JPH087297B2 - Optical circuit and optical fiber connection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of connecting an optical circuit and an optical fiber, which has a high degree of reliability and can be applied to the connection of fiber arrays.

[Problems to be solved by the prior art and the invention]

The connection technology between the optical circuit and the optical fiber is composed of three (1) optical axis adjustment technology, (2) fixing technology, and (3) end surface processing technology. Of these, the end surface treatment technique corresponds to the pretreatment for the connection work and can be separated from the other two.
Therefore, from the viewpoint of the optical axis adjusting technique and the fixing technique, the conventional techniques for connecting the optical circuit and the optical fiber can be roughly classified into two. The respective conceptual diagrams are shown in FIGS. 3 (a) and 3 (b) and FIGS. 4 (a) and 4 (b).

FIG. 3 (a) is a diagram showing a method focusing on the optical axis adjustment. In the figure, 11 is an optical fiber, and 12 is an optical circuit comprising an optical waveguide 13 and an optical circuit board 14. In the method shown in this figure, with the optical circuit 12 held in a fixed position, the end face of the optical fiber 11 held on the fine movement table is made to face the input end (or output end) of the optical circuit 12, and the optical fiber is moved by the fine movement table. 11 and optical circuit
Adjust the optical axis with 12. After that, the end face of the optical fiber 11 and the end face of the optical circuit 12 are fixed with an adhesive 15. This method is referred to as an edge-bonding type here.

Further, FIGS. 4 (a) and 4 (b) are views showing a method focusing on fixation. This method uses an array 17 having a V-groove 16 that fits exactly into the optical fiber 11. First, the optical circuit 12 is fixed to the holding plate 18, and the optical fiber 11 is fixed in the groove 16 of the array 17. Then, the array 17 is placed on the holding plate 18, and the optical fiber 11 is made to face the input end (or output end) of the optical circuit 12. After that, the array 17 is moved by the fine movement table to adjust the optical axes of the optical fiber 11 and the optical circuit 12, and after the adjustment, the array 17 is fixed to the holding plate 18 with the adhesive 15. This method is referred to as an array adhesive type here.

In both methods, the optical axis with the optical circuit is adjusted and then fixed, but there is a difference between the optical fiber and the array that perform the precise work on the fine movement table. Therefore, there are problems inherent in the bonding technique.

In other words, in the end face adhesive type, the optical axis adjustment is accurate because the optical axis adjustment is performed directly between the optical fiber and the optical circuit, but since the outer diameter of the optical fiber is as thin as about 125 μm and it is elastic, adhesive is used. There is a problem that the optical fiber is apt to move and the axis is apt to be displaced when applied to the end face or when the adhesive is cured. As a method of improving this problem, there is a method of providing a fiber holding portion 19 at the end portion of the optical fiber 11 as shown in FIG. 3 (b). However, in this method, since the fiber holding portion 19 is provided, when connecting a large number of fibers in an array, a new problem arises in that the interval between the optical fibers is determined by the size of the fiber holding portion and cannot be narrowed. Further, in the end face adhesive type, since the adhesive is present on the connection end face between the optical fiber and the optical circuit, the guided light passes through the adhesive. Therefore, there is a limitation on the adhesive that can be used in order not to increase the connection loss. That is, only an adhesive having no refractive index at the wavelength of the guided light and having a refractive index almost equal to that of the optical fiber can be used. In addition, since the adhesive generally has a large characteristic change due to temperature, the end face adhesive type has a problem in reliability.

On the other hand, in the array adhesive type, there are basically no problems in the fixing technique, which was a problem in the end face adhesive type. However, since the optical axes of each optical fiber and the optical circuit are indirectly adjusted, there is a problem of the optical axis adjustment in principle. That is, the minimum value of the connection loss is determined by the processing accuracy of the groove structure of the array and the structural accuracy of the optical fiber. Therefore, there is a problem that it is difficult to obtain the minimum connection loss value that can be determined from the waveguide structure. In particular, in the case of the single mode in which the core diameter of the optical fiber and the optical circuit is small, the problem of the optical axis adjustment becomes remarkable when the distance between the optical fibers becomes wide.

