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

Abstract

The purpose of the present invention is to provide an optical waveguide element that suppresses formation defects of modulation electrodes having segmented electrodes and has high product yield. An optical waveguide element is provided with: a substrate (1) in which an optical waveguide (10) is formed; and modulation electrodes (2S, 2G) which are disposed on the substrate (1) and which apply an electric field to the optical waveguide (10) in order to modulate light waves propagating through the optical waveguide (10), the optical waveguide element being characterized in that the modulation electrodes (2S, 2G) have: segmented electrodes (SE) which are disposed on the substrate (1) and which are disposed on the substrate (1); a plurality of optical waveguides arranged close to the optical waveguides (10) and along the optical waveguides (10); and a signal transmission unit (SS) that is electrically connected to the segmented electrode (SE) and transmits a modulation signal (S), the segmented electrode (SE) having a T-shaped shape including a transverse line (L1) and a vertical line (L2), the corners (K1, K2) of the ends of the transverse line (L1) being formed by an arc or two or more corners.

Description

Technical Field

[0001] The present invention relates to an optical waveguide element, an optical modulation device using the optical waveguide element, and an optical transmission device, and particularly relates to an optical waveguide element including: a substrate on which an optical waveguide is formed; and a modulation electrode disposed on the substrate and configured to apply an electric field to the optical waveguide in order to modulate light waves propagating in the optical waveguide. Background Art

[0002] In the field of optical communication or optical measurement, like an optical modulator, etc., an optical waveguide element having an optical waveguide formed on a substrate is mostly used. In recent years, in order to meet the requirements of miniaturization or low power consumption, the optical waveguide element constituting an optical modulator built in an optical transceiver device needs to be miniaturized.

[0003] In addition, in order to achieve velocity matching or impedance matching between light waves propagating in the optical waveguide and modulation signals (i.e., microwaves) propagating in the modulation electrode to realize broadband of the optical modulator, as shown in Patent Document 1 and Patent Document 2, a structure using segmented electrodes in the modulation electrode has also been proposed. Figure 1 This is an example of a modulation electrode using a segmented electrode SE. The modulation electrode includes: segmented electrodes SE disposed close to the optical waveguide 10 and arranged in plurality along the optical waveguide; and a signal transmission portion SS electrically connected to the segmented electrodes SE and configured to transmit modulation signals.

[0004] In Patent Document 1, the segmented electrodes are only formed on the ground electrode. In Patent Document 2, the segmented electrodes and radio frequency (RF) electrodes serving as signal transmission paths are disposed with a dielectric layer therebetween.

[0005] In a high bandwidth-coherent driver modulator (HB-CDM) or the like, the optical waveguide element (chip) itself is miniaturized. Compared with conventional optical modulators, the electrode width is thinner and the electrode thickness is also thinner. Therefore, due to the thinning of the electrodes, when forming a resist pattern for forming a pattern of the segmented electrodes, resist cracks (crazing) are likely to occur at portions with unbalanced stress within the resist pattern. If resist cracks occur, it will cause poor electrode formation, resulting in a significant reduction in the product yield.

[0006] In Figure 1 the modulation electrode using the segmented electrode SE, the ends of the horizontal line or the vertical line of the "T" shape constituting the segmented electrode SE, and the portion where the horizontal line and the vertical line intersect are at right angles. Stress is likely to concentrate inside such right-angle portions, thus causing resist cracks in the resist pattern.

[0007] Prior art documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Publication No. 6075576

[0010] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2016 - 194544 Summary of the invention

[0011] Problems to be solved by the invention

[0012] The problem to be solved by the present invention is to solve the above - mentioned problems and provide an optical waveguide element that suppresses the formation defects of a modulation electrode having a segmented electrode and has a high product yield. Further, an optical modulation device and an optical transmission device using such an optical waveguide element are provided.

[0013] Technical means for solving the problems

[0014] In order to solve the above - mentioned problems, the optical waveguide element, optical modulation device, and optical transmission device of the present invention have the following technical features.

[0015] (1) An optical waveguide element, comprising: a substrate on which an optical waveguide is formed; and a modulation electrode disposed on the substrate and configured to apply an electric field to the optical waveguide in order to modulate light waves propagating in the optical waveguide, wherein the modulation electrode has: a segmented electrode disposed close to the optical waveguide and arranged in a plurality along the optical waveguide; and a signal transmission part electrically connected to the segmented electrode and configured to transmit a modulation signal, the segmented electrode having a T - shaped configuration including a horizontal line L1 and a vertical line L2, and the corner of the end of the horizontal line L1 being formed by an arc or two or more corners.

