Optical waveguide element, optical modulator, and optical transmission device

Abstract

The utility model provides a kind of optical waveguide element capable of inhibiting the generation of DC drift caused by oxygen defect of substrate, optical modulator comprising the optical waveguide element, and optical transmission device comprising the optical modulator.The utility model's optical waveguide element (1) is characterized in that, comprising: substrate (10), by electro-optic crystal is formed and forms optical waveguide (80);Electrode (60), is placed on substrate (10);Electrode base layer (50), with the lower surface of electrode (60) contact configuration;And oxygen defect prevention layer (40), with the lower surface of electrode base layer (50) at least part and substrate (10) upper surface (substrate upper surface (10a)) at least part contact configuration, prevent the oxygen defect of substrate (10).

Description

Technical Field

[0001] This utility model relates to an optical waveguide element having an optical waveguide formed thereon, an optical modulator including the optical waveguide element, and an optical transmitting device including the optical modulator. Background Technology

[0002] In the fields of optical measurement and optical communication, optical waveguide elements are constructed using a substrate in which optical waveguides are formed. Optical waveguide elements in optical modulators utilize substrates made of materials with photoelectric effects, such as lithium niobate (LiNbO3: hereinafter also referred to as LN). In recent years, due to advancements in substrate fabrication technology, the thinning of substrates has become possible, and research and development are underway towards miniaturization and high density of optical waveguide elements.

[0003] Patent Document 1 discloses an optical waveguide device that achieves impedance matching by forming a thin-walled portion at the location of the electrode, forming a buffer layer between the substrate and the electrode, and adjusting the thickness of the thin-walled portion.

[0004] Patent Document 2 disclosed below discloses an optical waveguide device, which includes an optical waveguide formed in the surface of an electro-optic crystal substrate, a buffer layer formed on the optical waveguide, and a driving electrode formed on the buffer layer. The material of the buffer layer is a mixture of silicon oxide and at least one of the oxides of metal elements selected from Groups 3 to 8, Group 1b and Group 12b of the periodic table and semiconductor elements other than silicon, or a transparent insulator of silicon and an oxide of one or more of metal elements and semiconductor elements. This allows for long-term improvement of direct current (DC) drift characteristics.

[0005] Patent document 3 discloses an optical device that reduces light scattering loss caused by roughness on the upper or side surfaces of the optical waveguide by forming a ribbed optical waveguide on a substrate and configuring a buffer layer of SiO2 on the entire surface of the substrate, including the optical waveguide.

[0006] Patent Document 4 discloses an optical waveguide element having an optical waveguide formed on a substrate, electrodes arranged in a manner that sandwich the optical waveguide, and a dielectric layer arranged in a manner that covers the optical waveguide, thereby suppressing light scattering loss caused by surface roughness of the optical waveguide or light absorption loss caused by electrodes, etc., and mitigating stress caused by the dielectric layer covering the optical waveguide.

[0007] Patent Document 5 discloses an optical element having a substrate formed of lithium niobate crystal and electrodes disposed on the substrate. In this optical element, the contact metal, which is disposed on the electrode side and is to be contacted, is a metal material whose standard enthalpy of formation per coordination bond during oxidation is greater than that per coordination bond of niobium pentoxide, thereby suppressing DC drift. The poor adhesion between the substrate material (e.g., LN) and the electrode material (e.g., gold) can suppress electrode peeling by the presence of a contact metal layer as a separator. However, by using a metal material that suppresses oxygen loss from the substrate as the material constituting the contact metal layer, the generation of DC drift can be suppressed.

[0008] [Existing technical documents]

[0009] [Patent Literature]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2000-147444

[0011] [Patent Document 2] Japanese Patent Application Publication No. 5-257105

[0012] [Patent Document 3] Japanese Patent Application Publication No. 2012-53487

[0013] [Patent Document 4] Japanese Patent Application Publication No. 2024-107822

[0014] [Patent Document 5] Japanese Patent Application Publication No. 2019-174733 Utility Model Content

[0015] [The problem that the utility model aims to solve]

[0016] According to the technology disclosed in Patent Document 1, a buffer layer is formed between the substrate and the electrode, and the electrode is mounted on the buffer layer. However, since the adhesion between the electrode and the buffer layer may not be high, there is a problem that the electrode can easily peel off from the buffer layer.

[0017] According to the technology disclosed in Patent Document 2, DC drift is improved by using a mixture of silicon oxide and a specific oxide, or a transparent insulator composed of silicon and oxide, as a buffer layer disposed between the substrate and the electrode. However, this requires additional steps to manufacture such a specific mixture or oxide, and it is not easy to form a transparent insulator from a homogeneous mixture or compound, which may cause the characteristics of the optical waveguide device to become unstable.

[0018] According to the technology disclosed in Patent Document 3, for example, Figure 7As shown, a buffer layer 903 made of SiO2 is disposed on the entire surface of the substrate 901, including the ribs 902 forming the ribbed optical waveguide. Furthermore, an example is shown here where electrodes 904 are arranged in a manner that clamps the ribs 902. However, in the structure described, as... Figure 7 As illustrated, the following problem exists: when an electric field is applied to the ribbed optical waveguide, the charge carriers 905 in the buffer layer 903 move in the direction that cancels the electric field, resulting in DC drift.

[0019] According to the technology disclosed in Patent Document 4, for example, Figure 8 As shown, on a substrate 911 having ribs 912 forming ribbed optical waveguides, a dielectric layer 913 is disposed such that it covers the ribs 912 and partially covers the surface of electrodes 914 configured to sandwich the ribs 912. However, in the structure described, as... Figure 8 As schematically shown, the entire lower surface of electrode 914 is in direct contact with substrate 911. As a result, the metal constituting electrode 914 absorbs oxygen from substrate 911, causing oxygen defects in substrate 911. When an electric field is applied to the ribbed optical waveguide, charge carriers 915 in substrate 911 move in the direction of canceling the electric field, potentially causing DC drift. Furthermore, similar to the technology disclosed in Patent Document 3, when an electric field is applied to the ribbed optical waveguide, charge carriers 915 in dielectric layer 913 move in the direction of canceling the electric field, potentially causing DC drift.

