JPH0279805A - Method for connecting optical waveguide and optical fiber - Google Patents

Abstract

PURPOSE:To stably exhibit a fixing function by forming a fixing groove having a specific size and adjusting the optical axes of an optical fiber and an optical waveguide in the fixing groove, then dropping a fixing agent to the groove part behind the end face of the optical fiber and allowing the agent to flow to a prescribed position and to cure. CONSTITUTION:The fixing groove 3 which has the width W larger than the outside diameter of the optical fiber 4 and with which the depth of the groove bottom measured from the center of the core layer 3 of the optical waveguide 2 has the size larger than the radius R of the optical fiber 4 is formed near the end part of the optical waveguide 2 on an optical waveguide circuit substrate 1. The optical axes of the optical fiber 4 and the optical waveguide 2 are adjusted in the fixing groove 3; thereafter, the fixing agent 5 is dropped into the groove part behind the end face of the optical fiber and is allowed to flow to the prescribed position and to cure. The amt. of the adhesive agent is determined by the size of the fixing groove 3 and the interracial tension of the adhesive agent. Since the fixing groove 3 can be determined with the good size accuracy, the amt. of the adhesive agent can be controlled with high accuracy. The stress to be applied on the optical fiber 4 on curing of the adhesive agent is controlled in this way and the misalignment of the optical fiber 4 arising from the fixing is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a highly reliable method for connecting optical waveguides and optical fibers, which is essential for realizing optical waveguide circuits.

[Prior art/problems to be solved by the invention] The connection technology for optical waveguides and optical fibers consists of (1) end face processing technology, (2)
) optical axis adjustment technology, and (3) fixation technology. Of these three elements, the most technically difficult is fixation technology. In other words, in the commonly used end face connection method, there is a problem in that axis misalignment is likely to occur when fixing the fiber with a fixing agent such as adhesive after adjusting the optical axis between the fiber and the waveguide. .

FIG. 9 shows an example of a conventional fiber fixing method using end-face connection. In the figure, 1 is an optical circuit board, 2 is an optical waveguide, 2a is a core layer, 4 is an optical fiber, and 5 is an adhesive. In this method, the optical axis adjustment between the optical fiber and the optical circuit can be directly performed, so the optical axis adjustment can be achieved with extremely high precision. Therefore, the field distribution of the propagating light in the optical fiber and the field distribution of the optical waveguide The minimum splice loss determined by can be achieved. However, in this method, it is necessary to directly apply an adhesive near the fiber/waveguide connection interface to fix the fiber. At this time, it is difficult to control the amount and distribution of the adhesive dropped. Generally, when fixing fibers with adhesives as shown in Figure 9(b), if the adhesive has a large uneven distribution, asymmetrical stress will be created in the optical fiber when the adhesive hardens. , the optical fiber becomes easier to move. Furthermore, the magnitude of the asymmetric stress increases as the amount of adhesive increases. As a result, in the method shown in FIG. 9, the probability that axis misalignment will occur during fiber fixation is extremely high.

In order to solve this problem, it has been considered to provide a fiber holding section 6 at the end of the optical fiber 4, as shown in FIG.

However, this method has a problem in that when a large number of fibers are connected in an array, the spacing between the optical fibers is determined by the dimensions of the fiber holding portion 6, and therefore the fiber spacing cannot be narrowed. In addition to the above-mentioned problems, the methods shown in FIGS. 9 and 10 described above have the problem that when fixing these end faces, the fixing agent also enters the connection interface between the optical fiber and the optical waveguide, which causes the guided light to adhere. passes through the agent. therefore,
In order not to increase the connection loss, the types of adhesives that can be used are limited, and only adhesives that do not absorb at the wavelength of light propagating through the waveguide can be used.

Fiber array connections are performed in order to have the same function as having a fiber holding part and to enable connection of a large number of fibers. However, in this method, the alignment accuracy between each fiber and the waveguide is determined by the manufacturing accuracy of the array. Therefore, it is difficult to achieve the minimum splice loss that can be achieved with direct fiber splicing for all fibers in the array.

