JP3180859B2 - Manufacturing method of planar optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a planar optical waveguide formed by laminating an organic polymer material as an optical waveguide material.

[0002]

2. Description of the Related Art Conventionally, in the field of long-distance optical communication and optical information processing, integration of optical circuit elements has been promoted in order to realize high reliability, high speed, low loss, and miniaturization. Various planar optical waveguides have been studied as the main components. Conventionally, in these fields, single-mode optical transmission is mainly premised, and a waveguide having a diameter of 1
An optical waveguide having a configuration of 0 μm square or less and a relative refractive index difference of 1% or less has been manufactured.

[0003] As materials for optical waveguides, various materials such as oxide crystals, glass, semiconductors, and organic materials have been studied. Among them, organic materials have the lowest material cost and are excellent in mass productivity, so that they are expected to be applied to consumer products mainly for short-distance use. Also,
In general, spin coating is used for film formation using an organic material on a substrate, and a relatively good uniformity of film thickness can be obtained in a small area.

[0004]

As described above, a conventional method for manufacturing a planar optical waveguide using an organic material is to dissolve an organic polymer material in a solvent and form a film on a substrate by spin coating. It is a target. However,
With this method, it is difficult to form a film having a thickness of 10 μm or more and a uniform thickness in the plane.

Further, when a thick film is laminated, it generally takes a long time until all the solvent in the film evaporates. for that reason,
The time required for the lower polymer film, which has been coated and dried, to come into contact with the solvent is inevitably increased, and cracks called solvent stress cracking occur. Alternatively, there is a problem that the re-dissolution at the boundary surface gradually progresses, and as a result, a mixed layer of two organic polymer materials is formed, and the thickness of the mixed layer becomes nonnegligible with respect to the wavelength used. Was.

[0006] Solvent stress cracking becomes a structural light scattering center, and the mixed layer causes light scattering due to random fluctuations in the refractive index. Therefore, these two factors cause a loss in the planar optical waveguide. With respect to the above-mentioned mixed layer, an attempt has been made to define a combination of both using the concept of solubility parameter of a polymer material and a solvent (JP-A-62-6202).

However, this rule is intended to facilitate the dissolution, and does not express whether or not a mixed layer is generated. In particular, there has been a problem that the thickness of the mixed layer easily exceeds the wavelength used in the case of being in contact with a solvent for a long time or drying at a high temperature. The present invention
In view of the above problems, when stacking thick organic polymer materials,
An object of the present invention is to provide a method for manufacturing a planar optical waveguide which has no solvent stress cracking or re-dissolution, has a uniform coating film, and has low scattering loss.

[0008]

According to the present invention, there is provided a planar optical waveguide in which a cladding layer made of a first organic polymer material and a core layer made of a second organic polymer material are sequentially laminated on a surface of a substrate. A raw material solution prepared by dissolving the first organic polymer material or the second organic polymer material in a solvent is prepared,
First, a substrate is immersed in a raw material solution for a clad layer, and a first laminating step of drying is performed. Then, the substrate on which the clad layer is formed is immersed in a raw material solution for a core layer, and a second laminating step of drying is performed. Wherein the first laminating step and the second
In the laminating step, the above immersion is performed a plurality of times, and at least once, the substrate is turned upside down.
And during the drying In the coating film parallel to the vertical direction of the raw material solution in the substrate, no line drying while suppressing solvent evaporation from the coating film, also hit the said soaking
The board with the board surface parallel to the vertical direction.
A method for producing a planar optical waveguide, characterized by immersing the planar optical waveguide in a material solution .

It is most remarkable in the present invention that the immersion in the first and second laminating steps is performed a plurality of times and the substrate is turned upside down at least once. In the vertical direction, and drying while suppressing the amount of solvent evaporated from the coating film.

That is, in the first laminating step, the first
A raw material solution in which an organic polymer material is dissolved by a solvent is prepared, and the substrate is immersed in this raw material solution. The immersion is performed a plurality of times. At this time, the immersion is performed at least once by reversing the vertical position of the substrate. Thereby, a substantially uniform coating film can be formed on the substrate.

