Edge coupler and photonic integrated chip

Abstract

The invention relates to an edge coupler and a photonic integrated chip, the edge coupler comprises a core layer, a preset optical transmission direction of the core layer is set as a first direction, a second direction is parallel to a thickness direction of the core layer, and a third direction is perpendicular to the first direction and the second direction; the core layer has a first waveguide layer, a second waveguide layer, and a third waveguide layer stacked in a second direction; the core layer is provided with a main transmission light path; the core layer comprises: a first waveguide located in a first waveguide layer; the third waveguide is located on the third waveguide layer; the waveguide group is located on the second waveguide layer and comprises two first sub-waveguides; the waveguide group is used for coupling light to the main transmission light path; wherein in the first direction, the first sub-waveguide comprises a first section and a second section which are sequentially arranged in the first direction; in the first direction, the width of the first section in the third direction is linearly increased, and the width of the second section in the third direction is linearly decreased. According to the edge coupler, a mode field can be expanded without being limited by the waveguide size, the light constraint capability is optimized, and the coupling efficiency is higher.

Description

Technical Field

[0001] This application relates to the field of silicon photonics communication, and in particular to an edge coupler and a photonic integrated chip. Background Technology

[0002] In photonic integrated circuits, edge couplers are typically placed at the chip's edge to interface with external optical fibers or other optical components. Their main function is to change the mode field area, matching the large mode field of the external fiber or other optical component with the small mode field of the chip, thereby improving coupling efficiency. Current related technologies typically achieve mode field matching through gradual size changes. One such approach is the in-plane inverted cone coupler, which uses a single inverted cone structure as the core layer. The gradual change in the inverted cone structure allows for a slow change in the mode field, achieving mode field matching between the chip side and the fiber side.

[0003] However, this approach has significant drawbacks when applied to silicon photonic chips. In silicon photonic chips, the mode size of the waveguide is typically submicron, while the mode size of optical fiber is typically several to tens of micrometers. This necessitates increasing the waveguide size of the inverted cone scheme to achieve mode field matching with the optical fiber. However, increasing the waveguide size can easily lead to optical field leakage, resulting in higher coupling loss. Summary of the Invention

[0004] Based on this, this application provides an edge coupler that can achieve mode field matching between optical fiber and chip, while reducing optical field leakage, thereby improving coupling efficiency.

[0005] On one hand, this application provides an edge coupler, including a core layer, a preset optical transmission direction of the core layer is set as a first direction, a second direction is parallel to the thickness direction of the core layer, and a third direction is perpendicular to both the first and second directions; the core layer has a first waveguide layer, a second waveguide layer, and a third waveguide layer stacked along the second direction; the core layer has a main transmission optical path; the core layer includes: a first waveguide and a third waveguide; the first waveguide is located in the first waveguide layer; the third waveguide is located in the third waveguide layer; a waveguide group is located in the second waveguide layer, and the waveguide group includes two first sub-waveguides; the waveguide group is used to couple light to the main transmission optical path; wherein, along the first direction, the first sub-waveguide includes a first segment and a second segment arranged sequentially along the first direction; along the first direction, the width of the first segment in the third direction increases linearly; along the first direction, the width of the second segment in the third direction decreases linearly.

[0006] Optionally, the waveguide group has a first symmetry plane; the plane containing the first direction and the second direction is parallel to the first symmetry plane; the first symmetry plane is coplanar with the symmetry plane of the first waveguide and the symmetry plane of the third waveguide.

[0007] Optionally, the first waveguide is a tapered waveguide; the transmission optical path of the first waveguide constitutes the main transmission optical path, and the narrow end of the first waveguide corresponds to the chip side; the structure of the third waveguide is the same as that of the first sub-waveguide; the length of the third waveguide is greater than the length of the first sub-waveguide.

[0008] Optionally, the first waveguide is a stepped tapered waveguide of at least three orders; the height of the first waveguide increases from the chip side to the optical fiber side along the first direction, and the difference in the height of the increase is less than or equal to 10 nanometers.

[0009] Optionally, the first waveguide is a continuous rectangular waveguide or a segmented rectangular waveguide.

[0010] Optionally, the third waveguide is a strip waveguide, and along the first direction, the width of the third waveguide gradually increases from the chip side to the optical fiber side; the transmission optical path of the third waveguide, the first sub-waveguide, and the first waveguide together constitute the main transmission optical path.

[0011] Optionally, the waveguide assembly may also include a second sub-waveguide; wherein the second sub-waveguide is a strip waveguide, and the width of the second sub-waveguide gradually increases from the chip side to the optical fiber side along the first direction; the transmission optical path of the second sub-waveguide and the transmission optical path of the first waveguide together constitute the main transmission optical path; the structure of the third waveguide is the same as that of the first sub-waveguide.

[0012] Optionally, there may be multiple second waveguide layers, each containing a waveguide group.

[0013] Optionally, the edge coupler also includes a cladding layer that surrounds the first waveguide layer, the second waveguide layer, and the third waveguide layer; wherein the first waveguide layer is made of silicon; the second and third waveguide layers are made of silicon nitride; and the cladding layer is made of silicon dioxide.

[0014] On the other hand, this application also provides a photonic integrated chip, which includes the aforementioned edge coupler.

