JPH08160236A - Production of optical waveguide - Google Patents

Abstract

PURPOSE: To produce an optical waveguide which is less deformed and exhibits a good polarization characteristic by removing the upper part of an upper clad layer, which part has a large fluctuation width in refractive index, thereby molding the upper clad layer to have an adequate thickness. CONSTITUTION: The upper clad layer 31 is subjected to etching to remove the upper part thereof. The upper clad layer 31 is molded to have an adequate thickness corresponding to silicon, which is a substrate material, and the quartz glass formed on a substrate. As a result, the fluctuation width in refractive index along the thickness direction of the upper clad layer 31 is sufficiently lowered. Namely, the silicon wafer 1 is cut and divided into chips and thereafter, the chips are immersed into an HF-NH4 F soln. to carry out the wet etching of the quartz glass layer, i.e., waveguide layer, on the chip. As a result, the upper clad layer 31 on the chip is removed over the entire surface and the upper part thereof and the layer thickness is made to be about 30μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical waveguide using a flame deposition method.

[0002]

2. Description of the Related Art A conventional method for producing an optical waveguide using a flame deposition method is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-105111. FIG. 1 is a flowchart explaining this manufacturing method. In this method, first, while supplying SiCl ₄ , BBr ₃ and POCl ₃ to a flame burner, the glass particles produced in the flame are blown onto a silicon wafer to form porous glass particles to be a lower clad layer on the wafer. Layer (SiO ₂ + B ₂ O ₃ +
P ₂ O ₅ ) is formed. Next, SiCl ₄ , G is added to the burner.
While supplying eCl ₄ , BCl ₃ and POCl ₃ , glass particles produced in a flame are blown onto a silicon wafer to form a porous glass particle layer (SiO ₂ + GeO ₂ + B ₂ O) serving as a core on the lower clad layer. ₃ + P ₂ O
₅ ) to form. Since these glass fine particle layers are soot-shaped, the above-mentioned process for forming the glass fine particle layer is called sooting (step 100 in FIG. 1).

Subsequently, these two glass fine particle layers are sintered and then gradually cooled to form a transparent glass (step 20).
0). Next, the core layer thus formed is subjected to appropriate patterning to form a core having a desired optical waveguide pattern (step 300). Typically, multiple cores are formed at once for mass production.

After this, a glass fine particle layer to be an upper clad layer is sooted on the lower clad layer and the core in the same manner as the lower clad layer (step 400), and then sintered and gradually cooled to form an upper clad layer. A layer is formed (step 500). Finally, the silicon wafer is diced, and the portions where each core is formed are cut into chips (step 600). By doing so, it is possible to collectively manufacture a plurality of optical waveguides.

[0005]

According to the conventional manufacturing method,
When the glass waveguide layer and the substrate have different coefficients of thermal expansion like the above-mentioned quartz glass and silicon, non-uniform stress is generated inside the glass layer (mainly the upper clad layer) when the glass fine particle layer is made into transparent glass. appear. As a result, the refractive index becomes non-uniform inside the glass layer, and as a result, the transmission characteristics of the TE mode and the TM mode are affected differently, and the polarization characteristic deteriorates. Further, since the optical waveguide is deformed due to the generation of stress, when an optical fiber is connected to this optical waveguide by using an optical connector or the like, a positional deviation easily occurs between the core of the optical waveguide and the core of the optical fiber, Connection loss tends to increase.

Further, when the substrate is cut into chips, mechanical strain is generated and remains on the side portions of the glass waveguide layer.
This residual strain also makes the refractive index of the glass layer non-uniform and affects the transmission characteristics and deteriorates the polarization characteristics, which is a problem in manufacturing the optical waveguide.

The present invention has been made to solve the above problems, and an object of the present invention is to produce an optical waveguide exhibiting good polarization characteristics with little deformation.

[0008]

In order to solve the above problems, an optical waveguide manufacturing method according to the present invention comprises a lower clad layer formed on a substrate and a lower clad layer formed on the lower clad layer. A first step of preparing an optical waveguide substrate having a core, and a second step of spraying glass fine particles generated in a flame onto the optical waveguide substrate to form a glass fine particle layer to be an upper clad layer, A chip having a core formed by cutting the substrate on which the glass layer is formed by the third step of forming the upper clad layer by transparentizing the glass fine particle layer by subjecting the glass fine particle layer to heat treatment. And the upper step of the upper clad layer of this chip is removed to obtain the following refractive index difference ratio Δn Δn = (n−n ₂ ) / n ₂ × 10 with the lower clad layer. 0 [%] (n is the refractive index of the object, n ₂ is the refractive index of the lower cladding layer) expressed by the refractive index difference ratio Δn in the refractive index distribution along the layer thickness direction of the upper cladding layer. And a fifth step of molding the upper clad layer to a thickness such that the fluctuation range is about 0.05 [%] or less.