[0020] According to the technology disclosed in Patent Document 5, in a structure in which electrodes are mounted on a substrate having ribs forming a ribbed optical waveguide, a contact metal layer made of a metal material that suppresses oxygen loss from the substrate is disposed between the substrate and the electrodes. However, in this structure, considering conditions based on the standard enthalpy of formation of niobium pentoxide and the adhesion to the substrate, there is a problem that the metal material selected as the contact metal layer is limited. Furthermore, in Patent Document 5, the spacing between electrodes is 15 μm or 25 μm. When the spacing between electrodes is narrowed (e.g., 10 μm or less) to achieve miniaturization and high density of the optical waveguide element, the effect of light absorption caused by the contact metal layer may become larger.

[0021] This invention was made in view of the aforementioned problems, and its purpose is to provide an optical waveguide element capable of suppressing DC drift caused by oxygen defects in a substrate, an optical modulator including the optical waveguide element, and an optical transmitting device including the optical modulator.

[0022] [Technical means to solve the problem]

[0023] To address the aforementioned issues, the optical waveguide element, optical modulator, and optical transmission device of this invention possess the following technical features.

[0024] To achieve the aforementioned objective, the optical waveguide element of this utility model is characterized by comprising: a substrate, which is made of an electro-optic crystal and forms an optical waveguide; an electrode, disposed on the substrate; an electrode base layer, which is disposed in contact with the lower surface of the electrode; and an oxygen defect prevention layer, which is disposed in contact with at least a portion of the lower surface of the electrode base layer and at least a portion of the upper surface of the substrate, to prevent oxygen defects in the substrate caused by the electrode base layer.

[0025] According to the structure, an oxygen defect prevention layer, which exists between an electrode substrate layer and a substrate in contact with the lower surface of the electrode, separates the electrode substrate layer and the substrate in such a way that at least a portion of them are not in direct contact. By disposing an oxygen defect prevention layer between the electrode substrate layer and the substrate in this way, it is possible to prevent oxygen from the substrate from being taken away by the electrode substrate layer and the electrode disposed above the substrate, thereby suppressing the generation of DC drift caused by oxygen defects in the substrate.

[0026] In the structure described in this invention, the optical waveguide element may be configured such that the oxygen defect prevention layer is in full-surface contact with the lower surface of the electrode substrate layer.

[0027] According to the structure, by configuring the oxygen defect prevention layer 40 in such a way that the entire lower surface of the electrode base layer 50 does not directly contact the substrate 10, the oxygen of the substrate can be more reliably prevented from being taken away by the electrode base layer and the electrode disposed above the substrate, thereby more reliably suppressing the generation of DC drift caused by oxygen defects of the substrate.

[0028] In the structure described in this invention, the optical waveguide element may have the oxygen defect prevention layer disposed below the DC electrode to which a DC voltage is applied.

[0029] According to the structure, by distributing an oxygen defect prevention layer below the DC electrode, the generation of DC drift caused by oxygen defects in the substrate can be effectively suppressed.

[0030] In the structure of the optical waveguide element of this invention, the oxygen defect prevention layer is disposed below the electrode with a thickness of less than 1.0 μm.

[0031] According to the structure, by disposing an oxygen defect prevention layer below an electrode with a thickness of less than 1.0 μm disposed near the modulation section (active section) of the optical waveguide 80, the generation of DC drift caused by oxygen defects in the substrate can be effectively suppressed.

[0032] The optical waveguide element of this invention may have a reinforcing substrate bonded to the underside of the substrate via a bonding layer. The substrate is made of an LN substrate with a thickness of less than 1.0 μm, and a convex portion serving as the optical waveguide is formed on the upper surface of the substrate.

[0033] According to the structure, by using an LN thin plate with convex portions as optical waveguides as a substrate, miniaturization and high density of optical waveguide components can be achieved.

[0034] In the structure of the optical waveguide element of this utility model, the oxygen defect prevention layer is not formed on the surface of the convex portion.

[0035] According to the structure, in the convex portion that forms the optical waveguide and is subjected to an electric field, oxygen vacancies can be avoided to prevent DC drift caused by carrier movement in the layer.

[0036] In the structure described in this invention, the optical waveguide element has an arithmetic mean roughness Ra of the surface of the convex portion of less than 5.0 nm.

[0037] According to the structure described, the scattering of light waves caused by the surface of the convex portion can be suppressed.

[0038] In the structure described in this invention, the optical waveguide element may have an oxygen defect prevention layer made of a material with a refractive index of 1.3 or higher and a dielectric constant of 3.0 or higher.

[0039] Based on the structure described, a suitable material can be used as an oxygen defect prevention layer.

[0040] In the structure described in this invention, the optical waveguide element may be made of SiO2, where the oxygen defect prevention layer is composed of an average oxygen-to-silicon atomic ratio greater than 1.9.

[0041] According to the structure, the oxygen defect prevention layer is in a state of fully containing oxygen, which prevents oxygen from being taken away from the substrate, thereby suppressing the generation of DC drift caused by oxygen defects in the substrate.

[0042] In the structure described above, the optical waveguide element of this invention may have an inert gas content of 1.0 atm% to 3.0 atm in the oxygen defect prevention layer.

[0043] According to the structure, by setting the content of the inert gas in the oxygen defect prevention layer to a specific range, the strength and film stress of the oxygen defect prevention layer can be well balanced and adjusted.