[0015] The embodiments provided in this application expand the mode spot size in the second direction by vertically arranging three waveguide layers in the core layer and setting the first waveguide and the third waveguide in the first waveguide layer and the third waveguide in the third waveguide layer, respectively. At the same time, a waveguide group consisting of two first sub-waveguides is set in the middle second waveguide layer to expand the mode spot size in the third direction. This allows the mode field area of ​​the edge coupler to be expanded without being limited by the waveguide size, so that the edge coupler can match the mode field of the optical fiber or other optical components. Meanwhile, the first sub-waveguide has a first segment with a linearly increasing width and a second segment with a linearly decreasing width. This structure allows the first sub-waveguide to have the functions of mode field gradient and adjustment of effective refractive index at the same time. This allows the first sub-waveguide to optimize the optical confinement capability while realizing mode field expansion, so as to couple the light into the main transmission optical path, thereby reducing optical field leakage and improving coupling efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of an edge coupler provided in one embodiment of this application;

[0017] Figure 2 for Figure 1 Schematic diagram of the first sub-waveguide of the rhombus shape;

[0018] Figure 3 This is a cross-sectional schematic diagram of the edge coupler provided in two embodiments of this application;

[0019] Figure 4 These are schematic diagrams of the edge couplers provided in the three embodiments of this application;

[0020] Figure 5 Side view of the F1-F2 plane of the edge coupler provided in the three embodiments of this application;

[0021] Figure 6 This is a schematic diagram of the structure of the edge coupler provided in four embodiments of this application;

[0022] Figure 7 This is a schematic diagram of the structure of the edge coupler provided in the five embodiments of this application;

[0023] Figure 8 Side view of the F1-F2 plane of the edge coupler provided in the four embodiments of this application;

[0024] Figure 9 for Figure 7 Schematic diagram of the structure of the first waveguide in the middle;

[0025] Figure 10 This is a cross-sectional schematic diagram of the edge coupler provided in the six embodiments of this application;

[0026] Figures 11a-11b The mode field simulation diagrams of the edge couplers provided in the three embodiments of this application;

[0027] Figures 12a-12b Simulation diagrams of the coupling tolerance of the edge coupler provided in the three embodiments of this application;

[0028] Figure 13 This is a schematic diagram of the structure of a photonic integrated chip provided in another embodiment of this application.

[0029] Explanation of reference numerals in the attached figures

[0030] 1000, Photonic integrated chip; 100, Edge coupler; 110, Core layer; 111, First waveguide layer; 112, Second waveguide layer; 113, Third waveguide layer; 114, First waveguide; 1141, First step; 1142, Second step; 1143, Third step; 115, Second waveguide; 116, Waveguide group; 1161, First sub-waveguide; 11611, First segment; 11612, Second segment; 1162, Second sub-waveguide; 120, Cladding; 130, Buried oxide layer; 140, Silicon substrate; F1, First direction; F2, Second direction; F3, Third direction. Specific Implementation

[0031] To make the technical solution and beneficial effects of this application more apparent and understandable, a detailed description is provided below by listing specific embodiments. The accompanying drawings are not necessarily drawn to scale, and local features may be enlarged or reduced to more clearly show the details of the local features; unless otherwise defined, the technical and scientific terms used herein have the same meanings as those in the technical field to which this application pertains.

[0032] In photonic integrated circuits, the primary function of edge couplers is to achieve mode field matching between external optical fibers or other optical components and the chip, ensuring coupling efficiency. In edge coupler design, in addition to mode field area matching, optical confinement capability, applicability, and stability are also important considerations.

[0033] Taking the traditional in-plane inverted cone coupler as an example, this approach primarily achieves a gradual change in the mode field through the inverted cone structure, simultaneously realizing mode field matching between the chip side and the fiber side. However, this approach has significant shortcomings when applied to silicon photonic chips. In silicon photonic chips, because the refractive index of silicon is much higher than that of the cladding, the mode field diameter of the edge coupler integrated into the chip is further reduced, typically to the sub-micron level, while the mode field diameter of optical fiber is usually several to tens of micrometers. This makes it difficult for the gradual waveguide size to meet the size requirements for mode field area matching. Even if a larger waveguide size is used to achieve mode field matching with the optical fiber, the excessively large waveguide size will weaken the optical confinement capability, widen the optical path, and allow the optical field to easily extend into the silicon substrate, causing leakage and increasing coupling loss.

[0034] Furthermore, edge couplers also need to consider applicability and stability. For example, some technologies choose to only adapt to lens fibers or small-core fibers, avoiding direct optical coupling with larger fibers (such as the common standard SMF28 single-mode fiber). Even if this ensures coupling efficiency, its applicability is narrow. At the same time, the design of small mode fields also has stricter requirements for coupling tolerance, which poses challenges to end-face assembly, resulting in poor reliability and applicability of edge couplers.

[0035] Therefore, it is necessary to provide an edge coupler that, through its own structural design, can simultaneously meet multiple requirements such as mode field matching, strong optical confinement capability, applicability, and stability when performing optical coupling, thereby solving the problems of low coupling efficiency, poor applicability, and poor reliability of traditional edge couplers.

[0036] refer to Figure 1 As shown, this application provides an edge coupler 100. The edge coupler 100 includes a core layer 110. A preset optical transmission direction of the core layer 110 is defined as a first direction F1, a second direction F2 is parallel to the thickness direction of the core layer 110, and a third direction F3 is perpendicular to both the first direction F1 and the second direction F2. The core layer 110 has a first waveguide layer 111, a second waveguide layer 112, and a third waveguide layer 113 stacked along the second direction F2. The core layer 110 has a main transmission optical path and includes a first waveguide 114, a third waveguide 115, and a waveguide group 116.

