Optical waveguide element, optical modulator, and optical transmission device

Abstract

This optical waveguide element is provided with: an optical waveguide (31) disposed on the main surface of an optical substrate (30); and a control electrode (42) for controlling light waves propagating through the optical waveguide (31), the control electrode (42) including a first control electrode (43) and a second control electrode (44) facing each other on the main surface of the optical substrate (30) with the optical waveguide (31) interposed therebetween, the first control electrode (43) and the second control electrode (44) each including: common electrodes (43a, 44a) extending along the optical waveguide (31); a plurality of segment electrodes (43c, 44c) disposed closer to the optical waveguide (31) than the common electrodes (43a, 44a), the segment electrodes (43c, 44c) being divided along the direction in which the optical waveguide (31) extends; a plurality of connection electrodes (43b, 44b) that connect the plurality of segment electrodes (43c, 44c) to the common electrodes (43a, 44a), respectively; and auxiliary electrodes (43d, 44d) which extend in the direction in which the optical waveguide (31) extends, and which connect adjacent connection electrodes (43b, 44b) to each other.

Description

Technical Field

[0001] The present invention relates to an optical waveguide element, an optical modulator, and an optical transmission device. Background Art

[0002] In high-speed / high-capacity optical fiber communication systems, optical modulators incorporating optical modulation elements as optical waveguide elements are often used. The optical waveguide element is composed of an optical waveguide formed on a substrate and a control electrode for controlling the optical wave propagating in the optical waveguide. As the optical waveguide element for performing the optical modulation operation, a semiconductor optical modulation element using a semiconductor substrate such as an InP substrate and an LN optical modulation element using LiNbO3 (hereinafter also referred to as LN) for the substrate have been put into practical use.

[0003] The electrodes of the LN modulation element can be roughly divided into a signal electrode for applying a high-frequency electric field to the optical waveguide to propagate a high-frequency signal and a bias electrode for controlling the bias point (operating point). Since the bias point varies due to aging changes and changes in the operating temperature, the bias point variation amount, which is the amount of variation, is one of the parameters affecting the performance of the LN optical modulator. In the design of the bias electrode, it is required to consider reducing the control voltage and the bias point variation amount.

[0004] Patent Document 1 describes the following: In a structure in which an electric field is applied to an optical waveguide by a center electrode and a ground electrode that sandwich the optical waveguide in the plane of the operating substrate, a part of the conductor of the ground electrode is removed. In this optical modulator, by removing a part of the conductor of the ground electrode, the stress generated in the substrate due to the difference in the linear expansion coefficients of the metal material of the ground electrode and the substrate can be alleviated, and the bias point variation amount associated with changes in the operating temperature can be reduced.

[0005] On the other hand, in accordance with the requirements for further miniaturization and lower driving voltage of the optical modulation element, it is necessary to make the electrode gap (for example, the separation interval between the above-mentioned center electrode and the ground electrode sandwiching the optical waveguide) narrower, and it is required to arrange the electrode and the optical waveguide closer to each other. As a result, the stress generated by the electrode on the substrate due to the difference in the linear expansion coefficients is greater than before, which affects the bias point variation amount.

[0006] As one means of reducing the substrate stress generated by the electrode, it is considered to narrow the line width of the electrode itself to reduce the area of the electrode disposed near the optical waveguide.

[0007] However, narrowing the line width of the electrode may affect the manufacturing yield of the optical waveguide element due to defects in the electrode pattern during electrode formation, and may also affect the long-term reliability.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-098640 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] Based on the above background, an object of the present invention is to improve the manufacturing yield and / or long-term reliability in an optical waveguide element, and to reduce the variation in the bias point of the driving voltage.

[0013] Means for Solving the Problems

[0014] One aspect of the present invention is an optical waveguide element including: an optical waveguide disposed on a main surface of an optical substrate; and control electrodes for controlling light waves propagating in the optical waveguide, wherein the control electrodes include a first control electrode and a second control electrode that face each other across the optical waveguide on the main surface of the optical substrate, and the first control electrode and the second control electrode each include: a common electrode extending along the optical waveguide; a plurality of segmented electrodes disposed closer to the optical waveguide than the common electrode and divided along the extending direction of the optical waveguide; a plurality of connection electrodes connecting the plurality of segmented electrodes to the common electrode respectively; and an auxiliary electrode extending along the extending direction of the optical waveguide and connecting adjacent connection electrodes to each other.

[0015] According to another aspect of the present invention, the optical waveguide element further includes a high-frequency electrode disposed on the optical substrate for modulating light waves propagating in the optical waveguide to perform a modulation operation, and the control electrode is a bias electrode for controlling the bias point of the modulation operation.

[0016] According to another aspect of the present invention, a side of the auxiliary electrode facing the segmented electrode is disposed at a position closer to the segmented electrode than a position bisecting a distance between a side of the common electrode on the optical waveguide side and a side of the segmented electrode on the optical waveguide side.

[0017] According to another aspect of the present invention, a side of the auxiliary electrode facing the segmented electrode is disposed at a position closer to the common electrode than a position bisecting a distance between a side of the common electrode on the optical waveguide side and a side of the segmented electrode on the optical waveguide side.

[0018] According to another aspect of the present invention, a side of the auxiliary electrode facing the segmented electrode is disposed at a position bisecting a distance between a side of the common electrode on the optical waveguide side and a side of the segmented electrode on the optical waveguide side.

[0019] According to another aspect of the present invention, the thickness of the segmented electrode is 3 μm or less.

[0020] According to another aspect of the present invention, the width of the segmented electrode measured in a direction orthogonal to the extending direction of the optical waveguide is narrower than the width of the auxiliary electrode.

[0021] According to another aspect of the present invention, a low-elasticity layer is disposed between the control electrode and the optical substrate, and the low-elasticity layer is made of a low-elasticity material having an elastic modulus of one-tenth or less of that of the common electrode.

[0022] Another aspect of the present invention is an optical modulator, including: any one of the above optical waveguide elements as an optical modulation element; a housing that houses the optical waveguide element; an optical fiber that inputs light to the optical waveguide element; and an optical fiber that guides the light output from the optical waveguide element to the outside of the housing.

[0023] Another aspect of the present invention is an optical transmission device, including: any one of the above optical modulators; and an electronic circuit that generates an electric signal for causing the optical waveguide element to perform an optical modulation operation.

[0024] Advantageous Effects of the Invention

[0025] According to the present invention, in an optical waveguide element, it is possible to improve the manufacturing yield and / or long-term reliability, and reduce the variation in the bias point of the driving voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 FIG. is a diagram showing the structure of an optical modulator according to a first embodiment of the present invention.

