Silicon nitride grating coupler and silicon-based optical chip

Abstract

This application discloses a silicon nitride grating coupler and a silicon-based optical chip. The silicon nitride grating coupler exhibits high coupling efficiency when facing incident light of different wavelengths and modes. Specifically, it includes: a substrate; a first grating layer located on one side of the substrate; a second grating layer located on the side of the first grating layer opposite to the substrate, the second grating layer and the first grating layer being staggered, the duty cycle of the second grating layer being greater than that of the first grating layer, the second grating layer being used to change the scattering path of the incident light and guide the incident light to couple into the first grating layer; a third grating layer located on the side of the first grating layer opposite to the substrate, the third grating layer and the first grating layer also being staggered, the duty cycle of the third grating layer being less than that of the first grating layer, the third grating layer being used to reflect the diffracted light leaking from the first grating layer and guide the reflected light back to the coupling region of the first grating layer; and a waveguide layer connected to the first grating layer along the grating period arrangement direction of the first grating layer.

Description

Technical Field

[0001] This application belongs to the field of optical device technology, specifically relating to a silicon nitride grating coupler and a silicon-based optical chip. Background Technology

[0002] In the fields of optical communication and optical integration technology, grating couplers are key components that connect free-space light to waveguides, and their performance directly affects the efficiency of the entire optical system.

[0003] However, traditional grating couplers have a simple structure and cannot flexibly adjust the light field distribution to achieve optimal coupling when faced with incident light of different wavelengths and modes, resulting in coupling efficiency that is far lower than theoretically expected. At the same time, light is prone to leakage after entering the grating layer, which reduces the overall coupling efficiency. Summary of the Invention

[0004] In view of this, this application provides a silicon nitride grating coupler and a silicon-based optical chip, the main purpose of which is to improve the coupling efficiency of the grating coupler when facing incident light of different wavelengths and modes.

[0005] To achieve the above objectives, this application mainly provides the following technical solutions:

[0006] A first aspect of this application provides a silicon nitride grating coupler, comprising:

[0007] Substrate;

[0008] The first grating layer is located on one side of the substrate;

[0009] A second grating layer is located on the side of the first grating layer facing away from the substrate. The second grating layer and the first grating layer are arranged alternately. The duty cycle of the second grating layer is greater than that of the first grating layer. The second grating layer is used to change the scattering path of the incident light and guide the incident light to couple into the first grating layer.

[0010] A third grating layer is located on the side of the first grating layer opposite to the substrate. The third grating layer and the first grating layer are also arranged alternately. The duty cycle of the third grating layer is less than that of the first grating layer. The third grating layer is used to reflect the diffracted light leaked from the first grating layer and guide the reflected light back to the coupling region of the first grating layer.

[0011] A waveguide layer is connected to the first grating layer along the grating period arrangement direction of the first grating layer.

[0012] Optionally, the grating period of the first grating layer is 1.1 to 1.4 μm, and the duty cycle of the first grating layer is 0.3 to 0.7.

[0013] The grating period of the second grating layer is 1.1–1.4 μm, and the duty cycle of the second grating layer is 0.6–0.8.

[0014] The grating period of the third grating layer is 1.1 to 1.4 μm, and the duty cycle of the third grating layer is 0.2 to 0.6.

[0015] Optionally, in the horizontal direction, the distance between the starting point of the periodic arrangement of the second grating layer and the starting point of the periodic arrangement of the first grating layer is 0.5 to 1.3 μm.

[0016] Optionally, in the horizontal direction, the distance between the starting point of the periodic arrangement of the third grating layer and the starting point of the periodic arrangement of the first grating layer is 0.2 to 0.8 μm.

[0017] Optionally, a first spacer layer is provided between the second grating layer and the first grating layer, and the thickness of the first spacer layer is 0.2 to 1.2 μm.

[0018] Optionally, a second spacer layer is provided between the third grating layer and the first grating layer, and the thickness of the second spacer layer is also 0.2 to 1.2 μm.

