On-chip crossed optical waveguide design method and on-chip crossed optical waveguide

Abstract

The invention relates to the technical field of integrated photonics, in particular to a design method of an on-chip crossed optical waveguide and the on-chip crossed optical waveguide. The method comprises the following steps: crossing two straight waveguides to form a crossed optical waveguide of which the crossing angle is less than 90 degrees; performing preliminary design on the crossed area of the crossed optical waveguide to enable the initial structure parameter of the crossed area to be smaller than 4 microns multiplied by 4 microns; adopting a particle swarm optimization algorithm to optimize the initial structure parameters of the cross region so as to change the material refractive index distribution in the cross region, and obtaining the material refractive index distribution in the cross region when the light transmittance of the cross optical waveguide is maximum and the structure of the cross region meets the up-down and left-right symmetrical structure; taking the structure parameters of the corresponding intersection areas as target structure parameters of the intersection areas; and redesigning the crossed region of the crossed optical waveguide according to the target structure parameters so as to solve the problems that the occupied area of the crossed optical waveguide is relatively large, the small-angle crossed design is complicated and the three-dimensional processing difficulty is high.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated photonics, and particularly to a design method for an on-chip crossed optical waveguide and an on-chip crossed optical waveguide. Background Art

[0002] With the rapid development of information technology, photonic integrated chips are becoming an important supporting technology in the next-generation optical communication, optical computing, optical sensing and other fields due to their significant advantages in high-speed data transmission, low-power consumption operation, and high integration. Compared with traditional electronic chips, photonic integrated chips use optical signals for information transmission and processing, which can effectively reduce energy consumption while improving data transmission rate and bandwidth. Therefore, the design of highly integrated and high-performance photonic devices is the key to promoting the development of photonic integrated chips. Among them, the high-density interconnection technology of optical waveguides is particularly important.

[0003] Inside a photonic integrated chip, signal transmission between different functional units needs to be carried out through optical waveguides. In complex optical path designs, multiple optical signal channels often need to cross each other to achieve a more compact layout and a more efficient optical path design. Therefore, as a core structure, the crossed optical waveguide plays a crucial role in on-chip optical interconnection. An ideal crossed optical waveguide needs to have a compact size, high transmittance, and broadband characteristics to meet the requirements of high-density photon integration. However, the existing designs of crossed optical waveguides still have many limitations and it is difficult to simultaneously take into account high integration and the feasibility of manufacturing processes.

[0004] Currently, the common crossed optical waveguide structures mainly include the cross-crossing scheme. This scheme usually uses two straight waveguides to directly cross through an intermediate extended part or optimizes the structure of the crossing area through inverse design. Specifically, the simplest way is to directly cross two straight waveguides and design the parameters of the formed "cross" structure, which usually requires a structure area of 10 micrometers by 10 micrometers. The advantages of this method are simple design, mature processing technology, and the ability to achieve low loss and broadband characteristics. However, since the crossing angle of this structure is 90 degrees, its occupied area is large and it is not conducive to high-density integration. In addition, for the crossed optical waveguide with the structure of the crossing area optimized through inverse design, although the size is slightly reduced, about 4 micrometers by 4 micrometers, the crossing angle is still 90 degrees and it is also difficult to achieve high-density integration.

[0005] To reduce the size occupation of cross optical waveguides and improve the integration density of photonic integrated chips, some design schemes attempt to achieve a more compact layout by reducing the crossing angle. However, under the condition of small-angle crossing, the mode matching problem of optical signals becomes more complex, which easily introduces additional mode coupling effects and affects the overall performance of the device. Therefore, in some application scenarios, three-dimensional optical path interconnection integrated chip schemes have also been proposed to utilize different waveguide layers (such as the "sandwich" structure of silicon-silicon dioxide-silicon) or photonic crystal structures, etc., to achieve spatial separation of optical signals, thereby avoiding the need for waveguide crossing. However, the processing of three-dimensional optical waveguides involves complex stacked structures, with high manufacturing costs and extremely high requirements for process precision, making it difficult to popularize in large-scale production.

[0006] In summary, the existing cross optical waveguide technologies mainly have the following deficiencies: 1. Large occupied area: Due to the large crossing angle of traditional cross waveguides, the feasibility of high-density integration is limited.

[0007] 2. Complex small-angle crossing design: When the crossing angle is small, the mode matching and coupling problems between waveguides become more prominent, affecting the stability of the device.

