JP2019160959A - Optical module - Google Patents

Abstract

To make compact a circuit board connected with an OSA by an FPC, in an optical module.SOLUTION: An OSA 2 converts a luminous signal and an electric signal at least from one to the other. A circuit board 3 is provided with a circuit electrically connected with the OSA 2, and an FPC 4 connects the OSA 2 and the circuit board 3. The circuit board 3 has a groove 12 in one principal surface thereof. At the connection of the FPC 4 and the circuit board 3, the tip of the FPC 4 is inserted into the groove 12. At the connection, the principal surfaces of the FPC 4 and the circuit board 3 are arranged in the directions intersecting each other, and the principal surface at the tip of the FPC 4 abuts against the lateral face of a step formed by the groove 12.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical module.

  In an optical communication system, an optical module that converts one of optical signals and electrical signals to the other or bidirectionally is used. An optical module houses an optical subassembly (OSA), a circuit board made of a rigid board, and a flexible board for connecting the OSA and the circuit board in one housing.

  The OSA includes a light emitting device such as a laser diode (LD) and a light receiving device such as a photodiode (PD). The circuit board is formed with a conductor pattern such as wiring, and a driver circuit that outputs an electrical signal to the laser diode, an electronic circuit that constitutes a CDR (Clock Data Recovery) that separates the electrical signal output from the photodiode into a clock and data, etc. Parts are mounted. The flexible board is a so-called flexible printed circuit (FPC), and a signal line for transmitting an electric signal between the OSA and the circuit board is formed as a conductor pattern in the FPC.

  Conventionally, the circuit board and the FPC are connected by overlapping the main surface of the end portion of the FPC on the main surface of the circuit board, as shown in Patent Document 1 below. Also, a connector for connecting the FPC is mounted on the circuit board. Patent Document 2 listed below describes a technique for inserting and fixing the tip of an FPC into a through hole provided in a circuit board.

JP, 2006-55767, A Japanese Patent Laid-Open No. 2015-19021

  Optical modules have been increased in speed and size with the spread of broadband networks in recent years. However, in the structure in which the end surfaces and main surfaces of the circuit board and the FPC are overlapped and faced to each other, the area of the portion where the FPC is superimposed on the circuit board or the solder that joins the wiring between the FPC and the circuit board. The area used for attachment becomes relatively large. That is, a dead space where electronic components cannot be mounted on the circuit board increases. On the other hand, there is a limit to improving the mounting density of electronic components on a circuit board. For this reason, miniaturization of the circuit board is hindered, and further miniaturization of the optical module is difficult. In addition, in this structure, since it is necessary to provide a connection pad for solder connection between the circuit board and the FPC, there is a problem in that it is disadvantageous in terms of high frequency characteristics. The structure in which the connector is mounted on the circuit board also has a problem that it is difficult to reduce the size of the circuit board because the area where the electronic component can be mounted is reduced due to the occupied area of the connector. Further, when a through hole used for connecting an FPC is provided in the circuit board, a dead space related to mounting of electronic components is generated on both surfaces of the circuit board at that portion, and there is a problem that it is difficult to downsize the circuit board.

  The present invention has been made to solve the above-described problems, and reduces the dead space associated with the connection of the FPC to the circuit board, thereby reducing the size of the circuit board and thus the optical module.

  (1) An optical module according to the present invention includes an optical subassembly for converting an optical signal and an electrical signal from at least one to the other, a circuit board provided with a circuit electrically connected to the optical subassembly, An optical subassembly and a flexible board for connecting the circuit board, the circuit board having a step on one main surface thereof, and at the connection portion between the flexible board and the circuit board, The main surfaces of the substrate are arranged in a direction crossing each other, and the main surface of the tip portion of the flexible substrate is in contact with the side surface of the step.

  (2) The optical module according to (1) may be configured such that a groove into which the tip portion of the flexible substrate is inserted is provided on the main surface of the circuit substrate as the step.

  (3) In the optical module according to the above (1) and (2), an electronic component may be arranged at the back position of the connection portion on the other main surface of the circuit board.

  (4) In the optical modules according to (1) to (3), each of the printed wirings transmits the electrical signal, and is provided on the first signal line provided on the flexible board and the circuit board. The first signal line and the second signal line that have a second signal line and are joined to each other at the connection portion may have the same line width.

