Optical fiber cladding light stripper

Abstract

Multi-clad optical fiber cladding light stripper (CLS) comprising an inner cladding with one or more recessed surface regions to remove light propagating within the inner cladding. A CLS may comprise such recessed surface regions along two or more azimuthal angles about the fiber axis, for example to improve stripping efficiency. One or more dimensions, or spatial distribution, of the recessed surface regions may be randomized, for example to improve stripping uniformity across a multiplicity of modes propagating within a cladding. Adjacent recessed surface regions may abut, for example, end-to-end, as segments of a recess that occupies a majority, or even an entirety, of the length of a fiber surrounded by a heat sink. One or more dimensions, or angular position, of individual ones of the abutted recessed surface regions may vary, according to a regular or irregular pattern.

What is claimed is: 
     
         1 . An optical fiber apparatus, comprising:
 first and second lengths of fiber, each comprising an outer cladding over an inner cladding that is over a core; and   a cladding light stripper (CLS) comprising a third length of fiber optically coupling the first length of fiber to the second length of fiber, wherein the third length of fiber further comprises a core, and an inner cladding that has one or more surface regions recessed from a nominal cladding diameter to perturb light propagating in the inner cladding, wherein individual ones of the recessed surface regions have a longitudinal length that exceeds an arc length of the regions, and a depth that varies over the longitudinal length.   
     
     
         2 . The apparatus of  claim 1 , wherein adjacent ones of the recessed surface regions abut, end to end, and wherein one or more dimensions, or angular position about an axis of the third length of fiber, vary. 
     
     
         3 . The apparatus of  claim 2 , wherein a depth of adjacent ones of the recessed surface regions vary over the third length of fiber. 
     
     
         4 . The apparatus of  claim 3 , wherein the depth is statistically random within the plurality of recessed surface regions. 
     
     
         5 . The apparatus of  claim 3 , wherein the angular position varies over the longitudinal length. 
     
     
         6 . The apparatus of  claim 1 , further comprising a heat sink adjacent to the third length of fiber, the heat sink comprising a material absorbing of light that is to escape at the recessed surface regions, and dissipating of heat produced by the absorbing of the light. 
     
     
         7 . The apparatus of  claim 6 , wherein adjacent ones of the recessed surface regions abut, end to end, over at least a majority of the third length of fiber. 
     
     
         8 . The apparatus of  claim 1  wherein the recessed surface regions comprise a first set of recessed surface regions at a first angular position about the fiber axis, and a second set of recessed surface regions at a second angular position, wherein individual ones of the second set are positioned longitudinally between individual ones of the first set with no overlap between the adjacent ones of the first and second sets. 
     
     
         9 . The apparatus of  claim 1 , wherein:
 the core of first, second and third lengths of fiber has a first diameter;   the inner cladding of the first and second lengths of fiber both have the same cladding diameter; and   the third length of fiber lacks an outer cladding at least within the recessed surface regions.   
     
     
         10 . A fiber laser system, comprising:
 a source laser;   a pump laser;   a first length of fiber, wherein the first length of fiber has a core coupled to the source laser and surrounded by two or more cladding layers, and wherein a first of the cladding layers is coupled to the pump laser;   a second length of fiber, wherein the second length of fiber has a core surrounded by two or more cladding layers; and   a cladding light stripper (CLS) comprising a third length of fiber optically coupling the first length of fiber to the second length of fiber, wherein the third length of fiber further comprises a core, and an inner cladding that has one or more surface regions recessed from a nominal cladding diameter to perturb light propagating in the inner cladding, wherein individual ones of the recessed surface regions have a longitudinal length that exceeds a transverse width of the regions, and a depth that varies over the longitudinal length.   
     
     
         11 . The fiber laser system of  claim 10 , wherein adjacent ones of the recessed surface regions abut, end to end, and wherein a depth of adjacent ones of the recessed surface regions vary over the third length of fiber. 
     
     
         12 . The fiber laser system of  claim 10 , wherein the laser system has a power output of at least 500 W.