Optical integrated devices, optical integrated circuit wafers, and methods for manufacturing optical integrated devices

Abstract

This disclosure relates to optical integrated devices, optical integrated circuit wafers, and methods for manufacturing optical integrated devices. The optical integrated device includes a substrate and a waveguide having a hollow structure. The waveguide includes a first waveguide and a second waveguide, the second waveguide being optically coupled to the first waveguide and having a relative refractive index difference smaller than that of the first waveguide, and the waveguide converting a mode diameter to the mode diameter of an optical fiber according to the propagation of light. The optical integrated device includes a recessed portion formed near a cleavage line on the substrate, such that, with the cleavage end surface of the substrate protruding further in the axial direction of the optical waveguide than the output end surface of the second waveguide, the width of the output end surface is smaller than the core width of the optical fiber optically coupled to the output end surface.

Description

Technical Field

[0001] The implementation methods discussed in this article relate to optical integrated devices, optical integrated circuit wafers, and methods for manufacturing optical integrated devices. Background Technology

[0002] For example, optical devices such as optical couplers are known to extract light from optical integrated devices (photonic integrated circuits: PICs) used for high-speed optical communication. Responding to market demands for small-size, low-power, and high-capacity optical devices, Si photonic (SiPh) devices, where each component integrates a waveguide and an electrode substrate on a Si substrate, are attracting attention. A major advantage of SiPh devices is that large-scale optical integrated circuits composed of many components can be easily fabricated using high-resolution processing techniques used to manufacture CMOS. Miniaturization of optical devices is significant, and SiPh devices, where each component integrates a waveguide and an electrode substrate on a Si substrate, are gaining attention. To realize SiPh-PICs as modules for optical communication, it is necessary to route the Si waveguides included in the optical integrated device to the chip's end surface, connect the Si waveguides to optical fibers, and input and output light. In fiber optic coupling structures where Si waveguides are optically coupled to optical fibers, low coupling loss and high reliability are required; however, it is difficult to meet both requirements simultaneously.

[0003] In SiPh-PIC, thin Si wires within silicon oxide serve as optical waveguides; however, due to the large relative refractive index difference between Si and SiO2, the mode diameter of the waveguide is very small. Consequently, if the SiPh-PIC is directly connected to an optical fiber, significant optical loss occurs due to the mismatch between the mode diameter and the optical fiber. Therefore, optical coupling is performed using a mode diameter conversion structure. For optical coupling, lens coupling techniques, such as linking the optical coupler to the optical fiber via a lens, and docking (BJ) techniques, such as directly joining the optical coupler and the optical fiber, are known.

[0004] When using lens coupling technology, even if the mode diameter of the PIC's optical coupler itself is small, it can be increased to the normal diameter of a single-mode fiber (SMF) by using lenses. However, the output light mode of an optical coupler is typically polarization-dependent, and if a spatial coupling system using lenses is used, the polarization dependence of the coupling efficiency increases. Furthermore, constructing an optical system that sandwiches the lens between the chip and the fiber increases the device area, making it difficult to achieve small-size modules. In addition, there are cost issues such as increased manufacturing steps required to adjust the optical axis and the need for special adjustment devices.

[0005] In contrast, BJ technology can solve these problems regarding lens coupling technology; however, without using lenses, it is difficult to increase the output light mode diameter of the PIC to a level similar to that of the SMF with a normal diameter.

[0006] Therefore, the inverted cone spot size converter (SSC) structure exists as a structure frequently used in BJ connection technology. Figure 17 This is a schematic plan view of an inverted conical SSC structure. In the inverted conical SSC structure, the mode diameter of the waveguide is increased by gradually reducing the width of the Si waveguides 102 (102A, 102B) formed on the Si substrate 101, thereby making the mode diameter of the waveguide approach the mode diameter of an SMF with a normal diameter. However, in the inverted conical SSC structure, it is difficult to increase the mode diameter of the waveguide to approach the mode diameter of an SMF with a normal diameter (approximately 10 μm). Furthermore, as an advantage, this structure is constructed using only Si waveguides 102, making manufacturing easy. However, effective optical connectivity is limited to small-diameter core fibers with a small mode diameter (4 μm), requiring additional fusion welding of the small-diameter core fiber to the core fiber to mount the device onto the module. As a result, excessive loss occurs at the fusion weld between the small-diameter core fiber and the normal core fiber in the inverted conical SSC structure.

[0007] Therefore, as an optical coupler capable of increasing the diameter of the output light mode used to output light from the PIC, there exists, for example, an optical coupler with a hollow structure. Figure 18 This is a perspective view illustrating an example of an optical coupler 100 with a hollow structure. Figure 18 The hollow optical coupler 100 shown includes a Si substrate 101, an outer cladding layer 103 made of SiO2, and an optical waveguide 104 extending from the outer cladding layer 103 above the Si substrate 101 and 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 that increases the mode diameter by switching the mode diameter from the Si waveguide 105 to the SiO2 waveguide 106 and directly connects the SiO2 waveguide 106 to an SMF with a normal diameter. By allowing the portion between the Si substrate 101 and the optical waveguide 104 to become an air layer 107, the optical coupler 100 is configured to have a hollow structure. As a result, by using the relative refractive index difference between the SiO2 waveguide 106 and the air layer 107, light is confined to the front end portion of the SiO2 waveguide 106. The small relative refractive index difference between the SiO2 waveguide 106 and the air layer 107 allows for the realization of the same mode diameter as optical fibers with normal diameters.