[0044] In the structure described in this invention, the thickness of the oxygen defect prevention layer can be 10 nm to 200 nm.

[0045] According to the structure described, film formation can be stably performed to suppress oxygen vacancies and prevent DC drift caused by charge carriers in the layer.

[0046] In addition, to achieve the aforementioned objective, the optical modulator of this invention is characterized by comprising: the optical waveguide element; a frame for housing the optical waveguide element; an input optical fiber connected to the optical input portion of the optical waveguide element; and an output optical fiber connected to the optical output portion of the optical waveguide element.

[0047] The optical modulator of this invention may include a modulation electrode as the electrode for modulating the light wave propagating in the optical waveguide, and a signal amplification circuit inside the frame for amplifying the modulation signal applied to the modulation electrode.

[0048] In addition, to achieve the aforementioned objective, the optical transmitting device of this invention is characterized by comprising: the optical modulator; a light source for inputting light waves into the optical modulator; and a signal output circuit for outputting the modulated signal.

[0049] [Effects of the utility model]

[0050] This invention provides an optical waveguide element capable of suppressing DC drift caused by oxygen defects in a substrate, an optical modulator comprising the optical waveguide element, and an optical transmitting device comprising the optical modulator. Attached Figure Description

[0051] Figure 1 This is a plan view showing the overall structure of the optical waveguide element according to the first to third embodiments of this utility model.

[0052] Figure 2 The optical waveguide element relating to the first embodiment of this utility model is a waveguide element that represents a waveguide along the path of the waveguide. Figure 1 A cross-sectional view of line AA.

[0053] Figure 3 A derivative example of the optical waveguide element relating to the first embodiment of this utility model is shown as follows: Figure 1 A cross-sectional view of line AA.

[0054] Figure 4 The optical waveguide element relating to the second embodiment of this utility model is a waveguide element that represents a waveguide along the optical waveguide. Figure 1 A cross-sectional view of the BB line.

[0055] Figure 5 The optical waveguide element relating to the third embodiment of this utility model is a waveguide element that represents a waveguide along... Figure 1 A cross-sectional view of the BB line.

[0056] Figure 6 This is a plan view showing the optical modulator and optical transmitting device of this utility model.

[0057] Figure 7This is a diagram used to illustrate the subject matter involved in the technology disclosed in Patent Document 3.

[0058] Figure 8 This is a diagram used to illustrate the subject matter involved in the technology disclosed in Patent Document 4.

[0059] Explanation of icon numbers

[0060] 1: Optical waveguide element

[0061] 10, 901, 911: substrate

[0062] 10a: Upper surface of substrate

[0063] 15: Convex part

[0064] 15a: Surface

[0065] 20: Reinforcing substrate (supporting substrate)

[0066] 30: Bonding layer (intermediate layer)

[0067] 40: Oxygen Defect Prevention Layer

[0068] 40a, 40b, 50a, 60a: Side view

[0069] 50: Electrode substrate layer

[0070] 60, 904, 914: Electrodes

[0071] 70: Contact surface

[0072] 80: Optical waveguide

[0073] 80a: Optical input terminal

[0074] 80b, 80c: Optical output terminals

[0075] 91: Branch Office

[0076] 92: Combined wave department

[0077] 100: Light scattering suppression layer

[0078] 300: Optical modulator

[0079] 301: Frame

[0080] 302: Input fiber optic cable

[0081] 303: Output fiber optic cable

[0082] 304: Polarization Wave Synthesis Unit

[0083] 400: Optical Transmitting Device

[0084] 401: Signal Output Circuit

[0085] 402: Signal Amplification Circuit

[0086] 403: Light source

[0087] 902, 912: Ribs

[0088] 903: Buffer layer

[0089] 905, 915: Charge carriers

[0090] 913: Dielectric layer

[0091] L1, L11: Input light

[0092] L2, L21, L22: Output light

[0093] So: Electrical signal (modulated signal)

[0094] S: Amplified signal (modulated signal) Detailed Implementation

[0095] The embodiments of this utility model will now be described with reference to the accompanying drawings. The drawings referenced in this specification may not be to a precise scale relative to actual dimensions; rather, they are exaggerated or simplified to schematically illustrate the structure of this utility model. Furthermore, the numerical ranges described in this specification include both upper and lower limits, meaning that any value within the stated range can be selected.

[0096] As illustrated in the various embodiments, the optical waveguide element of the present invention generally comprises the following components: a substrate, which is made of an electro-optic crystal and forms an optical waveguide; an electrode, which is disposed on the substrate; an electrode base layer, which is disposed in contact with the lower surface of the electrode; and an oxygen defect prevention layer, which is disposed in contact with at least a portion of the lower surface of the electrode base layer and at least a portion of the upper surface of the substrate, to prevent oxygen defects in the substrate caused by the electrode base layer.

[0097] (First Implementation)

[0098] The optical waveguide element of the first embodiment of this utility model will be described below.

[0099] First, refer to Figure 1 The overall structure of the optical waveguide element 1 in this embodiment will be described. Figure 1 This is a plan view showing an overall structural example of the optical waveguide element 1 in this embodiment. Hereinafter, it will sometimes be referred to as... Figure 1 The left-right direction of the planar diagram shown is called the long side direction of optical waveguide element 1. Figure 1 The vertical direction of the planar diagram shown is called the width direction of the optical waveguide element 1.

[0100] exist Figure 1 The diagram shows an optical waveguide element 1, 80, formed on a substrate 10 as an optical waveguide 80. However, the optical waveguide 80 of this invention is not limited to this type. Figure 1 The MZ-type optical waveguide shown is not limited to a Mach-Zehnder type structure. Electrodes 60 are also suitably disposed on the upper surface of the substrate 10 (see reference). Figure 2 ) etc., but Figure 1 Illustrations omitted.

