| CPC G02B 6/03688 (2013.01) [C03B 37/01426 (2013.01); G02B 6/023 (2013.01); B08B 7/0042 (2013.01); C03B 2201/34 (2013.01); G02B 6/14 (2013.01)] | 10 Claims |

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1. A preform for speckle-free output optical fibers, drawn from it, whose cross-sectional structure comprises: a complex core structure and a reflective layer, the complex core structure comprising a circular inner core with a refractive index and a circular outer core with the same refractive index as the inner core, the inner core surrounded by a structured circular area with an average refractive index lower than the refractive index of the inner core and the outer core.
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