阅读说明：本技术 光调制器及光传输装置 (Optical modulator and optical transmission device ) 是由 宫崎德一 菅又彻 于 2019-01-23 设计创作，主要内容包括：在光调制器中,提高高频特性,并提高其稳定性。具备：光元件基板(102),具有光波导和控制在所述光波导中传播的光波的多个电极；及壳体(104),固定并收容所述光元件基板,所述壳体在壳体底面具备与所述多个电极分别电连接的多个信号输入端子(120等),与设置于所述光元件基板的所述多个电极分别电连接的所述多个信号输入端子分开配置于隔着该光元件基板而相对的两侧。(In an optical modulator, high frequency characteristics are improved and stability thereof is improved. The disclosed device is provided with: an optical element substrate (102) having an optical waveguide and a plurality of electrodes for controlling an optical wave propagating through the optical waveguide; and a case (104) that fixes and accommodates the optical element substrate, wherein the case includes a plurality of signal input terminals (120, etc.) electrically connected to the plurality of electrodes, respectively, on a bottom surface of the case, and the plurality of signal input terminals electrically connected to the plurality of electrodes provided on the optical element substrate are disposed on opposite sides of the optical element substrate with the optical element substrate interposed therebetween.)

1. An optical modulator is provided with:

an optical element substrate having an optical waveguide and a plurality of electrodes for controlling an optical wave propagating through the optical waveguide; and

a housing for fixing and accommodating the optical element substrate,

a plurality of signal input terminals electrically connected to the plurality of electrodes, respectively, are provided on one surface of the exterior of the case,

the plurality of signal input terminals are disposed on respective sides facing each other with the optical element substrate interposed therebetween, when viewed in a plan view in a direction perpendicular to one surface of the exterior of the housing.

2. The light modulator of claim 1,

the housing has a plurality of projections on the one face,

at least one of the protruding portions includes a fixing portion for mounting the housing to an external structure.

3. The light modulator of claim 2,

the signal input terminals constitute two terminal groups facing each other with the optical element substrate interposed therebetween,

the plurality of signal input terminals are arranged in two different protruding portions for each of the two terminal groups.

4. The light modulator of claim 2,

the plurality of signal input terminals are arranged at one of the protruding portions.

5. The light modulator of claim 3,

the fixing portion is disposed at the protruding portion where the signal input terminal is disposed.

6. The light modulator of any of claims 2-5,

the plurality of protruding portions are arranged on the one surface of the housing at positions substantially symmetrical with respect to a center line of at least one of a longitudinal direction and a width direction of the housing.

7. The light modulator of any of claims 2-6,

the plurality of signal input terminals are arranged on the one surface of the housing at positions substantially symmetrical with respect to a center line of at least one of a longitudinal direction and a width direction of the housing.

8. An optical transmission device, comprising:

the light modulator of any of claims 1-7; and

and a circuit board that outputs an electrical signal for causing the optical modulator to perform a modulation operation.

Technical Field

The present invention relates to an optical modulator and an optical transmission device using the same.

Background

In recent years, digital coherent transmission technology that has been applied to long-distance optical communication is also being applied to optical communication for metropolitan areas such as medium-distance and short-distance areas because of further increasing communication demand. In such digital coherent transmission, it is common to use LiNbO as an optical modulator₃A DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) modulator on a (LN) substrate. Hereinafter, LiNbO will be used₃The optical modulator of the substrate is called LN modulator.

Such an optical modulator includes a plurality of high-frequency electrodes for modulating a braking action on an optical element substrate housed therein, and a housing of the optical modulator is provided with a plurality of signal input terminals for inputting a high-frequency signal from an external drive circuit (for example, a driver integrated circuit) to the high-frequency electrodes.

Such a plurality of signal input terminals are generally provided in a line at the bottom of the housing as shown in patent document 1 so that the respective signal propagation paths from the signal input terminals to the high-frequency electrodes on the optical modulation element have the same electrical length (i.e., so that skew is reduced). However, with the progress of circuit technology, skew adjustment can be performed also in an integrated circuit. Therefore, when the modulation signal frequency is further increased with a further increase in the transmission capacity, it is more important to shorten the electrical length of the signal propagation path itself and reduce the high frequency loss rather than to reduce the skew. In this regard, the above-mentioned conventional techniques have room for improvement from the viewpoint of improvement of high-frequency characteristics and improvement of stability thereof.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-134131

Disclosure of Invention

Problems to be solved by the invention

In view of the above background, it is desirable to improve high-frequency characteristics and improve stability of an optical modulator.