[0037] The first waveguide 114 is located in the first waveguide layer 111. The third waveguide 115 is located in the third waveguide layer 113. Waveguide group 116 is located in the second waveguide layer 112 and includes two first sub-waveguides 1161. Waveguide group 116 is used to couple light to the main transmission optical path. (Referring to...) Figure 2 As shown, along the first direction F1, the first sub-waveguide 1161 includes a first segment 11611 and a second segment 11612 arranged sequentially along the first direction F1. Along the first direction F1, the width of the first segment in the third direction F3 increases linearly. Along the first direction F1, the width of the second segment in the third direction F3 decreases linearly.

[0038] Specifically, in the edge coupler 100, the core layer 110 refers to the area where waveguides are concentrated, and the waveguides in the core layer 110 all extend along a preset optical transmission direction. The cross-section of the waveguides can be rectangular, circular, ridge-shaped, or other shapes to provide transmission optical paths with different effects. The main transmission optical path refers to the main transmission path of light in the edge coupler 100, which can be composed of the transmission optical paths of at least one waveguide in the core layer 110. The first direction F1, the second direction F2, and the third direction F3 are all vectors, where the first direction F1 is parallel to the preset optical transmission direction; the second direction F2 is parallel to the thickness direction of the core layer 110; and the third direction F3 is perpendicular to the first direction F1 and the second direction F2. The cross-section of the core layer 110 is the plane containing the second direction F2 and the third direction F3 (hereinafter referred to as the F2F3 plane). The orientation of these three directions is not limited here; for example, the first direction F1 can be from the chip side to the fiber side or from the fiber side to the chip side. For ease of description, the waveguide will be referred to as having a length in the first direction F1, a height in the second direction F2, and a width in the third direction F3.

[0039] In this embodiment, reference Figure 1 As shown, the first waveguide 114, the two first sub-waveguides 1161 in waveguide group 116, and the third waveguide 115 are respectively arranged in three waveguide layers (111, 112, 113) stacked vertically along the second direction F2. At this time, in the F2F3 plane, the first waveguide 114 and the third waveguide 115 can expand the mode size of the edge coupler 100 in the second direction F2, and the specific expansion range can be determined according to the spacing between the two waveguides in the second direction F2. In the middle second waveguide layer 112, the two first sub-waveguides 1161 in waveguide group 116 are arranged horizontally along the third direction F3, and can expand the mode size of the edge coupler 100 in the third direction F3, and the specific expansion range can be determined according to the spacing between the two first sub-waveguides 1161 in the third direction F3. The expansion of the mode spot size in the second direction F2 combined with the expansion of the mode spot size in the third direction F3 can expand the mode field area of ​​the edge coupler 100, so that the expansion of the mode spot size and mode field area of ​​the edge coupler 100 is not limited by the size of a single waveguide. The mode spot shape can be adjusted by setting the parameters of each waveguide (such as position, size, structure) to achieve matching with the mode spot shape of the optical fiber, thereby improving the coupling efficiency.

[0040] This allows the edge coupler 100 to directly match optical fibers and optical components with various mode field areas, such as small mode field lens fibers or small core diameter fibers (e.g., UHNA3) and large mode field fibers (e.g., SMF28), while ensuring coupling efficiency. Furthermore, the direct matching of mode spot shapes gives the edge coupler 100 higher coupling tolerance, thereby reducing the requirements for end-face coupling processes and improving the applicability and reliability of the edge coupler 100.

[0041] Furthermore, such as Figure 2 As shown, in waveguide group 116, each first sub-waveguide 1161 has a first segment 11611 with linearly increasing width and a second segment 11612 with linearly decreasing width. That is, in the first direction F1, both ends of the first sub-waveguide 1161 on the chip side and the fiber side are narrow ends, and there is a width transition surface in the middle, which is parallel to the F2F3 plane. Among them, the first segment 11611 is the part from the narrow end on the chip side to the width transition surface, and the second segment 11612 is the part from the width transition surface to the narrow end on the fiber side. This allows the first sub-waveguide 1161 to have the functions of mode field gradient and adjustment of effective refractive index at the same time. In the process of light entering the edge coupler 100 from the chip side and then being output to the fiber side, the width of the first segment 11611 increases linearly, which can realize the expansion of the mode field area and ensure mode field matching. The width of the second segment 11612 decreases linearly, which makes the effective refractive index of the first sub-waveguide 1161 change, thereby enabling the light to be coupled into the main transmission optical path as much as possible. This achieves optimization of the optical confinement capability of the edge coupler 100.

[0042] Compared to related technologies that use a single in-plane inverted conical waveguide to form an edge coupler, this embodiment, through the synergy of multiple waveguides (first waveguide 114, third waveguide 115, and two first sub-waveguides 1161), can concentrate optical energy into a preset, smaller main transmission optical path, thereby helping to reduce the spread of the optical field toward the silicon substrate, thus reducing optical field leakage and improving coupling efficiency.

[0043] Furthermore, the effective refractive index of the first sub-waveguide 1161 can be further adjusted by adjusting the dimensions of the first sub-waveguide 1161, including the narrow end width, wide end width, and total length, in order to improve the coupling efficiency.

