JP2009253064A - Bidirectional optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bidirectional optical module which reduces the transmission of LD-generated signals to a PD through a stem, by a simple and cheap method without using a large-sized package and without electrically separating the stem therefrom. <P>SOLUTION: The bidirectional optical module has a metal stem 3 whereon a light emitting element 4 for emitting a transmitting light and a photodetector 5 for receiving a receiving light are mounted, a first lead pin group electrically connected with the light emitting element 4 passing through the stem 3 and a second lead pin group electrically connected with the photodetector and a grounding flange 11 positioned in the region or the vicinity region for mounting the light emitting element 4 in the surface opposite to the principal surface for mounting the light emitting element 4 and the photodetector, and connected with the stem 3 electrically and mechanically. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bidirectional optical module in which a light emitting element and a light receiving element are mounted in one package and used for transmission / reception of an optical signal.

  With the advancement of optical communication technology, PON (Passive), which enables higher-speed and large-capacity immediate communication at an appropriate cost, in the subscriber network (access system) represented by FTTH (Fiber To The Home) The introduction of the Optical Network system is progressing. The PON system adopts a single-core bidirectional communication system, reduces the number of fibers in the optical fiber transmission line between the station side and the user side, and realizes a high-speed service at the same low price as a metal cable. . Specifically, it is a wavelength division multiplexing (WDM: Wavelength Division Multiplexing) in which transmission and reception are performed with two wavelengths of a 1.31 μm band and a 1.55 μm band (or 1.49 μm band) using one optical fiber.

  In a single-core bidirectional optical module (Bi-D: Bi-Directional Module) for use in such a PON system, transmission light emitted from a light emitting element such as a laser diode (hereinafter referred to as LD) is coupled to an optical fiber. On the other hand, the received light transmitted through the optical fiber is coupled to a light receiving element (hereinafter referred to as PD) such as a photodiode. Many proposals have been made for a method and an apparatus for coupling an optical fiber and transmitted / received light.

  Conventionally, development has progressed because an optical module having a two-package structure using a CAN package containing a transmission LD and a CAN package containing a reception PD can be assembled by a conventional method. However, as described at the beginning, it is necessary to further reduce the cost by single-core bidirectional communication, which has a strong demand for low prices, and both LD and PD are built in one CAN package. Development is also underway for single-core bidirectional optical modules with a single package structure.

However, in “1 package Bi-D” in which a transmission LD and a reception PD are built in one CAN package, an electromagnetic field generated when the LD is driven becomes noise to a weak reception signal. The so-called electric crosstalk problem becomes apparent. In the problem of this electrical crosstalk, for example, a method is known in which the coupling of noise is cut off by electrically separating a stem on which an LD and a PD are mounted to reduce the electrical crosstalk (for example, Patent Documents). 1). Further, there is known a method for improving the structure and arrangement such as strengthening grounding as an LD drive wiring, arranging a shield on the PD side, and orthogonally crossing the LD and PD wiring boards (for example, Patent Document 2).
JP 2005-203553 A JP 2006-41234 A

  However, since the technique disclosed in Patent Document 1 separately and independently provides a metal plate for mounting LD and PD, it increases the space in the package and is difficult to apply to a CAN type package. ing. Also in Patent Document 2, the addition of a substrate for grounding reinforcement and the space for that increase. All of them require additional parts and space for grounding and shielding reinforcement, and increase the size and cost.

  FIG. 9 shows an example of a conventional single-core bidirectional optical module using a CAN-type single package. The package 1 includes an LD 4 that transmits signal light to a stem 3 on which a plurality of lead pins 2 are arranged. It is mounted via a heat sink member or the like for cooling, and a PD 5 that receives received light is mounted via a submount or the like. A cap 8 provided with a lens 7 for condensing transmission light (LD light) and reception light is attached so as to seal the LD 4 and PD 5 mounted on the stem 3 and other electronic components. A holder 9 for positioning and holding a sleeve member (not shown) that forms a connection with the optical fiber is attached and fixed to the cap 8.

  A WDM filter 6 that reflects the transmission light and transmits the reception light is arranged on the optical path of the lens 7 and the LD 4 and PD 5. The transmitted light emitted from the LD 4 is reflected by the WDM filter 6, collected by the lens 7, passes through the opening of the holder 9, and is incident on the fiber portion 10 a of the fiber stub 10 fixed to the sleeve member. To the optical fiber transmission line. The received light transmitted from the external optical fiber transmission line is emitted from the fiber portion 10a of the fiber stub 10, is collected by the lens 7 through the opening of the holder 9, is transmitted through the WDM filter 6, and is incident on the PD 5. Is done.

