JPH0792537B2 - Ferrule for optical connector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ferrule for an optical connector used for connecting optical fibers to each other or between an optical fiber and an optical element. The present invention relates to a ferrule for an optical connector used when the optical characteristics of the optical fiber are affected even by a slight bending of the optical fiber.

[Problems to be solved by conventional techniques and inventions]

There are various types of optical connectors used to easily connect and disconnect between optical fibers or between an optical fiber and an optical element, but the mainstream is, for example,
Like the F01 type single-core optical fiber connector specified in JIS C 5970, the optical fiber strand is a cylindrical rod (ferrule).
This is a method in which the end faces of the ferrules are butted against each other by fixing it in the center of the ferrule and inserting it into a hollow cylinder (alignment sleeve) having a precise inner diameter. The structure of this ferrule has a precise outer diameter and is composed of a fitting portion to be inserted into the alignment sleeve and a flange portion for holding the fitting sleeve in the plug housing. As a ferrule used for an optical connector according to this method, for example, as described in Japanese Patent Application No. 60-11082, it has a fine through hole having an inner diameter slightly larger than the outer diameter of an optical fiber element wire, and has a zirconia ceramic. There is one manufactured by pressing a cylindrical rod-shaped fitting portion configured by itself into a metal flange portion. The feature is that
(1) The hardness and bending strength of the fitting part are high, and the reliability is high. (2) The structure is simple and the cost is low. (3) Japanese Patent Application
As described in 60-244050, since the Young's modulus of zirconia ceramic is lower than other ceramics, by polishing the ferrule end surface into a convex spherical shape and connecting them by applying a pressing force to each other in the axial direction, Even when the fiber retracts from the end face of the ferrule, the ferrule tip is deformed so that the core portions of the fiber can be brought into close contact with each other, and stable connection characteristics can be realized.

On the other hand, among optical fibers, there is a polarization-maintaining optical fiber that can preserve the polarization state of propagating light. A polarization-maintaining optical fiber has a characteristic of retaining its polarization state when linearly polarized light is incident in the principal axis direction. As a parameter for evaluating the performance, the extinction ratio, which is the ratio of the component of the optical power on the output side when the linearly polarized wave is incident in the principal axis direction and the component in the direction orthogonal to the principal axis direction, is used. In the case of the holding optical fiber, a value of −40 to −50 dB has been realized. However, even in such a polarization-maintaining optical fiber, when stress is generated inside by bending the optical fiber, the extinction ratio may be significantly deteriorated due to birefringence occurring in the optical fiber.

When the above-mentioned zirconia ceramic ferrule is bonded to the optical fiber core wire, as shown in FIG. 4, first, the epoxy adhesive 2 is dropped on the end face of the flange portion of the fiber 1, and then the vacuum is applied from the tip of the ferrule. Fill the inside of the ferrule with adhesive by suction. After that, an optical fiber core wire is inserted into this ferrule and heated to cure the adhesive. At this time, as shown in FIG. 5, when the ferrule 1 has a structure in which the fitting portion 3 is press-fitted into the flange portion 4, the hole diameter of the flange portion 4 at the connecting portion between the fitting portion 3 and the flange portion 4 is Since it spreads abruptly, bubbles 5 tend to remain in this portion even if vacuum suction is performed when filling the adhesive.
When the adhesive is cured while leaving air bubbles inside the flange in this way, as shown in FIG. 6, the non-uniformly distributed adhesive causes volume contraction during curing, so It produces a slight bend. FIG. 6 is a cross-sectional view showing a state in which the optical fiber core wire is bonded to the ferrule 1 described above, and is exaggerated to show the influence of bubbles remaining inside the flange portion 4. In the case of the ferrule 1, even if the adhesive is dropped from the end face of the flange portion and vacuum suction is performed from the tip of the fitting portion, bubbles remain inside the flange, so the adhesive is unevenly distributed around the optical fiber strand. . When the adhesive is heated and cured in this state, the optical fiber element wire 6 is slightly bent due to the volume contraction of the adhesive. Such a minute bending of the optical fiber strand causes almost no problem in the case of a normal single-mode optical fiber, but may deteriorate the extinction ratio in the case of the above-mentioned polarization-maintaining optical fiber. .

