Optical circuit board

Abstract

An optical circuit board (1) according to the present disclosure has a substrate (10), a first optical element (20), a second optical element (30), a first transmission path (40), and a second transmission path (50). The first optical element (20) has a first interface (21) that is positioned on the substrate and through which an optical signal is input or output. The second optical element (30) has a second interface (31) that is positioned on the substrate and through which an optical signal is input or output. The first transmission path (40) has one end (41) through which an optical signal is input or output, and the other end (42) which is optically connected to the first interface (21). The second transmission path (50) has one end (51) through which an optical signal is input or output, and the other end (52) which is optically connected to the second interface (31). The first transmission path (40) is longer than the second transmission path (50). The optical coupling efficiency of the first transmission path (40) with the first interface (21) is higher than the optical coupling efficiency of the second transmission path (50) with the second interface (31).

Description

Optical circuit board

[0001] The present disclosure relates to optical circuit boards.

[0002] Conventionally, modules have been known in which semiconductor elements (hereinafter also referred to as optical elements) that convert electrical signals into optical signals are mounted on a substrate. These modules may be connected to transmission paths such as optical fiber cables or optical wave paths for transmitting the converted optical signals from the optical elements to the outside or transmitting optical signals from the outside to the optical elements.

[0003] Japanese Patent Application Laid-Open No. 2002-131586

[0004] An optical circuit board according to one aspect of the present disclosure includes a substrate, a first optical element, a second optical element, a first transmission path, and a second transmission path. The first optical element is located on the substrate and has a first interface through which an optical signal is input or output. The second optical element is located on the substrate and has a second interface through which the optical signal is input or output. The first transmission path has one end through which the optical signal is input or output, and the other end optically connected to the first interface. The second transmission path has one end through which the optical signal is input or output, and the other end optically connected to the second interface. The first transmission path is longer than the second transmission path. The optical coupling efficiency of the first transmission path with the first interface is higher than the optical coupling efficiency of the second transmission path with the second interface.

[0005] Fig. 1 is a schematic plan view showing the configuration of an optical circuit board according to a first embodiment. Fig. 2 is a schematic side view showing the configuration of an optical circuit board according to the first embodiment. Fig. 3 is a schematic side view showing the configuration of an optical circuit board according to a second embodiment. Fig. 4 is a schematic plan view showing the configuration of an optical circuit board according to a third embodiment.

[0006] Hereinafter, modes for carrying out an optical circuit board according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. Furthermore, the embodiments can be appropriately combined within the scope of not causing any contradiction in the processing content. Furthermore, the same components in the following embodiments will be given the same reference numerals, and duplicated explanations will be omitted.

[0007] Furthermore, in the following embodiments, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing precision or installation precision.

[0008] In the drawings referred to below, for ease of understanding, the X-axis, Y-axis, and Z-axis directions are defined as being orthogonal to each other, and an orthogonal coordinate system is shown in which the positive Z-axis direction is the vertically upward direction. The rotation direction around the vertical axis is also referred to as the θ direction.

[0009] A module (hereinafter also referred to as an optical circuit board) in which an optical element that converts an electrical signal into an optical signal is mounted on a substrate is known. This optical circuit board may be connected to a transmission path such as an optical fiber cable or an optical wave path for transmitting the converted optical signal from the optical element to the outside or transmitting an optical signal from the outside to the optical element.

[0010] Furthermore, in order to achieve both an expansion of the transmission band of an optical circuit board and a reduction in the size of the optical circuit board, an optical circuit board in which a plurality of semiconductor elements are mounted on one board has been proposed.

[0011] Here, when attempting to miniaturize an optical circuit board, it is conceivable to arrange multiple optical elements along the direction in which the transmission line extends (hereinafter also referred to as the transmission direction). However, such an arrangement results in differences in the lengths of the transmission lines connected to each optical element. Generally, the longer the transmission line, the lower the signal strength of the optical signal. Therefore, differences in the lengths of the transmission lines result in variations between optical elements in the signal strength output from the optical circuit board or in the signal strength input to the optical circuit board and then input to the optical elements.