  (5) In the optical module according to any one of (1) to (4), a first signal line that is a printed wiring provided on the flexible board and that transmits the electrical signal, and an upper surface of the step of the circuit board. And a second signal line joined to the first signal line at the upper end of the step, and the end of the first signal line on the circuit board side is at the height of the upper end of the step. It can be set as the structure located.

  (6) In the optical module according to any one of (1) to (5), the flexible substrate is configured such that a surface of the main surface of the flexible substrate that is in contact with the step is protruded, and the optical subassembly. It can be set as the structure which curves in the single direction along the direction which goes to the said circuit board.

  (7) In the optical module according to any one of (1) to (6), a first signal line that is a printed wiring provided on the flexible board and that transmits the electrical signal, and an upper surface of the step of the circuit board. A second signal line joined to the first signal line at an upper end of the step, and the first signal line is continuous from the optical subassembly side to the circuit board side, and It can be set as the structure provided in the surface at the side contact | abutted by the said level | step difference among the main surfaces of a flexible substrate.

  According to the present invention, the optical module can be further reduced in size.

1 is a schematic top view illustrating a configuration of an optical module according to a first embodiment of the present invention. It is a typical vertical sectional view of the principal part of the optical module in the position along the II-II line of FIG. It is the typical perspective view which looked at the connection part of FPC and a circuit board from diagonally upward. It is a typical vertical sectional view of the connection part of FPC and a circuit board. It is a typical top view of the connection part of FPC and a circuit board. It is a typical vertical sectional view of the connection part of FPC and a circuit board in the optical module which concerns on the 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted.

[First Embodiment]
FIG. 1 is a schematic top view showing a configuration of an optical module 1 according to the first embodiment of the present invention. FIG. 2 is a schematic vertical sectional view of the main part of the optical module 1 at a position along the line II-II in FIG. For convenience of explanation, FIGS. 1 and 2 show coordinate axes of an XYZ coordinate system, which is an orthogonal coordinate system. The XYZ coordinate system is a right-handed system. The optical module 1 has, for example, a substantially elongated rectangular parallelepiped shape, and the longitudinal direction is set to the X axis. In the following description, for convenience, the X axis and the Y axis are two horizontal axes, and the Z axis is the vertical direction.

  The optical module 1 includes an OSA 2, a circuit board 3, and an FPC 4 that connects the OSA 2 and the circuit board 3 as main functional parts, and a housing 5 that stores the main part. FIG. 1 shows a state in which the upper plate of the housing 5 is removed so that the main part arranged inside the housing 5 can be seen.

  The circuit board 3 is positioned horizontally in the housing 5. That is, the main surface of the circuit board 3 is along the XY plane, and the direction perpendicular to the main surface is the Z-axis direction. Here, FIG. 1 is a view of the optical module 1 as viewed from above, and the upper surface of the upper surface and the lower surface, which are the main surfaces of the circuit board 3, appears in front.

  One end of the optical module 1 in the longitudinal direction (right side in FIG. 1) is connected to a host device (not shown) such as a transmission device, and the other end (left side in FIG. 1) is connected to the optical fiber 6. Correspondingly, the OSA 2 is basically arranged close to the connection end with the optical fiber 6, and the circuit board 3 is arranged close to the connection end with the host device. Further, the optical module 1 includes, for example, an optical receptacle 7 between the OSA 2 and the optical fiber 6 as a connector for connecting the optical fiber 6, and, for example, a circuit board 3 as a connector for connection with a host device. A card edge connector 8 is provided at the end on the host device side.

  The optical module 1 of this embodiment is a transceiver having a transmission function and a reception function, and has, as OSA2, a TOSA (Transmitter Optical Subassembly) 2a for transmission and a ROSA (Receiver Optical Subassembly) 2b for reception. . The TOSA includes, for example, a laser diode, converts an electrical signal input from the circuit board 3 into an optical signal, and outputs the optical signal to the optical fiber 6a. On the other hand, the ROSA includes, for example, a photodiode, converts an optical signal input from the optical fiber 6 b into an electrical signal, and outputs the electrical signal to the circuit board 3. In the present embodiment, the TOSA 2a and the ROSA 2b are juxtaposed with an interval in the Y-axis direction.

