Optical waveguide element and optical modulator

Abstract

The present invention aims at effectively suppressing the case where a loss occurs in a propagating light in an optical waveguide element using a convex optical waveguide. The optical waveguide element of the present invention has a substrate (220) in which an optical waveguide (226a) is formed, and electrodes (230a, 230b) formed on the substrate to control an optical wave propagating in the optical waveguide, wherein the optical waveguide (226a) is composed of a convex portion (300) extending on the substrate, the electrodes (230a, 230b) are composed of a base layer (304a, 304b) and an upper layer (302a, 302b), the base layer (304a, 304b) is composed of Nb between the electrodes (230a, 230b) and the substrate, and the upper layer (302a, 302b) is formed on the base layer.

Description

Technical Field

[0001] The present invention relates to an optical waveguide element that uses an optical waveguide as a functional element, and an optical modulator that uses an optical modulation element that uses an optical waveguide element. Background Technology

[0002] In high-speed / high-capacity optical fiber communication systems, optical transmission devices incorporating waveguide-type optical modulators are frequently used. Among these, optical modulation elements using LiNbO3 (hereinafter also referred to as LN) as a substrate exhibiting electro-optic effects show less light loss and can achieve broadband optical modulation characteristics compared to optical modulation elements using semiconductor materials such as indium phosphide (InP), silicon (Si), or gallium arsenide (GaAs). Therefore, they are widely used in high-speed / high-capacity optical fiber communication systems.

[0003] On the other hand, the modulation methods in optical fiber communication systems have been influenced by the trend of increasing transmission capacity in recent years. Multi-level modulation such as QPSK (Quadrature Phase Shift Keying) and DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) and transmission systems that use polarization multiplexing for multi-level modulation have become mainstream.

[0004] The rapid popularization of internet services in recent years will lead to a further increase in the amount of communication information, and research on the miniaturization, broadbanding, and power saving of optical modulation elements is also constantly advancing.

[0005] As a countermeasure to miniaturize, broadband, and reduce power consumption of such optical modulation elements, optical modulators using ribbed or ridged optical waveguides (hereinafter collectively referred to as convex optical waveguides) formed by thinning an LN substrate (e.g., with a thickness of 20 μm or less) to further enhance the interaction between the signal electric field in the substrate and the waveguide light (i.e., to improve the electric field efficiency) are also being put into practical use (e.g., Patent Documents 1 and 2).

[0006] Currently, due to further increases in speed, research is ongoing on placing electrodes closer to convex optical waveguides to further improve electric field efficiency. Au (gold) is primarily used for electrode construction; however, Au has low adhesion to LN substrates, resulting in insufficient fixation strength in practical applications. Therefore, Ti (titanium) films are typically formed as the electrode base layer to ensure the electrode's fixation strength relative to the substrate.

[0007] However, in the view of the inventors of this invention, when the conventional electrodes having the above-described structure are positioned closer to the ribbed optical waveguide, the light waves propagating in the convex optical waveguide will experience significant light loss.

[0008] Prior art literature

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2007-264548

[0011] Patent Document 2: International Publication No. 2018 / 031916 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Based on the above background, in optical waveguide elements that use convex optical waveguides such as ribbed or crested optical waveguides, it is required to suppress the loss of propagating light by using electrodes placed close to the convex optical waveguide.

[0014] Solution for solving the problem

[0015] One aspect of the present invention relates to an optical waveguide element comprising: a substrate on which an optical waveguide is formed; and an electrode formed on the substrate for controlling light waves propagating in the optical waveguide, wherein the optical waveguide is composed of protrusions extending on the substrate, the electrode is composed of a base layer and an upper layer, the base layer being composed of Nb between the electrode and the substrate, and the upper layer being formed on the base layer.

[0016] According to another aspect of the invention, the substrate layer has a thickness of less than 30 nm.

[0017] According to another aspect of the invention, the substrate layer is formed on the substrate containing oxygen atoms, or on a film of oxide formed on the substrate.

[0018] According to another aspect of the invention, the substrate layer contains oxygen atoms, and the elemental ratio of Nb to oxygen, Nb / O, is 1.0 or higher.

[0019] According to another aspect of the invention, the electrode is composed of a plurality of electrodes arranged along the optical waveguide at a position sandwiching the optical waveguide on the substrate.

[0020] Another aspect of the present invention relates to an optical modulator comprising: any of the aforementioned optical waveguide elements, which are optical modulation elements for modulating light; a housing for housing the optical waveguide element; an optical fiber for inputting light to the optical waveguide element; and an optical fiber for guiding the light output from the optical waveguide element to the outside of the housing.