Means for solving the problems

One embodiment of the present invention includes: an optical element substrate having an optical waveguide and a plurality of electrodes for controlling an optical wave propagating through the optical waveguide; and a case that fixes and accommodates the optical element substrate, wherein a plurality of signal input terminals electrically connected to the plurality of electrodes are provided on one surface of the outside of the case, and the plurality of signal input terminals are separately arranged on each of the sides facing each other with the optical element substrate interposed therebetween when viewed in a plan view in a direction perpendicular to the one surface of the outside of the case.

According to another aspect of the present invention, the case has a plurality of protruding portions on the one surface, and at least one of the protruding portions has a fixing portion for attaching the case to an external structure.

According to another aspect of the present invention, the signal input terminals constitute two terminal groups facing each other with the optical element substrate interposed therebetween, and the plurality of signal input terminals are arranged in two different protruding portions for each of the two terminal groups.

According to another aspect of the present invention, the plurality of signal input terminals are disposed in one of the protruding portions.

According to another aspect of the present invention, the fixing portion is disposed at the protruding portion where the signal input terminal is disposed.

According to another aspect of the present invention, the plurality of protruding portions are arranged at positions substantially symmetrical with respect to a center line of at least one of a longitudinal direction and a width direction of the housing on the one surface of the housing.

According to another aspect of the present invention, the plurality of signal input terminals are arranged at substantially symmetrical positions with respect to a center line of at least one of a longitudinal direction and a width direction of the housing on the one surface of the housing.

Another aspect of the present invention relates to an optical transmission device including: any of the light modulators described above; and a circuit board that outputs an electric signal for causing the optical modulator to perform the modulation operation.

The present specification includes the entire contents of japanese patent application No. 2018-034768 filed on 28/2/2018.

Drawings

Fig. 1 is a plan view of an optical modulator according to an embodiment of the present invention.

Fig. 2 is a side view of an optical modulator of an embodiment of the present invention.

Fig. 3 is a bottom view of an optical modulator according to an embodiment of the present invention.

Fig. 4 is a plan view of an optical transmission device mounted with the optical modulator shown in fig. 1.

Fig. 5 is an AA cross-sectional view of the optical transmission device shown in fig. 4.

Fig. 6 is a BB cross-sectional view of the optical transmission device shown in fig. 4.

Fig. 7 is a bottom view showing a configuration of a first modification of the optical modulator according to the embodiment of the present invention.

Fig. 8 is a bottom view showing a configuration of a second modification of the optical modulator according to the embodiment of the present invention.

Fig. 9 is a bottom view showing a configuration of a third modification of the optical modulator according to the embodiment of the present invention.

Fig. 10 is a bottom view showing a configuration of a fourth modification of the optical modulator according to the embodiment of the present invention.

Fig. 11 is a bottom view showing a configuration of a fifth modification of the optical modulator according to the embodiment of the present invention.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is a plan view showing a structure of an optical modulator 100 according to an embodiment of the present invention, fig. 2 is a side view of the optical modulator 100, and fig. 3 is a bottom view of the optical modulator 100. The optical modulator 100 is mounted on a circuit board (for example, a circuit board 404 shown in fig. 4 described later) constituting an external circuit for modulating the optical modulator 100, and is electrically connected to the circuit for use.

The optical modulator 100 includes an optical element substrate 102, a modulator case 104 that houses the optical element substrate 102, an optical fiber 108 that allows light to enter the optical element substrate 102, and an optical fiber 110 that guides light output from the optical element substrate 102 to the outside of the modulator case 104.

The optical element substrate 102 is a DP-QPSK optical modulator, and includes, for example, four mach-zehnder optical waveguides provided on an LN substrate and four RF electrodes (high-frequency electrodes) 150, 152, 154, and 156 provided on the mach-zehnder optical waveguides, respectively, for modulating an optical wave propagating in the optical waveguide. The two lights output from the optical element substrate 102 are polarized and combined by, for example, a lens optical system (not shown), and are guided to the outside of the modulator case 104 through the optical fiber 110.

The modulator housing 104 is composed of a case 114a to which the optical element substrate 102 is fixed and a cover 114 b. Note that, although only a part of the cover 114b is shown on the left side of the drawing in fig. 1 for the sake of easy understanding of the structure inside the modulator case 104, actually, the cover 114b is disposed so as to cover the entire box-shaped case 114a, and the inside of the modulator case 104 is hermetically sealed.

The housing 114a is provided with four pins 120, 122, 124, 126 as signal input terminals for inputting high-frequency signals. These pins 120, 122, 124, 126 extend outwardly from the bottom surface (the surface shown in fig. 3) of the modulator housing 104. Here, the bottom surface of the modulator housing 104 corresponds to one surface of the exterior of the modulator housing 104.

