Stepped three-band grating coupler and reverse optimization method thereof

Abstract

The invention discloses a stepped three-band grating coupler and a reverse optimization method thereof, and belongs to the technical field of photonic devices and integration, and the reverse optimization method comprises the steps: determining a design target of the grating coupler, and defining an initial structure; defining optimization parameters including grating height and grating width according to the grating number; defining an optimization quality factor according to a design target of the grating coupler, and dynamically updating a weight coefficient of the quality factor; optimizing the width and height distribution of all gratings by using an improved direct binary search algorithm; and iterative optimization is continuously carried out until a design target is achieved, and width distribution corresponding to gratings with different heights in the optimized stepped grating structure is obtained. The problem that traditional grating diffraction has inherent wavelength dependence is effectively solved, and efficient coupling of three optical communication wavebands is achieved.

Description

Technical Field

[0001] The present invention relates to the field of photonic devices and integration, and particularly to a stepped triple-band grating coupler and its reverse optimization method. Background Art

[0002] Under the background of the rapid development of information technology, the development of integrated optoelectronic technology is changing with each passing day. Due to physical property limitations, traditional electrical interconnections are difficult to meet the development requirements of the information age. Therefore, optical interconnection that combines photonic carriers and electronic carriers is the future development trend. The silicon-on-insulator platform has gradually become one of the most mainstream technologies in the field of integrated optoelectronics due to its advantages such as high refractive index contrast, low loss, and low cost. With the gradual application of optoelectronic integrated devices in optical communication systems, how to efficiently and low-costly couple optical fibers with the waveguides of optoelectronic integrated chips has become a long-term challenging problem.

[0003] Currently, the technology of grating couplers for single bands is relatively mature, and there are many solutions. For dual-band gratings, in 2023, the team of Hon Ki Tsang used a genetic algorithm to optimize two independent gratings on a silicon layer and a polysilicon cladding layer. The experimental results show that the coupling efficiency of this grating coupler in the C band is -4.37 dB, and the coupling efficiency in the O band is -5.8 dB, achieving efficient coupling of dual-band optical signals. However, there are still the following problems or deficiencies in existing research:

[0004] 1. The current grating coupler technology is only limited to the research of single-band or dual-band coupling, and the development of grating couplers supporting three bands and above is still pending.

[0005] 2. The current dual-band coupler technology has a complex structure and requires special fabrication processes, which are not compatible with existing conventional chip fabrication processes, resulting in high production costs and poor fabricability during the fabrication process. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a stepped triple-band grating coupler based on reverse design, and adjust the structural parameters of the stepped grating through an optimization algorithm to achieve efficient coupling between an integrated photonic chip and an optical fiber system under three bands.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A stepped triple-band grating coupler is constructed on a silicon platform on an insulating substrate, and includes a base layer, a lower cladding layer, a waveguide layer, and an upper cladding layer from bottom to top; a stepped grating structure is arranged in the waveguide layer, and the stepped grating structure is composed of gratings with different widths and heights, and the stepped grating structure is based on reverse optimization design.

[0009] A further improvement of the technical solution of the present invention lies in that: the width distribution range of the stepped grating structure is 100 nm - 700 nm.

[0010] A further improvement of the technical solution of the present invention lies in that: the height distribution of the stepped grating structure is in a stepped distribution, and there are four height parameters, including 0 nm, 70 nm, 150 nm, and 220 nm, and the four height parameters are compatible with the silicon-based chip manufacturing process.

[0011] A further improvement of the technical solution of the present invention lies in that: the waveguide layer and the base layer are made of silicon, and the upper cladding and the lower cladding are made of silicon dioxide.

[0012] A reverse optimization method for a stepped triple-band grating coupler includes the following steps:

[0013] S1. Determine the design goal of the grating coupler and define the initial structure;

[0014] S2. Define the optimization parameters according to the number of gratings, including the grating height and the grating width;

[0015] S3. Define the optimization quality factor based on the design goal of the grating coupler and dynamically update the weight coefficient of the quality factor;

[0016] S4. Use an improved direct binary search algorithm to optimize the width and height distributions of all gratings;

[0017] S5. Continuously iterate and optimize until the design goal is achieved, and obtain the corresponding width distributions of the gratings with different heights in the optimized stepped grating structure.

