Optical waveguide, manufacturing method of optical waveguide, and photoelectric combined substrate and active optical cable using the same

Abstract

To provide an optical waveguide capable of reducing inspection man-hour and improving production efficiency.SOLUTION: An optical waveguide 1 includes a core 2 and a clad 3 covering the core 2. The optical waveguide 1 includes a mirror part 4 configured to change a direction of an optical path propagating through the core 2. The mirror part 4 includes a recess 19 formed on one side of the optical waveguide 1. The recess 19 is substantially shaped in a truncated quadrangular pyramid shape narrower toward a bottom face 20. A first face 6 rising up from the bottom face 20 of the recess 19 has a cross section of the core 2 being a reflection plane 5 of the optical path. The first face 6 of the recess 19 and a second face 7 neighboring the first face 6 are connected via a first curved part 8 protruding to an outside.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical waveguide, a method for manufacturing the same, and an optoelectronic hybrid board and an active optical cable using the same. More specifically, the present invention relates to an optical waveguide and a method for manufacturing the same that reduce the number of inspection steps for the optical waveguide and achieve high production efficiency, and an optoelectronic hybrid board and an active optical cable using the same. [Background technology]

[0002] In recent years, with the increase in the amount of information transmitted in electronic devices, optoelectronic hybrid boards that use optical wiring in addition to electrical wiring have come into widespread use, and these optoelectronic hybrid boards use optical waveguides as the optical wiring.

[0003] An optical waveguide is made up of a linear core and a cladding provided to cover the core, and optically connects between optical elements (for example, a light-emitting element and a light-receiving element). More specifically, light emitted from a light-emitting element such as a semiconductor laser is reflected at the boundary between the core and the cladding, and is received by a light-receiving element such as a photodiode, and communication is performed based on the brightness pattern or intensity pattern of the received light.

[0004] As an example of such an optical waveguide, Patent Document 1 discloses an optical waveguide 30, as shown in FIG. 21, which has a core layer 32 in which a core portion 31 is formed, a first clad layer 33 laminated on one surface of the core layer 32, a second clad layer 34 laminated on the other surface of the core layer 32, and a mirror portion 35 that penetrates through the second clad layer 34 and the core layer 32 and reaches the first clad layer 33.

[0005] The mirror portion 35 of the optical waveguide 30 is provided with an inclined surface 37 having a reflective surface 36, and the light emitted from the light-emitting element is reflected by the reflective surface 36, thereby causing the light to enter the core portion 31.

[0006] Therefore, for example, if the reflecting surface 36 of the mirror portion 35 is not formed in the correct position relative to the light-emitting element, sufficient light cannot enter the core portion 31, which may result in a poor connection, and therefore the position of the reflecting surface of the mirror portion relative to the light-emitting element is extremely important in an optical waveguide.

[0007] Therefore, before mounting optical elements on optical waveguides, two types of inspections are generally performed: a mirror position inspection to accurately check whether the reflective surface of the mirror is formed in the correct position, and an optical loss inspection to check for core chipping or foreign matter in the core. However, the mirror position inspection is usually performed using an image measurement system that automatically measures the dimensions and shape of the reflective surface of the mirror from images obtained by a CCD camera, which requires the introduction of an expensive system and takes time for measurement, which reduces the production efficiency of optical waveguides. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-127783 Summary of the Invention [Problem to be solved by the invention]

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical waveguide that reduces the number of inspection steps and improves production efficiency. [Means for solving the problem]

[0010] In light of these circumstances, the inventors conducted extensive research and discovered that by changing the shape of the mirror portion of an optical waveguide so that a first surface having a reflective surface of the optical path is connected to a second surface adjacent to the first surface via a first curved portion that protrudes outward, optical loss increases when the reflective surface comes into contact with the first curved portion, and that misalignment of the reflective surface of the mirror portion can be detected solely by optical loss inspection, thereby completing the present invention.

[0011] That is, the present invention has the following aspects. [1] An optical waveguide having a core and a clad covering the core, the optical waveguide has a mirror portion that changes the direction of an optical path propagating through the core, the mirror portion is a recess formed on one surface of the optical waveguide, The recess has a shape of a substantially quadrangular pyramid that narrows toward the bottom, a first surface rising from the bottom surface of the recess has a cross section of the core that serves as a reflection surface of an optical path; An optical waveguide in which a first surface of the recess and a second surface adjacent to the first surface are connected via a first curved portion that protrudes outward. [2] The optical waveguide described in [1], wherein the first surface of the recess and the second surface adjacent to the first surface are connected via the first curved portion protruding in a direction along the longitudinal direction of the optical waveguide. [3] The optical waveguide according to [1] or [2], wherein a first surface of the recess and a third surface adjacent to the first surface and located on the opposite side of the second surface are connected via a second curved portion that protrudes outward. [4] The optical waveguide according to any one of [1] to [3], wherein a width d of the reflecting surface of the optical path is narrower than a width w of the first surface of the recess. [5] The optical waveguide according to [4], wherein a width d of the reflecting surface of the optical path and a width w of the first surface of the recess satisfy the following formula (1): 10(μm)≦(wd) / 2 (1) [6] The optical waveguide according to [5], wherein a width d of the reflecting surface of the optical path and a width w of the first surface of the recess satisfy the following formula (2): 10(μm)≦(wd) / 2≦50(μm) (2) [7] The first curved portion of the recess extends to the bottom surface, An optical waveguide according to any one of [1] to [6], wherein in a cross section obtained by cutting the recess horizontally at the height of the bottom side of the reflecting surface of the optical path, the radius of curvature of the inclined portion formed by the first surface of the recess and the first curved portion is set to 10 μm or more. [8] The first curved portion of the recess extends to the bottom surface, The optical waveguide according to any one of [1] to [7], wherein in a cross section obtained by cutting the recess horizontally at the height of the bottom side of the reflecting surface of the optical path, the radius of curvature of the inclined portion formed by the first surface of the recess and the first curved portion is 10 μm or more and 80 μm or less. [9] An optoelectronic hybrid board having the optical waveguide according to any one of [1] to [8].

