Patent ID: 12210232

DESCRIPTION OF EMBODIMENTS

In the following embodiments and modification examples thereof, in order to solve the above-described problems, in an optical modulator including an optical modulation element and a relay substrate, in the vicinity of a connection portion at which a signal conductor pattern on the relay substrate is connected to a high-frequency input terminal, two ground conductor patterns sandwiching at least one signal conductor pattern are configured to include asymmetrically shaped portions sandwiching the signal conductor pattern, or are configured so that impedances to ground lines are different from each other, or/and the relay substrate between the adjacent signal conductor patterns is provided with a notch extending from a side of the relay substrate. Thus, in the optical modulator, intensities of space leaked microwaves and/or substrate leaked microwaves toward the adjacent signal conductor pattern are reduced, and crosstalk between the adjacent signal conductor patterns is reduced.

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

First Embodiment

First, a first embodiment of the present invention will be described.FIG.1is a plan view illustrating a configuration of an optical modulator100according to the first embodiment of the present invention,FIG.2is a side view of the optical modulator100, andFIG.3is a partial detail view of a part A inFIG.1.

The optical modulator100includes an optical modulation element102, a housing104that accommodates the optical modulation element102, an input optical fiber108for inputting light into the optical modulation element102, and an output optical fiber110that guides the light output from the optical modulation element102to an outside of the housing104.

The optical modulation element102is, for example, a DP-QPSK modulator that performs optical modulation of 400 Gb/s, and includes, for example, four Mach-Zehnder type optical waveguides provided on an LN substrate. The four Mach-Zehnder type optical waveguides are provided with four signal electrodes112a,112b,112c, and112d(hereinafter, collectively also referred to as a signal electrode112) that respectively modulate light waves propagating through the Mach-Zehnder type optical waveguide. In addition, as known in the related art, on a surface of the LN substrate of the optical modulation element102, for example, ground electrodes122a,122b,122c,122d, and122e(seeFIG.3and not illustrated inFIG.1) are provided so that each of the four signal electrodes112a,112b,112c, and112dincludes a coplanar waveguide (CPW).

Specifically, the ground electrodes122a,122b,122c,122d, and122e(hereinafter, collectively also referred to as a ground electrode122) are disposed so as to respectively sandwich the signal electrodes112a,112b,112c, and112dtherebetween in a surface of the LN substrate, and constitute a coplanar waveguide having a predetermined characteristic impedance in a predetermined operating frequency together with the four signal electrodes112a,112b,112c, and112d.

Four high-frequency electrical signals (modulation signals) are respectively input to the four signal electrodes112. These high-frequency electrical signals cooperate to control the propagation of the light wave in the four Mach-Zehnder type optical waveguides, and perform the operation of DP-QPSK modulation of 400 Gb/s as a whole.

Specifically, two pairs of high-frequency electrical signals, one pair of which includes two high-frequency electrical signals, are applied to the four respective signal electrodes112. The optical modulation element102is configured to generate two modulated light beams each of which is modulated by one pair of electrical signals. The two generated modulated light beams are respectively output from two output optical waveguides126aand126bthat form a part of the optical modulation element102. In the present embodiment, two high-frequency electrical signals forming one pair are applied to the signal electrodes112aand112bto generate modulated light output from the output optical waveguide126a, and other two high-frequency electrical signals forming another pair are applied to the signal electrodes112cand112dto generate modulated light output from the output optical waveguide126b. These two modulated light beams are combined into one beam by a polarization-combining part128including a polarization combining prism or the like, and then output to the outside of the housing104via the output optical fiber110.

The housing104includes a case114ato which the optical modulation element102is fixed and a cover114b. In order to facilitate understanding of the configuration inside the housing104, only a part of the cover114bis illustrated on the left side inFIG.1, but actually, the cover114bis disposed to cover the entire box-shaped case114aand hermetically seals the inside of the housing104. The case114ais made of a metal or a ceramic plated with gold, for example, and functions electrically as an electrical conductor. The housing104can be usually provided with a plurality of pins for DC control or the like, which are omitted inFIG.1.

In the case114a, electrical connectors116a,116b,116c, and116d(hereinafter, collectively also referred to as electrical connectors116), which are coaxial connectors including input signal terminals124a,124b,124c, and124d(hereinafter, collectively also referred to as a input signal terminal124) that input the high-frequency electrical signal to be applied to each of the signal electrodes112a,112b,112c, and112dof the optical modulation element102are provided.

Each of the electrical connectors116is, for example, a socket for a push-on coaxial connector, including a cylindrical ground conductor, and the input signal terminal124includes a center conductor (core wire) extending along a center line of the cylindrical ground conductor. Each of the cylindrical ground conductors is electrically connected and fixed to the case114a. Therefore, the case114aconstitutes a ground line that supplies a ground potential. Further, each of the input signal terminals124is electrically connected to one end of each of the signal electrodes112of the optical modulation element102, via a relay substrate118.

The other end of the signal electrode112of the optical modulation element102is terminated by a terminator120having a predetermined impedance. Thus, the electrical signals input to the one ends of the signal electrodes112respectively propagate in the signal electrodes112as traveling waves.

FIG.3illustrates a configuration of the relay substrate118and its surroundings. On the relay substrate118, signal conductor pattern330a,330b,330c, and330d(hereinafter, collectively also referred to as a signal conductor pattern330) and ground conductor pattern340a,340b,340c,340d, and340e(hereinafter, collectively also referred to as a ground conductor pattern340) are formed.

On the relay substrate118, a rear surface ground conductor (not illustrated) is formed on a rear surface facing a front surface (a surface illustrated inFIG.3in which the signal conductor pattern330and the ground conductor pattern340are formed). The rear surface ground conductor is fixed to the case114aof the housing104with, for example, solder, a brazing material, a conductive adhesive, or the like. Thus, the rear surface ground conductor becomes a ground line component. Each of the ground conductor patterns340is connected to the rear surface ground conductor and connected to the ground line through an appropriate via (not illustrated).

The ground conductor patterns340a,340b,340c,340d, and340eare provided so as to sandwich the respective signal conductor patterns330a,330b,330c, and330din a front surface of the relay substrate118. Thus, each of the signal conductor patterns330and the ground conductor pattern340form a coplanar waveguide.

In the present embodiment, the signal conductor pattern330extends in an upward-downward direction illustrated inFIG.3, and among sides of the relay substrate118, one end of a side on a lower side illustrated inFIG.3is connected to the input signal terminal124. Here, among the sides of the relay substrate118, a side on which the signal conductor pattern330and the input signal terminal124are connected is referred to as a signal input side318a.

Each of the signal electrodes112of the optical modulation element102is electrically connected to another end of the signal conductor pattern330of the relay substrate118, on an upper side illustrated inFIG.3among sides of the relay substrate118, by wire bonding using a conductor wire326, for example. The conductor wire326can be a gold wire, for example. Here, among the sides of the relay substrate118, a side on which the signal conductor pattern330and the signal electrode112of the optical modulation element102are connected is referred to as a signal output side318b. In the present embodiment, the signal input side318aand the signal output side318bform two sides facing each other in the relay substrate118in a plan view. Among the sides of the relay substrate118inFIG.3, the other two sides facing each other, other than the signal input side318aand the signal output side318bare referred to as side edges (lateral sides)318cand318d.

In the optical modulation element102, the respective ground electrodes122that constitute the coplanar waveguide together with the signal electrodes112are electrically connected to one ends of the respective ground conductor patterns340at the signal output side318bof the relay substrate118, by wire bonding using the conductor wires326, for example, in the same manner as described above. The wire bonding using the conductor wire326described above is an example, and the present invention is not limited to this. Instead of wire bonding of the conductor wire326, for example, ribbon bonding using a conductor ribbon such as a gold ribbon can be used.

In the present embodiment, regarding at least one signal conductor pattern330, each of the two ground conductor patterns340sandwiching the signal conductor pattern330on the relay substrate118is formed in an asymmetrical shape in a plan view with respect to the at least one signal conductor pattern330, in a rectangular connection area in the plan view including a signal connection portion at which the signal conductor pattern330and the input signal terminal124are connected. Here, the connection area is defined as a rectangle extending in a plane of the relay substrate118by setting a part of the signal input side318aas one side in a width direction. Further, the connection area is centered on the at least one signal conductor pattern330in the width direction. A width of the connection area is equal to a distance from the at least one signal conductor pattern330to the nearest adjacent signal conductor pattern330, and a height of the connection area is equal to a distance from the signal input side318ato an end of the signal connection portion farthest from the signal input side318a.

In the present embodiment, the input signal terminal124is directly connected to the signal conductor pattern330by soldering or the like, but the present embodiment is not limited to this. The input signal terminal124may be connected to the signal conductor pattern330via a conductor wire or a conductor ribbon by wire bonding or the like. In this case, the signal connection portion between the signal conductor pattern330and the input signal terminal124can be a range in which the conductor wire or the like is connected on the signal conductor pattern330. Therefore, in this case, the above-described “end of signal connection portion farthest from signal input side318a” is a “farthest wire connection portion from signal input side318aamong wire connection portions at which conductor wire or the like is connected at signal conductor pattern330”.