[0008] The optical integrated circuit wafer 110 on which a pair of optical couplers 100 with such a hollow structure are mounted will be described. Figure 19 This is a schematic plan view illustrating an example of an optical integrated circuit wafer 110, and Figure 20 It is along Figure 19 The diagram shows a cross-sectional view of the optical integrated circuit wafer 110 taken along line GG. The optical integrated circuit wafer 110 includes 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 front end portion of a SiO2 waveguide 106 included in one associated optical waveguide 104 of one associated optical coupler 100 is linked to the front end portion of a SiO2 waveguide 106 included in another associated optical waveguide 104 of another associated optical coupler 100. Then, with respect to the optical integrated circuit wafer 110, a pair of optical couplers 100 can be cut from the optical integrated circuit wafer 110 by cutting a dicing line DL located between the front end portions of the SiO2 waveguides 106 included in the optical couplers 100.

[0009] However, in the optical integrated circuit wafer 110, the optical coupler 100 has a hollow structure. When dicing the portion between the front end portions of one SiO2 waveguide 106 and the front end portions of another SiO2 waveguide 106, the front end portions of the SiO2 waveguide 106 are likely to be damaged. Therefore, there is a need for an optical integrated circuit wafer that can avoid damage to the SiO2 waveguide 106 during the dicing step.

[0010] Figure 21 This is a schematic plan view illustrating an example of an optical integrated circuit wafer 110A, and Figure 22 It is along Figure 21 The image shows a cross-sectional view taken from line HH of the optical integrated circuit wafer 110A. Additionally, by comparing with... Figure 19 and Figure 20 The optical integrated circuit wafer 110 shown has components with the same configuration assigned the same reference numerals, and repeated descriptions of the configuration and operation will be omitted. Figure 21 The illustrated optical integrated circuit wafer 110A includes a recessed portion 109 that separates the front end portion of a SiO2 waveguide 106 included in one of the optical waveguides 104 from the front end portion of a SiO2 waveguide 106 included in the other optical waveguide 104. The recessed portion 109 is formed on a Si substrate 101 in a separated state between the front end portion of one SiO2 waveguide 106 and the front end portion of the other SiO2 waveguide 106.

[0011] Therefore, when cutting the dicing line DL in the recessed portion 109 between one optical coupler 100 and another optical coupler 100 from the optical integrated circuit wafer 110A, the optical coupler 100 can be cut off without damaging the two front end portions of the optical coupler 100.

[0012] Figure 23This is a schematic plan view illustrating an example of an optical fiber coupling structure 120A, and Figure 24 It is along Figure 23 The diagram shows a cross-sectional view of line JJ of the fiber optic coupling structure 120A. The fiber optic coupling structure 120A has fiber optic 121 optically coupled to... Figure 22 The structure of the optical coupler 100 cut from the optical integrated circuit wafer 110A is shown.

[0013] As a structure for stable connection with optical coupler 100, optical fiber 121 sometimes has a structure in which capillary tubes 123, for example made of glass, are attached around core 122. By using capillary tubes 123 attached around core 122, the connection area with the cut end surface 101A of optical coupler 100 is increased and the BJ connection is stable.

[0014] However, in the optical coupler 100, the portion of the optical fiber 121 with capillary 123 that contacts the diced end surface 101A is small and has an asymmetrical structure. The portions of the capillary 123 that contact the diced end surface 101A are able to approach each other sufficiently; however, the portion of the optical coupler 100 that is optically coupled to the optical fiber 121 is far from the diced end surface 101A, and therefore adhesive is filled in this portion.

[0015] Patent Document 1: US Patent No. 9946029

[0016] Patent Document 2: US Patent No. 9823420

[0017] Patent Document 3: US Patent No. 10345524

[0018] Figure 25 This diagram illustrates an example of a problem with the fiber optic coupling structure 120A. In the fiber optic coupling structure 120A, the adhesive 124 filling the portion between the optical coupler 100 and the optical fiber 121 expands, contracts, and bulges according to temperature changes, causing the optical fiber 121 to potentially rotate due to the expansion and contraction of the adhesive 124 at the contact points at the corners of the cut end surface 101A. As a result, the optical axis located between the optical fiber 121 and the optical coupler 100 shifts due to the rotation of the optical fiber 121, thus increasing optical coupling loss. Therefore, losses caused by UV curing or high-temperature curing steps during manufacturing lead to reduced yield, or losses that depend on the temperature of the post-manufacturing operating environment result in insufficient reliability.

[0019] Therefore, one aspect of the present invention is to provide an optical integrated device, etc., capable of suppressing optical coupling loss when coupled with an optical fiber. Summary of the Invention

[0020] According to one aspect of an embodiment, an optical integrated device includes a substrate; and an optical waveguide disposed on the substrate and having a hollow structure. The optical waveguide includes a first optical waveguide and a second optical waveguide. The second optical waveguide is optically coupled to the first optical waveguide and has a relative refractive index difference smaller than that of the first optical waveguide. The optical waveguide converts a mode diameter to the mode diameter of an optical fiber according to the travel of light from the first optical waveguide to the second optical waveguide. The optical integrated device includes a recessed portion formed near a cleaved line on the substrate, such that the width of the output end surface of the second optical waveguide is smaller than the core width of the optical fiber optically coupled to the output end surface. The recessed portion is formed in a state in which the cleaved end surface of the substrate protrudes further than the output end surface of the second optical waveguide in the axial direction of the optical waveguide. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view illustrating an example of an optical coupler according to the first embodiment;

[0022] Figure 2 This is a schematic plan view of an optical coupler;

[0023] Figure 3 It is along Figure 2 The image shows a cross-sectional view of line AA of the optical coupler.

