Package for optical receiving module and optical receiving module

Abstract

The package for an optical receiving module has a conductive housing and a feedthrough portion. The first side wall of the housing has an inlet for introducing an optical signal in the optical axis direction. The second side wall of the housing is separated from the first side wall in the optical axis direction. The internal space of the housing is partitioned between the first side wall and the second side wall, and houses a light receiving element that converts an optical signal into a high-frequency signal. The feedthrough portion has a first surface, a second surface, and a third surface that respectively extend from the second side wall to the opposite side of the first side wall. The third surface is located between the first surface and the second surface. The feedthrough portion is formed of a dielectric material. The feedthrough portion has a ground wiring and a plurality of first conductive pads. The ground wiring is provided on at least one of the first surface and the second surface. The plurality of first conductive pads are provided on the third surface and are arranged side by side in the lateral direction at a certain interval. The plurality of first conductive pads are electrically connected to the ground wiring.

Description

[0001] This application claims priority based on Japanese Application No. 2020-019073 filed on February 6, 2020, and incorporates by reference the entire disclosure described in the above Japanese application. Technical Field

[0002] The present invention relates to a package for an optical receiving module and an optical receiving module. Background Art

[0003] A package for housing electronic components is disclosed in U.S. Patent Publication No. 2005 / 0207092. The package has a base body, a frame, and input / output terminals. A mounting portion for mounting the electronic components is provided on the bottom surface of the base body. The frame is disposed on the bottom surface of the base body and surrounds the mounting portion. A lid is mounted on the upper surface of the frame. The input / output terminals have circuit conductors for electrically connecting the inside and outside of the frame. The circuit conductors are strip lines or microstrip lines. The base body, the frame, and the lid are made of a metal material. The input / output terminals are made of an insulating material.

[0004] A package for housing an optical semiconductor element is disclosed in U.S. Patent No. 6036375. The package has a base body, a frame, and a lid for housing the optical semiconductor element. A mounting portion for mounting the optical semiconductor element is provided on the bottom surface of the base body. The optical semiconductor element is electrically connected to an electrical circuit located outside the bottom surface of the base body via external lead terminals. The frame is mounted on the base body and surrounds the mounting portion. A through hole for fixing an optical fiber is formed in the frame. The lid is mounted on the upper surface of the frame. The base body, the frame, and the lid are made of a metal material. Summary of the Invention

[0005] The present invention provides a package for an optical receiving module. The package for the optical receiving module has a conductive housing and a feedthrough portion. The conductive housing has a first side wall, a second side wall, and an internal space. A light inlet for introducing an optical signal in the optical axis direction is provided on the first side wall. The second side wall is separated from the first side wall in the optical axis direction. The internal space is partitioned between the first side wall and the second side wall. The internal space houses a light receiving element that converts an optical signal into a high-frequency signal. The feedthrough portion has a first surface, a second surface, and a third surface that respectively extend from the second side wall to the opposite side of the first side wall. The feedthrough portion is formed of a dielectric material. A plurality of first electrical wirings are provided facing the internal space and include at least one of a monitor wiring and a power supply wiring. A second electrical wiring is provided facing the internal space and transmits a high-frequency signal. A plurality of third electrical wirings are provided on the first surface, are electrically connected to the plurality of first electrical wirings, and are arranged in a lateral direction intersecting the optical axis direction. A fourth electrical wiring is provided on the second surface, is electrically connected to the second electrical wiring, and transmits the high-frequency signal transmitted by the second electrical wiring. A ground wiring is provided on at least one of the first surface and the second surface. A plurality of first conductive pads are provided on the third surface located between the first surface and the second surface, are arranged in the lateral direction at a certain interval from each other, and are electrically connected to the ground wiring. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a top view schematically showing the structure of an optical transceiver used in optical communication.

[0007] Figure 2 is a top view schematically showing the structure of an optical receiving module.

[0008] Figure 3 is a perspective view showing the appearance of the package.

[0009] Figure 4 is to Figure 3 a part of which is enlarged and shown as a perspective view. Figure 4 Only the part of the feedthrough portion protruding from the end wall is enlarged and shown.

[0010] Figure 5 is along Figure 4 sectional view taken along line V-V of

[0011] Figure 6 is a top view of the third surface viewed from the thickness direction of the feedthrough portion.

[0012] Figure 7 is a top view of the fourth surface viewed from the thickness direction of the feedthrough portion.

[0013] Figure 8 is an enlarged perspective sectional view showing a part of the appearance of the package. Figure 8Shows the case of observing the part protruding from the end wall among the feedthrough parts from the second surface side.

[0014] Figure 9 Is an oblique view showing a left-handed metamaterial composed of multiple mushroom-shaped structures (conductive pads). The multiple mushroom-shaped structures are arranged two-dimensionally within a specified area on a dielectric substrate.

[0015] Figure 10A Is a circuit diagram showing the metamaterial realized by multiple conductive pads in the form of a distributed constant circuit. Figure 10A Shows an equivalent circuit of a normal transmission line along the traveling direction of electromagnetic waves.

[0016] Figure 10B Is a circuit diagram showing the metamaterial realized by multiple conductive pads in the form of a distributed constant circuit. Figure 10B Shows an equivalent circuit of a transmission line in the case where a metamaterial structure is arranged in the middle.

[0017] Figure 11 Shows, as a comparative example, the end face in the case where no electromagnetic shielding film and multiple conductive pads are provided.

[0018] Figure 12 Is to represent Figure 11 An oblique view of a model of a waveguide of the part shown by the dashed line.

[0019] Figure 13 Is to represent Figure 12 A graph showing the relationship between the insertion loss of the waveguide shown and the frequency of electromagnetic waves.

[0020] Figure 14 Shows, as another comparative example, the case where only an electromagnetic shielding film is provided on the end face shown in Figure 11

[0021] Figure 15 Is to represent Figure 14 An oblique view of a model of a waveguide of the part shown by the dashed line.

[0022] Figure 16 Is to represent Figure 15 A graph showing the relationship between the insertion loss of the waveguide shown and the frequency of electromagnetic waves.

[0023] Figure 17 Is to represent Figure 14 An oblique view of a waveguide structure in the form where multiple conductive pads and wiring parts are further added to the structure shown.

[0024] Figure 18 Is to represent Figure 17 A graph showing the relationship between the insertion loss of the waveguide shown and the frequency of electromagnetic waves. ​

[0025] Figure 19 It is a perspective view showing the feedthrough part as the first modification example.

[0026] Figure 20 It is a top view showing the third surface of the feedthrough part of the first modification example.

[0027] Figure 21 It is a top view showing the fourth surface of the feedthrough part of the first modification example.

[0028] Figure 22 It is a perspective view showing the feedthrough part as the second modification example.

[0029] Figure 23 It is a cross-sectional view along Figure 22 the line XXIII - XXIII. Detailed Description of the Invention

[0030] [Problems to be Solved by the Present Invention]

[0031] In recent years, with the increase in the transmission speed in optical communication, the miniaturization of optical transceivers has been continuously developed. In an optical transceiver, for example, an optical transmission module, an optical reception module, and a circuit board electrically connected to these modules are housed in one housing. The optical transmission module, for example, incorporates a light-emitting element such as a laser diode. The optical reception module, for example, incorporates a light-receiving element such as a photodiode. The optical transmission module and the optical reception module each have a package for the optical transmission module and a package for the optical reception module. The optical transmission module outputs an optical signal. An optical signal is input to the optical reception module. When the direction of inputting and outputting the optical signal in each package is set as the optical axis direction, these packages are in front of the circuit board and are arranged adjacent to each other in a direction crossing the optical axis. The package for the optical reception module has a conductive housing and a dielectric feedthrough part. The housing has an internal space, and the light-receiving element is housed in the internal space. The feedthrough part is provided so as to extend from the inside (internal space) of the housing to the outside. A plurality of wirings for conducting the inside and the outside of the housing are provided in the feedthrough part. A circuit for driving the light-emitting element of the optical transmission module is arranged outside the optical transmission module, for example, on the above-mentioned circuit board.

[0032] In an optical transceiver having the structure described above, the higher the transmission speed of optical communication, the higher the frequency of electromagnetic noise generated from the wiring between the drive circuit and the optical transmission module. For example, as the frequency of the electrical signal increases, electromagnetic waves are easily radiated from the signal wiring that transmits the electrical signal. The radiated electromagnetic waves induce noise in other signal wirings through electromagnetic induction, and the SN ratio of the electrical signals transmitted in other signal wirings deteriorates. As described above, this electromagnetic noise causes crosstalk due to electromagnetic wave interference in the received signal within the optical reception module disposed adjacent to the optical transmission module. As described above, in the package for the optical reception module, a dielectric feedthrough portion is provided by penetrating a part of the conductive housing. Through this feedthrough portion, electromagnetic noise easily intrudes into the housing of the optical reception module.

