Optical waveguide element, optical modulator, optical modulation module, and optical transmitter

Abstract

To provide an optical waveguide element capable of effectively removing unwanted light propagating through a substrate while suppressing the optical absorption loss caused by a working electrode.SOLUTION: An optical waveguide element is provided, comprising a substrate, an optical waveguide formed on the substrate, and a working electrode for controlling light waves propagating through the optical waveguide, the working electrode being comprised of a first underlayer made of a first material and a first conductive layer provided on the first underlayer. A conductive pattern consists of a second underlayer made of a second material different from the first material and a second conductive layer provided on the second underlayer and is formed in a region of an area on the substrate other than a path of the optical waveguide from an input end to an output end.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical waveguide element, an optical modulator, an optical modulation module, and an optical transmitter. [Background technology]

[0002] Commercial optical fiber communication systems often use optical modulators incorporating an optical modulation element as an optical waveguide element, which consists of an optical waveguide formed on a substrate and a working electrode that controls the light wave by applying an electric field to the optical waveguide. Among them, optical modulation elements using LiNbO3 (hereinafter also referred to as LN) substrates, which have electro-optic effects, are widely used in optical fiber communication systems for high-speed, large-capacity backbone optical transmission networks and metro networks, as they can achieve low optical loss and high-speed optical modulation characteristics.

[0003] As one measure to make such optical modulation elements smaller, faster, and more energy-efficient, optical modulators that use a thin LN substrate to further strengthen the interaction between the signal electric field and the guided light in the substrate (i.e., to increase the electric field efficiency) and optical modulators that use a rib-type optical waveguide or a ridge-type optical waveguide (hereinafter collectively referred to as a convex optical waveguide) that is configured by forming a strip-shaped convex portion on the surface of an LN substrate are beginning to be put into practical use (e.g., Patent Documents 1 and 2).

[0004] Recently, it has also been proposed to use a metal material with a smaller optical absorption coefficient at the operating light wavelength for the base layer of the working electrode that applies an electric field to the optical waveguide (Patent Document 3). This prevents the metal of the base layer of the working electrode provided close to the optical waveguide from absorbing light propagating through the optical waveguide, which would otherwise cause optical absorption loss. In other words, this configuration reduces optical absorption loss in the optical waveguide, enabling the realization of a low-loss optical waveguide element.

[0005] On the other hand, so-called unwanted light, which does not contribute to the output light controlled by the working electrode and output from the optical waveguide to the outside of the substrate, may also propagate through the substrate of the optical waveguide element. For example, leakage light leaking into the substrate from the light input section, branch section, and / or junction section of the optical waveguide may propagate through the substrate as unwanted light. Depending on the route of the optical waveguide on the substrate, such unwanted light may recombine with the guided light propagating through the optical waveguide, causing noise in the output light. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-264548 [Patent Document 2] International Publication No. 2018 / 1031916 [Patent Document 3] Patent Application No. 2020-164627 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above background, it is desirable to realize a structure in an optical waveguide element that can effectively remove unwanted light propagating through a substrate while suppressing light absorption loss caused by a working electrode. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided an optical waveguide element including a substrate, an optical waveguide formed on the substrate, and a working electrode for controlling a light wave propagating through the optical waveguide, wherein the working electrode is composed of a first base layer made of a first material and a first conductive layer on the first base layer, and in addition to the working electrode, a conductor pattern is formed on the substrate in an area other than a path from an input end to an output end of the optical waveguide, and the conductor pattern has a thickness between the substrate and the working electrode. Other layers Without intervention Adjacent to the substrateThe second underlayer is made of a second material different from the first material, and the second conductive layer is formed on the second underlayer. According to another aspect of the present invention, the conductor pattern constituted by the second base layer and the second conductive layer is formed in a region on the substrate through which unwanted light propagates. According to another aspect of the present invention, the second material has a larger optical absorption coefficient at the wavelength of light propagating through the optical waveguide than the first material. According to another aspect of the present invention, the conductor pattern is a pattern that continues from a wiring electrode connected to the working electrode. According to another aspect of the present invention, the optical waveguide includes a Mach-Zehnder optical waveguide, and a radiation light waveguide is formed at a multiplexing portion of the Mach-Zehnder optical waveguide, which propagates radiation light leaking from the Mach-Zehnder optical waveguide without being multiplexed, and the conductor pattern is arranged to cover at least a portion of the radiation light waveguide. According to another aspect of the present invention, the first conductive layer and the second conductive layer are made of gold (Au), and the first material and the second material are made of a material that does not react with iodine. According to another aspect of the invention, the first material is niobium (Nb) and the second material is titanium (Ti). According to another aspect of the present invention, the first underlayer has a thickness of 30 nm or less, and the second underlayer has a thickness of 100 nm or more. According to another aspect of the present invention, the optical waveguide is a convex optical waveguide formed by a convex portion extending on the substrate. According to another aspect of the present invention, the optical waveguide is sandwiched between two working electrodes within the plane of the substrate, and the distance between the two working electrodes is 1.0 μm or more and 5.0 μm or less. According to another aspect of the present invention, the working electrode has a third base layer made of a third material different from the first material on the first conductive layer, and a third conductive layer on the third base layer, and in a cross section perpendicular to the extension direction of the optical waveguide, an end of the third base layer is covered by the third conductive layer. According to another aspect of the present invention, the third material is made of titanium (Ti) and the third conductive layer is made of gold (Au). Another aspect of the present invention is an optical modulator comprising: any one of the optical waveguide elements described above that is an optical modulation element that modulates light; a housing that accommodates the optical waveguide element; an optical fiber that inputs light to the optical waveguide element; and an optical fiber that guides light output by the optical waveguide element to the outside of the housing. Another aspect of the present invention is an optical modulation module including any one of the above optical waveguide elements that is an optical modulation element that modulates light, a housing that accommodates the optical waveguide element, an optical fiber that inputs light to the optical waveguide element, an optical fiber that guides light output by the optical waveguide element to the outside of the housing, and a drive circuit that drives the optical waveguide element. Yet another aspect of the present invention is an optical transmitter comprising the optical modulator or the optical modulation module, and an electronic circuit that generates an electrical signal for causing the optical waveguide element to perform a modulation operation. [Effects of the Invention]