[0021] It should be noted that this specification contains the entire contents of Japanese Patent Application No. 2020-164627, filed on September 30, 2020.

[0022] Invention Effects

[0023] According to the present invention, in optical waveguide elements using convex optical waveguides such as ribbed or ridged optical waveguides, the loss in propagating light can be effectively suppressed by electrodes disposed close to the convex optical waveguide. Attached Figure Description

[0024] Figure 1 This is a diagram showing the structure of an optical modulator according to one embodiment of the present invention.

[0025] Figure 2 It means Figure 1 The diagram shows the structure of the optical modulation element used in the optical modulator.

[0026] Figure 3 yes Figure 2 The optical modulation element shown is viewed in section III-III.

[0027] Figure 4 This is a graph showing the simulation results of light absorption loss when the substrate layer of the electrode uses various metals.

[0028] Figure 5 This is a graph showing the evaluation results of the electrode's fixation strength relative to the substrate when the electrode's base layer uses various metals.

[0029] Figure 6 This is a diagram showing the results of compositional analysis of a cross-section of an electrode structure portion when an electrode containing an Nb-containing substrate is formed on a substrate.

[0030] Figure 7 This is a diagram illustrating another example of the optical modulation element of the present invention. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the optical waveguide element shown in the following embodiments is an optical modulation element constructed using an LN substrate, but the optical waveguide element of the present invention is not limited thereto. The present invention is also applicable to optical waveguide elements using substrates other than LN substrates, and to optical waveguide elements having functions other than optical modulation.

[0032] Figure 1 This diagram illustrates the structure of an optical modulation element and an optical modulator, which are optical waveguide elements according to one embodiment of the present invention. In this embodiment, the optical waveguide element is an optical modulation element 102 that uses a Mach-Zehnder optical waveguide for optical modulation.

[0033] The optical modulator 100 houses the optical modulation element 102 inside the housing 104. It should be noted that the housing 104 is ultimately fixed with a cover (not shown) as a plate at its opening, and its interior is hermetically sealed.

[0034] The optical modulator 100 has: an input optical fiber 106 for inputting light into the housing 104; and an output optical fiber 108 for guiding the light modulated by the optical modulation element 102 to the outside of the housing 104.

[0035] The optical modulator 100 further includes: a connector 110 for receiving a high-frequency electrical signal from the outside that causes the optical modulating element 102 to perform optical modulation; and a relay substrate 112 for relaying the high-frequency electrical signal received by the connector 110 to one end of an electrode (e.g., a signal electrode) of the optical modulating element 102. Furthermore, the optical modulator 100 includes a terminator 114 with a predetermined impedance connected to the other end of the electrode of the optical modulating element 102. Here, the electrode of the optical modulating element 102 is electrically connected to the relay substrate 112 and the terminator 114 via bonding, for example, with a metal wire.

[0036] Figure 2 It means in Figure 1 The diagram shows the structure of the optical modulation element 102, which serves as an optical waveguide element, housed in the housing 104 of the optical modulator 100. The optical modulation element 102 is composed of an optical waveguide 224 formed on a substrate 220. The substrate 220 is, for example, an X-cut LN substrate with electro-optic effect that has been thinned to a thickness of less than 20 μm (e.g., 2 μm).

[0037] The optical waveguide is a convex optical waveguide (e.g., a ribbed or ridged optical waveguide) formed on the surface of the thin-film substrate 220, consisting of protrusions extending in a strip shape. Here, the refractive index of the LN substrate changes locally due to photoelastic effects when stress is applied. Therefore, in order to enhance the overall mechanical strength of the substrate, it is usually bonded to a support plate 222, such as glass, via an adhesive layer 350 (described later).

[0038] Optical waveguide 224 is, for example, a Mach-Zehnder waveguide, including two branches and two parallel waveguides 226a and 226b extending parallel to each other. Electrodes 230a, 230b, and 230c are also provided on the substrate 220 to control the propagation of light waves in the parallel waveguides 226a and 226b by changing the refractive index of the parallel waveguides 226a and 226b. Hereinafter, electrodes 230a, 230b, and 230c will also be collectively referred to as electrode 230.