[0033] [Effects obtained by the present invention]

[0034] According to the present invention, it is possible to provide a package for an optical reception module and an optical reception module that can reduce electromagnetic noise intruding into the optical reception module through the feedthrough portion.

[0035] [Description of embodiments of the present invention]

[0036] The package for an optical reception module according to one embodiment has a conductive housing and a feedthrough portion. The conductive housing has a first side wall, a second side wall, and an internal space. An introduction port for introducing an optical signal in the optical axis direction is provided on the first side wall. The second side wall is separated from the first side wall in the optical axis direction. The internal space is partitioned between the first side wall and the second side wall. The internal space houses a light receiving element that converts an optical signal into a high-frequency signal. The feedthrough portion has a first surface, a second surface, and a third surface that respectively extend from the second side wall to the opposite side of the first side wall. The feedthrough portion is made of a dielectric material. A plurality of first electrical wirings are provided facing the internal space and include at least one of a monitor wiring and a power supply wiring. A second electrical wiring is provided facing the internal space and transmits a high-frequency signal. A plurality of third electrical wirings are provided on the first surface, are electrically connected to the plurality of first electrical wirings, and are arranged in a lateral direction intersecting the optical axis direction. A fourth electrical wiring is provided on the second surface, is electrically connected to the second electrical wiring, and transmits the high-frequency signal transmitted by the second electrical wiring. A ground wiring is provided on at least one of the first surface and the second surface. A plurality of first conductive pads are provided on the third surface between the first surface and the second surface, and are arranged in a lateral direction at a certain interval from each other. The plurality of first conductive pads are electrically connected to the ground wiring.

[0037] In the package for the optical receiving module, a plurality of first conductive pads are provided on a third surface between a first surface and a second surface. The plurality of first conductive pads are arranged side by side in a lateral direction with a certain interval therebetween. Moreover, each of the first conductive pads is electrically connected to a ground wiring. In this case, the plurality of first conductive pads can form a left-handed metamaterial. Therefore, in the region around the plurality of first conductive pads, electromagnetic waves of a specific frequency determined by the shape and arrangement of the plurality of first conductive pads (such as the interval between the first conductive pads) are attenuated. That is, the electromagnetic noise is attenuated inside the feedthrough portion, so that the electromagnetic noise invading into the optical receiving module through the feedthrough portion can be reduced.

[0038] In the above-mentioned package for the optical receiving module, the feedthrough portion may also have an end surface intersecting the first surface and the second surface at one end in the optical axis direction. The feedthrough portion may further have an electromagnetic shielding film and a plurality of wiring portions. The electromagnetic shielding film is provided on the end surface separated from the first surface and is electrically connected to the ground wiring. The plurality of wiring portions are provided on the third surface and electrically connect the plurality of first conductive pads to the electromagnetic shielding film. In this case, a part of the electromagnetic noise attempting to invade into the housing through the feedthrough portion can be shielded by the electromagnetic shielding film. On this basis, the electromagnetic noise that cannot be prevented by the electromagnetic shielding film can be attenuated by the above action of the plurality of first conductive pads. Therefore, the electromagnetic noise invading into the optical receiving module through the feedthrough portion can be reduced more effectively. The electromagnetic shielding film and each of the first conductive pads of the plurality of first conductive pads are electrically connected through the plurality of wiring portions, so that the electrical connection between the plurality of first conductive pads and the ground wiring can be easily achieved.

[0039] In the above-mentioned package for the optical receiving module, the feedthrough portion may further have a plurality of second conductive pads. The plurality of second conductive pads are arranged side by side in a lateral direction with a certain interval therebetween on a fourth surface between the second surface and the third surface. The plurality of second conductive pads are electrically connected to the ground wiring. In this case, the plurality of second conductive pads can form a left-handed metamaterial in the same manner as the plurality of first conductive pads. Therefore, in the region around the plurality of second conductive pads, electromagnetic waves of a specific frequency determined by the shape and arrangement of the plurality of second conductive pads (such as the interval between the second conductive pads) are attenuated. Thereby, the invasion of electromagnetic noise into the optical receiving module through the feedthrough portion can be reduced more effectively.

[0040] In the above-mentioned package for the optical receiving module, the feedthrough portion may further have a conductive pattern and a plurality of wiring portions. The conductive pattern is provided on the third surface and extends laterally and is electrically connected to the ground wiring. The plurality of wiring portions are provided on the third surface and electrically connect the plurality of first conductive pads to the conductive pattern. With the structure as described above, the electrical connection between the plurality of first conductive pads and the ground wiring can also be easily achieved.

[0041] [Details of Embodiments of the Present Invention]

[0042] Hereinafter, a specific example of a package for an optical receiving module and an optical receiving module according to an embodiment of the present invention will be described with reference to the drawings. In addition, the present invention is not limited by the following examples, but is shown by the claims, and includes all changes within the scope equivalent to the claims. In the following description, the same or corresponding elements are denoted by the same reference numerals in the description of the drawings, and repeated descriptions are appropriately omitted.

[0043] Figure 1 FIG. 1 is a top view schematically showing the structure of an optical transceiver 1A used in optical communication. The optical transceiver 1A includes an optical receiving module 2, an optical transmitting module 3, a circuit board 4, and a housing 5. The optical receiving module 2 includes a package for an optical receiving module according to an embodiment of the present invention. The housing 5 is a rectangular parallelepiped-shaped hollow container extending in the optical axis direction, i.e., the direction A1. The housing 5 has a rectangular parallelepiped-shaped outer shape with the direction A1 as the length direction, and has an internal space inside. The housing 5 houses the optical receiving module 2, the optical transmitting module 3, and the circuit board 4 in the internal space. At one end of the housing 5 in the direction A1, a receiving port 5a and a transmitting port 5b are provided. An optical connector attached to the front end of the receiving optical fiber is inserted and removed at the receiving port 5a. An optical connector attached to the front end of the transmitting optical fiber is inserted and removed at the transmitting port 5b. The other end of the housing 5 in the direction A1 is open, and the connection terminals 4c of the circuit board 4 are exposed from the opening. The optical transceiver 1A communicates with other optical transceivers by optical signals in a two-core bidirectional manner using the transmitting optical fiber and the receiving optical fiber. Sometimes the receiving port 5a and the transmitting port 5b are collectively referred to as sockets. The optical transceiver 1A is manufactured, for example, to be insertable and removable in a cage (not shown) of a host system. When the optical transceiver 1A is inserted into the cage of the host system, the connection terminals 4c are electrically connected to the connection terminals (not shown) on the host system side, and power is supplied from the host system, enabling communication with the host system by electrical signals.

[0044] The optical receiving module 2 is, for example, a ROSA (Receiver Optical Sub-Assembly) incorporating a light-receiving element such as a photodiode. The optical receiving module 2 converts an optical signal input via a receiving optical fiber into an electrical received signal. The optical transmitting module 3 is, for example, a TOSA (Transceiver Optical Sub-Assembly) incorporating a light-emitting element such as a laser diode. The optical transmitting module 3 converts an electrical transmission signal into an optical signal and outputs the optical signal to a transmitting optical fiber. The optical transmitting module 3 may also incorporate an optical modulator. In this case, the optical transmitting module 3 uses the optical modulator to convert an electrical signal into an optical signal. The ROSA and the TOSA are sometimes collectively referred to as OSA (Optical Sub-Assembly). Inside the housing 5, the optical receiving module 2 and the optical transmitting module 3 are arranged close to each other in a direction A2 that intersects (orthogonal in one example) the direction A1. The direction A2 is, for example, the same as the direction in which the transmitting optical fiber and the receiving optical fiber are arranged. The direction A2 is, for example, a lateral direction that intersects the length direction, i.e., the direction A1. The miniaturization of the optical transceiver 1A is carried out, for example, by reducing the external dimensions of the housing 5 in the direction A1 and the external dimensions of the housing 5 in the direction A2, respectively. By miniaturizing the optical transceiver 1A, the number of optical transceivers that can be mounted on each transmission device increases, and thus the transmission capacity of the transmission device can be increased.

[0045] The circuit board 4 mounts, for example, a drive circuit 4a and a signal processing circuit 4b. The drive circuit 4a drives the optical transmitting module 3. The signal processing circuit 4b supplies a processing signal to the drive circuit 4a and processes the received signal output from the optical receiving module 2. The circuit board 4 is electrically connected to the optical transmitting module 3 via a flexible wiring board 6. The circuit board 4 is electrically connected to the optical receiving module 2 via a flexible wiring board 7. The transmission signal (drive signal) output from the drive circuit 4a is sent to the optical transmitting module 3 through the wiring formed on the circuit board 4 and the flexible wiring board 6. The received signal output from the optical receiving module 2 is sent to the signal processing circuit 4b through the flexible wiring board 7 and the wiring formed on the circuit board 4. The flexible wiring board has, for example, connection terminals at one end, and the connection terminals are connected to the circuit board 4 by solder.

