Method of producing a preform rod for an optical fiber.

摘要

A glass layer (2); is formed inside a silica glass tube (3) and another glass layer (1) having a refractive index higher than that of the abovementioned glass layer (2) is formed on said glass layer (2). After these glass layers (1,2) are formed, one end of the glass tube (3) is collapsed. While the internal pressure of the glass tube is being reduced below the atmospheric pressure, the glass tube is caused to collapse by heating, thereby yielding a preform for an optical fiber. The optical fiber produced from this preform has the difference in the refractive indices of the two orthogonal major axes (x, y) of at least 1.6 x 10-4 and maintains the linear polarization plane.