Optical Modulator and Optical Transmission Device Using the Same

Abstract

In an optical modulator, the problem is to effectively suppress the influence of leakage microwaves generated from the signal connection portion between the relay substrate and the signal input terminal and achieve good optical modulation characteristics. The optical modulator includes: a relay substrate having a signal conductor pattern and a ground conductor pattern, the signal conductor pattern connecting the signal input terminal to the signal electrode of the optical modulation element; and a housing that houses the optical modulation element and the relay substrate. Among them, for at least one signal conductor pattern, in a connection portion range that is rectangular in a top view and includes the signal connection portion where the signal conductor pattern is connected to the signal input terminal, the top view shapes of the two ground conductor patterns sandwiching the signal conductor pattern are formed to be asymmetric with each other. The above connection portion range has a width equal to the distance to the nearest adjacent signal conductor pattern and a height equal to the distance from the end of the signal connection portion farthest from the signal input side to the signal input side, with the above at least one signal conductor pattern as the center in the width direction.

Description

Technical Field

[0001] The present invention relates to an optical modulator having a relay substrate that relays the propagation of an electrical signal between a signal input terminal and a signal electrode of an optical modulation element, and an optical transmission device using the optical modulator. Background Art

[0002] In high-speed / large-capacity optical fiber communication systems, optical modulators incorporating waveguide-type optical modulation elements are often used. Among them, optical modulation elements using LiNbO3 (hereinafter also referred to as LN) having an electro-optic effect can achieve low optical loss and broadband optical modulation characteristics, and are therefore widely used in high-speed / large-capacity optical fiber communication systems.

[0003] In the optical modulation element using the LN substrate, a Mach-Zehnder type optical waveguide and signal electrodes for applying a high-frequency electrical signal as a modulation signal to the optical waveguide are provided. Further, these signal electrodes provided in the optical modulation element are connected to pins and connectors serving as signal input terminals provided in the housing of the optical modulator that houses the optical modulation element via a relay substrate provided in the housing. Thus, the pins and connectors serving as the signal input terminals are connected to a circuit board on which an electronic circuit for causing the optical modulator to perform a modulation operation is mounted, and thereby the electrical signal output from the electronic circuit is applied to the signal electrodes of the optical modulation element via the relay substrate.

[0004] The modulation method in optical fiber communication systems has been influenced by the recent trend of increasing transmission capacity, and multi-level modulation such as QPSK (Quadrature Phase Shift Keying) and DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying), and transmission systems incorporating polarization multiplexing into multi-level modulation have become mainstream. In addition to being used in backbone optical transmission networks, they are also being introduced into metropolitan area networks.

[0005] An optical modulator for performing QPSK modulation (QPSK optical modulator) and an optical modulator for performing DP-QPSK modulation (DP-QPSK optical modulator) include a plurality of Mach-Zehnder type optical waveguides having a so-called nested structure, and each of them has at least one signal electrode. Therefore, these optical modulators have a structure including a plurality of signal electrodes, and the high-frequency electrical signals applied to these signal electrodes cooperate to perform the above-described DP-QPSK modulation operation.

[0006] Figure 15FIG. 0 is a top view showing an example of the structure of a conventional optical modulator having such a relay substrate. The optical modulator 2200 includes an optical modulation element 2202 as a DP-QPSK modulator formed on, for example, an LN substrate, and a housing 2204 that houses the optical modulation element 2202. Here, the housing 2204 is composed of an outer shell 2214a and a cover 2214b. The optical modulator 2200 also has an input optical fiber 2208 and an output optical fiber 2210 that are fixed to the outer shell 2214a and input and output light to and from the optical modulation element 2202.

[0007] On the outer shell 2214a of the housing 2204, four signal input terminals 2224a, 2224b, 2224c, and 2224d (hereinafter, also collectively referred to as signal input terminals 2224) for inputting a high-frequency electrical signal for driving the optical modulation element 2202 from an external electronic circuit are further provided. Specifically, the signal input terminals 2224 are, for example, the center electrodes of high-frequency coaxial connectors, i.e., electrical connectors 2216a, 2216b, 2216c, and 2216d (hereinafter, also collectively referred to as electrical connectors 2216). The high-frequency electrical signals respectively input from the signal input terminals 2224 are input to one ends of four signal electrodes 2212a, 2212b, 2212c, and 2212d (hereinafter, also collectively referred to as signal electrodes 2212) provided on the optical modulation element 2202 via a relay substrate 2218 housed in the housing 2204, and are terminated by a terminator 2220 having a predetermined impedance provided at the other ends of the signal electrodes 2212.

[0008] The optical modulation element 2202 outputs two beams of modulated light from two output optical waveguides 2226a and 2226b, and the two output beams of light are combined into one beam by a polarization wave combining unit 2228 composed of a polarization wave combining prism or the like. The combined light is output to the outside of the housing 2204 via the output optical fiber 2210.

[0009] In such an optical modulator 2200 in which the high-frequency electrical signals respectively applied to the plurality of signal electrodes 2212 cooperate to perform modulation, it is preferable to input all the high-frequency electrical signals to the signal electrodes 2212 of the optical modulation element 2202 without being affected by noise or the like. On the other hand, the requirement for miniaturization of the optical modulator 2200 remains unchanged, and with the miniaturization of the housing 2204 of the optical modulator 2200, the miniaturization of the relay substrate 2218 continues to progress. As a result, in the narrow relay substrate 2218, a plurality of different high-frequency signals are propagated in close proximity, and the electrical crosstalk between the high-frequency signal lines formed on the relay substrate 2218 becomes increasingly difficult to ignore.

[0010] In addition, although commercial DP-QPSK modulators are currently mostly used at a transmission rate of 100 Gb / s, development for expanding this transmission rate to 400 Gb / s is also in progress. Generally, radiation during the transmission of high-frequency signals tends to increase as the transmission rate increases. Therefore, in the future, if the transmission rate is expanded, the problem of crosstalk between high-frequency signal lines generated on the above-mentioned relay substrate will become a more serious issue.

[0011] As a method for suppressing the above-mentioned crosstalk, although it is conceivable to increase the distance between adjacent high-frequency signal lines, this method violates the requirement for miniaturization of the optical modulator as described above and is difficult to adopt. Therefore, a method such as providing a via hole in the ground electrode provided between the high-frequency signal lines and connecting it to the ground layer on the back surface of the relay substrate to strengthen the ground electrode and improve the shielding effect between the high-frequency signal lines can be adopted.

[0012] However, for example, in a DP-QPSK modulator with a high transmission rate of 400 Gb / s or more than 400 Gb / s, just the above-mentioned via holes sometimes cannot sufficiently suppress the crosstalk between adjacent high-frequency signal lines completely.

[0013] At a high transmission rate of 400 Gb / s or more than 400 Gb / s as described above, among the leaked microwaves generated at the connection point between the signal input terminal to which the high-frequency signal is input and the conductor pattern of the relay substrate and its vicinity, in addition to the leaked microwaves propagating in the relay substrate 2218 (substrate leaked microwaves), the leaked microwaves radiated from the relay substrate 2218 and propagating in space (space leaked microwaves) also become the main cause of the above-mentioned crosstalk.

[0014] Figure 16 This is an explanatory diagram for explaining the generation and propagation of such leaked microwaves. Here, Figure 16 shows Figure 15 the relay substrate 2218 and its surroundings in the optical modulator 2200 shown. Ground electrodes 2222a, 2222b, 2222c, 2222d, and 2222e are provided in the optical modulation element 2202 such that the signal electrodes 2212 respectively form coplanar lines (CPW, Coplanar Waveguide).

[0015] In addition, signal conductor patterns 2230a, 2230b, 2230c, and 2230d (hereinafter collectively referred to as signal conductor pattern 2230) that connect four signal input terminals 2224 and four signal electrodes 2212 of the optical modulation element 2202 are formed on the relay substrate 2218. These signal conductor patterns 2230 and ground conductor patterns 2240a, 2240b, 2240c, 2240d, and 2240e disposed on the relay substrate 2218 while sandwiching the signal conductor pattern 2230 in the substrate surface direction together constitute a high-frequency signal line.

[0016] In Figure 16 the relay substrate 2218 shown, the high-frequency signal line formed by the signal conductor pattern 2230 and the ground conductor pattern 2240 is generally a coplanar line, and the propagation mode of the high-frequency signal propagating in this line is a coplanar mode (hereinafter referred to as the CPW mode). In contrast, the signal input terminal 2224 is generally composed of, for example, a coaxial connector, a pin, etc. as described above, and the propagation mode of the high-frequency signal up to the input to the relay substrate 2218 is a coaxial mode.

[0017] Therefore, in the four signal connection portions that connect the four signal input terminals 2224 and the four signal conductor patterns 2230 of the relay substrate 2218, a mode conversion from the coaxial mode to the CPW mode (i.e., different mode conversion) occurs. As a result, in the signal connection portion, a part of the energy of the high-frequency signal propagating in the coaxial mode is easily converted into the radiation mode, and a state in which leakage microwaves are likely to be generated is formed.

[0018] That is, each of the above signal connection portions functions as an approximate simple model and serves as a point source of leakage microwaves. The leakage microwaves are emitted as spherical waves 2290 from each signal connection portion, and become, for example, substrate leakage microwaves propagating inside the relay substrate 2218 and space leakage microwaves radiating from the relay substrate 2218 and propagating in space.

[0019] Moreover, crosstalk occurs between the four high-frequency electrical signals input through the four signal input terminals 2224 via such substrate leakage microwaves and space leakage microwaves. Crosstalk caused by such leakage microwaves is particularly likely to occur between adjacent signal conductor patterns.

[0020] That is, in the conventional optical modulator, it is required to subtract the crosstalk between high-frequency electrical signals via the above leakage microwaves and achieve good modulation characteristics.

[0021] In the past, in order to suppress high-frequency reflection, radiation, and / or leakage in a relay substrate, impedance matching was performed with higher precision between the impedance at the connection portion between the conductor pattern of the relay substrate and the above-described pin and the impedance of the high-frequency transmission paths formed by the conductor pattern and the pin, respectively (for example, refer to Patent Document 1).

[0022] However, although the above-described prior art is effective at a transmission rate of 100 Gb / s, it does not provide an effective solution for suppressing deterioration of modulation characteristics caused by crosstalk between adjacent signal conductor patterns via the above-described leaked microwaves, for example, at a transmission rate of 400 Gb / s or higher.

[0023] Prior Art Documents

[0024] Patent Documents

[0025] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-106091 Summary of the Invention

[0026] Problems to be Solved by the Invention

[0027] Based on the above background, in an optical modulator including a relay substrate that electrically connects the signal electrode of an optical modulation element and a signal input terminal, it is required to effectively suppress the influence of leaked microwaves generated from the signal connection portion between the relay substrate and the signal input terminal and achieve good optical modulation characteristics.

[0028] Means for Solving the Problems

[0029] One aspect of the present invention relates to an optical modulator, comprising: an optical modulation element having a plurality of signal electrodes; a plurality of signal input terminals for inputting electrical signals applied to each of the signal electrodes; a relay substrate formed with a plurality of signal conductor patterns and a plurality of ground conductor patterns, the signal conductor patterns electrically connecting the signal input terminals to the signal electrodes; and a housing for housing the optical modulation element and the relay substrate, wherein, with respect to at least one of the signal conductor patterns, in a connection portion range having a rectangular top view including a signal connection portion where the signal conductor pattern is connected to the signal input terminal, the top view shapes of the two ground conductor patterns sandwiching the signal conductor pattern on the relay substrate are formed to be asymmetric with respect to each other with respect to the at least one signal conductor pattern, the connection portion range is defined as a rectangle extending in the plane of the relay substrate with a part of a signal input side as one side in the width direction, the signal input side is a side of the relay substrate on which at least one of the signal conductor patterns is connected to the signal input terminal, the connection portion range has the at least one signal conductor pattern as the center in the width direction, the width of the connection portion range is equal to the distance from the at least one signal conductor pattern to the nearest adjacent signal conductor pattern, and the height of the connection portion range is equal to the distance from the signal input side to the end portion farthest from the signal input side in the signal connection portion.

[0030] According to another aspect of the present invention, the two ground conductor patterns are formed such that the distances from the respective edges of the two ground conductor patterns to the opposite edges of the at least one signal conductor pattern have different portions within the connection portion range.

[0031] According to another aspect of the present invention, the widths of the portions of the two ground conductor patterns formed within the connection portion range, measured in a direction orthogonal to the extending direction of the at least one signal conductor pattern, are different from each other.

[0032] According to another aspect of the present invention, one of the two ground conductor patterns does not include a portion formed within the connection portion range.

[0033] According to another aspect of the present invention, the relay substrate is provided with a cutout portion in a portion where one of the two ground conductor patterns is formed within the connection portion range, and the cutout portion extends from the signal input side and penetrates the thickness direction of the relay substrate.