[0012] Therefore, there is a need for a technology that can reduce variations in the intensity of signals output from an optical circuit board on which a plurality of optical elements are mounted.

[0013] First Embodiment First, the configuration of an optical circuit-board 1 according to a first embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic plan view showing the configuration of the optical circuit-board 1 according to the first embodiment. Fig. 2 is a schematic side view showing the configuration of the optical circuit-board 1 according to the first embodiment.

[0014] 1 , the optical circuit board 1 includes a substrate 10, a first optical element 20, a second optical element 30, a plurality of first transmission paths 40, a plurality of second transmission paths 50, and a connector 60. The optical circuit board 1 according to the embodiment can expand the transmission bandwidth by mounting a plurality of optical elements (the first optical element 20 and the second optical element 30) on the substrate 10.

[0015] The substrate 10 has, for example, a rectangular plate shape in a plan view. The substrate 10 has a mounting surface 101 on which the first optical element 20 and the second optical element 30 are mounted. The substrate 10 may be, for example, an organic substrate. Alternatively, the substrate 10 may be a semiconductor substrate.

[0016] The first optical element 20 and the second optical element 30 are optical elements including a photoelectric conversion circuit. The first optical element 20 and the second optical element 30 are located on the mounting surface 101 of the substrate 10. The first optical element 20 and the second optical element 30 may include a plurality of light-emitting elements (not shown) and a plurality of light-receiving elements (not shown). The plurality of light-emitting elements and the plurality of light-receiving elements are arranged, for example, along a direction (Y-axis direction) perpendicular to the transmission direction (X-axis direction).

[0017] The first optical element 20 and the second optical element 30 may be arranged in a row along the extension direction of the first transmission line 40 and the second transmission line 50 described below. In the example shown in FIG. 1 , the first optical element 20 and the second optical element 30 are arranged in a row along the X-axis direction. Specifically, the first optical element 20 is arranged on the positive side of the X-axis on the substrate 10, and the second optical element 30 is arranged on the negative side of the X-axis on the substrate 10. In this way, by arranging multiple optical elements (the first optical element 20 and the second optical element 30) along the transmission direction, the optical circuit board 1 can be made smaller. Specifically, the width of the substrate 10 can be shortened in the direction perpendicular to the transmission direction, in this case, the Y-axis direction.

[0018] The first optical element 20 has a first interface 21 including a plurality of input interfaces to which optical signals are input and a plurality of output interfaces to which optical signals are output. An optical signal emitted from a light-emitting element (not shown) of the first optical element 20 is output to the outside via the output interface. Furthermore, a light-receiving element (not shown) of the first optical element 20 receives the optical signal input via the input interface. In the following description, either the output interface or the input interface of the first interface 21 may be referred to as the first interface 21.

[0019] The second optical element 30 has a second interface 31 including a plurality of input interfaces to which optical signals are input and a plurality of output interfaces to which optical signals are output. An optical signal emitted from a light-emitting element (not shown) of the second optical element 30 is output to the outside via the output interface. Furthermore, a light-receiving element (not shown) of the second optical element 30 receives the optical signal input via the input interface. In the following description, either the output interface or the input interface of the second interface 31 may be referred to as the second interface 31.

[0020] The light-emitting element and the light-receiving element may be located directly below the first interface 21 and the second interface 31, or may be located via a waveguide (not shown) from the first interface 21 and the second interface 31. In other words, a waveguide for transmitting an optical signal may also be located inside the first optical element 20 and the second optical element 30.

[0021] The first transmission path 40 and the second transmission path 50 are optical signal transmission paths, such as optical fiber cables. The first transmission path 40 has a bent portion (see FIG. 2 ), but extends in a generally fixed direction, in this case, along the X-axis direction. An optical signal is input or output from one end 41 of the first transmission path 40, and the other end 42 is optically connected to the first interface 21. The one end 41 of the first transmission path 40 is connected to a connector 60, which will be described later. That is, the first transmission path 40 transmits an optical signal output from the first interface 21 of the first optical element 20 toward the connector 60. The first transmission path 40 also transmits an optical signal input from the connector 60 to the first interface 21 of the first optical element 20.

