US Patent 8,094,986

A double clad fiber includes a core, a first cladding provided so as to cover the core, and a second cladding provided so as to cover the first cladding. The second cladding has a plurality of pores extending in a length direction and arranged so as to surround the first cladding. In at least one fiber end, the second cladding has been removed by mechanical processing so that the at least one fiber end is formed by the core and the first cladding.

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