Optical Communication Element

Abstract

A COSA as an optical communication component that can prevent energy radiated in a package from causing performance degradation includes a DC block capacitor that is mounted on an upper surface of the package and located at a position different from those of a SiP chip and an optical modulator driver IC to cut off a DC signal included in a RF signal to be transmitted to the IC and a lid provided over an upper portion of the package. A separation projecting portion of the lid projecting toward an upper surface of the package separately defines a region where the capacitor is present and a region where the SiP chip and the IC are present. The separation projecting portion is connected to GND of the package, and the lid is at a GND potential.

Claims

1. An optical communication component comprising: a package having a flat plate shape; an optical communication element mounted on an upper surface of the package; an electronic circuit element mounted on the upper surface of the package and located at a position different from that of the optical communication element; a direct-current block device mounted on the upper surface of the package and located at a position different from those of the optical communication element and the electronic circuit element to cut off a direct-current signal included in a high-frequency signal transmitted to the electronic circuit element via a conductive pattern provided on the package; and a lid provided over an upper portion of the package to cover the optical communication element, the electronic circuit element, and the direct-current block device, the lid having a separation projecting portion that projects toward the upper surface of the package to separately define a region where the direct-current block device is present and a region where the optical communication element and the electronic circuit element are present.

2. The optical communication component according to claim 1, wherein the lid is at a ground potential.

3. The optical communication component according to claim 1, wherein the conductive pattern on the package includes RF wires placed to connect, as a whole, the direct-current block device, the electronic circuit element, and the optical communication element such that the direct-current block device is interposed between the RF wires.

4. The optical communication component according to claim 3, wherein a portion of each of the RF wires has a wiring structure in which the portion of the RF wire temporarily extends into an inner layer of the package via one metal via wire and then returns again to a surface layer via another metal via wire at another position.

5. The optical communication component according to claim 4, wherein a ground electrode is provided in a surface layer of the metal via wire and the ground electrode is electrically connected to a tip surface of the separation projecting portion of the lid.

6. The optical communication component according to claim 5, wherein the ground electrode and the tip surface of the separation projecting portion of the lid are maintained in an electrically connected state by adhesive fixation using an adhesive.

7. The optical communication component according to claim 6, wherein the adhesive is a non-conductive adhesive adhesively fixing a side wall of the separation projecting portion in the vicinity of the tip surface thereof to a top surface of the package or a conductive adhesive adhesively fixing the ground electrode to the tip surface of the separation projecting portion.

8. An optical communication component according to claim 1, wherein a material of the lid is a metal material having a high thermal conductivity and a material of the package has a thermal expansion coefficient close to that of a printed circuit board serving as a connection partner.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is an outer appearance perspective view when viewed from obliquely above in which a structural shape of a DC block in a package in an ICR as a known optical communication component is partially broken and exposed.

[0036] FIG. 2 is a partially enlarged view illustrating a result of simulating an electric field intensity of an RF signal in the package of the ICR illustrated in FIG. 1.

[0037] FIG. 3 is a diagram illustrating a cross section of an example of a basic structure of a COSA as a known optical communication component in a side surface direction.

[0038] FIG. 4 is a diagram illustrating a cross section of a basic structure of a COSA as an optical communication component according to a first embodiment of the present invention in the side surface direction.

[0039] FIG. 5 is a diagram illustrating a cross section of another example of a basic structure of a COSA as an optical communication component according to a comparative example in the side surface direction.

[0040] FIG. 6 is a diagram illustrating a cross section of a basic structure of a COSA as an optical communication component according to a second embodiment of the present invention in the side surface direction.

[0041] FIG. 7 is a cross-sectional view illustrating a partially broken conductive pattern of a grounded coplanar line including RF wires placed in a surface layer and GND electrodes disposed in an inner layer and in the surface layer, which is applicable to a package related to a principal portion of the COSA illustrated in FIG. 5.

[0042] FIG. 8 is a perspective view of a conductive pattern on the package illustrated in FIG. 7, which is partially illustrated in a cross section.

[0043] FIG. 9 is a cross-sectional view illustrating a partially broken conductive pattern including RF wires placed in an inner layer and GND electrodes disposed in the inner layer and in a surface layer, which is applicable to a package related to a principal portion of the COSA illustrated in FIG. 6.

DESCRIPTION OF EMBODIMENTS

[0044] Referring to the drawings, a detailed description will be given of an optical communication component according to each of embodiments of the present invention.

First Embodiment

[0045] FIG. 4 is a diagram illustrating a cross section of a basic structure of a COSA 20A as an optical communication component according to the first embodiment of the present invention in a side surface direction.

