JP6133023B2 - Optical module - Google Patents

Description

  The present invention relates to an optical module having a structure in which an optical device including a plurality of optical elements and a control device are connected by wiring.

  In recent years, there has been a demand for higher speed and larger capacity of optical communication, and in order to realize this, a parallel optical transmission system that transmits optical signals in parallel using a plurality of optical fibers or optical waveguides is used.

  In an integrated, miniaturized and high-density circuit, mutual inductance increases between adjacent wirings, and crosstalk occurs between signals. Furthermore, crosstalk increases when high-frequency signals are used. For this reason, the occurrence of crosstalk is a particular problem in optical devices that use high-frequency signals, and reduction of crosstalk is required in order to advance the miniaturization and density of optical modules.

  In order to reduce crosstalk between signals, in the technique described in Patent Document 1, in a wiring connecting a photoelectric element and an IC, a signal line connecting the photoelectric element and the IC and a ground line connected to the ground are provided. They are arranged alternately. The ground line is connected to the ground layer via a via formed in the middle of the ground line. With this configuration, the signal line is sandwiched between the ground lines, and the ground potential is strengthened by the ground connection via the via formed in the middle of the ground line, so that crosstalk between the signal lines can be reduced.

JP 2007-249194 A

The technique described in Patent Document 1 is configured to reduce crosstalk by forming a via for ground connection. However, a certain size is required for the via, and clearance is required around the via. . For this reason, it is difficult to apply to a downsized and high-density optical module that has been required in recent years.
An object of the present invention is to provide an optical module that can be reduced in size and increased in density and can reduce crosstalk as compared with the conventional one.

  One aspect of the present invention is an optical module, which includes a plurality of optical elements each having an anode terminal and a cathode terminal, a control device that exchanges signals with the optical element, the anode terminal, and the control device. A plurality of signal lines to be connected; a plurality of ground lines for connecting the cathode terminal and the control device; and a conductor for electrically connecting the ground lines to the ground. Each of the plurality of ground lines is alternately arranged in parallel, and any one of the cathode terminals and the ground line connected to the cathode terminal is connected to the conductive line. And is electrically connected to the ground via the conducting wire.

  The optical module according to the present invention can be miniaturized and densified, and can reduce crosstalk as compared with the conventional one.

It is the schematic of the optical module which concerns on 1st Embodiment. It is sectional drawing of the optical module which concerns on 1st Embodiment. (A) It is a figure which shows the signal waveform which concerns on an Example. (B) It is a figure which shows the signal waveform which concerns on a comparative example. It is a figure which shows the graph of PJrms which concerns on an Example and a comparative example. It is the schematic of the optical module which concerns on 2nd Embodiment. It is the schematic of the optical module which concerns on 3rd Embodiment. It is the schematic of the optical module of a comparative example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

(First embodiment)
FIG. 1 is a schematic diagram of an optical module 100 according to the present embodiment. The optical module 100 includes an optical device 102 having a plurality of light emitting elements 101, a control device 103 that transmits and receives signals to and from the optical device 102, and a substrate 104 that has a plurality of lines 104a and 104b through which signals pass and a ground pattern 107. Prepare.

The optical device 102 includes a plurality of light emitting elements 101, and the light emitting elements 101 are vertical cavity surface emitting lasers (VCSELs) that emit laser beams in the surface direction of the substrate. As the light emitting element 101, any light emitting element corresponding to a high frequency signal can be used. Each of the light emitting elements 101 has an anode terminal 106 a and a cathode terminal 106 b on the surface of the optical device 102. In this specification, a signal path related to each light-emitting element 101 is referred to as a channel. Although a total of three channels are shown in FIG. 1, it is not limited to this number.
In the present embodiment, the optical device 102 is mounted on the substrate 104, but may be provided integrally with the substrate 104. As the optical device 102, any configuration can be used as long as a plurality of optical elements are arranged in parallel so as to realize a parallel optical transmission system.

