Method of sealing air holes in an optical fiber

A method for sealing an end portion of an optical fiber, said method comprising:

• forming at said end portion of said optical fiber an end face that is substantially at right angles to an axial direction of said optical fiber in said end portion, wherein said optical fiber comprises a core and a cladding formed around said core, the cladding comprising a plurality of air holes extending in the axial direction, the core having a refractive index greater than a refractive index of the cladding;
• inserting a glass powder with a particle diameter of 1 μm or less into said air holes from said end face;
• and
• subsequently, fusing said glass powder by heating said end portion of said optical fiber, thereby sealing said air holes while maintaining a diameter of the cladding.