JPH04157403A - Light wave guide and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a light wave guide whose opening angle is large and transmission loss is small by forming a clad material having a nearly semicircular groove made of transparent material of a low refractive index and forming a core with a groove section charged with transparent material of high refractive index. CONSTITUTION:An intermediate material, the cross section shape of projected sections 26 of which is nearly square, and the projected section 26 comprises a photoresist 22 formed on a flat plate 21. When this flat plate 21 (intermediate material) is heated, the projected sections 26 is half-melted, and the surfaces of the projected sections 26 become smooth due to the surface tension of the material, and nearly semicircular resistmasters 30 are formed. An inverse mold for these resistmasters are formed to form a clad base material 44, which has the same shape as the inverse mold and is made of transparent material of a low refractive index. The surface of the nearly semicircular groove 43 of this clad material 44 becomes smooth. When this groove 43 is charged with transparent material 45 of high refractive index to form a core 46, the core 46 and clad base material 44 are tightly contacted with each other bringing about an alternating arranging state resulting in the formation of a light wave guide 50. By this constitution, a light wave guide, whose opening angle is large and transmission loss is small, can be obtained.

Description

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

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

This method begins with polycarbonate 5 with a refractive index of 1.59.
A solution in which acrylic monomer 52 was dispersed in 1 was cast into a film (FIG. 5(a)), and then a photomask 54 on which the necessary waveguide pattern was drawn was prepared as shown in FIG. 5(a). When the film 55 is brought into close contact with the film 55 and irradiated with ultraviolet rays, the acrylic monomer 52 in the portion irradiated with the ultraviolet rays polymerizes with the polycarbonate 51 to form a copolymer 56 (see Fig. 5).
b)). Next, when the film 55 is heated in vacuum to remove the unreacted acrylic monomer 52 from the film 55, the copolymer portion 57 has a lower refractive index than the polycarbonate portion 58 (refractive index 1.575). The core of the polycarbonate portion 58 formed in a pattern (with a refractive index of 1.
59), it becomes a cladding part (refractive index of 1.575) (FIG. 5(C)). Finally, a film-like plastic waveguide 60 is obtained by covering the surface of the film 55 with a low refractive index material 59.

Second Conventional Example FIG. 6 shows a molding method as a second conventional example. Figure 6(a)
As shown in , this molding method first coats a thin layer of photoresist 62 on a flat plate 61 made of glass or metal material, and then coats the layer of photoresist 62 through a mask 63 having a planar structure of an optical waveguide. Selective exposure. Next, as shown in FIG. 6(b), by removing only the exposed portion of the photoresist 62 using a developer, the pattern of the mask 63 made of the photoresist 62 is transferred onto the flat plate 61, and the projections 64 and Become.

The flat plate 6 is then melted using a material that dissolves the flat plate 61.
1 is selectively dissolved by a chemical etching method, and then the protrusion 64 is removed. Through this process, Figure 6(c)
), grooves 66 are formed in the flat plate 61 in accordance with the pattern of the mask 63, and these become the master 65 of the optical waveguide.

As shown in FIG. 6(d), using the master 65, a crat base material 70 is made of a light-transmitting plastic material with a low refractive index.
form.

Examples of methods for forming the cladding 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 of the master 65 by a sputtering method, and a nickel conductive film is formed on the groove side surface of the master 65. The nickel layer is thickened by electroforming.

Then, by peeling off the master 65, a stamper 67 is formed. Using the stamper 67, a clad base material 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 a similar form to the groove side surface of the master 65.

Next, as shown in FIG. 6(f), the clad base material 7
A transparent plastic with a high refractive index is made to flow in from one end of the groove 69 using capillary action, and after the resin is sufficiently filled in the groove 69, it is hardened to form the core 71. Then, as shown in FIG. 6(g), the entire surface on which the core 71 is formed is uniformly coated with a transparent plastic having a low refractive index, thereby forming a cladding layer 72 and obtaining an optical waveguide 80. . By using this manufacturing method, the materials of the core 71, the cladding base material 70, and the cladding layer 72 can be freely selected, so that the leading waveguide 80 can have a large aperture angle.

For example, the material of the core 71 may be a photocurable acrylic resin (trade name M210, manufactured by Toagosei Kagaku Co., Ltd., refractive index J ''1.54), and the material of the cladding base material 70 and the cladding layer 72 may be a similar photocurable resin. The optical waveguide 80 made by using an acrylic resin (trade name: Aronix M310, manufactured by Toagosei Kagaku Co., Ltd., refractive index n2=1.46) has a large aperture angle of 26.5 degrees.

