Patent Publication Number: US-2007116472-A1

Title: Package for optical transceiver module

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority to and the benefit of Korean Patent Application No. 2005-113006, filed Nov. 24, 2005, the disclosure of which is incorporated herein by reference in its entirety.  
     BACKGROUND  
      1. Field of the Invention  
      The present invention relates to a package for optical semiconductor devices, and more particularly, to a high-density small package for a monolithic-integrated bidirectional optical transceiver module.  
      2. Discussion of Related Art  
      Currently, while new services such as high-speed multimedia Internet, video conference, Internet protocol (IP) telephony, video on demand, Internet game, telecommuting, electronic commerce, tele-education, e-learning, distance learning, telemedicine, and so on are gradually being realized and a transmission capacity of a backbone network considerably increases, a transmission capacity of a subscriber network is hardly changed. This means that a bottleneck phenomenon may occur between subscribers and a backbone network when various multimedia services are provided using the subscriber network. Even neither x digital subscriber line (xDSL), which is currently the most widely used subscriber network solution, nor cable modem network can provide the above-mentioned services. There is a need for a new technology capable of accommodating all of data, sound, and video services with an inexpensive, simple network architecture and excellent scalability.  
      Recently, an Ethernet passive optical network (PON) technology has come into the spotlight as a new subscriber network technology. PONs roughly includes an asynchronous transfer mode (ATM) PON and an Ethernet PON (E-PON). The ATM PON has been developed to provide all of IP data service, video service, and high-speed service such as 10/100 Mbps Ethernet at a low cost and in a high speed. However, an ATM-PON standard is not suitable for subscriber networks because of its insufficient video transmission capability and bandwidth, and high complexity and cost. Accordingly, high-speed Ethernet, giga-byte Ethernet, and the like are developed and eventually an Ethernet PON having a bandwidth of 1.25 Gbps is emerged.  
      A monolithic integrated bidirectional optical transceiver module for an Ethernet PON comprises, on a single semiconductor chip, a photodetector for receiving an optical signal, a laser diode for transmitting the optical signal, a monitor photodetector for monitoring operation of the laser diode, an electronic device, and a package component. The monolithic integrated bidirectional optical transceiver module is intended to enable an electric signal converted from an optical signal by the photodetector to be input to the electronic device disposed in the module and thereby to be amplified and modulated, and intended to enable an electrical signal input to the electronic device to be converted into an optical signal by the laser diode and thereby to be transmitted to an optical fiber. Therefore, in a package for the monolithic integrated bidirectional optical transceiver module, a number of lead frames increases. Thus, signal lines of a small TO(Transceiver Optical)-can package having a diameter of 4.6 mm or 5.6 mm should be disposed at a high density in order to implement the module in a small size.  
      A conventional TO-can package for an optical transmission module is shown in  FIGS. 1A and 1B . As illustrated in  FIGS. 1A and 1B , the conventional TO-can package is configured using a stem  113 . A pair of lead terminals  105  for a photodiode and a lead terminal  112  for signal transmission pass through the stem  113  and are isolated from the stem  113  by a glass material  106 . In addition, a metal mount  901  on which a sub-mount  102  and a semiconductor laser  103  are mounted is mounted adjacent to the lead terminal  112  for signal transmission on an upper surface of the stem  113 . Also, another sub-mount  108  and a photodiode  107  for monitoring are mounted on a recessed floor  109  of the upper surface. Here, the photodiode  107  for monitoring is mounted at a position where laser beam is input, the laser beam being emitted from a surface opposite to an emitting surface of the semiconductor laser  103 . In  FIG. 1A , a reference numeral  114  denotes a lead terminal for grounding.  
      In this manner, the above-described conventional optical transmission module is configured by providing the stem  113  for a TO-can package, mounting the semiconductor laser  103  with the sub-mount  102  located on one side of the metal mount  901 , mounting the photodiode  107  for monitoring on the recessed floor  109  with the sub-mount  108 , and connecting between the semiconductor laser  103 /photodiode  107  and the lead terminals by wires  104 ,  110  and  111 .  
