Optical modulator and optical transmission device using the same

Abstract

The present invention provides an optical modulator and an optical transmitting device using the optical modulator. In an optical modulator having a relay substrate, the increase in crosstalk between signal conductor patterns on the relay substrate, which is associated with an increase in transmission rate, is effectively suppressed, thereby achieving good optical modulation characteristics. The optical modulator comprises: an optical modulation element having a plurality of signal electrodes; a plurality of signal input terminals for inputting electrical signals to the signal electrodes; a relay substrate having a plurality of signal conductor patterns and a plurality of ground conductor patterns for electrically connecting the respective signal input terminals to the respective signal electrodes; and a housing for accommodating the optical modulation element and the relay substrate, wherein at least one ground conductor pattern formed between adjacent signal conductor patterns on the relay substrate has at least one groove extending from the signal input terminal to the signal input side of the signal conductor pattern, the groove being formed so that the length extending from the signal input side is longer than the length of the signal input terminal extending on the signal conductor pattern.

Description

Technical Field

[0001] The present invention relates to an optical modulator including a relay substrate for relaying propagation of an electric signal between a signal input terminal and an electrode of an optical modulator, and an optical transmission device using the optical modulator. Background Art

[0002] High-speed and high-capacity optical fiber communication systems often use optical modulators incorporating waveguide-type optical modulation elements. Among these, optical modulators using LiNbO3 (hereinafter referred to as LN), which exhibits an electro-optical effect, as substrates are widely used due to their low optical loss and ability to achieve broadband optical modulation characteristics.

[0003] This optical modulator, using an LN substrate, is equipped with a Mach-Zehnder optical waveguide and signal electrodes for applying a high-frequency electrical signal as a modulation signal to the optical waveguide. Furthermore, these signal electrodes are connected to pins or connectors serving as signal input terminals on the housing of the optical modulator, via a relay substrate located within the housing. These signal input terminals, i.e., the pins or connectors, are connected to a circuit substrate equipped with the electronic circuitry that causes the optical modulator to perform modulation operations. Consequently, the electrical signals output from this electronic circuitry are applied to the signal electrodes of the optical modulator via the relay substrate.

[0004] The modulation method in the optical fiber communication system has been influenced by the trend of increasing transmission capacity in recent years. Multi-value modulation such as QPSK (Quadrature Phase Shift Keying) or DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying), or transmission standards that incorporate polarization multiplexing into multi-value 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 that performs QPSK modulation (QPSK optical modulator) or DP-QPSK modulation (DP-QPSK optical modulator) includes multiple Mach-Zehnder optical waveguides in a nested structure, known as a nested structure. Each of these Mach-Zehnder optical waveguides includes at least one signal electrode. Therefore, these optical modulators include multiple signal electrodes, and the high-frequency electrical signals multiplexed onto these signal electrodes cooperate to perform the DP-QPSK modulation described above.

[0006] Furthermore, in optical modulators that coordinate the high-frequency electrical signals supplied to multiple signal electrodes, all high-frequency electrical signals must be input to the signal electrodes of the optical modulator element without being affected by noise or other factors. However, the demand for miniaturization of optical modulators remains constant, and the miniaturization of relay boards has progressed along with the miniaturization of optical modulator housings. As a result, multiple different high-frequency signals are closely concentrated and propagated through the narrow relay board, creating increasingly difficult to ignore electrical crosstalk between the high-frequency signal lines on the relay board.

[0007] Furthermore, commercial DP-QPSK modulators are currently mostly used at a transmission rate of 100 Gb / s, but development is underway to increase this rate to 400 Gb / s. Going forward, as the transmission rate increases, crosstalk between high-frequency signal lines in the relay boards mentioned above will become a more serious issue.

[0008] One possible method for suppressing this crosstalk is to increase the distance between adjacent high-frequency signal lines. However, this approach violates the aforementioned requirement for miniaturization of optical modulators and is therefore difficult to implement. Therefore, methods such as providing vias in the ground electrodes between the high-frequency signal lines to connect them to the ground layer on the back of the relay substrate are being used to reinforce the ground electrodes and improve the shielding effect between the high-frequency signal lines (see, for example, Patent Document 1).

[0009] However, in a DP-QPSK modulator with a high transmission rate of 400 Gb / s or higher, the problem of insufficient crosstalk suppression arises if only the above-mentioned guide holes are used.

[0010] According to the experiments carefully conducted by the inventors of the present invention, in the above-mentioned high-transmission-rate DP-QPSK modulator, it can be seen that the above-mentioned crosstalk is not only the direct exchange of signal energy between close high-frequency signal lines, but also the influence of leakage of the high-frequency signal of the input part (signal input part) accompanied by the conversion of the signal propagation mode (hereinafter referred to as propagation mode conversion) at the input part of the relay substrate, which is mainly the high-frequency signal, cannot be ignored.

[0011] Specifically, connectors or pins are typically used to input high-frequency signals to optical modulators, so high-frequency signals propagate in a coaxial mode before being input to the relay substrate. In contrast, high-frequency signal lines installed on optical modulator substrates or relay substrates are typically coplanar lines, and the propagation mode in these lines is the coplanar wave (CPW) mode.

[0012] Therefore, a propagation mode conversion (i.e., heterogeneous mode conversion) occurs from the coaxial mode to the CPW mode in the signal input section of the relay board. Part of the high-frequency signal energy propagating in the coaxial mode is released into the relay board or into the air in a radial mode. Furthermore, this part of the high-frequency signal energy released into the relay board or into the air contributes to the generation of the aforementioned crosstalk.

[0013]

Prior technical literature

[0014] [Patent Literature]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-156947 Summary of the Invention

[0016] [Problems to be solved by the invention]

[0017] Based on the above background, in an optical modulator having a relay substrate that electrically connects each signal electrode of an optical modulator element to each signal input terminal, it is required to effectively suppress the increase in crosstalk between signal conductor patterns on the relay substrate that accompanies the increase in transmission rate, so as to achieve good optical modulation characteristics.

[0018]

Solutions to Solve the Problem

[0019] One embodiment of the present invention relates to an optical modulator comprising: an optical modulator 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 for electrically connecting each of the signal input terminals to each of the signal electrodes; and a housing for accommodating the optical modulator element and the relay substrate, wherein, on a signal input side of the relay substrate, the signal input terminal is configured to extend from the signal input side to the signal conductor pattern, the signal input side being a side through which the electrical signal from the signal input terminal is input to the signal conductor pattern, and in the relay substrate, on a surface on which the signal conductor pattern is formed, at least one of the ground conductor patterns formed between adjacent signal conductor patterns has at least one groove extending from the signal input side, the groove being formed so that a length extending from the signal input side is longer than a length extending from the signal input terminal from the signal input side.

[0020] According to another aspect of the present invention, the groove extends to a signal output side of the relay substrate, the signal output side being a side through which an electrical signal is output from the signal conductor pattern to the signal electrode of the light modulator.

[0021] According to another aspect of the present invention, the groove is formed so that a depth of an end portion of the groove at the signal input side measured from the surface is deeper than a depth of the groove at the other end portion of the groove measured from the surface.

[0022] According to another aspect of the present invention, the groove is formed so that the depth measured from the surface becomes deeper in a stepwise or continuous manner as it approaches the signal input side from the other end of the groove.

[0023] According to another embodiment of the present invention, the groove is formed on the signal input side to the back side of the relay substrate opposite to the surface, or is formed on the back side of the relay substrate opposite to the surface within a range of a predetermined distance from the signal input side.

[0024] According to another aspect of the present invention, a metal film is formed on the inner side surface of the groove, or on the inner side surface and bottom surface of the groove.

[0025] According to another embodiment of the present invention, a metal film is formed on the inner side surface and bottom surface of the groove, a grounding conductor is formed on the back surface of the relay substrate opposite to the surface, and a guide hole is formed on the bottom surface of the groove to connect the metal film on the bottom surface and the grounding conductor on the back surface.

[0026] According to another embodiment of the present invention, the groove does not extend to the signal output side of the relay substrate, and the entire groove is formed to pass through the back side of the relay substrate opposite to the surface, and the signal output side is the side where the electrical signal is output from the signal conductor pattern to the signal electrode of the optical modulator.

[0027] According to another aspect of the present invention, a metal film is formed on the inner side surface of the groove.

[0028] According to another aspect of the present invention, the groove is formed so that a length extending from the signal input side is longer than a width measured in a direction perpendicular to the extending direction.

