JP3461724B2 - Optical connector ferrule with fiber grating - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical connector ferrule with a fiber grating, and more particularly to an optical connector ferrule with a fiber grating incorporating a fiber grating whose core refractive index changes periodically in the longitudinal direction. It is a thing.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional SC type optical connector 1 (hereinafter referred to as "optical connector"). In the figure, 2 is a frame, 3 is an optical ferrule, 4 is a caulking ring, 4a is a ring, 5 is a spring, 6 is a stop ring, 7 is a boot, and 8 is a knob. The optical ferrule 3 is, for example, JIS C
It is applied to the optical connector established in 5973, and an optical ferrule body 9 in which an optical fiber is internally fixed
And an optical ferrule hold 10 that holds the optical ferrule body 9. Polishing such as PC (Physical Contact) polishing is applied to the tip surface 11 of the optical ferrule body 9. The caulking ring 4 is an optical ferrule hold 10
It is fixed by crimping to. The spring 5 includes a stop ring 6 inserted in a boot 7 and an optical ferrule hold 1.
The optical ferrule 3 is urged forward (left side in FIG. 5) by being inserted between the outer peripheral portion of 0 and a flange portion 12 which is provided in an annular shape. The optical ferrule 3 is restricted from protruding from the frame 2 by a protrusion restricting portion (not shown) formed in the frame 2.

By the way, in recent years, in order to detect a failure of an optical line, a dielectric multilayer filter is fitted in an optical connector for connecting a user's house and the optical line to allow communication light to pass therethrough and a test light to be transmitted. The introduction of an optical line monitoring system that reflects light to the side is considered. For example, in the optical connector 1 shown in FIG. 5, a filter is fitted into a slit formed by cutting the end portion of the optical ferrule 3 with a diamond saw and fixed with an adhesive. However, the work of fitting the slit filter into the optical ferrule 3 requires a lot of time and effort to set an angle with respect to the optical path, and thus requires a lot of man-hours.

Therefore, the present applicants have studied a technique for obtaining a function equivalent to that of a filter by using a fiber grating. Since the fiber grating 13 has a band reflection (blocking) characteristic, this characteristic is used to transmit the communication light and reflect the monitoring light of a specific wavelength. Therefore, its characteristics can be utilized in the above-mentioned monitoring system. FIG. 6 shows an optical connector using a fiber grating. As shown in FIG. 6, in the optical ferrule 3 of this optical connector, a long optical fiber 14 having a fiber grating 13 in advance at its tip is inserted. The fiber grating 13 is entirely housed in the optical ferrule 3. The portion of the optical fiber 14 other than the fiber grating 13 is pulled out to the rear of the optical ferrule 3 (right side in FIG. 6) as a pigtail portion. The reason why the fiber grating 13 is housed in the optical ferrule 3 over the entire length is that, if the linear expansion coefficient of the fiber grating 13 and the surroundings are different, stress distortion may be applied to the fiber grating 13 due to temperature change and the filter characteristics may change. Because there is.

[0005]

By the way, in the case of the optical connector shown in FIG. 6, it is difficult to secure the length of the optical ferrule 3 corresponding to the length of the fiber grating 13. That is, although the filter characteristic of the fiber grating 13 depends on the grating length, the length of the standard SC type optical connector ferrule is determined by the standard, and therefore the fiber grating length is required to realize the required filter characteristic. Has exceeded the standard ferrule length, and there was a problem that it could not be stored in the standard housing. Therefore, even if the temperature changes, it is possible to prevent the temperature characteristics of the fiber grating 13 from changing and stably obtain desired optical characteristics, and to develop an optical connector ferrule that can be housed in a standard housing. It was wanted.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an optical connector ferrule with a fiber grating which can obtain the following effects. (1) Since the fiber grating portion is located outside the optical connector ferrule, it is possible to secure a fiber grating of an arbitrary length corresponding to required optical filter characteristics. (2) By embedding the fiber grating in a resin in which the linear expansion coefficient is close to that of the optical fiber, the strength is improved, and stress distortion of the fiber grating due to temperature change is prevented from occurring and the desired optical characteristics are maintained. can get. (3) Strength is improved by filling a resin having a linear expansion coefficient close to that of the optical fiber in a rigid reinforcing sleeve having a linear expansion coefficient close to that of the optical fiber, and housing the fiber grating in the resin in a buried state. It is possible to obtain the desired optical characteristics by preventing the stress strain from occurring in the fiber grating due to temperature changes.