[0019] Optionally, a buffer layer is provided between the third grating layer and the substrate, the thickness of the buffer layer being 0.8–2.2 μm.

[0020] Optionally, a cover layer is provided on the side of the second grating layer opposite to the first grating layer, and the thickness of the cover layer is 2.0 to 6.0 μm.

[0021] Optionally, the thickness of the first grating layer is 0.2–0.8 μm;

[0022] The thickness of the second grating layer is 0.4–0.8 μm;

[0023] The thickness of the third grating layer is 0.6–0.8 μm.

[0024] A second aspect of this application provides a silicon-based optical chip, including a silicon nitride grating coupler as described in any of the preceding claims.

[0025] By employing the above technical solution, this application has at least the following beneficial effects:

[0026] Embodiments of this application provide a silicon nitride grating coupler and a silicon-based optical chip. The silicon nitride grating coupler, by setting a first grating layer, a second grating layer, and a third grating layer with different duty cycles and arranged in an alternating manner, can effectively control the scattering path of incident light. The second grating layer can change the scattering path of the incident light and guide it to couple into the first grating layer, which helps to achieve a more reasonable adjustment of the light field distribution for incident light under different conditions, thereby improving the coupling efficiency and making it closer to the theoretical expectation. Simultaneously, the third grating layer can reflect the diffracted light leaking from the first grating layer and guide the reflected light back to the coupling region of the first grating layer, effectively reducing light leakage and thus helping to maintain a high overall coupling efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a silicon nitride grating coupler according to an optional embodiment of this application;

[0028] Figure 2 This is a schematic diagram of the structure of a silicon nitride grating coupler, which is another optional embodiment of this application.

[0029] The reference numerals in the attached figures are as follows:

[0030] 1. Substrate; 2. First grating layer; 3. Second grating layer; 4. Third grating layer; 5. Waveguide layer; 6. First spacer layer; 7. Second spacer layer; 8. Buffer layer; 9. Cover layer. Detailed Implementation

[0031] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0033] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection 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.

[0034] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0035] An embodiment of the first aspect of this application provides a silicon nitride grating coupler, and an embodiment of the second aspect of this application provides a silicon-based optical chip.

[0036] Among them, silicon nitride grating couplers are used in silicon-based optical chips.

[0037] Specifically, silicon-based optical chips contain optical waveguide structures for transmitting optical signals. Taking optical communication as an example, when the optical signal transmitted by the optical fiber arrives at the silicon-based optical chip, the silicon nitride grating coupler can diffract the light emitted from the fiber, accurately focusing the light energy and guiding it to the optical waveguide inside the silicon-based optical chip. This successfully builds a bridge between the external light and the internal optical transmission path of the chip, enabling subsequent optical signal processing operations such as modulation and filtering, ensuring the smooth operation and high-efficiency performance of the entire optical communication system.

[0038] See here. Figure 1 and Figure 2 As shown, the silicon nitride grating coupler provided in the first aspect of this application includes: a substrate 1; a first grating layer 2 located on one side of the substrate 1; a second grating layer 3 located on the side of the first grating layer 2 facing away from the substrate 1; a third grating layer 4 located on the side of the first grating layer 2 opposite to the substrate 1; and a waveguide layer 5 connected to the first grating layer 2 along the grating period arrangement direction; wherein, the second grating layer 3 and the first grating layer 2 are arranged alternately, the duty cycle of the second grating layer 3 is greater than the duty cycle of the first grating layer 2, the second grating layer 3 is used to change the scattering path of the incident light and guide the incident light to couple into the first grating layer 2; the third grating layer 4 and the first grating layer 2 are also arranged alternately, the duty cycle of the third grating layer 4 is less than the duty cycle of the first grating layer 2, the third grating layer 4 is used to reflect the diffracted light leaked from the first grating layer 2 and guide the reflected light back to the coupling region of the first grating layer 2.