[0029] Another aspect of the present invention relates to an optical transmission device including: any one of the above-described optical modulators; and an electronic circuit that outputs an electrical signal for causing the optical modulator to perform a modulation operation.

[0030] Effects of the invention

[0031] According to the present invention, in an optical modulator including a relay substrate, an increase in crosstalk between signal conductor patterns on the relay substrate accompanying an increase in transmission rate can be effectively suppressed, thereby achieving excellent optical modulation characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a top view of the optical modulator according to the first embodiment of the present invention.

[0033] Figure 2 yes Figure 1 A side view of the light modulator is shown.

[0034] Figure 3 yes Figure 1 Detailed view of section A of the light modulator shown.

[0035] Figure 4 yes Figure 1 The illustrated diagram is a perspective view of the surface of a relay substrate used in the optical modulator, viewed from the side where signal input terminals are arranged.

[0036] Figure 5 This is a diagram showing a first modified example of the relay substrate used in the optical modulator according to the first embodiment.

[0037] Figure 6 This is a diagram showing a second modified example of the relay substrate used in the optical modulator of the first embodiment.

[0038] Figure 7 This is a diagram showing a third modified example of the relay substrate used in the optical modulator of the first embodiment.

[0039] Figure 8 This is a diagram showing a fourth modified example of the relay substrate used in the optical modulator of the first embodiment.

[0040] Figure 9 This is a diagram showing a fifth modified example of the relay substrate used in the optical modulator of the first embodiment.

[0041] Figure 10 This is a diagram showing the configuration of an optical transmission device according to a second embodiment of the present invention.

[0042] Description of labels

[0043] 100, 1002…optical modulator, 102…optical modulation element, 104…housing, 108…input optical fiber, 110…output optical fiber, 112a, 112b, 112c, 112d…signal electrode, 114a…housing, 114b…cover, 116a, 116b, 116c, 116d…electrical connector, 118, 518, 618, 718, 818, 918…relay Substrate, 120…terminator, 122a, 122b, 122c, 122d…ground electrode, 124a, 124b, 124c, 124d…signal input terminal, 126…conductor lead, 330a, 330b, 330c, 330d, 930a, 930b, 930c, 930d…signal conductor pattern, 340a, 340b, 340c, 340d, 340d 0e, 940a, 940b, 940c, 940d, 940e...ground conductor pattern, 350a, 350b, 350c, 350d, 350e, 550a, 550b, 550c, 550d, 550e, 650a, 650b, 650c, 650d, 650e, 750a, 750b, 750c, 750d, 750e, 850a, 850b 50b, 850c, 850d, 850e, 950a, 950b, 950c, 950d, 950e…slots, 418a…signal input side, 418b…input side surface, 418c…signal output side, 418d…output side surface, 418e…surface, 418f…back surface, 418g…right side surface, 418h…left side surface, 840…grounding conductor, 860…guide hole. DETAILED DESCRIPTION

[0044] The following embodiments and their variations address the aforementioned challenges without compromising the miniaturization requirements of optical modulators, at a cost comparable to or lower than conventional methods, while also taking into account ease of manufacture. Furthermore, they suppress the increase in crosstalk between adjacent signal conductor patterns on a relay substrate that accompanies increased transmission rates. Specifically, they simultaneously suppress the propagation of two radiated microwaves within the relay substrate: a radiated mode generated along the signal conductor pattern as high frequencies propagate through the pattern (hereinafter referred to as a propagating radiated microwave), and a radiated mode generated by heterogeneous mode conversion at the connection point between a signal input terminal and the signal conductor pattern (hereinafter referred to as a connection point radiated microwave). This suppresses the occurrence of high-frequency energy transfer between adjacent signal conductor patterns.

[0045] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0046] [First embodiment]

[0047] First, a first embodiment of the present invention will be described. Figure 1 and Figure 2 1 is a diagram showing the structure of the optical modulator 100 according to the first embodiment of the present invention. Figure 1 、 Figure 2 They are respectively a top view and a side view of the optical modulator 100 .

[0048] The optical modulator 100 includes an optical modulator 102 , a housing 104 that houses the optical modulator 102 , an input optical fiber 108 for allowing light to enter the optical modulator 102 , and an output optical fiber 110 that guides light output from the optical modulator 102 to the outside of the housing 104 .

[0049] The optical modulator 102 is a DP-QPSK modulator that performs optical modulation at, for example, 400 Gb / s, and includes, for example, four Mach-Zehnder optical waveguides disposed on an LN substrate. The four Mach-Zehnder optical waveguides are provided with four signal electrodes 112a, 112b, 112c, and 112d that modulate the light waves propagating through the Mach-Zehnder optical waveguides. Furthermore, as is known in the art, ground electrodes 122a, 122b, 122c, 122d, and 122e are provided on the surface of the LN substrate of the optical modulator 102, for example, to form a coplanar waveguide (CPW) (see FIG. 1 ). Figure 3 .exist Figure 1 (not shown in the figure).

[0050] Specifically, the ground electrodes 122a, 122b, 122c, 122d, and 122e are arranged within the plane of the LN substrate so as to sandwich the signal electrodes 112a, 112b, 112c, and 112d, respectively, and together with the four signal electrodes 112a, 112b, 112c, and 112d, form a coplanar line having a specified characteristic impedance at a specified operating frequency.

[0051] Four high-frequency electrical signals (modulation signals) are input to the four signal electrodes 112a, 112b, 112c, and 112d, respectively. These high-frequency electrical signals cooperate to control the propagation of light waves in the four Mach-Zehnder optical waveguides, performing 400 Gb / s DP-QPSK modulation as a whole.

[0052] The two lights output from the light modulator 102 are polarization-combined by, for example, a lens system (not shown), and are guided to the outside of the housing 104 via the output optical fiber 110 .

[0053] The housing 104 is composed of a shell 114a and a cover 114b that fix the light modulating element 102. Figure 1In the figure, only a portion of cover 114b is shown on the left. However, in reality, cover 114b is arranged to cover the entire box-shaped housing 114a, thereby hermetically sealing the interior of housing 104. Housing 114a is made of metal or, for example, gold-plated ceramic, and functions electrically as a conductor. Housing 104 is typically provided with multiple pins for DC control, etc., but these are omitted in this figure.

[0054] The housing 114a is provided with electrical connectors 116a, 116b, 116c, and 116d having signal input terminals 124a, 124b, 124c, and 124d. The signal input terminals 124a, 124b, 124c, and 124d input high-frequency electrical signals to be applied to the signal electrodes 112a, 112b, 112c, and 112d of the optical modulator 102. Furthermore, a relay substrate 118 is housed within the housing 104. As described later, on the relay substrate 118, signal conductor patterns 330a, 330b, 330c, 330d are formed to electrically connect the respective signal input terminals 124a, 124b, 124c, 124d to the respective ends of the signal electrodes 112a, 112b, 112c, 112d of the optical modulator 102; and ground conductor patterns 340a, 340b, 340c, 340d, 340e.

[0055] The other ends of the signal electrodes 112a, 112b, 112c, and 112d of the optical modulator 102 are terminated by a terminator 120 having a predetermined impedance. As a result, electrical signals input to one end of each of the signal electrodes 112a, 112b, 112c, and 112d propagate through the signal electrodes 112a, 112b, 112c, and 112d as traveling waves.

[0056] Electrical connectors 116a, 116b, 116c, and 116d are each a socket of a push-on coaxial connector, for example. The cylindrical grounding conductors of these electrical connectors 116a, 116b, 116c, and 116d are electrically connected to and fixed to housing 114a. Therefore, housing 114a corresponds to a structure connected to ground potential. Furthermore, signal input terminals 124a, 124b, 124c, and 124d are each composed of a central conductor (core wire) extending along the centerline of the cylindrical grounding conductor within each connector socket of electrical connectors 116a, 116b, 116c, and 116d.

[0057] Figure 3 yes Figure 1 The detailed diagram of the portion A in FIG. 1 is a diagram showing the structure of the relay substrate 118 and its surroundings. Figure 4 The surface 418e of the relay substrate 118 alone ( Figure 1 and Figure 3 A stereoscopic view of the device 100 as viewed from the side where the signal input terminal 124a, etc. is configured (see the side shown in the figure).

[0058] Signal conductor patterns 330 a , 330 b , 330 c , and 330 d and ground conductor patterns 340 a , 340 b , 340 c , 340 d , and 340 e are provided on the front surface 418 e of the relay substrate 118 .