[0034] Another aspect of the present invention relates to an optical modulator, comprising: an optical modulation element having a plurality of signal electrodes; a plurality of signal input terminals for inputting electrical signals applied to each of the signal electrodes; a relay substrate formed with a plurality of signal conductor patterns and a plurality of ground conductor patterns, the signal conductor patterns electrically connecting the signal input terminals to the signal electrodes; and a housing for housing the optical modulation element and the relay substrate, wherein a backside ground conductor is formed on a surface of the relay substrate opposite to the surface on which the ground conductor patterns are formed, and for at least one of the signal conductor patterns, in a connection portion range including a signal connection portion where the signal conductor pattern is connected to the signal input terminal, the two ground conductor patterns sandwiching the signal conductor pattern on the relay substrate are formed asymmetrically by the presence or absence of vias, or the number or diameter of the formed vias being different from each other, the connection portion range is defined as a rectangle extending in the plane of the relay substrate with a part of a signal input side as one side in the width direction, the signal input side is a side of the relay substrate on which at least one of the signal conductor patterns is connected to the signal input terminal, the connection portion range has the at least one signal conductor pattern as the center in the width direction, the width of the connection portion range is equal to the distance from the at least one signal conductor pattern to the nearest adjacent signal conductor pattern, and the height of the connection portion range is equal to the distance from the signal input side to the end portion farthest from the signal input side in the signal connection portion.

[0035] According to another aspect of the present invention, the optical modulation element is configured to generate two modulated light beams respectively modulated by a pair of the electrical signals, and the relay substrate is configured to propagate the pair of the electrical signals through a pair of adjacent signal conductor patterns.

[0036] Another aspect of the present invention relates to an optical transmission device, comprising: any one of the above optical modulators; and an electronic circuit for outputting an electrical signal for causing the optical modulator to perform a modulation operation.

[0037] It should be noted that this specification includes all the contents of Japanese Patent Application No. 2019-112845 filed on June 18, 2019.

[0038] Advantages of the Invention

[0039] According to the present invention, in an optical modulator having a relay substrate, it is possible to effectively suppress the influence of leakage microwaves generated from a signal connection portion between the relay substrate and the signal input terminal, and achieve good optical modulation characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a top view of the optical modulator according to the first embodiment of the present invention.

[0041] Figure 2 is Figure 1 a side view of the optical modulator shown in

[0042] Figure 3 is Figure 1 a detailed view of part A of the optical modulator shown in

[0043] Figure 4 is Figure 3 a detailed view of part B in the detailed view of part A shown in

[0044] Figure 5 a diagram showing the structure of a relay substrate of a first modification of the optical modulator according to the first embodiment

[0045] Figure 6 a diagram showing the structure of a relay substrate of a second modification of the optical modulator according to the first embodiment

[0046] Figure 7 a diagram showing the structure of a relay substrate of a third modification of the optical modulator according to the first embodiment

[0047] Figure 8 a diagram showing the structure of a relay substrate of a fourth modification of the optical modulator according to the first embodiment

[0048] Figure 9 a diagram showing the structure of a relay substrate of a fifth modification of the optical modulator according to the first embodiment

[0049] Figure 10 a diagram showing the structure of a relay substrate of a sixth modification of the optical modulator according to the first embodiment

[0050] Figure 11 a diagram showing the structure of a relay substrate of a seventh modification of the optical modulator according to the first embodiment

[0051] Figure 12 a diagram showing the structure of a relay substrate of an eighth modification of the optical modulator according to the first embodiment

[0052] Figure 13 a diagram showing the structure of a relay substrate of a ninth modification of the optical modulator according to the first embodiment

[0053] Figure 14 a diagram showing the structure of an optical transmission device according to the second embodiment of the present invention

[0054] Figure 15 shows an example of the structure of a conventional optical modulator

[0055] Figure 16 is an explanatory diagram for explaining the generation of leakage microwaves in a conventional optical modulator Detailed implementation mode

[0056] In the following embodiments and their modified examples for solving the above problems, in an optical modulator including an optical modulation element and a relay substrate, near the connection portion where the signal conductor pattern on the relay substrate is connected to the high-frequency input terminal, two ground conductor patterns sandwiching at least one signal conductor pattern are configured to include shape portions that are asymmetric with each other across the signal conductor pattern, or are configured to have different impedances to the ground wire, and / or a notch extending from the edge of the relay substrate is provided on the relay substrate between the adjacent signal conductor patterns. Thereby, in the above optical modulator, the intensity of spatial leakage microwaves and / or substrate leakage microwaves toward the adjacent signal conductor patterns can be reduced, and the crosstalk between the adjacent signal conductor patterns can be reduced.

[0057] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0058] [First Embodiment]

[0059] First, the first embodiment of the present invention will be described. Figure 1 FIG. is a plan view showing the structure of an optical modulator 100 according to the first embodiment of the present invention, Figure 2 is a side view of the optical modulator 100, Figure 3 is Figure 1 a partial detailed view of part A in.

[0060] The optical modulator 100 includes an optical modulation element 102, a housing 104 that houses the optical modulation element 102, an input optical fiber 108 for making light incident on the optical modulation element 102, and an output optical fiber 110 for guiding the light output from the optical modulation element 102 to the outside of the housing 104.

[0061] The optical modulation element 102 is, for example, a DP-QPSK modulator that performs optical modulation at 400 Gb / s, and includes, for example, four Mach-Zehnder type optical waveguides provided on an LN substrate. Four signal electrodes 112a, 112b, 112c, 112d (hereinafter, also collectively referred to as signal electrodes 112) for modulating the light waves propagating in the Mach-Zehnder type optical waveguides are provided in the four Mach-Zehnder type optical waveguides. Moreover, as is known in the prior art, on the surface of the LN substrate of the optical modulation element 102, for example, ground electrodes 122a, 122b, 122c, 122d, 122e are provided in such a manner that the four signal electrodes 112a, 112b, 112c, 112d respectively form coplanar lines (CPW, Coplanar Waveguide) (refer to Figure 3 . In Figure 1 not shown).

[0062] Specifically, the above-mentioned ground electrodes 122a, 122b, 122c, 122d, 122e (hereinafter, also collectively referred to as the ground electrode 122) are respectively arranged in the plane of the LN substrate surface with the signal electrodes 112a, 112b, 112c, 112d interposed therebetween, and together with the four signal electrodes 112a, 112b, 112c, 112d, form a coplanar line having a specified characteristic impedance at a specified operating frequency.

[0063] Four high-frequency electrical signals (modulation signals) are respectively input to the four signal electrodes 112. These high-frequency electrical signals cooperatively control the propagation of light waves in the above-mentioned four Mach-Zehnder type optical waveguides, and perform an operation of 400 Gb / s DP-QPSK modulation as a whole.

[0064] Specifically, two pairs of high-frequency electrical signals each composed of two high-frequency electrical signals are respectively applied to the four signal electrodes 112. The optical modulation element 102 generates two beams of modulated light modulated by each pair of electrical signals. The two generated beams of modulated light are respectively output from the two output optical waveguides 126a, 126b that form a part of the optical modulation element 102. In the present embodiment, two high-frequency electrical signals forming one pair are applied to the signal electrodes 112a, 112b to generate modulated light output from the output optical waveguide 126a, and the other two high-frequency electrical signals forming the other pair are applied to the signal electrodes 112c, 112d to generate modulated light output from the output optical waveguide 126b. After these two beams of modulated light are combined into one beam by a polarization wave combining unit 128 composed of a polarization wave combining prism or the like, they are output to the outside of the housing 104 via the output optical fiber 110.

[0065] The housing 104 is composed of a housing 114a that fixes the optical modulation element 102 and a cover 114b. It should be noted that, for the sake of facilitating the understanding of the structure inside the housing 104, in Figure 1 , only a part of the cover 114b is shown on the left side in the drawing, but in fact, the cover 114b is arranged to cover the entire box-shaped housing 114a to hermetically seal the inside of the housing 104. The housing 114a is made of metal or, for example, ceramic plated with gold, etc., and electrically functions as a conductor. Moreover, a plurality of pins for DC control or the like are usually provided on the housing 104, but are omitted in this drawing.

[0066] The housing 114a is provided with electrical connectors 116a, 116b, 116c, 116d (hereinafter, also collectively referred to as the electrical connectors 116) serving as coaxial connectors and having signal input terminals 124a, 124b, 124c, 124d (hereinafter, also collectively referred to as the signal input terminals 124).

[0067] The electrical connector 116 is a slot of a plug-in coaxial connector, for example, and includes a cylindrical ground conductor. The signal input terminal 124 is composed of a center conductor (core wire) extending along the center line of the cylindrical ground conductor. The cylindrical ground conductors are electrically connected and fixed to the housing 114a. Therefore, the housing 114a constitutes a ground line for supplying a ground potential. In addition, the signal input terminal 124 is electrically connected to one end of each of the signal electrodes 112 of the optical modulator 102 via the relay substrate 118.

[0068] The other end of the signal electrode 112 of the optical modulation element 102 is terminated by a terminator 120 having a predetermined impedance. Thus, the electrical signal input to each end of the signal electrode 112 propagates in the signal electrode 112 as a traveling wave.

[0069] Figure 3 The relay substrate 118 and its surrounding structure are shown. The relay substrate 118 is provided with signal conductor patterns 330a, 330b, 330c, 330d (hereinafter also collectively referred to as signal conductor patterns 330) and ground conductor patterns 340a, 340b, 340c, 340d, 340e (hereinafter also collectively referred to as ground conductor patterns 340).

[0070] The relay substrate 118 is connected to the front side (where the signal conductor pattern 330 and the ground conductor pattern 340 are formed) Figure 3 A back ground conductor (not shown) is formed on the back side opposite to the back side (shown in the figure). The back ground conductor is fixed to the housing 114a of the housing 104 by, for example, solder, brazing material, or a conductive adhesive. Thus, the back ground conductor becomes a grounding wire component. The ground conductor pattern 340 is connected to the back ground conductor via appropriate vias (not shown) and is connected to the ground wire.

[0071] The ground conductor patterns 340a, 340b, 340c, 340d, and 340e are provided so as to sandwich the signal conductor patterns 330a, 330b, 330c, and 330d within the surface of the relay substrate 118. Thus, the signal conductor patterns 330 and the ground conductor patterns 340 form coplanar lines.

[0072] In this embodiment, the signal conductor pattern 330 extends in the vertical direction as shown in the figure, and one end of the lower side of the side of the relay substrate 118 is connected to the signal input terminal 124. Here, the side of the side of the relay substrate 118 where the signal conductor pattern 330 is connected to the signal input terminal 124 is referred to as the signal input side 318a.

[0073] The signal electrodes 112 of the optical modulation element 102 are electrically connected to the other ends of the signal conductor patterns 330 of the relay substrate 118 at the upper side edge in the illustration among the edges of the relay substrate 118, respectively, by wire bonding using, for example, conductor leads 326. The conductor leads 326 can be, for example, gold leads. Here, the edge of the relay substrate 118 where the signal conductor pattern 330 is connected to the signal electrode 112 of the optical modulation element 102 is referred to as the signal output edge 318b. In the present embodiment, the signal input edge 318a and the signal output edge 318b constitute two opposite edges of the relay substrate 118 in the top view. Figure 3 The other two opposite edges of the relay substrate 118 among the edges, other than the signal input edge 318a and the signal output edge 318b, are referred to as side edges (lateral edges) 318c and 318d.

[0074] The ground electrodes 122 that form a coplanar line together with the signal electrodes 112 in the optical modulation element 102 are electrically connected to the respective one ends of the ground conductor patterns 340 at the signal output edge 318b of the relay substrate 118, respectively, in the same manner as described above by wire bonding using, for example, conductor leads 326. It should be noted that the wire bonding using the conductor leads 326 described above is an example and is not limited thereto. Instead of the wire bonding using the conductor leads 326, for example, tape bonding using a conductor tape such as a gold tape can be used.

[0075] In the present embodiment, with respect to at least one signal conductor pattern 330, in the connection portion range that is rectangular in the top view and includes the signal connection portion where the signal conductor pattern 330 is connected to the signal input terminal 124, the top view shapes of the two ground conductor patterns 340 sandwiching the signal conductor pattern 330 on the relay substrate 118 are formed to be asymmetrical with respect to the at least one signal conductor pattern 330. Here, the above connection portion range is defined as a rectangle that extends in the plane of the relay substrate 118 with a part of the signal input edge 318a as one edge in the width direction. Moreover, the connection portion range has the at least one signal conductor pattern 330 as the center in the width direction. The width of the connection portion range is equal to the distance from the at least one signal conductor pattern 330 to the nearest adjacent signal conductor pattern 330, and the height of the connection portion range is equal to the distance from the signal input edge 318a to the end portion farthest from the signal input edge 318a in the above signal connection portion.

