MANUFACTURE OF OPTICAL COUPLER

PROBLEM TO BE SOLVED: To manufacture an optical coupler which has small characteristic variation against temperature variation by drawing a fiber part and applying tension to an optical coupling part while monitoring a drawing stage movement distance after the drawing ends, and finishing the drawing process at the position where it has moved to a specific length. SOLUTION: A fiber 1, fixed with fiber clamps 2a and 2b, and 6a and 6b, is drawn by drawing stages 5a and 5b while heated and fused by a burner. This is carried out while monitor light is inputted to the center fiber and drawing is stopped when the branching degree of the monitor light on the output side reaches a specific value to obtain a coupler wire. Further, while a constant tension is applied, both ends of the fiber bundle fusion spliced part are fixed to a quartz glass plate with an adhesive. Thus, the constant tension is applied after the heating, fusion splicing, and drawing end, so the fiber part is drawn while the drawing stage movement distance is monitored to apply tension to the optical coupling part, and the drawing process is ended where it is moved to the specific length.