[10] An active optical cable having the optical waveguide according to any one of [1] to [8].

[11] providing an optical waveguide having a core and a cladding provided so as to cover the core; placing a mask having an opening on one surface of the optical waveguide; and forming a recessed portion that becomes a mirror portion on one surface of the optical waveguide by irradiating a laser beam onto the opening of the mask. The method for manufacturing an optical waveguide, wherein the shape of the opening of the mask is a modified square with all four corners protruding outward. [Effects of the Invention]

[0012] That is, with the optical waveguide of the present invention, the deviation of the reflecting surface of the mirror portion can be efficiently detected by only optical loss inspection, so that inspection of the mirror position is not necessary, and production efficiency can be improved. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view showing a main part of an optical waveguide according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along the line AA' in FIG. [Figure 3]FIG. 3 is a plan view of the optical waveguide of FIG. [Figure 4] FIG. 4 is a cross-sectional view of the first surface of the recess according to the first embodiment as viewed from the front. [Figure 5] FIG. 5 is a diagram showing a cross section obtained by cutting the recess in the horizontal direction at the height of the bottom side of the reflecting surface of the optical path of the optical waveguide according to the first embodiment. [Figure 6] FIG. 6 is a schematic diagram showing a method for forming a mirror portion of an optical waveguide according to one embodiment of the present invention by laser processing. [Figure 7] FIG. 7 is a diagram showing the process of forming a recess in the mirror portion by the laser field locus, as viewed from above the optical waveguide. [Figure 8] FIG. 8 is a plan view of a mask for forming a mirror portion according to the first embodiment. [Figure 9] FIG. 9 is a perspective view showing a main part of an optical waveguide according to the second embodiment of the present invention. [Figure 10] FIG. 10 is a plan view of the optical waveguide of FIG. [Figure 11] FIG. 11 is a perspective view showing a main part of an optical waveguide according to a third embodiment of the present invention. [Figure 12] FIG. 12 is a plan view of the optical waveguide of FIG. [Figure 13] FIG. 13 is a perspective view showing a main part of an optical waveguide according to a fourth embodiment of the present invention. [Figure 14] FIG. 14 is a plan view of the optical waveguide of FIG. [Figure 15] FIG. 15 is a diagram showing a cross section of the optical waveguide according to the first embodiment, obtained by cutting the recess in the horizontal direction at the height of the bottom side of the reflecting surface of the optical path. [Figure 16] FIG. 16 is a diagram showing a cross section of the optical waveguide according to the second embodiment, obtained by cutting the recess in the horizontal direction at the height of the bottom side of the reflecting surface of the optical path. [Figure 17] FIG. 17 is a diagram showing a cross section of the optical waveguide according to the third embodiment, obtained by cutting the recess in the horizontal direction at the height of the bottom side of the reflecting surface of the optical path. [Figure 18]FIG. 18 is a diagram showing a cross section of the optical waveguide according to the fourth embodiment, obtained by cutting the recess in the horizontal direction at the height of the bottom side of the reflecting surface of the optical path. [Figure 19] FIG. 19 is a diagram showing a cross section of the optical waveguide according to the reference example, taken by cutting the recess in the horizontal direction at the height of the bottom side of the reflecting surface of the optical path. [Figure 20] FIG. 20 is a diagram showing a cross section of the optical waveguide according to Comparative Example 1, obtained by cutting the recess in the horizontal direction at the height of the bottom side of the reflecting surface of the optical path. [Figure 21] FIG. 21 is an explanatory diagram showing another example of a conventional optical waveguide. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described below based on examples of embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below.

[0015] In this specification, when it is expressed as "P or more" (P is any number) or "Q or less" (Q is any number), it also means that "it is preferable that it is greater than P" or "it is preferable that it is less than Q."

[0016] In this specification, optical loss testing refers to testing the amount of optical loss by connecting a light source and a detector to the input and output ends of an optical waveguide, respectively, and calculating the difference in intensity between the input and output light. The light source can be, for example, a semiconductor device that emits light of a specific wavelength, such as a light-emitting diode. The detector can be, for example, a CCD detector that converts light into an electric charge and detects it.

[0017] First Embodiment FIG. 1 is a perspective view showing a main part of an optical waveguide 1 according to a first embodiment of the present invention. The optical waveguide 1 has a core 2 and a cladding 3 that covers the core 2. The optical waveguide 1 has a mirror portion 4 that changes the direction of the optical path propagating through the core 2. The mirror portion 4 consists of a recess 19 formed on one side of the optical waveguide 1. The shape of the recess 19 is an approximately quadrangular pyramid shape that narrows toward the bottom surface 20. A first surface 6 rising from the bottom surface 20 of the recess 19 has a cross section of the core 2 that becomes the reflection surface 5 of the optical path. The first surface 6 and a second surface 7 adjacent to the first surface 6 of the recess 19 are connected via a first curved portion 8 that protrudes outward. In FIG. 1, for the sake of convenience, the main part of the optical waveguide 1 is shown as a rectangular prism, and the core 2 and part of the mirror portion 4 are shown by dashed lines. These configurations are described in detail below.

