Positioning structure for silicon substrate

Abstract

To improve the accuracy of alignment with a silicon substrate.SOLUTION: The positioning structure of the silicon substrate includes a silicon substrate and a guide pin. The silicon substrate has a substrate surface on which at least one or more linear grooves are formed. The guide pin is located along the groove. The groove reaches a side surface of the silicon substrate, and the guide pin extends beyond the side surface to the outside of the silicon substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positioning structure for a silicon substrate. [Background technology]

[0002] Silicon photonics has attracted attention as a way to realize compact optical transceivers. Patent Document 1 discloses that optical connecting components are attached to a silicon photonics element in advance to optically connect the silicon photonics element and an optical waveguide. In Patent Document 1, the optical coupling between the silicon photonics element and the optical connecting components is achieved by active optical alignment, which positions the optical connecting components while checking the conduction of light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-90500 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, performing active optical alignment individually requires time and effort. For this reason, passive mounting, which allows mounting without checking optical continuity, is being considered. However, passive mounting has the problem of being difficult to adjust the position with high precision, resulting in large connection loss.

[0005] Therefore, an object of the present disclosure, which has been made in consideration of these points, is to provide a silicon substrate positioning structure that improves the accuracy of alignment with the silicon substrate. [Means for solving the problem]

[0006] In one embodiment, (1) the positioning structure for a silicon substrate comprises a silicon substrate having a substrate surface with at least one linear groove formed therein, and a guide pin positioned along the groove, the groove reaching a side surface of the silicon substrate, and the guide pin extending beyond the side surface to outside the silicon substrate.

[0007] (2) The silicon substrate positioning structure of (1) above can further include a connection receiving portion that is positioned relative to the silicon substrate by the guide pin passing through it.

[0008] (3) In the positioning structure for a silicon substrate described in (2) above, the silicon substrate may have an optical waveguide formed therein and a port formed on the side surface for inputting or outputting light to the optical waveguide, and the connection receiving portion may be a receptacle that is positioned relative to the silicon substrate by the guide pin passing through it.

[0009] (4) In the silicon substrate positioning structure of (3) above, the connection receiving portion can have a light-collecting element at a position corresponding to the port.

[0010] (5) In the silicon substrate positioning structure of (3) or (4) above, the guide pin penetrates the ferrule to which the optical fiber is connected, thereby positioning the silicon substrate, the connection receiving portion, and the ferrule.

[0011] (6) In the silicon substrate positioning structure of (5) above, the connection receiving portion may have a spacer on the side connected to the ferrule.

[0012] (7) In the silicon substrate positioning structure according to any one of (3) to (6) above, a refractive index matching material may be provided between the connection receiving portion and the silicon substrate.

[0013] (8) In the silicon substrate positioning structure according to any one of (1) to (7) above, the groove may have a V-shaped or inverted trapezoidal cross section.

[0014] (9) In any of the silicon substrate positioning structures (1) to (7) above, the substrate surface may be a {100} plane of the silicon crystal forming the silicon substrate, and the groove surface may include at least two {111} planes of the silicon crystal.

[0015] (10) In the silicon substrate positioning structure of (9) above, the guide pin can be positioned relative to the silicon substrate by having the cylindrical side surfaces contact the two {111} planes, respectively. [Effects of the Invention]

[0016] According to the embodiment of the invention, the accuracy of alignment with the silicon substrate can be improved. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view showing an example of a positioning structure for positioning a silicon substrate having an optical integrated circuit with respect to an optical fiber ferrule. FIG. [Figure 2] 2 is an exploded side view showing the positioning structure of FIG. 1 together with a ferrule. [Figure 3] 2A and 2B are three-view diagrams showing the silicon substrate on which the guide pins of FIG. 1 are mounted. [Figure 4] 4 is a cross-sectional view of the silicon substrate taken along line AA in FIG. 3. [Figure 5] 4 is a cross-sectional view taken along the line AA of FIG. 3 showing another example of the silicon substrate. [Figure 6] 2 is a diagram showing an end face of the receptacle of FIG. 1 on the ferrule side. [Figure 7] BB line cross-sectional view of FIG. [Figure 8] 2 is a diagram showing an end face of the ferrule of FIG. 1 on the receptacle side. [Figure 9]FIG. 10 is a perspective view showing another example of the positioning structure for the silicon substrate. [Figure 10] 10 is a side view showing an example of a positioning structure that does not include a receptacle for positioning a silicon substrate relative to an optical fiber ferrule. FIG. [Figure 11] FIG. 10 illustrates the signal strength of each channel connected by the positioning structure of the present disclosure in accordance with one embodiment compared to active implementation. [Figure 12] 12A to 12C are diagrams illustrating the mounting accuracy of the positioning structure of the present disclosure based on FIG. 11. [Figure 13] 12A to 12C are diagrams illustrating the mounting accuracy of the positioning structure of the present disclosure based on FIG. 11. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The drawings used in the following description are schematic. The dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0019] (Overall structure) A positioning structure 1 according to an embodiment of the present disclosure is a structure that provides accurate positioning for connecting a silicon substrate 10 to a ferrule 40 (see FIG. 2) to which one or more optical fibers are connected. As shown in the perspective view of FIG. 1, the positioning structure 1 includes a silicon substrate 10, guide pins 20, and a receptacle 30 that serves as a connection receiving portion. In this disclosure, the connector on the optical fiber side is referred to as a "plug," and the connector on the silicon substrate 10 side is referred to as a "receptacle." The ferrule 40 is a component that constitutes the plug. As will be described later, the receptacle 30 is not an essential component of the positioning structure 1 of the present disclosure.