The substrate 104 is a printed circuit board, and has a plurality of conductive lines 104a and 104b on the surface. The line 104a and the line 104b are arranged in parallel, and are alternately provided adjacent to each other. The number of lines 104a is at least as many as the anode terminals 106a, and the number of lines 104b is at least as many as the cathode terminals 106b.
Further, the substrate 104 has a ground pattern 107 (also referred to as a solid ground) on the surface as a ground. The ground pattern 107 is provided on both sides so as to be close to the plurality of lines 104a and 104b and to extend in the major axis direction of the plurality of lines 104a and 104b.

The control device 103 is an integrated circuit (IC) that generates a laser by applying a high frequency voltage to the light emitting element 101. The control device 103 has at least a total number of terminals (not shown) of the anode terminal 106a and the cathode terminal 106b. The control device 103 is placed on the substrate 104 so that the terminals of the control device 103 are in contact with the separate lines 104a and 104b. The control device 103 may be provided integrally with the substrate 104.
As the control device 103, any configuration can be used as long as it is connected to the anode terminal and the cathode terminal of the optical element by wiring and transmits and receives signals.

The anode terminals 106 a of the plurality of light emitting elements 101 are connected to different lines 104 a by the first wires 105. The anode terminal 106a, the first wire 105, and the line 104a thus connected function as signal lines. In addition, each cathode terminal 106 b of the plurality of light emitting elements 101 is connected to a separate line 104 b by a first wire 105. The cathode terminal 106b, the first wire 105, and the line 104b thus connected function as a ground line.
The anode terminal 106a and the cathode terminal 106b of one light emitting element 101, that is, related to the same channel, are connected to two adjacent lines 104a and 104b.

FIG. 2 is a cross-sectional view taken along line AA in FIG. 1 for explaining the connection relationship of the second wires 108. The plurality of lines 104b connected to the cathode terminal 106b are arranged in a direction perpendicular to the longitudinal direction of the line 104b, and a ground pattern 107 is provided so as to sandwich the group of lines 104b in the arrangement direction. . The line 104b located at one end in the arrangement direction of the line 104b group is connected to the ground pattern 107 provided on the one end side by a second wire 108. Similarly, the line 104b located at the other end in the arrangement direction of the line 104b group is connected to the ground pattern 107 provided on the other end side by a second wire 108.
The lines 104b are also connected to each other by the second wire 108. At this time, since the line 104a and the line 104b are alternately arranged, the two lines 104b sandwiching one line 104a are connected by the second wire 108. With this configuration, the plurality of lines 104b are all electrically connected to each other, and are connected to the ground pattern 107 and maintained at a common ground potential.

In the present embodiment, the connection structure between the line 104b and the ground pattern 107 is not limited to the above, and each of the plurality of lines 104b is electrically connected to the ground pattern 107 directly or indirectly. Any structure may be used. Direct means that the line 104 b is directly connected to the ground pattern 107 by the second wire 108. Indirectly, one line 104b is connected to another line 104b by the second wire 108, and the other line 104b (or another line 104b electrically connected to the other line 104b) is connected. It is connected to the ground pattern 107 by the second wire 108 (that is, the one line 104b is not directly connected to the ground pattern 107 but is electrically connected to the ground pattern 107). Point to.
For example, a structure in which each of the lines 104b and the ground pattern 107 are directly connected by the second wire 108 may be used. Alternatively, a structure in which the plurality of lines 104b and the ground pattern 107 are directly connected by the second wire 108, and the lines 104b are connected by the second wire 108, and at least one of the lines 104b connected to each other is connected. A structure in which the structure connected to the line 104b connected to the ground pattern 107 is mixed may be used.
In the present embodiment, the second wire 108 for connecting the line 104b to the ground is connected to the vicinity of the end of the line 104b on the optical device 102 side on the line 104b.
The connection position between the second wire 108 and the line 104b is preferably closer to the optical device 102 than the center in the longitudinal direction of the line 104b in order to obtain a sufficient crosstalk reduction effect. It is more preferable to be closer to the end.