[0018] <Optical waveguide> The optical waveguide 1 is composed of a core 2 and a cladding 3 that covers the core 2, and the optical waveguide 1 is formed in a strip shape. The thickness q of the optical waveguide 1 (see FIG. 2) is not particularly limited, but is usually 10 μm to 200 μm, preferably 60 μm to 150 μm, more preferably 80 μm to 120 μm, and even more preferably 90 μm to 110 μm. If the thickness q of the optical waveguide 1 is too small, the durability of the optical waveguide 1 tends to be poor, and if it is too large, it tends to be difficult to make the optical waveguide 1 thinner and lighter. The thickness q of the optical waveguide 1 refers to the overall thickness including the core 2 and cladding 3.

[0019] The core 2 of the optical waveguide 1 propagates incident light, which is reflected at the boundary between the core 2 and the cladding 3 . The thickness e of the core 2 (see FIG. 2) is not particularly limited, but is preferably 60 μm or more and 150 μm or less, more preferably 80 μm or more and 120 μm or less, and even more preferably 85 μm or more and 100 μm or less. Furthermore, the width d of the core 2 (hereinafter, the width d of the core 2 is synonymous with the width of the core cross section and the width of the reflecting surface 5) (see Figure 4) is not particularly limited, but is preferably 30 μm or more and 100 μm or less, more preferably 40 μm or more and 80 μm or less, and even more preferably 45 μm or more and 60 μm or less. If the thickness e and width d of the core 2 are too small, the durability of the core 2 tends to be poor, and if they are too large, it tends to be difficult to make the core thinner and lighter.

[0020] Examples of materials for forming the core 2 and clad 3 of the optical waveguide 1 include epoxy resins (e.g., glycidyl ether epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, alicyclic epoxy resins, etc.), polyimide resins, acrylic resins, etc., and among these, epoxy resins are preferred in terms of transparency, heat resistance, and fine patterning properties. These may be used alone or in combination of two or more. The refractive index of the core 2 is usually greater than the refractive index of the cladding 3 .

[0021] The core 2 and clad 3 of the optical waveguide 1 are both preferably formed from a resin having a linear expansion coefficient of 30 ppm / °C to 120 ppm / °C, more preferably from 30 ppm / °C to 90 ppm / °C, and even more preferably from 30 ppm / °C to 70 ppm / °C. When the linear expansion coefficients of the core 2 and clad 3 of the optical waveguide 1 are within the above ranges, warping of the optical waveguide 1 tends to be more effectively suppressed. The linear expansion coefficients of the core 2 and the normal clad 3 may be different from each other or may be the same.

[0022] The optical waveguide 1 has a mirror section 4 that changes the direction of the path of light propagating through the core 2. As shown in Fig. 2, the mirror section 4 is made of a recess 19 formed on one surface of the optical waveguide 1. When the one surface of the optical waveguide 1 is the upper surface, the shape of the recess 19 is a substantially quadrangular truncated pyramid that narrows toward a bottom surface 20 of the optical waveguide 1. In Fig. 2, a first curved section 8 and a fourth curved section 13, which will be described later, are shown by dashed lines.

[0023] The height h of the recess 19 depends on the thickness q of the optical waveguide 1 and the thickness e of the core 2, but is preferably 50 μm or more and 260 μm or less, more preferably 60 μm or more and 220 μm or less, and even more preferably 70 μm or more and 180 μm or less.

[0024] The longitudinal size s of the upper surface of the recess 19 is preferably 150 μm or more and 650 μm or less, more preferably 180 μm or more and 550 μm or less, and even more preferably 200 μm or more and 450 μm or less.

[0025] The longitudinal size t of the bottom surface 20 of the recess 19 is preferably 30 μm or more and 390 μm or less, more preferably 40 μm or more and 330 μm or less, and even more preferably 50 μm or more and 270 μm or less.

[0026] As described above, when the height h of the recess 19, the longitudinal size s of the upper surface, and the longitudinal size t of the bottom surface 20 are set within the above ranges, the angles of the inclined surfaces of the first surface 6 and the fourth surface 11, which will be described later, can be adjusted.

[0027] The width u of the recess 19 (see FIG. 3) is preferably 150 μm or more and 500 μm or less, more preferably 200 μm or more and 400 μm or less, and even more preferably 225 μm or more and 300 μm or less, although it depends on the width d (see FIG. 4) of the core 2. When the width u of the recess 19 is set within the above range, the positional deviation of the reflecting surface 5 can be efficiently detected by optical loss inspection.

[0028] The recess 19 of the mirror portion 4 has a first surface 6 that rises from the bottom surface 20 and has a cross section of the core 2 that serves as a reflecting surface 5 of the optical path, and a second surface 7 that is adjacent to the first surface 6.

[0029] In addition, the recess 19 of the mirror portion 4 has a third surface 9 (see Figure 3) adjacent to the first surface 6 and located on the opposite side of the second surface 7, and a fourth surface 11 located on the opposite side of the first surface 6.