[0022] The first transmission line 40, which serves as an optical fiber cable, includes a light transmitting portion 43 and a coating portion 44 that protects the light transmitting portion 43. The coating portion 44 may be made of, for example, resin. The light transmitting portion 43 may be, for example, a core, and the coating portion 44 may be, for example, a cladding. As shown in FIG. 2 , the other end 42 of the first transmission line 40 includes a bent portion 46. The bent portion 46 extends from the first transmission line 40 along the negative Z-axis direction. The tip of the bent portion 46 is connected to the first interface 21 of the first optical element 20. That is, an optical signal incident in the thickness direction of the substrate 10 (here, from the Z-axis direction) passes through the bent portion 46 and is transmitted in the X-axis direction. Similarly, an optical signal transmitted in the X-axis direction passes through the bent portion 46 and is transmitted in the thickness direction of the substrate 10 and is input to the first interface 21. In other words, the bent portion 46 is a structure that changes the direction of travel of light traveling through the light transmitting portion 43 so that it travels to the first interface 21 of the first optical element 20. As shown in FIG. 2, the first transmission line 40 having the bent portion 46 may be located above the second transmission line 50 .

[0023] The second transmission path 50 extends in a fixed direction, here along the X-axis direction. An optical signal is input or output from one end 51 of the second transmission path 50, and the other end 52 is optically connected to the second interface 31. The one end 51 of the second transmission path 50 is connected to a connector 60, which will be described later. That is, the second transmission path 50 transmits an optical signal output from the second interface 31 of the second optical element 30 toward the connector 60. The second transmission path 50 also transmits an optical signal input from the connector 60 to the second interface 31 of the second optical element 30.

[0024] The second transmission line 50, which is an optical fiber cable, includes a light transmitting portion 53 and a coating portion 54 that protects the light transmitting portion 53. The coating portion 54 may be made of, for example, resin. The light transmitting portion 53 may be, for example, a core, and the coating portion 54 may be, for example, a cladding. As shown in FIG. 2 , the other end 52 of the coating portion 54 has an inclined surface 56 that is inclined with respect to the second optical element 30. The inclined surface 56 reflects an optical signal incident in the thickness direction of the substrate 10, in this case, from the Z-axis direction, and introduces the optical signal into the light transmitting portion 53. Specifically, the inclined surface 56 reflects an optical signal output from the second interface 31 of the second optical element 30 toward the positive direction of the Z-axis and introduces the optical signal into the light transmitting portion 53 of the second transmission line 50. The inclined surface 56 also reflects light incident from the light transmitting portion 53 in the thickness direction of the substrate 10. Specifically, the inclined surface 56 reflects the optical signal output from the other end 52 of the second transmission line 50 in the negative direction of the Z axis, and introduces the signal into the second interface 31 of the second optical element 30. In other words, the inclined surface 56 is a structure for changing the direction of travel of the light traveling through the optical transmitting unit 53, and allowing the light to travel to the second interface 31 of the second optical element 30.

[0025] The connector 60 is located on the substrate 10, and one end 41 of the first transmission line 40 and one end 51 of the second transmission line 50 are connected to the connector 60. The connector 60 is located on the mounting surface 101. Specifically, the connector 60 is disposed at one end of the mounting surface 101 in the transmission direction. In the example shown in FIG. 1 , the connector 60 is located at the end of the mounting surface 101 on the negative side of the X-axis.

[0026] In the optical circuit board 1 configured as described above, the first optical element 20 and the second optical element 30 are arranged along the extending direction of the first transmission line 40 and the second transmission line 50, so that a difference occurs in length between the first transmission line 40 and the second transmission line 50. That is, as shown in Fig. 2 , the first optical element 20 is arranged farther from the connector 60 than the second optical element 30, so the first transmission line 40 connected to the first optical element 20 is longer than the second transmission line 50 connected to the second optical element 30. Specifically, the length from one end 41 to the other end 42 of the first transmission line 40 is longer than the length from one end 51 to the other end 52 of the second transmission line 50.