In the first step, glass fine particles produced in a flame are sprayed onto a substrate to form a glass fine particle layer to be the lower clad layer, and then glass fine particles produced in a flame are formed on the glass fine particle layer. To form a glass fine particle layer serving as a core, and then heat-treating these glass fine particle layers to make these glass fine particle layers transparent vitrified to form a lower clad layer and a core layer. Then, the core layer may be subjected to a patterning process to form a predetermined optical waveguide pattern, thereby producing an optical waveguide substrate. Further, the glass fine particle layer to be the lower clad layer is heat-treated to be transparent vitrified, then the glass fine particle layer to be the core is formed, and then heat-treated to be transparent vitrified to prepare an optical waveguide substrate. May be.

Further, the removal of the upper portion of the upper clad layer in the fifth step can be carried out by etching or polishing, and it is particularly preferable to carry out it by wet etching. The wet etching may be performed by using a HF-NH ₄ F solution as an etching solution.

When a silicon wafer is used as the substrate and silica glass fine particles are sprayed as the glass fine particles, the upper clad layer is coated with about 10 to 10 parts in the fifth step.
It is preferable to mold it to a thickness of about 30 μm. At this time, in the fifth step, it is more preferable to remove the upper part of the upper clad layer by about 10 to about 20 μm.

[0012]

According to the knowledge of the present inventors, in the method of manufacturing an optical waveguide using the flame deposition method, when the upper clad layer is formed, that is, when the glass fine particle layer to be the upper clad layer is made into transparent glass. The internal stress generated becomes larger in the portion of the upper cladding layer closer to the upper surface. Therefore, in the method for producing an optical waveguide of the present invention, among the upper clad layers,
By removing the upper part having a large internal stress and thus a large fluctuation range of the refractive index, the internal stress of the upper clad layer after the removal is sufficiently suppressed, and the fluctuation range of the refractive index along the layer thickness direction is about 0.05. % Or less, which is sufficiently small. Therefore, the optical waveguide manufactured according to the present invention is little deformed and exhibits good polarization characteristics.

In the method of removing the upper portion of the upper clad layer by wet etching in the present invention, the etching progresses also from the side surface of the glass waveguide layer.
The distorted portion formed on the side of the waveguide layer during chip formation is removed. As a result, fluctuations in the refractive index of the glass waveguide layer are further reduced, so that the optical waveguide manufactured by this method has very small deformation and exhibits extremely good polarization characteristics.

According to the knowledge of the present inventors, when a silicon wafer is used as a substrate and a silica-based glass fine particle layer is formed as the glass fine particle layer, the upper clad layer is formed to have a thickness of about μm or less. The fluctuation range of the refractive index of the upper clad layer along the layer thickness direction is about 0.05% or less.
When the upper clad layer is formed to a thickness of about 10 μm or more, a sufficient light confining action is obtained, and an optical waveguide having a sufficiently low transmission loss is manufactured. In particular, when the upper clad layer is formed to have a thickness of about 10 to about 30 μm, an optical waveguide in which the fluctuation range of the refractive index along the layer thickness direction of the upper clad layer is extremely low and the radiation loss of propagating light is sufficiently low is obtained. As it is obtained, it is very suitable.

When a silicon wafer is used as the substrate and a silica-based glass fine particle layer is formed as the glass fine particle layer, the strained portion of the waveguide layer is sufficiently removed by removing the upper clad layer by about 10 μm or more by wet etching. Will be removed. When the thickness of the removed portion of the upper clad layer is about 20 μm or less, the sagging of the side surface of the waveguide layer caused by etching can be sufficiently suppressed. As a result, an optical waveguide having a small amount of deformation and exhibiting good polarization characteristics is manufactured.

[0016]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 2 is a flow chart for explaining the method of manufacturing the optical waveguide of this embodiment. Further, FIGS.
It is process drawing which shows a part of manufacturing method of a present Example. In this example, a silicon wafer having a diameter of 4 inches and a thickness of 1.0 mm is prepared as a substrate, and a waveguide layer made of silica glass is formed on the wafer by the flame deposition method.