[0027] Figure 2 FIG. is showing Figure 1 a diagram showing the structure of an optical modulation element used in the optical modulator shown.

[0028] Figure 3 FIG. is Figure 2 a partial detailed view of part A of the bias electrode portion shown.

[0029] Figure 4 FIG. is Figure 3 a partial detailed view of part B of the bias electrode portion shown.

[0030] Figure 5 FIG. is Figure 4 a V-V cross-sectional view of part B shown.

[0031] Figure 6 FIG. is Figure 4 a VI-VI cross-sectional view of part B shown.

[0032] Figure 7 FIG. is a diagram showing the structure of an optical modulation element according to a first modification.

[0033] Figure 8This is a diagram showing the structure of the optical modulation element according to the second modification example.

[0034] Figure 9 This is a diagram showing the structure of the optical modulation element according to the third modification example.

[0035] Figure 10 This is a diagram showing the structure of the optical modulation element according to the fourth modification example.

[0036] Figure 11 This is a diagram showing the structure of the optical modulation element according to the fifth modification example.

[0037] Figure 12 This is a diagram showing the structure of the optical modulation element according to the sixth modification example.

[0038] Figure 13 This is a diagram showing the structure of the optical modulation element according to the sixth modification example.

[0039] Figure 14 This is a diagram showing the structure of the optical modulation element according to the seventh modification example.

[0040] Figure 15 This is Figure 14 the XV-XV cross-sectional view of the control electrode shown.

[0041] Figure 16 This is a diagram showing the structure of the optical transmission device according to the second embodiment of the present invention.

[0042] Figure 17 This shows the application of the control electrode of the present invention to Figure 2 an example of the structure of the bias electrode of the nested Mach-Zehnder optical waveguide in. Detailed Embodiment

[0043] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0044] [First Embodiment]

[0045] First, the first embodiment of the present invention will be described.

[0046] Figure 1 This is a diagram showing the structure of the optical modulator 1 using the optical modulation element as an optical waveguide element according to the first embodiment of the present invention.

[0047] The optical modulator 1 has a housing 2 and an optical modulation element 3 housed in the housing 2. The optical modulation element 3 is, for example, a DP-QPSK modulator structure. The housing 2 complies with, for example, the HB-CDM specification which is an industry standard (“Implementation Agreement for the High Bandwidth Coherent Driver Modulator (HB-CDM) OIF-HB-CDM-02.0” (issued by OIF on July 15, 2021)). In addition, a cover (not shown) which is a plate body is finally fixed to the opening of the housing 2, and its interior is hermetically sealed.

[0048] A signal pin 4 is provided on the housing 2, and this signal pin 4 is used to input a high-frequency electrical signal for modulating the optical modulation element 3 to a drive circuit 17 mounted on a relay substrate 14 described later. In addition, a signal pin 5 is provided on the housing 2, and this signal pin 5 is used to input an electrical signal for adjusting the operating point of the optical modulation element 3, etc., input a power supply for the operation of the drive circuit 17, and input and output a control signal required for operating the drive circuit 17.

[0049] In addition, the optical modulator 1 has an input optical fiber 6 for inputting light into the housing 2 and an output optical fiber 7 for guiding the light modulated by the optical modulation element 3 to the outside of the housing 2 on the same surface of the housing 2. In addition, the optical modulator 1 has a beam shifter 12 having both a beam shifting function and a polarization combining function.

[0050] The input optical fiber 6 and the output optical fiber 7 are respectively fixed to the housing 2 via brackets 8 and 9 which are fixing members. The light input from the input optical fiber 6 is collimated by a lens 11a disposed in the bracket 8, then passes through the beam shifter 12, and is input to the optical modulation element 3 via a lens 10a. However, this is an example, and the input of light to the optical modulation element 3 can also be performed according to the prior art. For example, the input optical fiber 6 is introduced into the housing 2 via the bracket 8, and the end face of the introduced input optical fiber 6 is connected to the end face of an optical substrate 30 (described later) of the optical modulation element 3.

[0051] The two beams of modulated light output from the optical modulation element 3 are respectively collimated by lenses 10b and 10c, and then combined into one beam by the polarization combining function of the beam shifter 12. The combined beam is converged by a lens 11b disposed in the bracket 9 and coupled to the output optical fiber 7.

[0052] In the housing 2 of the optical modulator 1, a relay substrate 14 and a terminator 16 having four terminal resistors 15a, 15b, 15c, and 15d with a specified impedance are also arranged. Hereinafter, the terminal resistors 15a, 15b, 15c, and 15d are collectively referred to as the terminal resistor 15. The electrical connection between the optical modulation element 3 and the terminal resistor 15 of the terminator 16 is performed, for example, by wire bonding or the like.

[0053] The relay substrate 14 includes a drive circuit 17. The drive circuit 17 amplifies the high-frequency electrical signal input from the signal pin 4 and outputs a drive signal for causing the optical modulation element 3 to perform a modulation operation. In addition, the relay substrate 14 relays the electrical signals, power supply, and control signals such as those for operating point adjustment input from the signal pin 5 to the optical modulation element 3. The conductor pattern of the relay substrate 14 is connected, for example, by wire bonding or the like to the pads (not shown) at one end of the electrodes constituting the optical modulation element 3. In addition, the relay substrate 14 is Figure 1 illustrated as a single substrate in the figure, but may also be configured by being divided into a plurality of substrates as needed. In addition, the drive circuit 17 may be mounted on the relay substrate 14 as Figure 1 shown, or may be arranged between the relay substrate 14 and the optical modulation element 3. In addition, instead of the signal pin 4, the interface for inputting the high-frequency electrical signal may also be an FPC (flexible printed circuit) provided outside the housing 2.

[0054] Figure 2 is a diagram showing an example of the structure of the optical modulation element 3 such as a DP-QPSK modulator.

[0055] The optical modulation element 3 is composed of an optical waveguide 31 (the entire thick dotted line shown) formed on one main surface ( Figure 2 the surface shown) of the optical substrate 30, and performs, for example, coherent multi-value modulation of more than 100 GBaud. The optical substrate 30 is, for example, an X-cut LN substrate having an electro-optic effect that is processed to a thickness of 20 μm or less (for example, 2 μm) and thinned. In addition, the optical waveguide 31 is a convex optical waveguide (for example, a rib-type optical waveguide or a ridge-type optical waveguide) formed on the surface of the thinned optical substrate 30 and composed of convex portions extending in a strip shape.

