An optical waveguide mode spot conversion device and a method of manufacturing the same

Abstract

The application relates to the technical field of integrated optical chip, in particular to an optical waveguide mode spot conversion device and a manufacturing method thereof. The device comprises a semiconductor substrate, a lower waveguide, a cladding layer and an upper waveguide layer. The cladding layer is arranged on the semiconductor substrate. The lower waveguide with a wedge structure is arranged in the cladding layer. The upper waveguide layer is arranged on the cladding layer and is used for coupling the lower waveguide with a small head end and an optical fiber. The first refractive index of the upper waveguide layer is smaller than the second refractive index of the lower waveguide and is larger than the third refractive index of the cladding layer. An etching stripe is arranged on the upper surface of the upper waveguide layer and is close to the small head end of the lower waveguide. The etching stripe is arranged based on the position of the small head end of the lower waveguide and extends from the end surface of the upper waveguide layer along the extension direction of the lower waveguide. The etching stripe is used for limiting the mode spot size on the end surface of the upper waveguide layer. The sensitivity of the small head end size of the wedge-shaped waveguide to the mode spot size conversion can be reduced. The optical polarization-related loss is reduced. The process difficulty is reduced, and the mismatch loss of the mode spot conversion is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of integrated optical chip, in particular to an optical waveguide mode spot conversion device and a manufacturing method thereof. BACKGROUND

[0002] Silicon optical waveguide has the characteristics of small mode spot size, high integration, and can provide low loss and high performance solutions for optical interconnection, and gradually develops and is applied.

[0003] Because the end face size of the silicon optical waveguide and the ordinary single-mode optical fiber is quite different, there is a problem of high mismatch loss when the end face coupling is performed between the silicon optical waveguide and the ordinary optical fiber.

[0004] Usually, a mode spot conversion device is used to convert the mode spot size of the silicon optical waveguide to the mode spot size of the optical fiber, so as to reduce the mismatch loss. For example, a wedge-shaped waveguide is used to realize the mode spot conversion device. The wedge-shaped waveguide (equivalent to the lower waveguide described below) includes a large head end and a small head end. The large head end is used to couple with the silicon optical waveguide; the small head end is used to couple with the optical fiber; the width of the small head end of the wedge-shaped waveguide is very small (about 100 nm). The width of the wedge-shaped waveguide gradually narrows from the large head end to the small head end, which can expand the mode spot size of the silicon optical waveguide, and realize the matching of the mode spot of the silicon optical waveguide and the mode spot of the optical fiber.

[0005] However, because the mode spot size is very sensitive to the width and thickness of the waveguide (such as the wedge-shaped waveguide) of the mode spot conversion device, the process tolerance is small, and the uniformity of the mode spot conversion device is poor. For example, the mode spot size of the small head end of the wedge-shaped waveguide in the mode spot conversion device is related to the polarization direction of the input light of the large head end, which is easy to produce a large polarization-dependent loss, and has a great influence on the performance of the optical integrated chip, especially the performance of the optical receiver.

[0006] Therefore, it is urgent to provide an optical waveguide mode spot conversion device and a manufacturing method thereof, which can reduce the sensitivity of the mode spot size (the mode spot size enlarged at the optical fiber coupling end) to the size of the end of the waveguide (i.e. the optical fiber coupling end) in the mode spot conversion device; reduce the optical polarization-dependent loss; reduce the process difficulty, and reduce the mismatch loss of the mode spot conversion between the silicon optical waveguide and the optical fiber. SUMMARY

[0007] The embodiments of the present application provide an optical waveguide mode spot conversion device and a manufacturing method thereof, which can reduce the sensitivity of the mode spot size (the mode spot size enlarged at the optical fiber coupling end) to the size of the end of the waveguide (i.e. the optical fiber coupling end) in the mode spot conversion device; reduce the optical polarization-dependent loss; reduce the process difficulty, and reduce the mismatch loss of the mode spot conversion between the silicon optical waveguide and the optical fiber.

[0008] In one aspect, the embodiments of the present application provide an optical waveguide mode spot conversion device, comprising:

[0009] a semiconductor substrate, a lower waveguide, a cladding layer, and an upper waveguide layer.

[0010] The cladding layer is arranged on the semiconductor substrate;

[0011] The lower waveguide is arranged in the cladding layer, the lower waveguide is a wedge-shaped structure, and a large end of the lower waveguide is used for connecting with a silicon optical waveguide;

[0012] The upper waveguide layer is arranged on the cladding layer, the upper waveguide layer is used for coupling with an optical fiber at a small end of the lower waveguide; a first refractive index of the upper waveguide layer is smaller than a second refractive index of the lower waveguide and greater than a third refractive index of the cladding layer;

[0013] An etching stripe is arranged on an upper surface of the upper waveguide layer and close to the small end of the lower waveguide; the etching stripe is arranged based on a position of the small end of the lower waveguide and extends from an end surface of the upper waveguide layer along an extension direction of the lower waveguide; the etching stripe is used for limiting a mode spot size on the end surface of the upper waveguide layer.

[0014] In the embodiment, the semiconductor substrate is composed of a silicon substrate and a silicon oxide buried layer; the lower waveguide corresponds to a wedge-shaped waveguide, and the upper waveguide layer corresponds to an auxiliary waveguide layer. The cladding layer includes an upper cladding layer and a lower cladding layer; the upper cladding layer is a dielectric layer, and the lower cladding layer is an insulator layer.