[0027] Generally, the longer the transmission path, the lower the signal strength of the optical signal. Therefore, if the optical coupling efficiency of the first transmission path 40 and the optical coupling efficiency of the second transmission path 50 are equal, the signal strength of the optical signal transmitted through the first transmission path 40, which has a longer transmission path length, will be lower than that of the optical signal transmitted through the second transmission path 50.

[0028] Therefore, the optical circuit board 1 according to the first embodiment is configured so that the optical coupling efficiency between the first transmission line 40 and the first interface 21 is higher than the optical coupling efficiency between the second transmission line 50 and the second interface 31. Specifically, as described above, the other end 42 of the first transmission line 40 has a bent portion 46, and the other end 52 of the second transmission line 50 has an inclined surface 56. In the second transmission line 50, the optical signal from the optical transmitting unit 53 is reflected and introduced into the second optical element 30. Therefore, a portion of the optical signal may not be reflected by the inclined surface 56, which may result in optical signal loss. The optical coupling efficiency of the second transmission line 50, which may result in optical signal loss, is lower than the optical coupling efficiency of the first transmission line 40 directly connected to the first interface 21. In other words, in a structure for changing the light propagation direction to input or output an optical signal to or from an optical element, the optical coupling efficiency of the first transmission line 40 is higher than the optical coupling efficiency of the second transmission line 50.

[0029] With this configuration, since the first transmission path 40 is longer than the second transmission path 50, there is a possibility that optical propagation loss will increase. However, the optical coupling loss between the optical signal transmitted by the first transmission path 40 and the first interface 21 is smaller than the optical coupling loss between the second transmission path 50 and the second interface 31. This makes it possible to reduce variations in signal strength between the optical signal transmitted by the first transmission path 40 and the optical signal transmitted by the second transmission path 50. More specifically, it is possible to reduce variations in signal strength between the optical signal output from the first interface 21 and the second interface 31, transmitted by the first transmission path 40 and the second transmission path 50, and output from the connector 60. It is also possible to reduce variations in signal strength between the optical signal input from the connector 60, transmitted by the first transmission path 40 and the second transmission path 50, and input to the first interface 21 and the second interface 31.

[0030] Furthermore, in the optical circuit board 1, the first optical element 20 and the second optical element 30 are arranged in a row along the extension direction of the first transmission path 40 and the second transmission path 50, so that the optical circuit board 1 can be made smaller in the direction perpendicular to the extension direction of the first transmission path 40 and the second transmission path 50, in this case, in the Y-axis direction.

[0031] 1 has been described as an example in which one each of the first optical element 20 and the second optical element 30 is mounted on the substrate 10, the number of optical elements mounted on the substrate 10 is not limited to this. For example, two or more each of the first optical element 20 and the second optical element 30 may be mounted. This point will be described later in the third embodiment.

[0032] 1 and 2 show an example in which the first transmission line 40 and the second transmission line 50 extend in the negative direction of the X-axis from the first optical element 20 and the second optical element 30, respectively, but the extending directions of the first transmission line 40 and the second transmission line 50 are not limited to this. For example, the second transmission line 50 may extend in the negative direction of the X-axis from the second optical element 30, and the first transmission line 40 may extend in the positive direction of the X-axis from the first optical element 20. In this case, the second transmission line 50 may be connected to a connector arranged at an end of the mounting surface 101 on the negative side of the X-axis, and the first transmission line 40 may be connected to a connector arranged at an end of the mounting surface 101 on the positive side of the X-axis.

[0033] Second Embodiment Fig. 3 is a schematic side view showing the configuration of an optical circuit board 1 according to a second embodiment. In the first embodiment, an example in which the second transmission line 50 is an optical fiber cable has been described, but the second transmission line 50 is not limited to this. For example, the second transmission line 50 may be an optical waveguide. Below, a second transmission line 70 as an optical waveguide will be described.

[0034] 3 , the second transmission line 70 serving as an optical waveguide has a core 73 and claddings 74 and 75. The second transmission line 70 is formed on the substrate 10 and extends in a certain direction, in this case, along the X-axis direction. One end 71 of the second transmission line 70 is connected to the connector 60, and the other end 72 faces the mirror surface of the mirror 80.