[0056] The optical substrate 30 is, for example, rectangular, and has two sides 32a and 32b extending in the vertical direction shown in the figure and opposite to each other, and two sides 32c and 32d extending in the horizontal direction shown in the figure and opposite to each other.

[0057] The optical waveguide 31 includes: an input waveguide 33 that receives input light (arrow toward the right in the figure) from the input optical fiber 6 on the upper side of the right edge 32b in the figure of the optical substrate 30; and a branching waveguide 34 that branches the input light into two beams of light with the same light quantity. Further, the optical waveguide 31 includes two modulation units that modulate each beam of light branched by the branching waveguide 34, namely, so-called nested Mach-Zehnder type optical waveguides 35a and 35b.

[0058] Regarding the nested Mach-Zehnder type optical waveguides 35a and 35b, the propagation direction of light is folded back by 180 degrees in the folding region 38 in the left part of the figure of the optical substrate 30, and the light is output from the edge 32b of the optical substrate 30 to the right in the figure through the output waveguides 36a and 36b.

[0059] The nested Mach-Zehnder type optical waveguides 35a and 35b each include two Mach-Zehnder type optical waveguides 37a, 37b and 37c, 37d respectively provided in two waveguide portions constituting a pair of parallel waveguides.

[0060] In the RF electrode portion 41 in the lower part of the figure of the nested Mach-Zehnder type optical waveguides 35a and 35b folded back in the folding region 38 in the left part of the figure on the optical substrate 30, four center electrodes 18 that propagate high-frequency electrical signals and are used to respectively perform modulation operations on the total four Mach-Zehnder type optical waveguides 37a, 37b, 37c, 37d constituting the nested Mach-Zehnder type optical waveguides 35a and 35b are respectively arranged between two parallel waveguides of the corresponding Mach-Zehnder type optical waveguide 37.

[0061] In Figure 2 , the center electrodes 18 respectively form a distributed constant line with a specified impedance together with ground electrodes (not shown) formed on the main surface of the optical substrate 30 in a manner that sandwiches these center electrodes 18 at positions separated by a certain distance according to the prior art.

[0062] Thus, the drive signals output from the drive circuit 17 are respectively input from the left in the figure of Figure 2 to the corresponding center electrodes 18, become traveling waves, and respectively propagate to the right in the figure in the center electrodes 18, and in the RF electrode portion 41, modulate the light waves propagating in the corresponding Mach-Zehnder type optical waveguide 37. Here, the center electrodes 18 correspond to the high-frequency electrodes in the present disclosure.

[0063] Further, in a bias electrode portion 40 of an upper portion of a nested Mach-Zehnder optical waveguide 35a, 35b that is folded back in a folded-back region 38, a control electrode 42 serving as a bias electrode is provided. The control electrode 42 compensates for variations in bias points caused by so-called DC drift in each of four Mach-Zehnder optical waveguides 37a, 37b, 37c, 37d of the nested Mach-Zehnder optical waveguides 35a, 35b to adjust an operating point. Further, on the optical substrate 30, a bias electrode 51 for adjusting the operating point of the nested Mach-Zehnder optical waveguides 35a, 35b is also formed.

[0064] Hereinafter, the Mach-Zehnder optical waveguides 37a, 37b, 37c, 37d are collectively referred to as Mach-Zehnder optical waveguide 37.

[0065] Figure 3 is Figure 2 a partial detailed view of portion A in, and is a diagram showing an electrode structure of the Mach-Zehnder optical waveguide 37d in the bias electrode portion 40. The electrode structures of the other Mach-Zehnder optical waveguides 37a, 37b, and 37c in the bias electrode portion 40 are also the same as the electrode structure of the Mach-Zehnder optical waveguide 37d shown in Figure 3 . In Figure 3 , light is incident from the right side of the drawing and exits to the left side of the drawing.

[0066] The bias electrode, i.e., the control electrode 42 provided in the bias electrode portion 40 includes one first control electrode 43 and two second control electrodes 44. On a main surface of the optical substrate 30, the first control electrode 43 is disposed between parallel waveguides 39a and 39b of the Mach-Zehnder optical waveguide 37d that is part of the optical waveguide 31. The two second control electrodes 44 are respectively disposed at positions facing the first control electrode 43 with the parallel waveguides 39a and 39b interposed therebetween.

[0067] Hereinafter, the parallel waveguides 39a, 39b are collectively referred to as parallel waveguide 39.

[0068] The first control electrode 43 and the second control electrodes 44 are made of, for example, gold (Au), and chromium (Cr) may be used as a base metal in order to improve the adhesion to the optical substrate 30.

[0069] In Figure 3 , the first control electrode 43 actually extends to the right side of the drawing and is given one potential from the relay substrate 14, and the two second control electrodes 44 extend to the left side of the drawing and are given the other potential from the relay substrate 14.

[0070] The electric field generated between the first control electrode 43 and the two second control electrodes 44 controls the light wave propagating in each parallel waveguide 39, and controls the bias point of the modulation operation in the Mach-Zehnder type optical waveguide 37d.

[0071] Figure 4 is Figure 3 a partial detailed view of part B of the bias electrode section 40 shown. In addition, Figure 5 and Figure 6 is Figure 4 the V-V sectional front view and the VI-VI sectional front view of part B shown.

[0072] In Figure 4 part B shown, a second control electrode 44 and a first control electrode 43 facing each other across a parallel waveguide 39b sandwiching the Mach-Zehnder type optical waveguide 37d are shown. In addition, in Figure 3 the other second control electrode 44 and the first control electrode 43 facing each other across another parallel waveguide 39a are also configured in the same structure as Figure 4 shown.

[0073] As Figure 4 shown, the first control electrode 43 includes: a common electrode 43a that extends along the parallel waveguide 39b; and a plurality of segmented electrodes 43c that are arranged closer to the parallel waveguide 39b than the common electrode 43a and are divided along the extending direction of the parallel waveguide 39b. In addition, the first control electrode 43 includes a plurality of connection electrodes 43b that connect the plurality of segmented electrodes 43c to the common electrode 43a respectively. In addition, the first control electrode 43 further includes an auxiliary electrode 43d that extends in the extending direction of the parallel waveguide 39b and connects adjacent connection electrodes 43b to each other.