[0044] According to an embodiment of the present invention, the edge coupler 100 expands the mode area in the second direction F2 by vertically arranging multiple waveguide layers in the core layer 110 and respectively providing a first waveguide 114 and a third waveguide 115 in the first waveguide layer 111 and the third waveguide layer 113; simultaneously, it expands the mode area in the third direction F3 by providing a waveguide group 116 composed of two first sub-waveguides 1161 in the intermediate second waveguide layer 112. This allows the mode area of ​​the edge coupler 100 to be expanded without being limited by the waveguide size, thus enabling... The mode field of the edge coupler 100 is directly matched with the mode field of the external optical fiber, which optimizes the coupling efficiency while improving applicability and stability. At the same time, the first sub-waveguide 1161 has a first segment 11611 with a linearly increasing width and a second segment 11612 with a linearly decreasing width, which enables the first sub-waveguide 1161 to have both mode field gradient and effective refractive index adjustment functions. This allows the first sub-waveguide 1161 to optimize the optical confinement capability while realizing mode field expansion, so as to couple the light into the main transmission optical path, thereby reducing optical field leakage and improving coupling efficiency.

[0045] It should be noted that, Figure 1 The dark areas shown represent multiple waveguide layers (111, 112, 113) in the core layer 110, while the colorless areas and the portion of each waveguide layer excluding the waveguide itself constitute the cladding 120. The cladding 120 is made of a material with a lower refractive index than the multiple waveguide layers (111, 112, 113) to create a refractive index difference. In the actual fabrication of the edge coupler 100, the multiple waveguide layers can be etched into one or more waveguides of specific dimensions, and then the cladding 120 is deposited to fill the waveguide gaps and the interlayer spaces, achieving both physical protection and optical isolation. Since etching and deposition are mature semiconductor processes, low-cost mass production can be achieved on silicon-based platforms, thus the fabrication cost of the edge coupler 100 is relatively low.

[0046] In some embodiments, waveguide group 116 has a first symmetry plane, the plane containing the first direction F1 and the second direction F2 (hereinafter referred to as the F1 F2 plane) is parallel to the first symmetry plane, and the first symmetry plane is coplanar with the symmetry plane of the first waveguide 114 and the symmetry plane of the third waveguide 115.

[0047] Specifically, the coupling efficiency of the edge coupler is also affected by polarization-dependent loss. Polarization-dependent loss refers to the loss in the edge coupler caused by the difference in coupling efficiency under different modes. It is usually determined by the difference in coupling loss between TE mode (Transverse Electric Mode) and TM mode (Transverse Magnetic Mode). Therefore, in some embodiments of this application, waveguide group 116, first waveguide 114, and third waveguide 115 are all set as symmetrical structures, and the planes of symmetry of the three are coplanar, in order to reduce polarization-dependent loss. Specifically, as shown in... Figure 1 As shown, waveguide group 116 has two first sub-waveguides 1161, which are symmetrically arranged in the second waveguide layer 112 along a first symmetry plane (not shown). The first waveguide 114 and the third waveguide 115 are waveguides that are symmetrical about the width of the first symmetry plane. At this time, in the F2F3 plane, the two first sub-waveguides 1161 are symmetrically arranged about the second direction F2, and their structures and dimensions are exactly the same. This can cancel the mode field distortion caused by TE mode and TM mode, and thus better balance the coupling efficiency of the edge coupler in TE mode or TM mode, and reduce polarization-dependent loss.

[0048] In some embodiments, there are multiple second waveguide layers 112, and each second waveguide layer 112 contains the waveguide group 116. For example, as Figure 3 As shown, the edge coupler 100 includes two second waveguide layers 112, each waveguide layer having two first sub-waveguides 1161. The design of multiple second waveguide layers 112 can better adjust the mode spot shape and mode field area, making the mode spot shape of the edge coupler 100 at the end face closer to the circle of the optical fiber, thereby further optimizing the coupling efficiency.

[0049] In some embodiments, reference Figure 4 As shown, the first waveguide 114 is a tapered waveguide; the transmission optical path of the first waveguide 114 constitutes the main transmission optical path, and the narrow end of the first waveguide 114 corresponds to the chip side. The structure of the third waveguide 115 is the same as that of the first sub-waveguide 1161. The length of the third waveguide 115 is greater than the length of the first sub-waveguide 1161.

[0050] Specifically, a tapered waveguide refers to an optical waveguide structure whose cross-sectional dimensions (width, height, or diameter) gradually change along the direction of light propagation. In the edge coupler 100, the waveguide constituting the main transmission optical path needs to have a relatively long, tapered cross-section to allow for gradual changes in the mode field area, where the cross-sectional gradient includes changes in width and / or height. Therefore, as... Figure 5 As shown, in this embodiment, the length of the first waveguide 114 is greater than the lengths of the third waveguide 115 and the first sub-waveguide 1161. The narrow end of the first waveguide 114 refers to the end with the smaller cross-sectional dimension in the F2F3 plane, corresponding to the chip; the other end of the first waveguide 114 is the wide end, corresponding to the optical fiber. When light is coupled into the wide end of the first waveguide 114 from the optical fiber side, the tapered structure of the first waveguide 114 can gradually compress the mode field area during light transmission through a structure with gradually decreasing width, confining the light to the narrow end for output to the chip side, enabling the chip to couple and transmit light with the optical fiber through the edge coupler 100. Similarly, when light is coupled into the narrow end of the first waveguide 114 from the chip side, the tapered structure of the first waveguide 114 can also gradually expand the mode field area through a structure with gradually increasing width, confining the light to the wide end for output to the optical fiber side.