[0016] (2) The optical waveguide element according to (1) above, wherein the end of the horizontal line L1 has a corner K1 close to the optical waveguide and a corner K2 far from the optical waveguide, and the corner K1 and the corner K2 are set to have a shape that is line - symmetric with respect to a center line parallel to the length direction of the horizontal line L1.

[0017] (3) The optical waveguide element according to (1) above, wherein the end of the horizontal line L1 has a corner K1 close to the optical waveguide and a corner K2 far from the optical waveguide, and with respect to the bend formed by an arc or two or more corners of the corner K1 and the corner K2, the corner K2 is formed more gently than the corner K1.

[0018] (4) The optical waveguide element according to (1) above, characterized in that the radius of curvature of the arc is 1 μm or more.

[0019] (5) The optical waveguide element according to (1) above, characterized in that the thickness of the segmented electrode is 3 μm or less, the width of the horizontal line L1 is 6 μm or less, and the width of the vertical line L2 is 5 μm or more.

[0020] (6) The optical waveguide element according to (5) above, characterized in that the thickness of the signal transmission part is 3 times or more the thickness of the segmented electrode, and a cross section perpendicular to the transmission direction of the modulation signal is formed in a multi-stage manner in the signal transmission part.

[0021] (7) An optical modulation device, characterized in that the optical waveguide element according to any one of (1) to (6) above is housed in a housing, and the optical modulation device includes an optical fiber for inputting or outputting light waves with respect to the optical waveguide.

[0022] (8) The optical modulation device according to (7) above, characterized in that an electronic circuit for amplifying the modulation signal of the modulation electrode input to the optical waveguide element is provided inside the housing.

[0023] (9) An optical transmission device, characterized in that it has the optical modulation device according to (7) above and an electronic circuit for outputting a modulation signal for causing the optical modulation device to perform a modulation operation.

[0024] Effects of the Invention

[0025] The present invention is an optical waveguide element, including: a substrate on which an optical waveguide is formed; and a modulation electrode disposed on the substrate and configured to apply an electric field to the optical waveguide in order to modulate light waves propagating in the optical waveguide. In the optical waveguide element, the modulation electrode has: a segmented electrode disposed close to the optical waveguide and arranged in a plurality along the optical waveguide; and a signal transmission part electrically connected to the segmented electrode and transmitting a modulation signal. The segmented electrode has a T-shaped configuration including a horizontal line L1 and a vertical line L2. The corner of the end of the horizontal line L1 is formed by an arc or two or more corners, so that the inner angle of the corner is 90 degrees or more, thereby suppressing the generation of resist cracks on the resist pattern when the segmented electrode is formed. As a result, the product yield of the optical waveguide element can also be improved.

[0026] Furthermore, an optical modulation device or an optical transmission device using the optical waveguide element can also be provided. Brief Description of the Drawings

[0027] Figure 1 ​is a diagram showing an example in which segmented electrodes are provided on both the signal electrode and the ground electrode.

[0028] Figure 2 is a plan view showing an example of the optical waveguide element of the present invention.

[0029] Figure 3 is a diagram for explaining the shape of the segmented electrode of the optical waveguide element of the present invention.

[0030] Figure 4 is a diagram for explaining the dimensions of the segmented electrode.

[0031] Figure 5 is a diagram for explaining other shapes of the segmented electrode.

[0032] Figure 6 is a diagram for explaining the state in which the segmented electrode and the signal transmission part are combined.

[0033] Figure 7 is a diagram for explaining the dimensions of the segmented electrode and the arrangement relationship between the segmented electrode and the signal transmission part.

[0034] Figure 8 is Figure 6 a cross-sectional view taken along the dotted line D of

[0035] Figure 9 is Figure 6 a cross-sectional view taken along the dotted line E of

[0036] Figure 10 is for explaining Figure 9 an application example of

[0037] Figure 11 is a diagram for explaining an example (one) of a substrate suitable for Z-cutting.

[0038] Figure 12 is a diagram for explaining an example (two) of a substrate suitable for Z-cutting.

