Abstract: A prism is produced by the steps of feeding a glass base material into a heating furnace, the glass base material having surfaces to be prism surfaces after forming, the Ra value of the surface roughness of the surface being less than the Ra value corresponding to #170, the glass base material having a predetermined dimensional ratio, grasping the glass base material with feeding means, and feeding the glass base material into a heating furnace to heat the glass base material to a temperature so that a minimum viscosity of the glass base material becomes equal to or more than 104 Pa·s and less than 106 Pa·s, drawing and forming the lower portion of the glass base material, and then cutting the glass base material to obtain a longer body having a desired dimension and prism surfaces with the Ra value of the surface roughness equal to or less than a quarter of the wavelength of incident light, and cutting the longer body into desired length.

Abstract: A prism is produced by the steps of feeding a glass base material into a heating furnace, the glass base material having surfaces to be prism surfaces after forming, the Ra value of the surface roughness of the surface being less than the Ra value corresponding to #170, the glass base material having a predetermined dimensional ratio, grasping the glass base material with feeding means, and feeding the glass base material into a heating furnace to heat the glass base material to a temperature so that a minimum viscosity of the glass base material becomes equal to or more than 104 Pa·s and less than 106 Pa·s, drawing and forming the lower portion of the glass base material, and then cutting the glass base material to obtain a longer body having a desired dimension and prism surfaces with the Ra value of the surface roughness equal to or less than a quarter of the wavelength of incident light, and cutting the longer body into desired length.

Abstract: In the capillary tube 22, the cross section of the outer surface is substantially square, and the cross section of the insertion hole 23 is substantially square. Sides La, Lb of the outer surface have high dimensional accuracy and the insertion hole 23 is made to allow two optical fibers 5, 6 to be inserted while adjoining each other and arranged in order therein. The phases of the outer surface and the insertion hole 23 are relatively offset with each other, so that angles &thgr;a, &thgr;b which the sides 23a, 23b of the insertion hole 23 form with flat surfaces 22a, 22b of the outer surface are acute angles of substantially 45°±0.5°. Consequently, the flat surface 22a becomes substantially parallel to the center line M that connects the centers of the cores 5a, 6a of the two optical fibers 5, 6 inserted in the insertion hole 23, and the flat surface 22b becomes substantially perpendicular to the center line M.