[0009] According to the present invention, in an optical waveguide element, it is possible to effectively remove unwanted light propagating through a substrate while suppressing light absorption loss caused by a working electrode. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing a configuration of a light modulation element according to a first embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the light modulation element shown in FIG. 1 taken along line II-II. [Figure 3] 3 is a cross-sectional view of the light modulation element shown in FIG. 1 taken along line III-III. [Figure 4] 4 is a cross-sectional view of the light modulation element shown in FIG. 1 taken along line IV-IV. [Figure 5] 10 shows the results of a simulation of the increase in optical absorption loss relative to the thickness of the first underlayer when various metals are used as the first underlayer. [Figure 6]FIG. 10 is a diagram showing an example of a conductor pattern provided adjacent to a working electrode in a modified example of the light modulation element according to the first embodiment. [Figure 7] FIG. 10 is a diagram showing another example of a conductor pattern provided adjacent to a working electrode in the modified example of the light modulation element according to the first embodiment. [Figure 8] FIG. 10 is a diagram showing another example of a conductor pattern provided adjacent to a working electrode in the modified example of the light modulation element according to the first embodiment. [Figure 9] FIG. 10 is a diagram showing an example of the configuration of wiring electrodes in a modified example of the light modulation element according to the first embodiment. [Figure 10] FIG. 10 is a diagram showing another example of the configuration of wiring electrodes in a modified example of the light modulation element according to the first embodiment. [Figure 11] FIG. 10 is a diagram showing another example of the configuration of wiring electrodes in a modified example of the light modulation element according to the first embodiment. [Figure 12] FIG. 3 is a diagram showing a modified example of the working electrode shown in FIG. [Figure 13] FIG. 4 is a diagram illustrating a configuration of an optical modulator according to a second embodiment of the present invention. [Figure 14] FIG. 10 is a diagram showing the configuration of an optical modulation module according to a third embodiment of the present invention. [Figure 15] FIG. 10 is a diagram illustrating a configuration of an optical transmitting device according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [First embodiment] 1 is a diagram showing the configuration of an optical modulation element 100, which is an optical waveguide element according to a first embodiment of the present invention. The optical modulation element 100 is composed of an optical waveguide 104 formed on a substrate 102. The substrate 102 is, for example, an X-cut LN substrate having an electro-optic effect that has been processed and thinned to a thickness of 20 μm or less (e.g., 2 μm). The optical waveguide 104 is a convex optical waveguide (e.g., a rib-type optical waveguide or a ridge-type optical waveguide) that is composed of a convex portion extending in a strip shape formed on the surface of the thinned substrate 102.

[0012] The substrate 102 is, for example, rectangular and has two opposing left and right sides 140a and 140b extending in the vertical direction in the figure, and two opposing upper and lower sides 140c and 140d extending in the horizontal direction in the figure.

[0013] The optical modulation element 100 configures a DP-QPSK optical modulator using two nested Mach-Zehnder optical waveguides 108a and 108b. The nested Mach-Zehnder optical waveguide 108a includes two Mach-Zehnder optical waveguides 110a and 110b. The nested Mach-Zehnder optical waveguide 108b includes two Mach-Zehnder optical waveguides 110c and 110d.

[0014] The Mach-Zehnder optical waveguides 110a and 110b have two parallel waveguides 112a and 112b, and two parallel waveguides 112c and 112d, respectively. The Mach-Zehnder optical waveguides 110c and 110d have two parallel waveguides 112e and 112f, and two parallel waveguides 112g and 112h, respectively.

[0015] Input light (arrow pointing rightward in the figure) enters input waveguide 106 of optical waveguide 104 at the lower side of left side 140a of substrate 102 in the figure. After the light propagation direction is turned back 180 degrees, it is split into two beams and QPSK-modulated by two nested Mach-Zehnder optical waveguides 108a and 108b. The two QPSK-modulated beams are output from the upper side of left side 140a of substrate 102 in the figure via output waveguides 126a and 126b, respectively (two arrows pointing leftward in the figure). The end of input waveguide 106 where the light is incident is the input end of the signal light, and the ends of output waveguides 126a and 126b from which the light is emitted are the output ends of the signal light.

[0016] After these two output lights are emitted from the substrate 102, they are combined into one optical beam by, for example, a polarization combiner, and are then sent to a transmission optical fiber as a DP-QPSK modulated optical signal.

[0017] For QPSK modulation in the nested Mach-Zehnder optical waveguide 108a, signal electrodes 114-1a and 114-1b, to which high-frequency electrical signals for modulation are input, are arranged between the two parallel waveguides 112a and 112b of the Mach-Zehnder optical waveguide 110a and between the two parallel waveguides 112c and 112d of the Mach-Zehnder optical waveguide 110b, respectively.

[0018] For QPSK modulation in the nested Mach-Zehnder optical waveguide 108b, signal electrodes 114-1c and 114-1d, to which high-frequency electrical signals for modulation are input, are arranged between the two parallel waveguides 112e and 112f of the Mach-Zehnder optical waveguide 110c and between the two parallel waveguides 112g and 112h of the Mach-Zehnder optical waveguide 110d, respectively.

[0019] The signal electrode 114-1a forms a coplanar transmission line together with the ground electrodes 114-2a and 114-2b that face each other across the parallel waveguides 112a and 112b, respectively, and the signal electrode 114-1b forms a coplanar transmission line together with the ground electrodes 114-2b and 114-2c that face each other across the parallel waveguides 112c and 112d, respectively.

[0020] The signal electrode 114-1c forms a coplanar transmission line together with the ground electrodes 114-2c and 114-2d that face each other across the parallel waveguides 112e and 112f, respectively, and the signal electrode 114-1d forms a coplanar transmission line together with the ground electrodes 114-2d and 114-2e that face each other across the parallel waveguides 112e and 112f, respectively.

[0021] Hereinafter, the nested Mach-Zehnder optical waveguides 108a and 108b will be collectively referred to as nested Mach-Zehnder optical waveguides 108. Furthermore, the Mach-Zehnder optical waveguides 110a, 110b, 110c, 110d, 110e, 110f, 110g, and 110h will be collectively referred to as Mach-Zehnder optical waveguides 110. Furthermore, the parallel waveguides 112a, 112b, 112c, 112d, 112e, 112f, 112g, and 112h will be collectively referred to as parallel waveguides 112. Furthermore, the signal electrodes 114-1a, 114-1b, 114-1c, and 114-1d will be collectively referred to as signal electrode 114-1. The ground electrodes 114-2a, 114-2b, 114-2c, 114-2d, and 114-2e are also collectively referred to as ground electrodes 114-2.

[0022] The signal electrode 114-1 and the ground electrode 114-2 are collectively referred to as the working electrodes 114. The signal electrode 114-1 and the ground electrode 114-2, which are the working electrodes 114, control the light waves propagating through the optical waveguide 104. The signal electrode 114-1 and the ground electrode 114-2 are the two working electrodes 114 that sandwich the parallel waveguide 112 of the optical waveguide 104 within the plane of the substrate 102.

[0023] The right ends of the signal electrodes 114-1a, 114-1b, 114-1c, and 114-1d are connected to signal wiring electrodes 118-1a, 118-1b, 118-1c, and 118-1d, respectively, and the left ends of the signal electrodes 114-1a, 114-1b, 114-1c, and 114-1d are connected to signal wiring electrodes 118-1e, 118-1f, 118-1g, and 118-1h, respectively.