FIG. 7 is a sectional view showing the structure of another example of a ferrule according to the prior art, which is called a capillary type. In the ferrule 7 shown in this figure, the fitting portion 8 and the flange 9 are made of an integral metal, and the ceramic capillary 10 having a fine hole for fixing the optical fiber element wire to the center of the fitting portion 8 is a ferrule. It has a structure that is pressed into the tip.
A hole 11 for venting air is provided near the base of the fitting portion 8, but since this hole 11 is away from the entrance of the fine hole 12 of the capillary 10, it is completely filled when the adhesive is filled in the ferrule. Bubbles cannot be removed. Also in this case
Since the inlet of 12 is located in the middle of the fitting portion 8 having a precise outer diameter, if the air vent hole is provided at a position reaching the inlet of the fine hole 12, the adhesive leaked from the hole is There is a risk that it will adhere to the surface of the fitting portion 8 that has been finished. Therefore, in the ferrule 7 described above, the air vent hole must be provided at the base of the fitting portion 8. As a result, air bubbles remain when the adhesive is filled, and the optical fiber strand is bent and extinguished. The ratio may be deteriorated.

Therefore, it is an object of the present invention to provide a ferrule for an optical connector, in which the extinction ratio is less deteriorated even when bonded to a polarization maintaining optical fiber.

[Means for Solving the Problems]

The present invention relates to an optical connector ferrule in which a cylindrical rod-shaped fitting portion having a fine strand insertion hole having an inner diameter slightly larger than the outer diameter of an optical fiber strand in the axial direction is press-fitted into a through hole of a flange portion. , The through hole is a core wire insertion area having a constant diameter slightly larger than the optical fiber core wire, a fitting portion holding area having a constant diameter substantially equal to the fitting portion,
And an intermediate region in which the diameter sharply changes monotonically between the core wire insertion region and the fitting portion holding region, and the flange portion has a boundary between the intermediate region of the through hole and the fitting portion holding region. An air vent hole for communicating the through hole with the outside is formed in the vicinity.

The air vent holes are symmetrical with respect to the axis of the flange portion.
The number of individual pieces or more than that is formed at uniform intervals around the axis.

〔Example〕

1 (a), (b) and FIG. 2 are views showing an embodiment of the present invention.

As shown in FIGS. 1 (a) and 1 (b), the ferrule 21 of this embodiment includes a fitting portion 22 to be inserted into the alignment sleeve and a flange portion for holding the fitting portion 22 in the plug housing. It consists of 23 and.

The fitting portion 22 is formed in a cylindrical rod shape having a fine wire insertion hole 24 having an inner diameter slightly larger than the outer diameter of the optical fiber wire in the axial direction. The flange portion 23 is composed of a large-diameter tubular portion 25 and a small-diameter tubular portion 26, and has a through hole 27 into which the optical fiber core wire is inserted and the fitting portion 22 is inserted in the axial direction thereof. is there. The through hole 27 has a large diameter portion in the tubular portion 25, that is, a fitting portion holding region 28, and a small diameter portion in the tubular portion 26, that is, a core wire insertion region 29 and between the core wire insertion region and the fitting portion holding region. It consists of an intermediate region where the diameter changes sharply and monotonically. An annular projection 31 having grooves 30, 30 is formed on the outer peripheral surface of the distal end portion of the tubular portion 25.

The fitting portion 22 has a rear end portion having a through hole 27 in the flange portion 23.
It is press-fitted into the large diameter portion 28 of the. Then, in the flange portion, air vent holes 32, 32 for communicating the through hole with the outside are formed in the vicinity of the boundary between the intermediate area of the through hole and the fitting portion holding area. In this case, vent hole 3
2, 32 are provided at symmetrical positions with respect to the axis of the flange portion 23.

In order to fix the optical fiber core wire to the ferrule 21 having the above structure, first, as in the case of FIG.
The adhesive is dripped on the end face of the. In this way, the adhesive moves downward by its own weight and fills the through hole 27. In this case, the air near the inlet of the wire insertion hole 24 in the through hole 27 is discharged to the outside through the air vent holes 32. Therefore,
At this time, no bubbles remain in the through holes 27, and the adhesive is evenly distributed in the through holes 27. Then, the element insertion hole 24 is filled with the adhesive by vacuum suction from the tip of the fitting portion 22. Then, the optical fiber core wire is inserted into the ferrule 21 and heated to cure the adhesive.

