Three-dimensional photonic integrated network based on vertical coupling structure and preparation method thereof, photonic integrated circuit and optical communication system

Abstract

A three-dimensional photon integrated network based on a vertical coupling structure comprises a silicon waveguide layer, a silicon nitride waveguide layer, a silicon-silicon nitride vertical coupler and a silicon nitride-silicon nitride vertical coupler, the silicon waveguide layer and the silicon nitride waveguide layer are arranged at intervals through a silicon dioxide isolation layer and are interconnected through the vertical coupler, and the silicon nitride waveguide layer and the silicon nitride waveguide layer are connected through a silicon dioxide isolation layer. The silicon nitride waveguide layer serves as an isolation connection channel, and low-crosstalk cross transmission of the silicon waveguide layer is achieved through weak interaction. According to the invention, through two vertical coupling structures, on-chip multi-level network communication can be realized, and the silicon-based cross waveguide network structure is constructed by virtue of the independence of each level of network and the vertical coupling structures.

Description

Technical Field

[0001] The present invention belongs to the technical fields of optical waveguide structures and semiconductor technologies, and particularly relates to a three-dimensional photonic integrated network based on a vertical coupling structure, a preparation method thereof, a photonic integrated circuit, and an optical communication system. By designing vertical couplers between silicon waveguides and silicon nitride waveguides and between silicon nitride waveguides, efficient optical field coupling between each vertical layer network is realized to construct a multi-layer communication network on a chip. At the same time, a silicon-based cross-waveguide network on the chip is realized by virtue of the independent nature of each layer communication network. Background Art

[0002] Silicon, as an indirect bandgap semiconductor, has good transparency and a relatively high refractive index in the near-infrared band. The near-infrared band is the main operating wavelength of optical fiber communication. Therefore, silicon is suitable as a material for optical components such as optical waveguides and optical modulators. Thanks to the existing semiconductor industry, silicon-based optoelectronic devices have developed rapidly, and on-chip optical wave devices in the communication band are relatively mature. Low-loss transmission and excellent optical field control capabilities in the 1550 nm communication band have been achieved. Silicon-based optoelectronics is a technology with great potential. It combines the mature process of silicon materials with the powerful capabilities of optoelectronics and is driving the development of next-generation high-speed communication, data processing, and sensing technologies.

[0003] At the same time, silicon nitride (Si 3 N 4 ) materials exhibit unique advantages compared with silicon (Si) materials, especially in terms of optical properties, mechanical strength, chemical stability, and electrical insulation, which play an important complementary role to the deficiencies of silicon materials. Its low optical loss, high hardness, high corrosion resistance, excellent high-temperature resistance, and biocompatibility make it an important choice in the fields of integrated photonics, microelectromechanical systems, power electronics, and biomedicine. It makes up for the deficiencies of silicon materials in terms of low optical loss, wide transparent band, and high reliability, and achieves good compatibility with silicon-based technologies, supporting the development of multi-functional heterogeneous integration.

[0004] Therefore, the combination of silicon and silicon nitride on-chip platforms is one of the important development directions of current on-chip integration technologies. The respective material characteristics of the two optimize the overall performance and expand the application scenarios. Silicon provides high-speed electronic processing capabilities and high-density integration characteristics, while silicon nitride complements wide-wavelength optical functions and low-loss characteristics. By combining the two, efficient integration of electronic and photonic functions can be achieved to meet the requirements of optoelectronic integration and complex on-chip systems.

[0005] However, there are challenges in mode matching between silicon waveguides and silicon nitride waveguides. How to achieve efficient coupling between the two waveguides remains a difficult problem, and the vertical combination of silicon and silicon nitride on-chip platforms results in the mutual independence between the two layers. Summary of the Invention

[0006] To overcome the deficiencies of the above-mentioned existing technologies, the present invention provides a silicon-based cross-waveguide network and an on-chip multi-level communication network based on a vertical coupling structure. By designing vertical couplers between silicon waveguides and silicon nitride waveguides and between silicon nitride waveguides, efficient mutual optical field coupling between each vertical-level network is achieved to construct an on-chip multi-level communication network. At the same time, an on-chip silicon-based cross-waveguide network is realized by virtue of the independent nature of each level of the communication network.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a three-dimensional photonic integration network based on a vertical coupling structure, which is characterized by comprising:

[0009] At least one silicon waveguide layer, including silicon waveguides with a rectangular cross-section, for transmitting optical signals in the 1550 nm band;

[0010] At least one silicon nitride waveguide layer, including silicon nitride waveguides with a rectangular cross-section, for low-loss transmission of optical signals in the 1550 nm band

[0011] A silicon-silicon nitride vertical coupler, with both ends respectively connected to the silicon waveguide and the silicon nitride waveguide, and composed of a silicon tapered waveguide and a silicon nitride tapered waveguide vertically overlapping and facing each other, for realizing vertical optical field coupling between the silicon waveguide layer and the silicon nitride waveguide layer;

[0012] A silicon nitride-silicon nitride vertical coupler, with both ends respectively connected to different silicon nitride waveguides, and composed of at least two layers of silicon nitride tapered waveguides vertically overlapping and facing each other, for realizing mutual coupling between different layers of silicon nitride waveguides;

[0013] Wherein, the silicon waveguide layer and the silicon nitride waveguide layer are arranged at intervals through a silicon dioxide isolation layer and interconnected through a vertical coupler. The silicon nitride waveguide layer serves as an isolation connection channel to achieve low-crosstalk cross-transmission of the silicon waveguide layer through weak interaction.

[0014] Preferably, the silicon-silicon nitride vertical coupler includes:

[0015] A silicon tapered waveguide, with an input end width of 500 nm, an output end width of 50 nm, and a tapered region length of 6 - 7 μm;

[0016] A silicon nitride tapered waveguide, with an input end width of 900 nm, an output end width of 50 nm, and a tapered region length of 6 - 7 μm;

[0017] Wherein, the vertical overlapping region length of the silicon tapered waveguide and the silicon nitride tapered waveguide is 5 - 10 μm, the spacing is 50 - 300 nm, and the center offset of the overlapping region ≤ 200 nm.

[0018] Preferably, the silicon nitride - silicon nitride vertical coupler includes:

[0019] A first silicon nitride tapered waveguide, with an input - end width of 900 nm, an output - end width of 50 nm, and a tapered - region length of 4 - 5 μm;

[0020] A second silicon nitride tapered waveguide, with an input - end width of 900 nm, an output - end width of 50 nm, and a tapered - region length of 5 - 7 μm;

[0021] Wherein, the vertical overlapping region length of the first and second silicon nitride tapered waveguides is 6 - 12 μm, the spacing is 30 - 200 nm, and the center offset of the overlapping region ≤ 150 nm.

[0022] Preferably, the thickness of the silicon dioxide isolation layer is 1 - 5 μm, and the refractive - index difference Δn between it and the silicon nitride waveguide ≥ 0.4, which is used to suppress inter - layer crosstalk.

[0023] Preferably, the network includes at least three silicon waveguide layers and four silicon nitride waveguide layers, and each layer is interconnected by a vertical coupler, supporting a three - dimensional optical - path topology.

[0024] Preferably, the silicon waveguide layer includes an electro - optic modulator and a photodetector, the silicon nitride waveguide layer includes a Mach - Zehnder interferometer or a ring resonator, and the silicon waveguide layer and the silicon nitride waveguide layer form a reconfigurable optical path through the silicon - silicon nitride vertical coupler and / or the silicon nitride - silicon nitride vertical coupler.

[0025] In a second aspect, the present invention also provides a preparation method for the above - mentioned three - dimensional photonic integrated network based on a vertical - coupling structure, which is characterized by including the following steps:

[0026] S1. Form a silicon - tapered structure of the silicon waveguide and the silicon - silicon nitride vertical coupler on a silicon substrate through deep - ultraviolet lithography and reactive - ion etching, and fabricate the silicon waveguide layer;

[0027] S2. Deposit a first silicon dioxide layer on the silicon waveguide layer and perform chemical - mechanical polishing;

