Optical waveguide element, optical modulator using optical waveguide element, and optical transmission device

Abstract

The purpose of the present invention is to provide an optical waveguide element in which a thin plate having an electro-optical effect and a holding substrate are joined with an intermediate layer interposed therebetween, said optical waveguide element suppressing DC drift and temperature drift by escaping charges accumulated at the interface between the thin plate and the intermediate layer. This optical waveguide element is provided with: a thin plate (1) having an electro-optical effect; a holding substrate (3) for holding the thin plate (1); and an intermediate layer (2) provided between the thin plate (1) and the holding substrate (3), an optical waveguide (10) being formed on the thin plate (1), and electrodes (E1-E3) for applying an electric field to the optical waveguide being provided on the thin plate, characterized in that a part of the electrodes reach the intermediate layer (2) through a through-hole (12) in the thin plate.

Description

Technical Field

[0001] The present invention relates to an optical waveguide element, an optical modulator device using the optical waveguide element, and an optical transmitting device, and in particular to an optical waveguide element comprising: a thin plate having an electro-optical effect; a holding substrate for holding the thin plate; and an intermediate layer provided between the thin plate and the holding substrate, wherein an optical waveguide is formed on the thin plate, and an electrode for applying an electric field to the optical waveguide is provided on the thin plate. Background Art

[0002] In the fields of optical measurement and optical communications, optical waveguide devices, such as optical modulators, are often used, utilizing substrates exhibiting the electro-optic effect, such as lithium niobate (LN). Electro-optic substrates exhibit a pyroelectric effect. Consequently, stress caused by the linear expansion difference between the substrate and contacting components due to external temperature fluctuations, as well as externally applied electric fields, can accumulate charge within the substrate, causing fluctuations in the drive voltage of the optical waveguide device, known as drift.

[0003] In conventional optical waveguide elements, the accumulation of charge at the interface between a buffer layer formed on a substrate and the substrate, particularly in order to suppress light absorption loss caused by electrodes, has become a problem. Methods have been proposed for diffusing charge by studying electrode structures, as shown in Patent Documents 1 to 3, and for preventing charge accumulation in the buffer layer by doping the buffer layer with other substances to increase conductivity, as shown in Patent Documents 4 or 5.

[0004] In recent years, optical modulators such as HB-CDM (High Bandwidth Coherent Driver Modulator) require that the driver circuit that drives the optical waveguide element be assembled together with the optical waveguide element in the housing, thereby miniaturizing the overall package. As optical waveguide elements become smaller and broadband, the thickness of the substrate that produces the electro-optical effect has been reduced to less than 1μm. Figure 1 As shown in FIG. 2, a thin plate 1 having an electro-optical effect and a holding substrate 3 formed of another material are used as a bonding substrate. A rib-shaped optical waveguide 10 is formed on the thin plate 1. In addition, electrodes E1 to E3 for applying an electric field to the optical waveguide 10 are formed on the thin plate 1. Figure 1 The thinner portion of the plate 1 is formed in Figure 2 A convex portion 11 is formed in the middle to cover the thin plate 1.

[0005] like Figure 1 or Figure 2As shown, an intermediate layer 2 is provided between the thin plate 1 and the holding substrate 3. The intermediate layer 2 is formed with a material having a lower refractive index than the thin plate 1, such as SiO2, with a thickness of several microns. In this way, the charge generated between not only the components in contact with the upper surface of the thin plate 1 but also the components in contact with the lower surface of the thin plate 1 becomes a problem. As shown in Patent Documents 6 to 8, a method of applying the technology of doping other substances in the above-mentioned buffer layer to the components in contact with the lower surface of the thin plate has also been proposed. However, due to the change in optical and electrical properties caused by doping, light absorption loss, and changes in the intensity and distribution of the electric field sometimes hinder the function as an optical waveguide element.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent No. 5360256

[0009] Patent Document 2: Japanese Patent No. 4927358

[0010] Patent Document 3: Japanese Patent No. 5298849

[0011] Patent Document 4: U.S. Patent No. 5,404,412

[0012] Patent Document 5: U.S. Patent No. 5,680,497

[0013] Patent Document 6: Japanese Patent Application Laid-Open No. 2021-105650

[0014] Patent Document 7: Japanese Patent Application Laid-Open No. 2021-173791

[0015] Patent Document 8: Japanese Patent Application Laid-Open No. 2021-173792 Summary of the Invention

[0016] Problems to be solved by the invention

[0017] The present invention aims to solve the aforementioned problems by providing an optical waveguide element comprising a thin plate having an electro-optical effect and a supporting substrate bonded via an intermediate layer. The optical waveguide element allows charge accumulated at the interface between the thin plate and the intermediate layer to escape, thereby suppressing DC drift and temperature drift. Furthermore, an optical modulator and an optical transmitter using the optical waveguide element are provided.