First, as shown in FIG. 3, a silicon wafer 1
A first glass fine particle layer 10 serving as a lower clad layer is formed thereon. Using an oxyhydrogen flame burner 50, while feeding a raw material gas such as SiCl _{4 which} is a raw material of the glass fine particles 10 into the oxyhydrogen flame together with a fuel (O ₂ , H ₂ ),
This is performed by directly spraying the silica-based glass particles generated in the flame onto the silicon wafer 1. Burner 50
Is repeatedly moved over the silicon wafer 1 to form a glass fine particle layer having a uniform thickness (FIG. 3). Subsequently, the second glass fine particle layer 20 serving as a core is formed on the first glass fine particle layer 10 by the same method (FIG. 4).

Since these glass fine particle layers are soot-shaped, the above process for forming the glass fine particle layer is called sooting (step 100 in FIG. 2).

When forming the first glass fine particle layer 10, the gases of BCl ₃ and POCl ₄ which are dopant raw materials are sent into the oxyhydrogen flame together with SiCl ₄ which is a glass raw material. When forming the second glass fine particle layer 20,
In addition to BCl ₃ and POCl ₄ , GeCl ₄ is fed as a raw material gas of a dopant for increasing the refractive index of the core.

Next, after heating the silicon wafer 1 on which the glass fine particle layers 10 and 20 are formed in a sintering furnace,
The glass fine particle layers 10 and 20 are annealed to be sintered (step 200 in FIG. 2). The two glass fine particle layers are made into transparent glass, whereby the lower clad layer 11 (SiO ₂ + B ₂ O ₃ + P ₂ O ₅ ) and the core layer 21 (SiO ₂ + GeO ₂ + B ₂ O ₃ + P ₂ ) are formed on the silicon wafer 1.
O ₅ ) will be formed (FIG. 5). in this way,
In this embodiment, the lower clad layer 11 and the core layer 21 are simultaneously made into transparent glass, so that the work is efficiently performed.

Next, in order to perform patterning processing on the core layer 21, a photoresist 60 having a predetermined optical waveguide pattern is formed on the upper surface of the core layer 21 by using a photolithography technique (FIG. 6). Thereafter, the core layer 21 is subjected to reactive ion etching, and then the photoresist 60 is removed to form the 1 × 8 branched core 22. The core 22 has a shape in which one core is branched into eight cores by a Y branch portion that is sequentially provided (FIG. 7).
The above is the core processing (step 300 in FIG. 2).

Although a single core 22 is shown in FIGS. 6 and 7, in reality, reactive ion etching is performed using a photoresist having a plurality of optical waveguide patterns, and as shown in FIG. , A plurality of cores 22 are formed on the wafer 1. As a result, the optical waveguide substrate of this example is completed.

Next, a third glass fine particle layer 30 to be an upper clad layer is sooted on the optical waveguide substrate (step 400 in FIG. 2). This is similar to the first glass fine particle layer 10 in that B, which is a dopant raw material in the oxyhydrogen flame.
This is performed by blowing the glass particles generated in the flame onto the upper surfaces of the core 22 and the lower cladding layer 11 while feeding the gas of Br ₃ and POCl ₄ together with SiCl ₄ (FIG. 8).

Thereafter, the glass fine particle layer 30 is sintered to obtain a dopant-added upper clad layer 31 (Si
O ₂ + B ₂ O ₃ + P ₂ O ₅ ) is formed (step 500 in FIG. 2). The upper clad layer 31 is combined with the lower clad layer 11 to form one clad, and the clad surrounds the side peripheral surface of the core 22 (FIG. 9).

The dopant concentration of the core and clad layers is set so that the relative refractive index difference of the optical waveguide is 0.3%. In this embodiment, the upper clad layer 31 contains 5.6 wt%.
B ₂ O ₃ and 3.3 wt% P ₂ O ₅ are added. Further, the core 22 contains 2.3 wt% of B ₂ O ₃ ,
1.6 wt% P ₂ O ₅ and 5.4 wt% GeO ₂ are added. 2.3 wt% B is contained in the lower clad layer 11.
₂ O ₃ and 1.6 wt% P ₂ O ₅ are added.
As a result, the refractive index of the core 22 is set to 1.4632, and the refractive indices of the upper and lower clad layers are set to 1.4588.

