JP3800985B2 - Manufacturing method of polymer waveguide - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a polymer waveguide. Road It relates to a manufacturing method.
[0002]
[Prior art]
The polymer waveguide is expected to be put to practical use because it has features such as easy production, easy area enlargement, and possible cost reduction.
[0003]
As this type of polymer material, acrylic, epoxy, polyimide, silicone, polysilane, and the like have been studied. For these materials, it is desired that parameters such as a refractive index and a thermal expansion coefficient hardly change with temperature change.
[0004]
For this reason, among the polymer materials, polyimide-based, epoxy-based, and polysilane-based polymer materials are attracting attention, and improvements in these polymer materials are attracting attention.
[0005]
For example, as shown in FIG. 9, an example in which a linear polysilane material is taken up for a polymer waveguide and a three-dimensional waveguide pattern is formed by ultraviolet irradiation (JP-A-6-222234), amorphous polysilane is used. Examples (JP-A-11-287916), examples using linear or branched polysilane (JP-A-8-267728), and the like.
[0006]
FIG. 9 is an external perspective view showing a conventional example of a polymer waveguide.
[0007]
In the figure, 20 indicates a core layer through which an optical signal propagates, and 21 indicates a cladding layer having a refractive index lower than that of the core.
[0008]
[Problems to be solved by the invention]
However, the above-described prior art has the following problems.
(1) The refractive index changes greatly with temperature. For this reason, the optical characteristics (propagation mode, power distribution, wavelength characteristics, etc.) of an optical circuit made of a polymer waveguide made of such a material are significantly changed, and desired performance cannot be obtained.
(2) When an electronic component or an optical component is solder-mounted in the vicinity of the polymer waveguide at around 200 ° C., the refractive index distribution of the polymer waveguide is changed from the initial value to another value, and the temperature is restored. The refractive index value does not return to the original value even if it is returned to. Due to the change in the refractive index distribution, the optical characteristics of the optical circuit constituted by the polymer waveguide as shown in (1) change.
(3) A method has been proposed in which a linear polysilane film is used and a three-dimensional waveguide is formed by irradiating the polysilane film with ultraviolet rays. Problems such as the above (1) and (2), There is a problem of polarization dependency of the refractive index and the like, and it has not been put to practical use. Also, even if the refractive index of the polymer film is changed significantly with good reactivity by irradiating with ultraviolet light, the refractive index change changes discontinuously with the irradiation light energy, or a large refractive index change is obtained. There is a problem that the irradiation energy must be increased. It is also difficult to realize a low-loss waveguide.
(4) To realize the waveguide, the lower cladding layer, the core layer, and the upper cladding layer must be formed. However, in the conventional configuration, the composition and material of each layer are often different, and the thermal expansion coefficient is low. Residual strain and microcracks are generated in each layer due to mismatching, and the scattering loss due to structural irregularities is increased due to poor wetting of the interface, and formation of a thick film is difficult.
[0009]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and has a low scattering loss, a small residual strain, and a polymer waveguide that does not generate microcracks. Road It is to provide a manufacturing method.
[0010]
[Means for Solving the Problems]
To achieve the above purpose Book In the polymer waveguide manufacturing method of the invention, a photobleaching type polymer solution that has been previously sensitized with ultraviolet rays and has a reduced refractive index is applied onto a substrate, and the polymer solution is heated and cured to form a lower cladding layer. Process, next, Apply a photobleaching polymer solution that has not been irradiated with UV light onto the lower cladding layer. , Forming a high refractive index polymer layer having a higher refractive index than the lower cladding layer by thermosetting; next, A photobleaching polymer solution that has been sensitized with ultraviolet rays in advance and has a reduced refractive index is applied onto the high refractive index polymer layer, and the polymer solution is heated and cured to have a refractive index lower than that of the high refractive index polymer layer. Forming an upper cladding layer; next, A photomask having a core pattern drawn thereon is disposed on the upper clad layer, and a high refractive index polymer layer is irradiated with ultraviolet rays from above the photomask to form a core layer having a substantially rectangular cross-sectional shape not irradiated with the ultraviolet rays, and And a step of changing to a side cladding layer having a reduced refractive index by irradiation with ultraviolet rays on both sides of the core layer.
[0011]
In the method of manufacturing a polymer waveguide according to the present invention, a photobleaching type polymer solution that has been sensitized with ultraviolet rays in advance and has a reduced refractive index is applied onto a substrate, and the polymer solution is heated and cured to form a lower cladding layer. Next, a photobleaching polymer solution that has not been irradiated with ultraviolet light is applied onto the lower cladding layer and cured by heating to form a high refractive index polymer layer having a higher refractive index than the lower cladding layer. Next, a photomask having a core pattern drawn thereon is disposed on the high refractive index polymer layer, and ultraviolet rays are irradiated from above the photomask so that the high refractive index polymer layer is not irradiated with the ultraviolet rays. A core layer having a substantially rectangular cross-section, and a step of changing to a side cladding layer having a reduced refractive index by irradiation with ultraviolet rays on both sides of the core layer; Photosensitized by reduced photobleaching type polymer solution of the refractive index is applied to a line, and a step of forming an upper clad layer by heating and curing the polymer solution.
[0012]
The method for producing a polymer waveguide according to the present invention is such that a photobleaching type polymer solution that is not irradiated with ultraviolet rays is applied on a substrate and applied, and then the polymer solution is heated and cured, or the polymer solution is heated and cured. A step of forming a lower clad layer by irradiating with ultraviolet rays to lower the refractive index after irradiating, next, Apply a photobleaching polymer solution that has not been irradiated with UV light onto the lower cladding layer. , Forming a high refractive index polymer layer having a higher refractive index than the lower cladding layer by thermosetting; next, A photobleaching polymer solution that has been sensitized with ultraviolet rays in advance and has a reduced refractive index is applied onto the high refractive index polymer layer, and the polymer solution is heated and cured to have a refractive index lower than that of the high refractive index polymer layer. Forming an upper cladding layer; next, A photomask having a core pattern drawn thereon is disposed on the upper clad layer, and a high refractive index polymer layer is irradiated with ultraviolet rays from above the photomask to form a core layer having a substantially rectangular cross-sectional shape not irradiated with the ultraviolet rays, and And a step of changing to a side cladding layer having a reduced refractive index by irradiation with ultraviolet rays on both sides of the core layer.
