Polymer optical waveguide and optical module

Abstract

According to the present invention, a polymer optical waveguide can be highly accurately positioned with respect to an optical circuit board in a simple configuration and with simple assembly work by engaging protrusions formed on a cladding with guide grooves formed in the optical circuit board.　This polymer optical waveguide comprises a core (11) and a cladding (12, 13) disposed around the core (11) and having a lower refractive index than the core (11). The cladding (12, 13) is provided with a protrusion (17) that extends along the periphery of the core (11) and engages with a guide groove (22) formed in an optical circuit board (20). A plurality of protrusions (17) are formed alongside each other in the width direction of the cladding (12, 13), and a single core (11) is disposed in a central part of each of the protrusions (17) in the width direction.

Description

Polymer Optical Waveguide and Optical Module

[0001] The present invention relates to a polymer optical waveguide and an optical module.

[0002] Silicon photonics, which is a technology for integrating silicon optical circuits on a silicon chip, has attracted attention. In silicon photonics, for example, as shown in Patent Document 1, a polymer optical waveguide that utilizes adiabatic coupling is known as a waveguide for transmitting an optical signal between a silicon optical waveguide formed in an optical integrated circuit and an optical fiber.

[0003] Japanese Patent Application Laid-Open No. 2014-81586

[0004] Patent Document 1 aims to reduce the propagation loss between a silicon optical waveguide and an optical fiber when a polymer optical waveguide is used. However, in order to adiabatically couple a polymer optical waveguide, it is necessary to expose a part of the core of the polymer optical waveguide and closely adhere it in a state of being positioned with high precision on the silicon optical integrated circuit side. As a result, high processing accuracy and assembly accuracy are required, so there are problems in terms of versatility, workability, and cost.

[0005] The present invention has been made in view of the above situation, and an object thereof is to provide a polymer optical waveguide and an optical module that can be coupled to an optical circuit board constituting a silicon optical integrated circuit with high precision in a simple configuration.

[0006] The above object of the present invention is achieved by the following configuration. (1) A polymer optical waveguide having a core and a clad arranged around the core and having a refractive index lower than that of the core, wherein the clad is provided with a protrusion that extends along the periphery of the core and engages with a guide groove formed in an optical circuit board, the protrusions are formed in a plurality side by side in the width direction of the clad, and a single core is arranged at the center in the width direction of each of the protrusions. (2) An optical module having the polymer optical waveguide according to (1) and the optical circuit board, wherein the optical circuit board has an optical waveguide coupled to the polymer optical waveguide.

[0007] According to the present invention, by engaging the protrusions formed on the cladding with guide grooves formed on the optical circuit board, the polymer optical waveguide can be positioned with high precision relative to the optical circuit board with a simple configuration and simple assembly work.

[0008] Figure 1 is a perspective view showing an example configuration of the optical module of the present invention. Figure 2 is a perspective view showing the coupling portion between the polymer optical waveguide and the optical circuit board of the first embodiment. Figure 3 is an exploded perspective view showing the coupling portion between the polymer optical waveguide and the optical circuit board. Figure 4 is a front view of the main part showing the coupling portion between the polymer optical waveguide and the optical circuit board. Figure 5 is an enlarged view of the main part of Figure 4 showing the protrusion and guide groove. Figure 6 is an enlarged view of the main part showing modification 1 of the protrusion and guide groove of the first embodiment. Figure 7 is an enlarged view of the main part showing modification 2 of the protrusion and guide groove of the first embodiment.

[0009] Hereinafter, preferred embodiments of the polymer optical waveguide and the optical module including the polymer optical waveguide of the present invention will be described as shown in the accompanying drawings.

[0010] <First Embodiment> Figure 1 is a perspective view showing an example of the configuration of the optical module of the present invention. Figure 2 is a perspective view showing the coupling portion between the polymer optical waveguide and the optical circuit board of the first embodiment. Figure 3 is an exploded perspective view showing the coupling portion between the polymer optical waveguide and the optical circuit board. Figure 4 is a front view of the main part showing the coupling portion between the polymer optical waveguide and the optical circuit board. Figure 5 is an enlarged view of the main part of Figure 4 showing the protrusions and guide grooves.