If the above-mentioned upside down is not performed, the thickness of the coating film below the substrate becomes larger than that above the substrate, and the thickness is not uniform. The plurality of immersions are performed until a desired clad layer coating thickness is obtained. Thereafter, the coating film is dried. Thereby, a clad layer is formed on the substrate.

That is, in forming a coating film, the substrate surface is immersed in a raw material solution while being arranged in a vertical direction by using an immersion method. Drying while suppressing the evaporation rate of the solvent. The applied film gels as drying proceeds, and finally reaches a film thickness defined by viscosity and drying time.

Here, if the drying time is sufficiently longer than the moving time due to the flow of the solution, a smooth film surface can be obtained in the film surface due to the surface tension of the gel film, and the excess solution moves downward, and the substrate moves downward. It is dripped from. In addition, if the orientation of the substrate is always constant in a plurality of immersions, the film thickness increases vertically downward. So, immerse several times, and
On the way, the direction of the substrate is turned upside down at least once. As a result, a uniform film thickness can be obtained in the plane.

The thickening of the cladding layer and the core layer can be obtained by repeating immersion and drying in a solvent in which an organic polymer material is dissolved in a solvent at a high concentration. At this time, when the coating is performed a plurality of times, the same organic polymer material that has already been dried or gelled is dissolved again to form a gel-like film. However, since the gel-like film has extremely poor fluidity, it can be easily thickened. In the drying, the substrate is hung so that the coating film on the substrate is in a vertical direction, and drying is performed while suppressing the amount of solvent evaporated from the coating film.

As a method of suppressing the amount of solvent evaporation, for example, in the case of forming a clad layer, a gas stream containing the same solvent vapor as the solvent used in preparing the raw material solution of the first organic polymer material is used. Heat while flowing over the surface of the coating. The heating temperature is preferably lower than the boiling point of the solvent. If the boiling point is higher than the boiling point, the surface of the clad layer to be formed may have irregularities, which may impair the function of the planar optical waveguide.

Next, in the second laminating step, the substrate on which the clad layer is formed is immersed a plurality of times in a raw material solution obtained by dissolving the second organic polymer material in a solvent. At this time, the substrate is turned upside down, the coating film is oriented vertically during drying, the amount of solvent evaporation is suppressed, and the means thereof are the same as those in the first laminating step. Thus, the clad layer and the core layer are sequentially laminated on the surface of the substrate. Further, an upper clad layer is laminated on this core layer as necessary. A third laminating step of laminating the upper clad layer will be described later.

Further, as the substrate, glass, resin,
Materials such as semiconductors and oxide crystals are used. As the first organic polymer material for forming the cladding layer, fluoroalkyl acrylate, polytrifluoroethyl methacrylate,
Silicon resin or the like is used. Polymethyl methacrylate or the like is used as the second organic polymer material for forming the core layer.

In preparing the raw material solution, the first
As the solvent for dissolving the organic polymer material, one or a mixture of two or more of methyl ethyl ketone, ethyl acetate, acetonitrile and the like is used. On the other hand, as a solvent for dissolving the second organic polymer material, methyl isobutyl ketone, acetic acid n
One or a mixture of two or more of butyl, toluene and chlorobenzene is used.

Next, when the second laminating step is performed after the first laminating step, the drying time until the solvent in the core layer raw material solution dries is t, and the solvent at the drying temperature in the second laminating step is t. Assuming that the dissolution rate of the first organic polymer material is A and the wavelength used of the planar optical waveguide to be manufactured is λ, the condition “A <λ / t” is satisfied between them. Preferably, a combination of the first organic polymer material and a solvent in the core layer raw material solution is selected.

That is, when the core layer raw material solution is applied on the clad layer and the core layer is laminated, the first organic polymer material of the already formed clad layer is changed to the core layer raw material. The contact time of the solution with the solvent is prolonged. For this reason, a mixed layer of the clad layer and the core layer is formed, and the thickness of the mixed layer may reach about the used wavelength λ at which optical loss occurs. Therefore, it is preferable to form the core layer under a condition that satisfies the relationship of “A <λ / t”.

