JP7249745B2 - Optical subassemblies and optical modules - Google Patents

Description

The present invention relates to optical subassemblies and optical modules.

Currently, most of the Internet and telephone networks are constructed by optical communication networks. An optical module used as an interface for routers/switches and transmission equipment, which are optical communication devices, plays an important role in converting electrical signals into optical signals. An optical module generally consists of an optical subassembly that houses optical elements, a printed circuit board (PCB) on which ICs for processing signals including modulated electrical signals are mounted, and a flexible printed circuit board that electrically connects them. It takes the form provided with hereinafter FPC).

In recent years, there has been a marked demand not only for higher speed optical modules, but also for lower prices, and the demand for low-cost optical modules capable of transmitting and receiving high-speed optical signals is increasing. For example, as an optical module that satisfies the above-described requirements, a TO-CAN package type optical subassembly or the like having a form in which lead terminals to be inserted into an FPC or the like protrude from a metal stem contained in a can-shaped package is used. It is known. The metal stem includes a substantially disk-shaped eyelet and a base that protrudes from the eyelet.

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

It is difficult to match the characteristic impedance to a desired value in a TO-CAN optical subassembly that uses lead terminals as an electrical interface. In order to prevent this, a dielectric substrate is inserted directly under the lead terminals, and the high dielectric constant of the dielectric substrate strengthens the electrical coupling with the pedestal, which acts as a ground conductor. prevent an increase.

Further, the connection between the lead terminal and the dielectric substrate is not wire connection but solder connection, thereby suppressing generation of an unnecessary inductance component. In addition, the configuration facilitates connection between the lead terminal and the dielectric substrate.

JP 2017-50357 A Japanese Unexamined Patent Application Publication No. 2011-134740

In recent years, there has been a remarkable demand for higher speed, and for example, the demand for optical modules with a transmission rate of 40 Gbit/s class or higher is increasing. In order to realize a design that meets such a demand for further speeding up, it is necessary to perform impedance matching more strictly, 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 must be a desired value determined from the dielectric constant of the dielectric filling the through hole and the diameter of the lead terminal. As a result, a large gap may occur between the pedestal and the lead terminal. The return current that propagates through the ground conductor bypasses the through hole and propagates to the dielectric substrate via the pedestal. It has become more difficult to strictly perform

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

In order to solve the above problems, an optical subassembly according to the present disclosure includes a first surface, a second surface arranged on the opposite side of the first surface, and an optical subassembly extending from the first surface to the second surface. a first through hole that penetrates to the surface of the eyelet; a first lead terminal that is inserted into the first through hole and transmits an electrical signal; the first through hole and the first a dielectric filled between the lead terminals of the device, an element mounting board mounted with an optical device that converts at least one of an optical signal and the electrical signal to the other, and a second device that transmits the electrical signal to the optical device a relay board including one conductor 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; 1 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; The first lead terminal and the first conductor pattern exposed from the dielectric are brazed on the surface side.

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

Further impedance matching can be achieved with the optical subassemblies and optical modules of the present disclosure.

FIG. 1 is an external view of the optical module according to the first embodiment. FIG. 2 is a schematic diagram showing the internal structure of the optical subassembly according to the first embodiment. FIG. 3 is a schematic diagram showing the 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 obtained by calculating 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, using 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 S11 characteristics at 30 GHz and 40 GHz for each diameter of the large-diameter portion for each protrusion amount from the first surface of the first lead terminal 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 this embodiment. A modulated electric signal is transmitted from a drive 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 contains an optical element and has an interface for transmitting and receiving outgoing light or incoming light. Optical subassembly 100 includes eyelet 120 and optical receptacle 2 . A 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 housed in a housing made of metal or the like to form the optical module 1. FIG.

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

FIG. 2 is a schematic perspective view showing the internal structure of the optical subassembly 100 according to the first embodiment of the present disclosure. The optical subassembly 100 has a conductive eyelet 120 made of metal, for example in the shape of a disk with a diameter of 5.6 mm. Eyelet 120 has a first side 121 and a second side 122 located opposite first side 121 . The eyelet 120 also has a first through hole 123 and a second through hole 126 penetrating from the first surface 121 to the second surface 122 .

The optical subassembly 100 also includes a pedestal 124 that protrudes from the first surface 121 of the eyelet 120 in the extending direction of the first through hole 123 . The pedestal 124 has a third surface 125 on which a device mounting substrate 140 mounted with an optical device 160 that converts at least one of an optical signal and an electrical signal to the other is mounted. The eyelet 120 and the base 124 constitute a stem.

