JP2021077858A - Optical sub-assembly - Google Patents

Abstract

To provide an optical sub-assembly that is small and easy to be manufactured, and has good high-frequency characteristics.SOLUTION: An optical sub-assembly includes an eyelet including a first surface, a second surface, and a plurality of through-holes, a plurality of lead terminals in which a differential electric signal is inputted, a lead connection surface extending in a normal direction of the first surface, and a first bonding surface adjacent to the lead connection surface. First and second conductor patterns are formed over the lead connection surface and the first bonding surface. The first and conductor patterns formed on the lead connection surface include a relay substrate which is connected with the lead terminals by soldering and the like and to which the differential electric signal is inputted, an element mounting portion including a second bonding surface on which third and fourth conductor patterns are formed, and an optical element that converts one of an optical signal and the differential electric signal into the other. The first and second conductor patterns are connected with the third and fourth conductor patterns by a bonding wire, and normal directions of the first and second bonding surfaces are the same directions.SELECTED DRAWING: Figure 3

Description

The present invention relates to an optical subassembly.

Currently, most of the Internet and telephone networks are built by optical communication networks. Optical modules used as interfaces for routers / switches and transmission devices, which are optical communication devices, play an important role in converting electrical signals into optical signals. An optical module is generally a printed circuit board (hereinafter referred to as PCB) on which an optical subassembly containing an optical element, an IC for processing a signal including a modulated electric signal, or the like is mounted, and a flexible printed circuit board that electrically connects between them. It takes a form equipped with (hereinafter referred to as FPC).

In recent years, there has been a remarkable demand for optical modules not only for high speed but also for low price, and there is an increasing demand for optical modules capable of transmitting and receiving high-speed optical signals at low cost. For example, as an optical module that satisfies the above requirements, it is known to use a TO-CAN type optical subassembly having a lead terminal that is inserted into an FPC protruding from a metal stem contained in a can-shaped package. ing. The metal stem includes a substantially disk-shaped eyelet and a pedestal provided so as to project from the eyelet.

Further, in recent years, the demand for optical modules is increasing in the field of an interface standard for connecting a control unit and a radio unit of a radio base station called a SFP (Common Public Radio Interface). CPRI is a standard for an interface that connects a radio control unit (Radio Equipment Control; REC) of a radio base station and a radio unit (Radio Equipment; RE). Baseband signal processing, control, and management in the digital domain are performed using REC. Using RE, amplification, modulation / demodulation, filtering, and the like of radio signals in the analog region are performed. By connecting the REC and the RE with an optical signal capable of long-distance transmission, the RE can be used in an outdoor installation space near the antenna away from the base station.

However, in order to support the outdoor installation of RE, it is necessary to operate even in a harsh temperature environment. Therefore, in addition to the price reduction due to market demand, it may be required to operate in a wide temperature range of 40 to 85 ° C. called I-Temp (Industrial temperature range). From the above requirements, the technical requirements for the TO-CAN type optical subassembly that can operate in a wide temperature range and have a wide band are high.

Generally, TO-CAN type optical subassembly is manufactured by modularizing a plurality of small electronic devices into standardized diameter eyelets. On the other hand, in order to use an eyelet having a diameter different from that conventionally used, it is essential to introduce a new manufacturing apparatus. Since the introduction of a new manufacturing device causes an increase in manufacturing cost, it is desirable to use an eyelet having the same diameter as the one used in the past. In the TO-CAN type package, a lead terminal held by a dielectric material such as glass is arranged in a through hole provided in a disk type eyelet. Since an electric signal is transmitted to the optical element using the lead terminal, the area where electronic components other than the lead terminal can be arranged is limited.

Further, when a component such as a temperature adjusting element is arranged, the substrate on which the optical element is mounted is electrically separated from the disk-shaped eyelet that serves as the ground. Therefore, it is difficult to maintain good characteristics of the optical element by grounding the substrate on which the optical element is mounted to the ground potential. Therefore, there is a lot of research on both miniaturization and high frequency characteristics.

Patent Document 1 below discloses a technique for transmitting a high-quality high-frequency signal to an optical element in a small TO-CAN type package.

Japanese Patent No. 4279134

In Patent Document 1, a technique of minimizing the area of the coaxial portion and maximizing the mounting area inside the TO-CAN by including a pair of lead terminals for transmitting a differential signal in one glass through hole is used. It is disclosed. However, it is necessary to provide two lines on the same plane as the area where the optical element is mounted, which limits the area where other components are mounted.

Further, the electronic components and lead terminals arranged inside the TO-CAN type package are connected by wire bonding. The wire bonding is not easy to connect when the orientations of the surfaces to which the wires are connected are different.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical subassembly that is small in size, easy to manufacture, and has good high frequency characteristics.

According to the optical subassembly according to one aspect of the present invention, the first surface, the second surface arranged on the opposite side of the first surface, and a plurality of penetrating surfaces from the second surface to the first surface. An eyelet including a through hole, a plurality of lead terminals inserted into the plurality of through holes and at least partially input with a differential electric signal, and a lead connection surface extending in the normal direction of the first surface. A first conductor pattern and a second conductor pattern are formed across the lead connection surface and the first bonding surface, including a first bonding surface adjacent to the lead connection surface, and formed on the lead connection surface. The first conductor pattern and the second conductor pattern are connected to the lead terminal with solder or a conductive adhesive, and a relay board into which the differential electric signal is input, and a relay board into which the differential electric signal is input. An element mounting portion including a second bonding surface on which a three-conductor pattern and a fourth conductor pattern are formed, and a mounting portion mounted on the element mounting portion, electrically connected to the third conductor pattern and the fourth conductor pattern, and light. The first conductor pattern and the second conductor pattern of the first bonding surface include the signal and an optical element that converts one of the differential electric signals into the other, and the second conductor pattern is the third conductor of the second bonding surface. The pattern and the fourth conductor pattern are connected by a bonding wire, and the normal directions of the first bonding surface and the second bonding surface are the same.