  FIG. 10 is a diagram showing the stem 3 on which the LD 4 and the PD 5 are mounted. The stem 3 is usually circular with a diameter of about 5.6 mm. As one package Bi-D, around the mounting area of the LD 4 and PD 5, a plurality of lead pins 2 are insulated sealing members 3 a such as low melting glass. It is arranged by. These lead pins 2 are used as power supply and input / output terminals for electrical signals, and each lead pin is connected to the LD 4 and PD 5 with a fine wire having a diameter of 25 μm.

  Since the region of the LD 4 mounted via the heat sink 4a and the region of the PD 5 mounted via the submount 5a are arranged close to each other within a narrow region, an electromagnetic field generated from the region of the LD 4 during LD driving However, it is easy to go around to the region of PD5, and the problem of electric crosstalk becomes remarkable. In addition, since the coaxial stem 3 on which the LD 4 and the PD 5 are mounted is manufactured by a general press process, it is not easy and realistic to electrically separate the ground conductor portions of the LD and PD. Not.

  The present invention has been made in view of the above-described circumstances, and the signal generated from the LD can be obtained in a simple and inexpensive manner without increasing the size of the package and without electrically separating the stem. An object of the present invention is to provide a bi-directional optical module in which propagation of light to a PD via a stem is reduced.

  The bidirectional optical module according to the present invention includes a metal stem on which a light emitting element for emitting transmission light and a light receiving element for receiving reception light are mounted, and a first electrically connected to the light emitting element that penetrates the stem. A lead pin group and a second lead pin group electrically connected to the light receiving element group, and a region where the light emitting element is mounted or its vicinity on a surface opposite to the main surface on which the light emitting element and the light receiving element are mounted Located in the region is a grounding flange electrically and mechanically connected to the stem.

  The grounding flange may be provided so as to be positioned between a region where the light emitting element is mounted and a region where the light receiving element is mounted, and the first lead pin group and the second lead pin group You may make it provide along the boundary part. Further, a convex portion is provided on the grounding flange side, the convex portion is fitted into a concave portion provided on the stem side so as to be positioned, and the grounding flange is fitted and coupled to a groove portion provided on the stem side. It is good also as a structure.

  According to the present invention, the interference of the electromagnetic field generated from the region of the light emitting element with the light receiving element can be efficiently reduced by the grounding flange provided on the stem. The grounding flange is simply configured to be mounted on the back side opposite to the main surface of the stem, so that the size of the package is not increased, and the LD is not electrically separated from the stem. It is possible to effectively reduce the signal generated from the signal propagating to the PD via the stem.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an outline of a bidirectional optical module according to the present invention, and FIG. 2 is a diagram for explaining a main part of the present invention. In the figure, 1 is a package, 2 is a lead pin, 3 is a stem, 3a is an insulating sealing member, 3b is a main surface, 3c is a back surface, 4 is a laser diode (LD), 4a is a heat sink, and 5 is a photodiode (PD). 5a is a submount, 6 is a WDM filter, 7 is a lens, 8 is a cap, 9 is a holder, 10 is a fiber stub, 10a is a fiber part, 11 is a grounding flange, and 12 is a terminal.

  The basic configuration of the bidirectional optical module according to the present invention is a single-core bidirectional optical module of a CAN type single package structure similar to that described with reference to FIGS. 9 and 10. For example, the configuration shown in FIG. is there. The package 1 has a laser diode 4 (hereinafter referred to as LD) for transmitting signal light mounted on a main surface (upper surface) 3b of a metallic stem 3 via a heat sink 4a for cooling, and receives received light. A photodiode 5 (hereinafter referred to as PD) for receiving light is mounted via a submount 5a or the like. A plurality of lead pins 2 are arranged by an insulating sealing member 3a such as low melting glass so as to surround the LD 4 and the PD 5.

  The LD 4 and PD 5 mounted on the stem 3 and other electronic components are sealed by attaching a cap 8 provided with a lens 7 for condensing transmission light (LD light) and reception light. A holder 9 for positioning and holding a sleeve member (not shown) that forms a connection with the optical fiber is attached and fixed to the cap 8. A WDM filter 6 that reflects the transmitted light and transmits the received light is disposed on the optical path between the lens 7 and the LD 4 and PD 5.