[0007]

In order to solve the above problems, the present invention inserts an optical fiber in which a fiber grating portion in which the refractive index of the core periodically changes in the longitudinal direction is inserted in the middle portion. Yes, insert the non-gratinged insertion part secured at the tip of the optical fiber, place the fiber grating part on the rear end side facing the tip surface to be polished, and place the reinforcing tube on the outside of the inserted optical fiber. The fiber grating part is covered and the linear expansion coefficient is 5.4 × 10 ⁻⁵ ( cm / c) inside the reinforcing tube.
An optical connector ferrule with a fiber grating according to claim 1, which is filled with a resin adjusted to m / K 2 . Further, according to the present invention, an optical fiber in which a fiber grating portion in which the refractive index of the core periodically changes in the longitudinal direction is formed in the middle portion is inserted, and the secured grating is not provided at the tip of the optical fiber. Insert the insertion part, place the fiber grating part on the rear end side facing the tip surface to be polished, and cover the outside of the inserted optical fiber with a rigid reinforcing sleeve with a linear expansion coefficient close to that of the optical fiber. The linear expansion coefficient is 5.4 × 10 inside the reinforcing sleeve.
An optical connector ferrule with a fiber grating according to claim 1, which is filled with a resin adjusted to ^-5 ( cm / cm / K ). Further, in the present invention, it is more preferable to adopt a configuration in which the intermediate portion of the optical fiber is located outside the optical ferrule that does not contact the optical ferrule.

According to the present invention, an optical fiber having a fiber grating formed in the middle portion is directly inserted into an optical connector ferrule with a fiber grating (hereinafter referred to as "optical ferrule"). The optical ferrule is arranged on the rear end side opposite to the polished front end surface, so that only the light of a specific wavelength is reflected by the fiber grating part, and the transmission light of other wavelengths is transmitted. Light characteristics that are transmitted are obtained.

As the resin to be filled in the reinforcing tube,
For example, epoxy resin or the like is adopted, and the fiber grating portion is embedded in the reinforcing tube. More specifically, this resin has a linear expansion coefficient close to that of the glass portion (bare fiber) of the optical fiber. For example, the linear expansion coefficient is 5.4 × 10 ⁻⁵ which is close to that of the glass portion of the optical fiber.
It is more preferable to adopt a material having ( cm / cm / K 2 ). As a result, the fiber grating portion and the resin around the fiber grating portion are integrally deformed (expanded or contracted) with respect to the temperature change, so that stress strain is prevented from occurring in the fiber grating portion and the resin is supported by the resin. The tensile strength is improved because the maintained state is maintained. Various structures can be adopted as the reinforcing tube, and it is possible to cover not only the optical fiber but also the entire optical ferrule. In this case, since the reinforcing tube is mounted over the optical ferrule and the optical fiber, it is possible to protect and store the area including the fiber grating portion from the optical ferrule of the optical fiber,
This ensures that the optical characteristics of the fiber grating section are maintained. It is more preferable that the reinforcing tube also has a linear expansion coefficient close to that of the glass portion of the optical fiber.