FIG.4is a partial detail view of a part B illustrated inFIG.3. In the present embodiment, as an example, the two ground conductor patterns340aand340bsandwiching the signal conductor pattern330aon the relay substrate118are formed in an asymmetrical shape with respect to the signal conductor pattern330bin a plan view, in a connection area450aincluding a signal connection portion at which the signal conductor pattern330band the input signal terminal124bare connected.

Here, the connection area450ais defined for the signal conductor pattern330a. That is, assuming that an extending direction of the signal input side318aof the relay substrate118is a width direction and a direction orthogonal to the extending direction is a height direction, the connection area450ais defined as a rectangular range having the signal input side318aas one side and having a predetermined width w11and a predetermined height d11centered on the signal conductor pattern330a. Here, the height d11is a distance from the signal input side318ato a far end of a signal connection portion at which the signal conductor pattern330aand the input signal terminal124aare connected (that is, an end far from the signal input side318a). Further, the width w11is equal to a distance (pitch) p1between patterns from the signal conductor pattern330ato the nearest adjacent signal conductor pattern330b.

The signal conductor pattern330aand the ground conductor patterns340aand340bare formed so that characteristic impedances of the signal conductor pattern330ahave the same value inside and outside the connection area450a.

In the same manner, in the present embodiment, the two ground conductor patterns340dand340esandwiching the signal conductor pattern330dare formed in an asymmetrical shape with respect to the signal conductor pattern330din a plan view, in the connection area450ddefined for the signal conductor pattern330d. The connection area450dis a rectangular range having a signal input side318aas one side, and has a width w14centered on the signal conductor pattern330dand a predetermined height d14. Here, the height d14is a distance from the signal input side318ato a far end of a signal connection portion between the signal conductor pattern330dand the input signal terminal124d, and the width w14is equal to a distance p2between patterns from the signal conductor pattern330dto the nearest adjacent signal conductor pattern330c. Further, the signal conductor pattern330dand the ground conductor pattern340dand340eare formed so that characteristic impedances of the signal conductor pattern330dhave the same value inside and outside the connection area450d.

More specifically, in the present embodiment, gaps (g11and g12inFIG.4) from respective edges of the two ground conductor patterns340aand340bto opposite edges of the signal conductor pattern330ahave different portions in the connection area450a, so that the two ground conductor patterns340aand340bsandwiching the signal conductor pattern330ahave an asymmetrical shape with respect to the signal conductor pattern330a.

In the same manner, gaps (g41and g42inFIG.4) from respective edges of the two ground conductor patterns340dand340eto opposite edges of the signal conductor pattern330dhave different portions in the connection area450d, so that the two ground conductor patterns340dand340esandwiching the signal conductor pattern330dhave an asymmetrical shape with respect to the signal conductor pattern330d. Here, g11and g12, and g41and g42are respectively set to have distances under a condition that, for example, the characteristic impedances of the signal conductor patterns330aand330dinside and outside the respective connection areas450aand450dare equal to each other.

In general, in a high-frequency signal line including a signal conductor and a ground conductor, the smaller the distance between the signal conductor and the ground conductor, the stronger the confinement of the high-frequency signal in the signal conductor.

In the relay substrate118, distances from the signal conductor pattern330ato the ground conductor patterns340aand340bare different from each other, in the connection area450a. Therefore, leaked microwaves generated from the signal connection portion between the signal conductor pattern330aand the input signal terminal124a(therefore, generated from the connection area450a) are biased in a direction in which a distance from the adjacent ground conductor pattern is large, that is, a direction of the opposite ground conductor pattern340awith the distance g11(>g12) (for example, in a direction range illustrated as a range sandwiched by arrows490aand490bof the alternate long and short dash lines inFIG.4), and will be emitted so as to have a larger intensity distribution than in other directions. On the other hand, since the signal conductor pattern330ais configured to have the same characteristic impedance inside and outside the connection area450a, the total amount of leaked microwaves generated from the signal connection portion is approximately the same as a case where g11and g12are configured to have the same value.

As a result, intensities of the leaked microwaves in a direction range other than the direction range sandwiched by the arrows490aand490bis relatively reduced, and crosstalk via the leaked microwaves from the signal conductor pattern330ato the adjacent signal conductor pattern330bis reduced.

According to the same principle, leaked microwaves generated from the signal connection portion between the signal conductor pattern330dand the input signal terminal124d(therefore, generated from the connection area450d) are emitted toward a direction of the opposite ground conductor pattern340ewith a distance g42(>g41) so as to have a larger intensity distribution than the other directions. As a result, intensities of the leaked microwaves propagating in a direction of the adjacent signal conductor pattern330care relatively reduced, and crosstalk via the leaked microwaves from the signal conductor pattern330dtoward the adjacent signal conductor pattern330cis reduced.

In particular, in an optical modulator that generates two modulated light beams, each of which is modulated by a pair of high-frequency electrical signals, such as the optical modulator100that performs DP-QPSK modulation, the two paired high-frequency electrical signals often carry information for a phase difference between each other. Therefore, crosstalk between the two paired high-frequency electrical signals also generates a phase noise in addition to an intensity noise, and can have a greater influence on the modulation characteristics of the optical modulator100than crosstalk between different pairs of high-frequency electrical signals.

Since the paired high-frequency electrical signals are generally relayed by using two adjacent signal conductor patterns on the relay substrate, it is extremely important to suppress crosstalk between two adjacent signal conductor patterns that respectively propagate the two paired high-frequency electrical signals.

The optical modulator100of the present embodiment is configured to respectively propagate two high-frequency electrical signals that form one pair of the two pairs of high-frequency electrical signals by the adjacent signal conductor patterns330aand330b, and to propagate an other two paired high-frequency electrical signals, by the other adjacent signal conductor patterns330cand330d. Then, with the above configuration, the crosstalk from the signal conductor pattern330ato the signal conductor pattern330b, that is, crosstalk from one of the two high-frequency electrical signals forming one pair to the other is reduced. Further, with the above configuration, the crosstalk from the signal conductor pattern330dto the signal conductor pattern330c, that is, crosstalk from one of the two high-frequency electrical signals forming the other pair to the other is also reduced. As a result, the optical modulator100can effectively reduce the influence of leaked microwaves and realize appropriate optical modulation characteristics.

In the present embodiment, the two ground conductor patterns340aand340b, and340dand340erespectively sandwiching the signal conductor patterns that are not sandwiched between the adjacent signal conductor patterns, that is, the signal conductor patterns330aand330dlocated at the left and right ends of the arrangement of the four signal conductor patterns330include an asymmetrical shape with respect to the signal conductor patterns330aand330din the connection area450aand450d, respectively, but the embodiment is not limited to this. In the same manner, for the signal conductor patterns330bor330crespectively sandwiched between the two signal conductor patterns330aand330c, or330band330d, the two ground conductor patterns340band340c, or340cand340d, which respectively sandwich the signal conductor patterns330bor330c, can have an asymmetrical shape with respect to the signal conductor pattern330bor330cin a predetermined connection area, respectively.

In this case, a width of the connection area for the signal conductor pattern sandwiched between the adjacent signal conductor patterns (that is, a width corresponding to w11or w14inFIG.4) can be equal to a distance to the nearest adjacent signal conductor pattern.

Next, a modification example of the relay substrate used in the optical modulator100will be described.

First Modification Example

FIG.5is a diagram illustrating a configuration of a relay substrate518according to a first modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate518can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.5, the same reference numerals as those inFIG.4are used for the same components as those of the components of the relay substrate118illustrated inFIG.4, and the above description ofFIG.4is adopted.

The relay substrate518has the same configuration as the relay substrate118, but has a difference that a ground conductor pattern540cis provided instead of the ground conductor pattern340c. Thus, in the relay substrate518, in addition to the signal conductor patterns330aand330d, regarding the signal conductor patterns330band330c, in connection areas550band550cdefined for these signal conductor patterns330band330c, the ground conductor patterns340band540cand the ground conductor patterns540cand340drespectively sandwiching the signal conductor patterns330band330care configured in an asymmetrical shape with respect to the signal conductor patterns330band330c, respectively.

In the same manner as the connection areas450aand450ddefined for the signal conductor patterns330aand330d, the connection areas550band550cdefined for the signal conductor patterns330band330care a rectangular range having a width w22and a predetermined height d22centered on the signal conductor pattern330b, and a rectangular range having a width w23and a predetermined height d23centered on the signal conductor pattern330c, respectively having the signal input side318aas one side.

The widths w22and w23can be values equal to distances from the signal conductor patterns330band330cto the nearest adjacent signal conductor pattern, respectively.

For example, in a case where the distance p1between the signal conductor patterns330aand330b, the distance p2between the signal conductor patterns330cand330d, and a distance p3between the signal conductor patterns330band330chave a relationship of p1>p2>p3, a distance to the nearest adjacent signal conductor pattern for both the signal conductor patterns330band330cis p3. Therefore, the widths w22and w23of the connection area550band550care both equal to p3.

