Optical waveguide element, optical modulation device using the same, and optical transmission device

Abstract

To provide an optical waveguide element that prevents an optical component from falling off due to internal stress generated at a joint portion between an optical waveguide member including a substrate on which an optical waveguide is formed and the optical component, and can simplify a manufacturing process for polishing a joint surface.SOLUTION: An optical waveguide element includes: an optical waveguide member including a substrate 1 on which an optical waveguide is formed; and an optical component 3 that is fixed to an end surface (B0) of the optical waveguide member on which an input portion or output portion of the optical waveguide is disposed, and that transmits input light to the input portion or output light from the output portion. A portion which is at least part of the optical waveguide member and to which the optical component 3 is fixed is provided with rougher portions (B1 and B2) than roughness of the end surface (B0) of the optical waveguide member including the input portion or the output portion.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an optical waveguide element and an optical modulation device and an optical transmission device using the same, and in particular to an optical waveguide element including an optical waveguide member including a substrate on which an optical waveguide is formed, and an optical component fixed to an end face of the optical waveguide member at which an input portion or an output portion of the optical waveguide is disposed, and which transmits input light to the input portion or transmits output light from the output portion. [Background technology]

[0002] In the fields of optical measurement technology and optical communication technology, optical waveguide elements using substrates on which optical waveguides are formed, such as optical modulators, are widely used. An optical modulator element (LN chip) is formed by forming a control electrode for controlling the light waves propagating through the optical waveguide in an optical waveguide element using a substrate having an electro-optic effect, such as lithium niobate (LN). The LN chip is mounted in a housing such as metal, and an optical lens is adhesively fixed to the end face of the optical waveguide element to input or output light waves to the optical waveguide of the optical waveguide element.

[0003] By using an optical lens, it is possible to provide an optical modulator with good coupling efficiency between the input light or output light and the optical waveguide. Even if the mounting position of the LN chip and the housing is misaligned, a configuration with low insertion loss can be realized by adjusting the position and angle of the lens.

[0004] As shown in Patent Document 1, in recent years, in an optical modulation device in which an optical waveguide element is mounted in a housing, it has been proposed to output two signal lights from the optical waveguide element and to polarize and combine them in order to accommodate miniaturization and broadband. Also, as shown in Fig. 1, a configuration has been proposed in which an input section and an output section of an optical waveguide 2 are arranged on one side of the optical waveguide element in order to input (L1) and output (L2) light waves from one side of the housing. In these optical waveguide elements, a plurality of input sections and output sections related to light waves are arranged on the same end surface of the substrate, so that the contact area between the substrate end surface and the optical components is also large.

[0005] In FIG. 1, an optical block (optical component) 3 on which optical lenses (31, 32) are formed (or held) is attached to one side of the optical waveguide element. FIG. 2(a) is a side view (lower side of FIG. 1) showing the state in which the optical waveguide element (substrate 1) and the optical block 3 are attached, and a reinforcing block 10 is bonded and fixed to the upper part of the end face side of the substrate 1 with an adhesive (not shown). The optical block 3 is bonded and fixed to the end faces of the substrate 1 and the reinforcing block 10 with an adhesive A. In addition, when the substrate 1 is made of a thin plate with a thickness of 30 μm or less or a thin film with a thickness of 1 μm or less, it is also possible to increase the mechanical strength of the substrate by bonding and arranging a holding substrate 11 to the thin plate (thin film) 1 as shown in FIG. 2(b). Hereinafter, only the substrate on which the optical waveguide is formed, or a structure in which at least one of a holding substrate and a reinforcing block is added to the substrate is referred to as an "optical waveguide member".

[0006] The optical block (optical component) is not limited to the optical lenses described above, but may be a component that integrally forms or holds other optical components such as a reflecting member or polarizer used for polarization synthesis, or a spacer for fixing a reflecting member or these components. In addition, the optical component that is adhesively fixed to the substrate 1 and the reinforcing block 10 is not limited to the optical block, but may also include a configuration in which an optical fiber fixed to a sleeve (cylinder)-shaped holding member or a V-groove substrate is directly attached to the end face of the substrate 1.

