Optical reception module and optical transmission / reception module

Abstract

An optical reception module (3) according to the present invention comprises a first substrate (30), a second substrate (40) that is disposed on the first substrate (30), a light-receiving element (50) that is disposed on the second substrate (40) and that converts an optical signal into an electrical signal, and an amplifier (60) that is disposed on the second substrate (40) and that amplifies the electrical signal inputted from the light-receiving element (50). The second substrate (40) is provided with a transmission line (70) that transmits the amplified signal outputted from the amplifier (60) to the first substrate (30), and the light-receiving element (50) is positioned on one side of a center line (C40) on the second substrate (40), said center line (C40) being a virtual line segment passing through the center of the second substrate (40) in plan view. The amplifier (60) is positioned on the center line (C40) or between the center line (C40) and the light-receiving element (50).

Description

Optical receiving module and optical transmitting and receiving module

[0001] The present invention relates to an optical receiver module and an optical transmitter / receiver module.

[0002] Modules for transmitting and receiving optical signals in optical communications have been provided. For example, Patent Document 1 discloses an optical receiver module including a substrate, a light receiving element mounted on a first surface of the substrate, an amplifier corresponding to the light receiving element mounted on the first surface of the substrate, an anode wiring pattern formed on the first surface of the substrate between an anode terminal of the light receiving element and the amplifier, and a cathode wiring pattern formed on the first surface of the substrate between a cathode terminal of the light receiving element and the amplifier.

[0003] Patent No. 6191348

[0004] As optical communications become broader and faster, there is a demand for improved transmission speeds of electrical signals in optical receiver modules. In particular, ultra-high-speed, broadband electrical signals exceeding 800 Gbit / s can lead to increased signal wiring and associated loss at high frequencies. Therefore, there is a demand for optimizing the flow of electrical signals transmitted within optical receiver modules to reduce communication degradation.

[0005] An object of one aspect of the present invention is to provide an optical receiver module and an optical transmitter / receiver module that reduce degradation of an electrical signal transmitted within the optical receiver module.

[0006] One aspect of the present invention is an optical receiving module comprising: a first substrate; a second substrate arranged on the first substrate; a photodetector arranged on the second substrate for converting an optical signal into an electrical signal; and an amplifier arranged on the second substrate for amplifying the electrical signal input from the photodetector, wherein the second substrate comprises a transmission line for transmitting the amplified signal output from the amplifier to the first substrate, and wherein, in a plan view, when an imaginary line segment passing through the center of the second substrate is taken as a center line, the photodetector is located on one side of the center line on the second substrate, and the amplifier is located on the center line or between the center line and the photodetector.

[0007] One aspect of the present invention is an optical transmitting and receiving module comprising: an optical transmitting module for transmitting optical signals; and an optical receiving module for receiving optical signals, wherein the optical receiving module comprises: a first substrate; a second substrate arranged on the first substrate; a photodetector arranged on the second substrate for converting an optical signal into an electrical signal; and an amplifier arranged on the second substrate for amplifying the electrical signal input from the photodetector, wherein the second substrate comprises a transmission line for transmitting the amplified signal output from the amplifier to the first substrate side, and wherein, in a plan view, when an imaginary line segment passing through the center of the second substrate is taken as a center line, the photodetector is located on one side of the center line on the second substrate, and the amplifier is located on the center line or between the center line and the photodetector.

[0008] According to one aspect of the present invention, it is possible to provide an optical receiver module and an optical transmitter / receiver module that reduce degradation of an electrical signal transmitted within the optical receiver module.

[0009] 1 is a block diagram schematically showing an example of the overall configuration of an optical transceiver module according to an embodiment. FIG. 2 is a plan view schematically showing an example of the configuration of an optical receiver module in the optical transceiver module according to an embodiment. FIG. 3 is a cross-sectional view showing a schematic cross section of the optical receiver module taken along line III-III shown in FIG. 2. FIG. 4 is a cross-sectional view schematically showing a cross section of a light receiving element provided in the optical receiver module in the optical transceiver module according to an embodiment taken along the YZ plane. FIG. 5 is a diagram schematically showing an equivalent circuit relating to an example of the circuit configuration of an amplifier provided in the optical receiver module in the optical transceiver module according to an embodiment. FIG. 6 is a schematic enlarged plan view of the optical receiver module, enlarging the area within the frame indicated by the dashed line in FIG. 2. FIG. 7 is a schematic side view of the area within the frame indicated by the dashed line in FIG. 2, as viewed from the -Y side.

[0010] Hereinafter, embodiments of the present invention will be described in detail. To facilitate understanding of the description, the same components in the drawings will be designated by the same reference numerals, and duplicate descriptions will be omitted as appropriate. Furthermore, the scale of each component in the drawings may differ from the actual scale.