Further, according to the present invention, the inserted non-grating inserted portion secured to the tip of the optical fiber is inserted, and the fiber grating portion is arranged on the rear end side opposite to the tip surface to be polished, and the inserted optical fiber is inserted. It is also possible to adopt a configuration in which a rigid reinforcing sleeve having a linear expansion coefficient close to that of the optical fiber is covered on the outside of the fiber to accommodate the fiber grating portion, and a resin having a linear expansion coefficient close to that of the optical fiber is filled in the reinforcing sleeve. The material of the reinforcing sleeve is, for example, LCP (Liquid Crystalline Polymer).
For example, thermotropic main chain type polymer liquid crystal) and glass are adopted. As the resin filled in the reinforcing sleeve, as described above, the glass portion of the optical fiber (bare fiber)
A linear expansion coefficient close to is adopted.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS. In the figure, reference numeral 20 is an optical connector ferrule with a fiber grating (hereinafter referred to as "optical ferrule"), 21 is an optical cord, 21a is an optical fiber (optical fiber single core wire), 22 is a reinforcing tube,
Reference numeral 23 is a resin (epoxy resin), and 24 is a shrink tube.

As shown in FIG. 1, the optical ferrule 20 is formed of zirconia or a hard material such as glass into a cylindrical shape, and as shown in FIG. 2, the optical ferrule 20 is inserted into a fine hole 26 penetrating on the central axis. The fiber 21 is internally fixed.
As shown in FIG. 1, the front end surface 27 of the optical ferrule 20 (lower left front side in FIG. 1) is PC-polished. Further, on the rear end side of the optical ferrule 20 (upper right rear side in FIG. 1), a protruding portion 28 having a diameter smaller than that of the other portion is provided. As shown in FIG. 2, one end 29 of the relatively flexible reinforcing tube 22 is inserted into the protrusion 28, and is prevented from coming off by the shrink tube 24 attached to the outside. As the reinforcing tube 22, it is preferable to use, for example, Hytrel (trademark of Toray DuPont Co., Ltd.) or the like.

As shown in FIG. 1, the optical fiber 21 has an insertion portion 30 which is a bare fiber portion which is inserted into the fine hole 26 and has no change in the refractive index at the tip, and the core is formed in the longitudinal direction by, for example, ultraviolet irradiation. Has a fiber grating portion 31 in which the refractive index of is periodically changed.
The insertion portion 30 is formed to have a length of about 10 mm from the tip of the optical fiber 21. The length of the fiber grating portion 31 is determined by the cutoff wavelength. In the present embodiment, the fiber grating portion 31 is formed to have a length of 30 to 40 mm corresponding to cutoff center wavelengths of 1.55 μm and 1.65 μm. However, when the cutoff center wavelength is only 1.55 μm, the length of the fiber grating portion 31 is 20 mm.
The degree is enough. The fiber grating unit 31 is
Since the insertion portion 30 is formed continuously to the rear end side, as shown in FIG. 2, when the insertion portion 31 is internally fixed to the fine hole 26, it is positioned immediately after the fine hole 26. Therefore, they are not inserted into the fine holes 26. By the way,
According to JIS 5973, the length from the end surface of the optical ferrule 20 to the mechanical reference surface is about 7 mm. The entire length of the fiber grating portion 31 is housed in the reinforcing tube 22 and is embedded in the resin 23 filled in the reinforcing tube 22. The epoxy resin used as the resin 23 has a coefficient of linear expansion close to that of the optical fiber 21a of 5.4.
It is adjusted to × 10 ^-5 ( cm / cm / K ). In addition,
Also in the following embodiments, a resin having a similar linear expansion coefficient is used as the resin used.

As shown in FIG. 1, the optical cord 21 includes an external reinforcing tube 32, Kevlar fibers 33 provided in layers on the inner surface side of the external reinforcing tube 32, and the Kevlar fiber 3.
And an inner reinforcing tube 34 which is disposed inside 3 and covers the optical fiber 21a. The internal reinforcing tube 34 is a tube made of nylon or Hytrel having a diameter of 0.9 mm. The insertion section 30 and the fiber grating section 31 are pulled out together with the inner reinforcement tube 34 from the outer reinforcement tube 32, the inner reinforcement tube 34 is removed, and then the insertion section 3 of the optical fiber core wire 25 is inserted.
The surface coating (not shown) on the 0 side is removed and the clad portion is exposed to be inserted into the optical ferrule 20. In the region where the fiber grating portion 31 of the intermediate portion which is not inserted into the fine hole 26 is formed, the core wire coating may be removed to the extent that the grating applying step is possible. Therefore, even when not completely removing the core wire coating. is there.

