CN112838139B

CN112838139B - Optical subassembly

Info

Publication number: CN112838139B
Application number: CN202011172760.2A
Authority: CN
Inventors: 野口大辅; 山本宽
Original assignee: Cambridge Optoelectronics Co ltd
Current assignee: Cambridge Optoelectronics Co ltd
Priority date: 2019-11-01
Filing date: 2020-10-28
Publication date: 2023-11-17
Anticipated expiration: 2040-10-28
Also published as: JP2021077858A; JP7419188B2; CN112838139A

Abstract

The invention provides an optical subassembly which is small, easy to manufacture and has good high-frequency characteristics. According to an optical subassembly, comprising: an aperture member comprising a first face, a second face, and a plurality of through holes; a plurality of lead terminals to which differential electrical signals are input; a relay substrate including 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 being formed across the lead connection surface and the first bonding surface, the first and second conductor patterns formed on the lead connection surface being connected to a lead terminal by solder or the like to input differential electrical signals; a component mounting part including a second joint surface formed with third and fourth conductor patterns; and an optical element for converting one of the optical signal and the differential electrical signal into the other, wherein the first and second conductor patterns of the first bonding surface are connected to the third and fourth conductor patterns by bonding wires, and the normal directions of the first and second bonding surfaces are in the same direction.

Description

Optical subassembly

Technical Field

The present invention relates to an optical subassembly.

Background

Currently, most of the internet, telephone networks, are built up from optical communication networks. Optical modules used as interfaces of routers/switches and transmission devices serving as optical communication devices play an important role in converting electrical signals into optical signals. The optical module generally has the following configuration: an optical subassembly housing an optical element; a printed substrate (hereinafter, referred to as PCB) equipped with an IC or the like that processes signals including modulated electrical signals; and a flexible printed circuit board (hereinafter, referred to as FPC) that electrically connects them.

In recent years, there has been an increasing demand for optical modules that can transmit and receive high-speed optical signals at low cost, as well as at high speed and low price. For example, as an optical module satisfying the above-mentioned requirements, it is known TO use an optical subassembly of TO-CAN type having a lead terminal protruding from a metal rod inserted FPC contained in a CAN-shaped package. The metal rod is configured to include a substantially disk-shaped eyelet member and a pedestal provided so as to protrude from the eyelet member.

In recent years, there has been an increasing demand for optical modules in the field of an interface standard for connecting a control unit and a radio unit of a radio base station, which is called CPRI (Common Public Radio Interface; common public radio interface). CPRI is a standard of an interface connecting a Radio controller (Radio Equipment Control; REC) and a Radio Equipment (RE) of a Radio base station. The REC is used for baseband signal processing, control, management, etc. in the digital region. The RE is used for amplification, modulation and demodulation, filtering, and the like of a wireless signal in an analog region. When the REC and the RE are connected by an optical signal capable of long-distance transmission, the RE can be used in an outdoor installation space near an antenna far from the base station.

However, in order to cope with outdoor installation of RE, it is necessary to be able to operate even in a severe temperature environment. Therefore, in addition to the market demands for lower price, there is a demand for operation in a wide temperature range of-40 to 85 ℃ called I-Temp (Industrial temperature range; industrial temperature range). According TO the above requirements, the TO-CAN optical subassembly capable of operating in a wide temperature range and having a wide frequency band has a high technical requirement.

Typically, TO-CAN type optical subassemblies are fabricated by modularizing a plurality of small electronic devices in standardized diameter aperture components. On the other hand, in order to use an aperture member having a diameter different from that of an aperture member conventionally used, a new manufacturing apparatus must be introduced. Since introduction of a new manufacturing apparatus increases manufacturing costs, it is desirable to use an eyelet member having the same diameter as an eyelet member used in the past. In the TO-CAN type package, a lead terminal held by a dielectric such as glass is disposed in a through hole provided in a disk-shaped eyelet member. Since the electrical signal is transmitted to the optical element using the lead terminal, the area in which the electronic component other than the lead terminal can be disposed is limited.

Further, when a member such as a temperature adjusting element is disposed, the substrate on which the optical element is mounted is electrically separated from the disk-shaped aperture member which is the ground. Therefore, it is difficult to satisfactorily maintain the characteristics of the optical element by connecting the substrate on which the optical element is mounted to the ground potential. Accordingly, studies have been actively conducted on achieving both miniaturization and high frequency characteristics.

Patent document 1 discloses a technology for transmitting a high-quality high-frequency signal TO an optical element in a small TO-CAN package.

Prior art literature

Patent literature

Patent document 1: japanese patent No. 4279134

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 discloses the following technique: by incorporating a pair of lead terminals for differential signal transmission into a glass through hole, the area of the coaxial section is minimized and the mounting area inside the TO-CAN is maximized. However, it is necessary to provide two lines on the same plane as the region where the optical element is mounted, and the region where other components are mounted is limited.