[0011] The optical module 100 shown in Figure 1 comprises a polymer optical waveguide 10 and an optical circuit board 20. In the illustrated example, the optical circuit board 20 is coupled to both longitudinal ends of the polymer optical waveguide 10. The optical module 100 is not limited to the above configuration, as long as at least one of the longitudinal ends of the polymer optical waveguide 10 is coupled to the optical circuit board 20.

[0012] (Optical Circuit Board 20) In this embodiment, the optical circuit board 20 is a silicon substrate and includes at least a silicon optical waveguide (not shown) that is optically coupled to the polymer optical waveguide 10. A photonic integrated circuit (PIC) is formed by integrating other optical elements on the optical circuit board 20. Note that the optical circuit board 20 is not limited to a silicon substrate. For example, it may be an inorganic substrate such as an InP (indium phosphide) substrate, a BT substrate using BT resin, or a glass substrate. Similarly, the optical waveguide provided on the optical circuit board 20 is not limited to a silicon optical waveguide. For example, it may be an inorganic waveguide such as a SiN waveguide.

[0013] As shown in Figure 3, the optical circuit board 20 has a substrate-side coupling portion 21 to which the longitudinal ends of the polymer optical waveguide 10 are coupled. The substrate-side coupling portion 21 is recessed linearly from the end of the optical circuit board 20 and has multiple guide grooves 22 arranged in a row in the width direction, and a substrate-side connection portion 23 consisting of a flat surface formed between adjacent guide grooves 22 in the width direction.

[0014] In the examples shown in Figures 2 to 5, the guide groove 22 has a pair of inclined surfaces 22a, 22a and a bottom portion 22b, and is formed in a trapezoidal shape with a tapered angle that decreases in width as the groove deepens. The shape of the guide groove 22 is not limited to this, and may be rectangular, semicircular, or a V-groove that is a standard design for optical fiber mounting.

[0015] The pitch of the guide grooves 22, which is the distance between the centers of adjacent guide grooves 22 in the width direction, is preferably 80 μm to 250 μm. The width of the guide grooves 22 is preferably 20 μm or more. The depth of the guide grooves 22 is preferably 5 μm to 100 μm. In this embodiment, the pitch of the guide grooves 22 (core 11 of the polymer optical waveguide 10) was set to 125 μm to match the pitch of the optical fiber. Similarly, the depth of the guide grooves 22 on the silicon substrate was set to 75 μm.

[0016] (Polymer Optical Waveguide 10) The polymer optical waveguide 10 shown in Figure 1 comprises a core 11, an underclad 12, and an overclad 13. In the polymer optical waveguide 10, a plurality of cores 11 are arranged in parallel along the direction of light propagation of the core 11 in the polymer optical waveguide 10 (hereinafter referred to in this specification as the "direction of light propagation in the polymer optical waveguide" or the "longitudinal direction of the polymer optical waveguide"). The underclad 12 has a lower refractive index than the core 11 and is located around the core 11. The overclad 13 has a lower refractive index than the core 11 and is located around the core 11 on the opposite side from the underclad 12.

[0017] As shown in Figure 1, a coupling portion 15 is formed at the longitudinal end of the polymer optical waveguide 10, which is coupled to the optical circuit board 20. Figures 2 to 5 are views of the main cross-section of the coupling portion 15 shown in Figure 1, viewed from the back. As shown in Figures 2 to 5, the coupling portion 15 has a coupling support portion 16 which is located at the longitudinal end of the underclad 12 and overlaps with the optical circuit board 20, and a projection portion 17 which is formed by recessing or notching the overclad 13 along the longitudinal direction. As a result, the area around the core 11 in the coupling portion 15 is covered by the coupling support portion 16 and the projection portion 17.

[0018] As shown in Figures 4 and 5, the projections 17 are arranged in a row (12 in the illustrated example) at predetermined intervals in the width direction of the polymer optical waveguide 10, and a flat connecting portion 18 is formed between adjacent projections 17. The projections 17 are formed along the core 11 on the coupling support portion 16, and a single core 11 is positioned in the width direction center of each projection 17. As a result, the pitch of the multiple cores 11 arranged in the width direction of the polymer optical waveguide 10 is the same as the pitch of the multiple guide grooves 22 formed in the optical circuit board 20. In addition, the longitudinal direction of the projections 17 is formed to be the same as or longer than the guide grooves 22.

