Composite PCB

Abstract

To provide a composite substrate which has a high light closing effect in an optical waveguide and is highly reliable.SOLUTION: A composite substrate 100 includes: an optical waveguide substrate 10 including a first optical waveguide; a support substrate 40 for supporting the optical waveguide substrate 10; a joint layer 20 provided between the optical waveguide substrate 10 and the supporting substrate 40; and a gap part 21 provided between the joint layers 20 in a direction perpendicular to the direction in which the first optical waveguide is extended. The optical waveguide substrate 10 and the supporting substrate 40 are joined to each other by the joint layer 20 and at least a part of the gap part 21 is overlapped with the first optical waveguide when is viewed from the thickness direction of the optical waveguide substrate 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composite substrate for use in an optical element. [Background technology]

[0002] A conventional technique for forming an optical waveguide is known, in which a composite substrate is formed by bonding two substrates, one of which is thinned and then ridge-processed. For example, Patent Document 1 describes a waveguide substrate and a base substrate, which are bonded together, with a non-bonded region at the bonding surface between the waveguide substrate and the base substrate, and this non-bonded region is filled with ultraviolet-curable resin. This creates a refractive index difference between the non-bonded region and the optical waveguide, thereby achieving a sufficient light confinement effect in the optical waveguide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-250352 Summary of the Invention [Problem to be solved by the invention]

[0004] The structure of Patent Document 1 has the problem of low long-term reliability because the resin filled in the non-bonded region may deform due to aging, which may affect the bond between the waveguide substrate and the base substrate. Also, depending on the resin material, there is a risk that some of the light propagating through the optical waveguide may leak into the resin, which may result in a deterioration of the light propagation characteristics.

[0005] The present invention has been made in view of the above, and a main object of the present invention is to realize a highly reliable composite substrate that has a high light confinement effect in an optical waveguide. [Means for solving the problem]

[0006] A composite substrate according to the present invention includes a waveguide substrate including a first optical waveguide, a support substrate supporting the waveguide substrate, a bonding layer provided between the waveguide substrate and the support substrate, and a gap provided between the bonding layers in a direction perpendicular to an extending direction of the first optical waveguide. an intermediate layer disposed between the bonding layer and the support substrate; the waveguide substrate and the support substrate are bonded to each other via the bonding layer, and at least a portion of the void portion overlaps with the first optical waveguide when viewed in a thickness direction of the waveguide substrate. the intermediate layer includes a second optical waveguide disposed opposite the first optical waveguide with the gap therebetween. . [Effects of the Invention]

[0007] According to the present invention, it is possible to realize a highly reliable composite substrate that has a high light confinement effect in an optical waveguide. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a first embodiment of the present invention. [Figure 2] 2A to 2C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a first embodiment of the present invention. [Figure 3] 2A to 2C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a first embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a second embodiment of the present invention. [Figure 5] 5A to 5C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a second embodiment of the present invention. [Figure 6] 5A to 5C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a third embodiment of the present invention. [Figure 8] FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a fourth embodiment of the present invention. [Figure 9] FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0010] (First embodiment) 1 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a first embodiment of the present invention. A composite substrate 100 for optical elements in this embodiment has a structure in which a waveguide substrate 10 is bonded to a support substrate 40 via a bonding layer 20 and an intermediate layer 30.

[0011] The waveguide substrate 10 is a substrate including a first optical waveguide, and is processed (ridge processing) to form a ridge portion 11 corresponding to the first optical waveguide by providing a step in a portion of the substrate so that the ridge portion 11 is thicker than the other portions. Examples of materials used for the waveguide substrate 10 include LN (LiNbO3: lithium niobate), LT (LiTaO3: lithium tantalate), and Si. When the wavelength of light passing through the first optical waveguide is 1.55 μm, the thickness of the waveguide substrate 10, including the ridge portion 11, is, for example, approximately 300 nm to 5 μm. More preferably, the thickness of the waveguide substrate 10 is determined to be within a range that satisfies the following formula (1), where λ (μm) is the wavelength of light passing through the first optical waveguide, and t (μm) is the thickness of the waveguide substrate 10 including the ridge portion 11. λ / 5≦t≦4×λ (1)