[0046] Figure 2 is a top view schematically showing the structure of the optical receiving module 2. As Figure 2 shown, this optical receiving module 2 has an optical receiving module package 10A, an optical socket portion 21, a splitter (optical demultiplexer) 22, N light-receiving elements 23, and a transimpedance amplifier (TIA) 24. N is an integer greater than or equal to 1, Figure 2An example where N is 4 is illustrated. Hereinafter, the optical receiver module package will be simply referred to as the package. Package 10A is a rectangular parallelepiped-shaped hollow container extending in direction A1. Package 10A has a housing 11 and a feedthrough portion 12. The housing 11 is made of a conductive body such as metal, for example. The housing 11 has a rectangular bottom plate 11a and side walls 11b. When viewed from above in the out-of-plane direction of the plate surface of the bottom plate 11a, the shape of the side walls 11b is a rectangular frame shape surrounding the plate surface of the bottom plate 11a. The side walls 11b include end walls 11ba, 11bb, side walls 11bc, and side walls 11bd. The end walls 11ba and 11bb are separated from each other in direction A1. That is, the end walls 11ba and 11bb are provided separately from each other in direction A1. For example, the wall surfaces of the end walls 11ba and 11bb are orthogonal to direction A1. The side walls 11bc and 11bd face each other in direction A2. For example, the wall surfaces of the side walls 11bc and 11bd are orthogonal to direction A2. The opening of the side wall 11b on the side opposite to the bottom plate 11a is closed by a cover plate 11c (refer to Figure 3 ). The internal space defined by the bottom plate 11a, the side walls 11b, and the cover plate 11c is, for example, hermetically sealed (airtight sealed). The internal space is divided in the optical axis direction between the end walls 11ba and 11bb. The feedthrough portion 12 is provided so as to penetrate the end wall 11bb (the second side wall), realizing electrical conduction between the internal space of the housing 11 and the outside. A part of the feedthrough portion 12 is located outside the housing 11. Conductive bonding is performed between this part of the feedthrough portion 12 and one end of the flexible wiring board 7 shown in Figure 1 . The feedthrough portion 12 has a portion facing the internal space of the housing 11 and a portion exposed outside the housing 11. For example, the portion exposed in the internal space is connected to the TIA 24 through a wire. The received signal output from the TIA 24 is transmitted to the outside of the housing 11 through the wire and the feedthrough portion 12. The portion of the feedthrough portion 12 that penetrates the end wall 11bb is in close contact with the end wall 11bb, and the internal space can be hermetically sealed.

[0047] The optical socket portion 21 is an inlet for introducing an optical signal obtained by wavelength multiplexing along the optical axis direction, i.e., direction A1. The optical socket portion 21 has a cylindrical shape centered on the optical axis along direction A1. The optical socket portion 21 is fixedly connected to the end wall 11ba (the first side wall) of the package 10A at one of its ends. The optical socket portion 21 houses a cylindrical sleeve. The sleeve is fitted with the cylindrical ferrule of an optical connector mounted at the front end of the receiving optical fiber. The optical socket portion 21 also houses a lens. The lens collimates (parallelizes) the optical signal output from the optical fiber. The collimated optical signal, i.e., collimated light, is introduced into the internal space of the package 10A along the optical axis direction through an opening formed in the end wall 11ba. That is, the end wall 11ba has a cylindrical opening, and the optical socket portion 21 is fixedly connected to the end wall 11ba to block the opening without a gap. The optical signal input from the receiving optical fiber is introduced into the internal space through the ferrule and the lens, and is spatially transmitted in the internal space and then incident on the optical splitter 22.

[0048] The optical splitter 22 is an optical component (optical demultiplexer) that demultiplexes an optical signal obtained by wavelength multiplexing into multiple wavelength components. The wavelength component refers to an optical signal of a single wavelength. The optical splitter 22 is housed inside the housing 11 and is optically coupled to the optical socket portion 21. The optical splitter 22 receives the optical signal output from the optical socket portion 21. The optical splitter 22 demultiplexes the optical signal into multiple wavelength components. The optical splitter 22 supplies these wavelength components to the respective corresponding light receiving elements 23. The multiple wavelength components are collimated light and are processed as optical signals having different peak wavelengths from each other. The optical signals having different peak wavelengths from each other are independent single optical signals, each transmitting different information. Therefore, the optical signal obtained by wavelength multiplexing transmits a large amount of information in the number of single optical signals obtained by multiplexing. For example, in Figure 2 the optical splitter 22 separates the optical signal obtained by wavelength multiplexing into 4 single optical signals. The optical signal obtained by wavelength multiplexing transmits 4 times the amount of information transmitted by a single optical signal.

[0049] N light-receiving elements 23 are housed inside the housing 11 and optically coupled to the optical splitter 22. For example, the N light-receiving elements 23 are mounted on the bottom plate 11a and arranged in the direction A2. Each light-receiving element 23 receives the corresponding wavelength component (a single optical signal) from the optical splitter 22 and generates an electrical signal corresponding to the light intensity of the wavelength component. Thus, each light-receiving element 23 converts the optical signal received from the optical splitter 22 into a current signal as a high-frequency signal. Optically coupled means that, for example, the optical splitter 22 and the light-receiving elements 23 are arranged such that the optical signal output from the optical splitter 22 enters the light-receiving element 23 and the conversion from the optical signal to the electrical signal is appropriately performed. Optical components such as an optical lens, an optical filter, and a mirror may be arranged between the optical splitter 22 and the light-receiving elements 23. For example, if the optical splitter 22, the light-receiving elements 23, the mirror, and the lens are arranged such that the optical signal output from the optical splitter 22 is reflected by the mirror and then condensed by a lens (condensing lens) and enters the light-receiving surface of the light-receiving element 23, the optical splitter 22 and the light-receiving elements 23 are optically coupled. In addition, the lens may also be mounted on the light-receiving element 23. Each light-receiving element 23 is electrically connected to the TIA 24. Each light-receiving element 23 supplies the generated current signal (photoelectric current) to the TIA 24. The TIA 24 converts the current signal received from each light-receiving element 23 into a received signal as a voltage signal. Each received signal generated in the TIA 24 is output to the outside of the optical receiving module 2 via the feedthrough portion 12 as described above. These received signals are transmitted, for example, to the signal processing circuit 4b on the circuit board 4 via the Figure 1 flexible wiring board 7 shown. In addition, when the optical signal input from the receiving optical fiber is a single optical signal having one peak wavelength, the optical splitter 22 is not required. When the optical splitter 22 is not mounted on the optical receiving module 2 as described above, the lens and the light-receiving element 23 may be arranged such that the optical signal output from the optical socket portion 21 directly enters the incident surface of the light-receiving element 23.

[0050] Figure 3It is a perspective view showing the appearance of the package 10A. As described above, the package 10A of the present embodiment has a housing 11 and a feedthrough portion 12. The housing 11 is a conductive container and has a bottom plate 11a, side walls 11b, and a cover plate 11c. The side walls 11b include end walls 11ba, 11bb, side walls 11bc, and 11bd. The end walls 11ba and 11bb face each other in the direction A1. For example, the wall surface of the end wall 11bb has a portion parallel to the wall surface of the end wall 11ba. The end walls 11ba and 11bb extend along a plane intersecting the direction A1 (i.e., along the direction A2). The end wall 11ba is located at one end of the housing 11 in the direction A1. The end wall 11bb is located at the other end of the housing 11 in the direction A1. The end wall 11bb is closer to the feedthrough portion 12 than the end wall 11ba, and the end wall 11ba is closer to the optical socket portion 21 than the end wall 11bb. The side walls 11bc and 11bd face each other in the direction A2. The side walls 11bc and 11bd extend along a plane intersecting the direction A2 (i.e., along the direction A1). For example, the wall surface of the side wall 11bd has a portion parallel to the wall surface of the side wall 11bc.

[0051] The feedthrough portion 12 is formed, for example, by including a dielectric material such as plastic or ceramic. The feedthrough portion 12 penetrates the end wall 11bb in the direction A1. The feedthrough portion 12 includes a portion inside the housing 11 and a portion outside the housing 11. As Figure 2As shown, a plurality of DC wirings 13 (first electrical wirings) and N high-frequency signal wirings 14 (second electrical wirings) are provided on the surface of a portion of the feedthrough portion 12 located inside the housing 11. The DC wiring 13 and the high-frequency signal wiring 14 face each other in the internal space of the housing 11. The plurality of DC wirings 13 includes at least one of a monitor wiring and a power supply wiring. The monitor wiring is, for example, a wiring that transmits signals from a temperature sensor or a light intensity monitor provided in the internal space. The power supply wiring is a wiring that supplies power from an external power source to the light receiving element 23, the TIA 24, or both. The power supply wiring may include a ground wiring (earth wiring) having a reference potential. The N high-frequency signal wirings 14 are, for example, coplanar transmission lines or microstrip transmission lines that transmit received signals as high-frequency signals. One end of each high-frequency signal wiring 14 is electrically connected to the TIA 24 via a wire (e.g., a bonding wire). For example, the TIA 24 has a pad for wire bonding, and the pad and one end of the TIA 24 side of the DC wiring 13 are connected by a wire. In the figure, each high-frequency signal wiring 14 including a pair of signal wirings in a differential mode is shown as an example, but each high-frequency signal wiring 14 may also include a single signal wiring. A ground wiring is provided around each high-frequency signal wiring 14. The high-frequency signal is generated based on the photocurrent converted from the optical signal by the light receiving element 23. For example, the TIA 24 amplifies the photocurrent and converts the amplified photocurrent into a voltage signal. The voltage signal output from the TIA 24 is further amplified by a limiting amplifier (LIA). After the amplified voltage signal is waveform-shaped by a clock and data recovery (CDR) circuit, its logical value is identified and becomes a digital signal.