[0039] Figure 13 is a diagram for explaining the optical transmission device of the present invention. Detailed Description of the Invention

[0040] Hereinafter, the present invention will be described in detail using preferred examples.

[0041] As Figure 2 and Figure 3 ​​​​​​​​​​​​As shown in the figure, the present invention is an optical waveguide element, comprising: a substrate formed with an optical waveguide 10; and modulation electrodes (2S, 2G) disposed on the substrate and configured to apply an electric field to the optical waveguide in order to modulate the light wave propagating in the optical waveguide 10. The optical waveguide element is characterized in that the modulation electrode has: segmented electrodes SE, which are disposed close to the optical waveguide and arranged in plurality along the optical waveguide; and a signal transmission part SS, which is electrically connected to the segmented electrodes SE and transmits a modulation signal. The segmented electrode SE has a T-shaped configuration including a horizontal line L1 and a vertical line L2, and the corner parts (K1, K2) at the ends of the horizontal line L1 are formed by arcs or two or more corners.

[0042] As the substrate used in the optical waveguide element, specifically, as the substrate having an electro-optic effect, substrates such as lithium niobate (LN), lithium tantalate (LT), lanthanum modified lead zirconate titanate (PLZT), etc., or substrates doped with MgO, etc. in these substrate materials can be used. In addition, it is also possible to directly or with an intermediate layer of some kind form a film by vapor growth of materials such as LN on a support substrate such as Si, glass, sapphire, etc. In addition, a substrate obtained by thin film processing of an electro-optic substrate after bonding a substrate having an electro-optic effect with another substrate can also be used. Furthermore, substrates made of semiconductor substrates or organic materials such as ethylene oxide (EO) polymers, and quartz substrates for planar lightwave circuits (PLC) can also be used. Different types of semiconductor films can also be grown on semiconductor substrates. Furthermore, since the substrate (waveguide layer) on which the optical waveguide is formed is very thin, for example, 1 μm or less, it is preferably to use a support substrate having a dielectric constant lower than that of the waveguide layer.

[0043] As a method for forming the optical waveguide, it is possible to locally form a portion with a high refractive index by methods such as thermal diffusion of Ti, etc. on an LN substrate or proton exchange method, etc., thereby forming an optical waveguide. In the present invention, it is possible to etch the surface of the substrate other than the optical waveguide or form grooves, etc. on both sides of the optical waveguide, thereby forming a rib-type optical waveguide on the substrate with a convex portion corresponding to the optical waveguide. In the optical waveguide element of the present invention, compared with a graded index (GI) type optical waveguide such as a diffused waveguide, a step index (SI) type optical waveguide that generates a discontinuous point of refractive index interruption such as a rib-type optical waveguide is particularly effective.

[0044] The LN substrate used in the present invention is not limited to X-cut or Z-cut. The following description will focus on an example of an optical waveguide device (chip) in which a rib-type optical waveguide having a height of 1 μm or less is formed using an X-cut LN substrate.

[0045] The main features of the optical waveguide element of the present invention are: (1) Figure 2 As shown, the modulation electrode (2S, 2G) has a segment electrode SE and a signal transmission part SS, the segment electrode SE is arranged in a manner close to the optical waveguide and a plurality of segments are arranged along the optical waveguide, and the signal transmission part SS is electrically connected to the segment electrode and transmits the modulation signal; (2) as Figure 3 As shown, the segment electrode SE has a T-shape including a horizontal line L1 and a vertical line L2 , and the corners ( K1 , K2 ) at the ends of the horizontal line L1 are formed by arcs or two or more corners.

[0046] In the optical waveguide device of the present invention, the segment electrode SE of the modulation electrode and the signal transmission portion SS are formed by different manufacturing steps.

[0047] The thickness of the segment electrode SE is 3 μm or less, preferably 1 μm or less, and is therefore formed by plating, evaporation, or sputtering. In addition, the signal transmission portion SS is formed by plating because it has a thickness more than three times that of the segment electrode. The thicker the film thickness of the resist pattern, the easier it is for the resist to crack. In addition, the thinner the thickness of the segment electrode SE, the less high-frequency loss, which can reduce the degradation of high-frequency characteristics.