[0008] 3. Difficult three-dimensional processing: Although three-dimensional optical path design can avoid waveguide crossing, its manufacturing process is complex and the cost is high, making it difficult to meet the requirements of large-scale manufacturing. Summary of the Invention

[0009] The purpose of the present invention is to provide a design method for on-chip cross optical waveguides and on-chip cross optical waveguides, which can solve the problems of large occupied area, complex small-angle crossing design, and difficult three-dimensional processing of existing cross optical waveguides.

[0010] To solve the above technical problems, an embodiment of the present invention provides a design method for on-chip cross optical waveguides, including the following steps: Cross two straight waveguides to form a cross optical waveguide with a crossing angle less than 90 degrees; Preliminarily design the crossing area of the cross optical waveguide so that the initial structural parameters of the crossing area are less than 4 micrometers by 4 micrometers; Adopt the particle swarm optimization algorithm to optimize the initial structural parameters of the crossing area, so as to change the refractive index distribution of the material in the crossing area, obtain the refractive index distribution of the material in the crossing area when the light transmittance of the cross optical waveguide is the largest and the structure of the crossing area satisfies the up-down, left-right symmetric structure, and use the corresponding structural parameters of the crossing area as the target structural parameters of the crossing area; Redesign the crossing area of the cross optical waveguide with the target structural parameters.

[0011] Optionally, the objective function of the particle swarm optimization algorithm is established with the maximum light transmittance of the cross optical waveguide as the objective; The target structural parameters are obtained through the following steps: S1. Initialize the particle swarm: In the preliminarily designed cross region, a number of initial particles are randomly generated, each particle represents a possible refractive distribution of the material, and each refractive distribution of the material corresponds to a structural parameter; S2. Calculate the light transmittance: Calculate the light transmittance of the cross optical waveguide under each refractive distribution of the material, and evaluate the optimization degree according to the objective function; S3. Update the particle velocity and position: Adjust the position of each particle according to its own local optimal solution and the global optimal solution of the entire particle swarm to converge towards the optimal solution; S4. Iterative optimization: Repeat steps S2 and S3 until the convergence condition is met to obtain the optimal solution. The convergence condition is that the transmittance reaches a preset percentage or the number of iterations reaches a preset number; S5. Obtain the target structural parameters according to the optimal solution.

[0012] Optionally, the crossing angle of the cross optical waveguide is 20°.

[0013] Optionally, the initial structural parameters of the cross region are 2 microns by 2 microns.

[0014] Optionally, the target structural parameters are 2 microns × 1.45 microns.

[0015] Optionally, the re - design of the cross region of the cross optical waveguide with the target structural parameters includes: Replace the nanoscale feature regions in the cross region with the target structural parameters with rectangular units, and fix the length of the rectangular units at 2 microns, and vary the width in the range of 20 nanometers to 30 nanometers; Among them, the nanoscale feature region is the region where the line width in the cross region is less than 10 nanometers.

[0016] Optionally, when the wavelength of the cross optical waveguide is 1550 nanometers, the preset percentage takes a value of 95%.

[0017] An embodiment of the present invention also provides an on - chip cross optical waveguide, and the on - chip cross optical waveguide is designed by the design method of the on - chip cross optical waveguide as described above.

[0018] The design method of the on - chip cross optical waveguide provided by the present invention has at least the following beneficial effects: By crossing two straight waveguides to form a crossed optical waveguide with a crossing angle less than 90 degrees, and preliminarily designing the crossing region of the crossed optical waveguide so that the initial structural parameters of the crossing region are less than 4 microns by 4 microns, a small-angle crossing design is achieved, maintaining a compact device size, which helps to improve the overall integration of the photonic integrated chip. Then, through the particle swarm optimization algorithm, the structural parameters of the crossing region are optimized to change the refractive index distribution of the material in the crossing region, and the refractive index distribution of the material in the crossing region when the light transmittance of the crossed optical waveguide is maximized and the structure of the crossing region satisfies the up-down, left-right symmetry structure is obtained, and the corresponding structural parameters of the crossing region are used as the final target structural parameters of the crossing region. Based on this, the design of the crossing region of the crossed optical waveguide is completed, optimizing the light field distribution in the crossing region, thereby reducing the mode mismatch effect and improving the transmission stability of the optical signal, without introducing additional three-dimensional processing steps, reducing the manufacturing complexity and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings, and these exemplary illustrations do not constitute a limitation on the embodiments.