[Problem to be solved by the invention]

However, according to the selective polymerization method, which is the first conventional method of manufacturing optical waveguides, it is difficult to increase the difference in refractive index between the polycarbonate part and the copolymer part. The aperture angle of the optical waveguide 60 formed of the above material was 12.6 degrees. In addition, the transmission loss of the optical waveguide made by this manufacturing method is 0.2 dB/a.
It was l+. Therefore, there was a problem in that the aperture angle could not 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 angle of incidence of the light beam incident on the optical waveguide is small. This means that the amount of light that can be transmitted by the light beam coupled to the optical waveguide is small.

On the other hand, according to the second conventional molding method, it is possible to have a large aperture angle, but the surface roughness of the wall inside the groove formed by the etching process, that is, the wall of the optical waveguide, is , has become very large, and the optical waveguides created using this method have problems in that they are almost unable to propagate light or have a large transmission loss.

Generally, the surface roughness of optical systems such as optical waveguides and lenses is 0.0.
It is necessary to keep the thickness within the order of 1 μm.

The present invention was made to solve the above-mentioned problems, and even with the photo-etching method, the aperture angle is large,
Moreover, it is an object of the present invention to provide a method for manufacturing a guiding waveguide with low transmission loss.

[Means to solve the problem]

In order to achieve this object, the method for manufacturing an optical waveguide according to the invention described in claim 1 includes the step of creating an intermediate material in which a protrusion made of photoresist formed on a flat plate has a substantially rectangular cross-sectional shape. a second step of heating the intermediate material to make the surface of the substantially rectangular protrusion smooth and to have a substantially semicircular cross-sectional shape to create a resist master for the optical waveguide; a third step of creating an inverted mold in which the cross-sectional shape of the resist master is inverted and the substantially semicircular projections of the resist master are formed as substantially semicircular grooves; a fourth step of creating a crat base material having the substantially semicircular groove formed to have the same cross-sectional shape, and filling the roughly semicircular groove of the crat base material with a translucent material having a high refractive index to form a core. and a fifth step of creating.

The optical waveguide according to the invention described in claim 2 includes a flat first cladding layer made of a light-transmitting material with a low refractive index, and a cross-sectional shape formed along one side of the first cladding layer that is approximately half-shaped. A circular groove is filled with a translucent material having a high refractive index, and the contact portion of the filling material with the groove includes a core that is smooth, and a low-reflection layer that is in close contact with one side of the first cladding layer that includes this core. a flat second cladding layer made of a transparent material with a refractive index;
Equipped with

[Effect]

According to the first aspect of the present invention, first, an intermediate material is prepared, which is made of a photoresist formed on a flat plate and has a protrusion having a substantially rectangular cross-sectional shape. The surface of this substantially square protrusion is somewhat rough. When the flat plate (intermediate material) having the protrusion with a substantially square cross-sectional shape is heated, the protrusion becomes semi-molten,
A resist master is created in which the surface of the protrusion becomes smooth due to the surface tension of the material, and the protrusion has a substantially semicircular cross-sectional shape. Create an inverted version of this register master. A clad base material of the same type as this inverted type and made of a light-transmitting material with a low refractive index is created.

The surface of the approximately semicircular groove of this clad base material becomes smooth.

When the groove is filled with a transparent material having a high refractive index to form a core, the outer periphery of the core becomes smooth, and the core and the cladding base material are closely interleaved and arranged alternately, forming an optical waveguide. .

The invention according to claim 2 provides a large refractive index difference between the high refractive index core and the low refractive index cladding layer, so that even when the incident angle of light is large, the light is totally reflected within the core. Since the corners are thick and the inner peripheral surface of the core is smooth, transmission loss when light is reflected can be reduced.

〔Example〕

An embodiment embodying the present invention will be described below with reference to the drawings. FIGS. 1(a) to 1(e) show the order of steps up to forming a resist master in the method for manufacturing an optical waveguide according to the present invention.

