JP2005308880A - Optical connector and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical connector which can be manufactured easily at low cost and can be easily assembled by using an ordinary ferrule, and to provide a manufacturing method of the optical connector. <P>SOLUTION: In the optical connector 10, an optical fiber 6 for optical connector made by connecting a first optical fiber 1 to a second optical fiber 3 having a core 3a diameter larger than the core 1a diameter of the first optical fiber 1 is inserted and fixed to an optical insertion hole 12 of the ferrule 11. Therein, the connection part 7 between the first optical fiber 1 and the second optical fiber 3 is stored in the optical insertion hole 12 and the end surface 5 of the second optical fiber 3 opposed to the first optical fiber 1 is positioned and fixed with respect to the connection end surface 13 of the ferrule 11. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical connector used for optical connection of an optical fiber and a manufacturing method thereof.

As an optical fiber used for optical communication, a single mode optical fiber (SMF) is generally used. A single mode optical fiber has a relatively small core diameter and MFD (MFD: mode field diameter) of about several to several tens of μm, so both optical fibers are used when optical fibers are optically connected using an optical connector or the like. Must be precisely aligned (positioned so that the optical axes of both optical fibers coincide).
As a method for improving the coupling efficiency of an optical fiber by expanding the core diameter of the optical fiber, a method using a microlens fiber or a core expanded optical fiber (also referred to as a TEC: Thermally expanded core) is known.

  FIG. 5 shows an example of a microlens fiber and an optical connector using it. 5A and 5B, a GRIN lens 24 (GRIN: graded index) is arranged between a single mode optical fiber 22 and a multimode optical fiber 23, and both the lens 24 and the microlens fiber 21 shown in FIGS. The optical fibers 22 and 23 are connected. As shown in FIG. 5C, the microlens fiber 21 can be used for assembling the optical connector 20 by being inserted and fixed in an optical fiber insertion hole 26 formed in the ferrule 25 of the optical connector. .

As an optical connector using the core expansion optical fiber, there is an invention described in Patent Document 1, for example. As shown in FIG. 6, the optical fiber preform 31 is heated and stretched to make the core 33 of the optical fiber 32 tapered as shown in FIG. There is a method of expanding the core 42 by diffusing the dopant by heating with a micro burner (not shown) or the like.
The invention described in Patent Document 2 is an optical connector in which two types of optical fibers having different eccentricities are connected and accommodated in a ferrule.
JP-A-11-109185 JP-A-5-119235

In the case of a microlens fiber as shown in FIG. 5, there is a complaint that it is difficult to manufacture and is expensive. Further, since it is difficult to obtain the reproducibility of the connection loss, there is a possibility that the loss becomes large when used for optical connector connection.
As shown in FIG. 6, the core-enlarged optical fiber obtained by heating and drawing is difficult to control the core diameter, and the clad diameter varies and is not uniform in the longitudinal direction. It is difficult to assemble an optical connector by inserting it into the insertion hole.
As shown in FIG. 7, in the core expansion optical fiber obtained by diffusion of the dopant, in order to obtain the target core diameter, the tension when holding the optical fiber, the arrangement of the burner with respect to the optical fiber, the supply pressure of the fuel gas, etc. Must be controlled with high accuracy, and it is difficult to manufacture and the yield is poor.
When a multimode optical fiber is used as an optical fiber inserted and fixed in the ferrule, the bending loss increases when the optical fiber drawn out to the rear end side of the ferrule (the side opposite to the joining end face) is bent. The handling property of the optical connector is deteriorated, which is not preferable.

  The present invention has been made in view of the above circumstances, and provides an optical connector that can be easily manufactured at low cost and can be easily assembled using a normal ferrule and a method for manufacturing the same. Is an issue.

In order to solve the above-described problems, the present invention provides an optical fiber for an optical connector in which a first optical fiber and a second optical fiber having a core diameter larger than the core diameter of the first optical fiber are connected. The optical fiber insertion hole of the ferrule is inserted and fixed, and the connection portion between the first optical fiber and the second optical fiber is accommodated in the optical fiber insertion hole, Provided is an optical connector characterized in that an end face facing the first optical fiber is positioned and fixed with respect to a joining end face of the ferrule.
In this optical connector, it is possible to adopt a single mode optical fiber as the first optical fiber and a graded index optical fiber as the second optical fiber.
Moreover, it is also possible to employ | adopt that the said connection part is a fusion splicing part and the outer diameter of this fusion splicing part is below the internal diameter of the said optical fiber insertion hole.