As described above, the conventional techniques can be roughly classified into the end face adhesive type and the array adhesive type, and there are theoretical problems in the fixing technique and the optical axis adjusting technique, respectively. Therefore, the present invention provides a highly reliable and versatile optical circuit / optical fiber connection method by adopting only the advantages of the end face adhesive type and the array adhesive type, without any theoretical problem in fixing and optical axis adjustment. It is a thing.

[Means for solving problems]

The present invention examines the end face adhesive and the array adhesive of the prior art in detail, and finds that the problem occurring in the connection technology is fixed or optical axis adjustment depending on the place where the adhesive is applied. The technology is based on the finding that the flow properties of adhesives are not actively used. That is, after adjusting the optical axis on the fine movement table, the problem in connection technology can be determined as fixed or optical axis adjustment depending on whether the place where the adhesive is applied is near or far from the end face of the optical fiber-optical circuit connection. Further, in the conventional technique, it is difficult to achieve both fixing and optical axis adjustment because the place where the adhesive is applied and the place where the adhesive is cured are almost the same.

Therefore, in the present invention, the adhesive guide block having a groove larger than the outer diameter of the optical fiber and the optical circuit are installed so that the input end or the output end of the optical circuit comes to the end face of the groove, and the optical fiber is installed. After adjusting the optical axis with the optical circuit in the groove, an adhesive was dropped onto the groove portion before the end face of the optical fiber, and the adhesive was caused to flow at a predetermined position by interfacial tension to cure the adhesive.

〔Example〕

First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 (a) to 1 (d) are views for explaining an embodiment of the present invention. In this figure, 21 is an optical fiber, 22 is an optical circuit including an optical waveguide 23 and an optical circuit board 24, 25 is an adhesive guide block having a groove 26, 27 is a holding plate, and 28 is an adhesive.

The adhesive guide block 25 and the groove 26 are grooves having a rectangular cross section, and the depth dimension and the width dimension thereof are set to be larger than the diameter of the optical fiber 21. Therefore, groove the optical fiber 21.
When the optical fiber 21 is inserted into the groove 26, the optical fiber 21 can freely move in the groove 26 in the width direction and the depth direction of the groove 26 with a certain dimension.

The optical fiber 21 and the optical circuit 21 are connected in the following procedure.

First, the optical circuit 22 and the adhesive guide block 25 are fixed to the upper surface of the holding plate 27. In this case, the adhesive guide block
The groove 26 of 25 is positioned so as to be on the extension line of the optical waveguide 23. That is, the adhesive guide block 25 and the optical circuit 22 are positioned so that the input end (or output end) of the optical circuit 22 comes to the end face of the groove 26. Next, the optical fiber 21 is held and inserted into the groove 26, and the end face of the optical fiber 21 is butted against the end face of the optical waveguide 23. In this case, the optical fiber 21 can move in the groove 26 in the depth direction and the width direction of the groove 26. Then, the optical axis of the optical fiber 21 and the optical circuit 22 is adjusted by moving the optical fiber 21 in the groove 26. Then, next, the groove 26 in front of the end face of the optical fiber 21
The adhesive 28 is dipped inside (see FIG. 1 (c)). In this way, the adhesive 28 flows in the groove 26 due to the interfacial tension (see FIG. 1 (d)). Then, when the adhesive 28 flows to a predetermined position, the adhesive 28 is solidified. Thus, the connection between the optical fiber 21 and the optical circuit 22 is completed (see FIGS. 1 (a) and 1 (b)).

In the above connecting method, since the optical fiber 21 can freely move within the groove 26 of the adhesive guide block 25, the optical axes of the optical fiber 21 and the optical circuit 22 can be directly adjusted. Further, since the flow characteristic of the adhesive 28 is positively utilized, there is no problem of fixing in principle. That is, since the adhesive is drip-dropped at a location far from the end faces of the optical fiber 21 and the optical circuit 22, the axis deviation due to the application of the adhesive does not occur. The adhesive 28 flows along the groove 26 of the adhesive guide block 25 in the direction of the joint surface between the optical fiber 21 and the optical circuit 22, but since the interfacial tension governs this flow, the adhesive 28 is applied to the optical fiber 21. Does not apply asymmetrical force. Unlike the prior art in which the place where the adhesive is applied and the place where the adhesive is cured are almost the same, since the flow of the adhesive is used in the above connection method, the axis to the optical fiber-optical circuit connection end surface or to the vicinity thereof is used. Adhesive can be applied and cured without deviation.