[0052] A portion of the feedthrough portion 12 located outside the housing 11 protrudes from the end wall 11bb in the direction A1. This portion of the feedthrough portion 12 has a first surface 12a and a second surface 12b. The first surface 12a and the second surface 12b extend from the end wall 11bb toward the opposite side of the end wall 11ba. The first surface 12a and the second surface 12b face each other in a direction A3 that intersects both the direction A1 and A2. The direction A1 is the longitudinal direction of the housing 11. When the direction A2 is set as the lateral direction, the direction A3 becomes the height direction. Both the first surface 12a and the second surface 12b are flat and parallel to each other. The first surface 12a and the second surface 12b extend along the directions A1 and A2. The first surface 12a and the second surface 12b are parallel to the optical axis direction (direction A1). The feedthrough portion 12 has an end face 12c that intersects the first surface 12a and the second surface 12b at one end in the optical axis direction (direction A1). The end face 12c connects the first surface 12a and the second surface 12b and extends along the end wall 11bb (i.e., along the direction A2). The end face 12c extends along a plane that intersects the protruding direction of the feedthrough portion 12 toward the outside of the housing 11 (i.e., the direction A1). For example, among the mutually orthogonal X-axis, Y-axis, and Z-axis, when the X-axis direction is set as the direction A1, the end face 12c becomes a plane parallel to the YZ plane. For example, the direction A2 corresponds to the Y-axis direction, and the direction A3 corresponds to the Z-axis direction. For example, when the shape of the end face 12c is rectangular when viewed from the direction A1, the length direction of its shape corresponds to the direction A2. The direction A2 is, for example, the lateral direction. The direction A3 intersects the direction A1 and the direction A2 and is, for example, the height direction. For example, the first surface 12a and the second surface 12b are parallel to the directions A1 and A2.

[0053] Figure 4 is a perspective view showing an enlarged part of Figure 3 . Figure 4 Only the portion of the feedthrough portion 12 that protrudes from the end wall 11bb is shown. As Figure 4 shown, M DC pads 15 and J ground pads 31 are provided on the first surface 12a. M is an integer greater than or equal to 2, and M is 6 in the illustrated example. J is an integer greater than or equal to 1, and J is 3 in the illustrated example. The DC pads 15 are examples of the third electrical wiring in the present embodiment. The ground pads 31 are examples of the ground wiring in the present embodiment. The M DC pads 15 and the J ground pads 31 are metal films fixed on the dielectric feedthrough portion 12. Each DC pad 15 is electrically connected to a corresponding DC wiring 13 via a wiring buried inside the feedthrough portion 12. Each DC pad 15 has an elongated shape extending along the direction A1. The M DC pads 15 are arranged along the end wall 11bb (i.e., along the direction A2 that intersects the direction A1). Each ground pad 31 is connected to a ground via a flexible wiring board 7 (refer to Figure 1) is connected to the reference potential of the circuit board 4 through the ground terminal. Each ground pad 31 is arranged between adjacent DC pads 15 or at both ends of the arrangement of the DC pads 15 along the direction A2. For example, as Figure 4 shown, one ground pad 31 is arranged between the third and fourth ones counted from the end of the six DC pads 15. Therefore, the three ground pads 31 are arranged such that three DC pads 15 are sandwiched between adjacent ground pads 31. In one example, the lengths of the DC pads 15 and the ground pads 31 in the direction A1 are in the range of 0.8 mm to 1.4 mm. The center-to-center spacing (pitch) of adjacent DC pads 15 in the direction A2 is in the range of 0.3 mm to 0.6 mm. The width Wa of the DC pads 15 in the direction A2 is in the range of 0.1 mm to 0.4 mm. For example, when the DC pads 15 with a width Wa of 0.4 mm are arranged along the direction A2 with a center-to-center spacing (pitch) of 0.6 mm, the distance between adjacent DC pads 15 becomes 0.2 mm.

[0054] The feed-through portion 12 is formed by laminating a plurality of dielectric layers 121 along the direction A3. The dielectric layer 121 is made of, for example, ceramics such as alumina or aluminum nitride. The dielectric layer 121 can also be formed of, for example, glass fiber, epoxy resin, etc. in the same manner as an existing printed circuit board. The feed-through portion 12 can also be a multilayer substrate in which a plurality of wiring layers and a plurality of dielectric layers 121 are laminated. For example, the feed-through portion 12 is a ceramic multilayer substrate. For example, the first surface 12a is the uppermost wiring layer in the height direction (direction A3). For example, the second surface 12b is the lowermost wiring layer in the height direction (direction A3). The feed-through portion 12 has a ground pattern 42. The ground pattern 42 is buried in the interlayer of two dielectric layers 121 located between the first surface 12a and the second surface 12b. The ground pattern 42 is a conductive layer extending along the first surface 12a and the second surface 12b, and is, for example, a metal layer. At least one dielectric layer 121 is sandwiched between the ground pattern 42 and the first surface 12a. At least one dielectric layer 121 is also sandwiched between the ground pattern 42 and the second surface 12b. In Figure 4 the example involved, only one layer of the ground pattern 42 is provided, but multiple layers of the ground pattern 42 can also be provided. In addition, when the adjacent two dielectric layers 121 in the direction A3 do not include the ground pattern 42, the dielectric layers 121 can include conductive patterns.

[0055] The feedthrough portion 12 also has J electromagnetic shielding films 43. These electromagnetic shielding films 43 are metal films fixed on the end face 12c. Each electromagnetic shielding film 43 is provided corresponding to a ground pad 31 one by one and is connected to the ground pad 31. For example, on the side where the first face 12a and the end face 12c intersect, the electromagnetic shielding film 43 is connected to the ground pad 31 and is electrically connected to the ground pad 31. Each electromagnetic shielding film 43 extends from the first face 12a to the second face 12b on the end face 12c and is connected to the ground pattern 42 in the middle. That is, each ground pad 31 is electrically connected to the ground pattern 42 via the electromagnetic shielding film 43. Thus, the ground pattern 42 and the electromagnetic shielding film 43 are defined as the reference potential.

[0056] The feedthrough portion 12 also has (J - 1) electromagnetic shielding films 44. The electromagnetic shielding films 44 are metal films formed on the end face 12c of the feedthrough portion 12. Each electromagnetic shielding film 44 extends along the arrangement direction of the DC pads 15 (i.e., direction A2). The electromagnetic shielding film 44 is separated from both the first face 12a and the ground pattern 42 in the area between the ground pattern 42 and the first face 12a on the end face 12c. That is, when viewed from above in the normal direction of the end face 12c (i.e., direction A1), a gap is provided between the electromagnetic shielding film 44 and the first face 12a. Also, a gap is provided between the electromagnetic shielding film 44 and the ground pattern 42. The dielectric layer 121 is exposed from these gaps. The length L1 of these gaps in the direction A2 is, for example, 6.2 mm. One end of the electromagnetic shielding film 44 is connected to one electromagnetic shielding film 43. The other end of the electromagnetic shielding film 44 is connected to another electromagnetic shielding film 43. Therefore, the electromagnetic shielding film 44 is electrically connected to the ground pad 31 and the ground pattern 42 via the electromagnetic shielding film 43 and is defined as the reference potential. The height of the electromagnetic shielding film 44 in the direction A3 orthogonal to the direction A2, that is, the width of the electromagnetic shielding film 44 in the direction A3, is determined corresponding to the thickness of the dielectric layer 121, for example. The width of the electromagnetic shielding film 44 is 0.466 mm in one example.

