JPH0380209A - Perrule for polarization maintaining optical fiber - Google Patents

Abstract

PURPOSE:To prevent the deterioration in extinction ratio by forming a groove as a route for air venting which communicates the part near the inlet of a fiber insertion hole to the outside to the joint part between a flange part and a fitting part. CONSTITUTION:A ferrule 1 consists of the fitting part 2 for fixing an optical fiber to the center and the flange part 3 for holding the coated optical fiber and the groove 5 is inscribed on the outside periphery at one end of the fitting part 2. An adhesive agent is packed into a through-hole 8 when the adhesive agent is dropped to the end face of the flange part 3 in order to fix the coated optical fiber to the ferrule 1. The air near the inlet of the fiber insertion hole 4 in the through-hole 8 is then discharged through the groove 5 to the outside. The remaining of bubbles in the through-hole 8 is, therefore, obviated and the adhesive agent is uniformly distributed into the through-hole 8. The adhesive agent is packed into the fiber insertion hole 4 as well by vacuum suction from the front end of the fitting part 2. The coated optical fiber is thereafter inserted into the ferrule 1 and is heated to cure the adhesive agent. The extinction ratio is improved in this way.

Description

Detailed Description of the Invention [Technical Field to which the Invention Pertains] The present invention relates to a ferrule that is attached to the end of an optical fiber and used in the connection between an optical fiber and an optical element or between optical fibers, and in particular for polarization-maintaining light. This relates to the structure of a ferrule used in cases where minute bends within the ferrule pose a problem in terms of optical properties, such as in fibers.

[Conventional technology]

The mainstream of optical connectors used to easily connect and disconnect optical fibers is to connect bare optical fibers to a cylindrical rod (ferrule), such as the FOI type single-core optical fiber connector specified in JISC5970. In this method, the ferrule is fixed at the center and held floating in the connector housing, then inserted into a hollow cylinder (alignment sleeve) with a precise inner diameter, and the end surfaces of the ferrules butt against each other.

In addition, in the connection between an optical fiber and an optical element, in order to accurately align the optical axes of each other, the ends of the optical fibers should be
Methods include fixing the ferrule in advance at the center of the ferrule, positioning it using a fine adjustment table, etc., and then fixing the ferrule, or inserting the ferrule into a precision sleeve, etc., and positioning the ferrule without adjustment.

As an example of a ferrule used in these cases, as described in Japanese Patent Laid-Open No. 170709/1986, a ferrule made of a single zirconia ceramic has a fine through hole with an inner diameter slightly larger than the outer diameter of the optical fiber. There is one that is manufactured by press-fitting a cylindrical rod-shaped fitting part made up of into a metal flange part. It has excellent characteristics such as (1) high reliability with high hardness and bending strength of the fitting part, and (2) simple structure and low cost.

On the other hand, some optical fibers include polarization-maintaining optical fibers that can preserve the polarization state of propagating light. A polarization-maintaining optical fiber has a property of maintaining its polarization state when linearly polarized light is input in the direction of its principal axis.

As a parameter to evaluate its performance, the extinction ratio, which is the ratio of the optical power on the output side in the principal axis direction and the component in the perpendicular direction when linearly polarized waves are incident in the principal axis direction, is used.
In the case of a relatively short polarization maintaining optical fiber, a value of -40 to -50 dB has been achieved. However, in such a polarization-maintaining optical fiber, if stress is generated inside the optical fiber by, for example, bending the optical fiber, birefringence will occur within the optical fiber, which may significantly deteriorate the extinction ratio.