In the present modification example, p1=p2=p3, and w11=w22=w23=W14=p1=p2=p3.

In the same manner as the heights d11and d14, the heights d22and d23are defined by a distance from the signal input side318ato a far end of the signal connection portion between the signal conductor pattern330band the input signal terminal124d, and a distance to a far end of the signal connection portion between the signal conductor pattern330cand the input signal terminal124c.

Specifically, in the same manner as the ground conductor patterns340aand340e, within the connection area550b, the ground conductor pattern540cis configured so that a gap g22between the ground conductor pattern540cand the signal conductor pattern330bis different from a gap g21(more specifically, larger than g21) between the signal conductor pattern330band the ground conductor pattern340b. Further, the ground conductor pattern540cis configured so that a gap g31between the ground conductor pattern540cand the signal conductor pattern330cis different from a gap g32(more specifically, greater than g32) between the signal conductor pattern330cand the ground conductor pattern340dwithin the connection area550c. In the relay substrate518as well, the signal conductor patterns330and the ground conductor patterns340a,340b,540c,340d, and340eare formed so that respective characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

Thus, in the relay substrate518, a gap g22is set to be larger than a gap g21within the connection area550b, so that leaked microwaves generated at the signal connection portion between the signal conductor pattern330band the input signal terminal124b(therefore, generated from the connection area550b) have a larger intensity distribution than the other angular ranges in an angular range sandwiched between arrows590cand590dof broken lines, for example, in a direction of the ground conductor pattern540c. As a result, an intensity of a part of the leaked microwave that reaches the adjacent signal conductor pattern330awithin the other angular range is relatively reduced.

That is, in the same manner as the relay substrate118, in the relay substrate518, an intensity of a part of the leaked microwave generated at the signal connection portion between the signal conductor pattern330aand the input signal terminal124athat reaches the adjacent signal conductor pattern330bis reduced, and an intensity of a part of the leaked microwave generated at the signal connection portion between the signal conductor pattern330band the input signal terminal124bthat reaches the adjacent signal conductor pattern330ais also reduced.

Therefore, in the relay substrate518, crosstalk between the signal conductor patterns330aand330brespectively propagating the two paired high-frequency electrical signals is effectively suppressed.

In the same manner, in the relay substrate518, an intensity of a part of the leaked microwave generated at the signal connection portion between the signal conductor pattern330dand the input signal terminal124dthat reaches the adjacent signal conductor pattern330cis reduced in the same manner as the relay substrate118, and an intensity of apart of the leaked microwave generated at the signal connection portion between the signal conductor pattern330cand the input signal terminal124c(therefore, generated from the connection area550c) that reaches the adjacent signal conductor pattern330dis also reduced by setting a gap g31to be larger than a gap g32within the connection area550c.

Therefore, in the relay substrate518, crosstalk between the signal conductor patterns330cand330d, which respectively propagate the other two high-frequency electrical signals forming the other pair, is effectively suppressed.

As a result, the relay substrate518can realize further appropriate optical modulation characteristics than the case where the relay substrate118is used.

Second Modification Example

FIG.6is a diagram illustrating a configuration of a relay substrate618according to a second modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate618can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.6, the same reference numerals as those inFIGS.4and5are used for the same components as those of the components of the relay substrates118and518illustrated inFIGS.4and5, and the above descriptions ofFIGS.4and5are adopted.

The relay substrate618is formed with the signal conductor patterns330, in the same manner as the relay substrates118and518. Therefore, in the relay substrate618, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate518.

The relay substrate618has the same configuration as the relay substrate118, but has a difference that ground conductor patterns640a,640c, and640eare provided instead of the ground conductor patterns340a,340c, and340e. In the relay substrate618as well, the signal conductor patterns330and the ground conductor patterns640a,340b,640c,340d, and640eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

In the relay substrate618according to the present modification example, two ground conductor patterns sandwiching at least one signal conductor pattern330are configured in an asymmetrical shape, by setting widths of respective portions formed within a connection area defined for the signal conductor pattern, measured in a direction orthogonal to an extending direction of the signal conductor pattern to be different from each other.

Specifically, in the relay substrate618, the ground conductor pattern640asandwiching the signal conductor pattern330atogether with the ground conductor pattern340bis configured in an asymmetrical shape with the ground conductor pattern340bwith respect to the signal conductor pattern330ain the connection area450a, by setting a width Wg11of a portion formed in the connection area450ato be different from a width Wg12of a portion formed in the connection area450ain the ground conductor pattern340b(specifically, for example, Wg11<Wg12).

In general, in a high-frequency signal line including a signal conductor and a ground conductor, the smaller the impedance from the ground conductor to a portion that supplies the ground potential (so-called ground line) (that is, the more so-called ground strengthening is sufficient), the stronger confinement of the high-frequency signal in the signal conductor.

In the relay substrate618, the formation widths Wg11and Wg12of the portions, formed in the connection area450a, in the ground conductor patterns640aand340bsandwiching the signal conductor pattern330aare different from each other. Thus, leaked microwaves generated from a signal connection portion between the signal conductor pattern330aand the input signal terminal124aare emitted toward a direction of a ground conductor pattern having a narrow formation width and a larger impedance to the ground line (for example, rear surface ground conductor) among the adjacent ground conductor patterns, that is, a direction of the ground conductor pattern640ahaving the formation width Wg11(<Wg12) (for example, in a direction range illustrated as a range sandwiched by arrows690aand690bof alternate long and short dash lines inFIG.6) so as to have a larger intensity distribution than in other directions.

Therefore, intensities of the leaked microwaves in a direction range other than the direction range sandwiched by the arrows690aand690bare relatively reduced. For example, crosstalk via the leaked microwave from the signal conductor pattern330atoward the adjacent signal conductor pattern330bis reduced.

Further, in the relay substrate618, formation widths Wg21and Wg22of the portions in the connection area550bof the ground conductor patterns340band640csandwiching the signal conductor pattern330bare different from each other. Thus, leaked microwaves generated from a signal connection portion between the signal conductor pattern330band the input signal terminal124bare emitted toward a direction of the ground conductor pattern640chaving the formation width Wg22narrower than Wg21and a larger impedance to the ground line (for example, in a direction range illustrated as a range sandwiched by arrows690cand690dof alternate long and short dash lines inFIG.6) so as to have a larger intensity distribution than the other directions.

Therefore, intensities of the leaked microwaves in a direction range other than the direction range sandwiched by the arrows690cand690dare relatively reduced. For example, crosstalk via the leaked microwave from the signal conductor pattern330btoward the adjacent signal conductor pattern330ais also reduced. As a result, in the same manner as the relay substrate518illustrated inFIG.5, crosstalk between the signal conductor patterns330aand330brespectively propagating the two paired high-frequency electrical signals is effectively suppressed.

In the same manner, in the relay substrate618, formation widths Wg31and Wg32of portions in the connection area550cof the ground conductor patterns640cand340dsandwiching the signal conductor pattern330chave an asymmetric relationship of Wg31<Wg32, and formation widths Wg41and Wg42of portions in the connection area450dof the ground conductor patterns340dand640esandwiching the signal conductor pattern330dhave an asymmetric relationship of Wg41>Wg42.

Therefore, in the relay substrate618, crosstalk from the signal conductor pattern330cto the adjacent signal conductor pattern330dvia the leaked microwave generated from the signal connection portion between the signal conductor pattern330cand the input signal terminal124cand crosstalk from the signal conductor pattern330dto the adjacent signal conductor pattern330cvia the leaked microwave generated from the signal connection portion between the signal conductor pattern330dand the input signal terminal124dare suppressed.

As a result, in the relay substrate618, in the same manner as the relay substrate518illustrated inFIG.5, crosstalk between paired high-frequency signals is further suppressed and appropriate optical modulation characteristics can be realized, as compared with the relay substrate118.

In particular, in the configuration of the relay substrate618, in the connection areas450a,550b,550c, and450d, although the formation widths of the ground conductor patterns640a,640b,640c,340d, and640eeach of which sandwiches the corresponding signal conductor pattern330are different from each other, distances from the respective signal conductor patterns330to opposite edges of the adjacent ground conductor patterns640a,340b,640c,340d,640eare equal to each other. Therefore, even when the formation widths of the ground conductor patterns640a,640b,640c,340d, and640esandwiching the signal conductor patterns330are changed, a change in the characteristic impedance of the signal conductor pattern330is small. Therefore, the relay substrate618can be easily configured so that the characteristic impedance of each of the signal conductor patterns330does not change inside and outside the connection areas450a,550b,550c, and450d. However, even when a difference in formation width in the connection area (for example, Wg11and Wg12) of the two ground conductor patterns sandwiching the signal conductor pattern is set large, a polarization direction of the leaked microwaves do not change as much as in the case of the relay substrates118and518.

