JP2020021911A - Optical subassembly and optical module - Google Patents

Abstract

To provide an optical subassembly capable of achieving further impedance matching.SOLUTION: An optical subassembly includes: an eyelet 120 including a first through hole 123 penetrating from a first surface 121 to a second surface 122; a first lead terminal 110 being inserted into the first through hole and transmitting an electric signal; a dielectric 130 filled between the first through hole and the first lead terminal; an element mounting substrate 140 mounted with an optical element 160 which converts at least one of an optical signal and an electric signal into the other; a relay substrate 150 including a first conductor pattern 152 which transmits the electric signal to the optical element; and a pedestal 124 protruding from the first surface towards an extension direction of the first through hole and placed with the relay substrate and the element mounting substrate. The first lead terminal includes a large diameter part 115 provided at an end part of a small diameter part 114 and having a larger diameter than the small diameter part. At least a part of the large diameter part is exposed from the dielectric on the first surface side, and the first lead terminal and the first conductor pattern are brazed and soldered.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical subassembly and an optical module.

  At present, most of the Internet and telephone networks are constructed by optical communication networks. 2. Description of the Related Art An optical module used as an interface of a router / switch or a transmission device, which is an optical communication device, plays an important role of converting an electric signal into an optical signal. An optical module generally includes an optical sub-assembly containing an optical element, a printed circuit board (hereinafter referred to as a PCB) on which an IC for processing a signal including a modulated electric signal is mounted, and a flexible printed circuit board (hereinafter referred to as a PCB) for electrically connecting them. In the following, a form having FPC) will be used.

  In recent years, demands for not only high-speed but also low-cost optical modules have been remarkable, and demand for optical modules that can transmit and receive high-speed optical signals at low cost has been increasing. For example, as an optical module satisfying the above requirements, for example, a TO-CAN package type optical sub-assembly having a form in which a lead terminal inserted into an FPC or the like protrudes from a metal stem included in a can-shaped package is used. It is known. The metal stem includes a substantially disc-shaped eyelet and a pedestal provided to protrude from the eyelet.

  Patent Documents 1 and 2 below disclose techniques for transmitting a 25 Gbit / s-class modulated electric signal to an optical element.

  It is difficult to match characteristic impedance to a desired value in a TO-CAN type optical subassembly using a lead terminal as an electrical interface, but in Patent Documents 1 and 2 below, the inductance is increased at the lead terminal. In order to prevent this, insert a dielectric substrate directly under the lead terminals, enhance the electrical coupling with the pedestal that serves as the ground conductor due to the high dielectric constant of the dielectric substrate, reduce the inductance by capacitance, and reduce the undesirable impedance. It is preventing the increase.

  Further, the connection between the lead terminal and the dielectric substrate is not a wire connection but a brazing, so that the generation of an unnecessary inductance component has been suppressed. Further, the connection between the lead terminals and the dielectric substrate is configured to be easy.

JP 2017-50357 A JP 2011-134740 A

  In recent years, there has been a remarkable demand for high speed, and for example, demand for an optical module having a transmission rate of 40 Gbit / s class or more has been increasing. In order to realize a design corresponding to such a demand for higher speed, it is necessary to more strictly perform impedance matching, but it has been a problem that it is not easy.

  In order to perform impedance matching more strictly, the diameter of the through hole provided in the eyelet needs to be a desired value determined from the dielectric constant of the dielectric filling the through hole and the lead terminal diameter, As a result, a large gap may be generated between the pedestal and the lead terminal. The return current propagating through the ground conductor bypasses the through-hole and propagates through the pedestal to the dielectric substrate. Was more difficult to do strictly.

  The present disclosure has been made in view of the above problems, and an object of the present disclosure is to more strictly perform impedance matching in an optical module in which a lead terminal and a dielectric substrate are soldered.

  In order to solve the above-described problems, an optical subassembly according to the present disclosure includes a first surface, a second surface disposed on a side opposite to the first surface, and a second surface arranged from the first surface. An eyelet including a first through-hole penetrating through the first through-hole, a first lead terminal inserted into the first through-hole and transmitting an electric signal, the first through-hole and the first through-hole. A dielectric material filled between the lead terminals, an element mounting substrate on which an optical element for converting at least one of an optical signal and the electric signal to the other is mounted, and a second element for transmitting the electric signal to the optical element. A relay board including the first conductive pattern, and a pedestal that protrudes from the first surface in a direction in which the first through hole extends, and on which the relay board and the element mounting board are mounted. The first lead terminal is provided at a small diameter portion and at an end of the small diameter portion. A large diameter portion having a large diameter, at least a part of the large diameter portion is exposed from the dielectric on the first surface side, and the first lead terminal and the first conductor The pattern is brazed.