[0028] S3. Prepare a first silicon nitride waveguide layer by low - pressure chemical vapor deposition, and etch to form a silicon - nitride tapered structure of the silicon - silicon nitride vertical coupler and a silicon - nitride tapered structure of the silicon nitride - silicon nitride vertical coupler;

[0029] S4. Deposit a second silicon dioxide layer on the silicon nitride waveguide layer and perform chemical - mechanical polishing;

[0030] S5. Prepare a second silicon nitride waveguide layer by low - pressure chemical vapor deposition, and etch to form a silicon - nitride tapered structure of the silicon nitride - silicon nitride vertical coupler;

[0031] S6. Repeat steps S4 - S5 to construct a multi - layer silicon nitride waveguide and vertical coupler structure layer by layer;

[0032] S7. Calibrate the overlap offset of each layer of vertical couplers through electron beam lithography;

[0033] S8. When constructing the silicon waveguide layer and each silicon nitride waveguide layer, appropriate integrated optical devices should be etched on each layer.

[0034] In a third aspect, the present invention provides a photonic integrated circuit, which is characterized by including the above - mentioned three - dimensional photonic integration network based on a vertical coupling structure, and integrating any two or more of a silicon - based electro - optical modulator array, a silicon nitride delay line network, a multi - dimensional optical cross - connection node, and a photonic neural network computing unit.

[0035] In a fourth aspect, the present invention provides an optical communication system, which is characterized by adopting the above - mentioned photonic integrated circuit to realize Tb / s - level optical switching, wavelength routing, or coherent optical signal processing.

[0036] The beneficial effects of the technical solution provided by the present invention are as follows:

[0037] 1. The vertical coupling structure of the present invention adopts an opposing conical structure, which can achieve efficient vertical conversion of optical field energy within a short distance, thereby realizing mutual communication between the silicon waveguide and the silicon nitride waveguide, as well as between the silicon nitride waveguides.

[0038] 2. The present invention proposes to construct an on - chip multi - level network communication system, and the multi - layer silicon nitride structure provides a higher dimension. At the same time, the multi - level network communication will further improve the signal transmission dimension and efficiency of the on - chip platform.

[0039] 3. The present invention proposes to construct a silicon - based cross - waveguide network structure, which realizes mutual vertical coupling between the silicon waveguide and the high - layer silicon nitride waveguide by virtue of the above - mentioned two vertical coupling structures, and uses the silicon nitride waveguide as an isolation connection channel for the vertical structure to realize the weak interaction between the silicon waveguide and the silicon nitride waveguide. This structure has high flexibility and scalability, and thus can further construct a large - scale on - chip cross - waveguide network. Brief Description of the Drawings

[0040] Figure 1 It is a schematic diagram of a silicon - based cross - waveguide;

[0041] Figure 2 It is a three - dimensional and two - dimensional schematic diagram of a multi - level vertical coupling structure;

[0042] Figure 3 It is a schematic diagram of the structure of a vertical coupler between silicon and silicon nitride. Among them, (a) is a three - dimensional schematic diagram, (b) is a two - dimensional schematic diagram, (c) is a schematic diagram of transmitted energy, and (d) is a transmittance curve graph;

[0043] Figure 4 It is a schematic structural diagram of a vertical coupler between silicon nitrides. Among them, (a) is a three-dimensional schematic diagram, (b) is a two-dimensional schematic diagram, (c) is a transmitted energy schematic diagram, and (d) is a transmittance curve graph;

[0044] Figure 5 It is a schematic diagram of a silicon-based cross-waveguide network and a multi-level network;

[0045] In the figure: 1 - silicon waveguide; 2 - silicon-silicon nitride opposing tapered structure; 3 - silicon nitride opposing tapered structure; 4 - silicon nitride waveguide. Specific embodiments

[0046] The following further explains in conjunction with the accompanying drawings and specific embodiments. These embodiments are only used to introduce the present invention in more detail and specifically, and do not limit the present invention in any form. After reading the present invention, various equivalent modifications made by those skilled in the art to the present invention all fall within the scope defined by the appended claims of this application.

[0047] The vertical coupler design of this embodiment is based on an on-chip silicon (Si) and silicon nitride (Si 3 N 4 ) platform, including two types: the vertical coupler between the silicon waveguide and the silicon nitride waveguide (heterogeneous material coupling) and the vertical coupler between the silicon nitride waveguides (homogeneous material coupling).