[0101] The MZ-type optical waveguide is a waveguide that includes at least one branch 91 and at least one combiner 92 as its basic components. The branch 91 is the portion that branches one optical waveguide 80 into two optical waveguides 80. The combiner 92 is the portion that connects the two optical waveguides 80 and combines them into one optical waveguide 80. The shape, size, and refractive index of the optical waveguide components such as the branch 91 and the combiner 92 can be adjusted to fit the optical waveguide 80, and optical couplers can also be configured. Furthermore, the MZ-type optical waveguide may also include two or more branch 91s or two or more combiners 92s.

[0102] Figure 1 The optical waveguide 80 of the optical waveguide element 1 shown is configured to propagate input light L11 from the optical input end 80a and output light L21 and output light L22 from the two optical output ends 80b and 80c. The optical waveguide 80 extends from the optical input end 80a along its long side and folds back, branching into two optical waveguides 80 at the branching point 91. The two branched optical waveguides 80 further branch at the branching point 91 to become four optical waveguides 80, and then further branch at the branching point 91 to become eight optical waveguides 80. The eight optical waveguides 80 extend side-by-side (…). Figure 1 The region near R1 is used as a modulation section (operating section) to modulate the light wave propagating in the optical waveguide 80. The eight optical waveguides 80 arranged side by side are combined into four optical waveguides 80 at the combining section 92, and then further combined into two optical waveguides 80, which are connected to the two optical output terminals 80b and 80c respectively. Thus, the input light L11 input from the optical input terminal 80a is appropriately modulated by the modulation section, and output light L21 and output light L22 are output from the two optical output terminals 80b and 80c.

[0103] At the optical input end 80a, optical output end 80b, and optical output end 80c, which serve as the ends of the optical waveguide 80, a spot size converter (SSC) or a grating section can be provided to change the cross-sectional diameter of the light wave. The structure of the spot size converter or grating section is not particularly limited and can be implemented using existing technology.

[0104] The cross-sectional structure of the optical waveguide element 1 in this embodiment will be described. Figure 2 The optical waveguide element 1 involved in this embodiment is defined as the waveguide element along the optical waveguide. Figure 1 A cross-sectional view of line AA. Figure 2 The image shows a cross-section of the optical waveguide element 1 that is orthogonal to the direction of its long side (a cross-section orthogonal to the direction of light propagation of the optical waveguide 80). Figure 2 The left-right direction of the cross-sectional view shown corresponds to the width direction of optical waveguide element 1. Hereinafter, it will sometimes be referred to as... Figure 2 The vertical direction of the cross-sectional view shown is called the height direction of the optical waveguide element 1.

[0105] The substrate 10 of the optical waveguide element 1 is made of a material with photoelectric effect. Materials with photoelectric effect can include lithium niobate (LN), lithium tantalate (LT), lead lanthanum zirconate titanate (PLZT), etc., and can also be doped with MgO, etc. Alternatively, vapor-grown films obtained from these materials, or composite substrates formed by bonding these materials to different types of substrates, can also be used.

[0106] The thickness of the substrate 10 is preferably 1.0 μm or less. The thickness of the substrate 10 refers to the height from the lower surface of the substrate 10 to the flat upper surface (upper surface 10a of the substrate) where the protrusion 15 is not formed. By making the substrate 10 a thin plate with a thickness of 1.0 μm or less, the driving voltage can be reduced and miniaturized.

[0107] An optical waveguide 80 is formed on a substrate 10 of the optical waveguide element 1. A convex portion 15 protruding from the flat upper surface 10a of the substrate is formed on the substrate 10. The convex portion 15 is provided in a portion corresponding to the optical waveguide 80, forming a convex optical waveguide as a path for the propagation of light waves.

[0108] There are no particular limitations on the method of forming the convex optical waveguide. For example, the convex portion 15 (rib) can be formed by etching the substrate 10, or the convex portion 15 (ridge) can be formed by forming grooves on both sides of the optical waveguide 80. In addition, Ti or the like can be diffused to the surface of the substrate 10 by thermal diffusion or proton exchange methods, corresponding to the convex optical waveguide, thereby further improving the refractive index. There are no particular limitations on the size of the convex portion 15, but it can be set to about 1.0 μm in width and height, similar to a conventional convex optical waveguide.

[0109] To improve the mechanical strength of the thinned substrate 10, such as Figure 2 As shown, a reinforcing substrate (support substrate) 20 can be disposed below the substrate 10. Furthermore, in Figure 2The lower part of the reinforcing substrate 20 is omitted from the diagram. The thickness of the reinforcing substrate 20 is not particularly limited; for example, it can be set to approximately 0.2 mm to 1.0 mm. Figure 2 As shown, the reinforcing substrate 20 can be bonded to the substrate 10 via a bonding layer (intermediate layer) 30, or it can be directly bonded to the substrate 10. The material of the reinforcing substrate 20 is not particularly limited, and for example, Si, glass, crystal, fused silica, synthetic silica, alkali glass, alkali-free glass, lead glass, borosilicate glass, sodium glass, sapphire, alumina, etc. can be used.

[0110] An electrode 60 is mounted on the substrate 10. In this embodiment, as... Figure 2 As shown, an oxygen defect prevention layer 40 is formed corresponding to the placement position of the electrode 60. The oxygen defect prevention layer 40 can be formed on the upper surface (upper surface 10a) of the substrate 10 using a sputtering method or the like.

[0111] An oxygen defect prevention layer 40 is disposed between the substrate 10 and the electrode base layer 50. The oxygen defect prevention layer 40 is configured such that its lower surface contacts the substrate 10 and its upper surface contacts the electrode base layer 50. The oxygen defect prevention layer 40, which separates the substrate 10 and the electrode base layer 50, serves to prevent oxygen from the substrate 10 from being taken away by the electrode base layer 50 (and thus the electrode 60 on its upper surface side).