The lower clad layer 11 has a layer thickness of about 40 μm,
The layer thickness of the upper clad layer 31 (the thickness from the upper surface of the core to the upper surface of the upper clad layer 31) is about 40 μm, and the core 2
2 is formed to have a cross section of 8 × 8 μm. As a result, a glass waveguide layer having a layer thickness of about 90 μm is formed on the silicon wafer 1.

Next, the silicon wafer 1 (FIG. 10) is diced using a dicing saw, and each portion where the cores 22 are formed is cut into chips. Each chip has a planar shape of 5 mm × 40 mm. These chips function as a 1 × 8 branch type optical waveguide.

The above procedure is the same as the conventional method for manufacturing an optical waveguide. Generally, in the method for producing an optical waveguide using the flame deposition method as described above, when the glass fine particle layer is heated in a sintering furnace and then gradually cooled, silicon as a substrate material is more likely to form the waveguide layer. Since the thermal expansion coefficient is larger than that of the constituent quartz glass, the silicon wafer contracts strongly.
As a result, stress is generated inside the glass waveguide layer in the direction along the laminated surface. In the method in which the lower clad layer and the core are formed and then the upper clad layer is formed, this stress is mainly generated in the upper clad layer, and the magnitude of the stress increases as it approaches the surface of the waveguide layer.

When stress is generated inside the glass, the refractive index of the stress generating portion increases due to the photoelastic effect. Since the magnitude of the stress inside the glass waveguide layer is larger as it is closer to the surface of the waveguide layer, the increase amount of the refractive index of the upper cladding layer is larger as it is closer to the surface of the waveguide layer. As a result, the difference in refractive index between the core and the upper clad layer is reduced, so that the light confinement action is weakened and the radiation loss is increased.

As described above, in the upper clad layer 31, the amount of increase in the refractive index changes along the layer thickness direction, so that the TE mode and the TM mode, which are waveguide modes, have different effects of the refractive index change, and As a result, the amount of increase in radiation loss differs between the TE mode and the TM mode. Therefore, the difference in transmission loss between the two modes, that is, the polarization characteristic becomes large. Since it is not preferable for communication if the transmission characteristics differ depending on the polarization direction, an increase in the transmission characteristics difference depending on the polarization direction can be said to be deterioration of the polarization characteristics.

In this embodiment, the upper cladding layer 31 is etched to remove the upper portion thereof, and the upper cladding layer 31 is removed.
Is formed into an appropriate thickness according to the substrate material of silicon and the silica-based glass to be formed on the substrate, thereby sufficiently reducing the fluctuation range of the refractive index along the layer thickness direction of the upper cladding layer 31. There is.

That is, in this embodiment, the silicon wafer 1 is cut into chips and the chips are cut into HF-NH.
Wet in ₄ F solution for 200 minutes to perform wet etching of the quartz glass layer on the chip, that is, the waveguide layer (Fig. 2).
Step 700). HF-NH ₄ as etching liquid
The reason why the F solution is used is that the stability as a solution and the uniformity of etching are taken into consideration.

As a result, the upper clad layer 3 on the chip is
1 (thickness: about 40 μm) is entirely etched to remove 10 μm on the upper portion, and the layer thickness becomes about 30 μm. The fabrication of the optical waveguide of this example is completed as described above.

In this embodiment, the upper portion of the upper cladding layer 31 having a large fluctuation range in refractive index is removed by wet etching. As a result, the fluctuation range of the refractive index of the upper clad layer 31 remaining after etching becomes small.

Further, generally, when the substrate is cut into chips, mechanical deformation occurs and strain remains on the side portions of the glass waveguide layer. This residual strain also causes a change in the refractive index of the waveguide layer and deteriorates the polarization characteristics.

In this embodiment, not only the upper portion of the glass waveguide layer but also the side portions thereof are removed by wet etching, so that the strained portion of the waveguide layer is removed. Therefore, according to the present embodiment, the effect of removing the upper portion of the upper cladding layer 31 and the effect of removing the strained portion of the waveguide layer are mixed, and the fluctuation range of the refractive index of the upper cladding layer 31 remaining after etching becomes extremely small. .

FIG. 11 is a graph showing the refractive index distribution along the layer thickness direction of the glass waveguide layer in the optical waveguide produced in this example. The abscissa axis of the graph represents the thickness of the glass layer from the upper surface of the silicon wafer 1 to each part of the glass waveguide layer, and the ordinate axis represents the refractive index difference between the glass waveguide layer and the lower cladding layer 11. The refractive index difference ratio Δn. The refractive index difference ratio Δn is measured by a known RNF (refractive near field) method. In addition, RNF
The method is described on page 370 of the Optical Engineering Handbook (Asakura Shoten, 1986).