[0019] In the illustrated example, the projection 17 is formed in a rectangular cross-section and has a pair of corners 17a, 17a formed on the protruding portion and a flat protruding surface 17b formed between the pair of corners 17a, 17a. The projection 17 is formed so that the pair of corners 17a, 17a of the protruding portion press against a pair of inclined surfaces 22a, 22a formed in the trapezoidal guide groove 22 by adjusting the height H and width W of the projection 17. As a result, the projection 17 engages with the guide groove 22 of the optical circuit board 20 so as to fit into a predetermined position. At this time, the connection portion 18 of the polymer optical waveguide 10 and the substrate-side connection portion 23 of the optical circuit board 20 are in close contact at a predetermined position.

[0020] The width of the connection portion 18 is made larger than the mode field diameter, which is determined by the size of the core 11 and the difference in refractive index between the core 11 and the cladding 12. This ensures sufficient distance between adjacent protrusions 17, 17, thereby suppressing crosstalk caused by the mixing of light propagating through adjacent cores 11, 11. Furthermore, the width of the protrusions 17 centered on the core 11 is made larger than the mode field diameter, and the thickness of the protruding portion 17 and the thickness of the coupling support portion 16 are made greater than half the mode field diameter. This prevents light from leaking out of the protrusions 17 and increasing the propagation loss of the core 11. The mode field diameter is 1 μm or more. The core height of the core 11 is 0.1 μm or more and 50 μm or less, with a more preferable core height of 0.5 μm or more and 30 μm or less. The core width of the core 11 is 0.5 μm or more and 50 μm or less, with a more preferable core width of 1 μm or more and 30 μm or less. This configuration results in a higher yield of the manufactured polymer optical waveguides and a higher mounting density of the cores 11. In this specification, "core width" refers to the width of the core in the direction perpendicular to the thickness direction of the polymer optical waveguide in a cross section perpendicular to the direction of light propagation in the polymer optical waveguide. "Core height" refers to the height of the core in the thickness direction of the polymer optical waveguide in a cross section perpendicular to the direction of light propagation in the polymer optical waveguide.

[0021] The connection portion 18 can be firmly fixed in close contact with the substrate-side connection portion 23 by providing a sheet-like adhesive sheet or adhesive. This allows the connection portion 15 of the polymer optical waveguide 10 and the substrate-side connection portion 21 to be fixed together. However, the method of fixing the polymer optical waveguide 10 and the optical circuit board 20 is not limited to the above. For example, by filling the guide groove 22 with a curable adhesive in advance, when the projection 17 is fitted into the guide groove 22, the guide groove 22 is filled with the curable adhesive, and then the adhesive in the guide groove 22 is cured by heat or light irradiation.

[0022] (Function and Effects) With the optical module configured as described above, the projection 17 of the polymer optical waveguide 10 can be engaged with a predetermined position in the guide groove 22 of the optical circuit board 20, thereby enabling smooth and highly accurate positioning of the polymer optical waveguide 10 to a predetermined coupling position. As a result, the core 11 of the polymer optical waveguide 10 and the silicon optical waveguide can be connected accurately with a simple configuration, and thus the loss of light propagation between the polymer optical waveguide and the silicon optical waveguide can be efficiently suppressed with a low-cost configuration.

[0023] Furthermore, since multiple protrusions 17 and guide grooves 22 are arranged in a row in the width direction, the polymer optical waveguide 10 positioned on the optical circuit board 20 is less likely to shift position. Therefore, the ease of assembly when attaching the polymer optical waveguide 10 to the optical circuit board 20 is further improved. In addition, the optical circuit board 20 to which the polymer optical waveguide 10 is coupled can be one that already has V-grooves formed as guide grooves 22 that can mount optical fibers, thus improving versatility.

[0024] The method of coupling the core 11 of the polymer optical waveguide 10 and the silicon optical waveguide on the optical circuit board 20 side can be by direct coupling, but is not limited to a predetermined coupling method. For example, a grid coupling may be used, or a configuration may be used in which a part of the core 11 of the polymer optical waveguide 10 and a part of the core of the silicon optical waveguide are exposed and brought into linear contact to perform evanescent coupling.

[0025] <Modification 1 of the First Embodiment> Next, modification 1 of the polymer optical waveguide 10 and optical circuit board 20 of the first embodiment will be described based on Figure 6. Figure 6 is an enlarged view of the main part showing modification 1 of the projection and guide groove of the first embodiment.