[0015] In some optional embodiments, the etching stripe includes a first etching stripe and a second etching stripe; the first etching stripe and the second etching stripe are symmetrically arranged based on a transverse position of the small end of the lower waveguide.

[0016] In some optional embodiments, the etching stripe includes a third etching stripe, and a transverse position between the third etching stripe and the small end of the lower waveguide is consistent.

[0017] In some optional embodiments, a thickness of the upper waveguide layer is greater than 5 μm.

[0018] In some optional embodiments, the device further includes a cover layer, the cover layer is arranged on the upper waveguide layer, and a fourth refractive index of the cover layer is greater than or equal to the first refractive index of the upper waveguide layer.

[0019] In some optional embodiments, the fourth refractive index of the cover layer ranges between 1.448 and 1.47.

[0020] In some optional embodiments, a stripe width of the etching stripe ranges between 10 μm and 20 μm; a stripe depth of the etching stripe ranges between 1 μm and 2 μm.

[0021] In some optional embodiments, an extension length of the etching stripe ranges greater than or equal to 1 / 6 of an extension length of the lower waveguide.

[0022] In some optional embodiments, the interval distance between the first etching stripe and the second etching stripe ranges from 2 μm to 10 μm.

[0023] In another aspect, the application provides a method for manufacturing an optical waveguide mode spot conversion device, comprising:

[0024] depositing a lower cladding layer on a semiconductor substrate;

[0025] forming a lower waveguide with a wedge structure on the lower cladding layer by using a microelectronic process; a large-end of the lower waveguide is used for connecting with a silicon optical waveguide;

[0026] depositing an upper cladding layer on the lower cladding layer, the upper cladding layer covering the lower waveguide;

[0027] depositing an upper waveguide layer on the upper cladding layer; the upper waveguide layer is used for coupling with an optical fiber at a small-end of the lower waveguide; an end surface of the upper waveguide layer is used for coupling with the optical fiber;

[0028] etching on an upper surface of the upper waveguide layer based on a position of the small-end of the lower waveguide to obtain an etching stripe; the etching stripe extends from the end surface of the upper waveguide layer along an extension direction of the lower waveguide; a first refractive index of the upper waveguide layer is smaller than a second refractive index of the lower waveguide and larger than a third refractive index of the upper cladding layer.

[0029] The embodiments of the application provide an optical waveguide mode spot conversion device, which comprises a semiconductor substrate, a lower waveguide, a cladding layer and an upper waveguide layer; the cladding layer is arranged on the semiconductor substrate; the lower waveguide is arranged in the cladding layer, the lower waveguide has a wedge structure, and a large-end of the lower waveguide is used for connecting with a silicon optical waveguide; the upper waveguide layer is arranged on the cladding layer, and the upper waveguide layer is used for coupling with an optical fiber at a small-end of the lower waveguide; a first refractive index of the upper waveguide layer is smaller than a second refractive index of the lower waveguide and larger than a third refractive index of the cladding layer; an etching stripe is arranged on an upper surface of the upper waveguide layer and close to the small-end of the lower waveguide; the etching stripe is arranged based on a position of the small-end of the lower waveguide and extends from an end surface of the upper waveguide layer along an extension direction of the lower waveguide; and the etching stripe is used for limiting a mode spot size on the end surface of the upper waveguide layer. The sensitivity of the mode spot size (the mode spot size after amplification at the optical fiber coupling end) to the size of the end of the waveguide (i.e. the optical fiber coupling end) in the mode spot conversion device can be reduced; the optical polarization related loss can be reduced; the process difficulty can be reduced, and the mismatch loss of the mode spot conversion between the silicon optical waveguide and the optical fiber can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0031] Figure 1 is an application scenario of a mode spot conversion device provided by the embodiments of the present application;

[0032] Figure 2A is a schematic view of an end surface structure of the mode spot conversion device in some embodiments;

[0033] Figure 2B is a schematic view of the mode spot conversion device along M-M in some embodiments; Figure 2A

[0034] Figure 2C is a schematic view of the mode spot conversion device along N-N in some embodiments; Figure 2A

[0035] is a schematic view of an end surface structure of an optical waveguide mode spot conversion device provided by the embodiments of the present application; Figure 3A

[0036] is a schematic view of the optical waveguide mode spot conversion device along O-O in some embodiments; Figure 3B Figure 3A is a schematic view of the optical waveguide mode spot conversion device along Q-Q in some embodiments;

[0037] Figure 3C Figure 3A is a schematic view of an end surface structure of another optical waveguide mode spot conversion device provided by the embodiments of the present application;

[0038] Figure 3D is a schematic view of the optical waveguide mode spot conversion device along R-R in some embodiments;

[0039] Figure 3E is a manufacturing method of an optical waveguide mode spot conversion device provided by the embodiments of the present application; Figure 3A

[0040] is a schematic view of an end surface structure of another optical wave mode spot conversion device provided by the embodiments of the present application. Figure 4 The meanings of the reference signs in the drawings are as follows:

[0041] Figure 5 The meanings of the reference signs in the drawings are as follows:

[0042] The meanings of the reference signs in the drawings are as follows:

[0043] ​​​1 - optical fiber; 2 - silicon optical waveguide; 3 - mode spot conversion device; 31 - wedge waveguide; 32 - silicon substrate; 33 - insulator layer; 34 - dielectric layer; 35 - auxiliary waveguide layer; 36 - silicon layer; 37 - silicon waveguide; 38 - silicon oxide buried layer; T1 - first etched stripe; T2 - second etched stripe; T3 - third etched stripe. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0045] The term "one embodiment" or "an embodiment" as used herein means that a particular feature, structure, or characteristic described can be included in at least one implementation of the present application. In the description of the application, it should be understood that the terms "upper", "top", "bottom", and "under" indicate the relative position or orientation of the device or element as shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can be explicitly or implicitly included one or more of the features. Moreover, the terms "first", "second", etc. are used to distinguish similar objects, and do not necessarily describe a particular order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than those illustrated or described herein.

