CN115933063A - Variable-period grating coupler based on genetic algorithm optimization - Google Patents
Variable-period grating coupler based on genetic algorithm optimization Download PDFInfo
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- CN115933063A CN115933063A CN202211590929.5A CN202211590929A CN115933063A CN 115933063 A CN115933063 A CN 115933063A CN 202211590929 A CN202211590929 A CN 202211590929A CN 115933063 A CN115933063 A CN 115933063A
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Abstract
The invention relates to a variable period grating coupler based on genetic algorithm optimization, which comprises: a substrate; the buried oxide layer is positioned on the surface of the substrate; the waveguide layer is arranged above the buried oxide layer and is internally provided with a grating structure with a variable period and a variable duty ratio; the grating structure enables the field intensity attenuation factor of the grating coupler to change along with the position; the parameters of the grating structure are determined by a genetic algorithm. The invention optimizes the multi-structure parameters of the grating coupler by adopting a genetic algorithm, has simple design method, reduces the labor and time cost of design, increases the freedom degree of design and can realize good application.
Description
Technical Field
The invention relates to the technical field of integrated optoelectronic devices, in particular to a variable-period grating coupler based on genetic algorithm optimization.
Background
Since silicon is an indirect bandgap semiconductor and is not suitable for making light sources, it is necessary to couple light from an external laser to a silicon optical chip using an optical fiber. With the great improvement of the integration level, the size of the silicon-based photonic device is smaller and smaller, the optical fiber mode spot and the waveguide mode spot have huge mode mismatch, and the coupling loss between a chip and an optical fiber is an important source of optical loss in a link. The grating coupling scheme has the advantages of simple manufacture, flexible position, large alignment tolerance and better suitability for wafer-level test.
The optical field matching factor is the overlap integral of the optical field coupled out by the grating coupler and the intrinsic optical field distribution in the optical fiber, represents the matching degree of the two, and mainly influences the coupling efficiency of the grating coupler. The coupling intensity of each place to light is the same, the optical field distribution of the uniform grating coupler is in an exponential attenuation mode, the optical field in the single-mode fiber is in a near Gaussian distribution, and the optical field coupled out by the grating coupler and the intrinsic optical field distribution in the fiber may have certain mismatch, so that the coupling loss of the grating coupler is increased.
Most of the design methods of the grating coupler are designed based on the design principle, and because the factors influencing the performance index of the grating coupler are more, the design of multivariable complex devices requires a large amount of design time and labor cost. The automatic device design method can save the design cost and increase the degree of freedom of device design on the basis of ensuring that the device index is reached, and provides a scheme for the design of the grating coupler with variable period. The genetic algorithm is a method for searching an optimal solution by simulating a natural evolution process, and a better optimization result can be obtained quickly when a complex combination optimization problem is solved.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a variable-period grating coupler optimized based on a genetic algorithm, which can reduce the manpower and time cost of design under the condition of ensuring the coupling efficiency and bandwidth.
The technical scheme adopted by the invention for solving the technical problem is as follows: a variable period grating coupler optimized based on a genetic algorithm is provided, which comprises:
a substrate;
the buried oxide layer is positioned on the surface of the substrate;
the waveguide layer is arranged above the buried oxide layer and is internally provided with a grating structure with variable periods and variable duty ratios; the grating structure enables the field intensity attenuation factor of the grating coupler to change along with the position; the parameters of the grating structure are determined by a genetic algorithm.
The parameters of the grating structure are determined by a genetic algorithm, and specifically comprise the following steps: taking the length, duty ratio, optical fiber position and angle of each period of the grating structure as optimization variables; real number coding is carried out on optimized variables, a group of optimized variables are used as a chromosome, genetic algorithm parameters are set, an initial population is generated at random, the fitness of each individual in the population is calculated, the individual is selected by taking the proportion of the fitness accounting for the total fitness as the selected proportion, part of chromosomes are exchanged among adjacent individuals, gene values on certain positions of the chromosomes in the population are varied, a next generation population is generated, and the optimal optimized variables are found through multiple iterations.
And when the next generation species group is generated, directly retaining the optimal individuals in the current species group into the next generation species group.
The fitness function FOM in the genetic algorithm is:
wherein, P wg For coupling power into the waveguide, P source Is the source power, wherein the power coupled into the waveguide varies as a function of the length of each period of the grating structure, duty cycle, fiber position and angle.
The substrate is a silicon substrate.
The buried oxide layer is made of silicon dioxide.
The waveguide layer is made of any one of silicon, silicon nitride, silicon oxynitride, germanium and lithium niobate.
Advantageous effects
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects: the invention optimizes the multi-structure parameters of the grating coupler by adopting a genetic algorithm, has simple design method, reduces the labor and time cost of design, increases the freedom degree of design and can realize good application in the C wave band. The device structure provided by the invention has a simple preparation process, is compatible with a CMOS (complementary metal oxide semiconductor) process, and reduces the processing cost.
Drawings
FIG. 1 is a schematic cross-sectional view of a variable period grating coupler optimized based on a genetic algorithm according to an embodiment of the present invention;
FIG. 2 is a flow chart of a genetic algorithm in an embodiment of the present invention;
FIG. 3 is a schematic diagram of the coupling efficiency of a variable period grating coupler optimized based on a genetic algorithm according to an embodiment of the present invention.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention can be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the claims appended to the present application.