[0076] It should be noted that, in the present embodiment, the signal input terminal 124 is configured to be directly connected to the signal conductor pattern 330 through solder or the like, but it is not limited thereto. The signal input terminal 124 may also be configured to be connected to the signal conductor pattern 330 through wire bonding or the like and via a conductor lead or a conductor tape. In this case, the signal connection portion between the signal conductor pattern 330 and the signal input terminal 124 may be set to the range where the above-mentioned conductor lead or the like is connected to the signal conductor pattern 330. Therefore, in this case, the "end portion of the signal connection portion farthest from the signal input edge 318a" may be set to "the lead connection portion of the lead connection portion of the conductor lead or the like connected to the signal conductor pattern 330 and farthest from the signal input edge 318a in the signal conductor pattern 330".

[0077] Figure 4 Yes Figure 3 is a partial detailed view of part B shown. In the present embodiment, as an example, in the connection portion range 450a including the signal connection portion where the signal conductor pattern 330b is connected to the signal input terminal 124b, the top view shapes of the two ground conductor patterns 340a and 340b sandwiching the signal conductor pattern 330a on the relay substrate 118 are formed to be asymmetric with respect to the signal conductor pattern 330b.

[0078] Here, the connection portion range 450a is defined for the signal conductor pattern 330a. That is, if the extending direction of the signal input edge 318a of the relay substrate 118 is set as the width direction and the direction orthogonal to this extending direction is set as the height direction, the connection portion range 450a is defined as a rectangular range having a signal input edge 318a as one side and having a predetermined width w11 and a predetermined height d11 with the signal conductor pattern 330a as the center. Here, the height d11 is the distance from the signal input edge 318a to the distal end of the signal connection portion where the signal conductor pattern 330a is connected to the signal input terminal 124a (that is, the end on the side far from the signal input edge 318a). Moreover, the width w11 is equal to the pattern pitch (spacing) p1 between the signal conductor pattern 330a and the nearest adjacent signal conductor pattern 330b.

[0079] It should be noted that the characteristic impedance of the signal conductor pattern 330a is formed to have the same value inside and outside the connection portion range 450a with the ground conductor patterns 340a and 340b.

[0080] Similarly, in the present embodiment, in the connection portion range 450d defined for the signal conductor pattern 330d, the top view shapes of the two ground conductor patterns 340d and 340e sandwiching the signal conductor pattern 330d are formed to be asymmetric with respect to each other about the signal conductor pattern 330d. The connection portion range 450d is a rectangular range with the signal input side 318a as one side, having a width w14 centered on the signal conductor pattern 330d and a specified height d14. Here, the height d14 is the distance from the signal input side 318a to the distal end of the signal connection portion between the signal conductor pattern 330d and the signal input terminal 124d, and the width w14 is equal to the pattern pitch p2 from the signal conductor pattern 330d to the nearest adjacent signal conductor pattern 330c. Moreover, the signal conductor pattern 330d and the ground conductor patterns 340d and 340e are formed such that the characteristic impedance of the signal conductor pattern 330d becomes the same value inside and outside the connection portion range 450d.

[0081] More specifically, in the present embodiment, the two ground conductor patterns 340a and 340b sandwiching the signal conductor pattern 330a have portions where the intervals (illustrated as g11 and g12) from the respective edges of the two ground conductor patterns 340a and 340b to the opposite edges of the signal conductor pattern 330a are different in the connection portion ranges 450a, thereby forming an asymmetric shape with respect to the signal conductor pattern 330a.

[0082] Similarly, the two ground conductor patterns 340d and 340e sandwiching the signal conductor pattern 330d have portions where the intervals (illustrated as g41 and g42) from the respective edges of the two ground conductor patterns 340d and 340e to the opposite edges of the signal conductor pattern 330d are different in the connection portion range 450d, thereby forming an asymmetric shape with respect to the signal conductor pattern 330d. Here, g11 and g12, and g41 and g42 are set on the condition that, for example, the characteristic impedances of the signal conductor patterns 330a and 330d inside and outside the respective connection portion ranges 450a and 450d become equal.

[0083] Generally, in a high-frequency signal line composed of a signal conductor and a ground conductor, the closer the distance between the signal conductor and the ground conductor, the stronger the confinement of the high-frequency signal to the signal conductor.

[0084] In the relay substrate 118, the distances from the signal conductor pattern 330a to the ground conductor patterns 340a and 340b are different within the connection portion range 450a. Therefore, the leaked microwaves generated from the signal connection portion between the signal conductor pattern 330a and the signal input terminal 124a (thus, generated from the connection portion range 450a) are skewed in the direction where the distance to the adjacent ground conductor pattern is large, that is, in the direction of the ground conductor pattern 340a that is separated by a distance g11 (>g12) (for example, within the direction range shown as the range sandwiched by the arrows 490a and 490b which are single-dotted lines in Figure 4 ), and are emitted in a manner having an intensity distribution larger than that in other directions. On the other hand, the signal conductor pattern 330a is configured to have the same characteristic impedance inside and outside the connection portion range 450a. Therefore, the total amount of the leaked microwaves generated from the above signal connection portion is approximately the same as the case where g11 and g12 have the same value.

[0085] As a result, the intensity of the leaked microwaves in the direction range outside the direction range sandwiched by the arrows 490a and 490b is relatively reduced, and the crosstalk via the leaked microwaves from the signal conductor pattern 330a to the adjacent signal conductor pattern 330b is reduced.

[0086] For the same principle, the leaked microwaves generated from the signal connection portion between the signal conductor pattern 330d and the signal input terminal 124d (thus, generated from the connection portion range 450d) are emitted in the direction of the ground conductor pattern 340e that is separated by a distance g42 (>g41), in a manner having an intensity distribution larger than that in other directions. As a result, the intensity of the leaked microwaves propagating in the direction of the adjacent signal conductor pattern 330c is relatively reduced, and the crosstalk via the leaked microwaves from the signal conductor pattern 330d to the adjacent signal conductor pattern 330c is reduced.

[0087] Especially in an optical modulator 100 such as an optical modulator that performs DP-QPSK modulation and generates two modulated lights respectively modulated by a pair of high-frequency electrical signals, in many cases, the phase difference between the pair of high-frequency electrical signals also carries information. Therefore, the crosstalk between the pair of high-frequency electrical signals generates not only intensity noise but also phase noise, and has a greater impact on the modulation characteristics of the optical modulator 100 compared to the crosstalk between different pairs of high-frequency electrical signals.

[0088] The above pair of high-frequency electrical signals are usually relayed using two adjacent signal conductor patterns on the relay substrate. Therefore, it is extremely important to suppress the crosstalk between the two adjacent signal conductor patterns through which the pair of high-frequency electrical signals are respectively propagated.

[0089] In the optical modulator 100 of the present embodiment, two high-frequency electrical signals that are one pair of two pairs of high-frequency electrical signals are respectively propagated through adjacent signal conductor patterns 330a and 330b, and the other two high-frequency electrical signals that are the other pair are propagated through another adjacent signal conductor patterns 330c and 330d. Moreover, with the above structure, crosstalk from the signal conductor pattern 330a to the signal conductor pattern 330b is reduced, that is, crosstalk from one of the two high-frequency electrical signals constituting a pair to the other is reduced. Further, with the above structure, crosstalk from the signal conductor pattern 330d to the signal conductor pattern 330c is also reduced, that is, crosstalk from one of the two high-frequency electrical signals constituting the other pair to the other is also reduced. As a result, in the optical modulator 100, the influence of leaked microwaves can be effectively reduced, and good optical modulation characteristics can be achieved.

[0090] It should be noted that in the present embodiment, with respect to the signal conductor patterns not sandwiched by adjacent signal conductor patterns, that is, the signal conductor patterns 330a and 330d located at the left and right ends of the arrangement of the four signal conductor patterns 330, the two ground conductor patterns 340a and 340b, and 340d and 340e sandwiching them respectively are formed in an asymmetrical shape with respect to the signal conductor patterns 330a and 330d within the connection portion ranges 450a and 450d, but it is not limited thereto. Similarly, with respect to the signal conductor patterns 330b or 330c sandwiched by two signal conductor patterns 330a and 330c or 330b and 330d respectively, the two ground conductor patterns 340b and 340c or 340c and 340d sandwiching the above signal conductor patterns 330b or 330c respectively can also be configured to have an asymmetrical shape with respect to the signal conductor patterns 330b or 330c within a specified connection portion range.

[0091] In this case, the width of the connection portion range of the signal conductor pattern sandwiched by adjacent signal conductor patterns (that is, Figure 4 the width corresponding to w11 or w14 in) can be set to a width equal to the distance to the nearest adjacent signal conductor pattern.

[0092] Next, a modified example of the relay substrate used in the optical modulator 100 will be described.

[0093] <First Modified Example>

[0094] Figure 5 is a diagram showing the structure of the relay substrate 518 of the first modified example, and is a diagram corresponding to Figure 4 a partial detailed view of the first embodiment shown. This relay substrate 518 can be used in place of the relay substrate 118 in the Figure 1 shown optical modulator 100. It should be noted that in Figure 5 with respect toFigure 4 The components of the relay substrate 118 that are the same as those shown are denoted by the same reference numerals as in Figure 4 and the description of the above-mentioned Figure 4 is cited.

[0095] The relay substrate 518 has the same structure as the relay substrate 118, but is different in that it has a ground conductor pattern 540c instead of the ground conductor pattern 340c. Thus, in the relay substrate 518, in addition to the signal conductor patterns 330a and 330d, with respect to the signal conductor patterns 330b and 330c as well, within the connection portion ranges 550b and 550c defined for the above-mentioned signal conductor patterns 330b and 330c, the ground conductor patterns 340b and 540c sandwiching the signal conductor patterns 330b and 330c, and the ground conductor patterns 540c and 340d are respectively configured to have shapes that are asymmetric with respect to the signal conductor patterns 330b and 330c.

[0096] It should be noted that the connection portion ranges 550b and 550c defined for the signal conductor patterns 330b and 330c are, similarly to the connection portion ranges 450a and 450d defined for the signal conductor patterns 330a and 330d, respectively, rectangular ranges having a width w22 and a specified height d22 with the signal input side 318a as one side and centered on the signal conductor pattern 330b, and rectangular ranges having a width w23 and a specified height d23 centered on the signal conductor pattern 330c.

[0097] The widths w22 and w23 can be set to values equal to the distances from the signal conductor patterns 330b and 330c to the nearest adjacent signal conductor patterns, respectively.

[0098] For example, when the distances p1 between the signal conductor patterns 330a and 330b, p2 between the signal conductor patterns 330c and 330d, and p3 between the signal conductor patterns 330b and 330c have the relationship p1 > p2 > p3, the distance from either of the signal conductor patterns 330b and 330c to the nearest adjacent signal conductor pattern becomes p3. Therefore, the widths w22 and w23 of the connection portion ranges 550b and 550c both become values equal to p3.

[0099] In this modification example, p1 = p2 = p3, and w11 = w22 = w23 = W14 = p1 = p2 = p3.

[0100] The heights d22 and d23, similar to the heights d11 and d14, are defined by the distance from the signal input edge 318a to the distal end of the signal connection portion between the signal conductor pattern 330b and the signal input terminal 124d, and the distance to the distal end of the signal connection portion between the signal conductor pattern 330c and the signal input terminal 124c.

[0101] Specifically, in the connection portion range 550b, the ground conductor pattern 540c is formed in the same manner as the ground conductor patterns 340a and 340e, such that the interval g22 between the ground conductor pattern 540c and the signal conductor pattern 330b is different from the interval g21 between the signal conductor pattern 330b and the ground conductor pattern 340b (more specifically, greater than g21). Moreover, in the connection portion range 550c, the ground conductor pattern 540c is formed in such a way that the interval g31 between the ground conductor pattern 540c and the signal conductor pattern 330c is different from the interval g32 between the signal conductor pattern 330c and the ground conductor pattern 340d (more specifically, greater than g32). It should be noted that in the relay substrate 518, the signal conductor pattern 330 and the ground conductor patterns 340a, 340b, 540c, 340d, 340e are formed such that the characteristic impedance of each of the signal conductor patterns 330 is the same inside and outside the connection portion ranges 450a, 550b, 550c, 450d.

[0102] Accordingly, in the relay substrate 518, by setting the interval g22 larger than the interval g21 within the connection portion range 550b, the intensity distribution of the leaked microwave generated in the signal connection portion between the signal conductor pattern 330b and the signal input terminal 124b (and thus generated from the connection portion range 550b) in the direction of the ground conductor pattern 540c has a greater intensity within the angle range sandwiched by the arrows 590c and 590d shown by the dotted line in the figure, for example, than in other angle ranges. As a result, the intensity of the portion of the above-mentioned leaked microwave that reaches the adjacent signal conductor pattern 330a within the above-mentioned other angle range is relatively reduced.

[0103] That is, in the relay substrate 518, in addition to the reduction in the intensity of the portion of the leaked microwave generated in the signal connection portion between the signal conductor pattern 330a and the signal input terminal 124a and reaching the adjacent signal conductor pattern 330b, similar to the relay substrate 118, the intensity of the portion of the leaked microwave generated in the signal connection portion between the signal conductor pattern 330b and the signal input terminal 124b and reaching the adjacent signal conductor pattern 330a is also reduced.