[0112] The material of the oxygen defect prevention layer 40 can be a dielectric material with a low refractive index and high transparency compared to the material of the substrate 10 (e.g., LN) and the material of the electrode 60 (e.g., gold (Au)). The refractive index of the material of the oxygen defect prevention layer 40 is preferably 1.3 or higher, and the dielectric constant of the material of the oxygen defect prevention layer 40 is preferably 3 or higher. Furthermore, it is preferable to select a material with low light absorption within the wavelength band of the light wave propagating in the optical waveguide 80. Specifically, as the material of the oxygen defect prevention layer 40, oxides or fluorides or nitrides of metal elements from groups 1 to 17 of the periodic table are preferred, such as SiO2, Al2O3, MgF2, La2O3, ZnO, HfO2, MgO, CaF2, Y2O3, etc.

[0113] When using SiO2 as the material for the oxygen defect prevention layer 40, it is preferable to have an average atomic number ratio O / Si greater than 1.9 (O / Si > 1.9). This ensures that the oxygen defect prevention layer 40 is sufficiently oxygen-containing, preventing oxygen from being removed from the substrate 10 and thus suppressing DC drift caused by oxygen defects in the substrate 10. The average atomic number ratio in the oxygen defect prevention layer 40 can be detected using Rutherford backscattering spectroscopy (RBS).

[0114] The content of inert gas (e.g., argon) in the oxygen defect prevention layer 40 is preferably set to 1.0 atm% to 3.0 atm%. The content of inert gas in the oxygen defect prevention layer 40 is the same as the average number of atoms and can be detected by Rutherford backscattering analysis (RBS analysis).

[0115] When there is a high amount of inert gas in the oxygen defect prevention layer 40, the density of the oxygen defect prevention layer 40 becomes low, which may result in insufficient strength. On the other hand, when there is a low amount of inert gas in the oxygen defect prevention layer 40, the density of the oxygen defect prevention layer 40 becomes high, and the film stress of the oxygen defect prevention layer 40 has a greater impact on the substrate 10, making it easier for the layer to peel off from the substrate 10. Therefore, by controlling the content of inert gas in the oxygen defect prevention layer 40 to the aforementioned range, the oxygen defect prevention layer 40 can be made physically stable. Furthermore, by appropriately adjusting the pressure of the inert gas used in film deposition based on sputtering or the film deposition rate, the content of inert gas in the oxygen defect prevention layer 40 can be controlled to the aforementioned range.

[0116] The thickness of the oxygen defect prevention layer 40 is preferably set within a specific range for the following reasons. If the thickness of the oxygen defect prevention layer 40 is too thick, the charge carriers in the oxygen defect prevention layer 40 may move due to the electric field, potentially causing DC drift. Furthermore, if the thickness of the oxygen defect prevention layer 40 is too thick, the film stress of the oxygen defect prevention layer 40 will have a greater impact on the substrate 10, making it easier for the layer to peel off from the substrate 10. Therefore, the thickness of the oxygen defect prevention layer 40 is preferably set to 200 nm or less, and more preferably 100 nm or less. On the other hand, since the oxygen defect prevention layer 40 is formed using methods such as sputtering, if the thickness is too thin, controlling the film thickness becomes difficult. From the viewpoint of process stability, the thickness of the oxygen defect prevention layer 40 is preferably set to 10 nm or more, and more preferably 20 nm or more. That is, the thickness of the oxygen defect prevention layer 40 is preferably 10 nm to 200 nm, and more preferably 20 nm to 100 nm.

[0117] The oxygen defect prevention layer 40 is configured between the substrate 10 and the electrode base layer 50, with its lower surface in contact with the substrate 10 and its upper surface in contact with the electrode base layer 50. The electrode base layer 50 exists between the oxygen defect prevention layer 40 and the electrode 60 and functions as an adhesive layer, improving the adhesion of the electrode 60 and preventing its peeling.

[0118] The material of the electrode substrate 50 is preferably selected with consideration for its adhesion to the substrate 10 and the oxygen defect prevention layer 40, and for example, Nb, Ti, Al, Mn, Cr, Ni, Pt, SiN, etc. can be used. The film formation method or the thickness of the electrode substrate 50 is not particularly limited. For example, the thickness of the electrode substrate 50 may be the same as or less than that of the oxygen defect prevention layer 40.

[0119] Electrode 60 is used for modulation of light waves propagating in optical waveguide 80 and is disposed near optical waveguide 80. Furthermore, in this embodiment, as... Figure 2 As shown, an example is illustrated where the electrode 60 is positioned between the optical waveguide 80 (X-cut substrate), but this can also be applied to a case where the electrode 60 is positioned above the optical waveguide 80 (Z-cut substrate). Furthermore, this specification primarily illustrates and describes a single-electrode structure, but it can also be applied to a differential electrode structure. The electrode 60 includes a modulation electrode that applies a modulation signal to the optical waveguide 80 or a DC electrode that applies a DC bias voltage.

[0120] The material of electrode 60 is not particularly limited as long as it is a metal material with low resistance and excellent impedance characteristics; Au, Ag, Cu, etc., can be used. The method of forming electrode 60 is also not particularly limited; conventional methods such as sputtering, vapor deposition, and plating can be used.

[0121] As described above, in this embodiment, an oxygen defect prevention layer 40 is formed on the upper surface (upper surface 10a) of a substrate 10 on which the protrusion 15 is formed, and an electrode 60 is formed on the upper surface of the oxygen defect prevention layer 40, with an electrode base layer 50 in between. That is, the optical waveguide element 1 of this embodiment is configured such that an oxygen defect prevention layer 40 is disposed on the upper surface 10a of the substrate, an electrode base layer 50 is disposed on the upper surface of the oxygen defect prevention layer 40, and an electrode 60 is disposed on the upper surface of the electrode base layer 50.