[0012] The bonding layer 20 is a layer that bonds the waveguide substrate 10 to the support substrate 40, and is provided between the waveguide substrate 10 and the support substrate 40. The waveguide substrate 10 is directly bonded to the support substrate 40 via the bonding layer 20, which has a bonding surface suitable for bonding, thereby enabling strong bonding to the support substrate 40. Examples of materials that can be used for the bonding layer 20 include amorphous Si, Ta2O5, and Al2O3. The thickness of the bonding layer 20 is, for example, 1 nm to 50 nm.

[0013] Between the waveguide substrate 10 and the support substrate 40, there is a gap 21 where the bonding layer 20 is not formed. The gap 21 is provided between the bonding layers 20 in a direction (the left-right direction in FIG. 1 ) perpendicular to the extension direction of the ridge portion 11, which is the first optical waveguide. When the ridge portion 11 of the waveguide substrate 10 is viewed in the thickness direction of the composite substrate 100, the gap 21 is provided so as to occupy an area at least larger than the area occupied by the ridge portion 11. That is, at least a portion of the gap 21 overlaps with the ridge portion 11 when viewed in the thickness direction of the waveguide substrate 10. This creates a refractive index difference between the ridge portion 11, which functions as the first optical waveguide, and the gap 21, thereby achieving an optical confinement effect in the ridge portion 11. The thickness of the gap 21 is equal to that of the bonding layer 20, and is, for example, 1 nm to 50 nm. The width of the gap 21 is, for example, 10 μm.

[0014] 1, if the thickness of the waveguide substrate 10 including the ridge portion 11 is t (μm) and the width of the void 21 is w (μm), then t and w preferably satisfy the relationship of the following formula (2), and more preferably the relationship of formula (3). This effectively prevents the waveguide substrate 10 from deforming toward the void 21 during the thin-plate processing step described below due to the presence of the void 21, or from deforming toward the opposite side of the void 21 due to expansion of air in the void 21 in a low-pressure environment. w≦30×t (2) w≦20×t (3)

[0015] On the other hand, in order for the voids 21 to fully exert the light trapping effect, it is preferable that the width w of the voids 21 is at least 5 μm or more.

[0016] The intermediate layer 30 is disposed between the bonding layer 20 and the support substrate 40, and is made of, for example, an amorphous material such as SiO2. A second optical waveguide 31 made of, for example, Si or SiN is provided inside the intermediate layer 30. This second optical waveguide 31 is disposed opposite the ridge portion 11 of the waveguide substrate 10, with a gap portion 21 sandwiched therebetween.

[0017] The second optical waveguide 31 may be formed, for example, buried inside the intermediate layer 30. In this case, the thickness of the intermediate layer 30 between the second optical waveguide 31 and the gap 21 is, for example, 2 μm or less. Alternatively, the second optical waveguide 31 may be formed, for example, in a state where at least a part of it is exposed on the surface of the intermediate layer 30 facing the gap 21. In this case, the thickness of the intermediate layer 30 between the second optical waveguide 31 and the gap 21 is zero.

[0018] Here, in order to achieve the desired optical coupling between light passing through the first optical waveguide (ridge portion 11) of the waveguide substrate 10 and light passing through the second optical waveguide 31 of the intermediate layer 30, it is preferable that the distance between these optical waveguides is, for example, about 500 nm or less. The thickness of the void portion 21 (thickness of the bonding layer 20) and the thickness of the intermediate layer 30 between the second optical waveguide 31 and the void portion 21 can be set so as to satisfy this condition. Furthermore, it is preferable that the distance from the interface between the intermediate layer 30 and the support substrate 40 to the second optical waveguide 31 be, for example, 1 μm or more.