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

A first lead terminal 110 for transmitting electrical signals 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 is filled. The eyelet 120, the dielectric 130, and the first lead terminal 110 form a coaxial line. Hereinafter, this coaxial line will be referred to as a "glass coaxial portion".

On the third surface 125, the element mounting board 140 described above and the relay board 150 for transmitting electrical signals to the optical element 160 are mounted. In the example shown in FIG. 2, the third surface 125 has a step between the area where the element mounting board 140 is mounted and the area where the relay board 150 is mounted. However, a configuration in which no step is provided between the two regions may be employed. Note that a spacer 170 is arranged between the relay substrate 150 and the third surface 125 in this embodiment. Although the details of the spacer 170 will be described later, both the surface of the spacer 170 in contact with the relay substrate 140 and the surface in contact with the third surface 125 are at ground potential.

However, as shown in FIG. 2, the area of the third surface 125 on which the element mounting substrate 140 is mounted is higher than the area on which the relay substrate 150 is mounted (in the direction orthogonal to the third surface 125). , near the center position of the eyelet 120). As will be described later, when matching the characteristic impedance of the glass coaxial portion to 50 ohms, the diameter of the first through hole 123 must be increased. Here, in view of the manufacturing process, it is desirable that the first through-hole 123 and the base 124 do not overlap when viewed from the extending direction of the first lead terminal 110 . That is, when viewed from the extending direction of the first lead terminal 110, the first through hole 123 and the pedestal 124 are configured so as not to overlap each other. It is desirable because the through hole 123 can be easily formed. If a configuration in which the first through-hole 123 and the pedestal 124 are not overlapped is adopted, the pedestal 124 must be provided so as to avoid the first through-hole 123 having a large diameter. It is necessary to shift the area where the On the other hand, the optical element 160 should be placed in the center position of the eyelet 120 . Therefore, the third surface 125 has a step so that the area where the element mounting substrate 140 on which the optical element 160 is mounted is placed at a higher position than the area where the relay substrate 150 is mounted. As a result, the diameter of the first through-hole 123 can be increased while maintaining the position of the optical element 160 at the central position without lowering the efficiency of the manufacturing process. Ohms can be matched. Sufficient characteristics can be obtained by matching to 50 ohms±10 ohms.

In this embodiment, the first lead terminal 110 that transmits the modulated electrical signal has a small diameter portion 114 and a large diameter portion 115 provided at the end of the small diameter portion 114 and having a larger diameter than the small diameter portion 114. include. At least part of large diameter portion 115 is exposed from first surface 121 on the first surface 121 side. The large diameter portion 115 and the first conductor pattern 152 placed on the relay substrate 150 are soldered. For example, the large-diameter portion 115 of the first lead terminal 110 and the relay board 150 are connected by solder 70 made of 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 electrical signal is transmitted linearly between the first lead terminal 110 and the relay board 150 . 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 further transmitted to the relay substrate 150 via the spacer 170, resulting in an increase in the inductance component. 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 portion 111 protruding from the first surface 121, the large-diameter portion 115 and the first It is possible to increase the capacitance component with the inner peripheral surface of the through hole 123 . Therefore, the inductance component can be mitigated 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 increases, the inductance component increases as the number of return current paths increases. Therefore, the necessity and merit of impedance matching by increasing the capacitive component between the large-diameter portion 115 and the first through-hole 123 are increased.

More preferably, the first conductor pattern 152 placed on the relay substrate 150 has a wide portion 154 at the 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, increasing the capacitance component, and as a result, further impedance matching can be achieved.

As disclosed in Japanese Unexamined Patent Application Publication No. 2014-107733, etc., there is a method of providing a return path on the surface layer of the relay substrate to prevent parasitic inductance. Components can be mounted on the surface of the relay substrate 150 by configuring impedance matching by increasing the capacitance component between the portion 115 and the first through hole 123 . That is, if a return path serving as a ground conductor is provided on the surface of the relay board 150, it becomes difficult to mount components on the surface of the relay board 150. It is no longer necessary to provide on the surface layer of the substrate 150, and components can be mounted on the surface of the relay substrate 150. FIG.

The optical device 160 may be a direct modulation laser, an electroabsorption modulator integrated laser, or a combination of a laser and a Mach-Zehnder modulator. , an electro-absorption modulator integrated laser (EML) is used. Therefore, the drive impedance is 50 ohms. The modulated electrical signal is transmitted to the interior of optical subassembly 100 by first lead terminal 110 .

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

However, the relative dielectric constant of glass, which is the dielectric 130 that holds 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. and end up. For example, in order to provide a coaxial line matched to 50 ohms with glass having a dielectric constant of 6.7, the first through hole 123 with a diameter of 2 mm or more is required. Therefore, the size of the optical module 1 is naturally determined under these restrictions. Sufficient characteristics can be obtained by matching to 50 ohms±10 ohms.