[0039] In this embodiment, by setting a first grating layer 2, a second grating layer 3, and a third grating layer 4 with different duty cycles and arranged in an alternating manner, the scattering path of the incident light can be effectively controlled. The second grating layer 3 can change the scattering path of the incident light and guide it to couple into the first grating layer 2, which helps to achieve a more reasonable adjustment of the light field distribution for different incident light conditions, thereby improving the coupling efficiency and making it closer to the theoretical expectation. Simultaneously, the third grating layer 4 can reflect the diffracted light leaking from the first grating layer 2 and guide the reflected light back to the coupling region of the first grating layer 2, effectively reducing light leakage and thus helping to maintain a high overall coupling efficiency.

[0040] Substrate 1 is the basic supporting part of the entire silicon nitride grating coupler. Specifically, substrate 1 can be a silicon wafer.

[0041] In this embodiment, a third grating layer 4, a first grating layer 2, and a second grating layer 3 are sequentially grown on one side of the substrate 1. All three layers are made of silicon nitride. In this embodiment, the third grating layer 4, the first grating layer 2, and the second grating layer 3 are grown sequentially on the substrate 1 from bottom to top. That is, the second grating layer 3 is the top grating, the first grating layer 2 is the middle grating, and the third grating layer 4 is the bottom grating.

[0042] Specifically, in the direction perpendicular to the substrate 1, the etched portion of the second grating layer 3 partially overlaps with the non-etched portion of the first grating layer 2, and vice versa. Furthermore, the second grating layer 3 has a larger duty cycle than the first grating layer 2. This causes a highly complex scattering process to be triggered when incident light reaches the second grating layer 3, resulting in scattering components pointing in different directions. The core function of the second grating layer 3 is to optimize and adjust the direction and intensity distribution of these scattering components, guiding the incident light along a specific path and making it easier to couple into the first grating layer 2. It should be noted that the second grating layer 3 enables the incident light to form a specific phase distribution pattern after scattering, allowing it to achieve a more ideal match with the existing optical field mode within the first grating layer 2 when it enters, ultimately achieving a highly efficient optical field coupling process and significantly improving the coupling efficiency and performance of the entire grating coupler. Furthermore, in the direction perpendicular to the substrate 1, the etched portion of the third grating layer 4 partially overlaps with the non-etched portion of the first grating layer 2, and vice versa. However, the duty cycle of the third grating layer 4 is smaller than that of the first grating layer 2. When light propagates in the first grating layer 2, due to diffraction effects and other factors, some light inevitably leaks out. This leaked light is then reflected by the third grating layer 4. It should be noted that the third grating layer 4, based on its staggered structure with the first grating layer 2 and its smaller duty cycle, can accurately redirect the reflected light back into the effective coupling region of the first grating layer 2. As a result, light that might have been lost due to leakage can be reused and continue to participate in the optical coupling and transmission process, thereby reducing the occurrence of optical leakage, improving the light utilization and coupling efficiency of the entire silicon nitride grating coupler, better maintaining the integrity of the optical signal during transmission, and enhancing its stability. This lays a solid foundation for the stable and reliable operation of optical communication and optical integrated systems, and effectively guarantees the efficient operation and continuous service capabilities of related systems in various application scenarios.

[0043] Understandably, in a grating structure, the duty cycle refers to the proportion of unetched portions within one cycle of the grating. For the second grating layer 3, when its duty cycle is greater than that of the first grating layer 2, its unetched portion is relatively larger per unit cycle. According to the Huygens-Fresnel principle, light can be considered as the superposition of wavelets emitted by countless secondary wave sources. In the second grating layer 3, due to the large duty cycle, the distribution and intensity of the secondary wave sources are significantly affected by the grating structure. When light passes through this layer, the increased unetched portion will change the emission direction and intensity of the secondary wave sources, thus causing a change in the direction of the scattered light. That is, a larger duty cycle makes it easier for light to form a new propagation direction through the unetched portion when propagating in the second grating layer 3, thereby optimizing the direction of the incident light scattering component and causing the incident light to travel in a direction that is easier to couple into the first grating layer 2. However, for the third grating layer 4, when its duty cycle is smaller than that of the first grating layer 2... It should be noted that when the duty cycle of the third grating layer 4 is too large, the optical field matching between the third grating layer 4 and the first grating layer 2 deteriorates. In other words, after light leaks from the first grating layer 2, due to the excessively large duty cycle of the third grating layer 4, the reflected light cannot be well recoupled into the coupling region of the first grating layer 2. Conversely, if the duty cycle of the third grating layer 4 is smaller than that of the first grating layer 2, although the reflective area is relatively smaller, the grating structure becomes more refined, allowing for better control of the light reflection direction and mode, enabling the reflected light to return to the coupling region of the first grating layer 2 more precisely.