[0051] Meanwhile, in this embodiment, the main transmission optical route is constructed using the first waveguide 114. The main function of the third waveguide 115 is to cooperate with other waveguide layers to increase the mode field area and improve the mode pattern shape, thereby reducing end-face coupling loss. Therefore, as... Figure 4 As shown, the structure of the third waveguide 115 can be the same as that of the first sub-waveguide 1161 to achieve the above-mentioned functions and optimize the optical confinement capability of the edge coupler 100. For the specific principle, please refer to the aforementioned description of the first sub-waveguide 1161, which will not be repeated here. Optionally, both the first sub-waveguide 1161 and the third waveguide 115 can adopt a refractive index gradient design along the first direction F1, for example, by using silicon oxynitride with different oxygen contents, thereby further optimizing their optical confinement capability to concentrate light onto the main transmission optical path and optimize coupling efficiency.

[0052] Furthermore, since the third waveguide 115 is located in the uppermost third waveguide layer 113, the vertical distance between the third waveguide 115 and the first waveguide 114 is greater than the vertical distance between the first sub-waveguide 1161 and the first waveguide 114, requiring a greater length to optimize inter-layer coupling efficiency. Therefore, as... Figure 5 As shown, the length of the third waveguide 115 is greater than the length of the first sub-waveguide 1161 to improve the overall coupling efficiency of the edge coupler 100.

[0053] It should be noted that, as Figure 4As shown, the edge coupler 100 also includes a buried oxide layer 130 and a silicon substrate 140, so that the core layer 110 can realize the optical transmission function. The specific principles of the buried oxide layer 130 and the silicon substrate 140 will not be elaborated here.

[0054] In some embodiments, reference Figure 4 and Figure 5 As shown, the first waveguide 114 is a stepped tapered waveguide of at least three orders. The height of the first waveguide 114 increases from the chip side to the optical fiber side along the first direction F1, and the difference in height is less than or equal to 10 nanometers.

[0055] Specifically, a third-order stepped conical waveguide refers to simulating the continuous gradient of a conical waveguide's height by setting three discrete, stepped conical waveguides along its height. For example... Figure 5 As shown, the first waveguide 114 at this time includes a first step 1141 at the bottom, a second step 1142 in the middle, and a third step 1143 at the top. The steps are... Figure 5 The shaded area is shown in the diagram. Each step width gradually changes within the same width range, where the initial value of the gradient width is determined by the waveguide process. For example, to ensure yield, the initial value of the gradient width is typically greater than 100 nanometers. The final value of the gradient width is affected by the mode field diameter of the fiber mated to the edge coupler 100. For example, when the fiber mated to the edge coupler 100 is a standard SMF28 single-mode fiber, the final value of the gradient width can be set around 450 nanometers, such as 400 nanometers. In this embodiment, both the width and height of the first waveguide 114 are gradient, which further improves its efficiency in changing the mode field area.

[0056] Meanwhile, compared to continuously tapered waveguides, the stepped tapered waveguide in this embodiment is simpler to fabricate, while the optical properties of both are similar. Furthermore, the higher the order, the closer the performance of the stepped tapered waveguide is to that of a continuously tapered waveguide. Therefore, the first waveguide 114 can also be a fourth-order, fifth-order, or other multi-order stepped tapered waveguide. Considering the actual fabrication complexity and cost, as well as the marginal benefit of performance improvement with increasing order, a third-order step is the optimal choice for this stepped tapered waveguide. Additionally, in this embodiment, the heights of the three tapered steps need to be identical to achieve the best simulation effect. However, since the fabrication process cannot precisely achieve perfect uniformity, the increasing height difference of the three tapered steps is limited to within 10 nanometers in this embodiment, thus balancing simulation performance and fabrication cost.

[0057] As a specific example, when the thickness of the first waveguide 114 is 220 nanometers, the heights of the three steps can be 70 nanometers, 150 nanometers, and 220 nanometers respectively, with the two increasing heights being 80 nanometers and 70 nanometers respectively, and the difference in increasing height is 10 nanometers.

[0058] It should be noted that in other embodiments, the first waveguide 114 may also be formed into a tapered waveguide by only varying the width or the height.

[0059] In some embodiments, reference Figure 6 As shown, the first waveguide 114 is a continuous rectangular waveguide, or, refer to... Figure 7 As shown, the first waveguide 114 is a segmented rectangular waveguide.

[0060] Specifically, due to the diverse coupling requirements between the chip and the optical fiber, in some scenarios, it may be necessary to couple the chip to the optical fiber through the intermediate second waveguide layer 112 or the upper third waveguide layer 113. In this case, the first waveguide 114 does not need to integrate a long, tapered cross-section structure to change the mode field area. Therefore, as... Figures 6-8 As shown, the first waveguide 114 can be a relatively short rectangular waveguide located near the chip's end face, and the length of the first waveguide 114 is much smaller than the lengths of the first sub-waveguide 1161 and the third waveguide 115. In this case, the function of the first waveguide 114 is to change the refractive index and cooperate with other waveguide layers to expand the mode field area, thereby reducing the end face coupling loss.

[0061] Meanwhile, the first waveguide 114 can be Figure 6 The continuous rectangular waveguide shown can also be Figure 7 The segmented waveguide shown is a waveguide composed of multiple rectangular waveguide segments spaced apart along the first direction F1. The specific structure can be illustrated as follows: Figure 9 As shown. Compared to traditional continuous rectangular waveguides, segmented waveguides offer the advantage of more adjustable parameters (such as adjusting the spacing width to regulate the duty cycle of the rectangular waveguide), thereby enabling fine-tuning of the coupled mode field shape. Optionally, the segmented waveguide can be a subwavelength structure, where the dimensions (width, thickness, and length) of each waveguide segment are smaller than the wavelength of light. Subwavelength structures allow for even finer adjustment of the coupled mode field shape; the specific principles are not elaborated here.

