JP2784503B2 - Guided optical waveguide and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide with a guide that can easily and reliably connect an optical waveguide to an optical fiber, and a method for manufacturing the same.

[Prior Art] In manufacturing an optical waveguide circuit, it is necessary to connect an optical fiber to an optical waveguide. Therefore, development of a simple and highly reliable optical fiber connection technology is required.

A method for forming an optical fiber alignment guide at the same time as patterning an optical circuit on a quartz glass-based optical waveguide substrate and making connection using this guide (JP-A-60-17406) is simple. It is expected as a highly reliable optical fiber connection technology. FIG. 9 is a diagram for explaining this connection method. In the figure, 1 is an optical circuit board, 2 is a ridge-shaped optical waveguide, 2a is a core layer, 2b is its buffer layer, 2c
Is a cladding layer. 3 is a fiber guide, 4 is an optical fiber, and 4a is its core layer. Since the width and depth of the guide groove surrounded by the guide 3 are appropriately set, the positioning between the optical fiber and the optical waveguide can be realized only by inserting the optical fiber 4 into the guide. In addition, since the position of the optical fiber 4 is mechanically determined by the guide 3, even if the temperature of the use environment fluctuates after the fixing of the optical fiber, no displacement occurs, and therefore, the reliability is extremely high. Highly efficient fiber connection can be realized.

As described above, in the conventional guide, the height of the upper surface of the guide is equal to the height of the surface of the optical waveguide, and the guide having a single structure has a fiber positioning function and a fiber fixing function. I have.

However, this method has been conventionally applied to a ridge-shaped optical waveguide, but it has been difficult to apply this method to an optical waveguide having a buried structure in which a thick clad layer is formed and a core is embedded. The reason for this is that when such an embedded optical waveguide is manufactured, the guide and the optical waveguide cannot be conventionally manufactured using a single photomask. For example, the manufacturing is performed based on the process shown in FIG. Because he was doing it. First, as shown in FIG. 10 (a), an optical waveguide core mask pattern is formed on the optical waveguide 2 'formed on the substrate 1 by photolithography using a photomask pattern 22a. Reference numeral 10 denotes a mask material.

Next, an optical waveguide core portion 2a is formed by dry etching (FIG. 10 (b)), and a buried cladding layer is formed thereon.
2c is formed (FIG. 10 (c)), and a mask material is again placed on the optical waveguide 2 embedded with the embedded cladding layer 2c.
11 is formed, and the guide mask is patterned by the photomask pattern 23b (FIG. 10 (d)).

Further, a fiber connection guide 3 to the optical waveguide 2 is formed by dry-etching the cladding layer 2c (FIG. 10 (e)).

[Problem to be Solved by the Invention] In such a conventional process, in the process shown in FIG. 10 (e), the guide pattern 23b is shifted by 1 μm with respect to the position of the optical waveguide 2 already formed. It is necessary to provide a pattern with an accuracy of within. However, since the optical waveguide formed in the lower layer to be aligned is transparent for both the core layer and the cladding layer, it has been extremely difficult to realize precise alignment visually.

A first object of the present invention is to solve the problem that it is difficult to form a guide by performing precise positioning on a buried optical waveguide with a guide having a conventional structure, and to provide a guide having a structure suitable for a buried waveguide. It is to provide an optical waveguide.

A second object of the present invention is to provide a method for manufacturing an optical waveguide having a guide having a structure suitable for a buried waveguide.

[Means for Solving the Problems] A guided optical waveguide according to the present invention is a guided optical waveguide having a guide portion for positioning an optical fiber and an optical waveguide near an end of the optical waveguide. It has a guide groove formed by a side wall and a bottom formed by processing a wave path, and the guide portion has a first guide for positioning an optical fiber and a second guide for fixing an optical fiber which are different in width, stacked in the height direction. It is provided and
The height of the upper surface of the first guide is equal to or less than the height of the upper surface of the core portion of the optical waveguide, and the central axis in the width direction of the first guide coincides with the central axis of the core portion. The distance from the contact point between the optical fiber and the first guide when the optical fiber is inserted into the first guide to the center of the optical waveguide core is equal to the radius of the optical fiber, and the second guide is provided above the first guide. And the height of the upper surface from the bottom is larger than the radius of the optical fiber, and the width is larger than the diameter of the optical fiber.

