Optical integrated device, optical integrated circuit wafer, and method for manufacturing optical integrated device

Abstract

To provide an optical integrated element, etc. with which it is possible to suppress optical coupling losses at the time it is coupled with an optical fiber.SOLUTION: An optical integrated element 1 comprises a substrate 2 and an optical waveguide 40 of a hollow structure which is located on the substrate 2. The optical waveguide 40 includes a first optical waveguide 4 and a second optical waveguide 5 the relative refractive index difference of which is smaller than the first optical waveguide 4 and which is optically coupled to the first optical waveguide, and converts a mode diameter to the mode diameter of an optical fiber in accordance with traveling of light from the first optical waveguide 4 to the second optical waveguide 5. The optical integrated element includes an indented part 7 which is formed in the vicinity of a dicing line of the substrate 2 so that, while a dicing end face 7A of the substrate protrudes in the axial direction of the optical waveguide 40 outward from an output end face 5A of the second optical waveguide 5, the width of the output end face 5A is smaller than the core width of an optical fiber that is optically coupled to the output end face 5A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical integrated device, an optical integrated circuit wafer, and a method for manufacturing an optical integrated device. [Background technology]

[0002] For example, optical devices such as optical couplers that extract light from photonic integrated circuits (PICs) used in high-speed optical communications are well known. Optical devices are required to be small, low-power, and high-capacity to meet market demands. To achieve this, SiPh (Si-Photonics) elements, in which waveguides and electrode substrates are integrated on a Si substrate, have attracted considerable attention. A major advantage of SiPh is its ability to easily fabricate large-scale optical integrated circuits consisting of numerous component devices by utilizing the high-precision process technology used in CMOS fabrication. Optical devices have become significantly smaller, and SiPh elements, in which waveguides and electrode substrates are integrated on a Si substrate, have attracted attention. To implement a SiP-PIC as an optical communications module, it is necessary to route the Si waveguide of the optical integrated element to the chip end face and connect the Si waveguide to an optical fiber for optical input and output. Optical fiber coupling structures that optically couple the Si waveguide to an optical fiber require low coupling loss and high reliability, but achieving both is difficult.

[0003] In SiPh-PIC, Si wires in silicon oxide are used as optical waveguides, but the large difference in relative refractive index between Si and SiO2 results in a small mode diameter for the guided light, and if the waveguide is directly coupled to an optical fiber, a large optical loss occurs due to a mismatch in mode diameter. Therefore, optical coupling is performed using a mode diameter conversion structure, and known optical coupling methods include lens coupling, which connects an optical coupler and optical fiber via a lens, and BJ (Butt Joint) coupling, which connects an optical coupler and optical fiber directly butt-jointed.

[0004] When using lens coupling, even if the mode diameter of the PIC optical coupler itself is small, the lens can be used to expand the mode diameter to that of a normal-diameter SMF (single-mode fiber). However, the output optical mode of an optical coupler is generally polarization-dependent, and when a spatial coupling system using a lens is used, the polarization dependence of the coupling efficiency becomes greater. In addition, constructing an optical system with a lens sandwiched between the chip and the optical fiber increases the device area, making it difficult to implement in a small module. Furthermore, there are cost issues, such as increased labor hours required for device manufacturing to adjust the optical axis or the need for special adjustment equipment.

[0005] On the other hand, BJ coupling can solve these problems associated with lens coupling, but it is difficult to increase the mode diameter of the output light from a PIC to the same level as the mode diameter of an SMF with a normal diameter without using a lens.

[0006] Therefore, one structure often used for BJ coupling is the inverse tapered SSC (Spot Size Converter) structure. Figure 17 is a schematic plan view of the inverse tapered SSC structure. The inverse tapered SSC structure gradually narrows the width of the Si waveguide 102 (102A, 102B) formed on the Si substrate 101 to widen the mode diameter of the guided light and approach the mode diameter of an SMF with a normal diameter. However, it is difficult to approach the mode diameter of an SMF with a normal diameter (mode diameter of approximately 10 μm) with the inverse tapered SSC structure. Another advantage is that it is easy to manufacture because it is composed only of the Si waveguide 102. However, since efficient optical connection can only be achieved with a thin-core fiber with a small mode diameter (4 μm), a thin-core fiber must be separately fused to a normal-core fiber to incorporate it into a module. Therefore, the inverse tapered SSC structure generates excess loss at the fusion point between the thin-core fiber and the normal-core fiber.

[0007] Therefore, an optical coupler with a hollow structure, for example, can be used as an optical coupler that can increase the mode diameter of the output light from the PIC. FIG. 18 is a perspective view showing an example of a hollow structure optical coupler 100. The hollow structure optical coupler 100 shown in FIG. 18 includes a Si substrate 101, a SiO2 cladding layer 103, and an optical waveguide 104 that extends from the cladding layer 103 to the Si substrate 101 and is surrounded by an air layer 107. The optical waveguide 104 includes a Si waveguide 105 and a SiO2 waveguide 106. The optical coupler 100 has a structure in which the Si waveguide 105 is converted into the SiO2 waveguide 106 to increase the mode diameter, and the SiO2 waveguide 106 is directly connected to a normal-diameter SMF. The optical coupler 100 has a hollow structure with an air layer 107 between the Si substrate 101 and the optical waveguide 104. As a result, the relative refractive index difference between the SiO2 waveguide 106 and the air layer 107 confines light up to the tip of the SiO2 waveguide 106. Because the relative refractive index difference between the SiO2 waveguide 106 and the air layer 107 is small, it is possible to achieve the same mode diameter as an optical fiber with a normal diameter.

