DOUBLE CLAD FIBER, ITS MANUFACTURING METHOD, AND PREFORM FOR MANUFACTURING DOUBLE CLAD FIBER

摘要

PROBLEM TO BE SOLVED: To provide a double clad fiber having a high NA with a simple structure, and also to provide its manufacturing method and a preform for manufacturing the double clad fiber.

SOLUTION: The double clad fiber 10 is composed of a core 11, an inner clad layer 12 enclosing the core, a hole forming layer 15 made up of a large number of holes 13 surrounding the inner clad layer and of a structure support 14 between these holes, and an outer clad layer 16 surrounding the hole forming layer. The double clad fiber 10 is characterized in that the structure support is composed of a material whose refractive index is lower than that of pure quartz and that the NA at the wavelength 1μm of the part surrounded by the inner clad layer is≥0.4.

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