[0013]
The method for producing a polymer waveguide according to the present invention is such that a photobleaching type polymer solution that is not irradiated with ultraviolet rays is applied on a substrate and applied, and then the polymer solution is heated and cured, or the polymer solution is heated and cured. A step of forming a lower clad layer by irradiating with ultraviolet light to lower the refractive index after irradiating the film; next, A step of applying a photobleaching polymer solution that is not irradiated with ultraviolet light onto the lower cladding layer and heat-curing to form a high refractive index polymer layer having a higher refractive index than the lower cladding layer; next, A photomask having a core pattern drawn thereon is disposed on the high refractive index polymer layer, and the high refractive index polymer layer is irradiated with ultraviolet rays from above the photomask to form a core layer having a substantially rectangular cross-sectional shape that is not irradiated with the ultraviolet rays. And a step of changing to a side cladding layer having a reduced refractive index by irradiation with ultraviolet rays on both sides of the core layer; next, A step of applying a photobleaching type polymer solution that has been sensitized with ultraviolet rays in advance and having a reduced refractive index on the core layer and the side cladding layer, and then heating and curing the polymer solution to form an upper cladding layer; It is what you have.
[0014]
According to the present invention, since the lower clad layer, the core layer, the side clad layer, and the upper clad layer formed on the substrate are all made of the same photobleaching material, distortion occurs in each layer. , And no microcracks are generated. Further, since the wettability of the interface is good when forming each layer, it becomes easy to uniformly apply the polymer solution, the interface can be formed uniformly, and a waveguide with low scattering loss can be realized.
[0015]
The present inventor uses the same photobleaching material, dissolves the material in an organic solvent to form a polymer solution, and adjusts the amount of ultraviolet light applied to the polymer solution, thereby forming a polymer layer using the polymer solution. It has been found that the refractive index of the polymer layer when formed can be easily controlled. This makes it possible to realize a polymer waveguide with low scattering loss.
[0016]
That is, the lower clad layer and the upper clad layer can be made to have a desired refractive index simply by applying a polymer solution irradiated with a desired amount of ultraviolet rays and heating and curing. The high refractive index polymer layer that becomes the core layer and the side cladding layer may be applied by using a polymer solution that is not irradiated with ultraviolet rays or irradiated with an ultraviolet ray less than a desired amount, and is cured by heating. After forming an upper clad layer on the high refractive index polymer layer, a photomask with a core pattern drawn is placed on the upper clad layer, and an ultraviolet ray is irradiated from above the photomask to obtain a substantially rectangular cross section. A polymer waveguide is obtained by forming a high refractive index core layer having a shape and a side cladding layer having a lower refractive index than the core layer on both sides of the core layer.
[0017]
Therefore, by using the polymer waveguide manufacturing method of the present invention, the controllability of the refractive index becomes extremely good, and it is possible to realize the desired waveguide structure parameter control with high accuracy. For this reason, when the polymer solution for photobleaching is irradiated with ultraviolet rays, the refractive index changes much more slowly than when the polymer solution becomes a polymer layer, and the refractive index changes. Therefore, a highly accurate waveguide structure can be realized. As a result, a waveguide structure device with good optical characteristics can be realized.
[0018]
The relative refractive index difference of the waveguide can be realized in a wide range from 0.3% to 6%. Thereby, an ultra-small waveguide device can be expected. Moreover, the relative refractive index difference can be adjusted by the irradiation amount and irradiation time of ultraviolet rays.
[0019]
In addition, by using the same photobleaching material, there is little risk of generation of strain in the waveguide and generation of microcracks due to the occurrence of residual strain, so that it can be formed into various substrates or sheets.
[0020]
Various materials can be used as the photo bleaching material. That is, since the same photobleaching material can be used for the lower clad layer, the core layer, the side clad layer, and the upper clad layer, the range of usable photobleaching materials is expanded.
[0021]
Using a polymer solution made of the same photobleaching material, applying a polymer solution in which the amount of ultraviolet rays applied to the polymer solution is changed and repeating the heat curing process three times to form a three-layer polymer layer, and then a photomask By irradiating ultraviolet rays through the waveguide, a waveguide can be realized by transferring the core pattern to the central high refractive index polymer layer. That is, the waveguide can be manufactured by a simple method, and the interface between the layers can be made uniform. Further, distortion is hardly generated in each layer, and generation of microcracks can be suppressed. Further, it can be manufactured at low cost.
[0022]
By irradiating ultraviolet rays in the polymer solution state, the controllability of the refractive index can be improved, so that a waveguide in which the refractive index structure is accurately controlled can be realized.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0024]
FIG. 1 is a cross-sectional view showing an embodiment of a polymer waveguide to which the polymer waveguide manufacturing method of the present invention is applied.
[0025]
The polymer waveguide shown in FIG. 1 is a substantially rectangular cross-sectional shape formed on the substrate 1, the lower cladding layer 2 formed on the substrate 1, and the lower cladding layer 2 and having a higher refractive index than the lower cladding layer 2. Core layer 3, side cladding layers 4-1 and 4-2 formed on both sides of core layer 3 on lower cladding layer 2 and having a lower refractive index than core layer 3, and core layer 3 and side cladding layer 4-4. 1 and 4-2 and an upper cladding layer 5a having a refractive index lower than that of the core layer 3, the lower cladding layer 2, the core layer 3, the side cladding layers 4-1, 4-2, and the upper cladding. The layer 5a is composed of the same photobleaching material.
[0026]
That is, in this polymer waveguide, each layer 2, 3, 4-1, 4-2, 5a is composed of the same material and the same composition, so that the thermal expansion coefficient mismatching as in the prior art is used. There is no risk of residual strain or microcracks in each layer 2, 3, 4-1, 4-2, 5a. The greatest feature of the present polymer waveguide is that a uniform interface can be formed because the interface between the layers 2, 3, 4-1, 4-2, and 5a has good wettability. For this reason, a waveguide having a uniform structure can be realized, and a reduction in scattering loss can be achieved. Furthermore, since the layers 2, 3, 4-1, 4-2, and 5a can be easily formed to a thickness of several μm to several tens of μm, a multimode waveguide can be easily formed in addition to the single mode. Furthermore, since the polymer waveguide is made of the same material and the same composition, the waveguide can be easily manufactured and cost reduction can be expected. In addition, each layer 2, 3, 4-1, 4-2, 5a is formed using polymers of the same material and the same composition, and the pre-bake and post-bake temperatures after applying the photobleaching polymer solution are determined for each layer. 2, 3, 4-1, 4-2, and 5a can be made the same, so that the manufacturing process can be easily managed. Furthermore, since the same material and the same composition of polymer are used for each of the layers 2, 3, 4-1, 4-2, and 5a, there is no residual strain and generation of microcracks as in the prior art, and various photobleaching is achieved. It is possible to use a polymer material for polishing.