  In the bidirectional optical module having the above configuration, the transmission light emitted from the LD 4 is reflected by the WDM filter 6, condensed by the lens 7, passes through the opening of the holder 9, and is fixed to the sleeve member. The light enters the fiber unit 10a and is sent to an external optical fiber transmission line. The received light transmitted from the external optical fiber transmission line is emitted from the fiber portion 10a of the fiber stub 10, is collected by the lens 7 through the opening of the holder 9, is transmitted through the WDM filter 6, and is transmitted through the PD5. Is incident on.

  In the present invention, in the bidirectional optical module having the above-described configuration, the grounding surface formed of a good electrical conductor such as copper on the back surface (lower surface) 3c side opposite to the main surface 3b side of the stem 3 on which the LD 4 and the PD 5 are mounted. A feature is that the flange 11 is provided by being electrically and mechanically connected. As shown in FIGS. 2 (A) and 2 (B), the grounding flange 11 is shaped so as to cross the back surface 3c of the stem 3 so as not to contact the plurality of lead pins 2, and at least one end thereof. It is assumed that the terminal is provided with a terminal 12 for electrical ground connection to the grounding part of the external device.

  The grounding flange 11 is provided by being electrically connected, for example, at a back surface position corresponding to the region of the LD 4 mounted on the central portion of the stem 3 or the vicinity thereof. The grounding flange 11 may be provided so as to be positioned between the LD4 mounting area and the LD5 mounting area. In addition, a first lead pin group L composed of LD drive lead pins and signal lead pins surrounding LD4, or a second lead pin group P composed of lead pins for PD bias voltage and preamplifier surrounding PD5. You may make it provide along the boundary part. As a method for electrically and mechanically connecting the grounding flange 11 to the back surface 3c of the stem 3, various methods can be used as will be described later.

  As described above, the grounding flange 11 is connected to the LD4 mounting region or the vicinity thereof, so that the driving current and signal current of the LD4 can be supplied to the grounding flange 11 at the shortest distance without passing through other regions. Can be effectively returned to the grounding circuit. As a result, it is possible to reduce the electromagnetic field caused by the drive current and signal current from interfering with the adjacent PD 5, reduce electrical crosstalk with respect to the PD 5, and prevent deterioration of communication characteristics.

3-7 is a figure explaining the example of a coupling | bonding with the various forms and stem of the grounding flange mentioned above.
FIG. 3 is a view showing a form in which the grounding flange 11 is partially electrically connected and coupled to the back surface 3c of the stem 3 at a position corresponding to the region of the LD4. For example, the portion 13 that electrically connects the grounding flange 11 can have an area range at least equivalent to that of the heat sink 4a immediately below the heat sink 4a on which the LD 4 is mounted on the main surface 3b of the stem 3. In the electrical connection portion 13, the stem 3 and the grounding flange 11 can be directly connected electrically, for example, with solder or the like. In this case, mechanical coupling can also be realized.

  In this configuration, when the heat sink 4a on which the LD 4 is mounted is formed of a conductive metal, the cathode electrode of the LD 4 can be directly connected to form a shortest grounding circuit that passes through the heat sink 4a and the connection portion 11a. be able to. The grounding flange 11 can also function as a heat radiator for the heat generated by the LD 4.

  4 and 5 are views showing a form in which the grounding flange 11 is electrically connected and coupled to the back surface 3c of the stem 3 at a position corresponding to the area between the LD4 and the PD5. As described with reference to FIG. 3, the portion where the grounding flange 11 is electrically connected may have the same area as the heat sink 4 a, but may be the entire length of the joint surface of the grounding flange 11. Good. Further, the grounding flange 11 may be formed in a shape along the LD 4 and the first lead pin group L surrounding the LD 4 as shown in FIG. Moreover, as shown in FIG. 5, you may make it form in shape along PD5 and the 2nd lead pin group P which surrounds this.

  FIG. 6 is a diagram illustrating a configuration example in which the grounding flange 11 is positioned and coupled to the stem 3. For example, a protrusion 11 a is integrally provided at a portion where the grounding flange 11 is connected to the stem 3, and a recess 14 into which the protrusion 11 a is fitted is provided on the stem 3 side. By fitting the protrusion 11a provided on the grounding flange 11 to the concave portion 14, the mounting of the grounding flange 11 can be positioned and the assembly can be facilitated. The protrusion 11a and the recess 14 may be closely fitted to form electrical connection and mechanical coupling. In this case, solder connection may be used together. The position of the recess 14 may be formed directly below the LD4 region described in FIGS. 3 to 5 or between the LD4 region and the PD5 region.