The housing 114a is made of a conductive material (for example, a metal such as stainless steel or a material coated with a metal thin film such as gold), and when the optical modulator 100 is mounted on an external structure such as a circuit board, the housing 114a is brought into contact with the external structure and connected to a ground (ground) line.

In the present embodiment, four pins 120, 122, 124, and 126 as signal input terminals are arranged on both sides facing each other with the optical element substrate 102 interposed therebetween, when viewed in a plan view from a direction perpendicular to one surface outside the modulator case 104 (i.e., the bottom surface of the modulator case 104). That is, the four leads 120, 122, 124, 126 are divided into two terminal groups each composed of the leads 120, 122 and 124, 126, and the leads 120, 122 constituting one terminal group are disposed on the lower side of the optical element substrate 102 in the figure and electrically connected to one ends of the RF electrodes 150, 152 via the conductor patterns 140, 142 on the relay substrate 130. The leads 124 and 126 constituting the other terminal group are disposed on the upper side of the optical element substrate 102 in the figure, and are electrically connected to one ends of the RF electrodes 154 and 156 of the optical element substrate 102 via the conductor patterns 144 and 146 on the relay substrate 132, respectively. The leads 120 and 122 and the conductor patterns 140 and 142, and the leads 124 and 126 and the conductor patterns 144 and 146 are electrically connected by, for example, solder (not shown). The conductor patterns 140 and 142 and the RF electrodes 150 and 152, and the conductor patterns 144 and 146 and the RF electrodes 154 and 156 are electrically connected to each other by a wire such as gold (Au).

The RF electrodes 150, 152, 154, and 156 are designed such that the characteristic impedance has a predetermined value in the operating frequency range, and the other ends of the RF electrodes 150, 152, 154, and 156 are terminated by terminations 160 having an impedance of the same value as the characteristic impedance.

Protrusions 300, 302, 304, 306 having the same height as each other from the bottom surface of the modulator case 104, that is, four corners of the bottom surface (the surface shown in fig. 3) of the housing 114a are provided. The distal ends of the projections 300, 302, 304, 306 are flat, and screw holes 310, 312, 314, 316 are provided in the distal ends to fix the modulator case 104 to an external structure. It should be noted that the threaded hole may not be provided in all of the projections 300, 302, 304, 306, and may be provided in at least one of the projections. In order to reduce the occurrence of strain during processing of the modulator housing 104, the projections 300, 302, 304, and 306 are preferably arranged at positions substantially symmetrical with respect to the center line in the longitudinal direction and/or the width direction of the modulator housing on the bottom surface of the modulator housing 104, as shown in fig. 3.

Fig. 4 is a top view of the optical transmission device 400 mounted with the optical modulator 100. Fig. 5 and 6 are a cross-sectional view AA and a cross-sectional view BB of the optical transmission device shown in fig. 4, respectively.

The optical transmission device 400 includes a circuit board 404 fixed in a device case 402. The optical modulator 100 is fixed and mounted on the circuit substrate 404 by attaching screws 410, 412, 414, 416 to the threaded holes 310, 312, 314, 316 of the modulator housing 104. Thus, an electronic component mounting space corresponding to the height of the protruding portions 300, 302, 304, 306 provided in the modulator case 104 can be secured between the bottom surface of the modulator case 104 and the circuit board 404.

Note that, since the optical modulator 100 and the circuit board 404 are housed in the device case 402, the optical modulator 100 and the circuit board 404 cannot be visually confirmed from the outside of the device case 402, but in fig. 4, for the sake of explanation, portions housed in the device case 402 are indicated by solid lines in addition to portions shielded by the modulator case 104 of the optical modulator 100.

On the circuit board 404, for example, a DSP (digital signal Processor) 420 and a DRV (Driver) 422 are mounted in the above-described secured electronic component mounting space. Further, an LD (Laser Diode) 424, a PD (Photo Diode) 426, and other electronic components (not shown) are mounted on other portions of the circuit board 404. The DSP420 is an arithmetic processing device for executing processing of a digital signal. DRV422 is a circuit for driving optical modulator 100. The LD424 causes laser light to enter the optical modulator 100 via the optical fiber 108. The PD426 is provided for digital coherent optical signal reception.

That is, the optical transmission device 400 includes the optical modulator 100 and the circuit board 404 that outputs an electrical signal for causing the optical modulator 100 to perform a modulation operation. The electric components mounted on the circuit board 404 are an example, and other electric components may be mounted. Since the sizes, thicknesses, and other shapes of the respective elements are various, they are not necessarily accurately shown in the drawings.

