JPH02211406A - Optical waveguide with fiber guide groove and its manufacture - Google Patents

Abstract

PURPOSE:To form the fiber guide groove in a buried type optical waveguide by using an Si substrate which has a recessed part and a projection part on the surface, and forming an optical waveguide in the recessed part and the fiber guide groove in the projection part. CONSTITUTION:The Si substrate 1 has the recessed part 1b and projection part 1a formed on the surface, a buffer layer 2b is formed on the recessed part 1b, and its top surface is the same in level with the top surface of the projection part 1a. On the buffer layer 2b, an optical waveguide core layer 2a and a clad layer 2c are formed and at the Si substrate projection part 1a nearby the end part of the optical waveguide core layer 2a, the fiber guide groove 4 for the positioning between an optical fiber and an optical waveguide 2 is formed so that the Si substrate surface is exposed. Thus, the fiber guide groove 4 is formed in the projection part 1a, so a fiber guide groove pattern and an optical waveguide pattern are formed at the same time by using one photomask and the fiber guide groove to the buried type optical waveguide can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a simple optical waveguide-to-optical fiber connection technology, which is a key technology for realizing an optical waveguide circuit.

[Conventional technology]

In order to realize a leading wave circuit, there is a need to develop a simple optical fiber connection technology to an optical waveguide. A method of forming a guide for optical fiber alignment on a silica-based optical waveguide substrate at the same time as forming an optical circuit pattern, and using this guide to connect fibers [JP 60-17406] is a simple and reliable method. It is expected to be a highly advanced optical fiber connection technology. FIG. 10 is an explanatory diagram of this connection method, and in the same figure, 11
12 is an optical circuit board, 12 is a ridge-shaped optical waveguide, and 12b is an optical circuit board.
is its buffer layer, 12a is its core layer, and 12C is its cladding layer. 13 is a fiber guide, 14 is an optical fiber, and 14a is its core layer.

Since the width and depth of the guide groove surrounded by the guide 13 are appropriately set, alignment of the optical fiber and the optical waveguide can be realized simply by inserting the optical fiber 14 into the guide. Moreover, since the position of the optical fiber 14 is determined mechanically by the guide 13, even if the temperature changes in the usage environment after the optical fiber is fixed, the position will not shift, and therefore the highly reliable fiber Connection can be achieved.

[Problem to be solved by the invention]

By the way, it has heretofore been difficult to apply the above guide groove connection method to a buried optical waveguide (an optical waveguide having a structure in which a thick cladding layer is formed and a core layer is buried). The reason for this is that when manufacturing a buried optical waveguide, conventionally,
This is because the guide and the optical waveguide cannot be formed at the same time using one photomask, and the guide and the optical waveguide are manufactured using the steps shown in FIG. 11, for example. First, as shown in FIG. 11(a), the core part 12a of the optical waveguide 12 is formed on the substrate 11, and after it is embedded with a cladding layer 12c, a mask is formed on the upper surface of the cladding layer as shown in FIG. 11(b). The material 15 is patterned using a photomask 16 on which a guide pattern is drawn. Next, the fiber guide 13 is etched by etching unnecessary parts of the cladding layer 12G as shown in FIG.
was forming. In such a process, it is necessary to form the guide pattern into a pattern with alignment accuracy within an error lμ1 with respect to the position of the optical waveguide 12 that has already been formed. However, the optical waveguide 12 formed in the lower layer has a core layer,
Since both the cladding layers are transparent, it is extremely difficult to achieve precise alignment.

As mentioned above, the conventional guide groove connection method has a problem in that it is difficult to apply to a buried optical waveguide. The first object of the present invention is to provide an optical waveguide having a fiber guide groove with a new structure that can be applied to a buried optical waveguide. An object of the present invention is to provide a method for manufacturing a guided optical waveguide.

[Means to solve the problem]

The fiber guide grooved optical waveguide of the present invention is a silica-based optical waveguide formed on a Si substrate having concave portions and convex portions formed on the surface, in which the silica-based optical waveguide buffer layer is
is formed in the i-substrate recess so that the height of its upper surface matches the height of the upper surface of the Si substrate convex part, and the silica-based optical waveguide core layer is formed on the buffer layer, Fiber for alignment between optical fiber and optical waveguide
It is characterized in that a guide groove is provided in a convex portion of the Si substrate near the end of the optical waveguide core layer.