[0008] An optical integrated circuit wafer 110 on which a pair of optical couplers 100 having such a hollow structure is mounted will be described. FIG. 19 is a schematic plan view showing an example of the optical integrated circuit wafer 110, and FIG. 20 is a cross-sectional view of the optical integrated circuit wafer 110 taken along line GG shown in FIG. 19. The optical integrated circuit wafer 110 has a pair of optical couplers 100 on a Si substrate 101. The optical integrated circuit wafer 110 is manufactured in a state in which the tip end of the SiO waveguide 106 of the optical waveguide 104 in one optical coupler 100 is connected to the tip end of the SiO waveguide 106 of the other optical waveguide 104 in the other optical coupler 100. The optical integrated circuit wafer 110 can be cut out into a pair of optical couplers 100 by dicing along a dicing line DL between the tip ends of the SiO waveguides 106 of the optical couplers 100.

[0009] However, in the optical integrated circuit wafer 110, the optical coupler 100 has a hollow structure, so there is a high possibility that the tip of the SiO2 waveguide 106 will be damaged when dicing between the tip of one SiO2 waveguide 106 and the tip of the other SiO2 waveguide 106. Therefore, there is a demand for an optical integrated circuit wafer that prevents damage to the SiO2 waveguide 106 during the dicing process.

[0010] Fig. 21 is a schematic plan view showing an example of an optical integrated circuit wafer 110A, and Fig. 22 is a cross-sectional view of the optical integrated circuit wafer 110A taken along line HH shown in Fig. 21. Note that the same components as those in the optical integrated circuit wafer 110 shown in Figs. 19 and 20 are designated by the same reference numerals, and descriptions of the overlapping components and operations will be omitted. The optical integrated circuit wafer 110A shown in Fig. 21 has a recessed portion 109 that separates the tip end of the SiO2 waveguide 106 of one optical waveguide 104 from the tip end of the SiO2 waveguide 106 of the other optical waveguide 104. The recessed portion 109 is formed on the Si substrate 101 in a state where the tip end of one SiO2 waveguide 106 is separated from the tip end of the other SiO2 waveguide 106.

[0011] Therefore, when dicing the optical integrated circuit wafer 110A along the dicing line DL in the recess 109 between one optical coupler 100 and the other optical coupler 100, the tips of the optical couplers 100 can be cut out without damaging each other.

[0012] Fig. 23 is a schematic plan view showing an example of an optical fiber coupling structure 120A, and Fig. 24 is a cross-sectional view of the optical fiber coupling structure 120A taken along line JJ shown in Fig. 23. The optical fiber coupling structure 120A has a structure in which an optical fiber 121 is optically coupled to an optical coupler 100 cut out from the optical integrated circuit wafer 110A shown in Fig. 22.

[0013] As one of the structures for stabilizing the connection with the optical coupler 100, the optical fiber 121 has a structure in which a capillary 123, which is a tiny block of glass or the like, is attached around the core 122. The capillary 123 around the core 122 increases the adhesive area with the dicing end face 101A of the optical coupler 100, thereby stabilizing the BJ coupling.

[0014] However, in the optical coupler 100, the contact area between the optical fiber 121 with the capillary 123 and the dicing end face 101A is small, resulting in an asymmetric structure. The contact area between the capillary 123 and the dicing end face 101A can be brought sufficiently close, but the area where the optical coupler 100 and the optical fiber 121 are optically coupled is farther away than the dicing end face 101A, and an adhesive is filled between them. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] U.S. Patent No. 9,946,029 [Patent Document 2] U.S. Patent No. 9,823,420 [Patent Document 3] U.S. Patent No. 10,345,524 Summary of the Invention [Problem to be solved by the invention]

[0016] 25 is an explanatory diagram showing an example of a problem with the optical fiber coupling structure 120A. However, in the optical fiber coupling structure 120A, the adhesive 124 filled between the optical coupler 100 and the optical fiber 121 expands and contracts in response to temperature changes. This may cause the optical fiber 121 to rotate due to expansion and contraction of the adhesive 124 at the corner of the dicing end face 101A, which is the contact point. As a result, the rotation of the optical fiber 121 may cause the optical axis between the optical fiber 121 and the optical coupler 100 to shift, resulting in increased optical coupling loss. This may result in loss during processes such as UV curing and high-temperature curing during manufacturing, reducing yield, or loss may occur depending on the temperature environment in which the product is used after commercialization, making it impossible to ensure sufficient reliability.