The output of the DRV422 is transmitted through conductor patterns 430, 432, 434, 436 provided on the circuit substrate 404 and is input to the pins 120, 122, 124, 126, respectively. Portions of the pins 120, 122, 124, 126 from the circuit substrate 404 to the modulator housing 104 may be provided with, for example, relay connectors 440, 442, 444, 446 to avoid impedance mismatches. In addition, the length of the leads 120, 122, 124, 126 may be shorter than the height dimension of the protrusions 300, 302, 304, 306, and in this case, the conductor patterns 430, 432, 434, 436 on the circuit board 404 and the leads 120, 122, 124, 126 may be connected via, for example, a relay adapter having a predetermined characteristic impedance.

In the optical modulator 100 having the above-described configuration, as shown in fig. 1 in particular, when viewed in a plan view from a direction perpendicular to one surface outside the modulator case 104 (i.e., the bottom surface of the modulator case 104), the plurality of pins 120, 122, 124, and 126 serving as signal input terminals are disposed on the respective sides facing each other with the optical element substrate 102 interposed therebetween, and are electrically connected to the plurality of RF electrodes 150, 152, 154, and 156 provided on the optical element substrate 102, respectively. Therefore, in the optical modulator 100, the electrical length from the RF electrodes 150, 152, 154, 156 to the pins 120, 122, 124, 126 as the signal input terminals can be shortened as compared with a conventional optical modulator in which a plurality of signal input terminals are arranged in a line. This can reduce the propagation loss of the electric signal, and improve the high-frequency characteristics of the modulator, such as a wider bandwidth and a reduction in driving power.

As shown in fig. 3, the leads 120, 122, 124, and 126 that are separately disposed on the opposite sides with the optical element substrate 102 interposed therebetween can be disposed at positions that are substantially symmetrical with respect to a center line 350 in the width direction of the modulator case 104 (a line extending in the longitudinal direction through the center in the width direction), for example, on the bottom surface of the modulator case 104. Therefore, even when machining strain is generated in the modulator case 104 when machining is performed for the modulator case 104 to install the pins 120 and the like, it is possible to prevent unevenness in machining strain such as asymmetric deformation of the modulator case 104 caused by temperature variation. As a result, the modulator case 104 is asymmetrically deformed, and the loss of the lens coupling system inside the modulator case 104 can be prevented from increasing.

Further, since the leads 120, 122, 124, and 126 are disposed on both sides facing each other with the optical element substrate 102 interposed therebetween, the distance between both end portions of the lead row disposed on each side can be made shorter than that of a conventional optical modulator in which all four signal input terminals are disposed in a row. Therefore, the generation of stress to the pins 120, 122, 124, 126 or an increase in the stress caused by the difference in the linear expansion coefficient between the modulator case 104 and the circuit substrate 404 can be suppressed. As a result, stable electrical connection between the leads 120, 122, 124, 126 and the conductor patterns 430, 432, 434, 436 on the circuit board 404 can be ensured, and temperature change and secular change in high-frequency characteristics can be suppressed.

Further, a space equal to or larger than the width of the optical element substrate 102 can be secured between the leads 120 and 122 and the leads 124 and 126, which are disposed on opposite sides of the optical element substrate 102. Therefore, by using this space, for example, as shown in fig. 4, conductor patterns 430, 432, 434, 436 can be formed as propagation paths of the high-frequency signal output from the DRV 422. As a result, the electrical length of the high-frequency propagation path between the DRV422 and the pins 120, 122, 124, and 126 can be shortened to reduce the propagation loss of the electrical signal, and the modulator can be made to have a wider band, and the drive power can be reduced, thereby obtaining a good optical modulation characteristic.

In the optical modulator 100, the projections 300, 302, 304, and 306 are provided in a part of the modulator housing 104, whereby an electronic component mounting space can be secured between the bottom surface of the modulator housing 104 and the circuit board 404.

Conventionally, as a method of securing an electronic component mounting space between the bottom surface of the modulator case and the circuit board, a method of providing a cutout in the modulator case and securing a mounting space for an electronic component by the cutout is known (japanese patent application laid-open No. 2017-134131). However, when the case is provided with a cut, a processing strain (for example, a processing deformation portion that degrades the flatness of the bottom surface of the case) is unevenly generated in the case due to the cut. Therefore, when the housing is screwed to the circuit board in the optical transmission device, there are problems that a fixing stress is generated in the housing, optical characteristics such as a light passing loss of the optical modulator are deteriorated, and the optical characteristics are changed (deteriorated) with time. For the same reason, the problem of the change or deterioration of the high-frequency characteristics of the optical modulator also occurs.