[0122] An oxygen defect prevention layer 40 is disposed between the substrate 10 and the electrode base layer 50. In this embodiment, the oxygen defect prevention layer 40 is configured to make full surface contact with the lower surface of the electrode base layer 50, and the upper surface of the substrate 10 and the lower surface of the electrode base layer 50 are separated by the oxygen defect prevention layer 40 and do not make direct contact.

[0123] The oxygen defect prevention layer 40 is made of a material that does not substantially remove oxygen from the substrate 10, and exists between the substrate 10 and the electrode base layer 50 and the electrode 60 as a separator, thus preventing oxygen from the substrate 10 from being removed by the electrode base layer 50 and the electrode 60. Therefore, the oxygen defect prevention layer 40 can prevent oxygen from the substrate 10 from being removed by the electrode base layer 50 and the electrode 60 disposed above the substrate 10, thereby suppressing the generation of DC drift caused by oxygen defects in the substrate 10.

[0124] In this embodiment, the widths of the stacked oxygen defect prevention layer 40, electrode substrate layer 50, and electrode 60 are all set to be the same. Specifically, as... Figure 2 As shown, the oxygen defect prevention layer 40 is formed such that its side surface 40a is consistent with the side surface 50a of the electrode substrate layer 50 and the side surface 60a of the electrode 60, and is not formed between the electrodes 60.

[0125] In this embodiment, the insight that charge carriers in the film on the surface 15a covering the convex portion 15 and the upper surface 10a of the substrate between the electrodes 60 are a factor in the generation of DC drift (see, for example, reference to...) Figure 7 and Figure 8 ),like Figure 2 As shown, the upper surface 10a of the substrate between the electrodes 60, including the surface 15a of the protrusion 15, is not covered with a specific material, thus exposing it to air. Furthermore, the surface 15a of the protrusion 15 refers to the upper surface and side surface of the protrusion 15 that protrudes from the upper surface 10a of the substrate.

[0126] Without covering the surface of the protrusion 15 with a specific material and allowing it to contact the air, in order to suppress the scattering of light waves caused by the surface 15a of the protrusion 15, the arithmetic mean roughness Ra of the surface 15a of the protrusion 15 is preferably set to 5.0 nm or less, and more preferably to 3.0 nm or less. The arithmetic mean roughness Ra of the protrusion 15 can be measured and calculated using an atomic force microscope (AFM). By reducing the roughness of the surface 15a of the protrusion 15 in this way, the scattering of light waves caused by the surface 15a of the protrusion 15 can be suppressed. Thus, without forming a light scattering suppression layer covering the surface 15a of the protrusion 15, the generation of DC drift caused by oxygen defects in the substrate 10 can be suppressed at the same time as the scattering of light waves.

[0127] On the other hand, such as Figure 3 As shown in the derivative example, a light scattering suppression layer 100 can also be formed by covering the surface 15a of the protrusion 15. The light scattering suppression layer 100 has the function of suppressing the scattering of light waves caused by the surface 15a of the protrusion 15. The light scattering suppression layer 100 can be made of, for example, the same material as the oxygen defect prevention layer 40, or it can be a film that does not generate carrier movement, such as a photosensitive insulating film (permanent film). Furthermore, a material that does not generate carrier movement can also be filled between the electrodes 60.

[0128] like Figure 3As shown, the light scattering suppression layer 100 is preferably formed in such a way that it only covers the surface 15a of the convex portion 15. The oxygen defect prevention layer 40 disposed below the electrode 60 and the light scattering suppression layer 100 covering the surface 15a of the convex portion 15 are preferably separated in the width direction and not connected. By limiting the position of the light scattering suppression layer 100 to the surface 15a of the convex portion 15 in this way, even if a material that generates charge carrier movement is used in the light scattering suppression layer 100, the scattering of light waves caused by the surface 15a of the convex portion 15 can be appropriately and effectively suppressed while minimizing the generation of DC drift.

[0129] exist Figure 2 In the figure, an oxygen defect prevention layer 40 is disposed below all electrodes 60, but the oxygen defect prevention layer 40 can also be selectively disposed according to the properties of the electrodes 60.

[0130] The oxygen defect prevention layer 40 serves to suppress DC drift caused by oxygen defects in the substrate 10, and is preferably disposed at least below the DC electrode to which a DC voltage such as a DC bias voltage is applied. For the reasons stated above, the oxygen defect prevention layer 40 may also be disposed only below the DC electrode. In this case, the oxygen defect prevention layer 40 may not be disposed below the modulation electrode to which the modulation signal is applied to the optical waveguide 80, or it may be disposed below the modulation electrode.

[0131] Furthermore, in the modulation section (functional section) of the optical waveguide 80, to prevent oxygen defects in the substrate 10, an oxygen defect prevention layer 40 may be provided only below the electrode 60 disposed near the modulation section (functional section). Specifically, if the thickness of the electrode 60 disposed near the modulation section (functional section) of the optical waveguide 80 is 1.0 μm or less, the oxygen defect prevention layer 40 may be provided only below the electrode 60 with a thickness of 1.0 μm or less. In this case, the oxygen defect prevention layer 40 may not be provided below the electrode 60 with a thickness exceeding 1.0 μm, or the oxygen defect prevention layer 40 may be provided below the electrode 60 with a thickness exceeding 1.0 μm.

