Two-dimensional grating coupler

Abstract

The invention discloses a two-dimensional grating coupler which comprises a two-dimensional grating, a focusing grating and a conical waveguide which are connected in sequence. The two-dimensional grating is used for converting nearly vertical incident light into emergent light propagating in a waveguide layer; the direction of the focusing grating is parallel to the propagation direction of the emergent light, and the focusing grating has preset duty ratio distribution, so that the emergent light is equal in optical path at the focal point of the focusing grating, and the emergent light is focused; the wide port of the conical waveguide is connected to the focusing grating, and the narrow port of the conical waveguide is located at the focus of the focusing grating and used for transmitting the focused emergent light.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and more specifically to an optical coupling device for use in a Photonic Integrated Circuit (PIC). Background Technology

[0002] With the explosive growth in bandwidth demands from data centers, high-performance computing, and optical communication networks, Integrated Optical Path (PIC) technology has become a key technology for solving optical interconnect bottlenecks due to its advantages of high integration, low power consumption, low cost, and potential high performance. In PIC systems, one of the core challenges in achieving high-performance optical interconnects is how to efficiently couple optical signals from external light sources (such as lasers) or transmission media (such as optical fibers) into the optical waveguides on the PIC chip, and how to couple optical signals from the PIC chip outwards.

[0003] Traditional coupling schemes mainly include edge coupling and grating coupling. Edge coupling typically requires precise chip edge polishing and alignment, placing extremely high demands on packaging processes and making it difficult to achieve multi-channel parallel coupling. Grating couplers, on the other hand, utilize periodic structures (gratings) to couple light beams vertically into and out of the chip plane. They offer significant advantages such as large alignment tolerance, ease of wafer-level testing, and good compatibility with planar processes, making them highly suitable for advanced optical interconnect architectures such as co-packaged optics (CPO) and optical input / output (OIO).

[0004] In optical interconnect scenarios, the distance between the transmitter and receiver is relatively long. For cost reasons, non-polarization-maintaining fiber is typically used between them. Therefore, the optical signal received at the receiver is not in a single polarization direction, making one-dimensional grating couplers unsuitable. That is, a two-dimensional grating coupler is required at the receiver to achieve efficient optical coupling that is insensitive to polarization.

[0005] like Figure 1 As shown, a traditional two-dimensional grating coupler consists of a two-dimensional grating and tapered waveguides. The two-dimensional grating converts incident light from a nearly perpendicular direction (with an angle of about 10° between the incident light and the normal direction of the plane containing the grating) into outgoing light that propagates within the waveguide layer along two tapered waveguides. Since the width of the two-dimensional grating (10µm-20µm) is significantly larger than the width of the waveguide (300nm-1000nm), a relatively long tapered waveguide (typically greater than 200µm) is needed to achieve a low-loss connection between the two-dimensional grating and the waveguide.

[0006] For optical interconnect chips, to achieve higher overall bandwidth, multiple channels (typically 8, 16, or 32) need to be arrayed. Due to the need for increased integration density, the channel spacing needs to be reduced, commonly less than 250µm. This reduction in channel spacing implies a reduction in the spacing of the two-dimensional grating couplers. To prevent interference between signals from different channels, the length of the tapered waveguide also needs to be shortened. However, the loss of the tapered waveguide increases as its length decreases, especially when the length is less than 200µm. For example, a channel spacing of 127µm implies a tapered waveguide length of less than 70µm, resulting in a significant increase in loss.

[0007] Therefore, there is an urgent need in this field for a novel two-dimensional grating coupler structure that can effectively shorten the length of the tapered waveguide while ensuring low insertion loss, adapt to the compact requirements of high-density channel arrays, and maintain good robustness to process deviations, so as to facilitate practical manufacturing and industrial applications. Summary of the Invention

[0008] This application provides a two-dimensional grating coupler with a compact structure. By introducing a focusing grating with a specific duty cycle distribution between a traditional two-dimensional grating and a tapered waveguide, it solves the technical problem of increased optical transmission loss caused by the shortening of the tapered waveguide length in high-density integration, and achieves a good balance between device compactness and low loss.

