JP2004295118A - Optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prevent the occurrence of cracking and stripping on a lower part cladding layer 2 and an upper part cladding layer 4, in an optical waveguide which is provided with a core layer 3 which becomes a light propagation region, the upper part cladding layer 4 covering the circumference of the core layer 3 and the lower part cladding layer 2, and is formed in such a manner that the upper part cladding layer 4 accompanies a volume shrinkage. <P>SOLUTION: A stress relaxation layer 5 comprising a material of which the storage modulus is smaller than that of the upper cladding layer 4 is formed between the upper cladding layer 4 and the lower cladding layer 2 on at least one part of the region with which the upper part cladding layer 4 and lower part cladding layer 2 are brought into contact with each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical waveguide that can be used for an optical interconnection, an optical modulator, an optical integrated circuit, an optical switch, a distributor, an optical transceiver module, and the like, and an optical communication device using the optical waveguide.

  In recent years, as the Internet becomes broadband, in order to spread access such as FTTH, a significantly low cost of an optical communication device is required. As an optical communication device, an optical transceiver module that converts light into an electric signal is used at an end of an optical communication device. In order to reduce the size and cost of the optical transceiver module, there has been proposed a method of forming an optical waveguide, which is a component in the module, from an organic polymer material (Non-Patent Document 1).

For example, a lower cladding layer is formed on a substrate, and a light propagation layer made of an organic polymer material is formed on the lower cladding layer. This light propagation layer forms a pattern by RIE or UV irradiation using photolithography to remove unnecessary portions. An upper clad layer is formed on the light propagation layer thus formed. In many cases, the lower cladding layer and the upper cladding layer are also formed from an organic polymer material.
Nobuo Miyadera, Polymer material for optical waveguides, Optical Alliance, p13, 2, (1999)

  However, when the upper cladding layer of the optical waveguide is formed from an organic-inorganic composite or a material with volume shrinkage upon curing such as a resin material, the volume of the upper cladding layer is shrunk when forming the upper cladding layer. There is a problem that cracks and peeling are likely to occur.

  An object of the present invention is to provide a novel structure of an optical waveguide that can effectively prevent the occurrence of cracks and peeling in a lower cladding layer and an upper cladding layer, and to provide an optical communication device using the optical waveguide. .

  The optical waveguide of the present invention is an optical waveguide including a core layer serving as a light propagation region, an upper clad layer and a lower clad layer covering the periphery of the core layer, and the upper clad layer is formed with volume shrinkage. In at least a part of a region where the upper clad layer and the lower clad layer are in contact with each other, a stress relaxation layer is provided between the upper clad layer and the lower clad layer to relieve a stress generated due to a volume shrinkage of the upper clad layer. It is characterized by having.

  According to the present invention, by providing a stress relaxation layer between the upper cladding layer and the lower cladding layer, the stress due to volume shrinkage during the formation of the upper cladding layer can be relaxed by the stress relaxation layer. For this reason, it is possible to effectively prevent cracks, peeling, and the like from occurring in the lower cladding layer and the upper cladding layer.

  The stress relaxation layer in the present invention is preferably formed from a material having a lower storage elastic modulus than the material of the upper cladding layer. In general, when a sinusoidally changing stress is applied to a polymer material, the strain has a sinusoidal waveform with the same frequency and a phase delayed by δ. Storage modulus is a measure of the energy stored and fully recovered per cycle and can be measured with a dynamic viscoelasticity measurement device.

When the upper cladding layer is formed from an organic-inorganic composite has a storage elastic modulus of the stress relaxing layer is preferably 100000kgf / cm ² or less at 30 ° C., further preferably 50000kgf / cm ² or less. Further, the stress relaxation layer can also be formed from an organic-inorganic composite. Although the lower limit of the storage elastic modulus of the stress relaxation layer is not particularly limited, it is generally preferable that the lower limit is 10,000 kgf / cm ² or more at 30 ° C. In the following, all storage elastic moduli are those at 30 ° C.

  In the present invention, the core layer and / or the lower cladding layer may be formed from an organic-inorganic composite.

  In the present invention, the organic-inorganic composite can be formed, for example, from an organic polymer and a metal alkoxide. Further, the organic-inorganic composite may be formed from at least one kind of metal alkoxide. In this case, it is preferably formed from at least two kinds of metal alkoxides.

  In the organic-inorganic composite, the refractive index of the finally formed organic-inorganic composite can be adjusted by appropriately adjusting the combination of the organic polymer and the metal alkoxide or the combination of at least two types of metal alkoxides. it can.

  As the metal alkoxide, a metal alkoxide having a polymerizable group that is polymerized by light or heat may be used. In this case, it is preferable to use a metal alkoxide having a polymerizable group that is polymerized by light or heat in combination with a metal alkoxide having no polymerizable group. Examples of the polymerizable group include a methacryloxy group, an acryloxy group, a vinyl group, and a styryl group.

  When a metal alkoxide having a polymerizable group is used, the polymerizable group of the metal alkoxide is preferably polymerized by light or heat.

  Examples of the metal alkoxide include alkoxides such as Si, Ti, Zr, Al, Nb, Sn, and Zn. In particular, alkoxides of Si, Ti, or Zr are preferably used. Therefore, alkoxysilane, titanium alkoxide, and zirconium alkoxide are preferably used, and in particular, alkoxysilane is preferably used.

  Examples of the alkoxysilane include tetraethoxysilane, tetramethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane, phenyltriethoxysilane (PhTES), phenyltrimethoxysilane ( PhTMS), diphenyldiethoxysilane, diphenyldimethoxysilane and the like.

  Examples of the alkoxysilane having a polymerizable group include 3-methacryloxypropyltriethoxysilane (MPTES), 3-methacryloxypropyltrimethoxysilane (MPTMS), 3-methacryloxypropylmethyldimethoxysilane, and 3-acryloxypropyltrimethoxysilane. Examples include methoxysilane, p-styryltriethoxysilane, p-styryltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and the like.

  Examples of the titanium alkoxide include titanium isopropoxide and titanium butoxide. Examples of the zirconium alkoxide include zirconium isopropoxide, zirconium butoxide, and the like. Examples of the niobium alkoxide include pentaethoxy niobium.

As the metal alkoxide, those described above can be used, and in general, the formulas M (OR) _n , R′M (OR) _n−1 , and R ′ ₂ M (OR) _n−2 (where, M is a metal, n is 2, 3, 4, or 5, and R and R 'each represent an organic group). Examples of the organic group include an alkyl group, an aryl group, and an organic group having the above-described polymerizable group. As described above, M includes Si, Ti, Zr, Al, Nb, Sn, Zn, and the like. In addition, as an alkyl group, a C1-C5 alkyl group is preferable.

  When the organic-inorganic composite is formed from an organic polymer and a metal alkoxide, the organic polymer is not particularly limited as long as it can form an organic-inorganic composite with the metal alkoxide. Examples of the organic polymer include a polymer having a carbonyl group, a polymer having a benzene ring, and a polymer having a naphthalene ring.

  Specific examples of the organic polymer include, for example, polyvinylpyrrolidone, polycarbonate, polymethyl methacrylate, polyamide, polyimide, polystyrene, polyethylene, polypropylene, epoxy resin, phenol resin, acrylic resin, urea resin, melamine resin, and the like. . From the viewpoint of forming an organic-inorganic composite having excellent optical transparency, polyvinyl pyrrolidone, polycarbonate, polymethyl methacrylate, polystyrene, epoxy resin, and a mixture thereof are preferably used.

