Manufacturing method of photonic band gap fiber and photonic band gap fiber

A manufacturing method of a photonic band gap fiber having a core portion and a cladding portion formed around an outer periphery of the core portion and having holes disposed to form photonic crystal which causes the core portion to act as a crystal defect, the manufacturing method comprising:

• a preliminary experiment process of measuring a hole diameter d0 and a distance-between-holes Λ0 realized in a preliminary experiment capillary body which is manufactured by first drawing a preliminary experiment preform having a plurality of holes formed along a longitudinal direction;
• calculating a confinement loss to a normalized wavelength λ/Λ which is obtained based on a wavelength λ normalized by an optional distance-between-holes Λ using a ratio d0/Λ0 of the hole diameter d0 and the distance-between-holes Λ0 of the measured preliminary experiment capillary body and the optional distance-between-holes Λ as design parameters;
• setting a distance-between-holes by calculating the set distance-between-holes Λ1 with respect to a desired transmission wavelength λ1 of a photonic band gap fiber to be manufactured using a value of the normalized wavelength λ/Λ in which the calculated confinement loss becomes about a minimum value;
• and
• second drawing of forming a manufacturing preform for manufacturing the photonic band gap fiber by using members made of a same material and having a same ratio of hole diameter to distance-between-holes as those of the preliminary experiment preform, and drawing the manufacturing preform by setting a distance-between-holes of the manufacturing preform to the set distance-between-holes Λ1, in a drawing temperature condition used for the first drawing of the preliminary experiment perform, wherein
• the photonic band gap filter manufactured by the manufacturing preform includes a core portion, and
• the core portion has a shape corresponding to a polygon.