[0018] Means for solving problems

[0019] In order to solve the above-mentioned problems, the optical waveguide element, the optical modulation device, and the optical transmission apparatus of the present invention have the following technical features.

[0020] (1) An optical waveguide element comprising: a thin plate having an electro-optical effect; a holding substrate for holding the thin plate; and an intermediate layer disposed between the thin plate and the holding substrate, wherein an optical waveguide is formed on the thin plate, and an electrode for applying an electric field to the optical waveguide is provided on the thin plate, wherein a portion of the electrode reaches the intermediate layer through a through hole in the thin plate.

[0021] (2) The optical waveguide element according to (1) above, wherein the intermediate layer is made of a material having a lower refractive index than that of the thin plate.

[0022] (3) The optical waveguide element according to (1) or (2) above, wherein a protective film is provided on the optical waveguide, and the protective film is in contact with the electrode.

[0023] (4) The optical waveguide element according to any one of (1) to (3) above, wherein the through hole has an opening diameter on the upper side larger than an opening diameter on the lower side.

[0024] (5) The optical waveguide element according to any one of (1) to (4) above, wherein a recess is formed on the upper surface of the electrode located above the through hole.

[0025] (6) The optical waveguide element according to any one of (1) to (5) above, wherein the electrode located in the intermediate layer is larger than the opening diameter of the lower side of the through hole.

[0026] (7) The optical waveguide element according to any one of (1) to (6) above, wherein the through hole is formed in an action portion of the electrode, and the action portion applies an electric field to the optical waveguide.

[0027] (8) The optical waveguide element according to (7) above, wherein the total length of the through hole formed in the action portion along the optical waveguide accounts for 50% or more of the total length of the action portion along the optical waveguide.

[0028] (9) An optical modulation device comprising: an optical waveguide element according to any one of (1) to (8) above; a housing for accommodating the optical waveguide element; and an optical fiber for inputting and outputting light waves to and from the optical waveguide element.

[0029] (10) The optical modulator device according to (9) above is characterized in that an electrode for modulating the light wave propagating in the optical waveguide is provided on the thin plate, and an electronic circuit for amplifying the modulated signal input to the electrode is provided inside or outside the housing.

[0030] (11) An optical transmitter comprising: the optical modulator according to (9) or (10) above; and an electronic circuit for outputting a modulation signal for causing the optical modulator to perform a modulation operation.

[0031] Effects of the Invention

[0032] According to the present invention, the optical waveguide element comprises: a thin plate having an electro-optical effect; a holding substrate for holding the thin plate; and an intermediate layer disposed between the thin plate and the holding substrate, wherein an optical waveguide is formed on the thin plate, and an electrode for applying an electric field to the optical waveguide is provided on the thin plate, wherein a portion of the electrode reaches the intermediate layer via a through hole in the thin plate, thereby enabling charges accumulated at the interface between the thin plate and the intermediate layer to escape toward the electrode, thereby suppressing drift phenomena.

[0033] Furthermore, it is also possible to provide an optical modulation device and an optical transmission apparatus using an optical waveguide element having such effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram showing a cross section of a conventional optical waveguide element.

[0035] Figure 2 This is a diagram showing another cross section of a conventional optical waveguide element.

[0036] Figure 3 It is a cross-sectional view showing an example of the optical waveguide element of the present invention.

[0037] Figure 4 This is a cross-sectional view showing another example of the optical waveguide element of the present invention.

[0038] Figure 5 Yes Figure 4 A cross-sectional view of an application example of an optical waveguide element.

[0039] Figure 6 Yes Figure 5 sectional views of other application examples of optical waveguide elements.

[0040] Figure 7 It is a diagram illustrating the structure of an electrode used in the optical waveguide element of the present invention.

[0041] Figure 8 This is a diagram illustrating a state where wiring is performed by ball bonding in the optical waveguide element of the present invention.

[0042] Figure 9 It is a plan view showing an example of the optical waveguide element of the present invention.

[0043] Figure 10 It is a diagram for explaining the working portion of the optical waveguide element of the present invention.