[0035] The clads 74 and 75 cover at least a portion of the core 73. Specifically, the second transmission line 70 has an upper clad 74 and a lower clad 75. The upper clad 74 covers the upper surface of the core 73. The lower clad 75 covers the lower surface of the core 73. In other words, the second transmission line 70 as an optical waveguide is formed by laminating the lower clad 75, the core 73, and the upper clad 74 in this order on the substrate 10.

[0036] The mirror 80 reflects the optical signal output from the second interface 31 or the core 73. As shown in FIG. 3 , the mirror 80 has a mirror surface facing the other end 72 of the second transmission line 70. The mirror 80 is formed by vapor-depositing a mirror surface on one surface of a rectangular pillar-shaped base made of silicon, glass, resin, metal, or the like. The mirror surface may be made of aluminum, silver, or gold. The mirror surface is inclined with respect to the surface of the substrate 10.

[0037] The mirror 80 reflects an optical signal incident in the thickness direction of the substrate 10, in this case, the Z-axis direction, and introduces the optical signal into the core 73. Specifically, the mirror 80 reflects an optical signal output from the output interface of the second interface 31 in the negative direction of the Z-axis, and introduces the optical signal into the core 73 of the second transmission line 70. The mirror 80 also reflects an optical signal incident from the core 73 in the thickness direction of the substrate 10. Specifically, the mirror 80 reflects an optical signal irradiated from the core 73 of the second transmission line 70 in the positive direction of the Z-axis, and inputs the optical signal to the input interface of the second interface 31.

[0038] Even when the second transmission line 70 is an optical waveguide in this way, the optical coupling efficiency between the first transmission line 40 and the first interface 21 is higher than the optical coupling efficiency between the second transmission line 70 and the second interface 31, as in the first embodiment. Specifically, in the second transmission line 70, the optical signal from the core 73 is reflected by the mirror surface of the mirror 80 and introduced into the second optical element 30. Therefore, a part of the optical signal may not properly enter the second interface 31, which may result in optical signal loss. Alternatively, the optical signal output from the second interface 31 and reflected by the mirror surface of the mirror 80 may not properly enter the core 73 of the second transmission line 70, which may result in optical signal loss. The optical coupling efficiency of the second transmission line 70, which may result in optical signal loss, is lower than the optical coupling efficiency of the first transmission line 40, which is directly connected to the first interface 21. In other words, in a structure for changing the direction of light propagation to input or output an optical signal to an optical element, the optical coupling efficiency of the first transmission path 40 is higher than the optical coupling efficiency of the second transmission path 70 as an optical waveguide.

[0039] According to this configuration, the first transmission path 40 is longer than the second transmission path 70, which may increase optical propagation loss, but the optical coupling loss between the optical signal transmitted by the first transmission path 40 and the first interface 21 is smaller than the optical coupling loss between the second transmission path 70 and the second interface 31. This makes it possible to reduce variations in signal strength between the optical signal transmitted by the first transmission path 40 and the optical signal transmitted by the second transmission path 70.

[0040] Third Embodiment Fig. 4 is a schematic plan view showing the configuration of an optical circuit board 1 according to a third embodiment. In the first embodiment, an example was shown in which one first optical element 20 and one second optical element 30, for a total of two, are mounted on the substrate 10, but the number of optical elements mounted on the substrate 10 is not limited to this. As shown in Fig. 4, two first optical elements 20 and two second optical elements 30, for a total of four, may be mounted on the substrate 10. In this case, the four optical elements 20, 30 may be arranged in a lattice pattern in plan view.

[0041] This allows more optical elements to be mounted on the substrate 10 compared to mounting one each of the first optical element 20 and the second optical element 30, thereby expanding the transmission bandwidth of the optical circuit board 1. Furthermore, by arranging the four optical elements 20, 30 in a lattice pattern, the optical circuit board 1 can be made more compact compared to arranging the four optical elements 20, 30 in a row.