[0074] Similarly, the second control electrode 44 includes: a common electrode 44a that extends along the parallel waveguide 39b and propagates a high-frequency signal; and a plurality of segmented electrodes 44c that are arranged closer to the parallel waveguide 39b than the common electrode 44a and are divided along the extending direction of the parallel waveguide 39b. In addition, the second control electrode 44 includes a plurality of connection electrodes 44b that connect the plurality of segmented electrodes 44c to the common electrode 44a respectively. In addition, the second control electrode 44 further includes an auxiliary electrode 44d that extends in the extending direction of the parallel waveguide 39b and connects adjacent connection electrodes 44b to each other.

[0075] Here, the auxiliary electrodes 43d and 44d can be respectively arranged at any positions where adjacent connection electrodes 43b and 44b can be connected to each other.

[0076] As Figure 5 and Figure 6As shown, in the present embodiment, each part of the first control electrode 43 and the second control electrode 44 is directly formed on the optical substrate 30.

[0077] In the optical modulation element 3 having the above structure, the segmented electrodes 43c and 44c disposed near the parallel waveguide 39 are divided along the extending direction of the parallel waveguide 39. Therefore, compared with the conventional bias electrode that is not divided, the substrate stress that may be generated in the vicinity of the parallel waveguide 39 in the optical substrate 30 can be reduced.

[0078] In addition, in the conventional bias electrode that is not divided along the extending direction of the parallel waveguide 39, when there is a defect in a part thereof, depending on the generation position of the defect, a state may occur in which most of the bias electrode is not applied with a bias voltage. In contrast, in the optical modulation element 3, the segmented electrodes 43c and 44c are respectively connected to the common electrodes 43a and 44a through the connection electrodes 43b and 44b. Therefore, even if there are defects in a part of the segmented electrodes 43c and 44c, the bias voltage from the common electrodes 43a and 44a can be normally supplied to the other segmented electrodes 43c and 44c. Therefore, in the optical modulation element 3, even when the line widths of the segmented electrodes 43c and 44c are set to be narrow in order to reduce the variation amount of the bias point, compared with the conventional optical modulation element using an undivided bias electrode, the manufacturing yield and long-term reliability can be improved.

[0079] Moreover, in the optical modulation element 3, adjacent connection electrodes 43b to each other and 44b to each other are connected through the auxiliary electrodes 43d and 44d. Therefore, even if there is a defect in the connection electrode 43b or 44b, the segmented electrode 43c or 44c connected to the defective connection electrode 43b or 44b can receive the supply of the bias voltage from the adjacent connection electrode 43b or 44b. Therefore, in the optical modulation element 3, even when the line widths of the connection electrodes 43b and 44b are set to be narrow in order to further reduce the variation amount of the bias point, the manufacturing yield and long-term reliability can be improved.

[0080] As described above, in the optical modulation element 3, the manufacturing yield and / or the long-term reliability can be improved, and the variation amount of the bias point of the driving voltage can be reduced.

[0081] As a preferred size of the first control electrode 43 and the second control electrode 44, in the present embodiment, the lengths a of the connection electrodes 43b and 44b respectively reaching the segmented electrodes 43c and 44c from the common electrodes 43a and 44a (refer to Figure 4) is greater than or equal to 1 μm and less than or equal to 10 μm. In addition, the width W1 of the auxiliary electrodes 43d and 44d and the width W2 of the connecting electrodes 43b and 44b are both greater than or equal to 1 μm and less than or equal to 10 μm. In addition, the width W3 of the segmented electrodes 43c and 44c measured in a direction orthogonal to the extension direction of the parallel waveguide 39b is greater than or equal to 1 μm and less than or equal to 10 μm. In addition, the spacing L between the segmented electrodes 43c and the segmented electrodes 44c measured in the extension direction of the parallel waveguide 39b is greater than or equal to 50 μm and less than or equal to 500 μm.

[0082] In this embodiment, bias voltage is supplied from the common electrodes 43a, 44a to the segment electrodes 43c, 44c via the connection electrodes 43b, 44b and the auxiliary electrodes 43d, 44d, respectively. Therefore, even if a conductor defect occurs in a part of the segment electrodes 43c, 44c, the bias point adjustment operation can be normally performed by the other segment electrodes 43c, 44c. Therefore, for example, the width W3 of the segment electrodes 43c, 44c can be configured to be narrower than the width W1 of the auxiliary electrodes 43d, 44d. Thus, the generation of substrate stress near the parallel waveguide 39 can be further suppressed, and the amount of bias point fluctuation can be further reduced.

[0083] In addition, Figure 5 and Figure 6 In the cross section of , the thickness t of the segment electrodes 43c and 44c is preferably 3 μm or less. This can reduce the substrate stress near the parallel waveguide 39 and reduce the amount of bias point variation.

[0084] Next, a modification example of the light modulation element 3 as the optical waveguide element will be described.

[0085] [First Modification]

[0086] In the above Figure 4 In the first control electrode 43 and the second control electrode 44 shown, the connection electrodes 43b and 44b are connected to the central portions of the segment electrodes 43c and 44c, respectively, in the length direction along the extending direction of the parallel waveguide 39. However, this is an example, and the connection electrodes 43b and 44b can be connected to any positions of the segment electrodes 43c and 44c, respectively.

[0087] For example, the connection electrodes 43 b and 44 b may be connected to one-side end portions of each of the segment electrodes 43 c and 44 c in the length direction along the extending direction of the parallel waveguide 39 .

[0088] Figure 7 4 is a diagram showing the structure of the control electrode 42 of the light modulator 3 according to the first modified example. Figure 7 is equivalent to the above Figure 4 Figure. Figure 7In the example shown, the connection electrodes 43b and 44b are respectively connected to the left end portions in the illustrated length direction along the extending direction of the parallel waveguide 39 of the respective segmented electrodes 43c and 44c. The first control electrode 43 and the second control electrode 44 sandwiching the parallel waveguide 39a can also be configured in the same manner as described above.

[0089] [Second Modified Example]

[0090] In the above-mentioned Figure 4 first control electrode 43 and second control electrode 44 shown, the positions of the auxiliary electrodes 43d and 44d can be arbitrary as long as they can connect adjacent connection electrodes 43b to each other and 44b to each other. However, the auxiliary electrodes 43d and 44d are respectively arranged close to the segmented electrodes 43c and 44c, or arranged close to the common electrodes 43a and 44a, thereby having different effects respectively.

[0091] As a second modified example of the optical modulation element 3, for example, the side of the auxiliary electrode 43d opposite to the segmented electrode 43c is arranged at a position closer to the segmented electrode 43c than the position bisecting the distance between the side of the common electrode 43a on the parallel waveguide 39 side and the side of the segmented electrode 43c on the parallel waveguide 39 side. Similarly, the side of the auxiliary electrode 44d opposite to the segmented electrode 44c is arranged at a position closer to the segmented electrode 44c than the position bisecting the distance between the side of the common electrode 44a on the parallel waveguide 39 side and the side of the segmented electrode 44c on the parallel waveguide 39 side.

