim 14  wherein said first curved length is characterized by a first radius of curvature and said second curved length is characterized by a second radius of curvature, and wherein the first and second radii of curvature are different and said first radius of curvature extends from within the cross sectional area of said first core and wherein said second radius of curvature extends from within the cross sectional area of said second core. 
   
   
       21 . The method of  claim 14  wherein providing a selected one of the first and second members comprises providing the selected member having when viewed in cross section a substantially circular outer perimeter and shaping the member to form the first straight length, wherein the substantially circular outer perimeter defines a geometrical center lying within the cross sectional area of a core of the member and wherein shaping comprises shaping such that the outer perimeter defines a new geometrical center that lies outside of the cross sectional area of the core of the member. 
   
   
       22 . The method of  claim 14  wherein providing first elongate member comprises an axially symmetric deposition process wherein material to form the first core is deposited on a first cylindrical substrate and wherein providing the second elongate member comprises an axially symmetric deposition process wherein material for forming the second core is deposited on a different cylindrical substrate. 
   
   
       23 . The method of  claim 14  comprising forming a hole in a region of the preform and inserting a stress-inducing elongate member in the hole for increasing the birefringence of a fiber drawn from the preform. 
   
   
       24 . The method of  claim 23  wherein the stress-inducing elongate member includes a dopant for varying the coefficient of thermal expansion of the stress-inducing elongate member, and wherein said stress-inducing elongate member is substantially free of an outermost region that is free of a concentration of the dopant. 
   
   
       25 . The method of  claim 24  including providing a stress-inducing region that includes an outermost region that includes a concentration of the dopant and substantially removing that outermost region. 
   
   
       26 . The method of  claim 23  comprising fusing said first and second elongate members together to form a fused assembly and forming the hole in the fused assembly.