  Further, an optical module according to the present disclosure includes the optical sub-assembly, a printed board, and a flexible board electrically connected to the printed board and the optical sub-assembly.

  According to the optical subassembly and the optical module of the present disclosure, further impedance matching can be realized.

FIG. 1 is an external view of the optical module according to the first embodiment. FIG. 2 is a schematic diagram illustrating an internal structure of the optical subassembly according to the first embodiment. FIG. 3 is a schematic diagram illustrating a cross-sectional structure of the optical subassembly according to the first embodiment. FIG. 4 is a schematic plan view of the optical subassembly according to the first embodiment. FIG. 5A is a table of data used for a high-frequency three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator) in the first embodiment. FIG. 5B is a graph in which the relationship between the protrusion amount of the lead terminal, the diameter of the large diameter portion, and the reflection characteristics according to the first embodiment is calculated by a high-frequency three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator). . FIG. 6 is a diagram comparing the behavior at 30 GHz and the behavior at 40 GHz with respect to the relationship between the diameter of the large diameter portion and the reflection characteristics. FIG. 7 is a graph showing the relationship between the S11 characteristics at 30 GHz and 40 GHz for each diameter of the large diameter portion according to the amount of protrusion of the first lead terminal from the first surface in the first embodiment. FIG. 8 is a schematic top view of the optical module according to the first embodiment.

  A first embodiment of the present disclosure will be described below with reference to the drawings.

  FIG. 1 is an external view of an optical module 1 for optical communication according to the present embodiment. A modulated electric signal is transmitted from a driving IC (not shown) mounted on the PCB 200 to the optical subassembly 100 via the FPC 300 connected to the PCB 200 by soldering or the like. The optical subassembly 100 has an interface that accommodates an optical element and transmits and receives outgoing light or incident light. The optical subassembly 100 includes an eyelet 120 and an optical receptacle 2. The specific structure of the optical receptacle 2 will be described later with reference to FIG. Although not shown, the optical subassembly 100, the PCB 200, and the FPC 300 are built in a case made of metal or the like, and the optical module 1 is configured.

  Here, as an example of the optical subassembly 100, an optical transmitter module (TOSA: Transmitter Optical Subassembly) that internally has a light emitting element such as a laser diode and converts an electric signal into an optical signal and transmits the signal, An optical receiver module (ROSA; Receiver Optical Subassembly) that has a light receiving element represented by a diode and converts received optical signals into electric signals, and a bidirectional module (BOSA; Bidirectional Optical Subassembly) incorporating both of these functions )and so on. The present invention can be applied to any of the above optical subassemblies, and in the present embodiment, an optical transmission module will be described as an example.

  FIG. 2 is a schematic perspective view illustrating the internal structure of the optical subassembly 100 according to the first embodiment of the present disclosure. The optical subassembly 100 has, for example, a disk-shaped conductive eyelet 120 having a diameter of 5.6 mm and made of metal. The eyelet 120 has a first surface 121 and a second surface 122 disposed on the opposite side of the first surface 121. Further, the eyelet 120 has a first through hole 123 and a second through hole 126 penetrating from the first surface 121 to the second surface 122.

  Further, the optical subassembly 100 includes a pedestal 124 protruding from the first surface 121 of the eyelet 120 in the direction in which the first through hole 123 extends. The pedestal 124 has a third surface 125 on which an element mounting substrate 140 on which an optical element 160 for converting at least one of an optical signal and an electric signal is converted to the other is mounted. The eyelet 120 and the pedestal 124 form a stem.

  In the present embodiment, the element mounting substrate 140 is made of a ceramic such as aluminum nitride having a thermal expansion coefficient close to that of the optical element 160, and the optical element 160 is die-bonded to the element mounting substrate 140. The element mounting board 140 has a metallized pattern on the front and back surfaces, and the back surface of the element mounting board 140 is connected to a pedestal 124 of a stem that serves as a ground conductor. On the surface (mounting surface) side of the element mounting substrate 140 on which the optical element 160 is mounted, a second conductor pattern 141 (see FIG. 8) serving as a transmission line is formed.

  A first lead terminal 110 for transmitting an electric signal is inserted into the first through hole 123 of the eyelet 120, and a dielectric material is provided between the first through hole 123 and the first lead terminal 110. 130 are filled. The eyelet 120, the dielectric 130, and the first lead terminal 110 form a coaxial line. Hereinafter, this coaxial line is referred to as a “glass coaxial section”.