  The present invention also relates to a method of manufacturing an optical connector in which an optical fiber is inserted and fixed in an optical fiber insertion hole of a ferrule, wherein the core diameter is larger than the core diameter of the first optical fiber and the first optical fiber. The tip of the second optical fiber is heated, the end faces of the two optical fibers are butted together and fusion spliced, and the two optical fibers are pulled oppositely while the tips of the two optical fibers are heated. For an optical connector obtained by adjusting the outer diameter of the fusion splicing portion to be equal to or smaller than the inner diameter of the optical fiber insertion hole by extending the fusion splicing portion between the two optical fibers. An optical connector manufacturing method is provided, wherein an optical fiber is inserted into the optical fiber insertion hole and bonded and fixed.

According to the optical connector of the present invention, the second optical fiber having a core diameter larger than the core diameter of the first optical fiber expands the core diameter and MFD on the ferrule joint end face side of the optical fiber, thereby reducing the connection loss. Can be reduced. Even when a high-power laser for video transmission or the like is used as the transmission light, burn-in due to dust or scratches can be suppressed.
According to the optical connector manufacturing method of the present invention, it is possible to easily and inexpensively manufacture an optical connector that is easy to insert into the optical fiber insertion hole of the ferrule, has low connection loss, and has excellent mechanical strength of the connection portion. It becomes possible.

The best mode for carrying out the present invention will be described below with reference to the drawings.
As shown in FIG. 1C, in the optical connector 10 of this embodiment, the optical fiber 6 for optical connectors is inserted and fixed in the optical fiber insertion hole 12 of the ferrule 11. In FIG. 1C, the housing of the optical connector 10 is not shown.

As shown in FIGS. 1A and 1B, an optical fiber 6 for an optical connector (hereinafter sometimes simply referred to as an optical fiber 6) is connected to the first optical fiber 1 at the end of the first light. A second optical fiber 3 having a core 3a diameter larger than the core 1a diameter of the fiber 1 is connected.
As the first and second optical fibers 1 and 3, for example, a single mode optical fiber 1 (hereinafter sometimes simply referred to as an SM fiber) is used as the first optical fiber 1, and a gray is used as the second optical fiber 3. A combination using the dead index optical fiber 3 (hereinafter sometimes simply referred to as GI fiber) can be exemplified.
The first optical fiber 1 and the second optical fiber 3 are connected by abutting one end faces 2 and 4 to each other.

The optical fiber 6 for optical connector is such that the second optical fiber 3 is directed to the joint end face 13 side of the ferrule 11, and the connection portion 7 between the first optical fiber 1 and the second optical fiber 3 is 11 in the optical fiber insertion hole 12. The end surface 5 of the second optical fiber 3 facing the first optical fiber 1 is positioned and fixed with respect to the joint end surface 13 of the ferrule 11. The optical fiber 6 for an optical connector can be bonded and fixed with an appropriate adhesive in the optical fiber insertion hole 12.
In FIG. 1, the end face 5 of the second optical fiber 3 is matched with the joining end face 13 of the ferrule 11, but the present invention is not particularly limited to this. The end face 5 of the optical fiber 3 may be smoothed, and the tip thereof may be protruded from the joining end face 13 of the ferrule 11 by a predetermined amount (for example, several μm).

Here, the outer diameter (diameter) of the connecting portion 7 of the optical fiber 6 is equal to or smaller than the inner diameter (diameter) of the optical fiber insertion hole 12.
In the present invention, the outer diameter of the connecting portion 7 means twice the maximum distance A from the center line C of the optical fiber 6 to the contour (outer periphery) of the optical fiber 6 in the vicinity of the connecting portion 7. .
In addition, the point where the distance from the center line C of the optical fiber 6 to the contour (outer periphery) of the optical fiber 6 is maximum may be a position corresponding to the outer periphery of the end faces 2 and 4 of both optical fibers 1 and 3. Alternatively, there is a possibility that the position is away from the outer periphery of the end faces 2 and 4 of the optical fibers 1 and 3.