[0019] The bonding layer 20 and the intermediate layer 30 can be formed by any appropriate method. For example, they can be formed by physical vapor deposition such as sputtering, vacuum deposition, or ion beam assisted deposition (IAD), chemical vapor deposition, or atomic layer deposition (ALD). The bonding layer 20 and the intermediate layer 30 can be formed at, for example, room temperature (25°C) to 300°C. Furthermore, the voids 21 in the bonding layer 20 can be formed by, for example, removing a portion of the bonding layer 20 by etching.

[0020] The support substrate 40 supports the waveguide substrate 10. Any appropriate substrate can be used as the support substrate 40. The support substrate 40 may be made of a single crystal or a polycrystalline material. It may also be made of a metal. The material constituting the support substrate 40 is preferably selected from the group consisting of silicon, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), and brass. The thickness of the support substrate 40 is, for example, 0.3 to 1 mm, but any other appropriate thickness can be adopted.

[0021] The silicon may be single crystal silicon, polycrystalline silicon, or high resistance silicon, and the support substrate 40 may be SOI (Silicon on Insulator).

[0022] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and has a composition represented by, for example, Si6-wAlwOwN8-w. Specifically, the sialon has a composition in which alumina is mixed into silicon nitride, where w represents the alumina mixing ratio. w is preferably 0.5 or more and 4.0 or less.

[0023] Typically, the sapphire is a single crystal having a composition of Al2O3, and the alumina is a polycrystalline material having a composition of Al2O3. The alumina is preferably translucent alumina.

[0024] Typically, the cordierite is a ceramic having a composition of 2MgO·2Al2O3·5SiO2, and the mullite is a ceramic having a composition in the range of 3Al2O3·2SiO2 to 2Al2O3·SiO2.

[0025] The composite substrate 100 described above is used, for example, as an optical element for optical communications that utilizes optical coupling between two optical waveguides. Although not shown, the composite substrate 100 may further include any layer. The type, function, number, combination, arrangement, etc. of such layers can be appropriately set depending on the purpose.

[0026] The composite substrate 100 can be manufactured in any appropriate shape. In one embodiment, the composite substrate 100 can be manufactured in the form of a so-called wafer. The size of the composite substrate 100 can be appropriately set depending on the purpose, for example, with the diameter of the wafer (substrate) being 50 mm to 150 mm.

[0027] 2 and 3 are diagrams showing an example of a manufacturing process for the composite substrate according to the first embodiment of the present invention.

[0028] 2(a) shows the preparation step in the manufacturing process of the composite substrate 100. In this step, an LN substrate 10A having a thickness of, for example, 0.3 mm is prepared. As mentioned above, an LT substrate or a Si substrate can also be used instead of the LN substrate, and in the following description, these will all be referred to as the "LN substrate 10A."

[0029] 2(b) shows the step of forming the bonding layer 20 in the manufacturing process of the composite substrate 100. In this step, the bonding layer 20 is formed by depositing an amorphous Si film to a thickness of, for example, 30 nm on the surface of the LN substrate 10A prepared in the preparation step of FIG.

[0030] 2(c) shows a step of removing the bonding layer 20 in the manufacturing process of the composite substrate 100. In this step, a part of the bonding layer 20 formed in the film forming step of FIG. 2(b) is removed by etching.

[0031] FIG. 2(d) shows the bonding step in the manufacturing process for the composite substrate 100. In this step, an intermediate layer 30 is first formed on a support substrate 40, and a second optical waveguide 31 is formed within the intermediate layer 30. For example, a support substrate 40 having an amorphous SiO2 layer formed thereon is prepared. After forming a Si or SiN film on the support substrate 40, the Si or SiN film is removed by etching except for the portion where the second optical waveguide 31 will be formed. Further, an amorphous SiO2 layer is entirely formed on the support substrate 40 on which the second optical waveguide 31 has been formed, thereby forming the intermediate layer 30. This allows the preparation of a support substrate 40 on which the second optical waveguide 31 has been formed within the intermediate layer 30. By performing the same steps as those shown in FIGS. 2(b) and 2(c) on this support substrate 40, a bonding layer 20 is formed on the intermediate layer 30 and a portion of the bonding layer 20 is then removed. 2(c) and the support substrate 40 obtained in the above process, the bonding layers 20 of the LN substrate 10A are activated by irradiating them with FAB (Fast Atom Beam), and the bonding layers 20 are then bonded together to form the composite substrate 100. In this bonding, the substrates removed by etching are bonded together using alignment marks so that they are aligned. The bonding accuracy is approximately ±2 μm.