[0024] The right ends of the ground electrodes 114-2a, 114-2b, 114-2c, 114-2d, and 114-2e in the figure are connected to the ground wiring electrodes 118-2a, 118-2b, 118-2c, 118-2d, and 118-2e, respectively, so that the signal wiring electrodes 118-1a, 118-1b, 118-1c, and 118-1d, together with the ground wiring electrodes 118-2a, 118-2b, 118-2c, 118-2d, and 118-2e adjacent to these signal wiring electrodes, form a coplanar transmission line.

[0025] Similarly, the left ends of the ground electrodes 114-2a, 114-2b, 114-2c, 114-2d, and 114-2e in the figure are connected to the ground wiring electrodes 118-2f, 118-2g, 118-2h, 118-2i, and 118-2j, respectively. As a result, the signal wiring electrodes 118-1e, 118-1f, 118-1g, and 118-1h, together with the ground wiring electrodes 118-2f, 118-2g, 118-2h, 118-2i, and 118-2j adjacent to these signal wiring electrodes, form a coplanar transmission line.

[0026] The signal wiring electrodes 118-1e, 118-1f, 118-1g, and 118-1h extending to the bottom side 140d of the substrate 102 in the drawing are terminated by a terminating resistor having a predetermined impedance outside the substrate 102.

[0027] As a result, high-frequency electrical signals input from the signal wiring electrodes 118-1a, 118-1b, 118-1c, and 118-1d extending to the upper side 140c of the substrate 102 in the figure become traveling waves and propagate through the signal electrodes 114-1a, 114-1b, 114-1c, and 114-1d, modulating the light waves propagating through the Mach-Zehnder optical waveguides 110a, 110b, 110c, and 110d, respectively.

[0028] Hereinafter, the signal wiring electrodes 118-1a, 118-1b, 118-1c, 118-1d, 118-1e, 118-1f, 118-1g, and 118-1h will be collectively referred to as signal wiring electrodes 118-1. The ground wiring electrodes 118-2a, 118-2b, 118-2c, 118-2d, 118-2e, 118-2f, 118-2g, 118-2h, 118-2i, and 118-2j will be collectively referred to as ground wiring electrodes 118-2. The signal wiring electrode 118-1 and the ground wiring electrode 118-2 will be collectively referred to as wiring electrodes 118. That is, the signal wiring electrode 118-1 and the ground wiring electrode 118-2 are wiring electrodes 118 connected to the working electrode 114.

[0029] The substrate 102 is also provided with a bias electrode 132a for adjusting the bias points of the Mach-Zehnder optical waveguides 110a and 110b, a bias electrode 132b for adjusting the bias points of the Mach-Zehnder optical waveguides 110c and 110d, and a bias electrode 132c for adjusting the bias points of the nested Mach-Zehnder optical waveguides 108a and 108b.

[0030] The multiplexing sections 128a and 128b of the nested Mach-Zehnder optical waveguides 108a and 108b are provided with two radiated light waveguides 130a and 130b and two radiated light waveguides 130c and 130d, respectively, for propagating radiated light leaking from the nested Mach-Zehnder optical waveguides 108a and 108b without being multiplexed. Similarly, the multiplexing sections 128c and 128d of the Mach-Zehnder optical waveguides 110a and 110b are provided with two radiated light waveguides 130e and 130f and two radiated light waveguides 130g and 130h, respectively. The multiplexing sections 128e and 128f of the Mach-Zehnder optical waveguides 110c and 110d are provided with two radiated light waveguides 130i and 130j and two radiated light waveguides 130k and 130m, respectively. The configuration and function of such a waveguide for emitted light are disclosed, for example, in Japanese Patent No. 4745432. Hereinafter, the multiplexing units 128a, 128b, 128c, 128d, 128e, and 128f will be collectively referred to as multiplexing unit 128. Furthermore, the waveguides for emitted light 130a, 130b, 130c, 130d, 130e, 130f, 130g, 130h, 130i, 130j, 130k, and 130m will be collectively referred to as waveguides for emitted light 130.

[0031] 2 is a cross-sectional view taken along the line II-II of the optical modulation element 100 shown in FIG. 1, showing a cross section of the substrate 102 in the working portion (the portion where the light wave is controlled by the working electrode) of the Mach-Zehnder optical waveguide 110a.

[0032] The back surface (the lower surface in the figure) of the substrate 102 is supported and reinforced by a support plate 142. The support plate 142 is made of, for example, glass. On the top surface of the substrate 102 in the figure, parallel waveguides 112a and 112b are configured as convex optical waveguides by convex portions 144a and 144b formed on the substrate 102, respectively. Note that the two dotted ellipses in the figure schematically represent light propagating through the parallel waveguides 112a and 112b, which are convex optical waveguides. Hereinafter, the convex portions on the substrate 102 that configure the optical waveguide 104, including the convex portions 144a and 144b, will be collectively referred to as convex portions 144.

[0033] The signal electrode 114-1a and the ground electrodes 114-2a and 114-2b sandwiching the parallel waveguides 112a and 112b within the plane of the substrate 102 are respectively composed of first underlayers 160a, 160b, and 160c made of a first material and first conductive layers 162a, 162b, and 162c formed on the first underlayers 160a, 160b, and 160c. In this embodiment, the first conductive layers 162a, 162b, and 162c are made of gold (Au). In this embodiment, the first material constituting the first underlayers 160a, 160b, and 160c is, for example, niobium (Nb). Niobium has a smaller optical absorption coefficient at the operating optical wavelengths of the optical modulation element 100 (for example, the 1.3 μm band and / or 1.55 μm band, which are wavelengths used for optical communications) than titanium, which has been conventionally used as an underlayer material for electrodes.

[0034] Therefore, the signal electrode 114-1a and the ground electrodes 114-2a and 114-2b can be formed closer to the parallel waveguides 112a and 112b than in the past. As a result, the optical modulation element 100 can efficiently generate an electric field in the parallel waveguides 112a and 112b (i.e., can improve the electric field efficiency), and can achieve optical modulation operation with a lower drive voltage and at a higher speed than in the past. For example, in this embodiment, the distance W between the signal electrode 114-1a and the ground electrode 114-2a, which are two working electrodes sandwiching the parallel waveguide 112a, is 1.0 μm or more and 5.0 μm or less.

[0035] The signal electrodes 114-1b, 114-1c, and 114-1d other than the signal electrode 114-1a and the ground electrodes 114-2c, 114-2d, and 114-2e other than the ground electrodes 114-2a and 114-2b are also configured in the same manner as the signal electrode 114-1a and the ground electrodes 114-2a and 114-2b. Hereinafter, the first base layer and the first conductive layer of the signal electrode 114-1 and the ground electrode 114-2 will also be collectively referred to as the first base layer 160 and the first conductive layer 162, respectively.