[0020] As shown in Fig. 2, a linear groove 12 is provided on a substrate surface 11 of a silicon substrate 10. The groove 12 reaches a side surface 13, which is one side surface of the silicon substrate 10. A guide pin 20 is positioned along the linear groove 12 and fixed thereto by adhesive or the like. The guide pin 20 extends beyond the side surface 13 to the outside of the silicon substrate 10.

[0021] The receptacle 30 is provided with a through hole 31 whose inner diameter is approximately equal to the outer diameter of the guide pin 20. The positioning structure 1 is formed by passing the guide pin 20 through the through hole 31 of the receptacle 30 and abutting the surface of the receptacle 30 facing the silicon substrate 10 against the side surface 13 of the silicon substrate 10 to secure the receptacle 30 in place. A portion of the receptacle 30 facing the silicon substrate 10 forms an overhang 32 that overhangs toward the silicon substrate 10. The overhang 32 is positioned so as to cover a portion of the substrate surface 11 and a portion of the guide pin 20 when the silicon substrate 10 and the receptacle 30 are connected. The upper portion of the guide pin 20 and the lower surface of the overhang 32 may be fixed with an adhesive or the like. The guide pin 20 is firmly fixed by being sandwiched between the groove 12 and the lower surface of the overhang 32.

[0022] The receptacle 30 can be connected to a ferrule 40 that is connected to a ribbon optical fiber cable 43. The ferrule 40 has a guide pin hole 41 that opens to a ferrule end face 42 facing the receptacle 30. The guide pin hole 41 has an inner diameter that is approximately equal to the outer diameter of the guide pin 20. The guide pin 20 is slidable within the guide pin hole 41. The guide pin 20, which protrudes from the receptacle end face 33 of the receptacle 30 that faces the ferrule 40, is inserted into and fitted into the guide pin hole 41, thereby connecting the receptacle 30 and the ferrule 40.

[0023] If necessary, a spacer 50 is disposed on the receptacle end face 33. The spacer 50 has a guide pin 20 and a hole 51 for passing light in the center. The spacer 50 is used to finely adjust the distance between the receptacle 30 and the ferrule 40. The spacer 50 adjusts the distance between the ferrule end face 42 and the light-collecting element 35, thereby increasing the optical coupling efficiency between the ferrule 40 and the silicon substrate 10.

[0024] The positioning structure 1 of the present disclosure can position the silicon substrate 10, the receptacle 30, and the ferrule 40 with high precision by having a common guide pin 20 fixed in a groove 12 of the silicon substrate 10 penetrate through the receptacle 30 and the ferrule 40.

[0025] (silicon substrate) Next, an example of the configuration of the silicon substrate 10 according to an embodiment will be described with reference to FIG.

[0026] The silicon substrate 10 is a silicon photonics substrate on which an optical integrated circuit 15, such as an optical transceiver, including a fine waveguide is formed. The optical integrated circuit 15 includes a silicon photonics chip in which optical elements and electronic elements are integrated on the silicon substrate 10. The silicon substrate 10 may have a rectangular shape in a plan view. However, the shape of the silicon substrate 10 is not limited to a rectangle. An optical waveguide connected to the optical integrated circuit 15 is formed inside the silicon substrate 10. One or more ports 16 for inputting or outputting light to the waveguide are formed on a side surface 13 of the silicon substrate 10. The number of ports 16 may be any number, such as 4, 6, 8, 12, or 16. The ports 16 may be arranged on the side surface 13 in a direction along the substrate surface 11. The ports 16 are not limited to being arranged in a single row, but may be arranged in multiple rows.