[0024] Figure 4 This is a schematic plan view of an optical integrated circuit wafer;

[0025] Figure 5 It is along Figure 4 The image shows a cross-sectional view taken from line BB of the optical integrated circuit wafer.

[0026] Figure 6 This is a schematic plan view of the fiber optic coupling structure;

[0027] Figure 7 It is along Figure 6 The cross-sectional view of the optical fiber coupling structure shown is taken from line CC.

[0028] Figure 8 This is a schematic plan view of the fiber optic coupling structure;

[0029] Figure 9A This is a diagram illustrating an example of an SOI substrate used for optical integrated circuit wafers;

[0030] Figure 9B This is a diagram illustrating an example of the formation steps of the first optical waveguide on an optical integrated circuit wafer;

[0031] Figure 9CThis is a diagram illustrating an example of the steps involved in forming the outer coating of an optical integrated circuit wafer;

[0032] Figure 10A This is a diagram illustrating an example of the resist step in forming an optical coupler on an optical integrated circuit wafer;

[0033] Figure 10B This is a schematic plan view of the optical integrated circuit wafer used to form the optical coupler;

[0034] Figure 10C It is along Figure 10B The image shows a cross-sectional view of the optical integrated circuit wafer taken from line DD.

[0035] Figure 11A This is a schematic plan view of the completed optical integrated circuit wafer;

[0036] Figure 11B It is along Figure 11A The image shown is a cross-sectional view of the completed optical integrated circuit wafer taken from line EE.

[0037] Figure 12 This is a schematic plan view illustrating an example of an optical fiber coupling structure according to the second embodiment;

[0038] Figure 13 This is a cross-sectional view of the fiber optic coupling structure according to the third embodiment;

[0039] Figure 14 This is a schematic plan view of an optical integrated circuit wafer according to the fourth embodiment;

[0040] Figure 15 This is a schematic plan view of an optical integrated circuit wafer according to the fifth embodiment;

[0041] Figure 16 This is a schematic plan view of the optical fiber coupling structure according to the sixth embodiment;

[0042] Figure 17 This is a schematic plan view of an inverted conical SSC structure;

[0043] Figure 18 This is a perspective view illustrating an example of an optical coupler with a hollow structure;

[0044] Figure 19 This is a schematic plan view illustrating an example of an optical integrated circuit wafer;

[0045] Figure 20 It is along Figure 19 The image shows a cross-sectional view of the optical integrated circuit wafer taken from line GG.

[0046] Figure 21This is a schematic plan view illustrating an example of an optical integrated circuit wafer;

[0047] Figure 22 It is along Figure 21 The image shows a cross-sectional view taken from line HH of the optical integrated circuit wafer.

[0048] Figure 23 This is a schematic plan view illustrating an example of an optical fiber coupling structure;

[0049] Figure 24 It is along Figure 23 The cross-sectional view of line JJ of the fiber coupling structure shown; and

[0050] Figure 25 This is a diagram illustrating an example of a problem with fiber optic coupling structures. Detailed Implementation

[0051] Preferred embodiments of the invention will be explained with reference to the accompanying drawings. Furthermore, the invention is not limited to the described embodiments. Additionally, the embodiments described below can be used in any suitable combination without conflicting with each other.

[0052] [a] First implementation method

[0053] Figure 1 This is a schematic cross-sectional view illustrating an example of an optical coupler 1 according to the first embodiment. Figure 1 The optical coupler 1 shown is a hollow-type optical integrated device. The optical coupler 1 includes: a Si substrate 2; an optical waveguide 40 disposed above the Si substrate 2 and having a hollow structure, in which the portion surrounding the optical waveguide 40 is a hollow cavity; and an outer cladding layer 3. The Si substrate 2 has a cut-end surface 7A formed when a pair of optical couplers 1 are cut from the optical integrated circuit wafer 10 described later. The hollow cavity is an air layer 6. The outer cladding layer 3 is, for example, a layer made of SiO2.

[0054] Optical waveguide 40 includes a first optical waveguide 4 and a second optical waveguide 5. The second optical waveguide 5 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 made of, for example, Si and is a semiconductor or dielectric material with a large relative refractive index difference. The first optical waveguide 4 has an SSC structure formed in an inverted tapered manner. The second optical waveguide 5 is made of, for example, SiO2. The second optical waveguide 5 includes a tapered portion 5B whose width increases toward the output end surface 5A, which serves as the front end. Furthermore, the optical fiber 21 optically coupled to the second optical waveguide 5 included in the optical coupler 1 is, for example, a single-mode fiber (SMF). The optical coupler 1 has the function of converting the mode diameter to the mode diameter of the SMF according to the travel of light from the first optical waveguide 4 to the second optical waveguide 5.

[0055] The optical coupler 1 includes a recessed portion 7 formed near a dicing line DL on the Si substrate 2. By forming the recessed portion 7, the width of the output end surface 5A is smaller than the core width of the optical fiber 21 optically coupled to the output end surface 5A in the axial direction of the optical waveguide 40, where it protrudes further than the output end surface 5A. The recessed portion 7 has a limited width and a recessed structure that is manufactured differently from the output end surface 5A and the dicing end surface 7A. By forming the recessed portion 7, the Si substrate 2 includes a wall surface 7B flush with the output end surface 5A and a bottom surface 7C extending vertically from the wall surface 7B.

