Capillary tube and method for manufacturing same

The capillary (3a) is provided with a glass capillary main body (9) configured in a long shape. The capillary main body (9) includes a housing part (10) for housing a part of the optical fibers (2a, 2b). The housing part (10) is provided with an opening part (11) which is formed in the first end surface (9a) of the capillary tube main body (9) and into which the optical fibers (2a, 2b) are inserted. The capillary main body (9) is provided with: a compressive stress layer (CSL) that is formed in the opening (11) and is observable by a two-dimensional birefringence method; a tensile stress layer (TSL) that is formed at a position separated from the compressive stress layer (CSL) toward the second end surface (9b) side of the capillary main body (9) and that can be observed by a two-dimensional birefringence method; and a stress neutral layer (NSL) which is formed between the compressive stress layer (CSL) and the tensile stress layer (TSL) and which can be observed by a two-dimensional birefringence method. 毛细管