[0009] The first aspect of this application discloses a two-dimensional grating coupler, comprising a two-dimensional grating, a focusing grating, and a tapered waveguide connected in sequence. The two-dimensional grating is used to convert incident light in a nearly perpendicular direction into outgoing light that propagates in the waveguide plane. The focusing grating is oriented parallel to the propagation direction of the outgoing light and has a preset duty cycle distribution, so that the outgoing light achieves equal optical path length at the focal point of the focusing grating, thereby achieving focusing of the outgoing light. The wide port of the tapered waveguide is connected to the focusing grating, and its narrow port is located at the focal point of the focusing grating for propagating the focused outgoing light.

[0010] According to the two-dimensional grating coupler of this application, by setting a focusing grating parallel to the direction of the outgoing light, the equivalent refractive index can be adjusted by utilizing the grating's duty cycle distribution, thus achieving convergence of the outgoing light. Since the outgoing light is converged by the focusing grating before entering the tapered waveguide, the length of the tapered waveguide can be significantly shortened without significantly increasing mode matching loss. This effectively overcomes the contradiction between long tapered waveguides and high integration density in traditional designs, achieving device miniaturization while ensuring good process compatibility and performance robustness.

[0011] In the two-dimensional grating coupler disclosed in this application, the duty cycle distribution of the focusing grating is set to satisfy the following relationship: ,in, , denoted as the equivalent refractive indices at two different locations on the focusing grating, and d as the dimension of the focusing grating in the direction of light propagation. The refractive index of the tapered waveguide (core layer) is... , These are the distances from the two locations to the narrow port of the tapered waveguide (i.e., the focal point of the focusing grating).

[0012] According to the two-dimensional grating coupler of this application, the above relationship clarifies the physical conditions for achieving equal optical path focusing. By precisely designing the duty cycle distribution to meet these conditions, it can be ensured that light waves emitted from different positions of the focusing grating are superimposed in phase at the narrow port (focal point) of the tapered waveguide, thereby obtaining a high-quality, low-loss focused spot and achieving efficient optical coupling.

[0013] In the two-dimensional grating coupler disclosed in this application, the focusing grating includes at least two grating units arranged along the propagation direction of the outgoing light, and each grating unit has the same or different duty cycle distribution.

[0014] The two-dimensional grating coupler of this application adopts a segmented design, which provides greater freedom and flexibility for the adjustment and processing of the duty cycle of the focusing grating.

[0015] In the two-dimensional grating coupler disclosed in this application, the two-dimensional grating is a focusing type two-dimensional grating.

[0016] According to the two-dimensional grating coupler of this application, the two-dimensional grating itself is also designed as a focusing grating with preliminary focusing function, which can form a "two-stage focusing" effect with the subsequent focusing grating. This design can further converge the optical field, allowing the use of shorter tapered waveguides and achieving a more compact design.

[0017] In the two-dimensional grating coupler disclosed in this application, the length of the tapered waveguide is less than 200µm, preferably less than 100µm, and more preferably less than 50µm.

[0018] In the two-dimensional grating coupler disclosed in this application, the tapered waveguide is one of a linear tapered waveguide, an exponential tapered waveguide, or a cosine tapered waveguide.

[0019] The two-dimensional grating coupler according to this application provides a variety of tapered waveguide profiles to choose from. Designers can select the most suitable tapered curve to achieve optimal transmission characteristics based on specific material systems, wavelengths, and bandwidth requirements.

[0020] In the two-dimensional grating coupler disclosed in this application, the two-dimensional grating and / or the focusing grating are formed by fully etching or partially etching the waveguide layer.

[0021] According to the two-dimensional grating coupler of this application, the grating structure can be realized through conventional semiconductor manufacturing processes, and has good manufacturability and compatibility with existing PIC production lines.

[0022] The two-dimensional grating coupler disclosed in this application also includes a reflective structure disposed below the two-dimensional grating, wherein the reflective structure is a metal reflector or a dielectric layer reflector.

[0023] According to the two-dimensional grating coupler of this application, the introduction of a bottom reflector can reflect the downward-leaking light back and perform the optical coupling process again, thereby significantly improving the optical coupling efficiency.

[0024] In the two-dimensional grating coupler disclosed in this application, the two-dimensional grating is directly connected to the focusing grating, or is connected through a patternless waveguide layer.