[0046] Referring to FIG. 4, the COSA 20A is similar to the COSA 20 in FIG. 3 in that a lid 27A has the projecting portion 27a and different from the COSA 20 in FIG. 3 in having a separation projecting portion 27b projecting toward the upper surface of the package 21 having the flat plate shape. The separation projecting portion 27b has a function of separately defining a region where the DC block capacitor 24a is present and a region where the SiP chip 25 serving as the optical communication element and the optical modulator driver IC 26 serving as the electronic circuit element are present.

[0047] The DC block capacitors 24a and 24b also cut off herein the DC signal included in the RF signal transmitted to the optical modulator driver IC 26, the TIA, and the like via the conductive pattern provided on the package 21. The conductive pattern may also be regarded as including the RF wires and the GND electrodes. This allows the DC block capacitors 24a and 24b to function as DC block devices protecting the various devices.

[0048] A one portion of the GND electrodes of the conductive pattern is electrically connected to a tip surface of the separation projecting portion 27b of the lid 27A. When a state of the connection is mechanically stable, sufficient contact is provided between the GND electrode and the tip surface of the separation projecting portion 27b. When the state of the connection is not mechanically stable, the GND electrode of the conductive pattern mentioned above and the tip surface of the separation projecting portion 27b mentioned above may also be bonded together using an adhesive or the like. However, when, e.g., a non-conductive adhesive is used as the adhesive, side walls of the separation projecting portion 27b in the vicinity of the tip surface thereof may be adhesively fixed appropriately to a top surface of the package 21 by using the adhesive so as to prevent the adhesive from being applied to the tip surface of the separation projecting portion 27b. Meanwhile, when a conductive adhesive is used as the adhesive, the tip surface of the separation projecting portion 27b may be adhesively fixed appropriately to the surface of the package 21 by using the adhesive. In either case, mechanical stability as well as an electrically connected state is maintained. When conduction is provided between the GND electrode and the tip surface of the separation projecting portion 27b of the lid 27A, the lid 27A is at a GND potential. Alternatively, the electrical connection between the lid 27A and the package 21 may also be provided not at the separation projecting portion 27b, but at another region such as an outer peripheral edge portion. In such a case, since the RF wires are placed on the surface of the package 21 to be brought into contact with the separation projecting portion 27b, when the lid 27A at the GND potential is brought closer thereto, it is required to give sufficient consideration so as not to affect a RF characteristic.

[0049] Note that, to the package 21 of the COSA 20A also, the laminated ceramic structure can be applied. For example, it is possible to connect the various devices with the RF wires included in the conductive pattern and place the metal via wires for routing and connection of the inner-layer GND electrode. However, it is also assumed that a detailed configuration of the conductive pattern is not specified herein except that the DC block capacitor 24a is interposed between the RF wires to be able to protect the optical modulator driver IC 26 serving as the electric circuit element.

[0050] The configuration is otherwise the same as in the case of the COSA 20. Specifically, the SiP chip 25 is configured by integrating an optical circuit, an optical modulator, a germanium optical receiver, and the like in one chip by using the silicon photonics technology of forming an optical element on a silicon substrate. An upper portion of the package 21 is covered with the lid 27A for protecting devices such as the optical modulator driver IC 26, the SiP chip 25, and the DC block capacitors 24a and 24b each mounted on the upper surface of the package 21. On the lower surface of the package 21, the solder BGA 31 for effecting connection and fixation to the printed circuit board as the connection partner is juxtaposed. The optical modulator driver IC 26 and the SiP chip 25 are connected and fixed by the individual Au bumps 32 provided in juxtaposition to the conductive pattern on the upper surface of the package 21.

[0051] Preferably, the lid 27A is formed of a metal material having a high thermal conductivity such as aluminum or a copper alloy and the like. Devices such as the optical modulator driver IC 26 and the TIA also generate heat during operation thereof, and accordingly a heat dissipation structure is used herein as countermeasures against heat generation. Specifically, the structure is such that the heat dissipation paste 28 is interposed between the projecting portion 27a corresponding to the inner projecting portion of the lid 27A and the upper surface of the optical modulator driver IC 26. Since the lid 27A used herein is also bonded to the package 21, the heat dissipation paste 28 may be applied appropriately to the inner projecting portion 27a of the lid 27A. This can provide a structure in which the heat generated from the optical modulator driver IC 26 is transferred to the lid 27A via the heat dissipation paste 28 present on the upper surface of the optical modulator driver IC 26 to be dissipated.