[0059] The ground conductor patterns 340a, 340b, 340c, 340d, and 340e are arranged so as to sandwich the signal conductor patterns 330a, 330b, 330c, and 330d within the surface 418e of the relay substrate 118. Thus, the signal conductor patterns 330a, 330b, 330c, and 330d, together with the ground conductor patterns 340a, 340b, 340c, 340d, and 340e, respectively, form a coplanar line.

[0060] like Figure 3 As shown, the signal electrodes 112a, 112b, 112c, and 112d of the optical modulator 102 are electrically connected to one end of the signal conductor patterns 330a, 330b, 330c, and 330d of the relay substrate 118, respectively, by wire bonding using, for example, conductor wires 126. The conductor wires 126 can be, for example, gold wires.

[0061] Furthermore, in the optical modulator 102, the ground electrodes 122a, 122b, 122c, 122d, and 122e, which constitute a coplanar line along with the signal electrodes 112a, 112b, 112c, and 112d, are electrically connected to one end of the ground conductor patterns 340a, 340b, 340c, 340d, and 340e of the relay substrate 118, respectively, by wire bonding using, for example, a conductor wire 126, as described above. The wire bonding using the conductor wire 126 described above is merely an example and is not limiting. Alternatively, ribbon bonding using, for example, a conductor ribbon such as a gold ribbon may be used instead of wire bonding using the conductor wire 126.

[0062] like Figure 3 、 Figure 4 As shown, the signal input terminals 124a, 124b, 124c, and 124d of the electrical connectors 116a, 116b, 116c, and 116d disposed on the housing 114a of the casing 104 are fixed and electrically connected to the other ends of the signal conductor patterns 330a, 330b, 330c, and 330d of the relay substrate 118, respectively. The above-mentioned fixing and electrical connection can be performed using, for example, solder, brazing material, or a conductive adhesive.

[0063] Here, in the relay substrate 118, the side connecting the signal conductor patterns 330a, 330b, 330c, 330d and the signal input terminals 124a, 124b, 124c, 124d, respectively, is referred to as the signal input side 418a, and the side surface of the relay substrate 118 with the signal input side 418a as one side is referred to as the input side side surface 418b. Furthermore, in the relay substrate 118, the side opposite to the signal input side 418a, that is, the side connecting the signal conductor patterns 330a, 330b, 330c, 330d and the signal electrodes 112a, 112b, 112c, 112d of the optical modulator 102, is referred to as the signal output side 418c, and the side surface of the relay substrate 118 with the signal output side 418c as one side is referred to as the output side side surface 418d. Furthermore, in Figure 3 In the example, the right side surface of the relay substrate 118 perpendicular to the input side surface 418b is referred to as the right side surface 418g, and the left side surface is referred to as the left side surface 418h. The surface of the relay substrate 118 opposite the front surface 418e is referred to as the back surface 418f.

[0064] On the signal conductor patterns 330a, 330b, 330c, and 330d of the relay substrate 118, as shown in FIG. Figure 3 As shown, the signal input terminals 124a, 124b, 124c, and 124d of the electrical connectors 116a, 116b, 116c, and 116d are arranged to extend a predetermined length L1 from the signal input side 418a. Here, the portions of the signal input side 418a and its vicinity where the signal conductor patterns 330a, 330b, 330c, and 330d connect to the signal input terminals 124a, 124b, 124c, and 124d are referred to as input connection points.

[0065] In particular, the relay substrate 118 of the optical modulator 100 of this embodiment has grooves 350a, 350b, 350c, 350d, and 350e, respectively, extending from the signal input side 418a (or input-side side 418b) in the ground conductor patterns 340a, 340b, 340c, 340d, and 340e on the surface 418e where the signal conductor patterns 330a, 330b, 330c, and 330d are formed. Furthermore, the grooves 350a, 350b, 350c, 350d, and 350e have a predetermined depth from the surface 418e of the relay substrate 118 itself (without penetrating the relay substrate 118). In this embodiment, as an example, the grooves 350a, 350b, 350c, 350d, and 350e are configured to have the same dimensions.

[0066] Hereinafter, the signal electrodes 112a, 112b, 112c, and 112d of the optical modulator 102 are collectively referred to as signal electrodes 112, and the ground electrodes 122a, 122b, 122c, 122d, and 122e are collectively referred to as ground electrodes 122. Furthermore, the electrical connectors 116a, 116b, 116c, and 116d are collectively referred to as electrical connectors 116, and the signal input terminals 124a, 124b, 124c, and 124d are collectively referred to as signal input terminals 124. Furthermore, the signal conductor patterns 330a, 330b, 330c, and 330d of the relay substrate 118 are collectively referred to as signal conductor pattern 330, and the ground conductor patterns 340a, 340b, 340c, 340d, and 340e are collectively referred to as ground conductor pattern 340. In addition, the grooves 350 a , 350 b , 350 c , 350 d , and 350 e are also collectively referred to as grooves 350 .

[0067] As described above, the four signal input terminals 124 serve as the center conductors of the four electrical connectors 116, which are coaxial connectors. Therefore, the propagation mode of the high-frequency electrical signals propagating through these signal input terminals 124 is a coaxial mode. Furthermore, as described above, the signal conductor patterns 330 on the relay substrate 118, together with the six ground conductor patterns 340, form coplanar lines, allowing the high-frequency electrical signals to propagate in a coplanar mode (CPW mode).

[0068] Therefore, a propagation mode conversion (heterogeneous mode conversion) from the coaxial mode to the CPW mode occurs at the input connection point where the signal conductor pattern 330 is connected to the signal input terminal 124. Consequently, connection point radiation microwaves are generated at each of the input connection points along with the heterogeneous mode conversion and propagate within the relay substrate 118.

[0069] Furthermore, when a high-frequency electrical signal propagates along the length of the signal conductor pattern 330 of the relay substrate 118, a propagating microwave is generated. The propagating microwave can propagate within the relay substrate 118. Furthermore, the propagating microwave is generated from various portions along the length of the signal conductor pattern 330. The generated microwave typically has a maximum intensity, for example, at the input connection point, and decreases as it moves away from the signal input side 418a.

[0070] The optical modulator 100 having the above-mentioned structure is provided with a groove 350 extending from the signal input edge 418a in the ground conductor pattern 340, so that the connection point radiated microwaves generated at the above-mentioned input connection point and the propagated radiated microwaves generated near the input connection point of the signal conductor pattern 330 are respectively prevented from propagating inside the relay substrate 118 by the air wall formed by the groove 350.

[0071] That is, in the optical modulator 100 , the presence of the groove 350 suppresses the transfer of high-frequency energy between the signal conductor patterns 330 that connect and propagate the radiated microwaves.

[0072] As a result, in the optical modulator 100, even when operating at a transmission rate of more than 400 Gb / s, the spacing between the signal conductor patterns 330 will not be increased (therefore, the size of the relay substrate 118 and the optical modulator 100 will not increase), and the crosstalk between the signal conductor patterns 330 will be effectively reduced at the same level or lower cost as before, thereby achieving good optical modulation characteristics.

[0073] Here, according to the knowledge of the inventors of the present invention, the size of the slot 350 is such that the length L1 of the signal input terminal 124 extending from the signal input side 418a on the signal conductor pattern 330 is defined as the length L1, the length L2 of the slot 350 extending from the signal input side 418a is defined as the length L2, and the width W measured in a direction perpendicular to the length direction is defined as the width W (refer to FIG. Figure 3 ), preferably having any of the following relationships. Here, the length L1 is the length of the signal input terminal 124 extending from the signal input side 418a on the signal conductor pattern 330 as described above. Hereinafter, the length L1 is referred to as the terminal extension length L1.

[0074] L2>L1 (1)

[0075] L2>W (2)

[0076] Furthermore, length L2 is the length of the slot 350 extending from the signal input side 418a along the slot 350. It should be noted that this does not refer to the distance between the signal input side 418a and the end of the slot 350 in a direction perpendicular to the signal input side 418a. For example, if the slot 350 is not straight but curved, this refers to the length measured along the curve (e.g., the length extending from the centerline of the slot 350 in the width direction). Furthermore, if the width W varies along the direction in which the slot 350 extends, it can be set to the average or maximum value of the widths of each portion.

[0077] Equation (1) indicates that the length L2 of the slot 350 extending from the signal input side 418a is longer than the terminal extension length L1 of the signal input terminal 124 extending from the signal input side 418a. Here, L2 > L1 is preferably because, at the input connection point, microwaves radiated from the connection point are generated over the range of the terminal extension length L1. Therefore, if the slot length L2 is shorter than the terminal extension length L1, the propagation suppression effect of the microwaves radiated from the connection point is reduced.