[0036] In the optical modulation element 100 according to this embodiment, a conductor pattern including a second base layer made of a second material different from the first material and a second conductive layer on the second base layer is formed particularly in a region on the substrate 102 through which unwanted light propagates. Here, the unwanted light refers to light that does not contribute to the output light (e.g., output signal light) that is controlled by the signal electrode 114-1 and output from the optical waveguide 104 to the outside of the substrate 102.

[0037] One example of the region through which unwanted light propagates is the region where the emitted light waveguide 130 through which unwanted emitted light propagates is formed. In the optical modulation element 100 shown in Fig. 1, conductor patterns 150a, 150b, 150c, and 150d are formed in the region on the substrate 102 where the emitted light waveguides 130a, 130d, 130e, and 130m are formed, so as to cover at least a portion of each of these emitted light waveguides.

[0038] 3 is a cross-sectional view taken along the line III-III in FIG. 1, showing a portion where the emitted light waveguide 130d is formed. A conductor pattern 150b is formed on the substrate 102 so as to cover the emitted light waveguide 130d. This conductor pattern 150b is composed of a second base layer 164a made of a second material different from the first material described above, and a second conductive layer 166a on the second base layer 164a.

[0039] In this embodiment, the second conductive layer 166a is made of gold (Au). The second material making up the second base layer 164a desirably has a larger optical absorption coefficient than the first material at the operating light wavelength of the optical modulation element 100. In this embodiment, the second material is titanium.

[0040] Conductive patterns 150a, 150c, and 150d formed to cover the emitted light waveguides 130a, 130e, and 130m, respectively, in FIG. 1 are configured in the same manner as the conductive pattern 150b shown in FIG.

[0041] Another example of a region on the substrate 102 through which unwanted light propagates is a rectangular region 172 surrounded by the dotted rectangle in the drawing, which is adjacent to a light incident portion 170 (i.e., a portion of the left side 140a in the drawing where the end of the input waveguide 106 is formed) where light is incident from outside the substrate 102 to the optical waveguide 104 in Fig. 1. In the optical modulation element 100 shown in Fig. 1, the conductor patterns 150e and 150f are formed so as to overlap with the rectangular region 172 while avoiding the input waveguide 106.

[0042] Fig. 4 is a cross-sectional view taken along the line IV-IV of the light modulation element 100 shown in Fig. 1. Similar to the conductor pattern 150b shown in Fig. 3, the conductor pattern 150e is composed of a second base layer 164b made of a second material formed on the substrate 102, and a second conductive layer 166b on the second base layer 164b. Also, similar to the conductor pattern 150b described above, the material constituting the second conductive layer 166b is gold, and the second material constituting the second base layer 164b is titanium.

[0043] 1, the width Wr of the rectangular region 172 in the direction perpendicular to the incident direction of light can be set to a width corresponding to the NA (numerical aperture) of the lens or optical fiber when the incident light is focused by a lens or directly incident from an optical fiber. Furthermore, the length Lr of the rectangular region 172 along the incident direction of light can be set to a length corresponding to the intensity of unwanted light that can enter the substrate 102 from the light incident section 170.

[0044] Hereinafter, the conductor patterns 150a, 150b, 150c, 150d, 150e, and 150f will also be collectively referred to as conductor pattern 150. In addition, the second base layer and second conductive layer of each of the conductor patterns 150 will also be collectively referred to as second base layer 164 and second conductive layer 166, respectively.

[0045] The optical modulation element 100 having the above configuration has a working electrode 114 that controls the light wave propagating through the parallel waveguide 112, and a conductor pattern 150 provided in a region of the substrate 102 through which unwanted light propagates. The second base layer 164 that constitutes the conductor pattern 150 is made of a second material that has a larger optical absorption coefficient at the operating light wavelength than the first material that constitutes the first base layer 160 of the working electrode 114, which needs to be placed close to the parallel waveguide 112.

[0046] As a result, the optical modulation element 100 can effectively remove unwanted light propagating through the substrate 102 while suppressing optical absorption loss that may occur in the parallel waveguide 112 due to the working electrode 114. As a result, the optical modulation element 100 can be driven at a lower voltage than conventional elements and can achieve modulation operation with good optical characteristics such as an extinction ratio. Note that the thickness of the second underlayer 164 is desirably 100 nm or more from the viewpoint of effectively absorbing unwanted light.

[0047] The material constituting the first underlayer 160 is not limited to niobium, and any material having a smaller optical absorption coefficient at the operating light wavelength than conventionally used titanium can be used, thereby making it possible to bring the working electrode 114 closer to the parallel waveguide 112 and improve the electric field efficiency of the optical modulation element 100 compared to conventional optical modulation elements. Fig. 5 shows simulation results of the increase in optical absorption loss in the parallel waveguide 112 relative to the thickness of the first underlayer 160 when the first underlayer 160 is made of various metals. Fig. 5 also shows calculation results when Ti, Al (aluminum), and Nb are used as the material for the first underlayer 160, in addition to when the first underlayer 160 is not used (when only an Au single film (first conductive layer 162) is used).

[0048] 5, the horizontal axis represents the thickness t of the first underlayer 160, and the vertical axis represents the amount of optical absorption loss per unit length (1 cm) of the parallel waveguide 112 adjacent to the first underlayer 160. In the simulation, Au was assumed for the first conductive layer 162, and the operating optical wavelength was assumed to be 1.55 μm. In addition, when calculating the optical absorption loss, the amount of optical absorption at the operating wavelength of 1.55 μm of each metal obtained from the optical absorption spectra of Ti, Al, and Nb was used.

[0049] The optical absorption loss α0 in the case of a single Au film (no underlying layer present) shown by line 200 is the background optical absorption loss in the above configuration, and the optical absorption loss in the first underlying layer 160 can be evaluated as the increase in optical absorption loss from this reference line.

[0050] Lines 202, 204, and 206 show the optical absorption loss when the metals constituting the first underlayer 160 are Ti, Al, and Nb, respectively. Of these metals, Ti, shown by line 202, has the greatest optical absorption loss, and the optical absorption loss increases significantly with increasing film thickness.

[0051] On the other hand, lines 204 and 206, which show the cases where Al and Nb, which do not include the operating wavelength in their optical absorption range, are used as the first underlayer 160, show that the optical absorption loss is significantly reduced compared to the case where Ti is used (line 202). Within the range of the evaluation results shown in Figure 5, the optical absorption loss is smallest when the first underlayer 160 is Al (line 204), and the optical absorption loss is almost constant with respect to the thickness of the underlayer. However, Al is generally known to have low adhesion strength to the substrate.

[0052] 5, it is desirable that the thickness of the first underlayer 160 made of Nb be 30 nm or less. If the thickness of the Nb underlayer is within this range, the optical absorption loss can be suppressed to 2α0 or less, which is twice the value α0 of a single Au film, or to one-third the value of approximately 6α0 in the case of a conventional first underlayer 160 using Ti.