Therefore, the configuration of the relay substrate618is appropriate when it is desired to suppress the influence of the leaked microwave while maintaining the consistency with the design in the related art (for example, pattern design in the related art for ground conductor pattern in relay substrate) as much as possible in the case where the influence of the leaked microwaves is relatively small.

Third Modification Example

FIG.7is a diagram illustrating a configuration of a relay substrate718according to a third modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate718can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.7, the same reference numerals as those inFIGS.4,5, and6are used for the same components as those of the components of the relay substrates118,518, and618illustrated inFIGS.4,5, and6, and the above descriptions ofFIGS.4,5, and6are adopted.

The relay substrate718is formed with the signal conductor patterns330in the same manner as the relay substrates118and518illustrated inFIGS.4and5. Therefore, in the relay substrate718, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate518.

The relay substrate718has the same configuration as the relay substrate118, but has a difference that ground conductor patterns740a,740c, and740eare provided instead of the ground conductor patterns340a,340c, and340e. In the relay substrate718as well, the signal conductor patterns330and the ground conductor patterns740a,340b,740c,340d, and740eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

In the relay substrate718according to the present modification example, one of two ground conductor patterns sandwiching at least one signal conductor pattern330is configured in an asymmetrical shape with respect to the signal conductor pattern, by not including a portion formed within a connection area defined for the signal conductor pattern.

Specifically, in the relay substrate718, the one ground conductor pattern740adoes not include a pattern formed within the connection area450a, so that the ground conductor patterns740aand340bsandwiching the signal conductor pattern330aare formed asymmetrically with respect to the signal conductor pattern330a. Further, in the relay substrate718, the one ground conductor pattern740cdoes not include a pattern formed within the connection area550b, so that the ground conductor patterns340band740csandwiching the signal conductor pattern330bare formed asymmetrically with respect to the signal conductor pattern330b.

In the same manner, in the relay substrate718, the one ground conductor pattern740cdoes not include a pattern formed within the connection area550c, so that the ground conductor patterns740cand340dsandwiching the signal conductor pattern330care formed asymmetrically with respect to the signal conductor pattern330c. Further, in the relay substrate718, the one ground conductor pattern740edoes not include a pattern formed within the connection area450d, so that the ground conductor patterns340dand740esandwiching the signal conductor pattern330dare formed asymmetrically with respect to the signal conductor pattern330d.

This relay substrate718corresponds to a case where Wg11, Wg22, Wg31, and Wg42are set to 0 (zero) in the relay substrate618inFIG.6of the second modification example described above. Therefore, in the relay substrate718, crosstalk via leaked microwaves between the signal conductor patterns330aand330brespectively propagating two paired high-frequency electrical signals, and crosstalk via leaked microwaves between the signal conductor patterns330cand330drespectively propagating the other two paired high-frequency electrical signals are further reduced, as compared with the relay substrate618. As a result, in a case where the relay substrate718is used, further appropriate optical modulation characteristics can be realized as compared with the case where the relay substrate618is used.

In the present modification example, for example, the one ground conductor pattern740adoes not include a pattern formed within the connection area450a, so that the ground conductor patterns740aand340bsandwiching the signal conductor pattern330aare formed asymmetrically with respect to the signal conductor pattern330a, but the present modification example is not limited to this. Instead of this, for example, the ground conductor patterns740aand340bsandwiching the signal conductor pattern330amay be formed asymmetrically with respect to the signal conductor pattern330a, by setting a range (area) in which the one ground conductor pattern740ais formed within the connection area450ato be smaller than a range (area) in which the other ground conductor pattern340bis formed within the connection area550b.

Fourth Modification Example

FIG.8is a diagram illustrating a configuration of a relay substrate818according to a fourth modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate818can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.8, the same reference numerals as those inFIGS.4and5are used for the same components as those of the components of the relay substrates118and518illustrated inFIGS.4and5, and the above description ofFIG.4is adopted.

The relay substrate818is formed with the signal conductor patterns330in the same manner as the relay substrates118and518of the first embodiment and the first modification example illustrated inFIGS.4and5. Therefore, in the relay substrate818, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate518.

The relay substrate818has the same configuration as the relay substrate118, but has a difference that ground conductor patterns840a,840b,840c,840d, and840eare provided instead of the ground conductor patterns340a,340b,340c,340d, and340e. In the relay substrate818as well, the signal conductor patterns330and the ground conductor patterns840a,840b,840c,840d, and840eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

In the relay substrate818according to the present modification example, a notched portion extending from the signal input side318aand penetrating the relay substrate818in a thickness direction is provided, at a portion at which one of the two ground conductor patterns sandwiching the signal conductor pattern330is formed, in a connection area for at least one signal conductor pattern330.

As an example, in the relay substrate818illustrated inFIG.8, a notched portion860aextending from the signal input side318aand penetrating the relay substrate818in the thickness direction is provided, at a portion at which one ground conductor pattern840bof the two ground conductor patterns840aand840bsandwiching the signal conductor pattern330ais formed, in the connection area450adefined for the signal conductor pattern330a. Thus, the ground conductor patterns840aand840bare configured in an asymmetrical shape with respect to the signal conductor pattern330ain the connection area450a.

InFIG.8, an outline of the relay substrate818is drawn with a thick line in order to clearly illustrate the notched portion860aand other notched portions860b,860c, and860dwhich will be described below. Further, inFIG.8, for the same purpose, broken lines and alternate long and short dash lines indicating the connection areas450a,550b,550c, and450dare drawn so as not to overlap the signal input side318aof the relay substrate818. However, the definitions of the connection areas450a,550b,550c, and450dhave the same manner as the definitions in the first embodiment and its modification examples described above.

Further, in the relay substrate818, the notched portion860bextending from the signal input side318aand penetrating the relay substrate818in the thickness direction is provided, at a portion at which one ground conductor pattern840bof the two ground conductor patterns840band840csandwiching the signal conductor pattern330bis formed, in the connection area550bdefined for the signal conductor pattern330b.

With the above configuration, in the relay substrate818, substrate leaked microwaves generated from a connection point between the signal conductor pattern330aand the input signal terminal124aand propagating in a substrate material of the relay substrate818is prevented from propagating to the adjacent signal conductor pattern330b, by a space formed by the notched portion860a. Further, substrate leaked microwaves generated from a connection point between the signal conductor pattern330band the input signal terminal124band propagating in the substrate material of the relay substrate818is prevented from propagating to the adjacent signal conductor pattern330a, by a space formed by the notched portion860b.

In the same manner, in the relay substrate818, the notched portion860cextending from the signal input side318aand penetrating the relay substrate818in the thickness direction is provided, at a portion at which one ground conductor pattern840dof the two ground conductor patterns840cand840dsandwiching the signal conductor pattern330cis formed, in the connection area550cdefined for the signal conductor pattern330c.

Further, in the relay substrate818, the notched portion860dextending from the signal input side318aand penetrating the relay substrate818in the thickness direction is provided, at a portion at which one ground conductor pattern840dof the two ground conductor patterns840dand840esandwiching the signal conductor pattern330dis formed, in the connection area450ddefined for the signal conductor pattern330d.

With the above configuration, in the relay substrate818, substrate leaked microwaves generated from a signal connection portion between the signal conductor pattern330cand the input signal terminal124cand propagating in the substrate material of the relay substrate818is prevented from propagating to the adjacent signal conductor pattern330d, by a space formed by the notched portion860c. Further, substrate leaked microwaves generated from a signal connection portion between the signal conductor pattern330dand the input signal terminal124dand propagating in the substrate material of the relay substrate818is prevented from propagating to the adjacent signal conductor pattern330c, by a space formed by the notched portion860d.

Therefore, in the relay substrate818, crosstalk via substrate leaked microwaves between the signal conductor patterns330aand330brespectively propagating two paired high-frequency electrical signals, and crosstalk via substrate leaked microwaves between the signal conductor patterns330cand330drespectively propagating the other two paired high-frequency electrical signals are further reduced. As a result, if the relay substrate818is used in the optical modulator100, appropriate optical modulation characteristics can be realized as the optical modulator100.

In the relay substrate818, if an inner wall of the notched portion860aor the like is metallized so as to extend from the ground conductor pattern840bor the like, the effect of suppressing the propagation of the substrate leaked microwaves as described above can be further enhanced.

Fifth Modification Example

FIG.9is a diagram illustrating a configuration of a relay substrate918according to a fifth modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate918can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.9, the same reference numerals as those inFIGS.4,5,6,7, and8are used for the same components as those of the components of the relay substrates118,518,618,718, and818illustrated inFIGS.4,5,6,7, and8, and the above descriptions ofFIGS.4,5,6,7, and8are adopted.

The relay substrate918is formed with the signal conductor patterns330in the same manner as the relay substrates118and518of the first embodiment and the first modification example illustrated inFIGS.4and5. Therefore, in the relay substrate818, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate518.

