JP3077188B2 - Manufacturing method of optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] As a conventional method of manufacturing this type of optical waveguide, various methods of manufacturing a plastic optical waveguide using a photolithography method have been devised.

First Conventional Example FIG. 5 shows a selective polymerization method as a first conventional example.

In this method, first, a solution in which an acrylic monomer 52 is dispersed in polycarbonate 51 having a refractive index of 1.59 is cast into a film (FIG. 5A), and then a photomask on which a necessary waveguide pattern is drawn is formed. When ultraviolet light is irradiated while the film 54 is brought into close contact with the film 55 produced in FIG. 5 (a), the acrylic monomer 52 in the portion irradiated with the ultraviolet light is polymerized with the polycarbonate 51 to form a copolymer 56 (FIG. 5 ( b)). Next, when the film 55 is heated in a vacuum to remove the unreacted acrylic monomer 52 from the film 55, the refractive index of the copolymer portion 57 becomes lower than that of the polycarbonate portion 58 (refractive index 1.57).
5), polycarbonate part 5 formed in a pattern
8 cores (refractive index 1.59), cladding (refractive index 1.5
75) (FIG. 5 (c)). Finally, a film-shaped plastic waveguide 60 is obtained by covering the surface of the film 55 with the low refractive index material 59.

Second Conventional Example FIG. 6 shows a molding method as a second conventional example. As shown in FIG. 6 (a), in this molding method, first, a layer of a photoresist 62 is thinly coated on a flat plate 61 made of glass or a metal material, and is then applied through a mask 63 having a planar structure of an optical waveguide. The layer of photoresist 62 is selectively exposed. Next, as shown in FIG. 6 (b), the photoresist 62 on the exposed portion is removed using a developer to remove the flat plate.
The pattern of the mask 63 by the photoresist 62 is transferred onto the surface 61, and becomes the projection 64. Next, the flat plate 61 is selectively melted by a chemical etching method using a material that dissolves the flat plate 61, and then the protrusion 64 is removed. By this step, as shown in FIG. 6 (c), a groove 66 is formed in the flat plate 61 according to the pattern of the mask 63, and this becomes the master 65 of the optical waveguide. As shown in FIG. 6 (d),
Using the master 65, a clad substrate 70 is formed of a low refractive index translucent plastic material.

Examples of the method of forming the clad base material 70 from the master 65 include a casting method and an injection molding method. In this case, a nickel conductive film is formed on the surface of the groove side surface of the master 65 by a sputtering method. The nickel layer is thickened by electroforming. Then, the stamper 67 is formed by releasing the master 65. Using the stamper 67, a clad substrate 70 having a groove having an optical waveguide pattern is formed by a known method such as a casting method or an injection molding method. As shown in FIG. 6 (e), the clad base material 70 has the same form as the groove-side surface of the master 65.

Next, as shown in FIG.
A high-refractive-index transparent plastic is caused to flow in from one end of the groove 69 by utilizing capillary action, and after the resin is sufficiently filled in the groove 69, the resin is cured to form the core 71. And
As shown in FIG. 6 (g), the entire surface on which the core 71 is formed is uniformly coated with a low-refractive-index translucent plastic to form a cladding layer 72, thereby forming an optical waveguide.
Get 80. According to this manufacturing method, the materials of the core 71, the clad base material 70, and the clad layer 72 can be freely selected, so that the optical waveguide 80 can have a large aperture angle. For example, an acrylic resin (trade name: M210, manufactured by Toa Gosei Chemical Co., Ltd., refractive index n ₁ = 1.54) as a material of the core 71, and a similar photocurable resin as a material of the clad base material 70 and the clad layer 72 Acrylic resin (trade name: Aronix M310, manufactured by Zinc Synthetic Chemical Company, refractive index n ₂ = 1.4
The aperture angle of the optical waveguide 80 formed by using 6) is as large as 26.5 degrees.

[Problems to be solved by the invention]

However, according to the selective polymerization method, which is the first conventional example, of such a conventional method for manufacturing an optical waveguide, it is difficult to increase the refractive index difference between the polycarbonate part and the copolymer part, and as a result, The aperture angle of the optical waveguide 60 formed of the above-mentioned material was 12.6 degrees. The transmission loss of the optical waveguide produced by this method was 0.2 dB / cm.
That is, there is a problem that the opening angle cannot be increased. The fact that the aperture angle cannot be made large means that the optical waveguide cannot be bent with a small radius of curvature, and at the same time, the acceptance angle of the light beam incident on the optical waveguide is small. Means that the amount of light beam that can be transmitted is small.