[0027] As described above, one or more grooves 12 are formed in the substrate surface 11 of the silicon substrate 10. The number of grooves 12 and the number of guide pins 20 arranged in the grooves 12 are preferably two or more to prevent rotation of the silicon substrate 10 and the receptacle 30 around the guide pins 20 during positioning. However, the number of grooves 12 may be one by combining with other rotation prevention means. In the example of FIG. 3 , two grooves 12 are arranged on the side surface 13 so as to be located on both sides of the array of ports 16. The grooves 12 extend linearly from a specific position on the substrate surface 11 to one side surface 13 of the silicon substrate 10. When there are multiple grooves 12, the grooves 12 extend parallel to each other. The extension direction of the grooves 12 may be perpendicular to the side surface 13.

[0028] The groove 12 may be two V-shaped grooves 12 as shown in the cross-sectional view of Fig. 4. The V-shaped groove 12 has two groove slopes 12a and 12b which are groove surfaces.

[0029] The substrate surface 11 is a {100} plane of the silicon crystal that forms the silicon substrate 10. The groove slopes 12a and 12b of the groove 12 are {111} planes of the silicon crystal. By performing anisotropic etching on the {100} plane of the substrate surface 11 using an alkaline aqueous solution such as a KOH solution, the V-shaped groove 12 can be formed with high precision. The groove slopes 12a and 12b of the V-shaped groove 12 form an angle θ of 54.7° with high precision with respect to the substrate surface 11. The angle θ of the groove slopes 12a and 12b is an angle strictly determined by the crystal planes of the silicon single crystal. Because the groove 12 is etched so that the groove slopes 12a and 12b are at the angle θ determined by the crystal planes, the angle, width, position, and the like can be easily controlled.

[0030] (Guide pin) The guide pin 20 is a highly accurate and rigid pin having a cylindrical shape with a precisely defined shape and size. The guide pin 20 can be made of a metal such as stainless steel, but is not limited to this. The guide pin 20 can also be made of a material such as ceramics or resin. The guide pin 20 is placed in the V-shaped groove 12, and is accurately positioned relative to the silicon substrate 10 by the cylindrical side surfaces contacting the groove slopes 12a and 12b. High-precision guide pins with a diameter of 698.5±0.5 μm are commercially available for use in single-mode optical fiber connectors, and these can be used as the guide pin 20. Other commercially available sizes of guide pins may also be used.

[0031] The pitch of the two V-shaped grooves 12, or the distance between the vertices of the V, can be the same as the distance between the centers of the guide holes that is standard for the ferrule 40. For example, the pitch of the V-shaped grooves 12 can be 4.6 mm. This allows commercially available ferrules 40 to be easily connected to the receptacle 30.

[0032] The shape of the groove 12 is not limited to a V-shape. For example, as shown in FIG. 5, the cross-sectional shape of the groove 12 may be an inverted trapezoid that narrows from the substrate surface 11 toward the interior of the silicon substrate 10. In this case, too, two groove slopes 12a and 12b, which are {111} planes of silicon crystal, are formed on either side of the groove bottom 12c by anisotropic etching. The guide pin 20 is positioned accurately with respect to the silicon substrate 10 by being placed in the inverted trapezoidal groove 12, with the cylindrical side surfaces of the guide pin 20 coming into contact with the groove slopes 12a and 12b.

[0033] (receptacle) Next, the receptacle 30 will be described with reference to Figures 6 and 7. The receptacle 30 may be made of any material, including resin. In addition to through holes 31 for the guide pins 20, the receptacle 30 has optical path holes 34 formed at positions corresponding to the ports 16 of the silicon substrate 10. The interior of the optical path holes 34 may be filled with air, or may be filled with an optical material that is transparent to the propagating light.

[0034] A focusing element 35 may be disposed inside the optical path hole 34, corresponding to each port 16. The focusing element 35 includes, for example, a lens. The focusing element 35 couples light emitted from an optical fiber hole 44 (see FIG. 8 ) in the ferrule end face 42 to the port 16 in the silicon substrate 10. The focusing element 35 couples light emitted from the port 16 in the silicon substrate 10 toward the optical fiber hole 44 in the ferrule end face 42. Therefore, the focusing element 35 can reduce connection loss in the receptacle 30 and increase the light coupling efficiency. In FIG. 7 , the focusing element 35 is provided at one location along the length of the optical path hole 34, but the focusing element 35 may have a size that extends over the entire length of the optical path hole 34. The focusing element 35 does not have to be provided inside the optical path hole 34. In that case, the length of the optical path hole 34 is appropriately adjusted so that light is coupled. Additionally, microlenses may be provided on the port 16 of the silicon substrate 10 and on the end face of the optical fiber disposed on the ferrule end face 42 .