The electronic component and the lead terminal disposed in the TO-CAN package are connected by wire bonding. In the wire bonding, when the surfaces to which the leads are connected are oriented differently, connection is not easy.

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

Means for solving the problems

An optical subassembly according to an aspect of the present invention, comprising: an aperture member including a first surface, a second surface disposed on an 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, at least a part of which is inputted with a differential electrical signal; a relay substrate including a lead connection surface extending in a normal direction of the first surface and a first bonding surface adjacent to the lead connection surface, wherein a first conductor pattern and a second conductor pattern are formed across the lead connection surface and the first bonding surface, and the first conductor pattern and the second conductor pattern formed on the lead connection surface are connected to the lead terminal by solder or conductive adhesive, and the differential electrical signal is input; an element mounting part including a second joint surface formed with a third conductor pattern and a fourth conductor pattern for inputting the differential electric signal; and an optical element mounted on the element mounting portion, electrically connected to the third conductor pattern and the fourth conductor pattern, and configured to convert one of the optical signal and the differential electrical signal into the other, wherein the first conductor pattern and the second conductor pattern of the first bonding surface are connected to the third conductor pattern and the fourth conductor pattern of the second bonding surface by bonding wires, and the normal directions of the first bonding surface and the second bonding surface are in the same direction.

In addition, the optical subassembly according to another aspect of the present invention further includes a temperature adjustment element disposed in contact with the first surface, for adjusting the temperature of the optical element.

In addition, the optical subassembly according to another aspect of the present invention further includes a sub-carrier mounted on the temperature adjustment element and mounted on the element mounting portion.

In the optical sub-assembly according to another aspect of the present invention, the center of gravity of the sub-carrier is offset toward the relay substrate side with respect to the center of gravity of the aperture member.

In addition, according to another aspect of the present invention, the bonding wires are three or more pairs.

In 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, in a surface adjacent to the second bonding surface, and the third conductor pattern and the fourth conductor pattern are disposed across the element mounting surface and the second bonding surface.

In addition, according to another aspect of the present invention, the plurality of lead terminals includes a pair of lead terminals to which corresponding signals are input, and the pair of lead terminals are fixed to a single through hole penetrating the aperture member through a dielectric.

In addition, according to another aspect of the present invention, the relay substrate further includes a first land pattern surface provided with a first land pattern connected to the ground in a surface adjacent to the first bonding surface, and the sub-carrier includes a second land pattern surface provided with a second land pattern connected to the ground in a surface parallel to the first land pattern surface, and the first land pattern is connected to the second land pattern by a bonding wire.

In the optical sub-assembly according to another aspect of the present invention, the first land pattern is disposed across the first bonding surface, and the first land pattern disposed on the first bonding surface is disposed on both sides of the first conductor pattern and the second conductor pattern.

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

In addition, according to another aspect of the present invention, the element mounting portion has a third ground pattern connected to the ground and extending at least across two adjacent surfaces.

Drawings

Fig. 1 is an external view of an optical module according to a first embodiment.

Fig. 2 is a schematic diagram showing a cross-sectional structure of a part of the optical module according to the first embodiment.

Fig. 3 is a schematic perspective view showing an optical subassembly of the first embodiment.

Fig. 4 is a schematic top view of the optical subassembly of the first embodiment, viewed from the Y-direction.

Fig. 5 is a schematic perspective view showing a state in which the relay substrate of the first embodiment is connected to the pedestal by solder or conductive adhesive.

Fig. 6 is a schematic perspective view showing the relay substrate according to the first embodiment.

Fig. 7 is a schematic perspective view showing the lever of the first embodiment.

Fig. 8 is a graph obtained by calculating the transmission characteristics (S21) of the optical module according to the first embodiment and the conventional examples 1 and 2 using a three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator; high-frequency structure simulator).

Fig. 9 is a schematic perspective view showing an optical subassembly of conventional example 1.

Fig. 10 is a schematic perspective view showing an optical subassembly of conventional example 2.

Fig. 11 is a schematic perspective view showing an optical subassembly of the second embodiment.

Fig. 12 is a schematic perspective view showing an optical subassembly of the third embodiment.

Fig. 13 is a schematic perspective view showing an optical subassembly of the third embodiment.

Fig. 14 is a schematic perspective view showing a state in which the relay substrate of the third embodiment is connected to the pedestal by solder or conductive adhesive.

Fig. 15 is a graph obtained by calculating the transmission characteristics (S21) of the optical module according to the third embodiment using a three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator; high-frequency structure simulator).