Further, the method for manufacturing an optical waveguide with a fiber guide groove of the present invention includes a buffer layer forming step of forming a silica-based optical waveguide buffer layer on a Si substrate having concave portions and convex portions formed on the surface; a polishing step of exposing the surface of the convex portion of the Si substrate and matching the height of the surface of the silica-based optical waveguide buffer layer formed on the concave portion of the Si substrate with the height of the convex portion of the Si substrate; A core layer forming step is performed in which an optical waveguide core layer is formed on the surface of the core layer on the top surface of the convex portion of the Si substrate using a single photomask on which the fiber guide groove pattern and the optical waveguide pattern are simultaneously drawn. A first photolithography step in which a fiber guide groove pattern is formed and the mask material is patterned by alignment so that the optical waveguide pattern is formed on the core layer surface on the upper surface of the recessed portion of the Si substrate; a core layer etching step of removing the quartz-based optical waveguide core layer and exposing the surface of the convex portion of the Si substrate; and a embedding step of forming a cladding layer on the substrate;
A second photolithography step of patterning a mask material so as to cover the area where the optical waveguide pattern is formed on the upper surface of the cladding layer, and removing unnecessary portions of the cladding layer and forming a fiber guide groove pattern formed by the core layer. A cladding layer etching process is carried out to expose the Si substrate concave portion, and an S etching process is performed using the fiber guide groove pattern formed in the core layer as a mask.
The method is characterized in that it consists of an Si substrate etching process in which the protrusions of the i-substrate are etched to form fiber guides and grooves.

The above cladding layer etching process involves
The fiber guide groove pattern formed in the core layer can be left by utilizing the difference in film thickness between the guide groove pattern forming part and other parts and the difference in etching speed between the core layer and the cladding layer.

In addition, in the buffer layer forming step, a (100) plane crystal is formed as the Si substrate, and in the first photolithography step, the fiber guide groove is formed on the Si substrate [11
0] direction, and by performing anisotropic etching of the Si substrate in the Si substrate etching step, a guide groove with high dimensional accuracy can be easily formed. The difference between the prior art and the present invention is that the conventional fiber guide grooved optical waveguide is
This is largely different from the present invention in that it is formed on a substrate. Also,
The conventional manufacturing method differs greatly from the manufacturing method of the present invention in that it is not possible to use a photomask on which a waveguide pattern and a guide pattern are drawn at the same time.

〔Example〕

Embodiment 1 FIG. 1 is a perspective view illustrating a first embodiment of the present invention. 1 is a Si substrate, 1a is a convex portion thereof, and 2b is a concave portion thereof. 2 is a quartz-based optical waveguide, 2a is a core layer, 2b is a buffer layer, and 2c is a cladding layer. The buffer layer 2b and the cladding layer 2c have the same refractive index, which is lower than the refractive index of the core layer 2a. 3 is a fiber guide core layer pattern (fiber guide groove pattern), and 4 is a fiber guide groove. The buffer layer 2b is formed on the Si substrate concave portion 1b, and its upper surface is at the same height as the upper surface of the Si/substrate convex portion 1a. The fiber guide groove 4 is formed in the convex portion of the Si substrate.

FIG. 2 is a sectional view for explaining the functions of this embodiment. 5 is an optical fiber, and 5a is its core layer.

The optical fiber 5 and the fiber guide groove 4 are in contact at three points A, B, and C. Here, A and B are fibers.
At the midpoint of the guide/core layer pattern 3 in the thickness direction, A
The straight line connecting C almost intersects with the center O of the waveguide core layer. B
is a point on the bottom surface of the fiber guide groove. The dimensions of the guide groove are: fiber radius R, guide groove width WI guide groove depth (
If D is the distance from the waveguide core center 0 to the guide bottom surface, it is set as D#R1W average 2R, so the alignment between the fiber and the waveguide can be achieved simply by inserting the fiber into the guide groove.

Such a guided optical waveguide can be manufactured by the method shown in FIG. FIG. 2A shows a step of forming an optical waveguide substrate by forming a silica-based optical waveguide buffer layer 2b on a Si substrate 1 having concave portions 1b and convex portions 1a. In this example, a flame deposition method [M, Kawachi et.
al, , Jan, J., Appl, Phys.
, Vol, 22. (1983), p. 193
Two pieces were used. That is, Si
After depositing a glass particulate film on the substrate 1, the glass particulate film is heated in an electric furnace to make it transparent vitrified.