FIG. 2 is a view showing a state in which an optical fiber core wire is bonded to the ferrule 21. In this figure, reference numeral 33 is an adhesive, 34 is an optical fiber core wire, and 35 is an optical fiber element wire. As shown in this figure, since the adhesive 33 is uniformly filled in the through holes 27, even when the adhesive 33 is hardened, the optical fiber element wire 35 is not bent.

Although two air vent holes are provided in the above embodiment,
The number of the air vent holes may be two or more.
In this case, it is preferable that the air vent holes are provided with a uniform interval around the axis of the flange portion in order to effectively release the air in the flange portion.

FIG. 3 is a result of measuring the extinction ratio when the ferrule according to the present invention and the ferrule according to the conventional technique are bonded to a polarization maintaining optical fiber, and the extinction ratio is measured when A is a conventional zirconia ferrule. As a result, B is the measurement result of the extinction ratio when the ferrule according to the present invention is used.
However, the fiber length is 5 m, and the extinction ratio of a single optical fiber is −
It is 46 dB. As is apparent from FIG. 3, when the ferrule according to the present invention is used, the extinction ratio is clearly improved as compared with the ferrule according to the conventional technique.

〔The invention's effect〕

As described above, the ferrule according to the present invention can be filled with the adhesive agent without leaving air bubbles inside the ferrule by the air vent hole provided in the flange portion, so that the minute bending of the optical fiber strand inside the ferrule does not occur. As a result, a high-performance optical connector can be realized without deteriorating the extinction ratio even when used in a polarization maintaining optical fiber.

Further, since two air vent holes are provided symmetrically about the axis of the flange portion, or a larger number of holes are provided with a uniform interval around the axis, the air inside the ferrule can be discharged more effectively.

[Brief description of drawings]

FIG. 1 (a) is a side sectional view of a ferrule for an optical connector shown as an embodiment of the present invention, and FIG. 1 (b) is a rear view thereof.
FIG. 2 is a side sectional view showing a state in which an optical fiber core wire is bonded to the ferrule shown in FIGS. 1 (a) and 1 (b), and FIG. 3 compares the characteristics of the ferrule according to the present invention and the ferrule according to the prior art. FIG. 4 is an explanatory view showing a method of filling the ferrule with the adhesive, FIG. 5 is a side sectional view showing a state when the ferrule according to the prior art is filled with the adhesive, and FIG. FIG. 7 is a side sectional view showing a state in which a ferrule according to the technique is adhered to an optical fiber, and FIG. 7 is a side sectional view showing the structure of another ferrule according to the conventional technique. 22 …… Mating part, 23 …… Flange part, 24 …… Element wire insertion hole,
27 …… Through hole, 32 …… Air vent hole, 34 …… Optical fiber core wire, 35 …… Optical fiber bare wire.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Etsuji Sugita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (56) Reference JP-A-61-170709 (JP, A) Sho 63-18307 (JP, A) JP 59-160115 (JP, A) JP 59-3408 (JP, A) JP 55-155316 (JP, A) JP 59-189309 (JP , A) Actually opened 58-54608 (JP, U) Actually opened 58-152214 (JP, U)

Claims (1)

[Claims] 1. An optical connector ferrule comprising a fitting portion to be inserted into an alignment sleeve and a flange portion for holding the fitting portion in a plug housing, wherein the fitting portion has an axial direction. It is formed in a cylindrical rod shape having a fine strand insertion hole having an inner diameter slightly larger than the outer diameter of the optical fiber strand, and the flange portion has a core wire insertion having a constant diameter slightly larger than the optical fiber core wire. A through hole formed of an area, a fitting portion holding area having a diameter substantially equal to that of the fitting portion, and an intermediate area in which the diameter sharply and monotonically changes between the core wire insertion area and the fitting portion holding area. And a rear end portion of the fitting portion is press-fitted into a through hole of the flange portion, and the flange portion is near a boundary between the intermediate region of the through hole and the fitting portion holding region. On the through hole and outside 2 air vent hole is formed which communicates, symmetrically to the axis of the air vent hole is the flange
A ferrule for an optical connector, characterized in that it is formed individually or in a larger number at even intervals around the axis.