The operation and effect of the optical ferrule 20 will be described below. In this optical ferrule 20, the fine holes 2
Since the work of internally fixing the optical fiber 21a to 6 can be performed by the same procedure as the work of inserting the optical fiber into the ferrule in the optical connector of the conventional configuration, it can be assembled easily and in a short time. That is, simply inserting the optical fiber 21 a in which the fiber grating portion 31 is formed in the intermediate portion into the fine hole 26 allows the insertion portion 30 to be housed in the fine hole 26, and the fiber grating portion 31 to be inserted into the fine hole 26. Since it can be arranged immediately after, it is no different from the work of inserting a normal optical fiber (bare fiber) into the optical ferrule of the optical connector having the conventional structure. Therefore, the fiber grating portion 31 can be arranged at the target position only by internally fixing the optical fiber 21a in the fine hole 26.

The reinforcing tube 22 and the contraction tube 24 are inserted into the optical fiber 21a in advance before the optical fiber 21a is inserted into the optical ferrule 20, and after the insertion portion 30 of the optical fiber 21a is inserted into the optical ferrule 20. The shrink tube 24 is heated and shrunk to fix the reinforcing tube 22. Before mounting, the reinforcing tube 22 is filled with the resin 23 in advance. At this time, the reinforcement tube 2
The other end 35 of 2 is inserted into the end of the optical cord 21. Then, the region from the fine hole 26 to the end of the optical cord 21 is housed in the frame 2 (not shown) to complete the optical connector.

In the completed optical connector, since the fiber grating portion 31 can be arranged at the closest distance from the fine hole 26, it becomes possible to adopt a long grating length without changing the design of the frame, and thereby the objective It is possible to secure a sufficient grating length for obtaining band reflection characteristics. In addition, the reinforcing tube 22
The length of the reinforcing tube 22 can be ensured by inserting the other end portion 35 into the end of the optical cord 21, which also contributes to the extension of the grating length.

Further, in this optical ferrule 20, the fiber grating portion 31 is provided with the reinforcing tube 22 and the resin 24.
Since it is protected by
The optical characteristic of No. 1 can be stably maintained. That is,
For example, when a bending force or an impact force is applied to the reinforcing tube 22, stress is absorbed by the elasticity of the reinforcing tube 22 itself and the viscosity of the resin 23, so that the stress imposed on the fiber grating portion 31 is significantly reduced. The optical characteristics of the fiber grating portion 31 are hardly affected.
The same applies to the tensile force. In the tensile test conducted by the applicants, the tensile strength of the fiber grating portion itself formed over the optical fiber single core wire of φ0.25 mm over 30 mm was 1.136 kgf. On the other hand, in the sample in which the optical ferrule is attached to the optical fiber single-core wire in which a part of the surface coating is removed to form the fiber grating portion, and the fiber grating portion is reinforced with the reinforcing tube 22 and the resin 23, In the tensile test conducted by applying a tensile load between the inner reinforcing tube 34 and the inner reinforcing tube 34, the tensile strength was increased to 3.750 kgf.

Further, in this optical ferrule 20, since the fiber grating portion 31 is embedded in the resin 23 having a linear expansion coefficient close to that of the optical fiber 21a, the resin 23 and the fiber grating portion 31 are affected by temperature change.
Since and are integrally deformed (expanded and contracted), stress strain is unlikely to occur in the fiber grating portion 31 in the process of deformation. Therefore, even if the fiber grating portion 31 is deformed due to the temperature change, the target optical characteristics can be surely obtained.