[0053] When the first conductive layer 162 and the second conductive layer 166 are made of gold, an etching solution containing iodine or iodide may be used as an etching solution for patterning these conductive layers in the manufacturing process of the light modulation element 100. In such a case, it is preferable to use a material that does not react with iodine (for example, Nb) for the first material that constitutes the first base layer 160 and the second material that constitutes the second base layer 164, rather than a material such as Al that has low resistance to iodine.

[0054] The emitted light waveguide 130 for removing unwanted light may be used as a monitor optical waveguide, and in this case, the end of the monitor waveguide is also the output end of the signal light.

[0055] <Modification> In the optical modulation element 100 described above, the conductor pattern 150 having the second base layer 164 and the second conductive layer 166 is formed so as to cover a portion of the emitted light waveguide for removing unwanted light. However, the location where the conductor pattern 150 is formed is not limited to the above. For example, the conductor pattern 150 may be formed in a region on the substrate 102 other than the path from the input end to the output end of the signal light of the optical waveguide 104, and the conductor pattern 150 may be formed in a region on the substrate 102 other than the path from the input end to the output end of the signal light of the optical waveguide 104.

[0056] In the above configuration, the conductor pattern 150 can be configured as follows in the region of the substrate 102 adjacent to the optical waveguide 104.

[0057] For example, the conductor pattern 150 may be provided adjacent to the working electrode 114. As an example, the light modulation element 100 may have a configuration as shown in Fig. 6 in the cross section taken along line II-II in Fig. 1. Fig. 6 is a cross section taken along line II-II corresponding to Fig. 2 described above.

[0058] 6, signal electrode 114-1a constituting the working electrode is formed by dividing it into two parts adjacent to parallel waveguides 112a and 112b, respectively, and may be configured with conductor pattern 150g sandwiched between the two signal electrodes 114-1a. In other words, working electrode 114 is provided adjacent to parallel waveguide 112, and conductor pattern 150g is formed so as to contact the side of working electrode 114 opposite to the side adjacent to parallel waveguide 112.

[0059] Similarly, the ground electrodes 114-2a and 114-2b constituting the working electrode 114 are formed adjacent to the parallel waveguides 112a and 112b, respectively, and conductor patterns 150h-1 and 150h-2 are formed to contact the side surfaces of the ground electrodes 114-2a and 114-2b opposite to the side surfaces adjacent to the parallel waveguides 112a and 112b.

[0060] Here, the conductive pattern 150g is composed of a second base layer 164c and a second conductive layer 166c, the conductive pattern 150h-1 is composed of a second base layer 164d-1 and a second conductive layer 166d-1, and the conductive pattern 150h-2 is composed of a second base layer 164d-2 and a second conductive layer 166d-2.

[0061] As another example in which the conductor pattern 150 is provided in a region other than the path from the input end to the output end of the optical waveguide 104, the optical modulation element 100 may have a configuration as shown in Fig. 7 in the cross section taken along II-II in Fig. 1. Fig. 7 is a cross section taken along II-II corresponding to Fig. 2 described above, and is an example in which the second base layer 164 is provided so as to extend into the adjacent working electrode 114 in the configuration described above in Fig. 6.

[0062] Specifically, the second underlayer 164c extends between the first underlayer 160a-1 and the first conductive layer 162a-1 of two adjacent signal electrodes 114-1a. The second underlayer 164d-1 extends between the first underlayer 160b and the first conductive layer 162b of the adjacent ground electrode 114-2a. Similarly, the second underlayer 164d-2 extends between the first underlayer 160b-2 and the first conductive layer 162b-2 of the adjacent ground electrode 114-2b.

[0063] As yet another example in which the conductor pattern 150 is provided in a region other than the path from the input end to the output end of the optical waveguide 104, the optical modulation element 100 may have a configuration as shown in Fig. 8 in the cross section taken along II-II in Fig. 1. Fig. 8 is a cross section taken along II-II corresponding to Fig. 2 described above, and is an example in which the first base layer 160 is provided so as to extend into the adjacent conductor pattern 150 in the configuration described above in Fig. 6. 6, 7, and 8, the first conductive layer 162 and the second conductive layer 166 are shown separately, but the materials for each may be different or the same. In particular, when the same material is used, the first conductive layer 162 and the second conductive layer 166 can be formed in the same process to improve process efficiency.

[0064] Specifically, the first foundation layer 160a-1 extends between the second foundation layer 164c and the second conductive layer 166c of two adjacent conductor patterns 150g. The first foundation layer 160b extends between the second foundation layer 164d-1 and the second conductive layer 166d-1 of the adjacent conductor pattern 150h-1. Similarly, the first foundation layer 160c extends between the second foundation layer 164d-2 and the second conductive layer 166d-2 of the adjacent conductor pattern 150h-2.

[0065] In the configuration of the above-described modified example, the wiring electrode 118 can have a second base layer 164 instead of the first base layer 160 in a portion other than the portion intersecting with the optical waveguide 104. For example, the wiring electrode 118 can have the first base layer 160 formed so as to be in contact with the optical waveguide 104 at least in the portion intersecting with the optical waveguide 104, and can include the second base layer 164 in other portions.

[0066] As an example, the optical modulator 100 may be configured as shown in FIG. 9 at the intersection of the ground wiring electrode 118-2f and the input waveguide 106 in FIG. 1. FIG. 9 is a cross-sectional view of the intersection of the ground wiring electrode 118-2f and the input waveguide 106, taken along a plane perpendicular to the extension direction of the input waveguide 106. In the configuration of FIG. 9, the ground wiring electrode 118-2f is configured, for example, of a first base layer 160d and a first conductive layer 162d at the intersection with the input waveguide 106, and of a second base layer 164e and the first conductive layer 162d at the portion other than the intersection. In the above configuration, it is desirable that the distance D from the center of the input waveguide 106 to the end of the second base layer 164e be larger than the mode field diameter of light in the input waveguide 106 to suppress optical absorption loss by the second base layer 164e.

[0067] As another example, the ground wiring electrode 118-2f can be configured as shown in Fig. 10. Fig. 10 shows an example in which the second base layer 164e in the configuration shown in Fig. 9 is extended up to an upper part of the first base layer 160d provided at the intersection between the ground wiring electrode 118-2f and the input waveguide 106.

[0068] As yet another example, the ground wiring electrode 118-2f can be configured as shown in Fig. 11. Fig. 11 shows an example in which the first base layer 160d in the configuration shown in Fig. 9 is extended up to the top of the second base layer 164e except for the intersection with the input waveguide 106.

[0069] [Second embodiment] Next, a second embodiment of the present invention will be described. This embodiment is an optical modulator using the optical modulation element 100 described above. Fig. 13 is a diagram showing the configuration of an optical modulator 400 according to the second embodiment. The optical modulator 400 has a housing 402, the optical modulation element 100 housed in the housing 402, and a relay substrate 406. A plate-shaped cover (not shown) is ultimately fixed to the opening of the housing 402, and the interior is hermetically sealed.