[0017] In one aspect, an object is to provide an optical integrated element or the like that can suppress optical coupling loss when coupled to an optical fiber. [Means for solving the problem]

[0018] An optical integrated device according to one embodiment includes a substrate and a hollow optical waveguide disposed on the substrate. The optical waveguide includes a first optical waveguide and a second optical waveguide having a smaller relative refractive index difference than the first optical waveguide and optically coupled to the first optical waveguide, and converts the mode diameter of the first optical waveguide into the mode diameter of the optical fiber as light travels from the first optical waveguide to the second optical waveguide. The optical integrated device includes a recess formed near a dicing line of the substrate such that the width of the output end face is smaller than the core width of the optical fiber optically coupled to the output end face, with the dicing end face of the substrate protruding in the axial direction of the optical waveguide relative to the output end face of the second optical waveguide. [Effects of the Invention]

[0019] According to one aspect, optical coupling loss when coupled to an optical fiber can be suppressed. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of an optical coupler according to a first embodiment. [Figure 2]FIG. 2 is a schematic plan view of an optical coupler. [Figure 3] FIG. 3 is a cross-sectional view of the optical coupler taken along line AA in FIG. [Figure 4] FIG. 4 is a schematic plan view of an optical integrated circuit wafer. [Figure 5] FIG. 5 is a cross-sectional view of the optical integrated circuit wafer taken along line BB in FIG. [Figure 6] FIG. 6 is a schematic plan view of an optical fiber coupling structure. [Figure 7] FIG. 7 is a cross-sectional view of the optical fiber coupling structure taken along line CC shown in FIG. [Figure 8] FIG. 8 is a schematic plan view of an optical fiber coupling structure. [Figure 9A] FIG. 9A is an explanatory diagram showing an example of an SOI substrate used in an optical integrated circuit wafer. [Figure 9B] FIG. 9B is an explanatory diagram showing an example of a process for forming a first optical waveguide in an optical integrated circuit wafer. [Figure 9C] FIG. 9C is an explanatory diagram showing an example of a process for forming a cladding layer of an optical integrated circuit wafer. [Figure 10A] FIG. 10A is an explanatory diagram showing an example of a resist process when forming an optical coupler on an optical integrated circuit wafer. [Figure 10B] FIG. 10B is a schematic plan view of the optical integrated circuit wafer when an optical coupler is formed. [Figure 10C] FIG. 10C is a cross-sectional view of the optical integrated circuit wafer shown in FIG. 10B taken along line DD. [Figure 11A] FIG. 11A is a schematic plan view of the completed optical integrated circuit wafer. [Figure 11B] FIG. 11B is a cross-sectional view of the completed optical integrated circuit wafer taken along line EE shown in FIG. 11A. [Figure 12] FIG. 12 is a schematic plan view showing an example of an optical fiber coupling structure according to the second embodiment. [Figure 13] FIG. 13 is a cross-sectional view of an optical fiber coupling structure according to the third embodiment. [Figure 14] FIG. 14 is a schematic plan view of an optical integrated circuit wafer according to the fourth embodiment. [Figure 15] FIG. 15 is a schematic plan view of an optical integrated circuit wafer according to a fifth embodiment. [Figure 16] FIG. 16 is a schematic plan view of the optical fiber coupling structure of Example 6. As shown in FIG. [Figure 17] FIG. 17 is a schematic plan view of the inverse tapered SSC structure. [Figure 18] FIG. 18 is a perspective view showing an example of an optical coupler having a hollow structure. [Figure 19] FIG. 19 is a schematic plan view showing an example of an optical integrated circuit wafer. [Figure 20] FIG. 20 is a cross-sectional view of the optical integrated circuit wafer taken along line GG in FIG. [Figure 21] FIG. 21 is a schematic plan view showing an example of an optical integrated circuit wafer. [Figure 22] FIG. 22 is a cross-sectional view of the optical integrated circuit wafer taken along line HH shown in FIG. [Figure 23] FIG. 23 is a schematic plan view showing an example of an optical fiber coupling structure. [Figure 24] FIG. 24 is a cross-sectional view of the optical fiber coupling structure taken along line JJ shown in FIG. [Figure 25] FIG. 25 is an explanatory diagram showing an example of a problem with an optical fiber coupling structure. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of an optical integrated device, an optical integrated circuit wafer, and a method for manufacturing an optical integrated device disclosed in the present application will be described in detail with reference to the drawings. Note that the present invention is not limited to these embodiments. Furthermore, the examples shown below may be combined as appropriate within the scope of not causing any contradiction. [Example]

[0022] FIG. 1 is a schematic cross-sectional view showing an example of an optical coupler 1 according to a first embodiment. The optical coupler 1 shown in FIG. 1 is a hollow optical integrated device. The optical coupler 1 includes a Si substrate 2, an optical waveguide 40 arranged on the Si substrate 2 and having a hollow structure surrounded by a cavity, and a cladding layer 3. The Si substrate 2 has a dicing end surface 7A formed when a pair of optical couplers 1 are cut out from an optical integrated circuit wafer 10, which will be described later. The cavity is an air layer 6. The cladding layer 3 is, for example, a layer of SiO2.