In the figure:

1-optical module, 2-optical receptacle, 3-optical package, 20-optical receptacle body, 20A-recess, 20B-insertion hole, 20C-taper, 20D-optical receptacle body, 20E-flange, 20F-optical package housing, 22-stub, 24-sleeve, 30-lens, 32-lens support, 50-optical fiber, 100-optical subassembly, 130-PCB, 140-FPC, 310-eyelet member, 311-first face, 312-second face, 313-pedestal, 314-dielectric, 315-through hole, 320-lead terminal, 320A-first lead terminal, 320B-second lead terminal, 320C-third lead terminal, 320D-fourth lead terminal, 320E-fifth lead terminal, 320F-sixth lead terminal, 330-relay substrate, 331-first conductor pattern, 332-second conductor pattern, 333-solder or conductive adhesive, 334-lead connection face, 335-first bonding face, 340-element mounting portion, 341-third conductor pattern, 342-fourth conductor pattern, 343-second bonding face, 344-element mounting face, 350-optical element, 360-temperature adjusting element, 370-sub-carrier, 380-bonding wire, 601-taper portion, 1202-first ground pattern, 1302-first ground pattern face, 1304-second ground pattern face, 1306-second ground pattern face, 1308-third ground pattern.

Detailed Description

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 according to a first embodiment. Differential electrical signals, control signals, and the like modulated are transmitted from a driver IC (not shown) mounted on the PCB130 to the optical subassembly 100 via the FPC140 connected to the PCB130 by solder, conductive adhesive, or the like. The FPC140 is a circuit board having flexibility. The optical subassembly 100 houses an optical element 350 (see fig. 3) and has an interface to send/receive outgoing or incoming light. The optical subassembly 100 includes an aperture member 310 (referenced in fig. 3) and an optical receptacle 2. Although not shown, the optical subassembly 100, the PCB130, and the FPC140 are housed in a case made of metal or the like to constitute the optical module 1.

Fig. 2 is a schematic diagram 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 of the first embodiment includes an optical receptacle 2 and an optical package 3. The optical receptacle 2 further includes an optical receptacle body 20, a stub 22, and a sleeve 24.

The optical receptacle body 20 of the first embodiment is configured to include an integrally formed resin member, and includes: an optical package accommodating portion 20f having a cylindrical outer shape; and a substantially cylindrical optical fiber insertion portion 20d having an outer diameter smaller than that of the optical package accommodation portion 20 f. One end surfaces of the optical package accommodating portion 20f and the optical fiber insertion portion 20d are coupled to each other.

The optical package housing portion 20f is formed with a circular concave portion 20a coaxially with the outer shape thereof, and is formed in a cylindrical shape.

An insertion hole 20b is formed in the optical receptacle body 20, and the insertion hole 20b extends from a front end surface of the optical fiber insertion portion 20d to a bottom surface of a recess 20a formed in the optical package accommodating portion 20f coaxially with the outer shape of the optical fiber insertion portion 20d. That is, the optical receptacle 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 front end of the inner wall surface of the insertion hole 20b has a tapered shape in which the diameter increases toward the outside. Therefore, the connector including the external optical fiber is easily inserted into the insertion hole 20b.

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

The stub 22 is constituted to contain zirconia or the like. The stub 22 is formed in a substantially cylindrical shape having a substantially same diameter as the insertion hole 20b formed in the optical fiber insertion portion 20d of the optical receptacle body 20, and holds the optical fiber 50 coaxial with the stub 22. The stub 22 is inserted and fixed into the optical fiber insertion portion 20d of the optical receptacle body 20 by press fitting or the like. The right end face of the stub 22 is angle ground. Thus, the light input to the optical fiber 50 is prevented from interfering with the reflected light thereof.

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 of the connector is coupled to the optical fiber 50 held by the stub 22.

The sleeve 24 is configured to include an open sleeve made of zirconia or the like. The sleeve 24 has a cylindrical shape with an inner diameter substantially equal to that of the insertion hole 20b, and is fitted into a groove provided in the inner wall surface of the optical receptacle body 20. The sleeve 24 allows adjustment of the position of the connector having the external optical fiber inserted into the optical fiber insertion portion 20d in the insertion hole 20 b.

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

The optical package 3 includes a rod including the above-described eyelet member 310 and the mount 313. The rod is formed of, for example, metal, and is electrically connected to a ground conductor formed on the FPC140 and electrically grounded.

The optical module 1 is assembled by adhesively fixing the joint surface of the optical receptacle body 20 and the first surface 311 of the grommet member 310. The optical receptacle body 20 and the grommet member 310 constitute a housing. The lens support portion 32 welded to the aperture member 310 and the lens 30 fitted into the lens support portion 32 are formed so as to enter into the recess 20a of the optical receptacle 2. That is, the lens 30 and the lens support 32 are accommodated in the recess 20a of the optical receptacle body 20. Further, the method of bonding the optical receptacle 2 and the optical package 3 is not limited thereto.