[0044] A waveguide layer 5 is disposed at the interface of the first grating layer 2. The waveguide layer 5 can confine light to its interior using the principle of total internal reflection, reducing scattering and loss during transmission. In practical applications, after light is coupled through the first grating layer 2 and other grating layers, the waveguide layer 5 can accurately receive and guide the light along its designated direction, thereby effectively transmitting the optical signal to other components of the optical communication or optical integrated system. It should be noted that the waveguide layer 5 ensures a smooth and efficient transition of light from the silicon nitride grating coupler into the internal waveguide structure of the silicon-based optical chip, avoiding additional light loss or signal distortion caused by interface mismatch, and further guaranteeing the performance and reliability of the entire optical communication link.

[0045] In some possible embodiments disclosed in this application, the grating period of the first grating layer 2 is 1.1 to 1.4 μm, and the duty cycle of the first grating layer 2 is 0.3 to 0.7; the grating period of the second grating layer 3 is 1.1 to 1.4 μm, and the duty cycle of the second grating layer 3 is 0.6 to 0.8; the grating period of the third grating layer 4 is 1.1 to 1.4 μm, and the duty cycle of the third grating layer 4 is 0.2 to 0.6.

[0046] In this embodiment, the grating period of the first grating layer 2 is 1.1–1.4 μm, and the duty cycle is 0.3–0.7. This parameter range allows the first grating layer 2 to effectively diffract incident light over a wide wavelength range. The grating period of the second grating layer 3 is also 1.1–1.4 μm, but the duty cycle of the second grating layer 3 is 0.6–0.8. The larger duty cycle can better alter the scattering path of the incident light. When the incident light reaches the second grating layer 3, due to the characteristics of its duty cycle, it can guide the incident light to couple into the first grating layer 2 at a more suitable angle and light field distribution. The grating period of the third grating layer 4 is 1.1–1.4 μm, and the duty cycle is 0.2–0.6. The smaller duty cycle means that the third grating layer 4 has a relatively larger reflection area. When light passes through the first grating layer 2, some of the light will leak due to diffraction and other reasons. The third grating layer 4 can use its structural characteristics to reflect this leaked light and guide it back to the coupling region of the first grating layer 2.

[0047] The grating period refers to the length of a complete repeating unit in the grating structure. For the first grating layer 2, its grating period is between 1.1 and 1.4 μm, providing good adaptability to different wavelengths of light. For the second grating layer 3, its grating period is also between 1.1 and 1.4 μm, which facilitates good optical synergy with the first grating layer 2 in the direction perpendicular to the substrate 1. For the third grating layer 4, its grating period is also between 1.1 and 1.4 μm, resulting in a regular grating structure for the entire silicon nitride grating coupler in the direction perpendicular to the substrate 1, which is beneficial for overall light control.

[0048] The duty cycle refers to the proportion of unetched portion within one grating cycle. For the first grating layer 2, its duty cycle is between 0.3 and 0.7, allowing for flexible adjustment of its optical properties. For the second grating layer 3, its duty cycle is between 0.6 and 0.8, greater than that of the first grating layer 2, enabling it to alter the incident light scattering path and guide light coupling into the first grating layer 2. For the third grating layer 4, its duty cycle is between 0.2 and 0.6, less than that of the first grating layer 2, effectively reflecting light. Through its staggered arrangement with the first grating layer 2, it guides the reflected light back to the coupling region of the first grating layer 2, thereby reducing light leakage and improving the overall coupling efficiency of the grating coupler.