[0052] In the case of the COSA 20A according to the first embodiment, on the inner side of the lid 27A, the separation projecting portion 27b as well as the projecting portion 27a for using the heat dissipation paste 28 is provided. The separation projecting portion 27b separately defines the region where the DC block capacitor 24a is present and the region where the electronic circuit element is present. Consequently, the energy of the RF signal reflected by the portion corresponding to the DC block and radiated in the inner space of the package 21 is confined to a space formed by inner walls of the lid 27A and the top surface of the package 21. As a result, it is possible to sufficiently prevent the energy radiated at an unintended place in the package 21 from returning as noise and causing performance degradation.

[0053] Also, in the case of the COSA 20A according to the first embodiment, as the metal material of the lid 27A, a copper alloy or the like having a relatively small thermal expansion coefficient difference with the LTCC as the material of the package 21 is used preferably. In this case, it is possible to provide a compact and high-performance optical communication component that is hardly affected by thermal expansion. However, for a cost reduction, aluminum having a relatively large thermal expansion coefficient difference with the LTCC as the material of the package 21 can also be used as a metal material of the lid 27A. In such a case, due to the presence of the separation projecting portion 27b other than the projecting portion 27a, the lid 27A has an improved mechanical strength. As a result, even when aluminum is used as the metal material of the lid 27A, influence of thermal expansion is reduced, and it is possible to provide a compact and low-cost optical communication component.

[0054] Note that, in the exemplified structure of the COSA 20A according to the first embodiment, the separation projecting portion 27b separately defines the region where the DC block capacitor 24a is present. However, in the COSA 20A, the conductive pattern provided on the package 21 also differs depending on a mode of each of the various devices mounted on the upper surface of the package 21. Accordingly, it is possible to provide the COSA 20A with a structure in which an additional separation projecting portion is provided to separately define even the region where the DC block capacitor 24b is present. In other words, the number of the separation projecting portions to be disposed and places where the separation projecting portions are to be disposed can freely be changed depending on various devices mounted on the package 21 and the conductive pattern for connection thereof.

Second Embodiment

[0055] FIG. 6 is a diagram illustrating a cross section of a basic structure of a COSA 20C as an optical communication component according to the second embodiment of the present invention in the side surface direction. Note that, in the second embodiment, referring to FIG. 5 illustrating a cross section of another example of a basic structure of a COSA 20B as an optical communication component according to a comparative example, a description will be given of a difference between the respective basic structures of the COSA 20C and the COSA 20B, while consideration is given thereto.

[0056] Referring to FIG. 5, the COSA 20B according to the comparative example is different from the COSA 20 in FIG. 3 in a routing and connection structure of a conductive pattern on a package 21B having a flat plate shape. To the package 21B, a laminated ceramic package 21Ba is applied, and routing of the RF wires 22, GND electrodes 23, and metal via wires described later is performed. The RF wires 22 are placed so as to connect, as a whole, the DC block capacitor 24a, the optical modulator driver IC 26, and the SiP chip 25 such that the DC block capacitor 24a is interposed between the RF wires 22. Note that the lid 27 is merely configured to have a heat dissipation projecting portion 27a.

[0057] In the laminated ceramic package 21Ba, the metal via wire connecting the GND electrode 23 on an upper surface of the package 21B and the solder BGA 31 in a direction of lamination is applied. Note that, around the metal via wire, via wires of the GND electrode 23 are similarly illustrated. Additionally, the metal via wire connecting the RF wire 22 connected to the DC block capacitor 24a on the upper surface of the package 21B and the solder BGA 31 in the direction of lamination is also applied. Still additionally, the metal via wire connecting the inner-layer GND electrode 23 of the package 21B and the solder BGA 31 in the direction of lamination is also applied.

[0058] The via wires of the GND electrodes 23 are placed so as to surround the metal via wire of the RF wire 22 and, by using a structure similar to that of a coaxial line, it is possible to implement a characteristic with reduced reflection and attenuation of the PF signal. Note that the GND electrodes 23 formed in layers underlying the RF wires 22 formed on the top surface of the package 21B include the GND electrode 23 and the metal via wire in the surface layer not shown, and a layout thereof is illustrated in FIG. 7 described later.