[0048] When forming the segment electrode SE, the corners of the segment electrode are Figure 3 The dotted frame areas A to C are formed by arcs or two or more angles (the inner angle of the polygon is 90 degrees or more) so that the resist pattern does not produce resist cracks. In particular, for the horizontal line L1 that is responsible for forming the electric field applied to the optical waveguide, the corners (K1, K2) at the ends of the horizontal line L1 are formed by arcs (see the dotted frame A') or two or more angles (see the dotted frame A") so that the resist cracks do not occur.

[0049] An enlarged view of the area A in the dashed box is dashed box A' or dashed box A".

[0050] In the dotted frame A', the corner K1 is formed by an arc with a curvature radius R1. In addition, the corner K2 is formed by an arc with a curvature radius R2. In order to suppress the occurrence of resist cracks, the curvature radius R1 (R2) of the arc is preferably 1 μm or more.

[0051] On the other hand, in the dashed-line box A", a corner K1 is formed by two corners. In addition, a corner K2 is formed by four corners. Whichever corner is used, the interior angle is set to be 90 degrees or more, more preferably 120 degrees or more. Compared with the case where the conventional corner is a right angle, the generation of resist cracks can be suppressed.

[0052] In the case where one corner is formed by a plurality of corners, it is preferable to increase the number of corners to increase the interior angle of each corner. However, if the interval between the first corner and the last corner is close, the effect of increasing the interior angle is weakened. Therefore, for example, it is preferable to set the interval between the first corner and the last corner to 0.2 μm or more.

[0053] Regarding the shapes of the corner K1 and the corner K2, they can be set to be line-symmetric with respect to the center line CL (refer to Figure 3 the dashed-line box A') parallel to the length direction of the horizontal line L1.

[0054] Specifically, the curvature radii R1 and R2 of the corners formed by arcs are set to the same size. Thus, since Figure 3 the shape of the end portion within the dashed-line box A' is symmetric up and down, the internal stress of the resist pattern near the corners arranged at the end portion of the horizontal line L1 can be made equal at the two corners (K1, K2). Thus, not only can the generation of resist cracks be suppressed, but also the strain of the resist pattern can be suppressed, thereby being able to suppress the deformation of the segmented electrode.

[0055] As another example, even in the case where the shapes of the corner K1 and the corner K2 are formed by two or more corners, by forming them to be line-symmetric with respect to the center line CL, the internal stress of the resist pattern arranged near the corners can be made equal at the two corners (K1, K2), thereby obtaining the same effect as the corner formed by the arc.

[0056] In addition, regarding the "bending" of the corner K1 and the corner K2 formed by an arc or two or more corners, the corner K2 can be formed more gently than the corner K1. Here, the so-called "bending" not only refers to the bending formed only by a curve, but also includes the bending formed by a broken line based on a plurality of corners.

[0057] Specifically, by setting the curvature radius of the corner to R1 < R2, the distance between the optical waveguide and the electrode can be kept constant, and stress relaxation and improvement of high-frequency characteristics can be achieved. By making the curvature radius of R1 5 μm or less, the influence of the expansion of the electrode interval and the reduction of the modulation efficiency can be suppressed. By making the curvature radius of R2 3 μm or more, the generation of resist cracks can be further suppressed.

[0058] Furthermore, if necessary, the curvature radius of the corner can also be set to R1 > R2.

[0059] In addition, in the case where a corner portion is formed by two or more corners, the sum of the interior angles of all the corners constituting the corner portion, or the sum of the lengths of the straight lines connecting a plurality of corners, is set such that the corner portion K2 is larger than the corner portion K1. Thereby, the distance between the optical waveguide and the segmented electrode can be kept longer and constant, which not only helps to relieve stress but also helps to improve high-frequency characteristics.

[0060] Next, Figure 4 the dimensions of the segmented electrode will be described.

[0061] Regarding the width of the segmented electrode, the width W1 of the horizontal line L1 is set to 6 μm or less, preferably 4 μm or less. Basically, for the horizontal line L1, being thinner is advantageous for high-frequency characteristics. The reason is that in the signal electrode, the larger the width of the horizontal line L1, the more the modulation signal makes the segmented electrode feel like protrusions and depressions protruding from the side of the signal electrode, so the high-frequency characteristics deteriorate. Therefore, it is more preferable that the width of the horizontal line L1 is narrower and the thickness is thinner.