Further, according to the optical subassembly according to another aspect of the present invention, a temperature adjusting element which is arranged in contact with the first surface and adjusts the temperature of the optical element is included.

Further, according to the optical subassembly according to another aspect of the present invention, the subcarrier is further mounted on the temperature control element and mounts the element mounting portion.

Further, according to the optical subassembly according to another aspect of the present invention, the center of gravity of the subcarrier is biased toward the relay board side with respect to the center of gravity of the eyelet.

Further, according to the optical subassembly according to another aspect of the present invention, the number of bonding wires is three or more.

Further, according to the optical subassembly according to another aspect of the present invention, the element mounting portion further includes an element mounting surface on which the optical element is mounted on a surface adjacent to the second bonding surface. The third conductor pattern and the fourth conductor pattern are arranged so as to straddle the element mounting surface and the second bonding surface.

Further, according to the optical subassembly according to another aspect of the present invention, the plurality of lead terminals include a pair of lead terminals into which corresponding signals are input, and the pair of lead terminals penetrate the eyelet. It is fixed by a dielectric to a single through hole.

Further, according to the optical subassembly according to another aspect of the present invention, the relay board is further provided with a first ground pattern grounded on the surface adjacent to the first bonding surface. The subcarrier has one ground pattern surface, and the subcarrier has a second ground pattern surface provided with a second ground pattern grounded on the ground on a surface parallel to the first ground pattern surface, and the first ground pattern surface is provided. The ground pattern is connected to the second ground pattern by a bonding wire.

Further, according to the optical subassembly according to another aspect of the present invention, the first ground pattern is arranged over the first bonding surface, and the first ground pattern is arranged on the first bonding surface. Are arranged on both sides of the first conductor pattern and the second conductor pattern.

Further, according to the optical subassembly according to another aspect of the present invention, the element mounting portion is a metal block.

Further, according to the optical subassembly according to the other aspect of the present invention, the element mounting portion is grounded to the ground and has a third ground pattern straddling at least two adjacent surfaces.

It is an external view of the optical module which concerns on 1st Embodiment. It is a schematic diagram which shows the cross-sectional structure of a part of the optical module which concerns on 1st Embodiment. It is a schematic perspective view which shows the optical sub-assembly which concerns on 1st Embodiment. It is a schematic plan view which looked at the optical sub-assembly which concerns on 1st Embodiment from the Y direction. It is a schematic perspective view which shows the state which the relay board which concerns on 1st Embodiment is connected to a pedestal by a solder or a conductive adhesive. It is a schematic perspective view which shows the relay board which concerns on 1st Embodiment. It is a schematic perspective view which shows the stem which concerns on 1st Embodiment. It is a graph which calculated the optical module which concerns on 1st Embodiment and the transmission characteristic (S21) of the prior art example 1 and the conventional example 2 using a three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator). It is a schematic perspective view which shows the optical sub-assembly which concerns on Conventional Example 1. FIG. It is a schematic perspective view which shows the optical sub-assembly which concerns on Conventional Example 2. It is a schematic perspective view which shows the optical subassembly which concerns on 2nd Embodiment. It is a schematic perspective view which shows the optical subassembly which concerns on 3rd Embodiment. It is a schematic perspective view which shows the optical subassembly which concerns on 3rd Embodiment. It is a schematic perspective view which shows the state which the relay board which concerns on 3rd Embodiment is connected to a pedestal by a solder or a conductive adhesive. It is a graph which calculated the transmission characteristic (S21) of the optical module which concerns on 3rd Embodiment using 3D electromagnetic field simulator HFSS (High Frequency Structure Simulator).

The 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 in the first embodiment. A differential electric signal, a control signal, or the like modulated in the optical subassembly 100 is transmitted from a drive IC (not shown) mounted on the PCB 130 via an FPC 140 connected to the PCB 130 by solder or a conductive adhesive or the like. To. The FPC 140 is a flexible circuit board. The optical subassembly 100 accommodates an optical element 350 (see FIG. 3) and includes an interface for transmitting and receiving emitted light or incident light. The optical subassembly 100 includes an eyelet 310 (see FIG. 3) and an optical receptacle 2. Although not shown, the optical sub-assembly 100, PCB 130, and FPC 140 are built in a metal housing, and the optical module 1 is configured.

FIG. 2 is a schematic view showing a cross-sectional structure of a part of the optical module 1 according to the first embodiment. As shown in FIG. 2, the optical module 1 according to the first 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 first embodiment is configured to include an integrally formed resin member, and is composed of an optical package accommodating portion 20f having a cylindrical outer shape and an outer diameter of the optical package accommodating portion 20f. It is provided with a substantially cylindrical optical fiber insertion portion 20d having a small outer diameter. One end surfaces of the optical package accommodating portion 20f and the optical fiber inserting portion 20d are connected to each other.