[0018] A further improvement of the technical solution of the present invention lies in that: in S1, the goal is to maximize the efficiency of waveguide coupling into a single-mode fiber at three wavelengths of 1310 nm, 1550 nm, and 1900 nm; the initial structure of the stepped grating is a stepped grating structure composed of a preset number of gratings with a width of 300 nm and heights of 0 nm, 70 nm, 150 nm, and 220 nm arranged in sequence.

[0019] A further improvement of the technical solution of the present invention lies in that: the grating height is denoted as h n , and the corresponding width is denoted as w n , during the optimization process, the distributions of a preset number of width parameters and a preset number of height parameters are adjusted. The adjustment range of the width parameter w n is from 100 nm to 700 nm, and the step size of each parameter adjustment is 10 nm. The adjustment range of the height parameter h n is 0 nm, 70 nm, 150 nm, and 220 nm.

[0020] A further improvement of the technical solution of the present invention lies in that: in S3, the expression of the figure of merit FOM is:

[0021] FOM = αT 1310nm + βT 1550nm + ωT 1900nm

[0022] wherein, T 1310nm 、T 1550nm 、T 1310nm respectively represent the coupling efficiencies from the waveguide to the single-mode grating at wavelengths of 1310 nm, 1550 nm, and 1900 nm, and α, β, and ω respectively represent the weight coefficients corresponding to the coupling efficiencies in different bands during the optimization process;

[0023] During the optimization process, the optimal coupling efficiency values T max-1310nm 、T max-1550nm and T max-1900nm for each band are monitored in real time, and the weight coefficients are dynamically updated according to their relative ratios;

[0024] The weight coefficients are set as:

[0025]

[0026] wherein, to balance the coupling efficiency values corresponding to the three wavelengths during the optimization process.

[0027] A further improvement of the technical solution of the present invention lies in that: S4 specifically includes the following steps:

[0028] S41 sets the initial width parameter and height parameter for the grating coupler, and then adjusts the width of each grating from 100 nm to 700 nm in steps of 10 nm in sequence;

[0029] S42 adjusts the height of each grating to 0 nm, 70 nm, 150 nm, and 220 nm;

[0030] S43 calculates the figure of merit FOM defined in S3 through simulation for each adjustment, and determines whether the convergence condition is satisfied;

[0031] If the current FOM value is improved compared with the optimal value, the current parameters are retained as the new optimization benchmark; if the FOM value does not reach the expected improvement, it immediately reverts to the previous valid parameter state and continues to adjust and optimize the parameters;

[0032] After the global optimization of any one of the grating parameters is completed, within a range of 20 nm centered on the parameter value corresponding to the global optimal efficiency, with a step size of 1 nm, local optimization is carried out. Using the same judgment criteria as in S43, the above-mentioned parameter adjustments and simulation calculations are respectively performed on the grating, so that the performance of the device continuously approaches the design target.

[0033] Due to the adoption of the above technical solutions, the technical progress achieved by the present invention is as follows:

[0034] 1. The present invention combines gratings with different heights and widths, and uses an inverse design algorithm to optimize the corresponding grating width and height distributions, effectively overcoming the problem that traditional grating diffraction has an inherent wavelength dependence, and realizing efficient coupling in three optical communication bands (1310 nm band, 1550 nm band, and 1900 nm band).

[0035] 2. The grating coupler in the present invention has the advantage of being compatible with the standard wafer process, providing a solid foundation for large-scale production and integration.

[0036] 3. The present invention realizes the adaptive balance optimization of the coupling efficiency corresponding to the three bands by dynamically updating the weight coefficients of the quality factor, effectively solving the problem of efficiency imbalance in multi-objective optimization.

