阅读说明：本技术 光调制器及光发送装置 (Optical modulator and optical transmission device ) 是由 宫崎德一 菅又徹 于 2019-01-11 设计创作，主要内容包括：在提高光传输装置壳体内的空间利用率的同时,抑制在将光调制器安装于光传输装置壳体内的情况下的光学特性及高频特性的初始变化及经年变化。光调制器(100)与在电路基板(404)上构成的电路电连接,具备收容光调制元件(102)的壳体(104)及从所述电路输入用于使所述光调制元件进行调制动作的电信号的信号输入部(120)等,所述壳体在与所述电路基板对向的底面(106)的一部分具有从该底面突出的第一突出部(130),所述信号输入部设置于所述第一突出部的上表面(132)。(The optical transmission device can improve the space utilization rate in the housing of the optical transmission device and can restrain the initial change and the aging change of the optical characteristic and the high-frequency characteristic when the optical modulator is installed in the housing of the optical transmission device. An optical modulator (100) is electrically connected to a circuit formed on a circuit board (404), and is provided with a housing (104) that houses an optical modulator element (102), a signal input unit (120) that inputs an electrical signal for causing the optical modulator element to perform a modulation operation from the circuit, and the like, wherein the housing has a first protruding portion (130) protruding from a bottom surface (106) facing the circuit board in a part of the bottom surface, and the signal input unit is provided on an upper surface (132) of the first protruding portion.)

1. An optical modulator electrically connected to a circuit formed on a circuit substrate, comprising:

a housing that houses the light modulation element; and

a signal input unit for inputting an electric signal for causing the optical modulation element to perform a modulation operation from the circuit,

the housing has a first protruding portion protruding from a bottom surface of the housing facing the circuit board,

the signal input part is arranged on the upper surface of the first protruding part.

2. The light modulator of claim 1,

the housing is provided with at least one screw hole on the upper surface of the first protruding portion.

3. The optical modulator of claim 1 or 2,

the bottom surface of the housing includes at least one screw hole in a portion other than the first protruding portion.

4. The optical modulator of any of claims 1-3,

the housing has a second projection at a portion of the bottom surface projecting therefrom,

the first and second protrusions have substantially equal heights from the bottom surface.

5. The light modulator of claim 4,

the housing is provided with at least one screw hole on an upper surface of the second protrusion.

6. An optical transmission device is provided with:

the optical modulator of any of claims 1 to 5; and

and the circuit board outputting an electric signal for causing the optical modulator to perform the modulation operation.

7. The optical transmission apparatus of claim 6,

the optical modulator further includes at least one spacer disposed between the bottom surface of the optical modulator and the circuit board, and having a height equal to a height of the first protruding portion from the bottom surface.

Technical Field

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

Background

In recent years, digital coherent transmission techniques that have been applied to long-distance optical communications have been increasingly applied to optical communications for metropolitan areas such as medium-distance and short-distance optical communications because of further increasing communication demands. In such digital coherent transmission, a DP-QPSK (Dual Polarization-Quadrature Phase shift keying) modulator using LiNbO3 (hereinafter, LN) substrate is typically used as an optical modulator. Hereinafter, an optical modulator using the LiNbO3 substrate is referred to as an LN modulator.

Such an optical modulator is used as an optical transmission device, for example, by connecting a drive element (or a drive circuit) that outputs an electrical signal for causing the optical modulator to perform a modulation operation. In general, the optical modulator or the driving element is disposed on a circuit board.

In particular, in an optical transmission device for short distance applications such as optical communication for metro-area, there is a high demand for suppressing the installation space of an optical modulator, a driving circuit, and the like, and miniaturization of the modulator and the like is desired. In order to miniaturize the optical modulator, there have been attempts to miniaturize the LN optical modulation element (for example, to reduce the area of an optical waveguide on the LN substrate), to miniaturize a space optical system for optically coupling output light from the optical waveguide on the LN substrate to an output optical fiber, to miniaturize a high-frequency (RF) signal input interface of the LN modulator (for example, to change from a coaxial connector to a flexible printed board), and the like.

In addition to the miniaturization of the optical modulator as described above, in order to improve the space utilization rate in the optical transmission device, an electronic component in which a notch is provided in a housing of the optical modulator and the drive circuit is disposed in a space secured by the notch has been studied (for example, see patent document 1).