  In the present invention, when the stress relaxation layer, the upper cladding layer and the other layers are formed from an organic-inorganic composite, the storage elastic modulus of each layer is determined by forming each layer using a solution for forming each layer. The sample can be determined by preparing a sample for measuring the storage elastic modulus under the conditions and measuring the storage elastic modulus of the sample.

  The organic-inorganic composite can be formed by applying a raw material solution and then heating and drying it. When a metal alkoxide having a polymerizable group is used, the metal alkoxide can be polymerized and cured by heating or light irradiation as necessary.

  In the present invention, the lower cladding layer may be a substrate having a lower refractive index than the core layer.

  In the present invention, the lower cladding layer may be formed on a substrate. Further, an upper substrate may be provided on the upper cladding layer.

  In the present invention, the upper cladding layer may be formed by laminating a plurality of layers. In this case, the plurality of layers may be layers formed from the same material. That is, the upper cladding layer may be formed by being applied a plurality of times. By performing the application in a plurality of times, it is possible to prevent the upper clad layer from being cracked or the upper clad layer from peeling off due to shrinkage during the formation of the upper clad layer.

  In the present invention, when the thickness of the core layer is H and the thickness of the stress relieving layer is t, the thickness t of the stress relieving layer may be in a range satisfying 0.05 μm ≦ t ≦ 0.25H. preferable. If the thickness of the stress relaxation layer is less than 0.05 μm, the effect of the present invention of reducing the occurrence of cracks and peeling may not be sufficiently obtained. In addition, when the thickness of the stress relaxation layer is larger than 0.25H, the degree of leakage of light from the stress relaxation layer may be increased. The more preferable thickness of the stress relaxation layer is 0.1 μm ≦ t ≦ 10 μm.

  In the present invention, the stress relaxation layer is preferably formed from a material having a refractive index that is not higher than the material of the core layer (that is, the refractive index is equal or lower). In particular, by using a material having a lower refractive index than the material of the core layer, it is possible to effectively prevent light from leaking from the stress relaxation layer.

  In the present invention, the stress relaxation layer may be formed from the same material as the core layer. By forming the stress relaxation layer from the same material as the core layer, the stress relaxation layer can be formed simultaneously with the formation of the core layer, and the manufacturing process can be simplified. In this case, the stress relaxation layer is formed integrally with the core layer.

  However, if the stress relaxation layer is formed of the same material as the core layer, light may leak from the stress relaxation layer to the outside. In such a case, it is preferable that a groove for separating the core layer and the stress relaxation layer is formed in the stress relaxation layer near the core layer, and the groove is filled with a material having a lower refractive index than the material of the stress relaxation layer. By forming such a groove, the stress relaxation layer can be separated from the core layer, so that light leakage from the stress relaxation layer can be prevented.

  The groove may be formed in the lower cladding layer. Further, it may be formed so as to pass through the lower cladding layer and reach the substrate. As described above, the groove is formed so as to reach the lower clad layer and further to the substrate, and the groove is filled with a material having good adhesion to each layer, whereby the adhesion between the layers can be increased.

  As a material for filling the inside of the groove, the same material as the upper clad layer is preferably used, but when the same material as the upper clad layer is used, the inside of the groove is filled with this material when forming the upper clad layer. At the same time.

  When the upper substrate is provided on the upper cladding layer, the groove may be formed in the upper substrate and the upper cladding layer.

As a method for preventing light from leaking from the stress relieving layer, irregularities may be formed at the interface between the stress relieving layer and the upper cladding layer. Such irregularities may be exemplified irregularities corresponding to the range of the surface roughness R _max 0.02~10μm.

  By forming irregularities at the interface between the stress relaxation layer and at least one of the upper cladding layer and the lower cladding layer, when irradiating ultraviolet rays to cure the upper cladding layer or the core layer, etc., the amount of ultraviolet irradiation for photocuring Can be made constant with high accuracy. That is, when the upper cladding layer or the core layer of the optical waveguide is formed from a photocurable resin, the refractive index of the resin changes according to the amount of ultraviolet irradiation at the time of curing. . Part of the ultraviolet light irradiated when curing the upper clad layer also penetrates into the lower clad layer, and the ultraviolet light is reflected at the interface on the opposite side of the lower clad layer, reaches the upper clad layer again, and the upper clad layer. Contributes to UV curing. The intensity of the ultraviolet light reflected in this manner is affected by variations in the refractive index and thickness of the lower cladding layer and varies, so that the refractive index of the upper cladding layer or the core layer varies.

  By forming irregularities at the interface between the stress relaxation layer and at least one of the upper cladding layer and the lower cladding layer, it is possible to reflect the ultraviolet rays irradiated to cure the upper cladding layer or the core layer at the irregularities, Ultraviolet rays can be prevented from reaching the lower cladding layer. For this reason, the amount of ultraviolet irradiation when the upper clad layer or the core layer is photocured can be controlled with good reproducibility and high accuracy, and the variation in the refractive index between the upper clad layer and the core layer can be reduced.

Uneven shape formed at the interface of the stress relaxation layer for the purpose as described above, is not particularly limited as long as it can scatter ultraviolet light having a wavelength of 400nm used for photocuring, a surface roughness R _max , 0.05 to 10 μm. Examples of the uneven shape include a stripe shape as shown in FIG. 28, an island shape as shown in FIG. 29, and a randomly formed island shape as shown in FIG.

In addition, as a method of reducing the occurrence of stray light due to light leakage from the stress relaxation layer and the occurrence of adverse effects such as noise, the stress relaxation layer may contain a light absorbing or scattering component. Examples of such light absorption or scattering components include carbon particles, oxides such as TiO ₂ and ZrO ₂ , and nitrides such as TiN and ZrN.

  In the present invention, it is preferable that an end face of the core layer through which light enters and / or exits is covered with a protective layer made of a transparent material. By forming such a protective layer, it is possible to prevent moisture from entering the core layer, adherence of contaminants, and the like.

  The protective layer is preferably formed from a material that is not higher than the refractive index of the core layer. Generally, the larger the difference in refractive index at the interface, the greater the loss due to reflection. Therefore, by forming such a protective layer, it is possible to reduce loss due to reflection when light enters the core layer.

  The protective layer is preferably formed from the same material as the upper clad layer. By forming the protective layer from the same material as the upper clad layer, the protective layer can be formed simultaneously with the formation of the upper clad layer, and the protective layer can be formed integrally with the upper clad layer.

  In the present invention, the corners of the core layer preferably have a rounded shape. By making the corners rounded, it is possible to prevent the corners of the core layer from being lost when forming the core layer.

  An optical communication device according to the present invention is characterized in that the optical waveguide according to the present invention is used as a medium for transmitting and / or receiving an optical signal.

  According to the present invention, since stress due to volume shrinkage during the formation of the upper cladding layer can be reduced by the stress relaxation layer, it is possible to effectively prevent the occurrence of cracks and peeling in the lower cladding layer and the upper cladding layer. Can be.

  Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within the scope of the gist of the present invention.