[0062] In addition, the width W2 of the vertical line L2 is set to 5 μm or more, preferably 10 μm or more. Without a certain thickness or more, the electrical connection between the segmented electrode SE and the signal transmission portion SS is unstable.

[0063] Regarding the length of the segmented electrode, the length S1 of the horizontal line L1 depends on the frequency processed by an optical modulator or the like. From a high-frequency perspective, it needs to be sufficiently short. Specifically, it is sufficient to be about one-fourth to one-eighth of the wavelength of the modulation signal, i.e., the microwave, and it can also be shorter than that. For example, when operating at a frequency of 100 GHz or less, the length S1 of the horizontal line L1 is ideally 400 μm or less.

[0064] Regarding the length S2 of the vertical line L2, similar to the width of the vertical line L2, basically, the longer it is, the more the overlapping area between the segmented electrode and the signal transmission portion increases, and the better the electrical connection between the two is. However, if the length S2 becomes longer, the interval between the branch waveguides of the Mach-Zehnder type optical waveguide also becomes larger, so the size of the optical waveguide element (chip) itself also becomes larger. Therefore, the length S2 is set to 100 μm or less.

[0065] In addition, as Figure 6 shown by the signal transmission portion SS of the signal electrode 2S, when the segmented electrodes SE are arranged on both sides of the signal transmission portion of the signal electrode or the ground electrode, for the vertical line L2, as Figure 6 shown by the segmented electrode in the right center, it is also possible to adopt a structure in which the vertical lines L2 of two segmented electrodes are connected in an "H" shape.

[0066] Regarding the radii of curvature (R1, R2) of the corners of the segmented electrodes, as described above, in order to avoid resist cracks, it is preferably set to 1 μm or more. However, since the size of the radius of curvature also affects the shape of the ends of the horizontal line L1, it is set to be equal to or less than the width W1 of the horizontal line L1, preferably less than half of the width W1, and more preferably equal to or less than 1 / 3 of the width W1.

[0067] Figure 5 FIG. is a diagram illustrating various shapes of the segmented electrodes.

[0068] Not only the ends of the horizontal line L1 of the segmented electrodes, as Figure 5 (a) shows, the intersection (region B in the dashed box) of the horizontal line L1 and the vertical line L2 can also be connected by an arc. Thereby, generation of resist cracks at the intersection of the horizontal line L1 and the vertical line L2 can be suppressed.

[0069] Figure 5 (b) is a shape in which an arc is formed on the vertical line L2 as shown in region B and connected to the horizontal line L1 which is a straight line, resulting in a shape where the intersection part becomes thinner. In the thinner part, the width of the resist film becomes narrower, so stress generation is also weak and resist cracks are not easily generated.

[0070] Figure 5 (c) is a diagram in which tapered shapes with gradually decreasing widths are formed at both ends of the horizontal line L1. Since the distance between the side of the horizontal line L1 on the optical waveguide side and the optical waveguide needs to be kept constant, the shape of the side away from the optical waveguide is changed. With this shape, the distance between the optical waveguide and the electrode can also be kept constant, so an effect of further improving the high-frequency characteristics can be expected.

[0071] Figure 5 (d) is a diagram in which the end of the vertical line L2 of the segmented electrode is formed at a right angle as in the past. Thereby, the possibility of resist cracks occurring in the resist pattern at the end of the vertical line L2 becomes high, but since the vicinity of the end is covered by the signal transmission part SS, the influence of the resist cracks is small.

[0072] Figure 5 (e) is a diagram in which the shape of the segmented electrode is set to a T shape biased to one side instead of a symmetric T shape. Assuming that the traveling direction of the propagating light in the optical waveguide is the right direction in the drawing, the modulation signal entering from the vertical line L2 becomes the same direction as the propagating light (forward modulation) when propagating to the right side of the horizontal line L1, so the modulation efficiency also becomes high. In addition, when propagating to the left side of the horizontal line L1, it becomes the opposite direction to the propagating light (reverse modulation). Therefore, by configuring as shown in Figure 5 (e), the interval of forward modulation can be extended and the interval of reverse modulation can be shortened. Depending on the situation, the horizontal line L1 can also be arranged only in the direction of forward modulation like an L shape.

[0073] As described above, the shape of the segmented electrode can be variously changed according to the desired characteristics of the optical waveguide element.