[0025] According to the two-dimensional grating coupler of this application, two component connection methods are provided. Direct connection helps to minimize the device length and achieve compactness. Transitioning through a section of unpatterned waveguide provides a buffer area for the light field before entering the focusing grating, which is beneficial for relaxing alignment tolerances and optimizing mode matching, and provides design flexibility.

[0026] In the two-dimensional grating coupler disclosed in this application, the two-dimensional grating coupler is composed of a waveguide layer and a cladding layer. The waveguide layer is made of silicon or silicon nitride, and the cladding layer is made of silicon dioxide or silicon oxynitride.

[0027] According to the two-dimensional grating coupler of this application, silicon and silicon nitride are the core waveguide materials in integrated photonics, while silicon dioxide and silicon oxynitride, which have relatively low refractive indices, are used as cladding materials. They can be widely used in mainstream photonic integrated circuits based on SOI (silicon-on-insulator) or silicon nitride platforms, and have wide applicability.

[0028] Compared with existing technologies, this application, by setting a focusing grating, can utilize existing PIC chip processing technology to achieve a significant reduction in the size of the grating coupler while maintaining stable performance, providing key technical support for the practical application of high-density, high-bandwidth optical interconnect chips. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a two-dimensional grating coupler in the prior art;

[0030] Figure 2 This is a schematic diagram of the two-dimensional grating coupler involved in this application;

[0031] Figure 3 This is a schematic diagram of the focusing grating in the two-dimensional grating coupler involved in this application;

[0032] Figure 4 This is a schematic diagram of the segmented grating in the two-dimensional grating coupler involved in this application. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments and accompanying drawings. It is to be understood that the illustrative embodiments of this disclosure are merely for explaining the present application and not for limiting it. Furthermore, for ease of description, the accompanying drawings show only the parts relevant to the present application, and not all of the structures or processes.

[0034] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Although the description of this application is presented in conjunction with preferred embodiments, this does not mean that the features of this invention are limited to this embodiment. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of this application. To provide a thorough understanding of this application, many specific details will be included in the following description. This application may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of this application, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0035] Unless the context otherwise specifies, the terms “contains,” “has,” and “includes” are synonyms. The phrase “A / B” means “A or B.” The phrase “A and / or B” means “(A and B) or (A or B).”

[0036] It should be understood that although terms such as "first," "second," etc., may be used herein to describe various components, units, or data, these components, units, or data should not be limited by these terms. These terms are used merely to distinguish one feature from another. For example, without departing from the scope of the exemplary embodiments, a first feature may be referred to as a second feature, and similarly, a second feature may be referred to as a first feature.

[0037] It should be understood that although directional terms such as "up," "down," "left," and "right" may be used here to describe the positional relationship between the various components, these directional terms are only for the convenience of understanding and are not intended to limit the scope of protection of this application.

[0038] It should be noted that in this specification, similar reference numerals and letters in the accompanying drawings indicate similar items. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0040] Figure 2 This is a schematic diagram of the two-dimensional grating coupler involved in this application. Figure 2 As shown, the two-dimensional grating coupler includes a two-dimensional grating 1, a focusing grating 2, and a tapered waveguide 3 connected in sequence. The two-dimensional grating 1 is used to convert nearly perpendicular incident light into outgoing light propagating within the waveguide layer. Here, "nearly perpendicular" means that the angle between the direction of the incident light and the normal direction of the plane containing the two-dimensional grating 1 (which is also the plane containing the waveguide layer) is very small, for example, less than or equal to 10°. The focusing grating 2 is parallel to the propagation direction of the outgoing light and has a preset duty cycle distribution, ensuring that the outgoing light has an equal optical path at the focal point of the focusing grating, thereby focusing the outgoing light. The wide port of the tapered waveguide 3 is connected to the focusing grating 2, and its narrow port is located at the focal point of the focusing grating 2, used to propagate the focused outgoing light.