As the resist coating process, as shown in FIG. 1(a),
First, a photoresist 22 is applied to one surface of a flat plate 21 made of a silicon wafer or glass by a spin code method. The material of the photoresist 22 is as follows:
Thick film bond type photoresist (product name: PMERP-G)
7900, manufactured by Tokyo Ohka Kogyo Co., Ltd.) is used. The spin code method is performed at 1500 + pm for 20 seconds. Then temperature 9
By performing a pre-baking process at 0 degrees for 10 minutes, a layer of photoresist 22 having a thickness of 15 μm is formed. The photoresist 22 is further coated on the surface coated with the photoresist 22 by a spin code method. The spin code method is performed at 1500 + pm for 20 seconds, followed by a pre-baking process at a temperature of 90 degrees Celsius for 30 minutes, thereby forming a layer of photoresist 22 with a thickness of 30 μm.

In the mask exposure step, as shown in FIG.
The layer of photoresist 22 is irradiated with ultraviolet rays 24 through mask 23.

As a result, the layer of photoresist 22 is selectively irradiated with ultraviolet light 23 . The shape of the mask 23 is, for example, a pitch of 60 μm for forming an optical waveguide array.
One opening 27 having a linear ant space shape with a width of 20 μm is used. Further, the amount of exposure to ultraviolet rays was 600 m1/a+f.

In the development process, as shown in FIG.
Product name P-5G stock solution, manufactured by Tokyo Ohka Kogyo Co., Ltd.) at a temperature of 25
Soak for 4 minutes at ℃. As a result, ultraviolet 2
The irradiated portions of the photoresist 22 are selectively dissolved, and the flat plate 21 is exposed.

As a rinsing step, as shown in FIG. 1(d), the selectively dissolved photoresist 22 is washed away with pure water. As a result, a protrusion 26 made of the layer of photoresist 22 and having a substantially trapezoidal cross-sectional shape is formed on the flat plate 21. The main protrusion 26 corresponds to the mask exposure process (first
(see Figure (b)), it is inevitable that the surface roughness will be about 1 μm. This is the mask exposure step (first step).
(See Figure (b)), the ultraviolet rays 24 irradiated onto the layer of the photoresist 22 are scattered in the material of the photoresist 22 due to material inhomogeneity, and therefore cannot travel straight through the material. There are two reasons.

In the process of forming similar protrusions 26 not only by the optical etching means (photolithography method) described above but also by chemical etching methods, it is extremely difficult for the chemical reaction to proceed unidirectionally in the material. Therefore, there was a problem in that the surface roughness became extremely large. Even if similar protrusions 26 were formed using a type of chemical etching method called anisotropic etching method, it was extremely difficult to suppress the surface roughness to within 0.01 μm. For the above reasons, conventionally, when manufacturing an optical waveguide using a molding method using a mold of the protrusion 26, the problem is that the wall surface of the optical waveguide has a large surface roughness, so the aperture angle is large and the transmission loss is high. It has been extremely difficult to manufacture high-quality optical waveguides with small values. As a post-baking process, as shown in FIG. 1(e), the protrusion 26 on the flat plate 21 that has undergone the rinsing process is heated at a temperature of 135 degrees for 30 minutes. As a result, the shape of the projection 26 changes over time as shown in FIGS. 2(a) to 2(d), and finally the surface roughness is within 0.01 μm and the cross-sectional shape is approximately It becomes a semicircle. This is because the material of the protrusion 26 is melted by heat, and a force acts on the material to reduce the surface area due to its surface tension. Therefore, the main protrusion 26 has a surface roughness of 0.
The effect is that the cross-sectional shape is approximately semicircular within 0.01 μm.

The protrusions 26D and the flat plate 21 that have undergone this post-bake step are collectively referred to as a resist master 30.

The resist master 30 is formed through the above steps.

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

As a conductive film forming step, as shown in FIG. 3(a), a nickel conductive film 31 with a thickness of 0.1 μm is deposited on the surface of the resist master 30 having the projections 26D by sputtering.
form in degrees.

As a first electroforming step, as shown in FIG. 3(b), a resist master 30 on which the nickel conductive film 31 is formed is
Then, a first nickel layer 3 of about 300 μm is formed by electroforming.
form 2. The first nickel layer 32 also includes the nickel conductive film 31 .

As a metal master forming step, as shown in FIG. 3(C), 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. Thereafter, the protrusions 26D remaining in the grooves of the first nickel layer 32 are completely removed by ultrasonic cleaning in acetone or a strong alkaline solvent. As a result, the resist master 30 is completely transferred to the first nickel layer 32, which is referred to as a metal master 33.