  On the third surface 125, the above-described element mounting board 140 and the relay board 150 for transmitting an electric signal to the optical element 160 are mounted. In the example illustrated in FIG. 2, an example is illustrated in which the third surface 125 has a step between a region where the element mounting substrate 140 is mounted and a region where the relay substrate 150 is mounted. However, a configuration in which no step is provided between both regions may be adopted. In this embodiment, a spacer 170 is arranged between the relay board 150 and the third surface 125. Although details of the spacer 170 will be described later, both surfaces of the spacer 170 in contact with the relay board 140 and the surface in contact with the third surface 125 are at the ground potential.

  However, as shown in FIG. 2, the region on the third surface 125 where the element mounting substrate 140 is mounted is higher than the region where the relay substrate 150 is mounted (in the direction orthogonal to the third surface 125). , Near the center of the eyelet 120). As described later, when matching the characteristic impedance of the glass coaxial portion to 50 ohms, it is necessary to increase the diameter of the first through hole 123. Here, in the manufacturing process, it is desirable that the first through-hole 123 and the pedestal 124 do not overlap when viewed from the extending direction of the first lead terminal 110. That is, when the first through-hole 123 and the pedestal 124 are not overlapped with each other when viewed from the extending direction of the first lead terminal 110, the first pedestal 124 and the eyelet 120 are integrally formed. It is desirable to easily form the through hole 123. If the first through hole 123 and the pedestal 124 do not overlap each other, the pedestal 124 needs to be provided so as to avoid the first through hole 123 having a large diameter. It is necessary to shift the region to be placed from the center position. On the other hand, the optical element 160 needs to be arranged at the center of the eyelet 120. Therefore, the third surface 125 has a step so that the region where the element mounting substrate 140 on which the optical element 160 is mounted is placed higher than the region where the relay substrate 150 is mounted. By doing so, it is possible to increase the diameter of the first through-hole 123 while keeping the position of the optical element 160 at the center without lowering the efficiency in the manufacturing process, and to reduce the characteristic impedance of the glass coaxial portion by 50. It can be matched to an ohm. Sufficient characteristics can be obtained by matching to 50 ohms ± 10 ohms.

  In the present embodiment, the first lead terminal 110 for transmitting the modulated electric signal includes a small-diameter portion 114 and a large-diameter portion 115 provided at an end of the small-diameter portion 114 and having a larger diameter than the small-diameter portion 114. Including. At least a part of the large-diameter portion 115 is exposed from the first surface 121 on the first surface 121 side. The large-diameter portion 115 and the first conductor pattern 152 placed on the relay board 150 are soldered. For example, the large-diameter portion 115 of the first lead terminal 110 and the relay board 150 are connected by the solder 70 made of a gold-tin alloy or the like.

  With such a configuration, further impedance matching can be realized in the optical module 1 in which the first lead terminal 110 and the relay board 150 are soldered.

  That is, when the first lead terminal 110 and the relay board 150 are soldered, the transmission of the electric signal between the first lead terminal 110 and the relay board 150 is performed linearly. On the other hand, the return current propagating through the ground conductor bypasses the first through hole 123, passes through the pedestal 124, and is transmitted to the relay board 150 via the spacer 170, so that the inductance component increases. This makes it more difficult to perform impedance matching. However, as described above, by configuring the first lead terminal 110 to have the large-diameter portion 115 at the first end 111 protruding from the first surface 121, the large-diameter portion 115 and the first The capacitance component between the through-hole 123 and the inner peripheral surface can be increased. Therefore, the inductance component can be reduced by the capacitance component, and impedance matching can be performed.

  In particular, as will be described later, when the characteristic impedance of the glass coaxial portion is set to around 50 ohms, it is necessary to increase the diameter of the first through hole 123, and the distance between the pedestal 124 and the first lead terminal 110 is increased. Increases, causing an increase in the inductance component with an increase in the path of the return current. Therefore, the necessity and merit of impedance matching by increasing the capacitance component between the large-diameter portion 115 and the first through hole 123 described above increase.

  More preferably, the first conductor pattern 152 mounted on the relay board 150 has a wide portion 154 at a portion where it is soldered to the large-diameter portion 115 of the first lead terminal 110. Is desirable. With such a configuration, the wide portion 154 can also serve as a stub, and the capacitance component can be increased. As a result, further impedance matching can be performed.

  In addition, as disclosed in Japanese Patent Application Laid-Open No. 2014-107733, there is a method of providing a return path on the surface layer of the relay board to prevent parasitic inductance, but in the present disclosure, as described above, a large diameter With a configuration in which impedance matching is performed by increasing the capacitance component between the portion 115 and the first through hole 123, components can be mounted on the surface of the relay board 150. That is, if a return path serving as a ground conductor is provided on the surface layer of the relay board 150, it becomes difficult to mount components on the surface of the relay board 150. It is not necessary to provide on the surface layer of the substrate 150, and it is possible to mount components on the surface of the relay substrate 150.