[0056] Figure 2 This is a schematic plan view of the optical coupler 1. It is desirable that the width w of the recessed portion 7 is smaller than the width of the capillary 22 included in the optically coupled fiber 21. Furthermore, the capillary 22 included in the fiber 21 has a square shape with a side length of approximately 1000 μm. The width w of the recessed portion 7 needs to be increased to a degree that does not obstruct the light emitted from the output end surface 5A of the second optical waveguide 5 included in the optical coupler 1 and radially propagating. Therefore, the width w of the recessed portion 7 can be expressed as w ≥ 2d*(λ / πD). Here, λ represents the wavelength of the light passing through the optical coupler 1, d represents the depth of the recessed portion 7, and D represents the mode diameter. The width w of the recessed portion 7 is smaller than the diameter of the front end of the SMF optically coupled to the output end surface 5A of the second optical waveguide 5 included in the optical coupler 1.

[0057] Figure 3 It is along Figure 2 The diagram shows a cross-sectional view of line AA of the optical coupler 1. Furthermore, the height of the recessed portion 7 needs to be increased to a degree that does not obstruct the light emitted from the output surface 5A of the second optical waveguide 5 included in the optical coupler 1 and propagating radially. Therefore, the height h of the recessed portion 7 can be expressed as h ≥ d*(λ / πD). The height h of the recessed portion 7 is the vertical distance between the bottom surface 7C of the recessed portion 7 formed on the Si substrate 2 and the upper surface of the second optical waveguide 5. Additionally, the depth d of the recessed portion 7 is, for example, 30 μm; the width w of the recessed portion 7 is, for example, 200 μm; and the height h of the recessed portion 7 is, for example, 100 μm.

[0058] By cutting the Si substrate 2 on the optical integrated circuit wafer 10 along the dicing line DL, the optical coupler 1 can be cut from the optical integrated circuit wafer 10. Therefore, the optical integrated circuit wafer 10 will be described. Figure 4 This is a schematic plan view of optical integrated circuit wafer 10, and Figure 5 It is along Figure 4 The cross-sectional view of line BB of the optical integrated circuit wafer 10 shown is shown.

[0059] Figure 4 The optical integrated circuit wafer 10 shown 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 disposed as one of the optical couplers 1A, a second substrate 2B disposed as the other optical coupler 1B, and a pair of recessed portions 7 formed near the dicing line DL between the first substrate 2A and the second substrate 2B.

[0060] Near the cleavage line DL connecting one optical coupler 1A and another optical coupler 1B, a pair of recessed portions 7 are formed on the Si substrate 2. As a result, the output end surface 5A of the second optical waveguide 5 included in one optical coupler 1A faces the output end surface 5A of the second optical waveguide 5 included in the other optical coupler 1B in a separated manner, and the width of the output end surface 5A of the second optical waveguide 5 is smaller than the core width of the SMF optically coupled to the output end surface 5A.

[0061] Next, the fiber coupling structure 20 that performs optical coupling to the optical fiber 21 relative to the optical coupler 1 cut from the optical integrated circuit wafer 10 will be described. Figure 6 This is a schematic plan view of the fiber optic coupling structure 20, and Figure 7 It is along Figure 6 The cross-sectional view of line CC of the fiber coupling structure 20 shown.

[0062] Figure 6 The fiber coupling structure 20 shown has a structure in which optical coupling is performed on the portion between the output end surface 5A of the second optical waveguide 5 and the optical fiber 21 via a capillary 22 included in the optical fiber 21 by filling an adhesive into the portion formed by the output end surface 5A and the recessed portion 7 of the second optical waveguide 5.

[0063] Figure 8 This is a schematic plan view of the fiber optic coupling structure 20. On the surfaces where the optical coupler 1 and the optical fiber 21 are optically coupled, the portion other than the recessed portion 7 corresponds to the contact surface D1, thereby increasing the contact area between the optical coupler 1 and the optical fiber 21. This allows for a robust 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 strengthened, preventing the risk of the optical fiber 21 rotating.

[0064] The method for manufacturing the optical coupler 1 will be described below. Figure 9A This is a diagram illustrating an example of a silicon-on-insulator (SOI) substrate used for an optical integrated circuit wafer 10. Figure 9AThe SOI substrate shown 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-shaped layer. The Si layer 13 is a layer used to form the first optical waveguide 4 included in the optical coupler 1. In addition, 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. In addition, for ease of explanation, there are cases where the Si substrate 11 is not shown in the figures, except for some figures. Furthermore, regarding the structure of the optical integrated circuit wafer 10, in addition to the fiber coupling structure, there may be structures required for modulators, optical receivers, etc., such as doping steps; however, it is assumed that such steps are omitted.

[0065] Figure 9B This is a diagram illustrating an example of the formation steps of a first optical waveguide 4 included in an optical integrated circuit wafer 10. Figure 9B On the SiO2 layer 12 shown, a first optical waveguide 4 is formed by etching a Si layer 13 disposed on the SiO2 layer 12. Specifically, a SiO2 film 12A is formed using plasma CVD, and a pattern of the first optical waveguide 4 is formed using photoresist. The pattern is formed such that the width of the first optical waveguide 4 is, for example, 460 nm, and the width of the front end of the inverted conical SSC is, for example, 140 nm. The pattern of the first optical waveguide 4 is formed by dry etching using the pattern as a mask. On the Si layer 13, a first optical waveguide 4 having an inverted conical SSC structure for increasing the mode diameter of the first optical waveguide 4 to the mode diameter of the second optical waveguide 5, and a Si optical waveguide 41 for guiding light to the first optical waveguide 4 are formed.