[0011] In the drawings, directions may be indicated by the X-axis, Y-axis, and Z-axis. The X-axis, Y-axis, and Z-axis are mutually orthogonal. The direction of the arrow in the X-axis direction is referred to as the +X direction or +X side, and the direction opposite the +X direction is referred to as the -X direction or -X side. The direction of the arrow in the Y-axis direction is referred to as the +Y direction or +Y side, and the direction opposite the +Y direction is referred to as the -Y direction or -Y side. The direction of the arrow in the Z-axis direction is referred to as the +Z direction or +Z side, and the direction opposite the +Z direction is referred to as the -Z direction or -Z side. In the following embodiments, "parallel" to the X-axis, Y-axis, Z-axis, or other direction includes an error of ±5° when the object is tilted relative to these axes or directions. Furthermore, in the embodiments, "orthogonal" includes an error of ±5° relative to 90°.

[0012] <Overall Configuration> An example of the overall configuration of an optical transceiver module 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram schematically showing an example of the overall configuration of the optical transceiver module 1 according to an embodiment. As shown in Fig. 1, the optical transceiver module 1 includes an optical transmitting module 2 and an optical receiving module 3. The optical transmitting module 2 is connected to an optical transmission medium 11. The optical receiving module 3 is connected to an optical transmission medium 12. Each of the optical transmission media 11 and 12 includes an optical fiber.

[0013] The optical transmission module 2 transmits an optical signal OS1. The optical signal OS1 transmitted from the optical transmission module 2 is transmitted to the outside via an optical transmission medium 11. The optical transmission module 2 includes, for example, a light-emitting element configured as a laser and a drive circuit for driving the light-emitting element. The light-emitting element emits light in response to a drive signal from the drive circuit. This results in the optical signal OS1.

[0014] The optical receiving module 3 receives an optical signal OS2. The optical signal OS2 received by the optical receiving module 3 is transmitted from the outside via an optical transmission medium 12. The optical receiving module 3 also converts the received optical signal OS2 into an electrical signal. The electrical signal converted by the optical receiving module 3 is processed by a signal processing circuit electrically connected to the optical receiving module 3. Here, the signal processing circuit may be provided inside the optical transmitting and receiving module 1 or may be provided outside the optical transmitting and receiving module 1. Note that a compensation circuit may be incorporated into the amplifier 60 of the optical receiving module 3, which will be described separately. In the following description, the electrical connection between component A and component B will simply be referred to as "connection."

[0015] <Optical Receiving Module 3> Next, the optical receiving module 3 will be described in detail with reference to Figs. 2 to 4. Fig. 2 is a plan view schematically showing an example configuration of the optical receiving module 3. Fig. 3 is a cross-sectional view showing a schematic cross section of the optical receiving module 3 taken along line III-III shown in Fig. 2. Fig. 4 is a cross-sectional view schematically showing a cross section of the light receiving element 50 provided in the optical receiving module 3 taken along the YZ plane. For ease of explanation, Fig. 3 omits illustration of the wiring 47 of the second substrate 40, which will be described separately, but illustrates the wiring 46.

[0016] 2, the optical receiving module 3 includes a first substrate 30, a second substrate 40, a light receiving element 50, and an amplifier 60. The optical receiving module 3 may further include other components. The components included in the optical receiving module 3 will be described in detail below.

[0017] <First Substrate 30> An example of the configuration of the first substrate 30 will be described. The first substrate 30 supports the second substrate 40. Examples of the first substrate 30 include a glass epoxy substrate, a resin substrate, a ceramic substrate, and a semiconductor substrate. The first substrate 30 may be, for example, a wiring substrate corresponding to the motherboard of the optical receiving module 3. The first substrate 30 may include, for example, a power supply circuit for supplying voltage to the amplifier 60 and a communication circuit for inputting and outputting various signals to and from the outside.

[0018] 2 and 3, the first substrate 30 has a first main surface 31, a second main surface 32, and a side surface 33. The first main surface 31 is disposed on the +Z side of the first substrate 30. The first main surface 31 faces the second substrate 40. The second main surface 32 is the surface opposite the first main surface 31. That is, the second main surface 32 is disposed on the -Z side of the first substrate 30. The side surface 33 connects the first main surface 31 and the second main surface 32. The first substrate 30 shown in FIG. 2 has a substantially rectangular outer shape in a plan view. However, the outer shape of the first substrate 30 is not limited to a substantially rectangular shape.

[0019] The first substrate 30 further includes wirings 34, 35, and 36. As shown in Fig. 2, the first substrate 30 may include a plurality of each of the wirings 34, 35, and 36. Each of the wirings 34, 35, and 36 is a conductor pattern disposed on the first main surface 31 of the first substrate 30.

[0020] Each of the wirings 34 and 35 is connected to, for example, a power supply circuit (not shown) included in the first substrate 30. When the amplifier 60 includes multiple amplifier circuits including operational amplifiers, the wiring 34 functions as a power supply path that supplies voltage from the power supply circuit to some of the multiple amplifier circuits. The wiring 35 also functions as a power supply path that supplies voltage from the power supply circuit to other of the multiple amplifier circuits. The wiring 34 is arranged in an area on the +X side of the second substrate 40 in a plan view. The wiring 35 is arranged in an area on the −X side of the second substrate 40 in a plan view.