  Note that the optical element 160 may be any of a direct modulation laser, an electroabsorption modulator integrated laser, and a combination of a laser and a Mach-Zehnder modulator. An electro-absorption modulator integrated laser (hereinafter, EML) is used. Therefore, the driving impedance is 50 ohms. The modulated electric signal is transmitted to the inside of the optical subassembly 100 by the first lead terminal 110.

  In an optical module for low-speed communication, the characteristic impedance of the glass coaxial portion does not need to be strictly matched to 50 ohms, and may be, for example, about 30 ohms. For example, by using a lead terminal diameter of 0.25 mm, a diameter of the dielectric 130 of 0.8 mm, and glass having a relative dielectric constant of 6.7 as the dielectric 130, a glass coaxial portion could be realized. . This is because, in low-speed applications, signal transmission is possible even with this characteristic impedance, so that miniaturization was prioritized. However, for example, in an optical module for high-speed communication having a transmission rate of 40 Gbit / s or more, a TO-CAN type package having a wide band and a characteristic impedance matched to 50 ohms is required.

  However, the relative permittivity of the glass, which is the dielectric material 130 holding the first lead terminal 110, is 4 to 7, and a physical space is required to match the characteristic impedance of the glass coaxial portion to 50 ohms. I will. For example, in order to provide a coaxial line matched to 50 ohms with glass having a relative dielectric constant of 6.7, the first through hole 123 having a diameter of 2 mm or more is required. Therefore, the size of the optical module 1 is naturally determined by the restriction. Sufficient characteristics can be obtained by matching to 50 ohms ± 10 ohms.

  In the present embodiment, the diameter of the large diameter portion 115 of the first lead terminal 110 is 1.6 times or more and 2.4 times or less the diameter of the second end portion 112 that is the small diameter portion 114. . As a specific example, the diameter of the first lead terminal 110 at the second end 112 is 0.25 mm, while the diameter of the large diameter portion 115 is 0.4 mm.

  FIG. 3 is a schematic diagram illustrating a cross-sectional structure of the optical subassembly 100 according to the present embodiment. As shown in FIG. 3, the optical subassembly 100 according to the present embodiment includes an optical receptacle 2 and an optical package 3. The optical receptacle 2 includes an optical receptacle main body 20, a stub 22, and a sleeve 24.

  The optical receptacle main body 20 according to the present embodiment is configured to include an integrally formed resin member, and has an optical package accommodating portion 20f having a cylindrical outer shape, and an outer diameter smaller than the outer diameter of the optical package accommodating portion 20f. A substantially cylindrical optical fiber insertion portion 20d having an outer diameter. One end surfaces of the optical package housing portion 20f and the optical fiber insertion portion 20d are connected to each other.

  The optical package accommodating portion 20f has a circular concave portion 20a formed coaxially with its outer shape, and has a cylindrical shape.

  The optical receptacle body 20 has a through hole 20b extending coaxially with the outer shape of the optical fiber insertion portion 20d from the tip end surface of the optical fiber insertion portion 20d and reaching the bottom surface of the concave portion 20a formed in the optical package housing portion 20f. Are formed. That is, the optical receptacle main body 20 is formed with the concave portion 20a and the through hole 20b penetrating from the concave portion 20a to the outside.

  The tapered portion 20c formed at the tip of the inner wall surface of the through hole 20b has a tapered shape whose diameter increases outward. Therefore, the connector including the optical fiber 50 is easily inserted into the through hole 20b.

  The optical fiber insertion portion 20d has a flange 20e formed along the outer periphery thereof.

  The stub 22 is configured to include zirconia and the like. The stub 22 has a substantially cylindrical shape having substantially the same diameter as the through hole 20b formed in the optical fiber insertion portion 20d of the optical receptacle main body 20, and holds the optical fiber 50 coaxial with the stub 22. The stub 22 is inserted and fixed in the optical fiber insertion portion 20d of the optical receptacle body 20 by press fitting or the like. The right end face of the stub 22 is obliquely polished. In this way, interference between the light input from the optical fiber 50 and the reflected light is prevented.

  The left side surface of the stub 22 of the optical receptacle 2 is in contact with a connector (not shown) having an optical fiber 50 inserted from the outside into the through hole 20b, and the optical fiber 50 provided in the connector and the stub 22 are held. With the optical fiber 50 to be connected.

  The sleeve 24 is configured to include elastic zirconia or the like. The sleeve 24 has a cylindrical shape having substantially the same diameter as the through hole 20b, and is embedded in a groove provided on the inner wall surface of the optical receptacle body 20. The position of the optical fiber 50 inserted into the optical fiber insertion portion 20d in the through hole 20b can be adjusted by the sleeve 24.