  FIG. 1 is a sectional view showing an optical waveguide according to one embodiment of the present invention. As shown in FIG. 1, a lower cladding layer 2 is formed on a substrate 1. A core layer 3 serving as a light propagation region is formed on a central portion of the lower cladding layer 2. On the core layer 3, an upper clad layer 4 is provided. The lower cladding layer 2 and the upper cladding layer 4 are formed from a material having a lower refractive index than the core layer 3. The core layer 3 has its periphery covered by the upper cladding layer 4 and the lower cladding layer 2 so that light can be propagated therein.

  In a region where the core layer 3 is not provided, a stress relaxation layer 5 is provided between the upper cladding layer 4 and the lower cladding layer 2. The stress relaxation layer 5 is formed of a material having a lower storage elastic modulus than the material of the upper cladding layer 4. Therefore, the stress caused by the volume shrinkage of the upper cladding layer 4 generated when the upper cladding layer 4 is formed can be reduced by the stress relaxation layer 5. For this reason, the occurrence of cracks and peeling in the lower cladding layer 2 and the occurrence of cracks and peeling in the upper cladding layer 4 can be effectively prevented.

  The thickness of the stress relaxation layer 5 is preferably not less than 0.05 μm, and is preferably not more than ４ of the thickness of the core layer 3. More preferably, it is in the range of 0.1 μm to 10 μm.

  In this embodiment, the lower cladding layer 2, the core layer 3, the upper cladding layer 4, and the stress relaxation layer 5 are all formed of an organic-inorganic composite. The substrate 1 is formed from a glass substrate.

  FIG. 2 is a sectional view showing an optical waveguide according to another embodiment of the present invention. In the embodiment shown in FIG. 2, the substrate has a lower refractive index than the core layer 3, and the substrate forms the lower cladding layer 2. Examples of a substrate that can be used as such a lower cladding layer 2 include quartz, Tempax glass, Pyrex (registered trademark) glass, and the like.

  FIG. 3 is a sectional view showing an optical waveguide according to another embodiment of the present invention. In this embodiment, the stress relaxation layer 5 is formed from the same material as the core layer 3. Therefore, the stress relaxation layer 5 is formed integrally with the core layer 3.

  The stress relaxation layer 5 is formed from a material having a lower storage elastic modulus than the material of the upper cladding layer. However, since the core layer 3 is formed of the same material, the refractive index is the same as that of the core layer 3.

  In this embodiment, since the stress relaxation layer 5 is formed from the same material as the core layer 3, the stress relaxation layer 5 can be formed simultaneously when the core layer 3 is formed. Therefore, the manufacturing process can be simplified. However, since it is formed of the same material as the core layer 3, the refractive index is the same, and light propagating in the core layer 3 may leak from the stress relieving layer 5 to the outside. Such light leakage can be suppressed by various methods described later.

  FIG. 4 is a sectional view showing an optical waveguide according to another embodiment of the present invention. In the embodiment shown in FIG. 4, the lower cladding layer 2 is formed from a substrate. Others are the same as the embodiment shown in FIG.

  FIG. 5 is a diagram showing an example of the cross-sectional shape of the core layer in the present invention. The core layer 3 shown in FIGS. 5A to 5D has a shape without corners or a shape with rounded corners. For this reason, when forming the core layer, chipping or the like hardly occurs.

  6 and 7 are cross-sectional views showing the steps of manufacturing the optical waveguide of the embodiment shown in FIG.

  As shown in FIG. 6A, a lower cladding layer 2 made of an organic-inorganic composite is formed on a glass substrate 1.

  Next, as shown in FIG. 6B, a core layer 3 made of an organic-inorganic composite is formed on the lower cladding layer 2. As the organic-inorganic composite of the core layer 3, an organic-inorganic composite having thermoplasticity is formed. Such an organic-inorganic composite having thermoplasticity can be formed, for example, from a solution containing a thermoplastic resin and a metal alkoxide. The core layer 3 is heated to be in a softened state, and then the mold 10 is pressed on the softened core layer 3 as shown in FIG. A concave portion 10a is formed in the mold 10, and the core layer 3 is formed according to the shape of the concave portion 10a. In addition, a stress relaxation layer 5 is formed in a peripheral portion of the concave portion 10a. In this embodiment, the mold 10 is formed from glass.

  Next, as shown in FIG. 7D, the mold 10 is removed, and as shown in FIG. 7E, the upper cladding layer 4 made of an organic-inorganic composite is provided on the core layer 3 and the stress relaxation layer 5. To form

  FIG. 8 is a side view showing a state in which the end of the optical waveguide manufactured as described above is cut. As shown in FIG. 8, the end of the optical waveguide can be cut by the dicing saw 11 to expose a good end face.

  FIG. 9 is a sectional view showing an optical waveguide according to still another embodiment according to the present invention. In the embodiment shown in FIG. 9, the lower clad layer 2 is formed on the substrate 1 and the stress relaxation layer 5 is formed of a material different from the material of the core layer 3 as in the embodiment shown in FIG.

  FIG. 10 is a sectional view showing a manufacturing process of the embodiment shown in FIG.

  As shown in FIG. 10A, a lower cladding layer 2 is formed on a substrate 1. Next, a core layer 3 is formed on the lower cladding layer 2 as shown in FIG. The core layer 3 is formed by forming the core layer 3 on the entire surface of the lower clad layer 2 and then patterning the same using photolithography and etching as shown in FIG.

  Next, as shown in FIG. 10C, a mask 12 is provided on the core layer 3, and the stress relaxation layer 5 is formed on a portion other than the core layer. After removing the mask 12, by forming an upper cladding layer on the stress relaxation layer 5 and the core layer 3, the optical waveguide shown in FIG. 9 can be formed.

  FIG. 11 is a sectional view showing an optical waveguide according to another embodiment of the present invention. In the embodiment shown in FIG. 11, a concave portion 2a is formed in the lower cladding layer 2, and a core layer 3 is formed in the concave portion 2a. The stress relaxation layer 5 is formed from the same material as the core layer 3.

  12 and 13 are views showing the manufacturing process of the embodiment shown in FIG.

  As shown in FIG. 12A, a lower cladding layer 2 is formed on a substrate 1. The lower cladding layer 2 is formed from an organic-inorganic composite having thermoplasticity. The lower clad layer 2 is heated and softened, and the mold 13 having the convex portion 13a protruding downward is pressed against the softened lower clad layer 2.

  As shown in FIG. 12B, a concave portion 2 a is formed in the lower clad layer 2 by the convex portion 13 a of the mold 13.

  Next, as shown in FIG. 13C, the mold 13 is removed, and the core layer 3 is formed on the lower clad layer 2 as shown in FIG. The core layer 3 is formed by being buried in the concave portion 2a, and a stress relaxation layer 5 is formed in a peripheral region thereof.

  Next, by forming an upper clad layer on the stress relaxation layer 5 and the core layer 3, the optical waveguide of the embodiment shown in FIG. 11 can be manufactured.

  The solution for forming the organic-inorganic composite of each layer used in the following examples is as follows.

(Clad layer forming solution)
13.2 g of 3-methacryloxypropyltriethoxysilane (MPTES), 16.8 g of ethanol, 1.6 g of hydrochloric acid (2N), and 2.4 g of phenyltriethoxysilane (PhTES) were mixed and left at 30 ° C. for 45 hours. Thus, a solution A was prepared. This solution A was used for forming a lower cladding layer and an upper cladding layer.