As the mold release film forming step, as shown in FIG. 3(d),
A nickel oxide film 34 is formed on the groove side surface of the metal master 33 by an anodic oxidation method or a dipping method in an oxidizing solution. As a result, a film having releasability is formed on the groove side surface of the metal master 33.

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

As the stamper forming process, as shown in FIG. 3(f),
The metal master 33 is peeled off from the metal master 33 and the second nickel layer 35 that have undergone the second electroforming process. As a result, the metal master 33 is completely transferred to the second nickel layer 35, and a stamper 40 is formed. This stamper 40 is used by being fixed to the mold 36.

Through the above steps, the stamper 40 is formed from the resist master 30. Therefore, stamper 4
The groove-side surface of the resist master 30 and the groove-side surface of the resist master 30 (surface on the protrusion 26D side) have the same form.

FIGS. 4(a) to 4(d) show the order of steps in the optical waveguide manufacturing method according to the present invention, from the stamper 40 to the final manufacturing of the optical waveguide 50 by the casting method.

As shown in FIG. 4(a), in the clad base material forming step, a transparent plate 41 is placed parallel to the plane of the groove side of the stamper 40 with a gap of about 200 μm. Next, a low refractive index ultraviolet curing resin 42 is filled in this gap.
Fill it. Next, ultraviolet rays 2 are transmitted through the transparent plate 41.
4 to completely cure the low refractive index ultraviolet curing resin 42.

Next, by peeling off the stamper 40 from the transparent plate 41 and the low refractive index ultraviolet curable resin 42, a clad base material 44 made of the transparent plate 41 and the low refractive index ultraviolet curable resin 42 and having a groove 43 is formed. be done. As the low refractive index ultraviolet curing resin 42, an acrylic resin (trade name: Aronix M310, manufactured by Toagosei Kagaku Co., Ltd., refractive index: 1.46) was used. The transparent plate 41 is made of a material that is transparent to near ultraviolet rays, such as UV-03 to improve adhesiveness with the low refractive index ultraviolet curing resin 42.
Examples include borosilicate glass whose surface has been treated by an ashing process.

The UV-03 ashing process is a widely used process in silicon integrated circuit formation processes. Furthermore, the transparent plate 41 also has the effect of reinforcing the optical waveguide 50.

As shown in FIG. 4(b), as a core forming step, a high refractive index ultraviolet curing resin 45 was injected into the groove 43 of the cladding base material 44 from its lower end using capillary action.

At this time, the high refractive index ultraviolet curing resin 45 injected into the groove 43 did not overflow from the groove 43 due to its surface tension and was filled only within the groove 43. After the high refractive index ultraviolet curable resin 45 was sufficiently filled in the groove 43, ultraviolet rays 24 were irradiated to completely cure the high refractive index ultraviolet curable resin 45 to form a core 46. The cross-sectional shape of the core 46 was approximately semicircular. If the high refractive index ultraviolet curable resin 45 is of a nature that does not cure in an oxygen atmosphere (air), it is necessary to cure it in an oxygen-free environment such as a nitrogen atmosphere. As the high refractive index ultraviolet curing resin 45, an acrylic resin (trade name Anilox M210, manufactured by Toagosei Kagaku Co., Ltd., refractive index 1.54) was used. This resin was easily cured even in an oxygen atmosphere (in air). Further, it took approximately 30 minutes to sufficiently fill the groove portion 43 with this resin. Further, it was confirmed that the surface roughness of the surface 46a of the core 46 after filling was within 0.01 μm due to surface tension.

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

As shown in FIG. 4(d), as a finishing step, the clad base material 44 and core 46 that have undergone the clad layer forming step are
The cladding layer 47 and the transparent plate 41 are provided with a surface roughness of 0.1 μm at appropriate positions by cutting, grinding, polishing, etc.
The final leading waveguide 50 is formed by forming the end portion 48 of the following degree.

The optical waveguide 50 manufactured through the steps detailed above with reference to FIGS. 1 to 4 has a pitch of 60 μm.
An optical waveguide array structure is obtained in which the width of the core 46 is 43 μm1 and the cross-sectional shape of the core 46 is approximately semicircular.

In addition, the present optical waveguide 50 is
When evaluated using e-Ne laser light, the aperture angle was 2.
6.5 degrees and transmission loss is 0. Very high quality optical waveguide properties of 1 dB/an or less were obtained.