[0092] Figure 8 is a diagram showing the structure of the control electrode 42 of the optical modulation element 3 of such a second modified example. Here, Figure 8 is equivalent to the above-mentioned Figure 4 diagram. In addition, in Figure 8 , for the sake of simplifying the drawings and facilitating understanding, in the first control electrode 43, only the boundary lines of the common electrode 43a, the connection electrode 43b, the segmented electrode 43c, and the auxiliary electrode 43d are shown by dotted lines. The same applies to the second control electrode 44.

[0093] As shown in Figure 8As shown, the extension line of the side of the auxiliary electrode 43d opposite to the segmented electrode 43c, i.e., the line EL1, is arranged at a position closer to the segmented electrode 43c than the line CL1 representing the position bisecting the distance between the side of the common electrode 43a on the parallel waveguide 39b side and the side of the segmented electrode 43c on the parallel waveguide 39b side. Similarly, the extension line of the side of the auxiliary electrode 44d opposite to the segmented electrode 44c, i.e., the line EL2, is arranged at a position closer to the segmented electrode 44c than the line CL2 representing the position bisecting the distance between the side of the common electrode 44a on the parallel waveguide 39b side and the side of the segmented electrode 44c on the parallel waveguide 39b side. In addition, the first control electrode 43 and the second control electrode 44 sandwiching the parallel waveguide 39a can also be configured in the same manner as described above.

[0094] Generally, the shorter the distance that the conductor pattern formed on the optical substrate 30 extends, the lower the probability of occurrence of conductor defects and the like. That is, in Figure 8 the structure shown, regarding the first control electrode 43, the probability of occurrence of conductor defects generated in the connection electrode 43b within the range from the connection portion with the auxiliary electrode 43d to the connection portion with the segmented electrode 43c is lower than the probability of occurrence of conductor defects generated in the range from the connection portion with the common electrode 43a to the connection portion with the auxiliary electrode 43d. Therefore, in Figure 8 the structure shown, the generation of conductor defects in the connection electrode 43b is restricted to the range from the connection portion with the common electrode 43a to the connection portion with the auxiliary electrode 43d, and the probability of ensuring an electrical detour path for this defect can be increased through the auxiliary electrode 43d. The same applies to the second control electrode 44. As a result, in Figure 8 the structure shown, the manufacturing yield and long-term reliability of the optical modulation element 3 can be further improved.

[0095] [Third Modified Example]

[0096] As a third modified example of the optical modulation element 3, for example, the side of the auxiliary electrode 43d opposite to the segmented electrode 43c is arranged at a position closer to the common electrode 43a than the position bisecting the distance between the side of the common electrode 43a on the parallel waveguide 39 side and the side of the segmented electrode 43c on the parallel waveguide 39 side. Similarly, the side of the auxiliary electrode 44d opposite to the segmented electrode 44c is arranged at a position closer to the common electrode 44a than the position bisecting the distance between the side of the common electrode 44a on the parallel waveguide 39 side and the side of the segmented electrode 44c on the parallel waveguide 39 side.

[0097] Figure 9 is a diagram showing the structure of the control electrode 42 of the optical modulation element 3 of such a third modified example. Here, Figure 9 is equivalent to the above-mentioned Figure 4 diagram. In addition, in Figure 9In Figure 8 Similarly, in the first control electrode 43, only the boundary lines of the common electrode 43a, the connection electrode 43b, the segmented electrode 43c, and the auxiliary electrode 43d are shown by dashed lines. The same applies to the second control electrode 44.

[0098] As Figure 9 shown, the extension line EL1 of the side of the auxiliary electrode 43d opposite to the segmented electrode 43c is arranged closer to the common electrode 43a than the line CL1 representing the position bisecting the distance between the side of the common electrode 43a on the parallel waveguide 39b side and the side of the segmented electrode 43c on the parallel waveguide 39b side. Similarly, the extension line EL2 of the side of the auxiliary electrode 44d opposite to the segmented electrode 44c is arranged closer to the common electrode 44a than the line CL2 representing the position bisecting the distance between the side of the common electrode 44a on the parallel waveguide 39b side and the side of the segmented electrode 44c on the parallel waveguide 39b side. In addition, the first control electrode 43 and the second control electrode 44 sandwiching the parallel waveguide 39a can also be configured in the same manner as described above.

[0099] In Figure 9 the structure shown, the auxiliary electrodes 43d and 44d are formed separately close to the common electrodes 43a and 44a and separated from the segmented electrodes 43c and 44c, so that the substrate stress that may be generated on the optical substrate 30 near the parallel waveguide 39 due to the auxiliary electrodes 43d and 44d can be reduced. Therefore, in Figure 9 the structure shown, the variation amount of the bias point of the Mach-Zehnder type optical waveguide 37d can be further reduced.

[0100] [Fourth Modification Example]

[0101] As a fourth modification example of the optical modulation element 3, for example, the side of the auxiliary electrode 43d opposite to the segmented electrode 43c is arranged at the position bisecting the distance between the side of the common electrode 43a on the parallel waveguide 39 side and the side of the segmented electrode 43c on the parallel waveguide 39 side. Similarly, the side of the auxiliary electrode 44d opposite to the segmented electrode 44c is arranged at the position bisecting the distance between the side of the common electrode 44a on the parallel waveguide 39 side and the side of the segmented electrode 44c on the parallel waveguide 39 side.

[0102] Figure 10 is a diagram showing the structure of the control electrode 42 of the optical modulation element 3 of such a fourth modification example. Here, Figure 10 is equivalent to the above Figure 4 diagram. In addition, in Figure 10 In Figure 8Similarly, in the first control electrode 43, only the boundary lines of the common electrode 43a, the connection electrode 43b, the segmented electrode 43c, and the auxiliary electrode 43d are shown by dashed lines. The same applies to the second control electrode 44.

[0103] As Figure 10 shown, the side of the auxiliary electrode 43d opposite to the segmented electrode 43c is arranged at the same position as the line CL1 indicating the position that bisects the distance between the side of the common electrode 43a on the parallel waveguide 39b side and the side of the segmented electrode 43c on the parallel waveguide 39b side. Similarly, the extension line, i.e., the line EL2, of the side of the auxiliary electrode 44d opposite to the segmented electrode 44c is arranged at the same position as the line CL2 indicating the position that bisects the distance between the side of the common electrode 44a on the parallel waveguide 39b side and the side of the segmented electrode 44c on the parallel waveguide 39b side. In addition, the first control electrode 43 and the second control electrode 44 sandwiching the parallel waveguide 39a can also be configured in the same manner as described above.

