Optical waveguides – With disengagable mechanical connector – Optical fiber/optical fiber cable termination structure
Reexamination Certificate
2001-03-20
2003-08-19
Kim, Robert H. (Department: 2882)
Optical waveguides
With disengagable mechanical connector
Optical fiber/optical fiber cable termination structure
C385S072000, C385S060000
Reexamination Certificate
active
06607306
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ferrule, made of thermoplastic resin, integrated with a flange into a monolithic structure, for use in an optical fiber connector, and a molding die therefor.
BACKGROUND OF THE INVENTION
Because conventional ferrules for use in optical fiber connectors are precision parts, such ferrules are manufactured from materials, such as metals, ceramics, and polycrystalline glass, using highly advanced technology including machining, and are thereby expensive products. A ferrule consists of a capillary portion, or capillary, and a flange. As for the capillary, excluding the flange, the injection molding technique is already being utilized by using ceramics, such as zirconia, where it is assumed that the die for the molding is formed to have dimensions approximately 20% greater than the product dimensions of the ferrule, in consideration of shrinkage caused during the ceramic burning process, and that precision working is applied to the capillary after burning. On the other hand, in order for a ferrule to satisfy the performance characteristics required when an optical fiber connector is connected, dimensional accuracy in terms of 1 &mgr;m is necessary. When taking into consideration such parameters as the die accuracy, molding characteristics, and burning characteristics, however, it is extremely difficult to satisfy such level of dimensional accuracy, which thereby constitutes a major cause for high manufacturing cost.
Therefore, to reduce the cost, developments and improvements of ferrules are in progress, including those for ferrules applied with injection molding, using thermoplastic resins. A die required for such injection molding may have a structure including a spool
51
, a runner
52
, a gate
53
, and a cavity
54
, as shown in
FIG. 7
, where a ferrule may be molded by casting molten resin into the die to flow through in this order. As shown in
FIG. 8
, this die is divisible at a parting line
55
into a stationary part fixed to the injection molding machine and a moving part movable in parallel with respect to the stationary part. The die has portions defining a cavity
56
for forming a capillary of the ferrule, and a core pin
57
for forming, in a connected structure, an optical fiber insertion hole including a guide hole part, a conical hole part, and a fine hole part, for inserting an optical fiber. The die also has a portion defining a cavity
58
for engaging with the core pin
57
, and a cavity
59
for forming a flange of the ferrule.
Here, it should be noted that, in a ferrule for use in an optical fiber connector, particularly important points may include: the outer diameter of the ferrule; the eccentricity of the axial part of the capillary to the fine hole part of the optical fiber insertion hole; and the state of all the guide hole part, the conical hole part, and the fine hole part, of the optical fiber insertion hole being made free from any protrusions and dents, thereby these holes being arranged in smooth succession. The outer diameter and eccentricity may deeply affect the performance and characteristics of the ferrule when it is assembled into an optical fiber connector, while the smoothness of the optical fiber insertion hole may prevent a fatal defect of insertion failure from occurring.
In the injection molding of a conventional ceramic ferrule, as described above, a stainless steel flange is press fit onto the ceramic (e.g., zirconia) capillary. In this injection molding using ceramics, the die for the molding is formed to have dimensions approximately 20% greater than the product dimensions of the ferrule, and, thereafter, precision post-process working is applied to obtain a ferrule having the product dimensions. This may cause a disadvantage in that material and working expenses would amount high, thereby forcing the cost to rise, and the weight would also get heavier.
Furthermore, in the injection molding of a conventional ceramic ferrule, where die dimensions are greater than the finished product dimensions for machine working the molded parts, the molding die has been employing a construction where a core pin for forming an optical fiber insertion hole including a guide hole part, a conical hole part, and a fine hole part, is integrated into a monolithic structure, and the front end portion of this core pin is inserted into the insertion opening of the cavity for forming the front end surface of the ferrule, and such constructions has caused no problems. In the injection molding using thermoplastic resin, however, because a finished ferrule is formed exactly in the same dimensions as the die dimensions, the core pin
57
tends to break when inserted into the insertion opening of the cavity
58
, if the gap between the core pin
57
and the insertion opening is narrow. Therefore, a relatively large gap is required between the core pin
57
and the insertion opening of the cavity
58
, which may cause a problem in the eccentricity between the core pin
57
and the insertion opening of the cavity
58
increases, and the core pin
57
may be bent due to pressure fluctuation in the resin when molded. One method to solve the problem could be to divide the core pin
57
between the circular conical part and the straight pin part. This however tends to leave parting marks and level differences in the ferrule after molding, which in turn may cause a new problem in that, when an optical fiber is inserted, the optical fiber is caught by such parting marks and gets broken. Breakage may be particularly likely to occur because thermoplastic resin is softer than optical fiber. Therefore, it is required that the core pin
57
is by all means integrated into a monolithic structure, and concentricity is maintained with high accuracy.
In addition, when forming the axial part of the capillary of the ferrule with the cylindrical cavity
56
, using a the thermoplastic resin, a problem may occur in that the front end part of the capillary is expanded to a trumpet-like shape as a result from the total effects of shrinkage and stretch due to quick cooling, pressure rise, and sink mark in the front end surface.
Moreover, when a gate for casting molten resin therethrough is connected to the flange of a complicated shape, fluctuations may occur in the flow and pressure of the molten resin when it passes through the complicated-shaped flange, which in turn may cause pressure fluctuation when the molten resin is cast into the cavity
56
for forming the axial part of the capillary. As a result, a problem occurs in that dispersion is caused to the roundness of the axial part of the capillary.
The present invention is made to solve the problems described above. Therefore, an object of the present invention is to provide a resin ferrule for use in an optical fiber that is capable of mass producing at low cost, reducing weight, preventing the front end part of the capillary from expanding to a trumpet-like shape, securing the roundness of the axial part of the capillary with high accuracy, and, furthermore, preventing eccentricity of the axial part to the optical fiber insertion hole, of the capillary from occurring, and to provide a proper molding die for such resin ferrule.
SUMMARY OF THE INVENTION
To solve the problems described above, inventors of the present invention have conducted tests on injection molding dies for various ferrules for use in optical fiber connectors since more than fifteen yeas ago. As a result, it has been known that, when a ring gate is employed, the outer diameter of the capillary of thermoplastic resin ferrules is correlated with the axial length, or width, of this gate, and the pressure preservation capability during the molding, and, thereby, specified dimensions of the targeted areas can be obtained by freely setting these correlated factors. Particularly, it has been found that, by having the flange of a complicated shape equipped with a ring gate of a very large axial width corresponding to ¼-½ the outer diameter of the capillary, fluctuations in the flow and pressure o
Kobayashi Hiroyuki
Ozeki Katsumi
Shinoki Norio
Takahashi Keiji
Daiichi Kasei Co., Ltd.
Kim Robert H.
Suchecki Krystyna
LandOfFree
Resin ferrule for use in optical fiber connector and molding... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Resin ferrule for use in optical fiber connector and molding..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resin ferrule for use in optical fiber connector and molding... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3123126