Manufacturing method for optical fiber and manufacturing apparatus for optical fiber

A manufacturing method for an optical fiber, comprising:

• drawing, while heating in a heating furnace, a lower end of an optical fiber preform that is to be an optical fiber having a core consisting of silica glass containing a rare earth element compound, wherein
• the heating furnace has a temperature profile in which a temperature of the heating furnace increases to a maximum temperature Tmax and then decreases from an upstream side of the heating furnace toward a downstream side of the heating furnace,
• the temperature profile has a changing point at which the temperature decreases more steeply on the downstream side from a position where the maximum temperature Tmax is reached,
• at the maximum temperature Tmax, a temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase,
• the temperature profile on the upstream side from the changing point is approximated based on a first normal distribution represented by below equation (1), and the temperature profile on the downstream side from the changing point is approximated based on a second normal distribution represented by below equation (2), and
• a temperature of the heating furnace causes a ratio σt/σb of a dispersion σt of the first normal distribution to a dispersion σb of the second normal distribution to be greater than or equal to 2,
• T
• =
• A
• ⁢
• exp
• ⁢
• {
• -
• x
• 2
• 2
• σ
• t
• 2
• }
• +
• B
• (
• x
• <
• x
• c
• )
• (
• 1
• )
• T
• =
• A
• ⁢
• exp
• ⁢
• {
• -
• (
• x
• -
• x
• 0
• )
• 2
• 2
• σ
• b
• 2
• }
• +
• B
• (
• x
• ≥
• x
• c
• )
• (
• 2
• )
• where
• T is a temperature at an arbitrary point in the heating furnace,
• A and B are constants,
• x is a distance to the arbitrary point from a reference point when the reference point is a position where the maximum temperature Tmax is reached and a direction from the reference point to the downstream side is a positive direction,
• xc is a distance from the reference point to a position where the changing point is reached, and
• x0 is a distance from the reference point to a position where T calculated by the equation (2) is a calculated maximum temperature Tmax.

A manufacturing method for an optical fiber, comprising:

• drawing, while heating in a heating furnace, a lower end of an optical fiber preform that is to be an optical fiber having a core consisting of silica glass containing a rare earth element compound, wherein
• the heating furnace has a temperature profile in which a temperature of the heating furnace increases to a maximum temperature Tmax and then decreases from an upstream side of the heating furnace toward a downstream side of the heating furnace,
• the temperature profile has a changing point at which the temperature decreases more steeply on the downstream side from a position where the maximum temperature Tmax is reached,
• at the maximum temperature Tmax, a temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase, and
• a ratio of a temperature Tc at the changing point and the maximum temperature Tmax represented by Tc/Tmax is greater than or equal to 0.5.