[0023] The optical waveguide 40 includes a first optical waveguide 4 and a second optical waveguide 5 that has a smaller relative refractive index difference than the first optical waveguide 4 and is optically coupled to the first optical waveguide 4. The first optical waveguide 4 is a semiconductor or dielectric optical waveguide made of, for example, Si, with a large relative refractive index difference. The first optical waveguide 4 has an inverted tapered SSC structure. The second optical waveguide 5 is made of, for example, SiO2. The second optical waveguide 5 has a tapered portion 5B whose width increases toward an output end face 5A, which is the tip. The optical fiber 21 optically coupled to the second optical waveguide 5 in the optical coupler 1 is, for example, a single-mode fiber (SMF). The optical coupler 1 has a function of converting the mode diameter of light traveling from the first optical waveguide 4 to the second optical waveguide 5 into the mode diameter of an SMF.

[0024] The optical coupler 1 has a recess 7 formed near a dicing line DL of the Si substrate 2. By forming the recess 7, the dicing end face 7A protrudes in the axial direction of the optical waveguide 40 compared to the output end face 5A, and the width of the output end face 5A becomes smaller than the core width of the optical fiber 21 optically coupled to the output end face 5A. The recess 7 has a limited width of the recess structure that makes the output end face 5A different from the dicing end face 7A. By forming the recess 7, the Si substrate 2 has a wall surface 7B that is flush with the output end face 5A and a bottom surface 7C that extends perpendicularly from the wall surface 7B.

[0025] FIG. 2 is a schematic plan view of the optical coupler 1. The width w of the recess 7 is preferably narrower than the capillary 22 of the optical fiber 21 to be optically coupled. The capillary 22 of the optical fiber 21 has a rectangular shape with sides of approximately 1000 μm. The width w of the recess 7 needs to be wide enough not to block the light that is emitted from the output end face 5A of the second optical waveguide 5 of the optical coupler 1 and spreads radially. Therefore, the width w of the recess 7 can be expressed as w≧2d*(λ / πD), where λ is the wavelength of the light passing through the optical coupler 1, d is the depth of the recess 7, and D is the mode diameter. The width w of the recess 7 is equal to or smaller than the tip diameter of the SMF to be optically coupled to the output end face 5A of the second optical waveguide 5 of the optical coupler 1.

[0026] 3 is a cross-sectional view of the optical coupler 1 taken along line AA in FIG. 2. Furthermore, the depth of the recess 7 needs to be deep enough so as not to block the light that is emitted from the output end face 5A of the second optical waveguide 5 of the optical coupler 1 and spreads radially. Therefore, the depth h of the recess 7 can be expressed as h≧d*(λ / πD). The depth h of the recess 7 is the distance in the vertical direction from the bottom surface 7C of the recess 7 formed in the Si substrate 2 to the top surface of the second optical waveguide 5. The depth d of the recess 7 is, for example, 30 μm, the width w of the recess 7 is, for example, 200 μm, and the depth h of the recess 7 is, for example, 100 μm.

[0027] The optical coupler 1 can be cut out from the optical integrated circuit wafer 10 by dicing the Si substrate 2 along dicing lines DL on the optical integrated circuit wafer 10. Now, the optical integrated circuit wafer 10 will be described. Fig. 4 is a schematic plan view of the optical integrated circuit wafer 10, and Fig. 5 is a cross-sectional view of the optical integrated circuit wafer 10 taken along line BB shown in Fig. 4.

[0028] 4 includes a Si substrate 2 and a pair of optical couplers 1 disposed on the Si substrate 2. The Si substrate 2 includes a first substrate 2A on which one optical coupler 1A is disposed, a second substrate 2B on which the other optical coupler 1B is disposed, and a pair of recesses 7 formed in the vicinity of a dicing line DL between the first substrate 2A and the second substrate 2B.

[0029] The pair of recesses 7 are formed near a dicing line DL of the Si substrate 2 that connects one optical coupler 1A and the other optical coupler 1B. As a result, the output end face 5A of the second optical waveguide 5 of one optical coupler 1A and the output end face 5A of the second optical waveguide 5 of the other optical coupler 1B face each other while being spaced apart, and the width of the output end face 5A of the second optical waveguide 5 is smaller than the core width of the SMF optically coupled to the output end face 5A.

[0030] Next, we will explain the optical fiber coupling structure 20 that optically couples an optical fiber 21 to the optical coupler 1 cut out from the optical integrated circuit wafer 10. Fig. 6 is a plan view schematic diagram of the optical fiber coupling structure 20, and Fig. 7 is a cross-sectional view of the optical fiber coupling structure 20 taken along line CC shown in Fig. 6.

[0031] The optical fiber coupling structure 20 shown in FIG. 6 is a structure in which an adhesive is filled in the output end face 5A of the second optical waveguide 5 and the recessed portion 7, and the output end face 5A of the second optical waveguide 5 and the optical fiber 21 are optically coupled via a capillary 22 in the optical fiber 21.

[0032] 8 is a schematic plan view of the optical fiber coupling structure 20. On the surface where the optical coupler 1 and the optical fiber 21 are optically coupled, the portion other than the recessed portion 7 becomes the contact surface D1, which increases the contact area between the optical coupler 1 and the optical fiber 21 and enables strong optical coupling between the optical coupler 1 and the optical fiber 21. As a result, the optical coupling between the optical coupler 1 and the optical fiber 21 is strong, and the risk of the optical fiber 21 rotating can be avoided.