[0044] Figure 11 It is a plan view showing the optical modulation device and optical transmission apparatus of the present invention. DETAILED DESCRIPTION

[0045] Hereinafter, the present invention will be described in detail using preferred examples.

[0046] like Figures 3 to 6 As shown, the optical waveguide element of the present invention comprises: a thin plate 1 having an electro-optical effect; a holding substrate 3 holding the thin plate 1; and an intermediate layer 2 disposed between the thin plate 1 and the holding substrate 3. An optical waveguide 10 is formed on the thin plate 1, and electrodes (E1 to E3) for applying an electric field to the optical waveguide are provided on the thin plate. The characteristic feature is that a portion of the electrodes reaches the intermediate layer 2 through a through hole 12 of the thin plate.

[0047] The thin plate 1 is a substrate formed from a material exhibiting an electro-optical effect. Specifically, it is a thin plate made of materials such as lithium niobate (LN), lithium tantalate (LT), or PLZT (lead lanthanum zirconate titanate), thinned to a thickness of several microns or less by mechanical methods such as grinding, or by methods such as smart cutting (a method of thinning by ion implantation and exfoliation). Alternatively, an intermediate layer 2 may be formed on a supporting substrate 3, and a vapor-phase grown film formed thereon from the aforementioned materials. Alternatively, various materials, such as semiconductor materials and organic materials, may be used.

[0048] As a method for forming an optical waveguide, the use of a rib-type optical waveguide in which the portion of the substrate corresponding to the optical waveguide is made convex by etching the substrate surface other than the optical waveguide or forming grooves on both sides of the optical waveguide can reduce light loss in the curved portion of the optical waveguide. Furthermore, a horizontal slot waveguide can also be used in which a slot waveguide structure is formed in the thickness direction by thinning the substrate. In addition, an optical waveguide can be formed by forming a high refractive index portion on the substrate surface using a thermal diffusion method, a proton exchange method, etc. A high refractive index material can also be diffused into the rib-type optical waveguide portion to form a composite optical waveguide. In particular, when using a bent optical waveguide, a rib-type optical waveguide with strong light confinement and a width or height of about 1 μm is used.

[0049] To achieve speed matching between the microwaves and light waves of the modulated signal, the thin plate 1 forming the optical waveguide is thinned by mechanical methods, smart cutting, or other methods to a thickness of 10 μm or less, more preferably 5 μm or less, and even more preferably less than 1 μm (the lower limit of the thickness is preferably 0.3 μm or greater). The height of the rib-shaped optical waveguide is preferably set to 1 μm or less. Alternatively, a vapor-grown film can be formed on the upper side of the supporting substrate and processed into the optical waveguide shape described above.

[0050] The thin plate (thin film) on which the optical waveguide is formed is bonded to a supporting substrate 3 via an intermediate layer 2, which functions as a lower cladding layer, to form a bonded substrate, thereby enhancing mechanical strength. The intermediate layer 2 preferably has a lower refractive index than the optical waveguide 10 and the thin plate 1 on which the optical waveguide is formed, minimizing light absorption in the communication band. Furthermore, a material with a thermal expansion coefficient close to that of the thin plate and a low dielectric constant is preferred. When using an inorganic material for the intermediate layer 2, SiO2, SiN, Al2O3, MgF, La2O3, ZnO, MgO, CaF2, Y2O3, etc. can be used, with SiO2 being particularly preferred. In the optical waveguide element of the present invention, even when SiO2 is used as the intermediate layer, doping treatment to enhance conductivity is unnecessary. Furthermore, the supporting substrate 3 is preferably the same substrate as the thin plate, or a low-dielectric-constant substrate such as Si or quartz.

[0051] like Figures 3 to 6 As shown, the optical waveguide element of the present invention is characterized in that a portion of the electrode E10 reaches the intermediate layer 2 via the through-hole 12 of the thin plate 1. Thus, the electrode E10 in the through-hole portion releases charge accumulated and moved at the interface between the thin plate 1 and the intermediate layer 2 into the electrode body, limiting the distance the charge moves. Consequently, temperature drift and DC drift can be effectively suppressed. Furthermore, the present invention can also be advantageously employed in structures where no electrode layer is disposed between the thin plate 1 and the supporting substrate 3.