[0037] 4. The present invention optimizes the width and height distributions of all gratings by applying an improved direct binary search algorithm, and combines the two-stage optimization strategy of global optimization and local optimization to find the optimal solution of the multi-objective problem in a large parameter space, maximizing the device performance. Brief Description of the Drawings

[0038] Figure 1 It is a cross-sectional schematic diagram of a stepped three-band grating coupler based on inverse optimization according to an embodiment of the present invention;

[0039] Figure 2 It is a schematic diagram of the optimization process of the stepped grating structure according to an embodiment of the present invention;

[0040] Figure 3 It is a simulated optical field distribution diagram of the embodiment of the present invention at three central wavelengths of 1310 nm, 1550 nm, and 1900 nm;

[0041] Figure 4 It is a coupling efficiency diagram of the embodiment of the present invention for light coupling from a waveguide to a single-mode fiber in the wavelength range of 1240 nm - 1348 nm;

[0042] Figure 5 It is a coupling efficiency diagram of the embodiment of the present invention for light coupling from a waveguide to a single-mode fiber in the wavelength range of 1510 nm - 1590 nm;

[0043] Figure 6 This is the coupling efficiency diagram of light from the waveguide to the single-mode fiber within the wavelength range of 1748nm - 2000nm for the embodiments of the present invention;

[0044] Among them, 1. Substrate layer, 2. Lower cladding layer, 3. Waveguide layer, 4. Upper cladding layer, 5. Step-type grating structure, 6. Single-mode fiber. Specific embodiments

[0045] The following further elaborates on the present invention in detail with reference to the accompanying drawings and embodiments:

[0046] Embodiment

[0047] As Figure 1 shown, this embodiment is a step-type three-band grating coupler based on reverse optimization, constructed on a silicon platform on an insulating substrate, which includes a substrate layer 1, a lower cladding layer 2, a waveguide layer 3, and an upper cladding layer 4 from bottom to top. Specifically, the materials of the waveguide layer 3 and the substrate layer 1 are silicon, and the materials of the upper cladding layer 4 and the lower cladding layer 2 are silicon dioxide.

[0048] The main structure of this embodiment is in the waveguide layer 3. The thickness of the waveguide layer 3 is 220nm. The main body of the grating coupler is a step-type grating structure 5. By combining gratings with different heights and widths and using the direct binary search algorithm to optimize the corresponding grating width and height distributions, the problem that traditional grating diffraction has an inherent wavelength dependence can be effectively overcome, ensuring that coupling between the integrated photon chip and the fiber system can be achieved in three bands centered at wavelengths of 1310nm, 1550nm, and 1900nm.

[0049] The width distribution range of the step-type grating structure 5 is 100nm - 700nm. The height distribution of the step-type grating structure 5 is in a step-type distribution, with four height parameters, including 0nm, 70nm, 150nm, and 220nm. These four height parameters are compatible with the silicon-based chip manufacturing process and can be adjusted according to the existing chip manufacturing process definitions.

[0050] As Figure 2 shown, the reverse optimization method of the step-type three-band grating coupler specifically includes the following steps:

[0051] S1. Determine the design objective of the grating coupler and define the initial structure;

[0052] Aiming to maximize the coupling efficiency of light from the waveguide into the single-mode fiber 6 at three wavelengths of 1310nm, 1550nm, and 1900nm; the initial structure of the step-type grating is a step-type grating structure 5 composed of 48 gratings with a width of 300nm and heights of 0nm, 70nm, 150nm, and 220nm arranged in sequence in a cyclic manner;

[0053] S2. Define the optimization parameters, where the grating height is denoted as h n , and the corresponding width is denoted as w n . During the optimization process, adjust the distribution of a preset number of width parameters and a preset number of height parameters. The width parameter w n is adjusted in the range of 100 nm to 700 nm, and the step size for each parameter adjustment is 10 nm. The height parameter h n is adjusted in the range of 0 nm, 70 nm, 150 nm, and 220 nm;

[0054] S3. Define the optimization figure of merit based on the design goal of the grating coupler and dynamically update the weight coefficients of the figure of merit;

[0055] The expression of the figure of merit FOM is:

[0056] FOM = αT 1310nm + βT 1550nm + ωT 1900nm

[0057] where T 1310nm , T 1550nm , T 1310nm respectively represent the coupling efficiency from the waveguide to the single-mode grating at wavelengths of 1310 nm, 1550 nm, and 1900 nm. α, β, and ω respectively represent the weight coefficients corresponding to the coupling efficiency in different wavelength bands during the optimization process;

[0058] During the optimization process, monitor the optimal coupling efficiency values T max-1310nm , T max-1550nm and T max-1900nm for each wavelength band in real time, and dynamically update the weight coefficients according to their relative ratios;

[0059] In this embodiment, the weight coefficients are set as:

[0060]

[0061] where, to balance the coupling efficiency values corresponding to the three wavelengths during the optimization process;

[0062] S4. Use the improved direct binary search algorithm to optimize the width and height distributions of all gratings;

[0063] S4 specifically includes the following steps:

[0064] S41. Set the initial width parameter and height parameter for the grating coupler, and then sequentially adjust the width of each grating from 100 nm to 700 nm with a step size of 10 nm;

[0065] S42 adjusts the height of each grating by 0 nm, 70 nm, 150 nm, and 220 nm;

[0066] S43 For each adjustment, the figure of merit FOM defined in S3 is calculated through simulation, and it is judged whether the convergence condition is satisfied;

[0067] If the current FOM value is improved compared with the optimal value, the current parameters are retained as the new optimization benchmark; if the FOM value does not reach the expected improvement, it immediately reverts to the previous valid parameter state, and the parameter adjustment and optimization continue;

[0068] S44 After the global optimization of any one grating parameter is completed, within a range of 20 nm centered on the parameter value corresponding to the global optimal efficiency, with a step size of 1 nm, local optimization is carried out. Using the same judgment criteria as S43, the above-mentioned parameter adjustment and simulation calculation are performed on 48 gratings respectively, so that the performance of the device continuously approaches the design target.

[0069] S5 Continuously iterate and optimize until the design target is reached, and obtain the width distribution corresponding to the gratings with different heights in the optimized stepped grating structure 5;

[0070] Perform a more detailed simulation performance analysis on the optimized grating coupler, and simulate and calculate the optical field distribution and coupling efficiency of the device at different wavelengths to verify whether the performance of the device meets the expectations.

[0071] Figure 3 This is the simulated optical field distribution diagram of the embodiment of the present invention. The device is simulated and analyzed by the three-dimensional finite difference time domain method. It shows the simulated optical field distribution diagrams of the designed three-band grating coupler during the coupling process at wavelengths of 1310 nm, 1550 nm, and 1900 nm. It can be seen that at the three wavelengths, the optical energy in the waveguide is well coupled to the single-mode fiber 6, which means that the designed grating coupler can realize the coupled transmission of TE0 mode optical signals in three bands.

[0072] Figure 4 、 5 、6 is the coupling efficiency diagram of the embodiment of the present invention. The device is simulated and analyzed by the three-dimensional finite difference time domain method. Figure 4 、 5 、6 are the coupling efficiency diagrams of the structure where the optical waveguide is coupled into the single-mode fiber 6 in the bands of 1240 nm - 1348 nm, 1510 nm - 1590 nm, and 1748 nm - 2000 nm respectively. It can be seen that the losses in the three bands are all less than 8.2 dB, meeting the design target.

[0073] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as the protection scope of the present invention.

[0074] In summary, the present invention effectively overcomes the problem of the inherent wavelength dependence of traditional grating diffraction and realizes efficient coupling in three optical communication bands (1310 nm band, 1550 nm band, and 1900 nm band).

Claims

1. A stepped triple-band grating coupler is built on a silicon platform on an insulating substrate, which includes a base layer (1), a lower cladding layer (2), a waveguide layer (3), and an upper cladding layer (4) from bottom to top; characterized in that: A stepped grating structure (5) is provided in the waveguide layer (3). The stepped grating structure (5) is composed of gratings with different widths and heights, and the stepped grating structure (5) is based on reverse optimization design.