The unit of the drying time "t" is time (Hr).
The unit of the dissolution rate “A” is μm / Hr, and the unit of the working wavelength “λ” is μm. “A” is obtained by measuring the thickness of the dissolved or swollen first organic polymer material per unit time.

For example, polymethyl methacrylate is used as the second organic polymer material for the core layer, methyl isobutyl ketone is used as the solvent for preparing the raw material solution, and the drying temperature in the second laminating step is 25 ° C. On the other hand, the used wavelength “λ” of the planar optical waveguide is 0.66 μm, and t = 6H
r. Then, λ / t = 0.11 μm / Hr. Therefore, in order to satisfy “A <0.11 μm / Hr”, a fluoroalkyl acrylate having a dissolution rate in the solvent at the above-mentioned drying temperature of less than 0.1 μm / Hr is used as the first organic polymer material.

Next, as the first organic polymer material, a fluoroalkyl acrylate is used, and as a means for suppressing the amount of solvent evaporation from the coating film during the drying, a solvent having the same concentration σ as the solvent in the raw material solution is used. Due to the gas stream containing steam,
Gas flow rate 2σCCM / cm ² per 1 cm ^{2 of} coating film area
It is preferable to use an atmosphere of less than. The unit “CCM” of the gas flow rate indicates “cc / min”.

Further, polymethyl methacrylate is used as the second organic polymer material, and one or more of methyl isobutyl ketone, n-butyl acetate, toluene and chlorobenzene are used as the solvent, and an atmosphere gas for drying is used when drying. It is preferable to control the dried coating film by the concentration of the solvent vapor mixed in the flow and the gas flow rate of the drying atmosphere.

Next, as described above, after forming the core layer on the clad layer, if necessary, an upper clad layer is formed so as to surround the core layer. In this case, for example, there is the following method. That is, in manufacturing a planar optical waveguide in which a clad layer and a core layer are sequentially laminated on the substrate, and an upper clad layer made of a third organic polymer material is further laminated on the core layer, After the second laminating step, a third laminating step of the same operation as the first laminating step is performed. In the above immersion, the substrate surface should be vertical.
The substrate is immersed in the raw material solution while being arranged parallel to the direction.

After the second laminating step, the third
In performing the laminating step, the drying time until the solvent in the raw material solution for the third organic polymer material is dried is represented by t, and the second time with respect to the solvent at the drying temperature in the third laminating step.
Assuming that the dissolution rate of the organic polymer material is A and the used wavelength of the planar optical waveguide to be manufactured is λ, “A <
The combination of the second organic polymer material and the solvent in the raw material solution for the upper cladding layer is selected so as to satisfy the condition of λ / t ”.

The third organic polymer material includes a thermosetting silicone resin, a fluororesin and the like. In addition, this third
In the laminating step, immersion in the raw material solution and drying are performed in the same manner as in the first laminating step. The same applies to the relationship of “A <λ / t”. It is to be noted that a flat optical waveguide having a plurality of waveguide layers can also be obtained by using a flat plate having an optical waveguide manufactured by any method as a substrate and applying the present invention thereto.

[0028]

In the present invention, the first laminating step and the second laminating step are performed, and immersion and drying are performed as described above. Therefore, the mixed layer formed at the interface between the cladding layer and the core layer does not have a large thickness compared to the wavelength used in the planar optical waveguide. Therefore, scattering loss due to the refractive index fluctuation at the interface hardly occurs, and a low-loss planar optical waveguide can be obtained.

The mechanism of the above-described solvent stress cracking is such that a solvent acts on craze generated at a microscopic stress concentration source existing on the surface of a coating film to cut a molecular chain. However, according to the present invention, the generation of the microscopic stress concentration source can be suppressed as much as possible, so that the solvent stress cracking does not occur even when the organic polymer material is laminated. In addition, according to the method of the present invention, the organic polymer material can be uniformly and smoothly coated on a large-area substrate.