[0039] Electrode 230 is configured, for example, as a coplanar transmission line with a specified impedance, in accordance with existing technology. Specifically, electrode 230a is a center electrode, formed in the plane of substrate 220 at a position sandwiched between the parallel waveguides 226a and 226b. Furthermore, electrodes 230b and 230c are ground electrodes, formed along these parallel waveguides at positions opposite to electrode 230a, respectively, across from parallel waveguides 226a and 226b.

[0040] Electrode 230 terminates the lower right end of substrate 220 in the diagram via terminator 114, thereby allowing a high-frequency signal input from the lower left end of substrate 220 via connector 110 to propagate as a traveling wave from left to right in the diagram. Thus, electrode 230 constitutes a signal line for controlling the light wave propagating from left to right in parallel waveguides 226a and 226b in the diagram.

[0041] Figure 3 yes Figure 2 The optical modulation element 102 shown is viewed in section III-III. The substrate 220 is bonded to, for example, glass, or support plate 222 via an adhesive layer 350. The parallel waveguide 226a, which is a convex optical waveguide, is formed by a protrusion 300 formed on the substrate 220. The height t1 of the protrusion 300, measured from the surface of the substrate 220, is 10 μm or less (e.g., 1 μm).

[0042] Electrodes 230a and 230b are disposed on substrate 220 with parallel waveguides 226a between them. Electrodes 230a and 230b are both formed on substrate 220 at a height t2. This height t2 is set such that the electrode 230 has a specified impedance and that the traveling wave of the high-frequency electrical signal propagating in the electrode 230 has a loss within a specified range and propagates at a specified speed.

[0043] The distance w2 between the electrode closest to the parallel waveguide 226a (electrode 230a in this embodiment) and the parallel waveguide 226a is, for example, more than 0.5 times and less than 2 times w1 (i.e., 0.5w1≤w2≤2w1). It should be noted that, of course, when electrodes 230a and 230b are symmetrically configured with respect to the parallel waveguide 226a as the center, the respective distances between electrodes 230a and 230b and the parallel waveguide 226a become the same distance w2.

[0044] Electrodes 230a and 230b have the same structure, consisting of upper layers 302a and 302b, and base layers 304a and 304b, respectively. Figure 3 Although electrode 230c is not shown, it should be understood that electrode 230c is composed of the same upper layer and base layer as electrode 230a and electrode 230b.

[0045] Hereinafter, the upper layers 302a, 302b and the upper layer of electrode 230c (not shown) will also be collectively referred to as upper layer 302, and the base layers 304a, 304b and the base layer of electrode 230c (not shown) will also be collectively referred to as base layer 304. That is, electrode 230 is composed of upper layer 302 and base layer 304.

[0046] The upper layer 302 is made of, for example, Au (gold), similar to the prior art. If the Au constituting the upper layer 302 is formed directly on the substrate 220, it does not have practically sufficient fixing strength to the substrate 220, so it is formed on the substrate 220 via the base layer 304.

[0047] Conventionally, the substrate layer, which is provided to ensure the fixation strength with the substrate, is usually made of Ti (titanium). The inventors of this invention have discovered that when an electrode is placed near a convex optical waveguide, the metal of the substrate layer constituting the electrode absorbs the light propagating in the convex optical waveguide, thereby causing a loss of propagating light in the convex optical waveguide (light absorption loss).

[0048] Furthermore, the inventors of this invention have obtained insights into the causes of such light absorption loss based on the following situations: the operating light wavelength of the optical modulation element (e.g., the light wavelength of 1.55 μm and / or 1.3 μm used in optical communication) exists in the light absorption domain of the metal of the substrate layer; and a portion of the mode field of the propagating light propagating in the convex waveguide extends towards the substrate portion near the convex waveguide.

[0049] Regarding the thickness of the substrate, a thicker substrate will result in greater light absorption loss. Therefore, the substrate needs to be made of a metal with good fixed strength that excludes the wavelength of the active light from the light absorption domain, and it needs to be formed with a thickness that can suppress light absorption loss to a certain level.

[0050] The inventors of this invention have repeatedly studied the raw materials and thickness of the substrate layer, and as a solution to maintain the fixing strength of the substrate at a practical level and suppress the light absorption loss mentioned above, they have found that it is effective to use Nb (niobium) instead of Ti, which has been used as a metal for the substrate layer in the past.

[0051] In accordance with the above understanding, in this embodiment, the substrate layer 304 is specifically composed of Nb with a film thickness t3. The formation of the substrate layer and the upper layer on the substrate 220 can be performed, for example, by electron beam evaporation (EB evaporation).