[0057] Figure 5 is along Figure 4 Cross-sectional view of the V - V line of. As Figure 5As shown, the feedthrough portion 12 has a third surface 12d and a fourth surface 12e inside. The third surface 12d and the fourth surface 12e are regions between adjacent dielectric layers 121 in the stacked dielectric layers 121. The third surface 12d is sandwiched by two dielectric layers 121 adjacent in the direction A3. The fourth surface 12e is sandwiched by two dielectric layers 121 adjacent in the direction A3. Therefore, although the third surface 12d and the fourth surface 12e do not face the outside like the first surface 12a and the second surface 12b, conductive patterns such as the conductive pads 17 and the wiring portions 18 described later can be formed in each of them. For example, the third surface 12d and the fourth surface 12e each correspond to a wiring layer in a multilayer substrate. The third surface 12d and the fourth surface 12e extend along a plane parallel to the first surface 12a and the second surface 12b. In the direction A3, the third surface 12d is located between the first surface 12a and the ground pattern 42. In the direction A3, the fourth surface 12e is located between the third surface 12d and the ground pattern 42. In the illustrated example, one layer of the dielectric layer 121 is sandwiched between the first surface 12a and the third surface 12d. Two layers of the dielectric layer 121 are sandwiched between the third surface 12d and the fourth surface 12e. One layer of the dielectric layer 121 is sandwiched between the fourth surface 12e and the ground pattern 42. The above-described electromagnetic shielding film 44 is provided in the region reaching from the third surface 12d to the fourth surface 12e at the end face 12c. The two layers of the dielectric layer 121 adjacent to the third surface 12d in the direction A3 can be in surface contact with each other. The two layers of the dielectric layer 121 adjacent to the fourth surface 12e in the direction A3 can be in surface contact with each other.

[0058] Figure 6 is a top view of observing the third surface 12d from the thickness direction of the feedthrough portion 12. The thickness direction of the feedthrough portion 12 is the stacking direction of the dielectric layers 121, corresponding to the direction A3. As Figure 6As shown, the feedthrough portion 12 has a plurality of conductive pads 17 (first conductive pads). The plurality of conductive pads 17 are buried in the interlayer of the dielectric layer 121 on the third surface 12d. As described above, in the region of the third surface 12d other than the conductive pads 17, the two-layer dielectric layers 121 sandwiching the third surface 12d can be in contact with each other. The conductive pads 17 are arranged in a region separated from the end surface 12c in the direction A1. The conductive pads 17 are periodically arranged at a certain interval along the first surface 12a and the end wall 11bb (i.e., along the direction A2). The planar shape of each conductive pad 17 may be the same shape as each other, and can be various shapes such as a rectangle, a square, a polygon, a circle, etc. When the planar shape of the conductive pad 17 observed from the direction A3 is a rectangle or a square, for example, a pair of opposite edges of each conductive pad 17 are along the direction A1, and the other pair of opposite edges are along the direction A2. The sizes of the conductive pads 17 are sufficiently small compared to the wavelength of the electromagnetic noise (electromagnetic wave) (in a typical case, the wavelength corresponding to the fundamental frequency of the high-frequency signal of the optical transmission module 3). This electromagnetic noise can be considered as harmful electromagnetic waves, and it is desired to prevent this electromagnetic noise from invading the internal space of the housing 11 through the feedthrough portion 12. For example, when the wavelength of the electromagnetic noise is 25 GHz, in other words, when it is not desired that electromagnetic waves with a frequency of 25 GHz or more invade the inside of the housing 11, the width W1 in the direction A2 and the length L2 in the direction A1 of each conductive pad 17 are both set to be less than or equal to 0.5 mm. In one embodiment, the width W1 and the length L2 of each conductive pad 17 are both 0.2745 mm. When the planar shape of each conductive pad 17 is a rectangle, the width W1 can be longer than the length L2, and the length L2 can also be longer than the width W1. When the dielectric layer 121 is made of ceramic, the lower limit values in manufacturing of the width W1 and the length L2 are both about 30 μm.

[0059] The capacitance between adjacent conductive pads 17 is determined by the interval D1 between the conductive pads 17 and the length L2 of the conductive pads 17 in the direction A1. The capacitance between the conductive pads 17 is set to a magnitude that can attenuate the electromagnetic noise of the assumed frequency. When the wavelength of the electromagnetic noise is the wavelength corresponding to the frequency of 25 GHz and the length of the conductive pad 17 in the direction A1 is 0.2745 mm, the interval D1 is set to 0.13 mm, for example. When the planar shape of the conductive pad 17 is a square, the arrangement period of the conductive pads 17 becomes 0.4045 mm. In this case, for example, a plurality of conductive pads 17 can be arranged approximately evenly with respect to the length L1 (6.2 mm) of the gap. In addition, the numerical examples of the respective dimensions shown here are inconsistent with Figure 6 the shapes shown in Figure 6This figure is not related to examples of specific dimensions and is used to illustrate how to configure multiple conductive pads 17.

[0060] The multiple conductive pads 17 are electrically connected to the ground pad 31. For this purpose, the feedthrough portion 12 of the present embodiment has a plurality of wiring portions 18. Each wiring portion 18 is provided in a one-to-one correspondence with each conductive pad 17 on the third surface 12d. Therefore, on the third surface 12d, the number of wiring portions 18 is equal to the number of conductive pads 17. Each wiring portion 18 extends from the corresponding conductive pad 17 toward the electromagnetic shielding film 44 in the protruding direction (direction A1) of the feedthrough portion 12. The planar shape of each wiring portion 18 is an elongated shape with the protruding direction of the feedthrough portion 12 as the length direction. Each wiring portion 18 electrically connects the corresponding conductive pad 17 and the electromagnetic shielding film 44. As shown above, the electromagnetic shielding film 44 is electrically connected to the ground pad 31. Therefore, each conductive pad 17 is electrically connected to the ground pad 31 via each wiring portion 18 and the electromagnetic shielding film 44 and is defined as the reference potential.

[0061] The size of each wiring portion 18 is smaller than the wavelength of the electromagnetic noise (in a typical case, the wavelength corresponding to the fundamental frequency of the high-frequency signal of the optical transmission module 3). The inductance of each wiring portion 18 is determined by the length L3 of each wiring portion 18 in the direction A1 and the width W2 of each wiring portion 18 in the direction A2. The length L3 is, in other words, the distance between each conductive pad 17 and the end face 12c. The width W2 is smaller than the width W1 of the conductive pad 17. For example, the width W2 is less than or equal to 1 / 2 of the width W1. The inductance of each wiring portion 18 together with the capacitance between the aforementioned conductive pads 17 is set to a size that can attenuate the electromagnetic noise of a specified frequency to a desired degree. For example, when the wavelength of the electromagnetic noise is the wavelength corresponding to a frequency of 25 GHz, the length L3 is set to be less than or equal to 0.5 mm (0.35 mm in one embodiment), and the width W2 is set to 0.033 mm, for example.

[0062] Figure 7 This is a top view of the fourth surface 12e as viewed from the thickness direction of the feedthrough portion 12. As Figure 7As shown, the feedthrough portion 12 has a plurality of conductive pads 19 (second conductive pads). The plurality of conductive pads 19 are embedded in the interlayer of the dielectric layer 121 in the fourth surface 12e. As described above, in the region of the fourth surface 12e other than the conductive pads 19, the two-layer dielectric layers 121 sandwiching the fourth surface 12e can be in contact with each other. The conductive pads 19 are arranged in a region separated from the end face 12c in the direction A1. The conductive pads 19 are periodically arranged at a certain interval along the first surface 12a and the end wall 11bb (i.e., along the direction A2). The planar shape, size, and arrangement of each conductive pad 19 are the same as those of the above-described conductive pad 17 and are set to a size capable of attenuating electromagnetic noise of a contemplated frequency. However, the planar shape and size of the conductive pads 19 only need to be the same as each other, and can be the same as or different from the planar shape and size of the conductive pads 17. The size of each conductive pad 19 is sufficiently small compared to the wavelength of the electromagnetic noise (electromagnetic wave) (in a typical case, the wavelength corresponding to the fundamental frequency of the high-frequency signal of the optical transmission module 3). This electromagnetic noise can be considered as harmful electromagnetic waves, and it is desired to prevent this electromagnetic noise from invading the internal space of the housing 11 through the feedthrough portion 12.

[0063] The plurality of conductive pads 19 are electrically connected to the ground pad 31. For this purpose, the feedthrough portion 12 of the present embodiment has a plurality of wiring portions 20. Each wiring portion 20 is provided in the fourth surface 12e in one-to-one correspondence with each conductive pad 19. Therefore, in the fourth surface 12e, the number of wiring portions 20 is equal to the number of conductive pads 19. Each wiring portion 20 extends from the corresponding conductive pad 19 toward the electromagnetic shielding film 44 in the protruding direction (direction A1) of the feedthrough portion 12. The planar shape of each wiring portion 20 is an elongated shape with the protruding direction of the feedthrough portion 12 as the longitudinal direction. Each wiring portion 20 electrically connects the corresponding conductive pad 19 and the electromagnetic shielding film 44. As shown above, the electromagnetic shielding film 44 is electrically connected to the ground pad 31. Therefore, each conductive pad 19 is electrically connected to the ground pad 31 and the ground pattern 42 via each wiring portion 20 and the electromagnetic shielding film 44 and is defined as the reference potential. The length and width of each wiring portion 20 are the same as those of the above-described wiring portion 18 and are set to a size capable of attenuating electromagnetic noise of a contemplated frequency to a desired degree. However, the length and width of the wiring portion 20 can be the same as or different from the length and width of the wiring portion 18.

