Double-clad, gain-producing fibers with increased cladding absorption while maintaining single-mode operation
AssigneeOFS Fitel, LLC
InventorThierry F. Taunay
Life of this patent
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Abstract
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.
Claims24
A double-clad, gain-producing optical fiber comprising:
- a core region having a longitudinal axis,
- a cladding region surrounding said core region, said core and cladding regions configured to support and guide the propagation of signal light in a fundamental transverse mode in the direction of said axis,
- said cladding region including a trench region surrounding said core region, an inner cladding region surrounding said trench region, and an outer cladding region surrounding said inner cladding region, said outer cladding region having a refractive index below that of said inner cladding region, said inner cladding region having a refractive index between that of said outer cladding region and said core region, and said trench region having a refractive index below that of said inner cladding region,
- at least said core region including at least one gain-producing species that provides gain to said signal light when suitable pumping energy is applied to said fiber, and
- said core and cladding regions being configured so that said fundamental mode is guided predominantly in said core region and the difference in refractive index Δntr between said trench region and said inner cladding region is, in absolute value, less than the difference in refractive index Δncore between said core region and said inner cladding region, thereby allowing the diameter of said core region and the cladding absorption of said fiber both to be increased as compared to a corresponding gain-producing fiber without said trench region while maintaining single-mode operation of said signal light.
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A method of increasing the cladding absorption of a double-clad, gain-producing fiber that includes a gain-producing core region, an inner cladding region surrounding said core region and an outer cladding surrounding said inner cladding region, said method including the steps of
- (a) forming a trench region between said core region and said inner cladding region;
- the diameter of said core region being greater than that of a corresponding double-clad, gain-producing fiber that does not have a trench region;
- (b) configuring said core, trench and inner cladding regions so that (i) the refractive index of said trench region is less than that of said inner cladding region and (ii) the difference in refractive index Δnt, between said trench and inner cladding regions is less than the difference in refractive index Δncore between said core region and said inner cladding region;
- and
- (c) configuring said core, trench and inner cladding regions so that the fundamental mode of signal light can be supported and guided in said core region and so that multimode pump light can be coupled into said core region via said inner cladding region.
Dependencies are inferred from the claim text.