[Core layer (stress relaxation layer) forming solution]
39.6 g of PhTES, 5.9 g of hydrochloric acid (0.05 N), and 53.6 g of N-methyl-2-pyrrolidone (NMP) were mixed and left at 30 ° C. for 19 hours. 19.1 g of this solution and 10.9 g of a solution in which 17.5 g of polymethyl methacrylate (PMMA) was dissolved in 82.5 g of NMP were mixed for 30 minutes to prepare a solution B. The solution B was used to form a core layer and a stress relaxation layer (when formed of the same material as the core layer).

(Solution for forming a stress relaxation layer)
39.6 g of PhTES, 5.9 g of hydrochloric acid (0.05 N), and 53.6 g of NMP were mixed and left at 30 ° C. for 19 hours to prepare a solution. 3.3 g of this solution and 16.7 g of a solution obtained by dissolving 17.5 g of PMMA in 82.5 g of NMP were mixed for 30 minutes to prepare a solution C. Using this solution C, a stress relaxation layer was formed.

The refractive index and the storage elastic modulus of the organic-inorganic composite prepared from the solutions A, B and C are as follows.
Solution A: refractive index about 1.50, storage elastic modulus about 27000 kgf / cm ²
Solution B: refractive index about 1.54, storage elastic modulus about 22000 kgf / cm ²
Solution C: refractive index about 1.50, storage elastic modulus about 20,000 kgf / cm ²

<Example 1>
The optical waveguide of the example shown in FIG. 3 was manufactured as follows.

  As shown in FIG. 6A, a solution A is spin-coated on a substrate 1 made of glass having a diameter of 76 mm and a thickness of 1 mm, and after being applied, the solution A is heated at 180 ° C. for 20 minutes using a heating furnace. The film was cured to form a lower cladding layer 2 having a thickness of about 5 μm. By the above heating, the methacryloxy group of MPTES is polymerized.

  Next, as shown in FIG. 6B, the solution B is dropped on the lower cladding layer 2 and dried at 120 ° C. for 5 hours to remove the solvent, thereby forming the core layer 3 having a thickness of about 50 μm. Formed.

  Next, the core layer 3 was heated to 140 ° C. and softened, and then, as shown in FIG. 6C, a glass mold 10 was pressed to transfer the shape of the mold 10 to the core layer 3. The width of the concave portion 10a of the mold 10 was 100 μm, the depth was 40 μm, and the radius of curvature of the corner was 10 μm.

  As described above, the core layer 3 and the stress relaxation layer 5 were simultaneously formed. The thickness of the stress relaxation layer 5 was about 10 μm. The thickness of the core layer 3 was about 50 μm.

Next, as shown in FIG. 7D, after the mold 10 is removed, as shown in FIG. 7E, the upper clad layer 4 (from the upper surface of the stress relaxation layer 5 to the upper surface of the upper clad layer 4) is removed. (Thickness: about 60 μm). The upper clad layer 4 is obtained by heating the solution A at 120 ° C. for 20 minutes to remove the solvent (ethanol) to obtain a highly viscous solution, and then dropping the solution on the core layer 3 and the stress relaxation layer 5. It was formed by irradiating ultraviolet rays for about 30 minutes with an ultraviolet irradiator having a wavelength of 365 nm and an intensity of 200 mW / cm ² (distance: 10 mm) for curing.

  When forming the upper cladding layer 4, it was formed twice. That is, half of the amount required for forming the upper cladding layer 4 was first applied, and after irradiating with ultraviolet rays, the other half of the solution was applied thereon and cured by irradiating with ultraviolet rays. By forming the upper cladding layer in a plurality of times as described above, it is possible to prevent cracks, peeling, and the like from occurring in the upper cladding layer. In the following examples, the upper cladding layer was similarly formed twice.

  In the organic-inorganic composite of the lower cladding layer 2 and the upper cladding layer 4, the methacryloxy group of MPTES is polymerized. The lower clad layer 2 is polymerized by heat, and the upper clad layer 4 is polymerized by ultraviolet irradiation.

  The reason why the upper clad layer 4 is cured by the irradiation of ultraviolet rays is that, when heating for polymerization, the core layer 3 and the stress relaxation layer 5 may be deformed because they have thermoplasticity. Therefore, in order to avoid the core layer 3 and the stress relaxation layer 5 from being deformed by heat, the upper cladding layer 4 is cured by irradiation with ultraviolet rays.

(Evaluation of stress relaxation effect)
In order to evaluate the stress relaxation effect of the stress relaxation layer, a lower cladding layer (thickness of about 5 μm) is formed on a glass substrate using solution A, and a stress relaxation layer (thickness of about 10 μm) is formed thereon using solution B. Was formed thereon, and an upper clad layer (about 60 μm in thickness) was formed thereon using the solution A to prepare a sample. As a result of preparing 50 samples and observing them with an optical microscope, peeling of the upper clad layer and the lower clad layer was observed in three samples.

  On the other hand, for comparison, a sample in which a lower clad layer and an upper clad layer were formed on a substrate was manufactured. In this sample, no stress relaxation layer was formed between the upper cladding layer and the lower cladding layer. When 50 of these samples were prepared and observed with an optical microscope, peeling of the upper clad layer and the lower clad layer was observed in 11 samples.

  From the above results, it can be seen that by providing the stress relaxation layer between the upper cladding layer and the lower cladding layer, the stress at the time of forming the upper cladding layer can be relaxed, and cracks and peeling can be prevented.

(Water resistance test)
In the same manner as described above, 50 samples in which a stress relaxation layer was formed between the upper clad layer and the lower clad layer were produced, and these samples were immersed in water at 23 ° C. for 24 hours. As a result, peeling of the upper clad layer and the lower clad layer was observed in five samples. On the other hand, 50 comparative samples without the stress relaxation layer were prepared in the same manner as above, and the same water resistance test was carried out. As a result, in the 20 samples, the separation between the upper clad layer and the lower clad layer was not observed. Admitted.

  From the above, it can be understood that the provision of the stress relaxation layer between the upper clad layer and the lower clad layer improves the water resistance.

<Example 2>
The optical waveguide of the example shown in FIG. 9 was manufactured.

  As shown in FIG. 10 (a), a glass substrate 1 having a diameter of 76 mm and a thickness of 1 mm is spin-coated using a solution A, and heated at 180 ° C. for 20 minutes using a heating furnace to form a lower portion having a thickness of about 2 μm. The clad layer 2 was formed.

  Next, the solution B was applied dropwise onto the lower cladding layer 2 and dried at 120 ° C. for 5 hours to remove the solvent, thereby forming a core layer 3 having a thickness of about 50 μm. This core layer 3 was patterned by photolithography and etching to form a core layer 3 having the shape shown in FIG.

  Next, as shown in FIG. 10C, a mask 12 is placed on the core layer 3, a solution C is applied by dripping, and dried at 120 ° C. for 5 hours to reduce the stress to a thickness of about 10 μm. Layer 5 was formed.

  After the mask 12 is removed, the solvent of the solution A is removed and a solution whose viscosity is increased is dropped and applied in the same manner as in the first embodiment, and thereafter, the upper clad layer 4 is irradiated with ultraviolet rays for about 30 minutes. (Thickness: about 60 μm).