[0070] The optical modulator 400 also has a signal pin 408 for inputting a high-frequency electrical signal used to modulate the optical modulation element 100, and a signal pin 410 for inputting an electrical signal used to adjust the operating point of the optical modulation element 100.

[0071] Furthermore, the optical modulator 400 has an input optical fiber 414 for inputting light into the housing 402 and an output optical fiber 420 for guiding the light modulated by the optical modulation element 100 to the outside of the housing 402, both on the same surface of the housing 402 (in this embodiment, the left surface shown in the figure).

[0072] Here, the input optical fiber 414 and the output optical fiber 420 are fixed to the housing 402 via supports 422 and 424, which are fixing members. Light input from the input optical fiber 414 is collimated by a lens 430 arranged in the support 422, and then input to the light modulation element 100 via a lens 434. However, this is just one example, and light can also be input to the light modulation element 100 according to conventional technology, for example, by introducing the input optical fiber 414 into the housing 402 via the support 422 and connecting the end face of the introduced input optical fiber 414 to the end face of the substrate 102 of the light modulation element 100.

[0073] The light output from the light modulation element 100 is coupled to an output optical fiber 420 via an optical unit 416 and a lens 418 disposed on a support 424. The optical unit 416 may include a polarization combiner that combines the two modulated lights output from the light modulation element 100 into one beam.

[0074] The relay substrate 406 relays high-frequency electrical signals input from the signal pins 408 and electrical signals for adjusting the operating point (bias point) and the like input from the signal pins 410 to the optical modulation element 100 by means of conductor patterns (not shown) formed on the relay substrate 406. The conductor patterns on the relay substrate 406 are connected to one end of the wiring electrodes 118 of the optical modulation element 100 by, for example, wire bonding. The optical modulator 400 also includes a terminator 412 having a predetermined impedance within the housing 402.

[0075] The optical modulator 400 having the above configuration is constructed using the optical modulation element 100 according to the first embodiment described above, and therefore can be driven at a lower voltage than conventional devices and can achieve modulation operation with good optical characteristics such as an extinction ratio.

[0076] [Third embodiment] Next, a third embodiment of the present invention will be described. This embodiment is an optical modulation module 500 using the optical modulation element 100 according to the first embodiment described above. Fig. 14 is a diagram showing the configuration of the optical modulation module 500 according to this embodiment. In Fig. 14, the same components as those in the optical modulator 400 according to the second embodiment shown in Fig. 13 are indicated by the same reference numerals as those shown in Fig. 13, and the description of Fig. 13 described above is used.

[0077] 13, the optical modulation module 500 differs from the optical modulator 400 in that it includes a circuit board 506 instead of the relay board 406. The circuit board 506 includes a drive circuit 508. The drive circuit 508 generates a high-frequency electrical signal for driving the optical modulation element 100 based on, for example, a modulation signal supplied from the outside via the signal pin 408, and outputs the generated high-frequency electrical signal to the optical modulation element 100.

[0078] The optical modulation module 500 having the above configuration is constructed using the optical modulation element 100 according to the first embodiment described above, and therefore can be driven at a lower voltage than conventional ones and can achieve modulation operation with good optical characteristics such as extinction ratio.

[0079] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described. This embodiment is an optical transmitting device 600 equipped with the optical modulator 400 according to the second embodiment. Fig. 15 is a diagram showing the configuration of the optical transmitting device 600 according to this embodiment. This optical transmitting device 600 has the optical modulator 400, a light source 604 that inputs light to the optical modulator 400, a modulator driving unit 606, and a modulation signal generating unit 608. Note that the optical modulation module 500 described above can also be used instead of the optical modulator 400 and the modulator driving unit 606.

[0080] The modulation signal generating unit 608 is an electronic circuit that generates an electrical signal for causing the optical modulator 400 to perform modulation operations. Based on transmission data provided from the outside, the modulation signal generating unit 608 generates a modulation signal, which is a high-frequency signal for causing the optical modulator 400 to perform optical modulation operations in accordance with the modulation data, and outputs the modulation signal to the modulator driving unit 606.

[0081] The modulator driver 606 amplifies the modulation signal input from the modulation signal generator 608 and outputs a high-frequency electrical signal for driving the signal electrode of the optical modulation element 100 included in the optical modulator 400. As described above, instead of the optical modulator 400 and the modulator driver 606, it is also possible to use an optical modulation module 500 in which, for example, a driver circuit 508 including a circuit equivalent to the modulator driver 606 is provided inside the housing 402.

[0082] The high-frequency electrical signal is input to the signal pin 408 of the optical modulator 400 to drive the optical modulation element 100. As a result, the light output from the light source 604 is modulated by the optical modulator 400, and is output from the optical transmitting device 600 as modulated light.

[0083] The optical transmitting device 600 having the above configuration uses the optical modulation element 100, and therefore, like the optical modulator 400 according to the second embodiment and the optical modulation module 500 according to the third embodiment described above, can be driven at a lower voltage than conventional devices and can achieve modulation operations with good optical characteristics such as extinction ratio, thereby achieving good optical transmission.

[0084] The present invention is not limited to the configurations of the above-described embodiments and their alternative configurations, and can be implemented in various forms without departing from the spirit of the present invention.

[0085] For example, in the light modulation element 100 according to the first embodiment, the conductor pattern 150 is formed in isolation on the substrate 102, but the conductor pattern 150 does not necessarily have to be formed in isolation. For example, the conductor pattern 150 may be formed so as to cover multiple regions on the substrate 102 through which unwanted light propagates.

[0086] Furthermore, for example, the wiring electrode 118, which does not need to be formed adjacent to the parallel waveguide 112, unlike the working electrode 114, may be formed from the same base layer and conductive layer as the conductor pattern 150, and the wiring electrode 118 and the conductor pattern 150 may be simultaneously formed on the substrate 102 in the same electrode formation process. In this case, at least a portion of the wiring electrode 118 and the conductor pattern 150 may be formed as a continuous pattern.

[0087] 1, the paths of the wiring electrode 118 and the wiring of the bias electrodes 132a, 132b, and 132c (hereinafter referred to as bias electrode wiring) are not limited to those shown in FIG. 1. The paths of the wiring electrode 118 and the bias electrode wiring on the substrate 102 are arbitrary, in accordance with conventional technology, as long as they do not affect the optical waveguide 104. For example, the wiring electrode 118 may extend linearly from the signal electrode 114-1 so as not to affect the optical waveguide 104. Furthermore, the bias electrode wiring may be formed along an arbitrary path, for example, to reach the side 140b opposite to the side 140a on which the input waveguide 106 and the output waveguides 126a and 126b are formed.

[0088] 2, the working electrode 114 is configured with the first base layer 160 and the first conductive layer 162, but is not limited to this. The working electrode 114 may have a multi-stage configuration including a third base layer made of a third material different from the first material on top of the first conductive layer 162, and a third conductive layer on the third base layer. This allows the impedance of the working electrode 114 to be set within a predetermined range while matching the speed of the electrical signal propagating through the working electrode 114 with the speed of the light wave propagating through the optical waveguide 104.