[0020] Figure 1 is a flowchart of a design method for an on-chip crossed optical waveguide provided according to an embodiment of the present invention; Figure 2 is a schematic structural diagram of a reverse design through the particle swarm optimization algorithm provided according to an embodiment of the present invention; Figure 3 is a schematic diagram of the transmittance of a crossed waveguide of a reverse design through the particle swarm optimization algorithm provided according to an embodiment of the present invention; Figure 4 is a schematic structural diagram of a crossed waveguide with a simplified structure provided according to an embodiment of the present invention; Figure 5 is a schematic diagram of the transmittance of a crossed waveguide with a simplified structure provided according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present invention, many technical details are proposed to help the reader better understand the present invention. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions required to be protected by the present invention can still be implemented. The following division of each embodiment is for convenience of description and should not constitute any limitation on the specific implementation manner of the present invention. Each embodiment can be combined and cross-referenced with each other without contradiction.

[0022] There is an urgent need for a new design method for crossed optical waveguides to achieve compact integration in the case of small-angle crossing, while maintaining good optical transmission performance, improving the integration degree of photonic chips and the feasibility of manufacturing processes.

[0023] Therefore, the present invention aims to solve the problem of integration degree limitation of existing crossed waveguides in the case of small-angle crossing. Specifically, the present invention realizes the efficient crossing of two waveguides within a small angle range by optimizing the waveguide structure and the design of the crossing region, while maintaining a compact device size, which helps to improve the overall integration degree of photonic integrated chips; at the same time, it can be compatible with existing photonic integrated manufacturing processes without introducing additional three-dimensional processing steps, thereby reducing manufacturing complexity and cost; in addition, this method is applicable to various on-chip photonic platforms, such as silicon photonics, silicon nitride photonics, etc., and can be widely used in fields such as optical communication and optical computing.

[0024] Compared with the traditional large-angle crossed waveguide scheme, the method of the present invention can provide higher integration degree on the premise of ensuring optical transmission performance, and provides a new solution for high-density photonic integration.

[0025] An embodiment of the present invention relates to a design method for an on-chip crossed optical waveguide. The implementation details of the design method for the on-chip crossed optical waveguide in this embodiment will be specifically described below. The following content is only the implementation details provided for convenient understanding and is not necessary for implementing this solution.

[0026] The specific process of the design method for the on-chip crossed optical waveguide in this embodiment can be as Figure 1 shown, including: Step 101, cross two straight waveguides to form a crossed optical waveguide with a crossing angle less than 90 degrees.

[0027] In one example, the crossing angle of the crossed optical waveguide is set to 20 degrees to achieve a compact device layout and take into account the mode matching and transmission stability of optical signals.

[0028] Step 102, preliminarily design the crossing region of the crossed optical waveguide so that the initial structural parameters of the crossing region are less than 4 microns by 4 microns.

[0029] In one example, a 2-micron by 2-micron reverse design region is introduced into the crossing region as the crossing region of the crossed optical waveguide.

[0030] Step 103, use the particle swarm optimization algorithm to optimize the initial structural parameters of the crossing region to change the refractive index distribution of the material in the crossing region, obtain the refractive index distribution of the material in the crossing region when the light transmittance of the crossed optical waveguide is the largest and the structure of the crossing region satisfies the up-down, left-right symmetric structure, and use the corresponding structural parameters of the crossing region as the target structural parameters of the crossing region.

[0031] In a specific implementation, after determining the angle of the crossing waveguide (20 degrees) and the size of the inverse design region (2 μm × 2 μm), this embodiment precisely optimizes the structural parameters of this region to improve the optical field distribution in the crossing region, reduce the mode mismatch effect, and improve the overall optical transmission efficiency. Specifically, an inverse design based on the particle swarm optimization algorithm is adopted, that is, the particle swarm optimization algorithm is used to perform an inverse design on this region to optimize its structural parameters, so that the crossing waveguide can maintain good optical transmission performance under the condition of small-angle crossing.

[0032] Basic principle: Inverse design is a computational method based on the optimization of the objective function and is commonly used in the design of optical devices for structural optimization to meet specific optical performance requirements. Particle swarm optimization is a bionic optimization algorithm that simulates the behavior of bird flocks or fish schools searching for the optimal food source. Through information sharing and adaptive adjustment among particles, it realizes the optimal search for the objective function. The application of this algorithm in the optical field is mainly reflected in the optimization of the required structural parameters, especially suitable for high-dimensional nonlinear problems such as optical field regulation and mode matching. In the design method of the present invention, particle swarm optimization is used to adjust the refractive index distribution of materials in the inverse design region, so that the optical signal is scattered and mode mismatched as little as possible in the crossing region, and the waveguide crossing process is successfully completed, thereby optimizing the transmittance.

