| 摘要 |
PURPOSE: To obtain a sharp transmission image having fewer Moire fringes and uniform brightness by randomly arranging picture elements each consisting of a core and a clad that have a specific refractive-index difference between them in the image fiber, each of which clads of any kind of the picture elements has an equal thickness to and a different diameter from those of the clads of the other kinds. CONSTITUTION: This image fiber is obtained by melting and integrating a number of picture elements each of which has a core consisting of GeO2 -SiO2 and a clad consisting of F-SiO2 . In this image fiber, at least two kinds of the picture elements each consisting of a core and a clad that have a specific refractive-index difference between them, each of which clads of any kind of the picture elements has an equal thickness to and a different diameter from those of the clads of the other kinds, are randomly arranged. Three kinds of silica optical fiber preforms having e.g. 3.5% of the same specific refractive-index difference and (outer diameter of the core)/(outer diameter of the clad) ratios of 0.645, 0.667 and 0.686 respectively are drawn to form three optical fibers having outer diameters of 200, 213 and 229μm respectively. At this time, these three kinds of optical fibers have equal clad thickness to each other, i.e., about 36μm. A number of the optical fibers thus obtained are cut into fibers having uniform length and the resulting fibers are uniformly mixed and packed into a silica tube to form the objective image fiber preform.
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