[0046] First, the application scenarios of the mode spot conversion device are exemplarily introduced.

[0047] Please refer to Figure 1 , Figure 1 The application scenario of the mode spot conversion device provided in the embodiments of the present application is shown in FIG. 1.

[0048] As Figure 1As shown, the end-face dimensions of silicon optical waveguide 1 and optical fiber 2 differ significantly, resulting in a large difference in the end-face mode size between optical fiber 2 and silicon optical waveguide 1. Therefore, when silicon optical waveguide 1 and optical fiber 2 are end-face coupled, there is a problem of high optical loss due to mode mismatch. A mode conversion device 3 is used to convert the mode size of silicon optical waveguide 1 to the mode size of optical fiber 2, or vice versa, to reduce the optical loss caused by mode mismatch.

[0049] Figure 2A These are schematic diagrams of the end face structure of the pattern conversion device in some embodiments; Figure 2B yes Figure 2A A schematic diagram of the cross-section of the intermediate mold spot conversion device along the MM; Figure 2C yes Figure 2A A schematic diagram of the intermediate mode conversion device along the cross section of NN. (See diagram below.) Figure 2A , Figure 2B and Figure 2C As shown, the mode conversion device 3 includes a wedge waveguide 31, which is used to amplify the mode along the extension direction of the wedge waveguide 31 (i.e., gradually amplify the mode from the large end to the small end).

[0050] like Figure 2B As shown, the wedge-shaped waveguide 31 has a uniform thickness; as Figure 2C As shown, the lateral width of the wedge waveguide 31 gradually decreases along its extension direction, and the end of the wedge waveguide 31 along its extension direction is the small end. The end face of the small end of the wedge waveguide 31 is parallel to... Figure 1 The end face of fiber 2 shown is matched and aligned; the end face of the large end of wedge waveguide 31 is aligned with... Figure 1 The end face connection of silicon optical waveguide 1 shown.

[0051] As mentioned earlier, the mode spot size at the small end of the wedge waveguide 31 is highly sensitive to the end face size of the small end of the wedge waveguide 31, resulting in small process tolerances and poor uniformity of the wedge waveguide 31. The mode spot size at the small end of the wedge waveguide 31 in the mode conversion device 3 is related to the polarization direction of the output light from the silicon optical waveguide 1. This can easily lead to significant polarization-dependent insertion loss at the small end of the wedge waveguide 31, which greatly affects the performance of the optical integrated chip (especially the performance of the optical receiver). Furthermore, limiting the material width of the end face where the mode spot is located by the trench, and thus limiting the mode spot size, increases process complexity.

[0052] Based on the above problems, the embodiment of the present application provides an optical waveguide mode spot conversion device, which comprises a semiconductor substrate, a lower waveguide, a cladding layer and an upper waveguide layer; the cladding layer is arranged on the semiconductor substrate; the lower waveguide is arranged in the cladding layer, the lower waveguide is in a wedge-shaped structure, and a large head end of the lower waveguide is used for being connected with a silicon optical waveguide; the upper waveguide layer is arranged on the cladding layer, and the upper waveguide layer is used for being coupled with an optical fiber at a small head end of the lower waveguide; a first refractive index of the upper waveguide layer is smaller than a second refractive index of the lower waveguide and greater than a third refractive index of the cladding layer; an etching stripe is arranged on an upper surface of the upper waveguide layer and close to the small head end of the lower waveguide; the etching stripe is arranged based on the position of the small head end of the lower waveguide and extends from an end surface of the upper waveguide layer along the extension direction of the lower waveguide; and the etching stripe is used for limiting the mode spot size on the end surface of the upper waveguide layer. By coupling the small head end of the wedge-shaped waveguide with the optical fiber through the auxiliary waveguide layer, the sensitivity of the mode spot size (the mode spot size amplified at the optical fiber coupling end) to the size of the end (i.e. the optical fiber coupling end) of the waveguide in the mode spot conversion device can be reduced, the optical polarization loss is reduced, by arranging the etching stripe, the mode spot size and position on the end surface of the auxiliary waveguide layer are limited, without arranging a groove, the process difficulty is reduced, and the mismatch loss of the mode spot conversion between the silicon optical waveguide and the optical fiber is reduced.

[0053] The following introduces a specific embodiment of an optical waveguide mode spot conversion device, Figure 3A is a schematic view of an end surface structure of a small head end of an optical waveguide mode spot conversion device provided by the embodiment of the present application; Figure 3B is Figure 3A is a schematic view of a section along O-O of the optical waveguide mode spot conversion device in Figure 3A The optical waveguide mode spot conversion device 3 (i.e. corresponding to the mode spot conversion device 3) comprises:

[0054] a semiconductor substrate, a lower waveguide, a cladding layer and an upper waveguide layer;

[0055] Specifically, the semiconductor substrate comprises a silicon substrate 32 and a silicon oxide buried layer 38; the lower waveguide is a wedge-shaped waveguide 31; the cladding layer comprises an upper cladding layer and a lower cladding layer, wherein the upper cladding layer is a dielectric layer 34, and the lower cladding layer is an insulator layer 33; and the upper waveguide layer is an auxiliary waveguide layer 35.