[0027]
As a material of the substrate 1 shown in FIG. 1, a substrate such as a semiconductor, glass, ceramics, magnetic material, or plastics, or a large-area substrate such as a printed substrate or a sheet can be used.
[0028]
The lower clad layer 2 formed on the substrate 1 is a layer in which a polymer layer for photobleaching is formed and then the polymer layer is irradiated with a desired amount of ultraviolet rays. By irradiating the ultraviolet rays, the polymer layer is refracted. The rate is 0. depending on the amount of UV irradiation. Decrease from several percent to several percent.
[0029]
Here, the photobleaching polymer layer is formed by applying a photobleaching polymer solution and then pre-baking (120 ° C. to 150 ° C.) for about 20 minutes and post baking (180 ° C. to 250 ° C.) for about 30 minutes. To be formed.
[0030]
Photobleaching materials include nitrone-containing silicone compounds, polysilane compounds, polysilane compounds with a desired amount of a silicone compound added, and polysilane compounds with a desired amount of a silicone compound and a photoacid generator added. It is done. As the amount of nitrone added increases, the refractive index of the nitrone decreases with irradiation of ultraviolet rays. It is preferable in terms of transmittance to use a branched polysilane compound having a branching degree of 2% or more as the polysilane compound. For example, polycondensation is carried out by heating a mixture of halosilanes composed of an organotrihalosilane compound, a tetrahalosilane compound, and a diorganodihalosilane compound, the organotrihalosilane compound and the tetrahalosilane compound being 2 mol% or more of the whole. Thus, the desired branched polysilane can be obtained. The branched polysilane compound is preferably bonded to a hydrocarbon group, an alkoxy group, or a hydrogen atom in addition to the Si atom. The branched polysilane compound is preferably deuterated or at least partially fluorinated branched polysilane compound from the viewpoint of low loss. The silicone compound is preferably crosslinkable or composed of an alkoxy group, or at least partially fluorinated in terms of reducing loss. The branched polysilane and the silicone compound will be described in detail later.
[0031]
A triazine-based material is preferably used as the photoacid generator from the viewpoint of photoreactivity, and a trichloromethyltriazine-based material is more preferable among the triazine-based materials. Even in the trichloromethyltriazine series, the light transmittance is high in the long wavelength region (1300 nm, 1550 nm band), the maximum absorption wavelength is substantially equal to the absorption wavelength in the ultraviolet wavelength region of the polysilane compound, and the polymer layer has a high melting point. It is preferable for improving the transmittance, the reactivity to the change of the refractive index due to ultraviolet irradiation, the temperature stability of the refractive index, and the like.
[0032]
The ultraviolet rays for forming the lower cladding layer 2 are irradiated so that the refractive index is ns. This refractive index ns is determined in consideration of the relative refractive index difference Δ with respect to the refractive index nw of the core layer expressed by the equation (1).
[0033]
[Expression 1]
Δ = (nw−ns) × 100% / nw
That is, when the polymer waveguide is for single mode transmission, the relative refractive index difference Δ is 0. It is preferable to select from a range of several% to 2.5%. When the polymer waveguide is for multimode transmission, the relative refractive index difference Δ is 0. It is preferable to select from a range of several% to 5%.
[0034]
Next, a polymer solution for photobleaching which is not irradiated with ultraviolet rays is applied on the lower clad layer, and prebaking (120 ° C. to 150 ° C.) for about 20 minutes and post baking (180 ° C. to 250 ° C.) for about 30 minutes. ) To form a cured high refractive index polymer layer.
[0035]
Next, a polymer solution for photobleaching previously irradiated with ultraviolet rays is applied onto the high refractive index polymer layer. The cured polymer layer is obtained by performing pre-baking (120 ° C. to 150 ° C.) for about 20 minutes and post-baking (180 ° C. to 250 ° C.) for about 30 minutes in the same manner as described above. This polymer layer is formed to have a low refractive index comparable to that of the lower cladding layer. That is, as will be described later, if the polymer solution for photobleaching is irradiated with a desired amount of ultraviolet rays in advance, when the polymer layer is formed using the solution, the refractive index of the polymer layer depends on the amount of ultraviolet irradiation. This is based on the finding of the inventor that the refractive index decreases.
[0036]
Next, a photomask (not shown) on which a waveguide pattern (core pattern) for light propagation is drawn is disposed on the upper clad layer, and a desired amount of ultraviolet rays is irradiated on the photomask. The polymer layer is sensitized by the irradiation of ultraviolet rays, and the region not irradiated with ultraviolet rays becomes a high refractive index core layer 3 having a substantially rectangular cross-sectional shape, and ultraviolet rays are irradiated to both sides of the core layer 3 to lower the refractive index. Side cladding layers 4-1 and 4-2 are formed. The refractive index nh of the side cladding layers 4-1 and 4-2 is controlled to a value substantially the same as that of the lower cladding layer 2 and the upper cladding layer 5a. The control of the refractive index can be adjusted by the irradiation amount of ultraviolet rays.
[0037]
In addition, the polymer layers of the upper clad layer 5a and the lower clad layer 2 may cause some ultraviolet photosensitivity by the ultraviolet ray irradiation through the photomask. In order to prevent this ultraviolet light exposure, the lower clad layer 2 and the upper clad layer 5a may be sufficiently irradiated with ultraviolet light so that the refractive index is substantially saturated.
[0038]
For example, the relative refractive index difference Δ before and after UV irradiation is the maximum in a polymer film formed using a polysilane solution (organic solvent: toluene) in which a silicone compound is added to a branched polysilane compound having a branching degree of 20%. 6% can be obtained. This relative refractive index difference Δ can be increased as the post-bake temperature is lower or the amount of ultraviolet irradiation is larger.
[0039]
Therefore, in order to set the relative refractive index difference Δ to a desired amount, when a high refractive index polymer layer is formed on the lower cladding layer 2, ultraviolet rays are irradiated on the polymer layer to change the refractive index. What is necessary is just to make it fall to some extent.
[0040]
FIG. 2 is a cross-sectional view showing another embodiment of the polymer waveguide to which the polymer waveguide manufacturing method of the present invention is applied.