(Evaluation of stress relaxation effect)
In the same manner as in Example 1, 50 samples in which a lower clad layer, a stress relaxation layer, and an upper clad layer were formed in this order on a substrate were produced. Here, the stress relaxation layer was formed from solution C. As a result of observation with an optical microscope in the same manner as in Example 1, peeling of the upper clad layer and the lower clad layer was observed in the two samples.

(Evaluation of water resistance)
As a result of performing a water resistance test on 50 samples similar to the above in the same manner as in Example 1, peeling was observed in 17 samples.

  From the above results, it can be seen that in this example as well as in Example 1, by providing the stress relaxation layer, the stress at the time of forming the upper cladding layer can be relaxed, and the occurrence of peeling can be suppressed. Further, it can be seen that the water resistance is also improved.

<Example 3>
The optical waveguide of the example shown in FIG. 11 was manufactured.

  As shown in FIG. 12A, a solution A is dropped on a glass substrate 1 having a diameter of 76 mm and a thickness of 1 mm, and heated at 180 ° C. for 20 minutes using a heating furnace while pressing a glass mold 13. Thus, the lower clad layer 2 was cured and formed. The mold 13 has a convex portion 13a, the width of the convex portion 13a is 100 μm, the height is 40 μm, and the radius of curvature of the corner portion is 10 μm.

  As shown in FIG. 13C, by removing the mold 13, the lower cladding layer 2 having the concave portion 2a was formed. The thickness of the lower cladding layer 2 is about 70 μm.

  Next, the solution B was dropped on the lower cladding layer 2 and dried at 120 ° C. for 5 hours to evaporate the solvent and harden. As a result, the core layer 3 was formed in the recess 2a, and the stress relaxation layer 5 was formed around the core layer 3.

  Next, the solution A was dropped thereon, and cured by irradiating ultraviolet rays for 30 minutes to form an upper clad layer 4 (thickness: about 30 μm).

<Example 4>
FIG. 14 is a sectional view showing an optical waveguide according to still another embodiment according to the present invention. In this embodiment, irregularities are formed at the interface 5a between the stress relaxation layer 5 and the upper cladding layer 4. By forming such irregularities 5a, it is possible to prevent light from the core layer 4 from leaking outside through the stress relaxation layer 5. The unevenness 5a is unevenness corresponding to a surface roughness _{Rmax of} about 1 μm.

As shown in FIG. 15A, a lower cladding layer 2 and a core layer 3 are formed on a substrate 1 in the same manner as in the first embodiment. As shown in FIG. 15B, the mold 14 in which the unevenness 14a is formed in the region corresponding to the stress relaxation layer and the concave portion 14b is formed in the region corresponding to the core layer is pressed against the core layer 3 as shown in FIG. The unevenness 14a has an unevenness corresponding to a surface roughness _{Rmax of} about 1 μm, and the unevenness is transferred to the surface of the stress relaxation layer 5.

  As shown in FIG. 15C, the mold 14 is removed, so that the surface of the stress relaxation layer 5 is formed with the irregularities 5a. Next, an optical waveguide shown in FIG. 14 is obtained by forming the upper cladding layer in the same manner as in the first embodiment.

  Light leakage in the manufactured optical waveguide was evaluated using an apparatus shown in FIG. In the apparatus shown in FIG. 18, an optical fiber having a core diameter of about 7 μm is provided, a laser beam 18 having a wavelength of 650 nm is introduced to one end face, and a core layer 3 of an optical waveguide is arranged on the other end face. The laser light incident on one end face of the core layer 3 passes through the core layer 3 and is emitted to the screen 17 from the other end face. By observing the spot of the light emitted to the screen 17 from the direction of the arrow, it is possible to observe the state of light leakage. As a result, in the case of the optical waveguide of this example, a sharp light spot corresponding to the core layer 3 was observed. On the other hand, when the optical waveguide of Example 1 was used, weak light was observed around the light spot. Therefore, in the case of Example 1, it is understood that light leaked from the stress relaxation layer.

  In the present example, it is considered that the light leaked to the stress relaxation layer was scattered above the optical waveguide due to unevenness at the interface between the stress relaxation layer and the upper cladding layer, and thus did not reach the screen.

<Example 5>
FIG. 16 is a sectional view showing an optical waveguide according to another embodiment of the present invention. In this embodiment, carbon particles 6 as a light absorbing component are contained at the interface of the stress relaxation layer 5 on the upper cladding layer 4 side.

  FIG. 17 is a sectional view showing a manufacturing process of the embodiment shown in FIG. As shown in FIG. 17A, carbon particles 6 are adhered on the tip end surface 15b of the mold 15 corresponding to the stress relieving layer. Press against core layer 3. Thereby, the carbon particles 6 are arranged in the stress relaxation layer 5. The core layer 3 is formed in a region corresponding to the concave portion 15a of the mold 15.

  As shown in FIG. 17C, by removing the mold 15, the surface of the stress relaxation layer 5 contains the carbon particles 6. Next, by forming the upper cladding layer 4 on the core layer 3 and the stress relaxation layer 5, the optical waveguide of the embodiment shown in FIG. 16 is manufactured.

  In this embodiment, as the carbon particles 6, carbon powder having an average particle size of about 1 μm was used.

  When the light leakage of the optical waveguide of this example was evaluated using the apparatus of FIG. 18 in the same manner as in Example 4, a sharp light spot was observed on the screen. It was confirmed that light leakage was prevented. This is probably because the light leaked to the stress relaxation layer was scattered or absorbed by the carbon particles contained in the stress relaxation layer and did not reach the screen.

<Example 6>
An optical waveguide was manufactured in the same manner as in Example 1, except that the thickness of the stress relaxation layer was changed to 0.02 μm, 0.05 μm, 0.1 μm, 0.3 μm, and 10 μm. Each sample of 50 optical waveguides was prepared and observed using an optical microscope. As a result, 18 samples were obtained when the stress relaxation layer had a thickness of 0.02 μm, and 10 samples when the thickness was 0.05 μm. , 0.1 μm, 4 samples, 0.3 μm, 3 samples, and 10 μm, 3 samples, peeling of the upper cladding layer and lower cladding layer was observed.

  From the above results, it is understood that the thickness of the stress relaxation layer is preferably 0.05 μm or more, and more preferably 0.1 μm or more.

  When the height of the core layer is 40 μm and the thickness of the stress relaxation layer is 10 μm or more, 50% or more of the light propagates through the stress relaxation layer while light propagates through the core layer at a distance of 20 mm. I found out. Similarly, when the height of the core layer was 80 μm and the thickness of the stress relaxation layer was 20 μm or more, it was found that 50% or more of the light leaked.

  From the above, when the height of the core layer is H, the thickness t of the stress relaxation layer is preferably in the range of 0.05 μm ≦ t ≦ 0.25H, and more preferably 0.1 μm ≦ t. It can be seen that ≦ 10 μm.

<Example 7>
FIG. 19 is a cross-sectional view of an optical waveguide according to still another embodiment of the present invention, as viewed from the side. As shown in FIG. 19, a protective layer 7 is provided on the end face 3a of the core layer 3 where light enters and / or exits. The protective layer 7 is formed from the same material as the upper clad layer 4. Therefore, the protective layer 7 is formed integrally with the upper clad layer 4.