[0041] Specifically, a two-dimensional grating coupler consists of a waveguide layer and cladding layers located on the top and bottom sides of the waveguide layer. The waveguide layer can be made of silicon or silicon nitride, while the cladding layer can be made of silicon dioxide or silicon oxynitride. The low-refractive-index cladding layer completely encloses the high-refractive-index waveguide layer, utilizing total internal reflection to achieve the propagation of light waves within the waveguide layer. For example, a two-dimensional grating coupler can be manufactured using SOI (Silicon-on-Insulator) platform technology. The buried oxide layer of the SOI wafer serves as the lower cladding layer, and the top silicon layer serves as the waveguide layer. A patterned structure of a two-dimensional grating 1, a focusing grating 2, and a tapered waveguide 3 is fabricated on the top silicon layer (i.e., the waveguide layer) using photolithography and etching processes. Then, silicon dioxide or silicon oxynitride is deposited on the etched structure using chemical vapor deposition (CVD) to form the upper cladding layer. This invention is also applicable to other material systems. For example, on a silicon nitride platform, a two-dimensional grating coupler with a working wavelength of 1310 nm or 1550 nm can be fabricated using a silicon nitride waveguide layer and a cladding material of silicon dioxide or silicon oxynitride.

[0042] Two-dimensional grating 1 and focusing grating 2 can be formed by full etching of the waveguide layer or by partial etching of the waveguide layer. Full etching refers to etching away all the material of the corresponding portion of the waveguide layer according to a pre-defined pattern structure, and then filling it with cladding material in subsequent processes. Partial etching refers to etching away a portion of the waveguide layer material in the depth direction according to a pre-defined pattern structure, but retaining the bottom portion of the waveguide layer, and then filling it with cladding material to maintain the continuity of the bottom of the waveguide layer. Generally, when the refractive index of the waveguide layer material is high (greater than or equal to 3), such as in silicon waveguide layers, partial etching can be applied. This reduces the etching depth, making it easier to process, while still ensuring the desired equivalent refractive index distribution is achieved. When the refractive index of the waveguide layer material is low (less than 3), such as in silicon nitride waveguide layers, full etching can be applied, replacing all the waveguide layer material corresponding to the pre-defined pattern structure with cladding material, thus ensuring the desired equivalent refractive index distribution is achieved.

[0043] Incident light with a non-uniform polarization direction is incident on a two-dimensional grating 1 from a nearly perpendicular direction. The grating 1 converts the light into outgoing light propagating within the waveguide layer. This outgoing light is split into two beams with mutually perpendicular propagation directions. Two focusing gratings 2 are connected downstream of the grating 1. The direction of the focusing grating 2 refers to the direction in which its scribe lines extend, which are parallel to the propagation directions of the two outgoing beams. Two tapered waveguides 3 are connected downstream of the two focusing gratings 2.

[0044] Although Figure 2 The two-dimensional grating 1 is directly connected to the focusing grating 2, but this application is not limited to this. The two-dimensional grating and the focusing grating can also be connected by a transitional unpatterned waveguide layer. Direct connection helps to minimize the device length and achieve compactness; transitioning through an unpatterned waveguide provides a buffer area for the light field before entering the focusing grating, which is beneficial for relaxing alignment tolerances and optimizing mode matching, and provides design flexibility.

[0045] Figure 3 This is a schematic diagram of the focusing grating in the two-dimensional grating coupler involved in this application. Figure 3 As shown, to achieve focusing of the emitted light at focal point F, it is necessary to ensure that the optical path lengths of emitted light from different positions on the focusing grating 2, such as the first position 21 located on the optical axis and the second position 22 located near the edge, are equal when reaching focal point F. The optical path length is defined as the product of the geometric path length and the refractive index of the medium along that path. Focal point F is the position of the narrow port of the focusing grating 2. For the emitted light at the first position 21, its optical path length is... For the emitted light at position 22, its optical path is 2, of which d is the equivalent refractive index of the focusing grating 2 at the first position 21, and d is the dimension (width, i.e. the short side dimension of the focusing grating 2 that is rectangular in the top view) of the focusing grating 2 in the direction of propagation of the outgoing light. The refractive index of the tapered waveguide (that is, the refractive index of the waveguide layer, such as the refractive index of silicon or silicon nitride). It is the distance from the first position 21 of the focusing grating 2 to the narrow port of the tapered waveguide 3 (that is, the geometric path length of the emitted light after passing through the first position 21 of the focusing grating 2 and propagating in the tapered waveguide 3). To focus the equivalent refractive index of grating 2 at the first position 22, This is the distance from the second position 22 of the focusing grating 2 to the narrow port of the tapered waveguide 3 (that is, the geometric path length of the outgoing light propagating within the tapered waveguide 3 after passing the second position 22 of the focusing grating 2). To achieve focusing of the outgoing light at the focal point F, it is necessary to ensure... Since the geometric path lengths of the emitted light at different positions of the focusing grating 2 propagating within the conical waveguide 3 are different, it is necessary to ensure that different positions of the focusing grating 2 have different equivalent refractive indices. The equivalent refractive index at different positions of the focusing grating 2 is determined by its duty cycle; therefore, the duty cycle distribution of the focusing grating 2 needs to be set to satisfy the above equation. In this application, the periodic variation of the focusing grating 2 is achieved by etching the waveguide layer and then filling it with cladding material. Furthermore, the refractive index of the waveguide layer material is greater than that of the cladding material. Here, the portion of the waveguide layer retained after etching is defined as the scribe line of the focusing grating 2. The width of the scribe line itself and the width between adjacent scribe lines are defined as the duty cycle of the focusing grating 2. Since the refractive index of the scribe line is relatively large, a larger duty cycle of the focusing grating 2 results in a larger equivalent refractive index. Therefore, the duty cycle distribution of the focusing grating 2 is set to gradually increase from the edge to the center.