  However, since the outer diameter of the connecting portion 7 is equal to or smaller than the inner diameter of the optical fiber insertion hole 12, the optical fiber 6 for an optical connector is not caught when inserted into the optical fiber insertion hole 12 of the ferrule 11, and smooth. Can be inserted into. Moreover, since the outer diameter of the portions other than the connection portion 7 of the optical fibers 1 and 3 is substantially equal to the inner diameter of the optical fiber insertion hole 12, the center line C of the optical fiber 6 is matched with the center line of the optical fiber insertion hole 12. Can do.

As the SM fiber 1, a quartz-based SM fiber in which both the core 1a and the cladding 1b are made of silica-based glass is generally used.
In general, the GI fiber 3 is a multimode optical fiber having a refractive index distribution parameter g defined in JIS C 6820 with respect to the refractive index distribution of the core 3a within a range of 1 ≦ g <3. In particular, when both the core 3a and the clad 3b are silica-based fibers made of silica-based glass, the refractive index gap between the SM fiber 1 and the GI fiber 3 is small (or substantially negligible). To preferred. In addition, if both the SM fiber 1 and the GI fiber 3 are silica optical fibers, it is easy to realize a connection with low connection loss by fusion splicing, which is preferable.

FIG. 2 is a schematic diagram illustrating how light propagates in the GI fiber 3. As shown in the figure, the light in the GI fiber 3 changes the distance from the central axis of the core 3a with a predetermined period P (also referred to as pitch length) that depends on the wavelength of the light, the refractive index distribution of the core 3a, and the like. And propagate while repeating convergence, divergence, and parallelization.
Therefore, the length of the GI fiber 3 is preferably ¼ wavelength or an odd multiple thereof (that is, [(2n−1) / 4] P, where n = 1, 2,...). As a result, the light emitted from the SM fiber 1 is emitted in a state of being collimated (collimated) at the end face 5 opposite to the side connected to the SM fiber 1 of the GI fiber 3, and high coupling is achieved. Efficiency can be realized. In addition, in this case, incident light from the end face 5 of the GI fiber 3 can also be incident on the core 1 a of the SM fiber 1 in a state of being converged in the GI fiber 3.

  The connection between the SM fiber 1 and the GI fiber 3 is not particularly limited as long as both optical fibers 1 and 3 can be handled in an integrated state. The connection loss due to the above is reduced, and the mechanical strength of the connection can be further improved.

Next, an example of a method for manufacturing the optical fiber for optical connector 6 described above by connecting the first optical fiber (SM fiber) 1 and the second optical fiber (GI fiber) 3 will be described.
First, as shown in FIG. 3A, the optical fibers 1 and 3 are respectively held by the holder 8, and the end faces 2 and 4 of the optical fibers 1 and 3 are brought close to each other, and both the optical fibers 1 and 3 are connected. The tip is heated by an arc 9 of an electrode (not shown).
And as shown in FIG.3 (b), the end surfaces 2 and 4 of both the optical fibers 1 and 3 are faced | matched and pressed and it fuse | melts. As a result, as shown in FIG. 3C, the cores 1 a and 3 a of both optical fibers 1 and 3 are fusion-connected at the fusion splicing portion 7. At this time, swelling occurs in the fusion splicing portion 7.

The outer diameter of the bulge of the fusion splicing portion 7 is larger than the optical fiber diameter. Therefore, as shown in FIG. 3 (d), both the optical fibers 1 and 3 are slightly pulled in opposite directions while the tips of the optical fibers 1 and 3 are melted due to the continuation of discharge or residual heat. By extending the fusion splicing part 7 between the optical fibers 1 and 3, the outer diameter of the fusion splicing part 7 is adjusted to be equal to or smaller than the inner diameter of the optical fiber insertion hole 12.
After allowing to cool, the holder 8 is removed, and as shown in FIG. 3E, the optical fiber 6 for optical connector in which the first optical fiber 1 and the second optical fiber 3 are fusion-connected can be obtained. .