[0030] The first surface 6 is usually formed so as to be inclined at 45° in the longitudinal direction relative to the bottom surface 20. By inclining this first surface 6 relative to the bottom surface 20, the reflective surface 5, which is the cross section of the core 2 on the first surface 6, plays the role of changing the direction of light propagated within the core 2 by 90° and making it incident on the light receiving section of the optical element, or conversely, changing the direction of light emitted from the light emitting section of the optical element by 90° and making it incident into the core 2.

[0031] The second surface 7 rises perpendicularly to the bottom surface 20, as shown in the plan view of the optical waveguide 1 in FIG. In FIG. 3, part of the core 2 is indicated by a dashed line.

[0032] The second surface 7 and a fourth surface 11 adjacent to the first surface 6 on the opposite side thereof are symmetrical to the first surface 6 .

[0033] Moreover, the first surface 6, the fourth surface 11, and the third surface 9 adjacent to and opposite the second surface 7 are in a symmetrical relationship with the second surface 7.

[0034] Furthermore, the second surface 7 and the third surface 9 may be provided with a protrusion 38 . The protrusions 38 are formed in the manufacturing process described below, and therefore, the protrusions 38 can be removed by scraping or the like.

[0035] The shape of the recess 19 is not limited to an approximately quadrangular pyramid shape consisting of the first surface 6, the second surface 7, the third surface 9, and the fourth surface 11, but includes, for example, a shape in which the second surface 7 and the third surface 9 are inclined with respect to the bottom surface 20, or a shape in which the fourth surface 11 rises perpendicularly to the bottom surface 20.

[0036] The first surface 6 and the second surface 7 adjacent to the first surface 6 are connected via a first curved portion 8 that protrudes outward. This is the greatest feature of the present invention. According to this configuration, if the reflecting surface 5 is shifted, for example, to the position of the reflecting surface 5', the reflecting surface 5' will be caught by the first curved portion 8, and when an optical loss test is performed, the optical loss will increase, making it possible to detect the positional shift of the reflecting surface 5.

[0037] That is, when the reflecting surface 5 is shifted to the position of the reflecting surface 5' and overlaps the first curved portion 8, not all of the light from the light source input to the optical waveguide 1 from the light-emitting side can reach the light-receiving side, and the amount of charge that can be converted on the light-receiving side decreases. By checking whether or not this decrease in the amount of charge exists, the positional shift of the reflecting surface 5 can be detected by optical loss inspection.

[0038] 4, the first curved portion 8 normally extends from the upper surface of the recess 19 of the mirror section 4 to the bottom surface 20, but does not necessarily have to extend to the bottom surface 20 because the reflective surface 5 overlaps the first curved portion 8, which allows misalignment of the reflective surface 5 to be detected by optical loss testing. In other words, the first curved portion 8 should preferably be located in the range from the upper surface of the recess 19 of the mirror section 4 to the bottom edge 5(b) of the reflective surface, and more preferably should be located in the range from the top edge 5(a) of the reflective surface to the bottom edge 5(b) of the reflective surface.

[0039] The shape of the first curved portion 8 will be described below using a cross section obtained by cutting the recess 19 horizontally at a height 5(c) up to the bottom side of the reflecting surface of the optical path.

[0040] As shown in FIG. 5, the first curved portion 8 protrudes in a direction along the longitudinal direction of the optical waveguide 1, and is connected to the first surface 6 and the second surface .

[0041] Furthermore, when the first curved portion 8 is connected to the second surface 7, it may be connected via a rounded edge portion 39. The edge portion 39 is formed in a manufacturing process to be described later, and therefore, the edge portion 39 can be removed by a grinding operation or the like.

[0042] In the cut surface, the first curved portion 8 is gently curved to connect to the first surface 6 and the second surface 7, but the first curved portion 8 may be bent sharply. However, in terms of achieving a good balance between the efficiency of manufacturing the optical waveguide 1 and the accuracy of the optical loss inspection, it is preferable that the first curved portion 8 be gently curved.

[0043] When the first curved portion 8 is gently curved, the lower limit of the radius of curvature r of the inclined portion 21 formed by the first surface 6 of the recess 19 and the first curved portion 8 is preferably typically 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. The upper limit of the radius of curvature r of the inclined portion 21 is, for example, preferably 80 μm or less, more preferably 70 μm or less, and even more preferably 65 μm or less. That is, the radius of curvature r of the inclined portion 21 formed by the first surface 6 of the recess 19 and the first curved portion 8 is preferably 10 μm or more and 80 μm or less. When the radius of curvature r is within the above range, it is possible to efficiently detect the positional deviation of the reflecting surface 5 by optical loss inspection. Here, the radius of curvature r of the inclined portion 21 means the radius of curvature r of the inclined portion 21 when viewed from a cross section obtained by cutting the recess 19 horizontally at the height up to the bottom side of the reflecting surface 5 (see FIG. 5, etc.).

[0044] In particular, when the first surface 6 and the third surface 9 adjacent to the first surface 6 and located on the opposite side of the second surface 7 are connected via a second curved portion 10 similar to the first curved portion 8, even if the position of the reflective surface 5 is shifted to the left or right in the width direction, this can be detected efficiently by optical loss inspection.

[0045] Furthermore, if the second surface 7 and the third surface 9 are connected to the fourth surface 11 adjacent to the first surface 6 on the opposite side thereof via the third curved portion 12 and the fourth curved portion 13, similar to the first curved portion 8, and if the fourth surface 11 has a reflective surface 5, then the positional deviation of the reflective surface 5 can also be detected efficiently on the fourth surface 11 by optical loss inspection.