Furthermore, the planar structure of the core 46 allowed optical transmission to be performed while maintaining the above-mentioned transmission loss even when the core 46 was bent with a radius of curvature of 2 mm or more.

Note that the present invention is not limited to the embodiments described above, and modifications can be made as appropriate.

For example, in the resist coating process shown in FIG.
It is also possible to attach it to As a result, the number of steps can be significantly reduced compared to coating by the spin code method.

In addition, in the mask exposure process shown in FIG. 1(b), by freely selecting the shape of the mask 23, only a few μm
It is also possible to form a core 46 (see FIG. 4) about the same width, or to branch or intersect it. Also, Fig. 4(a)
4(C), a resin such as TPX with excellent releasability is used as the transparent plate 41, and the transparent plate 41 is finally peeled off from the optical waveguide 50, thereby creating an optical waveguide 50 with flexibility. It is also possible to manufacture Furthermore, various other materials may be selected as the high refractive index ultraviolet curing resin 45 and the low refractive index ultraviolet curing resin 42 in FIGS. 4(a), 4(b), and 4(c). It is possible. An example of such a material is a fluorine-based resin (trade name: Defensa4), which is a high refractive index ultraviolet curing resin.
79-18, manufactured by Dainippon Ink and Chemicals, refractive index 1.5
3), and a fluororesin (trade name: Defensa 7710, manufactured by Dainippon Ink & Chemicals, Inc., refractive index: 1.40), which is a low refractive index ultraviolet curing resin. By changing this material, it is possible to change the aperture angle and transmission efficiency of the manufactured optical waveguide 50.

Moreover, the optical waveguide 50 can also be manufactured by curing other light-transmitting resin instead of the photocuring resin described in the embodiment as the material constituting the optical waveguide 50.

Further, in the clad base material forming step shown in FIG. 4(a), it is possible to use an injection molding method instead of the casting method described in the embodiment. As a result, the optical waveguide 50
This has the effect of improving manufacturing productivity.

Further, instead of using the capillary phenomenon in the embodiment as the core forming step in FIG. 4(b), the groove portion 43 may be filled with resin by a spin cord method.

Furthermore, the present optical waveguide 50 can be applied not only to optical transmission lines but also to optical splitters, optical couplers, other optical circuits, or optical integrated circuits.

Moreover, in addition to such a flat structure, it is also possible to form a three-dimensional structure by bending or overlapping each other.

〔Effect of the invention〕

As is clear from the detailed description above, according to the method for manufacturing an optical waveguide according to the present invention, even by the optical etching method,
It is possible to obtain an optical waveguide with a large aperture angle and small transmission loss.

[Brief explanation of drawings]

1 to 6 show embodiments embodying the present invention. FIG. 1 is a diagram showing the process of forming a resist master, and FIG. 2 is a diagram showing changes in the shape of a protrusion over time. Figure 3 shows the process of forming a stamper, Figure 4 shows the process of forming an optical waveguide by the casting method, and Figure 5 shows the selective polymerization method, which is a conventional method for manufacturing optical waveguides. FIG. 6 is a diagram showing the steps of a molding method, which is another conventional manufacturing method. 21...Flat plate 22...Photoresist 26...Protrusion 30...Resist master 41...Transparent plate 42.45...Transparent material 43...Groove 44...Clad base Material (first cladding layer) 46...
Core 47... Cladding layer (second cladding layer) 50... Optical waveguide

Claims (1)

[Scope of Claims] 1. A first step of creating an intermediate material in which a protrusion made of photoresist formed on a flat plate has a substantially rectangular cross-sectional shape; and heating the intermediate material to form the substantially rectangular protrusion. a second step of creating a resist master for the optical waveguide by making the surface of the resist master smooth and having a substantially semicircular cross-sectional shape; a third step of creating an inverted mold in which a portion is formed as a substantially semicircular groove, and the substantially semicircular groove is made of a light-transmitting material with a low refractive index and has a cross-sectional shape equal to that of the inverted mold; A light guide comprising: a fourth step of creating a cladding base material; and a fifth step of filling a substantially semicircular groove of the cladding base material with a translucent material having a high refractive index to create a core. Method of manufacturing wave channels. 2. A flat first cladding layer made of a light-transmitting material with a low refractive index, and a groove with a substantially semicircular cross section formed along one side of the first cladding layer. a flat plate made of a light-transmitting material with a low refractive index and closely adhered to one side of the first cladding layer including the core; An optical waveguide comprising: a second cladding layer having a shape;