[0056] the lower waveguide is arranged in the cladding layer, the lower waveguide is in a wedge-shaped structure, and a large head end of the lower waveguide is used for being connected with a silicon optical waveguide;

[0057] Specifically, the wedge waveguide 31 is arranged on the insulator layer 33; the insulator layer 33 is arranged on the buried silicon oxide layer 38; the buried silicon oxide layer 38 is arranged on the silicon substrate 32; and the big end of the wedge waveguide 31 is used to connect with the silicon optical waveguide 1. The dielectric layer 34 is arranged on the insulator layer 33 and surrounds the wedge waveguide 31.

[0058] The upper waveguide layer is arranged on the cladding layer, and is used to couple with the optical fiber at the small end of the lower waveguide; the first refractive index of the upper waveguide layer is smaller than the second refractive index of the lower waveguide and larger than the third refractive index of the cladding layer.

[0059] Specifically, the auxiliary waveguide layer 35 is arranged on the dielectric layer 34 and extends along the extension direction of the wedge waveguide 31; the auxiliary waveguide layer 35 is used to couple with the optical fiber 2 at the small end of the wedge waveguide 31; the first refractive index of the auxiliary waveguide layer 35 is smaller than the second refractive index of the wedge waveguide 31 and larger than the third refractive index of the dielectric layer 34. Figure 1

[0060] The upper surface of the upper waveguide layer is provided with an etching stripe near the small end of the lower waveguide; the etching stripe is arranged based on the position of the small end of the lower waveguide and extends along the extension direction of the lower waveguide from the end surface of the upper waveguide layer; and the etching stripe is used to limit the size of the mode spot on the end surface of the upper waveguide layer.

[0061] Specifically, the upper surface of the auxiliary waveguide layer 35 is provided with an etching stripe; the transverse position of the etching stripe is arranged based on the transverse position of the small end of the wedge waveguide 31 and extends along the extension direction of the wedge waveguide 31; and the etching stripe is used to limit the size and position of the mode spot on the end surface of the auxiliary waveguide layer 35.

[0062] In the above embodiments, by arranging the etching stripe, the area near the end surface of the upper waveguide layer (i.e. the auxiliary waveguide layer 35) where the mode spot appears has structural inhomogeneity, thereby limiting the size and position of the mode spot.

[0063] With reference to Figure 3A , Figure 3B and Figure 3C , in some optional embodiments, the etching stripe includes a first etching stripe T1 and a second etching stripe T2; the first etching stripe T1 and the second etching stripe T2 are symmetrically arranged based on the transverse position of the small end of the wedge waveguide 31 (i.e. the lower waveguide). In this way, the mode spot on the end surface of the auxiliary waveguide layer 35 is clamped between the first etching stripe T1 and the second etching stripe T2, i.e. the size and position of the mode spot are limited.

[0064] ​In some alternative embodiments, a thin film layer with a higher refractive index than silicon dioxide is generated using PECVD (Plasma Enhanced Chemical Vapor Deposition) technology as an auxiliary waveguide layer 35. The end face of this auxiliary waveguide layer 35 is used for matching and coupling with the end face of the optical fiber 2. Etching stripes are formed on the upper surface of the auxiliary waveguide layer 35, based on the lateral position of the small end of the wedge-shaped waveguide 31, which allows control over the mode size on the end face of the auxiliary waveguide layer 35. Without the need for trenches to form a complete rectangular waveguide, the extension of the end face mode size can be limited simply by etching stripes obtained from shallow etching of the upper surface, thus significantly reducing process complexity.

[0065] For example, such as Figure 3B As shown, since the first refractive index of the auxiliary waveguide layer 35 is less than the second refractive index of the wedge waveguide 31, the input light P will propagate in the wedge waveguide 31. Because the width of the wedge waveguide 31 gradually decreases along the direction of light propagation, the light will gradually pass through the dielectric layer 33 and enter the auxiliary waveguide layer 35. Finally, the light is output from the auxiliary waveguide layer 35 (the small end of the wedge waveguide) to the optical fiber 2. The mode size and position are limited by the first etched fringe T1 and the second etched fringe T2.

[0066] In the above embodiments, by setting an auxiliary waveguide layer 35 with a larger end face to match and couple with the end face of the optical fiber, the sensitivity of the mode spot size of the optical fiber to the waveguide tail end (i.e., the small end of the wedge waveguide 31) size of the mode spot conversion device can be reduced; optical polarization-dependent loss can be reduced; and the mismatch loss of mode spot conversion between silicon waveguide 1 and optical fiber 2 can be reduced, thereby improving the performance of the optical chip based on the above-mentioned mode spot conversion device. Furthermore, the end face of the auxiliary waveguide layer 35 can be set to be much larger than the end face size of the small end of the wedge waveguide 31. By setting etching stripes, the mode spot size and position on the end face of the auxiliary waveguide layer 35 can be limited, eliminating the need for trenches. Thus, when the end face of the auxiliary waveguide layer 35 is matched and coupled with the end face of the optical fiber 2, the alignment accuracy requirements can be reduced, and the process difficulty can be lowered. For example, compared to trench etching, the etching of etched stripes requires lower mechanical strength of the waveguide layer and cladding, has stronger anti-interference ability during etching, and improves alignment efficiency.