Here, the relay substrate918is configured by combining the feature configurations of the relay substrate718inFIG.7of the third modification example and the relay substrate818inFIG.8of the fourth modification example. That is, the relay substrate918has the same configuration as the relay substrate118, but has a difference that ground conductor patterns740a,840b,740c,840d, and740eare provided instead of the ground conductor patterns340a,340b,340c,340d, and340e. In the relay substrate918as well, the signal conductor patterns330and the ground conductor patterns740a,840b,740c,840d, and740eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

In particular, on the relay substrate918, the four notched portions860a,860b,860c,860dextending from the signal input side318aand penetrating the relay substrate918in a thickness direction are provided, at the same positions as the relay substrate818inFIG.8of the fourth modification example described above.

InFIG.9, in the same manner asFIG.8of the fourth modification example described above, an outline of the relay substrate918is drawn with a thick line in order to clearly illustrate the notched portion860aand other notched portions860b,860c, and860dwhich will be described below. Further, inFIG.9, for the same purpose, broken lines and alternate long and short dash lines indicating the connection areas450a,550b,550c, and450dare drawn so as not to overlap the signal input side318aof the relay substrate918. However, the definitions of the connection areas450a,550b,550c, and450dhave the same manner as the definitions in the first embodiment and its modification examples described above.

Thus, in the relay substrate918, in the same manner as the relay substrate818inFIG.7of the third modification example, crosstalk via substrate leaked microwaves is further reduced between the signal conductor patterns330aand330brespectively propagating the two paired high-frequency electrical signals, as compared with the case of the relay substrate718. In the same manner, crosstalk via substrate leaked microwaves is further reduced between the signal conductor patterns330cand330drespectively propagating the other two paired high-frequency electrical signals in the same manner as the relay substrate818, as compared with the case of the relay substrate718inFIG.7of the third modification example.

As a result, in a case where the relay substrate918is used for the optical modulator100, further appropriate optical modulation characteristics can be realized as the optical modulator100, as compared with the cases where the other relay substrates118,518,628,718, and818according to the first embodiment, the first modification example, the second modification example, the third modification example, and the fourth modification example illustrated inFIGS.4,5,6,7, and8described above are used.

In the same manner as the case of the relay substrate818, if an inner wall of the notched portion860aor the like is metallized so as to extend from the ground conductor pattern840bor the like, the effect of suppressing the propagation of the substrate leaked microwaves can be further enhanced.

Sixth Modification Example

FIG.10is a diagram illustrating a configuration of a relay substrate1018according to a sixth modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate1018can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.10, the same reference numerals as those inFIGS.4and5are used for the same components as those of the components of the relay substrates118and518illustrated inFIGS.4and5, and the above descriptions ofFIGS.4and5are adopted.

The relay substrate1018is formed with the signal conductor patterns330in the same manner as the relay substrates118and518of the first embodiment and the first modification example illustrated inFIGS.4and5. Therefore, in the relay substrate818, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate118.

In the relay substrate118inFIG.4of the first embodiment described above, for example, the ground conductor patterns340aand340bsandwiching the signal conductor pattern330aare formed in an asymmetrical shape with respect to the signal conductor pattern330awithin the connection area450a, so that intensities with which leaked microwaves generated within the connection area450areaches the adjacent signal conductor pattern330bis reduced. On the other hand, the relay substrate1018in the present modification example is formed so that within a connection area defined for at least one signal conductor pattern, respective portions, within the connection portion, of two adjacent ground conductor patterns sandwiching the signal conductor pattern have different impedances with respect to a ground line component (for example, a rear surface ground conductor of the relay substrate1018).

In particular, as an example, in the relay substrate1018, within the connection area defined for at least one signal conductor pattern, the respective portions, within the connection area, of the two adjacent ground conductor patterns sandwiching the signal conductor pattern have a difference in the presence or absence of vias (that is, the vias are provided only in one of the portions) so that the impedances are different from each other.

Specifically, the relay substrate1018has the same configuration as the relay substrate118of the first embodiment illustrated inFIG.4, but has a difference that ground conductor patterns1040a,1040b,1040c,1040d, and1040eare provided instead of the ground conductor patterns340a,340b,340c,340d, and340e. In the relay substrate1018as well, the signal conductor patterns330and the ground conductor patterns1040a,1040b,1040c,1040d, and1040eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

Six vias1062are formed in each of the ground conductor patterns1040band1040d. InFIG.10, reference numeral1062is attached to only one of the six vias in each of the ground conductor patterns1040band1040din order to avoid redundant description. It should be understood that in each of the ground conductor patterns1040band1040d, the other five circles drawn in the same size as the via1062to which the reference numeral is attached have the same manner as the via1062.

Specifically, in the adjacent ground conductor patterns1040aand1040bsandwiching the signal conductor pattern330a, only one ground conductor pattern1040bis connected to the rear surface ground conductor by the two vias1062, and such vias are not provided in the other ground conductor pattern1040a, within the connection area450adefined for the signal conductor pattern330a.

Further, in the adjacent ground conductor patterns1040band1040csandwiching the signal conductor pattern330b, only one ground conductor pattern1040bis connected to the rear surface ground conductor by the two vias1062, and such vias are not provided in the other ground conductor pattern1040c, within the connection area550bdefined for the signal conductor pattern330b.

In the same manner, in the adjacent ground conductor patterns1040cand1040dsandwiching the signal conductor pattern330c, only one ground conductor pattern1040dis connected to the rear surface ground conductor by the two vias1062, and such vias are not provided in the other ground conductor pattern1040c, within the connection area550cdefined for the signal conductor pattern330c.

Further, in the adjacent ground conductor patterns1040dand1040esandwiching the signal conductor pattern330d, only one ground conductor pattern1040dis connected to the rear surface ground conductor by the two vias1062, and such vias are not provided in the other ground conductor pattern1040e, within the connection area450ddefined for the signal conductor pattern330d.

As described above in relation to the relay substrate618according to the second modification example, in general, in a high-frequency signal line including a signal conductor and a ground conductor, the smaller the impedance from the ground conductor to a ground line (that is, the more so-called ground strengthening is sufficient), the stronger confinement of the high-frequency signal in the signal conductor.

Therefore, in the relay substrate1018, leaked microwaves generated in the connection area450aand550bhave higher intensities in a direction of the ground conductor patterns1040aand1040cthat are not connected to the rear surface ground conductor by the vias1062, respectively (therefore, the impedance to the rear surface ground conductor is higher), and intensities in the other direction are reduced. Therefore, in the relay substrate1018, in the same manner as in the relay substrate118, crosstalk via the leaked microwaves is reduced between the signal conductor patterns330aand330brespectively propagating the two paired high-frequency electrical signals. In the same manner, leaked microwaves generated in the connection area550cand450dhave higher intensities in a direction toward the ground conductor patterns1040cand1040ein which the via1062is not formed and an impedance to the rear surface ground conductor is higher, respectively, and intensities in the other direction are reduced. Therefore, in the relay substrate1018, crosstalk via the leaked microwaves is reduced between the signal conductor patterns330cand330drespectively propagating the other two paired high-frequency electrical signals.

As a result, even in a case where the relay substrate1018is used, appropriate optical modulation characteristics can be realized as the optical modulator100.

Seventh Modification Example

FIG.11is a diagram illustrating a configuration of a relay substrate1118according to a seventh modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate1118can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.11, the same reference numerals as those inFIGS.4,5, and10are used for the same components as those of the components of the relay substrates118,518, and1080illustrated inFIGS.4,5, and10, and the above descriptions ofFIGS.4,5, and10are adopted.

The relay substrate1118is formed with the signal conductor patterns330in the same manner as the relay substrates118and518of the first embodiment and the first modification example illustrated inFIGS.4and5. Therefore, in the relay substrate818, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate118.

In the same manner as the relay substrate1018inFIG.10of the sixth modification example described above, the relay substrate1118in the present modification example is formed so that within a connection area defined for at least one signal conductor pattern, respective portions, within the connection portion, of two adjacent ground conductor patterns sandwiching the signal conductor pattern have different impedances with respect to a ground line component (for example, a rear surface ground conductor of the relay substrate1118).

However, unlike the relay substrate1018, in the relay substrate1118, diameters of vias provided in the respective portions of the two adjacent ground conductor patterns sandwiching at least one signal conductor pattern within the connection area defined for the signal conductor pattern are different from each other, so that the impedances are different from each other.

Specifically, the relay substrate1118is different from the relay substrate1080in that ground conductor patterns1140a,1140c, and1140eare provided in place of the ground conductor patterns1040a,1040c, and1040e. In the relay substrate1118as well, the signal conductor patterns330and the ground conductor patterns1140a,1040b,1140c,1040d, and1140eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

The ground conductor patterns1140a,1140c, and1140ehave the same configuration as the ground conductor patterns1040a,1040c, and1040e, but have a difference that within the respective corresponding connection area450a,550b,550c,450d, the same number of vias1162as the vias1062having a diameter smaller than a diameter of the vias1062are provided. Here, inFIG.11, the reference numeral1162is attached to only one of the vias in each of the ground conductor patterns1140a,1140c, and1140ein order to avoid redundant description. It should be understood that in each of the ground conductor patterns1140a,1140c, and1140e, the other two, five, and two circles drawn in the same size as the via1162to which the reference numeral is attached have the same manner as the via1162.