[0052] Figure 4 This is part of the simulation results showing the increase in light absorption loss relative to the thickness of substrate 304 when various metals are used as the substrate 304. Figure 4In this paper, calculation results are shown for cases where Ti, Al (aluminum), and Nb are used as the substrate 304, in addition to the case where no substrate 304 is used (Au (upper layer 302) single film). Figure 4 In the diagram, the horizontal axis represents the thickness t3 of the substrate 304, and the vertical axis represents the light absorption loss per unit length (1 cm) of the parallel waveguide 226a. The simulation model used is similar to... Figure 3 The structure shown is similar, with w1 = 0.9 μm, w2 = 0.55 μm, t1 = 0.4 μm, t2 = 1.0 μm, t4 = 0.6 μm, and θ = 65°. Au is assumed to be the upper layer 302, and 1.55 μm is assumed to be the operating light wavelength. Here, t4 is the height of the protrusion 300 measured from the back side of the substrate 220, and θ is the angle of ascent of the side of the protrusion 300 relative to the surface of the substrate 220. Furthermore, when calculating the light absorption loss, the light absorption at the operating wavelength of 1.55 μm for each metal is used, obtained from the light absorption spectra of Ti, Al, and Nb.

[0053] The light absorption loss α0 of the Au monolayer (without a substrate layer) represented by line 400 is the light absorption loss in the above structure as background. The light absorption loss in the substrate layer 304 can be evaluated as the increase in light absorption loss from this baseline.

[0054] Lines 402, 404, and 406 represent the light absorption losses when the metals constituting the substrate layer 304 are Ti, Al, and Nb, respectively. Among these metals, Ti, represented by line 402, has the largest light absorption loss, which increases significantly along with its film thickness.

[0055] On the other hand, it can be seen that lines 404 and 406, representing the case where Al and Nb, whose operating wavelengths are not included in the light absorption domain, are set as substrate 304, show a significant reduction in light absorption loss compared to the case of Ti (line 402). Figure 4 Of the evaluation results shown, the light absorption loss is minimal when the substrate 304 is Al (line 404), and the light absorption loss is approximately constant relative to the thickness of the substrate. However, Al is generally known to have low bonding strength to the substrate.

[0056] Figure 5This table shows the results of evaluating the fixation strength of the electrodes relative to the LN substrate when various metals are used as the base layer. In this evaluation, the upper layer is Au with a thickness of 100 nm. The evaluation of fixation strength follows Japanese Industrial Standard JISK 5600-5-6:1999. Specifically, after the electrode layer is formed entirely on the substrate surface of the LN substrate, a cutter is used to make cuts in the electrode, forming 10 × 10 (totaling 100) rectangular samples of the same size on the LN substrate plane. Next, adhesive tape with adhesiveness specified in the above standard is attached to the 100 samples, and the fixation strength is evaluated based on the number of samples remaining on the LN substrate when the tape is peeled off. It should be noted that the base layer and the upper layer are formed on the LN substrate using EB vapor deposition.

[0057] Figure 5 Sample 01 shown is an Au single-layer film (without a substrate layer, only the top layer), with an adhesion rate of 0%. Samples 02-04 are samples that conventionally use Ti as a substrate layer, with an adhesion rate of 100% when the substrate layer thickness is 1 μm or more. In contrast, in samples 05-07 that use Al as a substrate layer, the adhesion rate is less than 100% regardless of the thickness, and a level of fixation strength that can withstand practical use is not obtained.

[0058] On the other hand, in sample 08-11, where Nb was used as a base layer, the adhesion rate was 100% at a thickness of 1 μm or more, indicating that sufficient fixation strength could be obtained in practical applications.

[0059] Figure 6 This is the result of cross-sectional compositional analysis of the portion of a sample containing electrodes formed on an LN substrate, where a Nb base layer and an Au top layer are formed. Figure 5 Similarly, the base layer and the upper layer were formed using EB vapor deposition. Figure 6 The horizontal axis represents position, and the vertical axis represents the component ratio (atomic percentage). Furthermore, in Figure 6 In the diagram, lines 610, 612, and 614 represent the positional changes in the component ratios of oxygen, Nb, and Au, respectively.

[0060] exist Figure 6 In the LN substrate near the interface 600 with the base layer, the oxygen content of the LN substrate decreases, while oxygen is present in the base layer in addition to Nb. On the other hand, at the interface 602 between the base layer and the upper layer, Au is present in the base layer and Nb is present in the upper layer. Therefore, the bonding force between the LN substrate and the Nb base layer can be considered to be based on the coupling of LN and Nb via oxygen, and the bonding force between the Nb base layer and the Au upper layer can be considered to be based on the coupling caused by the alloying of Nb and Au.