However, according to the findings of the inventors of the present application, if a conventional optical modulator having a notch in a housing is screwed to a circuit board in an optical transmission device, there is a possibility that optical characteristics of the optical modulator may be deteriorated such as light passing loss after the screw fixing, or the optical characteristics may be changed (deteriorated) with time.

In addition to the change or degradation of the optical characteristics as described above, there may be a problem of change or degradation of the high-frequency characteristics of the optical modulator.

The main cause of these problems is considered to be the occurrence of machining distortion (for example, the occurrence of a machining deformation portion that degrades the flatness of the bottom surface of the housing) and the unevenness of machining distortion due to the provision of a notch in the housing of the optical modulator, and the influence of a fixing stress generated when the housing is screwed.

That is, when a structure is formed in which a notch is provided in a part of a housing of an optical modulator in order to secure a space for arranging electrical components as in the optical modulator described in patent document 1, for example, in a cutting process for notch formation or the like, there is a possibility that processing distortion (also referred to as housing distortion) or unevenness in processing distortion may occur in the housing. When such a case in which machining distortion occurs is screwed to a circuit board, the case may be slightly deformed depending on the state of the machining distortion, the magnitude of fastening force at the time of screwing, the magnitude of stress, and the like. When a high-frequency drive IC or the like that generates heat is disposed in the cutout, a heat generating element is disposed in close proximity to the case, and the case is further distorted due to an increase in temperature of the heat generating element. Further, if the housing is kept at a high temperature with a long-term operation of the optical transmission device, the housing is distorted and the minute deformation is changed and expanded with time.

Further, the minute deformation occurring in the case causes a problem that the optical characteristics of the optical modulator are deteriorated due to the deformation of the LN substrate housed inside the case or the change in the positional relationship between optical components such as lenses constituting the spatial optical system. In addition, in a configuration in which a high-frequency connector is rigidly provided in the housing, such as the optical modulator disclosed in patent document 1, the above-described slight deformation of the housing also causes a change in the connection state between the high-frequency connector and the circuit board, resulting in deterioration of the optical transmission characteristics.

On the other hand, it is difficult to sufficiently suppress the occurrence of the distortion in the processing of the optical modulator housing and the change in the stress balance caused when the housing is screwed to the circuit board, only by taking time and effort (for example, reducing the variation in the processing conditions) in the processing conditions for the notch processing and the manufacturing conditions in the assembly process for screwing the optical modulator to the circuit board.

Disclosure of Invention

Problems to be solved by the invention

In view of the above-described circumstances, an object of the present invention is to improve the space utilization rate in an optical transmission device and to suppress initial changes and secular changes in optical characteristics and high-frequency characteristics when an optical modulator is mounted in the optical transmission device.

Means for solving the problems

One aspect of the present invention is an optical modulator electrically connected to a circuit formed on a circuit substrate, the optical modulator including: a housing that houses the light modulation element; and a signal input unit to which an electric signal for causing the light modulation element to perform a modulation operation is input from the circuit, wherein the housing has a first protruding portion protruding from a bottom surface of the housing, the bottom surface being a portion of the bottom surface facing the circuit board, and the signal input unit is provided on an upper surface of the first protruding portion.

According to another aspect of the present invention, the housing includes at least one screw hole in the upper surface of the first protruding portion.

According to another aspect of the present invention, the bottom surface of the housing includes at least one screw hole in a portion other than the first protruding portion.

According to another aspect of the present invention, the housing has a second protruding portion protruding from the bottom surface at a portion of the bottom surface, and heights of the first protruding portion and the second protruding portion from the bottom surface are substantially equal.

According to another aspect of the present invention, the housing has at least one screw hole on an upper surface of the second protrusion.

Another aspect of the present invention is an optical transmission device including any one of the optical modulators and the circuit board that outputs an electrical signal for causing the optical modulator to perform the modulation operation.

According to another aspect of the present invention, the optical transmission device further includes at least one spacer disposed between the bottom surface of the optical modulator and the circuit board, and having a height equal to a height of the first protruding portion from the bottom surface.