[0026] As shown in Figure 6, the projection 17A has an R-shape with a pair of smoothly curved corners 17Aa, 17Aa. The corners 17Aa may also be chamfered along the inclined surface 22a of the guide groove 22.

[0027] This configuration prevents the corners 17Aa of the projection 17A from chipping when the projection 17A is fitted into the guide groove 22. As a result, the installation of the polymer optical waveguide 10 onto the optical circuit board 20 becomes more stable. In addition, the contact area between the projection 17A and the guide groove 22 becomes larger, so the position of the projection 17A fitted into the guide groove 22 becomes more stable.

[0028] <Modification 2 of the First Embodiment> Next, modification 2 of the polymer optical waveguide 10 and optical circuit board 20 of the first embodiment will be described based on Figure 7. Figure 7 is an enlarged view of the main part showing modification 2 of the projection and guide groove of the first embodiment.

[0029] As shown in Figure 7, the projection 17B is formed so that its protruding surface 17Bb contacts the bottom 22b of the trapezoidal guide groove 22 by adjusting the height H and width W of the projection 17B. This configuration increases the contact area between the projection 17B and the guide groove 22. As a result, the projection 17B, which is fitted into the guide groove 22 at a predetermined position, becomes more stable, and misalignment becomes less likely.

[0030] It should be noted that the present invention is not limited to the embodiments described above. Combining the various components of the embodiments with each other, and modifying and applying them based on the description in the specification and well-known technology, are also intended to be done by those skilled in the art and are included within the scope of protection.

[0031] As described above, the following is disclosed in this specification: (1) A polymer optical waveguide having a core and a cladding disposed around the core and having a lower refractive index than the core, wherein the cladding is provided with projections that extend along the periphery of the core and engage with guide grooves formed in an optical circuit board, wherein a plurality of projections are arranged in the width direction of the cladding, and a single core is disposed in the width direction center of each projection. With this configuration, by engaging the projections formed on the cladding with guide grooves formed in the optical circuit board, the polymer optical waveguide can be positioned with high precision relative to the optical circuit board with a simple configuration and simple assembly work.

[0032] (2) The polymer optical waveguide according to (1), wherein the projection is made trapezoidal with a tapered angle. With this configuration, the projection is more easily guided smoothly into the guide groove, making it easier to position the polymer optical waveguide on the optical circuit board.

[0033] (3) The polymer optical waveguide according to (1) or (2), wherein the corners of the rectangular projections are curved. With this configuration, when the projections engage with the guide grooves, the contact area increases and the projections become less prone to chipping.

[0034] (4) A polymer optical waveguide according to any one of (1) to (3), wherein the distance between adjacent protrusions is greater than the mode field diameter. With this configuration, crosstalk can be prevented by the cores placed within adjacent protrusions.

[0035] (5) A polymer optical waveguide according to any one of (1) to (4), wherein the width of the projection in the width direction centered on the core is greater than the mode field diameter, and the thickness of the projection in the protruding direction is greater than half the mode field diameter. With this configuration, it is possible to prevent light propagating outside the cladding from leaking out and increasing the propagation loss of the core.

[0036] (6) A polymer optical waveguide as described in (4) or (5), wherein the mode field diameter is 1 μm or more. With this configuration, a polymer optical waveguide with stable light propagation performance can be obtained.

[0037] (7) A polymer optical waveguide according to any one of (1) to (6), wherein the height of the core is 0.5 μm or more and the width of the core is 1 μm or more. With this configuration, a polymer optical waveguide with stable light propagation performance can be obtained.

[0038] (8) A polymer optical waveguide according to any one of (1) to (7), wherein a connecting portion is formed between adjacent protrusions, which is bonded to a substrate-side connecting portion formed between adjacent guide grooves. With this configuration, the connection with the substrate is more stable.

[0039] (9) An optical module comprising the polymer optical waveguide described in any one of (1) to (8) and the optical circuit board, wherein the optical circuit board has an optical waveguide coupled to the polymer optical waveguide. With this configuration, an optical module that reduces propagation loss between the polymer optical waveguide and the optical circuit board can be easily and inexpensively obtained.

[0040] (10) The optical module described in (9), wherein the shape of the guide groove is a V-groove, which is a standard design for optical fiber mounting. This configuration improves versatility.