[0104] Therefore, in the relay substrate 518, crosstalk between the signal conductor patterns 330a and 330b that respectively propagate two paired high-frequency electrical signals can be effectively suppressed.

[0105] Similarly, in the relay substrate 518, in addition to the reduction in the intensity of the portion of the leaked microwave that reaches the adjacent signal conductor pattern 330c among the leaked microwaves generated at the signal connection portion between the signal conductor pattern 330d and the signal input terminal 124d, similar to the relay substrate 118, by setting the interval g31 larger than the interval g32 within the connection portion range 550c, the intensity of the portion of the leaked microwave that reaches the adjacent signal conductor pattern 330d among the leaked microwaves generated at the signal connection portion between the signal conductor pattern 330c and the signal input terminal 124c (therefore, generated from the connection portion range 550c) is also reduced.

[0106] Therefore, in the relay substrate 518, crosstalk between the signal conductor patterns 330c and 330d that respectively propagate another two paired high-frequency electrical signals can also be effectively suppressed.

[0107] As a result, in the relay substrate 518, better optical modulation characteristics can be achieved than in the case of using the relay substrate 118.

[0108] <Second Modification Example>

[0109] Figure 6 FIG. is a diagram showing the structure of the relay substrate 618 of the second modification example, and is equivalent to Figure 4 a partial detailed view of the first embodiment shown in FIG. This relay substrate 618 can be used in place of the relay substrate 118 in the Figure 1 shown optical modulator 100. It should be noted that in Figure 6 , regarding the components that are the same as those of the Figure 4 , Figure 5 shown relay substrates 118 and 518, the same reference numerals as those in Figure 4 , Figure 5 are used to denote them, and the description regarding Figure 4 , Figure 5 above is cited.

[0110] Similar to the relay substrates 118 and 518, the relay substrate 618 is formed with the signal conductor pattern 330. Therefore, in the relay substrate 618, connection portion ranges 450a, 550b, 550c, and 450d are defined for the signal conductor pattern 330 in the same manner as in the relay substrate 518.

[0111] The relay substrate 618 has the same structure as the relay substrate 118, but is different in that it has ground conductor patterns 640a, 640c, and 640e instead of the ground conductor patterns 340a, 340c, and 340e. It should be noted that in the relay substrate 618 as well, the signal conductor pattern 330 and the ground conductor patterns 640a, 340b, 640c, 340d, and 640e are formed such that the characteristic impedance of the signal conductor pattern 330 is the same inside and outside the connection portion ranges 450a, 550b, 550c, and 450d.

[0112] In the relay substrate 618 of this modification example, the widths measured in the direction orthogonal to the extending direction of the signal conductor pattern of the respective portions of the two ground conductor patterns sandwiching at least one signal conductor pattern 330 within the connection portion range defined for the signal conductor pattern are different from each other, and thus it is constituted by a shape asymmetric with respect to the signal conductor pattern.

[0113] Specifically, in the relay substrate 618, the ground conductor pattern 640a sandwiching the signal conductor pattern 330a together with the ground conductor pattern 340b makes the width 1Wg11 of the portion formed in the connection portion range 450a different from the width Wg12 of the portion formed in the connection portion range 450a in the ground conductor pattern 340b (specifically, for example, Wg11 < Wg12), and thus in the connection portion range 450a, it is constituted by a shape asymmetric with respect to the signal conductor pattern 330a with the ground conductor pattern 340b.

[0114] Generally, in a high-frequency signal line composed of a signal conductor and a ground conductor, the smaller the impedance from the ground conductor to the portion supplying the ground potential (so-called ground wire) (that is, the more sufficient the so-called ground strengthening), the stronger the confinement of the high-frequency signal to the signal conductor.

[0115] In the relay substrate 618, the formation widths Wg11 and Wg12 of the portions formed in the connection portion range 450a of the ground conductor patterns 640a and 340b sandwiching the signal conductor pattern 330a are different from each other. As a result, the leaked microwave generated from the signal connection portion between the signal conductor pattern 330a and the signal input terminal 124a is directed toward a certain direction of the ground conductor pattern having a larger impedance to the ground wire (for example, the back ground conductor) with a narrower formation width among the adjacent ground conductor patterns, that is, the direction of the ground conductor pattern 640a having the formation width Wg11 (< Wg12) (for example, within the direction range shown as being sandwiched by the arrows 690a and 690b as single-dot dash lines in Figure 6 and is emitted with a stronger intensity distribution than other directions.

[0116] Therefore, the intensity of the leaked microwave in the direction range outside the direction range sandwiched by the arrows 690a and 690b is relatively reduced. For example, the crosstalk of the leaked microwave from the signal conductor pattern 330a to the adjacent signal conductor pattern 330b is reduced.

[0117] In addition, in the relay substrate 618, the formed widths Wg21 and Wg22 of the portions within the connection portion range 550b in the ground conductor patterns 340b and 640c sandwiching the signal conductor pattern 330b are different from each other. Thus, the leaked microwave generated from the signal connection portion between the signal conductor pattern 330b and the signal input terminal 124b is directed toward the ground conductor pattern 640c having a greater impedance than the ground wire with the formed width Wg22 narrower than Wg21 (for example, within the direction range shown as the range sandwiched by the arrows 690c and 690d in Figure 6 ), and is emitted with a greater intensity distribution than in other directions.

[0118] Therefore, the intensity of the leaked microwave in the direction range outside the direction range sandwiched by the arrows 690c and 690d is relatively reduced. For example, the crosstalk of the leaked microwave from the signal conductor pattern 330b to the adjacent signal conductor pattern 330a is also reduced. As a result, similar to Figure 5 the relay substrate 518 shown, crosstalk between the signal conductor patterns 330a and 330b that respectively propagate two paired high-frequency electrical signals can be effectively suppressed.

[0119] Similarly, in the relay substrate 618, the formed widths Wg31 and Wg32 of the portions within the connection portion range 550c in the ground conductor patterns 640c and 340d sandwiching the signal conductor pattern 330c are in an asymmetric relationship of Wg31 < Wg32, and the formed widths Wg41 and Wg42 of the portions within the connection portion range 450d in the ground conductor patterns 340d and 640e sandwiching the signal conductor pattern 330d are in an asymmetric relationship of Wg41 > Wg42.

[0120] Therefore, in the relay substrate 618, crosstalk from the signal conductor pattern 330c to the adjacent signal conductor pattern 330d via the leaked microwave generated from the signal connection portion between the signal conductor pattern 330c and the signal input terminal 124c, and crosstalk from the signal conductor pattern 330d to the adjacent signal conductor pattern 330c via the leaked microwave generated from the signal connection portion between the signal conductor pattern 330d and the signal input terminal 124d can be suppressed.

[0121] As a result, in the relay substrate 618, similar to Figure 5Similarly, the relay substrate 518 shown can more effectively suppress crosstalk between paired high-frequency signals compared to the relay substrate 118, enabling good optical modulation characteristics.

[0122] Particularly in the structure of the relay substrate 618, in the connection portion ranges 450a, 550b, 550c, 450d, although the formation widths of the ground conductor patterns 640a, 640b, 640c, 340d, 640e are different from each other across the corresponding signal conductor patterns 330, the distances from the signal conductor pattern 330 to the opposite edges of the adjacent ground conductor patterns 640a, 340b, 640c, 340d, 640e are equal to each other. Therefore, even if the formation widths of the ground conductor patterns 640a, 640b, 640c, 340d, 640e sandwiching the signal conductor pattern 330 are changed, the change in the characteristic impedance of the signal conductor pattern 330 is small. Thus, in the structure of the relay substrate 618, it can be easily configured such that the characteristic impedance of each signal conductor pattern 330 does not change inside and outside the connection portion ranges 450a, 550b, 550c, 450d. However, even if the difference in the formation widths (e.g., Wg11 and Wg12) within the connection portion of the two ground conductor patterns sandwiching the signal conductor pattern is set large, the skew direction of the leaked microwave does not change as in the cases of the relay substrates 118 and 518.

[0123] Therefore, the structure of the relay substrate 618 is preferable when the influence of the leaked microwave is relatively small and when it is desired to achieve as much matching with the existing design (e.g., the existing pattern design of the ground conductor pattern of the relay substrate) as possible and suppress the influence of the leaked microwave.

[0124] <Third Modification Example>

[0125] Figure 7 FIG. shows the structure of the relay substrate 718 of the third modification example, which is equivalent to Figure 4 a partial detailed view of the first embodiment shown. This relay substrate 718 can be used in place of the relay substrate 118 in the Figure 1 optical modulator 100 shown. Note that, in Figure 7 , regarding the components that are the same as those of the relay substrates 118, 518, 618 shown in Figure 4 , Figure 5 , Figure 6 , the same reference numerals as those in Figure 4 , Figure 5 , Figure 6 are used, and the descriptions regarding Figure 4 , Figure 5 , Figure 6 cited above are incorporated.

[0126] The relay substrate 718 and Figure 4 , Figure 5 The relay substrates 118 and 518 shown similarly form a signal conductor pattern 330. Therefore, in the relay substrate 718, connection portion ranges 450a, 550b, 550c, and 450d identical to those of the relay substrate 518 are defined respectively with respect to the signal conductor pattern 330.

[0127] The relay substrate 718 has the same structure as the relay substrate 118, except that ground conductor patterns 740a, 740c, and 740e are provided instead of the ground conductor patterns 340a, 340c, and 340e. It should be noted that in the relay substrate 718 as well, the signal conductor pattern 330 and the ground conductor patterns 740a, 340b, 740c, 340d, and 740e are formed such that the characteristic impedance of the signal conductor pattern 330 becomes the same inside and outside the connection portion ranges 450a, 550b, 550c, and 450d.

[0128] In the relay substrate 718 of this modified example, one of the two ground conductor patterns sandwiching at least one signal conductor pattern 330 is formed in an asymmetrical shape with respect to the signal conductor pattern by a portion formed outside the connection portion range defined for the signal conductor pattern.

[0129] Specifically, in the relay substrate 718, the ground conductor patterns 740a and 340b sandwiching the signal conductor pattern 330a are formed to be asymmetrical with respect to the signal conductor pattern 330a because one of the ground conductor patterns, 740a, is not patterned within the connection portion range 450a. Also, in the relay substrate 718, the ground conductor patterns 340b and 740c sandwiching the signal conductor pattern 330b are formed to be asymmetrical with respect to the signal conductor pattern 330b because one of the ground conductor patterns, 740c, is not patterned within the connection portion range 550b.

[0130] Similarly, in the relay substrate 718, the ground conductor patterns 740c and 340d sandwiching the signal conductor pattern 330c are formed to be asymmetrical with respect to the signal conductor pattern 330c because one of the ground conductor patterns, 740c, is not patterned within the connection portion range 550c. Also, in the relay substrate 718, the ground conductor patterns 340d and 740e sandwiching the signal conductor pattern 330d are formed to be asymmetrical with respect to the signal conductor pattern 330d because one of the ground conductor patterns, 740e, is not patterned within the connection portion range 450d.

[0131] This relay substrate 718 corresponds to that in the aforementioned second modified example Figure 6In the relay substrate 618, Wg11, Wg22, Wg31, and Wg42 are set to 0 (zero). Therefore, in the relay substrate 718, the crosstalk of the leakage microwave via between the signal conductor patterns 330a and 330b that respectively propagate two high-frequency electrical signals forming a pair, and the crosstalk of the leakage microwave via between the signal conductor patterns 330c and 330d that respectively propagate the other two high-frequency electrical signals forming another pair are further reduced compared to the relay substrate 618. As a result, when the relay substrate 718 is used, better optical modulation characteristics can be achieved compared to the case of using the relay substrate 618.

[0132] It should be noted that in this modified example, for example, the ground conductor patterns 740a and 340b sandwiching the signal conductor pattern 330a are asymmetric with respect to the signal conductor pattern 330a because one of the ground conductor patterns 740a is not patterned within the connection portion range 450a. However, it is not limited to this. Instead, for example, the ground conductor patterns 740a and 340b sandwiching the signal conductor pattern 330a are asymmetric with respect to the signal conductor pattern 330a because the range (area) where one of the ground conductor patterns 740a is patterned within the connection portion range 450a is smaller than the range (area) where the other ground conductor pattern 340b is patterned within the connection portion range 550b.

[0133] <Fourth Modified Example>

[0134] Figure 8 It is a diagram showing the structure of the relay substrate 818 of the fourth modified example, and is equivalent to Figure 4 a partial detailed diagram of the first embodiment shown. This relay substrate 818 can be used in place of the relay substrate 118 in the Figure 1 shown optical modulator 100. It should be noted that in Figure 8 , regarding the components that are the same as those of the relay substrates 118 and 518 shown in Figure 4 , Figure 5 , the same reference numerals as those in Figure 4 , Figure 5 are used to represent them, and the description regarding Figure 4 above is cited.