[0089] For example, the signal electrode 114-1a and ground electrodes 114-2a and 114-2b shown in Fig. 2 can be configured as the signal electrode 114-1e and ground electrodes 114-2f and 114-2g shown in Fig. 12, respectively. In Fig. 12, the signal electrode 114-1e is configured with a first base layer 160a, a first conductive layer 162a, and a third base layer 180a and a third conductive layer 182a on the first conductive layer 162a. The ground electrode 114-2f is configured with a first base layer 160b, a first conductive layer 162b, and a third base layer 180b and a third conductive layer 182b on the first conductive layer 162b. Similarly, ground electrode 114-2g is composed of first base layer 160c, first conductive layer 162c, and third base layer 180c and third conductive layer 182c on first conductive layer 162c. Hereinafter, third base layers 180a, 180b, and 180c will be collectively referred to as third base layer 180, and third conductive layers 182a, 182b, and 182c will be collectively referred to as third conductive layer 182.

[0090] 12, the end of the third base layer 180 is covered with the third conductive layer 182 in a cross section perpendicular to the extension direction of the parallel waveguides 112, thereby preventing the third base layer 180 from being over-etched in the etching process used to form the electrode. Note that this multi-stage configuration of the working electrode 114 is not limited to the configuration of the first base layer 160 and the first conductive layer 162 shown in Fig. 12, but can also be applied to a configuration in which the base layer of the working electrode 114 is formed by both the first base layer 160 and the second base layer 164, as shown in Fig. 6, 7, or 8.

[0091] Furthermore, in the first embodiment, the optical modulation element 100 configured with the substrate 102 made of LN (LiNbO3) was shown as an example of the optical waveguide element according to the present invention, but the optical waveguide element according to the present invention is not limited to this. The optical waveguide element may be an element configured with a substrate made of any material (LN, InP, Si, etc.) and having any function (optical modulation, optical switch, optical directional coupler, etc.). Such an element may be, for example, a so-called silicon photonics waveguide device.

[0092] In the above-described embodiment, the substrate 102 is, for example, an X-cut LN substrate (so-called X-plate) (the normal direction of the substrate is the X-axis of the crystal axis), but a Z-cut LN substrate can also be used as the substrate 102.

[0093] As described above, the optical modulation element 100, which is the optical waveguide element according to the first embodiment, includes the substrate 102, the optical waveguide 104 formed on the substrate 102, and the working electrode 114 that controls light waves propagating through the parallel waveguides 112 of the optical waveguide 104. The working electrode 114 is composed of a first base layer 160 made of a first material and a first conductive layer 162 on the first base layer 160. Then, a conductive pattern 150 composed of a second base layer 164 made of a second material different from the first material and a second conductive layer 166 on the second base layer 164 can be formed in an area on the substrate 102 other than the path from the input end to the output end of the optical waveguide 104.

[0094] Specifically, in the optical modulation element 100, a conductor pattern 150 is formed in an area where unwanted light that is controlled by the working electrode 114 and does not contribute to the output light output from the substrate 102 propagates, the conductor pattern 150 being composed of a second base layer 164 made of a second material different from the first material, and a second conductive layer 166 on the second base layer 164.

[0095] These configurations make it possible to effectively remove unwanted light propagating through the substrate 102 while suppressing optical absorption loss that may occur due to the working electrode 114. As a result, it is possible to realize an optical modulation element 100 that can be driven at a lower voltage than conventional elements and has good optical characteristics.

[0096] Furthermore, the second material constituting the second underlayer 164 has a larger optical absorption coefficient at the wavelength of light propagating through the optical waveguide 104 than the first material constituting the first underlayer 160. With this configuration, unwanted light propagating through the substrate 102 can be more effectively removed.

[0097] Furthermore, the conductive pattern 150 may be a pattern that continues from the wiring electrode 118 connected to the working electrode 114. With this configuration, the conductive pattern 150 can be formed simultaneously with the formation of the wiring electrode 118, thereby simplifying the manufacturing process of the light modulation element 100.

[0098] The optical waveguide 104 also includes a nested Mach-Zehnder optical waveguide 108 and a Mach-Zehnder optical waveguide 110, and a waveguide 130 for emitted light is formed at a multiplexing section 128 of these Mach-Zehnder optical waveguides. The conductor pattern 150 is arranged so as to cover at least a portion of the waveguide 130 for emitted light. With this configuration, the conductor pattern 150 can effectively remove unwanted emitted light propagating through the waveguide for emitted light.

[0099] Furthermore, the first conductive layer 162 and the second conductive layer 166 are made of gold (Au), and the first material constituting the first foundation layer 160 and the second material constituting the second foundation layer are made of a material that does not react with iodine. With this configuration, an iodine-based etching solution can be used to pattern the first conductive layer 162 and the second conductive layer 166 in the manufacturing process of the light modulation element 100, which broadens the options for etching solutions in the manufacturing process and makes it easier to manufacture the light modulation element 100.

[0100] The first material constituting the first underlayer 160 is, for example, niobium (Nb), and the second material constituting the second underlayer 164 is, for example, titanium (Ti). With this configuration, it is possible to realize an optical modulation element 100 that can be driven at a lower voltage than conventional ones and has good optical characteristics, without using special materials.

[0101] Furthermore, the thickness of the first underlayer 160 is 30 nm or less, and the thickness of the second underlayer 164 is 100 nm or more. With this configuration, it is possible to more easily realize an optical modulation element 100 that can be driven at a lower voltage than conventional ones and has good optical characteristics.

[0102] The optical waveguide 104 is a convex optical waveguide formed by a convex portion 144 extending on the substrate 102. This configuration makes it possible to realize an optical modulation element 100 that can be driven at a lower voltage than conventional elements and has good optical characteristics.

[0103] The optical modulation element 100 also has two working electrodes 114 (specifically, a signal electrode 114-1 and a ground electrode 114-2) that sandwich the parallel waveguide 112 of the optical waveguide 104 within the plane of the substrate 102, and the distance between these two working electrodes 114 is 1.0 μm or more and 5.0 μm or less. This configuration makes it possible to easily realize an optical modulation element 100 that can be driven at a lower voltage than conventional elements and has good optical characteristics.

[0104] The working electrode 114 also has a third base layer made of a third material different from the first material on the first conductive layer 162, and a third conductive layer on the third base layer. In a cross section perpendicular to the extension direction of the optical waveguide 104, the end of the third base layer is covered with the third conductive layer.

[0105] Moreover, the third material is made of titanium (Ti), and the third conductive layer is made of gold (Au).

[0106] These configurations can prevent the third underlayer from being over-etched in the etching process when forming the electrodes.