How to solve the problems of the conventional fiber splicing method mentioned above (
In other words, it is a method that allows direct optical axis alignment of fibers and waveguides, and does not cause axis misalignment due to adhesive fixation.In addition, it is a method that allows even a large number of fibers to be arranged at narrow intervals. As a possible method), there is a method shown in FIG. 11 (Omori et al., Japanese Patent Application No. 62-332444).

The feature of this method is that the fiber 4 is attached to the guide block 30.
A fixing groove 3 having a width larger than the outer diameter of the fiber and a depth larger than the fiber radius is provided, and the fixing groove 3 allows the adhesive 5 to
The objective is to control the amount and distribution of the dripping.

That is, the optical circuit board 1 and the guide block 30 are mounted on the mounting board IO with their positions generally aligned. Then,
The fiber 4 is inserted into the fixing groove 3 and the optical axis with respect to the optical waveguide 2 is adjusted. In this case, as mentioned above, the dimensions of the fixing groove 3 are larger than the dimensions of the fiber 4, so that the fiber can move freely in the groove. After optical axis adjustment, fixing groove 3
Drop the adhesive on the side farthest from the fiber end face. Then, the adhesive starts to flow due to the interfacial tension between the fiber and the fixing groove, and spreads into the fixing groove. At this time, the amount and distribution of the adhesive near the connection end is determined by the dimensions of the fixing groove 3, as shown in FIG. 11(b). Therefore, by using this fixing groove, it becomes possible to easily control the amount and distribution of the adhesive, and as a result, it is possible to prevent the optical fiber from being misaligned due to the application and curing of the adhesive.

However, even when the above-mentioned method is used, if the depth of the fixing groove 3 is significantly deeper than the dimensions of the optical fiber, the adhesive distribution will be uneven, and strong asymmetric stress will act on the optical fiber. Axial misalignment occurred due to fixation. In order to prevent this, it is necessary to find the optimum condition for the depth of the fixing groove and form the fixing groove with this dimension. however,
In the past, this optimal condition was not clear, and even if it were, in the conventional method, the fixed groove and the optical waveguide were formed on separate substrates and then combined. It was difficult to adjust the depth to the optimum conditions described above.

Furthermore, in the conventional connection method using a fixing groove formed on a fixing block, it is necessary to mount the optical circuit board and the fixing block in combination on the mounting board, which increases the number of parts for fiber connection. Furthermore, because the number of assembly steps increases, there are limits to economic efficiency and reliability.

In addition, in the conventional fixed groove method, for the same reason as above, the position where the optical fiber can be connected to the optical circuit is limited to the end of the optical circuit board.

Therefore, there is a problem in that the degree of freedom in designing the optical circuit is limited.

The purpose of the present invention is to solve the problem that in the conventional connection method using fixed grooves, the controllability of groove depth was poor and the fixing function of the groove could not always be fully demonstrated, and to enable stable fixing function. An object of the present invention is to provide a method for connecting optical waveguides and optical fibers.

[Means to solve the problem]

The present invention provides a groove near the end of the optical waveguide on the optical waveguide circuit board, the width of which is larger than the outer diameter of the optical fiber, and the depth of the groove bottom measured from the center of the optical waveguide core layer is larger than the radius of the optical fiber. After adjusting the optical axes of the optical fiber and the optical waveguide in the fixing groove, the fixing agent 1 is dropped into the groove portion in front of the end surface of the optical fiber and allowed to flow to a predetermined position. , which is characterized by curing it.

The most significant feature of the present invention is that the fixing groove is formed in the optical waveguide substrate in order to enhance the controllability of the depth of the fixing groove and ensure that the fixing function of the groove is exerted.

In particular, in the present invention, the optimal conditions for the groove depth were found and the fixing grooves were formed under these conditions, thereby making it possible to fully exhibit the fixing function. That is, it is desirable that the depth of the fixing groove bottom, 6 μm, satisfies the relationship Red≦R+50 μm, (R near fiber radius (μm)).