[0062] It should be noted that when the first waveguide 114 is a rectangular waveguide, the first waveguide 114 needs to form the main transmission optical path together with the waveguides of other layers. Therefore, it is necessary to integrate a long cross-section gradient structure onto the other waveguides.

[0063] In some cases, when coupling with optical fiber is required through the third waveguide layer 113, a longer, tapered cross-section structure can be integrated onto the third waveguide 115. In this case, for example... Figure 6 and Figure 8 As shown, the length of the third waveguide 115 is greater than that of the first sub-waveguide 1161 and the first waveguide 114.

[0064] Specifically, refer to Figure 6As shown, the third waveguide 115 is a strip waveguide whose width gradually increases from the chip side to the fiber side along the first direction F1. The transmission optical path of the third waveguide 115, together with the transmission optical paths of the first sub-waveguide 1161 and the first waveguide 114, forms the main transmission optical path through optical field coupling. A strip waveguide is a waveguide with a constant thickness and a rectangular or trapezoidal cross-section. Strip waveguides are typically used to confine light along the waveguide path. In this embodiment, the cross-section of the third waveguide 115 is rectangular in all sections, classifying it as a strip waveguide. Furthermore, the width of the third waveguide 115 gradually increases from the chip side to the fiber side along the first direction F1. The third waveguide 115 has a narrow end and a wide end. The narrow end refers to the end with the smaller cross-sectional dimension in the F2F3 plane, corresponding to the chip; the other end of the third waveguide 115 is the wide end, corresponding to the fiber. In this embodiment, optical transmission between the first waveguide 114, the two first sub-waveguides 1161, and the third waveguide 115 is primarily achieved through evanescent wave coupling. After light travels from the two first sub-waveguides 1161 to the third waveguide 115, the mode field area of ​​the third waveguide 115 can be gradually adjusted through a width gradient until it matches the mode field formed with the fiber side or the first waveguide 114, thereby transmitting the light to the fiber side. Optionally, as... Figures 6-7 As shown, the width gradient rate of the third waveguide 115 can be inconsistent in different segments of the first direction F1, thereby better adjusting the effective refractive index and optimizing the optical confinement capability of the third waveguide 115. The specific principle is not elaborated here. This allows the edge coupler 100 to couple to the optical fiber through the third waveguide layer, thus increasing the applicable scenarios and improving the applicability of the edge coupler 100.

[0065] In other cases, refer to Figure 10 As shown, when coupling with the optical fiber via the second waveguide layer 112 is required, a second sub-waveguide 1162 can be set in the waveguide group 116. The second sub-waveguide 1162 is a strip waveguide, and its width gradually increases from the chip side to the optical fiber side along the first direction F1. The transmission optical path of the second sub-waveguide 1162, together with the transmission optical path of the first waveguide, constitutes the main transmission optical path. The structure, principle, and effect of the second sub-waveguide 1162 are similar to those of the aforementioned strip waveguide, and will not be elaborated here. Simultaneously, since the main transmission optical path no longer requires the participation of the third waveguide 115, the third waveguide 115 can also be set to the same structure as the first sub-waveguide 1161, so that the third waveguide 115 can better cooperate with the waveguides of other layers to achieve expanded mode field area and optimized optical confinement function. For details, please refer to the aforementioned description of the first sub-waveguide 1161, which will not be elaborated here. This enables the edge coupler 100 to couple with the optical fiber through the second waveguide layer 112, thereby increasing the applicable scenarios of the edge coupler 100 and improving its applicability.

[0066] It should be noted that when waveguide group 116 includes the second sub-waveguide 1162, waveguide group 116 can still maintain a symmetrical arrangement along the first symmetry plane to avoid polarization-dependent loss. That is, the width of the second sub-waveguide 1162 gradually changes symmetrically along the first symmetry plane, and the specific arrangement of the second sub-waveguide 1162 in the F2F3 plane can be as follows... Figure 10 As shown.

[0067] In some embodiments, various materials can be selected as the materials for the first waveguide layer 111, the second waveguide layer 112, and the third waveguide layer 113, such as silicon, silicon nitride, silicon oxynitride, lithium niobate, or III-V semiconductor compounds or various polymers. Correspondingly, materials with a refractive index lower than that of the waveguide layers can be selected as the material for the cladding 120, such as silicon nitride, silicon dioxide, or various polymers. For example, the first waveguide layer 111 is made of silicon, the second waveguide layer 112 and the third waveguide layer 113 are made of silicon nitride, and the cladding 120 is made of silicon dioxide. This makes the edge coupler 110 suitable for SOI (silicon-on-insulator) platforms and CMOS (Complementary Metal Oyide Semiconductor) process-friendly.

[0068] Optionally, since the edge coupler 100 needs to achieve interlayer coupling of light across multiple waveguide layers (111, 112, 113) via evanescent wave coupling, and the coupling efficiency of evanescent wave coupling is affected by the thickness of the cladding 120, and the thickness of the cladding 120 also affects the mode size of the edge coupler 100 in the vertical direction, the overall coupling efficiency of the edge coupler 100 can be optimized by adjusting the thickness of the cladding 120 between the waveguide layers. Specifically, when the edge coupler 100 is applied to an SOI platform, the thickness of the cladding 120 between the first waveguide layer 111 and the second waveguide layer 112 ranges from 400 nm to 500 nm; the thickness of the cladding 120 between the waveguide layer of the second waveguide layer 112 and the third waveguide layer 113 ranges from 200 nm to 500 nm. Here, 400 nm is the lower limit of the fabrication process for silicon and silicon nitride layers in the SOI platform, and 200 nm to 500 nm is the high-efficiency range for evanescent wave coupling. By setting the cladding 120 within the above range, we can ensure the interlayer coupling efficiency of the edge coupler 100, and select an appropriate cladding 120 thickness to optimize the pattern size of the edge coupler 100, thereby optimizing the overall coupling efficiency.