In contrast, in the optical modulator 100, the conventional notch is not provided, and the electronic component mounting space can be secured by the projections 300, 302, 304, and 306 provided on a part of the bottom surface of the modulator case 104. Therefore, in the optical modulator 100, most of the area of the bottom surface of the modulator case 104 can be formed as a uniform plane. Here, since the projections 300, 302, 304, 306 can be provided in a limited area required for providing the screw holes 310, 312, 314, 316, the occurrence of machining strain or unevenness thereof can be suppressed. From the viewpoint of reducing the processing strain of the modulator case 104 and securing the mounting space for the electrical components such as the DSP420 and the DRV422, the total area of the protruding portions 300, 302, 304, and 306 is preferably less than 50%, and more preferably 25% or less, with respect to the area of the bottom surface of the modulator case 104.

As a result, in the optical modulator 100, the occurrence of processing strain of the modulator case 104 is minimized, and the occurrence of minute deformation of the modulator case 104 when the optical modulator 100 is fixed to the circuit board 404 of the optical transmission device 400 can be suppressed, and the initial change of the optical characteristics of the optical modulator 100 and the aged change of the optical characteristics due to the aged change of the deformation stress can be suppressed.

In the present embodiment, the four leads 120, 122, 124, and 126 are disposed in two parts on both sides facing each other with the optical element substrate 102 interposed therebetween, but the number of leads and the manner of dividing the leads are not limited to this. For example, the four leads may be divided into three and one, and disposed on the opposite sides with the optical element substrate 102 interposed therebetween. Further, for example, six pins may be divided into three, four and two, or five and one, depending on the number of RF electrodes formed on the optical element substrate 102, and may be disposed on both sides facing each other with the optical element substrate 102 interposed therebetween. However, from the viewpoint of suppressing the processing strain of the modulator case 104 and the viewpoint of suppressing the stress generation at the connection portion between the lead and the external circuit board, the plurality of leads as the signal input terminals are more preferably arranged at positions substantially symmetrical with respect to the center line 350 in the width direction of the modulator case 104 and/or more preferably at positions substantially symmetrical with respect to the center line in the longitudinal direction on the bottom surface of the modulator case 104 as shown in fig. 3.

Next, a modification of the shape of the bottom surface of the modulator case and the arrangement of the pins will be described. Fig. 7, 8, 9, and 10 are diagrams showing the configuration of the bottom surface of the modulator housing that can be used in place of the modulator housing 104 having the layout shown in fig. 3. The positions of the pins on the bottom surface of the modulator housing can be changed by changing, for example, the shapes of the RF electrodes 150, 152, 154, and 156 on the optical element substrate 102, the shapes of the relay substrates 130 and 132, and the shapes of the conductor patterns 140, 142, 144, and 146 formed on the relay substrates 130 and 132. In fig. 7, 8, 9 and 10, the same components as those shown in fig. 1, 2 and 3 are denoted by the same reference numerals as those in fig. 1, 2 and 3, and the description of fig. 1, 2 and 3 is incorporated herein.

< first modification >

Fig. 7 is a diagram showing a configuration of a bottom surface of the optical modulator 100-1 according to the first modification of the optical modulator 100, and corresponds to a bottom view of the optical modulator 100 shown in fig. 3. The optical modulator 100-1 has the same configuration as the optical modulator 100, but is different in that four pins 720, 722, 724, 726 are separated into three pins 720, 722, 724 and one pin 726 on the bottom surface of the modulator case 104-1, and are disposed on opposite sides with the optical element substrate 102 interposed therebetween. The leads 720, 722, 724, 726 are connected to the RF electrodes 150, 152, 154, 156 on the optical element substrate 102 via, for example, a relay substrate having the same structure as the relay substrates 130, 132.

The optical modulator 100-1 is configured such that, similarly to the optical modulator 100, a plurality of pins 720, 722, 724, 726 serving as signal input terminals electrically connected to the plurality of RF electrodes 150, 152, 154, 156 provided on the optical element substrate 102 are disposed on opposite sides of the optical element substrate 102. Therefore, in the optical modulator 100-1, compared to a conventional optical modulator in which a plurality of signal input terminals are arranged in a line, the electrical length from the RF electrodes 150, 152, 154, 156 to the pins 720, 722, 724, 726 can be shortened to reduce the propagation loss of the electrical signal, and the high frequency characteristics can be improved by widening the frequency band of the modulator, reducing the driving power, and the like.

Further, since the leads 720, 722, 724, 726 are disposed on the opposite sides with respect to the optical element substrate 102, the distance between the two end portions of the lead row disposed on each side can be made shorter than that of a conventional optical modulator in which all four signal input terminals are disposed in a row. Therefore, generation of stress to the pins 720, 722, 724, 726 or increase thereof caused by the difference in linear expansion coefficient between the modulator housing 104 and the circuit substrate 404 can be suppressed. As a result, stable electrical connection between the leads 720, 722, 724, 726 and the conductor pattern on the circuit board can be ensured, and temperature change or secular change in high-frequency characteristics can be suppressed.