[0067] See Figure 3C In some optional embodiments, the etching stripe includes a third etching stripe T3, which is aligned with the lateral position of the small end of the wedge waveguide 31 (i.e., the lower waveguide mentioned above).

[0068] Thus, when the auxiliary waveguide layer 35 is thicker, the width of the mode spot on the end face of the auxiliary waveguide layer 35 can be more effectively limited; at the same time, the length of the mode spot can be limited.

[0069] For example, in some optional embodiments, the thickness of the auxiliary waveguide layer 35 (i.e. the upper waveguide layer mentioned above) is greater than 5 μm. When the thickness of the auxiliary waveguide layer 35 is greater than 5 μm, the effect on the mode spot width is greater, and the third etching stripe T3 is used to limit the mode spot size and position, which has a better mode spot size limiting effect, i.e. the target size is closer to the cross-sectional size of the fiber 2.

[0070] In some optional embodiments, the device further comprises a cover layer, which is arranged on the auxiliary waveguide layer 35 (i.e. the upper waveguide layer mentioned above), and the fourth refractive index of the cover layer is greater than or equal to the first refractive index of the auxiliary waveguide layer 35.

[0071] In this embodiment, when the fourth refractive index of the cover layer is greater than or equal to the first refractive index of the auxiliary waveguide layer 35, the first etching stripe and the second etching stripe can be used to well limit the transmission of light to the cover layer with a large refractive index, and thus well limit the mode spot size of the auxiliary waveguide layer 35 on the end face of the small end of the tapered waveguide 31.

[0072] In some optional embodiments, the fourth refractive index of the cover layer ranges from 1.448 to 1.47.

[0073] In some optional embodiments, the fourth refractive index of the cover layer is less than the first refractive index of the auxiliary waveguide layer 35.

[0074] In this embodiment, the third etching stripe mentioned above is used, i.e. only one stripe is etched, which can achieve a better control effect of the mode spot size and position, and make the mode spot closer to the tapered waveguide 31. Thus, the increase of the transmission loss caused by the process error of the width of the tapered waveguide 31 is reduced, and the process requirement is reduced.

[0075] In the above embodiments, the cover layer can be Figure 3A The epoxy resin shown in the figure can also be SiON or other low-refractive-index materials.

[0076] In some optional embodiments, the stripe width of the etching stripe ranges from 10 μm to 20 μm, and the stripe depth of the etching stripe ranges from 1 μm to 2 μm.

[0077] For example, Figure 3C The stripe width of the first etching stripe T1 and the second etching stripe T2 shown in the figure is 15 μm, and the stripe depth is 2 μm.

[0078] In some optional embodiments, the extension length of the etching stripe ranges from 1 / 6 to 1 of the extension length of the tapered waveguide 31 (i.e. the lower waveguide mentioned above).

[0079] For example, the extension length of the etching stripe ranges from 1 / 3 to 2 / 3. The mode spot size of the end face of the auxiliary waveguide layer 35 can be effectively limited, and the entire length of the tapered waveguide 31 does not need to be etched, such as the trench which needs to etch the entire length of the tapered waveguide. The process difficulty can be reduced and the process speed can be accelerated.

[0080] In some optional embodiments, the interval distance between the first etching stripe and the second etching stripe ranges from 2 μm to 10 μm.

[0081] For example, Figure 3C The interval distance between the first etching stripe T1 and the second etching stripe T2 is 8 μm to 10 μm. When the absolute value of the size error of the small end of the tapered waveguide 31 is greater than 10 nm, the mode spot size can be well controlled. For example, when the absolute value of the size error is in the range of 30 nm, the mode spot size can be well controlled. For example, the mode spot size can be controlled to be 6 μm to 7 μm.

[0082] In the above embodiments, when the mode spot of the auxiliary waveguide layer 35 (i.e. the upper waveguide layer) at the end of the optical waveguide mode conversion device 3 matches the mode spot of the optical fiber 2 under the structure limitation of the etching stripe, the mode spot size is large and the optical coupling loss is small. Moreover, the mode spot of the auxiliary waveguide layer 35 at the small end of the tapered waveguide 31 (i.e. the lower waveguide) is not sensitive to the size of the small end of the tapered waveguide 31, and the process tolerance is large.

[0083] In the above embodiments, by controlling the structure of the etching stripe, i.e. the position and size, the mode spot size of the auxiliary waveguide layer 35 (i.e. the upper waveguide layer) at the small end of the tapered waveguide 31 (i.e. the lower waveguide) can be controlled. Compared with the case where the auxiliary waveguide layer 35 is not provided, the mode spot size at the small end of the tapered waveguide 31 is too small, i.e. 3-4 μm, which causes the optical loss to be too large when the small end of the tapered waveguide 31 matches the optical fiber 2 with a size of about 9 μm. Also, without the mode spot limiting structure, the mode spot size extends too much in the transverse direction, which causes the mode spot size to be greater than 9 μm, and further causes the optical loss to be too large when the above matching is performed. Therefore, the sensitivity of the mode spot size to the size of the end of the above waveguide in the mode conversion device can be reduced, the optical polarization loss can be reduced, and the mismatch loss between the silicon optical waveguide and the optical fiber in the mode conversion can be reduced. In addition, the trench is not provided, and the process difficulty is reduced.