On the other hand, according to the molding method of the second conventional example, it is possible to increase the opening angle, but the surface roughness inside the groove formed by the etching step, that is, the surface roughness of the wall surface of the optical waveguide is reduced. However, the resulting optical waveguide has a problem that it can hardly propagate light or has a large transmission loss. Generally, the surface roughness of an optical system such as an optical waveguide and a lens must be kept within the order of 0.01 μm.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method of manufacturing an optical waveguide having a large aperture angle and a small transmission loss even by an optical etching method.

[Means for solving the problem]

In order to achieve this object, a method of manufacturing an optical waveguide according to the first aspect of the present invention is directed to a first method for producing an intermediate material in which a cross-sectional shape of a photoresist formed on a flat plate is substantially square. Heating the intermediate material,
A second step of making the surface of the substantially quadrangular projection smooth, and making the cross-sectional shape substantially semicircular to create a resist master of the optical waveguide; and the cross-sectional shape of the resist master is reversed, and A third step of forming an inverted mold in which the substantially semicircular protrusion is formed as a substantially semicircular groove; and a step of forming the inverted mold formed of a low-refractive-index translucent material and having the same cross-sectional shape as the inverted mold. The method includes a fourth step of forming a clad base having a substantially circular portion, and a fifth step of forming a core by filling a translucent material having a high refractive index into a substantially semicircular groove of the clad base.

[Action]

According to the first aspect of the present invention, first, an intermediate material having a substantially square cross section of a protrusion made of photoresist formed on a flat plate is prepared. The surface of the substantially quadrangular projection is slightly rough. When a flat plate (intermediate material) having a projection having a substantially quadrangular cross section is heated, the projection becomes a semi-melted state, the surface of the projection becomes smooth due to the surface tension of the material, and A resist master having a substantially semicircular cross section is created. Create an inverted version of this register master. A clad base material made of a low-refractive-index translucent material having the same shape as the inverted type is prepared. The surface of the substantially semicircular groove portion of the clad substrate becomes smooth. When the groove is filled with a high-refractive-index translucent material to form a core, the outer periphery of the core is smooth, and the core and the clad base material are in close contact and alternately arranged to form an optical waveguide. .

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIGS. 1 (a) to 1 (e) show the steps of a method for manufacturing an optical waveguide according to the present invention until a resist master is formed. As a resist coating step, as shown in FIG. 1 (a), first, a photoresist 22 is coated on one surface of a flat plate 21 made of a silicon wafer or glass by spin coating. Photoresist
As the material of No. 22, a thick film positive type photoresist (trade name: PMER P-G7900, manufactured by Tokyo Ohka Kogyo Co., Ltd.) is used.
The spin coating method is performed at 1500 rpm for 20 seconds. Then temperature 9
Perform a pre-bake process at 0 degrees for 10 minutes to achieve a layer thickness of 15
A layer of photoresist 22 of μm is formed. The photoresist 22 is further applied on the surface on which the photoresist 22 is applied by spin coating. Spin coating is performed at 1500 rpm for 20 seconds and then at 90 ° C for 3 seconds.
By performing a pre-bake step for 0 minutes, a layer of the photoresist 22 having a layer thickness of 30 μm is formed.

As a mask exposure step, as shown in FIG.
A mask 23 is placed on the layer of the photoresist 22 having a thickness of 30 μm, and the layer of the photoresist 22 is irradiated with ultraviolet rays 24 via the mask 23. As a result, the layer of the photoresist 22 is selectively irradiated with ultraviolet rays 23. As the shape of the mask 23, for example, a mask having a line-and-space shape with a pitch of 60 μm and a width of the opening 27 of 20 μm is used to form an optical waveguide array. Further, the exposure amount by ultraviolet rays is 600 mj / cm ² .

As a developing step, as shown in FIG. 1 (c), the layer of the photoresist 22 having undergone the mask exposure step is applied to a developer (trade name: P-5G stock solution, manufactured by Tokyo Ohka Kogyo Co., Ltd.) at a temperature of 25 ° C.
Soak for 4 minutes. As a result, the photoresist 22 in the portion irradiated with the ultraviolet rays 24 in the above step is selectively dissolved, and the flat plate 21 is exposed.