When bonding the aforementioned zirconia ceramic ferrule to an optical fiber, first drop the epoxy adhesive 13 onto the end surface of the flange portion 17 of the ferrule 16, as shown in FIG. As shown in (b),
The inside of the ferrule 16 is filled with the adhesive 13 by vacuum suction from the tip of the ferrule 16. Thereafter, an optical fiber is inserted into this ferrule 16 and heated to harden the adhesive. At this time, if the ferrule 16 has a structure in which the fitting part 19 is press-fitted into the flange part 17 as shown in FIG. Because the hole diameter suddenly widens, air bubbles 20 tend to remain in this area even if vacuum suction is applied when filling the adhesive.If the adhesive is cured with air bubbles left inside the flange, As shown in FIG. 11, the non-uniformly distributed adhesive causes volumetric contraction during curing, causing a slight bend in the optical fiber strand 15. Such minute bends in the optical fiber are caused by
There is almost no problem in the case of a normal single mode optical fiber, but in the case of the above-mentioned polarization maintaining optical fiber, the extinction ratio will be lowered.

Further, FIG. 12 is a cross-sectional view showing the structure of another example of a conventional ferrule called a capillary type.

In this case, the fitting part 26 and the flange part 27 are made of a single piece of metal, and a capillary 2 made of ceramic has a fine hole 30 for fixing the optical fiber at the center of the fitting part 26.
8 is press-fitted into the tip of the ferrule 29. There is one air vent hole 31 near the base of the fitting part 26, but since it is far from the entrance of the fine hole 30 of the capillary 28, it is difficult to completely eliminate air bubbles when filling the adhesive into the ferrule 29. In this case, since the entrance of the fine hole 30 is located in the middle of the fitting part 26 which has a precise outer diameter, leakage from the hole where the air vent hole is provided reaches near the entrance of the fine hole 30. There is a risk that the adhesive may adhere to the precisely finished surface of the fitting portion 26. Therefore, in the above-mentioned ferrule 29, there is no choice but to provide the air vent hole 31 at the root of the fitting portion 26, and air bubbles will remain when filling the adhesive. Also, even if it were possible to provide air vent holes near the entrances of the micropores,
A single hole cannot completely remove air bubbles on the opposite side of the hole. As a result, the optical fiber strands are bent due to volumetric shrinkage upon curing of the adhesive, resulting in deterioration of extinction ratio.

[Problem to be solved by the invention]

As explained above, in conventional ferrules, air bubbles cannot be completely removed from the inside of the ferrule when filled with adhesive, resulting in minute bends in the optical fiber inside the ferrule. As a result, there has been a problem in that a good extinction ratio cannot be obtained when a ferrule is bonded to connect a polarization-maintaining optical fiber and an optical element or optical fiber.

Therefore, the purpose of the present invention is to make it possible to completely remove the air bubbles inside the ferrule when it is filled with adhesive, and to create a polarized beam that does not cause deterioration of the extinction ratio even when bonded to a polarization-maintaining optical fiber. An object of the present invention is to provide a ferrule for holding optical fibers.

[Means to solve the problem]

The present invention provides a ferrule in which a cylindrical rod-shaped fitting portion having a fine wire through hole having an inner diameter slightly larger than the outer diameter of the optical fiber wire in the axial direction is press-fitted into the through hole of the flange portion. A groove is formed at the joint portion between the fitting portion and the fitting portion as an air vent path for communicating the vicinity of the entrance of the wire insertion hole to the outside.

It is preferable that the air venting paths are provided in two symmetrical directions about the axis of the flange portion, or in four paths at uniform intervals around the axis.

When the ferrule is used as an optical fiber terminal, the air venting path may be formed as a hole on the flange portion, or the fitting portion may include an optical lens at one end.

Furthermore, by providing a retaining means for the optical connector housing B on the flange portion, it can also be used for an optical connector.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention.

(a) is a cross-sectional view in the axial direction, and (b) is a cross-sectional view taken along line AA' shown in (a). As shown in FIG. 1, the 7-erule 1 of this embodiment consists of a fitting part 2 that fixes the optical fiber at the center and a flange part 3 that holds the optical fiber core.