[0046] It is preferable that the second curved portion 10, the third curved portion 12 and the fourth curved portion 13 have the same curvature radius r as the first curved portion 8, but they may be different from each other.

[0047] The radius of curvature r is usually determined after setting the width u (see FIG. 3) of the recess 19 of the mirror section 4. Therefore, if the radius of curvature r is too large, as shown in FIG. 4, the width w of the first surface 6 will be small, the area where the reflecting surface 5 can be arranged will be reduced, and the degree of freedom in designing the optical waveguide 1 will tend to be reduced.

[0048] That is, it is preferable that the width w of the first surface 6 is wider than the width d of the reflecting surface 5, in other words, the width d of the reflecting surface 5 is narrower than the width w of the first surface 6. In particular, if the relationship between the width w of the first surface 6 and the width d of the reflecting surface 5 satisfies the following formula (1), the positional deviation of the reflecting surface 5 can be detected more efficiently. In other words, the value of (wd) / 2 is 10 (μm) or more. 10(μm)≦(wd) / 2 (1) The value of (wd) / 2 may be 15 μm or more, or 20 μm or more. The value of (wd) / 2 may be 50 μm or less, or 45 μm or less. When the value of (wd) / 2 satisfies the above-mentioned condition, the positional deviation of the reflecting surface 5 can be detected more efficiently. For example, the relationship between the width w of the first surface 6 and the width d of the reflecting surface 5 satisfies the following formula (2). 10(μm)≦(wd) / 2≦50(μm)···(2)

[0049] The width w of the flat surface of the first surface 6 is preferably 70 μm or more and 140 μm or less, more preferably 80 μm or more and 120 μm or less, and even more preferably 85 μm or more and 100 μm or less. When the width w is set within the above range, the positional deviation of the reflecting surface 5 can be detected with higher accuracy.

[0050] <Method for manufacturing optical waveguide> Next, a method for manufacturing the optical waveguide 1 according to an embodiment of the present invention will be described. The optical waveguide 1 of this embodiment can be manufactured by the steps of preparing an optical waveguide 1 having a core 2 and a cladding 3 arranged to cover the core 2, and forming a recess 19 that will become the mirror portion 4 on one surface of the optical waveguide 1.

[0051] Methods for forming the recess 19 that will become the mirror portion 4 on one surface of the optical waveguide 1 include, for example, mechanical processing methods such as cutting and grinding, laser processing, electron beam processing, and imprinting. Among these, forming the mirror portion 4 by laser processing is preferred from the viewpoint of being able to form a mirror portion 4 with high dimensional accuracy. Hereinafter, a method for forming the mirror portion 4 by laser processing will be described.

[0052] 6 is a schematic diagram showing a method for forming recesses 19 that will become mirror portions 4 of optical waveguide 1 according to this embodiment by laser processing. When forming recesses 19 of mirror portion 4 by laser processing, for example, optical waveguide 1 is placed on a drive stage (not shown), and a mask 14 having a specially shaped opening 15, as will be described later, is placed on one surface of this optical waveguide 1, and a laser is irradiated onto openings 15 of mask 14 in the direction of white arrow 16. Then, by moving the drive stage in the direction indicated by the black arrow in the optical waveguide 1 for each laser irradiation, a recess 19 (see Figure 1) in the mirror section 4 can be formed as the area trajectory of the laser irradiation.

[0053] 7 shows the process of forming recesses 19 in the mirror section 4 by the area locus of the laser irradiation, as viewed from above the optical waveguide 1. That is, when the optical waveguide 1 placed on the drive stage moves in the direction indicated by the black arrow, the openings 15 in the mask move relatively in the opposite direction to the black arrow. At this time, differences in the number of times (time) exposed to the laser light result in differences in depth, and a recess 19 in the mirror part 4 having a predetermined inclined surface (first surface 6) and a reflective surface 5 on the first surface 6 are formed.

[0054] In the laser irradiation step, the optical waveguide 1 is moved relative to the fixed mask 14. However, the mask 14 may be moved while the optical waveguide 1 is fixed, or both may be moved. However, from the viewpoint of dimensional accuracy, it is preferable to move either one of them, and in particular, it is preferable to move the optical waveguide 1, since it is not necessary to move the laser irradiation device.

[0055] The light source of the laser is appropriately selected depending on the wavelength of the laser to be emitted, and examples thereof include various solid-state lasers such as a YAG laser, a YVO laser, a Yb laser, and a semiconductor laser, and various lasers such as a CO laser, a He—Ne laser, and an excimer laser.

[0056] The wavelength of the laser is appropriately selected depending on the material of the optical waveguide 1, but is preferably 150 nm or more and 950 nm or less, more preferably 200 nm or more and 850 nm or less, and even more preferably 300 nm or more and 750 nm or less.

[0057] As shown in Figure 8, the mask 14 is a plate-like body having an opening 15 that allows the laser to pass through and a shielding portion 17 that blocks the laser, and the shape of the opening 15 of the mask is a modified square with all four corners protruding outward.

[0058] The length v of one side of the square of the opening 15 in the mask 14, excluding the protruding portions at the four corners, is preferably 0.5 μm or more and 2.0 μm or less, more preferably 0.6 μm or more and 1.5 μm or less, and even more preferably 0.7 μm or more and 1.0 μm or less, although this depends on the sizes of the optical waveguide 1 and the core 2. When the length v of one side of the square of the opening 15 is set within the above range, the recess 19 of the mirror section 4 can be formed to the specified dimensions.