[0042] The present technology may also have the following configuration. (1) An optical circuit board (for example, an optical circuit board 1) includes a substrate (for example, a substrate 10), a first optical element (for example, a first optical element 20), a second optical element (for example, a second optical element 30), a first transmission path (for example, a first transmission path 40), and a second transmission path (for example, a second transmission path 50). The first optical element is located on the substrate and includes a first interface (for example, a first interface 21) through which an optical signal is input or output. The second optical element is located on the substrate and includes a second interface (for example, a second interface 31) through which an optical signal is input or output. The first transmission path has one end (for example, a first end 41) through which an optical signal is input or output, and the other end (for example, a second end 42) is optically connected to the first interface. The second transmission line has one end (for example, one end 51) from which an optical signal is input or output, and the other end (for example, the other end 52) is optically connected to the second interface. The first transmission line is longer than the second transmission line. The optical coupling efficiency of the first transmission line with the first interface is higher than the optical coupling efficiency of the second transmission line with the second interface. (2) The optical circuit board described in (1) above may have a connector (for example, connector 60) located on the substrate and to which one end of the first transmission line and one end of the second transmission line are connected, and the length from one end to the other end of the first transmission line may be longer than the length from one end to the other end of the second transmission line. (3) In the optical circuit board described in (1) or (2) above, the first transmission line may be an optical fiber cable having a bent portion at the other end, and the second transmission line may be an optical fiber cable having an inclined surface at the other end that is inclined toward the second optical element. (4) In the optical circuit board described in (1) or (2) above, the first transmission line may be an optical fiber cable, and the second transmission line (for example, the second transmission line 70) may be an optical waveguide formed by stacking a lower clad (for example, the lower clad 75), a core (for example, the core 73), and an upper clad (for example, the upper clad 74) on the substrate in this order. (5) In the optical circuit board described in any one of (1) to (4) above, the first optical element and the second optical element may be arranged in a row along the extension direction of the first transmission line and the second transmission line.(6) In the optical circuit board described in (5) above, the first transmission line may be located above the second transmission line. (7) The optical circuit board described in any one of (1) to (6) above may have at least four optical elements including a first optical element and a second optical element, and the four optical elements may be arranged in a lattice pattern in a plan view.

[0043] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0044] REFERENCE SIGNS LIST 1 Optical circuit board 10 Board 20 First optical element 21 First interface 30 Second optical element 31 Second interface 40 First transmission path 41 One end 42 Other end 50 Second transmission path 51 One end 52 Other end 60 Connector

Claims

1. An optical circuit board comprising: a substrate; a first optical element located on said substrate and having a first interface for inputting or outputting an optical signal; a second optical element located on said substrate and having a second interface for inputting or outputting an optical signal; a first transmission line having one end for inputting or outputting an optical signal and the other end optically connected to said first interface; and a second transmission line having one end for inputting or outputting an optical signal and the other end optically connected to said second interface, wherein said first transmission line is longer than said second transmission line, and the optical coupling efficiency of said first transmission line with said first interface is higher than the optical coupling efficiency of said second transmission line with said second interface.

2. An optical circuit board according to claim 1, further comprising: a connector located on said substrate to which said one end of said first transmission line and said one end of said second transmission line are connected, wherein the length from said one end to said other end of said first transmission line is longer than the length from said one end to said other end of said second transmission line.

3. An optical circuit board according to claim 1 or 2, wherein the first transmission path is an optical fiber cable having a bent portion at the other end, and the second transmission path is an optical fiber cable having an inclined surface at the other end that is inclined toward the second optical element.

4. An optical circuit board according to claim 1 or 2, wherein the first transmission line is an optical fiber cable, and the second transmission line is an optical waveguide in which a lower clad, a core, and an upper clad are laminated in this order on the board.

5. An optical circuit board according to any one of claims 1 to 4, wherein the first optical element and the second optical element are arranged in a row along the extension direction of the first transmission line and the second transmission line.

6. The optical circuit board according to claim 5, wherein the first transmission line is located above the second transmission line.

7. An optical circuit board according to any one of claims 1 to 6, comprising at least four optical elements including the first optical element and the second optical element, the four optical elements being arranged in a lattice pattern in plan view.

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