[0046] In this application, the focusing grating is typically designed as a single-segment grating, meaning the grating lines are a continuous strip of lines. However, this application is not limited to this; the focusing grating may also include at least two grating units arranged along the propagation direction of the emitted light, each grating unit having the same or different duty cycle distributions. Figure 4 This is a schematic diagram showing that the focusing grating in the two-dimensional grating coupler involved in this application is a segmented grating. For example... Figure 4As shown, the X-direction is the propagation direction of the emitted light. The focusing grating 2 includes a first grating unit 23 and a second grating unit 24 arranged along the X-direction. The first grating unit 23 and the second grating unit 24 are connected together by a continuous waveguide layer portion 25 between them, and the first grating unit 23 and the second grating unit 24 have the same duty cycle distribution. For a compact structure, the length of the tapered waveguide needs to be minimized. The shorter the length of the tapered waveguide, the greater the optical path difference between the emitted light at the center and edge positions of the focusing grating. Therefore, a greater difference in equivalent refractive index between the center and edge positions of the focusing grating is required. However, when the refractive index of the waveguide layer material is low, such as a silicon nitride waveguide layer, the difference in refractive index between the waveguide layer material and the cladding material is small. Compared with high-refractive-index waveguide layers, the equivalent refractive index difference is smaller under the same duty cycle. Therefore, it is necessary to increase the width of the focusing grating. Increasing the width of the focusing grating, i.e. Figure 4 The increased dimension in the X direction means an increase in the scribing length, which leads to a higher aspect ratio. However, an excessively large aspect ratio is detrimental to scribing processing and can cause a decrease in the processing quality of the focusing grating. Therefore, the robustness of the focusing grating can be improved by processing it in multiple grating units. The duty cycle of each grating unit can also be different, providing more flexibility in the design of the focusing grating.

[0047] Figure 2 and Figure 3 The tapered waveguide 3 shown is a linear tapered waveguide, meaning its edge contour is a straight line. However, this application is not limited to this; the tapered waveguide can also be an exponential tapered waveguide or a cosine tapered waveguide. By comprehensively optimizing the duty cycle distribution of the focusing grating and the shape of the tapered waveguide, the focusing effect and optical coupling efficiency can be further improved.

[0048] In this application, for ease of fabrication, two-dimensional gratings are typically designed as linear gratings, meaning the grating lines in both directions are straight and arranged in a uniform period. However, this application is not limited to this; the two-dimensional grating itself can also be designed as a focusing grating. By designing the two-dimensional grating with curved and / or non-uniformly periodically arranged grating lines, the two-dimensional grating itself can converge the emitted light. Designing the two-dimensional grating itself as a focusing grating with preliminary focusing function can form a "two-stage focusing" effect with subsequent focusing gratings. This design can further converge the light field, allowing the use of shorter tapered waveguides and achieving a more compact design.

[0049] In this application, by setting a focusing grating between the two-dimensional grating and the tapered waveguide, the length of the tapered waveguide can be effectively shortened without affecting the optical loss, so that the length of the tapered waveguide is less than 200µm, preferably less than 100µm, and more preferably less than 50µm.