[0041]
The difference from the embodiment shown in FIG. 1 is that a polymer layer formed by the same method as the method of forming the upper cladding layer 5a is used as the lower cladding layer 5b.
[0042]
That is, a polymer solution for photobleaching that has been irradiated with a desired amount of ultraviolet rays in advance is applied onto a substrate, prebaked (120 ° C to 150 ° C) for about 20 minutes, and postbaked (180 ° C to 250 ° C) for about 30 minutes. To obtain a cured polymer layer. A polymer layer and an upper clad layer are sequentially formed on the polymer layer in the same manner as the polymer waveguide shown in FIG. 1, and then a photomask is placed and irradiated with ultraviolet rays from above the photomask to obtain a high refractive index. A polymer waveguide having the structure shown in FIG. 2 can be realized by forming a core layer having a substantially rectangular cross section and side cladding layers on both sides of the core layer.
[0043]
In the polymer waveguide shown in FIGS. 1 and 2, if an ultraviolet cut layer (not shown) is formed on the upper surface of the upper clad layer 5a and the back surface of the substrate 1, the refractive index of the waveguide changes over a long period of time. Can be suppressed. For this ultraviolet cut layer, for example, KP-851 manufactured by Shin-Etsu Chemical Co., Ltd. can be used.
[0044]
1 and 2, post-baking of the polymer layers 2, 3, 4-1, 4-2, and 5b may be performed collectively after the formation of the upper cladding layer 5a. In that case, the prebake temperature may be increased or the heating time may be increased.
[0045]
FIG. 3 is a process diagram showing an embodiment of a method for producing a polymer waveguide according to the present invention.
[0046]
First, a polymer solution is prepared by dissolving a photobleaching polymer compound in an organic solvent.
[0047]
The photobleaching polymer material described above is used as the photobleaching polymer compound.
[0048]
Examples of the organic solvent include hydrocarbons having 5 to 12 carbon atoms, halogenated hydrocarbons, and ethers. Specific examples of the hydrocarbon type include pentane, hexane, heptane, cyclohexane, n-decane, n-dodecane, benzene, toluene, xylene, methoxybenzene and the like. Specific examples of halogenated hydrocarbons include carbon tetrachloride, chloroform, 1,2-dichloroethane, dichloromethane, chlorobenzene and the like. Specific examples of the ether type include diethyl ether, dibutyl ether, tetrahydrofuran and the like.
[0049]
As the polymer material for photobleaching, branched polymethylphenylsilane having a branching degree of 20% is used. 50% of a silicone compound (molecular weight: 650, side chain substituent: methyl, phenyl, methoxy, specific gravity: 1.13, viscosity: 0.7, liquid, nonvolatile content: 100) is added to this branched polymethylphenylsilane, A polymer solution is obtained by dissolving these in toluene. In this case, diethyl ether, dibutyl ether, tetrahydrofuran, etc. can be used.
[0050]
As a specific example of the polymer material for photobleaching, a branched polymethylphenylsilane having a branching degree of 20% is used, and a silicone compound (molecular weight: 650, side chain substituent: methyl, phenyl, methoxy, specific gravity: 1.13, viscosity: 0.7, liquid, non-volatile content: 100) is added 50%, and a polymer solution in which these are dissolved in toluene is mentioned (step S1).
[0051]
The polymer solution is irradiated with a desired amount of ultraviolet rays (step S2).
[0052]
Regarding the irradiation amount of the ultraviolet rays, as will be described later, the refractive index of the polymer film produced using the polymer solution can be controlled by the irradiation amount. The polymer solution irradiated with the ultraviolet light is applied on the substrate (step S3).
[0053]
As a coating method, a spin coating method, an extrusion coating method or the like is used. After the application, pre-baking (120 ° C. to 150 ° C.) for about 20 minutes and post-baking (180 ° C. to 250 ° C.) for about 30 minutes are performed to cure (lower clad layer) the polymer solution (steps S4 and S5). ).
[0054]
The photobleaching polymer solution obtained in step S1 is applied on the lower cladding layer (step S6).
[0055]
A high refractive index polymer layer is formed by performing pre-baking (120 ° C. to 150 ° C.) for about 20 minutes and post baking (180 ° C. to 250 ° C.) for about 30 minutes (steps S7 and S8).
[0056]
The polymer solution irradiated with the ultraviolet light obtained in step S2 is applied on the polymer layer obtained in step S8 (step S9).
[0057]
About 20 minutes of pre-baking (120 ° C. to 150 ° C.) and about 30 minutes of post-baking (180 ° C. to 250 ° C.) are performed to obtain a hardened low refractive index upper cladding layer (steps S10 and S11).
[0058]
A photomask is disposed on the upper cladding layer, and ultraviolet rays are irradiated from above the photomask (step S12).
[0059]
By changing the high refractive index polymer layer into a high refractive index core layer having a substantially rectangular cross-sectional shape that is not irradiated with ultraviolet light and a low refractive index side cladding layer that is not irradiated with ultraviolet light on both sides of the core layer, low scattering loss is achieved. A polymer waveguide can be realized (step S13).
[0060]
FIG. 4 is a process diagram showing another embodiment of the polymer waveguide manufacturing method of the present invention.
[0061]
The difference from the embodiment shown in FIG. 3 is that the method of forming the lower cladding layer is different. That is, the polymer solution obtained in Step P1 is applied on the substrate (Step P3), and then pre-baked (120 ° C. to 150 ° C.) for about 20 minutes and post-baked (180 ° C. to 250 ° C.) for about 30 minutes. To cure the polymer solution (steps P4 and P5) and to irradiate ultraviolet rays to obtain a lower clad layer having a low refractive index (step P6). The polymer solution obtained in the process P1 is irradiated with ultraviolet rays (process P2). Steps P7 to P14 are the same as steps S6 to S13 shown in FIG.
[0062]
FIG. 5 is a diagram showing the refractive index characteristics of a polymer film irradiated with ultraviolet rays, where the horizontal axis is the ultraviolet irradiation time axis and the vertical axis is the refractive index axis. The straight line L1 indicates the refractive index characteristic when the measurement wavelength is 633 nm, and the straight line L2 indicates the refractive index characteristic when the measurement wavelength is 1550 nm.