[0048] Please refer to Figure 3 , Figure 3 It is a schematic structural diagram of a vertical coupler from silicon to silicon nitride. As shown in the figure, the silicon-silicon nitride vertical coupler is composed of a silicon waveguide 1, a silicon nitride waveguide 4, and a silicon-silicon nitride opposing tapered structure 2.

[0049] Among them, the silicon waveguide 1 serves as a transmission channel for optical signals. In this embodiment, a rectangular waveguide structure is adopted, with a width of 500 nm and a height of 220 nm, supporting single-mode transmission in the 1550 nm band.

[0050] The silicon nitride waveguide 4 serves as a transmission channel for optical signals and also adopts a rectangular waveguide structure, but with different widths and heights. In this embodiment, the width is 900 nm and the height is 400 nm, which can achieve low-loss transmission in the 1550 nm band.

[0051] The silicon-silicon nitride opposing conical structure 2 is composed of a silicon conical waveguide 2-1 and a silicon nitride conical waveguide 2-2 placed vertically opposite to the silicon conical waveguide 2-1. Among them, the silicon conical waveguide gradually reduces (or expands) the cross-section from the silicon waveguide to achieve mode expansion or compression, and the silicon nitride conical waveguide realizes optical field coupling through mode overlap. This design of the conical waveguide enables the mutual conversion of the optical mode field from a small area (silicon waveguide) to a large area (silicon nitride waveguide). By placing the conical waveguides vertically opposite to each other, the optical field can be effectively guided from the silicon waveguide to the silicon nitride waveguide, or coupled from the silicon nitride waveguide into the silicon waveguide. The coupling process is divided into three stages: silicon waveguide → silicon nitride cone: the silicon waveguide mode gradually expands; silicon-silicon nitride opposing conical overlap region: the optical field is transferred through evanescent wave coupling; silicon cone → silicon nitride waveguide: the optical field is completely transferred to the silicon nitride waveguide. Through these three-step transitions, the transfer of the optical field is achieved. This coupling structure can achieve a coupling distance of 7μm and a coupling efficiency of 99%.

[0052] Please refer to Figure 4 , Figure 4 is a schematic structural diagram of a vertical coupler between silicon nitrides. As shown in the figure, the silicon nitride-silicon nitride vertical coupler is composed of a silicon nitride waveguide 4 and a silicon nitride opposing conical structure 3.

[0053] Among them, the silicon nitride waveguide 4 serves as a transmission channel for optical signals and still adopts a rectangular waveguide structure.

[0054] The silicon nitride opposing conical structure 3 is composed of a first silicon nitride conical waveguide 3-1 and a second silicon nitride conical waveguide 3-2 placed vertically opposite to the first silicon nitride conical waveguide 3-1, realizing the efficient conversion of the optical field between the silicon nitride conical waveguides. The conical waveguide realizes the transitional conversion of the optical field mode. The coupling process is divided into three stages: silicon nitride waveguide → silicon nitride cone: the mode gradually expands or compresses; opposing conical overlap region: the optical field is transferred through mode overlap; silicon nitride cone → target silicon nitride waveguide: the mode is fully adapted. An efficient mode transfer with 99% efficiency can be achieved at a distance of 7.2um.

[0055] The combination of the silicon and silicon nitride on-chip integrated platform in the present invention gives full play to the complementary advantages of the two in optical, electronic, and mechanical properties, further promoting the innovation and breakthrough of on-chip integration technology. By constructing a silicon-based cross-waveguide network and an on-chip multi-level communication network through an efficient vertical structure, the efficient interconnection between each level can be effectively achieved, and the information processing efficiency of the on-chip platform can be further improved.

[0056] Among them, the silicon waveguide and the silicon nitride can achieve low-loss transmission in the 1550nm band. The silicon waveguide and the silicon nitride waveguide are rectangular waveguides fabricated by semiconductor processes. The silicon waveguide is 220nm high and 500nm wide. The silicon nitride waveguide is 400nm high and 900nm wide.

