Optical ferrule

Details Optical ferrule Optical ferrule

2000-12-20

2002-02-19

Ullah, Akm E. (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber/optical fiber cable termination structure

C264S001250, C425S116000

Reexamination Certificate

active

06347890

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical ferrule, and more particularly, to an optical ferrule for establishing an optical connection between optical fibers without causing an optical loss.
2. Description of the Related Art
To connect optical fibers in a light communication system, a mono filamentary ferrule and a multistrand MT-type ferrule are employed, both of which are formed of a resin molding.
As shown in
FIG. 1
, mono filamentary ferrules
10
joined at their connecting end faces
1
a
are fixedly connected to each other by means of an adapter
4
, thereby establishing a connection between optical fibers respectively inserted in advance into fiber core insertion holes (more generally, optical fiber insertion holes)
1
b
of the ferrules.
As shown in
FIG. 2
, a multistrand MT-type ferrule comprises a ferrule body
1
that is formed into one piece and formed with a plurality of optical fiber insertion holes
1
b
and guide pin holes
2
having an inner diameter of about 125 &mgr;m. In establishing a connection between optical fibers, the optical fibers inserted into the optical fiber insertion holes
1
b
are fixedly bonded therein by an adhesive, and then connecting end faces
1
a
of ferrule bodies
1
of ferrules
10
are polished to a mirror-finished surface by using, for example, a lubricating oil having diamond abrasive grains dispersed therein. Next, guide pins
3
are inserted into the guide holes
2
of the ferrules
10
, and the connecting end faces of the ferrule bodies are abutted together, to thereby establish optical connection between the optical fibers.
In the case of the MT-type ferrule of this type, if the positional and dimensional accuracies of the guide pin holes are degraded, the optical axes of connected optical fibers are declined when the ferrule bodies are abutted together, which causes a large optical loss. Thus, it is necessary to form the guide pin holes in the ferrule body
1
with high accuracy. The mono filamentary ferrule is also required to be molded with high dimensional accuracy to reduce the optical loss since the connection accuracy of the optical fibers and the degree of optical loss are determined by the roundness and cylindricity of the periphery of the ferrule, the concentricity between the outer diameter of the ferrule and the optical fiber insertion hole, and the perpendicularity of the optical fiber insertion hole.
Conventionally, in order to mold optical ferrules with high accuracy, transfer molding of a resin (for example, a thermosetting resin such as an epoxy resin) that is small in the rate of mold shrinkage and has a high dimensional stability against aging has been employed for the production of optical ferrules. However, transfer molding takes time to thermally cure the resin filled in a mold, requiring a long molding cycle time, and hence it is not suited to mass production.
To obviate the problems, there has been recently proposed a technique in which a polyphenylene sulfide resin that is excellent in dimensional stability, high fluidity, and environmental resistance is subjected to injection molding which has a short molding cycle time. In this case, polyphenylene sulfide is ordinarily filled with a large amount of silica so as to make the thermal expansion coefficient of the molded ferrule and that of optical fibers close to each other, thereby reducing thermal stress generated in the ferrule. However, the silica filled in the resin is liable to fall off during the polishing of the connecting end face of the ferrule made of such a molding material, which makes it difficult to obtain a smoothed connecting end face.
To eliminate this problem, a method is proposed in which silica is subjected to surface-treatment by a silane coupling agent before it is filled in the resin, and a mixture of spherical silica and irregular-shaped silica is used as silica, to thereby prevent fall-off of silica (see Japanese Unexamined Patent Publication No. 6-299072). However, the proposed method still has the following problems:
First, the smoothness of the polished connecting end faces is insufficient, which makes it difficult to realize an excellent optical connection between optical fibers only by physical contact, i.e., by physically abutting the connecting end faces of the ferrules against each other.
Therefore, in connecting ferrules, conventionally, a matching agent such as silicone paste is applied to the polished end faces to prevent a change in refractive index, i.e., occurrence of an optical loss, from being caused in the gap between the optical fibers. However, the application of a matching agent must be carefully carried out so as not to allow dust or dirt to enter into the applied portion. Depending on the manner of applying the matching agent, bubbles may be produced in the agent applied portion to cause a markedly large optical loss. For these reasons, it is desired to develop ferrules which allow end faces of optical fibers to be connected to each other, without using a matching agent, i.e., solely by physical contact, such that no gap is formed between the optical fibers, thereby preventing occurrence of optical loss.
To establish a proper physical contact of ferrules, optical fibers are required to have ends thereof protruding from the polished end faces of the ferrules by about two to three &mgr;m.
In the case of the optical ferrule obtained by molding a resin filled with a large amount of silica, the connecting end face of the ferrule itself is hard since the hardness of silica is close to that of the optical fiber. Hence, the connecting end face of the optical fiber and that of the optical ferrule are both equally polished away, so that the length of protrusion of the optical fiber from the polished end face of the optical ferrule tends to become smaller than the required value. In such a case, a gap is produced between the connecting end faces of the optical fibers to cause a markedly large optical loss.
Further, MT-type optical ferrules are adapted to be connected via the guide pins that are inserted into the guide pin holes of the ferrule bodies, so that the guide pin holes may be damaged or broken if the operations of connecting and disconnecting the ferrules by fitting and removing the guide pins to and from the guide pin holes are repeated. This makes it impossible to carry out the connecting operation.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an optical ferrule that is excellent in smoothness of a connecting end face and allows an optical fiber to have a suitable length of protrusion from the connecting end face, whereby a connecting operation can be effected without using a matching agent and an optical loss between connected optical fibers can be reduced, with the optical ferrules hardly damaged even if it is subjected to repeated physical contact.
The present inventors made intensive study for attaining the above object, and found that when an optical ferrule is manufactured by injection molding, an intended optical ferrule can be obtained if a resin composition containing not only silica but also the below-mentioned whisker and exhibiting the below-mentioned melt viscosity is used as a molding material. Based on the finding, the present inventors have developed an optical ferrule of this invention.
According to the present invention, there is provided an optical ferrule which is a molding of a resin composition and which has an optical fiber insertion hole and a polished connecting end face. The resin composition contains, as essential constituents, a base resin, silica, and whisker.
The optical ferrule of this invention obtained by molding the aforementioned resin composition is not prone to produce burrs during the molding, has a high dimensional accuracy, is excellent in smoothness of the polished connecting end face thereof, and ensures an appropriate length of protrusion of an optical fiber from the polished end face. This makes it possible to realize physical contact between the ferrule and another ferrule without causi

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