As an example of the optical subassembly, there is: an optical transmitter subassembly (TOSA; transmitter Optical Subassembly) having a light emitting element such as a laser diode inside for converting an electrical signal into an optical signal for transmission; a light receiving subassembly (ROSA; receiver Optical Subassembly) having an optical receiving element typified by a photodiode inside and converting a received optical signal into an electrical signal; bi-directional optical subassemblies (BOSA; bidirectional Optical Subassembly) that incorporate both of their functions, and the like. The present application is also applicable to any of the above optical subassemblies, and in the first embodiment, an optical transmission subassembly is 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 an 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 aperture member 310, a mount 313, a lead terminal 320, a relay substrate 330, an element mount 340, an optical element 350, a temperature adjustment element 360, a sub-carrier 370, and a bonding wire 380.

The eyelet member 310 comprises: a first face 311; a second surface 312 disposed opposite to the first surface 311; and a plurality of through holes 315 penetrating from the second face 312 to the first face 311. Specifically, for example, the eyelet member 310 is in the shape of a disk having a diameter of 5.6mm, and is formed of a conductive material such as metal. The eyelet member 310 has a first surface 311 on a side of the disk shape facing the Z-axis direction and a second surface 312 on a side opposite to the first surface 311. The grommet member 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 the plurality of through holes 315, and at least a portion thereof is inputted with a differential electrical signal. Specifically, for example, the lead terminals 320 include first to sixth lead terminals 320A to 320F (see fig. 5), and the lead terminals 320 are inserted into the through holes 315 provided in the eyelet members 310. A gap between the through holes 315 where the lead terminals 320 are arranged is filled with a dielectric 314 such as glass. The dielectric 314 such as glass holds the lead terminals 320 in the through holes 315. Coaxial lines are formed by the eyelet members 310, the dielectric 314, and the lead terminals 320. In the embodiment shown in fig. 3, a differential electrical signal is input to the first lead terminal 320A and the second lead terminal 320B. A control signal for controlling the temperature adjustment 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 mount 313 is disposed on the first surface 311 side of the aperture member 310. In the first embodiment, the mount 313 is made of metal, and protrudes in the Z-axis direction from the first surface 311 of the eyelet member 310 toward the first lead terminal 320A and the second lead terminal 320B (see fig. 7). In the embodiment shown in FIG. 3, aperture member 310 is integrally formed with base 313. The eyelet member 310 and the mount 313 are at the same potential and form a rod. The rod of the first embodiment is formed by press working and is made of, for example, rolled steel having a thermal conductivity of 50 to 70[ W/mK ].

The relay substrate 330 is disposed on the Z-axis direction side of the mount 313. Specifically, for example, description will be given with reference to fig. 5 to 7. Fig. 5 is a diagram showing a state in which the relay substrate 330 is mounted on the mount 313, and is a diagram in which the eyelet member 310, the mount 313, the lead terminal 320, and the other structures than the relay substrate 330 are omitted. Fig. 6 is an enlarged view of the relay substrate 330. Fig. 7 is a schematic perspective view showing a lever. As shown in fig. 3 and 6, the relay substrate 330 is disposed on the X-axis direction side of the mount 313.

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

In addition, the relay substrate 330 has a first conductor pattern 331 and a second conductor pattern 332 formed across the lead connection surface 334 and the first bonding surface 335. Specifically, in the embodiment shown in fig. 3 to 6, the first conductor pattern 331 and the second conductor pattern 332 formed on the lead connection surface 334 and the first conductor pattern 331 and the second conductor pattern 332 formed on the first bonding surface 335 are seamlessly formed so as to have the same voltage with respect to the relay substrate 330. The first conductor pattern 331 and the second conductor pattern 332 are formed as a waveguide path through which differential electrical signals propagate. In particular, it is desirable that the first conductor pattern 331 and the second conductor pattern 332 have a taper portion 601 formed at a joint portion of the differential electrical signals. By forming the tapered portion 601, the impedance of the differential electrical signal can be prevented from abruptly changing at the joint 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 conductive adhesive 333, and a differential electrical signal is inputted thereto. In the embodiment shown in fig. 3 to 6, the first conductor pattern 331 is connected to the first lead terminal 320A by solder or conductive adhesive 333, and the second conductor pattern 332 is connected to the second lead terminal 320B by solder or conductive adhesive 333.

As described above, the relay substrate 330 is arranged such that the direction in which the lead connection surface 334 having a large area among the surfaces of the relay substrate 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. Thus, a plurality of members can be arranged in the aperture member 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 for differential electrical signal input are formed. Specifically, for example, the element mounting portion 340 includes a second bonding surface 343 on a surface facing the Y direction. The element mounting portion 340 has a third conductor pattern 341 and a fourth conductor pattern 342 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 bonding wires 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 connected to the first lead terminal 320A and the second lead terminal 320B, and a differential electrical signal is input thereto. Accordingly, differential electrical signals are input to the third conductor pattern 341 and the fourth conductor pattern 342 via the bonding wires 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, so that one of the optical signal and the differential electrical signal is converted into the other. Specifically, for example, the optical element 350 is a laser diode, and is mounted on the Y-direction surface of the element mounting portion 340. The optical element 350 receives differential electrical signals from the third conductor pattern 341 and the fourth conductor pattern 342, and converts the differential electrical signals into optical signals. When the optical element 350 functions as an optical receiving element, the optical element 350 receives an optical signal and converts the optical signal into a differential electrical signal. The converted differential electrical signal propagates to the first and second lead terminals 320A and 320B through the third and fourth conductor patterns 341 and 342, the bonding wire 380, the first and second conductor patterns 331 and 332. In the embodiment shown in fig. 3, the component mounting portion 340 is a substrate.