  The optical package 3 includes a spherical lens 30. Further, the optical package 3 includes a lens supporting portion 32 which is a cylindrical member having a bottom and made of metal and having an opening having substantially the same diameter as the lens 30 formed on the bottom surface. The opening of the lens support 32 is formed coaxially with the shape of the bottom surface of the lens support 32. The lens 30 is fitted into the opening of the lens support 32. That is, the lens support 32 supports the lens 30.

  The optical package 3 includes a stem including the eyelet 120 and the pedestal 124 described above.

  The sub-assembly 100 is assembled by bonding and fixing the joint surface between the concave portion 20a of the optical receptacle 2 and the first surface 121 of the eyelet 120. At this time, the lens support portion 32 welded to the eyelet 120 and the lens 30 fitted into the lens support portion 32 are formed so as to enter the concave portion 20a of the optical receptacle 2. That is, the lens 30 and the lens support portion 32 are housed in the concave portion 20 a of the optical receptacle main body 20. The method of bonding the optical receptacle 2 and the optical package 3 is not limited to this.

  FIG. 4 is a schematic plan view of the optical subassembly 100 according to the first embodiment shown in FIG. As shown in FIG. 3, a lens support 32 is welded to the first surface 121 of the eyelet 120. In FIG. 4, the position of the inner periphery 32a of the lens support 32 is indicated by a dashed line. ing. In the present embodiment, an eyelet 120 having a diameter of 5.6 mm is used. As the lens support portion 32 to be combined with the eyelet 120, an inner periphery 32a having a circular shape having a diameter of 3.2 mm is used. An example of use will be described.

  In the present embodiment, in order to match the characteristic impedance of the glass coaxial portion to 50 ohms, the diameter of the first through hole 123 is changed to the second lead terminal 116 into which the second lead terminal 116 for transmitting a DC signal is inserted. The diameter is 1.5 times or more the diameter of the through hole 126. On the other hand, if the diameter of the first through-hole 123 is too large, the degree of freedom of design in the eyelet 120 is reduced, so that the diameter of the first through-hole 123 is three times or less the diameter of the second through-hole 126. And As a specific example of the glass coaxial portion, a low dielectric glass having a relative dielectric constant of about 4 to 5 is used as the dielectric 130, and the diameter of the first through hole 123 is 1.5 mm. In addition, even when using a glass of a low dielectric material having a relative dielectric constant lower than 4 as the dielectric 130, in order to match the characteristic impedance of the glass coaxial portion to 50 ohms, the diameter of the first through-hole 123 is required. Needs to be about 1.2 mm. In this case, when the above-described lens supporting portion 32 having the inner circumference 32a having a diameter of about 3.2 mm is used, as shown in FIG. 4, the lens supporting portion 32 is viewed from the extending direction of the first through hole 123. The area of the first through hole 123 arranged on the inner circumference 32a side is equal to or more than 14% of the area on the inner circumference side of the lens support 32. When using a glass having a relative dielectric constant of about 7, the diameter of the first through hole 123 needs to be 2 mm or more in order to match the characteristic impedance of the glass coaxial portion to 50 ohms. In this case, when the above-described lens support portion 32 having the inner circumference 32a having a diameter of about 3.2 mm is used, the lens support portion 32 is disposed on the inner circumference 32a side of the lens support portion 32 when viewed from the extending direction of the first through hole 123. The area of the first through hole 123 occupies 40% of the area on the inner peripheral side of the lens support portion 32.

  Therefore, in the eyelet 120 according to the present embodiment, the area of the first through-hole 123 disposed on the inner peripheral side of the lens support portion 32 when viewed from the extending direction of the first through-hole 123 is such that the lens support portion is combined. The area defined by the diameter of 32, that is, 14% or more and 40% or less of the area on the inner peripheral side of the lens support portion 32.

  In order to match the characteristic impedance of the glass coaxial portion to 50 ohms, the diameter of the first through hole 123 needs to be 1.2 mm or more as described above. There is a gap of 0.5 mm or more between the gap and the gap. On the other hand, the relay board 150 needs to form a microstrip line having a characteristic impedance of 50 ohms, and depends on the thickness of the relay board 150 and the spacer 170 inserted between the relay board 150 and the eyelet 120 serving as the ground. The line width of the conductor pattern to be formed changes. When aluminum nitride is used as the material forming the relay substrate 150, its relative dielectric constant is 8.7. Therefore, when the thickness of the relay substrate 150 is 0.5 mm, the line width of the conductor pattern is 0.5 mm. There is a need to. However, in the present embodiment, the spacer 170 is interposed between the relay board 150 and the pedestal 124, and the spacer 170 raises the ground potential of the pedestal 124 to the upper surface thereof. Can be made as thin as 0.2 mm, for example. As a result, the line width of the first conductor pattern 152 formed on the relay board 150 can be set to 0.2 mm. As shown in FIG. 4, the spacer 170 including the ground conductor overlaps the dielectric 130 when viewed from the direction in which the first lead terminal 110 extends. The spacer 170 may be made of a ceramic such as aluminum nitride, for example, and a plurality of buried via holes may be provided in the ceramic substrate to make the front and back of the spacer 170 conductive. Alternatively, the spacer 170 may be formed of a metal plate having a thickness of 0.3 mm.