[0078] Furthermore, equation (2) indicates that the slot 350 is formed so that its length L2 extending from the signal input side 418a is longer than its width W measured in a direction perpendicular to the direction of extension. Here, L2 > W is preferably set because, if the length L2 of the slot 350 is shorter than its width W, microwaves propagating from the signal conductor pattern 330 near the signal input side 418a may not be adequately suppressed. Furthermore, if W > L2, the width of the slot 350 is unnecessarily increased, resulting in a decrease in the mechanical strength of the relay substrate 118.

[0079] In addition, Figure 3 In the embodiment, the terminal extension length L1 and the length L2 and width W of the slot 350 are shown using the signal input terminal 124a and the slot 350a as examples, but they can also be defined in the same way in the other slots 350b, 350c, 350d, and 350e. Moreover, in this embodiment, the five slots 350 are formed with the same size as each other, but this is not limited to this. In each slot 350, as long as the relationship of formula (1) or formula (2) is satisfied, the slots 350 can also be composed of different sizes. Moreover, the terminal extension length L1, the length L2 and width W of the slot 350, and the preferred conditions shown in formula (1) or formula (2) can also be defined and applied in the same way in the first to fifth modified examples described below.

[0080] Furthermore, if a metal film is formed on the inner surface of the groove 350 (if metallization is performed), the effect of suppressing the microwave radiation from the connection point and the propagation of the radiated microwave into the relay substrate 118 can be further enhanced. The metal film is preferably provided on at least two inner side surfaces of the groove 350 that face each other in the direction of the signal input side 418a. Furthermore, it is more preferable to also form a metal film on the bottom surface (the surface parallel to the surface 418e) and / or the end surface (the surface parallel to the input-side side surface 418b) of the groove 350.

[0081] Furthermore, in this embodiment, one groove 350 is provided in each of the five ground conductor patterns 340, but this is not limiting. To reduce crosstalk between adjacent signal input terminals 124 and / or between adjacent signal conductor patterns 330, at least one groove 350 is provided in the ground conductor pattern 340 formed between adjacent signal conductor patterns 330 (i.e., in this embodiment, the ground conductor patterns 340b, 340c, and 340d).

[0082] However, if grooves 350 are also formed in the ground conductor patterns 340a and 340e that are not sandwiched between adjacent signal conductor patterns 330, as in this embodiment, it is possible to reduce the propagation of microwave radiation and microwave propagation, for example, generated from the input connection points of the outermost signal conductor patterns 330a and 330d and reflected from and propagated to the right side 418g and left side 418h perpendicular to the input-side side surface 418b of the relay substrate 118. This can reduce, for example, the propagation of microwave radiation and microwave propagation, generated from and reflected from the connection points of the signal conductor patterns 330a and 330d, and the noise generated in the signal conductor patterns 330a and 330d due to these reflected microwaves.

[0083] In addition, in this embodiment, a single ground conductor pattern 340 is provided between each adjacent signal conductor pattern 330, but this is not limiting. Multiple ground conductor patterns 340 may be provided between adjacent signal conductor patterns 330. In this case, a groove similar to groove 350 may be formed in at least one ground conductor pattern 340 provided between adjacent signal conductor patterns 330. Alternatively, a groove similar to groove 350 may be provided in each of the multiple ground conductor patterns 340 provided between adjacent signal conductor patterns 330 that is adjacent to (closest to) each signal conductor pattern 330.

[0084] In this embodiment, the signal conductor patterns 330 are each formed as a straight line extending perpendicular to the signal input side 418a, as an example. However, the present invention is not limited thereto. The signal conductor patterns 330 may be formed as a straight line or a curved line that is not perpendicular to the signal input side 418a, depending on the spacing between the signal input terminals 124, the spacing between the signal electrodes 112 in the optical modulation element 102, or other electrical requirements.

[0085] In addition, Figure 3 In the figure, the pattern spacing between the signal conductor pattern 330 and the ground conductor pattern 340 is depicted as being substantially constant, but the present invention is not limited thereto. In accordance with conventional techniques, the pattern spacing may be different in the portion within the length L2 from the signal input side 418a where the slot 350 is formed, and in the portion other than the portion, in order to maintain the distributed impedance of the coplanar line formed by the signal conductor pattern 330 and the ground conductor pattern 340 within a predetermined range of values ​​within the operating frequency range of the optical modulator 102.

[0086] Next, a modification of the relay substrate 118 that can be used in the optical modulator 100 according to the first embodiment will be described.

[0087] <First Modification>

[0088] Figure 5 This is a diagram showing the structure of a relay substrate 518 according to a first modification. Figure 1 The optical modulator 100 shown in the figure can be used instead of the relay substrate 118. Figure 5 In, about Figure 4 The same components as the relay substrate 118 shown in FIG. Figure 4 The same reference numerals as in Figure 4 Description.

[0089] Figure 5 The relay substrate 518 shown has Figure 4 The relay substrate 118 shown in FIG. 1 has the same structure as the relay substrate 118 shown in FIG. 1 , but differs in that grooves 550a, 550b, 550c, 550d, and 550e are provided instead of grooves 350a, 350b, 350c, 350d, and 350e. Grooves 550a, 550b, 550c, 550d, and 550e have the same structure as grooves 350a, 350b, 350c, 350d, and 350e, but differ in that, instead of extending to the signal output edge 418c of the relay substrate 518, where electrical signals are output from the signal conductor pattern 330 to the signal electrode 112 of the optical modulator 102, each groove 550a, 550b, 550c, 550d, and 550e is formed entirely from the front surface 418e of the relay substrate 518 to the back surface 418f opposite to the front surface 418e.

[0090] Furthermore, grooves 550a, 550b, 550c, 550d, and 550e differ from grooves 350a, 350b, 350c, 350d, and 350e in that a metal film is formed (metallized) on each of their three inner side surfaces. Hereinafter, grooves 550a, 550b, 550c, 550d, and 550e will also be collectively referred to as grooves 550.

[0091] The relay substrate 518 having the above-mentioned structure is formed such that the grooves 550 extending from the signal input side 418a on the surface 418e of the relay substrate 518 are formed so as to penetrate the entirety of the grooves 550 to the back side 418f of the relay substrate 518. Figure 4 Compared to the case of relay substrate 118 shown, the propagation of the two connection-point radiated microwaves and the propagation-radiated microwaves generated at and near the input connection point within relay substrate 518 can be further suppressed. Furthermore, in this variation, a metal film is formed on the inner side surfaces of all three slots 550, thereby further enhancing the effect of suppressing the propagation of the connection-point radiated microwaves and the propagation-radiated microwaves compared to relay substrate 118. Consequently, the effect of reducing the transfer of high-frequency energy between signal conductor patterns 330 via the connection-point radiated microwaves and the propagation-radiated microwaves is further enhanced than in the case of relay substrate 118.

[0092] <Second Modification>

[0093] Figure 6 This is a diagram showing the structure of a relay substrate 618 according to a second modification. Figure 1 The optical modulator 100 shown in the figure can be used instead of the relay substrate 118. Figure 6 In, about Figure 4 The same components as the relay substrate 118 shown in FIG. Figure 4 The same reference numerals as in Figure 4 Description.

[0094] Figure 6 The relay substrate 618 shown has Figure 4 The relay substrate 118 shown has the same structure as the one shown, but differs in that grooves 650a, 650b, 650c, 650d, and 650e are provided instead of grooves 350a, 350b, 350c, 350d, and 350e. Grooves 650a, 650b, 650c, 650d, and 650e have partially the same structure as grooves 350a, 350b, 350c, 350d, and 350e, but differ in that they extend from the signal input side 418a of the relay substrate 618 to the signal output side 418c of the relay substrate 618, where the electrical signal is output from the signal conductor pattern 330 to the signal electrode 112 of the optical modulator 102.

[0095] In other words, this modification is equivalent to Figure 3 In the interconnect substrate 118 shown in FIG. 1 , the length L2 of the groove 350 is set to be equal to the width Ws of the interconnect substrate 118 (see FIG. 1 ). Figure 3 ) have the same value (L2 = Ws). Hereinafter, the grooves 650a, 650b, 650c, 650d, and 650e are also collectively referred to as grooves 650. Note that this example is merely an example, and the groove 350 does not form a straight line (L2 = Ws).