[0066] Figure 9C This diagram illustrates an example of the formation steps of the outer coating layer 3 on the optical integrated circuit wafer 10. After the first optical waveguide 4 is formed on the SiO2 layer 12, as shown... Figure 9C As shown, a SiO2 film 12A is formed on the first optical waveguide 4 and the SiO2 layer 12, and an outer cladding layer 3 of the SiO2 layer 12 is formed on the Si substrate 11. Specifically, the outer cladding layer 3 is formed by forming the SiO2 film on the Si substrate 11 using a plasma CVD method. The thickness of the outer cladding layer 3 is assumed to be, for example, 5 μm. The first optical waveguide 4 is formed with the first optical waveguide 4 surrounded by the SiO2 layer; therefore, light confined within the Si propagates through the waveguide due to the relative refractive index difference between Si and SiO2.

[0067] Figure 10A This is a diagram illustrating an example of the resist step in forming an optical coupler 1 included in an optical integrated circuit wafer 10. (See diagram for example.) Figure 10A As shown, the photoresist layer 15 is disposed at the following location, where a photoresist layer is formed. Figure 9C The cavity shown is an air layer 6 disposed on the outer covering layer 3.

[0068] Figure 10B This is a schematic plan view of the optical integrated circuit wafer 10 during the formation of the optical coupler 1, and Figure 10C It is along Figure 10B The image shows a cross-sectional view taken from line DD of the optical integrated circuit wafer 10. (Regarding...) Figure 10B The optical integrated circuit wafer 10 shown has SiO2 layer 12 and Si layer 13 disposed on it. Figure 10A Dry etching is performed on the portion of the optical integrated circuit wafer 10 other than the portion masked by the photoresist layer 15. Then, as a result of this dry etching, the air layer 6 hollows out the portion surrounding the optical waveguide 40, which includes the first optical waveguide 4 and the second optical waveguide 5. As a result, a pair of optical couplers 1 with a hollow form are formed on the optical integrated circuit wafer 10. Specifically, dry etching is performed on the SiO2 layer 12 using this pattern as a mask, and then wet etching is performed on the Si substrate 11 to form a hollow structure in which the portion surrounding the SiO2 layer 12 is surrounded by the air layer 6. Due to the relative refractive index difference between the SiO2 layer 12 and the air layer 6, this structure functions as the optical coupler 1.

[0069] Figure 11A This is a schematic plan view of the completed optical integrated circuit wafer 10. On the optical integrated circuit wafer 10, a pair of recessed portions 7 are formed on the Si substrate 11 near the output end surface 5A of the second optical waveguide 5 included in the optical coupler 1 by etching. The depth D of the recessed portion 7 is, for example, 30 μm; the width w of the recessed portion 7 is, for example, 200 μm; and the height h of the recessed portion 7 is, for example, 100 μm.

[0070] Figure 11B It is along Figure 11A The image shown is a cross-sectional view of line EE taken from the completed optical integrated circuit wafer 10. (About...) Figure 11B The optical integrated circuit wafer 10 shown is... Figure 1 The pair of optical couplers 1 shown can be cut by cutting the dicing line DL included in the recessed portion 7 and formed on the Si substrate 11 (2). Alternatively, the cutting can be achieved by, for example, stealth cutting using a laser, blade cutting, scribing, etc.

[0071] The optical coupler 1 according to the first embodiment includes a first optical waveguide 4 and a second optical waveguide 5. The second optical waveguide 5 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 recessed portion 7, which is formed near a cleaving line DL on the Si substrate 2 such that the width of the output end surface 5A is smaller than the core width of the optical fiber 21, and in this state, the output end surface 5A protrudes further than the cleaving end surface 7A in the axial direction of the optical waveguide 40. As a result, optical coupling loss during optical coupling with the optical fiber 21 can be suppressed. It can be connected to an optical fiber 21 with a normal diameter, allowing for a large tolerance profile. Furthermore, regarding the wall surface 7B of the recessed portion 7 on the Si substrate 2 included in the optical coupler 1, high reliability can be ensured because the rotation of the optical fiber 21 is suppressed by the expansion and contraction of the adhesive caused by increasing the contact area during optical coupling on the optical fiber 21.

[0072] Optical coupler 1 converts the mode diameter to the mode diameter of optical fiber 21 based on the travel of light from the first optical waveguide 4 to the second optical waveguide 5. As a result, optical coupling between optical coupler 1 and optical fiber (i.e., SMF) can be performed.

[0073] The width w of the recessed portion 7 included in the optical coupler 1 is calculated based on w≥2d*(λ / πD). As a result, the recessed portion 7 can be increased to a degree that does not block the light emitted from the output end surface 5A of the second optical waveguide 5 included in the optical coupler 1 and spread radially.

[0074] The height h of the recessed portion 7 of the optical coupler 1 is calculated based on h ≥ d*(λ / πD). As a result, the recessed portion 7 can be increased to a degree that does not block the light emitted from the output end surface 5A of the second optical waveguide 5 included in the optical coupler 1 and spread radially.