At this time, the thickness of the buffer layer 2b was formed so that it was thicker than the step difference between the concave and convex portions of the Si substrate.

FIG. 2B shows a step of polishing the surface of the optical waveguide substrate to expose the surface of the convex portion of the Si substrate and flatten the surface. <c> in the figure is a step of forming an optical waveguide core layer 2C on the optical circuit board. Here, the flame deposition method was used again.

In the same figure (d), the fiber guide core layer pattern 3 and the optical waveguide pattern 2a are drawn simultaneously using one photomask pattern.
This is a photolithography process in which the mask material 10 is patterned by aligning the mask material 10 so that it is located on the convex portion of the Si substrate.

Here, amorphous 5i (a-
3i) A membrane was used.

FIG. 3(e) shows a step of removing unnecessary portions of the quartz-based optical waveguide film by etching using a mask material 10 to form an optical waveguide core layer pattern 2a and a fiber guide core layer pattern 3. Here, reactive ion etching (RIE-) using a fluorine-based etching gas was used as the etching method. Etching was continued until unnecessary portions of the core layer were completely removed. At this time, the surface of the Si convex portion is exposed in the fiber guide groove. , (f) in the same figure shows the step of forming the cladding layer 2c and embedding the lower layer pattern, and (g) of the same figure shows the step of patterning the mask material 10a so as to cover the region where the optical waveguide is formed on the upper surface of the cladding layer 2c. be.

FIG. 6(h) shows a step in which unnecessary portions of the cladding layer are removed by etching to expose the fiber guide core layer pattern 3 and the Si substrate in the guide groove portion sandwiched therebetween. In this step, if the end of etching is properly determined, the fiber guide core layer pattern 3 can be left and the Si substrate surface in the area between them can be exposed. this is,
This is due to the reason shown in Figure 4. In other words, when a buried cladding layer is formed, the film thickness of the former part is thicker than the latter part in the part where the core layer is the underlying layer and the part without the core layer (Fig. 4a).
). In addition, the etching rate is slightly different between the cladding layer and the core layer, and the etching rate of the core layer is slightly slower than that of the cladding layer (about 1 to 20%). Therefore, in the case of a two-layer structure in which a core layer and a cladding layer are formed on a convex portion of a Si substrate as in this example, the amount of etching required is small, so that the above-mentioned difference in film thickness and slight difference in etching speed can be avoided. Therefore, it is possible to leave the core layer and expose the Si substrate surface (Fig. 4, c).

In contrast, in the case of a conventional optical waveguide in which a buffer layer, core layer, and cladding layer are formed on a flat Si substrate, S
Because deep etching to the buffer layer is required to expose the i-substrate, and because there is no difference in etching speed between the buffer layers, the fiber guide core layer pattern changes as the etching progresses. As a result, a clear step cannot be formed as shown in FIG. 5. Therefore, it is difficult to accurately determine the guide groove width.

After this, using the fiber guide core layer pattern 3 remaining after the above etching process as a mask, the Si substrate is etched so as to satisfy the depth condition shown in FIG. 2, as shown in FIG. 1. Optical waveguides with fiber guide grooves can be formed.

As described above, in this example, since the guide groove is formed on the upper surface of the convex portion of the Si substrate, the etching depth in FIG. 3(h) can be made shallow. As a result, the optical waveguide It is now possible to utilize the difference in film thickness and the slight difference in etching speed between the core layer and cladding layer, making it possible to
It is now possible to expose the surface of the Si substrate in the area between the guide core layer patterns 3 while leaving them intact. A fiber guide groove can be formed by etching the Si substrate using this fiber guide core layer pattern 3 as a mask. In this way, the present invention has made it possible to form a fiber guide groove and an optical waveguide using one photomask when forming a guide groove in a buried optical waveguide.

In the cladding layer etching process shown in FIG. 3(h), in order to expose the Si substrate surface in the area between while leaving the fiber guide core layer pattern 3, the method described in this embodiment is used. Alternatively, it is also possible to use a buried mask method [JP-A-62-94936]. That is, in the embedding process shown in FIG.
In this method, the mask is used as a mask in the cladding layer etching process shown in FIG. However, compared to this method,
The manufacturing method of this embodiment is advantageous in that the number of processes is small.