[0132] (Second Implementation)

[0133] The second embodiment of this utility model will be described. Compared with the first embodiment, the optical waveguide element 1 of the second embodiment differs in that the width of the oxygen defect prevention layer 40 is set to be greater than the width of the electrode substrate layer 50 and the electrode 60. For components having the same function as those in the first embodiment, descriptions are simplified or omitted, and the same reference numerals are used.

[0134] Figure 4 The optical waveguide element 1 involved in this embodiment is defined as the waveguide element along the optical waveguide. Figure 1 A cross-sectional view of the BB line.

[0135] The widths of the stacked oxygen defect prevention layer 40, electrode substrate layer 50, and electrode 60 do not necessarily need to be the same, such as... Figure 4 As shown, the width of the oxygen defect prevention layer 40 can also be set to be greater than the widths of the electrode substrate layer 50 and the electrode 60. Specifically, as... Figure 4 As shown, the oxygen defect prevention layer 40 is formed such that its side surface 40a is located closer to the protrusion 15 forming the optical waveguide 80 than the side surface 50a of the electrode substrate layer 50 and the side surface 60a of the electrode 60. The surface 15a of the protrusion 15 can be in contact with air, or it can be as shown in the diagram. Figure 3 As shown, a light scattering suppression layer 100 is formed on the surface 15a of the convex portion 15.

[0136] In this embodiment, compared to the first embodiment, the oxygen defect prevention layer 40 is formed over a wider area covering the upper surface 10a of the substrate. By increasing the width of the oxygen defect prevention layer 40 disposed between the substrate 10 and the electrode base layer 50 and the electrode 60, even if the alignment of the electrode 60 is misaligned, the alignment tolerance can be ensured so that it remains in a position that does not remove oxygen from the substrate 10. As a result, it is possible to more reliably prevent oxygen from the substrate 10 from being removed by the electrode base layer 50 and the electrode 60, thereby more reliably suppressing the generation of DC drift caused by oxygen defects in the substrate 10.

[0137] (Third implementation method)

[0138] The third embodiment of this utility model will be described. Compared with the first and second embodiments, the optical waveguide element 1 of the third embodiment differs in that the width of the oxygen defect prevention layer 40 is smaller, and a portion of the lower surface of the electrode substrate layer 50 is in direct contact with the substrate 10. For components having the same function as those in the embodiments, descriptions are simplified or omitted, and the same reference numerals are used.

[0139] Figure 5 The optical waveguide element 1 involved in this embodiment is defined as the waveguide element along the optical waveguide. Figure 1 A cross-sectional view of the BB line.

[0140] Electrode 60 is configured to apply an electric field to optical waveguide 80 formed on protrusion 15. The substrate 10 sandwiched between electrodes 60 of protrusion 15, or a substrate 10 near it, forms the electric field path. For the substrate 10 along the electric field path, it is preferable to reliably suppress oxygen defects. On the other hand, for substrates 10 located away from the electric field path, the oxygen defect prevention layer 40 may not necessarily be provided. That is, in this embodiment, while allowing a portion of the lower surface of the electrode base layer 50 to contact the substrate 10, the oxygen defect prevention layer 40 is provided only at locations that have the effect of suppressing DC drift.

[0141] The oxygen defect prevention layer 40 can be disposed biased toward the side where the convex portion 15 of the optical waveguide 80 is formed, for example, as shown in the example. Figure 5 As shown, it can also be configured such that one end (side 40b) of the portion away from the protrusion 15 is located inside the electrode substrate layer 50 in the width direction. The distance D in the width direction between the side 40b of the oxygen defect prevention layer 40 located away from the protrusion 15 and the side 60a of the electrode 60 (refer to...) Figure 5 For example, a thickness of 5.0 μm or more is preferred. This prevents oxygen from the substrate 10 from being removed by the electrode substrate layer 50 and the electrode 60, thereby suppressing DC drift caused by oxygen defects in the substrate 10. Furthermore, the surface 15a of the protrusion 15 can be in contact with air, or it can be as follows: Figure 3 As shown, a light scattering suppression layer 100 is formed on the surface 15a of the convex portion 15.

[0142] When the side surface 40b of the oxygen defect prevention layer 40 is disposed inside the width direction of the electrode substrate layer 50, the electrode substrate layer 50 has a surface that contacts the upper surface of the oxygen defect prevention layer 40, and has a portion that directly contacts the substrate 10 at a location away from the protrusion 15 (the contact surface 70 between the electrode substrate layer 50 and the substrate 10). The contact surface 70 between the electrode substrate layer 50 and the substrate 10 is disposed at a position at least 5.0 μm away from the side surface 60a of the electrode 60. Furthermore, in Figure 5 There is no optical waveguide 80 on the left side. Figure 5 The contact surface 70 between the electrode base layer 50 and the substrate 10 on the left side of the electrode 60 is wider than that of the other electrodes 60.

[0143] The lower surface of the electrode substrate layer 50 is uneven rather than flat. The uneven lower surface of the electrode substrate layer 50 also has the following advantages: the contact area between the lower surface of the electrode substrate layer 50 and each layer (substrate 10 and oxygen defect prevention layer 40) is increased, which can improve the tightness through the anchoring effect.

[0144] The optical modulator and optical transmitting device of this invention will be described below. This invention provides an optical modulator and optical transmitting device utilizing the optical waveguide element 1 of the various embodiments described above.

[0145] Figure 6 This is a plan view showing the optical modulator 300 and the optical transmitting device 400 of this utility model. Figure 6 The optical modulator 300 shown includes an optical waveguide element 1, a housing 301, an input optical fiber 302, and an output optical fiber 303. Here, as an example, the case where the optical waveguide element 1 of this embodiment is applied to a high-bandwidth coherent driver modulator (HB-CDM) will be described.