  A terminal connected to the circuit board 3 through the FPC 4 is provided on the circuit board 3 side of the OSA 2. In the example illustrated in the present embodiment, the terminal is formed with a conductor pattern on the surface of the ceramic substrate 9 integrated with the OSA 2, for example. Further, when the OSA 2 is mounted on a printed board, the terminal can be provided on the printed board. In addition, when it only describes as a printed circuit board, the said board | substrate shall be a rigid board | substrate fundamentally.

  The circuit board 3 is a printed board. The circuit board 3 is, for example, a multilayer board, and in particular in the example shown in the present embodiment, is a double-sided board that can mount electronic components on both main surfaces. The circuit board 3 is provided with a circuit electrically connected to the OSA 2. Specifically, a conductor pattern such as wiring is formed on the circuit board 3, and a driving circuit or ROSA that outputs an electrical signal to the TOSA, for example, is provided on the main surface of the circuit board 3, that is, the upper surface 3u and the lower surface 3d. An integrated circuit (IC) or the like is mounted as an electronic component 10 constituting a CDR or the like that separates an electrical signal output from the clock into data and data. The electronic component 10 also includes a control IC (microcomputer) that controls driving of the TOSA and ROSA, a power supply circuit, and a resistor and a capacitor.

  The FPC 4 electrically connects the OSA 2 and the circuit board 3. Specifically, a signal line 11 (first signal line) that connects the OSA 2 and the circuit board 3 is formed by printed wiring in the FPC 4, and an electric signal is transmitted from the circuit board 3 to the TOSA via the signal line 11. To the circuit board 3 from the ROSA. In the present embodiment, two OSAs 2 (2a, 2b) are connected to the circuit board 3 by separate FPCs 4 (4a, 4b).

  Next, a connection structure between the OSA 2 using the FPC 4 and the circuit board 3 will be described.

  FIG. 3 is a schematic perspective view of the connecting portion between the FPC 4 and the circuit board 3 as viewed obliquely from above. FIG. 4 is a schematic vertical sectional view of a connection portion between the FPC 4 and the circuit board 3. FIG. 4 shows coordinate axes of the XYZ coordinate system common to FIGS. 1 and 2.

  The circuit board 3 has a groove 12 on the upper surface 3u into which the tip of the FPC 4 is inserted. The groove 12 has a function of locking the tip of the FPC 4 at a target position where the signal line 20 (second signal line) of the circuit board 3 and the signal line 11 (first signal line) of the FPC 4 are connected. This function makes it easy to keep the signal line at the tip of the FPC 4 at the connection target position on the circuit board 3 when both signal lines are joined by solder or the like.

  The shape of the groove 12 is basically set so as to fulfill the function. Specifically, the width of the groove 12 (dimension in the X direction) is set larger than the thickness of the FPC 4, and the length of the groove 12 (dimension in the Y direction) is set larger than the width of the FPC 4. In the example illustrated in the present embodiment, the groove 12 into which the FPC 4a is inserted (referred to as a groove 12a) and the groove 12 into which the FPC 4b is inserted (referred to as a groove 12b) are a single continuous groove. It is formed as. In this regard, the groove 12a and the groove 12b can also be formed as two grooves separated from each other. In this case, the groove 12a and the groove 12b can be formed by shifting the positions in the X direction from each other.

  Further, the depth of the groove 12 and the vertical cross-sectional shape are also determined so as to fulfill the above-described function. In this respect, the groove 12 has a depth up to the middle of the thickness of the circuit board 3 and is not a hole penetrating the circuit board 3. That is, the groove 12 contributes to the above-described function by limiting the vertical position of the tip portion of the FPC 4. Further, as a point different from the hole, the lower surface located on the back side of the groove 12 does not become a dead space in the circuit formation in the circuit board 3 and can be used as, for example, an arrangement space or wiring space for the electronic component 10. 3 and, in turn, the optical module 1 can be downsized.

  Regarding the vertical cross-sectional shape of the groove 12, for example, as shown in FIG. 4, it can be a rectangular groove having a vertical side surface and a horizontal bottom surface. Moreover, the vertical cross-sectional shape of the groove | channel 12 can also be made into other shapes, such as a U shape. Note that the groove 12 forms a step on the main surface of the circuit board 3 with the lower end positioned at the bottom and the open end of the upper surface as the upper end.