The present specification includes the entire contents of japanese patent application No. 2018-003443 filed on 12/1/2018.

Drawings

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

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

Fig. 3 is a bottom view of the optical modulator of the first embodiment of the present invention.

Fig. 4 is a plan view of an optical transmission device in which the optical modulator according to the first embodiment of the present invention is mounted.

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

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

Fig. 7 is a top view of an optical modulator of a second embodiment of the present invention.

Fig. 8 is a front view of an optical modulator of a second embodiment of the present invention.

Fig. 9 is a bottom view of the optical modulator of the second embodiment of the present invention.

Fig. 10 is a plan view of an optical modulator according to a third embodiment of the present invention.

Fig. 11 is a front view of an optical modulator of a third embodiment of the present invention.

Fig. 12 is a bottom view of the optical modulator of the third embodiment of the present invention.

Fig. 13 is a left side view of the light modulator shown in fig. 12.

Detailed Description

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

[ first embodiment ]

First, an optical modulator according to a first embodiment of the present invention will be described. Fig. 1 is a plan view showing the structure of an optical modulator 100 according to a first embodiment of the present invention, fig. 2 is a front 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 modulator 102, a housing 104 that houses the optical modulator 102, an optical fiber 108 that introduces light into the optical modulator 102, and an optical fiber 110 that guides light output from the optical modulator 102 to the outside of the housing 104.

The optical modulator 102 is an optical modulator used in, for example, a DP-QPSK optical modulator including 4 mach-zehnder optical waveguides provided on an LN substrate and 4 high-frequency electrodes (RF electrodes) provided on the mach-zehnder optical waveguides to modulate an optical wave propagating in the optical waveguide. The 2 light beams output from the light modulator 102 are polarized and synthesized by, for example, a lens optical system (not shown) housed in the housing 104, and are guided to the outside of the housing 104 via the optical fiber 110.

The housing 104 includes 4 socket electrodes 120, 122, 124, and 126 connected to 4 RF electrodes (not shown) included in the optical modulator 102. The socket electrodes 120, 122, 124, 126 constitute female high-frequency connectors (RF connectors), and are inserted into corresponding 4 signal pins provided on an external circuit board, to which electric signals (high-frequency signals) are input from circuits formed on the external circuit board.

That is, the socket electrodes 120, 122, 124, and 126 correspond to signal input portions for inputting an electrical signal for causing the optical modulator 102 to perform a modulation operation from a circuit formed on an external circuit substrate. In the present embodiment, the signal input portion has been described as a female-type socket-type electrode, but may be male-type or may be configured such that a signal pin extends from the case 104. In addition, the general optical modulator includes not only an RF section for inputting a high-frequency signal but also a dc signal input section for bias control or the like, but is not particularly shown in this embodiment or the like.

In the optical modulator 100 of the present embodiment, a part of the bottom surface 106 of the housing 104 facing the circuit board on which the optical modulator 100 is mounted has a protrusion 130 (fig. 2 and 3) as a first protrusion protruding from the bottom surface 106. Socket electrodes 120, 122, 124, and 126 as signal input portions are provided on an upper surface (top surface) 132 of the protruding portion 130.

Screw holes 140a, 140b, 140c, and 140d are provided in the bottom surface 106 of the case 104 in regions where the protruding portions 130 are not provided.

Next, an example of mounting the optical modulator 100 on a circuit board to the outside will be described. 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 in the direction indicated by the arrow AA and a cross-sectional view in the direction indicated by the arrow BB of the optical transmission device shown in fig. 4, respectively.

The optical transmission device 400 includes a circuit board 404 fixed in a housing 402, and the optical modulator 100 is mounted on the circuit board 404. Note that, since the optical modulator 100 and the circuit board 404 are housed in the housing 402, the optical modulator 100 and the circuit board 404 cannot be visually confirmed from the outside of the housing 402, but in fig. 4, for the sake of explanation, portions housed in the housing 402 are indicated by solid lines except for portions of the circuit board 404 hidden by the housing 104 of the optical modulator 100.