As described above, the above connection method uses the adhesive guide block having the groove larger than the outer diameter of the optical fiber, and only takes advantage of the end face adhesive type and the array adhesive type in order to utilize the flow characteristics of the adhesive. It can be said that it is a connection method.

 Next, this embodiment will be described more specifically.

FIG. 2 is a diagram showing a schematic configuration of a connecting device used for implementing the present invention. In the figure, 31 is a 5-axis fine movement table for holding the optical fiber 21, 32 is an optical circuit 22 and an adhesive guide block.
It is a three-axis fine movement table that holds a holding plate 27 on which 25 is mounted. The fine movement tables 31 and 32 are driven by the drive systems 33 and 34, respectively, and the optical fiber 2
1. The position of the holding plate 27 is controlled. Drive system 33,34
Is controlled by the control system 35. Microtremor 31,3
In the vicinity of 2, a UV light source 36, an image pickup tube 37, and an adhesive drip device 38 are installed. The UV light source 36 is controlled by the control system 35, and the output of the image pickup tube 37 is input to the control system 35 via the image processing system 39. The adhesive drip device 38 is adapted to be driven by the drive device 40, and the drive device 40 is controlled by the control system 35. On the other hand, a He-Ne laser is incident on the optical fiber 21 from the laser light source 41. Further, laser light is incident on the optical circuit 22 on the holding plate 21 as described later, but this light is received by the light receiver 43 through the multimode optical fiber 42 for light reception, and its output is input to the control system 35. It is supposed to be done. The optical circuit 22 is an optical circuit made of quartz and is composed of two linear waveguides. The core part
A ridge type single mode optical waveguide having a 10 μm opening, and the waveguide spacing is 500 μm.

As shown in FIG. 3 (a), the length of the end surface of the optical circuit 22 is 5 m.
A quartz holding plate of m, width 3 mm, and thickness 1 m, which has 300 μm wide and 500 μm deep rectangular grooves 26 machined at intervals of 500 μm, has an adhesive guide block 25 made of ceramic so that the center of the groove and the waveguide are aligned. Fixed to 27. A holding plate 27 having an optical circuit 22 and an adhesive guide block 25 mounted thereon was attached to a triaxial fine movement table 32 by a vacuum chuck. A 5-axis precision fine movement table with a rotating mechanism at one end of a single mode silica optical fiber 21 with an outer diameter of 125 μm.
It was held at 31 by a vacuum chuck, and He-Ne laser light from a laser light source 41 was incident on the other end. Adhesive guide block for the optical fiber 21 by the image pickup tube 37 and the image processing system 39.
After installing in the groove 26 portion of 25, while monitoring the output light from the other end of the optical waveguide 23 with the receiving multimode optical fiber 42 and the optical receiver 43, the optical axis adjustment of the optical fiber 21 and the optical waveguide 23 is precisely performed. went. The UV photo-curable adhesive 28 was put into the drip device 38, and one drop of the adhesive 28 was dropped by the drive device 40 into the groove 26 portion of the adhesive guide block 25 as shown in FIG. The flow of the adhesive 28 along the groove 26 portion is measured by the image pickup tube 37 and the image processing system 39, and the optical circuit 22-the optical fiber 21 is connected to the end face 10
When the adhesive 28 came to the position of μm, it was irradiated with UV light. As a result, the adhesive 28 was cured and the optical fiber 21 could be fixed, as shown in FIG. At that time, the optical circuit after the optical axis adjustment
The output light intensity from 22 and the output light intensity after the adhesive was cured were the same, and there was no excess loss due to connection. As is clear from the above description, the role of the adhesive guide block 25 is to adjust the optical axis of the optical fiber 21 in the groove portion and to flow the adhesive. Therefore, it is necessary for the structure of the adhesive guide block to have a groove larger than the outer diameter of the optical fiber.

In this embodiment, since the silica glass made of the same material as that of the optical fiber is used as the adhesive guide block, the critical surface tension of the groove surface and the critical surface tension of the optical fiber surface are substantially equal to each other as shown in FIG. 1 (d). The flow velocity of the adhesive along the surface and the flow velocity of the adhesive along the surface of the optical fiber became almost equal, and it became easy to control the flow characteristics of the adhesive.