[0104] In Figure 10 the structure shown, the improvement effects of the manufacturing yield and long-term reliability of the structure of the second modification example and the reduction effect of the bias point variation amount of the structure of the third modification example can be exerted evenly. Figure 8 Figure 9

[0105] [Fifth Modification Example]

[0106] The segmented electrode 43c of the first control electrode 43 and the segmented electrode 44c of the second control electrode 44 that are opposite to each other with the parallel waveguide 39 in between do not have to be configured symmetric with respect to the line of the parallel waveguide 39 as Figure 4 shown.

[0107] For example, as a fifth modification example of the optical modulation element 3, the segmented electrode 44c of the second control electrode 44 is arranged at a position offset along the extending direction of the parallel waveguide 39 from the position symmetric with respect to the line of the parallel waveguide 39 with respect to the segmented electrode 43c of the first control electrode 43.

[0108] Figure 11 is a diagram showing the structure of the control electrode 42 of the optical modulation element 3 of such a fifth modification example. Here, Figure 11 corresponds to the above Figure 4 . In Figure 11 the example shown, the segmented electrode 44c of the second control electrode 44 is arranged at a position offset by a distance L / 2 along the extending direction of the parallel waveguide 39 from the position symmetric with respect to the line of the parallel waveguide 39 with respect to the segmented electrode 43c of the first control electrode 43. Here, L is the arrangement pitch between the segmented electrodes 43c and between the segmented electrodes 44c.

[0109] [Sixth Modified Example]

[0110] As a sixth modified example of the optical modulation element 3, a low-elasticity layer made of a low-elasticity material having an elastic coefficient of one-tenth or less of that of the control electrode 42 can be disposed between the control electrode 42 and the optical substrate 30. As the low-elasticity material constituting the low-elasticity layer 45, for example, resin can be used.

[0111] Figure 12 and Figure 13 are diagrams showing the structure of the optical modulation element 3 of such a sixth modified example. Here, Figure 12 and Figure 13 correspond to the above-mentioned Figure 5 and Figure 6 . In Figure 12 and Figure 13 , as an example, a low-elasticity layer 45 having the above-mentioned elastic coefficient is formed on the main surface of the optical substrate 30, and common electrodes 43a and 44a are formed on the low-elasticity layer 45.

[0112] Accordingly, in the optical modulation element 3 of the sixth modified example, the substrate stress generated at the boundary between the control electrode 42 and the optical substrate 30 can be alleviated, and the variation amount of the bias point can be further reduced.

[0113] In addition, in the examples shown in Figure 12 and Figure 13 , the low-elasticity layer 45 is disposed below the common electrodes 43a and 44a, but it is not limited thereto, and it may be disposed below the entire control electrode 42 or any part thereof. For example, in addition to being disposed below the common electrodes 43a and 44a, the low-elasticity layer 45 may be disposed below the entire connection electrodes 43b and 44b or any part thereof.

[0114] However, from the viewpoint of effectively applying an electric field from the control electrode 42 to the parallel waveguide 39, it is preferable not to provide the low-elasticity layer 45 below the segmented electrodes 43c and 44c. In addition, from the viewpoint of ensuring the reliability of voltage supply from the common electrodes 43a and 44a to the segmented electrodes 43c and 44c, it is preferable not to provide the low-elasticity layer 45 below the auxiliary electrodes 43d and 44d, and to ensure the adhesion strength between the auxiliary electrodes 43d and 44d and the optical substrate 30.

[0115] [Seventh Modified Example]

[0116] As a seventh modified example of the optical modulation element 3, the low-elasticity layer 45 shown in the sixth modified example has one or more through-holes extending in the thickness direction of the low-elasticity layer 45, and the control electrode 42 is configured to extend to the main surface of the optical substrate through the above through-holes.

[0117] Figure 14 andFigure 15 FIG. Figure 15 is a diagram showing the structure of the optical modulation element 3 representing such a seventh modification. Here, Figure 14 corresponds to the above-mentioned Figure 3 . In addition, Figure 15 is Figure 14 the XV-XV cross-sectional view in Figure 14 . In the example shown in Figure 14 , a plurality of through-holes 48 (circles shown by dotted lines in the figure) having a circular shape in plan view are arranged in a matrix in the low-elasticity layer 45 below each of the common electrodes 43a of the first control electrode 43 and the common electrode 44a of the second control electrode 44. In addition, Figure 14 in Figure 14 , as an example, only one through-hole 48 is labeled with a reference numeral, but all the circles shown by the dotted lines in the figure represent the through-holes 48.

[0118] Moreover, as shown in Figure 15 , for example, the common electrode 44a of the second control electrode 44 extends through the inside of the through-hole 48 (rectangle shown by the dotted line in the figure) to the main surface of the optical substrate 30. The common electrode 43a of the first control electrode 43 also extends through the inside of the through-hole 48 to the main surface of the optical substrate 30 in the same manner as Figure 15 .

[0119] Accordingly, the control electrode 42 is in direct contact with the optical substrate 30 through the inside of the through-hole 48. Therefore, even when the low-elasticity layer 45 is made of resin, for example, the adhesion between the control electrode 42 and the optical substrate 30 can be improved, and the reliability of the optical modulation element 3 can be improved.

[0120] In addition, from the viewpoint of ensuring the adhesion between the control electrode 42 and the optical substrate 30, the through-hole 48 preferably has a diameter r (see Figure 14 ) of 1 μm or more and 25 μm or less. In addition, from the same viewpoint, the arrangement intervals d1 and d2 of the through-holes 48 in the extending direction of the parallel waveguide 39 and the direction orthogonal thereto are preferably 50 μm or more and 500 μm or less.

[0121] In addition, the through-hole 48 is not limited to a circular shape and can have any shape in plan view. In this case, the through-hole 48 is preferably configured such that its opening area on the optical substrate 30 side is the same as that of the through-hole having a circular shape in plan view with a diameter of 1 μm or more and 25 μm or less. In addition, the through-hole 48 is not limited to a matrix shape and can be arranged in any regular pattern or irregular pattern. In this case, the arrangement interval between the through-holes 48 is also preferably 50 μm or more and 500 μm or less.