[0135] The relay substrate 818 is formed with signal conductor patterns 330 in the same manner as the relay substrates 118 and 518 of the first embodiment and the first modified example shown in Figure 4 , Figure 5 . Therefore, in the relay substrate 818, connection portion ranges 450a, 550b, 550c, and 450d that are the same as those of the relay substrate 518 are defined for the signal conductor patterns 330, respectively.

[0136] The relay substrate 818 has the same structure as the relay substrate 118, except that it has ground conductor patterns 840a, 840b, 840c, 840d, 840e instead of the ground conductor patterns 340a, 340b, 340c, 340d, 340e. It should be noted that in the relay substrate 818, the signal conductor pattern 330 and the ground conductor patterns 840a, 840b, 840c, 840d, 840e are formed such that the characteristic impedance of the signal conductor pattern 330 is the same inside and outside the connection portion ranges 450a, 550b, 550c, 450d.

[0137] In the relay substrate 818 of this modification, in the connection portion range of at least one signal conductor pattern 330, a cutout portion is provided that extends from the signal input side 318a and penetrates the thickness direction of the relay substrate 818 in a part of one of the two ground conductor patterns sandwiching the signal conductor pattern 330.

[0138] As an example, in Figure 8 In the shown relay substrate 818, in the connection portion range 450a defined for the signal conductor pattern 330a, a cutout portion 860a is provided in a part of the ground conductor pattern 840b of one of the two ground conductor patterns 840a, 840b sandwiching the signal conductor pattern 330a, which extends from the signal input side 318a and penetrates the thickness direction of the relay substrate 818. Thus, the ground conductor patterns 840a, 840b have asymmetric shapes with respect to the signal conductor pattern 330a in the connection portion range 450a.

[0139] It should be noted that in Figure 8 In order to clearly show the cutout portion 860a and other cutout portions 860b, 860c, 860d described later, the outline of the relay substrate 818 is depicted by thick lines. Moreover, in Figure 8 For the same purpose, the dashed lines and dotted lines indicating the connection portion ranges 450a, 550b, 550c, 450d are drawn so as not to overlap with the signal input side 318a of the relay substrate 818. However, the definition of the connection portion ranges 450a, 550b, 550c, 450d is the same as the definition in the above-described first embodiment and its modifications.

[0140] In addition, in the relay substrate 818, in the connection portion range 550b defined for the signal conductor pattern 330b, a cutout portion 860b is provided in a part of the ground conductor pattern 840b of one of the two ground conductor patterns 840b, 840c sandwiching the signal conductor pattern 330b, and the cutout portion 860b extends from the signal input side 318a and penetrates the thickness direction of the relay substrate 818.

[0141] With the above structure, in the relay substrate 818, the substrate leakage microwave generated at the connection point between the signal conductor pattern 330a and the signal input terminal 124a and propagating within the substrate material of the relay substrate 818 is prevented from propagating to the adjacent signal conductor pattern 330b by the space formed through the cutout portion 860a. Moreover, the substrate leakage microwave generated at the connection point between the signal conductor pattern 330b and the signal input terminal 124b and propagating within the substrate material of the relay substrate 818 is prevented from propagating to the adjacent signal conductor pattern 330a by the space formed through the cutout portion 860b.

[0142] Similarly, in the relay substrate 818, in the connection portion range 550c defined for the signal conductor pattern 330c, a cutout portion 860c is provided in a part of one of the two ground conductor patterns 840c and 840d sandwiching the signal conductor pattern 330c. The cutout portion 860c extends from the signal input side 318a and penetrates the thickness direction of the relay substrate 818.

[0143] In addition, in the relay substrate 818, in the connection portion range 450d defined for the signal conductor pattern 330d, a cutout portion 860d is provided in a part of one of the two ground conductor patterns 840d and 840e sandwiching the signal conductor pattern 330d. The cutout portion 860d extends from the signal input side 318a and penetrates the thickness direction of the relay substrate 818.

[0144] With the above structure, in the relay substrate 818, the substrate leakage microwave generated at the signal connection portion between the signal conductor pattern 330c and the signal input terminal 124c and propagating within the substrate material of the relay substrate 818 is prevented from propagating to the adjacent signal conductor pattern 330d by the space formed through the cutout portion 860c. Moreover, the substrate leakage microwave generated at the signal connection portion between the signal conductor pattern 330d and the signal input terminal 124d and propagating within the substrate material of the relay substrate 818 is prevented from propagating to the adjacent signal conductor pattern 330c by the space formed through the cutout portion 860d.

[0145] Therefore, in the relay substrate 818, the crosstalk via the substrate leakage microwave between the signal conductor patterns 330a and 330b that respectively propagate two high-frequency electrical signals forming a pair, and the crosstalk via the substrate leakage microwave between the signal conductor patterns 330c and 330d that respectively propagate two other high-frequency electrical signals forming another pair are further reduced. As a result, if the relay substrate 818 is used in the optical modulator 100, good optical modulation characteristics can be achieved for the optical modulator 100.

[0146] Note that in the relay substrate 818, if metallization is performed on the inner wall of the notch portion 860a or the like so as to extend from the ground conductor pattern 840b or the like, the effect of suppressing the propagation of microwave leakage from the substrate as described above can be further improved.

[0147] <Fifth Modification Example>

[0148] Figure 9 FIG. is a diagram showing the structure of the relay substrate 918 of the fifth modification example, and is equivalent to Figure 4 a partial detailed view of the first embodiment shown in FIG. This relay substrate 918 can be used in place of the relay substrate 118 in the Figure 1 shown optical modulator 100. Note that in Figure 9 , regarding the components identical to those of the relay substrates 118, 518, 618, 718, 818 shown in Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , the same reference numerals as those in Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 are used, and the description regarding Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 above is incorporated by reference.

[0149] In the relay substrate 918, signal conductor patterns 330 are formed in the same manner as in the relay substrates 118 and 518 of the first embodiment and the first modification example shown in Figure 4 , Figure 5 . Therefore, in the relay substrate 818, connection portion ranges 450a, 550b, 550c, and 450d identical to those of the relay substrate 518 are defined for the signal conductor patterns 330, respectively.

[0150] Here, the relay substrate 918 is obtained by combining the relay substrate 718 in Figure 7 of the aforementioned third modification example and the Figure 8It is composed of the characteristic structural combination of the relay substrate 818 in []. That is, the relay substrate 918 has the same structure as the relay substrate 118, but the difference is that it has the ground conductor patterns 740a, 840b, 740c, 840d, 740e instead of the ground conductor patterns 340a, 340b, 340c, 340d, 340e. It should be noted that in the relay substrate 918, the signal conductor pattern 330 and the ground conductor patterns 740a, 840b, 740c, 840d, 740e are also formed so that the characteristic impedance of the signal conductor pattern 330 becomes the same inside and outside the connection part ranges 450a, 550b, 550c, 450d.

[0151] Especially in the relay substrate 918, at the same positions as those of the relay substrate 818 in the aforementioned fourth modification example Figure 8 four cutout parts 860a, 860b, 860c, 860d that extend from the signal input side 318a and penetrate the thickness direction of the relay substrate 918 are provided.

[0152] It should be noted that in Figure 9 the outline of the relay substrate 918 is depicted with thick lines in order to clearly show the cutout part 860a and other cutout parts 860b, 860c, 860d described later, in the same way as in the Figure 8 of the above-mentioned fourth modification example. Moreover, in Figure 9 for the same purpose, the dotted lines and single-dot-and-dash lines indicating the connection part ranges 450a, 550b, 550c, 450d are depicted in a manner that does not overlap with the signal input side 318a of the relay substrate 918. However, the definition of the connection part ranges 450a, 550b, 550c, 450d is the same as the definition in the above-mentioned first embodiment and its modification examples.

[0153] Thus, in the relay substrate 918, between the signal conductor patterns 330a and 330b that respectively propagate two high-frequency electrical signals that form a pair, the crosstalk of the microwave leaking through the substrate is further reduced compared to the case of the relay substrate 718 in the Figure 7 of the third modification example, in the same way as the relay substrate 818 in the Figure 7 of the third modification example. Similarly, between the signal conductor patterns 330c and 330d that respectively propagate the other two high-frequency electrical signals that form another pair, the crosstalk of the microwave leaking through the substrate is further reduced compared to the case of the relay substrate 718 in the

[0154] As a result, when the relay substrate 918 is used in the optical modulator 100, compared with using the above-mentioned Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8Compared with the other relay substrates 118, 518, 628, 718, 818 of the first embodiment, the first modification, the second modification, the third modification, and the fourth modification shown, better optical modulation characteristics can be achieved as the optical modulator 100.

[0155] It should be noted that, similar to the case of the relay substrate 818, if the inner walls of the cutout portions 860a, etc. are metallized so as to extend from the ground conductor patterns 840b, etc., the effect of suppressing the propagation of leaked microwaves on the substrate can be further improved.

[0156] <Sixth Modification>

[0157] Figure 10 FIG. showing the structure of the relay substrate 1018 of the sixth modification, which is equivalent to Figure 4 a partial detailed view of the first embodiment shown. This relay substrate 1018 can be used in place of the relay substrate 118 in the optical modulator 100 shown. It should be noted that, in Figure 1 the same reference numerals are used to denote the components that are the same as those of the relay substrates 118 and 518 shown in Figure 10 , and the description of Figure 4 , Figure 5 is cited for the components that are the same as those of the relay substrates 118 and 518 shown in Figure 4 , Figure 5 . Figure 4 , Figure 5

[0158] The relay substrate 1018 is formed with signal conductor patterns 330 in the same manner as the relay substrates 118 and 518 of the first embodiment and the first modification shown in Figure 4 , Figure 5 . Therefore, in the relay substrate 818, for the signal conductor patterns 330, connection portion ranges 450a, 550b, 550c, 450d that are the same as those of the relay substrate 118 are defined.

[0159] In the relay substrate 118 of Figure 4 in the above-described first embodiment, for example, the ground conductor patterns 340a and 340b sandwiching the signal conductor pattern 330a are formed in an asymmetric shape with respect to the signal conductor pattern 330a within the connection portion range 450a, thereby reducing the intensity of the leaked microwaves generated within the connection portion range 450a from reaching the adjacent signal conductor pattern 330b. In contrast, in the relay substrate 1018 of this modification, in the connection portion range defined for at least one signal conductor pattern, each part within the connection portion range where two adjacent ground conductor patterns sandwich the signal conductor pattern is formed to have a different impedance with respect to the ground wire component (for example, the back surface ground conductor of the relay substrate 1018).

[0160] Particularly in the relay substrate 1018, as an example, within the connection portion range defined for at least one signal conductor pattern, the presence or absence of via holes in each part within the connection portion range of two adjacent ground conductor patterns sandwiching the signal conductor pattern is different (that is, via holes are provided only in one of these parts), whereby the impedance is different.

[0161] Specifically, the relay substrate 1018 has the same structure as the relay substrate 118 of the Figure 4 first embodiment shown, but is different in that instead of the ground conductor patterns 340a, 340b, 340c, 340d, 340e, it has ground conductor patterns 1040a, 1040b, 1040c, 1040d, 1040e. It should be noted that in the relay substrate 1018 as well, the signal conductor pattern 330 and the ground conductor patterns 1040a, 1040b, 1040c, 1040d, 1040e are formed such that the characteristic impedance of the signal conductor pattern 330 is the same inside and outside the connection portion ranges 450a, 550b, 550c, 450d.

[0162] Six via holes 1062 are respectively formed in the ground conductor patterns 1040b and 1040d. It should be noted that in Figure 10 , in order to avoid a lengthy description, only one of the six via holes is labeled 1062 in each of the ground conductor patterns 1040b and 1040d. The other five circles depicted in the same size as the labeled via hole 1062 in the ground conductor patterns 1040b and 1040d can be understood as the same via holes 1062.

[0163] Specifically, within the connection portion range 450a defined for the signal conductor pattern 330a, only one of the adjacent ground conductor patterns 1040a, 1040b sandwiching the signal conductor pattern 330a, namely the ground conductor pattern 1040b, is connected to the back ground conductor through two via holes 1062, and no such via holes are provided in the other ground conductor pattern 1040a.

[0164] In addition, within the connection portion range 550b defined for the signal conductor pattern 330b, only one of the adjacent ground conductor patterns 1040b, 1040c sandwiching the signal conductor pattern 330b, namely the ground conductor pattern 1040b, is connected to the back ground conductor through two via holes 1062, and no such via holes are provided in the other ground conductor pattern 1040c.

[0165] Similarly, in the connection portion range 550c defined for the signal conductor pattern 330c, only one of the adjacent ground conductor patterns 1040c and 1040d sandwiching the signal conductor pattern 330c is connected to the backplane ground conductor through two vias 1062, and such vias are not provided in the other ground conductor pattern 1040c.