The circuit board 404 is mounted with a DSP (Digital Signal Processor) 410, a DRV (Driver) 420, an LD (Laser Diode) 430, a PD (Photo Diode) 440, and other electronic components (not shown). The DSP410 is an arithmetic processing device for executing processing of a digital signal. DRV420 is a circuit for driving optical modulator 100. The LD430 injects laser light into the optical modulator 100 via the optical fiber 108. The PD440 is provided for digital coherent optical signal reception. The electric components mounted on the circuit board 404 are examples, and other electric components may be mounted.

The output of the DRV420 is output from electrode pins 450, 452, 454, 456 provided in the circuit substrate 404. As shown in fig. 5, the electrode pins 450, 452, 454, and 456 are provided on the circuit board 404 so as to extend upright from a component mounting surface (a surface on the upper side in the figure) of the circuit board 404 toward the upper side in the figure from a conductor pattern for signal output of the DRV420 mounted on the circuit board 404. The optical modulator 100 is electrically connected to the DRV420 by fitting the socket electrodes 120, 122, 124, 126 provided on the protrusion 130 to the electrode pins 450, 452, 454, 456 provided on the circuit board 404.

The screw holes 140a, 140b, 140c, and 140d of the housing 104 are fastened to screws 462a, 462b, 462c, and 462d inserted into the circuit board 404 via tubular spacers 460a, 460b, 460c, and 460d disposed at the respective positions of the screw holes, and the optical modulator 100 is fixed to the circuit board 404.

The spacers 460a, 460b, 460c, and 460d have the same height as or higher than the height of the protrusion 130 measured from the bottom surface 106 of the housing 104 (the surface facing the circuit board 404) of the optical modulator 100, and the protrusion 130 and the spacers 460a, 460b, 460c, and 460d ensure a space for mounting electrical components such as the DSP410 and the DRV420 between the bottom surface 106 of the optical modulator 100 and the circuit board 404. This improves the space utilization efficiency in the housing 402 of the optical transmission device 400.

In particular, the bottom surface 106 of the housing 140 of the optical modulator 100 of the present embodiment is not provided with a notch as in the conventional art, and the protrusion 130 is provided in the portion. Therefore, in the optical modulator 100, most regions of the bottom surface 106 of the housing 104 can be configured to be the same plane. Here, the protrusion 130 can be limited to a minimum area region required for housing the socket electrodes 120, 122, 124, 126 as the signal input portions, and occurrence and unevenness of machining distortion can be minimized, so that disturbance of the uniformity of the bottom surface 106 due to the protrusion 130 can be minimized.

As a result, in the optical modulator 100, the occurrence of the machining distortion of the housing 104 is minimized, and the occurrence of minute deformation of the housing 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 optical modulator 100, socket electrodes 120, 122, 124, and 126, which are signal input portions to which an electrical signal (high-frequency signal) for causing the optical modulator 100 to perform an optical modulation operation is input, are provided on an upper surface (top surface) 132 of a protrusion portion 130 protruding from the bottom surface 106 of the housing 104. Therefore, in the optical modulator 100, the electrode pins 450, 452, 454, and 456 rising from the conductor pattern for signal output of the driving circuit formed on the circuit substrate 404 are in contact with and electrically connected to the socket electrodes 120, 122, 124, and 126 of the optical modulator 100 in the vicinity of the corresponding conductor pattern.

That is, in the optical modulator 100, the distance between the conductor pattern for signal output of the drive circuit formed on the circuit substrate 404 and the signal input portion (the socket electrode 120 and the like) of the optical modulator 100 (and thus the propagation distance of the high-frequency signal output from the drive circuit) can be made significantly smaller than that of a conventional optical modulator (for example, the optical modulator described in patent document 1). Therefore, the distortion at the time of fixing the case can be reduced between the conductor pattern and the signal input portion, and the disturbance of the high-frequency characteristics can be reduced, and the initial change and the secular change of the high-frequency characteristics can be suppressed.

In order not to apply stress to the protruding portion 130 when the screws 462a, 462b, 462c, and 462d are fastened, the height of the spacers 460a, 460b, 460c, and 460d may be, for example, a height with a negative tolerance of zero with respect to the height of the protruding portion 130 or a height with a predetermined dimension higher than the height of the protruding portion 130.