The method of manufacturing a guided optical waveguide according to the present invention includes a first step of forming an optical waveguide core portion forming mask pattern and a first guiding mask pattern for positioning an optical fiber on a surface of the optical waveguide; Waveguide core and first
A second step of forming a guide pattern; and a third step of forming a buried cladding layer on the surface of the optical waveguide while removing the mask on the core pattern and leaving the mask on the first guide.
A fourth step of forming a second guide mask pattern for fixing the optical fiber on the buried cladding layer surface, and a fourth step of forming the second guide mask pattern formed on the buried cladding layer surface and the buried cladding layer. A fifth step of etching unnecessary portions of the optical waveguide to a desired depth using the one guide mask pattern as a mask.

Further, the method of manufacturing a guided optical waveguide according to the present invention includes a first step of forming a mask pattern for forming an optical waveguide core portion and a first guide mask pattern for positioning an optical fiber on the surface of the optical waveguide. A second step of forming the optical waveguide core portion and the first guide pattern, and a third step of removing the mask on the core pattern and the mask on the first guide to form a buried cladding layer on the surface of the optical waveguide. Forming a second guide mask pattern for fixing the optical fiber on the surface of the buried cladding layer, and forming the second guide mask pattern formed on the surface of the buried cladding layer and the first guide embedded inside the buried cladding layer. A fifth step of etching an unnecessary portion of the optical waveguide to a desired depth using the pattern for use as a mask.

[Operation] The present invention has two configurations as a guide having a structure suitable for an embedded optical waveguide, a first guide for positioning the optical fiber and the waveguide, and a second guide having an optical fiber fixing function. A guide consisting of elements is used. In the first guide for positioning, the height of the upper surface of the guide is equal to or lower than the upper surface of the core of the optical waveguide. The center position of the groove width of the first guide coincides with the center of the optical waveguide core, whereby horizontal fiber waveguide alignment can be realized. In addition, the distance from the contact point between the first guide and the optical fiber to the center of the optical waveguide core is set to be substantially equal to the radius of the optical fiber, thereby realizing vertical alignment between the fiber waveguides. it can. The second guide having an optical fiber fixing function is formed above the upper surface of the first guide, and the height from the contact point between the substrate and the lower surface of the fiber to the upper surface of the second guide is set to be sufficiently larger than the radius of the optical fiber. I do. In consideration of practicality, it is preferable to make the radius larger than the radius by 10 μm or more. The groove width is set larger than the groove width of the first guide and slightly larger than the optical fiber diameter.

The purpose of the second guide is to provide a fixing function as described above. If the height of the fiber guide is low compared to the radius of the optical fiber (ie, without the second guide), applying an adhesive around the optical fiber will
A large non-uniformity is likely to occur in the distribution. When there is a large non-uniformity in the adhesive distribution, asymmetrical stress acts on the optical fiber when the adhesive is cured, and the optical fiber is easily moved.
Moreover, the magnitude of the asymmetric stress increases as the amount of the adhesive increases.

As a result, when the height of the fiber guide is smaller than the radius of the optical fiber, the probability of occurrence of axial misalignment when fixing the fiber becomes extremely high. The second guide of the present invention
This is to solve the above problem. That is,
In fixing the optical fiber, when a fixing agent such as an adhesive is dropped, the fixing agent starts flowing due to the interfacial tension between the optical fiber and the second guide, and spreads through the first and second guides. At this time, the amount and distribution of the fixing agent can be easily controlled by using the second guide having a height sufficiently larger than the radius of the optical fiber. Displacement can be prevented.

In order to manufacture the above-described optical waveguide with a guide, in the present invention, in forming a guide having a double structure of the first and second guides, the first guide and the optical waveguide are formed by using one photomask. At the same time,
Subsequently, a second guide is formed by a process using a different type of photomask after the formation of the buried cladding layer.

Example An example of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a perspective view for explaining a first embodiment of the present invention. 1 is a substrate, 2 is an optical waveguide comprising an optical waveguide core 2a and an optical waveguide buried cladding layer 2c, 2a 'is a core layer provided for forming the core 2a, 3 is a guide, and a first guide 3a And the second guide 3b. In this embodiment, the upper surface 31 of the first guide is formed at substantially the same height as the upper surface of the core 2a. The upper surface of the second guide 3b is at the same height as the surface of the buried cladding layer 2c. In this embodiment, the substrate 1 is a Si substrate, and the optical waveguides 2a and 2c are quartz optical waveguides.