[0069] It should be noted that the above description of the thickness range of the cladding 120 is exemplary. In some other embodiments, the thickness of the cladding 120 may also be other ranges, and the specific thickness may be adjusted according to process adaptability.

[0070] against Figure 4In addition to the three embodiments shown, this application also provides a specific example and simulation results to verify that it can be interfacing with SMF28 single-mode fiber with low coupling loss. In this example, the edge coupler 100 uses a standard SOI wafer. The topmost silicon layer serves as the first waveguide layer 111, with a thickness of 220 nm. The buried oxide layer below it has a thickness of 2.5 μm, and the bottommost silicon substrate has a thickness greater than 700 μm. Two silicon nitride layers, each 300 nm thick, are deposited on top of the wafer as the second waveguide layer 112 and the third waveguide layer 113, respectively. The cladding thickness between the second waveguide layer 112 and the third waveguide layer 113 is 200 nm, and the cladding thickness between the second waveguide layer 112 and the first waveguide layer 114 is 400 nm. The third-direction F3 spacing between the two first sub-waveguides 1161 is 5.15 μm, and the cladding material 120 is silicon dioxide. The light source used in this simulation has a wavelength of 1310 nm. At a wavelength of 1310 nm, the refractive index of silicon 1310 is 3.48, the refractive index of silicon dioxide is 1.468, and the refractive index of silicon nitride is 1.96508. 1310 nm belongs to the O band (Original Band).

[0071] The dimensional parameters of each waveguide in the edge coupler 100 are as follows: In the first waveguide 114, the height of the first step 1141 is 70 nm, the height of the second step 1142 is 150 nm, and the height of the third step 1143 is 220 nm. The width of each of the three steps gradually increases from 100 nm to 400 nm, with the gradual change length of the first step 1141 being 155 μm; the gradual change length of the second step 1142 being 150 μm; and the gradual change length of the third step 1143 being 80 μm. The height of both first sub-waveguides 1161 is 300 nm, and the width gradually increases from 150 nm to 320 nm and then gradually decreases back to 150 nm. The length of the first segment 11611 of the first sub-waveguide 1161 in the first direction F1 is 155 μm, and the length of the second segment 11612 in the first direction F1 is 80 μm. The height of the third waveguide 115 is 300 nanometers, and the width of the third waveguide 115 gradually increases from 150 nanometers to 320 nanometers and then gradually decreases back to 150 nanometers. The first segment of the third waveguide 115 has a length of 155 micrometers in the first direction F1, and the second segment of the third waveguide 115 has a length of 100 micrometers in the first direction F1.

[0072] Based on the above parameters, simulations were performed using the FDTD (Finite-Difference Time-Domain) software. The selected mode light source was an SMF28 single-mode fiber fundamental mode with a mode field diameter of 9.2 micrometers. The results show that... Figures 11a-11b and Figures 12a-12b The simulation results. Among them, Figures 11a-11bThis diagram shows the mode field diagrams of the edge coupler 100 under different cross-sections in TE and TM modes. From left to right, they represent the fiber-side end face, the middle section of the edge coupler 100, and the chip-side end face. Figure 11a Corresponding to TE mode, Figure 11b Corresponding to TM mode. In Figures 11a-11b In the diagram, the horizontal axis represents the dimension of the third direction F3, and the vertical axis represents the dimension of the second direction F2, both in micrometers. Figures 12a-12b This represents the conditions under which the edge coupler 100 is offset in different propagation directions and the coupling loss in different modes. Among these, Figure 12a Corresponding to the offset of the third party towards F3, Figure 12b This corresponds to the offset in the second direction, F2. In Figures 12a-12b In the diagram, the horizontal axis represents the size of the propagation direction offset in micrometers, and the vertical axis represents the coupling loss in decibels; TE and TM represent the coupling loss in TE mode and TM mode, respectively; PDL represents polarization-dependent loss; and X represents coupling tolerance.

[0073] refer to Figures 11a-11b As shown, in the O-band, the mode field area and mode spot shape of the edge coupler 100 are highly similar in both TE and TM modes. Combined with... Figure 12a and Figure 12b It can be concluded that the loss of edge coupler 100 is 1.83 dB in TE mode and 1.87 dB in TM mode, with a PDL of 0.05 dB. Typically, the PDL of a conventional edge coupler with polarization insensitivity is 0.1 dB, and the PDL of edge coupler 100 in this embodiment is significantly lower than that of conventional edge couplers. Therefore, the edge coupler of this embodiment exhibits low coupling loss when coupled with standard SMF28 single-mode fiber, enabling direct coupling connection with SMF28 single-mode fiber in the O-band. Furthermore, edge coupler 100 also has low polarization-dependent loss, meeting the polarization insensitivity requirements of O-band optical communication systems and demonstrating excellent applicability.

[0074] refer to Figures 12a-12b As shown, the coupling tolerance of the edge coupler 100 in this embodiment is ±2.2 micrometers for 1 dB in the third direction F3 and ±1.5 micrometers for 1 dB in the second direction F3, which exceeds the coupling tolerance of conventional tapered waveguides.