[0007] 2(a) and (b), in order to bond an optical component 3 to an optical waveguide component such as a substrate 1 (including a holding substrate 11) or a reinforcing block 10, the end faces of the optical waveguide component and the optical component to be bonded are formed into a mirror-like state. When such mirror-like end faces are placed opposite each other and bonded with an adhesive, the surface area becomes smaller than when the bonding surfaces are rough, and the anchor effect cannot be obtained, which causes a decrease in the adhesive strength between the two.

[0008] On the other hand, a ferroelectric material such as LN is used for the substrate constituting the optical waveguide element, and a material such as LN is also used for the reinforcing block in order to match the linear expansion coefficient with that of the substrate 1 . In contrast, glass (organic glass, optical glass, etc.) and plastic are used as materials for optical components. Therefore, the thermal expansion coefficient (linear expansion coefficient) of the LN substrate, holding substrate, and reinforcing block that constitute the optical waveguide member and the optical block (optical component) is 5×10 -6 The difference may be more than / ℃. Furthermore, as long as there is no adverse effect on the optical waveguide of the substrate 1, by using the same material for the reinforcing block and the holding substrate 11, not only the linear expansion coefficient but also the Vickers hardness can be matched, thereby improving the surface accuracy when the substrate is cut.

[0009] The size of the optical waveguide element is about 0.5 to 3 mm in chip width, and about 1 to 2 mm in total thickness of the reinforcing block and the substrate of the optical waveguide element. In particular, in the case of polarization combining or a folded structure in which the input and output are on the same end face as shown in Fig. 1, the chip width becomes larger than 1.5 mm, and the bonding area between the optical block (optical component) 3 and the substrate 1 becomes larger, so that it is easily affected by the difference in thermal expansion coefficient between the substrate (including the holding substrate) or the reinforcing block and the optical component.

[0010] If the thermal expansion coefficients of the components to be joined are different, internal stress will occur in the joint due to changes in environmental temperature, leading to problems such as changes in optical characteristics, cracks in the joint, or loss of optical components. This tendency is particularly pronounced when the thermal expansion coefficients differ in directions parallel to the joint surface, such as the thickness direction (Y-axis direction) and width direction (X-axis direction) of the optical waveguide element, as shown in Figure 2(a).

[0011] As a method for solving such a problem, the applicant of the present invention has proposed a method for reducing the area of ​​the joint portion, as shown in Patent Document 2.

[0012] Furthermore, in order to mirror-finish the bonding surfaces, the end faces must be polished after the substrates are cut, which creates the problem of increased processing time. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2020-003701 A [Patent Document 2] Patent Application No. 2020-062129 (Application date: March 31, 2020) Summary of the Invention [Problem to be solved by the invention]

[0014] The problem to be solved by the present invention is to provide an optical waveguide element that solves the above-mentioned problems, prevents the detachment of an optical component due to internal stress generated at a joint between an optical waveguide member including a substrate on which an optical waveguide is formed and an optical component, and can simplify the manufacturing process relating to the polishing process of the joint surface, and also to provide an optical modulation device and an optical transmission device that utilize the optical waveguide element. [Means for solving the problem]

[0015] In order to solve the above problems, the optical waveguide element and the optical modulation device and optical transmission device using the same according to the present invention have the following technical features. (1) An optical waveguide element including an optical waveguide member including a substrate on which an optical waveguide is formed, and an optical component fixed to an end face of the optical waveguide member on which an input section or an output section of the optical waveguide is disposed, and transmitting input light to the input section or transmitting output light from the output section, the optical waveguide member for The optical component is fixed The corner formed by the end face and the bottom face connected to the end face and on which the optical waveguide is not formed is removed. providing a cutout portion, and providing a portion on at least a part of a surface forming the cutout portion that is rougher than the roughness of an end surface of the optical waveguide member including the input portion or the output portion; from an end face of the optical waveguide member including the input portion or the output portion At least a portion of the coarse portion to The adhesive for bonding the optical components is In succession The present invention is characterized in that it is provided.

[0017] ( 2 ) the above( 1) is characterized in that the depth of the cutout portion is set in the range of 5 μm or more and 300 μm or less from the end face including the input portion or the output portion.

[0018] ( 3 ) Above (1) Or (2) In the optical waveguide element described in the above, the coefficient of thermal expansion of the optical component in a direction parallel to the end face of the optical waveguide member is different from that of at least a part of a member constituting the end face of the optical waveguide member.