Embodiment 2 FIG. 6 is a perspective view illustrating a second embodiment of the present invention. A (100) plane crystal is used as the Si base substrate. The optical waveguide 2 is formed in the Si substrate recess 1b, and the guide groove 4 is formed in the Si substrate recess 1b.
It is provided on the substrate convex portion 1a in parallel to the [110] direction. The guide groove has a V-groove shape, and its side wall is formed by a 5i (111) plane 4a. This is formed by anisotropic etching of a Si substrate, as will be described later. Further, the optical waveguide end portion 20 was shaped to protrude convexly.

FIG. 7 is a sectional view for explaining the function of the fiber guide groove of this embodiment. Angle θ between the guide groove side wall 4a and the substrate surface, optical fiber 50 radius R1, waveguide core layer 2a
When the thickness h is, the interval W of the fiber guide core layer pattern 3 is W-2[(R/sinθ) (h/(2tanθ)
) to satisfy the following relationship. If these dimensions are set, the distance from the contact points A and B between the optical fiber 5 and the guide groove 4 to the center 0 of the optical waveguide core layer will be R, so simply inserting the optical fiber 5 into the guide groove 4 will result in a distance of R. The centers of the optical waveguide core layer 2a and the optical fiber core layer 5a coincide, and alignment between the fiber waveguides can be realized. In this Example 1, the ■groove was formed by anisotropic etching of the (100) surface of the Si substrate, so θ=54.74°
becomes. Therefore, the optical fiber outer diameter is 125 μx (R=
62.5μII), when the waveguide core layer thickness h=8μl,
The optimum spacing W of the fiber guide core layer pattern 3 is:
It becomes 148μ shoulder.

The fiber guide groove having such a structure can be basically manufactured by the same method as that of the first embodiment. That is,
To form the fiber guide core layer pattern 3, the Si substrate may be anisotropically etched after following the process similar to that shown in FIG. For anisotropic etching of the Si substrate, for example, an alkaline etching solution such as ethylenediamine pyrocatechol is used. When the optical waveguide substrate is immersed in the etching solution, the Si substrate is etched using the fiber guide core layer pattern 3 made of a silica-based glass film and the optical waveguide 2 as a mask, thereby forming a V-groove in the Si substrate.

The advantage of the guide groove structure of this embodiment is that, compared to the guide groove structure of the first embodiment, it is easier to improve the machining accuracy of the guide groove. That is, when the above etching solution is used, the relationship between the Si crystal plane and the etching rate is (1
00): (110): (111)=50:30
:3, so when a (111) plane appears, that plane will not be etched any further. For this reason, fiber
As long as the interval W between the guide core layer patterns 3 is precisely formed, the guide groove dimensions can be determined accurately, and therefore, there is no need to control the etching depth. In contrast, Example 1
In this case, it was necessary to precisely control the distance W of the fiber guide core layer pattern 3 as well as the depth of the guide groove.In addition, in this example, as shown in FIG. The reason why the convex portion 1a is made to protrude is as follows. If the waveguide end 20 is flat, the (111) plane 4 also exists on the Si substrate directly under the waveguide end 20, as shown in FIG.
a appears, and as a result, the end surfaces of the optical fiber 5 and the optical waveguide 2 cannot be brought into contact with each other, as shown in FIG. 2(b). When the waveguide end 20 is made to protrude into the convex portion of the Si substrate, a liquid crystal surface 4a' which is not a (111) plane appears as shown in FIG. 9, and as a result, the Si substrate at the bottom of the optical waveguide is etched. As shown in FIG. 6(b), it becomes possible to bring the fiber and the waveguide end into contact with each other.

As described above, in this embodiment, when forming the guide groove in the convex portion of the Si substrate, the V-groove shape is formed by anisotropic etching, so that the guide groove only needs to be formed precisely in its width. As a result, it became easy to form precision guide grooves.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