When bonding wires, in the case where the surfaces to which both ends of the bonding wire 380 are connected are directed in different directions, it is necessary to change the direction of the bonding object after bonding the bonding wire 380 to one terminal. As described above, since the normal directions of the first bonding surface and the second bonding surface are the same direction (the positive direction of the Y axis in the first embodiment as shown in fig. 3), it is not necessary to change the orientation of the optical subassembly 100 to be bonded. The normal directions are the same, and the angle between the first bonding surface 335 and the second bonding surface 343 is small enough that the direction of the bonding object does not need to be changed after bonding the bonding wire 380 to one surface and before bonding the bonding wire 380 to the other surface. That is, the first joint surface 335 and the second joint surface 343 are both oriented in the same direction (in the first embodiment, as shown in fig. 3, the positive direction of the Y axis), and the first joint surface 335 and the second joint surface 343 are substantially parallel to each other. Thus, the fabrication of the optical subassembly 100 is facilitated.

The temperature adjusting element 360 is disposed in contact with the first surface 311, and adjusts the temperature of the optical element 350. Specifically, for example, the temperature adjustment element 360 is a peltier element, and is disposed in contact with the first surface 311. The temperature adjustment element 360 cools the optical element 350 based on the control signals input from the third and fourth lead terminals 320C and 320D. In addition, the temperature adjustment element 360 may be omitted in the case where temperature adjustment is not required.

Further, in general, it is desirable that the differential electrical signal supplied to the optical element 350 be combined with a conductor pattern connected to the ground. The peltier element is configured by sandwiching both sides of the semiconductor element that moves heat by an insulating substrate. Therefore, when the temperature adjustment element 360 is a peltier element, the aperture member 310 and the element mounting portion 340 are insulated, and therefore, the ground potential cannot be supplied to the element mounting portion 340. However, according to the first embodiment, the path through which the differential electrical signal passes from the first lead terminal 320A and the second lead terminal 320B to the optical element 350 is formed as a waveguide path through which the differential electrical signal propagates. Therefore, as described later, even if the element mounting portion 340 is not connected to the ground, the high-frequency characteristics of the optical subassembly 100 can be improved.

The sub-carrier 370 is mounted on the temperature adjustment element 360 and on the element mounting portion 340. Specifically, for example, the sub-carrier 370 is disposed at a distance from the mount 313 in the X-axis direction on the Z-axis direction side of the temperature adjustment element 360.

The sub-carrier 370 is preferably composed of an insulating material having a relatively high thermal conductivity and a coefficient of thermal expansion close to that of the optical element 350. In the first embodiment, the sub-carrier 370 is formed of, for example, ceramic. Ceramics, whether metallic or nonmetallic, include inorganic solid materials such as shaped bodies, powders, films, etc. of inorganic compounds such as oxides, carbides, nitrides, borides, etc. For example, as the ceramic for the subcarrier 370, aluminum nitride having a thermal conductivity of 170 to 200[ W/mK ] is preferable. The surface of the sub-carrier 370 facing the Y-axis direction is provided with the element mounting portion 340.

The bonding wire 380 electrically connects the first and second conductor patterns 331 and 332 of the first bonding surface 335 and the third and fourth conductor patterns 341 and 342 of the second bonding surface 343. Specifically, three or more bonding wires 380 electrically connect the first conductor pattern 331 and the third conductor pattern 341. Similarly, 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 is disposed close to the bonding wire 380 connecting the second conductor pattern 332 and the fourth conductor pattern 342. Thus, three or more pairs of bond wires 380 form a waveguide path through which differential electrical signals propagate. By connecting three or more pairs of bonding wires 380, inductance parasitic on the bonding wires 380 can be reduced, and good transmission characteristics can be obtained.

Fig. 8 is a graph obtained by calculating transmission characteristics (S21) of the optical module with respect to the structure shown in fig. 3 and the structures of conventional examples 1 and 2 using a three-dimensional electromagnetic field simulator HFSS (High Frequency Structure Simulator; high frequency structure simulator).