[0019] ( 4 ) (1) to ( 3 ) The optical waveguide element according to any one of claims 1 to 5, wherein a spot size conversion portion is provided at least at one of an input portion and an output portion of the optical waveguide.

[0021] ( 5 ) (1) to ( 4 ) The optical waveguide element according to any one of claims 1 to 5, wherein the roughness Ra of the rough portion is 50 nm or more.

[0022] ( 6 ) (1) to ( 5 ) is characterized in that the distance between the input section or the output section and the position where the rough portion is formed is set in the range of 5 μm or more and 300 μm or less.

[0024] (7) In the optical waveguide element according to any one of (1) to (6), in the region in which the rough portion is formed At the corner of A curved surface is formed. The roughness of the curved surface is It is characterized by having a smaller roughness than other rough areas.

[0025] ( 8 ) (1) to ( 7) is an optical modulation device comprising an electrode for modulating a light wave propagating through the optical waveguide, the optical waveguide element being housed in a housing, and an optical fiber for inputting or outputting a light wave to or from the optical waveguide.

[0026] ( 9 ) the above( 8 ) is characterized in that the housing includes an electronic circuit for amplifying a modulating signal input to the optical waveguide element.

[0027] ( 10 ) the above( 8 ) or ( 9 and an electronic circuit that outputs a modulation signal that causes the optical modulation device to perform a modulation operation. Effect of the Invention

[0028] The present invention relates to an optical waveguide element including an optical waveguide member including a substrate on which an optical waveguide is formed, and an optical component fixed to an end face of the optical waveguide member on which an input section or an output section of the optical waveguide is disposed, and transmitting input light to the input section or transmitting output light from the output section, for The optical component is fixed The corner formed by the end face and the bottom face connected to the end face and on which the optical waveguide is not formed is removed. providing a cutout portion, and providing a portion on at least a part of a surface forming the cutout portion that is rougher than the roughness of an end surface of the optical waveguide member including the input portion or the output portion; from an end face of the optical waveguide member including the input portion or the output portion At least a portion of the coarse portion to The adhesive for bonding the optical components is In succession Since the rough portion is provided, it is possible to increase the bonding strength with the optical component side at the rough portion and prevent the optical component from falling off. Moreover, since the rough portion of the bonding surface other than the optical waveguide portion that needs to be mirror-finished for performance reasons can be used as is, it is also possible to simplify the manufacturing process related to the polishing process of the bonding surface. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a plan view showing an example of a conventional optical waveguide element. [Diagram 2] 2 is a side view of the optical waveguide element of FIG 1. (a) shows the case where the substrate 1 is thick, and (b) shows the case where a supporting substrate 11 is bonded to a thin plate (thin film) 1. [Diagram 3] 1A is a side view illustrating an optical waveguide element according to a first embodiment of the present invention, in which (a) shows a case where an adhesive is applied to a rough portion B1, and (b) shows a case where an adhesive is applied to more rough portions (B1, B2) than in (a). [Figure 4] 4A to 4C are diagrams illustrating a part of a process for manufacturing the optical waveguide element of FIG. [Diagram 5] 10A is a side view illustrating an optical waveguide element according to a second embodiment of the present invention, in which (a) shows an optical component arranged parallel to the surface of rough portion B3, and (b) shows an optical component arranged tilted relative to the surface of rough portion B3. [Figure 6] 6A to 6C are diagrams illustrating a part of a process for manufacturing the optical waveguide element of FIG. 5. [Figure 7] FIG. 11 is a side view illustrating a third embodiment of the optical waveguide element of the present invention. [Figure 8] FIG. 11 is a side view illustrating an optical waveguide element according to a fourth embodiment of the present invention. [Figure 9] 1A and 1B are diagrams illustrating an example in which a spot size conversion portion is used in the optical waveguide element of the present invention. [Figure 10] 4A to 4C are diagrams illustrating regions in which "rough portions" are formed in the optical waveguide element of the present invention. [Figure 11] 1 is a plan view illustrating an optical modulation device and an optical transmission device according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The optical waveguide element of the present invention will be described in detail below using preferred examples. As shown in Figs. 3 to 10, the optical waveguide element of the present invention comprises an optical waveguide member including a substrate 1 on which an optical waveguide is formed, and an optical component 3 fixed to an end face (B0) of the optical waveguide member where an input or output part of the optical waveguide is arranged and transmits input light to the input part or transmits output light from the output part, and is characterized in that at least a part of the optical waveguide member, where the optical component 3 is fixed, is provided with portions (B1 to B6) rougher than the roughness of the end face (B0) of the optical waveguide member including the input part or the output part. In the following description, an example in which a substrate 1 is combined with a holding substrate 11 and a reinforcing block 10 will be mainly described as an optical waveguide member.