[0032] 2(d), the composite substrate 100 may be heated to a predetermined temperature, for example, about 400° C. In this way, the optical propagation characteristics of the optical waveguide in the waveguide substrate 10 can be improved while maintaining the bonding strength of the bonding layer 20.

[0033] Fig. 3(e) shows the composite substrate 100 obtained after the bonding step of Fig. 2(d). In this composite substrate 100, the portions removed from the bonding layer 20 on the LN substrate 10A side and the bonding layer 20 on the support substrate 40 side are integrated by the bonding step, thereby forming a gap 21 between the LN substrate 10A and the intermediate layer 30, as shown in Fig. 3(e).

[0034] Fig. 3(f) shows a thinning step in the manufacturing process of composite substrate 100. In this step, LN substrate 10A is polished to a predetermined thickness to thin composite substrate 100 after the bonding step shown in Fig. 3(e). For example, LN substrate 10A can be polished to a thin plate using grinding, CMP (Chemical Mechanical Polish), surface planarization using a gas cluster ion beam, or the like.

[0035] 3(g) shows the ridge processing step in the manufacturing process of the composite substrate 100. In this step, the LN substrate 10A thinned in the thinning process of FIG. 3(f) is further subjected to the above-mentioned ridge processing to form a ridge portion 11 that functions as an optical waveguide, thereby forming a waveguide substrate 10 including a first optical waveguide. For example, the ridge processing can be performed by processing using laser light or dry etching such as RIE (Reactive Ion Etching).

[0036] Through the above steps, composite substrate 100 having the structure shown in FIG. 1 is manufactured.

[0037] (Second embodiment) 4 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a second embodiment of the present invention. A composite substrate 110 for optical elements according to this embodiment has a structure in which a cladding layer 50 is further disposed between the waveguide substrate 10 and the bonding layer 20, compared to the composite substrate 100 shown in FIG. 1 described in the first embodiment.

[0038] The cladding layer 50 is provided to protect the waveguide substrate 10 from irradiation with the FAB when the activation process of the bonding layer 20 is performed in the bonding step described with reference to Fig. 2(d). The cladding layer 50 is made of, for example, an amorphous material such as SiO2, similar to the intermediate layer 30. The thickness of the cladding layer 50 is, for example, about 10 nm.

[0039] 4, where t (μm) is the total thickness of the waveguide substrate 10 including the ridge portion 11 and the cladding layer 50, and w (μm) is the width of the void 21, t and w preferably satisfy the relationship of the aforementioned formula (2), and more preferably satisfy the relationship of formula (3). This effectively prevents the waveguide substrate 10 and the cladding layer 50 from deforming toward the void 21 during the thinning process due to the presence of the void 21, or from deforming toward the opposite side of the void 21 due to expansion of air in the void 21 in a low-pressure environment, as with the first embodiment. Furthermore, as with the first embodiment, the width w of the void 21 is preferably at least 5 μm or greater in order for the void 21 to fully exert its light-confining effect.

[0040] 5 and 6 are diagrams showing an example of a manufacturing process for a composite substrate according to the second embodiment of the present invention.

[0041] 5(a) shows a preparation step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 2(a) described in the first embodiment, an LN substrate 10A having a thickness of, for example, 0.3 mm is prepared, and an amorphous SiO film having a thickness of, for example, 10 nm is formed on the surface of this LN substrate 10A, thereby producing an LN substrate 10A having a cladding layer 50.

[0042] Fig. 5(b) shows a film-forming step of the bonding layer 20 in the manufacturing process of the composite substrate 110. In this step, the bonding layer 20 is formed by depositing amorphous Si to a thickness of, for example, 30 nm on the surface of the cladding layer 50 formed on the LN substrate 10A prepared in the preparation step of Fig. 5(a) using a method similar to the step of Fig. 2(b) described in the first embodiment.