[0063]
The figure shows that a photobleaching polymer solution (for example, the polymer solution used in step S1 of FIG. 3) is irradiated with a desired amount of ultraviolet rays, and the polymer solution irradiated with ultraviolet rays is applied on a Si substrate for about 20 minutes. This is a result of evaluating the refractive index of a polymer film cured by performing pre-baking (120 ° C. to 150 ° C.) and post-baking (180 ° C. to 250 ° C.) for about 30 minutes.
[0064]
Here, a 150 W mercury xenon lamp (output: 1200 mW / cm) is used as an ultraviolet light source. ² ) Was used. Ultraviolet rays from a light source were propagated through a fiberscope (diameter 10 mm), and a container containing a polymer solution was placed at a position where the emitted light spread to a diameter of about 100 mm. A plurality of types of polymer solutions with different ultraviolet irradiation times were prepared, and a polymer film was prepared using them. As these polymer solutions, polymer solutions obtained by adding a silicone compound to the aforementioned polysilane were used.
[0065]
From the figure, it can be seen that the refractive index of the polymer film decreases substantially in proportion to the ultraviolet irradiation time. As described above, a polymer film is formed on a Si substrate using a polymer solution that does not irradiate ultraviolet rays, and the relative refractive index difference Δ between the case where the polymer film is not irradiated with ultraviolet rays and the case where the polymer film is irradiated is examined. The relative refractive index difference Δ was 6% at the maximum.
[0066]
Therefore, when the ultraviolet irradiation time in the characteristic diagram shown in FIG. 5 is extended, it is expected that the refractive index further decreases and the maximum relative refractive index difference Δ is obtained.
[0067]
In the present invention, by using the polymer film having the characteristics shown in FIG. 5, the lower cladding layer, the upper cladding layer, or both can be formed of the same polymer material.
[0068]
【Example】
Next, a waveguide having the structure shown in FIG. 1 will be prototyped and the results of optical propagation loss measurement at a wavelength of 1300 nm will be described.
[0069]
On a substrate 1 made of quartz glass having a diameter of 76.2 mm (about 3 inches) and a thickness of 1 mm, the above-described branched polysilane compound of a polymer solution (branching degree is 20%) not irradiated with ultraviolet rays is 50% silicone. A polymer solution for photobleaching in toluene organic solvent to which the compound was added was spin-coated under the conditions of a rotation speed of 1000 rpm and 20 seconds. After spin coating of the polymer solution, the polymer solution was pre-baked (120 ° C. to 150 ° C., about 20 minutes) and post-baked (180 ° C. to 250 ° C., about 30 minutes), and cured to a thickness of about 8 μm. A membrane was obtained. The lower clad layer 2 was obtained by irradiating the cured film with ultraviolet rays having an energy of 18000 mJ. A polymer solution was applied on the lower clad layer 2 under the spin coating conditions, and then heated under the pre-bake and post conditions to form a high refractive index cured film having a thickness of about 8 μm.
[0070]
On the cured film, a polymer solution that has been irradiated with ultraviolet rays for 180 minutes in advance is applied under the spin coating conditions, and then heated under the pre-bake and post-bake conditions. A cured film of the upper clad layer 5a having a refractive index was formed. A photomask was placed on the upper clad layer 5a, and ultraviolet rays with energy of 18000 mJ were irradiated from above the photomask. As a result, a polymer waveguide as shown in FIG. 1 was obtained. The relative refractive index difference Δ was about 5%. As a result of measuring the optical propagation loss characteristic at a wavelength of 1300 nm of this waveguide, a low loss characteristic of 0.12 dB / cm could be realized. That is, a polymer waveguide with very little scattering loss could be realized.
[0071]
Here, the present invention is not limited to the above embodiments. For example, a part of the lower cladding layers 2 and 5b shown in FIGS. ₂ Or SiO ₂ A layer to which a dopant for controlling the refractive index is added may be provided. Further, the pre-bake or post-bake time may be several minutes or more or several hours or more. Further, as the branched polysilane compound and the silicone compound, the following compounds can be used.
(Branched polysilane compound)
Examples of the polysilane used in the present invention include branched polysilane compounds instead of linear polysilanes.
[0072]
The branched polysilane is a polysilane containing Si atoms having 3 or 4 bonded to adjacent Si atoms. On the other hand, in the linear polysilane, the number of bonds between Si atoms and adjacent Si atoms is two.
[0073]
Usually, since the valence of the Si atom is 4, those having 3 or less bonds among the Si atoms present in the polysilane are bonded to a hydrocarbon group, an alkoxy group or a hydrogen atom in addition to the Si atom. Yes. As such a hydrocarbon group, an aliphatic hydrocarbon group which may be substituted with a halogen having 1 to 10 carbon atoms and an aromatic hydrocarbon group having 6 to 14 carbon atoms are preferable.
[0074]
Specific examples of the aliphatic hydrocarbon include chain groups such as a methyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a decyl group, a trifluoropropyl group and a nonafluorohexyl group, and a cyclohexyl group and a methylcyclohexyl group. Examples include alicyclic groups such as groups.
[0075]
Specific examples of the aromatic hydrocarbon group include a phenyl group, a p-tolyl group, a biphenyl group, and an anthracyl group.
[0076]
As an alkoxy group, a C1-C8 thing is preferable and a methoxy group, an ethoxy group, a phenoxy group, an octyloxy group etc. are mentioned as a specific example. Among these, a methyl group and a phenyl group are particularly preferable in view of ease of synthesis.
[0077]
In the case of a branched polysilane, the number of Si atoms having 3 or 4 bonds with adjacent Si atoms is preferably 2% or more of the total number of Si atoms in the branched polysilane. Branched polysilane and linear polysilane of less than 2% have high crystallinity, and microcrystals are easily formed in the film, thereby causing scattering and lowering transparency.
[0078]
The polysilane used in the present invention is produced by a polycondensation reaction by heating a halogenated silane compound to 80 ° C. or higher in an organic solvent such as n-decane or toluene in the presence of an alkali metal such as sodium. be able to. The synthesis can also be performed by an electrolytic polymerization method or a method using metal magnesium and metal chloride.
[0079]
In order to obtain a branched polysilane, a halosilane compound comprising an organotrihalosilane compound, a tetrahalosilane compound, and a diorganodihalosilane compound, wherein the organotrihalosilane compound and the tetrahalosilane compound are 2 mol% or more of the total amount. What is necessary is just to polycondense by heating.
[0080]
Here, the organotrihalosilane compound is a Si atom source having a bond number of 3 with an adjacent Si atom, and one tetrahalosilane compound is an Si atom source having a bond number of 4 with an adjacent Si atom. Become. The network structure can be confirmed by measuring an ultraviolet absorption spectrum or a silicon nuclear magnetic resonance spectrum.