[0021] The wiring 36, together with the transmission line 70, functions as a transmission path for transmitting an electrical signal output to, for example, a signal processing circuit. The wiring 36 is arranged in a region on the −Y side of the second substrate 40 in a plan view so as to be connected to the transmission line 70. Note that the electrical signal transmitted to the signal processing circuit via the transmission line 70 and the wiring 36 corresponds to an amplified signal amplified by an amplifier 60, which will be described separately.

[0022] <Second Substrate 40> Next, an example of the configuration of the second substrate 40 will be described. The second substrate 40 is disposed on the upper surface (first main surface 31 in this example) of the first substrate 30. Here, high-frequency AC electrical signals output from the light-receiving element 50 and the amplifier 60 are transmitted through various wirings disposed on the second substrate 40. Therefore, from the viewpoint of reducing transmission loss and degradation of the electrical signals, the second substrate 40 is preferably a quartz substrate with a low relative dielectric constant. However, the second substrate 40 is not limited to a quartz substrate. The second substrate 40 may be another substrate, such as a ceramic substrate.

[0023] 2 and 3, the second substrate 40 has a first main surface 41, a second main surface 42, and a side surface 43. The first main surface 41 is disposed on the +Z side of the second substrate 40. The first main surface 41 supports the light-receiving element 50 and the amplifier 60. The second main surface 42 is the surface opposite to the first main surface 41. In other words, the second main surface 42 is disposed on the −Z side of the second substrate 40. The side surface 43 connects the first main surface 41 and the second main surface 42.

[0024] 2 has a substantially rectangular outer shape in a plan view, however, the outer shape of the second substrate 40 is not limited to a substantially rectangular shape.

[0025] 2, the second substrate 40 has four side surfaces 43. Of the four side surfaces 43, the side surface located on the +Y side corresponds to a first side surface 431. Of the four side surfaces 43, the side surface located on the −Y side corresponds to a second side surface 432. Of the four side surfaces 43, the side surface located on the +X side corresponds to a third side surface 433. Of the four side surfaces 43, the side surface located on the −X side corresponds to a fourth side surface 434.

[0026] The first side surface 431 and the second side surface 432 face each other. Furthermore, the first side surface 431 and the second side surface 432 each extend parallel to the X-axis direction. The third side surface 433 and the fourth side surface 434 face each other. Furthermore, the third side surface 433 and the fourth side surface 434 each extend parallel to the Y-axis direction. However, the number of side surfaces 43 of the second substrate 40 is not limited to four.

[0027] The second substrate 40 further has wiring 44 and 45. When the amplifier 60 includes a plurality of amplifier circuits, the wiring 44, together with the wiring 34 of the first substrate 30, functions as a power supply path that supplies voltage from the power supply circuit to some of the plurality of amplifier circuits. The wiring 45, together with the wiring 35 of the first substrate 30, functions as a power supply path that supplies voltage from the power supply circuit to other of the plurality of amplifier circuits.

[0028] The second substrate 40 may have a plurality of wirings 44 and 45. The wirings 44 are conductor patterns disposed in a region on the +X side of the first main surface 41 of the second substrate 40 and on the third side surface 433 of the second substrate 40. One end of the wiring 44 is connected to a power supply pad of the amplifier 60. The other end of the wiring 44 is connected to the wiring 34 of the first substrate 30. As a result, for example, voltage from a power supply circuit provided on the first substrate 30 is supplied to the amplifier 60 through the wirings 34 and 44. That is, the power supply circuit and the amplifier 60 can be connected through the wirings 34 and 44, which are conductor patterns, without using thin conductor wires such as bonding wires. This improves the reliability of the optical receiving module 3. Furthermore, by overlapping the region of the wiring 44 disposed on the third side surface 433 of the second substrate 40 with the wiring 34 of the first substrate 30, the second substrate 40 can be easily positioned at a desired position on the first substrate 30. That is, alignment of the second substrate 40 can be easily performed.

[0029] In the wiring 44, the region arranged on the third side surface 433 is preferably formed along the inner wall of the castellation recessed into the second substrate 40. This makes it possible to avoid the use of bonding wires, which can be a major cause of degradation of electrical signals, and as a result, degradation of electrical signals can be suppressed.

[0030] The wiring 45 is a conductor pattern disposed in a region on the −X side of the first main surface 41 of the second substrate 40 and on the fourth side surface 434 of the second substrate 40. One end of the wiring 45 is connected to a power supply pad of the amplifier 60. The other end of the wiring 45 is connected to the wiring 35 of the first substrate 30. As a result, for example, voltage from a power supply circuit provided on the first substrate 30 is supplied to the amplifier 60 via the wiring 35 and the wiring 45. That is, the power supply circuit and the amplifier 60 can be connected via the wiring 35 and the wiring 45, which are conductor patterns, without using thin conductor wires such as bonding wires. This further improves the reliability of the optical receiving module 3. Furthermore, by overlapping the region of the wiring 45 disposed on the fourth side surface 434 of the second substrate 40 with the wiring 35 of the first substrate 30, the second substrate 40 can be easily positioned at a desired position on the first substrate 30. That is, alignment of the second substrate 40 can be further facilitated.