[0061] exist Figure 6In the Nb substrate, the Nb / O ratio is 1.2. When considering various Nb oxides such as NbO and NbO2, the Nb / O ratio in the Nb substrate only needs to be 1.0 or higher, and can be considered preferably 1.2 or higher.

[0062] It should be noted that the presence of oxygen in the Nb substrate layer up to the vicinity of interface 602 can be considered as oxygen infiltration from the LN substrate, or oxygen present in the ambient atmosphere infiltration into the substrate layer.

[0063] Reference Figure 3 Therefore, in this embodiment, the substrate 304 is composed of Nb, and the elemental ratio of Nb to oxygen in the substrate 304 is 1.2.

[0064] In addition, according to Figure 4 For lines 406 and 400, the thickness of the Nb substrate layer is preferably 30 nm or less. If the thickness of the Nb substrate layer is within this range, the light absorption loss can be suppressed to 2α0 or less, which is twice the value α0 under an Au single film, or about one-third or less of the value 6α0 conventionally used with a Ti substrate layer. In this embodiment, w2 = 2.0 μm, and the thickness t3 of the Nb substrate layer 304 is, for example, 10 nm. The light absorption loss in the parallel waveguide 226a is 6.0 dB / cm at this time.

[0065] Since the base layer of the electrode 230, which controls the light wave of the parallel waveguide 226a as a convex optical waveguide, is made of Nb, the optical modulation element 102 with the above structure can maintain the fixing strength of the electrode 230 to the substrate 220 at a level that can withstand practical use. Moreover, compared with conventional optical waveguide elements that use Ti as the base layer, the light absorption loss in the parallel waveguide 226a can be effectively suppressed to less than 1 / 3.

[0066] It should be noted that the present invention is not limited to the structure of the above-described embodiments and their variations, and can be implemented in various forms without departing from its spirit.

[0067] For example, in the above embodiment, the substrate 220 is an LN substrate, but the material of the substrate 220 is not limited to LN. The substrate 220 having a base layer 304 formed of Nb can be made of a material whose components contain oxygen, such as lithium tantalate (LiTaO3). Alternatively, if the base layer 304 is formed on a coating of oxide formed on the substrate 220, such as a buffer layer made of SiO2, the substrate 220 can be a semiconductor such as InP, or a Si substrate used in so-called silicon-based photonic devices.

[0068] Furthermore, in the above embodiment, the base layer 304 and the upper layer 302 of the electrode 230 are formed by EB vapor deposition, but the formation method of the electrode 230 is not limited to EB vapor deposition. For example, the base layer 304 and the upper layer 302 of the electrode 230 can be formed by vapor deposition methods other than EB vapor deposition or sputtering methods.

[0069] Furthermore, in this embodiment, the optical modulation element 102 is shown as an optical modulation element that performs optical modulation operation by constructing an optical waveguide 224 comprising a single Mach-Zehnder optical waveguide including a pair of parallel waveguides 226a, 226b. However, the structure of the electrode 230, as an example electrode, is not limited to an optical modulation element composed of a single Mach-Zehnder optical waveguide. Figure 3 The electrode 230 shown above, which also has a substrate layer 304, can also be used for, for example... Figure 7 The optical modulation element 702 shown uses two nested Mach-Zehnder waveguides to perform DP-QPSK modulation. In such an optical modulation element for DP-QPSK modulation, there is a demand for further miniaturization, broadband, and power saving. On the other hand, due to the limitation of the area of ​​the parallel waveguides and electrodes on the substrate 720, the spacing between the waveguides and electrodes becomes narrower, and thus the problem of light absorption loss becomes more obvious.

[0070] In the optical modulation element 702, for example, electrodes 730a, 730b, 730c, and 730d extending along parallel waveguides 726a, 726b, 726c, and 726d (dashed lines in the diagram) formed as convex optical waveguides on the same substrate 720 as substrate 220 can be configured to be connected to the optical modulation element 702. Figure 3 The electrode 230 shown also has a structure consisting of an upper layer 302 and a base layer 304. Therefore, in such an optical modulation element performing DP-QPSK modulation, light absorption loss in parallel waveguides 726a and the like can be reduced, resulting in good modulation characteristics.