[0049] In some possible embodiments disclosed in this application, the distance between the starting point of the second grating layer 3 and the starting point of the first grating layer 2 in the horizontal direction is 0.5 to 1.3 μm.

[0050] Here, the horizontal direction refers to the direction parallel to the plane of substrate 1. For the grating layer, it is a periodically arranged structure with a starting point for this periodic arrangement. This starting point can be understood as the position where the periodic repeating units of the grating begin, much like the starting connection point of a "chain" composed of repeating identical units.

[0051] Specifically, the distance between the starting points of the periodic arrangement of the second grating layer 3 and the starting points of the periodic arrangement of the first grating layer 2 is between 0.5 and 1.3 μm. After light is processed in the second grating layer 3, it needs to enter the first grating layer 2 to complete the subsequent coupling process. This distance acts as a transition in the light transmission path. It should be noted that, from the perspective of light field distribution, the light field mode generated by the light in the second grating layer 3 needs to match the light field mode in the first grating layer 2 to achieve efficient coupling. The 0.5–1.3 μm interval allows for some adjustment of the light field. From the perspective of light propagation, this interval is like a "light channel adjustment zone." If the interval is too small or there is no interval, the light may produce unnecessary scattering or reflection due to the sudden change in the two grating structures, resulting in reduced coupling efficiency. In this embodiment, the 0.5–1.3 μm interval can guide the light to enter the first grating layer 2 at a more suitable angle and in a more suitable manner.

[0052] In some possible embodiments disclosed in this application, the distance between the starting point of the third grating layer 4 and the starting point of the first grating layer 2 in the horizontal direction is 0.2 to 0.8 μm.

[0053] In this embodiment, when light partially leaks during propagation in the first grating layer 2, the third grating layer 4 is responsible for reflecting this leaked light and guiding it back to the coupling region of the first grating layer 2. The spacing of 0.2–0.8 μm provides a suitable spatial adjustment range for the light reflection and recoupling process.

[0054] Specifically, when the leaked light propagates from the first grating layer 2 to the third grating layer 4 and is reflected, the 0.2 to 0.8 μm interval allows the light to be properly adjusted in this space when it returns to the first grating layer 2, so as to better adapt to the light field structure of the first grating layer 2 and thus more effectively recouple into the first grating layer 2.

[0055] In some possible embodiments disclosed in this application, a first spacer layer 6 is provided between the second grating layer 3 and the first grating layer 2, and the thickness of the first spacer layer 6 is 0.2 to 1.2 μm.

[0056] In this embodiment, a first spacer layer 6 with a thickness of 0.2–1.2 μm is disposed between the second grating layer 3 and the first grating layer 2, which can effectively reduce potential optical interference between the two grating layers. When light is scattered in the second grating layer 3, without the spacer layer, it may directly interact with the first grating layer 2, producing some unnecessary reflection, refraction, or scattering. The presence of the first spacer layer 6 acts as a buffer region, providing a transition phase for light before it enters the first grating layer 2, reducing this direct interaction that could lead to chaotic light fields, thereby reducing interlayer crosstalk and improving the purity of optical signal transmission. Furthermore, light can obtain a suitable phase change after passing through the first spacer layer 6, allowing it to better match the light field mode within the first grating layer 2 when it enters, thereby improving optical coupling efficiency.

[0057] The first spacer layer 6 can be made of silicon dioxide.

[0058] Specifically, the thickness of the first spacer layer 6 can be 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, etc. It is understood that the thickness of the first spacer layer 6 can also be other values ​​besides those mentioned above, as long as the thickness of the first spacer layer 6 is within the range of 0.2 to 1.2μm. It should be noted that for incident light of different wavelengths and modes, adjusting the thickness of the first spacer layer 6 can optimize the optical field distribution, allowing the silicon nitride grating coupler to better adapt to various optical communication scenarios.

[0059] In some possible embodiments disclosed in this application, a second spacer layer 7 is provided between the third grating layer 4 and the first grating layer 2, and the thickness of the second spacer layer 7 is also 0.2 to 1.2 μm.