[0096] In the relay substrate 618 having the above structure, the propagation of the radiated microwaves generated from the respective portions in the longitudinal direction of the signal conductor pattern 330 into the relay substrate 618 is continuously suppressed by the slot 650 from the signal input side 418a to the signal output side 418c. Figure 4 Compared with the relay substrate 118, the high frequency energy transfer between the signal conductor patterns 330 can be further reduced. Moreover, by forming the groove 650 in such a manner as to extend from the signal input side 418a to the signal output side 418c, the structure of the relay substrate 618 is simplified, so that Figure 4 The relay substrate 118 is easier to manufacture than the relay substrate 118 .

[0097] Furthermore, the aforementioned effect of reducing high-frequency energy transfer is enhanced by forming a metal film on two inner side surfaces of each slot 650 (i.e., two inner side surfaces that face each other in the direction of the signal input side 418a of the relay substrate 618). Furthermore, forming a metal film on the bottom surface of each slot 650 (the surface parallel to the surface 418e) also reduces the energy of microwaves that propagate within the relay substrate 618 and radiate into the air from the bottom surface, further reducing crosstalk between the signal conductor patterns 330.

[0098] Here, when a metal film is formed on the bottom surface of the groove 650, when the relay substrate 618 is secured to the housing 104 using solder or brazing material, the solder or brazing material exposed from the rear surface 418f of the relay substrate 618 may reach the metal film on the bottom surface of the groove 650 and, in some cases, follow the metal film on the inner surface of the groove 650 to reach the ground conductor pattern 340. Such solder or brazing material reaching the ground conductor pattern 340 may hinder the welding of the wires in the ground conductor pattern 340, for example, when bonding wires between the ground electrode 122 of the optical modulator 102 and the ground conductor pattern 340. Therefore, in the event that solder or brazing material reaches the ground conductor pattern 340 via the metal film of the groove 650, a metal film may not be formed on the bottom surface of the groove 650, for example, near the signal output side 418c.

[0099] Furthermore, in this variation, the slot 650 is provided at the signal output side 418c. Therefore, when the high-frequency signal confinement strength of the signal conductor pattern 330 is weak or there is a discrepancy in the propagation mode matching at the signal output point of the signal output side 418c (the connection point between the signal conductor pattern 330 and the signal electrode 112), the presence of the slot 650 may cause propagation mode disturbance (such as reflection or radiation of the high-frequency electrical signal) at the signal output point of the signal output side 418c. Therefore, this variation is particularly preferred for designs that can sufficiently ensure the high-frequency signal confinement strength of the signal conductor pattern 330, simplify the structure of the relay substrate 618 for ease of manufacture, and further reduce crosstalk between the signal conductor patterns 330.

[0100] <Third Modification>

[0101] Figure 7 This is a diagram showing the structure of a relay substrate 718 according to a third modified example. Figure 1 In the illustrated optical modulator 100 , it is used instead of the relay substrate 118 . Figure 7 Different from Figure 4 , the structure of the relay substrate 718 is shown using a three-sided view instead of a three-dimensional view. Figure 7 In, about Figure 4Elements identical to the relay substrate 118 shown are denoted by the same reference numerals as those in Figure 4 and the description thereof above is incorporated by reference. Figure 4 .

[0102] Figure 7 The relay substrate 718 shown has the same structure as the relay substrate 118 shown in Figure 4 , except that grooves 750a, 750b, 750c, 750d, and 750e are provided in place of grooves 350a, 350b, 350c, 350d, and 350e.

[0103] Grooves 750a, 750b, 750c, 750d, and 750e are different from groove 350 in that the depth of the end of the grooves 750a, 750b, 750c, 750d, and 750e measured from the surface 418e at the signal input side 418a is formed deeper than the depth of the grooves 750a, 750b, 750c, 750d, and 750e measured from the surface 418e at the other end of the grooves 750a, 750b, 750c, 750d, and 750e. Specifically, the bottom surface of the grooves 750a, 750b, 750c, 750d, and 750e is formed in a stepped shape and is formed to penetrate to the back surface 418f of the relay substrate 518 within a range of a predetermined distance L3 (e < b) from the signal input side 418a.

[0104] That is, the grooves 750a, 750b, 750c, 750d, and 750e are formed such that their depth becomes deeper in a stepped shape (two levels in this modification example) and reaches the back surface 418f at a predetermined distance L3 from the signal input side 418a. Conversely, the depth of the grooves 750a, 750b, 750c, 750d, and 750e becomes shallower in a stepped shape as it approaches the signal output side 418c. Hereinafter, the grooves 750a, 750b, 750c, 750d, and 750e are also collectively referred to as groove 750.

[0105] In the relay substrate 718 having the above structure, since the portion of the groove 750 within the range of the predetermined distance L3 from the signal input side 418a is provided to penetrate to the back surface 418f, the input connection point and the connection points in its vicinity can effectively suppress the radiation of microwaves and the propagation of the radiated microwaves into the relay substrate 718, similarly to the case of Modification Example 1.

[0106] Furthermore, in relay substrate 718, slots 750 are formed to extend longer toward signal output edge 418c than slots 350 in relay substrate 118, and their depth decreases in a stepwise manner. Therefore, the disturbance in the propagation mode in signal conductor pattern 330 caused by the presence of slots 750 gradually decreases as the signal output edge 418c is approached, and no disturbance occurs at signal output edge 418c. Furthermore, the amount of microwaves radiated from various portions of signal conductor pattern 330 along its length gradually decreases as the signal output edge 418c is approached. Therefore, even though the depth of slots 750 gradually decreases as the signal output edge 418c is approached, the amount of microwaves radiated from various portions of signal conductor pattern 330 that propagate within relay substrate 718 can be suppressed to a substantially constant value along the length of signal conductor pattern 330.

[0107] Therefore, in the relay substrate 718, the disturbance of the propagation mode of the signal conductor pattern 330 caused by the presence of the groove 750 is smoothly eliminated as it approaches the signal output edge 418c, and the high-frequency energy transfer between the microwave radiated through the above-mentioned connection point and the signal conductor pattern 330 that propagates the radiated microwave can be effectively reduced.

[0108] Here, in this variation, the specified distance L3 of the portion where the groove 750 extends to the back side 418f of the relay substrate 718 preferably satisfies any one of the following for the same reason as the length L2 on the relay substrate 118 (the above-mentioned suppression of microwave radiation at the connection point and propagation of the radiated microwaves).

[0109] L3>L1 (3)

[0110] L3>W (4)

[0111] In equations (3) and (4), L1 and W are the terminal extension length and the width of the groove 750 , respectively, which are defined in the same manner as in the example of the interconnect substrate 118 described above.

[0112] Furthermore, in this modified example, the depth of the groove 750 is formed in two steps, gradually deepening until reaching the back surface 418f. However, the number of steps is not limited to two. For example, the number of steps may be one. In other words, the depth of the groove 750 may be constant from the position of the predetermined distance L3 to the end of the groove 750. Alternatively, the number of steps may be three or more.

[0113] Alternatively, the depth of the groove 750 may continuously increase from the end of the groove 750. In this case, the bottom surface of the groove 750 may also reach the back surface 418f at the signal input side 418a (ie, L3 = 0).

[0114] In this variation, the groove 750 at least reaches the back surface 418f at the signal input side 418a, but this is not limiting. The groove 750 only needs to be deeper at the signal input side 418a as measured from the front surface 418e than at the end of the groove 750. For example, the groove 750 need not reach the back surface 418f at the signal input side 418a to achieve the same effects as described above.

[0115] In this modification, similar to interconnect substrates 118 , 518 , and 618 , a metal film is formed on the two inner side surfaces of groove 750 or on the two inner side surfaces and the bottom surface of groove 750 , thereby enhancing the effect of reducing high-frequency energy transfer.

[0116] <Fourth Modification>

[0117] Figure 8 This is a diagram showing the structure of a relay substrate 818 according to a fourth modification. Figure 1 The optical modulator 100 shown in the figure can be used instead of the relay substrate 118. Figure 8 In, about Figure 4 The same components as the relay substrate 118 shown in FIG. Figure 4 The same reference numerals as in Figure 4 Description.

[0118] Figure 8 The relay substrate 818 shown has Figure 4 Relay substrate 818 has the same structure as relay substrate 118 shown, but differs in that a grounding conductor 840 is provided on rear surface 418f, which is in contact with housing 104 and thus at ground potential. Furthermore, relay substrate 818 differs from relay substrate 118 in that grooves 850a, 850b, 850c, 850d, and 850e are provided instead of grooves 350a, 350b, 350c, 350d, and 350e. Hereinafter, grooves 850a, 850b, 850c, 850d, and 850e will also be collectively referred to as grooves 850.