[0084] In some optional embodiments, the auxiliary waveguide layer 35 (i.e. the upper waveguide layer) includes silicon-rich silicon dioxide. For example, Figure 3AAs shown, the auxiliary waveguide layer 35 is made of silicon-rich silicon oxide (SRO) thin film. Specifically, the silicon-rich silicon oxide thin film can be achieved by increasing the flow rate of silane in the process based on the silicon dioxide growth process. Silicon has a higher refractive index than silicon-rich silicon oxide, and silicon-rich silicon oxide has a higher refractive index than silicon dioxide.

[0085] By controlling the silicon content, and thus the first refractive index of the silicon-rich silica film, the width of the wedge waveguide 31 gradually decreases along the direction of light transmission, causing the light transmitted in the wedge waveguide 31 to gradually enter the auxiliary waveguide layer 35. Similarly, when light propagates in the reverse direction in the wedge waveguide 31, the light from the auxiliary waveguide layer 35 gradually enters the wedge waveguide 31 along the reverse light transmission direction.

[0086] In some optional embodiments, silicon dioxide with a refractive index less than 1.45 is used as the cladding material for the wedge waveguide 31, and the refractive index of this cladding material is less than the first refractive index of the auxiliary waveguide layer 35. For example, the cladding material is... Figure 3A Insulating layer 33.

[0087] In the mode conversion device, the waveguide (such as the wedge waveguide 31 mentioned above) is at a distance... Figure 3A When the silicon substrate 32 with a high refractive index is close to the waveguide in the mode conversion device, the transmitted light can easily leak into the silicon substrate 32, resulting in optical loss. Existing technologies typically use the method of partially removing the silicon substrate to reduce loss, but this method has problems such as high process difficulty, easy damage to the mode conversion device, and weak mechanical strength.

[0088] In the above embodiments, an insulating layer 33 and a dielectric layer 34 are present between the auxiliary waveguide layer 35 and the silicon substrate 32. By modulating the thickness of the insulating layer 33, the distance between the mode field (i.e., mode spot) of the auxiliary waveguide layer 35 and the silicon substrate 32 is increased, thus avoiding or reducing mode field leakage of the auxiliary waveguide layer 35. This simplifies the process and improves the reliability of the device. Furthermore, without the need for trenches, the mode spot size is limited by setting etching stripes, further simplifying the process.

[0089] For example, the insulating layer 33 is obtained using shallow trench isolation (STI) technology; the dielectric layer 34 contains an inter-metal dielectric (IMD).

[0090] For example, the wedge-shaped waveguide 31 is a silicon nitride waveguide. During the transmission of light in the mode conversion device 3, it is gradually converted from the silicon nitride waveguide (the wedge-shaped waveguide 31) to the silicon-rich silicon dioxide thin film waveguide (the auxiliary waveguide layer 35).

[0091] In some optional embodiments, the tapering structure of the taper waveguide 31 from the large end to the small end can be linearly transformed, or a non-linear structure can be used to reduce the length of the optical waveguide mode spot conversion device 3, reduce the volume of the optical waveguide mode spot conversion device 3, and save costs.

[0092] In some optional embodiments, the first refractive index of the auxiliary waveguide layer 35 is in the range of 1.45-1.6, such as 1.453. The third refractive index of the dielectric layer 34 can be 1.448. Specifically, according to the second refractive index of the taper waveguide 31 (such as 2.0), and the distance between the bottom of the auxiliary waveguide layer 35 and the bottom of the taper waveguide 31, the light is slowly converted from the silicon nitride waveguide to the silicon-rich silicon dioxide film waveguide, and the mode spot conversion efficiency is ensured.

[0093] Since the distance between the top of the taper waveguide 31 and the bottom of the auxiliary waveguide layer 35 is too large, it increases the difficulty of light conversion from the auxiliary waveguide layer 35 to the taper waveguide 31, resulting in an increase in the length of the optical waveguide mode spot conversion device 3. In some optional embodiments, the distance between the top of the taper waveguide 31 and the bottom of the auxiliary waveguide layer 35 is in the range of 0-2 μm. In this distance range, the length of the optical waveguide mode spot conversion device 3 can be effectively reduced.

[0094] Since light will be transmitted along materials with a large refractive index, in some optional embodiments, the second refractive index of the taper waveguide 31 is greater than 1.45. For example, the taper waveguide 31 can be a silicon waveguide or other high refractive index (such as a refractive index greater than 1.45) material waveguide. In this way, the light is quickly converted from the taper waveguide 31 to the auxiliary waveguide layer 35.

[0095] In some optional embodiments, the taper waveguide 31 includes a silicon nitride waveguide or a silicon waveguide.

[0096] In some optional embodiments, the two end faces of the taper waveguide 31 are rectangular, and the thickness of the taper waveguide 31 is uniform.

[0097] In some optional embodiments, the length of the small end of the taper waveguide 31 is less than 130 nm. Specifically, since the small end of the taper waveguide 31 is no longer used for fiber coupling, the impact of the size of the small end of the taper waveguide 31 on light loss is greatly reduced, and the size of the end face of the small end of the taper waveguide 31 can be controlled to be less than 130 nm, thereby reducing the process difficulty of the taper waveguide 31. However, the existing scheme often needs to control the end face size of the taper waveguide 31 to be within 10 nm, which is relatively difficult in terms of process.