[0071] As described above, the optical modulation element 102 shown in this embodiment, which is an optical waveguide element, includes: a substrate 220 on which an optical waveguide 224 is formed; and an electrode 230 formed on the substrate 220 to control the light wave propagating in the optical waveguide 224. Here, the optical waveguide 224 is composed of a protrusion (e.g., a protrusion 300) extending on the substrate 220. Furthermore, the electrode 230 is composed of a base layer 304 and an upper layer 302, wherein the base layer 304 is composed of Nb between the electrode 230 and the substrate 220, and the upper layer 302 is formed on the base layer 304.

[0072] According to this structure, by using Nb as the base layer of electrode 230, the light absorption loss caused by the presence of electrode 230 can be effectively reduced in optical waveguide 224 (e.g., parallel waveguide 226a), which is a convex optical waveguide.

[0073] Furthermore, the substrate 304 has a thickness of less than 30 nm. Based on this structure, the light absorption loss in the optical waveguide 224 caused by the presence of the electrode 230 can be reduced to 1 / 3 compared to conventional structures using a Ti substrate.

[0074] Furthermore, the substrate 304 is formed on the substrate 220 containing oxygen atoms, or on a film of oxide formed on the substrate 220. According to this structure, a practically usable level of fixing force can be ensured between the Nb-based substrate 304 and the substrate made of LN or the like.

[0075] Furthermore, the substrate 304 contains oxygen atoms, and the Nb / O ratio is 1.0 or higher. Based on this structure, a more reliable level of fixing force can be ensured between the Nb-based substrate 304 and the substrate made of LN or similar materials, thus guaranteeing practical stability.

[0076] Furthermore, the electrode 230 on the substrate 220 is composed of a plurality (e.g., two) electrodes 230a, 230b arranged along the parallel waveguide 226a at a position sandwiching the parallel waveguide 226a constituting the optical waveguide 224. According to this structure, by approaching the arranged electrodes with the parallel waveguide 226a apart, the light absorption loss of the propagating light in the parallel waveguide 226a can be effectively suppressed.

[0077] Furthermore, an optical modulator 100 is constructed by comprising an optical modulation element 102 as an optical waveguide element, a housing 104 housing the optical modulation element 102, an input optical fiber 106 for inputting light to the optical modulation element 102, and an output optical fiber 108 for guiding the light output from the optical modulation element 102 to the outside of the housing 104. This optical modulator 100 utilizes the optical modulation element 102, which suppresses light absorption losses in the convex optical waveguide (e.g., parallel waveguide 226a) caused by the presence of the electrode 230, thus achieving excellent optical modulation and transmission characteristics.

[0078] Label Explanation

[0079] 100… Optical modulator, 102, 702… Optical modulation element, 104… Housing, 106… Input fiber, 108… Output fiber, 110… Connector, 112… Repeater substrate, 114… Terminator, 220, 720… Substrate, 222… Support plate, 224, 724… Optical waveguide, 226a, 226b, 726a, 726b, 726c, 726d… Parallel waveguide, 230, 230a, 230b, 230c, 730a, 730b, 730c, 730d… Electrode, 300… Protrusion, 302, 302a, 302b… Upper layer, 304, 304a, 304b… Base layer, 350… Adhesive layer, 600, 602… Interface.

Claims

1. An optical waveguide element, comprising: A substrate having an optical waveguide formed thereon; and Electrodes, formed on the substrate, control the light waves propagating in the optical waveguide, wherein... The optical waveguide is formed by protrusions extending on the substrate. The electrode comprises a base layer and a top layer. The base layer is composed of Nb and oxygen atoms between the top layer and the substrate. The top layer is formed on top of the base layer. In the substrate layer, the elemental ratio of Nb to oxygen (Nb / O) is greater than 1.

0.

2. The optical waveguide element according to claim 1, wherein, The substrate layer has a thickness of less than 30 nm.

3. The optical waveguide element according to claim 1 or 2, wherein, The substrate layer is formed on the substrate containing oxygen atoms, or on a film of oxide formed on the substrate.

4. The optical waveguide element according to claim 1 or 2, wherein, The electrode is composed of a plurality of electrodes arranged on the substrate along the optical waveguide at a position sandwiching the optical waveguide.

5. An optical modulator, comprising: The optical waveguide element according to any one of claims 1 to 4 is an optical modulation element for modulating light; Housing that houses the optical waveguide element; Optical fiber, inputting light into the optical waveguide element; and The optical fiber guides the light output from the optical waveguide element to the outside of the housing.

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