Specifically, within the connection area450adefined for the signal conductor pattern330a, one ground conductor pattern1140bsandwiching the signal conductor pattern330ais connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1140ais connected to the rear surface ground conductor by the vias1162having the same number (that is, two in this example) and the diameter smaller than the diameter of the via1062.

Further, within the connection area550bdefined for the signal conductor pattern330b, one ground conductor pattern1140bsandwiching the signal conductor pattern330bis connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1140cis connected to the rear surface ground conductor by the vias1162having the same number and the diameter smaller than the diameter of the via1062.

In the same manner, within the connection area550cdefined for the signal conductor pattern330c, one ground conductor pattern1040dsandwiching the signal conductor pattern330cis connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1140cis connected to the rear surface ground conductor by the vias1162having the same number and the diameter smaller than the diameter of the via1062.

Further, within the connection area450ddefined for the signal conductor pattern330d, one ground conductor pattern1040dsandwiching the signal conductor pattern330dis connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1140eis connected to the rear surface ground conductor by the vias1162having the same number and the diameter smaller than the diameter of the via1062.

Thus, in the relay substrate1118, in the same manner as the relay substrate1018inFIG.10of the sixth modification example described above, leaked microwaves generated in the connection areas450aand550brespectively have higher intensities in a direction toward the ground conductor patterns1040aand1040cin which the vias1162having small diameters are provided and impedances with the rear surface ground conductor are higher, and intensities in the other direction are reduced. Therefore, in the relay substrate1118, in the same manner as in the relay substrate1018, crosstalk via the leaked microwaves is reduced between the signal conductor patterns330aand330brespectively propagating the two paired high-frequency electrical signals.

In the same manner, in the relay substrate1118, leaked microwaves generated in the connection area550cand450drespectively have higher intensities in a direction to the ground conductor patterns1140cand1140ein which the vias1162having small diameters are provided and impedances with the rear surface ground conductor are higher, and intensities in the other direction are reduced. Therefore, in the relay substrate1118, in the same manner as the relay substrate1018inFIG.10of the sixth modification example described above, crosstalk via the leaked microwaves is also reduced between the signal conductor patterns330cand330drespectively propagating the other two paired high-frequency electrical signals.

As a result, even in a case where the relay substrate1118is used, appropriate optical modulation characteristics can be realized as the optical modulator100.

Eighth Modification Example

FIG.12is a diagram illustrating a configuration of a relay substrate1218according to an eighth modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate1218can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.12, the same reference numerals as those inFIGS.4,5,10, and11are used for the same components as those of the components of the relay substrates118,518,1018, and1118illustrated inFIGS.4,5,10, and11, and the above descriptions ofFIGS.4,5,10, and11are adopted.

The relay substrate1218is formed with the signal conductor patterns330in the same manner as the relay substrates118and518of the first embodiment and the first modification example illustrated inFIGS.4and5. Therefore, in the relay substrate1218, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate118.

In the same manner as the relay substrates1018and1118in the sixth modification example and the seventh modification example illustrated inFIGS.10and11, the relay substrate1218is configured so that respective portions of two adjacent ground conductor patterns sandwiching at least one signal conductor pattern within a connection area defined for the signal conductor pattern are formed to have different impedances with respect to a ground line component (for example, the rear surface ground conductor of the relay substrate1118).

However, unlike the relay substrates1018and1118, in the relay substrate1218, the numbers of vias provided in the respective portions of the two adjacent ground conductor patterns sandwiching at least one signal conductor pattern within the connection area defined for the signal conductor pattern are different from each other, so that the impedances are different from each other.

Specifically, the relay substrate1218is different from the relay substrate1118in that the ground conductor patterns1240a,1240c, and1240eare provided in place of the ground conductor patterns1140a,1140c, and1140e. In the relay substrate1218as well, the signal conductor patterns330and the ground conductor patterns1240a,1040b,1240c,1040d, and1240eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

Within the connection area450adefined for the signal conductor pattern330a, one ground conductor pattern1140bsandwiching the signal conductor pattern330ais connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1140ais connected to the rear surface ground conductor by a smaller number of vias1062(that is, one in this example).

Further, within the connection area550bdefined for the signal conductor pattern330b, one ground conductor pattern1140bsandwiching the signal conductor pattern330bis connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1240cis connected to the rear surface ground conductor by a smaller number of vias1062(one in this example).

In the same manner, within the connection area550cdefined for the signal conductor pattern330c, one ground conductor pattern1040dsandwiching the signal conductor pattern330cis connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1240cis connected to the rear surface ground conductor by a via1062which number is smaller than the number of the two vias1062on the ground conductor pattern1040d.

Further, within the connection area450ddefined for the signal conductor pattern330d, one ground conductor pattern1040dsandwiching the signal conductor pattern330dis connected to the rear surface ground conductor by the two vias1062and the other ground conductor pattern1240eis connected to the rear surface ground conductor by the vias1162having a diameter smaller than diameters of a smaller number of vias1062a via1062which number is smaller than the number of the two vias1062on the ground conductor pattern1040d.

Thus, in the relay substrate1218, in the same manner as the relay substrate1118of the seventh modification example illustrated inFIG.11described above, leaked microwaves generated in the connection areas450aand550brespectively have higher intensities in a direction toward the ground conductor patterns1040aand1040cin which the smaller number of vias1062as compared with the ground conductor pattern1040bare provided and impedances with the rear surface ground conductor are higher, and intensities in the other direction are reduced. Therefore, in the relay substrate1218, in the same manner as in the relay substrate1118, crosstalk via the leaked microwaves is reduced between the signal conductor patterns330aand330brespectively propagating the two paired high-frequency electrical signals.

In the same manner, in the relay substrate1218, leaked microwaves generated in the connection area550cand450drespectively have higher intensities in a direction to the ground conductor patterns1140cand1140ein which the smaller number of vias1062as compared with the ground conductor pattern1040dare provided and impedances with the rear surface ground conductor are higher, and intensities in the other direction are reduced. Therefore, in the relay substrate1218, in the same manner as in the relay substrate1118, crosstalk via the leaked microwaves is also reduced between the signal conductor patterns330cand330drespectively propagating the other two paired high-frequency electrical signals.

As a result, even in a case where the relay substrate1218is used, appropriate optical modulation characteristics can be realized as the optical modulator100.

Ninth Modification Example

Each feature configuration within the connection area illustrated in each of the above-described modification examples can be combined and/or overlapped in one relay substrate. The present modification example illustrates examples of such a relay substrate.

FIG.13is a diagram illustrating a configuration of a relay substrate1318according to a ninth modification example, and is a diagram corresponding to the partial detail view of the first embodiment illustrated inFIG.4. The relay substrate1218can be used instead of the relay substrate118in the optical modulator100illustrated inFIG.1. InFIG.12, the same reference numerals as those inFIGS.4,5,6,7,8,10are used for the same components as those of the components of the relay substrates118,518,618,718,818, and1018illustrated inFIGS.4,5,6,7,8,10, and the above descriptions ofFIGS.4,5,6,7,8,10are adopted.

The relay substrate1318is formed with the signal conductor patterns330in the same manner as the relay substrates118and518of the first embodiment and the first modification example illustrated inFIGS.4and5. Therefore, in the relay substrate1318, the connection areas450a,550b,550c, and450dare defined for each of the signal conductor patterns330, in the same manner as the relay substrate118.

In the relay substrate1318according to the ninth modification example, the feature configurations of the relay substrates118,618, and718the first embodiment, the second modification example, and the third modification example illustrated inFIGS.4,6, and7are respectively applied to the connection areas450a,550b, and550cdefined for the signal conductor patterns330a,330b, and330c, and the feature configurations of the relay substrates118and1018of the first embodiment and the sixth modification example illustrated inFIGS.4and10are applied to the signal conductor pattern330din an overlapped manner.

The relay substrate1318has the same configuration as the relay substrate118, but has a difference that ground conductor patterns1340cand1340dare provided instead of the ground conductor patterns340cand340d. In the relay substrate1318as well, the signal conductor patterns330and the ground conductor patterns340a,340b,1340c,1340d, and340eare formed so that characteristic impedances of the signal conductor patterns330are the same inside and outside the connection areas of450a,550b,550c, and450d.

The relay substrate1318has the ground conductor patterns340aand340bin the same manner as the relay substrate118. Thus, crosstalk via leaked microwaves generated from the connection area450atoward the signal conductor patterns330ato330bis suppressed for the reason described above in relation to the relay substrate118.