[0119] The groove 850 has the same structure as the groove 350, but is different from the groove 350 in that a metal film is formed on its bottom surface and two inner side surfaces and six guide holes 860 are provided on its bottom surface. Figure 8 In order to facilitate understanding, only the guide hole at the right end of the groove 850 is marked with the number 860, but it should be understood that the five guide holes on the left side of the guide hole marked with the number 860 and depicted by a circle with the same diameter as the guide hole are also guide holes 860.

[0120] These vias 860 electrically connect the metal film on the bottom surface of the groove 850 to the ground conductor 840 formed on the back surface 418f of the relay substrate 818. Thus, the ground conductor 840 on the back surface 418f is electrically connected to the ground conductor pattern 340 on the front surface 418e via the vias 860 and the metal film formed on the bottom surface and two inner side surfaces of the groove 850.

[0121] Since the relay substrate 818 having the above-described structure includes the via 860 connecting the metal film on the bottom surface of the slot 850 to the ground conductor 840 on the back surface 418f of the relay substrate 818, it is possible to block the two radiated microwaves (the connection point radiated microwave and the propagation radiated microwave) from passing under the slot 850 and propagating within the relay substrate 818. Therefore, in the relay substrate 818, the transfer of high-frequency energy between the signal conductor patterns 330 via the two radiated microwaves can be further suppressed.

[0122] In addition, the ground conductor pattern 340 on the surface 418e is connected to the ground conductor 840 on the back surface 418f by a guide hole 860 whose length is shorter than the thickness of the relay substrate 818, thereby achieving a higher grounding effect (such as uniformity of ground potential distribution) than the relay substrate 118. In addition, in this embodiment, the number of guide holes is set to 6, but it is not limited to this. Moreover, the outer diameters of the guide holes are set to the same structure for all, but they can be set to different outer diameters as long as they are within the range that achieves the above-mentioned effect. In particular, when the outer diameter of the guide hole on the connection point side of the signal input terminal and the signal conductor pattern is larger than the outer diameters of the other guide holes, it is possible to achieve a higher grounding effect (such as uniformity of ground potential distribution) at the connection point between the signal input terminal and the signal conductor pattern, where the two radiated microwaves are likely to be generated, while maintaining the mechanical strength of the substrate.

[0123] <Fifth Modification>

[0124] Figure 9 This is a diagram showing the structure of a relay substrate 918 according to a fifth modification. Figure 1 The optical modulator 100 shown in the figure can be used instead of the relay substrate 118. Figure 9 In, about Figure 4 The same components as the relay substrate 118 shown in FIG. Figure 4 The same reference numerals as in Figure 4 Description.

[0125] Figure 9 The relay substrate 918 shown has Figure 4The relay substrate 118 shown has the same structure as shown, but instead of the signal conductor patterns 330a, 330b, 330c, 330d, signal conductor patterns 930a, 930b, 930c, 930d are provided.

[0126] The signal conductor patterns 930a, 930b, 930c, and 930d have the same structures as the signal conductor patterns 330a, 330b, 330c, and 330d, respectively, but their planar shapes on the relay substrate 918 are different from those of the signal conductor patterns 330a, 330b, 330c, and 330d.

[0127] Specifically, whereas signal conductor patterns 330a, 330b, 330c, and 330d are each formed as a straight line extending in a direction perpendicular to signal input side 418a, signal conductor patterns 930a and 930d are each formed to include a straight line extending at an angle in a direction different from the direction perpendicular to signal input side 418a. Furthermore, signal conductor patterns 930b and 930c each include a curved portion.

[0128] Thus, on the signal input side 418a of the relay substrate 918, the ends of the signal conductor patterns 930a and 930b are arranged adjacent to each other on the right side of the diagram to form one group, while the ends of the signal conductor patterns 930c and 930d are arranged adjacent to each other on the left side of the diagram to form another group. This grouping of the ends of the signal conductor pattern 930 on the signal input side 418a can be used, for example, when the optical modulation element 102 is a compact, integrated modulator such as a DP-QPSK modulator, to input two groups of high-frequency electrical signals to two nested Mach-Zehnder modulators that modulate two orthogonally polarized beams.

[0129] Relay substrate 918 differs from relay substrate 118 in that ground conductor patterns 940a, 940b, 940c, and 940d are provided instead of ground conductor patterns 340a, 340b, 340c, and 340d. Ground conductor patterns 940a, 940b, 940c, and 940d are also collectively referred to as ground conductor pattern 940 hereinafter.

[0130] The ground conductor pattern 940 has the same structure as the ground conductor pattern 340 , but the edges of the ground conductor pattern 940 adjacent to the signal conductor pattern 930 are formed by straight lines and / or curved lines in order to form a coplanar line corresponding to the shape of the signal conductor pattern 930 .

[0131] Interconnect substrate 918 also differs from interconnect substrate 118 in that grooves 950a, 950b, 950c, 950d, and 950e are provided instead of grooves 350a, 350b, 350c, 350d, and 350e. Hereinafter, grooves 950a, 950b, 950c, 950d, and 950e are also collectively referred to as grooves 950.

[0132] Here, the grooves 950a, 950b, 950c, 950d, and 950e have the same structure as the grooves 350a, 350b, 350c, 350d, and 350e, but are different from the grooves 350a, 350b, 350c, 350d, and 350e in the following points.

[0133] First, in Figure 4 The relay substrate 118 is provided with a groove 350 in each ground conductor pattern 340. Figure 9 In the relay substrate 918, no grooves are provided in the ground conductor patterns 940a and 940e that are not sandwiched between adjacent signal conductor patterns 930. In the relay substrate 918, the propagation radiation microwaves that propagate from the signal conductor patterns 930a and 930d toward the right side 418g and left side 418h of the relay substrate 918, respectively, do not directly reach other signal conductor patterns 930 and therefore rarely contribute to crosstalk between the signal conductor patterns 930.

[0134] Furthermore, in the relay substrate 918, the ends of the signal input side 418a of the signal conductor patterns 930b and 930c are separated so as not to cause intentional crosstalk. Therefore, in the relay substrate 918, no groove is provided in the ground conductor pattern 940c sandwiched between the signal conductor patterns 930b and 930c.

[0135] Furthermore, in the relay substrate 918, two grooves 950a and 950b, each formed of a straight line and a curved line, are provided in the ground conductor pattern 940b sandwiched between the signal conductor patterns 930a and 930b, respectively, along the shapes of the signal conductor patterns 930a and 930b. Furthermore, in the relay substrate 918, two grooves 950c and 950d, each formed of a curved line and a straight line, are provided in the ground conductor pattern 940d sandwiched between the signal conductor patterns 930c and 930d, respectively, along the shapes of the signal conductor patterns 930c and 930d.

[0136] In the relay substrate 918 having the above-described structure, the number and shape of the slots provided in the ground conductor pattern 940 are determined according to the shape of the signal conductor pattern 930. Specifically, slots are not provided in the propagation path of radiated microwaves (in this variation, the portion of the relay substrate 918 where the ground conductor patterns 940a, 940c, and 940d are formed) that does not substantially contribute to crosstalk between adjacent signal conductor patterns 330. Consequently, the relay substrate 918 can simplify its processing steps and can be manufactured easily and inexpensively.

[0137] In addition, in the relay substrate 918, in the propagation path (in this modified example, the substrate portion on which the ground conductor patterns 940b and 940d are formed) of two radiated microwaves (connection point radiated microwaves and propagation radiated microwaves) clamped by two signal conductor patterns 930 and which will generate crosstalk between the signal conductor patterns 930, a groove 950 including a straight line portion or a curved line portion along the shape of the signal conductor pattern 930 is provided at a position adjacent to each signal conductor pattern 930 having a curved line portion.

[0138] This prevents the two radiated microwaves from propagating within the relay substrate 918 between adjacent signal conductor patterns 930 , and also suppresses propagation of unnecessary microwaves radiated from the curved portion of the signal conductor pattern 930 .

[0139] Furthermore, in this variation, two slots 950a and 950b, and slots 950c and 950d, are provided in ground conductor patterns 940b and 940d, respectively, each comprising a single ground conductor pattern. However, this is not limiting. For example, ground conductor pattern 940b can be divided into two parts, with slot 950a formed in the right portion of the division and slot 950b in the left portion. Similarly, ground conductor pattern 940d can be divided into two parts, with slot 950c formed in the right portion of the division and slot 950d in the left portion.

[0140] [Second embodiment]

[0141] Next, a second embodiment of the present invention is described. This embodiment is an optical transmission device equipped with the optical modulator 100 of the first embodiment and any of the optical modulators 100 including the relay substrates 518, 618, 718, 818, and 918 of the first to fifth modifications of the first embodiment.