[0098] In the above embodiments, an upper waveguide layer is disposed on the cladding, and the upper waveguide layer is used for coupling with the optical fiber at the small end of the lower waveguide; the first refractive index of the upper waveguide layer is less than the second refractive index of the lower waveguide and greater than the third refractive index of the cladding; etching stripes are disposed on the upper surface of the upper waveguide layer near the small end of the lower waveguide; the etching stripes are disposed based on the position of the small end of the lower waveguide and extend from the end face of the upper waveguide layer along the extension direction of the lower waveguide; the etching stripes are used to limit the mode spot size on the end face of the upper waveguide layer. This can reduce the sensitivity of the mode spot size (the mode spot size magnified at the optical fiber coupling end) to the size of the end of the waveguide (i.e., the optical fiber coupling end) in the mode conversion device; reduce optical polarization-dependent loss; reduce process difficulty; and reduce the mismatch loss of mode conversion between silicon optical waveguide and optical fiber.

[0099] Figure 4 This application provides a method for manufacturing an optical waveguide mode conversion device. This specification provides method operation steps as shown in the embodiments or flowcharts, but based on conventional or non-inventive labor, more or fewer operation steps may be included. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only execution order. In actual system or server products, the method can be executed sequentially according to the embodiments or drawings, or in parallel (e.g., in a parallel processor or multi-threaded processing environment). Specifically, as shown... Figure 4 As shown, the method includes:

[0100] S402: Deposit a cladding layer on a semiconductor substrate.

[0101] For example, in semiconductor substrates Figure 3A An insulating layer 33 (i.e., the aforementioned lower cladding layer) is deposited on the buried silicon oxide layer 38 shown.

[0102] S404: A wedge-shaped lower waveguide is formed on the lower cladding using microelectronic processes; the larger end of the lower waveguide is used to connect to a silicon optical waveguide.

[0103] Specifically, a wedge-shaped waveguide is formed on the insulating layer using microelectronic processes; the larger end of the wedge-shaped waveguide 31 is used to connect to the silicon optical waveguide.

[0104] For example, in Figure 3A A wedge-shaped waveguide 31 is formed on the insulating layer 33 using microelectronic processes. Specifically, the insulating layer 33 is formed by depositing and filling silicon oxide. A silicon nitride protective layer is formed on the insulating layer 33 using plasma chemical vapor deposition and low-pressure chemical vapor deposition (LPCVD) techniques.

[0105] S406: Deposit an upper cladding layer on the lower cladding layer, the upper cladding layer covering the lower waveguide.

[0106] Specifically, a dielectric layer is deposited on the insulating layer, and the dielectric layer covers the wedge-shaped waveguide.

[0107] For example, such as Figure 3A An inter-metal dielectric (IMD) is deposited on the insulating layer 33 and then ground smooth to obtain a dielectric layer 34. This dielectric layer 34 serves as the middle protective layer of the optical waveguide mode conversion device 3.

[0108] S406: An upper waveguide layer is deposited on the upper cladding; the upper waveguide layer is used to couple to an optical fiber at the small end near the lower waveguide.

[0109] Specifically, an auxiliary waveguide layer is deposited on the dielectric layer; the auxiliary waveguide layer is used for coupling with an optical fiber at the small end of the wedge-shaped waveguide.

[0110] For example, a silicon-rich silicon dioxide thin film layer is deposited using plasma chemical vapor deposition technology to obtain an auxiliary waveguide layer 35, and then the auxiliary waveguide layer 35 is ground smooth.

[0111] S408: Based on the position of the small end of the lower waveguide, etching is performed on the upper surface of the upper waveguide layer to obtain etching stripes; the etching stripes extend from the end face of the upper waveguide layer along the extension direction of the lower waveguide; the first refractive index of the upper waveguide layer is less than the second refractive index of the lower waveguide and greater than the third refractive index of the upper cladding layer.

[0112] Specifically, based on the lateral position of the small end of the wedge waveguide (i.e., the lower waveguide mentioned above), the auxiliary waveguide layer (i.e., the upper waveguide mentioned above) is etched along the extension direction of the wedge waveguide to form etching stripes; the first refractive index of the auxiliary waveguide layer is less than the second refractive index of the wedge waveguide and greater than the third refractive index of the dielectric layer.

[0113] For example, the auxiliary waveguide layer 35 is etched using photolithography and etching techniques to form etching stripes; then epoxy resin is filled into the surface of the auxiliary waveguide layer 35 to form etching stripes with silicon nitride waveguide as the core, and the dielectric layer is a protective layer for the silicon nitride waveguide.

[0114] Figure 5 This is a schematic diagram of the end face structure of another optical mode conversion device provided in the application embodiment. In some optional embodiments, Figure 5 The buried silicon oxide layer 38 shown can be a silicon dioxide layer.

[0115] In some alternative embodiments, inFigure 3A Before the wedge-shaped waveguide 31 is formed on the insulator layer 33 by microelectronic process, the silicon layer 36 is deposited on the buried silicon oxide layer 38, and the silicon waveguide 37 is formed by etching the silicon layer 36; then the silicon dioxide is deposited on the silicon waveguide 37 as the insulator layer 33, and is polished.

[0116] In the embodiment, the optical wave mode spot conversion device 3 adopts a Figure 5 The silicon waveguide 37 is used to couple the light from the waveguide 31 to the silicon waveguide 37. Thus, other silicon optical devices such as modulators, detectors, etc. can also be integrated in the silicon waveguide 37.