  When connecting the first optical fiber 1 and the second optical fiber 3, the second optical fiber 3 having a length sufficient for gripping the optical fiber can be used. After the connection with the first optical fiber 1, the second optical fiber 3 is cut and the end face 5 is precisely polished, so that the predetermined length can be adjusted. The end face 5 of the second optical fiber 3 may be polished together with the joining end face 13 of the ferrule 11 after the optical fiber 6 for optical connector is inserted into the optical fiber insertion hole 12.

In manufacturing the optical connector 10 of the present embodiment using the optical fiber for optical connector 6 described above, it was obtained by the fusion splicing of the first optical fiber 1 and the second optical fiber 3 as described above. The optical fiber 6 for an optical connector is inserted into the optical fiber insertion hole 12 of the ferrule 11, the connecting portion 7 of the optical fiber 6 is accommodated in the optical fiber insertion hole 12, and the optical fiber 6 is bonded and fixed.
In order to position the end face 5 of the optical fiber 6 with respect to the joint end face 13 of the ferrule 11, the optical fiber 6 may be precisely positioned when the optical fiber 6 is inserted into the optical fiber insertion hole 12. Alternatively, when the optical fiber 6 is inserted into the optical fiber insertion hole 12, the position may be roughly aligned, and after bonding and fixing, the bonding end surface 13 may be precisely positioned.

By using the optical connector 10 as described above, the core diameter of the portion exposed to the joining end face 13 of the ferrule 11 becomes the diameter of the core 3a of the second optical fiber 3, and the core diameter of the first optical fiber 1 is larger than the core diameter. Therefore, an optical connector with high coupling efficiency and low insertion loss can be obtained. For example, as shown schematically in FIG. 4, even when foreign matter 14 such as dust adheres to the joining end face 13 of the ferrule 11, the insertion loss of the optical connector can be suppressed to a level sufficient for optical transmission. it can.
Since the core diameter of the outgoing end face of the optical fiber for optical connectors is large, outgoing light such as a laser is diffused, and adverse effects such as seizure due to dust or scratches can be mitigated.

When the second optical fiber exposed to the joint end face of the ferrule is a GI fiber, and the length of the GI fiber is 0.25 P or an odd multiple thereof, as described above, the light coupling at the end face of the GI fiber The efficiency can be improved, which is preferable.
When the first optical fiber drawn out to the rear end side of the ferrule (the side opposite to the joining end face) is an SM fiber, the bending loss is relatively small even if the first optical fiber is bent. The handleability is good, which is preferable.

According to the optical connector manufacturing method described above, an optical connector that can be easily inserted into the optical fiber insertion hole of the ferrule, has low connection loss, and has excellent mechanical strength of the connection portion can be manufactured easily and at low cost. become.
When the outer diameter of the fusion splicing part of both optical fibers is reduced to be equal to or smaller than the original outer diameter of the optical fiber, the optical fiber for the optical connector can be applied to the assembly of a normal optical connector. It can be smoothly inserted into the optical fiber insertion hole.

In order to compare the characteristics of an optical connector using a normal SM fiber and the optical connector of the present invention, the following tests were performed.
As the SM fiber of the comparative example, a normal SM fiber having a core diameter of 9 μm, a cladding diameter of 125 μm, and a coating diameter of 0.9 mm was used.
As the optical connector of the example, an optical fiber for an optical connector in which a GI fiber (GI 50) having a core diameter of 50 μm and a cladding diameter of 125 μm was connected to an SM fiber was used. The length of the GI fiber was adjusted to 0.25 times the pitch length P within the range of 0.5 to 10 mm.
As the ferrule, a substantially cylindrical glass ferrule having a diameter of 2.5 mm was used.

Each optical fiber was inserted into a ferrule optical fiber insertion hole and polished to assemble an optical connector.
First, the insertion loss of the optical connector when the ferrule joining end face was clean was measured. The insertion loss of the optical connector was measured as the insertion loss when the optical connectors having the same type of optical fiber fixed internally were butt-connected.
Next, the joining end surface of the ferrule was repeatedly pressed against the dust-contaminated pad (see FIG. 4). After contamination, the insertion loss of the optical connector was measured again.
The measurement results of the above test are shown in Table 1.

