Optical fiber preform manufacturing method

1. A method of manufacturing an optical fiber preform, comprising:

supporting a drilling jig in a radial direction of a preform that is cylinder-shaped;

moving the drilling jig in a longitudinal direction of the preform; and

forming a plurality of slits each extending in the longitudinal direction and directed from an outer side of the preform toward a center the perform; and

forming a plurality of holes each extending in the longitudinal direction and connecting with an end of one of the plurality of slits in a depth direction of the one of the plurality of slits, wherein

a width of each of the plurality of slits is smaller than a diameter of each of the plurality of holes.

2. The method according to claim 1 , wherein the depth of each of the plurality of slits is equal to or larger than 2 millimeters and equal to or smaller than 20 millimeters.

3. The method according to claim 1 , wherein the width of each of the plurality of slits is equal to or larger than 0.5 millimeter and equal to or smaller than a quarter of a diameter of each of the plurality of holes.

4. The method according to claim 1 , further comprising eliminating the plurality of slits by heating the preform.

5. The method according to claim 4 , wherein the preform is heated to be in a temperature range of a softening point temperature ±1% of the preform.

6. The method according to claim 1 , further comprising:

accommodating the preform in a glass tube; and

integrating the preform with the glass tube.

7. The method according to claim 6 , wherein the preform and the glass tube are integrated by heating the preform to be in a temperature range of a softening point temperature ±1% of the preform.