  FIG. 7 is a diagram illustrating another configuration example in which the grounding flange 11 is coupled to the stem 3. In this example, a concave groove 15 is provided on the back surface 3c side of the stem 3 so as to pass directly under the LD4 region or between the LD4 region and the PD5 region, and the grounding flange 11 is provided in the concave groove 15. Fitting the edges together. In this case, as in the case of FIG. 6, the grounding flange 11 and the concave groove 15 may be closely fitted to form an electrical connection and a mechanical connection, and a solder connection is used in combination. You may do it.

  FIG. 8 is a diagram showing the result of verifying the effect of reducing the electric crosstalk by the above-described grounding flange. FIG. 8A shows the code error rate (BER) on the vertical axis and the reception sensitivity (dBm) on the horizontal axis. FIG. 8B shows the noise power (dBm) on the vertical axis and the frequency (GHz) on the horizontal axis.

  As shown in FIG. 8A, when the LD is off (in a state where the LD in the same package is not driven), the smallest PD error rate is obtained with the smallest PD reception sensitivity. On the other hand, when the LD is turned on, the reception sensitivity deteriorates due to the influence of noise propagation (electric crosstalk) from the LD to the PD. This deterioration in reception sensitivity is said to be a crosstalk penalty, whereas the reception sensitivity of a conventional product (non-grounded reinforcement) with a BER of 1.0E-13 is greatly degraded to 2.0 dB. In the case of the product of the present invention (ground reinforcement), about 0.8 dB, which is less than half of the conventional product.

In addition, as shown in the frequency characteristics of noise power in FIG. 8B, in the region of 1 GHz or less where the frequency is low, the difference from the noise floor is about 3.5 dB in the case of the conventional product (ground non-reinforced). On the other hand, in the case of the product of the present invention (ground reinforcement), it was 1.0 dB.
From the above results, by arranging the grounding flange on the back side of the stem in the region where the LD is mounted or in the vicinity thereof as in the present invention, the electrical noise generated from the LD is reduced to the PD. It is possible to suppress the propagation of the electric crosstalk and reduce the electric crosstalk.

It is a figure explaining the outline of the bidirectional | two-way optical module by this invention. It is a figure explaining the principal part of this invention. In this invention, it is a figure which shows an example which electrically connects the flange for grounding to the back surface of a stem. In this invention, it is a figure which shows the other example which electrically connects the grounding flange to the back surface of a stem. In this invention, it is a figure which shows the other example which electrically connects the flange for grounding to the back surface of a stem. It is a figure which shows an example which positions the flange for earthing | grounding by this invention to a stem. It is a figure which shows an example which couple | bonds the grounding flange by this invention with a stem. It is a figure explaining the result of having verified the effect of the present invention. It is a figure explaining the outline of the conventional bidirectional optical module. It is a figure explaining the outline of the stem of the conventional bidirectional optical module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Package, 2 ... Lead pin, 3 ... Stem, 3a ... Insulation sealing member, 3b ... Main surface, 3c ... Back surface, 4 ... Laser diode (LD), 4a ... Heat sink, 5 ... Photodiode (PD), 5a ... Submount, 6 ... WDM filter, 7 ... Lens, 8 ... Cap, 9 ... Holder, 10 ... Fiber stub, 10a ... Fiber part, 11 ... Grounding flange, 11a ... Protrusion, 12 ... Terminal, 13 ... Connection part, 14 ... concave, 15 ... concave groove.

Claims (5)

A metal stem on which a light emitting element that emits transmission light and a light receiving element that receives reception light are mounted, a first lead pin group that is electrically connected to the light emitting element that penetrates the stem, and the light receiving element group A bi-directional optical module comprising a second lead pin group electrically connected to
For grounding electrically and mechanically connected to the stem on the surface opposite to the main surface on which the light emitting element and the light receiving element are mounted, located in a region where the light emitting element is mounted or in the vicinity thereof A bidirectional optical module comprising a flange.   The bidirectional optical module according to claim 1, wherein the grounding flange is provided so as to be positioned between a region where the light emitting element is mounted and a region where the light receiving element is mounted.   3. The bidirectional optical module according to claim 1, wherein the grounding flange is provided along a boundary portion between the first lead pin group and the second lead pin group.   The bidirectional according to any one of claims 1 to 3, wherein a convex portion is provided on the grounding flange, and the convex portion is positioned by fitting into a concave portion provided on the stem side. Optical module.   The bidirectional optical module according to any one of claims 1 to 3, wherein the grounding flange is fitted and coupled to a groove provided on the stem side.

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