[0059] Furthermore, the shape of the four protruding protrusions 18 at the four corners of the opening 15 is preferably a circle with a circle superimposed on the corner of the square, and the center x of the approximately circular circle is preferably located at the corner of the square. The radius y of the circle is appropriately selected depending on the radius of curvature r, but is preferably 0.03 mm to 0.45 mm, more preferably 0.04 mm to 0.3 mm, and even more preferably 0.05 mm to 0.3 mm. When the radius y of the circle is set within the above range, the positional deviation of the reflecting surface 5 can be detected more efficiently.

[0060] In this embodiment, the shape of the opening 15 in the mask 14 is a modified square with all four corners protruding outward, but this square does not necessarily have straight sides, and may have curved sides as long as this does not violate the spirit of the present invention. Also, for the same purpose, the lengths of the sides of the square do not need to be strictly the same. Furthermore, the shape of the protrusion 18 of the opening 15 is not limited to the above-described substantially circular shape in which circles are superimposed on the four corners of the square, but may be, for example, an ellipse or another shape in which the four corners of the square are superimposed. However, a substantially circular shape in which circles are superimposed on the four corners of the square is preferable in that it allows the dimensions of the first curved portion 8 of the recess 19 of the mirror section 4 to be formed with high precision.

[0061] <Optical communication module> The optical waveguide 1 of this embodiment can be used for optical wiring of an optoelectronic hybrid board. An optical communication cable (for example, an active optical cable) can be obtained by connecting various cables to an optoelectronic hybrid board using the optical waveguide 1 of this embodiment. Therefore, the production efficiency of the optoelectronic hybrid board using the optical waveguide 1 and the optical communication cable using the optoelectronic hybrid board is improved.

[0062] <Second embodiment> FIG. 9 is a perspective view showing a main part of an optical waveguide 40 according to the second embodiment of the present invention, and FIG. 10 is a plan view of the optical waveguide 40 according to the second embodiment. The optical waveguide 40 according to the second embodiment differs in that the second surface 7 and the third surface 9 do not have the convex portions 38 that are provided on the second surface 7 and the third surface 9 of the optical waveguide 1 of the first embodiment shown in Fig. 3, i.e., they are changed to flat surfaces. The rest of the configuration is the same as that of the optical waveguide 1 of the first embodiment shown in Fig. 1, and the same parts are designated by the same numbers and the numbers will be omitted.

[0063] As a method for manufacturing the optical waveguide 40, for example, the convex portions 38 (see FIG. 3) provided on the second surface 7 and the third surface 9 of the optical waveguide 1 according to the first embodiment can be removed by a grinding operation or the like, thereby producing an optical waveguide 40 that does not have the convex portions 38.

[0064] Even with the configuration of the optical waveguide 40 according to the second embodiment, if the position of the reflecting surface 5 is shifted, the positional shift of the reflecting surface 5 can be detected by optical loss inspection.

[0065] <Third embodiment> FIG. 11 is a perspective view showing a main part of an optical waveguide 41 according to the third embodiment of the present invention, and FIG. 12 is a plan view of the optical waveguide 41 according to the third embodiment. The optical waveguide 41 according to the third embodiment differs from the optical waveguide 1 of the first embodiment shown in Fig. 3 in that the connecting portion between the first curved portion 8 and the second surface 7, the connecting portion between the second curved portion 10 and the third surface 9, the connecting portion between the third curved portion 12 and the third surface 9, and the connecting portion between the fourth curved portion 13 and the second surface 7 do not have the rounded edge portion 39 that is provided in the connecting portion between the first curved portion 8 and the second surface 7, the connecting portion between the second curved portion 10 and the third surface 9, the connecting portion between the third curved portion 12 and the third surface 9, and the connecting portion between the fourth curved portion 13 and the second surface 7. The rest of the configuration is the same as that of the optical waveguide 1 of the first embodiment shown in Fig. 1, and the same parts are designated by the same numbers and the reference numerals therefor will be omitted.

[0066] As a method for manufacturing the optical waveguide 41, for example, the curved edge portions 39 (see FIG. 3) provided in the connecting portion between the first curved portion 8 and the second surface 7 of the optical waveguide 1 according to the first embodiment, the connecting portion between the second curved portion 10 and the third surface 9, the connecting portion between the third curved portion 12 and the third surface 9, and the connecting portion between the fourth curved portion 13 and the second surface 7 can be removed by a grinding operation or the like, thereby producing an optical waveguide 41 that does not have the edge portions 39.

[0067] Even with the configuration of the optical waveguide 41 of this third embodiment, if the position of the reflecting surface 5 is shifted, the positional shift of the reflecting surface 5 can be detected by optical loss inspection. Furthermore, by not forming the edge portion 39 (see Figure 3), the shape of the opening of the mirror portion 4 approaches a rectangular shape as shown in Figure 12, which increases the rigidity of the optical waveguide 41 and tends to result in excellent mechanical strength.