[0064] Figure 8 is a partial cross-sectional view showing an enlarged part of the appearance of the package 10A. Figure 8 is a view of a part of the portion of the feedthrough portion 12 protruding from the end wall 11bb as viewed from the second surface 12b side. As Figure 8As shown, N high-frequency signal pads 16 (fourth electrical wiring) are provided on the second surface 12b of the feedthrough portion 12. N is an integer greater than or equal to 1, and N is 4 in the illustrated example. Each high-frequency signal pad 16 is a transmission line for transmitting high-frequency signals transmitted through each high-frequency signal wiring 14. Each high-frequency signal pad 16 is composed of, for example, a pair of signal pads 16a and 16b. The signal pad 16a is arranged with the signal pad 16b in the direction A2. In the case where the high-frequency signal is a differential signal (differential transmission method), the above-described two signal pads 16a and 16b are used. For example, the signal pad 16a is used for the positive-phase component (positive signal) of the differential signal, and the signal pad 16b is used for the negative-phase component (negative signal) of the differential signal. Ground pads 16c are provided adjacent to each of the signal pads 16a and 16b. For example, the ground pads 16c are arranged on both sides of the pair of signal pads 16a and 16b in the direction A2. The adjacent high-frequency signal pads 16 share the ground pads 16c. The signal pads 16a and 16b are denoted by the symbol S, and the ground pads 16c are denoted by the symbol G. Sometimes, the structure in which the ground pads 16c are arranged on both sides of the pair of signal pads 16a and 16b is called a GSSG structure. In the case where the high-frequency signal is a differential signal, the N high-frequency signal pads 16 include 2×N signal pads 16a and 16b. Alternatively, N differential signals can be transmitted through 2×N signal pads 16a and 16b. The signal pads 16a and 16b and the ground pads 16c are metal films and are fixedly connected to the dielectric feedthrough portion 12. The ground pad 16c is defined as the reference potential. The signal pads 16a and 16b and the ground pads 16c form a coplanar line. Each high-frequency signal pad 16 is connected to the corresponding high-frequency signal wiring 14 via wiring buried inside the feedthrough portion 12 (see Figure 2)Electrically connected. Another flexible substrate is disposed in a superposed manner on the second surface 12b for conductive bonding with the flexible wiring substrate 7. Each high-frequency signal pad 16 is connected to the circuit substrate 4 via this other flexible substrate. In the figure, as an example, each high-frequency signal pad 16 including the signal pads 16a and 16b for the differential transmission method described above is shown, but in the case where the differential transmission method is not adopted, each high-frequency signal pad 16 may each include a single signal pad. In the case of the differential transmission method, one of the differential signals having a positive-phase component and an inverted-phase component (for example, the positive-phase component) is input to the signal pad 16a, and the other of the differential signals (for example, the inverted-phase component) is input to the signal pad 16b. The positive-phase component and the inverted-phase component are a pair of complementary signals. For example, when the positive-phase component increases, the inverted-phase component decreases, and when the positive-phase component decreases, the inverted-phase component increases. When the positive-phase component reaches the maximum value (peak), the inverted-phase component reaches the minimum value (lowest value), and when the positive-phase component reaches the minimum value (lowest value), the inverted-phase component reaches the maximum value (peak). The amplitude of the positive-phase component is the same as the amplitude of the inverted-phase component. The average value of the amplitude of the positive-phase component is consistent with the average value of the amplitude of the inverted-phase component. The positive-phase component has a phase different from that of the inverted-phase component by 180°.

[0065] Between the ground pattern 42 and the second surface 12b, at least one layer of dielectric layer 121 is interposed. Each ground pad 16c is electrically connected to the ground pattern 42 via the electromagnetic shielding films 43 and 45 provided on the end face 12c. In the present embodiment, the ground pattern 42 is provided for impedance adjustment of the high-frequency signal pads 16. That is, the ground pattern 42 can form a microstrip-type transmission line together with each high-frequency signal pad 16. As long as the characteristic impedance of the transmission line formed by the high-frequency signal pads 16 can be adjusted to a desired value, the ground pattern 42 may not be provided. For example, the high-frequency signal pads 16 may form a coplanar-type transmission line.

[0066] The effects obtained by the package 10A of the present embodiment described above will be described. In recent optical transceivers, a circuit (drive circuit) that drives a light-emitting element incorporated in an optical transmission module is sometimes provided outside the optical transmission module. In this case, electromagnetic noise is generated from the wiring that connects the drive circuit and the optical transmission module due to the high-frequency signal (drive signal) output from the drive circuit. In particular, when an electroabsorption modulator integrated laser diode (EML) is used as the light-emitting element incorporated in the optical transmission module, the drive voltage of the EML is usually high (for example, an amplitude of 2V), so the electromagnetic noise also becomes large. In addition, in recent optical communication systems, for example, transmission speeds such as 50 Gbits / s or 100 Gbits / s are being achieved, and the high-speed trend is continuously developing. The faster the transmission speed of optical communication becomes, the higher the frequency of the drive signal becomes. The higher the frequency of the drive signal becomes, the greater the electromagnetic noise (electromagnetic wave) radiated from the wiring between the drive circuit and the optical transmission module becomes. The radiation of electromagnetic noise as described above becomes significant when the transmission speed of the optical communication system is greater than or equal to 10 Gbits / s.

[0067] On the other hand, due to the miniaturization of optical transceivers accompanying the increase in communication data volume in recent years, the optical transmission module is mostly arranged close to the optical reception module. The above-mentioned electromagnetic noise may cause crosstalk due to electromagnetic wave interference to the received signal in the optical reception module arranged adjacent to the optical transmission module. In the package of the optical reception module, a dielectric feedthrough portion is provided by penetrating a part of the conductive frame. In the existing optical reception module, electromagnetic noise may invade into the package through the dielectric feedthrough portion.

[0068] In the region between the ground pattern 42 and the second surface 12b among the end faces 12c, a plurality of electromagnetic shielding films 45 are provided corresponding to the ground pads 16c. Alternatively, the ground pad 16c may be connected to the ground pattern 42 through a via hole that penetrates the dielectric layer 121. Thereby, the reference potential of the ground pad 16c is more stabilized. Regardless of which structure, the region between the ground pattern 42 and the second surface 12b has a shielding effect of blocking high electromagnetic noise. In contrast, in the region between the ground pattern 42 and the first surface 12a, there are few electromagnetic shielding films and via holes, so electromagnetic waves with a frequency of 10 GHz or more will invade.

[0069] In order to suppress the intrusion of external electromagnetic waves as described above, in the package 10A of the present embodiment, a plurality of conductive pads 17 are provided on the third surface 12d between the first surface 12a and the ground pattern 42. These conductive pads 17 are arranged at a certain interval along the wall surfaces of the first surface 12a and the end wall 11bb. That is, they are arranged in the direction A2 parallel to the first surface 12a and parallel to the wall surface of the end wall 11bb. Moreover, each conductive pad 17 is electrically connected to the ground pad 31, and thus is set to the reference potential. In this case, the plurality of conductive pads 17 can form a left-handed metamaterial. Therefore, in the region around the plurality of conductive pads 17, electromagnetic waves of a specific frequency determined by the shape and arrangement of the plurality of conductive pads 17 (the interval between the conductive pads 17, etc.) are attenuated. The left-handed metamaterial structure of the present embodiment particularly effectively attenuates electromagnetic waves invading from the out-of-plane direction (direction A1) of the end face 12c. That is, the electromagnetic noise traveling toward the internal space of the housing 11 inside the feedthrough portion 12 is attenuated, and thus the electromagnetic noise invading into the optical receiving module through the feedthrough portion 12 can be reduced.

[0070] Here, the left-handed metamaterial will be described. Figure 9 It is a perspective view showing an example of a left-handed metamaterial. This left-handed metamaterial is composed of a plurality of conductive pads 51 each constituting a mushroom structure. The plurality of mushroom structures are two-dimensionally arranged over multiple rows and columns on the dielectric substrate 50. Each conductive pad 51 is connected to a ground pattern (not shown) on the lower surface via a metal vias (not shown) provided in the dielectric substrate 50. The cross-sectional area of the metal vias is reduced to be less than or equal to 1 / 10 of the area of the conductive pad 51. In this left-handed metamaterial, minute unit cells (Unit cell) such as metal sheets (the conductive pads 51 in Figure 9 are arranged periodically at intervals less than or equal to the wavelength of the target electromagnetic wave. The shape and arrangement of each unit cell are set corresponding to the wavelength of the target electromagnetic wave. Thereby, an artificial member with a negative dielectric constant and permeability that does not exist in natural materials can be realized. Sometimes the structure as described above is called an electromagnetic band gap (EBG; Electromagnetic Band Gap) structure.