[0031] In the wiring 45, the region arranged on the fourth side surface 434 is preferably formed along the inner wall of the castellation recessed into the second substrate 40. This makes it possible to avoid the use of bonding wires, which can be a major cause of degradation of electrical signals, and as a result, degradation of electrical signals can be suppressed.

[0032] The second substrate 40 further has wiring 46 and 47. Each of the wiring 46 and 47 is a conductor pattern disposed (wired) on the first main surface 41 between the light receiving element 50 and the amplifier 60. The wiring 46 functions as a transmission path for transmitting an electrical signal output from the light receiving element 50 to the amplifier 60. The wiring 47 functions as a power supply path for a bias voltage supplied to the light receiving element 50. The wiring 47 may be connected to the amplifier 60. That is, the bias voltage supplied to the light receiving element 50 may be supplied from the amplifier 60 via the wiring 47.

[0033] The second substrate 40 further includes a transmission line 70. The transmission line 70 transmits the amplified signal output from the amplifier 60 to the first substrate 30. As shown in FIG. 2, the transmission line 70 is disposed in an area on the −Y side of the second substrate 40 in a plan view. In the example shown in FIGS. 2 and 3, one end of the transmission line 70 is connected to the output terminal 65 of the amplifier 60. The other end of the transmission line 70 is connected to the wiring 36 of the first substrate 30. The transmission line 70 transmits the amplified signal output from the amplifier 60 to the wiring 36 of the first substrate 30. Details of an example configuration of the transmission line 70 will be described separately with reference to FIGS. 6 and 7.

[0034] The second substrate 40 preferably further includes a ground electrode 40G connected to ground. The ground electrode 40G is disposed, for example, on the second main surface 42 of the second substrate 40. The ground electrode 40G is preferably disposed in a region that overlaps at least the amplifier 60 and the transmission line 70 in a plan view. Alternatively, the ground electrode 40G may be disposed over substantially the entire area of ​​the second main surface 42.

[0035] The second substrate 40 preferably further includes a plurality of through holes 48 that penetrate the second substrate 40 in the Z-axis direction. A conductive film made of, for example, a metal material is formed on the inner wall of each of the plurality of through holes 48. The conductive film formed on the inner wall of the through hole 48 is connected to the ground electrode 40G of the second substrate 40. The plurality of through holes 48 are arranged, for example, in a region that overlaps with the transmission line 70 in a plan view.

[0036] The second substrate 40 may also include other through holes. The other through holes are arranged, for example, in a region that overlaps with the amplifier 60 in a plan view. It is preferable that the conductive films formed on the inner walls of the through holes that overlap with the amplifier 60 in a plan view are connected to the amplifier 60 and the ground electrode 40G, respectively. Note that the through holes that overlap with the amplifier 60 in a plan view are omitted in FIG. 2 .

[0037] <Light-receiving element 50> Next, an example of the configuration of the light-receiving element 50 will be described. The light-receiving element 50 receives the optical signal OS2 transmitted from the outside through the optical transmission medium 12. Furthermore, the light-receiving element 50 outputs an electrical signal in response to receiving the optical signal OS2. In other words, the light-receiving element 50 converts the optical signal OS2 into an electrical signal. An example of the light-receiving element 50 is a photodiode. However, the light-receiving element 50 is not limited to a photodiode as long as it converts the optical signal OS2 into an electrical signal.

[0038] The light-receiving element 50 is disposed on the second substrate 40. The light-receiving element 50 may be bonded to the first main surface 41 of the second substrate 40 via a conductive bonding member such as a gold-tin alloy (AuSn). Preferably, there are multiple light-receiving elements 50. By providing multiple light-receiving elements 50, it is possible to receive an optical signal OS2 containing multiple types of light with different wavelengths. This makes it possible to receive a wideband optical signal OS2 via the multiple light-receiving elements 50. In the example shown in FIG. 2, four light-receiving elements 50 are disposed on the first main surface 41 of the second substrate 40. The four light-receiving elements 50 respectively receive the four types of light contained in the optical signal OS2. However, the number of light-receiving elements 50 is not limited to four. The number of light-receiving elements 50 may be one or more.

[0039] Even when multiple light receiving elements 50 are provided, the optical signal OS2 may be transmitted through a single optical fiber as the optical transmission medium 12. In this case, the multiple types of light contained in the optical signal OS2 are transmitted in a multiplexed state. The multiplexed multiple types of light are separated by a spectrometer. The spectrometer is disposed in the transmission path of the optical signal OS2 before reaching the light receiving element 50. Furthermore, the multiple types of light separated by the spectrometer reach each of the multiple light receiving elements 50. However, the multiple types of light contained in the optical signal OS2 may be transmitted through each of multiple optical fibers as the optical transmission medium 12 so as to reach each of the multiple light receiving elements 50. In this case, a spectrometer does not need to be disposed in the transmission path of the optical signal OS2.