[0050] In this application, a reflective structure can also be set below the two-dimensional grating. For example, during the PIC chip manufacturing process, a metal mirror or a dielectric layer mirror can be prepared in advance directly below the two-dimensional grating. This allows the incident light that passes directly through the two-dimensional grating but is not coupled into the waveguide layer to be reflected back to the two-dimensional grating for secondary optical coupling, which can significantly improve the optical coupling efficiency.

[0051] This invention provides a compact two-dimensional grating coupler. By introducing a focusing grating with a specific duty cycle distribution between a traditional two-dimensional grating and a tapered waveguide, effective focusing of the outgoing light is achieved, significantly reducing the length of the tapered waveguide to below 200 μm, and preferably even less than 50 μm, while maintaining low coupling loss. This design not only significantly reduces device size and increases integration density, but also ensures equal optical path lengths for incident light at different positions reaching the focal point by precisely controlling the duty cycle distribution of the focusing grating, thereby achieving efficient focusing and improving coupling efficiency. Furthermore, this invention supports various optimized configurations, such as segmented focusing grating designs, the use of linear, exponential, or cosine-shaped tapered waveguides, and the use of bottom-reflective structures, further enhancing beam focusing and coupling performance. These improvements work together to make the two-dimensional grating coupler of this invention outstanding in terms of bandwidth, loss, and integration density, making it particularly suitable for high-density multi-channel integrated optical interconnect systems and providing an ideal solution for data centers, high-performance computing, and optical communication networks.

[0052] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Where there is no conflict, the embodiments and features described in the embodiments of this application can be combined with each other. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A two-dimensional grating coupler, characterized in that, It includes a two-dimensional grating, a focusing grating, and a tapered waveguide connected in sequence: The two-dimensional grating is used to convert nearly vertical incident light into outgoing light that propagates within the waveguide layer. The focusing grating is parallel to the propagation direction of the emitted light. The focusing grating has a preset duty cycle distribution, so that the emitted light achieves equal optical path length at the focal point of the focusing grating, thereby focusing the emitted light. The tapered waveguide has its wide port connected to the focusing grating and its narrow port located at the focal point of the focusing grating, for propagating the focused outgoing light.

2. The two-dimensional grating coupler as described in claim 1, characterized in that, The duty cycle distribution of the focusing grating is set to satisfy the following relationship to achieve focusing: in, , Here, represents the equivalent refractive index at two different positions on the focusing grating, and d represents the dimension of the focusing grating in the direction of propagation of the outgoing light. The refractive index of the tapered waveguide is... , These are the distances from two different positions on the focusing grating to the narrow port of the tapered waveguide.

3. The two-dimensional grating coupler as described in claim 1, characterized in that, The focusing grating includes at least two grating units arranged along the propagation direction of the emitted light, wherein each grating unit has the same or different duty cycle distribution.

4. The two-dimensional grating coupler as described in claim 1, characterized in that, The two-dimensional grating is a focusing type two-dimensional grating.

5. The two-dimensional grating coupler according to claim 1, characterized in that, The length of the tapered waveguide is less than 200µm, preferably less than 100µm, and more preferably less than 50µm.

6. The two-dimensional grating coupler according to claim 1, characterized in that, The tapered waveguide is one of a linear tapered waveguide, an exponential tapered waveguide, or a cosine tapered waveguide.

7. The two-dimensional grating coupler according to claim 1, characterized in that, The two-dimensional grating and / or the focusing grating are formed by fully etching or partially etching the waveguide layer.

8. The two-dimensional grating coupler according to claim 1, characterized in that, It also includes a reflective structure disposed below the two-dimensional grating, wherein the reflective structure is a metal reflector or a dielectric layer reflector.

9. The two-dimensional grating coupler according to claim 1, characterized in that, The two-dimensional grating is directly connected to the focusing grating, or is connected via a patternless waveguide layer.

10. The two-dimensional grating coupler according to claim 1, characterized in that, The two-dimensional grating coupler consists of a waveguide layer and a cladding layer. The waveguide layer is made of silicon or silicon nitride, and the cladding layer is made of silicon dioxide or silicon oxynitride.

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