The optical module of conventional example 1 includes an optical subassembly on which the temperature adjustment element 360 is not mounted. Specifically, the optical subassembly of conventional example 1 has the structure shown in fig. 9. The optical subassembly of conventional example 1 includes a conductive rod composed of a metal having a diameter of 5.6 mm. The stem includes an eyelet member 310 having a through hole 315, and a lead terminal 320 is secured to the through hole 315 by a dielectric 314 such as glass. Coaxial lines are formed by the eyelet members 310, the dielectric 314, and the lead terminals 320. The impedance of the coaxial line is integrated to 25Ohm. The lead terminal 320 penetrates a hole provided in the eyelet member 310, and a part thereof protrudes. The tip of the protruding lead terminal 320 is bonded to a conductor pattern mounted on the surface of the relay substrate 330 of the mount 313 protruding perpendicularly from the eyelet member 310 by AuSn solder. In the relay substrate 330, a microstrip line is formed by the pedestal 313 protruding from a rod as the ground potential and the conductor pattern. Further, the component mounting portion 340 is bonded to the mount 313. The element mounting portion 340 is formed of 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 having conductor patterns on the front and rear surfaces, and the conductor patterns on the rear surface are connected to a rod that is a ground potential. An optical element 350 is mounted on the element mounting portion 340.

The optical module of conventional example 2 includes an optical subassembly having a temperature adjustment element 360 mounted thereon. Specifically, the optical subassembly of conventional example 2 has the structure shown in fig. 10. The optical sub-assembly of conventional example 2 includes a temperature adjustment element 360 and a sub-carrier 370 in the central portion of the region of conventional example 1 where the mount 313 is provided. The sub-carrier 370 is formed of ceramic or metal having high thermal conductivity in order to improve heat dissipation. The stand 313 is provided separately at two positions on both sides of the temperature adjustment element 360 and the sub-carrier 370. The relay substrate 330 is disposed on the pedestal 313 separated at two places. The element mounting portion 340 on which the optical element 350 is mounted on the sub-carrier 370, and transmits and receives differential electrical signals to and from the lead terminal 320 via the separate relay substrate 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 rear surfaces thereof. The temperature adjustment element 360 is a peltier element, and therefore, the temperature adjustment element 360 has an insulating substrate at a portion facing the aperture member 310 and the sub-carrier 370. Therefore, the ground potential is not supplied to the back surface of the element mounting portion 340 on which the optical element 350 is mounted.

As shown in fig. 8, in the optical subassembly of conventional example 1, since the ground potential is supplied to the back surface of the element mounting portion 340, the transmission characteristics are high even in the high frequency range. However, the optical subassembly of conventional example 1 does not include the temperature adjustment element 360, and thus cannot be used in a high-temperature environment.

On the other hand, the optical subassembly of conventional example 2 includes the temperature adjustment element 360, and thus can be used in a high-temperature environment. However, as shown in fig. 8, in the optical subassembly of conventional example 2, since the ground potential is not supplied to the back surface of the element mounting portion 340, the transmission characteristics are degraded in the high frequency range.

In contrast, the optical subassembly 100 of the first embodiment includes the temperature adjustment element 360, and thus, can be used in a high-temperature environment. Further, as shown in fig. 8, the optical subassembly 100 of the first embodiment has higher transmission characteristics with respect to the high frequency characteristics, compared with the conventional example 2. Unlike conventional example 2, in the first embodiment, the relay substrate 330 is not divided, and thus, a waveguide path for propagating a differential electric signal is formed. The waveguide is formed across two perpendicular sides of the substrate. Therefore, unlike conventional example 2, in the first embodiment, the differential electrical signal is propagated from the lead terminal 320 to the front of the optical element 350 in a state where the electrical coupling between the differential electrical signals is maintained. Thus, even in a state where the ground potential is not supplied directly below the element mounting portion 340, the electromagnetic field propagates in the TEM mode without causing a transition to the higher-order mode by the electric coupling between the differential electric signals. Thus, 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 disposed across the element mounting surface 344 and the second bonding surface 343 on which the optical element 350 is mounted. Specifically, for example, the component mounting portion 340 is integrally formed with the sub-carrier 370. The third conductive pattern 341 and the fourth conductive pattern 342 are formed across the Y-direction facing surface and the Z-direction facing surface of the element mounting portion 340. As in the first embodiment, the third conductor pattern 341 and the fourth conductor pattern 342 are formed as a waveguide for propagating a differential electrical signal in the element mounting portion 340.

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

The relay substrate 330 includes a lead connection surface 334 extending in the normal direction of the first surface 311 and a first bonding surface 335 adjacent to the lead connection surface 334. In the second embodiment, the relay substrate 330 includes the lead connection surface 334 in the surface facing the X-axis direction and the first bonding surface 335 in the surface facing the Z-axis 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 bonding wires 380. In the second embodiment, the first conductor pattern 331 formed on the Z-direction surface of the relay substrate 330 is electrically connected to the third conductor pattern 341 formed on the Z-direction surface of the element mounting portion 340. The second conductor pattern 332 formed on the Z-direction surface of the relay substrate 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 substrate 330 and the element mounting portion 340 connected by wire bonding are both surfaces facing the Z direction. Therefore, joining can be easily performed. In addition, as in the first embodiment, the direction in which the lead connection surface 334 having a large area among the surfaces of the relay substrate 330 faces is arranged substantially perpendicular to the direction in which the surfaces of the third conductor pattern 341 and the fourth conductor pattern 342 face, and thus a plurality of members can be arranged in the aperture member 310 and can be easily manufactured.

