JP4784460B2 - Optical communication module - Google Patents

Description

  The present invention relates to an optical communication module.

Patent Document 1 listed below describes a radiation noise reduction device for reducing the influence of radiation noise generated from a cable connected to a printed board on a frame ground (FG). This radiation noise reduction device has an FG electrode provided on a printed circuit board and connected to a shielded cable, an SG electrode (SG: signal ground), and a capacitor element provided between the FG electrode and the SG electrode. The noise current generated by radiation noise and flowing to the frame ground is shunted to the signal ground.
JP 2003-283177 A

  Since an optical communication module such as an optical transceiver module operates at a high speed on the order of GHz, in order to reduce the influence (generation of noise current) of the radiation noise as described above on the frame ground, the FG electrode and the SG electrode It is desirable to set the capacitance of the capacitor inserted between them to several pF or more. In addition, this capacitor must have a withstand voltage against an AC voltage of 500 V or more as defined in the IEC standard (IEC: International Electro-technical Commission). However, a chip-type capacitor used in an optical communication module does not have the above-described capacity and withstand voltage, and it is difficult to develop a capacitor having such a capacity and withstand voltage. Therefore, an object of the present invention is to provide an optical communication module that can reduce the influence of radiation noise on the frame ground while maintaining a relatively high withstand voltage.

  The present invention provides a metal first package, a laser diode housed in the first package, a first lead pin connected to the first package, and an anode terminal and a cathode terminal of the laser diode. An optical transmission module having second and third lead pins connected to each other, a front surface and a back surface, and an electronic circuit having a signal ground potential connected to the second and third lead pins is connected to the front surface. A circuit board provided on the top surface; a first electrode provided on the front surface; connected to the first lead pin; and provided on the back surface, the first substrate sandwiching the circuit board. A second electrode connected to the signal ground potential and electrically connected to the first package, the optical transmission module and the circuit board And the first electrode and the second electrode are electrically insulated in the case to form a capacitance with the circuit board interposed therebetween. And The present invention further includes an optical receiver module, and the optical receiver module includes a metal second package, a photodiode housed in the metal second package, and the metal second package. A ground lead pin connected to the package, and the ground lead pin is connected to the second electrode on the circuit board and insulated from the metal case.

  Thus, the first electrode connected to the metal case, the circuit board, and the second electrode form a capacitance (capacitor). Therefore, a part of the influence of the radiation noise generated by the bias current of the laser diode flowing on the second and third lead pins on the case can be borne by the second electrode via this capacitor. . Thereby, the influence which radiation noise has on a case (frame ground) can be reduced. Further, there is no need to newly provide a capacitor element between the first electrode and the second electrode. In addition, the capacitor constituted by the first electrode, the circuit board, and the second electrode has a relatively large withstand voltage because the base of the circuit board has an insulating property.

  According to the present invention, it is possible to reduce the influence of radiation noise on the frame ground while maintaining a relatively high withstand voltage.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, if possible, the same elements are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 is a diagram for explaining a configuration of an optical communication module 2 according to the embodiment. The optical communication module 2 is a small optical transceiver including a TOSA 4a (TOSA: Transmitter Optical Sub-Assembly), a ROSA 4b (ROSA: Receiver Optical Sub-Assembly), a circuit board 5, and a case 6. The TOSA 4 a and the ROSA 4 b are fixed to the side wall 6 a of the case 6, and the circuit board 5 is accommodated in the case 6. The case 6 is made of a metal material and serves as a frame ground. The base of the circuit board 5 is made of an insulating prepreg, and a circuit pattern is provided on the base.

  The TOSA 4a is an optical transmission module having a laser diode 7 and a package 8 (first package) that accommodates the laser diode 7. The laser diode 7 has an anode terminal and a cathode terminal (not shown), and emits laser light according to the supplied bias current. The package 8 is made of a metal material, but is insulated from any electronic element (for example, the laser diode 7) included in the TOSA 4a. The TOSA 4a further includes a stem 10a provided at one end 10 of the package 8, and lead pins 12a to 12c extending from the stem 10a. The laser diode 7 is accommodated in the other end portion 14 of the package 8, and the laser light emitted from the laser diode 7 is output to the outside from the end portion 14. The lead pins 12 a are connected to the package 8, but are insulated from any of the electronic elements of the TOSA 4 a housed in the package 8. The lead pin 12 b is connected to the anode terminal of the laser diode 7, and the lead pin 12 c is connected to the cathode terminal of the laser diode 7. The package 8 is a coaxial type package, and has a flange 16a and a flange 16b on the side surface. A groove 18 is provided between the flange 16a and the flange 16b. The TOSA 4 a is fixed to the side wall 6 a by fitting the side wall 6 a of the case 6 into the groove 18. In this way, the case 6 of the optical communication module 2 and the package 8 of the TOSA 4a are electrically connected.