The conventional method using a fixing groove differs greatly from the present invention in that the fixing groove is formed in a fixing block, and the optical circuit board and the fixing groove are assembled on a mounting board. Further, the conventional method does not have a concept of optimal design of groove depth, and in this point as well, it differs greatly from the present invention, which introduces the concept of optimal design of groove depth.

〔Example〕

Embodiment 1 FIG. 1 shows step by step a method for connecting an optical waveguide and a fiber end using a fixing groove formed on an optical circuit board, which is an embodiment of the present invention. In the figure, 1 is a Si substrate, 2 is a quartz optical waveguide, 2a is a core layer, 3 is a fixing groove, 4 is an optical fiber, 4a is a core layer, and 5 is an adhesive. In this embodiment, the fixing groove 3 was formed by etching. Figure 1 (a
) shows a step of forming a fixing groove 3 near the end of the optical waveguide 2 by etching. In this example, the quartz optical waveguide 2 was etched by reactive ion etching (RIE) using a fluorocarbon gas, and then the Si substrate was etched. Figure 2 shows
The dimensions of the formed fixing groove and the fiber are compared. The optical fiber used had an outer diameter of 125 μm. Therefore, in the same figure, R (fiber radius) = 62.5μ
It is m.

On the other hand, the fixed groove width W=200 μm is false, and it is set so that one side W/2=100 μm with respect to the center of the optical waveguide core layer. The fixed groove depth d was set to d = 90μ. The fixing groove in this example is, as described above, RIE
Since it was formed using the above method, it was possible to manufacture the above-mentioned dimensions with high precision.

FIG. 1(b) shows a step of inserting the fiber 4 into the formed fixing groove 3 and adjusting the optical axis. The fixed groove dimensions were manufactured under the conditions of W>2R and d>R as mentioned above, so the fixed groove 3
The fiber 4 can be moved freely within the fiber. Therefore, precise optical axis adjustment could be achieved. After adjusting the optical axis, the optical fiber was pressed against the end of the optical waveguide with a predetermined pressure.

FIG. 1(c) shows a step of dropping adhesive 5 near the end of the fixing groove on the side farther from the end surface of the optical fiber to fix it. In this example, an ultraviolet curing adhesive was used. The adhesive 5 dropped near the end of the fixed groove flows in the groove toward the fiber waveguide connection part due to the interfacial tension between the optical fiber 4 and the fixed groove 3. Once the adhesive has flowed to the desired position, the adhesive is irradiated with ultraviolet rays to cure the adhesive, thereby completing the fixation of the optical fiber. FIG. 3 is a cross-sectional view of the place where the adhesive has flowed at this time. As shown in the figure, the amount of adhesive is determined by the dimensions of the fixing groove and the interfacial tension of the adhesive. Since the dimensions of the fixing groove of the present invention can be determined with high precision, the amount of adhesive can be controlled with high precision. As a result, it is possible to control the stress applied to the optical fiber as the adhesive hardens, and it is possible to prevent the axis of the optical fiber from shifting due to fixing. If we explain how stress is applied using Figure 3,
It will look like this: Stresses F and F in mutually different directions act from the adhesive present on the sides of the optical fiber. However, the two side walls of the fixed groove are at the same distance (W/2) from the center of the optical waveguide core. Therefore, the amount of adhesive between the fiber and the sidewall is approximately equal on both sides, and therefore lF, 1
The relationship ``-11F, l holds true.As a result, the stresses acting on the optical fiber from the sides cancel each other out.-On the other hand, the adhesive present below the optical fiber pulls the optical fiber downward. A stress F acts. If this F is kept below a predetermined value, the axis of the fiber will not shift due to fixing. This boundary value can be considered as Fo shown in Figure 4. , is a cross-sectional view of the vicinity of the connection between the waveguide and the fiber, taken along the longitudinal direction. 20 is the connection end surface of the fiber and the waveguide. It is a frictional force. Therefore, the stress F is smaller than the frictional force F. In this example, the fixed groove depth d is 90 μm.
(approximately 30 μm larger than the fiber radius), F
, > F was satisfied, and it was possible to prevent the fiber axis from shifting due to fixation.