The optical package accommodating portion 20f is formed with a circular recess 20a coaxial with its outer shape, and has a cylindrical shape.

The insertion hole 20b in the optical receptacle main body 20 extends from the tip surface of the optical fiber insertion portion 20d coaxially with the outer shape of the optical fiber insertion portion 20d and reaches 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 an insertion hole 20b penetrating from the recess 20a to the outside.

The tapered portion 20c formed at the tip of the inner wall surface of the insertion hole 20b has a tapered shape whose diameter increases outward. Therefore, it is easy to insert the connector provided with the external optical fiber into the insertion hole 20b.

A flange 20e is formed in the optical fiber insertion portion 20d 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 insertion 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 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 diagonally polished. In this way, interference between the light input to the optical fiber 50 and the 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 external optical fiber inserted into the insertion hole 20b from the outside, and the external optical fiber included in the connector and the stub 22 are held by the connector. The optical fiber 50 is coupled to the optical fiber 50.

The sleeve 24 includes a split sleeve made of zirconia or the like. The inner diameter of the sleeve 24 has a cylindrical shape having substantially the same diameter as the insertion hole 20b, and is embedded in a groove provided on the inner wall surface of the optical receptacle main body 20. The sleeve 24 allows the position of the connector including the external optical fiber to be inserted into the optical fiber insertion portion 20d to be adjusted in the insertion hole 20b.

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

Further, the optical package 3 includes a stem including the above-mentioned eyelet 310 and pedestal 313. The stem is made of metal, for example, and is electrically connected to a ground conductor formed on the FPC 140 and electrically grounded.

The optical module 1 is assembled by adhesively fixing the joint surface between the optical receptacle main body 20 and the first surface 311 of the eyelet 310. The housing is composed of the optical receptacle main body 20 and the eyelet 310. The lens support portion 32 welded to the eyelet 310 and the lens 30 fitted in the lens support portion 32 are formed so as to enter the recess 20a of the optical receptacle 2. That is, the lens 30 and the lens support portion 32 are housed in the recess 20a of the optical receptacle main body 20. The method of adhering the optical receptacle 2 and the optical package 3 is not limited to this.

Examples of optical subassembly include an optical transmission subassembly (TOSA) that has a light emitting element such as a laser diode inside and converts an electric signal into an optical signal and transmits it, and a photodiode inside. An optical subassembly (ROSA) that has a light receiving element and converts the received optical signal into an electrical signal, and a bidirectional optical subassembly (BOSA) that includes both of these functions. )and so on. The present invention can be applied to any of the above optical subassemblies, and in the first embodiment, the optical transmission subassembly will be described as an example.

FIG. 3 is a schematic perspective view showing an optical subassembly 100 included in the optical module 1 according to the first embodiment of the present disclosure. FIG. 4 is a view of the optical subassembly 100 included in the optical module 1 according to the first embodiment of the present disclosure as viewed from the Y-axis direction.

The optical subassembly 100 includes, for example, an eyelet 310, a pedestal 313, a lead terminal 320, a relay board 330, an element mounting portion 340, an optical element 350, a temperature adjusting element 360, a subcarrier 370, and a bonding wire. 380 and.

The eyelet 310 includes a first surface 311 and a second surface 312 arranged on the opposite side of the first surface 311 and a plurality of through holes 315 penetrating from the second surface 312 to the first surface 311. Specifically, for example, the eyelet 310 has a disk shape with a diameter of 5.6 mm and is formed of a conductive material such as metal. The eyelet 310 has a first surface 311 on the side of the disk shape facing the Z-axis direction and a second surface 312 on the side opposite to the first surface 311. Further, the eyelet 310 has a plurality of through holes 315 penetrating from the first surface 311 to the second surface 312.

The lead terminal 320 is inserted into a plurality of through holes 315, and a differential electric signal is input to at least a part thereof. Specifically, for example, the lead terminal 320 includes the first lead terminal 320A to the sixth lead terminal 320F (see FIG. 5), and each lead terminal 320 is inserted into a through hole 315 provided in the eyelet 310. .. A dielectric 314 such as glass is filled in the gap of the through hole 315 in which each lead terminal 320 is arranged. A dielectric 314 such as the glass holds each lead terminal 320 in each through hole 315. A coaxial line is composed of an eyelet 310, a dielectric 314, and each lead terminal 320. In the embodiment shown in FIG. 3, a differential electric signal is input to the first lead terminal 320A and the second lead terminal 320B. A control signal for controlling the temperature adjusting element 360 is input to the third lead terminal 320C and the fourth lead terminal 320D. An output monitor and a temperature monitor are connected to the fifth lead terminal 320E and the sixth lead terminal 320F.

The pedestal 313 is arranged on the first surface 311 side of the eyelet 310. In the first embodiment, the pedestal 313 is made of metal and projects from the first surface 311 of the eyelet 310 in the vicinity of the first lead terminal 320A and the second lead terminal 320B in the Z-axis direction (). (See FIG. 7). In the embodiment shown in FIG. 3, the eyelet 310 and the pedestal 313 are integrally formed. The eyelet 310 and the pedestal 313 have the same potential, and both form a stem. The stem according to the first embodiment is molded by press working, and is made of, for example, rolled steel having a thermal conductivity of 50 to 70 [W / m · K].