[0043] Fig. 5(c) shows the step of removing the bonding layer 20 in the manufacturing process of the composite substrate 110. In this step, similar to the step of Fig. 2(c) described in the first embodiment, a part of the bonding layer 20 formed in the film formation step of Fig. 5(b) is removed by etching.

[0044] FIG. 5(d) shows the bonding step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 2(d) described in the first embodiment, an intermediate layer 30 is first formed on a support substrate 40, and a second optical waveguide 31 is formed inside the intermediate layer 30. A bonding layer 20 is then formed on the intermediate layer 30 of the support substrate 40, and a portion of the layer is then removed. The LN substrate 10A obtained in the removal step of FIG. 5(c) and the support substrate 40 obtained in the above step are then activated, and the bonding layers 20 are then bonded together to form the composite substrate 110. In this bonding, the substrates removed by etching are bonded together via alignment marks so that they are aligned. The bonding accuracy can be approximately ±2 μm.

[0045] Fig. 6(e) shows the composite substrate 110 obtained after the bonding step of Fig. 5(d). In this composite substrate 110, the portions removed from the bonding layer 20 on the LN substrate 10A side and the bonding layer 20 on the support substrate 40 side are integrated by the bonding step, so that a void 21 is formed between the cladding layer 50 and the intermediate layer 30, as shown in Fig. 6(e).

[0046] Fig. 6(f) shows a thinning process in the manufacturing process of the composite substrate 110. In this process, similar to the process of Fig. 3(f) described in the first embodiment, the LN substrate 10A of the composite substrate 110 after the bonding process shown in Fig. 6(e) is polished to a predetermined thickness to be thinned.

[0047] Fig. 6(g) shows a ridge processing step in the manufacturing process of the composite substrate 110. In this step, similar to the step of Fig. 3(g) described in the first embodiment, ridge processing is performed on the LN substrate 10A thinned in the thinning processing step of Fig. 6(f), to form a ridge portion 11 that functions as an optical waveguide, thereby forming a waveguide substrate 10 including a first optical waveguide.

[0048] Through the above steps, composite substrate 110 having the structure shown in FIG. 4 is manufactured.

[0049] (Third embodiment) 7 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a third embodiment of the present invention. A composite substrate 120 for optical elements according to this embodiment differs from the composite substrate 100 of the first embodiment shown in FIG. 1 in that the intermediate layer 30 is not provided between the waveguide substrate 10 and the support substrate 40, and the waveguide substrate 10 is bonded to the support substrate 40 via a bonding layer 20.

[0050] In this embodiment, as in the first embodiment, if the thickness of the waveguide substrate 10 including the ridge portion 11 is t (μm) and the width of the void portion 21 is w (μm), then t and w preferably satisfy the relationship of the above-mentioned formula (2), and more preferably satisfy the relationship of formula (3). Furthermore, in order for the void portion 21 to fully exert its light trapping effect, the width w of the void portion 21 is preferably at least 5 μm or more.

[0051] 2(a) to 2(c) described in the first embodiment are performed on composite substrate 120 of this embodiment, and then in the step of Fig. 2(d), intermediate layer 30 is not formed, but bonding layer 20 is formed on support substrate 40 and a portion of it is removed, and the bonding layers 20 formed on LN substrate 10A and support substrate 40 are bonded to each other. By performing the steps of Fig. 3 on composite substrate 120 thus formed, composite substrate 120 having the structure shown in Fig. 7 can be manufactured.

[0052] (Fourth embodiment) 8 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a fourth embodiment of the present invention. A composite substrate 130 for optical elements according to this embodiment has a structure in which a cladding layer 50 is further disposed between the waveguide substrate 10 and the bonding layer 20, compared to the composite substrate 120 shown in FIG. 7 described in the third embodiment.