[0081]
It is preferable that the halogen atom which each of the organotrihalosilane compound, the tetrahalosilane compound, and the diorganodihalosilane compound used as the raw material for polysilane has is a chlorine atom. Examples of the substituent other than the halogen atom that the organotrihalosilane compound and the diorganodihalosilane compound have include the above-described hydrocarbon group, alkoxy group, or hydrogen atom.
[0082]
The branched polysilane is not particularly limited as long as it is soluble in an organic solvent and can form a transparent film by coating. Preferable examples of such an organic solvent include hydrocarbon-based, halogenated hydrocarbon-based, and ether-based organic solvents having 5 to 12 carbon atoms.
[0083]
Specific examples of the hydrocarbon type include pentane, hexane, heptane, cyclohexane, n-decane, n-dodecane, benzene, toluene, xylene, methoxybenzene and the like. Specific examples of halogenated hydrocarbons include carbon tetrachloride, chloroform, 1,2-dichloroethane, dichloromethane, chlorobenzene and the like. Specific examples of the ether include diethyl ether, dibutyl ether, tetrahydrofuran and the like.
(Silicone compound)
The silicone compound used in the present invention is represented by Formula 1.
[0084]
[Chemical 1]
[0085]
(In the chemical formula 1, R1 to R12 are an aliphatic hydrocarbon group optionally substituted with a halogen having 1 to 10 carbon atoms or a glycidyloxy group, an aromatic hydrocarbon group having 6 to 12 carbon atoms, or 1 carbon atom. A group selected from the group consisting of alkoxy groups of ˜8, which may be the same or different, and a, b, c and d are integers including 0 and the sum of which is 1 or more.
Specific examples of the aliphatic hydrocarbon group possessed by the silicone compound include chain groups such as methyl group, propyl group, butyl group, hexyl group, octyl group, decyl group, trifluoropropyl group, and glycidyloxypropyl group. And alicyclic groups such as a cyclohexyl group and a methylcyclohexyl group. Specific examples of the aromatic hydrocarbon group include a phenyl group, a p-tolyl group, and a biphenyl group. Specific examples of the alkoxy group include methoxy group, ethoxy group, phenoxy group, octyloxy group, ter-butoxy group and the like.
[0086]
The types of R1 to R12 in Formula 1 and the values of a, b, c, and d are not particularly important as long as they are compatible with polysilane and an organic solvent and the film is transparent. In consideration of compatibility, it is preferable to have a group similar to the hydrocarbon group of the polysilane used. For example, when a phenylmethyl type polysilane is used, it is preferable to use the same phenylmethyl type or diphenyl type silicone compound. Moreover, the silicone compound which has 2 or more of alkoxy groups in 1 molecule so that at least 2 is a C1-C8 alkoxy group among R1-R12 can be utilized as a crosslinking agent. Examples thereof include methylphenylmethoxysilicone and phenylmethoxysilicone containing 15 to 35% by weight of alkoxy groups.
[0087]
Methylphenylmethoxysilicone and phenylmethoxysilicone preferably have a molecular weight of 10,000 or less, particularly preferably 3000 or less.
[0088]
Here, the present inventor has found that when the branching degree of the branched polysilane compound is 2% or more, the light transmittance can be further improved as the branching degree becomes higher. In addition, by setting the compounding ratio of the silicone compound to be added within the optimum range, the thermal stability of the refractive index, which has been difficult with conventional materials, can be greatly improved. As a result, it is possible to expect a polymer material and a polymer film whose refractive index hardly changes even when the temperature changes from room temperature to a high temperature of about 280 ° C.
[0089]
Further, by using a branched type for the polysilane compound, it is possible to realize a polymer material having a very small refractive index dependency on polarization and a polymer film using the polymer material.
[0090]
Furthermore, in order to reduce light absorption loss due to light absorption groups such as CH groups and OH groups, absorption can be achieved by using polysilane compounds or silicone compounds that are deuterated or at least partially halogenated, especially fluorinated. The optical loss due to the base can be greatly reduced. As a result, it is possible to realize a low light propagation loss polymer material with very little wavelength dependency and a polymer film using the same, and it is possible to expand the application to a wide range as optical materials and components.
[0091]
In addition, by using a crosslinkable or alkoxy group that is a silicone compound, it can be uniformly added to a branched polysilane compound, and it is easily soluble in an organic solvent such as toluene and is nanometer. By using the polymer solution, a uniform structure or film having no light scattering center can be formed.
[0092]
Furthermore, since both the branched polysilane compound and the silicone compound can be easily dissolved in an organic solvent such as toluene, the branched polysilane compound and the silicone compound can be easily mixed in a desired compounding ratio in the same organic solvent.
[0093]
Furthermore, the polymer material solution can be applied onto various substrates, and even if the film is formed by heating in a temperature range of 100 ° C. to 280 ° C., the refractive index of the film is within the above temperature range. The inventor has found that there is little change. As a result, the polymer film can be used as various optical films. For example, an electronic component or an optical component can be soldered in the vicinity of the present polymer film, or a temperature can be controlled for the characteristics of the electronic device or the optical device by providing a heater in the vicinity of the present film.
[0094]
Further, if a polymer structure having a transparent refractive index and good thermal stability or an ultraviolet cut layer is formed on the surface of the polymer film, the optical characteristics can be stabilized for a long period of time.
[0095]
In addition, this invention is not limited to the said Example. For example, in FIG. 1 and FIG. ₂ Or SiO ₂ A layer to which a dopant for controlling the refractive index is added may be provided. The pre-bake or post-bake time may be several minutes or more, or several hours or more. Furthermore, a heating method may be used in which pre-baking and post-baking are successively increased from a low temperature gradually to a post-baking temperature and maintained for a desired time, and then the temperature is gradually decreased to room temperature.
[0096]
FIG. 6 is a process diagram showing a modification of the method for producing a polymer waveguide of the present invention.
[0097]
As shown in the figure, the formation of a high refractive index core layer having a substantially rectangular cross-sectional shape by irradiation of the core layer with ultraviolet rays and a low refractive index side cladding layer on both sides of the core layer is performed before the upper cladding layer is formed. After that, an upper clad layer having a low refractive index may be formed.
