JPH04298704A - Ferrule - Google Patents

Abstract

PURPOSE:To lower coefft. of thermal expansion so as to suppress the contraction by cooling after injection molding and to improve surface roughness by compounding an inorg. filler with a thermoplastic org. high-polymer material. CONSTITUTION:The ferrule 1 is formed by injection-molding the thermoplastic org. high-polymer material compounded with the inorg. filler having <=10mum average grain size. This inorg. filler acts to suppress the contraction by the cooling after injection molding by lowering the coefft. of thermal expansion. Glass beads, SIRASU balloons, glass fibers, carbon fibers, etc., are used for this filler. The ferrule 1 is so formed that its outer peripheral surface 1a to be fitted onto the cylindrical rod of a connector for optical fibers has out of roundness. In addition, a through-holes 2 to be inserted with an optical fiber cable 20 is bored at the axial center of the ferrule. The surface roughness is extremely approximated to the surface roughness of metallic molds by confining the average grain size of the inorg. filler to <=10mum. The ferrule having a desired size and shape is thus obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrule used in an optical fiber connector.

0002

[Background Art] In order to form an optical fiber communication network,
Optical fiber connectors are required to interconnect optical fibers. When connecting optical fibers using this optical fiber connector, it is important to accurately align the axes of the optical fibers with small diameter cores and connect them to keep the transmission loss at the connection part as low as possible. becomes. To align and connect optical fibers, align the center of the core of the optical fiber with the center of the cylindrical rod based on the outer diameter of the cylindrical rod, and then insert a pair of optical fibers into the cylindrical rod with the center of the optical fiber as the axis. Optical fibers are connected by inserting and holding the ferrules from both ends of the cylindrical rod and bringing the connecting end surfaces into close contact. In this case, in order to accurately align and connect the optical fibers, the outer peripheral surface of the ferrule is required to be a perfect circle. Here, there is a minimum circumscribed circle center method as a center definition method in roundness measurement. That is, as shown in FIG. 3, this is a method of performing shape analysis based on the center of the smallest circumscribed circle that circumscribes the shape obtained by measurement. And the difference D between these concentric circles
is the roundness, and as can be seen from the figure, it can be said that the influence of surface roughness affects the roundness.

[0003] Therefore, the surface roughness of a ferrule desired in the market as a ferrule for an optical connector is required to be approximately 1.0 to 2.0 μm according to JIS standard Rmax. However, even if the surface roughness of the mold used for thermoplastic organic polymer ferrule molding is processed to a good level and injection molding is performed, the surface roughness of the resulting thermoplastic polymer ferrule will vary depending on the molding conditions and mold temperature. It is difficult to obtain a desired surface roughness due to factors other than the mold, such as the properties of the molding material. This is because thermoplastic organic polymers generally have a large coefficient of thermal expansion and therefore shrink significantly when cooled after injection molding. It is well known that attempts have been made to reduce the coefficient of thermal expansion of thermoplastic organic polymers by blending inorganic substances with them as a means of reducing and alleviating this property. This inorganic filler is blended with an average diameter of 20 μm or more.
100μm fiber or average particle size 20μm~1
00 μm beads are used in a weight ratio of 10 to 50%.

0004

[Problems to be Solved by the Invention] However, the surface roughness of a ferrule injection molded with a composition consisting of a thermoplastic organic polymer and the above-mentioned inorganic filler is less than that of the mold. Significantly decreased. This tendency is more pronounced in the case of injection molding using a thermoplastic organic polymer material containing a larger amount of inorganic filler. For this reason, as a measure to improve the reduction in surface roughness caused by the addition of inorganic fillers, the filling weight ratio of the inorganic filler to the thermoplastic organic polymer has been kept low. However, keeping the mixing ratio of the inorganic filler with the thermoplastic organic polymer at a low level eliminates the effect of reducing the coefficient of thermal expansion, which is the original purpose of adding the inorganic filler, and makes it difficult to obtain a ferrule with the desired size and shape. was difficult.

[0005] Accordingly, an object of the present invention is to provide a ferrule which can suppress shrinkage due to cooling by reducing the coefficient of thermal expansion and has a good surface roughness.

[0006]

[Means for Solving the Problems] The ferrule of the present invention is characterized in that it is made of a thermoplastic polymer material blended with an inorganic filler having an average particle size of 10 μm or less.