Therefore, according to the present invention, there is provided a method for manufacturing a planar optical waveguide having a uniform coating film, low scattering loss and no solvent stress cracking or re-dissolution during lamination of an organic polymer material. can do.

[0031]

【Example】

Embodiment 1 A method for manufacturing a planar optical waveguide according to an embodiment of the present invention will be described with reference to FIGS. This example is shown in FIG.
Basically, as shown in FIG.
This is to manufacture a planar optical waveguide in which a cladding layer 1 made of an organic polymer material and a core layer 2 made of a second organic polymer material are sequentially laminated.

Finally, in the planar optical waveguide, as shown in FIG. 2D, an upper clad layer 15 is formed so as to wrap the core layer 2 around the core layer 2. An upper substrate 45 is provided on 15. In manufacturing the planar optical waveguide, first, FIG.
As shown in FIG. 1, a clad layer raw material solution 10 in which a first organic polymer material is dissolved in a solvent (FIG. 1A) and a core layer raw material solution 20 in which a second organic polymer material is dissolved in a solvent (FIG. 1F)
Prepare

[0033] Then, first, FIG. 1 (A), the as (B), the substrate 4 in the cladding layer for raw material solution 10, the group
A first laminating step is performed in which the plate is immersed while the plate surface is arranged parallel to the vertical direction, and is then pulled up and dried (FIG. 1C). The first lamination step is performed a plurality of times as shown in FIGS. In the meantime, the lower end 41 and the upper end 4 of the substrate 4 are at least once before the next immersion.
2 is inverted in the vertical direction (FIGS. 1B to 1D).

At the time of drying (FIGS. 1C and 1E), while the coating 11 of the raw material solution 10 on the substrate is parallel to the vertical direction, the amount of solvent evaporated from the coating 11 is suppressed. Perform drying. The suppression of the amount of solvent evaporation is performed, for example, while applying a vapor stream of the solvent vapor used for the cladding layer raw material solution to the surface of the coating film 11.

Next, after the cladding layer 1 is formed on the surface of the substrate 4, the substrate 4 is immersed in the core layer raw material solution 20, as shown in FIG. Next, as in the case of the formation of the clad layer, immersion, upside down, and drying are performed in a vertical state while suppressing the amount of solvent evaporation. As a result, FIG.
As shown in (G), the cladding layers 1 and
An intermediate 40 in which the core layers 2 are sequentially laminated is obtained.

Next, as shown in FIGS. 2A to 2D,
In the intermediate 40, the etching mask 3 was formed on the upper surface of the core layer 2 by photolithography, and etching was performed by dry etching to produce the channel type optical waveguide 22 (FIGS. 2A to 2C). Further, an upper cladding layer 15 was formed around the optical waveguide 22 as necessary in the same manner as in the first laminating step, and an upper substrate 45 was further provided thereon. Thus, a planar optical waveguide having a channel-type optical waveguide is manufactured.

Embodiment 2 Next, a specific example of the manufacture of the planar optical waveguide shown in Embodiment 1 will be described with reference to FIGS. 2 and 3 to 6. That is, as shown in FIG.
A fluoroalkyl acrylate (OP-10, manufactured by Daikin Industries, Ltd.) is used as the first organic polymer material for the cladding layer 1 by using an immersion method on a substrate 4 made of a glass material of m.
0; refractive index 1.39).

Although methyl ethyl ketone was used as the solvent for dissolving the first organic polymer material, other solvents such as ethyl acetate, acetonitrile and the like, or a mixed solvent thereof are also possible. After drying, subsequently, as a second organic polymer material for the core layer, polymethyl methacrylate (refractive index;
1.49). As a solvent, a mixed solvent of methyl isobutyl ketone and monochlorobenzene was used.

