Abstract: A single crystal non-linear optical transmission line is manufactured by using a cladding made of a glass material that eliminates or reduces the formation of an uneven inner wall of an optical fiber cladding made of a glass mother material. The improved glass material suppresses the elution of metal mono-oxides on the inner wall and results in a high yield of non-defective fiber manufacturing. A glass mother material, such as SF1, having a low concentration of lead oxide does not contribute to the elution problem common to higher concentration glass mother materials. A glass mother material having no metal oxides also overcomes the problem of elusion since substitute molecules, such as TaC6, do not elute in water or in acid solutions. These glass materials can be used to successfully form a non-defective core having a low refractive index layer of the inner wall and make possible single mode propagation of a laser light in a single crystal non-linear optical transmission line.

Abstract: A method of coating the ends of a fiber wavelength-conversion element with a macromolecular film. This serves to protect the crystal core and change in quality without changing the state of the core end surface.