The ground conductor pattern1340chas the same configuration as the ground conductor pattern340c, but is configured so that the formation width Wg22of a portion within the connection area550bis narrower than the formation width Wg21of a portion within the connection area550bof the opposite ground conductor pattern340bsandwiching the signal conductor pattern330b, in the same manner as the relay substrate618of the second modification example illustrated inFIG.6. Thus, crosstalk via leaked microwaves generated from the connection area550btoward the signal conductor patterns330bto330ais suppressed for the reason described above in relation to the relay substrate618.

Further, the ground conductor pattern1340cdoes not include a pattern formed in the connection area550cin the same manner as the relay substrate718of the third modification example illustrated inFIG.7. The ground conductor pattern1340dis formed in the same shape as the ground conductor pattern340dwithin the connection area450d. Therefore, crosstalk via leaked microwaves generated from the connection area550ctoward the signal conductor patterns330cto330dis suppressed for the reason described above in relation to the relay substrate718.

Further, in the connection area450dof the relay substrate1318, in the same manner as in the relay substrate118of the first embodiment illustrated inFIG.4, gaps (g41and g42inFIG.13) between respective edges facing the signal conductor pattern330dand edges of the signal conductor pattern330drespectively facing the edges are different from each other, so that the ground conductor patterns1340dand340esandwiching the signal conductor pattern330dare formed in an asymmetrical shape with respect to the signal conductor pattern330din the connection area450d. Further, in the connection area450dof the relay substrate1318, in the same manner as in the relay substrate1018of the sixth modification example illustrated inFIG.10, only the ground conductor pattern1340dis connected to the rear surface ground conductor by the two vias1062, and such vias are not provided at the ground conductor pattern340e. Therefore, in the relay substrate1318, crosstalk via leaked microwaves generated from the connection area450dtoward the signal conductor patterns330dto330cis suppressed for the reason described above in relation to the relay substrates518and1018of the second modification example and the sixth modification example illustrated inFIGS.5and10.

As a result, even in a case where the relay substrate1318is used, appropriate optical modulation characteristics can be realized as the optical modulator100.

The method of combining and overlapping the feature configurations of the relay substrates118,518,618,718,818,918,1018,1118, and1218when constructing one relay substrate is not limited to the configuration of the relay substrate1318described above. These feature configurations can be combined and/or overlapped in any manner for the purpose of suppressing crosstalk via leaked microwaves and/or substrate leaked microwaves between adjacent signal conductor patterns, based on the above-described crosstalk suppression principle related to these relay substrates.

Second Embodiment

Next, a second embodiment of the present invention will be described. The present embodiment provides an optical transmission apparatus on which any optical modulator of the optical modulator100according to the first embodiment and the optical modulators100using the relay substrates518,618,718,818,918,1018,1118,1218,1318according to the modification examples is mounted.

FIG.14is a diagram illustrating a configuration of an optical transmission apparatus according to the present embodiment. An optical transmission apparatus2100includes an optical modulator2102, a light source2104that inputs light to the optical modulator2102, a modulation signal generation part2106, and a modulation data generation part2108.

The optical modulator2102can be any optical modulator of the optical modulator100according to the first embodiment and the optical modulators100using the relay substrates518,618,718,818,918,1018,1118,1218, and1318according to the modification examples described above. Here, in order to avoid redundant description and facilitate understanding, the optical modulator2102is assumed to be the optical modulator100according to the first embodiment, hereinafter.

The modulation data generation part2108receives transmission data given from the outside, generates modulation data for transmitting the transmission data (for example, data obtained by converting or processing transmission data into a predetermined data format), and outputs the generated modulation data to the modulation signal generation part2106.

The modulation signal generation part2106is an electronic circuit (drive circuit) that outputs an electrical signal for causing the optical modulator2102to perform a modulation operation, generates a modulation signal which is a high-frequency signal for making the optical modulator2102perform an optical modulation operation according to the modulation data, based on the modulation data which is output by the modulation data generation part2108, and inputs the generated modulation signal to the optical modulator2102. The modulation signal includes four high-frequency electrical signals corresponding to the four signal electrodes112a,112b,112c, and112dof the optical modulation element102provided in the optical modulator2102. Here, the high-frequency electrical signals input to the signal electrodes112aand112bform a pair, and output light output from one output optical waveguide126aof the optical modulation element102is modulated. Further, the high-frequency electrical signals input to the signal electrodes112cand112dform the other pair, and output light output from the other output optical waveguide126bof the optical modulation element102is modulated.

The four high-frequency electrical signals are input from the input signal terminals124a,124b,124c, and124dof the respective electrical connectors116a,116b,116c, and116dof the optical modulator2102to the signal conductor patterns330a,330b,330c, and330don the relay substrate118, and are input to the signal electrodes112a,112b,112c, and112dof the optical modulation element102via the signal conductor pattern330aor the like.

Thus, the light output from the light source2104is, for example, DP-QPSK modulated by the optical modulator2102and output as modulated light from the optical transmission apparatus2100.

In particular, in the optical transmission apparatus2100, as the optical modulator2102, any optical modulator of the optical modulator100according to the first embodiment and the optical modulators100using the relay substrates518,618,718,818,918,1018,1118,1218,1318according to the modification examples is used. Therefore, in the optical transmission apparatus2100, it is possible to effectively reduce an increase in crosstalk between the high-frequency electrical signals for driving the optical modulation element102due to the above-described space leaked microwaves, particularly, crosstalk via space leaked microwaves between the signal lines propagating the two paired high-frequency electrical signals. Therefore, in the optical transmission apparatus2100, it is possible to ensure stable and appropriate optical modulation characteristics, and to realize stable and appropriate transmission characteristics.

The present invention is not limited to the configurations of the embodiments and the modification examples described above, and can be realized in various aspects without departing from the spirit thereof.

For example, the above-described relay substrates118,518,618,718,818,918,1018,1118,1218, and1318are examples of a configuration in which regarding at least one signal conductor pattern330, the two ground conductor patterns sandwiching the signal conductor pattern are asymmetrically formed in the connection area, and the present invention is not limited to these. As long as the two ground conductor patterns sandwiching the signal conductor pattern are asymmetrically formed in the corresponding connection area, the two ground conductor patterns can be formed in any shape and/or any number of vias can be arranged in any position.

In this case, in a case where at least one signal conductor pattern330and the adjacent signal conductor pattern330respectively propagate two paired high-frequency signals, the two ground conductor patterns sandwiching the at least one signal conductor pattern330are desirable to be formed to reduce intensities of leaked microwaves generated from the corresponding connection area in a direction toward the adjacent signal conductor pattern330. Specifically, among the two ground conductor patterns sandwiching the at least one signal conductor pattern330, an impedance of the ground conductor pattern on a side farther from the adjacent signal conductor pattern330with respect to the ground line component can be increased. Alternatively, a distance between the at least one signal conductor pattern and the far-side ground conductor pattern can be increased to reduce a confinement intensity of the far-side high-frequency signal. A more specific configuration for increasing the impedance and decreasing the confinement intensity is clear from the feature configurations of the relay substrates118,518,618,718,818,918,1018,1118,1218, and1318described above.

Further, in the relay substrates118,518,618,718,818,918,1018,1118,1218, and1318described above, the signal conductor pattern330is configured so that characteristic impedances of the signal conductor pattern330are not changed inside and outside the connection area450aand the like, but the present invention is not limited to this. The signal conductor pattern330may be configured so that the characteristic impedances of the signal conductor pattern330are changed inside and outside the connection area450aand the like. Even in this configuration, if the two adjacent ground conductor patterns sandwiching the signal conductor pattern are formed asymmetrically in the corresponding connection area, it is possible to reduce propagation intensities of leaked microwaves generated from the connection area in a specific direction, as compared with a case where these ground conductor patterns are formed symmetrically.

Further, in the above-described relay substrates118,518,618,718,818,918,1018,1118,1218, and1318, one ground conductor pattern is formed between two adjacent signal conductor patterns330, but the present invention is not limited to this. The ground conductor pattern sandwiched between the two adjacent signal conductor patterns330may be divided into two and formed. For example, the ground conductor pattern540csandwiched between the signal conductor patterns330band330cinFIG.5may be formed as, for example, two ground conductor patterns divided between the connection areas550band550c.

Further, in the relay substrates418and518according to the fourth and fifth modification examples illustrated inFIGS.8and9, the two notched portions are provided in one ground conductor pattern (for example, the two notched portions860aand860bin the ground conductor pattern840b), but the present invention is not limited to this. For example, the notched portions860aand860bmay be formed as one notch that covers a range of the notched portions860aand860bby removing a part of the relay substrate818between the notched portions860aand860b.

Further, for example, in the above-described relay substrates118,518,618,718,818,918,1018,1118,1218, and1318, the signal conductor pattern330is illustrated to have a straight line shape from the signal input side318atoward the signal output side318b, but the present invention is not limited to this. In the same manner as the related art, the signal conductor pattern330can include different shapes, for example, each including a curved portion or a portion having a different width.