The relay board 330 is arranged on the X-axis direction side of the pedestal 313. Specifically, for example, it will be described with reference to FIGS. 5 to 7. FIG. 5 is a diagram showing a state in which the relay board 330 is mounted on the pedestal 313, and is a diagram in which configurations other than the eyelet 310, the pedestal 313, the lead terminal 320, and the relay board 330 are omitted. FIG. 6 is an enlarged view of the relay board 330. FIG. 7 is a schematic perspective view showing the stem. As shown in FIGS. 3 and 6, the relay board 330 is arranged on the X-axis direction side of the pedestal 313.

The relay board 330 includes a lead connecting surface 334 extending in the normal direction of the first surface 311 and a first bonding surface 335 adjacent to the lead connecting surface 334. Specifically, in the embodiment shown in FIGS. 3 to 6, the relay board 330 includes a lead connecting surface 334 on the surface facing the X-axis direction and a first bonding surface 335 on the surface facing the Y direction.

Further, in the relay board 330, the first conductor pattern 331 and the second conductor pattern 332 are formed so as to straddle the lead connection surface 334 and the first bonding surface 335. Specifically, in the embodiment shown in FIGS. 3 to 6, the relay substrate 330 is formed on the first conductor pattern 331 and the second conductor pattern 332 formed on the lead connection surface 334 and on the first bonding surface 335. The first conductor pattern 331 and the second conductor pattern 332 are seamlessly formed so as to have the same voltage. The first conductor pattern 331 and the second conductor pattern 332 are formed as a waveguide that propagates a differential electric signal. In particular, it is desirable that the first conductor pattern 331 and the second conductor pattern 332 have a taper 601 formed at the coupling portion of the differential electric signal. By forming the taper 601 it is possible to prevent the impedance of the differential electric signal from suddenly changing at the coupling portion. As a result, the high frequency characteristics can be improved.

Further, the first conductor pattern 331 and the second conductor pattern 332 formed on the lead connection surface 334 are connected to the lead terminal 320 by solder or a conductive adhesive 333, and a differential electric signal is input. In the embodiments shown in FIGS. 3 to 6, the first conductor pattern 331 is connected to the first lead terminal 320A by solder or a conductive adhesive 333, and the second conductor pattern 332 is soldered to the second lead terminal 320B. Alternatively, they are connected with a conductive adhesive 333.

As described above, in the relay board 330, the direction in which the lead connection surface 334 having a large area among the surfaces of the relay board 330 faces is substantially perpendicular to the direction in which the surfaces of the third conductor pattern 341 and the fourth conductor pattern 342 face. Is placed in. Thereby, a large number of parts can be arranged on the eyelet 310 and can be easily manufactured.

The element mounting portion 340 includes a second bonding surface 343 on which a third conductor pattern 341 and a fourth conductor pattern 342 into which a differential electric signal is input are formed. Specifically, for example, the element mounting portion 340 includes a second bonding surface 343 on the surface facing the Y direction. Further, in the element mounting portion 340, the third conductor pattern 341 and the fourth conductor pattern 342 are formed on the second bonding surface 343. The first conductor pattern 331 and the second conductor pattern 332 of the first bonding surface 335 are connected to the third conductor pattern 341 and the fourth conductor pattern 342 of the second bonding surface 343 by the bonding wire 380. In the embodiment shown in FIG. 3, the third conductor pattern 341 is electrically connected to the first conductor pattern 331 formed on the relay substrate 330 by wire bonding. Similarly, the fourth conductor pattern 342 is electrically connected to the second conductor pattern 332 formed on the relay substrate 330 by wire bonding.

As described above, the first conductor pattern 331 and the second conductor pattern 332 are input with the differential electric signal connected to the first lead terminal 320A and the second lead terminal 320B. Therefore, a differential electric signal is input to the third conductor pattern 341 and the fourth conductor pattern 342 via the bonding wire 380.

The optical element 350 is mounted on the element mounting portion 340 and is electrically connected to the third conductor pattern 341 and the fourth conductor pattern 342 to convert one of the optical signal and the differential electric signal into the other. Specifically, for example, the optical element 350 is a laser diode, and is mounted on the surface of the element mounting portion 340 facing the Y direction. The optical element 350 receives a differential electric signal from the third conductor pattern 341 and the fourth conductor pattern 342, and converts the differential electric signal into an optical signal. When the optical element 350 functions as a light receiving element, the optical element 350 receives an optical signal and converts the optical signal into a differential electric signal. The converted differential electric signal passes through the third conductor pattern 341 and the fourth conductor pattern 342, the bonding wire 380, the first conductor pattern 331 and the second conductor pattern 332, and the first lead terminal 320A and the second conductor pattern 332. It is propagated to the second lead terminal 320B. In the embodiment shown in FIG. 3, the element mounting portion 340 is a substrate.

When performing wire bonding, if the surfaces to which both ends of the bonding wire 380 are connected face different directions, it is necessary to change the direction of the bonding target after bonding the bonding wire 380 to one terminal. As in the above configuration, the normal directions of the first bonding surface and the second bonding surface are the same direction (in the first embodiment, the positive direction of the Y axis as shown in FIG. 3), so that the bonding target can be used. It is not necessary to change the direction of a certain optical subassembly 100. It should be noted that the normal directions are the same to the extent that it is not necessary to change the direction of the bonding target after bonding the bonding wire 380 to one surface and before bonding the bonding wire 380 to the other surface. , Indicates that the angle formed by the first bonding surface 335 and the second bonding surface 343 is small. That is, the first bonding surface 335 and the second bonding surface 343 both face the same direction (in the first embodiment, the positive direction of the Y axis as shown in FIG. 3), and the first bonding surface 335 and the second bonding surface 335 and the second The bonding surface 343 is a surface substantially parallel to each other. Therefore, the production of the optical subassembly 100 becomes easy.