In the rinsing step, as shown in FIG. 1D, the selectively dissolved photoresist 22 is washed away with pure water. As a result, a projection 26 having a substantially trapezoidal cross-sectional shape formed from the layer of the photoresist 22 is formed on the flat plate 21. In the mask exposure step (see FIG. 1 (b)), it is inevitable that the projections 26 have a surface roughness of about 1 μm. This is because, in the mask exposure step (see FIG. 1 (b)), the ultraviolet rays 24 applied to the layer of the photoresist 22 are scattered in the material of the photoresist 22 due to a cause such as inhomogeneity of the material. One reason is that you cannot go straight inside.

It is very difficult for the chemical reaction to proceed unidirectionally in the material not only in the photo-etching means (photolithography technique) described above but also in the process of forming the similar protrusions 26 by the chemical etching technique. Therefore, there is a problem that the surface roughness becomes very large. Even if similar projections 26 are formed using a kind of chemical etching technique called anisotropic etching technique, it has been very difficult to keep the surface roughness within 0.01 μm. For the reasons described above, conventionally, when the optical waveguide is manufactured by the molding method using the mold of the protrusion 26, the aperture angle is large due to the problem that the surface roughness of the wall surface of the optical waveguide is large. It is very difficult to manufacture a high quality optical waveguide such as a small optical waveguide. As a post-baking step, as shown in FIG. 1 (e), the projection 26 on the flat plate 21 that has undergone the rinsing step is heated at a temperature of 135 degrees for 30 minutes. As a result, the shape of the protrusion 26 changes every moment as shown in FIGS. 2 (a) to 2 (d) when viewed temporally, and finally the surface roughness is within 0.01 μm and the cross-sectional shape is substantially half. It becomes circular. This is because a force acts on the material of the protruding portion 26 so as to reduce the surface area due to its surface tension due to melting by heat. For this reason, there is an effect that the main projections 26 have a surface roughness of 0.01 μm or less and have a substantially semicircular cross-sectional shape by the post-baking step.

The projecting portion 26D and the flat plate 21 that have undergone the post-baking process are
Collectively, it is referred to as a resist master 30.

Through the above steps, a resist master 30 is formed.

FIG. 3 shows the order of steps from the register master 30 to the formation of the stamper 40 in the method of manufacturing an optical waveguide according to the present invention.

As a conductive film forming step, as shown in FIG.
A nickel conductive film 31 is formed with a thickness of about 0.1 μm on the surface of the resist master 30 having the projections 26D by a sputtering method.

In the first electroforming step, as shown in FIG. 3 (b), a resist master 30 having the nickel conductive film 31 formed thereon is formed.
Next, a first nickel layer 32 of about 300 μm is formed by electroforming. The first nickel layer 32 includes the nickel conductive film 31.
Is also included.

As shown in FIG. 3 (c), as a metal master forming step, the flat plate 21 is peeled off from the resist master 30 and the first nickel layer 32 that have undergone the first electroforming step. afterwards,
The protrusion 26D remaining in the groove of the first nickel layer 32 is completely removed by an ultrasonic cleaning method in acetone or a strong alkaline solvent. This makes the resist master 30 completely first
The shape transferred to the nickel layer 32 is referred to as a metal master 33.

In the release film forming step, as shown in FIG. 3D, a nickel oxide film 34 is formed on the groove-side surface of the metal master 33 by an anodizing method or a dipping method in an oxidizing solution. As a result, a film is formed on the groove-side surface of the metal master 33 with releasability.

In the second electroforming step, as shown in FIG. 3 (e), a second nickel layer 35 of about 300 μm is formed on the metal master 33 on which the nickel oxide film 34 has been formed by electroforming.

As a stamper forming step, as shown in FIG. 3 (f), the metal master 33 and the second
The metal master 33 is separated from the nickel layer 35. As a result, the metal master 33 is completely transferred to the second nickel layer 35, and the stamper 40 is formed. The stamper 40 is used by being fixed to a mold 36.

Through the above steps, the stamper 40 is formed from the resist master 30. Therefore, the groove-side surface of the stamper 40 and the groove-side surface of the resist master 30 (projections 26D
Side surface).