In the present example, the controllability of the flow characteristics of the adhesive was improved by using the photo-curable adhesive that can accelerate the curing speed of the adhesive, but the thermosetting or two-liquid mixed type adhesive is used as the adhesive. Only the controllability of the rheological properties of the agent changes and does not alter the essence of the invention.

Example 2 In Example 1, Teflon (limit surface tension γ _c = 18.5 dyne / cm), epoxy resin (γ _c = 50), titanium oxide (γ _c = 110) was used as an adhesive guide block,
The flow characteristics of the adhesive were investigated when a silica optical fiber (γ _c = 78) was used as the optical fiber. As a result, as the difference between the surface tension of the optical fiber surface and the limit surface tension increases, the flow of the adhesive along the optical fiber surface or groove surface becomes faster, and the adhesive does not get wet on the optical circuit / optical fiber connection interface. It was difficult to fix the optical fiber. Of the adhesive guide blocks, the epoxy resin and titanium oxide managed to fix the optical fiber, but Teflon could not be used at all. As is clear from this result, if the difference between the critical surface tension of the groove surface of the adhesive guide block and the critical surface tension of the optical fiber surface is within 30 dynes / cm, the optical fiber is not wetted with the adhesive at the connection interface. Can be fixed.

Example 3 In Example 1, an adhesive having a refractive index of 1.45 was used as the adhesive, and the connection end face of the optical circuit was not polished to make the connection according to the present invention. As a result, when the adhesive was wet to the connection interface and then cured, the connection loss was improved by about 2 dB compared with the case where it was cured immediately before the connection interface. This is because the adhesive having a refractive index almost equal to 1.46 of quartz was used, so that the mating of the connection interface and the effect as oil acted. As is clear from this result,
The present invention is an optical circuit optical fiber splicing method that can complement the edge treatment technology.

〔The invention's effect〕

As described above, according to the present invention in which the flow of the adhesive can be used, unlike the prior art in which the optical axis adjustment and the fixing are contradictory to each other, the adhesive guide having a groove having a larger diameter than the optical fiber outer diameter is provided. Since the block is used, the optical axis adjustment and the fixing can be matched. Further, since the place where the adhesive is applied can be controlled, there is an advantage in improving the reliability of the connection and also an advantage that the loss due to the structural irregularity of the connection interface can be reduced. That is, the present invention has an advantage of being versatile enough to meet various connection requirements by selecting an optimum adhesive guide block and adhesive according to the states of the optical fiber and the optical circuit to be connected.

[Brief description of drawings]

1 (a) to 1 (d) are views showing an embodiment of the present invention, which are process diagrams showing a method for connecting an optical circuit and an optical fiber, and FIG. 2 shows a connecting device used in the embodiment. Schematic configuration diagram, third
FIGS. 4A and 4B are conceptual diagrams showing a conventional end face adhesive type connection method, and FIGS. 4A and 4B are conceptual diagrams showing a conventional array adhesive type connection method. 21 …… optical fiber, 22 …… optical circuit, 25 …… adhesive guide block, 26 …… groove, 28 …… adhesive.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Morio Kobayashi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (56) Reference JP-A-60-95410 (JP, A)

Claims (5)

[Claims] 1. An adhesive guide block having a groove larger than the outer diameter of the optical fiber and an optical circuit are installed so that an input end or an output end of the optical circuit comes to an end face of the groove, and the optical fiber is set to the above. An optical circuit characterized in that after adjusting the optical axis with the optical circuit in the groove, an adhesive is drip-dipped in the groove portion before the end face of the optical fiber, and the adhesive is caused to flow at a predetermined position by interfacial tension to cure the adhesive. And optical fiber connection method. 2. The adhesive guide block according to claim 1, wherein the critical surface tension of the groove surface is ± 30 dynes / cm with respect to the critical surface tension of the optical fiber surface. Optical circuit and optical fiber connection method. 3. The method for connecting an optical circuit and an optical fiber according to claim 1, wherein the adhesive guide block is made of quartz having a surface tension almost equal to that of a silica optical fiber. 4. The optical circuit and the optical fiber according to claim 1, wherein the adhesive has an index of refraction which is less than 0.01 from the index of refraction of the optical circuit. Connection method. 5. The method for connecting an optical circuit and an optical fiber according to claim 1, wherein a photo-curable adhesive is used as the adhesive.