FIG. 5 shows the results of an experiment to clarify the conditions for preventing the influence of stress below the fiber. In the experiment, a fixed groove with a width of 200 μm was used to measure the amount of increase in connection loss due to adhesive curing when the groove depth was changed. C on the horizontal axis is the difference between the fiber radius R and the groove depth d, that is, C
=d-R.

This reveals that there is almost no increase in loss due to adhesive curing up to C=50 μm. Therefore, the upper limit of the fixed groove depth is considered to be d≦R+50 μm.

Next, we examined the lower limit of the fixed groove depth. In the case of C=0μ-, in principle, just by inserting the fiber into the fixing groove, the position in the height direction will match, and since this position is determined mechanically, no position shift will occur due to fixing. it is conceivable that. However, when the dimensions were set in this way, it became difficult to move the fiber laterally in the groove and adjust the optical axis. This is because the optical fiber and the fixed groove bottom are always in contact with each other, and the friction between them makes it difficult for the optical fiber to move. From this, it was found that in order to adjust the optical axis in the groove, the fixed groove needs to be set deeper than the fiber radius.

As a result of the above study, the optimal condition for the fixed groove depth is R<d≦R
It turned out to be +50μ faith.

Note that, unlike the depth, the width of the fixing groove of the present invention does not essentially affect the fiber position associated with adhesive fixation (therefore, in principle, it may be set arbitrarily). However, in practice, a rough guideline for groove width is determined by considering economy and workability.In other words, if the groove width is too wide, a large amount of adhesive must be used to spread the adhesive into the groove. is required, which is not economical.Furthermore, when connecting a plurality of fibers to the same waveguide end face, if a wide groove is used, the fibers cannot be connected with high density.

In this example, the width was set to 500 μm or less in consideration of setting an appropriate amount of adhesive to be dropped for fixing.

Embodiment 2 FIG. 6 is a diagram showing a second embodiment of the present invention, in which solder 51 is used as the fixing agent. Even when solder is used, there is basically no difference from the first embodiment. However, in this embodiment, a feature of the second embodiment is that a metal film 31 is formed on the side wall and bottom of the fixing groove 3, as shown in FIG. 2(a).

Further, in FIG. 2B, a metal foot fiber coated with metal 11141 is used as the optical fiber 4. In order to cause the solder 51 to flow into the fixing groove, the sample may be heated above the melting point of the solder, and once the solder 51 has flowed to a desired location, the sample may be cooled.

Example 3 In Examples 1 and 2, a buried structure quartz optical waveguide is used as the optical waveguide, and a groove with a structure etched to the Si substrate is used as the fixing groove, but the present invention is of course limited to these. It's not something you can do. FIG. 7 shows an example of a structure other than the above-mentioned structure.

FIG. 7(a) is an example using a ridge-type optical waveguide 20a. In this example, the substrate l is also etched. Although FIG. 7(b) uses a buried waveguide,
This is an example in which the groove was formed only in the optical waveguide section and the substrate was not machined. This structure is possible if the buffer layer of the optical waveguide is sufficiently thick.

Embodiment 4 FIG. 8 shows an example in which a plurality of fixing grooves are formed on a substrate in order to apply the connection method of the present invention to a plurality of fiber connections. FIG. 4(a) shows a case where the present invention is applied to a large number of waveguide arrays. In this example, in order to narrow the waveguide spacing,
The width of the fixed groove 30 is 140 μm, and the thickness of the wall 35 between the fixed grooves is 2.
It was set to 0 μm.