FIGS. 4 (a) to 4 (d) show a process sequence from the stamper 40 to the final production of the optical waveguide 50 by the casting method in the optical waveguide production method according to the present invention.

As shown in FIG. 4 (a), as a cladding base material forming step, the transparent plate 41 is positioned parallel to the plane of the groove side of the stamper 40 with a small gap of about 200 μm. Next, the low refractive index ultraviolet curable resin 42 is filled in the gap. Next, ultraviolet rays 24 are irradiated through the transparent plate 41 to completely cure the low refractive index ultraviolet curable resin. Next, by peeling the stamper 40 from the transparent plate 41 and the low-refractive-index ultraviolet curable resin 42, a clad substrate 44 having the groove 43 and comprising the transparent plate 41 and the low-refractive-index ultraviolet curable resin 42 is formed. You. As the low refractive index ultraviolet curable resin 42, an acrylic resin (trade name: Aronix M310, manufactured by Zinc Synthetic Chemical Company, refractive index: 1.46) was used. The use of a material transparent to near-ultraviolet rays as the transparent plate 41, for example, low refractive index borosilicate glass surface-treated with UV-O ₃ ashing process to enhance the adhesion between the ultraviolet curable resin 42 Is mentioned. UV-O ₃ ashing process is a process that is widely used in silicon integrated circuit formation process. Further, the transparent plate 41 also has an effect as a reinforcing material of the optical waveguide 50.

As shown in FIG. 4 (b), as a core forming step, a high-refractive-index ultraviolet curable resin 45 was injected into the groove 43 of the clad base material 44 from one end thereof using a capillary phenomenon. At this time, the high refractive index ultraviolet curable resin 45 injected into the groove 43 was filled only in the groove 43 without overflowing from the groove 43 due to the surface tension. High refractive index UV curable resin 45 is groove 43
After sufficiently filling the inside, the core was formed by irradiating ultraviolet rays 24 to completely cure the high refractive index ultraviolet curable resin 45.
The cross-sectional shape of the core 46 was substantially semicircular. If the high refractive index ultraviolet curable resin 45 does not cure in an oxygen atmosphere (in the air), it must be cured in an inorganic oxygen environment such as a nitrogen atmosphere. An acrylic resin (trade name: Anilox M210, manufactured by Zinc Synthetic Chemical Co., Ltd., refractive index: 1.54) was used as the high refractive index ultraviolet curable resin 45.
This resin was easily cured even in an oxygen atmosphere (in air). It took approximately 30 minutes to sufficiently fill the groove 43 of the present resin. The surface 46a of the core 46 after filling is
It was confirmed that the surface roughness was within 0.01 μm due to the surface tension.

As shown in FIG. 4 (c), as a clad layer forming step, a plane of about 200 μm is formed on the plane on the core 46 side of the clad base material 44 on which the core 46 is formed by the core forming step. Transparent plate 41 with a small distance gap
Are positioned plane-parallel. Next, the low refractive index ultraviolet curable resin 42 is filled in the gap. Next, ultraviolet rays are irradiated through the transparent plate 41 to completely cure the low-refractive-index ultraviolet curing resin 42 to form a clad layer 47.

As shown in FIG. 4 (d), as a finishing step, the clad base material 44, the core 46, the clad layer 47, and the transparent plate 41, which have been subjected to the clad layer forming step, are appropriately cut, ground, polished, or the like by means such as cutting. An end portion 48 having a surface roughness of about 0.1 μm or less is formed at an appropriate position, and a final optical waveguide 50 is formed.

As described above, the optical waveguide 50 manufactured through the steps described in detail with reference to FIGS. 1 to 4 has an optical waveguide having a pitch of 60 μm, a width of the core 46 of 43 μm, and a cross-sectional shape of the core 46 substantially semicircular. It has an array structure.

In addition, when the present optical waveguide 50 was evaluated using He-Ne laser light having a wavelength λ = 632.8 nm, the aperture angle was 26.5 degrees, and the transmission loss was 0.1 dB / cm or less. Was obtained.

In addition, optical transmission could be performed with the transmission loss maintained for the bend having a curvature radius of 2 mm or more as the planar structure of the core 46.