[0068] <Fourth embodiment> FIG. 13 is a perspective view showing a main part of an optical waveguide 42 according to the fourth embodiment of the present invention, and FIG. 14 is a plan view of the optical waveguide 42 according to the fourth embodiment. This optical waveguide 42 differs from the optical waveguide 1 of the first embodiment shown in FIG. 3 in that the second surface 7 and the third surface 9 do not have the convex portions 38 that are present on the second surface 7 and the third surface 9 of the optical waveguide 1 of the first embodiment shown in FIG. 3, and in that the connecting portion between the first curved portion 8 and the second surface 7, the connecting portion between the second curved portion 10 and the third surface 9, the connecting portion between the third curved portion 12 and the third surface 9, and the connecting portion between the fourth curved portion 13 and the second surface 7 of the optical waveguide 42 do not have the rounded edge portions 39 that are present on the connecting portion between the first curved portion 8 and the second surface 7, the connecting portion between the second curved portion 10 and the third surface 9, the connecting portion between the third curved portion 12 and the third surface 9, and the connecting portion between the fourth curved portion 13 and the second surface 7 of the optical waveguide 1 of the first embodiment shown in FIG. The other configurations are the same as those of the optical waveguide 1 of the first embodiment shown in FIG. 1, and the same parts are assigned the same numbers and the numbers are omitted.

[0069] As a method for manufacturing the optical waveguide 42, for example, the convex portions 38 (see FIG. 3) provided on the second surface 7 and the third surface 9 of the optical waveguide 1 according to the first embodiment, and the rounded edge portions 39 (see FIG. 3) provided on the connecting portion between the first curved portion 8 and the second surface 7 of the first embodiment, the connecting portion between the second curved portion 10 and the third surface 9, the connecting portion between the third curved portion 12 and the third surface 9, and the connecting portion between the fourth curved portion 13 and the second surface 7 of the optical waveguide 1 according to the first embodiment can be removed by a grinding operation or the like, thereby making it possible to manufacture an optical waveguide 42 that does not have the convex portions 38 (see FIG. 3) and the edge portions 39 (see FIG. 3).

[0070] Even with the configuration of the optical waveguide 42 according to the fourth embodiment, if the position of the reflecting surface 5 is shifted, the positional shift of the reflecting surface 5 can be detected by optical loss inspection. [Example]

[0071] Next, specific examples of the present invention will be described.

[0072] [Example 1] First, an optical waveguide was prepared, which had a core (thickness e: 100 μm, core width (width of the reflecting surface) d: 45 μm) and a cladding covering this core. Then, as a mask to be used during laser irradiation to form the mirror portion of the optical waveguide, a mask was prepared in which the shape of the opening was a modified square with all four corners protruding outward, the length v of one side of the square was 0.75 mm, and the radius y of the circle was 0.05 mm. Next, the prepared optical waveguide was placed on a drive stage, a mask with a specially shaped opening was placed on one side of the optical waveguide, and laser irradiation (wavelength 248 nm) was performed using a YAG laser. Then, for each laser irradiation, the optical waveguide was moved to form a recess that would become a mirror portion so that the longitudinal size s of the top surface of the recess, the longitudinal size t of the bottom surface, and the height h of the recess were approximately 230 μm, approximately 60 μm, and approximately 80 μm, respectively, thereby producing the optical waveguide of Example 1. The shape of the mirror portion (recess) of the optical waveguide of Example 1 is shown in FIG. Note that Figures 15 to 20 are schematic views of a cross section cut horizontally at the height of the base of the reflecting surface of the optical path, and the size and shape of each part are appropriately exaggerated to make it easier to understand.

[0073] [Examples 2 to 4, Reference Example] The optical waveguides of Examples 2 to 4 and the Reference Example were fabricated in the same manner as Example 1, except that the shape of the opening in the mask was changed as follows: That is, in Examples 2 to 4 and the Reference Example, the shape of the opening was a modified square with all four corners of the square protruding outward, and the radius y of the circle of the protruding parts at the four corners of the square was changed as shown in Table 1 below. The shapes of the mirror portions (recesses) of the optical waveguides of Examples 2 to 4 and Reference Example are shown in FIGS.

[0074] [Comparative Example 1] An optical waveguide for Comparative Example 1 was fabricated in the same manner as in Example 1, except that the shape of the opening of the mask was changed to a square with one side measuring 0.75 μm (that is, a conventional mask with no protrusions at the opening). The shape of the mirror portion (recess) of the optical waveguide of Comparative Example 1 is shown in FIG.

[0075] The width w of the flat surface of the first surface and the radius of curvature r of the inclined portion of the cut surface obtained by cutting the optical waveguides of Examples 1 to 4, Reference Example, and Comparative Example 1 horizontally at the height of the bottom side of the reflecting surface with respect to the mirror portion (recess) were measured using a digital microscope (VHX-7000, manufactured by Keyence Corporation). The obtained values are shown in Table 1 below. These values were then substituted into the following formula (1) to calculate the detectable range of positional deviation of the reflecting surface. The calculated values are also shown in Table 1 below. 10(μm)≦(wd) / 2 (1)

[0076] (Evaluation of positional deviation of reflecting surface) A large number of optical waveguides were fabricated for each of Examples 1 to 4, Reference Example, and Comparative Example 1, and these were subjected to mass-produced high-speed continuity testing (optical loss testing) of polymer optical wiring waveguides using an optical tester with an optical wiring waveguide high-speed continuity testing device (manufactured by Synergy Opto Systems Co., Ltd.), and the positional deviation of the reflecting surface was evaluated by measuring the loss with the optical tester. Note that the optical waveguides fabricated in large numbers for Examples 1 to 4, Reference Example, and Comparative Example 1 include those in which the reflecting surface of the mirror portion is misaligned. Whether the reflective surface of the mirror was in the correct position was confirmed by the brightness of the light displayed on the measurement screen of the optical tester. An optical waveguide with a misaligned reflective surface of the mirror was displayed more than 30% darker than an optical waveguide with the reflective surface of the mirror in the correct position. If there is anything dark displayed on the optical tester measurement screen, it means that the positional deviation of the reflective surface of the mirror part can be identified in the optical loss test, and is marked with a circle (O).If there is nothing dark displayed on the optical tester measurement screen, it means that the positional deviation of the reflective surface of the mirror part cannot be identified in the optical loss test, and is marked with an × (X).The results are shown in Table 1 below.