       FIGS. 2A and 2B  show another conventional TO-can package for an optical transmission module. The TO-can package shown in  FIGS. 2A and 2B  has the same structure as the conventional TO-can package described above with reference to  FIGS. 1A and 1B , except that it uses a new mount  101  to enhance a radio frequency (RF) characteristic. Therefore, the reference numerals used in  FIGS. 1A and 1B  are also used in  FIGS. 2A and 2B . In  FIGS. 2A and 2B , the mount  101  is formed of a metal having excellent electric conductivity and thermal conductivity. The mount  101  has a side surface  101   b  on which a semiconductor laser  103  is mounted, and a circumferential surface  101   a  surrounding a lead terminal  112  for signal transmission. The semiconductor laser  103  is mounted on the side surface  101   b  using a sub-mount  102 . The mount  101  is disposed on an upper surface of the stem  113  so that the semiconductor laser  103  is positioned substantially in a center of the upper side of the stem  113  and the circumferential surface  101   a  is concentric with the lead terminal  112  for signal transmission. In this TO-can package, the circumferential surface  101   a  of the mount  101  is formed to have substantially the same diameter as a through hole into which the lead terminal  112  for signal transmission is inserted.  
      However, the conventional arts set forth above are intended to develop a TO-can package for an optical semiconductor laser or optical semiconductor photodiode. More specifically, the TO-can package for only an optical semiconductor laser or optical semiconductor photodiode generally comprises one or two high-speed signal lead wires, one direct current (DC) signal lead wire, and one ground lead wire. Thus, the TO-can package has a drawback in that a density of the signal lines on a stem having a diameter of 4.6 mm or 5.6 mm is very low. Therefore, since the TO-can package set forth above is difficult to apply to a monolithic integrated bidirectional optical transceiver module, a new TO-can package is required.  
      In other words, a monolithic integrated bidirectional optical transceiver module comprises a trans-impedance amplifier chip for primarily amplifying a signal photoelectrically converted by an optical semiconductor photodiode, and a single optical semiconductor chip including an optical semiconductor laser, a monitor photodiode and an optical semiconductor photodiode. Therefore, a package for the module needs a total of nine signal lead wires including at least one high-speed signal transmission lead wire for the optical semiconductor laser, one lead wire for the monitor photodiode, two high-speed signal transmission lead wires for the trans-impedance amplifier, one DC signal lead wire for the trans-impedance amplifier, and four ground lead wires for controlling signal interference between the optical semiconductor laser and optical semiconductor photodiode. The single optical semiconductor chip may further comprise an optical amplifier upon demands. In this case, the package may further require one signal lead wire for the optical amplifier and one signal lead wire for checking operational performance of the trans-impedance amplifier. Accordingly, the package requires a total of eleven signal lead wires.  
      However, the conventional arts have a limit in that only four or five lead wires are allowed to be formed within the same package size, e.g., a diameter of 4.6 mm or 5.6 mm because they utilize only the upper surface and one side surface of the metal mount  901  or  101  formed on the stem  113 , as seen in  FIGS. 1A, 1B ,  2 A and  2 B.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a high-density package for miniaturizing a monolithic integrated bidirectional optical transceiver module developed to implement an Ethernet passive optical network (PON) technology. In other words, the present invention is directed to provide a package for an optical transceiver module capable of significantly increasing signal density within the same size.  
      One aspect of the present invention provides a package for an optical transceiver module, comprising a stem having through holes; a metal mount positioned on an upper surface of the stem; a signal line disposed in the metal mount; and a plurality of lead wires protruding from a lower surface of the stem and electrically connected to an optical device mounted on the metal through the through holes.  
      The signal line may pass through the metal mount and be isolated from the metal mount by an insulator.  
      The signal line may be separately fabricated, and be disposed in a groove of the metal mount.  
      The lead wires may extend parallel to the largest surface of the metal mount.  
      One of the lead wires may pass through the metal mount and be disposed for intended impedance matching upon high-speed signal transmission.  
      An end of one of the lead wires may be exposed on a side surface of the metal mount for intended impedance matching upon high-speed signal transmission.  
      The lead wires may be united as a lead-wire group having a same characteristic.  
      The optical device may include a bidirectional semiconductor device in which an optoelectronic device for transmitting an optical signal, a monitor photoelectronic device for monitoring operation of the optoelectronic device, and a photoelectronic device for receiving the optical signal are monolithically integrated.  