[0166] In addition, in the connection portion range 450d defined for the signal conductor pattern 330d, only one of the adjacent ground conductor patterns 1040d and 1040e sandwiching the signal conductor pattern 330d is connected to the backplane ground conductor through two vias 1062, and such vias are not provided in the other ground conductor pattern 1040e.

[0167] Associated with the relay substrate 618 of the second modification, as described above, generally, in a high-frequency signal line composed of a signal conductor and a ground conductor, the smaller the impedance from the ground conductor to the ground wire (i.e., the more sufficient the so-called ground strengthening), the stronger the confinement of the high-frequency signal to the signal conductor.

[0168] Therefore, in the relay substrate 1018, the leaked microwaves generated in the connection portion ranges 450a and 550b have greater intensity in a certain direction of the ground conductor patterns 1040a and 1040c that are not connected to the backplane ground conductor through the vias 1062 (thus, having a higher impedance to the backplane ground conductor), and the intensity in other directions is reduced. Therefore, in the relay substrate 1018, similar to the relay substrate 118, crosstalk via the leaked microwaves is reduced between the signal conductor patterns 330a and 330b that respectively propagate two high-frequency electrical signals that will form a pair. Similarly, the leaked microwaves generated in the connection portion ranges 550c and 450d have greater intensity in the direction of the ground conductor patterns 1040c and 1040e that do not form the vias 1062 and have a higher impedance to the backplane ground conductor, and the intensity in other directions is reduced. Therefore, in the relay substrate 1018, crosstalk via the leaked microwaves is also reduced between the signal conductor patterns 330c and 330d that respectively propagate two other high-frequency electrical signals that will form a pair.

[0169] As a result, when the relay substrate 1018 is used, good optical modulation characteristics can also be achieved for the optical modulator 100.

[0170] <Seventh Modification>

[0171] Figure 11 is a diagram showing the structure of the relay substrate 1118 of the seventh modification, and is equivalent to Figure 4 a partial detailed diagram of the first embodiment shown. This relay substrate 1118 is in Figure 1It can be used to replace the relay substrate 118 in the optical modulator 100 shown. It should be noted that in Figure 11 regarding the components identical to those of the relay substrates 118, 518, and 1080 shown in Figure 4 , Figure 5 , Figure 10 , the same reference numerals as those in Figure 4 , Figure 5 , Figure 10 are used to denote them, and the descriptions regarding Figure 4 , Figure 5 , Figure 10 above are incorporated by reference.

[0172] The relay substrate 1118 is formed with a signal conductor pattern 330 in the same manner as the relay substrates 118 and 518 in the first embodiment and the first modification shown in Figure 4 , Figure 5 . Therefore, in the relay substrate 818, connection portion ranges 450a, 550b, 550c, and 450d identical to those of the relay substrate 118 are defined for the signal conductor pattern 330, respectively.

[0173] The relay substrate 1118 is the same as the relay substrate 1018 in Figure 10 of the above-described sixth modification. In the connection portion range defined for at least one signal conductor pattern, respective portions within the connection portion range of two adjacent ground conductor patterns sandwiching the signal conductor pattern are formed to have different impedances with respect to a ground wire component (e.g., the back surface ground conductor of the relay substrate 1118).

[0174] However, in the relay substrate 1118, different from the relay substrate 1018, the diameters of the via holes provided in respective portions within the connection portion range defined for the signal conductor pattern by two adjacent ground conductor patterns sandwiching at least one signal conductor pattern are different, whereby the above-mentioned impedances are different.

[0175] Specifically, the relay substrate 1118 is different from the relay substrate 1080 in that it includes ground conductor patterns 1140a, 1140c, and 1140e instead of the ground conductor patterns 1040a, 1040c, and 1040e. It should be noted that in the relay substrate 1118 as well, the signal conductor pattern 330 and the ground conductor patterns 1140a, 1040b, 1140c, 1040d, and 1140e are formed such that the characteristic impedance of the signal conductor pattern 330 is the same inside and outside the connection portion ranges 450a, 550b, 550c, and 450d.

[0176] The ground conductor patterns 1140a, 1140c, and 1140e have the same structure as the ground conductor patterns 1040a, 1040c, and 1040e, but are different in that through-holes 1162 having the same number as the through-hole 1062 and a smaller diameter than the through-hole 1062 are provided in the corresponding connection portion ranges 450a, 550b, 550c, and 450d, respectively. Here, in Figure 11 in order to avoid redundant description, only one of the through-holes in the ground conductor patterns 1140a, 1140c, and 1140e is labeled 1162. In the ground conductor patterns 1140a, 1140c, and 1140e, the other two, five, and two circles drawn in the same size as the labeled through-hole 1162 can be understood as the same through-hole 1162.

[0177] Specifically, in the connection portion range 450a defined for the signal conductor pattern 330a, one ground conductor pattern 1140b sandwiching the signal conductor pattern 330a is connected to the back ground conductor through two through-holes 1062, and the other ground conductor pattern 1140a is connected to the back ground conductor through through-holes 1162 having the same number (i.e., two in this example) and a smaller diameter than the through-hole 1062.

[0178] In addition, in the connection portion range 550b defined for the signal conductor pattern 330b, one ground conductor pattern 1140b sandwiching the signal conductor pattern 330b is connected to the back ground conductor through two through-holes 1062, and the other ground conductor pattern 1140c is connected to the back ground conductor through through-holes 1162 having the same number and a smaller diameter than the through-hole 1062.

[0179] Similarly, in the connection portion range 550c defined for the signal conductor pattern 330c, one ground conductor pattern 1040d sandwiching the signal conductor pattern 330c is connected to the back ground conductor through two through-holes 1062, and the other ground conductor pattern 1140c is connected to the back ground conductor through through-holes 1162 having the same number and a smaller diameter than the through-hole 1062.

[0180] In addition, in the connection portion range 450d defined for the signal conductor pattern 330d, one ground conductor pattern 1040d sandwiching the signal conductor pattern 330d is connected to the back ground conductor through two through-holes 1062, and the other ground conductor pattern 1140e is connected to the back ground conductor through through-holes 1162 having the same number and a smaller diameter than the through-hole 1062.

[0181] Thus, in the relay substrate 1118, similar to that of the above sixth modification Figure 10Similarly, in the relay substrate 1018, the leaked microwaves generated in the connection portion ranges 450a and 550b have greater intensities in the directions toward the via holes 1162 with small diameters and the ground conductor patterns 1040a and 1040c having higher impedances with respect to the backside ground conductor, and the intensities in other directions are reduced. Therefore, in the relay substrate 1118, similar to the relay substrate 1018, crosstalk via the leaked microwaves is reduced between the signal conductor patterns 330a and 330b that respectively propagate two high-frequency electrical signals that will form a pair.

[0182] Similarly, in the relay substrate 1118, the leaked microwaves generated in the connection portion ranges 550c and 450d have greater intensities in the directions toward the via holes 1162 with small diameters and the ground conductor patterns 1140c and 1140e having higher impedances with respect to the backside ground conductor, and the intensities in other directions are reduced. Therefore, in the relay substrate 1118, similar to the relay substrate 1018 in the above-described sixth modification Figure 10 crosstalk via the leaked microwaves can also be reduced between the signal conductor patterns 330c and 330d that respectively propagate two high-frequency electrical signals that will form another pair.

[0183] As a result, when the relay substrate 1118 is used, good optical modulation characteristics can also be achieved as the optical modulator 100.

[0184] <Eighth Modification>

[0185] Figure 12 FIG. is a diagram showing the structure of the relay substrate 1218 of the eighth modification, and is a diagram corresponding to a partial detailed view of the first embodiment shown in Figure 4 This relay substrate 1218 can be used in place of the relay substrate 118 in the optical modulator 100 shown in Figure 1 Note that, in Figure 12 , with regard to the constituent elements that are the same as those of the relay substrates 118, 518, 1018, and 1118 shown in Figure 4 , Figure 5 , Figure 10 , Figure 11 the same reference numerals as those in Figure 4 , Figure 5 , Figure 10 , Figure 11 are used, and the descriptions regarding Figure 4 , Figure 5 , Figure 10 , Figure 11 above are incorporated by reference.

[0186] The relay substrate 1218 and Figure 4 , Figure 5The relay substrates 118 and 518 of the first embodiment and the first modification shown are similarly formed with the signal conductor pattern 330. Accordingly, in the relay substrate 1218, connection portion ranges 450a, 550b, 550c, and 450d that are the same as those of the relay substrate 118 are defined for the signal conductor pattern 330, respectively.

[0187] The relay substrate 1218 and Figure 10 , Figure 11 similarly to the relay substrates 1018 and 1118 in the sixth modification and the seventh modification shown, respective portions within the connection portion ranges defined for the signal conductor pattern by two adjacent ground conductor patterns sandwiching at least one signal conductor pattern are formed to have different impedances with respect to a ground line component (e.g., the back surface ground conductor of the relay substrate 1118).

[0188] However, in the relay substrate 1218, different from the relay substrates 1018 and 1118, the number of via holes provided in respective portions within the connection portion ranges defined for the signal conductor pattern by two adjacent ground conductor patterns sandwiching at least one signal conductor pattern is different, whereby the above-described impedances are different.

[0189] Specifically, the relay substrate 1218 is different from the relay substrate 1118 in that the relay substrate 1218 includes ground conductor patterns 1240a, 1240c, and 1240e in place of the ground conductor patterns 1140a, 1140c, and 1140e. Note that in the relay substrate 1218 as well, the signal conductor pattern 330 and the ground conductor patterns 1240a, 1040b, 1240c, 1040d, and 1240e are formed such that the characteristic impedance of the signal conductor pattern 330 is the same inside and outside the connection portion ranges 450a, 550b, 550c, and 450d.

[0190] Moreover, in the connection portion range 450a defined for the signal conductor pattern 330a, one of the ground conductor patterns 1140b sandwiching the signal conductor pattern 330a is connected to the back surface ground conductor through two via holes 1062, and the other ground conductor pattern 1140a is connected to the back surface ground conductor through a smaller number (i.e., one in this example) of via holes 1062.

[0191] In addition, in the connection portion range 550b defined for the signal conductor pattern 330b, one of the ground conductor patterns 1140b sandwiching the signal conductor pattern 330b is connected to the back surface ground conductor through two via holes 1062, and the other ground conductor pattern 1240c is connected to the back surface ground conductor through a smaller number (one in this example) of via holes 1062.

[0192] Similarly, within the connection range 550c defined for the signal conductor pattern 330c, one ground conductor pattern 1040d sandwiching the signal conductor pattern 330c is connected to the backplane ground conductor through two vias 1062, and the other ground conductor pattern 1240c is connected to the backplane ground conductor through a smaller number (one in this example) of vias 1062.

[0193] In addition, within the connection range 450d defined for the signal conductor pattern 330d, one ground conductor pattern 1040d sandwiching the signal conductor pattern 330d is connected to the backplane ground conductor through two vias 1062, and the other ground conductor pattern 1240e is connected to the backplane ground conductor through a smaller number (one in this example) of vias 1062.

[0194] Thus, in the relay substrate 1218, similar to Figure 11 the relay substrate 1118 in the seventh modification example shown, the leakage microwaves generated in the connection ranges 450a and 550b have greater intensities in the directions towards the ground conductor patterns 1040a and 1040c with higher impedance to the backplane ground conductor due to having a smaller number of vias 1062 than the ground conductor pattern 1040b, and the intensities in other directions are reduced. Therefore, in the relay substrate 1218, similar to the relay substrate 1118, crosstalk via the leakage microwaves is reduced between the signal conductor patterns 330a and 330b that respectively propagate two high-frequency electrical signals that will form a pair.

[0195] Similarly, in the relay substrate 1218, the leakage microwaves generated in the connection ranges 550c and 450d have greater intensities in the directions towards the ground conductor patterns 1140c and 1140e with higher impedance to the backplane ground conductor due to having a smaller number of vias 1062 than the ground conductor pattern 1040d, and the intensities in other directions are reduced. Therefore, in the relay substrate 1218, similar to the relay substrate 1118, crosstalk via the leakage microwaves can also be reduced between the signal conductor patterns 330c and 330d that respectively propagate two high-frequency electrical signals that will form another pair.

[0196] As a result, when using the relay substrate 1218, good optical modulation characteristics can be achieved for the optical modulator 100.

[0197] <Ninth Modification Example>

[0198] The respective characteristic structures within the connection ranges shown in the above-described modification examples can be mixed and / or repeatedly provided in one relay substrate. This modification example shows an example of such a relay substrate.

[0199] Figure 13FIG. is a diagram showing the structure of the relay substrate 1318 according to the ninth modification example, and is equivalent to Figure 4 a partial detailed view of the first embodiment shown in Figure 1 . This relay substrate 1218 can be used in place of the relay substrate 118 in the Figure 12 optical modulator 100 shown in Figure 4 . Note that in Figure 5 , regarding the components identical to those of the relay substrates 118, 518, 618, 718, 818, 1018 shown in Figure 6 , Figure 7 , Figure 8 , Figure 10 , the same reference numerals as those in Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 10 are used, and the descriptions regarding Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 10 above are cited.