[0075] The optical coupler 1 is constructed by partially filling the area formed by the output end surface 5A of the second optical waveguide 5 and the recessed portion 7 with adhesive, and performs optical coupling to the optical fiber 21 relative to the output end surface 5A of the second optical waveguide 5. As a result, the optical coupler 1 is capable of optical coupling to the optical fiber 21.

[0076] On the optical integrated circuit wafer 10, a pair of optical couplers 1, each having the same structure, are disposed on the Si substrate 2 with the optical couplers 1 facing each other in a separated manner at the dicing line DL. As a result, a pair of optical couplers 1 can be cut from the optical integrated circuit wafer 10 by cutting along the dicing line DL.

[0077] In a conventional optical integrated circuit wafer 110A, to prevent damage to the optical coupler 100 during the dicing process, the recessed portion 109 is configured to protrude beyond the front end of the SiO2 waveguide 106 included in the hollow coupler. Therefore, when a portion of the recessed portion 109 is diced and the diced end surface 101A contacts the capillary 123 included in the optical fiber 121, the contact surface has an asymmetric structure, causing the optical axis to shift due to the rotation of the optical fiber 121 caused by the bulging, expansion, and contraction of the adhesive.

[0078] In contrast, regarding the optical integrated circuit wafer 10 according to this embodiment, the width of the recessed portion 7 is limited, and the width of the capillary 22 leading to the optical fiber 21 is not increased. This results in a specific portion of the diced end surface 7A located between the surface and bottom surface of the chip, capable of being bonded to the capillary 22, being located at both ends of the recessed portion 7. Therefore, when the target portion and the capillary 22 included in the optical fiber 21 are bonded using an adhesive, even if the adhesive entering the recessed portion 7 bulges, expands, and contracts due to heat, rotation of the optical fiber 21 can be prevented. In other words, optical coupling loss caused by optical axis misalignment can be suppressed. Furthermore, compared to the contact area used in conventional structures, the bonding strength is improved because the contact area between the capillary 22 included in the optical fiber 21 and the diced end surface 7A is increased. Therefore, while using an optical coupler 1 capable of connecting to an optical fiber 21 with a normal diameter, the contact area between the optical fiber 21 and the diced end surface 7A of the optical integrated circuit wafer 10 can be increased. As a result, rotation of the optical fiber 21 caused by the expansion and contraction of the adhesive can be suppressed, thereby suppressing optical coupling loss.

[0079] Furthermore, for ease of explanation, the above description uses the case where the material of the first optical waveguide 4 is Si and the material of the second optical waveguide 5 is SiO2 as an example; however, the materials are not limited to those mentioned above. For example, SiN, SiON, etc., can be used, as long as the refractive index of the first optical waveguide 4 is greater than the refractive index of the second optical waveguide 5, appropriate modifications can be made. The material of the first optical waveguide 4 is a material including Si, and the material of the second optical waveguide 5 is a material including Si and having a specific refractive index smaller than that of the first optical waveguide 4. In addition, the material of the first optical waveguide 4 includes, for example, Si, SiN, SiON, SiO2, etc. In some cases, when the material used for the first optical waveguide 4 is SiN and the material used for the second optical waveguide 5 is SiO2, a structure that converts the Si waveguide to a SiN waveguide can exist immediately before the SiN waveguide.

[0080] As an example, the following situation is described, in which, in optical coupler 1, optical waveguide 40 has a hollow structure and is formed by an air layer 6 surrounded by a hollow cavity; however, instead of air layer 6, an optical waveguide surrounded by adhesive can be used, which can be modified appropriately.

[0081] Furthermore, as an example, a case is described in which the recessed portion 7 is formed such that the orientation of the output end surface 5A of the second optical waveguide 5 included in the optical coupler 1 according to the first embodiment is the same as the orientation of the diced end surface 7A on the Si substrate 2. However, the orientation of the output end surface 5A of the second optical waveguide 5 is not limited to this. The orientation of the output end surface 5A of the optical coupler 1 may be different from the orientation of the diced end surface 7A, and its embodiment is described below as a second embodiment. In addition, by assigning the same reference numerals to components having the same structure as the optical coupler 1 according to the first embodiment, repeated descriptions of this structure and its operation will be omitted.

[0082] [b]Second Implementation

[0083] Figure 12 This is a schematic plan view illustrating an example of an optical fiber coupling structure 20A according to the second embodiment. The optical coupler 1 is disposed on the Si substrate 2 such that the orientation of the output end surface 5A, included in the second optical waveguide 5, is tilted relative to the orientation of the diced end surface 7A. Then, a recessed portion 71 is formed near the dicing line DL on the Si substrate 2 at a position between the output end surface 5A and the diced end surface 7A.

[0084] For the fiber coupling structure 20A, optical coupling can be achieved at the portion between the output end surface 5A of the second optical waveguide 5 and the optical fiber 21 by filling the portion formed by the recessed portion 71 and the output end surface 5A of the second optical waveguide 5 with adhesive, via the capillary 22 attached to the core 25 of the optical fiber 21.

[0085] Furthermore, as an example, a case is described in which the recessed portion 7 is formed such that the orientation of the output end surface 5A of the second optical waveguide 5 included in the optical coupler 1 according to the first embodiment is the same as the orientation of the diced end surface 7A on the Si substrate 2. However, the orientation of the diced end surface 7A is not limited to this, and its implementation is described below as a third embodiment.