  In addition, when the first lead terminal 110 has the large-diameter portion 115, a manufacturing advantage can be obtained in addition to the above-described advantages in terms of characteristics. That is, it is preferable to reduce the area of the relay board 150 for cost reduction. However, if the first lead terminal 110 and the first conductor pattern 152 formed on the relay board 150 are separated from each other when the mounting variation occurs, the first lead terminal 110 and the first conductor pattern 152 The solder 70 made of a gold-tin alloy or the like is not attached during the process, and the production yield is deteriorated. In order to solve this problem, the first end 111 of the first lead terminal 110 is configured to have the large-diameter portion 115 so that even if the position of the relay board 150 is slightly shifted, the first lead terminal 110 It is possible to join the first end 111 and the first conductor pattern 152 of the relay board 150 with the solder 70. As a result, the size of the relay board 150 can be reduced, which can contribute to cost reduction.

  Next, when the first lead terminal 110 having a diameter of 0.25 mm is used, the diameter of the large diameter portion 115 and the amount of protrusion of the first lead terminal 110 from the first surface 121 are changed. FIGS. 5A and 5B show the results of calculating the reflection characteristics using a high-frequency three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator). FIG. 5A is a table of data used for the simulator, and FIG. 5B is a graph showing calculation results of a high-frequency three-dimensional electromagnetic field simulator HFSS corresponding to the simulation numbers (S1 to S25) described in FIG. 5A. The amount of protrusion of the first lead terminal 110 from the first surface 121 means the distance between the end surface of the large-diameter portion 115 and the first surface 121 in the direction in which the first through hole 123 extends. . In FIG. 5B, the horizontal axis represents the frequency of the transmitted electric signal, and the vertical axis represents the electric signal transmitted from the second end 112 of the first lead terminal 110, which is transmitted to the first end 111. The signal level when returning to the second end 112 is shown again. Therefore, it is desirable that S11 [dB], which is the value on the vertical axis, be a small value.

  As shown in FIG. 5B, the behavior of the diameter of the large-diameter portion 115 and the amount of protrusion (pin height) of the first lead terminal 110 are different between the 30 GHz band and the 40 GHz band. The diameter of the portion 115 is preferably 0.55 mm or more, but conversely, it is optimally about 0.35 mm in the 30 GHz band.

  FIG. 6 is a diagram comparing the behavior at 30 GHz and the behavior at 40 GHz with respect to the relationship between the diameter of the large diameter portion 115 and the reflection characteristics. In this simulation, the protrusion amount (pin height) of the first lead terminal 110 is set to 0.1 mm, and the diameter of the small diameter portion 114 is set to 0.25 mm.

  In order to realize a broadband transmission path, S11 is preferably -15 dB or less in a wide frequency range. As shown in FIG. 6, when the diameter of the large diameter portion 115 is 0.4 mm to 0.6 mm when the first lead terminal 110 having the small diameter portion 114 having a diameter of 0.25 mm is used, transmission is performed. It can be seen that S11 can be -15 dB or less regardless of whether the frequency of the electric signal is 30 GHz or 40 GHz. Therefore, the diameter of the large diameter portion 115 of the first lead terminal 110 in this embodiment is 1.6 to 2.4 times the diameter of the small diameter portion 114 such as the second end 112. Is desirable.

  FIG. 7 is a graph showing the relationship between the S11 characteristics at 30 GHz and 40 GHz for each diameter of the large diameter portion for each protrusion amount (pin height) of the first lead terminal 110 from the first surface 121. is there. In FIG. 7, the protrusion amount (pin height) of the first lead terminal 110 is shown in a range of 0.2 mm or less. The reason for selecting this range is as follows. First, if the protrusion amount (pin height) of the first lead terminal 110 is set to be larger than 0.2 mm, the distance between the outer peripheral surface of the large-diameter portion 115 and the inner peripheral surface of the first through hole 123 becomes larger. As a result, the capacitance component between the outer peripheral surface of the large diameter portion 115 and the inner peripheral surface of the first through hole 123 becomes small. In addition, the air that is interposed between the outer peripheral surface of the large diameter portion 115 and the inner peripheral surface of the first through hole 123 is not the dielectric 130 but air, so that the outer peripheral surface of the large diameter portion 115 is The relative dielectric constant between the first through hole 123 and the inner peripheral surface becomes small. Therefore, the above-mentioned capacitance component becomes small. Furthermore, since the relative dielectric constant around the large diameter portion 115 decreases, the inductance component increases. Therefore, it is difficult to reduce the inductance component by the capacitance component, and it becomes difficult to match the characteristic impedance. Therefore, in the present embodiment, the protrusion amount (pin height) of the first lead terminal 110 is in a range of 0.2 mm or less.