2. The stepped three-band grating coupler according to claim 1, wherein: The width distribution range of the stepped grating structure (5) is 100nm - 700nm.

3. The stepped three-band grating coupler according to claim 1, wherein: The height distribution of the stepped grating structure (5) is in a stepped distribution, with four height parameters, including 0nm, 70nm, 150nm, and 220nm, and the four height parameters are compatible with the silicon-based chip manufacturing process.

4. The stepped three-band grating coupler according to claim 1, wherein: The materials of the waveguide layer (3) and the base layer (1) are silicon, and the materials of the upper cladding (4) and the lower cladding (2) are silicon dioxide.

5. An inverse optimization method for a stepped three-band grating coupler, characterized in that: Applied to the stepped three-band grating coupler according to any one of claims 1 to 4, it includes the following steps: S1. Determine the design objective of the grating coupler and define the initial structure; S2. Define the optimization parameters according to the number of gratings, including the grating height and the grating width; S3. Define the optimization figure of merit based on the design objective of the grating coupler, and dynamically update the weight coefficient of the figure of merit; S4. Use an improved direct binary search algorithm to optimize the width and height distributions of all gratings; S5. Continuously iterate and optimize until the design objective is achieved, and obtain the width distributions corresponding to the gratings with different heights in the optimized stepped grating structure (5).

6. The reverse optimization method of the stepped triple-band grating coupler according to claim 5, wherein: In S1, the objective is to maximize the efficiency of waveguide coupling into the single-mode fiber (6) at three wavelengths of 1310nm, 1550nm, and 1900nm; the initial stepped grating structure is a stepped grating structure (5) composed of a preset number of gratings with a width of 300nm and heights of 0nm, 70nm, 150nm, and 220nm arranged in sequence.

7. The reverse optimization method of the stepped three-band grating coupler according to claim 5, characterized in that: The grating height is denoted as h n , and the corresponding width is denoted as w n , during the optimization process, the distributions of a preset number of width parameters and a preset number of height parameters are adjusted. The width parameter w n is adjusted in the range of 100 nm to 700 nm, and the step size of each parameter adjustment is 10 nm. The height parameter h n is adjusted in the ranges of 0 nm, 70 nm, 150 nm, and 220 nm.

8. The reverse optimization method of the stepped three-band grating coupler according to claim 5, characterized in that: In S3, the expression of the figure of merit FOM is: FOM = αT 1310nm + βT 1550nm + ωT 1900nm Among them, T 1310nm , T 1550nm , T 1310nm respectively represent the coupling efficiencies from the waveguide to the single-mode grating at wavelengths of 1310 nm, 1550 nm, and 1900 nm, and α, β, and ω respectively represent the weight coefficients corresponding to the coupling efficiencies in different wavelength bands during the optimization process; During the optimization process, the optimal coupling efficiency values T for each band max-1310nm , T max-1550nm and T max-1900nm are monitored in real time, and the weight coefficients are dynamically updated according to their relative ratios; The weight coefficient is set as: Among them, to balance the coupling efficiency values corresponding to the three wavelengths during the optimization process.

9. The reverse optimization method of the stepped three-band grating coupler according to claim 8, wherein: S4 specifically includes the following steps: S41. Set the initial width parameter and height parameter for the grating coupler, and then adjust the width of each grating from 100nm to 700nm with a step of 10nm in sequence; S42. Adjust the height of each grating to 0nm, 70nm, 150nm, and 220nm; S43. Each adjustment calculates the figure of merit FOM defined in S3 through simulation and judges whether the convergence condition is met; If the current FOM value is improved compared to the optimal value, retain the current parameters as the new optimization benchmark; if the FOM value does not reach the expected improvement, immediately roll back to the previous valid parameter state and continue to adjust and optimize the parameters; After the global optimization of any one grating parameter is completed, within a range of 20nm centered on the parameter value corresponding to the global optimal efficiency, with a step of 1nm, perform local optimization, and use the same judgment criterion as in S43 to perform the above parameter adjustment and simulation calculation on the grating respectively, so that the performance of the device continuously approaches the design objective.

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