[0052] Figure 3 and Figure 1 Similarly, by forming the electrodes E1 to E3 in the thin portion of the thin plate 1, the through hole 12 penetrating the thin plate 1 can be easily formed. Figure 4 and Figure 2 Similarly, electrodes E1 to E3 are formed so as to cover the convex portion 11 of the thin plate 1. When a through-hole 12 is provided in a thin plate 1 having such a thickness, as will be described later, the height of the through-hole 12 increases, and the through-hole 12 can be tapered, with the opening diameter on the upper side being different from the opening diameter on the lower side. Therefore, the concave portion E11 on the upper surface of the electrode E1 can be easily formed.

[0053] In addition, Figure 3 and Figure 4 In the embodiment, the electrodes E1 to E3 are set as electrodes having two steps, but the present invention is not limited thereto and may be electrodes having three or more steps or electrodes without steps.

[0054] Figure 5 and Figure 6The figure shows the case where a protective film 4 is arranged on the optical waveguide 10. As the protective film 4, it is preferred that a material with a lower refractive index than the optical waveguide 10 and less light absorption in the communication band be used, and a material with a low dielectric constant be used. When an inorganic material is used for the protective film 4, SiO2, SiN, Al2O3, MgF, La2O3, ZnO, MgO, CaF2, Y2O3, etc. can be used. When an organic material is used for the protective film 4, a resin such as a resist is preferred, which has a low Young's modulus and is easy to pattern. For example, materials such as polyamide resins, melamine resins, phenolic resins, amino resins, and epoxy resins can be used. Figure 5 A protective film 4 is also formed under the electrodes E1 to E3. Figure 6 No protective film is formed beneath the electrodes. In either case, to release charge accumulated at the interface between thin plate 1 and protective film 4, a portion of electrodes E1 to E3 is configured to contact this interface. This structure effectively suppresses drift even when the material of protective film 4 is susceptible to charge accumulation. This charge is released at the interface between thin film 1 and protective film 4.

[0055] Figure 7 This figure shows the structure of an electrode reaching the intermediate layer via the through-hole 12 .

[0056] The through hole 12 is formed in a tapered shape in which the opening diameter W1 at the upper side is larger than the opening diameter W2 at the lower side. Figure 7 The angle θ of the tapered portion shown is 80° or less. This allows the charge-releasing electrode E10 to be uniformly formed deep within the through-hole. The electrode is preferably formed within the through-hole by dry film formation such as evaporation or sputtering, or by plating after forming a base metal by dry film formation. However, as described above, by increasing the opening diameter (opening width) W1 on the upper side of the thin plate 1, the dry film formation target can be formed deep, allowing the plating layer to grow even deeper.

[0057] Furthermore, the shape of the through hole 12 can reduce the internal stress applied to the thin plate 1 and suppress drift even if the electrode in the through hole expands thermally, and the expansion direction can be not only left and right in the drawing but also upward.

[0058] Furthermore, it is convenient to fill the electrode portion disposed within the through-hole with an electrode forming material such as a ground electrode or signal electrode (e.g., a metal such as Au, Cu, or Ag). However, even if only the through-hole portion is filled with a semiconductor such as Si, the desired effect can be achieved. When a semiconductor is used in the through-hole portion, these materials generally have lower linear expansion coefficients and thermal conductivity than metals. Therefore, when temperature changes are applied to the optical waveguide element, changes in shape and temperature of the through-hole portion can be minimized, thereby minimizing temperature changes and stresses imparted to the sheet 1.

[0059] exist Figure 7 In the figure, the size (width W3) of the electrode E10 located in the middle layer 2 is wider than the opening diameter (width W2) on the lower side of the through hole 12. On the lower side of the through hole 12, the middle layer 2 is hollowed out. As a result, the surface area of ​​the electrode E10 in contact with the interface between the thin plate 1 and the middle layer 2 can be increased. In addition to improving the effect of releasing charge, it also has the effect of preventing the electrode (E1) body from peeling off. In fine electrodes such as segmented electrodes, there is a problem of electrode peeling due to insufficient etching caused by wet etching of the base electrode during electrode formation. Therefore, it is also possible to include an electrode peeling countermeasure in the root portion of the segment. Figure 7 The electrode portion E10 has a shape in which the width W3 is widened. Figures 3 to 6 As shown, it is of course possible to adopt a shape in which the width W3 is the same as the opening diameter W2 on the lower side of the through hole.

