JPS62231913A - Plastic ferrule for optical fiber connector - Google Patents

Abstract

PURPOSE:To make a core pin thick and to prevent it from breaking by altering the sectional shape of the optical fiber holding and fixing insertion hole of a ferrule and making its cross section larger than that of an optical fiber. CONSTITUTION:The upper part 1 and lower part 2 of a main mold body where the core pin 3 is fitted are coupled by applying pressure, liquid resin is injected through a resin injection hole 4 and solidified, and then the molds are opened to take a ferrule 8 out. The optical fiber 9 is inserted into the ferrule 8 formed as mentioned above. The strength of the core pin 3 is large, so an insertion hole for fiber holding and fixation is easily formed in the axial direction of the ferrule 8. The insertion hole is made long in the axial direction of the ferrule 8 to prevent the optical fiber 9 from curving in the ferule 8 and also increase the adhesion area, so that the optical fiber 9 is fixed tightly to the ferrule.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in ferrules for optical fiber connectors used in optical communications.

(Prior Art) An optical fiber having a structure in which two optical fibers are fixed in each ferrule, and the ferrules are arranged such that the ends of the optical fibers are aligned and connected to each other in the axial direction. In connectors, high precision is required in the dimensions of the ferrule that determines the accuracy of the butt position of both optical fibers, and therefore the manufacturing cost thereof occupies a large proportion of the manufacturing cost of the entire connector. Conventionally, plastic ferrules made by integral molding have been attempted in order to reduce the manufacturing cost of ferrules, but the manufacturing process is shown in Figure 5, published in IEICE technical report 0QIE81-32. A mold like this is used.

The core pin 3 in FIG. 5 is cylindrical and has an extremely thin diameter of about 125 μm, which is approximately the same as the outer diameter of the optical fiber.

For this reason, it has the drawback of being easily broken and having poor mass productivity. In addition, since the length cannot be increased, the part of the ferrule that holds the optical fiber becomes shorter, making it easier for the optical fiber to bend inside the ferrule, and not allowing enough bonding area between the ferrule and the optical fiber. Therefore, there were various problems such as the need for careful adhesion.

(Problems to be Solved by the Invention) An object of the present invention is to provide a plastic ferrule for an optical fiber connector that is easy to manufacture and has stable characteristics.

(Means for Solving the Problems) The plastic ferrule of the present invention is a line including a plurality of tangents circumscribing at least three points on the circumference of a cross section perpendicular to the axial direction of the optical fiber. It has a structure having a columnar optical fiber holding/fixing insertion hole that surrounds the periphery and includes the optical fiber.

This differs from conventional plastic ferrules in that the insertion hole has a non-circular cross-section, and its cross-sectional area is sufficiently larger than the cross-sectional area of the optical fiber.

FIG. 1 is a sectional view of a mold for molding the plastic ferrule of the present invention, in which 1 is the upper part of the mold body, 2 is the lower part of the mold body, and 3 is for molding the insertion hole for holding and fixing the optical fiber in the ferrule. 4 is a resin injection port. The core pin 3 is precisely positioned at the center of the ferrule in the upper mold body 1 and the lower mold body 2. The cross-sectional shape of the core bin 3 is generally polygonal in many cases, but is not limited to a polygonal shape.

As an example of a polygon, if an equilateral triangle with a height h as shown in FIG. 2 is used, the bending strength of this triangular core pin 5 and a circular core pier 6 with a radius r inscribed inside the triangular core pin 5 are compared as follows.
It will look like this:

Here, 11 is the moment of inertia of the triangular core pin 5, and I2 is the moment of inertia of the circular core pin 6.

As is clear from equations [1] and (2), 11 is approximately three times as large as I2, and therefore, the triangular core pin 5 is approximately three times stronger in bending than the circular core pin 6.

Also, as shown in Figure 3, it is circumscribed to a circle with radius r, and radius 1
The cross-sectional quadratic Mome/H of the polygonal core pin 7 having a hexagonal cross-section inscribed in the circle 0r.

The result is as follows.

As is clear from equations (2) and (3), 13 is approximately 480 times larger than I2. Although the hole shown in FIG. 3 has a polygonal shape that contacts the optical fiber at three points, the number of contact points may be greater. Alternatively, each corner of this polygon may be rounded. Next, the ferrule is formed as follows.

As shown in FIG. 1, the upper part 1 of the mold body to which the core bin 3 is attached and the lower part 2 of the mold body are joined together by applying pressure. Liquid resin is injected from the resin injection port 4.

After the resin hardens, open the mold and remove the ferrule.

FIG. 4 is a cross-sectional view of the optical fiber inserted into the ferrule formed in this way, where 8 is the ferrule and 9 is the ferrule.
is an optical fiber, IO is a polygonal hole, and 11 is an adhesive.

Even with such a molding method, since the strength of the core bin is high, it is easy to form an insertion hole for holding and fixing a long optical fiber in the axial direction of the ferrule.

By making the insertion hole longer in the axial direction of the ferrule, it is possible to prevent the optical fiber from bending within the ferrule, and the adhesive area is increased, so that the optical fiber is firmly fixed to the ferrule. Furthermore, since there is a large gap between the ferrule and the optical fiber, it is easy to fill with adhesive when assembling the beans. These effects make it possible to realize an optical fiber connector that is less susceptible to environmental changes such as temperature changes and has stable characteristics.

(Effects of the Invention) As explained above, the plastic ferrule for an optical fiber connector of the present invention has a cross-sectional shape of the insertion hole for holding and fixing the optical fiber in the ferrule that is changed so that its cross-sectional area is larger than the cross-sectional area of the optical fiber. By increasing the size of the ferrule, the core pin can be made thicker to prevent it from breaking, making it suitable for mass production. Also, by using this ferrule,
An optical fiber connector with stable characteristics can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a mold for molding the plastic ferrule of the present invention, Figure 2 is a comparison between a circular core pin and a triangular core pin, Figure 3 is a comparison between a circular core pin and a polygonal core pin, and Figure 4 is a comparison between a circular core pin and a polygonal core pin. 5 is a cross-sectional view of the plastic ferrule of the present invention with an optical fiber inserted therein, and FIG. 5 is a cross-sectional view of a conventional mold for molding the plastic ferrule. 1... Upper part of the mold body 2... Lower part of the mold body 3...
・Core bin 4... Resin injection port 5... Triangular core pin 6... Circular core pin 7... Polygonal core pin 8... Ferrule 9... Optical fiber
10... Polygonal hole 11... Adhesive patent applicant Nippon Telegraph and Telephone Corporation Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a plastic ferrule for an optical fiber connector having an insertion hole for fixing an optical fiber accurately in the center, the insertion hole circumscribes at least three points on the circumference of a cross section perpendicular to the axial direction of the optical fiber. 1. A plastic ferrule for an optical fiber connector, characterized in that the optical fiber is surrounded by a line including a plurality of tangent lines, and is a columnar insertion hole that encloses the optical fiber.