[0041] (11) The optical module according to (9), wherein a connecting portion formed between adjacent protrusions and a substrate-side connecting portion formed between adjacent guide grooves are bonded together with an adhesive. With this configuration, the polymer optical waveguide and the optical circuit board can be bonded together at the same time as the work of fitting the protrusions into the guide grooves for positioning.

[0042] (12) The optical module according to (9), wherein the protruding surface formed at the end of the projection is brought into close contact with the bottom of the guide groove. With this configuration, the contact area between the projection of the polymer optical waveguide and the guide groove of the optical circuit board is increased, so that the positioning of the polymer optical waveguide on the optical circuit board is more stable.

[0043] (13) The optical module according to (9), wherein the polymer optical waveguide and the optical waveguide are connected by evanescent coupling, facing coupling, or grating coupling. According to this configuration, since the polymer optical waveguide and the optical waveguide on the optical circuit board side can be connected by a coupling method according to the application, the versatility is improved.

[0044] As described above, various embodiments have been described with reference to the drawings. Needless to say, the present invention is not limited to such examples. It is obvious that those skilled in the art can conceive of various modification examples or correction examples within the scope described in the claims, and it is naturally understood that they also belong to the technical scope of the present invention. Also, within the scope not departing from the gist of the invention, the components in the above embodiments may be arbitrarily combined.

[0045] This application is based on a Japanese patent application (Japanese Patent Application No. 2024-166657) filed on September 25, 2024, the content of which is incorporated herein by reference.

[0046] 10 Polymer optical waveguide 11 Core 12 Underclad (clad) 13 Overclad (clad) 15 Coupling part 16 Coupling support part 17, 17A, 17B Protrusion part 17a, 17Aa Corner part 17b, 17Bb Protruding surface 18 Connection part 20 Optical circuit board 21 Board-side coupling part 22 Guide groove 22a Inclined surface 22b Bottom 23 Board-side connection part 30 Polymer optical waveguide 30A Polymer optical waveguide 35 Coupling part 36 Coupling support part 37, 37A Protrusion part 38 Edge part 40 Optical circuit board 41, 41A Board-side coupling part 42, 42A Guide groove 43 Edge part 44 Central protrusion part 100 Optical module

Claims

1. A polymer optical waveguide comprising a core and a cladding disposed around the core and having a lower refractive index than the core, wherein the cladding is provided with projections that extend along the periphery of the core and engage with guide grooves formed in an optical circuit substrate, and the projections are formed in a plurality of rows in the width direction of the cladding, with a single core positioned at the width center of each projection.

2. The polymer optical waveguide according to claim 1, wherein the projection is made trapezoidal with a tapered angle.

3. The polymer optical waveguide according to claim 1, wherein the corners of the rectangular projections are curved.

4. The polymer optical waveguide according to claim 1, wherein the distance between adjacent protrusions is greater than the mode field diameter.

5. The polymer optical waveguide according to claim 4, wherein the width of the projection in the width direction centered on the core is greater than the mode field diameter, and the thickness of the projection in the protruding direction is greater than half the mode field diameter.

6. The polymer optical waveguide according to claim 4, wherein the mode field diameter is 1 μm or more.

7. The polymer optical waveguide according to claim 1, wherein the height of the core is 0.5 μm or more, and the width of the core is 1 μm or more.

8. The polymer optical waveguide according to claim 1, wherein a connecting portion is formed between adjacent protrusions, which is bonded to a substrate-side connecting portion formed between adjacent guide grooves.

9. An optical module comprising the polymer optical waveguide according to any one of claims 1 to 8 and the optical circuit board, wherein the optical circuit board has an optical waveguide coupled to the polymer optical waveguide.

10. The optical module according to claim 9, wherein the shape of the guide groove is a V-groove, which is a standard design for optical fiber mounting.

11. The optical module according to claim 9, wherein a connecting portion formed between adjacent protrusions and a substrate-side connecting portion formed between adjacent guide grooves are bonded together with an adhesive.

12. The optical module according to claim 9, wherein the protruding surface formed at the end of the projection is brought into close contact with the bottom of the guide groove.

13. The optical module according to claim 9, wherein the polymer optical waveguide and the optical waveguide are connected by evanescent coupling, direct pairing, or lattice coupling.

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