[0071] In Figure 9The direction of the traveling electromagnetic wave is shown by an arrow. In the region near the above-described member, the electromagnetic wave is transmitted as a backward wave (arrow R1). Therefore, if this member is disposed in a waveguide or the like in which the electromagnetic wave is transmitted as a forward wave (arrow R2), the electromagnetic wave cannot exist in a specific frequency region around this member. Accordingly, it is possible to block the electromagnetic noise that attempts to pass around this member. In addition, current caused by electromagnetic noise is not induced in the DC wiring disposed around this member.

[0072] The plurality of conductive pads 17 in the present embodiment correspond to Figure 9 a corresponding amount of the conductive pads 51 in a two-dimensional arrangement shown in FIG. 51 that cross the traveling direction of the electromagnetic wave. In addition, the wiring portion 18 corresponds to a metal via hole. Even in a corresponding amount in a one-dimensional arrangement, the left-handed metamaterial has the above-described function. The plurality of conductive pads 17 and Figure 9 the conductive pads 51 can be arranged two-dimensionally along the directions A2 and A1 in the same manner. In addition, in this case, for the plurality of conductive pads 17 shown in the figure, the plurality of conductive pads 17 arranged on the side opposite to the end face 12c in the direction A1 can be Figure 9 connected to the ground pattern 42 via the metal via holes provided in the dielectric layer 121 in the same manner as the conductive pads 51.

[0073] In the present embodiment, a resonance circuit is formed by the capacitance between adjacent conductive pads 17 and the inductance between each conductive pad 17 and the ground pad 31. The above-described specific frequency corresponds to the resonance frequency of this resonance circuit. The capacitance between adjacent conductive pads 17 is mainly determined by the interval D1 between adjacent conductive pads 17 and the length L2 of each conductive pad 17. The inductance between each conductive pad 17 and the ground pad 31 is mainly determined by the length L3 and the width W2 of the wiring portion 18.

[0074] As in the present embodiment, the package 10A may have an electromagnetic shielding film 44. The electromagnetic shielding film 44 is provided separated from the first surface 12a on the end surface 12c and is electrically connected to the ground pad 31. Each wiring portion 18 extends from each conductive pad 17 toward the electromagnetic shielding film 44 in the protruding direction (direction A1) of the feedthrough portion 12, and electrically connects each conductive pad 17 and the electromagnetic shielding film 44. In this case, a part of the electromagnetic noise attempting to invade the housing 11 through the feedthrough portion 12 can be shielded by the electromagnetic shielding film 44. In addition, the electromagnetic noise not sufficiently attenuated by the electromagnetic shielding film 44 can be attenuated by the above-described action of the plurality of conductive pads 17. Therefore, the electromagnetic noise invading the optical receiving module 2 through the feedthrough portion 12 can be reduced more effectively. By electrically connecting the electromagnetic shielding film 44 and the conductive pad 17 via the wiring portion 18, the electrical connection between the conductive pad 17 and the ground pad 31 can be easily achieved.

[0075] As in the present embodiment, the package 10A may have a plurality of conductive pads 19 electrically connected to the ground pad 31. The plurality of conductive pads 19 are provided on the fourth surface 12e between the second surface 12b and the third surface 12d, and are arranged at a certain interval from each other along the first surface 12a and the end wall 11bb in the same manner as the plurality of conductive pads 17. On the fourth surface 12e, a plurality of wiring portions 20 are arranged in the same manner as the plurality of wiring portions 18. The plurality of conductive pads 19 are connected to the plurality of wiring portions 20 one-to-one and are electrically connected to the ground pad 31. The plurality of wiring portions 20 may be connected to the ground pad 31 via the above-described electromagnetic shielding film 44. In this case, the plurality of conductive pads 19 can form a left-handed metamaterial in the same manner as the plurality of conductive pads 17. Therefore, the plurality of conductive pads 19 can attenuate electromagnetic waves of a specific frequency determined by the shape and arrangement (interval between the conductive pads 19, etc.) of the plurality of conductive pads 19 in the surrounding area. Thereby, the electromagnetic noise invading the optical receiving module 2 through the feedthrough portion 12 can be reduced more effectively.

[0076] In the present embodiment, as described above, by adjusting the interval D1 between adjacent conductive pads 17 and the length L2 of each conductive pad 17, the cutoff frequency for electromagnetic noise can be changed to a desired value. At this time, if the interval D1 is increased, the number of conductive pads 17 will decrease accordingly. The metamaterial of the present embodiment is similar to a distributed constant circuit, and the more the number of conductive pads 17 per unit length, the better.

[0077] Figure 10A and Figure 10B is a circuit diagram in which the metamaterial realized by the plurality of conductive pads 17 is equivalently represented by a distributed constant circuit. Figure 10A Shows an equivalent circuit of a normal transmission line along the traveling direction of electromagnetic waves. Figure 10BShows the transmission line equivalent circuit in the case where a metamaterial structure is disposed midway. In Figure 10B with respect to a part E1 of the circuit of Figure 10A a capacitor 61 and an inductor 62 equivalent to the metamaterial structure are added.

[0078] Embodiment

[0079] In order to confirm the above effects of the package 10A according to the above embodiment, the present inventor performed a simulation implemented by a computer. Figure 11 As a comparative example, the end face 12c in the case where the electromagnetic shielding film 44, the plurality of conductive pads 17, and the plurality of conductive pads 19 are not provided is shown. In this case, Figure 11 the portion indicated by the dashed line F1 of Figure 12 is regarded as a waveguide composed only of a dielectric. Figure 4 is a perspective view showing a waveguide 70 as a model of this waveguide. In this simulation, the width W of the waveguide 70 in the direction A2 (corresponding to the length L1 of r ) is set to 6.2 mm, and the height h1 is set to 0.852 mm. It is assumed that the waveguide 70 is filled with alumina. The relative dielectric constant ε of alumina

[0080] If the calculation is performed only focusing on the TE10 mode in the waveguide direction, the relationship between the insertion loss of this waveguide 70 and the frequency of the electromagnetic wave becomes Figure 13 the graph shown. If the insertion loss becomes effective, the cut-off frequency is about 9 GHz. Therefore, electromagnetic noise at frequencies higher than 9 GHz is not attenuated and is conducted in the waveguide 70 in the waveguide direction. For example, the transmission speed used in 100GBASE-LR4 etc. is 25 Gbits / s. In this case, electromagnetic noise with a fundamental frequency of 25.78125 GHz radiated by the drive signal can be conducted in this waveguide. According to this calculation result, it can be seen that in order to block the electromagnetic noise with a fundamental frequency of 25.78125 GHz at the transmission speed of 25 Gbits / s to -30 dB, for example, in theory, it is only necessary to set the width W to be less than or equal to 1.9 mm. However, since the actual feedthrough portion 12 cannot form a complete waveguide structure, it is desirable to set it to a width that is sufficiently short with respect to the wavelength of the electromagnetic noise, for example, 1 / 4 of less than 1.9 mm. Since a plurality of DC pads 15 are arranged and provided on the first surface 12a, it is difficult to set the width W of the waveguide to the size as described above.

[0081] Figure 14is shown as another comparative example with respect to Figure 11 the case where only the electromagnetic shielding film 44 is provided on the end face 12c shown. Gaps F2 and F3 are provided between the electromagnetic shielding film 44 and the upper and lower surfaces of the waveguide. Figure 15 is Figure 14 a perspective view of the waveguide 71 shown as a model of the portion of the waveguide represented by the dashed line F1. In this simulation, the width of the electromagnetic shielding film 44 in the direction A2 is set to be the same as the width W of the waveguide 71 (6.2 mm), and the height (width in the direction A3) h2 of the electromagnetic shielding film 44 is set to 0.47 mm. Figure 16 is a graph showing Figure 15 the relationship between the insertion loss of the waveguide shown and the frequency of the electromagnetic wave. Referring to Figure 16 , it can be seen that by providing only the electromagnetic shielding film 44, there is almost no change compared to the Figure 13 graph shown, and the effect of shielding electromagnetic noise is insufficient.

[0082] Figure 17 is a perspective view of the waveguide 72 showing the mode (i.e., the above-described embodiment) in which a plurality of conductive pads 17, 19 and wiring portions 18, 20 are further added to the structure shown in Figure 14 . In this simulation, the width W1 and length L2 of each conductive pad 17 shown in Figure 6 are both set to 0.2745 mm, the width W2 of the wiring portion 18 is set to 0.033 mm, and the length L3 is set to 0.35 mm. In addition, the interval D1 between adjacent conductive pads 17 is set to 0.13 mm. The same applies to the conductive pad 19 and the wiring portion 20. Figure 18 is a graph showing Figure 17 the relationship between the insertion loss of the waveguide shown and the frequency of the electromagnetic wave. Compared with Figure 13 and Figure 16 , it can be seen that a peak P1 where the absolute value of the insertion loss increases is found near the frequency of 25 GHz. That is, according to the above-described embodiment, it is possible to attenuate electromagnetic noise near a desired frequency in the feedthrough portion 12 and effectively suppress the intrusion of electromagnetic noise into the interior of the housing of the optical reception module 2.