[0031] The material of the substrate 1 used in the optical waveguide element of the present invention can be a ferroelectric material having an electro-optic effect, specifically, a substrate such as lithium niobate (LN), lithium tantalate (LT), or PLZT (lead lanthanum zirconate titanate), or a vapor-deposited film made of these materials. In addition, various materials such as semiconductor materials and organic materials can also be used as the substrate of the optical waveguide element.

[0032] The thickness of the substrate 1 on which the optical waveguide is formed may be set to 10 μm or less, more preferably 5 μm or less, in order to strengthen the confinement of the light waves propagating through the optical waveguide and improve the modulation efficiency. In such a case, in order to reinforce the mechanical strength of the substrate 1, a holding substrate 11 having a thickness of 0.2 to 1 mm is attached by direct bonding or via an adhesive. The material of the holding substrate may be LN, quartz, Si, molten glass, alumina, or the like. In the optical waveguide element of the present invention, the term "substrate on which an optical waveguide is formed" does not simply mean a single substrate, but also includes the case where a vapor-deposited film is formed on a supporting substrate and the film (thin film) is processed into an optical waveguide.

[0033] As a method for forming an optical waveguide in the substrate 1, a method of thermally diffusing a high refractive index material such as Ti into the substrate, or a method of forming a high refractive index portion by a proton exchange method can be used. It is also possible to form a rib-type optical waveguide in which the portion of the substrate corresponding to the optical waveguide is convex by a method such as etching the substrate portion other than the optical waveguide or forming grooves on both sides of the optical waveguide. Furthermore, it is also possible to use a rib-type optical waveguide together with an optical waveguide by a thermal diffusion method or the like.

[0034] Furthermore, when using a narrow optical waveguide such that the mode field diameter (MFD) of the optical waveguide is 1 μm or less, a spot size converter (SSC) that changes the MFD at the input or output part of the optical waveguide can be provided as a part of the optical waveguide. As described later, when an SSC is present, the "rough part" of the present invention is formed at a position that does not affect the light wave propagating through the SSC.

[0035] A reinforcing block 10 is placed and fixed to the upper part of the end face side of the substrate 1 where the input and output parts of the light waves are formed. A material with a Vickers hardness similar to that of the reinforcing substrate 11 is used for the reinforcing block 10 in order to improve the surface accuracy when the substrate is cut. As long as there is no adverse effect on the optical waveguide of the substrate 1, using the same material as the holding substrate 11 makes it possible to match not only the Vickers hardness but also the linear expansion coefficient. The end face of the reinforcing block 10 (the surface on the same side as the end face of the substrate 1) is used as a bonding surface for bonding optical components such as an optical block, if necessary.

[0036] The optical components include optical blocks that hold optical lenses, reflecting members, polarizers, etc., sleeve (cylindrical)-shaped holding members that hold the vicinity of the end of an optical fiber, or V-groove substrates, etc. Materials that make up the optical components include glass materials such as organic glass and optical glass, and plastic materials.

[0037] The thermal expansion coefficient (linear expansion coefficient) of the LN substrate in the Z-axis direction is 4.0×10 -6 / °C, and in the X-axis (Y-axis) direction, it is 14.0×10 -6 / °C. For example, if an optical component is made of optical glass material such as BK-7, the linear expansion coefficient is 7.1×10 -6 When an optical component is attached to an LN substrate, if the X-axis or Y-axis exists on the bonding surface of the LN substrate, the difference in the linear expansion coefficient between the two is 5.0×10 -6 / °C or more, and the difference becomes significant. As a result, the optical components may become misaligned or peel off or fall off due to temperature changes in the substrate, environment, etc.