In the optical subassembly 100 according to the second embodiment shown in fig. 11, the center of gravity of the sub-carrier 370 may be offset toward the relay substrate 330 with respect to the center of gravity of the aperture member 310. According to this fitting method, the upper part of the glass coaxial part can be used stably as the fitting area, and therefore, there is an advantage in downsizing.

In the optical subassembly 100 according to the second embodiment, the temperature adjustment element 360 may not be included, or three or more pairs of bonding wires 380 may be provided.

Next, a third embodiment will be described. Note that the same configuration as in the first and second embodiments is not described. As described above, according to the first embodiment, the electromagnetic field does not cause conversion to the higher order mode due to the electrical coupling between the differential electrical signals, and therefore, the differential electrical signals propagate as the TEM mode. Thus, good transmission characteristics can be obtained. However, as shown in the simulation result of fig. 8, when the intermediate substrate 330 is not supplied with the ground potential, the frequency band exhibiting good response characteristics is limited to 25GHz. According to the third embodiment, an optical semiconductor laser incorporating an electric field absorption type optical modulator exhibiting good response characteristics even in a high frequency region of 30GHz or more can be realized.

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, viewed from another direction. Fig. 14 is a schematic perspective view showing a state in which the relay substrate 330 of the third embodiment is connected to the mount 313 by solder or conductive adhesive 333.

The relay substrate 330 further has a first large-scale pattern surface 1302 on a surface adjacent to the first bonding surface 335, and the first large-scale pattern surface 1302 is provided with a first large-scale pattern 1202 connected to the ground. Specifically, the relay substrate 330 has a first land pattern 1202 connected to the ground on a surface opposite to the lead connection surface 334 (i.e., a surface facing the-X axis direction). In the example shown in fig. 13, the first land pattern 1202 is disposed on the entire surface of the surface opposite to the lead connection surface 334.

The first land pattern 1202 is disposed across the first joint surface 335. Specifically, for example, the first ground pattern 1202 is disposed across the first bonding surface 335 from a surface opposite to the lead connection surface 334. The first land patterns 1202 disposed on the first bonding surface 335 are disposed on both sides of the first conductor patterns 331 and the second conductor patterns 332.

The first land pattern 1202 may be disposed on the-X axis direction side of the first conductor pattern 331 and the second conductor pattern 332 of the first junction surface 335. According to this structure, the first conductive pattern 331 and the second conductive pattern 332 are surrounded by the first land pattern 1202 except for the portion disposed so as to straddle the wire connection surface 334 from the first bonding surface 335.

The sub-carrier 370 has a second ground pattern surface 1306 on a surface parallel to the first ground pattern surface 1302, and the second ground pattern surface 1306 is provided with a second ground pattern 1304 connected to the ground. Specifically, for example, the sub-carrier 370 has a second ground pattern 1304 connected to the ground on the side facing the-X axis direction. In the example shown in fig. 13, the second ground pattern 1304 is disposed on the entire surface of the second ground pattern surface 1306.

The second large pattern 1304 may be disposed across a surface adjacent to the second large pattern surface 1306. Specifically, for example, the second ground pattern 1304 may be arranged so as to cross from the second ground pattern surface 1306 to the surface of the sub-carrier 370 in the Y-axis direction. That is, the second large pattern 1304 may be disposed on the entire surface of the sub-carrier 370 that contacts the relay substrate 330. Further, the sub-carrier 370 may also be a block of metal.

The first large pattern 1202 is connected to the second large pattern 1304 by bonding wires 380. Specifically, for example, the first large pattern 1202 provided on the first large pattern surface 1302 of the relay substrate 330 is connected to the second large pattern 1304 provided on the second large pattern surface 1306 of the sub-carrier 370 via the bonding wire 380.

The element mounting portion 340 has a third ground pattern 1308 connected to the ground and extending at least across two adjacent surfaces. Specifically, for example, the element mounting portion 340 has a third land pattern 1308 connected to the ground on the second bonding surface 343. The third large pattern 1308 is disposed on both sides of the third conductor pattern 341 and the fourth conductor pattern 342. The third large scale pattern 1308 is connected to the first large scale 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 large pattern 1308 may be arranged so as to cross the surface on the back side of the second bonding surface 343 via the surface adjacent to the second bonding surface 343. The third land pattern 1308 arranged on the back side of the second bonding surface 343 is connected to the ground by being connected to the second land pattern 1304 arranged on the Y-axis direction surface of the sub-carrier 370.