[0060] In addition, when a voltage is applied to the electrode, the lines of force also leak out of the thin plate, and the accumulation of charge occurs not only at the interface between the thin plate and the intermediate layer, but also in the intermediate layer 2. Therefore, in order to obtain the effect of releasing the charge in the intermediate layer, the depth D1 of the electrode portion E10 into the intermediate layer is preferably more than 100nm. In addition, it is also possible to completely penetrate from the intermediate layer 2 to the holding substrate 3 below. In addition, in a structure in which multiple intermediate layers are stacked between the holding substrate 3 and the thin plate 1, this structure is also effective. In this case, it is preferred to form the electrode portion to a depth that reaches the intermediate layer formed by an insulator such as SiO2.

[0061] The electrode portion E10 extending into the through-hole 12 and into the intermediate layer may alter the electric field distribution formed by the electrode. Therefore, from the perspective of electric field efficiency, the distance L1 from the electrode end (the side of the electrode facing the optical waveguide) to the through-hole 12 (the upper opening of the through-hole) must be at least one times the mode field diameter (MFD) of the light propagating through the optical waveguide 10. Furthermore, from the perspective of optical absorption loss, the distance L2 from the optical waveguide 10 to the through-hole (the upper opening of the through-hole) must be at least three times the MFD.

[0062] Figure 8This is an example of a structure in which a ball bond (BB) for wiring is performed directly above the through-hole 12. Ball bonding typically involves crimping a metal ball to create a wiring connection. However, when ball bonding is performed on electrodes formed on a thin plate, such as LN, there are problems such as cracking of the thin plate due to heat and processing stress during crimping, and drift caused by charge accumulation in the thin plate.

[0063] In the optical waveguide element of the present invention, a recess E11 can be formed on the upper surface of the electrode E1 located above the through-hole 12. By using this recess E11 as a wiring connection, the heat and compressive stress during press-bonding are dispersed by the recess, preventing stress concentration on the sheet 1. Furthermore, by making the opening width W4 of the recess E11 in the through-hole 12 slightly smaller than the ball size for ball bonding (approximately 30 to 40 μm), the metal ball is less likely to shift during wiring, enabling stable bonding. Reference numeral 5 denotes the bonded wire (wiring).

[0064] In the present invention, the through hole 12 is preferably formed in an action portion of the electrode, and this action portion applies an electric field to the optical waveguide 10 .

[0065] Figure 9 This is a top view of an example of an optical waveguide element according to the present invention. The optical waveguide 10 is bent, and various electrodes are formed along the optical waveguide 10. Ground electrodes EG1 and EG2 are arranged to sandwich a signal electrode ES. An electric field corresponding to the modulation signal is applied to the optical waveguide between the signal electrode ES and the ground electrode (EG1 or EG2). Furthermore, an electric field for phase adjustment is applied to the optical waveguide via the DC bias electrode EB and the ground electrodes (EG2, EG3). The active portion of the electrode refers to the portion where the signal electrode, DC bias electrode, etc. are arranged.

[0066] The portion of each electrode indicated by the oblique lines indicates the position where the through hole 12 is formed, and a portion E10 of the electrode enters the through hole. Figure 8 The recessed portion shown in the figure is connected to wiring such as the Au wire 5.

[0067] The through hole 12 is preferably formed at one or more locations below the ground electrode, the signal electrode, or the DC bias electrode in the electric field action portion of the optical waveguide element. Figure 9 In the embodiment, no through-hole is formed below the signal electrode ES. However, in order to reduce propagation loss when a microwave signal serving as a modulated signal propagates, it is preferable to configure the surface of the signal electrode to have as few irregularities as possible.

[0068] Furthermore, if Figure 10 As shown in FIG. 1 , the total length of the through holes 12 formed in the active portion along the optical waveguide preferably accounts for 50% or more of the total length L of the active portion along the optical waveguide 10. Specifically, Figure 10In the upper ground electrode, the sum of the lengths of the through holes (L1+L2) preferably accounts for at least 50% of the total length L. Furthermore, in the lower ground electrode, when twelve circular through holes having a diameter of L3 are formed, the sum of the lengths of the through holes (L3×12) preferably accounts for at least 50% of the total length L.

[0069] Typically, charge accumulated at the interface between the thin plate and the intermediate layer in the voltage application section moves along the thin plate, causing drift. However, as described above, by dividing more than 50% of the thin plate in the electric field application section by through-holes 12, and electrically connecting the divided sections by a portion of electrode E10, the movement of charge is sufficiently limited. As a result, drift can be effectively suppressed. Furthermore, the through-holes only need to be formed at a distance of at least 50%, and can be divided into multiple sections.