[0040] As shown in FIG. 2 , in a plan view, the light receiving elements 50 are located on one side of the center line C40 on the second substrate 40. Specifically, in a plan view, the four light receiving elements 50 are located on the first side surface 431 side of the second substrate 40 with respect to the center line C40. Here, the center line C40 is a virtual line segment passing through the center of the second substrate 40. In the example shown in FIG. 2 , the center line C40 passes through the center of the second substrate 40 and extends parallel to the X-axis direction. Furthermore, the four light receiving elements 50 are arranged parallel to the center line C40. The center of the second substrate 40 through which the center line C40 passes corresponds to the center of the second substrate 40 in the in-plane direction. In the example shown in FIG. 2 , the in-plane direction of the second substrate 40 is a plane parallel to the XY plane.

[0041] Next, a configuration example of each light receiving element 50 will be described in more detail with reference to Fig. 4. As shown in Fig. 4, the light receiving element 50 includes a light receiving portion 51, a first electrode 52, a second electrode 53, and a support substrate 54.

[0042] The light receiving unit 51 converts the optical signal OS2 into an electrical signal. As shown in Fig. 4, the light receiving unit 51 includes a p-type semiconductor layer 51a, an i-type semiconductor layer 51b, and an n-type semiconductor layer 51c. The p-type semiconductor layer 51a, the i-type semiconductor layer 51b, and the n-type semiconductor layer 51c are stacked in the Z-axis direction. However, the light receiving unit 51 may be configured with only the p-type semiconductor layer 51a and the n-type semiconductor layer 51c without including the i-type semiconductor layer 51b.

[0043] An example of the p-type semiconductor layer 51a is p-type indium gallium arsenide (InGaAs). An example of the i-type semiconductor layer 51b is undoped InGaAs. An example of the n-type semiconductor layer 51c is n-type indium phosphide (InP). However, the materials constituting the p-type semiconductor layer 51a, the i-type semiconductor layer 51b, and the n-type semiconductor layer 51c are not limited to these.

[0044] The first electrode 52 is connected to the p-type semiconductor layer 51a. The first electrode 52 corresponds to the anode terminal. The first electrode 52 is connected to the wiring 46 of the second substrate 40. The first electrode 52 outputs the electrical signal converted by the light receiving unit 51 to the input terminal 64 of the amplifier 60 via the wiring 46 (see FIG. 3). The first electrode 52 is an example of the "output terminal" of the light receiving element 50. The second electrode 53 is connected to the n-type semiconductor layer 51c. The second electrode 53 corresponds to the cathode terminal. The second electrode 53 is connected to the wiring 47 of the second substrate 40.

[0045] The support substrate 54 is a substrate that supports the light receiving unit 51. As shown in Fig. 4, the support substrate 54 is disposed on the +Z side of the light receiving element 50. In contrast, the light receiving unit 51 faces the support substrate 54 and is disposed on the -Z side of the support substrate 54.

[0046] The optical signal OS2 enters the support substrate 54, passes through the support substrate 54, and then reaches the light-receiving unit 51. That is, the light-receiving element 50 has a so-called back-illuminated configuration in which the optical signal OS2 enters from a component located on the opposite side of the light-receiving unit 51 (the support substrate 54 in the example shown in FIG. 4 ). The back-illuminated configuration of the light-receiving element 50 allows the light-receiving unit 51 and the first electrode 52 to face the first main surface 41 of the second substrate 40. Therefore, the first electrode 52 and the input terminal 64 of the amplifier 60 can be connected via the wiring 46 of the second substrate 40 (see FIG. 3 ). Incidentally, the electrical signal output from the first electrode 52 of the light-receiving element 50 to the input terminal 64 of the amplifier 60 is a high-frequency AC signal. Therefore, if the first electrode 52 of the light-receiving element 50 and the input terminal 64 of the amplifier 60 are connected by a thin conductor such as a bonding wire, the electrical signal may be significantly degraded during transmission. On the other hand, by connecting the first electrode 52 of the light receiving element 50 and the input terminal 64 of the amplifier 60 via the wiring 46 of the second substrate 40, degradation of the electrical signal output from the first electrode 52 can be reduced.

[0047] In optical communications, near-infrared rays are generally used as the optical signal OS2. The support substrate 54 is not limited to any material as long as it has the property of transmitting the light contained in the optical signal OS2. Examples of the support substrate 54 include a semiconductor substrate such as InP and a glass substrate. However, the optical signal OS2 is not limited to near-infrared rays.