[0107] Moreover, the optical modulator 400 according to the second embodiment includes an optical modulation element 100 that modulates light, a housing 402 that houses the optical modulation element 100, an input optical fiber 414 that inputs light to the optical modulation element 100, and an output optical fiber 420 that guides the light output by the optical modulation element 100 to the outside of the housing 402.

[0108] Moreover, the optical modulation module 500 according to the third embodiment includes an optical modulation element 100, a housing 402 that houses the optical modulation element 100, an input optical fiber 414 that inputs light to the optical modulation element 100, an output optical fiber 420 that guides the light output by the optical modulation element 100 to the outside of the housing 402, and a drive circuit 508 that drives the optical modulation element.

[0109] In addition, the optical transmitting device 600 of the fourth embodiment includes the optical modulator 400 of the second embodiment or the optical modulation module 500 of the third embodiment, and a modulation signal generating unit 608 which is an electronic circuit that generates an electrical signal to cause the optical modulation element 100 to perform a modulation operation.

[0110] These configurations make it possible to realize an optical modulator 400, an optical modulation module 500, or an optical transmitter 600 that can be driven at a lower voltage than conventional devices and has good optical characteristics. [Explanation of symbols]

[0111] 100...Optical modulator, 102...Substrate, 104...Optical waveguide, 106...Input waveguide, 108a, 108b...Network-type map-type optical waveguide, 110, 110a, 110b, 110c, 110d...Map-type optical waveguide, 112, 112a, 112b, 112c, 112d, 112e, 112f, 112g, 112h...Parallel waveguide, 114 ...working electrodes, 114-1, 114-1a, 114-1b, 114-1c, 114-1d, 114-1e...signal electrodes, 114-2, 114-2a, 114-2b, 114-2c, 114-2d, 114-2e, 114-2f, 114-2g...graph electrodes, 118...wiring electrodes, 118-1, 118-1a, 118-1b, 118-1c, 118 -1d, 118-1e, 118-1f, 118-1g, 118-1h...signal wiring electrodes, 118-2, 118-2a, 118-2b, 118-2c, 118-2d, 118-2e, 118-2f, 118-2g, 118-2h, 118-2i, 118-2j...graph wiring electrodes, 126a, 126b...output waveguides, 128, 128a, 128 b, 128c, 128d, 128e, 128f...combining unit, 130, 130a, 130b, 130c, 130d, 130e, 130f, 130g, 130h, 130i, 130j, 130k, 130m...radiated light waveguide, 132a, 132b, 132c...basis electrodes, 140a, 140b, 140c, 140d...side, 142...support plate, 144,144a, 144b... protruding portions, 150, 150a, 150b, 150c, 150d, 150e, 150f, 150g, 150h-1, 150h-2... conductive patterns, 160, 160a, 160a-1, 160a-2, 160b, 160c, 160d... first base layer, 162, 162a, 162a-1, 162a-2, 162b, 162c, 162d... first conductive layer, 164, 164a, 164b, 164c, 164d-1, 164d-2, 164e... second base layer, 166, 166a, 166b, 166c, 166d-1, 166d-2... second conductive layer, 1 70...light incident portion, 172...rectangular area, 180, 180a, 180b, 180c...third base layer, 182, 182a, 182b, 182c...third conductive layer, 200, 202, 204, 206...line, 402...housing, 406...relay board, 408, 410...signal pin, 412...terminator, 414...input optical fiber, 416...optical unit, 418, 430, 434...lens, 420...output optical fiber, 422, 424...support, 506...circuit board, 508...drive circuit, 600...optical transmitter, 604...light source, 606...modulator drive unit, 608...modulation signal generation unit.

Claims

1. An optical waveguide element including a substrate, an optical waveguide formed on the substrate, and a working electrode that controls an optical wave propagating through the optical waveguide, The working electrode is a first underlayer made of a first material; a first conductive layer on the first underlayer; It consists of In addition to the working electrode, a conductor pattern is formed on the substrate in an area other than a path from the input end to the output end of the optical waveguide, the conductor pattern is composed of a second base layer made of a second material different from the first material and adjacent to the substrate without any other layer interposed between them, and a second conductive layer on the second base layer. Optical waveguide element.

2. the conductor pattern constituted by the second base layer and the second conductive layer is formed in a region on the substrate through which unwanted light propagates; The optical waveguide element according to claim 1 .

3. the second material has a larger optical absorption coefficient at the wavelength of light propagating through the optical waveguide than the first material; 3. The optical waveguide element according to claim 1.

4. the conductor pattern is a pattern continuing from a wiring electrode connected to the working electrode; 4. The optical waveguide element according to claim 1.

5. the optical waveguide includes a Mach-Zehnder optical waveguide, a waveguide for radiated light that propagates radiated light leaking from the Mach-Zehnder optical waveguide without being multiplexed is formed at a multiplexing portion of the Mach-Zehnder optical waveguide; the conductor pattern is arranged so as to cover at least a portion of the emitted light waveguide; 5. The optical waveguide element according to claim 1.

6. the first conductive layer and the second conductive layer are made of gold (Au), and the first material and the second material are made of a material that does not react with iodine. The optical waveguide element according to claim 1 .

7. The first material is niobium (Nb) and the second material is titanium (Ti).

7. The optical waveguide element according to claim 1.

8. the thickness of the first underlayer is 30 nm or less; The thickness of the second underlayer is 100 nm or more. The optical waveguide element according to claim 7 .

9. the optical waveguide is a convex optical waveguide formed by a convex portion extending on the substrate; 9. The optical waveguide element according to claim 1.

10. the two working electrodes sandwiching the optical waveguide within the plane of the substrate; The distance between the two working electrodes is 1.0 μm or more and 5.0 μm or less. The optical waveguide element according to claim 9 .

11. the working electrode has a third base layer made of a third material different from the first material on the first conductive layer, and a third conductive layer on the third base layer; In a cross section perpendicular to the extending direction of the optical waveguide, an end portion of the third underlayer is covered with the third conductive layer. The optical waveguide element according to claim 1 .

12. the third material is titanium (Ti); The third conductive layer is made of gold (Au). The optical waveguide element according to claim 11.

13. The optical waveguide element according to any one of claims 1 to 12, which is an optical modulation element for modulating light; a housing that houses the optical waveguide element; an optical fiber for inputting light into the optical waveguide element; an optical fiber that guides the light output from the optical waveguide element to the outside of the housing; An optical modulator comprising:

14. The optical waveguide element according to any one of claims 1 to 12, which is an optical modulation element for modulating light; a housing that houses the optical waveguide element; an optical fiber for inputting light into the optical waveguide element; an optical fiber that guides the light output from the optical waveguide element to the outside of the housing; a drive circuit for driving the optical waveguide element; An optical modulation module comprising:

15. an optical modulator according to claim 13 or an optical modulation module according to claim 14; an electronic circuit for generating an electrical signal for causing the optical waveguide element to perform a modulation operation; An optical transmitting device comprising:

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