  20, a protective layer 7 is provided on the end face 3a of the core layer 3 as in the embodiment shown in FIG. In the embodiment shown in FIG. 20, this protective layer 7 is also provided below the substrate 1.

  In the embodiment shown in FIGS. 19 and 20, the thickness of the protective layer 7 is about 50 μm. By covering the end face 3a with the protective layer 7, the light output increased by about 3%.

  It is considered that the formation of the protective layer 7 can prevent moisture from infiltrating into the core layer and adhesion of contaminants, thereby improving light output characteristics.

Example 8
FIG. 21 is a sectional view showing an optical waveguide according to still another embodiment of the present invention. In the embodiment shown in FIG. 21, a groove 8 separating the core layer 3 and the stress relaxation layer 5 is formed in the stress relaxation layer 5 near the core layer 3. The groove 8 is filled with the same material as the upper clad layer 4. Therefore, a material having a lower refractive index than the stress relaxation layer 5 is filled in the groove 8. For this reason, light propagating in the core layer 3 is reflected by the material in the groove 8. Therefore, it is possible to prevent light from leaking from the stress relaxation layer 5.

  The groove 8 can be formed using a dicing saw or the like after forming the core layer 3 and the stress relaxation layer 5 in the same manner as in the first embodiment. After forming the groove 8, the upper cladding layer 4 is formed in the same manner as in the first embodiment, so that the same material as the upper cladding layer 4 is filled in the groove 8.

  In the present embodiment, the groove 8 may be formed with a dicing saw or the like after FIG. 6B without performing the step of forming a convex shape by pressing the mold against the core layer 3 (FIG. 6C). Since the stress relaxation layer 5 and the core layer 3 are completely separated from each other by the groove 8, similar results can be obtained. In this case, the thickness of the core layer is equal to the thickness of the stress relaxation layer.

  Note that, also in the present embodiment, it is preferable that the upper cladding layer 4 is formed in plural times. For example, it is preferable that a predetermined amount of the solution A is applied, and the solution is irradiated with ultraviolet light to cure and fill the groove 8, and then the other half of the solution A is applied and irradiated with ultraviolet light and cured to form. . The same applies to the following embodiments.

<Example 9>
FIG. 22 is a sectional view showing an optical waveguide according to still another embodiment of the present invention.

  In this embodiment, a groove 8 for separating the core layer 3 and the stress relaxation layer 5 is formed in the stress relaxation layer 5 near the core layer 3 in the embodiment shown in FIG. It is filled with material. By forming such a groove 8 as in the eighth embodiment, light leakage from the core layer 3 can be prevented.

  The grooves 8 can be formed using a dicing saw after forming the core layer 3 and the stress relaxation layer 5. By forming the upper cladding layer 4 after forming the groove 8, the same material as the upper cladding layer 4 can be filled in the groove 8.

<Example 10>
FIG. 23 is a sectional view showing an optical waveguide according to still another embodiment of the present invention.

  This embodiment is different from the eighth embodiment shown in FIG. 21 in that an upper substrate 9 is provided on the upper cladding layer 4. As the upper substrate 9, for example, a glass substrate can be used. Others are the same as the eighth embodiment shown in FIG.

<Example 11>
This embodiment is an embodiment in which the upper substrate 9 is provided on the upper cladding layer 4 in the embodiment 9 shown in FIG. Others are the same as the ninth embodiment.

<Example 12>
FIG. 25 is a sectional view showing still another optical waveguide according to the present invention.

  In this embodiment, the grooves 8 are also formed in the upper cladding layer 4 and the upper substrate 9. The groove 8 is filled with the same material 19 as the upper cladding layer 4.

  In the present embodiment, the upper substrate 9 is provided on the upper cladding layer 4, and thereafter, the groove 8 is formed using a dicing saw, and the formed groove 8 is filled with the same material 19 as the upper cladding layer 4. Can be formed.

  Also in this embodiment, light leakage from the core layer 3 can be prevented as in the above embodiment.

<Example 13>
FIG. 26 is a sectional view showing still another embodiment according to the present invention.

  In this embodiment, grooves 8 are also formed in the upper cladding layer 4 and the upper substrate 9. As in Example 12 shown in FIG. 25, after providing the upper substrate 9 on the upper cladding layer 4, a groove 8 is formed using a dicing saw, and the same material 19 as the upper cladding layer 4 is formed in the groove 8. Can be formed.

  Also in this embodiment, the formation of the groove 8 can prevent light from leaking from the core layer 3.

  In the above Examples 8 to 13, the same material as that of the upper cladding layer 4 is exemplified as the material to be filled in the groove 8, but the present invention is not limited to this, and the material of the stress relaxation layer 5 Other materials having a low refractive index may be used.

  In each of the above embodiments, the mold is pressed and molded while the core layer is softened by heating, but the present invention is not limited to this. For example, the core layer may be formed into a predetermined shape by applying a liquid having viscosity and curing the liquid by irradiating ultraviolet rays or the like while pressing the mold against the liquid. For example, a solution is prepared by mixing 3.6 g of MPTMS, 16.8 g of ethanol, 1.6 g of hydrochloric acid (2N), and 11.7 g of PhTES. The solution is left at 30 ° C. for 45 hours, and then heated at 120 ° C. for 20 minutes. The solvent may be removed to form a highly viscous liquid, and this liquid may be used to irradiate ultraviolet rays with the mold pressed as described above to form a predetermined shape.

  Further, in the above embodiment, each layer of the optical waveguide is formed from an organic-inorganic composite, but an optical waveguide in which any one of these layers is formed from an organic-inorganic composite may be used. Alternatively, each layer may be formed from a material other than the organic-inorganic composite.

<Example 14>
FIG. 27 is a perspective view showing an optical transmission system using an optical transceiver module as an optical communication device of the present invention. Optical transmitting / receiving modules 20 and 23 are connected to both ends of the optical fiber 26. The optical transmitting and receiving modules 20 and 23 are provided with Y-branch optical waveguides 27 and 28 formed from the optical waveguides of the first embodiment, respectively. The ends of the optical fiber 26 are connected to the ends of the Y-branch optical waveguides 27 and 28, and the laser diodes 21 and 24 and the photodiodes 22 and 25 are connected to the branch ends of the Y-branch optical waveguides 27 and 28, respectively. Have been. As the optical fiber 26, a glass multimode optical fiber having a core diameter of 50 μm is used.

  When a pulse wave of 100 kHz was incident from the laser diode 21 of the optical transceiver module 20, the pulse wave could be reproduced from the photodiode 25 of the optical transceiver module 23. Also, the signal from the laser diode 24 was able to be received by the photodiode 22. Therefore, it was confirmed that the module functioned as an optical transmission / reception module.

  In the following Examples 15 to 19, in order to prevent the ultraviolet rays irradiated when photocuring the upper clad layer and the like from reaching the lower clad layer, the unevenness is formed at the interface between the stress relaxation layer and the clad layer. Will be described.