[0033] Next, a method for manufacturing the optical coupler 1 will be described. FIG. 9A is an explanatory diagram showing an example of an SOI (Silicon on Insulator) substrate used in the optical integrated circuit wafer 10. The SOI substrate shown in FIG. 9A includes a Si substrate 11(2), a SiO2 layer 12 stacked on the Si substrate 11, and a Si layer 13 stacked on the SiO2 layer 12. The SiO2 layer 12 is a box layer. The Si layer 13 is a layer for forming the first optical waveguide 4 in the optical coupler 1. The thickness of the Si substrate 11 is, for example, 750 μm, the thickness of the SiO2 layer 12 is, for example, 2.5 μm, and the thickness of the Si layer 13 is, for example, 250 μm. For ease of explanation, the Si substrate 11 may be omitted from the drawings in some cases. Furthermore, the optical integrated circuit wafer 10 may include structures such as modulators and photodetectors that require additional processes, such as doping, in addition to the present structure; however, these processes will be omitted here.

[0034] FIG. 9B is an explanatory diagram showing an example of a process for forming the first optical waveguide 4 of the optical integrated circuit wafer 10. The first optical waveguide 4 is formed on the SiO layer 12 shown in FIG. 9B by etching the Si layer 13 on the SiO layer 12. Specifically, a SiO film 12A is formed using plasma CVD, and the pattern of the first optical waveguide 4 is formed using photoresist. The width of the first optical waveguide 4 is, for example, 460 nm, and the width of the tip of the SSC reverse taper is, for example, 140 nm. Using this pattern as a mask, the pattern of the first optical waveguide 4 is formed by dry etching. In the Si layer 13, the first optical waveguide 4 with a reverse tapered SSC structure for enlarging the mode diameter of the first optical waveguide 4 to the mode diameter of the second optical waveguide 5 and the Si optical waveguide 41 for guiding light to the first optical waveguide 4 are formed.

[0035] FIG. 9C is an explanatory diagram showing an example of a process for forming the cladding layer 3 of the optical integrated circuit wafer 10. After forming the first optical waveguide 4 on the SiO2 layer 12, an SiO2 film 12A is formed on the first optical waveguide 4 and the SiO2 layer 12, thereby forming the cladding layer 3 of the SiO2 layer 12 on the Si substrate 11 as shown in FIG. 9C. Specifically, the cladding layer 3 is formed by depositing an SiO2 film on the Si substrate 11 using a plasma CVD method. The thickness of the cladding layer 3 is set to, for example, 5 μm. The first optical waveguide 4 is surrounded by the SiO2 layer, and light is confined within the Si due to the relative refractive index difference between Si and SiO2, and the light propagates through the waveguide.

[0036] Fig. 10A is an explanatory diagram showing an example of a resist process when forming the optical coupler 1 of the optical integrated circuit wafer 10. As shown in Fig. 10A, a photoresist layer 15 is arranged in a portion where a cavity of the air layer 6 on the cladding layer 3 shown in Fig. 9C is to be formed.

[0037] FIG. 10B is a schematic plan view of the optical integrated circuit wafer 10 during the formation of the optical coupler 1, and FIG. 10C is a cross-sectional view of the optical integrated circuit wafer 10 shown in FIG. 10B along line DD. The optical integrated circuit wafer 10 shown in FIG. 10B is fabricated by dry-etching the SiO layer 12 and a portion of the Si layer 13 other than the portion masked with the photoresist layer 15 on the optical integrated circuit wafer 10 shown in FIG. 10A. This dry etching creates an air layer 6 that creates a cavity around the optical waveguide 40 having the first optical waveguide 4 and the second optical waveguide 5. As a result, a pair of hollow optical couplers 1 are formed on the optical integrated circuit wafer 10. Specifically, the SiO layer 12 is dry-etched using this pattern as a mask, followed by wet-etching the Si substrate 11, thereby forming a hollow structure in which the SiO layer 12 is surrounded by the air layer 6. The optical coupler 1 functions due to the relative refractive index difference between the SiO layer 12 and the air layer 6.

[0038] 11A is a schematic plan view of the completed optical integrated circuit wafer 10. In the optical integrated circuit wafer 10, a pair of recesses 7 are formed on the Si substrate 11 by etching the Si substrate 11 near the output end face 5A of the second optical waveguide 5 of the optical coupler 1. The depth D of the recesses 7 is, for example, 30 μm, the width w of the recesses 7 is, for example, 200 μm, and the depth h of the recesses 7 is, for example, 100 μm.

[0039] Fig. 11B is a cross-sectional view of the completed optical integrated circuit wafer 10 taken along the line E-E shown in Fig. 11A. The optical integrated circuit wafer 10 shown in Fig. 11B can be cut into a pair of optical couplers 1 shown in Fig. 1 by dicing along dicing lines DL in the recessed portions 7 on the Si substrate 11(2). Dicing can be achieved by, for example, stealth dicing using a laser, blade dicing, scribing, or the like.