The temperature adjusting element 360 is arranged in contact with the first surface 311 to adjust the temperature of the optical element 350. Specifically, for example, the temperature adjusting element 360 is a Peltier element and is arranged in contact with the first surface 311. The temperature adjusting element 360 cools the optical element 350 based on the control signals input from the third lead terminal 320C and the fourth lead terminal 320D. If the temperature adjustment is not necessary, the temperature adjustment element 360 may be omitted.

Normally, it is desirable that the differential electric signal supplied to the optical element 350 is coupled with a conductor pattern grounded on the ground. Further, the Peltier element is configured by sandwiching both sides of the semiconductor element that transfers heat with an insulating substrate. Therefore, when the temperature adjusting element 360 is a Peltier element, the eyelet 310 and the element mounting portion 340 are insulated from each other, so that the ground potential cannot be supplied to the element mounting portion 340. However, according to the first embodiment, the path through which the differential electric signal passes from the first lead terminal 320A and the second lead terminal 320B to the optical element 350 is formed as a waveguide that propagates the differential electric signal. To. Therefore, as will be described later, the high frequency characteristics of the optical subassembly 100 can be improved even if the element mounting portion 340 is not grounded.

The subcarrier 370 is mounted on the temperature adjusting element 360, and the element mounting unit 340 is mounted. Specifically, for example, the subcarrier 370 is arranged on the Z-axis direction side of the temperature adjusting element 360 at a distance from the pedestal 313 in the X-axis direction.

It is desirable that the subcarrier 370 is made of an insulating material having a high thermal conductivity and a coefficient of thermal expansion close to that of the optical element 350. In the first embodiment, the subcarrier 370 is formed of, for example, ceramic. Ceramics, whether metal or non-metals, include molded bodies of inorganic compounds such as oxides, carbides, nitrides and borides, and inorganic solid materials such as powders and films. For example, as the ceramic used for the subcarrier 370, aluminum nitride having a thermal conductivity of 170 to 200 [W / m · K] is desirable. Further, the element mounting portion 340 is mounted on the surface of the subcarrier 370 facing the Y-axis direction.

The bonding wire 380 electrically connects the first conductor pattern 331 and the second conductor pattern 332 of the first bonding surface 335 with the third conductor pattern 341 and the fourth conductor pattern 342 of the second bonding surface 343. Specifically, the three or more bonding wires 380 electrically connect the first conductor pattern 331 and the third conductor pattern 341. Similarly, the three or more bonding wires 380 electrically connect the second conductor pattern 332 and the fourth conductor pattern 342. The bonding wire 380 connecting the first conductor pattern 331 and the third conductor pattern 341 and the bonding wire 380 connecting the second conductor pattern 332 and the fourth conductor pattern 342 are arranged in close proximity to each other. As a result, the three or more pairs of bonding wires 380 are formed as a waveguide that propagates the differential electric signal. By connecting with three or more pairs of bonding wires 380, the inductance parasitic on the bonding wires 380 can be reduced and good transmission characteristics can be obtained.

In FIG. 8, the transmission characteristics (S21) of the optical module for the configuration shown in FIG. 3 and the configurations of Conventional Example 1 and Conventional Example 2 were calculated using a three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator). It is a graph.

The optical module of the conventional example 1 is equipped with an optical sub-assembly that does not include the temperature adjusting element 360. Specifically, the optical subassembly of Conventional Example 1 has the configuration shown in FIG. The optical subassembly of Conventional Example 1 includes a conductive stem made of a metal having a diameter of 5.6 mm. The stem includes an eyelet 310 provided with a through hole 315, and a lead terminal 320 is fixed to the through hole 315 with a dielectric material 314 such as glass. A coaxial line is formed by the eyelet 310, the dielectric 314, and the lead terminal 320. The impedance of the coaxial line is matched to 25 Ohm. The lead terminal 320 penetrates the hole provided in the eyelet 310, and a part thereof protrudes. The tip of the protruding lead terminal 320 is joined to the conductor pattern on the surface of the relay board 330 mounted on the pedestal 313 vertically protruding from the eyelet 310 with AuSn solder. A microstrip line is formed on the relay board 330 by the pedestal 313 protruding from the stem, which is the ground potential, and the conductor pattern. Further, the element mounting portion 340 is die-bonded to the pedestal 313. The element mounting portion 340 is formed of a ceramic such as aluminum nitride having a coefficient of thermal expansion close to that of the optical element 350. The element mounting portion 340 is a microstrip line including a conductor pattern on the front and back surfaces, and the conductor pattern on the back surface is connected to a stem having a ground potential. An optical element 350 is mounted on the element mounting unit 340.