[0142] Figure 10This diagram shows the configuration of an optical transmission device according to this embodiment. The optical transmission device 1000 includes an optical modulator 1002 , a light source 1004 for causing light to enter the optical modulator 1002 , a modulation signal generator 1006 , and a modulation data generator 1008 .

[0143] The optical modulator 1002 can be any of the optical modulator 100 of the first embodiment described above, or the optical modulator 100 including the relay substrates 518, 618, 718, 818, and 918 of the first to fifth modifications of the first embodiment. To avoid redundant description and facilitate understanding, the optical modulator 1002 is hereinafter referred to as the optical modulator 100 including the relay substrate 118.

[0144] The modulation data generation unit 1008 receives transmission data assigned from the outside, generates modulation data for transmitting the transmission data (for example, converts or processes the transmission data into data of a prescribed data format), and outputs the generated modulation data to the modulation signal generation unit 1006 .

[0145] The modulation signal generator 1006 is an electronic circuit (driver circuit) that outputs an electrical signal for causing the optical modulator 1002 to perform a modulation operation. Based on the modulation data output by the modulation data generator 1008, it generates a modulation signal, which is a high-frequency signal for causing the optical modulator 1002 to perform an optical modulation operation in accordance with the modulation data, and inputs the modulation signal to the optical modulator 1002. This 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 1002.

[0146] The four high-frequency electrical signals are input from the respective signal input terminals 124a, 124b, 124c, 124d of the electrical connectors 116a, 116b, 116c, 116d of the optical modulator 1002 to the signal conductor patterns 330a, 330b, 330c, 330d of the relay substrate 118, and are then input to the signal electrodes 112a, 112b, 112c, 112d of the optical modulator element 102 via these signal conductor patterns 330a, etc.

[0147] As a result, the light output from the light source 1004 is modulated by, for example, DP-QPSK by the optical modulator 1002 , becomes modulated light, and is output from the optical transmission device 1000 .

[0148] In particular, in the optical transmitter 1000, any one of the optical modulator 100 according to the first embodiment and the optical modulator 100 including the relay substrates 518, 618, 718, 818, and 918 according to the first to fifth modifications of the first embodiment is used as the optical modulator 1002. Therefore, in the optical transmitter 1000, the increase in crosstalk between the plurality of high-frequency electrical signals driving the optical modulator 102, which is associated with an increase in the transmission rate, is effectively reduced, and stable and excellent optical modulation characteristics can be ensured, thereby achieving stable and excellent transmission characteristics.

[0149] The present invention is not limited to the configurations of the above-described embodiment and its modified examples, and can be implemented in various forms without departing from the spirit and scope of the invention.

[0150] For example, in the above-described embodiment and modified examples, the preferred dimensional conditions expressed by equations (1) and (2) regarding groove 350 described in the description of relay substrate 118 are also applicable to grooves 550, 650, 750, 850, and 950 in relay substrates 518, 618, 718, 818, and 918. In this case, the groove length L2 is defined as the length along which the groove extends. Therefore, it should be noted that in the example of groove 950, the groove length L2 is measured along the shape of groove 950, which is formed by a straight line or a curve.

[0151] Furthermore, for example, even if the characteristic portions of the relay substrates 118, 518, 618, 718, 818, and 918 shown in the above-described embodiments and modifications are combined to form a single relay substrate, the same effects as those shown in the above-described modifications can be achieved. For example, a plurality of grooves having structures similar to the grooves 350, 550, 650, 750, 850, and 950 may be interspersed with a plurality of ground conductor patterns, with at least one groove provided in each of at least one ground conductor pattern formed on the surface 418e.

[0152] Alternatively, in relay substrates 618, 718, and 918, a metal film may be provided on the entire inner surface of grooves 650, 750, and 950, and a metal film may be provided on rear surface 418f, with the same guide holes provided as in relay substrate 818. Alternatively, in relay substrate 618, the depth of grooves 650 may vary in a stepwise or continuously manner, similar to relay substrate 718. In this case, for example, the depth of grooves 650 may vary in a stepwise or continuously manner within the range not reaching rear surface 418f.

[0153] As described above, the optical modulator 100 includes an optical modulator element 102 having a plurality of signal electrodes 112; a plurality of signal input terminals 124 for inputting electrical signals applied to the respective signal electrodes 112; and a relay substrate 118 having a plurality of signal conductor patterns 330 and a plurality of ground conductor patterns 340 formed thereon for electrically connecting the respective signal input terminals 124 to the respective signal electrodes 112. Furthermore, the optical modulator 100 includes a housing 104 for housing the optical modulator element 102 and the relay substrate 118. On the signal input side 418a of the relay substrate 118, where electrical signals from the signal input terminals 124 are input to the signal conductor patterns 330, the signal input terminals 124 are arranged so as to extend from the signal input side 418a to the signal conductor patterns 330. On the surface 418e of the relay substrate 118 where the signal conductor patterns 330 are formed, at least one ground conductor pattern 340 formed between adjacent signal conductor patterns 330 includes at least one groove 350 extending from the signal input side 418a. Furthermore, the groove 350 is formed so that the length extending from the signal input side 418 a is longer than the length extending from the signal input terminal 124 from the signal input side 418 a .

[0154] According to this structure, the slots 350 provided in the relay substrate 118 suppress the propagation of two radiated microwaves within the relay substrate 118: a radiation mode (propagation radiated microwaves) generated from the signal conductor pattern 330 near the input connection point accompanying the propagation of a high-frequency signal, and a radiation mode (connection point radiated microwaves) generated due to heterogeneous mode conversion at the connection point between the signal input terminal 124 and the signal conductor pattern 330. This suppresses the occurrence of high-frequency energy transfer between adjacent signal conductor patterns 330. Specifically, in the optical modulator 100, the simple slots 350 provided in the relay substrate 118 suppress this high-frequency energy transfer, thereby ensuring ease of manufacture and effectively suppressing the increase in crosstalk between the signal conductor patterns 330 associated with increased transmission rates without compromising the miniaturization requirements of the optical modulator 100 or increasing costs. This allows for the realization of excellent optical modulation characteristics.

[0155] Alternatively, the optical modulator 100 may use a relay substrate 618 having a groove 650 different from the groove 350. The groove 650 is formed to extend to the signal output side 418c of the relay substrate 118, which is the side through which the electrical signal is output from the signal conductor pattern 330 to the signal electrode 112 of the optical modulator 102.

[0156] With this structure, the propagation of microwaves radiated from various portions of the signal conductor pattern 330 along its longitudinal direction into the relay substrate 618 is continuously suppressed by the slots 650 from the signal input side 418a to the signal output side 418c. Consequently, compared to the relay substrate 118, the transfer of high-frequency energy between the signal conductor patterns 330 can be further reduced. Furthermore, by forming the slots 650 from the signal input side 418a to the signal output side 418c, the relay substrate 618 can be simplified in structure, thereby facilitating manufacture.

[0157] In addition, the optical modulator 100 may use a relay substrate 718 having a groove 750 different from the groove 350. The groove 750 is formed so that the depth of the groove 750 at the end of the signal input side 418a measured from the surface 418e of the relay substrate 718 is deeper than the depth of the groove 750 at the other end measured from the surface 418e.

[0158] According to this structure, the depth of the slot 750 is formed to become shallower as it moves away from the signal input side 418a. Therefore, the disturbance in the propagation mode of the signal conductor pattern 330 caused by the presence of the slot 750 decreases as it approaches the signal output side 418c. Furthermore, the areas with greater disturbance in the propagation mode correspond to the deeper portions of the slot 750. Therefore, the deeper slot portions effectively suppress the propagation of microwaves generated in areas where this disturbance is greater. Therefore, in the relay substrate 718, the disturbance in the propagation mode of the signal conductor pattern 330 caused by the presence of the slot 750 is smoothly eliminated as it approaches the signal output side 418c. This allows the transfer of high-frequency energy between microwaves radiated through the connection points and between the signal conductor pattern 330 that propagates the radiated microwaves to a certain level along the length of the signal conductor pattern 330.

[0159] Furthermore, in the relay substrate 718, the groove 750 can be formed so that its depth, as measured from the surface 418e of the relay substrate 718, increases in a stepwise or continuously manner as it approaches the signal input side 418a from the other end of the groove 750. This configuration allows a groove having a varying depth to be formed with a simple structure.