However, other solvents that do not form a mixed layer of the clad layer and the core layer even when they are in contact with the fluoroalkyl acrylate of the first organic polymer material for 10 hours or more are acetic acid. There are n-butyl, toluene, and a mixed solvent thereof. 25 of these solvents
All dissolution rates for the fluoroalkyl acrylate at 0 ° C. were less than 0.1 μm per hour. Table 1 shows these film forming conditions.

The etching shown in FIGS. 2B to 2D and the formation of the upper cladding layer 15 and the upper substrate 45 are performed by a known method. As the upper cladding layer 15,
A non-solvent low refractive index resin such as a silicone resin was used. Glass was used as the upper substrate 45.

[0041]

[Table 1]

In the above method, the first organic polymer material is dried by using the same saturated vapor of methyl ethyl ketone as the solvent.
A gas diluted to 20% (ie, saturated vapor concentration σ = 0.2) with an inert gas such as N ₂ gas was used as a dry gas. Gas flow rate (cc / min / cm ² / cm ² = CCM / c) passing through the unit channel cross-sectional area per 1 cm ^{2 of} coating film
The film thickness distribution after drying is shown in FIG. 3 using m ⁴ ) as a parameter. The horizontal axis in the figure is the position (ymm) from the lower end to the upper end of the substrate, and the vertical axis is the film thickness Tμm of the first organic polymer material.
Is shown.

As can be seen from FIG.
At less than CM / cm ⁴ , the evaporation rate of the solvent is low and the solution can easily move downward, so that the solution converges to the film thickness specified by the surface tension and the film thickness in the plane is almost uniform. It turns out that it becomes. Here, since the concentration σ of the saturated vapor and the flow rate are in a proportional relationship, if the flow rate is less than 2σCCM / cm ⁴ , a uniform film is always obtained.

Next, FIG. 4 shows the film thickness distribution after film formation when the concentration of the first organic polymer material is 12 wt% under the conditions shown in Table 1 in the same manner as in FIG. In the figure, the black point is the result of dipping in the same direction twice, and the white point is the result of upside down. It can be seen that the in-plane uniformity of the film thickness is improved by the upside down.

Next, FIG. 5 shows that the second
The film thickness distribution after immersion in the organic polymer material four times is shown in the same manner as in FIG. In the above immersion, immersion was performed twice in the same direction, and then inverted upside down and immersed twice. As a result, a thick film exhibiting good uniformity was obtained. FIG. 6 shows a change in film thickness when a polymethyl methacrylate film is formed on a 76 × 26 mm ² substrate under the conditions shown in Table 1 and the gas flow rate of the solvent vapor is changed. As is known from the figure, the film thickness can be adjusted over a wide range by changing the gas flow rate of the solvent vapor during drying.

As shown in Table 1, even when the drying time for forming the core layer is 6 hours, the thickness of the mixed layer does not reach the working wavelength of 0.66 μm. Therefore, when this is used as a two-dimensional optical waveguide, scattering at the interface between the cladding layer and the core layer is not observed, and the propagation loss is 0.2%.
It was as low as dB / cm. As described above, according to the present invention, it is possible to obtain a planar optical waveguide having a uniform coating film and low scattering loss, without the occurrence of solvent stress cracking and re-dissolution when laminating an organic polymer material.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a method for manufacturing a planar optical waveguide according to a first embodiment.

FIG. 2 is an explanatory view following FIG. 1 showing the method for manufacturing the planar optical waveguide.

FIG. 3 is a diagram showing a relationship between a flow rate of a dry gas, a substrate position, and a film thickness when a fluoroalkyl acrylate is formed in Example 2.

FIG. 4 is a diagram showing the relationship between the upside down of the substrate, the substrate position, and the film thickness when a fluoroalkyl acrylate is formed in Example 2;

FIG. 5 is a view showing a state where the substrate is turned upside down in the second embodiment;
FIG. 4 is a diagram showing a relationship between a substrate position and a film thickness when polymethyl methacrylate is formed.

FIG. 6 is a diagram showing a relationship between a flow rate of a dry gas and a film thickness when polymethyl methacrylate is formed in Example 2.