[0048] It is preferable to arrange an optical thin film such as an anti-reflection film 541 on the +Z side surface of the support substrate 54. This can reduce the optical reflectance of the optical signal OS2 on the +Z side surface of the support substrate 54. As a result, it is possible to prevent a situation in which the amount of light of the optical signal OS2 reaching the light receiving unit 51 is reduced.

[0049] 4, the +Z side surface of the support substrate 54 includes a curved region 542 that protrudes toward the +Z side. That is, the support substrate 54 functions as a convex lens that focuses the optical signal OS2 onto the light receiving unit 51. That is, the support substrate 54 is used as a focusing lens for a back-illuminated photodiode. With such a simple configuration, the optical signal OS2 can be focused onto the light receiving unit 51, thereby reducing costs. Furthermore, the light receiving unit 51 can be made smaller, and the amount of light of the optical signal OS2 received by the light receiving unit 51 can be increased.

[0050] The light receiving element 50 may further include an insulating layer 58 to prevent, for example, a short circuit between the first electrode 52 and the second electrode 53, a short circuit between the first electrode 52 and the support substrate 54, a short circuit between the second electrode 53 and the support substrate 54, etc.

[0051] <Amplifier 60> Next, an example of the configuration of the amplifier 60 will be described. The amplifier 60 amplifies the electrical signal input from the light receiving element 50. The amplifier 60 shown in FIGS. 2 and 3 is a trans-impedance amplifier (TIA). However, the type of amplifier 60 is not limited to a TIA. Other examples of the amplifier 60 include a preamplifier, a limiting amplifier, and an auto-gain controller. The amplifier 60 may also include other components such as an equalizer. By including an equalizer in the amplifier 60, the electrical signal input from the light receiving element 50 can be amplified more efficiently.

[0052] The amplifier 60 is disposed on the second substrate 40. The amplifier 60 may be flip-chip mounted on the first main surface 41 of the second substrate 40 via a bonding member such as a copper (Cu) pillar and a tin-silver alloy (AgSn).

[0053] As shown in FIGS. 2 and 3 , the amplifier 60 is disposed on the first main surface 41 of the second substrate 40, facing the light-receiving element 50. Also, as shown in FIG. 2 , the amplifier 60 is disposed on the center line C40 of the second substrate 40, or between the center line C40 and the light-receiving element 50. This allows the distance between the amplifier 60 and the light-receiving element 50 to be shortened. That is, the wiring 46 connecting the input terminal 64 of the amplifier 60 and the first electrode 52 of the light-receiving element 50 can be shortened. The electrical signal output from the first electrode 52 of the light-receiving element 50 is a weak signal having a high frequency. By shortening the distance between the amplifier 60 and the light-receiving element 50, degradation of the electrical signal output from the first electrode 52 of the light-receiving element 50 can be reduced and transmission to the amplifier 60 can be ensured.

[0054] An example of the circuit configuration of the amplifier 60 will be described with reference to FIG. 5 . FIG. 5 is a diagram schematically illustrating an equivalent circuit relating to an example of the circuit configuration of the amplifier 60. When a plurality of light-receiving elements 50 are provided on the second substrate 40, the amplifier 60 preferably includes a plurality of amplifier circuits 60a connected to the plurality of light-receiving elements 50, respectively. Each amplifier circuit 60a includes an operational amplifier 67 that amplifies an electrical signal input from the first electrode 52 of the light-receiving element 50 via an input terminal 64. In the example shown in FIG. 5 , three operational amplifiers 67 are connected in series. However, the number of operational amplifiers 67 is not limited to this. The amplified signal amplified by the operational amplifier 67 is output via an output terminal 65. Each of the plurality of amplifier circuits 60a is connected to a different transmission line 70 (71a, 71b) via, for example, two output terminals 65. The amplified signal output from each of the plurality of amplifier circuits 60a is output to a signal processing circuit via the respective transmission line 70 and the wiring 36 of the first substrate 30. 5 shows an example of an equivalent circuit for one amplifier circuit 60a, but the equivalent circuits for the other amplifier circuits 60a may be similar. In the example shown in FIG. 5, the bias voltage to the light receiving element 50 is supplied from the amplifier circuit 60a.

[0055] The output terminals 65 of the amplifier 60 (each amplifier circuit 60a) preferably correspond to two output terminals that respectively output a first signal and a second signal corresponding to an inverted signal of the first signal as amplified signals. Since the amplified signals output from the amplifier 60 are AC electrical signals having a high frequency, outputting the first signal and the second signal separately can reduce degradation of the amplified signals due to noise, etc. When the amplifier 60 includes a plurality of amplifier circuits 60a, each amplifier circuit 60a preferably has two output terminals 65 that respectively output the first signal and the second signal.

[0056] <Transmission Line 70> Next, an example of the configuration of the transmission line 70 will be described in detail with reference to Figures 6 and 7. Figure 6 is a schematic enlarged plan view of the optical receiving module 3, enlarging the area within the frame V indicated by the dashed line in Figure 2. Figure 7 is a schematic side view of the area within the frame V indicated by the dashed line in Figure 2, viewed from the -Y side. For ease of explanation, only the side surface 43 (second side surface 432) of the second substrate 40 and the transmission line 70 are shown in Figure 7.