  The ROSA 4b is an optical receiving subassembly having a photodiode and a package (second package) made of a metal material that accommodates the photodiode (the portion excluding the sleeve from the optical receiving subassembly corresponds to the optical receiving module) .) This package is covered with a sleeve made of a resin material. This package is insulated from any of the electronic elements housed in the ROSA 4b. The ROSA 4b is provided with a groove 18a similarly to the TOSA 4a, and the side wall 6a of the case 6 is fitted into the groove 18a. Thereby, ROSA4b is fixed to the side wall 6a. The ROSA 4b package is insulated from the side wall 6a by a sleeve made of a resin material covering the package. The ROSA 4b has a plurality of lead pins, and each lead pin has a plurality of electrodes made of a metal material provided on the first surface M1 (front surface) of the circuit board 5, and an electrode 26 described later (FIG. 3). For example). One lead pin (ground lead pin) of the plurality of lead pins of the ROSA 4b is connected to the package and the electrode 26 of the ROSA 4b. This lead pin is insulated from both the electronic element housed in the package of ROSA 4 b and the case 6.

  The optical communication module 2 further includes a plurality of electrodes such as electrodes 20a to 20c made of a metal material. The electrodes 20 a to 20 c are provided on the first surface M <b> 1 of the circuit board 5. As shown in FIG. 2, each of the lead pins 12a to 12c is soldered to each of the electrodes 20a to 20c. FIG. 2 is a diagram illustrating the arrangement of the electrodes 20a to 20c. As shown in FIG. 2, the electrodes 20a to 20c are arranged at equal intervals. The distance between the electrode 20a (first electrode) and the electrode 20b is the same as the distance L1 between the electrode 20a and the electrode 20c, and is about 250 μm. The electrodes 20a to 20c have substantially the same shape, and the planar shape of each of the electrodes 20a to 20c has a width L2 of about 800 μm and a length L3 of about 2000 μm. The electrode 20a connected to the lead pin 12a is sandwiched between the electrode 20b and the electrode 20c. The electrode 20 a is insulated from any electronic element provided on the circuit board 5. The lead pins 12a are connected to the package 8 of the TOSA 4a, and the package 8 is connected to the case 6 of the optical communication module 2. Therefore, the electrode 20 a is electrically connected to the case 6 of the optical communication module 2. That is, an electrode 20a that is electrically connected to the case 6 (frame ground) is provided on the circuit board 5.

  The optical communication module 2 further includes an electronic circuit 24. The electronic circuit 24 has a signal ground potential (signal ground potential) and is provided on the first surface M1 of the circuit board 5 on which the electrodes 20a to 20c are provided. The electronic circuit 24 is an IC or the like having an amplifier circuit or a drive circuit for the laser diode 7, and is electrically connected to the electrode 20b and the electrode 20c.

  The optical communication module 2 further includes an electrode 26 (second electrode), a substrate 28, a ground layer 30, and a circuit board 32. The electrode 26, the substrate 28, the ground layer 30, and the circuit board 32 are included in the circuit board 5. A laminated structure is formed on top. FIG. 3 is a cross-sectional view taken along the line I-I shown in FIG. 2 and shows a laminated structure provided on the circuit board 5. The electrode 26 is provided on the second surface M2 (back surface) of the circuit board 5, the substrate 28 is provided on the electrode 26, the ground layer 30 is provided on the substrate 28, and the circuit board 32 is provided on the ground layer 30. Is provided. The electrode 26 is disposed so as to overlap the electrode 20a with the circuit board 5 interposed therebetween, and has substantially the same planar shape as the electrode 20a. The electrode 26 is a signal ground. The substrate 28 is disposed so as to overlap the circuit board 5 with the electrode 26 interposed therebetween, and has substantially the same planar shape as the circuit board 5. The board | substrate 28 consists of a prepreg similar to the circuit board 5, for example. The thickness L4 of the substrate 28 is about 148 μm. The ground layer 30 is a layer made of a metal material, and is disposed so as to overlap the circuit board 5 with the electrode 26 and the board 28 interposed therebetween, and has substantially the same planar shape as the circuit board 5. The circuit board 32 is made of, for example, the same prepreg as the circuit board 5, and an electronic circuit is provided on the circuit board 32. The ground layer 30 ensures electrical isolation between the electronic circuit provided on the circuit board 32 and the electronic circuit provided on the circuit board 5.