The optical module of the conventional example 2 is equipped with an optical sub-assembly equipped with a temperature adjusting element 360. Specifically, the optical subassembly of Conventional Example 2 has the configuration shown in FIG. The optical subassembly of the conventional example 2 includes a temperature adjusting element 360 and a subcarrier 370 in the central portion of the region where the pedestal 313 of the conventional example 1 is provided. The subcarrier 370 is made of ceramic or metal having high thermal conductivity in order to improve heat dissipation. The pedestal 313 is separately provided at two locations on both sides of the temperature adjusting element 360 and the subcarrier 370. The relay board 330 is arranged on a pedestal 313 separated in two places. The element mounting unit 340 on which the optical element 350 is mounted is mounted on the subcarrier 370 and transmits / receives a differential electric signal to / from the lead terminal 320 via the separated relay board 330. The two relay boards 330 and the element mounting portion 340 each form a microstrip line including a conductor pattern on the front and back surfaces. Since the temperature adjusting element 360 is a Peltier element, the temperature adjusting element 360 has an insulating substrate in a portion facing the eyelet 310 and the subcarrier 370. Therefore, the ground potential is not supplied to the back surface of the surface on which the optical element 350 of the element mounting portion 340 is mounted.

As shown in FIG. 8, in the optical subassembly of the conventional example 1, since the ground potential is supplied to the back surface of the element mounting portion 340, the transmission characteristic is high even in a high frequency region. However, since the optical subassembly of Conventional Example 1 does not include the temperature adjusting element 360, it cannot be used in a high temperature environment.

On the other hand, since the optical subassembly of Conventional Example 2 includes a temperature adjusting element 360, it can be used in a high temperature environment. However, as shown in FIG. 8, in the optical subassembly of the conventional example 2, since the ground potential is not supplied to the back surface of the element mounting portion 340, the transmission characteristic deteriorates in a high frequency region.

On the other hand, since the optical subassembly 100 of the first embodiment includes the temperature adjusting element 360, it can be used in a high temperature environment. Further, as shown in FIG. 8, the optical subassembly 100 according to the first embodiment has a high transmission characteristic in terms of high frequency characteristics as compared with the conventional example 2. In the first embodiment, unlike the conventional example 2, since the relay board 330 is not divided, a waveguide for propagating the differential electric signal is formed. The waveguide is formed across two vertical surfaces of the substrate. Therefore, in the first embodiment, unlike the conventional example 2, the differential electric signal is propagated in a state where the electrical coupling between the differential electric signals is maintained from the lead terminal 320 to immediately before the optical element 350. As a result, even when the ground potential is not supplied directly under the element mounting portion 340, the electromagnetic field does not convert to the higher-order mode due to the electrical coupling between the differential electric signals, and the TEM mode is used. Propagated as. Therefore, good transmission characteristics can be obtained.

FIG. 11 is a perspective view of an optical subassembly 100 included in the optical module 1 according to the second embodiment. In the optical subassembly 100 shown in FIG. 11, the third conductor pattern 341 and the fourth conductor pattern 342 are arranged so as to straddle the element mounting surface 344 and the second bonding surface 343 on which the optical element 350 is mounted. Specifically, for example, the element mounting portion 340 is integrally formed with the subcarrier 370. The third conductor pattern 341 and the fourth conductor pattern 342 are formed so as to straddle the surface of the element mounting portion 340 toward the Y direction and the surface toward the Z direction. Similar to the first embodiment, the third conductor pattern 341 and the fourth conductor pattern 342 are formed as a waveguide for propagating the differential electric signal on the element mounting portion 340.

Further, the element mounting portion 340 further includes an element mounting surface 344 on which the optical element 350 is mounted on a surface adjacent to the second bonding surface 343. Specifically, for example, the element mounting unit 340 includes an element mounting surface 344 on which the optical element 350 is mounted on a surface facing the Y direction. The optical element 350 is mounted on a surface of the element mounting portion 340 facing the Y direction, and is connected to a third conductor pattern 341 and a fourth conductor pattern 342 formed on the surface.

The relay board 330 includes a lead connecting surface 334 extending in the normal direction of the first surface 311 and a first bonding surface 335 adjacent to the lead connecting surface 334. In the second embodiment, the relay board 330 includes a lead connecting surface 334 on the surface facing the X-axis direction and a first bonding surface 335 on the surface facing the Z direction.

The first conductor pattern 331 and the second conductor pattern 332 of the first bonding surface 335 are connected to the third conductor pattern 341 and the fourth conductor pattern 342 of the second bonding surface 343 by the bonding wire 380. In the second embodiment, the first conductor pattern 331 formed on the surface of the relay board 330 toward the Z direction is electrically different from the third conductor pattern 341 formed on the surface of the element mounting portion 340 facing the Z direction. Be connected. The second conductor pattern 332 formed on the Z-direction surface of the relay board 330 is electrically connected to the fourth conductor pattern 342 formed on the Z-direction surface of the element mounting portion 340.

Even in such a configuration, the surfaces of the relay board 330 and the element mounting portion 340 that are connected by wire bonding are both surfaces that face the Z direction. Therefore, bonding can be easily performed. Further, as in the first embodiment, the direction in which the lead connection surface 334 having a large area among the surfaces of the relay board 330 faces is substantially perpendicular to the direction in which the surfaces of the third conductor pattern 341 and the fourth conductor pattern 342 face. By arranging in the eyelet 310, a large number of parts can be arranged in the eyelet 310 and easily manufactured.

Further, the optical subassembly 100 of the second embodiment shown in FIG. 11 may be characterized in that the center of gravity of the subcarrier 370 is biased toward the relay board 330 with respect to the center of gravity of the eyelet 310. With this mounting method, it is possible to stably use the area directly above the glass coaxial portion as a mounting area, which is advantageous in miniaturization.

The optical subassembly 100 of the second embodiment may also have a configuration that does not include the temperature adjusting element 360, or may have a configuration in which three or more pairs of bonding wires 380 are provided.