[0040] The optical coupler 1 of the first embodiment includes a first optical waveguide 4 and a second optical waveguide 5 that has a smaller relative refractive index difference than the first optical waveguide 4 and is optically coupled to the first optical waveguide 4. The optical coupler 1 includes a recess 7 formed near the dicing line DL of the Si substrate 2 so that the width of the output end face 5A is smaller than the core width of the optical fiber 21 when the output end face 5A protrudes in the axial direction of the optical waveguide 40 relative to the dicing end face 7A. As a result, optical coupling loss during coupling with the optical fiber 21 can be reduced. Because the optical fiber 21 can be connected to a standard diameter optical fiber 21, a wide tolerance curve can be achieved. Furthermore, the wall surface 7B of the recess 7 of the Si substrate 2 in the optical coupler 1 increases the contact area during optical coupling with the optical fiber 21, thereby suppressing rotation of the optical fiber 21 due to expansion and contraction of the adhesive, thereby achieving high reliability.

[0041] The optical coupler 1 converts the mode diameter into the mode diameter of the optical fiber 21 in accordance with the progression of light from the first optical waveguide 4 to the second optical waveguide 5. As a result, the optical coupler 1 can be optically coupled to an SMF optical fiber.

[0042] The width w of the recessed portion 7 of the optical coupler 1 is calculated as w≧2d*(λ / πD). As a result, the recessed portion 7 can be made wide enough not to block the light that is emitted from the output end face 5A of the second optical waveguide 5 of the optical coupler 1 and spreads radially.

[0043] The depth h of the recess 7 of the optical coupler 1 is calculated as h≧d*(λ / πD). As a result, the recess 7 can be made deep enough not to block the light that is emitted from the output end face 5A of the second optical waveguide 5 of the optical coupler 1 and spreads radially.

[0044] The optical coupler 1 fills the output end face 5A of the second optical waveguide 5 and the recess 7 with adhesive to optically couple the optical fiber 21 to the output end face 5A of the second optical waveguide 5. As a result, the optical coupler 1 can optically couple the optical fiber 21.

[0045] The optical integrated circuit wafer 10 has a pair of optical couplers 1 of the same structure arranged opposite each other across a dicing line DL on a Si substrate 2. As a result, the pair of optical couplers 1 can be cut out from the optical integrated circuit wafer 10 by dicing along the dicing line DL.

[0046] In the conventional optical integrated circuit wafer 110A, in order to prevent damage to the optical coupler 100 during dicing, the recessed portion 109 is provided beyond the tip of the SiO2 waveguide 106 of the hollow coupler. Therefore, when the portion of the recessed portion 109 is diced and the dicing end face 101A is brought into contact with the capillary 123 of the optical fiber 121, the contact surface becomes asymmetric, and the expansion and contraction of the adhesive causes the optical fiber 121 to rotate, resulting in misalignment of the optical axis.

[0047] In contrast, in the optical integrated circuit wafer 10 of this embodiment, the width of the recess 7 is limited and does not extend to the width of the capillary 22 of the optical fiber 21. Therefore, the dicing end surface 7A, which can be bonded to the capillary 22, is located at both ends of the recess 7 from the bottom to the top of the chip. Therefore, when the capillary 22 of the optical fiber 21 is bonded to this portion with adhesive, rotation of the optical fiber 21 can be prevented even if the adhesive that has entered the recess 7 expands and contracts due to heat. In other words, coupling loss due to misalignment of the optical axis can be suppressed. Furthermore, the bonding area between the capillary 22 of the optical fiber 21 and the dicing end surface 7A is increased compared to conventional structures, thereby enhancing bonding strength. Therefore, while using an optical coupler 1 that can connect to optical fibers 21 of normal diameters, the contact area between the optical fiber 21 and the dicing end surface 7A of the optical integrated circuit wafer 10 is increased. As a result, rotation of the optical fiber 21 due to expansion and contraction of the adhesive is suppressed, thereby suppressing optical coupling loss.

[0048] For ease of explanation, the first optical waveguide 4 is made of Si and the second optical waveguide 5 is made of SiO2. However, the present invention is not limited to these materials and may be made of, for example, SiN or SiON. The materials may be changed as appropriate as long as the refractive index of the first optical waveguide 4 is higher than that of the second optical waveguide 5. The first optical waveguide 4 is made of a material containing Si, and the second optical waveguide 5 is made of a material containing Si with a lower relative refractive index than that of the first optical waveguide 4. The first optical waveguide 4 may be made of, for example, Si, SiN, SiON, or SiO2. When the first optical waveguide 4 is made of SiN and the second optical waveguide 5 is made of SiO2, a structure may be formed in which the Si waveguide and the Si and SiN waveguides are converted into each other up to just before the SiN waveguide.

[0049] The optical coupler 1 is exemplified as a case where a hollow optical waveguide 40 formed by an air layer 6 that is surrounded by a void is arranged, but instead of the air layer 6, an optical waveguide surrounded by adhesive may also be used, and modifications can be made as appropriate.