[0053] In this embodiment, as in the second embodiment, if the total thickness of the waveguide substrate 10 including the ridge portion 11 and the cladding layer 50 is t (μm) and the width of the void 21 is w (μm), then t and w preferably satisfy the relationship of the above-mentioned formula (2), and more preferably satisfy the relationship of formula (3). Furthermore, in order for the void 21 to fully exert its light trapping effect, the width w of the void 21 is preferably at least 5 μm or more.

[0054] 5(a) to 5(c) described in the second embodiment are performed on composite substrate 130 of this embodiment, and then in the step of Fig. 5(d), intermediate layer 30 is not formed, but bonding layer 20 is formed on support substrate 40 and a portion of it is removed, and bonding layers 20 formed on LN substrate 10A and support substrate 40 are bonded to each other. By performing the steps of Fig. 6 on composite substrate 130 thus formed, composite substrate 130 having the structure shown in Fig. 8 can be manufactured.

[0055] (Variation) FIG. 9 is a schematic cross-sectional view showing the general configuration of a composite substrate according to a modified example of the present invention. In the composite substrates 100 and 110 described in the first and second embodiments, respectively, the surface of the waveguide substrate 10 may be covered with a cladding film 60, as shown in FIGS. 9(a) and 9(b), respectively. The cladding film 60 is formed using, for example, an amorphous SiO2 material, similar to the intermediate layer 30 and the cladding layer 50. For example, the cladding film 60 can be formed by depositing SiO2 on the surface of the waveguide substrate 10 using a technique such as sputtering. In this case, it is preferable to employ a technique that allows the cladding film 60 to be deposited also on the sidewalls of the ridge portion 11.

[0056] 9(a) and 9(b) show examples in which a clad film 60 is formed on the surface of the waveguide substrate 10 in the composite substrates 100 and 110, respectively, but a clad film 60 may also be formed on the surface of the waveguide substrate 10 in the composite substrates 120 and 130 described in the third and fourth embodiments, respectively.

[0057] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0058] (1) The composite substrates 100 to 130 each include a waveguide substrate 10 including a first optical waveguide, a support substrate 40 supporting the waveguide substrate 10, a bonding layer 20 provided between the waveguide substrate 10 and the support substrate 40, and a void 21 provided between the bonding layer 20 in a direction perpendicular to the extension direction of the first optical waveguide. The waveguide substrate 10 and the support substrate 40 are bonded to each other via the bonding layer 20, and at least a portion of the void 21 overlaps with the first optical waveguide when viewed in the thickness direction of the waveguide substrate 10. This configuration makes it possible to realize a composite substrate that has a high optical confinement effect in the optical waveguide and is highly reliable.

[0059] (2) The composite substrates 100, 110 have an intermediate layer 30 disposed between the bonding layer 20 and the support substrate 40. The intermediate layer 30 also includes a second optical waveguide 31 disposed opposite the first optical waveguide of the waveguide substrate 10 with a gap 21 sandwiched therebetween. This makes it possible to realize an optical element for optical communication that utilizes optical coupling between two optical waveguides.

[0060] (3) The intermediate layer 30 can be made of SiO2, and the second optical waveguide 31 can be made of either Si or SiN. In this way, the second optical waveguide 31 can have excellent optical propagation characteristics.

[0061] (4) The second optical waveguide 31 is formed so as to be buried inside the intermediate layer 30 or so as to have a portion of its surface exposed to the void 21, and the thickness of the intermediate layer 30 between the second optical waveguide 31 and the void 21 can be 2 μm or less. In this way, desired optical coupling can be achieved between light passing through the first optical waveguide of the waveguide substrate 10 and light passing through the second optical waveguide 31 of the intermediate layer 30.

[0062] (5) The waveguide substrate 10 has a ridge portion 11 that corresponds to the first optical waveguide of the waveguide substrate 10 and is thicker than other portions. In the composite substrates 100 and 120, if the thickness of the waveguide substrate 10 including the ridge portion 11 is t (μm) and the width of the void portion 21 is w (μm), it is preferable that t and w satisfy the formula "5 μm≦w≦30×t." This can prevent deformation of the waveguide substrate 10.