<Example 15>
[Core layer (stress relaxation layer) forming solution]
3-methacryloxypropyltriethoxysilane (MPTES): 5.5 ml
Phenyltrimethoxysilane (PhTMS): 5.8 ml
Aqueous solution containing hydrochloric acid as reaction catalyst (concentration 2N hydrochloric acid): 1.65 ml
Ethanol: 20.5 ml
After mixing, MPTES and PhTMS were hydrolyzed and polycondensed by standing for 24 hours. 4 ml of the obtained polycondensate was placed in a Petri dish, 10 mg of 1-hydroxy-cyclohexyl-phenyl-ketone was dissolved as a polymerization initiator, and the mixture was heated at 100 ° C. to evaporate ethanol to remove about 1 g. A viscous liquid was obtained. Trimethylethoxysilane: 3 ml in 1 g of this viscous liquid
Trifluoroacetic anhydride: 0.8 ml
Was mixed and left for 24 hours, and then heated and dried at 100 ° C., thereby removing excess trimethylethoxysilane and trifluoroacetic anhydride by evaporation to prepare a solution D. Using this solution D, a core layer and a stress relaxation layer were formed.

(Clad layer forming solution)
Solution E was prepared in the same manner as the solution for forming the core layer (stress relaxation layer), except that the amount of the PhTMS was 4.5 ml. Using this solution E, an upper clad layer and a lower clad layer were formed.

The refractive index and the storage modulus of the organic-inorganic composite prepared from the solutions D and E are as follows.
Solution D: refractive index 1.519, storage modulus about 27000 kgf / cm ²
Solution E: refractive index 1.515, storage elastic modulus about 28000 kgf / cm ²

  FIG. 31 is a cross-sectional view illustrating the optical waveguide of this example. As shown in FIG. 31, unevenness 5a is formed at the interface between stress relaxation layer 5 and upper cladding layer 4. By forming such irregularities 5a, the stress relaxation layer 5 itself can absorb ultraviolet rays and can prevent the ultraviolet rays from reaching the lower cladding layer 2. For this reason, the amount of ultraviolet irradiation when the upper clad layer 4 or the core layer 3 is photocured can be set with high reproducibility and high accuracy.

The unevenness 5a is a stripe-shaped unevenness as shown in FIG. 28, and has a shape in which semi-cylindrical columns having a radius of 0.3 μm are arranged in stripes at intervals of 0.5 μm. The unevenness 5a corresponds to a surface roughness _{Rmax of} 0.3 μm.

  FIG. 32 and FIG. 33 are cross-sectional views for explaining the steps of manufacturing the optical waveguide of the embodiment shown in FIG.

  First, as shown in FIG. 32 (a), a solution E is dropped on the glass substrate 1, and while pressing a silicone rubber mold 13, an ultraviolet lamp having a central wavelength of 365 nm and an intensity of 100 mW is used. The lower clad layer 2 was formed by irradiating with ultraviolet rays for 30 minutes to cure. The mold 13 has a convex portion 13a, and the convex portion 13a has a width of 7 μm and a height of 7 μm. Therefore, the core layer formed by the convex portions 13a becomes a so-called single mode optical waveguide in the optical communication wavelength band of 1300 nm or 1550 nm.

  Next, as shown in FIG. 32 (b), the solution D is poured into the groove of the lower cladding layer 2, and as shown in FIG. The core layer 3 and the stress relaxation layer 5 were formed by irradiating ultraviolet rays for 30 minutes using an ultraviolet lamp having a wavelength and hardening. The average thickness of the stress relaxation layer 5 is 0.5 μm. As shown in FIG. 32 (b), the mold 14 has irregularities 14a corresponding to the irregularities 5a of the stress relaxation layer.

  Next, as shown in FIG. 33 (d), the mold 14 is removed, the solution E is dropped on the core layer 3 and the stress relaxation layer 5, and the upper glass substrate 9 is placed thereon, and in this state, Using an ultraviolet lamp having a central wavelength of 365 nm, ultraviolet rays were irradiated for 30 minutes to cure, thereby forming the upper cladding layer 4.

  As described above, 50 samples of the optical waveguide of the example shown in FIG. 31 were manufactured, and the refractive index of the upper cladding layer was measured. The refractive index of the upper cladding layer was measured using a prism coupler device after removing the upper glass substrate. As a result, the variation in the refractive index of the upper cladding layer was ± 0.007%.

  For comparison, 50 samples of an optical waveguide were prepared in the same manner as in the above example except that no unevenness was formed on the surface of the stress relaxation layer, and the refractive index of the upper cladding layer was measured. As a result, in this comparative sample, the variation in the refractive index of the upper cladding layer was ± 0.015%.

  From the above, it can be seen that by forming irregularities on the surface of the stress relaxation layer, the refractive index of the upper cladding layer can be controlled with high accuracy.

<Example 16>
An optical waveguide having the structure shown in FIG. 34 was manufactured in the same manner as in Example 15 above. In the embodiment shown in FIG. 34, irregularities 5b are formed at the interface between lower cladding layer 2 and stress relaxation layer 5. The unevenness 5b has the same shape as that of the fifteenth embodiment. The unevenness 5b can be formed on the surface of the lower cladding layer 2 by forming an uneven shape in a corresponding portion of the mold 13 shown in FIG. Also in this example, it was confirmed that the refractive index of the upper cladding layer 4 could be controlled as in the case of Example 15 described above.

<Example 17>
An optical waveguide shown in FIG. 35 was manufactured in the same manner as in the above-described Examples 15 and 16. In the embodiment shown in FIG. 35, unevenness 5a is formed at the interface between stress relaxation layer 5 and upper clad layer 4, and unevenness 5b is formed at the interface between stress relaxation layer 5 and lower clad layer 2. . By forming the irregularities at both interfaces in this way, the variation in the refractive index of the upper cladding layer 4 was further improved and could be reduced to ± 0.006%.

<Example 18>
An optical waveguide was formed in the same manner as in Example 15, except that the uneven shape formed on the stress relaxation layer was an island shape shown in FIG. The size of the islands in the unevenness is 0.3 μm in width, 0.5 μm in depth, and 0.5 μm in height, and the distance between adjacent islands is 0.5 μm. This unevenness corresponds to a surface roughness R _{max of} 0.5 μm.

  In this example, the variation in the refractive index of the upper cladding layer could be reduced to ± 0.006%.

<Example 19>
An optical waveguide was manufactured in the same manner as in Example 15, except that the unevenness formed on the stress relaxation layer was made into an island shape as shown in FIG. The size of one island is 0.3 μm in width, 0.3 μm in depth and 0.5 μm in height, and the density at which the islands are dispersed is such that the area of the island surface is about 40 times the surface area of the entire stress relaxation layer. %. This unevenness corresponds to a surface roughness R _{max of} 0.5 μm.

  In this example, the variation in the refractive index of the upper cladding layer could be reduced to ± 0.007%.

<Example 20>
[Core layer (stress relaxation layer) forming solution]
3-methacryloxypropyltriethoxysilane (MPTES): 4.0 ml
Diphenyldiethoxysilane (DPhDES): 3.3 ml
Aqueous solution containing hydrochloric acid as reaction catalyst (concentration 2N hydrochloric acid): 1.18 ml
Ethanol: 15ml
After mixing, MPTES and DPhDES were hydrolyzed and polycondensed by standing for 24 hours. 4 ml of the obtained polycondensate was placed in a Petri dish, 10 mg of 1-hydroxy-cyclohexyl-phenyl-ketone was dissolved as a polymerization initiator, and the mixture was heated at 100 ° C. to remove ethanol by evaporation. A viscous liquid was obtained. Trimethylethoxysilane: 3 ml in 1 g of this viscous liquid
Trifluoroacetic anhydride: 0.8 ml
Was mixed and allowed to stand for 24 hours, and then heated and dried at 100 ° C. to remove excess trimethylethoxysilane and trifluoroacetic anhydride by evaporation, thereby preparing a solution F. Using this solution F, a core layer and a stress relaxation layer were formed.