[0050] In the optical coupler 1 of Example 1, the recess 7 is formed so that the orientation of the output end face 5A of the second optical waveguide 5 is the same as the orientation of the dicing end face 7A on the Si substrate 2. However, the orientation of the output end face 5A of the second optical waveguide 5 is not limited to this. The orientation of the output end face 5A of the optical coupler 1 may be different from the orientation of the dicing end face 7A, and such an embodiment will be described below as Example 2. Note that the same components as those of the optical coupler 1 of Example 1 are denoted by the same reference numerals, and descriptions of the overlapping components and operations will be omitted. [Example]

[0051] 12 is a plan view schematic diagram showing an example of an optical fiber coupling structure 20A of Example 2. The optical coupler 1 is disposed on the Si substrate 2 so that the output end face 5A of the second optical waveguide 5 is oriented obliquely with respect to the dicing end face 7A. Then, a recess 71 is formed in the Si substrate 2 near the dicing line DL between the output end face 5A and the dicing end face 7A.

[0052] The optical fiber coupling structure 20A can optically couple the output end face 5A of the second optical waveguide 5 and the optical fiber 21 via the capillary 22 of the optical fiber 21 by filling the output end face 5A of the second optical waveguide 5 and the recessed portion 71 with adhesive.

[0053] In the example 1, the recess 7 is formed so that the orientation of the output end face 5A of the second optical waveguide 5 in the optical coupler 1 is the same as the orientation of the dicing end face 7A on the Si substrate 2. However, the orientation of the dicing end face 7A is not limited to this, and such an embodiment will be described below as Example 3. [Example]

[0054] 13 is a cross-sectional view of an optical fiber coupling structure 20A of Example 3. A dicing end face 7A1 is formed on the Si substrate 2, and is inclined obliquely from a vertical direction Y perpendicular to the axial direction X of the optical waveguide 40. A recess 72 is formed in the Si substrate 2 near a dicing line DL between the output end face 5A and the dicing end face 7A1.

[0055] The optical fiber coupling structure 20A can optically couple the output end face 5A of the second optical waveguide 5 and the optical fiber 21 via the capillary 22 of the optical fiber 21 by filling the output end face 5A of the second optical waveguide 5 and the recessed portion 72 with adhesive. [Example]

[0056] Fig. 14 is a schematic plan view of an optical integrated circuit wafer 10A of Example 4. The Si substrate 2 shown in Fig. 14 has a first substrate 2A on which one optical coupler 1A is arranged, a second substrate 2B on which the other optical coupler 1B is arranged, and a recessed portion 7 formed near a dicing line DL between the first substrate 2A and the second substrate 2B.

[0057] The optical integrated circuit wafer 10A has a routing optical waveguide 8 arranged on a first substrate 2A and a second substrate 2B, with an optical waveguide 40 in one optical coupler 1A and an optical waveguide 40 in the other optical coupler 1B in parallel, separated by a dicing line DL. The routing optical waveguide 8 is, for example, an optical waveguide having an input portion 8A for inputting test light.

[0058] Furthermore, limiting the width of the recessed portion 7 increases the degree of freedom in routing the waveguides used for wafer inspection before dicing, etc. In the conventional optical integrated circuit wafer 110A, recessed portion 109 is provided in the area of the dicing line DL to simplify dicing, so it is not possible to route the optical waveguide in the portion of recessed portion 109. However, in the optical integrated circuit wafer 10A of this embodiment, the width of recessed portion 7 is limited, so it is possible to route the routed optical waveguide 8 across the dicing line DL other than in recessed portion 7, and therefore the routed optical waveguide 8 can be used before dicing. [Example]

[0059] Fig. 15 is a schematic plan view of an optical integrated circuit wafer 10B according to a fifth embodiment. The Si substrate 2 shown in Fig. 15 has a first substrate 2A on which one optical coupler 1A is arranged, a second substrate 2B on which the other optical coupler 1B is arranged, and a recessed portion 7 formed near a dicing line DL between the first substrate 2A and the second substrate 2B. The optical integrated circuit wafer 10B has a routing waveguide 9 that passes from one optical coupler 1A through the recessed portion 7 to the other optical coupler 1B across the dicing line DL. The routing waveguide 9 is an optical waveguide through which test light is input.

[0060] A method of light incidence that does not use an optical end face is to use a grating coupler, which allows light to be incident from the surface of the chip on the optical integrated circuit wafer 10B. With a grating coupler, optical measurements are possible even before dicing, but incorporating this grating coupler into the product chip increases the chip area. Therefore, to prevent the chip area from increasing, it is placed outside the product chip and used as a sacrificial port during dicing. By limiting the width of the recess 7, the waveguide can be routed from the dicing line DL on the optical end face, increasing the degree of freedom. [Example]

[0061] Fig. 16 is a schematic plan view of an optical fiber coupling structure 20B of Example 6. Note that the same components as those of the optical coupler 1 of Example 1 are given the same reference numerals, and explanations of the overlapping components and operations will be omitted. The optical fiber coupling structure 20B shown in Fig. 16 has a Si substrate 2, three optical couplers 1 arranged on the Si substrate 2, three recesses 73, and an optical fiber array 21A having three cores 25A. The Si substrate 2 has a recess 73 formed for each optical coupler 1.

[0062] The optical fiber coupling structure 20B is a structure in which an adhesive is filled into the output end face 5A and recessed portion 73 of the second optical waveguide 5 in the optical coupler 1, and the output end face 5A of the second optical waveguide 5 and the core 25A of the optical fiber array 21A are optically coupled via the capillary 22. In other words, the second optical waveguides 5 of three optical couplers 1 can be optically coupled to the three cores 25A in the optical fiber array 21A.