[0200] Similar to the relay substrates 118 and 518 of the first embodiment and the first modification example shown in Figure 4 , Figure 5 , the relay substrate 1318 of the ninth modification example is formed with signal conductor patterns 330. Therefore, in the relay substrate 1318, connection portion ranges 450a, 550b, 550c, 450d identical to those of the relay substrate 118 are defined respectively for the signal conductor patterns 330.

[0201] For the connection portion ranges 450a, 550b, 550c defined for the signal conductor patterns 330a, 330b, 330c, the characteristic structures of the relay substrates 118, 618, and 718 of the first embodiment, the second modification example, and the third modification example shown in Figure 4 , Figure 6 , Figure 7 are respectively applied to the relay substrate 1318 of the ninth modification example, and the characteristic structures of the relay substrates 118 and 1018 of the first embodiment and the sixth modification example shown in Figure 4 and Figure 10 are repeatedly applied to the signal conductor pattern 330d.

[0202] The relay substrate 1318 has the same structure as the relay substrate 118, but is different in that it has ground conductor patterns 1340c and 1340d instead of ground conductor patterns 340c and 340d. It should be noted that in the relay substrate 1318 as well, the signal conductor pattern 330 and the ground conductor patterns 340a, 340b, 1340c, 1340d, and 340e are formed such that the characteristic impedance of the signal conductor pattern 330 becomes the same inside and outside the connection portions 450a, 550b, 550c, and 450d.

[0203] The relay substrate 1318 has ground conductor patterns 340a and 340b in the same manner as the relay substrate 118. Thus, for the above reasons in association with the relay substrate 118, crosstalk of leaked microwaves from the signal conductor pattern 330a to 330b via the connection portion 450a can be suppressed.

[0204] The ground conductor pattern 1340c has the same structure as the ground conductor pattern 340c, but similar to Figure 6 the relay substrate 618 of the second modification example shown, the formation width Wg22 of the portion within the connection portion 550b is narrower than the formation width Wg21 of the portion within the connection portion 550b of the ground conductor pattern 340b that sandwiches the signal conductor pattern 330b. Thus, for the above reasons in association with the relay substrate 618, crosstalk of leaked microwaves from the signal conductor pattern 330b to 330a via the connection portion 550b can be suppressed.

[0205] In addition, the ground conductor pattern 1340c is similar to Figure 7 the relay substrate 718 of the third modification example shown, and no pattern is formed within the connection portion 550c. Also, the ground conductor pattern 1340d is formed in the same shape as the ground conductor pattern 340d within the connection portion 450d. Therefore, for the above reasons in association with the relay substrate 718, crosstalk of leaked microwaves from the signal conductor pattern 330c to 330d via the connection portion 550c can be suppressed.

[0206] In addition, in the connection portion 450d of the relay substrate 1318, similar to Figure 4 the relay substrate 118 of the first embodiment shown, within the range of the connection portion 450d, the ground conductor patterns 1340d and 340e that sandwich the signal conductor pattern 330d are asymmetric with respect to the signal conductor pattern 330d due to the differences in the intervals (g41 and g42 shown in the figure) between their respective edges opposite to the signal conductor pattern 330d and the edges of the signal conductor pattern 330d opposite to those edges. Further, in the connection portion 450d of the relay substrate 1318, similar to Figure 10Similarly to the relay substrate 1018 of the sixth modification example shown, only the ground conductor pattern 1340d is connected to the backside ground conductor through two via holes 1062, and such via holes are not provided in the ground conductor pattern 340e. Therefore, in the relay substrate 1318, similar to Figure 5 , Figure 10 the relay substrates 518 and 1018 of the second and sixth modification examples shown, for the above reasons, crosstalk of leaked microwaves from the signal conductor pattern 330d to 330c via the connection portion range 450d can be suppressed.

[0207] As a result, when the relay substrate 1318 is used, good optical modulation characteristics can also be achieved as the optical modulator 100.

[0208] Note that the combination and overlapping manners of the characteristic structures of the relay substrates 118, 518, 618, 718, 818, 918, 1018, 1118, and 1218 when forming one relay substrate are not limited to the structure of the above relay substrate 1318. Based on the above crosstalk suppression principle, the above characteristic structures can be combined and / or overlapped in any form in association with the above relay substrates for the purpose of suppressing crosstalk of leaked microwaves between adjacent signal conductor patterns and / or leaked microwaves via the substrate.

[0209] [Second Embodiment]

[0210] Next, a second embodiment of the present invention will be described. This embodiment is an optical transmission device equipped with the optical modulator 100 of the first embodiment and any one of the optical modulators of its modification examples that use the relay substrates 518, 618, 718, 818, 918, 1018, 1118, 1218, and 1318.

[0211] Figure 14 FIG. shows the structure of the optical transmission device of this embodiment. This optical transmission device 2100 includes an optical modulator 2102, a light source 2104 that makes light incident on the optical modulator 2102, a modulation signal generation unit 2106, and a modulation data generation unit 2108.

[0212] The optical modulator 2102 can be set to any one of the optical modulator 100 of the first embodiment and the optical modulators of its modification examples that use the relay substrates 518, 618, 718, 818, 918, 1018, 1118, 1218, and 1318. Here, in order to avoid redundant descriptions and facilitate understanding, hereinafter, the optical modulator 2102 is set to the optical modulator 100 of the first embodiment.

[0213] The modulation data generation unit 2108 receives transmission data provided from the outside, generates modulation data for transmitting the transmission data (for example, data obtained by converting or processing the transmission data into a prescribed data format), and outputs the generated modulation data to the modulation signal generation unit 2106.

[0214] The modulation signal generation unit 2106 is an electronic circuit (drive circuit) that outputs an electrical signal for causing the optical modulator 2102 to perform a modulation operation. Based on the modulation data output from the modulation data generation unit 2108, the modulation signal generation unit 2106 generates a high-frequency signal, that is, a modulation signal, for causing the optical modulator 2102 to perform an optical modulation operation in accordance with the modulation data, and inputs the modulation signal to the optical modulator 2102. The modulation signal is composed of four high-frequency electrical signals corresponding to the four signal electrodes 112a, 112b, 112c, and 112d of the optical modulation element 102 included in the optical modulator 2102. Here, the high-frequency electrical signals input to the signal electrodes 112a and 112b form a pair and modulate the output light output from one output optical waveguide 126a of the optical modulation element 102. Further, the high-frequency electrical signals input to the signal electrodes 112c and 112d form another pair and modulate the output light output from the other output optical waveguide 126b of the optical modulation element 102.

[0215] The four high-frequency electrical signals are input from the signal input terminals 124a, 124b, 124c, and 124d of the electrical connectors 116a, 116b, 116c, and 116d of the optical modulator 2102 to the signal conductor patterns 330a, 330b, 330c, and 330d of the relay substrate 118, and are input to the signal electrodes 112a, 112b, 112c, and 112d of the optical modulation element 102 via the signal conductor patterns 330a and the like.

[0216] As a result, the light output from the light source 2104 is modulated by the optical modulator 2102, for example, by DP-QPSK modulation, and the modulated light is output from the optical transmission device 2100.

[0217] In particular, in the optical transmission device 2100, as the optical modulator 2102, any one of the optical modulator 100 of the first embodiment and the optical modulators 100 using the relay substrates 518, 618, 718, 818, 918, 1018, 1118, 1218, and 1318, which are modified examples thereof, is used. Therefore, in the optical transmission device 2100, it is possible to effectively reduce an increase in crosstalk between high-frequency electrical signals for driving the optical modulation element 102 due to the above-described spatial leakage microwave, and in particular, crosstalk via the spatial leakage microwave between signal lines through which two paired high-frequency electrical signals propagate. Therefore, in the optical transmission device 2100, it is possible to ensure stable and good optical modulation characteristics and to achieve stable and good transmission characteristics.

[0218] It should be noted that the present invention is not limited to the structures of the above-described embodiments and their modified examples, and can be implemented in various forms without departing from its gist.

[0219] For example, the above-described relay substrates 118, 518, 618, 718, 818, 918, 1018, 1118, 1218, 1318 are an example of a structure in which two ground conductor patterns sandwiching at least one signal conductor pattern are formed asymmetrically in the corresponding connection portion range with respect to at least one signal conductor pattern 330, but are not limited thereto. The two ground conductor patterns sandwiching the signal conductor pattern may be formed asymmetrically in the corresponding connection portion range, may be formed in any shape, and / or any via holes may be arranged in any number at any position.

[0220] In this case, when at least one signal conductor pattern 330 and an adjacent signal conductor pattern 330 propagate two high-frequency signals that are paired together, it is preferable that the two ground conductor patterns sandwiching the at least one signal conductor pattern 330 are formed such that the intensity in the direction toward the adjacent signal conductor pattern 330 is reduced in the leakage microwave generated from the corresponding connection portion range. Specifically, the impedance of the ground conductor pattern on the side far from the adjacent signal conductor pattern 330 among the two ground conductor patterns sandwiching the at least one signal conductor pattern 330 with respect to the ground wire component may be increased, or the distance between the at least one signal conductor pattern and the ground conductor pattern on the far side may be increased to reduce the trapped intensity of the high-frequency signal on the far side. The more specific structures for increasing the impedance and reducing the trapped intensity are clearly known from the characteristic structures of the above-described relay substrates 118, 518, 618, 718, 818, 918, 1018, 1118, 1218, 1318.

[0221] In addition, in the above-described relay substrates 118, 518, 618, 718, 818, 918, 1018, 1118, 1218, 1318, the characteristic impedance of the signal conductor pattern 330 is set not to change inside and outside the connection portion range 450a, etc., but is not limited thereto. The signal conductor pattern 330 may change the characteristic impedance of the signal conductor pattern 330 inside and outside the connection portion range 450a, etc. Even in such a configuration, as long as the two adjacent ground conductor patterns sandwiching the signal conductor pattern are configured asymmetrically in the corresponding connection portion range, compared with the case where the ground conductor pattern is formed symmetrically, the propagation intensity of the leakage microwave generated from the connection portion range in a specific direction can be reduced.

[0222] In addition, in the above-described relay substrates 118, 518, 618, 718, 818, 918, 1018, 1118, 1218, 1318, a ground conductor pattern is formed between two adjacent signal conductor patterns 330, but it is not limited thereto. The ground conductor pattern sandwiched between two adjacent signal conductor patterns 330 may be divided into two parts. For example, in Figure 5 the ground conductor pattern 540c sandwiched between the signal conductor patterns 330b and 330c may be formed as two ground conductor patterns divided between, for example, the connection part ranges 550b and 550c.

[0223] In addition, in Figure 8 , Figure 9 in the relay substrates 418 and 518 of the fourth and fifth modified examples shown, two cutout portions are provided in one ground conductor pattern (for example, two cutout portions 860a and 860b are provided in the ground conductor pattern 840b), but it is not limited thereto. For example, the cutout portions 860a and 860b may be formed by removing the part of the relay substrate 818 between them to form one cutout portion including the cutout portions 860a and 860b.

[0224] In addition, for example, in the above-described relay substrates 118, 518, 618, 718, 818, 918, 1018, 1118, 1218, 1318, the signal conductor pattern 330 is depicted in a straight line from the signal input side 318a toward the signal output side 318b, but it is not limited thereto. The signal conductor pattern 330 may be formed in the same manner as the prior art, for example, and may include a curved portion or portions having different widths and may be formed in different shapes, respectively.

[0225] In addition, in the above-described embodiment, with respect to at least two signal conductor patterns 330, the portions of the two ground conductor patterns sandwiching them within the corresponding connection part ranges are formed in an asymmetrical shape with respect to the corresponding signal conductor pattern, or are formed to have different impedances with respect to the ground wire components, but it is not limited thereto.

[0226] When it is sufficient to reduce only the leakage microwaves generated from a specific signal conductor pattern due to, for example, the respective shapes of the signal conductor patterns 330 formed in the relay substrate 118 or the like, the characteristics of the optical modulation element 102, etc., only for that specific signal conductor pattern, the portion within the corresponding connection part range may be formed in an asymmetrical shape with respect to the corresponding signal conductor pattern, or may have different impedances with respect to the ground wire components.

[0227] In addition, in the relay substrates 1018, 1118, and 1218 of the sixth, seventh, and eighth modified examples described above, the ground conductor pattern sandwiching the signal conductor pattern makes the impedance of the portion within the corresponding connection portion range different from that of the ground wire component by varying the number or diameter of the via holes provided in the portion within the corresponding connection portion range. However, the present invention is not limited thereto.

[0228] The ground conductor pattern sandwiching the signal conductor pattern only needs to have a different impedance from that of the ground wire component in the portion within the corresponding connection portion range, and the via holes can be provided in any different form. For example, the ground conductor pattern sandwiching the signal conductor pattern can be configured such that the density of the via holes provided in the portion within the corresponding connection portion range is different. Here, the density of the via holes can be represented by the number of via holes provided per unit area or the area of the via holes provided per unit area. This is because the larger the number or area of the via holes, the lower the impedance of the backplane ground conductor as a ground wire component.