Further, a space equal to or larger than the width of the optical element substrate 102 can be secured between the leads 720, 722, 724 and the leads 726 that are disposed on the opposite sides with the optical element substrate 102 interposed therebetween. Therefore, by using this space, a conductor pattern as a propagation path of a high-frequency signal output from a driver circuit such as the DRV422 can be formed on the circuit board. As a result, the electrical length of the high-frequency propagation path between the driver circuit and the pins 720, 722, 724, and 726 can be shortened, the propagation loss of the electric signal can be reduced, the frequency band of the modulator can be widened, the driving power can be reduced, and the like, and thus, favorable optical modulation characteristics can be obtained.

In the optical modulator 100-1, similarly to the optical modulator 100, the projections 300, 302, 304, and 306 are provided on a part of the bottom surface of the modulator case 104-1. That is, since no notch as in the conventional art is provided in the modulator housing 104-1, it is possible to minimize the occurrence of processing strain or unevenness thereof in the modulator housing 104-1, and to suppress the aged change in optical characteristics due to the initial change in optical characteristics and the aged change in deformation stress of the optical modulator 100-1, as in the optical modulator 100.

< second modification >

Fig. 8 is a diagram showing a configuration of a bottom surface of the optical modulator 100-2 according to the second modification of the optical modulator 100, and corresponds to a bottom view of the optical modulator 100 shown in fig. 3. The optical modulator 100-2 has the same configuration as the optical modulator 100, but is different in that two protruding portions 800 and 802 are further formed on the bottom surface of the modulator case 104-2, and the leads 120 and 122 are disposed on the flat distal end portion of one protruding portion 800, and the leads 124 and 126 are disposed on the flat distal end portion of the other protruding portion 802.

That is, the leads 120, 122, 124, and 126 as signal input terminals disposed on both sides facing each other with the optical element substrate 102 interposed therebetween are separated to form two terminal groups facing each other with the optical element substrate 102 interposed therebetween, and are disposed at the tip ends of two different protruding portions 800 and 802 for each of the terminal groups. Here, the height of the protrusions 800, 802 measured from the bottom surface of the modulator housing 104-2 is formed to be equal to or lower than the protrusions 300, 302, 304, 306 provided with the screw holes 310, 312, 314, 316. The projections 800 and 802 are disposed at positions substantially symmetrical with respect to a center line 850 in the width direction of the modulator case 104-2, for example.

The optical modulator 100-2 has the same configuration as the optical modulator 100, and therefore has advantages such as improvement of the high-frequency characteristics, stability of the optical characteristics and the high-frequency characteristics, and improvement of secular change, which are possessed by the optical modulator 100. Further, since the optical modulator 100-2 fixes the lead 120 and the like to the circuit board by, for example, solder, and the relay connector 440 and the like are not interposed, it is possible to reduce high-frequency propagation loss and high-frequency signal reflection, and to realize an optical transmission device having more excellent high-frequency characteristics. Also, there is an advantage in cost.

In the optical modulator 100-2, the lead 120 or the like is disposed at the distal end portion of the protruding portions 800 and 802, and therefore, the distance between the portion of the modulator case 104-2 where the lead 120 or the like is provided and the circuit board can be made significantly close to each other, so that the reproducibility of high-frequency connection is improved, and the modulator case 104-2 is less likely to be affected by deformation of the circuit board or the like. Therefore, the variation of the high-frequency characteristics with time can be suppressed.

Further, as with the optical modulator 100, since the plurality of leads 120 and the like are disposed on both sides facing each other with the optical element substrate 102 interposed therebetween, it is possible to avoid the generation of stress in the high-frequency connection portion (solder fixing portion) due to the difference in linear expansion between the modulator case 104-2 and the circuit substrate, as compared with the conventional configuration in which the plurality of leads are all disposed in a row. Such stress is particularly likely to occur in a structure in which the modulator case and the circuit substrate face each other via the proximity of the pins as in the optical modulator 100-2, and therefore the stress suppressing effect described above, which is caused by equally dividing the plurality of pins 120 on both sides facing each other with the optical element substrate 102 interposed therebetween, is extremely important.

The protruding portions 800 and 802 provided with the leads 120 and the like do not need to be in contact with the circuit board, and a gap of about 50 μm to 1mm may be provided. Such a gap portion may be a space only or may be filled with solder. In addition, a relay member formed to be thin may be used in the gap portion.