[0057] The vertical coupler between the silicon waveguide and the silicon nitride waveguide is connected to the silicon waveguide and the silicon nitride waveguide at both ends, and can achieve efficient vertical coupling of the optical field between the silicon waveguide and the silicon nitride waveguide. The vertical coupler between the silicon waveguide and the silicon nitride waveguide adopts an opposing tapered structure. By reasonably selecting the lengths of each coupling region and optimizing the structure and length of the tapered waveguide, efficient vertical coupling of the optical field between the silicon waveguide and the silicon nitride waveguide can be achieved within a short distance.

[0058] The vertical coupler between the silicon nitride waveguides is connected to the silicon nitride waveguides at both ends, and can achieve effective mutual coupling between the upper and lower silicon nitride waveguides. It adopts an opposing tapered structure. By designing a reasonable cone region length and shape, efficient vertical coupling of the optical field from the silicon waveguide to the silicon nitride waveguide can be achieved within a short distance.

[0059] An optical signal at 1550 nm is input from the silicon waveguide, and after passing through the vertical coupler between the silicon waveguide and the silicon nitride waveguide, it is efficiently coupled to the upper-layer silicon nitride waveguide, and then the optical field energy is transferred to another layer of silicon nitride waveguide through the vertical coupler between the silicon nitride waveguides. Thus, mutual communication between the silicon waveguide and the silicon nitride waveguide and between the silicon nitride waveguides can be achieved, and a multi-level on-chip communication network can be further constructed.

[0060] Please refer to Figure 5 , Figure 5 for the schematic diagram of the silicon-based cross-waveguide network and the multi-level network; through the vertical coupler between silicon and silicon nitride and the vertical coupler between silicon nitrides, efficient transfer of the optical field from the silicon waveguide layer to the upper silicon nitride layer can be achieved. Since the silicon waveguide and the silicon nitride waveguide have relatively independent properties in the vertical direction, independent signal transmission of the silicon waveguide and the silicon nitride waveguide can be achieved in the corresponding vertical direction, thereby constructing a silicon-based cross-waveguide network structure, where the silicon nitride waveguide serves as an isolation connection channel for the vertical structure to achieve weak interaction between the silicon waveguide and the silicon nitride waveguide. This structure has high scalability and flexibility. By its isolation in the vertical direction and cross-placement of multiple silicon waveguides and silicon nitride waveguides, a silicon-based cross-waveguide network is formed. At the same time, the vertical coupling structure serves as an information channel between different levels, and a three-dimensional photonic integrated network, that is, a multi-level network, can be constructed. With the multi-layer silicon nitride structure to achieve a multi-level on-chip network and through the vertical coupling structure to achieve mutual communication between different-level networks, the design dimension of the on-chip photonics platform will be expanded, and the information processing capacity and speed of the on-chip platform are also expected to be further improved.

Claims

1. A three-dimensional photonic integrated network based on a vertical coupling structure, characterized in that: include: At least one silicon waveguide layer, comprising a silicon waveguide with a rectangular cross section, for transmitting an optical signal in the 1550 nm band; At least one silicon nitride waveguide layer, comprising a silicon nitride waveguide with a rectangular cross section, for low-loss transmission of optical signals in the 1550nm band A silicon-silicon nitride vertical coupler, with two ends connected to the silicon waveguide and the silicon nitride waveguide respectively, wherein the silicon tapered waveguide and the silicon nitride tapered waveguide are vertically overlapped and placed opposite to each other, and is used to realize vertical coupling of the optical field from the silicon waveguide layer to the silicon nitride waveguide layer; A silicon nitride-silicon nitride vertical coupler, with two ends respectively connected to different silicon nitride waveguides, is composed of at least two layers of silicon nitride tapered waveguides vertically overlapped and placed opposite to each other, for achieving mutual coupling between different layers of silicon nitride waveguides; The silicon waveguide layer and the silicon nitride waveguide layer are arranged at intervals through a silicon dioxide isolation layer and interconnected through a vertical coupler. The silicon nitride waveguide layer serves as an isolation connection channel to achieve low crosstalk cross transmission of the silicon waveguide layer through weak interaction.