In this 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, which is the small-diameter portion 114. . As a specific example, the diameter of the first lead terminal 110 at the second end portion 112 is 0.25 mm, while the diameter of the large diameter portion 115 is 0.4 mm.

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

The optical receptacle body 20 according to the present embodiment includes an integrally formed resin member, and has an optical package housing portion 20f having a cylindrical outer shape and an outer diameter smaller than that of the optical package housing portion 20f. and a substantially cylindrical optical fiber insertion portion 20d having an outer diameter. The optical package accommodating portion 20f and the optical fiber insertion portion 20d are connected at their one end surfaces.

A circular concave portion 20a is formed coaxially with the outer shape of the optical package housing portion 20f to form a cylindrical shape.

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

A tapered portion 20c formed at the tip of the inner wall surface of the through hole 20b has a tapered shape in which the diameter increases toward the outside. Therefore, the connector having the optical fiber 50 can be easily inserted into the through hole 20b.

A flange 20e is formed along the outer periphery of the optical fiber insertion portion 20d.

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

The left side surface of the stub 22 of the optical receptacle 2 is brought into contact with a connector (not shown) having an optical fiber 50 inserted into the through hole 20b from the outside, and the optical fiber 50 and the stub 22 are held by the connector. coupling with the optical fiber 50 is performed.

The sleeve 24 is made of elastic zirconia or the like. The sleeve 24 has a cylindrical shape with substantially the same diameter as the through hole 20 b and is embedded in a groove provided in the inner wall surface of the optical receptacle main body 20 . The sleeve 24 allows the position of the optical fiber 50 inserted into the optical fiber insertion portion 20d to be adjusted within the through hole 20b.

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

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

The subassembly 100 is assembled by adhesively fixing the joint surface between the concave portion 20 a of the optical receptacle 2 and the first surface 121 of the eyelet 120 . At this time, the lens supporting portion 32 welded to the eyelet 120 and the lens 30 fitted in the lens supporting portion 32 are formed to be inserted into the concave portion 20 a of the optical receptacle 2 . That is, the lens 30 and the lens supporting portion 32 are accommodated in the concave portion 20 a of the optical receptacle body 20 . The method for bonding the optical receptacle 2 and the optical package 3 is not limited to this.

4 is a schematic plan view of the optical subassembly 100 according to the first embodiment shown in FIG. 2. FIG. As shown in FIG. 3, the lens supporting portion 32 is welded to the first surface 121 of the eyelet 120, and in FIG. ing. In this embodiment, an eyelet 120 with a diameter of 5.6 mm is used, and the lens supporting portion 32 combined with this eyelet 120 has a circular inner circumference 32a with a diameter of 3.2 mm. An example of use will be described.

In this 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 set to the second diameter through which the second lead terminal 116 for transmitting the DC signal is inserted. It 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 design freedom within the eyelet 120 is reduced. and As a specific example of the glass coaxial portion, a low dielectric glass having a 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. Note that even when a low-dielectric glass material having a dielectric constant lower than 4 is used as the dielectric 130, the diameter of the first through-hole 123 must be equal to should be about 1.2 mm. In this case, if the lens supporting portion 32 having the inner circumference 32a with a diameter of about 3.2 mm is used, as shown in FIG. The area of the first through hole 123 arranged on the inner periphery 32a side is 14% or more of the area of the lens supporting portion 32 on the inner periphery side. When glass having a dielectric constant of about 7 is used, the diameter of the first through hole 123 must be 2 mm or more in order to match the characteristic impedance of the glass coaxial portion to 50 ohms. In this case, if the above-described lens support portion 32 having an inner circumference 32a with a diameter of about 3.2 mm is used, then the lens support portion 32 is arranged 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 thus formed occupies 40% of the area of the inner peripheral side of the lens supporting portion 32 .

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

In order to match the characteristic impedance of the glass coaxial portion to 50 ohms, as described above, the diameter of the first through hole 123 must be 1.2 mm or more. 124, a gap of 0.5 mm or more is created. On the other hand, the relay substrate 150 must form a microstrip line with a characteristic impedance of 50 ohms. The line width of the conductor pattern formed in . When aluminum nitride is used as the material forming the relay board 150, its dielectric constant is 8.7. There is a need to. However, in this embodiment, the spacer 170 is interposed between the relay substrate 150 and the base 124, and the spacer 170 raises the ground potential of the base 124 to the upper surface thereof. can be made as thin as 0.2 mm, for example. As a result, it is possible to set the line width of the first conductor pattern 152 formed on the relay board 150 to 0.2 mm. As shown in FIG. 4, the spacer 170 including the ground conductor overlaps the dielectric 130 when viewed from the extending direction of the first lead terminal 110 . The spacer 170 may be made of a ceramic such as aluminum nitride, and a plurality of embedded via holes may be provided in the ceramic substrate so that the front and back surfaces of the spacer 170 are electrically connected. Alternatively, the spacer 170 may be made of a metal plate with a thickness of 0.3 mm.