[0057] 6 and 7, the transmission line 70 includes a pair of signal lines 71a and 71b and a pair of ground lines 72a and 72b. That is, the transmission line 70 has a GSSG differential line configuration.

[0058] The signal line 71a and the signal line 71b are, for example, conductor patterns arranged adjacent to each other in the X-axis direction. The signal line 71a transmits one of the first signal and the second signal output from the amplifier 60. The signal line 71b transmits the other of the first signal and the second signal output from the amplifier 60. For convenience, the following description will be given assuming that the signal line 71a transmits the first signal and the signal line 71b transmits the second signal. However, the signal line 71a may transmit the second signal and the signal line 71b may transmit the first signal.

[0059] Each of the pair of ground lines 72a, 72b is a conductor pattern connected to the ground electrode 40G via a conductor film formed on the inner wall of the through hole 48 in the second substrate 40. Some of the multiple through holes 48 are arranged at a predetermined interval in a region overlapping the ground line 72a in a plan view. Other of the multiple through holes 48 are arranged at a predetermined interval in a region overlapping the ground line 72b in a plan view.

[0060] A pair of ground lines 72a and 72b are arranged with the signal lines 71a and 71b in between. In the example shown in Fig. 2, the ground line 72a is arranged on the -X side of the signal line 71a. The ground line 72b is arranged on the +X side of the signal line 71b.

[0061] By providing the transmission line 70 with a GSSG differential line configuration, it is possible to further reduce the degradation of the amplified signal transmitted through the transmission line 70 due to noise and the like.

[0062] 2 , each of the signal lines 71a, 71b and the ground lines 72a, 72b includes a region on the first main surface 41 of the second substrate 40 that extends parallel to the Y-axis direction and a region on the side surface 43 (second side surface 432) of the second substrate 40 that extends parallel to the Z-axis direction. For each of the signal lines 71a, 71b and the ground lines 72a, 72b, the region on the side surface 43 (second side surface 432) is preferably disposed on the inner wall of a castellation recessed inward of the second substrate 40. Connecting each of the signal lines 71a, 71b and the ground lines 72a, 72b to the wiring 36 via the castellation on the side surface 43 reduces the inductance component and reduces degradation of the electrical signal. Furthermore, alignment of the first substrate 30 and the second substrate 40 can be easily performed.

[0063] One end of each of the signal lines 71a, 71b and the ground lines 72a, 72b is connected to a different output terminal 65 of the amplifier 60. The other end of each of the signal lines 71a, 71b and the ground lines 72a, 72b is connected to a plurality of wirings 36 of the first substrate 30, respectively. That is, the pair of signal lines 71a, 71b can be connected to the wirings 36 of the first substrate 30 without using thin conductor wires such as bonding wires. Similarly, the pair of ground lines 72a, 72b can be connected to the wirings 36 of the first substrate 30 without using thin conductor wires such as bonding wires. This further improves the reliability of the optical receiving module 3. Furthermore, because the transmission path of the amplified signal output from the amplifier 60 does not include thin conductor wires such as bonding wires, degradation of the transmitted amplified signal can be further reduced. Furthermore, by overlapping the areas on the second side surface 432 of the second substrate 40 with the wiring 36 of the first substrate 30 in each of the signal lines 71 a, 71 b and the ground lines 72 a, 72 b, the second substrate 40 can be easily disposed in a desired position on the first substrate 30. In other words, the alignment of the second substrate 40 can be performed even more easily.

[0064] When the amplifier 60 includes multiple amplifier circuits 60a, the second substrate 40 includes multiple transmission lines 70, each connected to a different amplifier circuit 60a. In this case, the ground lines 72a and 72b may be shared between adjacent transmission lines 70 in the X-axis direction. In the example shown in FIGS. 6 and 7 , between two adjacent transmission lines 70, the ground line 72b of the transmission line 70 located on the −X side and the ground line 72a of the transmission line 70 located on the +X side are shared. This allows the total number of ground lines 72a and 72b to be reduced while maintaining the differential line configuration for the multiple transmission lines 70. As a result, the optical receiving module 3 can be made smaller and less expensive.

[0065] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as set forth in the claims.