< third modification >

Fig. 9 is a diagram showing a configuration of a bottom surface of the optical modulator 100-3 according to a third modification of the optical modulator 100, and corresponds to a bottom view of the optical modulator 100 shown in fig. 3. The optical modulator 100-3 is similar to the optical modulator 100 in that four leads 910, 912, 914, 916 are disposed on opposite sides of the optical element substrate 102. Here, the leads 910, 912, 914, 916 are electrically connected to the RF electrodes 150, 152, 154, 156 on the optical element substrate 102, respectively, via a relay substrate similar to the relay substrate 130, for example. Further, in the optical modulator 100-3, similarly to the optical modulator 100, the four protrusions 900, 902, 904, and 906 are provided at positions substantially symmetrical with respect to a center line 950 in the width direction and a center line 952 in the longitudinal direction of the modulator housing 104-3 on the bottom surface of the modulator housing 104-3, and the four protrusions 900, 902, 904, and 906 are provided with screw holes 920 and 922, 924 and 926, 930 and 932, and 934 and 936, respectively.

However, in the optical modulator 100-3, unlike the optical modulator 100, the pins 910 and 912 are provided in the protrusion 900 provided with the screw holes 920 and 922, and the pins 914 and 916 are provided in the protrusion 902 provided with the screw holes 924 and 926.

In the optical modulator 100-3, in addition to the same effects as those of the optical modulator 100, the strength and accuracy of fixing to the circuit substrate of the pin 910 or the like that transmits the high-frequency signal between the modulator case 104-3 and the circuit substrate can be improved by reducing the number of the extra processing portions on the bottom surface of the case as compared with the optical modulator 100-2 of the second modification. Further, since the distance between the modulator case 104-3 and the circuit board can be shortened at the connection portion of the lead 910 or the like, it is possible to prevent the reliability of fixing the lead 910 or the like to the circuit board and the stability of the high-frequency characteristics from being lowered due to the difference in linear expansion between the modulator case 14-3 and the circuit board.

In the optical modulator 100-3, since the screw-fixing protrusions 904 and 906 having substantially the same shape as the protrusions 900 and 902 provided with the pins 910 and the like are arranged substantially symmetrically with respect to the center line 952 in the longitudinal direction of the modulator case 104-3, the fixing stability is further improved as compared with the optical modulator 100-2 of the second modification.

< fourth modification >

Fig. 10 is a diagram showing a configuration of a bottom surface of an optical modulator 100-4 according to a fourth modification of the optical modulator 100, and corresponds to a bottom view of the optical modulator 100 shown in fig. 3. The light modulator 100-4 has the same structure as the light modulator 100, but does not have four corner protrusions 300, 302, 304, 306 on the bottom surface of the modulator housing 104-4. The bottom surface of the modulator housing 104-4 has one protrusion 1000 at the position of the pins 120, 122, 124, 126, and has another protrusion 1002 at a position substantially symmetrical with respect to the center of the modulator housing 104-4. These protrusions 1000, 1002 have a substantially symmetrical shape with respect to, for example, a center line 1050 in the width direction of the modulator case 104-4, and the protrusions 1000, 1002 are arranged at positions substantially symmetrical with respect to, for example, a center line 1052 in the length direction of the modulator case 104-4.

The heights of the tip portions of the protrusions 1000 and 1002 measured from the bottom surface of the modulator case 104-4 are the same. Further, screw holes 1010, 1012, 1014, 1016 are provided at four corners of the flat distal end portion of the projection 1000, and the pins 120, 122, 124, 126 are arranged. Screw holes 1020, 1022, 1024, 1026 are provided at four corners of the flat distal end portion of the projection 1002.

The optical modulator 100-4 has the same effect as that of the optical modulator 100. In particular, the optical modulator 100-4 has a smaller number of processed parts than the optical modulator 100-3 of the third modification, and the pins 120, 122, 124, and 126 are provided on the bottom surface, that is, the tip end surface of the protrusion 1000. Therefore, in the optical modulator 100-4, the stability and uniformity of the connection state of the pins 120, 122, 124, and 126 to the circuit substrate are improved as compared with the optical modulator 100-3. As a result, an optical transmission device with less variation in high-frequency characteristics among the high-frequency transmission channels formed by the pins 120, 122, 124, and 126 can be realized.

< fifth modification >

Fig. 11 is a diagram showing a configuration of a bottom surface of an optical modulator 100-5 according to a fifth modification of the optical modulator 100, and corresponds to a bottom view of the optical modulator 100 shown in fig. 3. The optical modulator 100-5 has the same configuration as the optical modulator 100, but the pins 1120, 1122 and the pins 1124, 1126 disposed on the bottom surface of the modulator case 104-5 on opposite sides with the optical element substrate 102 inside the modulator case 104-5 interposed therebetween are disposed at positions offset from each other along the longitudinal direction of the optical element substrate 102 or the modulator case 104-5. Here, the pins 1120, 1122, 1124, and 1126 are connected to the RF electrodes 150, 152, 154, and 156 of the optical element substrate 102, respectively, as are the pins 120, 122, 124, and 126.