[0070] exist Figure 9 In FIG. 5 , a through hole is also provided just below the connection portion of the wiring 5 connected to the electrode, but a through hole may be formed at a position different from the above position depending on the application. Figure 9 , the structure of the folded waveguide is exemplified, but the present invention is not limited thereto. However, in the case of the folded waveguide, the DC bias electrode EB and the signal electrode ES can be formed relatively close to each other. Therefore, by sharing the ground electrode EG2 of each electrode, the number of locations where through holes are formed in the entire optical waveguide element can be reduced while achieving the same effect.

[0071] like Figure 11 As shown, the optical waveguide element (plate 1) of the present invention is housed in a housing CA made of metal or other materials, and the exterior of the housing is connected to the optical waveguide element via an optical fiber F. This allows for a compact optical modulator MD. Of course, optical fibers can be directly connected to the incident or outgoing portion of the optical waveguide in plate 1, and optical connections can also be made via a spatial optical system. Reference numeral 6 denotes a reinforcing member that overlaps with substrate 1 along the end face of plate 1 and is used when optical components such as optical fibers are directly bonded to the end face of substrate 1. Reference numeral Lin represents incident light, and Lout represents outgoing light.

[0072] An optical transmitter OTA can be constructed by connecting an electronic circuit (digital signal processor DSP) that outputs a modulation signal S0, which causes the optical modulator MD to perform a modulation operation, to the optical modulator MD. The modulation signal S applied to the optical waveguide element requires amplification, which is why a driver circuit DRV is used. The driver circuit DRV and the digital signal processor DSP can be located outside the housing CA, or they can be located inside the housing CA. In particular, locating the driver circuit DRV inside the housing further reduces propagation losses in the modulation signal from the driver circuit.

[0073] Industrial Applicability

[0074] As described above, the present invention can provide an optical waveguide element in which a thin plate having an electro-optical effect is bonded to a supporting substrate via an intermediate layer, thereby allowing charge accumulated at the interface between the thin plate and the intermediate layer to escape, thereby suppressing DC drift and temperature drift. Furthermore, an optical modulator and an optical transmitter using the optical waveguide element can be provided.

[0075] Label Description

[0076] 1 thin plate (LN substrate)

[0077] 2. Intermediate layer (SiO2)

[0078] 3. Hold the substrate

[0079] 4. Protective film

[0080] 10 Optical waveguide

[0081] 11 Base board protrusion

[0082] 12 through holes

[0083] E1~E3 electrodes

[0084] Part of an E10 electrode

Claims

1. An optical waveguide element comprising: a thin plate having an electro-optical effect; a holding substrate holding the thin plate; and an intermediate layer disposed between the thin plate and the holding substrate, wherein an optical waveguide is formed on the thin plate, and an electrode for applying an electric field to the optical waveguide is provided on the thin plate, characterized in that: A portion of the electrode reaches the intermediate layer through the through hole of the thin plate.

2. The optical waveguide element according to claim 1, wherein The intermediate layer is made of a material having a lower refractive index than that of the thin plate.

3. The optical waveguide element according to claim 1 or 2, wherein: A protective film is disposed on the optical waveguide, and the protective film is in contact with the electrode.

4. The optical waveguide element according to any one of claims 1 to 3, wherein The through hole has an upper opening diameter larger than a lower opening diameter.

5. The optical waveguide element according to any one of claims 1 to 4, characterized in that A recess is formed on the upper surface of the electrode located above the through hole.

6. The optical waveguide element according to any one of claims 1 to 5, characterized in that The size of the electrode located in the intermediate layer is larger than the opening diameter of the lower side of the through hole.

7. The optical waveguide element according to any one of claims 1 to 6, wherein: The through hole is formed in an action portion of the electrode, and the action portion applies an electric field to the optical waveguide.

8. The optical waveguide element according to claim 7, wherein The total length of the through-holes formed in the action portion along the optical waveguide accounts for 50% or more of the entire length of the action portion along the optical waveguide.

9. An optical modulation device, characterized in that: The optical waveguide device comprises: the optical waveguide device according to any one of claims 1 to 8; a housing for accommodating the optical waveguide device; and an optical fiber for inputting and outputting light waves to and from the optical waveguide device.

10. The optical modulation device according to claim 9, wherein: The thin plate is provided with electrodes for modulating light waves propagating in the optical waveguide, and an electronic circuit for amplifying the modulated signal input to the electrodes is provided inside or outside the housing.

11. An optical transmitting device, characterized in that: A light modulator according to claim 9 or 10; and an electronic circuit for outputting a modulation signal for causing the light modulator to perform a modulation operation.

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