[0077] [Table 1]

[0078] As shown in Table 1 above, in Examples 1 to 4, the presence or absence of positional deviation of the reflective surface could be evaluated simply by performing an optical loss test, whereas in Comparative Example 1, which is a conventional product, the presence or absence of positional deviation of the reflective surface could not be evaluated simply by performing an optical loss test. In the reference example, the width of the core (width of the reflecting surface) d was larger than the width w of the flat surface of the first surface, so it was not possible to evaluate whether or not a positional shift of the reflecting surface had occurred. However, by making the width of the core (width of the reflecting surface) d smaller than the width w of the flat surface of the first surface, it becomes possible to evaluate whether or not a positional shift of the reflecting surface has occurred. [Industrial Applicability]

[0079] The optical waveguide of the present invention can be widely used in high-speed signal transmission technology. [Explanation of symbols]

[0080] 1 Optical waveguide (first embodiment) 2 cores 3. Clad 4 Mirror section 5 Reflective surface 5' Misaligned reflecting surface 5(a) Upper edge of the reflecting surface 5(b) Base of the reflecting surface 5(c) Height to the bottom of the reflecting surface 6 First Side 7 Second Side 8 First curved section 9 The Third Side 10 Second curved portion 11 The Fourth Side 12 Third bend 13 Fourth Curve 14 Mask 15 Opening 17 Shielding part 18 Mask protrusions 19 Recess 20 bottom 21 Slope 30 Optical waveguide 31 Core 32 Core layer 33 First cladding layer 34 Second cladding layer 35 Mirror section 36 Reflective surface 37 Slope 38 Convex part 39 Edge 40 Optical waveguide (second embodiment) 41 Optical waveguide (third embodiment) 42 Optical waveguide (fourth embodiment) d Core width (width of the reflecting surface) e Core thickness h Recess height q Thickness of the optical waveguide r Radius of curvature of the slope s The longitudinal size of the top surface of the recess t: The longitudinal size of the bottom surface of the recess u Recess width v Length of one side of the mask opening w Width of the first face x Center of protrusion y Mask opening radius

Claims

1. An optical waveguide having a core and a clad covering the core, the optical waveguide has a mirror portion that changes the direction of an optical path propagating through the core, the mirror portion is a recess formed on one surface of the optical waveguide, The recess has a shape of a substantially quadrangular pyramid that narrows toward the bottom, a first surface rising from the bottom surface of the recess has a cross section of the core that serves as a reflection surface of an optical path; An optical waveguide in which a first surface of the recess and a second surface adjacent to the first surface are connected via a first curved portion that protrudes outward.

2. 2. The optical waveguide according to claim 1, wherein a first surface of the recess and the second surface adjacent to the first surface are connected via the first curved portion protruding in a direction along the longitudinal direction of the optical waveguide.

3. 2. The optical waveguide according to claim 1, wherein a first surface of the recess and a third surface adjacent to the first surface and located opposite the second surface are connected via a second curved portion protruding outward.

4. 3. The optical waveguide according to claim 2, wherein a width d of the reflecting surface of said optical path is narrower than a width w of the first surface of said recess.

5. 5. The optical waveguide according to claim 4, wherein a width d of the reflecting surface of the optical path and a width w of the first surface of the recess satisfy the following formula (1): 10 (μm)≦(w-d) / 2...(1)

6. 6. The optical waveguide according to claim 5, wherein a width d of the reflecting surface of the optical path and a width w of the first surface of the recess satisfy the following formula (2): 10 (μm)≦(w-d) / 2≦50 (μm)...(2)

7. the first curved portion of the recess extends to the bottom surface; 2. The optical waveguide according to claim 1, wherein in a cross section obtained by cutting the recess horizontally at the height of the bottom side of the reflecting surface of the optical path, the radius of curvature of the inclined portion formed by the first surface of the recess and the first curved portion is set to 10 μm or more.

8. the first curved portion of the recess extends to the bottom surface; 8. The optical waveguide according to claim 7, wherein in a cross section obtained by cutting the recess horizontally at the height of the bottom side of the reflecting surface of the optical path, the radius of curvature of the inclined portion formed by the first surface of the recess and the first curved portion is 10 μm or more and 80 μm or less.

9. An optoelectronic hybrid substrate having the optical waveguide according to any one of claims 1 to 8.

10. An active optical cable comprising the optical waveguide according to any one of claims 1 to 8.

11. providing an optical waveguide having a core and a cladding provided so as to cover the core; placing a mask having an opening on one surface of the optical waveguide; and forming a recessed portion that becomes a mirror portion on one surface of the optical waveguide by irradiating a laser beam onto the opening of the mask. The method for manufacturing an optical waveguide, wherein the shape of the opening of the mask is a modified square with all four corners protruding outward.

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