2. The three-dimensional photonic integrated network based on the vertical coupling structure according to claim 1, characterized in that: The silicon-silicon nitride vertical coupler comprises: Silicon tapered waveguide, with an input width of 500nm, an output width of 50nm, and a tapered region length of 6-7μm; Silicon nitride tapered waveguide, with an input width of 900nm, an output width of 50nm, and a tapered region length of 6-7μm; The vertical overlapping region of the silicon tapered waveguide and the silicon nitride tapered waveguide has a length of 5-10 μm, a spacing of 50-300 nm, and an offset of the center of the overlapping region of ≤200 nm.

3. The three-dimensional photonic integrated network based on vertical coupling structure according to claim 1, characterized in that: The silicon nitride-silicon nitride vertical coupler comprises: The first silicon nitride tapered waveguide has an input end width of 900 nm, an output end width of 50 nm, and a tapered region length of 4-5 μm; The second silicon nitride tapered waveguide has an input end width of 900 nm, an output end width of 50 nm, and a tapered region length of 5-7 μm; The length of the vertical overlapping region between the first and second silicon nitride tapered waveguides is 6-12 μm, the spacing is 30-200 nm, and the center offset of the overlapping region is ≤150 nm.

4. The three-dimensional photonic integrated network based on vertical coupling structure according to claim 1, characterized in that: The thickness of the silicon dioxide isolation layer is 1-5 μm, and the refractive index difference between the silicon dioxide isolation layer and the silicon nitride waveguide is Δn≥0.4, which is used to suppress interlayer crosstalk.

5. The three-dimensional photonic integrated network based on vertical coupling structure according to claim 1, characterized in that: The network comprises at least three silicon waveguide layers and four silicon nitride waveguide layers, each layer is interconnected by vertical couplers, and supports a three-dimensional optical path topology structure.

6. The three-dimensional photonic integrated network based on a vertical coupling structure according to any one of claims 1 to 5, characterized in that: The silicon waveguide layer includes an electro-optic modulator and a photodetector, the silicon nitride waveguide layer includes a Mach-Zehnder interferometer or a ring resonator, and the silicon waveguide layer and the silicon nitride waveguide layer form a reconfigurable optical path through the silicon-silicon nitride vertical coupler and / or the silicon nitride-silicon nitride vertical coupler.

7. A method for preparing a three-dimensional photonic integrated network based on a vertical coupling structure as claimed in any one of claims 1 to 6, characterized in that: The steps include: S1. Forming a silicon waveguide and a silicon-silicon nitride vertical coupler silicon cone structure on a silicon substrate by deep ultraviolet lithography and reactive ion etching to produce a silicon waveguide layer; S2. Depositing a first silicon dioxide layer on the silicon waveguide layer and chemically mechanically polishing it; S3. preparing a first silicon nitride waveguide layer by low pressure chemical vapor deposition, and etching to form a silicon nitride tapered structure of a silicon-silicon nitride vertical coupler and a silicon nitride tapered structure of a silicon nitride-silicon nitride vertical coupler; S4. Depositing a second silicon dioxide layer on the silicon nitride waveguide layer and chemically mechanically polishing it; S5. preparing a second silicon nitride waveguide layer by low pressure chemical vapor deposition, and etching to form a silicon nitride-silicon nitride vertical coupler silicon nitride conical structure; S6. Repeat steps S4-S5 to construct a multilayer silicon nitride waveguide and vertical coupler structure layer by layer; S7. Calibrate the overlap offset of each layer of vertical couplers by electron beam lithography; S8. When constructing the silicon waveguide layer and each silicon nitride waveguide layer, suitable integrated optical devices should be etched on each layer.

8. A photonic integrated circuit, characterized in that: A three-dimensional photonic integrated network based on a vertical coupling structure comprising any one of claims 1 to 6, and integrating any two or more of a silicon-based electro-optical modulator array, a silicon nitride delay line network, a multi-dimensional optical cross-connection node, and a photonic neural network computing unit.

9. An optical communication system, characterized in that: The photonic integrated circuit of claim 8 is used to realize Tb / s-level optical switching, wavelength routing or coherent optical signal processing.

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