It is preferable that the reinforcing tube 22 has a coefficient of linear expansion close to that of the optical fiber 21a. This more reliably prevents stress strain from occurring in the fiber grating portion 31 due to temperature change. It is possible to obtain the desired optical characteristics more reliably. The HYTREL used as the material of the reinforcing tube 22 of the present embodiment is inexpensive and can be reduced in cost.

A second embodiment of the present invention will be described below with reference to FIGS. 3 and 4. In the figure, the same components as those in FIGS. 1 and 2 are designated by the same reference numerals to simplify the description. In the optical ferrule 20a of the present embodiment, the insertion portion 30 of the optical fiber 21a exposed at the end of the optical cord 21.
Is inserted into the fine hole 26, and the fiber grating portion 31
Is stored in a relatively rigid reinforcing sleeve 36 and is embedded in the resin 23 filled in the reinforcing sleeve 36.

The reinforcing sleeve 36 is made of LCP or glass, and its linear expansion coefficient is close to that of the glass portion of the optical fiber 21a. Particularly, in the case of the reinforcing sleeve 36 formed of glass, the linear expansion coefficient thereof can easily be made very close to that of the glass portion of the optical fiber 21a, and the change in the optical characteristics of the fiber grating portion 31 with respect to the temperature change can be made extremely small. be able to. Incidentally, the linear expansion coefficient of the glass material of this embodiment is 1.2 × 10 ⁻⁶ / K. Further, LCP (liquid crystal polymer) can be used for the reinforcing sleeve 36. Here, the thermotropic main chain type of wholly aromatic polyester is used, and the linear expansion coefficient is 6.0 × 10.
^-6 / K. One end 37 of the reinforcing sleeve 36 is inserted into and fixed to the optical ferrule 20a, and the other end 38 is inserted into the end of the inner reinforcing tube 34. Accordingly, the rigidity of the reinforcing sleeve 36 allows the internal reinforcing tube 3 to pass through the fine holes 26.
Since the optical fibers 21a arranged between the four terminals are stably supported on the same straight line, the fiber grating portion 31 is prevented from being deformed due to the action of external force, such as being bent, and the fiber grating portion 31 is deformed only by the temperature change. To be done. Therefore, the occurrence in the fiber grating portion 31 is surely prevented. In addition, the optical fiber 21
Since a can be bent only within the optical cord 21, the bending radius can be maintained.

Therefore, according to the optical ferrule 20a, since the fiber grating portion 31 is protected and housed in the reinforcing sleeve 36 having rigidity, the optical characteristics of the fiber grating portion 31 can be reliably maintained. Further, since the reinforcing sleeve 36 itself has a linear expansion coefficient close to that of the glass portion of the optical fiber 21a, it is possible to reduce a change in the temperature characteristics of the fiber grating portion 31 and to reliably obtain the desired optical characteristics. it can.

The optical ferrule, optical cord, etc. are shown in FIG.
It is needless to say that various configurations can be adopted without being limited to the configuration shown in FIG.

[0025]

As described above, according to the optical connector ferrule with the fiber grating of the present invention,
With the configuration in which the optical fiber in which the fiber grating in which the refractive index of the core periodically changes in the longitudinal direction is formed in the middle portion is inserted, the following excellent effects are exhibited. (1) By simply forming and inserting a fiber grating portion in the middle of the target optical fiber, the optical fiber can be easily assembled by the same operation as in the case of the standard optical connector ferrule. (2) Since the intermediate portion of the inserted optical fiber is located outside the optical ferrule that does not contact the optical ferrule, there is no restriction on the fiber grating length, and the degree of freedom in filter design is improved. (3) Since the shape can be used as it is from the standard optical connector ferrule, the cost can be reduced.

The secured insertion portion without a grating is inserted at the tip of the optical fiber, the fiber grating portion is arranged at the rear end side facing the tip surface to be polished, and the reinforcing tube is provided outside the inserted optical fiber. By covering the entire length of the fiber grating part with a cover and filling the reinforcing tube with resin whose linear expansion coefficient is close to that of the optical fiber, the resin and the fiber grating part are deformed integrally with temperature change. As a result, stress distortion due to deformation does not occur in the fiber grating portion, so that an excellent effect that target optical characteristics can be reliably obtained is achieved.