[0122] [Second Embodiment]

[0123] Next, a second embodiment of the present invention will be described. This embodiment is an optical transmission device 60 equipped with the optical modulator 1 of the first embodiment or its modified example. Figure 16 It is a diagram showing the structure of the optical transmission device 60 of this embodiment. The optical transmission device 60 includes an optical modulator 1, a light source 61, and a modulation signal generation unit 62. The modulation signal generation unit 62 is an electronic circuit that generates a high-frequency signal (modulation signal) for causing the optical modulator 1 to perform a modulation operation. The modulation signal generation unit 62 generates, for example, four modulation signals to be input to the optical modulation element 3 included in the optical modulator 1 based on transmission data given from the outside, and inputs them to the signal pins 4 of the optical modulator 1. Thereby, the optical modulator 1 modulates the light from the light source 61 incident from the input optical fiber 6 and outputs the modulated light via the output optical fiber 7.

[0124] In the optical transmission device 60 having the above structure, since the above-described optical modulator 1 that reduces the amount of bias point variation and improves the manufacturing yield and long-term reliability is used, an optical transmission device with high transmission quality can be realized at low cost.

[0125] [Other Embodiments]

[0126] In Figure 2 the structure shown, the bias electrode 51 for adjusting the operating point of the nested Mach-Zehnder optical waveguides 35a and 35b can also be configured in the same manner as Figure 4 the control electrode 42 shown. Figure 17 It is a diagram showing an example of the bias electrode 51 configured in the same manner as the control electrode 42. In the illustrated example, two bias electrodes 51 sandwiching one parallel waveguide 35a1 (see Figure 2 ) of the nested Mach-Zehnder optical waveguide 35a are each configured in the same manner as the first control electrode 43 and the second control electrode 44.

[0127] In the above-described first embodiment or its modified example, the bias electrode portion 40 is arranged at a position upstream of the RF electrode portion 41 along the light propagation direction in the optical waveguide 31, but depending on the arrangement of the optical waveguides on the optical substrate 30 (for example, in a structure that does not include the folded-back region 38, etc.), it may also be arranged at a position downstream of the RF electrode portion 41. Alternatively, two bias electrode portions 40 may be arranged at positions sandwiching the RF electrode portion 41 along the light propagation direction in the optical waveguide 31.

[0128] The various modifications in the above-described first embodiment can be arbitrarily combined to form an optical waveguide element (for example, the optical modulation element 3). For example, the segmented electrode 43c and the connection electrode 43b shown in the first modification, and the electrode structures in a top view L-shape formed by the segmented electrode 43c and the connection electrode 43b respectively can be combined and applied in all other modifications. Additionally, for example, the structures of the sixth modification and the seventh modification can be combined with all other modifications.

[0129] Moreover, the optical waveguide element in the present invention is not limited to the optical modulation element 3 that uses a nested Mach-Zehnder type optical waveguide for optical modulation operation, and can be various optical waveguide elements that use an optical waveguide formed in an arbitrary pattern to achieve arbitrary functions. For example, in addition to the Mach-Zehnder type optical waveguide, the optical waveguide element can also be an element that includes a directional coupler type waveguide and / or a Y-branch waveguide, etc., and realizes functions such as an optical switch.

[0130] In addition, the present invention is not limited to the structures and their alternative structures in the above-described embodiments, and can be implemented in various ways without departing from its gist.

[0131] [Structure supported by the above-described embodiments]

[0132] The above-described embodiments and modifications support the following structures.

[0133] (Structure 1) An optical waveguide element having: an optical waveguide disposed on a main surface of an optical substrate; and a control electrode for controlling light waves propagating in the optical waveguide, wherein the control electrode includes a first control electrode and a second control electrode that are opposed to each other with the optical waveguide interposed therebetween on the main surface of the optical substrate, and the first control electrode and the second control electrode each include: a common electrode extending along the optical waveguide; a plurality of segmented electrodes disposed closer to the optical waveguide than the common electrode and divided along the extending direction of the optical waveguide; a plurality of connection electrodes connecting the plurality of segmented electrodes to the common electrode respectively; and an auxiliary electrode extending along the extending direction of the optical waveguide and connecting adjacent connection electrodes to each other.

[0134] In the optical waveguide element according to Structure 1, voltage is supplied from the common electrode to each segmented electrode via the connection electrode and the auxiliary electrode. Therefore, even if the line width of the segmented electrode is narrow and conductor defects occur in a part of the segmented electrodes, the light waves propagating in the optical waveguide can be normally controlled by other segmented electrodes. Therefore, in the optical waveguide element according to Structure 1, the segmented electrodes can be formed thinner to reduce the amount of variation in the bias point, and the manufacturing yield and long-term reliability of the optical waveguide element can be improved.

[0135] (Structure 2)The optical waveguide element according to Structure 1, wherein the optical waveguide element further includes a high-frequency electrode disposed on the optical substrate for modulating the light wave propagating in the optical waveguide to perform a modulation operation, and the control electrode is a bias electrode for controlling the bias point of the modulation operation.

[0136] In the optical waveguide element according to Structure 2, in a bias electrode having a generally higher design freedom than the high-frequency electrode formed as a high-frequency transmission line, the electrode line width can be made narrower to reduce the bias point variation.

[0137] (Structure 3)The optical waveguide element according to Structure 1 or 2, wherein the side of the auxiliary electrode opposite to the segmented electrode is disposed at a position closer to the segmented electrode than the position bisecting the distance between the side of the common electrode on the optical waveguide side and the side of the segmented electrode on the optical waveguide side.

[0138] In the optical waveguide element according to Structure 3, the generation of conductor defects in the connection electrode can be restricted to the range from the common electrode to the auxiliary electrode, and the probability of ensuring an electrical detour path for the defect through the auxiliary electrode can be increased. Therefore, in the optical waveguide element according to Structure 3, the manufacturing yield and long-term reliability of the optical waveguide element can be further improved.

[0139] (Structure 4)The optical waveguide element according to Structure 1 or 2, wherein the side of the auxiliary electrode opposite to the segmented electrode is disposed at a position closer to the common electrode than the position bisecting the distance between the side of the common electrode on the optical waveguide side and the side of the segmented electrode on the optical waveguide side.

[0140] In the optical waveguide element according to Structure 4, the auxiliary electrode is formed close to the common electrode and far from the segmented electrode, so that the substrate stress that may be generated in the optical substrate near the optical waveguide due to the auxiliary electrode can be reduced. Therefore, in the optical waveguide element according to Structure 4, the amount of bias point variation can be further reduced.