[0146] In the optical modulator 300, an optical waveguide element 1 is housed within a housing 301. An input optical fiber 302 is connected to the optical input section of the optical waveguide element 1, including an optical input terminal 80a, and an output optical fiber 303 is connected to the optical output section, including optical output terminals 80b and 80c. By connecting the optical waveguide element 1 within the housing 301 to the outside of the housing 301 using optical fibers in this way, a compact optical modulator 300 can be provided. Furthermore, a spatial optical system can be provided between the optical input section and the input optical fiber 302, and between the optical output section and the output optical fiber 303. Additionally, the optical waveguide element 1 has two optical output terminals 80b and 80c. In this case, as... Figure 6 As shown, the optical modulator 300 can be configured to have a polarization wave combining unit 304, which combines the polarization waves of the light output from the two optical output terminals 80b and 80c and guides the light to the output optical fiber 303.

[0147] like Figure 6 As shown, an optical transmitting device 400 can be constructed by connecting a signal output circuit 401 that generates a high-frequency signal, i.e., an electrical signal So (modulation signal), for modulation, and a signal amplification circuit 402 that amplifies the electrical signal So to generate an amplified signal S (modulation signal). The signal output circuit 401 or the signal amplification circuit 402 can be configured outside the housing 301 of the optical modulator 300, but by configuring them inside the housing 301, efficient transmission of the modulation signal and miniaturization of the optical transmitting device 400 can be achieved.

[0148] Alternatively, the light source 403 can be mounted on the light transmitting device 400, and the light emitted by the light source 403 (input light L1) can be input to the light input terminal 80a of the optical waveguide element 1. In this way, the light output from the light source 403 can be modulated by the optical modulator 300, and the modulated light (output light L2) can be output from the light transmitting device 400.

[0149] The optical waveguide element 1 of this embodiment can be applied to various devices related to optical measurement technology or optical communication technology. The optical waveguide element 1 of this embodiment can be installed inside a transceiver or in a pluggable module. The pluggable module includes an electrical interface that can be plugged into and removed relative to the optical transmission device and an optical interface that can be connected to an optical fiber connector, enabling the optical transmission device to achieve high-performance transceiver functionality.

[0150] The optical waveguide element 1 of this embodiment can also be installed in packaged modules such as co-packaged optics (CPO) or near-packaged optics (NPO), or in sub-assemblies such as integrated coherent transmit-receive optical sub-assemblies (IC-TROSA) or coherent optical sub-assemblies (COSA). Furthermore, it can be assembled into optical circuits utilizing silicon photonics technology. The optical waveguide element 1 of this embodiment achieves the effect of suppressing DC drift, providing excellent operational stability in various devices.

[0151] The embodiments described above are provided for ease of understanding of this utility model and are not intended to limit the scope of this utility model. The main point of the components disclosed in the embodiments is that they also include all design modifications or equivalents that fall within the technical scope of this utility model. In addition, the technical ideas obtained by appropriately combining the concepts illustrated in the various embodiments are also included in this utility model.

Claims

1. An optical waveguide element, characterized in that, include: The substrate is made of electro-optic crystals and forms an optical waveguide; Electrodes are mounted on the substrate; An electrode substrate layer is configured to contact the lower surface of the electrode; as well as An oxygen defect prevention layer is disposed in contact with at least a portion of the lower surface of the electrode substrate and at least a portion of the upper surface of the substrate to prevent oxygen defects in the substrate caused by the electrode substrate.

2. The optical waveguide element according to claim 1, characterized in that, The oxygen defect prevention layer is configured to make full surface contact with the lower surface of the electrode substrate layer.

3. The optical waveguide element according to claim 1 or 2, characterized in that, The oxygen defect prevention layer is disposed below the DC electrode to which the DC voltage is applied.

4. The optical waveguide element according to claim 1 or 2, characterized in that, The oxygen defect prevention layer is disposed below the electrode, which has a thickness of less than 1.0 μm.

5. The optical waveguide element according to claim 1 or 2, characterized in that, It has a reinforced substrate bonded to the underside of the substrate via a bonding layer. The substrate is composed of a lithium niobate substrate with a thickness of less than 1.0 μm. A convex portion serving as the optical waveguide is formed on the upper surface of the substrate.

6. The optical waveguide element according to claim 5, characterized in that, The oxygen defect prevention layer is not formed on the surface of the convex portion.

7. The optical waveguide element according to claim 5, characterized in that, The arithmetic mean roughness Ra of the surface of the convex portion is less than 5.0 nm.

8. The optical waveguide element according to claim 1 or 2, characterized in that, The oxygen defect prevention layer is made of a material with a refractive index of 1.3 or higher and a dielectric constant of 3.0 or higher.

9. The optical waveguide element according to claim 1 or 2, characterized in that, The material constituting the oxygen defect prevention layer is SiO2, and the average atomic ratio of oxygen to silicon is greater than 1.

9.

10. The optical waveguide element according to claim 1 or 2, characterized in that, The inert gas content in the oxygen defect prevention layer is 1.0 atm% to 3.0 atm.

11. The optical waveguide element according to claim 1 or 2, characterized in that, The thickness of the oxygen defect prevention layer is 10 nm to 200 nm.

12. An optical modulator, characterized in that, It comprises: an optical waveguide element as described in claim 1 or 2; a housing for accommodating the optical waveguide element; an input optical fiber connected to the optical input portion of the optical waveguide element; and an output optical fiber connected to the optical output portion of the optical waveguide element.

13. The optical modulator according to claim 12, characterized in that, The device includes a modulation electrode that modulates the light wave propagating in the optical waveguide, and a signal amplification circuit that amplifies the modulation signal applied to the modulation electrode is located inside the housing.

14. An optical transmitting device, characterized in that... It has: the optical modulator as described in claim 13; A light source inputs light waves into the light modulator; and The signal output circuit outputs the modulated signal.

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