Further, in the above-described embodiment, for at least two signal conductor patterns330, the two ground conductor patterns sandwiching each signal conductor pattern330are formed in an asymmetrical shape with respect to the corresponding signal conductor pattern in a portion within the corresponding connection area, or the impedances with respect to the ground line component is set to be different from each other, but the present invention is not limited to this.

In a case where it is sufficient to reduce only leaked microwaves generated from one specific signal conductor pattern, due to respective shapes of the signal conductor patterns330formed on the relay substrate118and the like, characteristics of the optical modulation element102, or the like, regarding only the specific signal conductor pattern, a portion within the corresponding connection area is formed in an asymmetrically with respect to the corresponding signal conductor pattern, or impedances to the ground line component is different from each other.

Further, in the relay substrates1018,1118, and1218according to the sixth modification example, the seventh modification example, and the eighth modification example described above, the ground conductor patterns sandwiching the signal conductor pattern is configured so that the number of vias or the diameters of the vias provided at a portion within the corresponding connection area are different from each other and the impedances of the portion with respect to the ground line component are different from each other, but the present invention is not limited to this.

As long as the ground conductor patterns sandwiching the signal conductor pattern are provided so that the impedances of the portion within the corresponding connection area with respect to the ground line component are different from each other, the vias can be provided in any different manner. For example, the ground conductor patterns sandwiching the signal conductor pattern may be configured so that densities of the vias provided in the corresponding connection area are different from each other. Here, the density of vias can be represented by the number of vias provided per unit area or an area of the vias provided per unit area. This is because the larger the number of vias or the area of the vias, the lower the impedance with the rear surface ground conductor which is the ground line component.

Further, in the above-described embodiment, the optical modulation element102is a DP-QPSK modulator configured by using an LN substrate, but the present invention is not limited to this. For example, the optical modulation element102may be any optical modulation element configured by using a semiconductor substrate.

As described above, the optical modulator100according to the above-described embodiment includes the optical modulation element102including a plurality of signal electrodes112, and a plurality of input signal terminals124afor inputting electrical signals to be respectively applied to the signal electrode112. Further, the optical modulator100includes the relay substrate518on which a plurality of signal conductor patterns330that electrically connect the input signal terminal124and the signal electrode112, a plurality of ground conductor patterns340, and the like are formed, and the housing104that accommodates the optical modulation element102and the relay substrate118. Then, in the optical modulator100, for example, as illustrated in the description of the relay substrates118and518as examples, for at least one signal conductor pattern, for example, the signal conductor pattern330b, the two ground conductor patterns340band540csandwiching the signal conductor pattern330bon the relay substrate518are formed in an asymmetrical shape in a plan view with respect to the signal conductor pattern330bin the connection area550bincluding a signal connection portion at which the signal conductor pattern330band the input signal terminal124bare connected. Here, the connection area550bis a rectangular range in the plan view, having the width w22equal to a distance to the nearest adjacent signal conductor pattern (for example, the distance p1to the signal conductor pattern330a) by being centered on the signal conductor pattern330b, which is the at least one signal conductor pattern and having the height d22equal to a distance from the signal input side318aon which the at least one signal conductor pattern330bis connected to the input signal terminal124bto a far end of the signal connection portion among sides of the relay substrate518.

With this configuration, for example, a propagation direction of space leaked microwaves generated from the connection area550band propagating in a space is biased and crosstalk from the signal conductor pattern330bto at least one adjacent signal conductor pattern (for example, signal conductor pattern330a) is suppressed, so that it is possible to realize appropriate optical modulation characteristics.

Further, as illustrated in the relay substrates118and518as an example, in the optical modulator100, for example, the two ground conductor patterns340aand340bsandwiching the signal conductor pattern330amay be configured so that the distances g11and g12from the respective edges facing the signal conductor pattern330ato the opposite edges of the signal conductor pattern330aare different from each other in the connection area450a.

With this configuration, without increasing a size of the relay substrate118or the like, for example, a propagation direction of space leaked microwaves generated from the connection area450aand propagating in a space is biased to suppress crosstalk from the signal conductor pattern330ato the adjacent signal conductor pattern330b, so that it is possible to realize appropriate optical modulation characteristics.

Further, as illustrated in the relay substrate618as an example, in the optical modulator100, for example, the two ground conductor patterns640aand340bsandwiching the signal conductor pattern330amay be configured so that the widths Wg11and Wg12of the portions formed in the connection area450a, measured in a direction orthogonal to an extending direction of the signal conductor pattern330aare different from each other.

With this configuration, without increasing a size of the relay substrate618, for example, a propagation direction of space leaked microwaves generated from the connection area450aand propagating in a space is biased to suppress crosstalk from the signal conductor pattern330ato the adjacent signal conductor pattern330b, so that it is possible to realize appropriate optical modulation characteristics.

Further, as illustrated in the relay substrate718as an example, in the optical modulator100, for example, one of the two ground conductor patterns740aand340bsandwiching the signal conductor pattern330a, for example, the ground conductor pattern740amay not include a portion formed within the connection area450a.

With this configuration, without increasing a size of the relay substrate718, for example, a propagation direction of space leaked microwaves generated from the connection area450aand propagating in a space is biased to suppress crosstalk from the signal conductor pattern330ato the adjacent signal conductor pattern330b, so that it is possible to realize appropriate optical modulation characteristics.

Further, as illustrated by an example in the relay substrate818as an example, for example, the optical modulator100may have a configuration in which the notched portion860aextending from the signal input side318aand penetrating the relay substrate818in the thickness direction is provided at a portion of the connection area450aat which one of the two ground conductor patterns840aand840bsandwiching the signal conductor pattern330ais formed.

With this configuration, for example, the propagation of substrate leaked microwaves generated from the connection area450aand propagating in the relay substrate818is blocked, and crosstalk from the signal conductor pattern330atoward the adjacent signal conductor pattern330bis suppressed, so that it is possible to realize appropriate optical modulation characteristics.

Further, as illustrated in the relay substrates1018,1118,1218and the like as an example, for example, the optical modulator100may have a configuration in which in a portion of the ground conductor patterns1040a,1040b, and the like sandwiching the signal conductor pattern330awithin the connection area450a, the presence or absence of vias connected to the rear surface ground conductor provided on the rear surface of the relay substrate1018or the like, or the number or a density of vias are different from each other.

With this configuration, a characteristic impedance of the signal conductor pattern300hardly changes by providing the vias in the ground conductor pattern1040or the like sandwiching the signal conductor pattern300, so that pattern design of the ground conductor pattern1040in the connection area450aor the like becomes easy. That is, appropriate optical modulation characteristics can be realized by suppressing crosstalk via space leaked microwaves between the adjacent signal conductor patterns330without complicating the design.

Further, the optical modulator100can use, for example, the optical modulation element102that performs DP-QPSK modulation, which is configured to generate two modulated light beams, each of which is modulated by a pair of electrical signals, and the relay substrate118and the like may be configured to propagate the pair of electrical signals by a pair of signal conductor patterns adjacent to each other, for example, the signal conductor patterns330aand330b.

With this configuration, crosstalk propagated by the adjacent signal conductor patterns300between the two paired high-frequency electrical signals can be effectively reduced, so that it is possible to realize appropriate optical modulation characteristics.

Further, the optical transmission apparatus according to the second embodiment described above includes the modulation operation on the optical modulator100using any of the relay substrates described in the first embodiment or the modification examples thereof, the modulation signal generation part2106which is an electronic circuit that outputs an electrical signal for causing the optical modulator100to perform a modulation operation, and the like. With this configuration, for example, the propagation of leaked microwaves, which becomes noticeable as the transmission rate is increased, is suppressed and crosstalk and the like between a plurality of high-frequency electrical signals that drive the optical modulation element102is effectively reduced, so it is possible to realize stable and appropriate transmission characteristics.

REFERENCE SIGNS LIST

100,2102,2200. . . optical modulator102,2202. . . optical modulation element104,1604,2204. . . housing108,2208. . . input optical fiber110,2210. . . output optical fiber112,112a,112b,112c,112d,2212,2212a,2212b,2212c,2212d. . . signal electrode114a,2214a. . . case114b,2214b. . . cover116,116a,116b,116c,116d,2216,2216a,2216b,2216c,2216d. . . electrical connector118,518,618,718,818,918,1018,1118,1218,1318,2218. . . relay substrate120,2220. . . terminator122,122a,122b,122c,122d,122e,2222a,2222b,2222c,2222d,2222e. . . ground electrode124,124a,124b,124c,124d,2224,2224a,2224b,2224c,2224d. . . input signal terminal126a,126b. . . output optical waveguide318a. . . signal input side318b. . . signal output side318c,318d. . . side edge326. . . conductor wire330,330a,330b,330c, and330d,2230,2230a,2230b,2230c,2230d. . . signal conductor pattern340,340a,340b,340c,340d, and340e,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 pattern450a,550b,550c,450d. . . connection area860a,860b,860c,860d. . . notched portion1062,1162. . . via2100. . . optical transmission apparatus2104. . . light source2106. . . modulation signal generation part2108. . . modulation data generation part2290. . . spherical wave