[0059] Referring to FIG. 6, the COSA 20C is different from the COSA 20B in FIG. 5 in that a laminated ceramic package 21Aa is applied as a routing and connection structure in a conductive pattern on a package 21A having a flat plate shape. Various devices provided on an upper surface of the package 21A are the same as those used in the case of the first embodiment. The lid 27A is configured to have the projecting portion 27a and also have the separation projecting portion 27b. Note that, as illustrated in the first embodiment, as the material of the lid 27A, the metal material having the high thermal conductivity is used and, as the material of the package 21A, the LTCC material or the like having the thermal expansion coefficient closer to that of the printed circuit board as the connection partner is used.

[0060] The laminated ceramic package 21Aa has a wiring structure in which a portion of the RF wire 22 temporarily extends into the inner layer of the package 21A via one of metal via wires 29 and then returns again to the surface layer via another of the metal via wires 29 at another position. The RF wires 22 are placed so as to connect, as a whole, the DC block capacitor 24a, the optical modulator driver IC 26, and the SiP chip 25 such that the DC block capacitor 24a is interposed between the RF wires 22. Note that the GND electrodes 23 formed in the layers overlaying and underlying the RF wires 22 formed in the inner layer of the package 21A have metal via wires not shown, and a layout thereof is illustrated in FIG. 9 described later.

[0061] In the case of the COSA 20C also, the separation projecting portion 27b separately defines the region where the DC block capacitor 24a is present and the region where the electronic circuit element is present. Consequently, the energy of the RF signal reflected by the portion corresponding to the DC block and radiated in an inner space of the package 21A is confined to a space formed by the inner walls of the lid 27A and a top surface of the package 21A. As a result, it is possible to prevent the energy radiated at an unintended place in the package 21A from returning as noise and causing performance degradation.

[0062] Additionally, in the case of the COSA 20C, the portions of the RF wires 22 connecting the DC block capacitor 24a and the optical modulator driver IC 26 are placed in the inner layer of the package 21A and, in the surface layer of the inner-layer portion in which the RF wires 22 are placed, the GND electrode 23 is disposed. Such a configuration allows the tip surface of the separation projecting portion 27b of the lid 27A to come into contact with the GND electrode 23 on the upper surface of the package 21A and be electrically connected thereto without bringing the tip surface of the separation projecting portion 27b into contact with the RF wire 22.

[0063] In other words, such a form allows the space in which the DC block is provided to be provided as a closed space. Elements forming the closed space include the GND electrode 23 on the top surface of the package 21A to be connected to the tip surface of the separation projecting portion 27b of the lid 27A and inner walls of the lid 27A at the GND potential in such a state of connection. Such elements also include the GND electrode 23 formed on an end side of the top surface of the package 21A to be bonded to an end surface of an edge portion of the lid 27A.

[0064] In the COSA 20C having such a configuration, the energy of the RF signal reflected by the DC block portion and radiated in the inner space of the package 21A is confined to a space formed by the lid 27A at the GND potential and the GND electrode 23 on the upper surface of the package 21A. A confining effect achieved by the COSA 20C is more remarkable than that achieved by the COSA 20A in the first embodiment.

[0065] In other words, the COSA 20C in the second embodiment achieves the same actions and effects as those achieved by the COSA 20A in the first embodiment and can more reliably prevent occurrence of performance degradation. As a result, it is possible to provide a compact and low-cost optical communication component having an excellent RF characteristic. In particular, in the case of the COSA 20C, the portions of the RF wires 22 are placed in the inner layer of the package 21A to allow the tip surface of the separation projecting portion 27b of the lid 27A to be connected mechanically solidly to the GND electrode 23 on the top surface of the package 21A. As a result, to maintain a connected state, bonding the side walls in the vicinity of the tip surface of the separation projecting portion 27b of the lid 27A and the top surface of the package 21A together using, e.g., the non-conductive adhesive 30 or the like is effective, as illustrated in FIG. 6. When the non-conductive adhesive 30 is used, it is preferable to prevent the adhesive 30 from being applied to the tip surface of the separation projecting portion 27b and provide conduction between the GND electrode 23 and the lid 27A through the tip surface of the separation projecting portion 27b. Meanwhile, when the conductive adhesive is used, the tip surface of the separation projecting portion 27b and the GND electrode 23 on the upper surface of the package 21A are adhesively fixed to each other by using the adhesive. In either case, it is possible to provide a form in which mechanical stability and an electrically connected state are simultaneously maintained. Alternatively, as described in the first embodiment, it is also possible to provide electrical connection between the lid 27A and the package 21 not at the separation projecting portion 27b, but at another place, and points to be considered in that case are also as described above. In this state, the lid 27A is at the GND potential.