(Clad layer forming solution)
A solution G was prepared in the same manner as the solution for forming the core layer (stress relaxation layer), except that the amount of DPhDES was changed to 2.5 ml. Using this solution G, an upper clad layer and a lower clad layer were formed.

The refractive index and the storage elastic modulus of the organic-inorganic composite prepared from the solutions F and G are as follows.
Solution F: refractive index 1.547, storage modulus about 25,000 kgf / cm ²
Solution G: refractive index 1.542, storage elastic modulus about 26000 kgf / cm ²

  An optical waveguide was produced in the same manner as in Example 19, except that the above-mentioned solutions were used as a solution for forming a core layer (stress relaxation layer) and a solution for forming a cladding layer.

  In this example, the variation in the refractive index of the upper clad could be reduced to ± 0.007.

1 is a cross-sectional view showing an optical waveguide according to one embodiment of the present invention. FIG. 11 is a cross-sectional view showing an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. The figure which shows the example of the cross-sectional shape of the core layer in this invention. FIG. 4 is a diagram showing a manufacturing process of the embodiment shown in FIG. 3. FIG. 4 is a diagram showing a manufacturing process of the embodiment shown in FIG. 3. FIG. 4 is a diagram showing a manufacturing process of the embodiment shown in FIG. 3. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 10 is a sectional view showing the manufacturing process of the embodiment shown in FIG. 9. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 12 is a diagram showing a manufacturing process of the embodiment shown in FIG. 11. FIG. 12 is a diagram showing a manufacturing process of the embodiment shown in FIG. 11. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 15 is a sectional view showing a manufacturing step of the embodiment shown in FIG. 14. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 17 is a sectional view showing the manufacturing process of the example shown in FIG. 16. FIG. 2 is a schematic view showing an apparatus for performing a light propagation test on an optical waveguide according to an embodiment of the present invention. FIG. 11 is a side sectional view showing an optical waveguide according to still another embodiment according to the present invention. FIG. 11 is a side sectional view showing an optical waveguide according to still another embodiment according to the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 2 is a perspective view showing an optical transmission system using an optical transmission / reception module. The perspective view which shows an example of the uneven | corrugated shape formed in the interface of a stress relaxation layer and an upper clad layer or a lower clad layer. FIG. 9 is a perspective view showing another example of the uneven shape formed at the interface between the stress relaxation layer and the upper clad layer or the lower clad layer. FIG. 13 is a perspective view showing still another example of the uneven shape formed at the interface between the stress relaxation layer and the upper clad layer or the lower clad layer. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 32 is a sectional view showing a step of manufacturing the optical waveguide of the example shown in FIG. 31. FIG. 32 is a sectional view showing a step of manufacturing the optical waveguide of the example shown in FIG. 31. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention. FIG. 13 is a cross-sectional view illustrating an optical waveguide according to another embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Lower clad layer 3 ... Core layer 4 ... Upper clad layer 5 ... Stress relaxation layer 6 ... Carbon particles 7 ... Protective layer 8 ... Groove 9 ... Upper substrate 10 ... Mold 11 ... Dicing saw 12 ... Mask 13, 14 , 15 ... type 16 ... optical fiber 17 ... translucent screen 18 ... laser beam 20, 23 ... optical transmitting and receiving module 21, 24 ... laser diode 22, 25 ... photodiode 26 ... optical fiber 27, 28 ... Y branch optical waveguide

Claims (26)

A core layer serving as a light propagation region, comprising an upper clad layer and a lower clad layer covering the periphery of the core layer, wherein the upper clad layer is an optical waveguide formed with shrinkage in volume,
At least a part of a region where the upper clad layer and the lower clad layer are in contact with each other, between the upper clad layer and the lower clad layer, a stress relieving layer that relieves stress generated due to volume shrinkage of the upper clad layer. An optical waveguide, which is provided.   The optical waveguide according to claim 1, wherein the upper clad layer is formed of an organic-inorganic composite.   The optical waveguide according to claim 1, wherein the stress relaxation layer is formed of a material having a lower storage elastic modulus than a material of the upper cladding layer. The optical waveguide according to claim 3, the storage modulus of the stress relaxing layer, characterized in that at 100000kgf / cm ² or less at 30 ° C..   The optical waveguide according to claim 1, wherein the stress relaxation layer is formed of an organic-inorganic composite.   The optical waveguide according to any one of claims 1 to 5, wherein the core layer and / or the lower clad layer are formed of an organic-inorganic composite.   The optical waveguide according to claim 2, 5 or 6, wherein the organic-inorganic composite is formed from an organic polymer and a metal alkoxide.   7. The optical waveguide according to claim 2, wherein the organic-inorganic composite is formed from at least one kind of metal alkoxide.   The optical waveguide according to any one of claims 1 to 8, wherein the lower cladding layer is a substrate.   The optical waveguide according to claim 1, wherein the lower cladding layer is formed on a substrate.   The optical waveguide according to claim 1, wherein an upper substrate is provided on the upper clad layer.   The optical waveguide according to any one of claims 1 to 11, wherein the upper clad layer is formed by stacking a plurality of layers.   The thickness t of the stress relaxation layer is within a range satisfying 0.05 μm ≦ t ≦ 0.25H, where H is the thickness of the core layer and t is the thickness of the stress relaxation layer. 13. The optical waveguide according to any one of 1 to 12.   The optical waveguide according to any one of claims 1 to 13, wherein the stress relaxation layer is formed of a material having a refractive index not higher than a material of the core layer.   The optical waveguide according to any one of claims 1 to 13, wherein the stress relaxation layer is formed of the same material as the core layer.   The optical waveguide according to claim 15, wherein the stress relaxation layer is formed integrally with the core layer.   A groove separating the core layer and the stress relaxation layer is formed in the stress relaxation layer near the core layer, and the groove is filled with a material having a lower refractive index than the material of the stress relaxation layer. 17. The optical waveguide according to claim 15, wherein   The optical waveguide according to claim 17, wherein the groove is also formed in the lower cladding layer.   The optical waveguide according to claim 18, wherein the groove is formed so as to reach the substrate through the lower clad layer.   The said upper board | substrate is provided on the said upper clad layer, The said groove | channel is formed also in the said upper board | substrate and the said upper clad layer, The Claims any one of Claims 17-19 characterized by the above-mentioned. Optical waveguide.   The optical waveguide according to any one of claims 1 to 16, wherein an unevenness is formed at an interface between the stress relaxation layer and at least one of the upper clad layer and the lower clad layer.   22. The optical waveguide according to claim 1, wherein the stress relaxation layer contains a light absorbing and / or scattering component.   The optical waveguide according to claim 22, wherein the light absorbing and / or scattering component is a carbon particle.   The optical waveguide according to any one of claims 1 to 23, wherein an end face of the core layer from which light enters and / or exits is covered with a protective layer made of a transparent material.   25. The optical waveguide according to claim 1, wherein a corner of the core layer has a rounded shape. An optical communication device using the optical waveguide according to any one of claims 1 to 25 as a medium for transmitting and / or receiving an optical signal.

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