[0141] (Structure 5)The optical waveguide element according to Structure 1 or 2, wherein the side of the auxiliary electrode opposite to the segmented electrode is disposed at the position bisecting the distance between the side of the common electrode on the optical waveguide side and the side of the segmented electrode on the optical waveguide side.

[0142] In the optical waveguide element according to Structure 5, the improvement effects of the manufacturing yield and long-term reliability and the reduction effect of the bias point variation can be exerted evenly.

[0143] (Structure 6)The optical waveguide element according to any one of Structures 1 to 5, wherein the thickness of the segmented electrode is 3 μm or less.

[0144] The optical waveguide element according to Structure 6 can reduce the substrate stress near the optical waveguide and thus reduce the variation in the bias point.

[0145] (Structure 7) The optical waveguide element according to any one of Structures 1 to 6, wherein the width of the segmented electrode measured in a direction orthogonal to the extending direction of the optical waveguide is narrower than the width of the auxiliary electrode.

[0146] The optical waveguide element according to Structure 7 can further suppress the generation of substrate stress near the optical waveguide, thereby further reducing the variation in the bias point.

[0147] (Structure 8) The optical waveguide element according to any one of Structures 1 to 7, wherein a low-elasticity layer is disposed between the control electrode and the optical substrate, and the low-elasticity layer is made of a low-elasticity material having an elastic modulus of one-tenth or less of that of the common electrode.

[0148] The optical waveguide element according to Structure 8 can relieve the substrate stress generated at the boundary between the control electrode and the optical substrate, and further reduce the variation in the bias point.

[0149] (Structure 9) An optical modulator includes: the optical waveguide element according to any one of Structures 1 to 8 as an optical modulation element; a housing that houses the optical waveguide element; an optical fiber that inputs light to the optical waveguide element; and an optical fiber that guides the light output from the optical waveguide element to the outside of the housing.

[0150] The optical modulator according to Structure 9 can improve the manufacturing yield and / or long-term reliability, and reduce the variation in the bias point of the drive voltage.

[0151] (Structure 10) An optical transmission device includes: the optical modulator according to Structure 9; and an electronic circuit that generates an electrical signal for causing the optical waveguide element to perform an optical modulation operation.

[0152] The optical transmission device according to Structure 10 can inexpensively realize an optical transmission device with high transmission quality because it uses an optical modulator that improves the manufacturing yield and / or long-term reliability and reduces the variation in the bias point of the drive voltage.

[0153] Description of Reference Numerals

[0154] 1…Optical modulator, 2…Housing, 3…Optical modulation element, 4, 5…Signal pins, 6…Input optical fiber, 7…Output optical fiber, 8, 9…Supports, 10a, 10b, 10c, 11a, 11b…Lenses, 12…Beam shifter, 14…Relay substrate, 15, 15a, 15b, 15c, 15d…Terminal resistors, 16…Terminator, 17…Driver circuit, 18…Center electrode, 30…Optical substrate, 31…Optical waveguide, 32a, 32b, 32c, 32d…Edges, 33…Input waveguide, 34…Branch waveguide, 35, 35a, 35b…Nested Mach-Zehnder type optical waveguide, 36a, 36b…Output waveguide, 37a, 37b, 37c, 37d…Mach-Zehnder type optical waveguide, 38…Folding region, 39a, 39b…Parallel waveguides, 40, 40a, 40b…Bias electrode portions, 41…RF electrode portion, 42…Control electrode, 43…First control electrode, 44…Second control electrode, 43a, 44a…Common electrodes, 43b, 44b…Connection electrodes, 43c, 44c…Segmented electrodes, 43d, 44d…Auxiliary electrodes, 45…Low elastic layer, 48…Through hole, 49…R portion, 51…Bias electrode, 60…Optical transmission device, 61…Light source, 62…Modulation signal generation unit.

Claims

1. An optical waveguide element having: an optical waveguide disposed on a main surface of an optical substrate; and control electrodes for controlling light waves propagating in the optical waveguide, wherein, the control electrodes include a first control electrode and a second control electrode that face each other with the optical waveguide interposed therebetween on the main surface of the optical substrate, the first control electrode and the second control electrode each include: a common electrode extending along the optical waveguide; a plurality of segmented electrodes disposed closer to the optical waveguide than the common electrode and divided along the extending direction of the optical waveguide; a plurality of connection electrodes connecting the plurality of segmented electrodes to the common electrode respectively; and auxiliary electrodes extending along the extending direction of the optical waveguide and connecting adjacent ones of the connection electrodes to each other.

2. The optical waveguide element according to claim 1, wherein, the optical waveguide element further includes a high-frequency electrode disposed on the optical substrate for modulating light waves propagating in the optical waveguide to perform a modulation operation, the control electrodes are bias electrodes for controlling a bias point of the modulation operation.

3. The optical waveguide element according to claim 1 or 2, wherein, a side of the auxiliary electrode facing the segmented electrode is disposed at a position closer to the segmented electrode than a position bisecting a distance between a side of the common electrode on the optical waveguide side and a side of the segmented electrode on the optical waveguide side.

4. The optical waveguide element according to claim 1 or 2, wherein, a side of the auxiliary electrode facing the segmented electrode is disposed at a position closer to the common electrode than a position bisecting a distance between a side of the common electrode on the optical waveguide side and a side of the segmented electrode on the optical waveguide side.

5. The optical waveguide element according to claim 1 or 2, wherein, a side of the auxiliary electrode facing the segmented electrode is disposed at a position bisecting a distance between a side of the common electrode on the optical waveguide side and a side of the segmented electrode on the optical waveguide side.

6. The optical waveguide element according to any one of claims 1 to 5, wherein, the thickness of the segmented electrode is 3 μm or less.

7. The optical waveguide element according to any one of claims 1 to 6, wherein, a width of the segmented electrode measured in a direction orthogonal to the extending direction of the optical waveguide is narrower than a width of the auxiliary electrode.

8. The optical waveguide element according to any one of claims 1 to 7, wherein, a low-elasticity layer is disposed between the control electrodes and the optical substrate, and the low-elasticity layer is made of a low-elasticity material having an elastic modulus of one-tenth or less of that of the common electrode.

9. An optical modulator comprising: the optical waveguide element according to any one of claims 1 to 8 as an optical modulation element; a housing for housing the optical waveguide element; an optical fiber for inputting light to the optical waveguide element; and an optical fiber for guiding light output from the optical waveguide element to the outside of the housing.

10. An optical transmission device comprising: the optical modulator according to claim 9; and an electronic circuit for generating an electrical signal for causing the optical waveguide element to perform an optical modulation operation.

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