[0086] [c] Third Embodiment

[0087] Figure 13This is a cross-sectional view of the fiber coupling structure 20A according to the third embodiment. A diced end surface 7A1 is formed on the Si substrate 2, diagonally inclined from the vertical direction Y, which is orthogonal to the axial direction X of the optical waveguide 40. A recessed portion 72 is formed near the dicing line DL on the Si substrate 2, located between the output end surface 5A and the diced end surface 7A1.

[0088] Regarding the fiber coupling structure 20A, optical coupling can be performed at the portion between the output end surface 5A of the second optical waveguide 5 and the optical fiber 21 via a capillary 22 attached near the core 25 of the optical fiber 21 by filling the portion formed by the recessed portion 72 and the output end surface 5A of the second optical waveguide 5 with adhesive.

[0089] [d] Fourth Implementation Method

[0090] Figure 14 This is a schematic plan view of the optical integrated circuit wafer 10A according to the fourth embodiment. Figure 14 The Si substrate 2 shown includes a first substrate 2A having an optical coupler 1A, a second substrate 2B having another optical coupler 1B, and a recessed portion 7 formed near a cut line DL in the portion located between the first substrate 2A and the second substrate 2B.

[0091] The optical integrated circuit wafer 10A includes a routing optical waveguide 8 disposed across a dicing line DL on a first substrate 2A and a second substrate 2B, parallel to an optical waveguide 40 included in one optical coupler 1A and another optical waveguide 40 included in another optical coupler 1B. The routing optical waveguide 8 is an optical waveguide that includes an input unit 8A, for example, for receiving test light input.

[0092] Furthermore, by limiting the width of the recessed portion 7, the degree of freedom in routing the waveguide used for testing the wafer can be increased before the dicing process is performed. For a conventional optical integrated circuit wafer 110A, to simplify the dicing process, a recessed portion 109 is provided across the entire area of ​​the dicing line DL, making it impossible to route the optical waveguide within the recessed portion. In contrast, for the optical integrated circuit wafer 10A according to this embodiment, the width of the recessed portion 7 is limited, thus allowing the routing optical waveguide 8 to be routed across the dicing line DL outside the recessed portion 7, enabling the routing optical waveguide 8 to be used as long as the dicing process has not yet been performed.

[0093] [e] Fifth Implementation

[0094] Figure 15 This is a schematic plan view of the optical integrated circuit wafer 10B according to the fifth embodiment. Figure 15The Si substrate 2 shown includes a first substrate 2A with an optical coupler 1A, a second substrate 2B with another optical coupler 1B, and a recessed portion 7 located near a dicing line DL in the portion between the first substrate 2A and the second substrate 2B. The optical integrated circuit wafer 10B includes a routing waveguide 9 that passes from one optical coupler 1A through the recessed portion 7 across the dicing line DL and through the other optical coupler 1B. The routing waveguide 9 is an optical waveguide that receives input test light. The routing waveguide 9 has a terminal 9A.

[0095] As a light incidence method that does not utilize the optical end surface, there exists a grating coupler for inputting light from the chip surface of the optical integrated circuit wafer 10B. With a grating coupler, optical measurements can be performed before the dicing process; however, if the grating coupler is placed inside the manufactured chip, the chip area increases. Therefore, to prevent this increase in chip area, the grating coupler is placed outside the manufactured chip and used as a discard port during the dicing process. By limiting the width of the recessed portion 7, waveguide routing from the dicing line DL on the optical end surface is also possible, thus increasing the degrees of freedom.

[0096] [f] Sixth implementation method

[0097] Figure 16 This is a schematic plan view of the fiber optic coupling structure 20B according to the sixth embodiment. Furthermore, by assigning the same reference numerals to components having the same structure as those in the optical coupler 1 according to the first embodiment, repeated descriptions of the structure and its operation will be omitted. Figure 16 The fiber coupling structure 20B shown includes a Si substrate 2, three optical couplers 1 (1D) disposed on the Si substrate 2, three recessed portions 73, and an optical fiber array 21A including three cores 25A. On the Si substrate 2, each of the recessed portions 73 is formed at intervals of the optical couplers 1.

[0098] The fiber optic coupling structure 20B has the following structure: by filling the portion formed by the recessed portion 73 and the output end surface 5A of the respective second optical waveguide 5 included in the optical coupler 1 with adhesive, optical coupling is performed via capillary 22 between each of the output end surfaces 5A included in the respective second optical waveguide 5 and the core 25A of the fiber array 21A. In other words, optical coupling can be performed between the second optical waveguide 5 included in the respective three optical couplers 1 and the three cores 25A included in the fiber array 21A.

[0099] Each of the components in the unit shown in the accompanying drawings is not always physically configured as shown in the drawings. In other words, the specific shape of the individual unit or integrated unit is not limited to that shown in the drawings; however, all or part of the unit can be configured by functionally or physically separating or integrating any unit, depending on various loads or usage conditions.