[0035] The positioning structure 1 may have a refractive index matching agent between the silicon substrate 10 and the receptacle 30. The refractive index matching agent may be liquid or solid. The refractive index matching agent may be an ultraviolet-curable resin that functions as an adhesive between the silicon substrate 10 and the receptacle 30. By having a refractive index matching agent, it is possible to reduce loss due to reflection or the like at the interface between the port 16 of the silicon substrate 10 and the optical path hole 34 of the receptacle 30.

[0036] (ferrule) The ferrule 40 is a connector component commonly used to mechanically connect multiple optical fibers together. A mechanically transferable (MT) ferrule for a multi-fiber optical connector can be used as the ferrule 40. The ferrule 40 functions as a terminal for holding multiple optical fibers. The ferrule 40 aligns the ends of the optical fibers of a ribbon optical fiber cable 43 with optical fiber holes 44 in a ferrule end face 42. The ferrule 40 may be made of a resin such as PPS (Poly Phenylene Sulfide). The material of the ferrule 40 is not limited to resin, and it may be made of other materials such as glass or ceramics.

[0037] 8, the ferrule 40 has a ferrule end face 42 with a plurality of optical fiber holes 44, each in which the tip of an optical fiber is positioned, and guide pin holes 41, into which a connection guide pin 20 is inserted, at both ends. The tip of each optical fiber may be polished and positioned to slightly protrude from the ferrule end face 42. The optical path holes 34 of the receptacle 30 are positioned opposite the optical fiber holes 44 when the receptacle 30 and the ferrule 40 are connected using the guide pins 20. The ferrule 40 has high dimensional accuracy at the submicron level.

[0038] The ferrule 40 can be positioned by fitting with the guide pin 20 by inserting the guide pin 20 into the guide pin hole 41. The ferrule 40 is configured to be detachable between the guide pin 20 and the receptacle 30. A fastener or the like may be provided between the plug including the ferrule 40 and the receptacle 30 to fix the connected state.

[0039] As configured as described above, by using the positioning structure 1 of the present disclosure, the silicon substrate 10, the receptacle 30, and the plug including the ferrule 40 can be positioned and connected with high precision using the guide pin 20 as a reference. In particular, accurate positioning is possible because the positioning between the silicon substrate 10 and the guide pin 20 uses the V-shaped groove 12 having an angle that is accurately determined by the crystal orientation of the silicon single crystal, and the guide pin 20 whose size is accurately determined.

[0040] Furthermore, by making the pitch of the two grooves 12 the same as the spacing between the guide holes adopted as the standard for the ferrule 40, each fiber of the ribbon optical fiber cable 43 can be easily connected to the port 16 of the optical integrated circuit 15 on the silicon substrate 10 using a commercially available ferrule 40.

[0041] Furthermore, when the positioning structure 1 of the present disclosure is applied to a silicon substrate 10 having an optical integrated circuit 15 and used to connect the ferrule 40 to each optical fiber, high-precision alignment is possible, enabling high-precision connection in passive mounting. Also, the positioning structure 1 of the present disclosure can detachably connect the silicon substrate 10 on which the optical integrated circuit 15 is mounted and the ferrule 40 connected to the ribbon optical fiber cable 43.

[0042] In another embodiment, the positioning structure 1A may be configured as shown in the perspective view of FIG. 9. In this case, the shape of the receptacle 30 differs from that shown in FIG. 1 and does not include the protruding portion 32. Therefore, the receptacle 30 in FIG. 9 does not cover the silicon substrate 10 and a portion of the guide pin 20. However, in the positioning structure 1A in FIG. 9, the guide pin 20 is accurately positioned relative to the silicon substrate 10 and fixed with an adhesive or the like. This allows the positioning structure 1A to accurately position the silicon substrate 10, the receptacle 30, and the ferrule 40, similar to the positioning structure 1 in FIG. 1.

[0043] 10, the positioning structure 1B may be configured not to include the receptacle 30. The positioning structure 1B of FIG. 10 may be directly connected to the ferrule 40. In this case, the guide pins 20 are inserted into the guide pin holes 41 of the ferrule 40, and each port 16 on the side surface 13 of the silicon substrate 10 can be directly connected to the tip of an optical fiber disposed in each optical fiber hole 44 on the ferrule end face 42. Even in this configuration, the guide pins 20 are positioned with high precision relative to the silicon substrate 10, so that the silicon substrate 10 and the ferrule 40 can be positioned and connected with high precision.