  FIG. 7 is a schematic diagram of an optical module that does not have the second wire 108 and the ground pattern 107. The optical module includes an optical device 2 having a plurality of optical elements 1, a control device 3 for controlling the optical device 2, and a substrate 4 having a plurality of lines 4a and 4b on the surface. The control device 3 is disposed on the substrate 4 so as to be in contact with the plurality of lines 4a and 4b. Each of the plurality of lines 4a and 4b is connected to one end of the wire 5, and the other end of the wire 5 is connected to an anode terminal 6a and a cathode terminal 6b attached to each of the plurality of optical elements 1. The wiring connecting the line 4 a and the anode terminal 6 a and the wiring connecting the line 4 b and the cathode terminal 6 b are alternately arranged along the surface of the substrate 4. With this configuration, signals are exchanged between the plurality of optical elements 1 and the control device 3 via the lines 4a and 4b, the wires 5, and the terminals 6a and 6b. This configuration can be applied to the case where either a light emitting element or a light receiving element is used as the optical element 1.

In the case of the optical module shown in FIG. 7, since the line 4b connected to the cathode electrode 6b is connected to the ground on the control device 3 side, an electric signal flows from the cathode electrode 6b to the control device 3. For this reason, it is conceivable that the electrical signal from the cathode electrode 6b generates an electromagnetic wave in the line 4b and causes crosstalk with the adjacent line.
On the other hand, in the optical module 100 according to the present embodiment, conduction to the ground pattern 107 is formed in the vicinity of the end of the line 104b on the optical device 102 side. Thereby, at least a part of the electric signal from the cathode electrode 106b to the control device 103 flows to the ground pattern 107 in the middle of the line 104b. As a result, in the line 104b, an electric signal flowing from the connection position with the second wire 108 to the control device 103 side is reduced, thereby reducing electromagnetic waves generated in the line 104b and reducing crosstalk in the adjacent line. The Further, the crosstalk reduction effect due to the alternate arrangement of the signal lines and the ground lines also occurs at the same time.

  Further, since the lines 104b and between the lines 104b and the ground pattern 107 are connected by wire connection, a minute optical module that has been difficult to apply in the past, specifically, the pitch (interval) between the lines 104b is 250 μm. It can be applied to the following minute circuits.

  In particular, in the configuration of the present embodiment, the closest lines 104b are connected to each other, so that the connection is simple and stable. In addition, since the signal is connected to the ground pattern 107 on both sides of the plurality of lines 104b, a signal from the cathode terminal 106b can be efficiently passed to the ground pattern 107, and as a result, a high crosstalk reduction effect can be obtained.

In the present embodiment, it is important to reduce crosstalk while arranging the line 104a group and the line 104b group for electrically connecting the optical device 102 and the control device 103 with high density. For this purpose, at least one of the plurality of lines 104b is connected to the ground pattern 107 by the second wire 108, and 104b not connected to the ground pattern 107 is also connected by the second wire 108. One is connected to the line 104 b connected to the ground pattern 107 by the second wire 108. Therefore, in each line 104b, an electric signal flowing after the position connected to the second wire 108 (on the control device 103 side) can be reduced, and crosstalk can be reduced as compared with the conventional case. In this way, by connecting the second wire 108 for electrical connection to the ground pattern 107 in the line 104b, crosstalk due to an electrical signal after the connection point can be reduced. In order to increase the crosstalk reduction effect by flowing an electric signal through the ground pattern 107, the position where the second wire 108 is connected on the line 104b is preferably in the vicinity of the end of the line 104b on the optical device 102 side. . For example, the optical device 102 may be closer to the middle point of the line 104b.
However, since the crosstalk due to the electrical signal after the connection point with the second wire in the line 104b can be reduced, if the connection point with the second wire 108 exists on the ground line, the crosstalk reduction effect of this embodiment Can be obtained. Therefore, for example, even when the second wire 108 is connected in the vicinity of the end of the line 104b on the control device 103 side, as long as the second wire 108 is connected at least at a position separated from the control device 103, As described above, it is possible to obtain a higher crosstalk reduction effect than when the control device 103 is grounded.

(Example)
By measuring the transmission characteristics through experiments, the crosstalk reduction effect of the present invention was verified.

  As an example, an optical module having the configuration of the first embodiment was produced. However, the number of channels (the number of light emitting elements) was 12. The pitch between the line 104a and the line 104b was 125 μm. The second wire 108 in each channel was connected to a point within 100 μm in the direction of the control device 103 from the point where the first wire 105 was connected on the line 104b.