The fitting part 2 is formed in the shape of a cylindrical rod having a fine wire insertion hole 4 having an inner diameter slightly larger than the outer diameter of the optical fiber in its axial direction, and has four holes on the outer periphery of one end. A groove 5 is carved. The flange portion 3 is a large diameter cylindrical portion 6
and a small-diameter cylindrical part 7, which has a through hole 8 into which the optical fiber is inserted from one end in the axial direction and the fitting part 2 is inserted from the other end. It consists of a large diameter part 9 in the section 6 and a small diameter part 10 in the cylindrical part 7,
The rear end portion of the large diameter portion 9 is formed in a tapered shape and continues to the small diameter portion 10 .

The rear end of the fitting portion 2 is press-fitted into the large diameter portion 9 of the through hole 8 of the flange portion 3 . Here, the groove 5 serves as an air vent that communicates the vicinity of the entrance of the wire insertion hole 4 with the outside.
Four grooves 5 are provided at uniform intervals around the axis of the flange portion.

In order to fix the optical fiber core to the ferrule 1 having the above-described structure, adhesive is first dropped onto the end surface of the flange portion 3, as in the case of FIG. 10. In this way, the adhesive moves downward under its own weight and is filled into the through hole 8. In this case, air in the vicinity of the wire insertion hole 4 in the through hole 8 is exhausted to the outside through the air vent groove 5. Therefore, at this time, no air bubbles remain in the through hole 8, and the adhesive is uniformly distributed within the through hole 8. Then, the adhesive is also filled into the wire insertion hole 4 by vacuum suction from the tip of the fitting part 2. Thereafter, an optical fiber is inserted into this ferrule 1 and heated to harden the adhesive.

FIG. 2 is a diagram showing a state in which a coated optical fiber is adhered to the ferrule 1. In this figure, reference numeral 13 indicates adhesive;
4 is a coated optical fiber, and 15 is a bare optical fiber. As shown in this figure, since the adhesive 13 is uniformly filled in the through hole 8, even when the adhesive 13 hardens, the optical fiber 15 does not bend.

In addition, in the above embodiment, air vent grooves were provided at four locations, but they may also be provided at two locations symmetrically with respect to the axis of the flange portion.
Alternatively, it is also possible to provide four or more force points symmetrically about the axis of the flange portion.

FIG. 3 shows the results of measuring the extinction ratios of 46 ferrules of the present invention attached to polarization-maintaining optical fibers and 49 ferrules of conventional ferrules attached to polarization-maintaining optical fibers. A is the measurement result of the extinction ratio when a conventional zirconia ferrule is used, and 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 the single optical fiber is -46 dB.
It is. As is clear from FIG. 3, when the ferrule according to the present invention is used, the extinction ratio is clearly improved compared to the ferrule according to the prior art.

FIG. 4 shows an example of a collimator constructed using the ferrule according to the present invention, in which 21 is a lens, and 22 is a sleeve for fixing the lens 21 and the ferrule 1.

FIG. 5 shows a second example of a collimator constructed by applying the present invention, in which a lens 21 is provided directly at the tip of the fitting part 18 of the ferrule 23.

In this way, by configuring the fitting portion of the ferrule to include an optical lens, it is possible to further reduce the size of the coupling portion with the optical element.

FIG. 6 shows an example of an LD module configured using the ferrule according to the present invention, where 24 is an LD chip, 22 is an LD module, and 24 is an LD chip.
Chip 24. Lens 21. This is a sleeve that fixes the ferrule l.

FIG. 7 shows an example in which the ferrule according to the present invention is used as a polarization-maintaining optical fiber terminal, and is used for direct connection to the optical waveguide 25.

FIG. 8 shows another embodiment of the ferrule according to the present invention.

32 is a ferrule, 33 is a fitting portion, and 34 is a flange portion. This is an example in which a hole 12 is provided in the flange portion instead of a groove as a path for air venting, and like the groove, it has the function of communicating the inside and outside of the flange portion.

In order to use the ferrule according to the present invention in an optical connector, FIG. 9 shows a ferrule in which a keyway 11 is provided on the outer periphery of the flange portion as a means for connecting to an optical connector housing. (a)
is a cross-sectional view in the axial direction, and (b) is a cross-sectional view taken along the line AA' shown in (a).