[0033] Objective function setting: Particle swarm optimization needs to define an objective function to enable the algorithm to continuously optimize the structural parameters to meet the performance requirements. In this embodiment, the objective function of the particle swarm optimization algorithm is established with the maximum optical transmittance of the crossing optical waveguide as the goal, and is set as follows: , where represents the optical transmittance of the crossing waveguide. At the target wavelength (for example, 1550 nm), the transmittance of the crossing waveguide reaches or approaches 95%. Therefore, the goal of the particle swarm optimization algorithm is to find the optimal structural parameters to maximize the value of this objective function.

[0034] The particle swarm optimization process (that is, the process of obtaining the target structural parameters) is as follows: S1. Initialize the particle swarm: In the preliminarily designed crossing region (for example, within the 2 µm × 2 µm inverse design region), several initial particles are randomly generated. Each particle represents a possible refractive distribution of the material, and each distribution is set to be symmetric about the x direction up and down to ensure that the generated structure can meet the simultaneous transmission in the forward and reverse directions; among them, each refractive distribution of the material corresponds to a structural parameter; S2. Calculate the optical transmittance: Use the three-dimensional full-wave electromagnetic solution method (the finite-difference time-domain method is adopted in this embodiment) to calculate the optical transmittance of the crossing waveguide under each refractive distribution of the material, and evaluate its optimization degree according to the objective function; S3. Update the particle velocity and position: Adjust the position of each particle according to its own historical optimal solution (local optimum) and the global optimal solution of the entire particle swarm to converge towards the optimal solution (i.e., the highest cross-waveguide transmittance). S4. Iterative optimization: Repeat steps S2 and S3 until the convergence condition is met to obtain the optimal solution. The convergence condition is that the transmittance reaches a preset percentage or the number of iterations reaches a preset number. The preset percentage can be 95%. S5. Optimization result: After iterative optimization by the particle swarm algorithm, the obtained cross-region structure is symmetric up and down, with structural parameters of 2 µm × 1.45 µm, and the structure is as Figure 2 shown, greatly reducing the size of the cross region and ensuring that the transmittance of the cross-waveguide reaches 94%. See Figure 3 .

[0035] Step 104, redesign the cross region of the crossed optical waveguide with the target structural parameters again.

[0036] In one example, after the inverse design is completed using the particle swarm optimization algorithm, although a cross-waveguide structure with a high transmittance is obtained, the feature size in some optimized regions may be too small, such as less than 10 nm, making it difficult to accurately manufacture through existing micro-nano processing technologies (such as photolithography or electron beam lithography). Therefore, on the premise of ensuring that the outer contour remains unchanged, the present invention further optimizes the process feasibility of the optimized structure, that is, structure simplification. In the actual manufacturing process of micro-nano optical devices, the process capabilities are usually limited by the following factors: the minimum manufacturable feature size (too small a pitch may lead to processing defects, such as pattern collapse or reduced resolution), and the manufacturing cost (extremely fine structures require longer processing times, increasing the manufacturing cost and difficulty). Therefore, in this embodiment, structure simplification is carried out on the basis of optimization so that the final design can be compatible with standard complementary metal-oxide-semiconductor (CMOS)-compatible photolithography or electron beam lithography processes.

[0037] In a specific implementation, in order to improve the process feasibility while maintaining the optimized performance, this embodiment uses rectangular units to replace the complex small structures inside the optimized region. Keeping the outer contour unchanged, that is, the structure size is still 2 µm × 1.45 µm, replace the optimized complex nano-scale feature region (line width less than 10 nm) inside with easy-to-process rectangular units, and set the length to be fixed at 2 µm, and the width varies in the range of 20 nm - 30 nm to adapt to different refractive index distributions and processing accuracy requirements. The simplified cross-waveguide structure is as Figure 4 shown, and at the same time, the transmittance of the cross-waveguide after structure simplification is as Figure 5As shown, it corresponds to the cases where the rectangular widths are 20 nm and 30 nm. For the incident wavelength of 1550 nm, the corresponding bandwidth is increased, and the process standard and high transmittance can be taken into account simultaneously. The processing defects caused by too small structures are avoided, and the repeatability of large-scale manufacturing is improved.

[0038] It can be seen that the present invention is exactly a design and implementation method of an efficient on-chip cross optical waveguide proposed for the technical problems, which can achieve efficient transmission of optical signals within a small angle range and provide a more optimized solution for high-density photon integration.

[0039] Specifically, the present invention optimizes the cross waveguide design, combines the particle swarm optimization algorithm for inverse design, and simplifies the structure on the basis of optimization to adapt to the existing micro-nano processing technology, and realizes an efficient on-chip cross optical waveguide solution. This method improves the integration degree of the photon integration chip, makes the optical path design more compact, optimizes the optical field distribution in the cross region at the same time, and improves the transmission stability of optical signals. The structure simplification strategy avoids ultra-small feature sizes, ensures that the design can be compatible with standard photolithography or electron beam exposure processes, reduces the manufacturing cost, and improves the CMOS processing consistency. In addition, the present invention does not require additional three-dimensional processing steps, is applicable to mainstream photon integration platforms such as silicon photonics and silicon nitride, and provides an efficient and reliable new solution for the design and manufacturing of high-density photon chips.