  At the connecting portion between the FPC 4 and the circuit board 3, the front end portion of the FPC 4 is inserted into the groove 12 with its main surface facing sideways. That is, the main surface of the front end portion of the FPC 4 and the main surface of the circuit board 3 are arranged so as to intersect each other. Basically, the front end portion of the FPC 4 and the circuit board 3 are arranged so that their main surfaces are substantially perpendicular to each other. Thus, by connecting the FPC 4 to the circuit board 3 in an upright manner, the area occupied by the connection portion on the circuit board 3, for example, the main surface of the front end of the FPC 4 is superimposed on the main surface of the circuit board 3. The structure can be made smaller than the structure in which the FPC 4 is connected to the circuit board 3 by mounting a connector on the circuit board 3. Therefore, also in this respect, the dead space for circuit formation in the circuit board 3 is suppressed, and the circuit board 3 can be downsized, and the optical module 1 can be downsized.

  The main surface of the front end portion of the FPC 4 is in contact with the side surface of the step of the groove 12. Specifically, in FIG. 2 or FIG. 4, the main surface of the tip portion of the FPC 4 is brought into contact with the right side surface of the groove 12. In this embodiment, the OSA 2 is located on the upper left side of the groove 12 in FIG. 2 or FIG. 4, and the OSA 2 side end of the FPC 4 has its main surface horizontal, and the terminals of the OSA 2 provided on the ceramic substrate 9 etc. Connected to. The FPC 4 is curved in a single direction along the direction from the OSA 2 toward the circuit board 3 so that the main surface 4u on the side that comes into contact with the step between the two main surfaces is convex. That is, the FPC 4 is bent downward from the OSA 2 side toward the circuit board 3 side, and has no inflection point in the middle. As a result, the main surface 4u of the FPC 4 facing upward at the end portion on the OSA 2 side is directed to the right at the end portion on the circuit board 3 side, and is in contact with the right side surface of the groove 12. At that time, the front end portion can be pressed against the side surface of the groove 12 by using the force acting rightward on the front end portion of the FPC 4 on the circuit board 3 side due to the elasticity of the FPC 4 to extend the deflection.

  FIG. 5 is a schematic top view of a connection portion between the FPC 4 connected to one OSA 2 and the circuit board 3, and a signal line 11 provided in the FPC 4 as a first signal line and a circuit as a second signal line. An example of the pattern of each signal line 20 provided on the substrate 3 is shown. In addition, the vertical sectional view along the IV-IV line in FIG. 5 corresponds to FIG.

  For example, in the FPC 4, as a signal line 11 between the OSA 2 and the circuit on the circuit board 3, a pair of high frequency signal lines 11s for transmitting a high frequency signal in a differential format and a ground electrode 11g for transmitting a ground potential are formed. Is done. In the example shown in FIG. 5, the ground electrodes 11g are disposed on both sides of the pair of high-frequency signal lines 11s, respectively, so that a shielding effect on the high-frequency signal lines 11s can be expected.

  On the other hand, a signal line 20 is formed on the upper surface 3u of the circuit board 3 as a printed wiring corresponding to each signal line 11 of the FPC 4. That is, as the signal line 20, a pair of high-frequency signal lines 20s connected to the high-frequency signal line 11s and a ground electrode 20g connected to the ground electrode 11g are provided. Corresponding to the arrangement of the ground electrode 11g on both sides of the high-frequency signal line 11s, the ground electrode 20g is also arranged on both sides of the high-frequency signal line 20s.

  The signal line 11 and the signal line 20 that are joined to each other are configured so as to achieve impedance matching at the joined part. In particular, the high-frequency signal line 11s and the high-frequency signal line 20s that are joined to each other have the same line width, and impedance matching is achieved at the joint.

  The signal line 11 and the signal line 20 are joined by, for example, solder 21 at a connection portion between the FPC 4 and the circuit board 3. Specifically, the signal line 11 is a curved main surface 4u of the two main surfaces 4u, 4d of the FPC 4, that is, is curved convexly as shown in FIG. It is formed on the main surface on the side in contact with. As shown in FIG. 4, the signal line 11 reaches the upper end of the step on the right side of the groove 12 on the circuit board 3 side. On the other hand, the signal line 20 is disposed on the upper surface 3u on the right side of the groove 12, and the end of the signal line 20 is located at the upper end of the step on the right side of the groove 12 as shown in FIG. Therefore, the signal line 11 and the signal line 20 come into contact with or approach each other at the upper end of the step on the right side of the groove 12 and are joined with the solder 21 at the corresponding portion. Incidentally, in the conventional structure in which the main surface 4d at the tip of the FPC 4 is superimposed on the main surface of the circuit board 3, the signal line formed on the upper main surface 4u of the FPC 4 and the upper surface 3u of the circuit board 3 are formed. In order to connect to the signal line, for example, vias and connection pads are provided. On the other hand, in the connection structure of this embodiment mentioned above, since the contact and approach location of the signal track | line 11 and the signal track | route 20 are joined directly, degradation of a high frequency characteristic can be suppressed. Note that the joining member is not limited to solder, and the signal lines 11 and 20 can be electrically connected using other materials such as conductive resin.