It should be noted that the present invention is not limited to the above-described embodiment, and can be appropriately modified. For example, the first
In the resist coating step shown in FIG. 5A, a sheet-like photoresist can be attached to the flat plate 21 by thermal fusion. As a result, the number of steps can be considerably reduced compared to the spin coating method.

In the mask exposure step shown in FIG.
Only a few μm by freely choosing the shape of the mask 23
It is also possible to form a core 46 of about width (see FIG. 4) or to branch and cross it. FIG. 4 (a)
4 (c), a resin such as TPX having excellent releasability is used as the transparent plate 41, and the transparent plate 41 is finally peeled off from the optical waveguide 50 to thereby provide a flexible optical waveguide 50. Can also be produced. FIG. 4 (a)
Various other materials can be selected as the high-refractive-index UV-curable resin 45 and the low-refractive-index UV-curable resin 42 in FIGS. 4 (b) and 4 (c). Examples of such a material include a fluorine resin (trade name: Defensa 479-18, manufactured by Dainippon Ink and Chemicals, Inc., refractive index: 1.53) which is a high refractive index ultraviolet curable resin, and a low refractive index ultraviolet curable resin. Fluorinated resin (trade name Defensa 7710, manufactured by Dainippon Ink and Chemicals, refractive index 1.40) and the like. Optical waveguide manufactured by changing this material
It is possible to reduce the aperture angle of 50 and the transmission efficiency.

Further, the optical waveguide 50 can also be manufactured by curing other translucent resin instead of the photocurable resin described in the embodiment as a material constituting the optical waveguide 50.

In addition, in the clad base material forming step shown in FIG. 4A, an injection molding method can be used instead of the casting method described in the embodiment. Thereby, the optical waveguide 50
This has the effect of improving the productivity of the production of

Further, instead of utilizing the capillary phenomenon in the embodiment as the core forming step in FIG. 4B, the groove 43 may be filled with resin by a spin coating method.

Further, the present optical waveguide 50 can be applied not only to an optical transmission line but also to an optical distributor, an optical coupler, and other optical circuits or optical integrated circuits.

In addition to such a flat structure, a three-dimensional structure can be obtained by bending or overlapping.

〔The invention's effect〕

As is clear from the above, according to the method for manufacturing an optical waveguide according to the present invention, it is possible to obtain an optical waveguide having a large aperture angle and a small transmission loss even by a photoetching method. It works.

[Brief description of the drawings]

1 to 6 show an embodiment of the present invention. FIG. 1 is a view showing a process of forming a resist master, and FIG. 2 is a view showing a temporal change in shape of a projection. FIG. 3, FIG. 3 is a view showing a process of forming a stamper, FIG. 4 is a view showing a process of forming an optical waveguide by a casting method, and FIG. 5 is a diagram of a selective polymerization method which is a conventional method of manufacturing an optical waveguide. FIG. 6 is a diagram showing steps of a molding method which is another conventional manufacturing method. 21 Flat plate 22 Photoresist 26 Projection 30 Resist master 41 Transparent plate 42, 45 Translucent material 43 Groove 44 Cladding base material (first cladding layer) 46 …… Core 47 …… Clad layer (second clad layer) 50 …… Optical waveguide

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Chisato Kobayashi 9-35, Horitadori, Mizuho-ku, Nagoya, Aichi Prefecture Inside Brother Industries, Ltd. Address Brother Industries, Ltd. (56) References JP-A-48-48139 (JP, A) JP-A-58-149008 (JP, A) JP-A-1-73302 (JP, A) JP-A-1- 271710 (JP, A) JP-A-2-191906 (JP, A) JP-A-3-15805 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/12-6 /14

Claims (1)

(57) [Claims] A first step of forming an intermediate material having a substantially rectangular cross-sectional shape of a photoresist formed on a flat plate; and heating the intermediate material to form a surface of the substantially rectangular projection. And a second step of forming a resist master of the optical waveguide by making the cross-sectional shape substantially semicircular, and the cross-sectional shape of the resist master is inverted, and the substantially semicircular projection of the resist master is A third step of forming an inverted mold formed as a substantially semi-circular groove, and a clad base made of a low-refractive-index translucent material and having the substantially semi-circular groove formed in the same cross-sectional shape as the inverted mold. And a fifth step of forming a core by filling a translucent material having a high refractive index into a substantially semicircular groove of the clad base material. Method.