FIG. 2 is a sectional view for explaining a positioning function of the guide of FIG. In the figure, 4 is an optical fiber,
4a is the core layer. As described above, the height of the upper surface 31 of the first guide 3a is set substantially equal to the height of the upper surface of the optical waveguide core 2a. Therefore, the width W of the groove of the first guide 3a is substantially equal to the diameter D of the optical fiber 4 (W
D) Set and guide the optical waveguide core 2a from the bottom of the guide.
By setting the height H to the center of the optical fiber 4 approximately equal to the radius D / 2 of the optical fiber 4 (HD / 2), the optical fiber 4 is inserted into the guide 3 so that the position of the optical fiber between the optical waveguides is reduced. Matching is realized. At this time, the points of contact between the optical fiber and the first guide are the three points A, B, and C shown in FIG. 2, and the distance between these points and the center 0 of the optical waveguide core 2a is
A0B0C0D / 2. Therefore, the positioning between the optical fiber and the waveguide can be performed only by inserting the optical fiber 4 into the guide 3.

FIG. 3 is a perspective view for explaining a fixing function of the guide.
For example, as shown in FIG. 3A, when the fixing agent 5 is dropped near the end of the guide 3 farther from the fiber end surface so that the fixing agent does not flow around the connection surface between the fiber and the optical waveguide,
The fixing agent 5 flows in the groove toward the fiber waveguide connecting portion due to the interfacial tension between the optical fiber 4 and the second guide 3b. When the fixative has flowed to the desired location, the fixative is cured. For curing, for example, if the fixing agent is an ultraviolet curing adhesive, ultraviolet irradiation is performed, and if the fixing agent is solder, the substrate temperature may be lowered.

As described above, by applying the fixing agent using the interfacial tension between the guide and the fiber, there is an advantage that the degree of freedom in selecting a usable fixing agent is increased. That is, according to this method, it is possible to prevent the fixing agent from being applied to the connection end face between the optical waveguide and the optical fiber, and thus it is possible to use the solder or the adhesive having large light absorption as described above. Become.

FIG. 3 (b) is a cross-sectional view at the place where the fixing agent has flowed. As shown in the figure, the amount of the fixing agent is determined by the dimensions of the second guide and the first guide and the interfacial tension of the fixing agent. As a result, the amount and distribution of the fixing agent are controlled, and the optical fiber can be stably fixed.

FIG. 4 is a diagram for explaining an example of a method for manufacturing the optical waveguide with guide of the present embodiment. FIG. 2A shows a step of forming an optical waveguide core portion mask pattern 12a and a first guide film thickness 13a on the upper surface of a core layer 2a 'of a quartz optical waveguide formed on a Si substrate 1. For this purpose, as shown in FIG. 5, after a mask material 10 is formed on the upper surface of the silica-based optical waveguide core layer 2a ', one optical waveguide pattern 22a and a first guide pattern 23a are drawn on this substrate. A photolithography technique using the photomask 20 and an etching technique may be applied. In this embodiment, amorphous Si (a-
Si) was used. In FIG. 4 (a), the optical waveguide mask pattern 12a and the first guide mask pattern 13a can be formed collectively by using one photomask, so that the positioning accuracy of both is extremely high and the error is 0.1 to 0.2 μm. Within. FIG. 4 (b) shows a step of etching the unnecessary portion of the silica-based optical waveguide core layer to form the optical waveguide core portion 2a and the first guide 3a. For this purpose, for example, reactive ion etching may be applied. In this example, the first guide 3a is also etched, but the first guide portion can be left unetched. 4th
FIG. 3C shows a step of removing the mask material on the optical waveguide 2a while leaving the mask pattern 13a of the first guide. FIG. 4D shows a step of forming a silica-based optical waveguide cladding layer 2c and embedding the optical waveguide core 2a, the first guide 3a, and the first guide mask pattern 13a. FIG. 4E shows a step of forming a second guide mask pattern 13b and the like on the upper surface of the buried cladding layer 2c. Here, as shown in FIG. 6, the second mask material 11 is formed on the upper surface of the buried cladding layer 2c.
Then, a photolithography technique using a second photomask on which the second guide pattern 23b and the like are drawn is used. In this step, it is necessary to align and form the second guide mask pattern with respect to the embedded optical waveguide core 2a and the first guide 3a. In this case, as described above, the width of the second guide is larger than that of the first guide, and since the function of the second guide is not fiber alignment but fixed, the position of the second guide relative to the lower layer pattern is reduced. The deviation tolerance is sufficiently large. Therefore,
The alignment of the second guide mask with respect to the lower layer pattern in this step can be easily performed.

FIG. 4 (f) shows that the silica-based optical waveguide is etched to a desired depth by using the second guide mask pattern 13b and the first guide mask pattern 13a embedded in the cladding layer 2c as a mask, thereby forming an optical waveguide with a guide. This is the step of performing
In this embodiment, the quartz optical waveguide is etched,
After exposing the surface of the Si substrate, the depth of the guide was set to a desired value by further etching the Si substrate.
If the optical waveguide buffer layer is sufficiently thick, the etching of the Si substrate becomes unnecessary.

