Patent ID: 8177439

Claim:
A capillary tube for holding an optical fiber, the capillary tube comprising: an insertion hole for inserting and fixing the optical fiber; a cylindrical surface as an outer circumferential surface; and a groove formed in the cylindrical surface in an axial direction thereof, the groove having inner side surfaces and a bottom, wherein regions from the cylindrical surface to both the inner side surfaces of the groove each form a projecting curved surface, and regions from both the inner side surfaces of the groove to the bottom of the groove form at least one recessed curved surface, the capillary tube is inserted to an external cylindrical tube having an inner circumferential surface that is a cylindrical surface, and the capillary tube and the external cylindrical tube are relatively rotated, with an adhesive filled between the capillary tube and the external cylindrical tube, for positioning the capillary tube in a circumferential direction relative to the external cylinder tube.