[0074] Figure 6 FIG. is a view for explaining a case where the signal transmission portion SS and the segmented electrode SE are overlapped and arranged. In addition, in order to easily understand the shape of the segmented electrode, the portion overlapping with the signal transmission portion is also shown exposed.

[0075] In addition, Figure 7 is a view extracting Figure 6 a pair of segmented electrodes across the optical waveguide 10, and is a view for explaining the size of the segmented electrode and the arrangement relationship between the segmented electrode and the signal transmission portion. Regarding the size of the segmented electrode, it is the same as Figure 4 the same.

[0076] Figure 6 On the left side of is a normal segmented electrode (SE), and the respective segmented electrodes are separately arranged. In contrast, as described above, Figure 6 on the right side of , the segmented electrode SE has an "H" shape in which the vertical lines L2 of the two segmented electrodes located on both sides of the signal transmission path are connected. Of course, in the case of the "H" shape, the area of the overlapping portion between the vertical line L2 and the signal transmission portion SS becomes larger, so that electrical connection can be more reliably performed.

[0077] Figure 7 The electrode interval G1 between the segmented electrode SE of the signal electrode 2S shown in and the segmented electrode SE of the ground electrode 2G is preferably arranged close to the optical waveguide 10 within a range that does not absorb the light wave propagating in the optical waveguide 10. For example, the interval G1 is set to be 2 times or more the mode field diameter of the light wave propagating in the optical waveguide 10, and becomes 3 μm or more.

[0078] Regarding the interval G3 between the vertical line L1 of the segmented electrode SE and the signal transmission portion SS, when the two are too close, the electric field formed by the signal transmission portion SS directly affects the optical waveguide 10. Therefore, although it also depends on the size of the width W1 of the horizontal line L1 of the segmented electrode SE, the interval G3 is preferably set to 1 μm or more. Of course, the interval G3 must be smaller than the length S2 of the vertical line L2 of the segmented electrode SE (G3 < S2). On the contrary, the minimum value of the length S2 is set to a value having a margin by adding the alignment accuracy between the segmented electrode and the signal transmission portion to the interval G3.

[0079] Figure 7 The interval G2 between the two signal transmission portions (2S(SS), 2G(SS)) in is 10 μm or more, but in order not to increase the size of the optical waveguide element (chip), it is preferably set to 100 μm or less.

[0080] Figure 8 is Figure 6 a cross-sectional view taken along the dash-dotted line D of Figure 9 is Figure 6 a cross-sectional view taken along the dash-dotted line E of Figure 8 and Figure 9 As shown in

[0081] Figure 10 is Figure 9 an application example of

[0082] In the above description, the X-cut LN substrate has been mainly described, but the technology related to the optical waveguide element of the present invention can of course also be applied to the Z-cut LN substrate and the like. Figure 11 and Figure 12 illustrate the electrode configuration applied to the Z-cut LN substrate. As shown in Figure 9 is a cross-sectional view of the vertical line L2 passing through the segmented electrode SE.

[0083] In Figure 11 an example of applying an electric field to two optical waveguides 10 using one signal electrode 2S and one ground electrode 2G is shown.

[0084] In addition, in Figure 12 is a diagram showing an example of a case where the electric signals applied to the electrodes are G, S+, S-, G (G is the ground potential, and S+ and S- are differential signals with opposite phases). In the drawings, the electric signal S+ is represented by 2S+, and the electric signal S- is represented by 2S-.

[0085] In addition, the symbol BF represents a buffer layer.

[0086] Next, an example of applying the optical waveguide element of the present invention to an optical modulation device or an optical transmission device will be described. Hereinafter, an optical modulation device using the optical waveguide element will be described, but the present invention is not limited thereto, and it can also be applied to an optical phase modulator, an optical modulator having a polarization wave synthesis function, an optical waveguide element integrated with more Mach-Zehnder type optical waveguides, a bonding device with an optical waveguide element made of other materials such as silicon, a device for sensor applications, etc. Furthermore, of course, it can be applied to HB-CDM.