Claims

1. An optical integrated device, the optical integrated device comprising: substrate; as well as An optical waveguide, wherein the optical waveguide is disposed on the substrate and has a hollow structure, wherein... The optical waveguide includes: First optical waveguide; and A second optical waveguide, optically coupled to the first optical waveguide and having a relative refractive index difference smaller than that of the first optical waveguide, and The optical waveguide converts the mode diameter into the mode diameter of the optical fiber based on the travel of light from the first optical waveguide to the second optical waveguide, and The optical integrated device includes a recessed portion formed near a dicing line on the substrate, such that the width of the recessed portion, including the output end surface of the second optical waveguide, is less than the width of a glass block made of a capillary mounted on the end of the optical fiber optically coupled to the output end surface. The recessed portion is formed in a state where the dicing end surface of the substrate protrudes further in the axial direction of the optical waveguide than the output end surface of the second optical waveguide, and the recessed portion has a width calculated using Equation 1: w≥2d*(λ / πD) λ: wavelength d: Depth of the recessed portion w: Width of the recessed portion w < the diameter of the front end of the glass block of the optical fiber, and D: Pattern diameter.

2. The optical integrated device according to claim 1, wherein, The recessed portion has a height calculated using the following formula 2: h≥d*(λ / πD) λ: wavelength d: Depth of the recessed portion h: the height of the recessed portion, and D: The diameter of the pattern.

3. The optical integrated device according to claim 1, wherein, The first optical waveguide is made of a material including Si, and The material of the second optical waveguide is a material comprising Si and having a specific refractive index that is smaller than that of the material used in the first optical waveguide.

4. The optical integrated device according to claim 1, wherein, The optical waveguide is disposed on the substrate such that the surface of the output end is inclined relative to the surface of the cut end.

5. The optical integrated device according to claim 1, wherein, The cut-off end surface is formed on the substrate in a direction that is diagonally inclined from a vertical direction orthogonal to the axial direction of the optical waveguide.

6. The optical integrated device according to claim 1, wherein, The optical fiber is coupled to the output end surface of the second optical waveguide by filling the portion formed by the output end surface of the second optical waveguide and the recessed portion with adhesive.

7. An optical integrated circuit wafer, the optical integrated circuit wafer comprising: substrate; as well as A pair of optical integrated devices, each of which is disposed on the substrate and includes an optical waveguide having a hollow structure, wherein... Each of the optical waveguides includes: First optical waveguide, and A second optical waveguide, optically coupled to the first optical waveguide and having a relative refractive index difference smaller than that of the first optical waveguide, and Each of the optical waveguides converts its mode diameter to the mode diameter of the optical fiber based on the travel of light from the first optical waveguide to the second optical waveguide, and The optical integrated circuit wafer includes a pair of recessed portions formed near a dicing line connecting portions between one optical integrated device and the other of the pair of optical integrated devices. The dicing line is positioned on the substrate such that the width of the recessed portion including the output end surface of each of the second optical waveguides is less than the width of a glass block made of a capillary mounted on the end of the optical fiber optically coupled to the output end surface. The pair of recessed portions are formed in a state in which the output end surface of the second optical waveguide included in one of the pair of optical integrated devices faces the output end surface of the second optical waveguide included in the other of the pair of optical integrated devices in a separated manner, and the recessed portion has a width calculated by Equation 1: w≥2d*(λ / πD) λ: wavelength d: Depth of the recessed portion w: Width of the recessed portion w < the diameter of the front end of the glass block of the optical fiber, and D: Pattern diameter.

8. The optical integrated circuit wafer according to claim 7, wherein, The substrate includes: A first substrate, on which the aforementioned optical integrated device is disposed. A second substrate, on which the other optical integrated device is disposed, and The recessed portion is disposed near the cut line located between the first substrate and the second substrate, and The optical integrated circuit wafer includes another optical waveguide disposed across the dicing line on the first substrate and the second substrate, parallel to the optical waveguides included in the one optical integrated device and the other optical integrated device.

9. The optical integrated circuit wafer according to claim 7, wherein, The substrate includes: A first substrate, on which the aforementioned optical integrated device is disposed. A second substrate, on which the other optical integrated device is disposed, and The recessed portion is disposed near the cut line located between the first substrate and the second substrate, and The optical integrated circuit wafer includes another optical waveguide that passes from one optical integrated device to the other optical integrated device through the recessed portion across the dicing line.

10. A method for manufacturing an optical integrated device by dicing an optical integrated device from an optical integrated circuit wafer, the optical integrated circuit wafer comprising: substrate; as well as A pair of optical integrated devices, each of which is disposed on the substrate and includes an optical waveguide having a hollow structure, and Each of the optical waveguides includes: First optical waveguide, and A second optical waveguide, optically coupled to the first optical waveguide and having a relative refractive index difference smaller than that of the first optical waveguide, and The optical waveguide converts the mode diameter into the mode diameter of the optical fiber based on the travel of light from the first optical waveguide to the second optical waveguide. The method for manufacturing the optical integrated device includes the following steps: A recessed portion is formed near a cleaving line connecting one optical integrated device to the other optical integrated device in the pair of optical integrated devices. The cleaving line is positioned on the substrate such that the width of the recessed portion including the output end surface of each of the second optical waveguides is less than the width of a glass block made of a capillary mounted on the end of an optical fiber optically coupled to the output end surface of each of the second optical waveguides. The recessed portion is formed in a state in which the output end surface of the second optical waveguide included in one of the pair of optical integrated devices faces the output end surface of the second optical waveguide included in the other of the pair of optical integrated devices in a separated manner. The recessed portion has a width calculated by Equation 1: w≥2d*(λ / πD) λ: wavelength d: Depth of the recessed portion w: Width of the recessed portion w < the diameter of the front end of the glass block of the optical fiber, and D: Model diameter; and The one optical integrated device and the other optical integrated device are cut from the optical integrated circuit wafer by cutting the dicing lines included in the recessed portion.

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