  As a comparative example, an optical module having the configuration shown in FIG. 7 was produced. Conditions other than that the ground line is not connected to the ground pattern in the middle, that is, the number of channels, the pitch between lines, and the like are the same as in the configuration of the embodiment.

First, eye patterns of signal waveforms were measured in the examples and comparative examples. If the eye pattern of the signal waveform is clear, it can be said that there is little noise. FIG. 3A is an eye pattern of a signal waveform in one channel of the embodiment, and FIG. 3B is an eye pattern of a signal waveform in the same channel of the comparative example. 3A and 3B, the horizontal axis represents time, and the vertical axis represents voltage.
3A and 3B, it can be seen that the eye pattern of the example is clearer than the comparative example. Therefore, it was confirmed that the configuration according to the example reduces noise, that is, crosstalk is reduced as compared with the comparative example.

  Next, PJrms was measured in order to quantitatively verify the crosstalk reduction effect of the example. PJrms can be measured by a known method. PJrms is the rms value of periodic jitter (PJ), and is used as an index of crosstalk noise. The smaller the crosstalk, the smaller the value of PJrms.

Two samples were prepared under the conditions of the above-described example, and six samples were prepared under the conditions of the above-described comparative example, and PJrms was measured respectively. FIG. 4 is a graph of PJrms measurement results. The horizontal axis in FIG. 4 is the channel number, and the vertical axis is the value of PJrms. The result of the example is indicated by a solid line in FIG. 4, and the result of the comparative example is indicated by a broken line in FIG. There are 12 channels (CH1 to CH12) in each module, but four of them (CH6 to CH9) are shown so that the difference can be easily understood.
In the comparative example, the value of PJrms is around 1.7, whereas in the example, the value of PJrms is reduced to around 1.2. Therefore, it was confirmed that the crosstalk is significantly reduced by the configuration according to the example as compared with the comparative example.
In addition to the four channels shown in FIG. 4, the crosstalk reduction effect was confirmed although the reduction effect was different because the characteristics were different for each channel.

(Second Embodiment)
FIG. 5 is a schematic diagram of the optical module 200 according to the present embodiment. In the optical module 100 according to the first embodiment, the line 104 b is connected to the ground pattern 107 by the second wire 108. On the other hand, the optical module 200 according to this embodiment is connected to the ground pattern 107 by the second wire 108 on the cathode terminal 106 b of the light emitting element 101. Even with such a configuration, it is possible to obtain an effect of reducing crosstalk by flowing at least part of the signal in the ground line to the ground pattern 107.

The optical module 200 includes components common to the optical module 100 according to the first embodiment, and only the connection position of the second wire 108 is different.
In the optical module 200, the cathode terminals 106 b of the light emitting elements 101 are connected to each other by the second wire 108 and further connected to the ground pattern 107 by the second wire 108.

  One cathode terminal 106b is connected to the two closest cathode terminals 106b by a second wire 108. That is, since the anode terminal 106a and the cathode terminal 106b are alternately arranged, the two cathode terminals 106b sandwiching one anode terminal 106a are connected by the second wire 108. However, the outermost one of the plurality of cathode terminals 106 b is connected to the nearest one cathode terminal 106 b by the second wire 108 and further connected to the ground pattern 107 by the second wire 108. With this configuration, all of the plurality of cathode terminals 106b are electrically connected to each other, and are connected to the ground pattern 107 and maintained at the ground potential.

(Third embodiment)
FIG. 6 is a schematic diagram of an optical module 300 according to the present embodiment. In the optical module 100 according to the first embodiment, the line 104 b is connected to the ground pattern 107 by the second wire 108. On the other hand, the optical module 300 according to the present embodiment is connected to the ground pattern 107 by the second wire 108 on the first wire 105 that connects the cathode terminal 106b and the line 104b. Even with such a configuration, it is possible to obtain an effect of reducing crosstalk by flowing at least part of the signal in the ground line to the ground pattern 107.

The optical module 300 includes components common to the optical module 100 according to the first embodiment, and only the connection position of the second wire 108 is different.
In the optical module 300, the first wire 105 connecting the cathode terminal 106b and the line 104b is connected to each other by the second wire 108, and further connected to the ground pattern 107 by the second wire 108.