[0063] (6) The composite substrates 110 and 130 have a cladding layer 50 disposed between the waveguide substrate 10 and the bonding layer 20. This configuration allows the waveguide substrate 10 to be protected when the bonding layer 20 is activated.

[0064] (7) The cladding layer 50 can be made of SiO2. In this way, the cladding layer 50 can be made of any material depending on the application.

[0065] (8) The waveguide substrate 10 has a ridge portion 11 that corresponds to the first optical waveguide of the waveguide substrate 10 and is thicker than other portions. In the composite substrates 110 and 130, if the total thickness of the waveguide substrate 10 including the ridge portion 11 and the cladding layer 50 is t (μm) and the width of the void 21 is w (μm), it is preferable that t and w satisfy the formula "5 μm≦w≦30×t." This can prevent deformation of the waveguide substrate 10.

[0066] (9) The composite substrates 100 to 130 may also have a cladding film 60 that covers the waveguide substrate 10. This improves the optical propagation characteristics of the first optical waveguide of the waveguide substrate 10 and protects the waveguide substrate 10 from the external environment.

[0067] (10) The waveguide substrate 10 can be made of any of LiNbO3, LiTaO3, Si, and SiC. In this way, the waveguide substrate 10 can be made of any material depending on the application.

[0068] The present invention is not limited to the above-described embodiment, and can be implemented using any components without departing from the spirit of the present invention.

[0069] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0070] 10: Waveguide substrate 10A: LN substrate 11: Ridge portion (first optical waveguide) 20: Bonding layer 21:Void part 30: Middle class 31: Second optical waveguide 40: Support substrate 50: Cladding layer 60: Clad film 100, 110, 120, 130: Composite board

Claims

1. a waveguide substrate including a first optical waveguide; a support substrate that supports the waveguide substrate; a bonding layer provided between the waveguide substrate and the support substrate; a gap provided between the bonding layers in a direction perpendicular to an extending direction of the first optical waveguide; an intermediate layer disposed between the bonding layer and the support substrate; the waveguide substrate and the support substrate are bonded to each other via the bonding layer, At least a portion of the void overlaps with the first optical waveguide when viewed in a thickness direction of the waveguide substrate, The intermediate layer includes a second optical waveguide disposed opposite the first optical waveguide with the gap therebetween.

2. The composite substrate according to claim 1 , The bonding layer is made of amorphous Si and Ta. ２ O ５ , Al ２ O ３ It consists of either Composite board.

3. The composite substrate according to claim 1 , The intermediate layer is made of SiO ２ It consists of The second optical waveguide is made of either Si or SiN.

4. The composite substrate according to claim 1 , the second optical waveguide is formed in a state where it is buried inside the intermediate layer or where a part of the surface thereof is exposed to the void portion, A composite substrate, wherein the thickness of the intermediate layer between the second optical waveguide and the gap is 2 μm or less.

5. The composite substrate according to any one of claims 1 to 4, the waveguide substrate has a ridge portion that is thicker than other portions corresponding to the first optical waveguide; A composite substrate, wherein t and w satisfy the following formula, where t (μm) is the thickness of the waveguide substrate including the ridge portion, and w (μm) is the width of the void portion. 5 μm≦w≦30×t

6. The composite substrate according to any one of claims 1 to 4, A composite substrate having a cladding layer disposed between the waveguide substrate and the bonding layer.

7. The composite substrate according to claim 6, The cladding layer is made of SiO ２ A composite substrate consisting of:

8. The composite substrate according to claim 6, the waveguide substrate has a ridge portion that is thicker than other portions corresponding to the first optical waveguide; A composite substrate, wherein t and w satisfy the following formula, where t (μm) is the total thickness of the waveguide substrate including the ridge portion and the cladding layer, and w (μm) is the width of the gap portion. 5 μm≦w≦30×t

9. The composite substrate according to any one of claims 1 to 4, A composite substrate having a cladding film covering the waveguide substrate.

10. The composite substrate according to any one of claims 1 to 4, The waveguide substrate is made of LiNbO ３ , LiTaO ３ , Si, or SiC.

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