In the case of optical connection between SM optical fibers, if the optical connector is dirty, the insertion loss is significantly worse than when it is cleaned.
On the other hand, in the case of the optical connector of the example, even if the optical connector is dirty, a decrease in insertion loss is suppressed as compared to when it is clean. As a result, it has been found that, even when used in an environment that is not necessarily maintained clean, according to the present invention, an optical connector having sufficient characteristics for connector connection can be obtained.

  The present invention can be used for optical connection of optical fibers in various fields such as optical communication and optical measurement.

BRIEF DESCRIPTION OF THE DRAWINGS (a) Longitudinal sectional view and (b) End view showing an example of an optical fiber used in the optical connector of the present invention, and (c) A schematic configuration diagram showing an example of an optical connector using the optical fiber. It is the schematic explaining the mode of propagation of the light in GI fiber. It is drawing which shows an example of the manufacturing method of the optical fiber for optical connectors of this invention, (a) shows a mode that the single mode optical fiber and the graded index optical fiber are heated, (b) shows both optical fibers (C) shows a state where both optical fibers are fused, (d) shows a state where the connecting portion of both optical fibers is further extended, and (e) shows the obtained optical connector. FIG. It is a schematic diagram which shows an example of the ferrule end surface of the optical connector to which foreign materials, such as dust, adhered. It is the schematic block diagram which shows an example of the optical connector using (a) longitudinal cross-sectional view and (b) end elevation which show the conventional micro lens fiber, and (c) this. (A) is the schematic which shows an example of the preform before heat-stretching, (b) is the schematic which shows an example of the core expansion optical fiber obtained by heat-stretching. (A) is the schematic which shows an example of the optical fiber before diffusing a dopant, (b) is the schematic which shows an example of the core expansion optical fiber obtained by the spreading | diffusion of a dopant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st optical fiber (SM fiber), 2 ... End surface of 1st optical fiber, 3 ... 2nd optical fiber (GI fiber), 4, 5 ... End surface of 2nd optical fiber, 6 ... Optical connector Optical fiber (optical fiber), 7 ... connection part (fusion splicing part), 10 ... optical connector, 11 ... ferrule, 12 ... optical fiber insertion hole, 13 ... joining end face of ferrule.

Claims (4)

  An optical fiber for an optical connector formed by connecting a first optical fiber (1) and a second optical fiber (3) having a core (3a) diameter larger than the core (1a) diameter of the first optical fiber. (6) is inserted and fixed in the optical fiber insertion hole (12) of the ferrule (11), and the connection portion (7) between the first optical fiber and the second optical fiber is in the optical fiber insertion hole. An optical connector (1), wherein an end face (5) of the second optical fiber facing the first optical fiber is positioned and fixed with respect to a joining end face (13) of the ferrule. 10).   The optical connector (10) of claim 1, wherein the first optical fiber is a single mode optical fiber and the second optical fiber is a graded index optical fiber. The optical connector according to claim 1, wherein the connecting portion is a fusion splicing portion, and an outer diameter of the fusion splicing portion is equal to or smaller than an inner diameter of the optical fiber insertion hole.
An optical connector manufacturing method in which an optical fiber is inserted and fixed in an optical fiber insertion hole (12) of a ferrule (11),
Both ends of the first optical fiber (1) and the second optical fiber (3) having a core (3a) diameter larger than the core (1a) diameter of the first optical fiber are heated. The end faces (2, 4) of the optical fibers are butted and spliced together, and further, while the tip ends of both optical fibers are heated, the two optical fibers are pulled in the opposite direction, and the spliced splicing part (7) between the optical fibers. The outer diameter of the fusion splicing part is adjusted to be equal to or smaller than the inner diameter of the optical fiber insertion hole, and the optical fiber for optical connector (6) obtained by fusion splicing of the two optical fibers is used as the optical fiber. A method of manufacturing an optical connector (10), wherein the optical connector (10) is inserted into an insertion hole and fixed by adhesion.

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