As described above, in the present embodiment, the mask pattern of the first guide is formed simultaneously with the mask pattern of the optical waveguide, so that the position of the first guide with respect to the optical waveguide can be precisely adjusted. It became.

Further, since the height of the second guide is sufficiently higher than the radius of the optical fiber, the optical fiber can be stably fixed with an adhesive or the like after the optical fiber is inserted into the guide. Therefore, this enables the connection of the self-alignment fiber to the embedded optical waveguide.

Embodiment 2 By using the guide according to the present invention, the second guide for fixing is provided even when the height of the first guide having the positioning function is significantly lower than the height of the optical waveguide core. Therefore, the optical fiber can be fixed stably.

FIG. 7 shows the case where the height of the first guide is low.
3 shows an example of a guide structure. FIG. 7A shows an example of a structure in which the groove shape of the first guide is concave, and the first guide and the optical fiber are in contact with the edge A, the point C and the groove bottom B of the guide. It is. In this case, the dimensions of the first guide are 0A0B0CD / 2 (O is the center of the optical waveguide core, D
Is the fiber diameter). FIG. 7 (b)
Is an example in which the groove shape of the first guide has a V-groove shape, and the first guide and the optical fiber are in contact at points A and B of the V-groove surface. The dimensions of the guide are set to 0A0BD / 2.

The guide having the structure shown in FIG. 7A can be manufactured with basically the same dimensions as those shown in FIG. That is, the first guide 3a and the optical waveguide 2a are patterned using a single photomask on the mask material 10, and both are formed using this mask pattern. For the second guide 3b, after embedding the cladding layer, a mask material 11 is formed on the surface of the cladding layer 2c, and the guide 3b may be formed on the mask material 11 by using a mask pattern patterned using a second photomask.
In the guide of this embodiment, the height of the first guide 3a is set lower than that of the embodiment of FIG. Therefore, in the case of this embodiment, the mask thickness to be embedded as the first guide mask pattern 13a may be small. Since the embedding of the mask material is easier as the mask thickness is smaller, the structure of this embodiment is easier to manufacture than the guide structure of FIG.

The guide having the structure shown in FIG. 7B may be obtained by etching the quartz optical waveguide in the same manner as described above, and then anisotropically etching the Si substrate. At the same time, as shown in FIG. 8, the first guide can be formed without using a buried mask. That is, first, the first guide 3a and the optical waveguide 2a are simultaneously formed using one photomask (FIG. 8A). Next, after removing all the remaining mask material, both the first guide 3a and the optical waveguide 2a are embedded in the cladding layer 2c (FIG. 8B), and then the second guide mask pattern 13b formed on the cladding surface is removed. Then, the quartz optical waveguide is etched to expose the surface of the Si substrate (FIG. 8 (c)). At this time, since the etching rate of the core layer is slightly lower than the etching rate of the cladding layer, if the end point of the etching of the quartz-based optical waveguide is carefully detected, the quartz-based optical waveguide of the first guide portion 3a is left with a small amount. Thus, the Si substrate at the bottom of the guide can be exposed.
Lastly, if the anisotropic etching of the Si substrate is performed, the V-shaped silicon substrate is used as a mask with the quartz optical waveguide remaining in the first guide portion.
A groove can be formed (FIG. 8 (d)).

As described above, according to the present invention, even if the height of the upper surface of the first guide is considerably lower than the radius of the optical fiber, the second guide is provided, so that the stable and reliable use of the guide is achieved. Highly efficient optical fiber connection is possible. Therefore, there is an effect that the degree of freedom in designing the structure of the first guide is increased.

Although the embodiments described above relate to a quartz optical waveguide formed on a Si substrate, it goes without saying that the optical waveguide of the present invention is also effective for other material systems. The present invention can be applied to any optical waveguide using a material capable of removing unnecessary portions by etching to form the first guide and the second guide. In addition, in the present embodiment, an example in which an unnecessary portion is removed by etching in forming the optical waveguide core is described, but the effect of the present invention is not limited to this structure. For example, mask unnecessary parts with a mask,
The present invention can also be applied to a diffusion type optical waveguide in which a dopant is diffused only into a core portion.

