Double-clad, gain-producting fibers with increased cladding absorption while maintaining single-mode operation

摘要

The cladding absorption of single-mode, double-clad, gain-producing fibers is increased in fiber designs that includes a trench region disposed between the core and inner cladding regions. Increased cladding absorption is achieved while maintaining single-mode operation. The cladding region includes a trench region surrounding thecore region, an inner cladding region surrounding the trench region, and an outer cladding region surrounding the inner cladding region, the outer cladding region having a refractive index below that of the inner cladding region, the inner cladding region having a refractive index between that of the outer cladding region and the core region, and the trench region having a refractive index below that of the inner cladding region, the difference in refractive index ”n tr between the trench region and the inner cladding region being, in absolute value, less than the difference in refractive index ”n core between the core region and the inner cladding region, thereby allowing the diameter of the core region and the cladding absorption of the fiber both to be increased as compared to a corresponding gain-producing fiber without the trench region while maintaining single-mode operation of the signal light.