By configuring the first lead terminal 110 to have the large-diameter portion 115, it is possible to obtain not only the advantages of the characteristics described above but also the advantages of manufacturing. That is, it is preferable to reduce the area of the relay substrate 150 for cost reduction. However, when mounting variations occur, if the first lead terminal 110 and the first conductor pattern 152 formed on the relay substrate 150 are separated from each other, the first lead terminal 110 and the first conductor pattern 152 may become separated from each other. The solder 70 made of a gold-tin alloy or the like does not stick between them, which deteriorates the manufacturing yield. To solve this problem, by configuring the first end portion 111 of the first lead terminal 110 as the large-diameter portion 115, even if the position of the relay substrate 150 is slightly deviated, the first lead terminal 110 and the first conductor pattern 152 of the relay board 150 can be joined with the solder 70 . Moreover, 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 with 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. FIG. 5A and FIG. 5B show the results of calculation of reflection characteristics by a high-frequency three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator). FIG. 5A is a table of data used in the simulator, and FIG. 5B is a graph showing calculation results of the high-frequency three-dimensional electromagnetic field simulator HFSS corresponding to the simulation numbers (S1 to S25) shown in FIG. 5A. The amount of protrusion of first lead terminal 110 from first surface 121 means the distance between the end surface of large-diameter portion 115 and first surface 121 in the extending direction of first through-hole 123 . . In FIG. 5B, the horizontal axis represents the frequency of the transmitted electrical signal, and the vertical axis represents the electrical signal transmitted from the second end 112 side of the first lead terminal 110, which is transmitted to the first end 111, Again, it represents the signal level upon returning to the second end 112 . 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 diameter of the large-diameter portion 115 and the amount of protrusion (pin height) of the first lead terminal 110 in particular differ between the 30 GHz band and the 40 GHz band. The diameter of the portion 115 is preferably 0.55 mm or more, but in the 30 GHz band, the optimum diameter is about 0.35 mm.

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 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 wideband transmission line, S11 is preferably −15 dB or less over a wide frequency range. As shown in FIG. 6, in the case of using the first lead terminal 110 in which the diameter of the small diameter portion 114 is 0.25 mm, if the diameter of the large diameter portion 115 is 0.4 mm to 0.6 mm, the transmission It can be seen that S11 can be reduced to -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 should be 1.6 to 2.4 times the diameter of the small-diameter portion 114 such as the second end portion 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 of the first lead terminal 110 by the protrusion amount (pin height) from the first surface 121. be. In addition, in FIG. 7, the projection amount (pin height) of the first lead terminal 110 is shown in the 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 made 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 Since they are separated from each other, 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, instead of the dielectric 130, air is interposed between the outer peripheral surface of the large-diameter portion 115 and the inner peripheral surface of the first through hole 123, so that the outer peripheral surface of the large-diameter portion 115 and the first The dielectric constant between the through hole 123 of 1 and the inner peripheral surface becomes small. Therefore, the capacitance component mentioned above becomes small. Furthermore, the inductance component increases due to the decrease in the dielectric constant around the large-diameter portion 115 . Therefore, it becomes difficult to relax the inductance component with the capacitance component, and characteristic impedance matching becomes difficult. Therefore, in the present embodiment, the protrusion amount (pin height) of the first lead terminal 110 is set to 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 is It can be seen that the smaller the value, the smaller the S11. 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 protrusion amount (pin height) of the first lead terminal 110 in the optical module 1 according to this embodiment is preferably 0 to 0.2 mm.

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

Further, in this embodiment, the element mounting board 140 and the relay board 150 are connected by a plurality of first wires 182 . Such a configuration suppresses an increase in inductance component and enables impedance matching in a high frequency region.