In the figure, 35 is a ferrule, and 36 is a flange portion.

〔Effect of the invention〕

As detailed above, the ferrule of the present invention allows the adhesive to be filled inside the ferrule without leaving any air bubbles inside the ferrule due to the air vent path provided at the joint between the fitting part and the flange part. As a result, even when used as a polarization-maintaining optical fiber, a high-performance optical fiber terminal can be realized without deteriorating the extinction ratio.

Further, by arranging two air vent paths symmetrically about the axis of the flange portion, or by arranging four air vent paths at uniform intervals around the axis, the air inside the ferrule can be more effectively discharged.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the ferrule according to the present invention, FIG. 2 is a cross-sectional view showing a state in which an optical fiber is bonded to the ferrule according to the present invention, and FIG. 3 is a cross-sectional view showing the ferrule according to the present invention and the conventional technology. A graph showing a comparison of the characteristics of ferrules, FIGS. 4 and 5 are cross-sectional views showing an embodiment of a collimator constructed using a ferrule according to the present invention, and FIG. 6 is a diagram showing an embodiment of an LD module constructed according to the present invention. FIG. 7 is a cross-sectional view showing an example in which the ferrule according to the present invention is used as an optical fiber terminal, FIG. 8 is a cross-sectional view showing another embodiment of the present invention, and FIG. 9 is a cross-sectional view showing the present invention. FIG. 10 is a cross-sectional view showing an example of the structure of a ferrule applied to an optical connector. FIG. FIG. 11 is a cross-sectional view showing a state in which an optical fiber is bonded to a conventional ferrule, and FIG. 12 is a cross-sectional view showing another example of the conventional ferrule. 1.16.23.29.32.35... Ferrule 2
．． 18.19.26.33...Mating part, 3.17,2
7, 34. 36... Flange portion, 4... Element wire insertion hole, 5... Groove, 6... Large diameter cylindrical portion, 7... Small diameter cylindrical portion, 8... Penetration Hole, 9...Large diameter part, 10...
Small diameter part, 11... Keyway, 12... Hole, 1
3... Adhesive, 14... Optical fiber core, 15
...Optical fiber wire, 20...Bubble, 21...
・Lens, 22... Sleeve, 24... LD chip, 25... Leading waveguide, 28... Capillary, 30... Fine hole, 31... Air vent hole, (α) No.! Enta 15 20 25 Itto 35 40 45 1jo) and (dB) 1ro fL table/79ru//z tb (≧1) - Ichinomikou ai - 7fu#lt/ -Tsum- Meneike 3 Someda l Natsume Menda 5 (0) (b) ゐ?田■ (α) (b) Figure 0 ((1) Name z

Claims (5)

[Claims] (1) A ferrule attached to the end of an optical fiber that propagates linearly polarized light, which is formed into a cylindrical rod shape and has a strand insertion opening with an inner diameter slightly larger than the outer diameter of the optical fiber strand in the axial direction. It consists of a fitting part and a cylindrical flange part having a through hole into which the fitting part is inserted at one end and into which the optical fiber core is inserted and fixed at the other end, and the fitting part inserted into the flange part. For a polarization-maintaining optical fiber, the joint portion of the flange portion and the fitting portion has at least two grooves that are air vent paths that communicate the vicinity of the entrance of the wire insertion port of the portion with the outside. Ferrule. (2) The ferrule for a polarization-maintaining optical fiber according to claim 1, wherein two grooves are formed symmetrically about the axis of the flange portion, or four grooves are formed at uniform intervals around the axis. (3) The ferrule for a polarization-maintaining optical fiber according to claim 1 or 2, wherein the air venting path is a hole formed in a flange portion. (4) The ferrule for a polarization-maintaining optical fiber according to claim 1, 2 or 3, further comprising an optical lens at one end of the strand insertion opening of the fitting portion. (5) Claim 1, 2 or 4, characterized in that the flange portion has means for engaging with the optical connector housing on the outer periphery thereof.
Ferrule for polarization-maintaining optical fiber described in .