[0066] The electronic circuit element to be used in the optical communication component comes in various types such as a type that requires heat dissipation and a type that requires a potential at a back surface thereof to be reduced to the GND potential. For example, the optical modulator driver IC 26 illustrated in each of FIGS. 3, 4, 5, and 6 is of a type that requires heat dissipation and also requires a potential at a back surface thereof to be reduced to the GND potential. This results from flip-chip mounting of the optical modulator driver IC 26 with the back surface thereof facing upward. The SiP chip 25 illustrated in each of the drawings mentioned above is also flip-chip mounted.

[0067] When consideration is given to such circumstances, there is a case where a paste for which a material having an optimal property is to be selected and which need not necessarily have a strong bonding force, such as a thermally conductive paste having an excellent heat dissipation property or a low-resistance conductive paste, may be applied. In such a point also, it can be said that the form in the second embodiment in which a bonding area can be increased to ensure a bonding strength between the lid 27A and the package 21A is advantageous. In other words, by ensuring the bonding strength between the lid 27A and the package 21A as appropriate, it is possible to use the optical communication component for a long period without separating the lid 27A from the package 21A in a range of −5° C. to 85° C. corresponding to an operating temperature of the optical communication component. In such a case, it is possible to provide the optical communication component excellent in mechanical stability and long-term reliability.

[0068] A structure in which the portions of the RF wires 22 connecting the DC block capacitor 24a and the optical modulator driver IC 26 are placed in the inner layer of the package 21A and the GND electrode 23 is disposed in the surface layer, such as that of the COSA 20C, has various advantages. This structure allows a structure in which the RF wires 22 are circumferentially surrounded by the GND electrodes 23 to be provided, which is effective in improving a characteristic compared to the grounded coplanar line applicable to a case where the RF wires 22 are on the top surface of the package 21A. In other words, by also covering the upper portions of the RF wires 22 with the GND electrodes 23, it is possible to reduce likelihood of entrance of noise from the outside and reduce radiation of the RF signal to the outside.

[0069] The following will add technical supplementary notes with respect to the laminated ceramic package 21Ba of the COSA 20B according to the comparative example described above and the laminated ceramic package 21Aa of the COSA 20C according to the second embodiment.

[0070] FIG. 7 is a cross-sectional view illustrating a partially broken conductive pattern applicable to the package 21B related to a principal portion of the COSA 20B according to the comparative example described above. The conductive pattern on the laminated ceramic package 21Ba is a grounded coplanar line including the RF wires 22 placed in the surface layer and the GND electrodes 23 disposed in the inner layer and in the surface layer. FIG. 8 is a perspective view of the conductive pattern on the package 21B, which is partially illustrated in a cross section. Note that, in FIG. 7, the layout of the GND electrode 23 in the surface layer and the metal via wires 29, which is not illustrated in FIG. 5, is also illustrated.

[0071] FIG. 9 is a cross-sectional view illustrating a partially broken conductive pattern applicable to the package 21A related to a principal portion of the COSA 20C according to the second embodiment described above. The conductive pattern on the laminated ceramic package 21Aa includes the RF wires 22 placed in the inner layer and the GND electrodes 23 disposed in the inner layer and in the surface layer. In other words, FIG. 9 illustrates a form in which the inner-layer RF wires 22 are surrounded by the GND electrodes 23 in the surface layer and in the inner layer and by the metal via wires 29 in the inner layers. Note that, in FIG. 9, a layout of the metal via wires 29 not illustrated in FIG. 6 is also illustrated.

[0072] In each of the modes in FIGS. 7 to 9, a line form of a structure (GSSG structure) in which the GND electrode 23 is absent between the two RF wires 22 serving as the differential lines is illustrated. However, as in the case of the ICR 10 illustrated in FIG. 1, a line form of a structure (GSGSG) in which the GND electrodes 23 are interposed between the two RF wires 22 can also be used instead. Therefore, the optical communication component of the present invention is not limited to the configuration disclosed in each of the embodiments.

[0073] Note that, in the exemplified structure of the COSA 20C according to the second embodiment also, the separation projecting portion 27b separately defines the region where the DC block capacitor 24a is present. However, in the COSA 20C, the conductive pattern provided on the package 21A also differs depending on a mode of each of the various devices mounted on the upper surface of the package 21A. Accordingly, it is possible to provide the COSA 20C with a structure in which, in the same manner as described in the first embodiment, an additional separation projecting portion is provided to separately define even the region where the DC block capacitor 24b is present. In other words, the number of the separation projecting portions are to be disposed and places where the separation projecting portions are to be disposed can freely be changed depending on various devices mounted on the package 21A and the conductive pattern for connection thereof.