[0007]

[Function] According to the structure of the present invention, by blending an inorganic filler into the thermoplastic organic polymer material, the thermal expansion coefficient can be reduced and shrinkage due to cooling after injection molding can be suppressed. Furthermore, by setting the average particle size of the inorganic filler to 10 μm or less, the surface roughness becomes extremely close to that of the mold, making it possible to obtain a ferrule with desired dimensions and shape. Therefore, the alignment of the optical fibers can be properly connected, and the adhesion between the opposing connection end surfaces can also be improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A ferrule according to an embodiment of the present invention will be explained based on FIGS. 1 and 2. That is, this ferrule 1 is formed as shown in FIG. 2 by injection molding a thermoplastic organic polymer material containing an inorganic filler having an average particle size of 10 μm or less. The inorganic filler reduces the thermal expansion coefficient to suppress shrinkage due to cooling after injection molding, and glass beads, glass balloons, glass fibers, carbon fibers, etc. are used as the inorganic filler. Further, the ferrule 1 is formed so that the outer circumferential surface 1a, which is fitted into a cylindrical rod (not shown) of an optical fiber connector, is a perfect circle, and the through hole 2 through which the optical fiber cable 20 is inserted is axially formed. It's drilled into my heart. The through hole 2 is connected to the first straight pipe part 3 via a first straight pipe part 3 that opens in the connection end surface 10 and is provided only at the end on the connection side, and a first tapered part 4 that widens toward the insertion side. The third straight pipe part 7 is connected to the second straight pipe part 5 via a second tapered part 6 expanding toward the insertion side and is open to the insertion end surface 11.

The inner diameter of the first straight pipe section 3 is set to be slightly larger (about 0.5 μm) than the outer diameter of the optical fiber 21.
The optical fiber 21 can be fitted inside. The inner diameter of the second straight pipe section 5 is approximately 0.3 mm to 0.7 mm, and is set slightly smaller than the outer diameter of the jacket 22 that covers the optical fiber 21, so that the jacket 22 is not inserted and the optical fiber 21 is loosely fitted. It is designed so that it will be done. Further, the inner diameter of the third straight pipe section 7 is set to a size that allows the jacket 22 to be inserted therein.

Next, the operation of attaching the exposed end of the optical fiber 21 of the optical fiber cable 20 to the ferrule 1 will be explained. That is, an adhesive (not shown) is injected into the through hole 2 in advance, and the optical fiber 21 is inserted from the insertion end surface 11 of the ferrule 1 into the third straight tube section 7, the second tapered section 6, and the second straight tube section. 5 and the first tapered part 4 in order, and then inserted into the first straight pipe part 3. At this time, the inner diameters of the third straight pipe part 7 and the second straight pipe part 5 are considerably larger than the outer diameter of the optical fiber 21, and the second tapered part 6 and Since the first tapered portion 4 has a shape that expands toward the insertion side, the optical fiber 21 is smoothly guided to the first straight tube portion 3. Further, the inner diameter of the second straight pipe portion 5 is the same as that of the jacket 22.
The jacket 22 is not inserted into the second straight pipe part 5 and the optical fiber 2
1 is inserted loosely. As described above, since the inner diameter of the second straight pipe section 5 is set to a size that allows the optical fiber 21 to be fitted loosely, the adhesive can be smoothly injected into the second straight pipe section 5 without causing any missing parts. In addition to the first straight tube section 3, the second straight tube section 5 can be bonded reliably, and the adhesive strength of the optical fiber 21 can be improved.

[0011] Furthermore, when connecting the optical fiber 21,
A pair of ferrules 1 with optical fibers 21 attached thereto as described above are inserted into a cylindrical rod so that the connection end surfaces 10 face each other. In this case, the average particle size of the added inorganic filler was 10 μm.
As the following, in addition to the original cooling shrinkage rate reduction effect,
The roundness of the outer circumferential surface 1a of the ferrule 1 is increased, and the surface roughness is improved. The table below shows experimental data on surface roughness due to differences in particle size.

As is clear from this table, it can be seen that the surface roughness is significantly improved.

Since the surface roughness of the ferrule 1 is improved as described above, it is possible to connect the optical fibers 21 with their axes accurately abutting each other. In addition, when connecting, the opposing connection end faces 10 with exposed end faces of the optical fibers 21 are polished to a mirror finish and then brought into close contact.As mentioned above, the small particle size of the inorganic filler improves the close contact. becomes good, and the misalignment of ferrule 1,
It can prevent tilting.

Note that the shape of the ferrule 1 is not limited to that shown in FIG.

[0015]

[Effects of the Invention] According to the ferrule of the present invention, by blending an inorganic filler with a thermoplastic organic polymer material,
By reducing the coefficient of thermal expansion, shrinkage due to cooling after injection molding can be suppressed. Furthermore, the average particle size of the inorganic filler was
By setting it to 0 μm or less, the surface roughness becomes extremely close to that of the mold, and a ferrule with desired dimensions and shape can be obtained. Therefore, the alignment of the optical fibers can be properly connected, and the adhesion between the opposing connection end surfaces can also be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional front view of a ferrule according to an embodiment of the present invention.

FIG. 2 is a perspective view of this ferrule.

FIG. 3 is an explanatory diagram showing the relationship between surface roughness and roundness.

[Explanation of symbols]

1 Ferrule

Claims (1)

[Claims] 1. A ferrule characterized in that it is made of a thermoplastic polymer material blended with an inorganic filler having an average particle size of 10 μm or less.