[0038] In addition, for the metal housing that houses the optical waveguide element, a material with a linear expansion coefficient close to that of the substrate used for the optical waveguide element is selected. Stainless steel is often used for LN substrates, and the linear expansion coefficient of stainless steel is 17.3×10 -6 / °C, the difference in linear expansion coefficient between the optical components becomes large, so the optical components are not bonded to the housing, but are bonded and held solely by the substrate 1 or the reinforcing block 10. When an element with a low linear expansion coefficient such as quartz glass is used for the holding substrate 11, a material with a low linear expansion coefficient such as Kovar may be used for the housing.

[0039] 3 to 10, the optical waveguide element of the present invention is characterized in that a "rougher portion" than the surface roughness of end face B0 where the input or output portion of the light waves is formed is formed in at least a part of the optical waveguide member such as substrate 1, holding substrate 1 (if a holding substrate is present) 11 that holds substrate 1, or reinforcing block 10 placed on substrate 1, in a portion facing optical component 3 (shaded portion D in FIG. 10). Note that, for reference, the "rough portion" shown in each figure is exaggerated in appearance compared to the actual unevenness of the roughness. 3, 7 and 8 show a state in which the "rough portion" is recessed into the substrate 1 side from the end face B0 on ​​which the input or output portion is formed, but in Fig. 5, it shows a state in which it protrudes from the end face B0. Naturally, it is also possible to combine the two. Furthermore, it is preferable to set the depth of the cutout (the distance from end face B0 to B2 in FIG. 3, and the distance from end face B0 to B5 in FIG. 7) in the range of 5 μm to 300 μm. The deeper the cut, the greater the anchor effect of adhesive A can be, but if it is too deep, the mechanical strength of the substrate and other components constituting the optical waveguide member will be weakened.

[0040] In Fig. 3, a cutout is provided in part of the holding substrate 11, and "rough parts" (B1, B2) are formed on at least a part of the surface on which the cutout is formed. Then, the adhesive for bonding the optical component 3 is provided only on the rough part B1 in Fig. 3(a), and on both the rough parts B1 and B2 in Fig. 3(b), which makes up for the lack of adhesive on the substrate end face B0 and enables the optical component 3 to be firmly fixed to the substrate 1 side.

[0041] As shown in Figures 3 and 7, curved surfaces (R, R1, R2) are provided between rough portions (B1 and B2, B4 and B5, B5 and B6). By doing so, for example, stress concentration at the corners formed by the "rough portions" (B1, B2) is dispersed, so that the occurrence of cracks, etc. in the holding substrate 11 can be suppressed. In particular, when the distance between the curved surface and the substrate 1 is 300 μm or less, the effect of cracks, etc. on the optical waveguide of the substrate 1 can be reduced, which is more preferable. Of course, the risk of occurrence of cracks, etc. increases, but the effect of the present invention can be obtained even without providing curved surfaces at the corners formed by the "rough portions".

[0042] Furthermore, when providing a curved surface, if the surface of the curved surface is as rough as or rougher than the adjacent rough parts, the internal stress of the adhesive that has penetrated into those parts is likely to cause stress concentration on the curved surface, which may lead to cracks on the curved surface, etc. To avoid this, it is preferable to finish the curved surface to be smoother than the other rough parts (B1 to B6).

[0043] The shape of the "notch" is not limited to that shown in Fig. 3 and 7, and for example, it is also possible to form the notch by chamfering the corners of the holding substrate 11 as shown in Fig. 8. The part to be chamfered may be a corner of the substrate 1 or the reinforcing block 10.

[0044] FIG. 4 shows an example of a method for forming an end face including a "rough part" as shown in FIG. 3. FIG. 4 explains an example using a holding substrate 11, but the same applies to the case where there is no holding substrate 11 and only a thick substrate 1. When cutting into chips (single optical waveguide elements) with the reinforcing block 10 attached to the substrate 1, the holding substrate 11 is notched with a cutting blade C1, and then the chips are cut with a cutting blade C2 having a thinner blade thickness than the cutting blade C1. The mesh of the cutting blade C1 is coarser than that of the cutting blade C2, and the "rough part" of the present invention is formed on the surface with which the cutting blade C1 comes into contact. The fine-meshed cutting blade C2 is used for the portion including the end face of the substrate 1 where the input or output part of the optical waveguide element is arranged, and the end face is finished smoothly (mirror-like).

[0045] To finish the curved surface R in Fig. 3 more smoothly than the other rough parts (B1 to B6), it is possible to locally mechanically process only the curved surface R using a narrower grindstone or electron beam after Fig. 4(a), etc. The smoothness can also be adjusted by adjusting the shape, material, rotation speed, feed speed, etc. of the cutting blade.