The embodiment of the invention relates to a variable-period grating coupler optimized based on a genetic algorithm, which comprises a substrate 1, a buried oxide layer 2 and a waveguide layer 3 as shown in figure 1. The substrate 1 is made of silicon, the buried oxide layer 2 is located above the substrate 1 and made of silicon dioxide, the waveguide layer 3 is placed above the buried oxide layer 2 and made of one of silicon, silicon nitride, silicon oxynitride, germanium and lithium niobate, and the waveguide layer 3 is internally etched to form a grating structure with a variable period and a variable duty ratio. The grating structure with variable period and duty ratio makes the field intensity attenuation factor of the grating coupler change with the position, thereby changing the mode field of the grating coupler and improving the mode field matching of the grating coupler and the optical fiber in approximate Gaussian distribution. The grating coupling strength and the mode field distribution can be optimized by optimizing the parameters of the grating structure, and the parameters of the grating structure are optimized by adopting a genetic algorithm in the embodiment.
In the embodiment, the length and the duty ratio of each period of the grating structure to be optimized and the position and the angle of the optical fiber are used as optimization variables, and the genetic algorithm is used for optimizing the multi-structure parameters of the grating coupler by utilizing the characteristic that the genetic algorithm is insensitive to the size of a solution space. As shown in fig. 2, first, real number coding is performed on optimized variables, a set of optimized variables is used as a chromosome, genetic algorithm parameters are set, an initial population is generated randomly, fitness of each individual in the population is calculated, the individual is selected according to the selected proportion of the fitness accounting for the total fitness, part of chromosomes are exchanged among adjacent individuals, gene values of certain positions of the chromosomes in the population are varied, a next generation population is generated, and the optimal optimized variables are found through multiple iterations. The elite sense is adopted when the next generation population is generated, namely, the optimal individual in the current generation population is directly reserved in the next generation population, and the introduction of the elite sense can ensure convergence to the global optimal solution.
The fitness of the individual is calculated through a fitness function, and the fitness function FOM in the embodiment is as follows:
wherein, P wg For coupling power into the waveguide, P source Is the source power, wherein the power coupled into the waveguide varies as a function of the length of each period of the grating structure, duty cycle, fiber position and angle.
For the input light in the TE mode, light is coupled into the waveguide using a silicon nitride variable period grating coupler. As shown in fig. 3, the optimization can achieve a coupling efficiency of over-3 dB, with a-1 dB bandwidth of the grating coupler reaching 45nm around the 1550nm center wavelength. Therefore, the device has the advantages of small size, high coupling efficiency, larger bandwidth and simple process. Therefore, the invention optimizes the multi-structure parameters of the grating coupler by adopting a genetic algorithm, has simple design method, reduces the labor and time cost of design, increases the freedom degree of design, ensures that the minimum size parameter of the designed device is not less than the minimum characteristic size under the existing silicon photofabrication technology, and can realize good application.
Claims (7)
1. A variable period grating coupler optimized based on a genetic algorithm, comprising:
a substrate;
the buried oxide layer is positioned on the surface of the substrate;
the waveguide layer is arranged above the buried oxide layer and is internally provided with a grating structure with a variable period and a variable duty ratio; the grating structure enables the field intensity attenuation factor of the grating coupler to change along with the position; the parameters of the grating structure are determined by a genetic algorithm.
2. The variable-period grating coupler optimized based on the genetic algorithm as claimed in claim 1, wherein the parameters of the grating structure are determined by the genetic algorithm, specifically: taking the length, duty ratio, optical fiber position and angle of each period of the grating structure as optimization variables; real number coding is carried out on optimized variables, a group of optimized variables are used as a chromosome, genetic algorithm parameters are set, an initial population is generated at random, the fitness of each individual in the population is calculated, the individual is selected by taking the proportion of the fitness accounting for the total fitness as the selected proportion, part of chromosomes are exchanged among adjacent individuals, gene values on certain positions of the chromosomes in the population are varied, a next generation population is generated, and the optimal optimized variables are found through multiple iterations.
3. The genetic algorithm optimization-based variable period grating coupler of claim 2, wherein the next generation population is generated by directly retaining the optimal individuals in the current population into the next generation population.
4. The genetic algorithm optimization-based variable period grating coupler of claim 1, wherein the fitness function FOM in the genetic algorithm is:
wherein, P wg For coupling power into the waveguide, P source Is the power of the light source, wherein the power coupled into the waveguide is based on the length of each period of the grating structure, the duty cycle, the fiber positionAnd the angle of the lever.
5. The genetic algorithm optimization-based variable period grating coupler of claim 1, wherein the substrate is a silicon substrate.
6. The genetic algorithm optimization-based variable period grating coupler of claim 1, wherein the material of the buried oxide layer is silicon dioxide.
7. The genetic algorithm optimization-based variable period grating coupler of claim 1, wherein the waveguide layer is made of any one of silicon, silicon nitride, silicon oxynitride, germanium and lithium niobate.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116502545A (en) * | 2023-06-26 | 2023-07-28 | 国科大杭州高等研究院 | Genetic algorithm, application and microstructure optical probe for wide-angle coupling structure |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116502545A (en) * | 2023-06-26 | 2023-07-28 | 国科大杭州高等研究院 | Genetic algorithm, application and microstructure optical probe for wide-angle coupling structure |
| CN116502545B (en) * | 2023-06-26 | 2023-09-26 | 国科大杭州高等研究院 | Genetic algorithm, application and microstructure optical probe for wide-angle coupling structure |
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