In the optical waveguide with a fiber guide groove according to the first aspect, a Si substrate having concave portions and convex portions on the surface is used, an optical waveguide consisting of a buffer layer, a core layer, and a cladding layer is formed in the concave portion, and a fiber guide groove is formed in the convex portion. By providing guide grooves, it is now possible to simultaneously pattern the fiber guide groove pattern and the optical waveguide pattern using one photomask, making it possible to form fiber guide grooves in embedded optical waveguides. Become. Further, according to the manufacturing method of claim 2, it is possible to manufacture an optical waveguide with an embedded fiber guide groove. Furthermore, according to the manufacturing method of claim 3, the number of processes can be reduced compared to other manufacturing methods.Furthermore, according to the manufacturing method of claim 4, guide grooves are formed in the protrusions of the Si substrate. , set the guide groove to S.
Since it is formed by i-substrate anisotropic etching, if only the width of the guide groove is set accurately, there is no need to control the depth direction, and guide grooves with high dimensional accuracy can be easily manufactured.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the first embodiment of the present invention, and FIG. 2 is a perspective view of the first embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating the structure of the guide groove in the embodiment of
a) to (h) are process diagrams of the method for manufacturing an optical waveguide with a guide groove of the present invention, Fig. 4 (a) to (C) and Fig. 5 (a).
~(C) is an explanatory diagram of the formation process of the fiber guide core layer pattern, FIG. 6 is a perspective view of the second embodiment of the present invention, and FIG. 7 is an explanation of the guide groove structure of the second embodiment. cross-sectional view,
8 (a), (b) and 9 (a), (b) are explanatory diagrams of the structure of the optical waveguide end in this example, and 10.
This figure is a perspective view of a conventional optical waveguide with a guide, and FIG. 11 is a process diagram showing the process of forming a guide in a buried optical waveguide by a conventional method. DESCRIPTION OF SYMBOLS 1...Si substrate, 1a...Si substrate convex part, 1b...
- Si substrate recess, 2... optical waveguide, 2a... optical waveguide core layer, 2b... optical waveguide buffer layer, 2c...
Optical waveguide cladding layer, 3... Fiber guide core layer pattern, 4... Fiber guide groove, 4a... Guide groove side wall (Si (111) surface), 5... Optical fiber 5a...・Optical fiber core N, 10 + l O
a...Mask material.

Claims (4)

[Claims] (1) In a silica-based optical waveguide formed on a Si substrate having concave portions and convex portions formed on its surface, the silica-based optical waveguide buffer layer is located in the concave portion of the Si substrate, and the height of its upper surface is the same as that of the Si substrate. The quartz-based optical waveguide core layer is formed on the buffer layer, and a fiber guide groove for aligning the optical fiber and the optical waveguide is formed to match the height of the upper surface of the convex portion. An optical waveguide with a fiber guide groove, characterized in that the fiber guide groove is provided on a convex portion of a Si substrate near an end of the optical waveguide core layer. (2) On a Si substrate with depressions and protrusions formed on the surface,
A buffer layer forming step of forming a silica-based optical waveguide buffer layer, polishing the substrate surface to expose the surface of the convex portion of the Si substrate, and increasing the height of the surface of the silica-based optical waveguide and buffer layer formed on the concave portion of the Si substrate. A polishing step to match the height of the convex portion of the Si substrate, a core layer forming step to form an optical waveguide core layer on the substrate, and a single sheet in which the fiber guide groove pattern and the optical waveguide pattern are drawn simultaneously. using a photomask, and positioned so that the fiber guide groove pattern is formed on the surface of the core layer on the top surface of the convex portion of the Si substrate, and the optical waveguide pattern is formed on the surface of the core layer on the top surface of the concave portion of the Si substrate. a first photolithography step for patterning the mask material; a core layer etching step for removing unnecessary portions of the quartz-based optical waveguide core layer and exposing the surface of the convex portions of the Si substrate; and forming a cladding layer on the substrate. a second photolithography step of patterning a mask material so as to cover the region where the optical waveguide pattern is formed on the upper surface of the cladding layer; removing unnecessary portions of the cladding layer and forming a core layer; A cladding layer etching process that exposes the concave portion of the Si substrate while leaving the fiber guide groove pattern formed in the core layer, and a Si substrate etching process that etches the convex portion of the Si substrate using the fiber guide groove pattern formed in the core layer as a mask to form the fiber guide groove. A method for manufacturing an optical waveguide with a fiber guide groove, comprising the steps of: substrate etching process. (3) In the cladding layer etching process, the difference in film thickness between the fiber guide groove pattern forming part and other parts and the difference in etching speed between the core layer and the cladding layer are utilized to 3. The method of manufacturing an optical waveguide with fiber guide grooves according to claim 2, wherein a guide groove pattern remains. (4) In the buffer layer forming step, a (100) plane crystal is used as the Si substrate, and in the first photolithography step, the fiber guide groove is formed on the Si substrate [11
0] direction, and the above-mentioned S
3. The method of manufacturing an optical waveguide with a fiber guide groove according to claim 2, wherein an anisotropic etching of the Si substrate is performed in the i-substrate etching step.