Subsequently, the third embodiment will be described. The description of the same configurations as those of the first embodiment and the second embodiment will be omitted. As described above, according to the first embodiment, the differential electric signal is propagated as the TEM mode because the electromagnetic field does not cause conversion to the higher order mode due to the electrical coupling between the differential electric signals. To. Therefore, good transmission characteristics can be obtained. However, as shown by the simulation result of FIG. 8, when the ground potential is not supplied to the relay board 330, the band showing good response characteristics is limited to 25 GHz. According to the third embodiment, it is possible to realize an optical semiconductor laser in which an electric field absorption type optical modulator that exhibits good response characteristics even in a high frequency region of 30 GHz or more is integrated.

FIG. 12 is a perspective view of an optical subassembly 100 included in the optical module 1 according to the third embodiment. FIG. 13 is a perspective view of the optical subassembly 100 included in the optical module 1 according to the third embodiment from another direction. FIG. 14 is a schematic perspective view showing a state in which the relay board 330 according to the third embodiment is connected to the pedestal 313 with solder or a conductive adhesive 333.

The relay board 330 further has a first ground pattern surface 1302 provided with a first ground pattern 1202 grounded on the surface adjacent to the first bonding surface 335. Specifically, the relay board 330 has a first ground pattern 1202 grounded on a surface opposite to the lead connection surface 334 (that is, a surface facing the −X axis direction). In the example shown in FIG. 13, the first ground pattern 1202 is arranged on the entire surface of the surface opposite to the lead connection surface 334.

The first ground pattern 1202 is arranged so as to straddle the first bonding surface 335. Specifically, for example, the first ground pattern 1202 is arranged so as to straddle the first bonding surface 335 from the surface opposite to the lead connection surface 334. The first ground pattern 1202 arranged on the first bonding surface 335 is arranged on both sides of the first conductor pattern 331 and the second conductor pattern 332.

The first ground pattern 1202 may also be arranged on the −X axis direction side of the first conductor pattern 331 and the second conductor pattern 332 of the first bonding surface 335. According to this configuration, the first conductor pattern 331 and the second conductor pattern 332 are surrounded by the first ground pattern 1202 except for the portion arranged from the first bonding surface 335 to the lead connection surface 334.

The subcarrier 370 has a second ground pattern surface 1306 provided with a second ground pattern 1304 grounded on the surface parallel to the first ground pattern surface 1302. Specifically, for example, the subcarrier 370 has a second ground pattern 1304 grounded on a surface facing the −X axis direction. In the example shown in FIG. 13, the second ground pattern 1304 is arranged on the entire surface of the second ground pattern surface 1306.

The second ground pattern 1304 may be arranged so as to straddle a surface adjacent to the second ground pattern surface 1306. Specifically, for example, the second ground pattern 1304 may be arranged so as to straddle the surface of the subcarrier 370 in the Y-axis direction from the second ground pattern surface 1306. That is, the second ground pattern 1304 may be arranged on the entire surface of the subcarrier 370 in contact with the relay board 330. Further, the subcarrier 370 may be a metal block.

The first ground pattern 1202 is connected to the second ground pattern 1304 by a bonding wire 380. Specifically, for example, the first ground pattern 1202 provided on the first ground pattern surface 1302 of the relay board 330 is bonded to the second ground pattern 1304 provided on the second ground pattern surface 1306 of the subcarrier 370. Connected by 380.

The element mounting portion 340 is grounded and has a third ground pattern 1308 that spans at least two adjacent surfaces. Specifically, for example, the element mounting portion 340 has a third ground pattern 1308 grounded on the second bonding surface 343. The third ground pattern 1308 is arranged on both sides of the third conductor pattern 341 and the fourth conductor pattern 342. The third ground pattern 1308 is connected to the first ground pattern 1202 provided on the first bonding surface 335 by a bonding wire 380. The element mounting portion 340 may be a metal block.

The third ground pattern 1308 may be arranged so as to pass through a surface adjacent to the second bonding surface 343 and to a surface on the back side of the second bonding surface 343. The third ground pattern 1308 arranged on the back surface of the second bonding surface 343 is grounded by being connected to the second ground pattern 1304 arranged on the surface of the subcarrier 370 in the Y-axis direction. To.

The plurality of lead terminals include a pair of lead terminals into which corresponding signals are input. Specifically, for example, the first lead terminal 320A and the second lead terminal 320B are a pair of lead terminals. A pair of differential electric signals are input to the first lead terminal 320A and the second lead terminal 320B. The pair of lead terminals are fixed by a dielectric 314 to a single through hole 315 penetrating the eyelet 310. For example, a pair of lead terminals (first lead terminal 320A and second lead terminal 320B) are fixed to a single through hole 315 by glass, and the impedance of the pair of lead terminals is designed to match the differential 100 Ohm.

The third conductor pattern 341 and the fourth conductor pattern 342 shown in FIGS. 12 and 13 are in the case where the optical element 350 is an electric field absorption type optical element. When an electric field absorption type optical element is used, the differential signal is generally modulated by using a drive IC having an output impedance of 100 Ohm. Therefore, since the impedances of the third conductor pattern 341 and the fourth conductor pattern 342 to which the differential signal is input are designed to match 100 Ohm, the pattern width is narrower than that of the first embodiment and the second embodiment. Is.

