Optical fiber preform production method and optical fiber production method

An optical fiber preform production method for producing a core preform which extends along a center axis and constitutes a part of an optical fiber preform and in which a refractive index profile defined along a radial direction on a cross-section orthogonal to the center axis is adjusted to a predetermined shape, the method comprising

• a glass synthesis step of sequentially stacking glass particles synthesized while a doping amount of a refractive index adjusting agent M is adjusted on an inner peripheral surface or an outer peripheral surface of a glass deposition substrate extending along a direction matched with the center axis to thereby produce, to produce a glass preform as the glass preform to be the core preform, the glass preform having a cross-section in which a plurality of glass layers are concentrically arranged so as to be matched with the cross-section of the core preform and surround the center axis,
• wherein the optical fiber preform production method further comprises a pretreatment step executed prior to the glass synthesis step, the pretreatment step of:
• for one of a cross-section of an i-th (=1 to m) core preform sample among m (an integer of 2 or more) core preform samples produced in the past and the number of the glass layers constituting an i-th glass preform sample having become the i-th core preform sample, dividing an arbitrarily set adjustment region into n (an integer of 2 or more) sections along the radial direction and for the other, dividing a region corresponding to the adjustment region along the radial direction to correspond to the n division sections on one-to-one basis;
• creating glass synthesis actual-result data including actual measurement data of a relative refractive index difference of a k-th (=1 to n) division section in the i-th core preform sample as refractive index profile data and including doping amount data of the refractive index adjusting agent M doped to the k-th division section in the i-th glass preform sample as production condition data;
• calculating a correlation between a deviation of the actual measurement data of the relative refractive index difference with respect to a target value and the doping amount data of the refractive index adjusting agent M from glass synthesis actual-result data of the k-th division section of each of the m core preform samples;
• and
• calculating a theoretical doping amount of the refractive index adjusting agent M in which an absolute value of the deviation is minimized from the correlation in the k-th division section of each of the m core preform samples, and
• wherein the glass synthesis step sequentially forms one or more glass layers belonging to a k-th glass synthesis section corresponding to the k-th division section of each of the m core preform samples on the inner peripheral surface or the outer peripheral surface of the glass deposition substrate, in a state in which the doping amount of the refractive index adjusting agent M to be supplied at the time of synthesizing the glass particles is adjusted to the theoretical doping amount.