[0046] FIG. 5 shows an example in which the optical component 3 is arranged away from the end face B0 of the input or output part of the substrate 1. In the optical waveguide element of FIG. 5, at least a part (B3) of the rough part formed on the holding substrate 11 protrudes toward the optical component 3 side from the end face B0 of the substrate 1 on which the input or output part is formed. In FIG. 5(a), the optical component 3 is arranged parallel to the surface of the rough part B3, but in FIG. 5(b), the optical component 3 is arranged tilted with respect to the surface of the rough part B3. The configuration of FIG. 5(b) not only holds the optical component more stably than the configuration of FIG. 5(a), but also contributes to suppressing the reflected light to the optical waveguide by reflecting the light wave on the surface of the optical component 3 on the substrate 1 side. Note that, although there is no adhesive between the optical component and the end face B0 in FIG. 5, an adhesive may be inserted.

[0047] Figure 6 shows an example of a method for forming an end face including a "rough portion" as shown in Figure 5. A reinforcing block 10 is fixed to the substrate 1 (including the holding substrate 11), and when cutting into individual chips, a cutting blade C3 is inserted from the reinforcing block side, and then another cutting blade C4, which is thinner than the cutting blade C3, is used to cut into chips. At this time, the "rough portion" B3 can be formed by making the mesh of the cutting blade C4 coarser than that of the cutting blade C3.

[0048] Figures 3 to 6 show an example in which a cutting blade is applied perpendicularly to the surface of the substrate 1, etc., but as shown in Figure 7, it is also possible to form grooves and form rough portions (B4 to B6) on the surface of the grooves by cutting from the lateral direction of Figure 7 (a direction parallel to the surface of the substrate 1).

[0049] 9 is an end view of an optical waveguide member showing a spot size conversion section (SSC) provided at the input section or output section of the optical waveguide 1. In order to prevent the light waves propagating through the SSC from being scattered by the "rough section", it is necessary to form the "rough section" outside the mode field diameter (MFD) of the SSC (dotted line S indicates the boundary part of the MFD). More preferably, it is formed at a position 5 μm or more away from the MFD. Reference numeral 4 denotes an adhesive layer that connects the holding substrate 11 (including the substrate 1 and the SSC) and the reinforcing block 10.

[0050] The SSC can be formed either by directly processing the optical waveguide, such as by gradually changing the waveguide width at the end of the optical waveguide formed on the substrate 1, or by forming a separate SSC at the end of the optical waveguide formed on the substrate 1. In the former configuration, the optical component is fixed to the end of the optical waveguide on which the SSC is formed, a holding substrate, or a reinforcing block, while in the latter configuration, the optical component is fixed to an SSC, holding substrate, or reinforcing block that is separate from the optical waveguide. In the configuration in which an SSC is formed, the SSC also constitutes part of the optical waveguide member.

[0051] FIG. 10 is a diagram for explaining the region where the rough portion is formed. FIG. 10 shows a surface on which the light wave input portion 20 and output portion 21 are arranged. If a rough portion D is present near the light wave input portion 20 or output portion 21, the internal stress generated by bonding the rough portion to the optical component also affects the optical waveguide, and in the worst case, changes the refractive index of the optical waveguide. For this reason, as shown in FIG. 10, a "rough portion" (D) is formed in an area a certain distance (S1 to S3) away from the optical waveguide (20, 21). This distance (S1 to S3) is preferably set to 5 μm or more. More preferably, it is 10 μm or more.

[0052] Furthermore, the roughness of the rough portion (D) is preferably 50 nm or more in terms of arithmetic mean roughness Ra from the viewpoint of increasing the bonding strength of the adhesive. The roughness of the end face of the substrate 1 on which the input and output parts are formed must be set to 10 nm or less.

[0053] In the region D in FIG. 10 where the rough portion can be formed, not only the "rough portion" as shown in FIG. 3, FIG. 5 or FIG. 7, but also saw marks running horizontally, vertically or even diagonally parallel to the surface of FIG. 10 can be used as the "rough portion". Note that up to this point, the edge surface (B0) of the substrate and the rough portion of the holding substrate have been described as being not on the same plane but having a step, but they may be on the same plane. Such a same plane can be formed by making the blade thickness of the cutting blade C1 and the cutting blade C2 in FIG. 4 the same, or by making the blade thickness of the cutting blade C3 and the cutting blade C4 in FIG. 5 the same. The "same plane" here is a concept that includes a step due to the processing accuracy that occurs when cutting with different cutting blades.