  As shown in FIG. 7, when the protrusion amount (pin height) of the first lead terminal 110 is changed in the range of 0 to 0.2 mm, the protrusion amount (pin height) of the first lead terminal 110 becomes It can be seen that the smaller the value, the smaller S11 can be. However, even if the protrusion amount (pin height) of the first lead terminal 110 is changed in the range of 0 to 0.2 mm, S11 at each frequency (30 GHz, 40 GHz) is changed. The amount of change is very small, and it can be seen that the ideal diameter of the large diameter portion 115 is about 0.5 mm in any situation. Therefore, it can be said that the projection amount (pin height) of the first lead terminal 110 in the optical module 1 according to the present embodiment is desirably 0 to 0.2 mm.

  FIG. 8 is a schematic top view of the optical module 1 according to the present embodiment. In the present embodiment, as shown in FIG. 8, vias 142 serving as pillars of the ground potential and castellations 144 are arranged on both sides of the high-frequency line. The via 142 has a through hole filled with a conductor, and conducts between the front and back surfaces of the element mounting substrate 140 (the mounting surface on which the optical element 160 is mounted and the rear surface). The castellation 144 has a concave notch provided from the front surface to the rear surface of the element mounting substrate 140, and a metal film is formed on the inner peripheral surface of the concave shape. The castellations 144 conduct the front and back surfaces of the element mounting substrate 140 (the mounting surface on which the optical element 160 is mounted and the rear surface). The ground pattern 146 provided on the front surface (mounting surface) side of the element mounting board 140 is electrically connected to the ground layer on the back surface of the element mounting board 140 via vias 142, castellations 144, and the like. The position of the via 142 is not particularly limited if the purpose is merely conduction between the front and back surfaces, but the position and the number of the via 142 are important from the viewpoint of high frequency. In the case of the present embodiment, a high-frequency signal is transmitted from the relay board 150 to the element mounting board 140 by the plurality of first wires 182, and then passes through the second conductor pattern 141 on the element mounting board 140 to the second Is transmitted to the modulation element 186 via the wire 184. As the modulation element 186 in this embodiment, for example, an electro-absorption modulator can be used. In the transmission section of the high-frequency electric signal, it is advantageous in terms of characteristics that a ground potential exists around the high-frequency electric signal in order to confine the electromagnetic field of the high-frequency signal. In the present embodiment, the ground pattern 146 on the front surface of the element mounting substrate 140 and the ground layer on the back surface are connected by vias 142 and castellations 144 near the connection between the relay substrate 150 and the element mounting substrate 140. I have. Further, since there is a region connecting the ground pattern 146 on the front surface (mounting surface) of the element mounting substrate 140 and the ground layer on the back surface of the element mounting substrate 140, deterioration of high frequency characteristics can be further reduced.

  In the present embodiment, the element mounting board 140 and the relay board 150 are connected by a plurality of first wires 182. With such a configuration, an increase in the inductance component is suppressed, and impedance matching in a high frequency region is enabled.

  On the other hand, transmission of an electric signal from the element mounting board 140 to the optical element 160 is communicated by one second wire 184. This is because it is necessary to reduce the electrode size of the optical element 160 in order to suppress an increase in the parasitic capacitance in the optical element 160. Therefore, in order to suppress the occurrence of an inductance component in the second wire 184, the ground plane 146 is provided on the element mounting board 140 of the present embodiment on both sides of the second wire 184 to provide a strong ground pattern. It constitutes a track. In order to strengthen the ground, a castellation 144 is provided on the light emitting point side of the optical element 160, and a via 142 is provided on the rear side, so that the pedestal 124 serving as a strong ground and the ground pattern 146 are connected in the shortest way. I am trying to. The ground pattern 146 of the element mounting board 140 is connected to the ground potential of the pedestal 124 via the first connection part (for example, via 142) and the second connection part (for example, castellation 144). When viewed from a direction orthogonal to the mounting surface on which the optical element 160 is mounted, a line connecting the first connection part and the second connection part connects the second conductor pattern 141 and the optical element 160. The configuration intersects with the second wire 184. With this configuration, even if the connection between the optical element 160 and the element mounting board 140 is, for example, a connection using a single second wire 184, the increase in the inductance component can be reduced, and up to a high-frequency region. Impedance matching can be realized.