[0075] It should be noted that the edge coupler 100 in this embodiment can also be adapted to other wavebands, such as the C-band (Conventional Band), by adjusting the size of each waveguide to change its effective refractive index.

[0076] Another embodiment of this application provides a photonic integrated chip, see reference.Figure 13 As shown, the photonic integrated chip 1000 includes the aforementioned edge coupler 100.

[0077] According to the photonic integrated chip 1000 of this embodiment, the coupling efficiency between the photonic integrated chip 1000 and the optical fiber can be effectively improved by the internal edge coupler 100. At the same time, the coupling tolerance of the photonic integrated chip 1000 can also be improved and the manufacturing cost can be reduced.

[0078] In this application, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "height," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the purpose of simplifying the description of this application and do not indicate that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. In other words, they should not be construed as limitations on this application.

[0079] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating the relative importance of the indicated features or the number of indicated technical features. Therefore, a feature specified as "first" or "second" may explicitly include at least one of those features. In this application, "multiple" means at least two, such as two, three, etc.; "several" means at least one, such as one, two, three, etc., unless otherwise explicitly specified.

[0080] In this application, unless otherwise expressly defined, the terms "installation," "connection," "linking," "fixing," "setting," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can also refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0081] In this application, unless otherwise expressly defined, the terms "above," "on top of," "over," "above," "below," "below," "below," or "below" for "first feature over second feature" can refer to the first and second features being in direct contact, or to the first and second features being in indirect contact through an intermediate medium. Furthermore, "above," "over," and "below" for "first feature over second feature" can mean the first feature is directly above or diagonally above the second feature, or simply indicates that the horizontal height of the first feature is higher than the horizontal height of the second feature. Similarly, "below," "below," and "below" for "first feature over second feature" can mean the first feature is directly below or diagonally below the second feature, or simply indicates that the horizontal height of the first feature is lower than the horizontal height of the second feature.

[0082] It should be understood that the above embodiments are exemplary and are not intended to include all possible embodiments covered by the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of this application that may not be explicitly described. Therefore, the above embodiments only illustrate several embodiments of this application and do not limit the scope of protection of this patent application.

Claims

1. An edge coupler, characterized in that, It includes a core layer, wherein a preset light transmission direction of the core layer is set as a first direction, a second direction is parallel to the thickness direction of the core layer, and a third direction is perpendicular to both the first and second directions; The core layer has a first waveguide layer, a second waveguide layer, and a third waveguide layer stacked along a second direction; the core layer has a main transmission optical path; The core layer includes: A first waveguide and a third waveguide; the first waveguide is located in the first waveguide layer; the third waveguide is located in the third waveguide layer; A waveguide assembly, located in a second waveguide layer, comprising two first sub-waveguides; the waveguide assembly is used to couple light to the main transmission optical path; wherein... Along the first direction, the first sub-waveguide includes a first segment and a second segment arranged sequentially along the first direction; along the first direction, the width of the first segment in a third direction increases linearly; along the first direction, the width of the second segment in a third direction decreases linearly.

2. The edge coupler according to claim 1, characterized in that, The waveguide group has a first symmetry plane; the plane containing the first direction and the second direction is parallel to the first symmetry plane; the first symmetry plane is coplanar with the symmetry plane of the first waveguide and the symmetry plane of the third waveguide.

3. The edge coupler according to claim 1, characterized in that, The first waveguide is a tapered waveguide; the transmission optical path of the first waveguide constitutes the main transmission optical path, and the narrow end of the first waveguide corresponds to the chip side; The structure of the third waveguide is the same as that of the first sub-waveguide; the length of the third waveguide is greater than that of the first sub-waveguide.

4. The edge coupler according to claim 3, characterized in that, The first waveguide is a stepped tapered waveguide of at least three orders; The height of the first waveguide increases from the chip side to the optical fiber side along the first direction, and the difference in the height increase is less than or equal to 10 nanometers.

5. The edge coupler according to claim 1, characterized in that, The first waveguide is a continuous rectangular waveguide or a segmented rectangular waveguide.

6. The edge coupler according to claim 5, characterized in that, The third waveguide is a strip waveguide, and along the first direction, the width of the third waveguide gradually increases from the chip side to the optical fiber side; the third waveguide, together with the transmission optical path of the first sub-waveguide and the transmission optical path of the first waveguide, constitute the main transmission optical path.

7. The edge coupler according to claim 5, characterized in that, The waveguide group further includes a second sub-waveguide; wherein... The second sub-waveguide is a strip waveguide, and along the first direction, the width of the second sub-waveguide gradually increases from the chip side to the optical fiber side; the transmission optical path of the second sub-waveguide and the transmission optical path of the first waveguide together constitute the main transmission optical path; The structure of the third waveguide is the same as that of the first sub-waveguide.

8. The edge coupler according to claims 1-7, characterized in that, There are multiple second waveguide layers; each second waveguide layer contains the waveguide group.

9. The edge coupler according to any one of claims 1-7, characterized in that, The edge coupler further includes a cladding layer that surrounds the first waveguide layer, the second waveguide layer, and the third waveguide layer; wherein... The first waveguide layer is made of silicon; the second and third waveguide layers are made of silicon nitride; and the cladding is made of silicon dioxide.

10. A photonic integrated chip, characterized in that, The photonic integrated chip includes: The edge coupler according to any one of claims 1-9.

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