[0063] Furthermore, the components of each unit shown in the figure do not necessarily have to be physically configured as shown in the figure. In other words, the specific form of distribution and integration of each unit is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc. [Explanation of symbols]

[0064] 1 Optical coupler 2. Si substrate 2A First board 2B Second board 3 Cladding layer 4. First Optical Waveguide 5 Second optical waveguide 5A output end face 7. Depression 7A dicing edge 10. Optical integrated circuit wafer 21 Optical Fiber 40 Optical waveguide

Claims

1. An optical integrated device having a substrate and an optical waveguide disposed on the substrate and surrounded by air, The optical waveguide is a first optical waveguide; a second optical waveguide that has a smaller relative refractive index difference than the first optical waveguide and is optically coupled to the first optical waveguide, and converts a mode diameter into a mode diameter of an optical fiber according to the progression of light from the first optical waveguide to the second optical waveguide; The optical integrated device comprises: an optical integrated device having a recess formed near a dicing line of the substrate so that, in a state where the dicing end face of the substrate protrudes in the axial direction of the optical waveguide compared to the output end face of the second optical waveguide, the width of the recess including the output end face is smaller than the width of a glass block formed by a capillary attached to an end of the optical fiber that is optically coupled to the output end face.

2. The recessed portion is [Equation 1] 2. The integrated optical element according to claim 1, wherein the integrated optical element has a width calculated by:

3. The recessed portion is [Equation 2] 3. The optical integrated device according to claim 1, wherein the optical integrated device has a depth calculated by:

4. 4. The optical integrated element according to claim 1, wherein the material of the first optical waveguide is a material containing Si, and the material of the second optical waveguide is a material containing Si and having a smaller relative refractive index than the material of the first optical waveguide.

5. The optical waveguide is 5. The optical integrated device according to claim 1, wherein the optical integrated device is disposed on the substrate so that the output end face is oblique to the dicing end face.

6. The substrate is 5. The optical integrated device according to claim 1, wherein the dicing end faces are formed so as to be inclined obliquely from a vertical direction orthogonal to an axial direction of the optical waveguide.

7. 6. The optical integrated device according to claim 1, wherein an adhesive is filled into the output end face of the second optical waveguide and the recessed portion, and the optical fiber is optically coupled to the output end face of the second optical waveguide.

8. A substrate; a pair of optical integrated devices disposed on the substrate and having optical waveguides surrounded by air, The optical waveguide is a first optical waveguide; a second optical waveguide within the optical waveguide, the second optical waveguide having a smaller relative refractive index difference than the first optical waveguide and optically coupled to the first optical waveguide, wherein a mode diameter is converted into a mode diameter of an optical fiber according to the progression of light from the first optical waveguide to the second optical waveguide; The optical integrated circuit wafer comprises: an output end face of a second optical waveguide of one of the pair of optical integrated elements and an output end face of the second optical waveguide of the other of the pair of optical integrated elements facing each other while being spaced apart, and a pair of recesses formed in the vicinity of a dicing line of the substrate connecting the one optical integrated element and the other optical integrated element such that the width of the recessed portion including the output end face of the second optical waveguide is smaller than the width of a glass block formed by a capillary attached to an end of the optical fiber that is optically coupled to the output end face.

9. The substrate is a first substrate on which the one optical integrated element is arranged, a second substrate on which the other optical integrated element is arranged, and the recessed portion formed in the vicinity of the dicing line between the first substrate and the second substrate, The optical integrated circuit wafer comprises:

9. The optical integrated circuit wafer according to claim 8, further comprising another optical waveguide arranged on the first substrate and the second substrate, the optical waveguide in one of the optical integrated elements and the optical waveguide in the other of the optical integrated elements being parallel to each other across the dicing line.

10. The substrate is a first substrate on which the one optical integrated element is arranged, a second substrate on which the other optical integrated element is arranged, and the recessed portion formed in the vicinity of the dicing line between the first substrate and the second substrate, The optical integrated circuit wafer comprises:

9. The optical integrated circuit wafer according to claim 8, further comprising another optical waveguide passing from said one optical integrated element to said other optical integrated element via said recess, across said dicing line.

11. A substrate; a pair of optical integrated circuit elements disposed on the substrate and having optical waveguides surrounded by air, the optical waveguides including a first optical waveguide and a second optical waveguide having a relative refractive index difference smaller than that of the first optical waveguide and optically coupled to the first optical waveguide; a method of manufacturing an optical integrated element, comprising: cutting the optical integrated element from the optical integrated circuit wafer; an output end face of a second optical waveguide of one of the pair of optical integrated elements and an output end face of the second optical waveguide of the other of the pair of optical integrated elements are opposed to each other while being spaced apart, and a recessed portion is formed in the vicinity of a dicing line of the substrate connecting between the one optical integrated element and the other optical integrated element so that the width of the recessed portion including the output end face is smaller than the width of a glass block formed by a capillary attached to an end of the optical fiber optically coupled to the output end face; a dicing line in the recessed portion, whereby the one optical integrated element and the other optical integrated element are cut out from the optical integrated circuit wafer;

Images