[0083] First Modified Example

[0084] Figure 19 is a perspective view showing the feedthrough portion 12A as the first modified example of the above-described embodiment. In addition, Figure 20 and Figure 21is a top view showing the third surface 12d and the fourth surface 12e of the feedthrough portion 12A of this modified example. This modified example has two differences compared with the above-described embodiment. One point is that the feedthrough portion 12A does not have the electromagnetic shielding film 44. Another point is that the feedthrough portion 12A has the conductive pattern 46 on the third surface 12d and the conductive pattern 47 on the fourth surface 12e.

[0085] The conductive pattern 46 is a metal film and is buried between the dielectric layers 121 on the third surface 12d. The conductive pattern 47 is a metal film and is buried between the dielectric layers 121 on the fourth surface 12e. The conductive patterns 46 and 47 extend from one side surface to the other side surface of the feedthrough portion 12A along the direction A2. The conductive patterns 46 and 47 are electrically connected to each other via the metal films formed on both side surfaces of the feedthrough portion 12A, for example. The conductive patterns 46 and 47 are exposed from the dielectric layer 121 at the end face 12c of the feedthrough portion 12A and are in contact with the electromagnetic shielding film 43. Therefore, the conductive patterns 46 and 47 are electrically connected to the ground pad 31 via the electromagnetic shielding film 43 and are defined as the reference potential. The width W3 of the conductive patterns 46 and 47 in the direction A1 can be set to be the same as the width of the electromagnetic shielding film 44 in the direction A3, for example. The width W3 is 0.47 mm, for example.

[0086] As Figure 20 shown, the wiring portion 18 extends from the conductive pad 17 toward the conductive pattern 46 along the direction A1. The end portion of the wiring portion 18 on the side opposite to the conductive pad 17 is connected to the conductive pattern 46. Thus, the wiring portion 18 electrically connects the conductive pad 17 and the conductive pattern 46. Therefore, the conductive pad 17 is electrically connected to the ground pad 31 via the conductive pattern 46 and the electromagnetic shielding film 43 and is defined as the reference potential. Similarly, as Figure 21 shown, the wiring portion 20 extends from the conductive pad 19 toward the conductive pattern 47 along the direction A1. The end portion of the wiring portion 20 on the side opposite to the conductive pad 19 is connected to the conductive pattern 47. Thus, the wiring portion 20 electrically connects the conductive pad 19 and the conductive pattern 47. Therefore, the conductive pad 19 is electrically connected to the ground pad 31 and the ground pattern 42 via the conductive pattern 47 and the electromagnetic shielding film 43 and is defined as the reference potential.

[0087] The method for electrically connecting the wiring portions 18 and 20 to the ground pad 31 is not limited to the above-described embodiment, and various methods such as this modified example can be used, for example. Regardless of which method is used, by electrically connecting the conductive pads 17 and 19 to the ground pad 31, the same effects as those of the above-described embodiment can be achieved. In addition, according to this modified example, the electrical connection between the plurality of conductive pads 17 and 19 and the ground pad 31 can be easily realized.

[0088] Second Modified Example

[0089] Figure 221 is a perspective view showing a feed-through portion 12B as a second modified example of the above-mentioned embodiment. Figure 23 is along Figure 22 The difference between this variant and the above embodiment is that the electromagnetic shielding film 44 of the feed-through portion 12B extends to the ground pattern 42 and is connected to the ground pattern 42. In this case, the electromagnetic gap between the ground pattern 42 and the electromagnetic shielding film 44 disappears, so a higher shielding effect can be obtained with respect to electromagnetic noise than in the above embodiment. In this case, Figure 7 The plurality of conductive pads 19 and the plurality of wiring portions 20 shown may be omitted.

[0090] The package for optical receiving module and the optical receiving module involved in the present invention are not limited to the above-mentioned embodiments and various modifications, and other various modifications can be performed. For example, in the above-mentioned embodiment, a plurality of conductive pads 19 and a plurality of wiring parts 20 are provided on the fourth surface 12e, but in the case where the gap between the electromagnetic shielding film 44 and the ground pattern 42 can be shielded by other means as in the second modification, or in the case where the distance between the first surface 12a and the ground pattern 42 is short in the first modification, the plurality of conductive pads 19 and the plurality of wiring parts 20 can also be omitted. In the above-mentioned embodiment, the conductive pads 17 and 19 are electrically connected to the ground pad 31 via the ground pattern 42, but the conductive pads 17 and 19 can also be electrically connected to the ground pad 31 or the ground pattern 42 via other elements (such as via holes that penetrate the dielectric layer 121). In the above embodiment, the conductive pads 17 and 19 are electrically connected to the ground pad 31 on the first surface 12 a and the ground pad 16 c on the second surface 12 b , but the conductive pads 17 and 19 only need to be connected to at least one of them.

Claims

1. An encapsulation for an optical receiving module, comprising: A conductive housing having a first sidewall, a second sidewall, and an internal space. The first sidewall is provided with an inlet for introducing an optical signal along the optical axis direction. The second sidewall is separated from the first sidewall in the optical axis direction. The internal space is partitioned between the first sidewall and the second sidewall and houses a light-receiving element for converting the optical signal into a high-frequency signal; and A feedthrough portion having a first surface, a second surface, and a third surface that respectively extend from the second sidewall to the opposite side of the first sidewall and is made of a dielectric material. The feedthrough portion has: A plurality of first electrical wirings that are arranged facing the internal space and include at least one of a monitor wiring and a power wiring; A second electrical wiring that is arranged facing the internal space and transmits the high-frequency signal; A plurality of third electrical wirings that are arranged on the first surface, are electrically connected to the plurality of first electrical wirings, and are arranged in a lateral direction intersecting the optical axis direction; A fourth electrical wiring that is arranged on the second surface, is electrically connected to the second electrical wiring, and transmits the high-frequency signal transmitted by the second electrical wiring; A ground wiring that is arranged on at least one of the first surface and the second surface; and A plurality of first conductive pads that are arranged on the third surface between the first surface and the second surface, are arranged at a certain interval from each other in the lateral direction, The plurality of first conductive pads are electrically connected to the ground wiring.

2. The encapsulation for an optical receiving module according to claim 1, wherein, At one end of the feedthrough portion in the optical axis direction, there is also an end face intersecting the first surface and the second surface, The feedthrough portion further has: An electromagnetic shielding film that is arranged separated from the first surface on the end face and is electrically connected to the ground wiring; and A plurality of wiring portions that are arranged on the third surface and electrically connect the plurality of first conductive pads to the electromagnetic shielding film.

3. The encapsulation for an optical receiving module according to claim 2, wherein, The width of each of the plurality of wiring portions in the lateral direction is smaller than the width of each of the plurality of first conductive pads in the lateral direction.

4. The encapsulation for an optical receiving module according to claim 1, wherein, The feedthrough portion further has: A conductive pattern that is arranged on the third surface, extends in the lateral direction, and is electrically connected to the ground wiring; and A plurality of wiring portions that are arranged on the third surface and electrically connect the plurality of first conductive pads to the conductive pattern.

5. The encapsulation for an optical receiving module according to claim 4, wherein, The width of each of the plurality of wiring portions in the lateral direction is smaller than the width of each of the plurality of first conductive pads in the lateral direction.

6. The encapsulation for an optical receiving module according to claim 1, wherein, The feedthrough portion further has a fourth surface located between the second surface and the third surface, The feedthrough portion further has a plurality of second conductive pads that are arranged at a certain interval from each other in the lateral direction on the fourth surface. The plurality of second conductive pads are electrically connected to the ground wiring.

7. The package for an optical receiving module according to claim 6, wherein, The feed-through portion further has: a conductive pattern provided on the fourth surface, extending in the lateral direction, and electrically connected to the ground wiring; and a plurality of wiring portions provided on the fourth surface, electrically connecting the plurality of second conductive pads to the conductive pattern.

8. The package for an optical receiving module according to claim 7, wherein, The lateral width of each of the plurality of wiring portions is smaller than the lateral width of each of the plurality of second conductive pads.

9. The package for an optical receiving module according to any one of claims 1 to 8, wherein, The feed-through portion further has at least one dielectric layer between the first surface and the third surface.

10. The package for an optical receiving module according to any one of claims 1 to 9, wherein, The feed-through portion further has at least one dielectric layer between the second surface and the third surface.

11. An optical receiving module, comprising: the package for an optical receiving module according to any one of claims 1 to 10; and the light receiving element received in the internal space of the housing.

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