[0054] The optical waveguide element of the present invention is provided with a modulation electrode on a substrate 1 for modulating light waves propagating through the optical waveguide, and is housed in a housing CA as shown in Fig. 11. Furthermore, an optical fiber F for inputting and outputting light waves to and from the optical waveguide can be provided to configure an optical modulation device MD. The optical fiber can be arranged not only outside the housing CA as shown in Fig. 11, but also introduced and fixed inside the housing via a through-hole penetrating the side wall of the housing.

[0055] An optical transmitter OTA can be configured by connecting an electronic circuit (digital signal processor DSP) that outputs a modulation signal that causes the optical modulation device MD to perform a modulation operation to the optical modulation device MD. Since the modulation signal applied to the optical waveguide element needs to be amplified, a driver circuit DRV is used. The driver circuit DRV and digital signal processor DSP can be placed outside the housing CA, but they can also be placed inside the housing CA. In particular, by placing the driver circuit DRV inside the housing, it is possible to further reduce the propagation loss of the modulation signal from the driver circuit. [Industrial Applicability]

[0056] As described above, according to the present invention, it is possible to provide an optical waveguide element that can prevent the optical component from falling off due to internal stress generated at the joint between the optical waveguide member including the substrate on which the optical waveguide is formed and the optical component, and can simplify the manufacturing process related to the polishing process of the joint surface. It is also possible to provide an optical modulation device and an optical transmission device that use the optical waveguide element. [Explanation of symbols]

[0057] 1 Board 2 Optical waveguide 3 Optical block (optical components) 10 Reinforcement block A Bonding surface (adhesive) MD Optical Modulation Device OTA Optical Transmitter B1~B6 Rough part

Claims

1. An optical waveguide element comprising an optical waveguide member including a substrate on which an optical waveguide is formed, and an optical component fixed to an end face of the optical waveguide member on which an input section or an output section of the optical waveguide is disposed, the optical component transmitting input light to the input section or transmitting output light from the output section, a cutout portion is provided in the optical waveguide member by removing a corner formed by an end face to which the optical component is fixed and a bottom face connected to the end face and on which the optical waveguide is not formed; providing a portion rougher than the roughness of an end face of the optical waveguide member including the input portion or the output portion on at least a part of a surface forming the notch portion; an adhesive for bonding said optical components is continuously provided from an end face of said optical waveguide member including said input portion or said output portion to at least a part of said rough portion;

2. 2. The optical waveguide element according to claim 1, wherein the depth of the cutout portion is set in the range of 5 μm to 300 μm from the end face including the input portion or the output portion.

3. 3. The optical waveguide element according to claim 1, wherein the coefficient of thermal expansion of the optical component in a direction parallel to the end face of the optical waveguide member is different from that of at least a part of a material constituting the end face of the optical waveguide member.

4. 4. The optical waveguide element according to claim 1, further comprising a spot size conversion portion provided at least at one of an input portion and an output portion of the optical waveguide.

5. 5. The optical waveguide element according to claim 1, wherein the roughness Ra of the rough portion is 50 nm or more.

6. 6. The optical waveguide element according to claim 1, wherein the distance between the input portion or the output portion and the position where the rough portion is formed is set in the range of 5 μm or more and 300 μm or less.

7. 7. The optical waveguide element according to claim 1, wherein a curved surface is formed at a corner within the region in which the rough portion is formed, and the roughness of the curved surface is smaller than that of other rough portions.

8. 8. An optical modulation device comprising an optical waveguide element according to claim 1, comprising an electrode for modulating an optical wave propagating through the optical waveguide, the optical waveguide element being housed in a housing, and comprising an optical fiber for inputting or outputting an optical wave to the optical waveguide.

9. 9. The optical modulation device according to claim 8, further comprising an electronic circuit disposed inside said housing for amplifying a modulation signal input to said optical waveguide element.

10. 10. An optical transmitter comprising: an optical modulation device according to claim 8; and an electronic circuit for outputting a modulation signal for causing the optical modulation device to perform a modulation operation.

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