  Here, the position of the end of the signal line 11 on the circuit board 3 side can be the height of the upper end of the step or slightly above it. That is, the signal line 11 is not formed in a portion disposed below the upper end of the step at the tip portion of the FPC 4 on the circuit board 3 side. As a result, as shown in FIG. 4, the signal line 11 does not extend below the signal line 20 located on the upper surface 3 u of the circuit board 3 at the connection portion between the signal line 11 and the signal line 20. In the structure, unnecessary resonance hardly occurs at the connection portion between the signal line 11 and the signal line 20. Therefore, the effect of preventing the deterioration of the high-frequency characteristics of the signals transmitted through the high-frequency signal lines 11 s and 20 s can be obtained by using the high-frequency signal line 11 s as the structure.

  In the above-described example, the signal line 11 is continuously provided from the OSA 2 side to the circuit board 3 side, and is provided on the main surface 4 u on the side that comes into contact with the step between the two main surfaces of the FPC 4. It faces the signal line 20 at the upper end. On the other hand, the signal line 11 is formed on the main surface 4d on the opposite side of the FPC 4 in at least a part of the path from the OSA 2 side to the circuit board 3 side, and the signal line 11 is routed via the middle in the path. A structure in which the main surface 4u on the side in contact with the step is pulled out and connected to the signal line 20 is conceivable. For example, the structure can be adopted for the ground electrode 11g. On the other hand, with respect to the high-frequency signal line 11s, a deviation in impedance between the via and other portions can affect the high-frequency characteristics of the signal transmitted through the high-frequency signal line 11s. Therefore, in this embodiment, the structure shown in the above example is used to suppress the deterioration of the characteristics of the signal transmitted through the high-frequency signal line 11s. Note that, in the connection portion between the ceramic substrate 9 of the OSA 2 and the FPC 4, the high-frequency signal line 11 s is drawn to the main surface 4 d through the via at the end of the FPC 4 and the conductor pattern provided on the surface of the ceramic substrate 9. It may be electrically connected.

  As shown in FIGS. 1 and 2, the position of the groove 12 in the X direction in the circuit board 3 is relatively close to the OSA 2. Here, since the OSA 2 and the circuit board 3 are in a position shifted in the Z direction, the electronic component 10 can be disposed between the OSA 2 and the upper surface 3 u of the circuit board 3. Therefore, by arranging the OSA 2 and the circuit board 3 so as to have an overlapping part in a plan view and using the upper surface 3u of the circuit board 3 in the overlapping part as a component mounting region, the optical module 1 can be further improved. Miniaturization can be achieved. In this case, the position of the groove 12 in the X direction can be on the right side of the example shown in the figure.

[Second Embodiment]
FIG. 6 is a schematic vertical sectional view of a connection portion between the FPC 4 and the circuit board 3 of the optical module 1 according to the second embodiment of the present invention, which can be compared with FIG. 4 of the first embodiment. . FIG. 4 shows a connection portion between the FPC 4 and the circuit board 3 of the optical module 1 shown in FIG. The optical module 1 of the present embodiment is obtained by replacing the connection portion in FIG. 2 with the structure shown in FIG. 6, and other configurations are basically the same as those in the first embodiment.

  Specifically, in the optical module 1 of the present embodiment, a component different from the first embodiment is a circuit board, and a circuit board 3B is used instead of the circuit board 3 of the first embodiment. The difference between the circuit board 3B and the circuit board 3 is that the step 30 on the surface of the circuit board with which the tip of the FPC 4 abuts is not formed by a groove. That is, the groove 12 of the circuit board 3 has steps on both sides in the width direction, whereas the step 30 of the circuit board 3B is only on one side.