[0066] Note that aspects of the present invention are, for example, as follows: <1> An optical receiving module comprising: a first substrate; a second substrate arranged on the first substrate; a light-receiving element arranged on the second substrate, which converts an optical signal into an electrical signal; and an amplifier arranged on the second substrate, which amplifies the electrical signal input from the light-receiving element, wherein the second substrate comprises a transmission line which transmits the amplified signal output from the amplifier to the first substrate side, and wherein, in a plan view, when an imaginary line segment passing through the center of the second substrate is taken as a center line, the light-receiving element is located on one side of the center line on the second substrate, and the amplifier is located on the center line or between the center line and the light-receiving element. <2> The optical receiving module according to <1>, wherein the second substrate includes a first main surface supporting the light receiving element and the amplifier, a second main surface opposite the first main surface and facing the first substrate, and one or more side surfaces connecting the first main surface and the second main surface, and the transmission line is a conductor pattern arranged on the first main surface and the side surface of the second substrate, respectively. <3> The optical receiving module according to <2>, wherein the transmission line has a differential line configuration including a pair of signal lines transmitting the amplified signal and a pair of ground lines arranged on either side of the pair of signal lines and connected to ground, respectively, and the pair of signal lines and the pair of ground lines are arranged on the first main surface and the side surface of the second substrate, respectively. <4> The optical receiving module according to <2> or <3>, wherein the light receiving element is a back-illuminated photodiode, and an output terminal of the light receiving element is connected to an input terminal of the amplifier via a conductor pattern wired on the first main surface of the second substrate. <5> The optical receiving module according to any one of <1> to <4>, wherein a plurality of the light receiving elements are arranged on one side of the center line on the second substrate, and the plurality of the light receiving elements are arranged parallel to the center line.<6> An optical transmitting and receiving module comprising an optical transmitting module for transmitting an optical signal and an optical receiving module for receiving the optical signal, wherein the optical receiving module comprises: a first substrate; a second substrate arranged on the first substrate; a photodetector arranged on the second substrate for converting an optical signal into an electrical signal; and an amplifier arranged on the second substrate for amplifying the electrical signal input from the photodetector, wherein the second substrate comprises a transmission line for transmitting the amplified signal output from the amplifier to the first substrate side, and wherein, in a plan view, when an imaginary line segment passing through the center of the second substrate is taken as a center line, the photodetector is located on one side of the center line on the second substrate, and the amplifier is located on the center line or between the center line and the photodetector.

[0067] This application claims priority based on Japanese Patent Application No. 2024-042805, filed on March 18, 2024, the entire contents of which are incorporated herein by reference.

[0068] REFERENCE SIGNS LIST 1 Optical transmitting and receiving module 2 Optical transmitting module 3 Optical receiving module 11, 12 Optical transmission medium 30 First substrate 31 First main surface 32 Second main surface 33 Side surface 34, 35, 36 Wiring 40 Second substrate 41 First main surface 42 Second main surface 43 Side surface 44, 45, 46, 47 Wiring C40 Center line 50 Light receiving element 51 Light receiving section 52 First electrode 53 Second electrode 54 Support substrate 60 Amplifier 64 Input terminal 65 Output terminal 70 Transmission line 71a, 71b Signal line 72a, 72b Ground line

Claims

1. An optical receiving module comprising: a first substrate; a second substrate arranged on said first substrate; a photodetector arranged on said second substrate for converting an optical signal into an electrical signal; and an amplifier arranged on said second substrate for amplifying the electrical signal input from said photodetector; wherein said second substrate comprises a transmission line for transmitting the amplified signal output from said amplifier to said first substrate; and wherein, in a plan view, when an imaginary line segment passing through the center of said second substrate is taken as the center line, said photodetector is located on one side of said center line on said second substrate, and said amplifier is located on said center line or between said center line and said photodetector.

2. The optical receiving module according to claim 1, wherein the second substrate includes a first main surface that supports the light receiving element and the amplifier, a second main surface that is opposite to the first main surface and faces the first substrate, and one or more side surfaces that connect the first main surface and the second main surface, and the transmission line is a conductor pattern that is respectively arranged on the first main surface and the side surfaces of the second substrate.

3. The optical receiving module according to claim 2, wherein the transmission line has a differential line configuration including a pair of signal lines that transmit the amplified signal and a pair of ground lines that are arranged on either side of the pair of signal lines and are each connected to ground, and the pair of signal lines and the pair of ground lines are each arranged on the first main surface and the side surface of the second substrate.

4. The optical receiving module according to claim 2, wherein the light receiving element is a back-illuminated photodiode, and the output terminal of the light receiving element is connected to the input terminal of the amplifier via a conductor pattern wired on the first main surface of the second substrate.

5. An optical receiving module according to claim 1 or claim 2, wherein a plurality of the light receiving elements are arranged on one side of the center line on the second substrate, and the plurality of light receiving elements are arranged parallel to the center line.

6. An optical transmitting and receiving module comprising an optical transmitting module for transmitting optical signals and an optical receiving module for receiving optical signals, wherein the optical receiving module comprises: a first substrate; a second substrate arranged on the first substrate; a photodetector arranged on the second substrate for converting optical signals into electrical signals; and an amplifier arranged on the second substrate for amplifying the electrical signals input from the photodetector, wherein the second substrate comprises a transmission line for transmitting the amplified signal output from the amplifier to the first substrate side, and wherein, in a plan view, when an imaginary line segment passing through the center of the second substrate is taken as the center line, the photodetector is located on one side of the center line on the second substrate, and the amplifier is located on the center line or between the center line and the photodetector.

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