[0229] In addition, in the above-described embodiment, the optical modulation element 102 is a DP-QPSK modulator formed using an LN substrate. However, the present invention is not limited thereto. For example, the optical modulation element 102 can be any optical modulation element formed using a semiconductor substrate.

[0230] As described above, the optical modulator 100 of the above-described embodiment includes: an optical modulation element 102 having a plurality of signal electrodes 112; and a plurality of signal input terminals 124 for inputting an electrical signal applied to each signal electrode 112. Further, the optical modulator 100 includes: an intermediate substrate 518 formed with a plurality of signal conductor patterns 330, a plurality of ground conductor patterns 340, etc., the signal conductor pattern 330 electrically connecting the signal input terminal 124 and the signal electrode 112; and a housing 104 for housing the optical modulation element 102 and the intermediate substrate 118. In the optical modulator 100, for example, as shown in the description of the intermediate substrates 118 and 518, regarding at least one signal conductor pattern, for example, the signal conductor pattern 330b, in a connection portion range 550b including a signal connection portion where the signal conductor pattern 330b is connected to the signal input terminal 124b, the top view shapes of two ground conductor patterns 340b and 540c sandwiching the signal conductor pattern 330b on the intermediate substrate 518 are asymmetric with respect to the signal conductor pattern 330b. Here, the connection portion range 550b is a range having a rectangular top view: centered on the signal conductor pattern 330b as the at least one signal conductor pattern, having a width w22 equal to a distance (for example, a distance p1 to the signal conductor pattern 330a) to the nearest adjacent signal conductor pattern, and having a height d22 equal to a distance from a signal input side 318a to a distal end of the signal connection portion, the signal input side 318a being a side of the intermediate substrate 518 on the side where the at least one signal conductor pattern 330b is connected to the signal input terminal 124b.

[0231] According to this structure, for example, it is possible to deflect the propagation direction of the spatial leakage microwave generated from the connection portion range 550b and propagating in space, suppress crosstalk from the signal conductor pattern 330b to at least one adjacent signal conductor pattern (for example, the signal conductor pattern 330a), and achieve good optical modulation characteristics.

[0232] Further, as shown in an example in the intermediate substrates 118 and 518, the optical modulator 100 may be configured such that, for example, in a connection portion range 450a, distances g11 and g12 from respective edges opposite to the signal conductor pattern 330a to an opposite edge of the signal conductor pattern 330a of two ground conductor patterns 340a and 340b sandwiching the signal conductor pattern 330a are different from each other.

[0233] According to this structure, without increasing the size of the intermediate substrate 118 or the like, for example, it is possible to deflect the propagation direction of the spatial leakage microwave generated from the connection portion range 450a and propagating in space, suppress crosstalk from the signal conductor pattern 330a to the adjacent signal conductor pattern 330b, and achieve good optical modulation characteristics.

[0234] In addition, as shown in an example in the relay substrate 618, the optical modulator 100 may be configured such that, for example, the widths Wg11 and Wg12 measured in a direction orthogonal to the extending direction of the signal conductor pattern 330a of the portions formed in the connection portion range 450a of the two ground conductor patterns 640a and 340b sandwiching the signal conductor pattern 330a are different from each other.

[0235] According to this structure, without increasing the size of the relay substrate 618, for example, by deflecting the propagation direction of the spatial leakage microwave generated from the connection portion range 450a and propagating in space, crosstalk from the signal conductor pattern 330a to the adjacent signal conductor pattern 330b can be suppressed, and good optical modulation characteristics can be achieved.

[0236] In addition, as shown in an example in the relay substrate 718, the optical modulator 100 may be configured such that, for example, one of the two ground conductor patterns 740a and 340b sandwiching the signal conductor pattern 330a, for example, the ground conductor pattern 740a does not include a portion formed within the connection portion range 450a.

[0237] According to this structure, without increasing the size of the relay substrate 718, for example, by deflecting the propagation direction of the spatial leakage microwave generated from the connection portion range 450a and propagating in space, crosstalk from the signal conductor pattern 330a to the adjacent signal conductor pattern 330b can be suppressed, and good optical modulation characteristics can be achieved.

[0238] In addition, as shown in an example in the relay substrate 818, the optical modulator 100 may be configured such that, for example, a cutout portion 860a is provided in a portion where one of the two ground conductor patterns 840a and 840b sandwiching the signal conductor pattern 330a is formed in the connection portion range 450a, and the cutout portion 860a extends from the signal input side 318a and penetrates the thickness direction of the relay substrate 818.

[0239] According to this structure, it is possible to block the propagation of, for example, the substrate leakage microwave generated from the connection portion range 450a and propagating within the relay substrate 818, suppress crosstalk from the signal conductor pattern 330a to the adjacent signal conductor pattern 330b, and achieve good optical modulation characteristics.

[0240] In addition, as shown in an example by the relay substrates 1018, 1118, 1218, etc. for the optical modulator 100, for example, in the portions of the ground conductor patterns 1040a, 1040b, etc. sandwiching the signal conductor pattern 330a within the connection portion range 450a, the presence or absence of via holes connected to the backside ground conductor provided on the backside of the relay substrates 1018, etc., or the number or density of the via holes are different from each other.

[0241] According to this structure, the characteristic impedance of the signal conductor pattern 300 hardly changes by providing via holes in the ground conductor pattern 1040 or the like sandwiching the signal conductor pattern 300. Therefore, the pattern design of the ground conductor pattern 1040 in the connection portion range 450a or the like becomes easy. That is, crosstalk between adjacent signal conductor patterns 330 leaking microwave via space can be suppressed without complicating the design, and good optical modulation characteristics can be achieved.

[0242] In addition, the optical modulator 100 can use an optical modulation element 102 that performs, for example, DP-QPSK modulation and is configured to generate two modulated lights respectively modulated by a pair of electrical signals. The relay substrate 118 or the like propagates the pair of electrical signals through a pair of adjacent signal conductor patterns, for example, signal conductor patterns 330a and 330b.

[0243] According to this structure, crosstalk between a pair of two high-frequency electrical signals propagated through adjacent signal conductor patterns 300 can be effectively reduced, and good optical modulation characteristics can be achieved.

[0244] In addition, the optical transmission device of the second embodiment described above includes an optical modulator 100 using any one of the relay substrates shown in the first embodiment or a modified example thereof, a modulation signal generation unit 2106 or the like as an electronic circuit that outputs an electrical signal for causing the optical modulator 100 to perform a modulation operation. According to this structure, propagation of leaked microwave, which becomes significant, for example, as the transmission rate increases, can be suppressed, crosstalk between a plurality of high-frequency electrical signals for driving the optical modulation element 102 can be effectively reduced, and stable and good transmission characteristics can be achieved.

[0245] Reference Numeral Explanation

[0246] 100, 2102, 2200... optical modulators, 102, 2202... optical modulation elements, 104, 1604, 2204... housings, 108, 2208... input optical fibers, 110, 2210... output optical fibers, 112, 112a, 112b, 112c, 112d, 2212, 2212a, 2212b, 2212c, 2212d... signal electrodes, 114a, 2214a... outer casings, 114b, 2214b... covers, 116, 116a, 116b, 116c, 116d, 2216, 2216a, 2216b, 2216c, 2216d... electrical connectors, 118, 518, 618, 718, 818, 918, 1018, 1118, 1218, 1318, 2218... relay substrates, 120, 2220... terminators, 122, 122a, 122b, 122c, 122d, 122e, 2222a, 2222b, 2222c, 2222d, 2222e... ground electrodes, 124, 124a, 124b, 124c, 124d, 2224, 2224a, 2224b, 2224c, 2224d... signal input terminals, 126a, 126b... output optical waveguides, 318a... signal input side, 318b... signal output side, 318c, 318d... side edges, 326... conductor leads, 330, 330a, 330b, 330c, 330d, 2230, 2230a, 2230b, 2230c, 2230d... signal conductor patterns, 340, 340a, 340b, 340c, 340d, 340e, 540c, 640a, 640c, 640e, 740a, 740c, 740e, 840a, 840b, 840c, 840d, 840e, 1040a, 1040b, 1040c, 1040d, 1040e, 1140a, 1140c, 1140e, 1240a, 1240c, 1240e, 1340c, 1340d, 2240a, 2240b, 2240c, 2240d, 2240e... ground conductor patterns, 450a, 550b, 550c, 450d... connection part ranges, 860a, 860b, 860c, 860d... cutout parts, 1062, 1162... via holes, 2100... optical transmission device, 2104... light source, 2106... modulation signal generation unit, 2108... modulation data generation unit, 2290... spherical wave.

Claims

1. An optical modulator, comprising: An optical modulation element having a plurality of signal electrodes; A plurality of signal input terminals for inputting an electrical signal applied to each of the signal electrodes; The relay substrate is formed with a plurality of signal conductor patterns and a plurality of ground conductor patterns, and the signal conductor patterns electrically connect the signal input terminals to the signal electrodes; and a housing that houses the optical modulation element and the relay substrate, wherein with respect to at least one of the signal conductor patterns, in a connection portion range that is rectangular in a top view and includes a signal connection portion where the signal conductor pattern is connected to the signal input terminal, the top view shapes of the two ground conductor patterns sandwiching the signal conductor pattern on the relay substrate are formed to be asymmetric with respect to each other with respect to at least one of the signal conductor patterns, the connection portion range is defined as a rectangle that extends in the plane of the relay substrate with a part of a signal input side as one side in the width direction, and the signal input side is the side of the relay substrate where at least one of the signal conductor patterns is connected to the signal input terminal, the connection portion range is centered in the width direction on at least one of the signal conductor patterns, the width of the connection portion range is equal to the distance from at least one of the signal conductor patterns to the nearest adjacent signal conductor pattern, the height of the connection portion range is equal to the distance from the signal input side to the end of the signal connection portion that is the farthest from the signal input side, each of the signal conductor patterns extends linearly from the signal input side toward the signal output side in a top view, and the signal output side is the side of the relay substrate where the signal conductor pattern is connected to the signal electrode.

2. The optical modulator according to claim 1, wherein, The two ground conductor patterns are formed such that the distances from the respective edges of the two ground conductor patterns to the opposite edges of at least one of the signal conductor patterns have different portions within the connection portion range.

3. The optical modulator according to claim 1, wherein, The widths of the portions of the two ground conductor patterns formed within the connection portion range, measured in a direction orthogonal to the extending direction of at least one of the signal conductor patterns, are different from each other.

4. The optical modulator according to claim 1, wherein, One of the two ground conductor patterns does not include a portion formed within the connection portion range.

5. The optical modulator according to claim 1, wherein, The relay substrate is provided with a cutout portion in a portion where one of the two ground conductor patterns is formed within the connection portion range, and the cutout portion extends from the signal input side and penetrates the thickness direction of the relay substrate.

6. The optical modulator according to claim 1, wherein, The optical modulation element is configured to generate two modulated light beams respectively modulated by a pair of the electrical signals, The relay substrate is configured to propagate the pair of electrical signals through a pair of adjacent signal conductor patterns.

7. An optical modulator, comprising: An optical modulation element having a plurality of signal electrodes; A plurality of signal input terminals for inputting an electrical signal applied to each of the signal electrodes; The relay substrate is formed with a plurality of signal conductor patterns and a plurality of ground conductor patterns, and the signal conductor patterns electrically connect the signal input terminals to the signal electrodes; and a housing that houses the optical modulation element and the relay substrate, wherein the relay substrate is formed with a back surface ground conductor on a surface opposite to the surface where the ground conductor pattern is formed. Regarding at least one of the signal conductor patterns, within a connection portion range including a signal connection portion where the signal conductor pattern is connected to the signal input terminal, two of the ground conductor patterns sandwiching the signal conductor pattern on the relay substrate are formed asymmetrically by the number or diameter of the formed vias being different from each other. The connection portion range is defined as a rectangle that extends in the plane of the relay substrate with a part of the signal input side as one side in the width direction, and the signal input side is the side of the relay substrate where at least one of the signal conductor patterns is connected to the signal input terminal. The connection portion range has at least one of the signal conductor patterns as the center in the width direction. The width of the connection portion range is equal to the distance from at least one of the signal conductor patterns to the nearest adjacent signal conductor pattern. The height of the connection portion range is equal to the distance from the signal input side to the farthest end portion in the signal connection portion from the signal input side.

8. The optical modulator according to claim 7, wherein, The light modulation element is configured to generate two modulated light beams respectively modulated by a pair of the electrical signals. The relay substrate is configured to propagate the pair of electrical signals through a pair of adjacent signal conductor patterns.

9. An optical transmission device, wherein, Comprising: The optical modulator according to any one of claims 1 to 8; and An electronic circuit that outputs an electrical signal for causing the optical modulator to perform a modulation operation.

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