Method of producing an elliptic core optical fiber, and a processed preform used for producing elliptic core optical fiber

A method of producing an elliptic core optical fiber, in which a original preform having a circular core disposed at the center of a circular clad is processed to flatten on its periphery to form a processed preform that is then drawn with heating into an elliptic core optical fiber, characterized in that the aspect ratio of the processed preform for obtaining the desired aspect ratio of the elliptic core of the elliptic core optical fiber is obtained from the correlation between the aspect ratios of processed preforms and the aspect ratios of elliptic cores, which correlation is obtained for the material of the processed preform and the conditions of the drawing with heating;

• the core radius/clad radius ratio of the original preform for obtaining the desired core area/(core+clad) area ratio of the elliptic core optical fiber is obtained from the correlation between the aspect ratios and core area/(core+clad) area ratios of processed preforms, which correlation is obtained with the core radius/clad radius ratio as a parameter;
• and the original preform with the obtained core radius/clad radius ratio is processed to form the processed preform with said aspect ratio.