      The metal mount may have a trans-impedance amplifier mounted thereon, the trans-impedance amplifier amplifying and modulating an electric signal converted by the photoelectronic device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
       FIGS. 1A and 1B  are diagrams illustrating a conventional TO-can package for an optical transmission module;  
       FIGS. 2A and 2B  are diagrams illustrating another conventional TO-can package for an optical transceiver module;  
       FIG. 3A  is a perspective view of a package for an optical transceiver module according to a first exemplary embodiment of the present invention;  
       FIG. 3B  is another perspective view of the package of  FIG. 3A  when viewed from the opposite side;  
       FIG. 4A  is a perspective view of a package for an optical transceiver module according to a second exemplary embodiment of the present invention;  
       FIG. 4B  is another perspective view of the package of  FIG. 4A  when viewed from the opposite side; and  
       FIG. 5  is a perspective view of a package for an optical transceiver module according to a third exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Hereinafter, an exemplary embodiment of the present invention will be described in detail. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various types. Therefore, the present embodiment is provided for complete disclosure of the present invention and to fully inform the scope of the present invention to those ordinarily skilled in the art. Like elements are denoted by like reference numerals throughout the drawings. Matters related to the present invention and well-known in the art will not be described in detail when deemed that such description would detract from the clarity and concision of the disclosure.  
       FIG. 3A  is a perspective view of a package for an optical transceiver module according to a first exemplary embodiment of the present invention, and  FIG. 3B  is another perspective view of the package of  FIG. 3A  when viewed from the opposite side.  
      Referring to  FIGS. 3A and 3B , the package for an optical transceiver module according to this embodiment includes a stem  213 , a metal mount  201 , signal lines  204  (hereinafter, referred to as “connection signal lines” to be distinguished from other signal lines or lead wires), and a plurality of lead wires  206 ,  207 ,  207   a,    208  and  209 .  
      The stem  213  is a component of the TO(Transceiver Optical)-can package, and has through holes that pass through the upper surface and lower surface thereof. The through holes may be formed to have a cross section of circular shape, oval shape, or the like. The stem  213  further includes a step portion  213   a  in the upper surface thereof for connection with a cap or an optical fiber cable (not shown in the drawings).  
      The metal mount  201  is made of a metal or alloy having excellent durability and thermal conductivity, and mounted on the upper surface of the stem  213 . A laser diode, a monitor photodetector, and a photodetector are mounted on one side surface of the metal mount  201 . The laser diode converts an electric signal such as a radio frequency (RF) signal into an optical signal and emits the optical signal, the monitor photodetector monitors operation of the laser diode, and the photodetector receives an optical signal and converts the optical signal into an electric signal. In this embodiment, a bidirectional semiconductor device  202  in which the laser diode, the monitor photodetector, and the photodetector are monolithically integrated is used. In  FIG. 3A , reference numerals  202   a,    202   b  and  202   c  respectively denote the laser diode, monitor photodetector, and photodetector in the monolithic integrated bidirectional semiconductor device  202 . Also, the one side surface of the metal mount  201  denotes the largest surface which is nearly orthogonal to the upper surface of the stem  213  and on which the optical device  202  is mounted.  
      In addition, a trans-impedance amplifier  203  and capacitors  205   a  and  205   b  are mounted on the one side surface of the metal mount  201  or the other side surface thereof facing the one side surface. The trans-impedance amplifier  203  amplifies and modulates the electric signal converted by the laser diode  202   a,  the capacitor  205   a  removes noise of the trans-impedance pre-amplifier  203 , and the capacitor  205   b  removes noise for direct current (DC) stabilization. The three connection signal lines  204  are disposed to pass through the metal mount  201  and to be exposed on the one side surface and the other side surface. Meanwhile, an impedance-matching resistor and a capacitor may be additionally mounted on the one side surface or the other side surface of the metal mount  201  upon demands.  
      The lead wires  206 ,  207 ,  207   a,    208  and  209  are disposed to extend substantially parallel to the one side surface and the other side surface of the metal mount  201 . In addition, the lead wires  206 ,  207 ,  207   a,    208  and  209  protrude from the lower surface of the stem  213 , extended through the through holes of the stem, and electrically connected to the optical device  202  mounted on the one side surface of the metal mount  201  through bonding wires  210 ,  211  and  212 (hereinafter, referred also to as “wires”).  
      One lead wire  206  among the lead wires is disposed to pass through the metal mount  201 , with an end of the lead wire  206  protruding from another side surface facing a side surface joined to the upper surface of the stem  213 . This is to consider intended impedance for high-speed signal transmission. The end of the lead wire  206  is connected to the laser diode  202   a  positioned on the other side surface of the metal mount  201  through the wire  210 .  