The secured insertion portion without a grating is inserted at the tip of the optical fiber, the fiber grating portion is arranged at the rear end side opposite to the tip surface to be polished, and the linear expansion is performed outside the inserted optical fiber. If a structure is adopted in which the entire length of the fiber grating part is stored by covering a rigid reinforcing sleeve whose coefficient is close to that of the optical fiber, and a resin whose linear expansion coefficient is close to that of the optical fiber is used in the reinforcing sleeve.
Since the linear expansion coefficient of the fiber grating part and the members around it is uniform, the resin, the reinforcing sleeve, and the fiber grating part are integrally deformed due to temperature changes, causing stress strain in the fiber grating part due to the deformation. Since it does not exist, it has an excellent effect that the desired optical characteristics can be surely obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of an optical connector ferrule with a fiber grating of the present invention.

FIG. 2 is a front sectional view showing the optical connector ferrule with a fiber grating shown in FIG.

FIG. 3 is a perspective view showing a second embodiment of an optical connector ferrule with a fiber grating of the present invention.

4 is a front sectional view showing the optical connector ferrule with the fiber grating of FIG. 3. FIG.

FIG. 5 is an exploded perspective view showing a conventional optical connector.

FIG. 6 is a front view showing a conventional example of an optical ferrule in which a fiber grating portion is internally fixed.

[Explanation of symbols]

2 ... Frame, 20 ... Optical connector ferrule with fiber grating (optical ferrule), 20a ... Optical connector ferrule with fiber grating (optical ferrule), 21a ... Optical fiber (bare fiber), 22 ...
Reinforcement tube, 23 ... Resin, 27 ... Tip surface, 30 ... Insertion part, 31 ... Fiber grating part, 36 ... Reinforcement sleeve.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Hosoya 1440 Rosaki, Sakura City, Chiba Fujikura Ltd. Sakura Factory (72) Inventor Kenichi Tomita 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Naoki Nakao 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Shigenori Goto 1-11-5 Tajiri, Ichikawa City, Chiba Prefecture Suzuki Giken (56) Reference JP-A-9-269435 (JP, A) JP-A-10-307231 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/00 -6/02 G02B 6/10 G02B 6/16-6/24 G02B 6/36-6/44

Claims (3)

(57) [Claims] 1. An optical fiber (21a) in which a fiber grating portion (31) in which the refractive index of the core periodically changes in the longitudinal direction is formed in the middle portion is inserted and secured at the tip of the optical fiber. Insert the non-gratinged insertion part (30) and polish the tip surface (2
7) The fiber grating portion is arranged on the rear end side opposite to 7), and the reinforcing tube (2
2) is covered to accommodate the fiber grating part, and the linear expansion coefficient is 5.4 × 10 ⁻⁵ ( cm / c ) in the reinforcing tube.
The optical connector ferrule (20) with a fiber grating according to claim 1, wherein the resin (23) adjusted to m / K 2 is filled. 2. An optical fiber (21a) in which a fiber grating portion (31) in which the refractive index of the core periodically changes in the longitudinal direction is formed in the middle portion is inserted and secured at the tip of the optical fiber. Insert the non-gratinged insertion part (30) and polish the tip surface (2
7), the fiber grating portion is arranged on the rear end side, the outer side of the inserted optical fiber is covered with a rigid reinforcing sleeve (36) having a linear expansion coefficient close to that of the optical fiber, and the fiber grating portion is accommodated. 2. An optical connector ferrule with a fiber grating according to claim 1, wherein a resin whose linear expansion coefficient is adjusted to 5.4 × 10 ⁻⁵ ( cm / cm / K ) is filled therein.
a). 3. The optical connector ferrule with a fiber grating according to claim 1, wherein an intermediate portion of the optical fiber is located outside the optical ferrule that does not contact the optical ferrule.