In the present embodiment, the structure in which 4 spacers 460a, 460b, 460c, 460d are used so as to correspond to all 4 screw holes 140a, 140b, 140c, 140d is not limited to this. For example, a spacer (460a or the like) may be used for at least one of the 4 screw holes 140a, 140b, 140c, 140 d. Even with such a configuration, the spacer and the protruding portion 130 can secure a space for mounting the electrical component between the bottom surface 106 and the circuit board 404.

In the present embodiment, the bottom surface 106 is provided with 4 screw holes 140a, 140b, 140c, and 140d at four corners of the bottom surface 106 except for the portion where the protruding portion 130 is provided, but the present invention is not limited thereto. The number and arrangement of the screw holes provided in the bottom surface 106 except for the portion where the protruding portion 130 is provided may be any number and arrangement of 1 or more as long as the mounting space of the electrical component can be secured between the bottom surface 106 and the circuit board by using the spacer 460a or the like in the portion of the screw holes.

[ second embodiment ]

Next, an optical modulator according to a second embodiment of the present invention will be described. Fig. 7, 8, and 9 are a plan view, a front view, and a bottom view respectively showing the structure of the optical modulator 700 according to the second embodiment of the present invention, and correspond to fig. 1, 2, and 3 respectively showing the structure of the optical modulator 100 according to the first embodiment. In fig. 7, 8, and 9, the same components as those of the optical modulator 100 shown in fig. 1, 2, and 3 are referred to in the description of fig. 1, 2, and 3.

The optical modulator 700 of the second embodiment has the same configuration as the optical modulator 100 of the first embodiment, but differs in that it includes a housing 704 instead of the housing 104. The housing 704 has the same configuration as the housing 104, but differs in that a first protrusion is provided instead of the protrusion 130 as the protrusion 730. Similarly to the protrusion 130, the protrusion 730 protrudes from a part of the bottom surface 706 of the housing 704 facing the circuit board on which the optical modulator 700 is mounted, and includes, on its upper surface (top surface) 732, socket electrodes 120, 122, 124, and 126 (fig. 8 and 9) as signal input portions.

However, the protrusion 730 further includes screw holes 740a and 740b on the upper surface 732, unlike the protrusion 130. In the present embodiment, the screw holes 740a and 740b are provided at positions sandwiching the 4 socket electrodes 120, 122, 124, and 126 arranged in a row on the upper surface 732 from both end portions in the arrangement direction.

Thus, in the optical modulator 700, when the electrical connection is made to the drive circuit (circuit) formed on the external circuit board via the socket electrodes 120, 122, 124, and 126, the projecting portion 730 can be stably fixed to the circuit board so as to include the respective intervals by using the screw holes 740a and 740b at the position very close to the high-frequency connector portion. As a result, compared to the case of the optical modulator 100 of the first embodiment, the distance between the conductor pattern for signal output of the drive circuit configured on the circuit substrate and the signal input portion (the socket electrode 120 and the like) of the optical modulator 700 (and thus the propagation distance of the high-frequency signal output from the drive circuit) can be more stably set and maintained, and the secular change in the high-frequency characteristics of the optical modulator 700 can be more favorably suppressed.

In the present embodiment, the two screw holes 740a and 740b are provided on the upper surface 732 of the protruding portion 730 at positions sandwiching the socket electrodes 120, 122, 124, and 126 from both ends in the arrangement direction thereof, but the present invention is not limited thereto. For example, the number of screw holes provided in upper surface 732 may be any number, such as one or more, and the arrangement of these screw holes in upper surface 732 may be any.

[ third embodiment ]

Next, an optical modulator according to a third embodiment of the present invention will be described. Fig. 10, 11, and 12 are a plan view, a front view, and a bottom view respectively showing the structure of an optical modulator 1000 according to a third embodiment of the present invention, and correspond to fig. 1, 2, and 3 respectively showing the structure of the optical modulator 100 according to the first embodiment. In addition, fig. 13 is a left side view of the optical modulator 1000 shown in fig. 11 with respect to a front view of the optical modulator 1000.

In fig. 10, 11, and 12, the same components as those of the optical modulator 100 shown in fig. 1, 2, and 3 are referred to in the description of fig. 1, 2, and 3.

The optical modulator 1000 of the third embodiment has the same configuration as the optical modulator 100 of the first embodiment, but differs in that a housing 1004 is provided instead of the housing 104. The case 1004 has the same configuration as the case 104, but is different in that a protrusion 1030 is provided in addition to the protrusion 130.