The plurality of lead terminals includes a pair of lead terminals to 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 electrical signals is input to the first lead terminal 320A and the second lead terminal 320B. A pair of lead terminals are secured to a single through hole 315 through aperture member 310 by dielectric 314. 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 be integrated as a differential 100Ohm.

The third conductor pattern 341 and the fourth conductor pattern 342 shown in fig. 12 and 13 are patterns in the case where the optical element 350 is an electric field absorption type optical element. In the case of using an electric field absorption type optical element, a differential signal is generally modulated using a drive IC having an output impedance of 100 Ohm. Therefore, the impedance of the third conductor pattern 341 and the fourth conductor pattern 342 to which the differential signal is input is designed so as to be 100Ohm, and thus has a smaller pattern width than those of the first and second embodiments.

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 the high-frequency region of 30GHz 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; high-frequency structure simulator). It is understood that by supplying the ground potential to the third large pattern 1308 of the element mounting portion 340, the transmission characteristics of 30GHz or more are improved.

The first land pattern surface 1302 and the second land pattern surface 1306 may be provided not on the surface facing the-X axis direction but on the surface facing the Z axis direction. Specifically, for example, the relay substrate 330 may have a first land pattern 1202 connected to the ground on a surface facing the Z-axis direction. The sub-carrier 370 may also have a second ground pattern 1304 connected to the ground on the face facing the Z-axis direction. In this case, even when the relay substrate 330 is shorter than the mount 313 in the Z-axis direction, the first land pattern 1202 is exposed. Further, the first land pattern 1202 and the second land pattern 1304 are parallel, and thus can be connected by the bonding wire 380.

In the present specification, the term "eyelet member 310" is used to indicate a metal disk, but the eyelet member 310 has no substantial meaning in the shape of a disk, and may have another shape such as a polygonal column.

Claims

1. An optical subassembly, comprising:

an aperture member including a first surface, a second surface disposed on an 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, at least a part of which is inputted with a differential electrical signal;

a relay substrate including a lead connection surface extending in a normal direction of the first surface and a first bonding surface adjacent to the lead connection surface, wherein a first conductor pattern and a second conductor pattern are formed across the lead connection surface and the first bonding surface, and the first conductor pattern and the second conductor pattern formed on the lead connection surface are connected to the lead terminal by solder or conductive adhesive, and the differential electrical signal is input;

an element mounting part including a second joint surface formed with a third conductor pattern and a fourth conductor pattern for inputting the differential electric signal; and

An optical element which is mounted on the element mounting portion, is electrically connected to the third conductor pattern and the fourth conductor pattern, and converts one of the optical signal and the differential electrical signal into the other,

the first conductor pattern and the second conductor pattern of the first bonding surface are connected to the third conductor pattern and the fourth conductor pattern of the second bonding surface by bonding wires,

the normal directions of the first joint surface and the second joint surface are the same.

2. The optical subassembly of claim 1, wherein the optical subassembly comprises,

the optical element further includes a temperature adjusting element disposed in contact with the first surface for adjusting the temperature of the optical element.

3. An optical subassembly as claimed in claim 2, wherein,

the temperature control device further includes a sub-carrier mounted on the temperature control element and mounted on the element mounting portion.

4. An optical subassembly according to claim 3, wherein,

the center of gravity of the sub-carrier is offset toward the relay substrate side with respect to the center of gravity of the aperture member.

5. The optical subassembly of any one of claims 1 to 4, wherein,

The bonding wires are three or more pairs.

6. The optical subassembly of any one of claims 1 to 4, wherein,

the element mounting portion further includes an element mounting surface on which the optical element is mounted in a surface adjacent to the second bonding surface,

the third conductor pattern and the fourth conductor pattern are disposed across the element mounting surface and the second bonding surface.

7. The optical subassembly of claim 1, wherein the optical subassembly comprises,

the plurality of lead terminals include a pair of lead terminals to which corresponding signals are inputted,

the pair of lead terminals are fixed to a single through hole penetrating the eyelet member through a dielectric.

8. An optical subassembly according to claim 3, wherein,

the relay substrate further has a first ground pattern surface provided with a first ground pattern connected to the ground in a surface adjacent to the first bonding surface,

the sub-carrier has a second ground pattern surface in a surface parallel to the first ground pattern surface, the second ground pattern having a second ground pattern connected to the ground,

the first large pattern is connected to the second large pattern by a bonding wire.

9. The optical subassembly of claim 8, wherein the optical subassembly comprises,

the first land pattern is disposed across the first bonding surface,

the first land pattern disposed on the first bonding surface is disposed on both sides of the first conductor pattern and the second conductor pattern.

10. The optical subassembly of claim 8, wherein the optical subassembly comprises,

the element mounting portion is a metal block.

11. The optical subassembly of claim 8, wherein the optical subassembly comprises,

the element mounting portion has a third ground pattern connected to the ground and extending at least across two adjacent surfaces.