[0117] The manufacturing method of the optical wave mode spot conversion device provided by the present application can reduce the sensitivity of the mode spot size (the mode spot size amplified at the fiber coupling end) to the size of the end of the waveguide (i.e. the fiber coupling end) in the mode spot conversion device, reduce the optical polarization dependent loss, reduce the process difficulty by setting the etching stripes, and reduce the mismatch loss of the mode spot conversion between the silicon optical waveguide and the optical fiber.

[0118] In summary, the embodiment of the present application provides an optical wave mode spot conversion device and a manufacturing method thereof. The optical wave mode spot conversion device comprises a semiconductor substrate, a lower waveguide, a cladding layer, and an upper waveguide layer. The cladding layer is arranged on the semiconductor substrate. The lower waveguide is arranged in the cladding layer. The lower waveguide has a wedge-shaped structure. The large end of the lower waveguide is used to connect with a silicon optical waveguide. The upper waveguide layer is arranged on the cladding layer. The upper waveguide layer is used to couple with an optical fiber at the small end of the lower waveguide. The first refractive index of the upper waveguide layer is smaller than the second refractive index of the lower waveguide and larger than the third refractive index of the cladding layer. Etching stripes are arranged on the upper surface of the upper waveguide layer and close to the small end of the lower waveguide. The etching stripes are arranged based on the position of the small end of the lower waveguide and extend from the end surface of the upper waveguide layer along the extension direction of the lower waveguide. The etching stripes are used to limit the mode spot size on the end surface of the upper waveguide layer. The sensitivity of the mode spot size (the mode spot size amplified at the fiber coupling end) to the size of the end of the waveguide (i.e. the fiber coupling end) in the mode spot conversion device can be reduced. The optical polarization dependent loss can be reduced. The process difficulty can be reduced. The mismatch loss of the mode spot conversion between the silicon optical waveguide and the optical fiber can be reduced.

[0119] The above description is merely a specific implementation of the present application. However, the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0120] Furthermore, those skilled in the art will recognize that, while certain embodiments described herein include certain features that are not included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the application and form different embodiments, for example, in the claims. For example, in the claims, any of the claimed embodiments can be used in any combination.

Claims

1. An optical waveguide mode spot conversion device, characterized by, The application relates to a semiconductor waveguide structure, which comprises a semiconductor substrate, a lower waveguide, a cladding layer, an upper waveguide layer and a cover layer. The cladding layer is arranged on the semiconductor substrate. The lower waveguide is arranged in the cladding layer and has a wedge structure, and a large-end of the lower waveguide is used for connecting with a silicon optical waveguide. The upper waveguide layer is arranged on the cladding layer and is used for coupling with an optical fiber at a small-end of the lower waveguide; a first refractive index of the upper waveguide layer is smaller than a second refractive index of the lower waveguide and larger than a third refractive index of the cladding layer. An etching stripe is arranged on an upper surface of the upper waveguide layer and close to the small-end of the lower waveguide; the etching stripe is arranged based on a position of the small-end of the lower waveguide and extends from an end surface of the upper waveguide layer along an extension direction of the lower waveguide; the etching stripe is used for limiting a mode spot size on the end surface of the upper waveguide layer; a stripe width of the etching stripe ranges from 10 mu m to 20 mu m. A stripe depth of the etching stripe ranges from 1 mu m to 2 mu m. The cover layer is arranged on the upper waveguide layer, and a fourth refractive index of the cover layer is greater than or equal to the first refractive index of the upper waveguide layer. The etching stripe comprises a first etching stripe and a second etching stripe; the first etching stripe and the second etching stripe are symmetrically arranged based on a transverse position of the small-end of the lower waveguide.

2. The apparatus of claim 1, wherein, The etching stripe comprises a third etching stripe, and a transverse position of the third etching stripe is consistent with that between the third etching stripe and the small-end of the lower waveguide.

3. The apparatus of claim 1, wherein, A thickness of the upper waveguide layer is greater than 5 mu m.

4. The apparatus of claim 3, wherein, The fourth refractive index of the cover layer ranges from 1.448 to 1.

47.

5. The apparatus of any one of claims 1 to 4, wherein, An extension length of the etching stripe ranges from greater than or equal to 1 / 6 of an extension length of the lower waveguide.

6. The apparatus of any one of claims 1 to 4, wherein, A spacing distance between the first etching stripe and the second etching stripe ranges from 2 mu m to 10 mu m.

7. The apparatus of claim 2, wherein, The method comprises the following steps.

8. A method of fabricating an optical waveguide mode spot conversion device, comprising: A lower cladding layer is deposited on a semiconductor substrate. A lower waveguide with a wedge structure is formed on the lower cladding layer by using a microelectronic process; a large-end of the lower waveguide is used for connecting with a silicon optical waveguide. An upper cladding layer is deposited on the lower cladding layer, and the upper cladding layer covers the lower waveguide. An upper waveguide layer is deposited on the upper cladding layer; the upper waveguide layer is used for coupling with an optical fiber at a small-end of the lower waveguide. An etching stripe is etched on an upper surface of the upper waveguide layer based on a position of the small-end of the lower waveguide; a stripe width of the etching stripe ranges from 10 mu m to 20 mu m; a stripe depth of the etching stripe ranges from 1 mu m to 2 mu m; the etching stripe extends from an end surface of the upper waveguide layer along an extension direction of the lower waveguide; a first refractive index of the upper waveguide layer is smaller than a second refractive index of the lower waveguide and larger than a third refractive index of the upper cladding layer. A cover layer is deposited on the upper waveguide layer, and a fourth refractive index of the cover layer is greater than or equal to the first refractive index of the upper waveguide layer. ​

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