The refractive index difference ratio Δn is expressed as Δn = (n−n ₂ ) / n ₂ × 100 [%]. Here, n is the refractive index of each part of the glass waveguide layer, and n ₂ is the refractive index of the lower cladding layer. The refractive index n ₂ of the lower clad layer is a design value determined by the type of dopant added to the silica glass and its concentration.

As shown in FIG. 11, in the optical waveguide manufactured according to this example, the fluctuation range of the refractive index in the upper cladding layer is about 0.05%, and the refractive index difference ratio of the core (about 0. (3%), the fluctuation range of the refractive index is suppressed to the extent that the refractive index distribution can be said to be almost uniform.

This means that the internal stress of the upper cladding layer 31 is sufficiently small, and therefore the optical waveguide manufactured according to this example has a small deformation.

According to the knowledge of the present inventors, when the substrate material is silicon and the glass constituting the waveguiding layer is a silica-based glass containing quartz as the main component as in this embodiment, the upper portion When the clad layer is formed to have a thickness of about 30 μm or less, the fluctuation range of the refractive index of the upper clad layer along the layer thickness direction is about 0.
It will be less than 05%. In addition, the upper clad layer is about 10 μm
When molded to the above thickness, a sufficient light confining action is obtained, and an optical waveguide having a sufficiently low transmission loss is manufactured. In particular, when the upper clad layer is molded to a thickness of about 10 to about 20 μm, the fluctuation range of the refractive index along the layer thickness direction is extremely low,
Since the radiation loss of propagating light is also sufficiently low, an optical waveguide exhibiting extremely good polarization characteristics with little deformation can be obtained.

The inventors of the present invention, for comparison with the above-mentioned embodiment, performed etching to reduce the thickness of the upper clad layer to about 30 μm.
Instead of increasing the thickness to 30 m, the upper clad layer has a thickness of 30 μm from the beginning.
To form an optical waveguide (Comparative Example 1). After forming the upper clad layer on the silicon wafer 1,
As in Example 1, the wafer 1 is cut into chips.
This chip has the same plane shape (5 mm × 4) as that of the first embodiment.
0 mm).

This method adjusts the thickness of the upper clad layer by paying attention to the fact that the thicker the upper clad layer is, the larger the fluctuation range of the refractive index is. It is something to reduce.

The inventors of the present invention and the comparative example 1 prepared the optical waveguides according to their polarization characteristics,
The transmission loss and the connection loss with an optical connector containing eight optical fibers were measured. The measurement was performed on each core branched into eight. The following table shows the maximum and minimum values of the results measured for each branch core.

[0046]

[Table 1]

As shown in this table, the optical waveguide manufactured according to this example has a sufficiently small fluctuation range of the refractive index and, as a result, exhibits good polarization characteristics and connection with an optical connector. The loss is also small enough.

The variation of the transmission loss between the branch cores is small, which is preferable. The optical waveguide manufactured in Comparative Example 1 also exhibits sufficiently good polarization characteristics by adjusting the thickness of the upper clad layer to be formed, and the connection loss is sufficiently low. However, the method of Comparative Example 1 does not remove the strained portion of the waveguide layer that occurs when the silicon wafer 1 is made into chips. Since the influence of this strained portion is greater in the branch core closer to the side surface of the waveguide layer, in the optical waveguide according to Comparative Example 1, as shown in Table 1, the polarization characteristics and the transmission loss are slightly different among the branch cores. ing.

On the other hand, the optical waveguide according to the present embodiment is
Since the distorted portion of the waveguide layer is removed, not only good polarization characteristics are exhibited, but also variations in polarization characteristics and transmission loss are reduced, which is very suitable.

Further, for comparison with the present embodiment, the inventors of the present invention have performed an upper clad layer 31 by wet etching.
An optical waveguide was manufactured by making the thickness of the removed portion larger than that of this example (Comparative Example 2).

That is, in the method of Comparative Example 2, after forming the upper clad layer 31 to a thickness of about 59 μm, the silicon wafer 1 was made into chips (the plane shape of the chips is the same as that of the embodiment), and then this. chips immersed about 600 minutes to HF-NH ₄ F solution. By this wet etching,
The thickness of the upper clad layer 31 on the chip is set to about 30 μm, which is the same as in the embodiment.