[Explanation of symbols]

 1. . . 9. cladding layer, . . 14. a raw material solution of the first organic polymer material; . . 1. upper cladding layer; . . Core layer, 20. . . 21. a raw material solution of a second organic polymer material; . . 2. channel-type optical waveguide; . . 3. etching mask; . . Substrate, 41. . . Lower end, 42. . . Upper end, 45. . . Upper substrate,

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Satoru Kato 41, Chukumi Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory, Inc. (72) Inventor Tadashi Ichikawa, Nagakute-cho, Aichi-gun, Aichi, Japan 41, Yokomichi 1 Inside Toyota Central Research Laboratory Co., Ltd. (56) References JP-A-62-150302 (JP, A) JP-A-1-129206 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) G02B 6/12-6/14

Claims (5)

(57) [Claims] 1. A method for manufacturing a planar optical waveguide, comprising: laminating a clad layer made of a first organic polymer material and a core layer made of a second organic polymer material on a surface of a substrate in order. A raw material solution prepared by dissolving a coalescing material or a second organic polymer material in a solvent was prepared, and a first laminating step of immersing the substrate in a raw material solution for a cladding layer and drying was performed, and then the cladding layer was formed. A method of performing a second laminating step of immersing a substrate in a raw material solution for a core layer and drying, wherein in the first laminating step and the second laminating step, the immersion is performed a plurality of times and at least once. The substrate is turned upside down, and at the time of drying, the coating of the raw material solution on the substrate is parallel to the vertical direction, and drying is performed while suppressing the amount of solvent evaporated from the coating.
No, and in the above immersion, arrange the substrate surface parallel to the vertical direction.
A method for manufacturing a planar optical waveguide, wherein a substrate is immersed in a raw material solution while being placed . 2. The method according to claim 1, wherein when the second laminating step is performed after the first laminating step, the drying time until the solvent in the core layer raw material solution is dried is t, and the drying time in the second laminating step is The first for the solvent at temperature
When the dissolution rate of the organic polymer material is A and the used wavelength of the planar optical waveguide to be manufactured is λ, “A
A method for manufacturing a planar optical waveguide, comprising selecting a combination of the first organic polymer material and a solvent in the core layer raw material solution such that the condition of <λ / t ”is satisfied. 3. The method according to claim 1, wherein the first organic polymer material is a fluoroalkyl acrylate, and the same organic solvent as the solvent in the raw material solution is used as means for suppressing the evaporation of the solvent from the coating film during the drying. Gas flow rate of 2σ per 1 cm ^{2 of} coating film area
A method for manufacturing a planar optical waveguide, comprising using an atmosphere of less than CCM / cm ² . 4. The method according to claim 1, wherein polymethyl methacrylate is used as the second organic polymer material, and one or more of methyl isobutyl ketone, n-butyl acetate, toluene and chlorobenzene are used as the solvent. A method of manufacturing a planar optical waveguide, wherein the thickness of a dried optical film is controlled by the concentration of a solvent vapor mixed into a gas flow for drying and the gas flow rate of the gas for drying. 5. The method according to claim 1, wherein a clad layer and a core layer are sequentially laminated on the substrate, and a third layer is formed on the core layer.
In producing a planar optical waveguide formed by laminating an upper clad layer made of an organic polymer material, a method of performing a third laminating step of the same operation as the first laminating step after the second laminating step is provided. When performing the third laminating step after the second laminating step, the drying time until the solvent in the raw material solution for the third organic polymer material dries is t, Assuming that the dissolution rate of the second organic polymer material is A and the wavelength used of the planar optical waveguide to be manufactured is λ, the above condition is satisfied so that “A <λ / t” is satisfied. selects a combination of a solvent for the raw material solution in the second organic polymeric material and the upper cladding layer, also hitting the above immersion, distribution parallel to the substrate surface in a vertical direction
A method for manufacturing a planar optical waveguide, wherein a substrate is immersed in a raw material solution while being placed .