[0044] (Evaluation of positioning structure) FIG. 11 is a graph showing the signal strength of light transmitted when connecting the silicon substrate 10, receptacle 30, and ferrule 40 using the positioning structure 1 shown in FIG. 1, compared with the signal strength when connecting in the most loss-free manner using active mounting. This test was conducted using six channels Ch.A to Ch.F connecting the six ports 16 on the silicon substrate 10 with the six optical fiber ends on the ferrule end face 42 on the ferrule 40. In FIG. 11, the "x" (cross) indicates the signal strength when connected using active optical alignment. The "o" (circle) indicates the signal strength of the channel connected using passive optical alignment using the method disclosed herein. According to this graph, the difference in signal strength between active and passive mounting was 1.48 dB on average, with a maximum of 2.46 dB.

[0045] 12 and 13 are graphs showing the relationship between misalignment and loss during active mounting. The horizontal axis of FIG. 12 indicates misalignment from left to right (hereinafter referred to as the "horizontal direction") when viewing the side surface 13 from the front. From FIG. 12, a loss of 2.46 dB corresponds to a misalignment in the horizontal direction of approximately 1.7 μm. The horizontal axis of FIG. 13 indicates a misalignment in the direction perpendicular to the substrate surface 11 (hereinafter referred to as the "vertical direction"). From FIG. 13, a loss of 2.46 dB corresponds to a misalignment in the vertical direction of approximately 1.5 μm. From the above, the maximum misalignment from the best position when using the positioning structure 1 of the present disclosure was 1.7 μm.

[0046] As described above, by using the positioning structure 1 of the present disclosure for connecting a silicon photonics substrate and an optical fiber, even mounting using passive optical alignment can be performed with high precision, with an error of 1.7 μm or less, compared to active mounting. Therefore, by using the positioning structure 1 of the present disclosure, low-loss connection can be achieved between the silicon substrate 10, the receptacle 30, and the ferrule 40, even without active optical alignment.

[0047] Although the above-described embodiments have been described as typical examples, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments and examples, and various modifications and / or changes can be made without departing from the scope of the claims. [Explanation of symbols]

[0048] 1, 1A, 1B Positioning structure 10 Silicon substrate 11 Substrate surface 12 grooves 12a,12b Groove slope (groove surface) 12c Bottom of groove 13 Side 15 Optical Integrated Circuits 16 ports 20 guide pin 30 Receptacle (connection receiving part) 31 Through hole 32 Overhang hole 33 Receptacle end face 34 Optical hole 35 Condenser element 40 ferrules 41 Guide pin hole 42 Ferrule end face 43 Ribbon Fiber Optic Cable 44 optical fiber holes 50 spacer 51 holes

Claims

1. a silicon substrate having a substrate surface on which at least one linear groove is formed; a guide pin positioned along the groove; The groove reaches a side surface of the silicon substrate, and the guide pin extends beyond the side surface to the outside of the silicon substrate.

2. The silicon substrate positioning structure according to claim 1 , further comprising a connection receiving portion that is positioned relative to the silicon substrate by the guide pin passing through the connection receiving portion.

3. an optical waveguide is formed inside the silicon substrate, and a port for inputting or outputting light to the optical waveguide is formed on the side surface of the silicon substrate; 3. The silicon substrate positioning structure according to claim 2, wherein the connection receiving portion is a receptacle that is positioned relative to the silicon substrate by the guide pin passing therethrough.

4. The silicon substrate positioning structure according to claim 3 , wherein the connection receiving portion has a light-collecting element at a position corresponding to the port.

5. 4. The silicon substrate positioning structure according to claim 3, wherein the silicon substrate, the connection receiving portion, and the ferrule are positioned by the guide pin penetrating a ferrule to which an optical fiber is connected.

6. 6. The silicon substrate positioning structure according to claim 5, wherein the connection receiving portion has a spacer on a side connected to the ferrule.

7. 4. The silicon substrate positioning structure according to claim 3, further comprising a refractive index matching material between said connection receiving portion and said silicon substrate.

8. The silicon substrate positioning structure according to claim 1 , wherein the groove has a V-shaped or inverted trapezoidal cross section.

9. 2. The silicon substrate positioning structure according to claim 1, wherein the substrate surface is a {100} plane of the silicon crystal forming the silicon substrate, and the groove surface includes at least two {111} planes of the silicon crystal.

10. 10. The silicon substrate positioning structure according to claim 9, wherein the guide pin is positioned with respect to the silicon substrate by contacting cylindrical side surfaces with the two {111} faces, respectively.

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