[0160] In addition, in the relay substrate 718, the groove 750 is formed at the signal input edge 418a to the back side 418f opposite to the surface 418e of the relay substrate 718, or is formed within a range of a specified distance L3 from the signal input edge 418a to the back side 418f opposite to the surface 418e of the relay substrate 718.

[0161] According to this structure, the propagation suppression effect of the connection point radiation microwave and the propagation radiation microwave in the relay substrate 718 can be enhanced at the signal input edge 418a or its vicinity where the connection point radiation microwave and the propagation radiation microwave are most likely to occur.

[0162] Furthermore, a metal film may be formed on the inner side surfaces of the grooves 350, 650, 750, and 950 of the interconnect substrates 118, 618, 718, and 918. This configuration can enhance the effect of suppressing microwave radiation and propagation at the connection points within the interconnect substrates.

[0163] Furthermore, a metal film may be formed on the bottom surfaces of the grooves 350, 650, 750, and 950 of the relay substrates 118, 618, 718, and 918. This structure can suppress microwaves radiated from the connection points propagating within the relay substrate and from the bottom surfaces of the grooves into the air, further enhancing the crosstalk suppression effect between the signal conductor patterns 330.

[0164] Furthermore, the optical modulator 100 can use a relay substrate 818 having a groove 850 different from the groove 350. A grounding conductor 840 is formed on the back surface 418f of the relay substrate 818, which is opposite to the front surface 418e. A guide hole 860 is formed on the bottom surface of the groove 850 to connect the metal film on the bottom surface to the grounding conductor 840 on the back surface 418f of the relay substrate 818.

[0165] This structure further prevents microwaves from being radiated from the connection point and from propagating through the bottom of the slot 850 and into the interior of the relay substrate 818 due to the formation of the via 860 connecting the metal film on the bottom surface of the slot 850 to the ground conductor 840 on the back surface 418f of the relay substrate 818. Therefore, in the relay substrate 818, the transfer of high-frequency energy between microwaves radiated from the connection point and the signal conductor pattern 330 that propagates the radiated microwaves can be further suppressed.

[0166] Alternatively, the optical modulator 100 may use a relay substrate 518 having a groove 550 different from the groove 350. The groove 550 does not extend to the signal output edge 418 c of the relay substrate 518, where an electrical signal is output from the signal conductor pattern 330 to the signal electrode 112 of the optical modulator 102. Instead, the groove 550 is formed so as to extend entirely through the rear surface 418 f of the relay substrate 518, which is opposite to the front surface 418 e.

[0167] According to this structure, each of the grooves 550 extends entirely through the back surface 418f of the relay substrate 518 opposite the front surface 418e, thereby further suppressing the connection point radiation microwaves generated at and near the input connection point and the propagation of the radiation microwaves within the relay substrate 518.

[0168] Furthermore, the relay substrate 518 has a metal film formed on the inner side of the groove 550 extending from the front surface 418e to the back surface 418f. This structure further enhances the effect of suppressing microwave radiation from the connection points and the propagation of the radiated microwaves, thereby further enhancing the effect of reducing the transfer of high-frequency energy between the signal conductor patterns 330 that radiate the microwaves.

[0169] Furthermore, in the relay substrates 118, 518, 618, 718, 818, and 918 of the optical modulator 100, the slots 350, 550, 650, 750, 850, and 950 are formed such that the length L2 extending from the signal input side 418a is longer than the width W measured in a direction perpendicular to the extending direction. This structure effectively suppresses microwave radiation from connection points generated at various portions of the signal conductor pattern 330 along the longitudinal direction as high-frequency signals propagate, as well as the propagation of the radiated microwaves within the relay substrate.

[0170] Furthermore, the optical modulator 100 including any of the relay substrates 118, 518, 618, 718, 818, and 918 described above, together with the modulation signal generating unit 1006, an electronic circuit that outputs an electrical signal for causing the optical modulator 100 to perform a modulation operation, constitutes the optical transmitter 1000. This configuration further reduces crosstalk between the multiple high-frequency electrical signals driving the optical modulator 102, which is associated with increased transmission rates, and enables stable and excellent transmission characteristics to be achieved.

Claims

1. An optical modulator comprising: A light modulation element having a plurality of signal electrodes; a plurality of signal input terminals for inputting electrical signals applied to the respective signal electrodes, wherein the plurality of signal input terminals are central conductors of an electrical connector serving as a coaxial connector; a relay substrate having a plurality of signal conductor patterns and a plurality of ground conductor patterns for electrically connecting the signal input terminals to the signal electrodes, wherein the plurality of signal conductor patterns and the plurality of ground conductor patterns together constitute a coplanar line; and The housing accommodates the light modulator and the relay substrate, wherein: The signal input terminal is arranged on the signal input side of the relay substrate so as to extend from the signal input side onto the signal conductor pattern, and the signal input side is a side where the electrical signal from the signal input terminal is input to the signal conductor pattern. In the relay substrate, on the surface where the signal conductor patterns are formed, at least one of the ground conductor patterns formed between adjacent signal conductor patterns has at least one groove extending from the signal input side. The groove is formed to extend from the signal input side to a length longer than the length of the signal input terminal extending from the signal input side, wherein The groove extends to a signal output side of the relay substrate, where the signal output side is a side through which an electrical signal is output from the signal conductor pattern to the signal electrode of the light modulation element.

2. The optical modulator according to claim 1, wherein The groove is formed on the signal input side to the back surface of the relay substrate opposite to the front surface, or is formed within a range of a predetermined distance from the signal input side to the back surface of the relay substrate opposite to the front surface.

3. The optical modulator according to claim 1, wherein A metal film is formed on the inner side surface of the groove, or on the inner side surface and bottom surface of the groove.

4. The optical modulator according to claim 1, wherein A metal film is formed on the inner side and bottom surface of the groove. A grounding conductor is formed on the back surface of the relay substrate opposite to the front surface. A via connecting the metal film on the bottom surface and the grounding conductor on the back surface is formed on the bottom surface of the groove.

5. The optical modulator according to claim 1, wherein A metal film is formed on the inner side surface of the groove.

6. The optical modulator according to claim 1, wherein The groove is formed so that a length extending from the signal input side is longer than a width measured in a direction perpendicular to the extending direction.

7. An optical modulator comprising: A light modulation element having a plurality of signal electrodes; a plurality of signal input terminals for inputting electrical signals applied to the respective signal electrodes, wherein the plurality of signal input terminals are central conductors of an electrical connector serving as a coaxial connector; a relay substrate having a plurality of signal conductor patterns and a plurality of ground conductor patterns for electrically connecting the signal input terminals to the signal electrodes, wherein the plurality of signal conductor patterns and the plurality of ground conductor patterns together constitute a coplanar line; and The housing accommodates the light modulator and the relay substrate, wherein: The signal input terminal is arranged on the signal input side of the relay substrate so as to extend from the signal input side onto the signal conductor pattern, and the signal input side is a side where the electrical signal from the signal input terminal is input to the signal conductor pattern. In the relay substrate, on the surface where the signal conductor patterns are formed, at least one of the ground conductor patterns formed between adjacent signal conductor patterns has at least one groove extending from the signal input side. The groove is formed to extend from the signal input side to a length longer than the length of the signal input terminal extending from the signal input side, wherein The groove is formed so that a depth of an end portion of the groove at the signal input side measured from the surface is deeper than a depth of the groove at the other end portion of the groove measured from the surface.

8. The optical modulator according to claim 7, wherein The groove is formed so that the depth measured from the surface becomes deeper in a stepwise or continuous manner as it approaches the signal input side from the other end of the groove.

9. The optical modulator according to claim 7, wherein The groove is formed on the signal input side to the back surface of the relay substrate opposite to the front surface, or is formed within a range of a predetermined distance from the signal input side to the back surface of the relay substrate opposite to the front surface.

10. The optical modulator according to claim 7, wherein A metal film is formed on the inner side surface of the groove, or on the inner side surface and bottom surface of the groove.

11. The optical modulator according to claim 7, wherein A metal film is formed on the inner side and bottom surface of the groove. A grounding conductor is formed on the back surface of the relay substrate opposite to the front surface. A via connecting the metal film on the bottom surface and the grounding conductor on the back surface is formed on the bottom surface of the groove.

12. The optical modulator according to claim 7, wherein A metal film is formed on the inner side surface of the groove.

13. The optical modulator according to claim 7, wherein The groove is formed so that a length extending from the signal input side is longer than a width measured in a direction perpendicular to the extending direction.

14. An optical transmitting device comprising: The optical modulator according to any one of claims 1 to 13; and The electronic circuit outputs an electrical signal for causing the optical modulator to perform a modulation operation.

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