[Effects of the Invention] As described above, according to the present invention, a fiber connection guide is provided with two components according to its function, that is, a first guide for positioning an optical waveguide and an optical fiber, and a fixing of an optical fiber. And a second guide for performing the above.
For the first guide, a mask pattern for the first guide is formed simultaneously with the mask pattern for the core portion of the optical waveguide, and the first guide is formed by etching using this mask. Precision positioning with one guide was realized. About the second guide,
Since the positional deviation tolerance with respect to the optical waveguide is large, it is possible to form the buried cladding by etching using a mask pattern formed on the surface of the cladding layer. As a result, the second guide can have a sufficient height to stably fix the optical fiber.

Therefore, according to the present invention, connection of a self-alignment fiber to an optical waveguide having a buried structure has become possible.

[Brief description of the drawings]

FIG. 1 is a perspective view of a first embodiment of the present invention, FIG. 2 is a cross-sectional view for explaining an alignment function of a first guide of the first embodiment, and FIG. 3 is a fiber of a second guide of the first embodiment. FIG. 4 is an explanatory view of a fixing function, FIG. 4 is an explanatory view of an example of a manufacturing method of the optical waveguide with a guide according to the first embodiment, and FIG. 5 is a method of FIG. FIG. 6 is an explanatory view of a step of forming, FIG. 6 is an explanatory view of a step of forming a mask pattern of a second guide in the method of FIG. 4, and FIG. 7 is another embodiment of a guide structure of an optical waveguide with a guide according to the present invention. FIG. 8 is an explanatory view of an example of a method for manufacturing a guided optical waveguide having the structure of FIG. 7 (b), FIG. 9 is an explanatory view of the structure of a conventional guided optical waveguide, FIG. FIG. 4 is an explanatory view of a step of forming a guide in a buried optical waveguide by a conventional method. DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... optical waveguide, 2a ... core part, 2b ... buffer layer, 2c ... clad layer, 3 ... guide, 3a ... 1st guide, 3b ... 2nd guide, 4 ... ... optical fiber, 5 ...
... Fixing agent, 10,11 ... Mask material, 12a ... Mask pattern for optical waveguide core, 13a ... Mask pattern for first guide, 13b ... Mask pattern for second guide, 20,21 ... Photo mask , 22a …… Mask pattern of optical waveguide core part, 2
3a... First guide mask pattern, 23b... Second guide mask pattern.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasushi Omori 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-61-267010 (JP, A) JP-A Sho 63-21611 (JP, A) Japanese Utility Model Showa 63-8706 (JP, U) JP-B 63-25644 (JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 6/30 G02B 6/12

Claims (3)

(57) [Claims] 1. A guided optical waveguide having a guide for positioning an optical fiber and the optical waveguide near an end of the optical waveguide, wherein the guide is formed by processing the optical waveguide. And a guide groove constituted by a bottom portion, and the guide portion is provided with a first guide for positioning an optical fiber and a second guide for fixing an optical fiber having different widths stacked in a height direction, The height of the upper surface of the first guide is equal to or less than the height of the upper surface of the core portion of the optical waveguide, and the central axis in the width direction of the first guide coincides with the central axis of the core portion;
Further, when the optical fiber is inserted into the first guide, the distance from the contact point between the optical fiber and the first guide to the center of the optical waveguide core is equal to the radius of the optical fiber, and the second guide is An optical waveguide provided at an upper portion of the first guide, wherein a height of the upper surface from the bottom portion is larger than a radius of the optical fiber and a width is larger than a diameter of the optical fiber. 2. A first step of forming a mask pattern for forming an optical waveguide core and a first mask pattern for positioning an optical fiber on a surface of the optical waveguide, and a step of forming an optical waveguide core and a first guide. Forming the second pattern
Removing the mask on the core pattern and forming a buried cladding layer on the surface of the optical waveguide while leaving the mask on the first guide; and a second guide for fixing the optical fiber. A fourth step of forming a mask pattern for use on the surface of the buried cladding layer, a mask pattern for the second guide formed on the surface of the buried cladding layer and a mask pattern for the first guide embedded inside the buried cladding layer, And a fifth step of etching an unnecessary portion of the optical waveguide to a desired depth. 3. A first step of forming a mask pattern for forming an optical waveguide core portion and a mask pattern for a first guide for positioning an optical fiber on a surface of the optical waveguide, and the optical waveguide core portion and the first guide. Forming the second pattern
A third step of removing the mask on the core pattern and the mask on the first guide and forming a buried cladding layer on the surface of the optical waveguide; and a second guide mask pattern for fixing an optical fiber. Forming on the surface of the buried cladding layer; using the second guide mask pattern formed on the buried cladding layer surface and the first guide pattern buried inside the buried cladding layer as a mask, thereby eliminating the need for an optical waveguide. And a fifth step of etching the portion to a desired depth.