The protrusion 1030 is a second protrusion configured to protrude from a part of the bottom surface 1006 of the housing 1004 similarly to the protrusion 130 as the first protrusion, and the height from the bottom surface 1006 is equal to the height of the protrusion 130. Thus, in the optical modulator 1000, by providing the protrusion 1030 as the second protrusion, the facing area (for example, contact area) between the optical modulator 1000 and the circuit board can be enlarged, and the optical modulator 1000 can be mounted on the circuit board more stably.

In the present embodiment, as shown in fig. 12, the protruding portion 1030 as the second protruding portion is provided at a position symmetrical to the protruding portion 130 as the first protruding portion with respect to the center line 1200 in the width direction of the case 1004 extending in the longitudinal direction of the case 1004, but the present invention is not limited thereto. Even if the protrusion 1030 is disposed at an arbitrary position regardless of the arrangement of the protrusion 130, the light modulator 1000 can be mounted more stably on the circuit board.

Further, as shown in fig. 12, when the protrusion 1030 and the protrusion 130 are arranged substantially symmetrically, the case 1004 becomes a member having a symmetrical structure, and unevenness in machining distortion of the case 1004 generated at the time of machining the case 1004 is further reduced as compared with the case of the case 104, and the remaining machining stress is also symmetrical. As a result, it is possible to further suppress the occurrence of minute distortion due to unevenness in processing distortion in the case 1004 of the optical modulator 1000 when the optical modulator 1000 is fixed to the circuit substrate, and this is a more preferred embodiment. Therefore, in the optical modulator 1000, initial changes in optical characteristics and/or high-frequency characteristics and their secular changes at the time of mounting on a circuit board can be further suppressed.

In general, in a DP-QPSK modulator, which is an example of an optical modulator to which the configuration of the optical modulator 100, 700, or 1000 can be applied, 2 output lights from the optical modulator 102 propagate along the center line 1200 in the width direction of the housing 104, 704, or 1004 and in a symmetrical arrangement with respect to the center line 1200. Further, many optical elements such as lenses for combining the 2 output beams and guiding the combined beams to the optical fiber 108 are arranged symmetrically with respect to the width direction center line 1200.

Therefore, if the housings 104, 704, and 1004 are configured symmetrically as in the present embodiment and the shape change that may occur in the housings is a change that is symmetrical about the center line 1200, the secular change in optical characteristics and the temperature variation in the optical modulators 100, 700, and 1000 can be more effectively suppressed than when the housings are configured asymmetrically.

In the present embodiment, the screw holes are not provided on the upper surface 132 of the protrusion 130 and the upper surface 1032 of the protrusion 1030, but the present invention is not limited thereto. For example, at least one screw hole may be provided on the upper surface 132 and/or 1032 to screw the protrusion 130 and/or the protrusion 1030 to the circuit board. Accordingly, similarly to the optical modulator 700 in the second embodiment, the distance between the conductor pattern for signal output of the driving circuit formed on the circuit substrate and the signal input portion (e.g., the socket electrode 120) of the optical modulator 1000 can be further stably maintained, and the secular change in the high-frequency characteristics of the optical modulator 1000 can be more favorably suppressed.

Further, although the optical modulator including the optical modulation element having 4 RF electrodes using LN as the substrate has been described in each of the above embodiments, the present invention is not limited to this, and is similarly applicable to an optical modulator having RF electrodes of a number other than 4 and/or an optical modulator using a material other than LN as the substrate.

Description of the reference symbols

100. 700, 1000 … optical modulator, 102 … optical modulation element, 104, 704, 1004 … housing, 106, 706, 1006 … bottom surface, 108, 110 … optical fiber, 120, 122, 124, 126 … socket electrode, 130, 730, 1030 … protrusion, 132, 732 … top surface, 140a, 140b, 140c, 140d, 740a, 740b … screw hole, 400 … optical transmission device, 402 … housing, 404 … circuit substrate, 450, 452, 454, 456 … electrode pin, 460a, 460b, 460c, 460d … spacer, 462a, 462b, 462c, 462d … screw, 1200 … width direction centerline.