  The overall vertical sectional view of the main part of the optical module 1 of the present embodiment corresponding to the partial cross section of FIG. 6 is basically the same as that of FIG. 2 except for the connecting portion between the FPC 4 and the circuit board 3 as described above. OSA2 is located at the upper left of the circuit board 3, and the FPC 4 is connected to the OSA2 with one end thereof being horizontal, and the main surface 4u on the upper side at the one end protrudes between the OSA2 and the circuit board 3. And the other end is connected perpendicularly to the circuit board 3.

  As shown in FIG. 6, a level difference is provided on the upper surface 3 u of the circuit board 3 </ b> B by the step 30, and the upper step surface 31, the lower step surface 32 lower than the upper step surface 31, and the upper step surface 31 and the lower step surface 32 are vertically aligned. A side surface 33 is formed to connect in the direction. Incidentally, the upper surface 31 and the lower surface 32 are horizontal surfaces, and the side surfaces are vertical surfaces, for example. In FIG. 6, the upper step surface 31 is located on the right side of the step 30, the lower step surface 32 is located on the left side of the step 30, and the side surface 33 faces the surface to the left side. The tip of the main surface 4u of the FPC 4 on the circuit board 3 side is in contact with the side surface 33 of the step 30. The joining of the signal line 11 of the FPC 4 and the signal line 20 of the circuit board 3 by the solder 21 or the like is performed in a state in which the front end portion of the FPC 4 is in contact with and locked to the step 30 as in the first embodiment. Can do.

  For example, the step 30 can be formed by making the number of layers of the multilayer substrate different between the upper step surface 31 side and the lower step surface 32 side.

  Also in the present embodiment, as in the first embodiment, the dead space in the portion where the FPC 4 is connected to the circuit board 3 can be suppressed, and the circuit board 3 can be downsized, and thus the optical module 1 can be downsized.

  1 optical module, 2 optical subassembly (OSA), 3, 3B circuit board, 4 flexible printed circuit board (FPC), 5 housing, 6 optical fiber, 7 optical receptacle, 8 card edge connector, 9 ceramic substrate, 10 electronic components 11 signal line, 11 g ground electrode, 11 s high frequency signal line, 12 groove, 20 signal line, 21 solder, 30 step, 31 upper step surface, 32 lower step surface, 33 side surface.

Claims (7)

An optical subassembly for converting optical and electrical signals from at least one to the other;
A circuit board provided with a circuit electrically connected to the optical subassembly;
A flexible board connecting the optical subassembly and the circuit board;
The circuit board has a step on one main surface thereof,
At the connection portion between the flexible substrate and the circuit substrate, the principal surfaces of the two substrates are arranged in a direction intersecting each other, and the principal surface of the tip portion of the flexible substrate is in contact with the side surface of the step. ,
An optical module characterized by The optical module according to claim 1,
A groove into which the tip end portion of the flexible substrate is inserted in the main surface of the circuit board as the step;
An optical module characterized by The optical module according to claim 1 or 2,
An optical module, wherein an electronic component is disposed at a back position of the connection portion on the other main surface of the circuit board. In the optical module according to any one of claims 1 to 3,
Each of which is a printed wiring for transmitting the electrical signal, and has a first signal line provided on the flexible substrate and a second signal line provided on the circuit board,
The first signal line and the second signal line joined to each other at the connection portion have the same line width;
An optical module characterized by In the optical module according to any one of claims 1 to 4,
A first signal line that is a printed wiring that is provided on the flexible substrate and transmits the electrical signal;
A second signal line provided on an upper surface of the step of the circuit board and joined to the first signal line at an upper end of the step;
The terminal on the circuit board side of the first signal line is located at the height of the upper end of the step;
An optical module characterized by In the optical module according to any one of claims 1 to 5,
The flexible substrate is curved in a single direction along a direction from the optical subassembly toward the circuit board, with a surface of the main surface of the flexible substrate being abutted against the step being convex. An optical module. The optical module according to any one of claims 1 to 6,
A first signal line that is a printed wiring that is provided on the flexible substrate and transmits the electrical signal;
A second signal line provided on an upper surface of the step of the circuit board and joined to the first signal line at an upper end of the step;
The first signal line is continuously provided from the optical subassembly side to the circuit board side, and is provided on a surface of the main surface of the flexible substrate that is in contact with the step,
An optical module characterized by

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