[0060] In this embodiment, when light leaks from the first grating layer 2 and propagates to the third grating layer 4, the presence of the second spacer layer 7 reduces additional reflections that may occur due to direct contact between the two grating layers. Without the second spacer layer 7, the light may experience unexpected reflections during its journey from the first grating layer 2 to the third grating layer 4 due to the abrupt change at the interface, thus interfering with the normal propagation path of the light. The thickness range of 0.2–1.2 μm provides a transition region for light propagation, allowing the light to gradually adjust its propagation state within this region, reducing unnecessary reflections, and enabling the light to reach the third grating layer 4 more effectively for reflection and recoupling back to the first grating layer 2.

[0061] The second spacer layer 7 can also be made of silicon dioxide.

[0062] Specifically, the thickness of the second spacer layer 7 can be the same as or different from the thickness of the first spacer layer 6, as long as the thickness of the second spacer layer 7 is within the range of 0.2 to 1.2 μm. It should be noted that a thickness of 0.2 to 1.2 μm in the second spacer layer 7 will result in different optical path changes in the second spacer layer 7, and different optical path changes will cause phase changes in the light, so that the light can achieve ideal phase adjustment during its propagation from the first grating layer 2 to the third grating layer 4 or its reflection back.

[0063] In some possible embodiments disclosed in this application, a buffer layer 8 is provided between the third grating layer 4 and the substrate 1, and the thickness of the buffer layer 8 is 0.8 to 2.2 μm.

[0064] In this embodiment, the buffer layer 8 reduces the light reflection interference from the substrate 1. The buffer layer 8 can also be made of silicon dioxide.

[0065] Specifically, the thickness of the buffer layer 8 can be 0.8μm, 0.9μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, etc. When light propagates in the third grating layer 4, some light may propagate towards the substrate 1. Without the buffer layer 8, the interface between the substrate 1 and the third grating layer 4 may cause strong reflection, preventing light from propagating effectively in the grating coupler. The buffer layer 8 provides a transition region before the light reaches the substrate 1, reducing the reflectivity of the substrate 1 and allowing more light to propagate in the grating coupler in the intended direction, thereby improving light utilization and transmission efficiency.

[0066] In some possible embodiments disclosed in this application, a cover layer 9 is provided on the side of the second grating layer 3 facing away from the first grating layer 2, and the thickness of the cover layer 9 is 2.0 to 6.0 μm.

[0067] In this embodiment, by providing the cover layer 9, the second grating layer 3 can be protected, preventing external dust, moisture or other impurities from contacting the second grating layer 3, which would lead to increased light loss or disordered light field distribution of the second grating layer 3.

[0068] The capping layer 9 is located at the top of the entire silicon nitride grating coupler and is the outermost structural part of the silicon nitride grating coupler. In practical applications, the capping layer 9 is in direct contact with the external environment or subsequent optical components.

[0069] Specifically, the capping layer 9 can be made of silicon dioxide to protect the grating structure inside the silicon nitride grating coupler. Furthermore, the thickness of the capping layer 9 is between 2.0 and 6.0 μm, allowing light to enter the target element at an optimal angle and with appropriate intensity distribution, thereby improving the efficiency and accuracy of optical coupling.

[0070] In some possible embodiments disclosed in this application, the thickness of the first grating layer 2 is 0.2 to 0.8 μm; the thickness of the second grating layer 3 is 0.4 to 0.8 μm; and the thickness of the third grating layer 4 is 0.6 to 0.8 μm.

[0071] The varying thicknesses of the grating layers help to adjust the optical field pattern. The first grating layer 2 has a thickness between 0.2 and 0.8 μm, the second grating layer 3 has a thickness between 0.4 and 0.8 μm, and the third grating layer 4 has a thickness between 0.6 and 0.8 μm. When light propagates between these grating layers, the thickness of each layer affects the propagation path and the optical field distribution. For example, the relatively thick second grating layer 3 (0.4–0.8 μm) can better guide the scattering of incident light, allowing its resulting optical field pattern to better match the optical field pattern of the first grating layer 2. This matching helps improve the coupling efficiency of light from the second grating layer 3 to the first grating layer 2 and reduces light loss during coupling. The thickness of the third grating layer 4 (0.6–0.8 μm) effectively reflects light leaking from the first grating layer 2. The thicker third grating layer 4 can provide sufficient reflective interface and optical path, allowing the leaked light to have a suitable phase change during reflection, which is more conducive to recoupling into the first grating layer 2 and improving the light utilization of the entire grating coupler.