On the other hand, a single second wire 184 is used for transmission of electrical signals from the device mounting board 140 to the optical device 160 . This is because the electrode size of the optical element 160 needs to be reduced in order to suppress an increase in parasitic capacitance in the optical element 160 . Therefore, in order to suppress the generation of the inductance component in the second wire 184, the device mounting substrate 140 of the present embodiment is provided with strong ground patterns 146 on the left and right sides of the second wire 184 to provide a grounded coplanar structure. constitutes the line. 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 at the shortest distance. I'm trying to A ground pattern 146 of the element mounting board 140 is connected to the ground potential of the pedestal 124 via a first connecting portion (for example via 142) and a second connecting portion (for example castellation 144). , the line segment connecting the first connection portion and the second connection portion connects the second conductor pattern 141 and the optical element 160 when viewed from the direction orthogonal to the mounting surface on which the optical element 160 is mounted. It is configured to intersect with the second wire 184 . With this configuration, even if the connection between the optical device 160 and the device mounting board 140 is, for example, a connection by a single second wire 184, it is possible to reduce the increase in the inductance component, and the Impedance matching can be achieved.

In the present specification, the word eyelet is used to represent a metal disk, but it is not essential that the eyelet 120 has a disk shape, and other shapes such as a polygonal prism may be used.

The optical subassembly 100 may include a bias to a laser diode, which is the optical element 160, a bias to a photodiode for monitoring rear output, and a thermistor terminal for monitoring the laser temperature.

1 optical module, 2 optical receptacle, 3 optical package, 20 optical receptacle body, 20a concave portion, 20b through hole, 20c taper portion, 20d optical fiber insertion portion, 20e flange, 20f optical package housing portion, 22 stub, 24 sleeve, 30 Lens 32 Lens supporting portion 32a Inner circumference 50 Optical fiber 70 Solder 100 Optical subassembly 110 First lead terminal 111 First end 112 Second end 114 Small diameter portion 115 Large Radial portion 116 Second lead terminal 120 Eyelet 121 First surface 122 Second surface 123 First through hole 124 Base 125 Third surface 126 Second through hole 130 Dielectric body 140 element mounting board 141 second conductor pattern 142 via 144 castellation 146 ground pattern 150 relay board 152 first conductor pattern 154 wide portion 160 optical element 170 spacer 182 first 184 second wire, 186 modulating element, 200 PCB, 300 FPC.

Claims (12)

an eyelet including a first surface, a second surface arranged 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 that is inserted into the first through hole and transmits an electrical signal;
a dielectric filled between the first through hole and the first lead terminal;
a device mounting board on which an optical device for converting at least one of an optical signal and the electrical signal to the other is mounted;
a relay board including a first conductor pattern that transmits the electrical signal to the optical element;
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 includes a small-diameter portion and a large-diameter portion provided only at one end of the small-diameter portion and having a larger diameter than the small-diameter portion,
a portion of the large diameter portion is exposed from the dielectric and protrudes from the first surface on the first surface side;
the portion of the large-diameter portion of the first lead terminal and the first conductor pattern are soldered ;
The other portion of the large diameter portion is inside the first through hole and is not exposed from the dielectric.
optical subassemblies. The optical subassembly of claim 1, comprising:
The first conductor pattern has a wide portion soldered to the large diameter portion,
optical subassemblies. 3. 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 than the diameter of the small diameter portion.
optical subassemblies. An optical subassembly according to any one of claims 1 to 3,
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 subassemblies. An optical subassembly according to any one of claims 1 to 4,
a lens support welded to the first surface;
a lens secured to the aperture of the lens support;
The area of the first through-hole arranged on the inner peripheral side of the lens supporting portion when 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 supporting portion, is 40% or less,
optical subassemblies. 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 subassemblies. An optical subassembly according to any one of claims 1 to 6,
The electrical signal has a transmission rate of 40 Gbit/s or higher.
optical subassemblies. An optical subassembly according to any one of claims 1 to 7,
a second through hole penetrating from the first surface to the second surface;
a second lead terminal that is inserted into the second through hole and transmits 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 subassemblies. 9. An optical subassembly according to any one of claims 1 to 8,
The device mounting board further includes a second conductor pattern for transmitting the electrical signal to the optical device,
wherein the first conductor pattern and the second conductor pattern are connected by a plurality of first wires,
optical subassemblies. An optical subassembly according to any one of claims 1 to 9,
The device mounting board is
a second conductor pattern provided on the mounting surface side of the optical element and transmitting the electrical signal to the optical element;
a first connection portion and a second connection portion that electrically connect the mounting surface and the back surface of the element mounting board and are connected to the ground potential of the pedestal;
a ground pattern provided on the mounting surface side and connected to a 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 connecting portion, the second connecting portion, and the ground pattern constitute a grounded coplanar line,
optical subassemblies. An optical subassembly according to any one of claims 1 to 10,
further comprising a ground conductor that overlaps with the dielectric when viewed from the extending direction of the first lead terminal;
optical subassemblies. 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 subassembly,
optical module.

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