Capillary tube for holding optical fiber

#The present invention relates to a capillary tube for holding an optical fiber, particularly, a capillary tube for holding an optical fiber in which one or a plurality of insertion holes are formed into which such optical fiber is inserted and held.

#As is commonly known, a glass capillary tube for holding an optical fiber (hereinafter, glass capillary tube), in which an insertion hole is formed into which the optical fiber is inserted and held, is used for holding the optical fiber in alignment with an optical axis of an optical component such as optical waveguide-type device. The glass capillary tube is fixed to an end surface of the optical component in a straight line in such a way that a central axis of the insertion hole and the optical axis of the optical component are precisely positioned. In this case, both the optical component and the glass capillary tube are usually provided on the same flat surface of a substrate (or casing or holder).

#As specific examples, Patent Document 1 below discloses a glass capillary tube of which an exterior surface is substantially rectangular in shape (composed of four flat portions) and in a center of which an insertion hole, into which a single-core optical fiber is inserted and held, is formed, and an optical component is connected to the glass capillary tube in a straight line. According to Patent Document 1, positioning of an optical axis of the optical fiber inserted into and held by the insertion hole, and an optical axis of the optical component, are determined by utilizing the flat portions on the exterior surface of the glass capillary tube.

#FIG. 1 is a perspective view illustrating a glass capillary tube for holding an optical fiber, and an overview structure of its periphery related to a first embodiment of the present invention;

#FIG. 2(a) is a front view of a vertical cross-section of the glass capillary tube for holding an optical fiber related to the first embodiment, and FIG. 2(b) is a side view of the vertical cross-section;

#FIG. 3 is a front view of the vertical cross-section illustrating the glass capillary tube for holding an optical fiber, and an overview structure of its periphery related to the first embodiment;

#Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

#FIG. 1 represents a glass capillary tube for holding an optical fiber and an overview structure of its periphery related to a first embodiment of the present invention. As illustrated in the same drawing, the glass capillary tube 1 includes an insertion hole 3 through which a single-core optical fiber 2 is inserted and held within, and an optical waveguide device 5 serving as an optical component with a core 4 is firmly adhered to and in-line with an end (front end) of the optical fiber in an optical axis direction. This firmly adhered glass capillary tube 1 and the optical waveguide device 5 are packaged and housed within a casing (holder) 6. In this case, a front end 3a of the insertion hole 3 in the glass capillary tube 1 and a rear end 4a of the core 4 in the optical waveguide device 5 are pushed against and connected to each other in alignment at an adhering surface of the glass capillary tube 1 and the optical waveguide device 5.

#FIG. 2(a) is a vertical cross-sectional view in which the glass capillary tube 1 is cut at a right angle to the optical axis, and FIG. 2(b) is a vertical cross-sectional view in which the glass capillary tube 1 is cut along the optical axis. As illustrated in FIG. 2(a), an exterior surface 7 of the glass capillary tube 1 is composed of two flat portions 8, 9, and two partial cylindrical portions 10, 11 connecting with the flat portions 8, 9. In particular, the exterior surface 7 is composed of a first flat portion 8, which serve as a benchmark, a second flat portion 9 parallel to the flat portion 8, a first partial cylindrical portion 10 connecting from an end of the first flat portion 8 in a widthwise direction to an end of the second flat portion 9 in the widthwise direction, and a second partial cylindrical portion 11 connecting from another end of the first flat portion 8 in the widthwise direction to another end of the second flat portion 9 in the widthwise direction. The first partial cylindrical portion 10 and the second partial cylindrical portion 11 have the same central axis X (axis of origin) and are defined by a common radius, and a total region (total surface area) of the two partial cylindrical portions 10, 11 covers at least 20% (with an upper limit at about 80%) of an entire region (entire surface area) of the exterior surface 7.