  The first wire 105 related to one cathode terminal 106b is connected by the second wire 108 to the first wire 105 related to the two closest cathode terminals 106b. That is, since the anode terminals 106 a and the cathode terminals 106 b are alternately arranged, the first wires 105 related to the two cathode terminals 106 b sandwiching one anode terminal 106 a are connected by the second wire 108. Will be. However, the first wire 105 relating to the outermost one of the plurality of cathode terminals 106b is connected to the first wire 105 relating to the nearest one cathode terminal 106b by the second wire 108, and further to the ground. The pattern 107 is connected to the second wire 108. With this configuration, the first wires 105 related to the plurality of cathode terminals 106b are all electrically connected to each other, and are connected to the ground pattern 107 and maintained at the ground potential.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention.

The essence of the present invention is to electrically connect to a ground pattern on a ground line (including a cathode terminal) connecting an optical device and a control device in the optical module. Therefore, the connection methods for connecting to the ground pattern in the middle of the line, on the cathode terminal, or on the wire described in the above embodiment may be combined with each other.
The cathode terminal and the terminal of the control device are directly connected by the first wire without going through the line on the substrate, and the second wire is connected between the first wire and between the first wire and the ground pattern. You may connect by a wire.

  The wiring connecting the ground line and the ground pattern is not limited to a wire, and any conductive wire can be used. Further, bumps may be formed on the line (or cathode terminal) and the ground pattern, and wiring may be formed by connecting the bumps with a conductor.

When the optical module functions as a light receiving module, a light receiving element such as a photodiode may be used instead of the light emitting element. In that case, the control device receives and processes the high-frequency signal from the light receiving element via the wire and the terminal.
As the optical module according to the present invention, any optical element can be used as long as it is an optical element that emits or receives light by transmitting and receiving a high-frequency signal through an anode terminal and a cathode terminal.

100, 200, 300 Optical module 101 Light emitting element 102 Optical device 103 Control device 104 Substrate 104a, 104b Line 105 First wire 106a, 106b Terminal of optical device 107 Ground pattern 108 Second wire

Claims (4)

A substrate having a plurality of conductive lines formed in parallel on the surface;
A plurality of optical elements each having an anode terminal and a cathode terminal;
A control device for exchanging signals with the optical element;
A plurality of signal lines connecting the anode terminal and the control device;
A plurality of ground lines connecting the cathode terminal and the control device;
A conductive wire for electrically connecting the ground wire to the ground;
A second conducting wire that connects one end of each of the plurality of lines to the anode terminal or the cathode terminal;
With
The signal line and the ground line are composed of the line and the second conductive line,
And respectively they are arranged in parallel alternately before Symbol plurality of signal lines each of the plurality of ground lines,
Any part of the previous SL ground line is connected to the conductor, it is electrically connected to the ground via the conductor lines,
All adjacent two ground lines are connected to each other by the conducting wire,
An optical module, wherein two of the plurality of ground lines located on the outermost side are connected to the ground by the conducting wire . The control device is provided in contact with the other end of each of the plurality of lines,
The optical module according to claim 1 , wherein the conducting wire is connected to a position closer to the optical element than a center in a longitudinal direction of each of the plurality of lines . A substrate having a plurality of conductive lines formed in parallel on the surface;
A plurality of optical elements each having an anode terminal and a cathode terminal;
A control device for exchanging signals with the optical element;
A plurality of signal lines connecting the plurality of anode terminals and the control device;
A plurality of ground lines connecting the plurality of cathode terminals and the control device;
A conductive wire for electrically connecting the ground wire to the ground;
With
Each of the plurality of anode terminals and each of the plurality of cathode terminals are alternately arranged in a row,
The cathode terminal is connected to the conducting wire, and is electrically connected to the ground via the conducting wire;
All the two adjacent cathode terminals are connected to each other by the conducting wire,
An optical module, wherein two cathode terminals located on the outermost side among the plurality of cathode terminals are connected to the ground by the conducting wire . A substrate having the optical element and the control device on a surface, and a ground pattern formed on the surface;
The ground optical module according to any one of claims 1-3, characterized in that the said ground pattern.