According to the third embodiment, by supplying the ground potential to the element mounting portion 340, the high frequency characteristics are stabilized, and good transmission characteristics are exhibited even in a high frequency region of 30 GHz or more. FIG. 15 is a graph obtained by calculating the transmission characteristics (S21) of the optical module 1 according to the third embodiment using a three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator). It can be seen that the transmission characteristic of 30 GHz or more is also improved by supplying the ground potential to the third ground pattern 1308 of the element mounting portion 340.

The first ground pattern surface 1302 and the second ground pattern surface 1306 may be provided on a surface facing the Z-axis direction instead of a surface facing the −X-axis direction. Specifically, for example, the relay board 330 may have a first ground pattern 1202 grounded on a surface facing the Z-axis direction. The subcarrier 370 may have a second ground pattern 1304 grounded on a surface oriented in the Z-axis direction. In this case, the first ground pattern 1202 is exposed even when the relay board 330 is shorter than the pedestal 313 in the Z-axis direction. Further, since the first ground pattern 1202 and the second ground pattern 1304 are parallel to each other, they can be connected by the bonding wire 380.

In this specification, the term eyelet 310, which represents a metal disk, is used, but the fact that the eyelet 310 has a disk shape has no essential meaning, and other shapes such as polygonal prisms may be used. ..

1 Optical module, 2 Optical conductor, 3 Optical package, 20 Optical conductor body, 20a recess, 20b insertion hole, 20c taper, 20d optical fiber insertion part, 20e flange, 20f optical package housing, 22 stubs, 24 sleeves, 30 Lens, 32 lens support, 50 optical fiber, 100 optical subassembly, 130 PCB, 140 FPC, 310 eyelet, 311 first surface, 312 second surface, 313 pedestal, 314 dielectric, 315 through hole, 320 lead terminal, 320A 1st lead terminal, 320B 2nd lead terminal, 320C 3rd lead terminal, 320D 4th lead terminal, 320E 5th lead terminal, 320F 6th lead terminal, 330 relay board, 331 1st conductor pattern, 332 2nd conductor Pattern, 333 solder or conductive adhesive, 334 lead connection surface, 335 first bonding surface, 340 element mounting part, 341 third conductor pattern, 342 fourth conductor pattern, 343 second bonding surface, 344 element mounting surface, 350 Optical element, 360 temperature control element, 370 sub-carrier, 380 bonding wire, 601 taper, 1202 1st ground pattern, 1302 1st ground pattern surface, 1304 2nd ground pattern, 1306 2nd ground pattern surface, 1308 3rd ground pattern ..

Claims (11)

An eyelet including a first surface, a second surface arranged on the opposite side of the first surface, and a plurality of through holes penetrating from the second surface to the first surface.
A plurality of lead terminals inserted into the plurality of through holes and at least partially input with a differential electric signal,
A first conductor pattern and a first conductor pattern including a lead connection surface extending in the normal direction of the first surface and a first bonding surface adjacent to the lead connection surface, straddling the lead connection surface and the first bonding surface. A two-conductor pattern is formed, and the first conductor pattern and the second conductor pattern formed on the lead connection surface are connected to the lead terminal with solder or a conductive adhesive, and the differential electric signal is input. With the relay board
An element mounting portion including a second bonding surface on which the third conductor pattern and the fourth conductor pattern into which the differential electric signal is input are formed, and
An optical element mounted on the element mounting portion, electrically connected to the third conductor pattern and the fourth conductor pattern, and converting one of an optical signal and the differential electric signal into the other.
Including
The first conductor pattern and the second conductor pattern on the first bonding surface are connected to the third conductor pattern and the fourth conductor pattern on the second bonding surface by a bonding wire.
The normal directions of the first bonding surface and the second bonding surface are the same.
An optical sub-assembly that is characterized by this. The optical subassembly according to claim 1, further comprising a temperature adjusting element that is arranged in contact with the first surface and adjusts the temperature of the optical element. The optical subassembly according to claim 2, further comprising a subcarrier mounted on the temperature adjusting element and mounting the element mounting portion. The optical subassembly according to claim 3, wherein the center of gravity of the subcarrier is biased toward the relay board side with respect to the center of gravity of the eyelet. The optical subassembly according to any one of claims 1 to 4, wherein the bonding wires have three or more pairs. The element mounting portion further includes an element mounting surface on which the optical element is mounted on a surface adjacent to the second bonding surface.
The third conductor pattern and the fourth conductor pattern are arranged so as to straddle the element mounting surface and the second bonding surface.
The optical subassembly according to any one of claims 1 to 5. The plurality of lead terminals include a pair of lead terminals into which corresponding signals are input.
The pair of lead terminals are fixed by a dielectric to a single through hole penetrating the eyelet.
The optical subassembly according to claim 1. The relay board further has a first ground pattern surface provided with a first ground pattern grounded on the surface adjacent to the first bonding surface.
The subcarrier has a second ground pattern surface on which a second ground pattern grounded on the ground is provided on a surface parallel to the first ground pattern surface.
The first ground pattern is connected to the second ground pattern by a bonding wire.
The optical subassembly according to claim 3. The first ground pattern is arranged so as to straddle the first bonding surface.
The first ground pattern arranged on the first bonding surface is arranged on both sides of the first conductor pattern and the second conductor pattern.
The optical subassembly according to claim 8. The optical subassembly according to claim 8, wherein the element mounting portion is a metal block. The optical subassembly according to claim 8, wherein the element mounting portion is grounded and has a third ground pattern that spans at least two adjacent surfaces.

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