The thickness of the upper clad layer 31 after etching is the same as that of the example, but in the example, the upper clad layer 3 is formed.
1 is removed by about 10 μm, whereas Comparative Example 2 is removed by about 29 μm.

Also in the case of Comparative Example 2, the upper portion of the upper clad layer 31 having a large fluctuation range of the refractive index is removed by etching, as in the present Example. Further, as a result of the etching progressing also from the side surface of the glass waveguide layer, the side portion of the waveguide layer is removed similarly to the upper portion of the upper cladding layer 31, and the strained portion of the waveguide layer is removed. When the refractive index distribution of the glass waveguide layer of the optical waveguide thus manufactured was measured by the RNF method, the fluctuation range of the refractive index of the upper cladding layer 31 was 0.05% or less, which was sufficiently small. It was

However, in the method of Comparative Example 2, since the thickness of the side portion of the glass layer removed by etching is large, the sagging of the side surface of the waveguide layer caused by etching becomes remarkable. When attempting to connect the optical waveguide and the optical connector by bringing the flat end surface of the optical connector into contact with the end surface having such surface sagging, positional deviation and angular deviation are caused between the cores of the optical waveguide and the optical fiber. Is likely to occur. This is not preferable because it increases the transmission loss of the optical line.

The inventors of the present invention measured the polarization characteristics, transmission loss and connection loss with an optical connector containing eight optical fibers of the optical waveguide prepared in Comparative Example 2 above. The following table shows the maximum value and the minimum value of the results measured for each branch core, and the measurement results for the optical waveguides manufactured according to the examples are also shown.

[0056]

[Table 2]

As shown in this table, the polarization characteristic of the optical waveguide according to Comparative Example 2 is sufficiently small. However, the variation among the branch cores is larger than that of the embodiment, and the transmission loss and the connection loss are also larger.

According to the knowledge of the present inventors, when the substrate material is silicon and the glass constituting the waveguiding layer is a silica-based glass whose main component is quartz, as in this embodiment, etching is performed. Is about 10 μm above the upper clad layer 31.
With the above removal, the strained portion of the waveguide layer can be sufficiently removed. In addition, the upper clad layer 31 formed by etching
If the thickness of the removed portion is about 20 μm or less, the sagging of the side surface of the waveguide layer can be sufficiently suppressed. Therefore, in the case where the substrate material is silicon and the type of glass forming the waveguiding layer is silica-based glass whose main component is quartz, removing the upper portion of the upper cladding layer by about 10 to about 20 μm reduces deformation. It is possible to manufacture an optical waveguide that exhibits extremely good polarization characteristics and has sufficiently low connection loss and transmission loss even when connected to an optical connector.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, even when the substrate material or the type of glass forming the waveguide layer is different from that of this embodiment, the upper portion of the upper clad layer is removed by an appropriate thickness,
By molding to an appropriate thickness according to various conditions, the fluctuation range of the refractive index of the upper cladding layer can be sufficiently suppressed. This makes it possible to manufacture an optical waveguide that exhibits little deformation, exhibits excellent polarization characteristics, and has a small connection loss with the optical connector.

[0060]

As described above in detail, in the method of manufacturing an optical waveguide of the present invention, the upper clad layer having a large fluctuation range of the refractive index is removed and the upper clad layer is formed to an appropriate thickness. By doing so, the fluctuation range of the refractive index of the upper clad layer after the removal is sufficiently reduced to about 0.05% or less. Therefore, according to the present invention, it is possible to manufacture an optical waveguide exhibiting good polarization characteristics with little deformation.

In the method of using wet etching of the present invention, the fact that the etching also proceeds from the side surface of the glass waveguide layer is utilized to remove the strained portion formed on the side portion of the waveguide layer during chip formation. This further reduces the variation of the refractive index of the glass waveguide layer. Therefore, according to this method, it is possible to fabricate an optical waveguide which has very small deformation and exhibits extremely good polarization characteristics.

When a silicon wafer is used as the substrate and a silica-based glass fine particle layer is formed as the glass fine particle layer, if the upper clad layer is molded to a thickness of about 10 to about 30 μm, the refractive index fluctuation of the upper clad layer is Since the width is sufficiently suppressed and the radiation loss of the propagating light is also sufficiently reduced, it is possible to manufacture a suitable optical waveguide exhibiting good polarization characteristics. In particular, the upper clad layer is about 10 to about 20μ.
Molding to a thickness of m makes it possible to produce an optical waveguide exhibiting extremely good polarization characteristics, which is very suitable.

