Optical fiber preform, production method thereof, and optical fiber produced from the preform

A method for producing an optical fiber preform, the method comprising:

• (a) a preparing step in which:
• (a1) an effective glass pipe to become a portion of the optical fiber preform, an auxiliary glass pipe, an effective glass rod to become a portion of the optical fiber preform, an auxiliary glass member made of a material selected from the group consisting of highly pure silica glass, fluorine-doped silica glass, diphosphorus pentaoxide-doped silica glass, and chlorine-doped silica glass, and a heat source are prepared;
• (a2) a glass pipe is assembled by connecting the auxiliary glass pipe to one end of the effective glass pipe;
• and
• (a3) a glass rod is assembled by connecting the auxiliary glass member to one end of the effective glass rod;
• (b) a diameter-reduced-portion-forming step in which a first diameter-reduced portion is formed at the auxiliary glass pipe, and a second diameter-reduced portion is formed in the vicinity of the effective glass pipe's end to which no auxiliary glass pipe is connected;
• (c) a glass-rod-inserting step in which the glass rod is inserted into the glass pipe;
• (d) a glass-rod-fixing step in which the auxiliary glass member is fixed to the glass pipe at the first diameter-reduced portion;
• and
• (e) a unifying step in which the glass pipe and the glass rod is heat-unified from the second diameter-reduced portion to the first diameter-reduced portion.

An optical fiber preform, being produced by the method comprising:

• (a) a preparing step in which a glass pipe, a glass rod, and a heat source are prepared;
• (b) a diameter-reduced-portion-forming step in which an inner diameter of the glass pipe is reduced at two longitudinal locations for forming a first diameter-reduced portion and a second diameter-reduced portion;
• (c) a glass-rod-inserting step in which the glass rod is inserted into the glass pipe;
• (d) a glass-rod-fixing step in which the glass rod is fixed to the glass pipe at the first diameter-reduced portion;
• and
• (e) a unifying step in which the glass pipe and the glass rod is heat-unified from the second diameter-reduced portion to the first diameter-reduced portion;
• the optical fiber preform having a core noncircularity of at most 1.5%.

An optical fiber, being produced from an optical fiber preform having a core noncircularity of at most 1.5%;

• the optical fiber preform being produced by the method comprising:
• (a) a preparing step in which a glass pipe, a glass rod, and a heat source are prepared;
• (b) a diameter-reduced-portion-forming step in which an inner diameter of the glass pipe is reduced at two longitudinal locations for forming a first diameter-reduced portion and a second diameter-reduced portion;
• (c) a glass-rod-inserting step in which the glass rod is inserted into the glass pipe;
• (d) a glass-rod-fixing step in which the glass rod is fixed to the glass pipe at the first diameter-reduced portion;
• and
• (e) a unifying step in which the glass pipe and the glass rod is heat-unified from the second diameter-reduced portion to the first diameter-reduced portion;
• the optical fiber having a polarization mode dispersion of at most 0.15 ps/km1/2 at a wavelength of 1,550 nm.