  In this specification, the term “eyelet” representing a metal disk is used. However, the eyelet 120 has a disk shape and has no essential meaning, and may have another shape such as a polygonal pillar.

  Note that the optical subassembly 100 may include a bias for a laser diode as the optical element 160, a bias for a photodiode for monitoring a rear output, and a thermistor terminal for monitoring a laser temperature.

REFERENCE SIGNS LIST 1 optical module, 2 optical receptacle, 3 optical package, 20 optical receptacle main body, 20 a concave portion, 20 b through hole, 20 c tapered portion, 20 d optical fiber insertion portion, 20 e flange, 20 f optical package housing portion, 22 stub, 24 sleeve, 30 Lens, 32 Lens support, 32a Inner circumference, 50 Optical fiber, 70 Solder, 100 Optical subassembly, 110 First lead terminal, 111 First end, 112 Second end, 114 Small diameter, 115 Large Diameter part, 116 second lead terminal, 120 eyelet, 121 first surface, 122 second surface, 123 first through hole, 124 pedestal, 125 third surface, 126 second through hole, 130 dielectric Body, 140 element mounting board, 141 second conductor pattern, 142 via, 144 castellation, 146 glau Cable pattern, 150 relay board, 152 first conductor pattern, 154 wide part, 160 optical element, 170 spacer, 182 first wire, 184 second wire, 186 modulation element, 200 PCB, 300 FPC.

Claims (12)

An eyelet including a first surface, a second surface disposed on the opposite side of the first surface, and a first through hole penetrating from the first surface to the second surface. ,
A first lead terminal inserted into the first through-hole and transmitting an electric signal;
A dielectric filled between the first through hole and the first lead terminal;
An element mounting board on which an optical element for converting at least one of the optical signal and the electric signal to the other is mounted,
A relay board including a first conductor pattern that transmits the electric signal to the optical element;
A pedestal on which the relay board and the element mounting board are mounted, protruding from the first surface in a direction in which the first through hole extends,
The first lead terminal includes a small-diameter portion, and a large-diameter portion provided at an end of the small-diameter portion and having a larger diameter than the small-diameter portion,
At least a portion of the large diameter portion is exposed from the dielectric on the first surface side,
The first lead terminal and the first conductor pattern are soldered,
Optical sub-assembly. The optical subassembly according to claim 1, wherein:
The first conductor pattern has a wide portion brazed to the large diameter portion,
Optical sub-assembly. An optical subassembly according to claim 1 or 2,
The diameter of the large diameter portion is 1.6 times or more and 2.4 times or less the diameter of the small diameter portion;
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 3, wherein
The distance between the end surface of the large diameter portion and the first surface in the extending direction of the first through hole is 0 mm or more and 0.2 mm or less.
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 4, wherein:
A lens support welded to the first surface;
A lens fixed to the opening of the lens support portion,
The area of the first through hole disposed on the inner peripheral side of the lens support portion, as viewed from the extending direction of the first through hole, is 14% or more of the area of the inner peripheral side of the lens support portion; Less than 40%,
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 5,
The characteristic impedance of the coaxial line formed by the eyelet, the dielectric, and the first lead terminal is 50 ± 10 ohms.
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 6, wherein
A transmission rate of the electric signal is 40 Gbit / s or more;
Optical sub-assembly. The optical subassembly according to claim 1, wherein:
A second through hole penetrating from the first surface to the second surface;
A second lead terminal inserted into the second through-hole and transmitting a DC signal,
The diameter of the first through hole is 1.5 times or more and 3 times or less the diameter of the second through hole.
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 8, wherein:
The element mounting board further includes a second conductor pattern that transmits the electric signal to the optical element,
The first conductor pattern and the second conductor pattern are connected by a plurality of first wires,
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 9, wherein:
The element mounting board,
A second conductor pattern provided on the mounting surface side of the optical element and transmitting the electric signal to the optical element;
A first connection portion connected to a ground potential of the pedestal, and a second connection portion, which conducts the mounting surface and the back surface of the element mounting substrate;
A ground pattern provided on the mounting surface side and further connected to the ground potential of the pedestal via the first connection portion and the second connection portion;
The second conductor pattern and the optical element are connected by a second wire,
The second conductor pattern, the first connection portion, the second connection portion, and the ground pattern constitute a grand coplanar line.
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 10, wherein:
Further including a ground conductor overlapping with the dielectric when viewed from the extending direction of the first lead terminal,
Optical sub-assembly. An optical subassembly according to any one of claims 1 to 11,
A printed circuit board,
A flexible substrate electrically connected to the printed circuit board and the optical sub-assembly,
Optical module.

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