When a silicon wafer is used as the substrate and a silica-based glass fine particle layer is formed as the glass fine particle layer, the upper part of the upper clad layer is about 10 to about 20 μm.
When only m is removed, the strained portion of the waveguide layer is sufficiently removed and the sag of the side surface of the waveguide layer is sufficiently suppressed.
An optical waveguide exhibiting good polarization characteristics can be manufactured.

[0064]

[Brief description of drawings]

FIG. 1 is a flowchart illustrating a conventional method of manufacturing an optical waveguide.

FIG. 2 is a flow chart illustrating a method of manufacturing an optical waveguide of this example.

FIG. 3 is a first process chart showing the manufacturing method of the present embodiment.

FIG. 4 is a second process chart showing the manufacturing method of the present embodiment.

FIG. 5 is a third process chart showing the manufacturing method of the present embodiment.

FIG. 6 is a fourth process chart showing the manufacturing method of the present embodiment.

FIG. 7 is a fifth process chart showing the manufacturing method of the present embodiment.

FIG. 8 is a sixth process chart showing the manufacturing method of the present embodiment.

FIG. 9 is a seventh process chart showing the manufacturing method of the present embodiment.

FIG. 10 is a plan view showing a silicon wafer 1 having a plurality of cores 22 formed therein.

FIG. 11 is a graph showing the refractive index distribution along the layer thickness direction of the glass waveguide layer in the optical waveguide manufactured according to this example.

[Explanation of symbols]

1 ... Silicon wafer, 10 ... First glass fine particle layer,
11 ... Lower clad layer, 20 ... Second glass fine particle layer,
21 ... Core layer, 22 ... 1 × 8 branch core, 30 ... Third glass fine particle layer, 31 ... Upper clad layer, 50 ... Oxygen flame burner, 60 ... Photoresist.

Claims (6)

[Claims] 1. A lower clad layer formed on a substrate,
A first step of preparing an optical waveguide substrate having a core formed on the lower clad layer, and glass fine particles to be an upper clad layer by spraying glass fine particles generated in a flame onto the optical waveguide substrate. The second step of forming a layer, the third step of heat-treating the glass fine particle layer to make the glass fine particle layer transparent vitrified to form an upper clad layer, and the glass layer formed by the above steps. A fourth step of cutting the formed substrate into chips having the core, and removing the upper portion of the upper clad layer of the chips to obtain the following refractive index difference ratio with the lower clad layer. _{Δn Δn = (n-n 2} ) / n 2 × 100 [%] (n is the refractive index of the object, n ₂ is the refractive index of the lower clad layer) layer of the upper cladding layer and is represented by A fifth step of molding the upper clad layer to a thickness such that the fluctuation range of the refractive index difference ratio Δn in the refractive index distribution along the direction is about 0.05 [%] or less. And a method for manufacturing an optical waveguide. 2. In the first step, glass fine particles produced in a flame are sprayed onto a substrate to form a glass fine particle layer serving as the lower clad layer, and then the glass fine particle layer is produced on the glass fine particle layer in a flame. The glass fine particles are sprayed to form a glass fine particle layer serving as the core, and thereafter, these glass fine particle layers are heat-treated to be transparent vitrified, and the lower clad layer, and the above A step of forming the core layer to be a core, and subsequently subjecting the core layer to a patterning process to form a plurality of the cores having a predetermined optical waveguide pattern, thereby producing the optical waveguide substrate. The method for producing an optical waveguide according to claim 1, which is characterized in that. 3. The method of manufacturing an optical waveguide according to claim 1, wherein the fifth step is a step of performing wet etching on the glass layer on the chip. 4. The wet etching is HF-NH
_The method for producing an optical waveguide according to claim 3, wherein the 4F solution is used as an etching solution. 5. A silicon wafer is used as the substrate, and silica-based glass fine particles are sprayed as the glass fine particles. In the fifth step, the upper clad layer is coated with about 10
The method for producing an optical waveguide according to claim 1, wherein the optical waveguide is molded to a thickness of about 30 μm. 6. The method of manufacturing an optical waveguide according to claim 5, wherein in the fifth step, the upper portion of the upper clad layer is removed by about 10 to about 20 μm.