[0072] Specifically, the thickness of the first grating layer 2, the second grating layer 3, and the third grating layer 4 is preferably 0.8 μm.

[0073] It will be readily understood by those skilled in the art that the aforementioned advantageous methods can be freely combined and superimposed without conflict.

[0074] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A silicon nitride grating coupler, characterized in that, include: Substrate (1); The first grating layer (2) is located on one side of the substrate (1); A second grating layer (3) is located on the side of the first grating layer (2) away from the substrate (1). The second grating layer (3) and the first grating layer (2) are arranged alternately. The duty cycle of the second grating layer (3) is greater than that of the first grating layer (2). The second grating layer (3) is used to change the scattering path of the incident light and guide the incident light to couple into the first grating layer (2). A third grating layer (4) is located on the side of the first grating layer (2) opposite to the substrate (1). The third grating layer (4) and the first grating layer (2) are also arranged alternately. The duty cycle of the third grating layer (4) is smaller than that of the first grating layer (2). The third grating layer (4) is used to reflect the diffracted light leaked from the first grating layer (2) and guide the reflected light back to the coupling region of the first grating layer (2). Waveguide layer (5) is connected to the first grating layer (2) along the grating period arrangement direction of the first grating layer (2).

2. The silicon nitride grating coupler according to claim 1, characterized in that, The grating period of the first grating layer (2) is 1.1 to 1.4 μm, and the duty cycle of the first grating layer (2) is 0.3 to 0.

7. The grating period of the second grating layer (3) is 1.1 to 1.4 μm, and the duty cycle of the second grating layer (3) is 0.6 to 0.

8. The grating period of the third grating layer (4) is 1.1 to 1.4 μm, and the duty cycle of the third grating layer (4) is 0.2 to 0.

6.

3. The silicon nitride grating coupler according to claim 1, characterized in that, In the horizontal direction, the distance between the starting point of the periodic arrangement of the second grating layer (3) and the starting point of the periodic arrangement of the first grating layer (2) is 0.5 to 1.3 μm.

4. The silicon nitride grating coupler according to claim 1, characterized in that, In the horizontal direction, the distance between the starting point of the periodic arrangement of the third grating layer (4) and the starting point of the periodic arrangement of the first grating layer (2) is 0.2 to 0.8 μm.

5. The silicon nitride grating coupler according to claim 1, characterized in that, A first spacer layer (6) is provided between the second grating layer (3) and the first grating layer (2), and the thickness of the first spacer layer (6) is 0.2 to 1.2 μm.

6. The silicon nitride grating coupler according to claim 1, characterized in that, A second spacer layer (7) is provided between the third grating layer (4) and the first grating layer (2), and the thickness of the second spacer layer (7) is also 0.2 to 1.2 μm.

7. The silicon nitride grating coupler according to claim 1, characterized in that, A buffer layer (8) is provided between the third grating layer (2) and the substrate (1), and the thickness of the buffer layer (8) is 0.8 to 2.2 μm.

8. The silicon nitride grating coupler according to claim 1, characterized in that, The second grating layer (3) has a cover layer (9) on the side opposite to the first grating layer (2), and the thickness of the cover layer (9) is 2.0 to 6.0 μm.

9. The silicon nitride grating coupler according to claim 1, characterized in that, The thickness of the first grating layer (2) is 0.2–0.8 μm; The thickness of the second grating layer (3) is 0.4–0.8 μm; The thickness of the third grating layer (4) is 0.6 to 0.8 μm.

10. A silicon-based optical chip, characterized in that, Including the silicon nitride grating coupler as described in any one of claims 1-9.

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