[0040] The step division of the above various methods is only for clear description. When implemented, they can be combined into one step or some steps can be split into multiple steps. As long as the same logical relationship is included, they are all within the protection scope of the present invention; adding insignificant modifications to the algorithm or process or introducing insignificant designs, but not changing the core design of its algorithm and process are all within the protection scope of the invention.

[0041] Another embodiment of the present invention relates to an on-chip cross optical waveguide, and the on-chip cross optical waveguide of this embodiment is designed by the design method of the on-chip cross optical waveguide described in the above embodiment.

[0042] It is not difficult to find that this embodiment is a waveguide component embodiment corresponding to the above method embodiment, and this embodiment can be implemented in cooperation with the above method embodiment. The relevant technical details and technical effects mentioned in the above embodiment are still valid in this embodiment. In order to reduce repetition, they will not be elaborated here. Correspondingly, the relevant technical details mentioned in this embodiment can also be applied to the above embodiment.

[0043] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present invention. In actual applications, various changes can be made to them in form and details without departing from the spirit and scope of the embodiments of the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, the protection scope of the embodiments of the present invention should be subject to the scope defined by the claims.

Claims

1. A design method for an on-chip cross optical waveguide, characterized in that The method includes: Cross two straight waveguides to form a crossed optical waveguide with a crossing angle less than 90 degrees; Conduct a preliminary design on the crossing area of the crossed optical waveguide to make the initial structural parameters of the crossing area less than 4 microns by 4 microns; Adopt a particle swarm optimization algorithm to optimize the initial structural parameters of the crossing area, so as to change the refractive index distribution of the material in the crossing area, obtain the refractive index distribution of the material in the crossing area when the light transmittance of the crossed optical waveguide is the largest and the structure of the crossing area satisfies the up-down, left-right symmetric structure, and use the corresponding structural parameters of the crossing area as the target structural parameters of the crossing area; Redesign the crossing area of the crossed optical waveguide with the target structural parameters.

2. The design method of the on-chip cross optical waveguide according to claim 1, characterized in that The objective function of the particle swarm optimization algorithm is established with the goal of maximizing the light transmittance of the crossed optical waveguide; The target structural parameters are obtained through the following steps: S1. Initialize the particle swarm: Randomly generate a number of initial particles in the preliminarily designed crossing area. Each particle represents a possible refractive distribution of the material, and each refractive distribution of the material corresponds to a structural parameter; S2. Calculate the light transmittance: Calculate the light transmittance of the crossed waveguide under each refractive distribution of the material, and evaluate the degree of optimization according to the objective function; S3. Update the particle velocity and position: Make each particle adjust its position according to its own local optimal solution and the global optimal solution of the entire particle swarm to converge towards the optimal solution; S4. Iterative optimization: Repeat steps S2 and S3 until the convergence condition is met to obtain the optimal solution. The convergence condition is that the transmittance reaches a preset percentage or the number of iterations reaches a preset number; S5. Obtain the target structural parameters according to the optimal solution.

3. The design method of the on-chip cross optical waveguide according to claim 1, wherein The crossing angle of the crossed optical waveguide is 20°; 4. The design method of the on-chip crossed optical waveguide according to claim 3, characterized in that, The initial structural parameters of the crossing area are 2 microns by 2 microns; 5. The design method of the on-chip crossed optical waveguide according to claim 4, characterized in that, The target structural parameters are 2 microns × 1.45 microns; 6. The design method of the on-chip crossed optical waveguide according to claim 5, characterized in that The redesign of the crossing area of the crossed optical waveguide with the target structural parameters includes: Replace the nanoscale feature area in the crossing area with the target structural parameters with rectangular units, and fix the length of the rectangular unit at 2 microns, and make the width vary within the range of 20 nanometers to 30 nanometers; Among them, the nanoscale feature area is the area where the line width in the crossing area is less than 10 nanometers; 7. The design method of the on-chip cross optical waveguide according to claim 2, characterized in that When the wavelength of the crossed optical waveguide is 1550 nanometers, the preset percentage takes a value of 95%; 8. An on-chip crossed optical waveguide, characterized in that, The on-chip crossed optical waveguide is designed by the design method of the on-chip crossed optical waveguide according to any one of claims 1 to 7.

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