Even in the above arrangement, since the leads 1120, 1122, 1124, and 1126 are arranged on the opposite sides with the optical element substrate 102 interposed therebetween, the same effect as that of the optical modulator 100 can be obtained in the optical modulator 100-5. That is, in the optical modulator 100-5, compared to a conventional optical modulator in which a plurality of signal input terminals are arranged in a line, the electrical length from the RF electrodes 150, 152, 154, 156 to the pins 1120, 1122, 1124, 1126 can be shortened to reduce the propagation loss of the electrical signal, and the high frequency characteristics can be improved by widening the frequency band of the modulator, reducing the driving power, and the like.

Further, the distance between both end portions of the pin row disposed on each side with the optical element substrate 102 interposed therebetween can be shortened as compared with a conventional optical modulator in which all four signal input terminals are disposed in a row, and generation of stress or increase in stress to the pins 1120, 1122, 1124, and 1126 can be suppressed. As a result, stable electrical connection between the leads 1120, 1122, 1124, and 1126 and the conductor pattern on the circuit board can be ensured, and temperature change or secular change in high-frequency characteristics can be suppressed.

Further, since a space equal to or larger than the width of the optical element substrate 102 is secured between the leads 1120 and 1122 and the leads 1124 and 1126 disposed on the opposite sides with the optical element substrate 102 interposed therebetween, a conductor pattern such as a propagation path of a high-frequency signal can be formed on the circuit substrate by using the space. As a result, the electrical length of the high-frequency propagation path between the driver circuit and the pins 1120, 1122, 1124, and 1126 can be shortened, thereby reducing the propagation loss of the electrical signal, widening the frequency band of the modulator, reducing the driving power, and the like, and obtaining good optical modulation characteristics.

In the optical modulator 100-5, as in the optical modulator 100, since the projections 300, 302, 304, and 306 are provided in a part of the bottom surface of the modulator case 104-5, and no cut as in the conventional art is provided, it is possible to minimize the occurrence of processing strain or unevenness thereof in the modulator case 104-5, and to suppress an initial change in optical characteristics of the optical modulator 100-5 and an aged change in optical characteristics due to an aged change in deformation stress.

In the above-described embodiment, the modulator cases 104, 104-1, 104-2, 104-3, 104-4, and 104-5 each have the plurality of projections 300 and the like on the bottom surface thereof, but the present invention is not limited thereto. At least one protrusion may be provided as long as a space for mounting an electronic component can be secured between the bottom surface of the modulator case 104 or the like and the external circuit board.

As described above, the optical modulator 100 of the above embodiment includes: an optical element substrate 102 having an optical waveguide, a plurality of RF electrodes 150 for controlling light waves propagating through the optical waveguide, and the like; and a modulator case 104 that houses the optical element substrate 102. The modulator case 104 includes a plurality of pins 120 and the like as signal input terminals electrically connected to the plurality of RF electrodes 150 and the like, respectively, and the plurality of pins 120 and the like are disposed on opposite sides of the optical element substrate 102.

This improves the high-frequency characteristics and stability of the optical modulator 100.

In the above embodiments, the optical modulator including the optical element substrate having four RF electrodes using LN as a substrate is shown, but the present invention is not limited to this, and is also applicable to an optical modulator having four RF electrodes other than LN and/or an optical modulator using a material other than LN as a substrate.

Description of the reference symbols

100. 100-1, 100-2, 100-3, 100-4, 100-5 … optical modulator, 102 … optical element substrate, 104-1, 104-2, 104-3, 104-4, 104-5 … modulator housing, 108, 110 … optical fiber, 114a … housing, 114b … cover, 120, 122, 124, 126, 720, 722, 724, 726, 910, 912, 914, 916, 1120, 1122, 1126, … pin, 130, 132 … relay substrate, 140, 142, 144, 146, 430, 432, 434, 436 … conductor pattern, 150, 152, 154, 156 … RF electrode (high frequency electrode), 160 … terminator, 300, 302, 304, 306, 800, 802, 900, 1014, 904, 906, 1000, 1002 … protrusion, 310, 312, 314, 316, 920, 312, 922, 926, 930, 934, 930, 1010, 1012, 1022, 1024, 1020, 1024, 24 threaded hole, 24, 350. 850, 950, 952, 1050, 1052 … centerline, 400 … optical transmission device, 402 … device housing, 404 … circuit substrate, 410, 412, 414, 416 … screw, 420 … DSP, 422 … driver circuit (DRV), 424 … LD, 426 … PD, 440, 442, 444, 446 … relay connector.