As a result, the optical waveguide furnaces 2 could be arranged with a center line spacing of 160 μm. FIG. 2B shows an example in which fiber connections are realized at arbitrary positions on the substrate for a plurality of waveguides, and a multistage interference system is constructed by combining a plurality of directional couplings. According to the present invention, the fixing groove 3 can be provided at any position on the optical waveguide substrate, so even when a complex optical interference system as shown in the figure is formed using an optical waveguide, it is not necessary. Accordingly, it is possible to install a signal monitor port.

Finally, in the above embodiments describing the present invention, etching technology is used to form the fixing grooves, but it goes without saying that the means for forming the fixing grooves is not limited to this. An essential condition for the fixing groove of the present invention is that it be precisely formed on the optical circuit board. Therefore, for example, C
o. It is also fully possible to apply techniques such as laser machining and mechanical grinding to groove formation.

[Effects of the Invention] As explained above, according to the present invention, in the fiber-end splicing method using a fixing groove having a groove larger than the outer diameter of the optical fiber, the fixing groove can be formed into a desired size on an optical circuit board. Since the fibers were formed with high precision, it became possible to control the amount of fixative used when fixing the fibers, and therefore the stress acting on the fibers.

Further, according to the present invention, since the fixing groove is also formed on the optical waveguide circuit board, the number of parts and assembly steps when mounting the optical waveguide can be reduced. Therefore, there are great advantages in improving the reliability of parts and making them more economical.

Furthermore, according to the present invention, the connection between the optical waveguide and the optical fiber can be realized at any position on the optical waveguide circuit board.
This has the advantage that the degree of freedom in designing the optical waveguide circuit is greatly improved.

In particular, the depth of the fixing groove is 4μm, so that Red≦R+50μm.
By setting so as to satisfy the ``Long-tailed'' relationship, the end fiber can be connected without increasing loss due to hardening of the fixative.

[Brief explanation of the drawing]

16), (b), (c) to FIG. 8 (a), (b) are diagrams explaining the present invention in detail, and FIG. 1 is a diagram showing the steps of the first embodiment of the present invention. Figure 2 is an explanatory diagram showing the relationship between the dimensions of the optical fiber and the fixing groove, Figure 3 is an explanatory diagram showing the adhesive distribution and stress in the fixing groove, and Figure 4 is an explanatory diagram showing the relationship between the optical fiber and the dimensions of the fixing groove. An explanatory diagram for explaining stress, Figure 5 is a diagram showing the measurement results of the relationship between groove depth and loss increase due to fixing, and Figures 6 (a) and (b) are the second embodiment of the present invention. FIGS. 7(a) and 7(b) are process diagrams, and FIG. 8(a) is a perspective view showing another example of the fixing groove structure. (b) is a plan view of an example in which the present invention is applied to a plurality of fiber connections. FIGS. 9(a) and (b) are illustrations of the conventional end-face connection method, FIG. 10 is an illustration of the conventional end-face connection method using a fiber block, and FIGS. 11(a) and (b) are illustrations of the conventional end-face connection method. FIG. 3 is an explanatory diagram of a connection method using a conventional fixing groove. , 1... Si substrate, 2... Optical waveguide,
2a, 20a...) A layer, 3...Fixing groove, 4...Optical fiber/XI, 4a...
Core layer, 5, 51...Fixing agent, 6...
Fiber holding part, 30...Guide pro tsuku,
31...Metal film, 41...Metal film.

Claims (2)

[Claims] (1) Fixing near the end of the optical waveguide on the optical waveguide circuit board, the width of which is larger than the outer diameter of the optical fiber, and the depth of the groove bottom measured from the center of the optical waveguide core layer is larger than the radius of the optical fiber. After forming a groove and adjusting the optical axes of the optical fiber and optical waveguide in the fixing groove, a fixing agent is dropped into the groove portion in front of the optical fiber end face and allowed to flow to a predetermined position. A method for connecting optical waveguides and optical fibers, which is characterized by curing. (2) The optical waveguide/optical fiber according to claim 1, wherein the depth dμm of the bottom of the fixing groove satisfies the relationship R<d≦R+50μm (R: fiber radius (μm)). Connection method.