[0098]
That is, the polymer solution obtained in step T1 is applied on the substrate (step T3), and then pre-baked (120 ° C. to 150 ° C.) for about 20 minutes and post-baked (180 ° C. to 250 ° C.) for about 30 minutes. To cure the polymer solution (steps T4 and T5), and irradiate the cured polymer solution with ultraviolet rays to obtain a lower refractive index lower cladding layer (step T6). A polymer solution for photobleaching is applied on the lower clad layer (step T7), and pre-baking and post-baking are performed under the above conditions to form a high refractive index polymer layer (steps T8 and T9). A photomask is placed on the high refractive index polymer layer, and ultraviolet rays are irradiated from above the photomask (step T10). The polymer solution obtained in step T1 is irradiated with ultraviolet rays (step T2), the obtained polymer solution is applied on the polymer layer obtained in step T10, and polymerized by pre-baking and post-baking under the above conditions. A waveguide is obtained (steps T11 to T14).
[0099]
In this way, the refractive index of the core layer and the side cladding layer can be controlled in a fairly wide range, and the relative refractive index difference Δ can be selected from a wider range.
[0100]
Next, a method for manufacturing the polymer waveguide of the present invention shown in FIGS. 1 and 2 will be described together.
[0101]
FIG. 7 illustrates the present invention. Application of polymer waveguide manufacturing method FIG. 8 is a cross-sectional view of the polymer waveguide, and FIG.
[0102]
There are three methods for forming the lower clad two layers on the substrate 1.
[0103]
The first method is a method in which a polymer solution for photobleaching is applied on the substrate 1 and then pre-baking and post-baking are heated, and then ultraviolet rays are irradiated to obtain a desired refractive index (step R2-1). .
[0104]
The second method is a method in which a photobleaching polymer solution is applied onto the substrate 1 and then pre-baking and post-baking are performed while simultaneously irradiating with ultraviolet rays to obtain a desired refractive index (step R2-2). .
[0105]
The third method is a method in which a polymer solution for photobleaching that has been irradiated with a desired amount of ultraviolet rays in advance is applied onto the substrate 1 and then pre-baking and post-baking are performed to obtain a desired refractive index (step R2-3). ).
[0106]
Next, a method for changing the high refractive index polymer layer 6 into a core layer and a side cladding layer will be described.
[0107]
In the first method, a photobleaching polymer solution is applied on the lower cladding layer 2 (5b), followed by pre-baking and post-baking heating to form a core pattern on the cured high refractive index polymer film 6. Is placed on the high refractive index core layer 3 that has not been irradiated with ultraviolet rays, and the both sides of the core layer 3 are irradiated with ultraviolet rays. This is a method of forming the side cladding layers 4-1 and 4-2 having a refractive index (step R3-1).
[0108]
In the second method, a polymer solution for photobleaching previously irradiated with a desired amount of ultraviolet light is applied on the lower cladding layer 2 (5b), and then pre-baking and post-baking are performed to form the polymer film 6. The core layer 3 having a desired refractive index through an exposure process through a photomask and a side cladding layer 4-1 having a desired low refractive index on both sides of the core layer 3, 4-2 is formed (step R3-2).
[0109]
Next, a method for forming the upper cladding layer 5a will be described.
[0110]
The first method is a method of applying a photobleaching polymer solution that has been irradiated with a desired amount of ultraviolet rays in advance after exposure (step R6), and then heating the prebake and postbake to obtain a desired refractive index. (Step R5a-1).
[0111]
The second method is a method of applying pre-baking and post-baking after applying a polymer solution for photobleaching on the core layer obtained in step 3-1 (step R5a-2).
[0112]
The third method is a method of heating the pre-bake and post-bake after applying the polymer solution for photobleaching obtained in step 3-2 (step R5a-2).
[0113]
A step of forming a high refractive index core layer and a low refractive index side cladding layer on both sides of the core layer by performing exposure (step R7) using a photomask after step 5a-2. As a result, the polymer waveguide 8 as shown in FIGS. 1 and 2 can be finally realized even after the process R5a-1. In addition to irradiating ultraviolet rays using a transparent glass substrate or sapphire substrate as the substrate of the polymer waveguide of the present invention from the upper clad layer of the substrate, a lower photomask is placed on the substrate to transmit ultraviolet rays to the substrate You may make it irradiate from. Furthermore, by providing an ultraviolet cut layer on the upper clad layer of the waveguide and the back surface of the substrate, a waveguide structure having a stable refractive index can be realized over a long period of time.
[0114]
In the above, according to the present invention,
(1) Since the lower clad layer, core layer, side clad layer, and upper clad layer formed on the substrate are all made of the same photobleaching material, strain is generated in each layer or strain remains. Or microcracks do not occur due to strain. Further, since the wettability of the interface is good when forming each layer, it becomes easy to apply the polymer solution uniformly, the interface can be formed uniformly, and a waveguide with low scattering loss can be realized.
(2) When the same photobleaching material is used, the material is dissolved in an organic solvent to form a polymer solution, and the polymer layer is formed using the solution by adjusting the amount of ultraviolet rays irradiated to the polymer solution. The refractive index of the polymer layer can be easily controlled. That is, the lower clad layer and the upper clad layer can realize a desired refractive index simply by applying a polymer solution irradiated with a desired amount of ultraviolet rays and heating and curing. The polymer layer that becomes the core layer and the side cladding layer may be applied with a polymer solution that is not irradiated with ultraviolet rays or irradiated with ultraviolet rays that is less than the above irradiation amount, and is cured by heating. By forming an upper clad layer on the core layer and the side clad layer, and then placing a photomask with a core pattern on the upper clad layer and irradiating the photomask with a desired amount of ultraviolet rays. A polymer waveguide can be realized by forming a high-refractive index core layer having a substantially rectangular cross-sectional shape and a side clad layer whose refractive index is lowered by irradiating ultraviolet rays on both sides of the core layer.
(3) Since the controllability of the refractive index can be made extremely high, desired waveguide structure parameters can be realized with high accuracy. That is, when the polymer solution for photobleaching is irradiated with ultraviolet rays, the refractive index changes much more slowly than when the polymer layer is irradiated with ultraviolet rays, and the controllability of the refractive index is very good. As a result, a more accurate waveguide structure can be realized.
(4) The relative refractive index difference Δ can take a wide range from 0.3% to 6%. As a result, an ultra-small waveguide device can be expected.
(5) Since the same photobleaching material is used, there is little risk of occurrence of strains in the waveguide and microcracks due to the occurrence of residual strains. Therefore, it can be formed on various substrates and flexible sheets. .