  The prepreg constituting the base of the circuit board 5 has a withstand voltage against an AC voltage of about 60 V per 1 μm thickness, and the thickness L5 of the circuit board 5 is about 65 μm. Therefore, the circuit board 5 theoretically has a withstand voltage against a relatively high AC voltage of about 3900V. The circuit board 5 has a dielectric constant of about 5.0. The electrode 20a and the electrode 26 are electrically insulated in the case 6, and therefore the electrode 20a, the circuit board 5 and the electrode 26 form a capacitance having a capacity of about 0.7 pF (a parallel plate capacitor is formed). .)

  Next, functions and effects of the optical communication module 2 will be described. The optical communication module 2 generates a relatively large amount of radiation noise from a location where the TOSA 4a and ROSA 4b and the circuit board 5 are connected (region indicated by symbol E in FIG. 1). In particular, radiation noise generated from a location where the TOSA 4a and the circuit board 5 are connected is large. A relatively large bias current (several tens of mA) supplied to the laser diode 7 of the TOSA 4a flows at a location where the TOSA 4a and the circuit board 5 are connected. This bias current is modulated to the signal frequency. Electromagnetic induction noise is generated by the current thus modulated. Due to the generation of the electromagnetic induction noise, the radiation noise generated from the connection portion between the TOSA 4a and the circuit board 5 becomes particularly remarkable. In addition, the wiring pattern on the circuit board 5 and the lead pins 12a to 12c each have a unique resonance frequency. When this resonance frequency and the signal frequency of the bias current overlap, the radiation noise further increases. Use of the optical communication module 2 can reduce the influence of such radiation noise on the frame ground.

  In the optical communication module 2, the electrode 20a connected to the frame ground, the circuit board 5, and the electrode 26 connected to the signal ground form a capacitance having a capacity of several pF or less (about 0.7 pF) (parallel). A flat capacitor is formed.) Therefore, part of the influence of radiation noise on the frame ground can be borne by the signal ground via this capacitor. Thereby, the influence which radiation noise has on a frame ground can be reduced. Further, it is not necessary to newly provide a capacitor element between the frame ground and the signal ground. In addition, the capacitor constituted by the electrode 20a, the circuit board 5, and the electrode 26 has a dielectric strength voltage with respect to an AC voltage of about 3900 V, and therefore conforms to the IEC standard for dielectric strength voltage. As described above, the optical communication module 2 can reduce the influence of radiation noise on the frame ground while maintaining a relatively high withstand voltage.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

It is a figure for demonstrating the structure of the optical communication module which concerns on embodiment. It is a figure which shows arrangement | positioning of an electrode. It is a figure which shows the laminated structure provided on the circuit board.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Optical communication module 5, 32 ... Circuit board, 4a ... TOSA, 4b ... ROSA, 6 ... Case, 6a ... Side wall, 7 ... Laser diode, 8 ... Package, 10, 14 ... End part, 10a ... Stem, 12a , 12b, 12c ... lead pins, 16a, 16b ... flanges, 18, 18a ... grooves, 20a, 20b, 20c, 26 ... electrodes, 24 ... electronic circuit, 28 ... substrate, 30 ... ground layer.

Claims (1)

A metal first package, a laser diode accommodated in the first package, a first lead pin connected to the first package, and an anode terminal and a cathode terminal of the laser diode, respectively. An optical transmission module having second and third lead pins;
An optical receiver module including a second package made of metal, a photodiode housed in the second package, and a ground lead pin electrically connected to the second package;
Has a front surface and a back surface, said second and third lead pins are connected, have a signal ground potential, the circuit board on which the electronic circuit provided on the surface including a driving circuit for driving the laser diode When,
A first electrode provided on the surface and connected to the first lead pin;
A second electrode provided on the back surface, arranged to overlap the first electrode across the circuit board, and connected to the signal ground potential;
A metal case that is electrically connected to the first package and that houses the optical transmission module and the circuit board;
The first electrode and the second electrode are electrically insulated within the case to form a capacitance with the circuit board interposed therebetween, and the ground lead pin is formed on the circuit board with the second electrode. An optical communication module, wherein the optical communication module is electrically connected to an electrode and insulated from the metal case .

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