[0087] As Figure 13 shown, the optical waveguide element has an optical waveguide 10 formed on a substrate 1 and a modulation electrode (not shown) for modulating the light wave propagating in the optical waveguide 10, and is housed in a frame CA. Furthermore, by providing an optical fiber (F) for inputting / outputting light waves to / from the optical waveguide, an optical modulation device MD can be constituted. In Figure 13 , the optical fiber F is introduced into the frame through a through-hole penetrating the side wall of the frame and is directly bonded to the optical waveguide element (chip). It is not limited thereto, and an optical block including an optical lens or a lens barrel can also be used to optically couple with the optical waveguide 10 in the optical waveguide element. In addition, in order to stably bond with the optical fiber or the optical block, a reinforcing member 3 can also be arranged overlapping the end face of the optical waveguide substrate 1.

[0088] By connecting an electronic circuit (digital signal processor DSP) that outputs a modulation signal So for causing the optical modulation device MD to perform a modulation operation to the optical modulation device MD, an optical transmission device OTA can be constituted. In order to obtain the modulation signal S applied to the optical waveguide element, it is necessary to amplify the modulation signal So output from the digital signal processor DSP. Therefore, in Figure 13 , a drive circuit DRV is used to amplify the modulation signal. The drive circuit DRV or the digital signal processor DSP can also be arranged outside the frame CA, but can also be arranged inside the frame CA. In particular, by arranging the drive circuit DRV inside the frame, the propagation loss of the modulation signal from the drive circuit can be further reduced.

[0089] Industrial Applicability

[0090] As described above, according to the present invention, an optical waveguide element that suppresses the formation defect of a modulation electrode having a segmented electrode and has a high product yield can be provided. Furthermore, an optical modulation device and an optical transmission device using such an optical waveguide element can be provided.

[0091] Explanation of Symbols

[0092] 1: Substrate (waveguide layer)

[0093] 3: Reinforcing member

[0094] 10: Rib-type optical waveguide

[0095] 2G: Ground electrode

[0096] 2S: Signal electrode

[0097] SE: Segment electrode

[0098] SS: Signal transmission section

[0099] L1: Horizontal line

[0100] L2: Vertical line

[0101] K1, K2: Corners

[0102] R1, R2: Radius of curvature

Claims

1. An optical waveguide element, comprising: a substrate on which an optical waveguide is formed; and a modulation electrode disposed on the substrate and configured to apply an electric field to the optical waveguide in order to modulate light waves propagating in the optical waveguide, wherein the optical waveguide element is characterized in that the modulation electrode has: segmented electrodes disposed close to the optical waveguide and arranged in plurality along the optical waveguide; and a signal transmission portion electrically connected to the segmented electrodes and configured to transmit a modulation signal, the segmented electrode has a T-shaped configuration including a horizontal line L1 and a vertical line L2, and corners at ends of the horizontal line L1 are formed by an arc or two or more corners.

2. The optical waveguide element according to claim 1, wherein ends of the horizontal line L1 have a corner K1 close to the optical waveguide and a corner K2 away from the optical waveguide, the corner K1 and the corner K2 are set to be symmetric with respect to a center line parallel to the length direction of the horizontal line L1.

3. The optical waveguide element according to claim 1, wherein ends of the horizontal line L1 have a corner K1 close to the optical waveguide and a corner K2 away from the optical waveguide, with respect to the curvature formed by an arc or two or more corners at the corner K1 and the corner K2, the corner K2 is formed more gently than the corner K1.

4. The optical waveguide element according to claim 1, wherein the radius of curvature of the arc is 1 μm or more.

5. The optical waveguide element according to claim 1, wherein the thickness of the segmented electrode is 3 μm or less, the width of the horizontal line L1 is 6 μm or less, and the width of the vertical line L2 is 5 μm or more.

6. The optical waveguide element according to claim 5, wherein the thickness of the signal transmission portion is 3 times or more the thickness of the segmented electrode, and in the signal transmission portion, a cross-section perpendicular to the transmission direction of the modulation signal is formed in a multi-stage manner.

7. An optical modulation device, wherein the optical waveguide element according to any one of claims 1 to 6 is housed in a housing, and the optical modulation device includes an optical fiber configured to input or output light waves with respect to the optical waveguide.

8. The optical modulation device according to claim 7, wherein an electronic circuit for amplifying a modulation signal input to the modulation electrode of the optical waveguide element is provided inside the housing.

9. An optical transmission device, wherein the optical modulation device according to claim 7 and an electronic circuit for outputting a modulation signal for causing the optical modulation device to perform a modulation operation are provided.

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