      Two lead wires  207  among the lead wires are connected to the trans-impedance amplifier  203  through the wires  211 . The trans-impedance amplifier  203  is connected to the photodetector  202   c  for optical signal reception, to one end of a middle connection signal line among the three connection signal lines  204 , and to the capacitor  205   a  for removing impedance amplifier&#39;s noise through other wires.  
      One lead wire  207   a  among the lead wires transmits a DC signal, and is connected to the capacitor  205   a  for removing impedance amplifier&#39;s noise through the wire  211 .  
      Three lead wires  208  among the lead wires are respectively connected to the other ends of the three connection signal lines  204  through the wires  212 . Here, one of the three lead wires  208  is connected to the other end of the middle connection signal line among the three connection signal lines  204  through the noise-removal capacitor  205   b  for DC stabilization, and another of the three lead wires  208  is electrically connected to the monitor photodetector  202   b  through the connection signal line  204 .  
      Remaining four lead wires  209  among the lead wires are ground lead wires for controlling signal interference between the laser diode  202   a  and the photodetector  202   c.  Each lead wire except the ground lead wires is isolated from the stem  213  by insulators  214  such as a glass insulator and a ceramic insulator. Similarly, the connection signal lines  204  are isolated from the metal mount  201  by the insulator  214  such as a glass insulator and a ceramic insulator.  
      Each lead wire described above is designed to have specific intended impedance by coaxial-cable impedance matching. For example, each lead wire is designed to have intended impedance by the size of the lead wire protruding from the lower surface of the stem  213  and by intervals between the lead wires. In addition, in the present invention, lead wires having the same characteristic are united in an oval shape such that a signal density increases.  
       FIG. 4A  is a perspective view of a package for an optical transceiver module according to a second exemplary embodiment of the present invention, and  FIG. 4B  is another perspective view of the package of  FIG. 4A  when viewed from the opposite side.  
      Referring to  FIGS. 4A and 4B , the package for an optical transceiver module according to the second embodiment is characterized in that connection signal lines are separately fabricated and disposed in a groove  201   a  of a metal mount  201 , unlike the package for an optical transceiver module of the first embodiment.  
      In other words, in this embodiment, the connection signal lines are not fabricated together with the metal mount  201 . A connection signal line block  204   a  that is separately fabricated is mounted after the groove  201   a  of   shape is formed in the metal mount  201 . With this structure, it is easy and simple to fabricate the connection signal lines being disposed in the metal mount, and thus the package manufacturing process can be simplified compared to the first embodiment.  
      Meanwhile, the groove  201   a  of the metal mount can be formed in a proper shape like   other than the shape mentioned above. The connection signal line can be formed of a conductor coated on or filled in the inner circumference surface of a via having a circular cross-section, or of a conductor having a quadrangular cross-section, like the connection signal lines of the first embodiment. Similarly, lead wires can be formed to have another cross-section such as a circular cross-section other than the quadrangular cross-section.  
       FIG. 5  is a perspective view of a package for an optical transceiver module according to a third exemplary embodiment of the present invention.  
      Referring to  FIG. 5 , the package for an optical transceiver module according to the third embodiment is characterized in that a lead wire  206  passing through a metal mount  201  is not exposed on an upper side surface of the metal mount  201  but an end  206   a  of the lead wire  206  is exposed on the one side surface, unlike the package of the first embodiment. Here, the one side surface of the metal mount  201  indicates a surface on which a monolithic integrated bidirectional semiconductor device  202  is mounted.  
      The lead wire  206  is designed considering intended impedance upon high-speed signal transmission. With the structure described above, the lead wire  206  can be designed to pass through the metal mount  201  or to be exposed on one surface of the metal mount  201 , thereby increasing the freedom degree of design.  
      Meanwhile, the package for an optical transceiver module according to third embodiment may be implemented so that a separately fabricated connection signal line block is disposed in a groove of the metal mount  201 , like the connection signal line block of the second embodiment.  
      As described above, the present invention allows lead wires to be connected to both of one side surface and the opposite surface of a metal mount mounted on a stem, thereby increasing a signal density more than two times in a package having the same size. In other words, the present invention can increase the density of lead wires included in a TO-can package having a diameter of 4.6 mm or 5.6 mm in order to miniaturize a monolithic integrated bidirectional module for a 1.25 Gbps Ethernet Passive Optical Networks.  
      While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.