(6) Various materials can be used as the photo bleaching material. That is, since the same photobleaching material can be used for the lower clad layer, upper clad layer, side clad layer, and core layer, the range of usable photobleaching materials is expanded.
(7) Using a polymer solution made of the same photobleaching material, a polymer solution is formed by repeating the application of the polymer solution in which the irradiation amount of ultraviolet rays to the polymer solution and the heat curing process are repeated three times, Thereafter, the waveguide can be realized by transferring the core pattern to the central polymer layer by irradiating the photomask with ultraviolet rays. That is, a waveguide can be realized by a simple method, and the interface between the layers can be made uniform. Further, distortion is hardly generated in each layer, and generation of microcracks can be suppressed. Furthermore, the waveguide can be manufactured at low cost.
(8) The refractive index controllability can be improved by irradiating the polymer in solution with ultraviolet rays, and a waveguide in which the refractive index structure is accurately controlled can be realized.
[0115]
【The invention's effect】
In short, according to the present invention, the following excellent effects are exhibited.
[0116]
Polymer waveguide with low scattering loss, little residual strain, and no microcracks Road Provision of a manufacturing method can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a polymer waveguide to which a polymer waveguide manufacturing method of the present invention is applied.
FIG. 2 is a cross-sectional view showing another embodiment of a polymer waveguide to which the polymer waveguide manufacturing method of the present invention is applied.
FIG. 3 is a process diagram showing an embodiment of a method for producing a polymer waveguide according to the present invention.
FIG. 4 is a process diagram showing another embodiment of the method for producing a polymer waveguide of the present invention.
FIG. 5 is a diagram showing a refractive index characteristic of a polymer film irradiated with ultraviolet rays.
FIG. 6 is a process diagram showing a modification of the polymer waveguide manufacturing method of the present invention.
[Fig. 7] of the present invention. Application of polymer waveguide manufacturing method It is sectional drawing of a polymer waveguide.
FIG. 8 is a general process diagram showing a method of manufacturing a polymer waveguide according to the present invention.
FIG. 9 is an external perspective view showing a conventional example of a polymer waveguide.
[Explanation of symbols]
1 Substrate
2 Lower cladding layer
3 Core layer
4-1, 4-2 Side cladding layer
5a Upper cladding layer

Claims (4)

Previously reduced photobleaching type polymer solution of the UV in photosensitized by the refractive index is applied to a substrate, forming a lower clad layer by heating and curing the polymer solution, then, is irradiated ultraviolet the polymer solution of photobleaching type non coated onto the lower cladding layer, and a step of heating and curing to form a high refractive index polymer layer having a refractive index higher than the lower clad layer, then pre ultraviolet The photobleaching type polymer solution that has been sensitized with a low refractive index is applied onto the high refractive index polymer layer, and the polymer solution is heated and cured to have a refractive index lower than that of the high refractive index polymer layer. forming an upper clad layer, then, a photomask depicted with a core pattern on said upper cladding layer disposed, the high bending by irradiating ultraviolet rays from above the photomask And a step of changing the refractive index polymer layer into a core layer having a substantially rectangular cross-sectional shape that is not irradiated with ultraviolet rays, and a side cladding layer having a reduced refractive index that is irradiated with the ultraviolet rays on both sides of the core layer. A method of manufacturing a polymer waveguide. Previously reduced photobleaching type polymer solution of the UV in photosensitized by the refractive index is applied to a substrate, forming a lower clad layer by heating and curing the polymer solution, then, is irradiated ultraviolet A non-photobleaching polymer solution is applied onto the lower clad layer and heated and cured to form a high refractive index polymer layer having a higher refractive index than the lower clad layer ; A photomask having a core pattern drawn thereon is disposed on the refractive index polymer layer, and the high refractive index polymer layer is irradiated with ultraviolet rays from above the photomask to form a core layer having a substantially rectangular cross-sectional shape that is not irradiated with the ultraviolet rays. and a step of the ultraviolet on both sides of the core layer is varied in a side cladding layer reduced in the refractive index is irradiated, then photosensitized with advance UV on said core layer and said side cladding layer Method for producing a polymer optical waveguide, characterized in that a step of reduced photobleaching type polymer solution of the refractive index is applied to form the upper clad layer by heating and curing the polymer solution Te. Photobleaching type polymer solution that has not been irradiated with ultraviolet light is applied to the substrate, and after application, the polymer solution is heat-cured, or after the polymer solution is heat-cured, it is exposed to ultraviolet light to sensitize it. forming a lower cladding layer by lowering the refractive index, then the polymer solution of photobleaching type not ultraviolet irradiation is applied onto the lower clad layer, the lower cured pressurized heat A step of forming a high refractive index polymer layer having a higher refractive index than that of the cladding layer; and then, a photobleaching polymer solution which has been previously sensitized with ultraviolet rays and has a reduced refractive index is applied on the high refractive index polymer layer. was applied to a step of forming the polymer solution and cured by heating to form a low upper cladding layer refractive index than the high refractive index polymer layer, then the core pattern on said upper cladding layer The photomask he arranged, the core layer having a substantially rectangular cross-sectional shape which is not ultraviolet irradiation the UV the high refractive index polymer layer is irradiated from above of the photomask, and both sides of the UV of the core layer irradiated And a step of changing to a side cladding layer having a reduced refractive index. Photobleaching type polymer solution that has not been irradiated with ultraviolet light is applied to the substrate, and after application, the polymer solution is heat-cured, or after the polymer solution is heat-cured, it is exposed to ultraviolet light to sensitize it. Forming a lower clad layer by lowering the refractive index, and then applying a photobleaching polymer solution that is not irradiated with ultraviolet light onto the lower clad layer, followed by heating and curing to form the lower clad layer. Forming a high refractive index polymer layer having a refractive index higher than that of the layer, and then placing a photomask having a core pattern on the high refractive index polymer layer, and irradiating ultraviolet rays from the photomask. Irradiated to change the high refractive index polymer layer into a core layer having a substantially rectangular cross-sectional shape that is not irradiated with ultraviolet rays, and a side cladding layer having a reduced refractive index that is irradiated with the ultraviolet rays on both sides of the core layer. A step of, then a reduced photobleaching type polymer solution of the refractive index is photosensitized in advance UV on said core layer and said side cladding layer was applied, the upper and cured by heating the polymer solution And a step of forming a clad layer.