Spectral filtering channel optimization design method based on target characteristics

Abstract

The invention relates to a spectral filtering channel optimization design method based on target characteristics, which comprises the following steps of: generating m candidate solutions for each layer of film of a filtering channel, performing crossover variation on the candidate solutions by combining a genetic algorithm, expanding a candidate solution set, repeatedly debugging the weight in an optimization algorithm, simplifying the calculation amount of the optimization algorithm, and improving the optimization efficiency. Then, on the basis of considering the diversity of target characteristic peaks, constructing a target function # imgabs0 # containing a penalty term, and obtaining a film system combination of an optimal filtering channel from a varied candidate solution set, so that the central wavelength and bandwidth of the filtering channel are freely regulated and controlled, and meanwhile, coupling overlapping among a plurality of characteristic peaks of the same target is prevented; the limitation of an existing optimization algorithm is effectively overcome, and the pertinence of a design result is higher.

Description

Technical Field

[0001] The present invention relates to the technical field of spectral imaging and optical thin films, and in particular to a method for optimizing the design of spectral filtering channels based on target characteristics. Background Art

[0002] In the field of spectral detection, accurate identification of the spectral characteristics of the target is crucial for key application areas such as remote sensing detection and biomedical diagnosis. The filter channel, as a core component in the spectral detection system, realizes the selective transmission of light of a specific wavelength while effectively suppressing out-of-band radiation. The filter channel plays a vital role in distinguishing the spectral characteristics of different targets. Specifically, the spectral characteristic peaks of different targets are different, and complex targets may exhibit multiple characteristic peaks. Therefore, in order to improve the accuracy and reliability of target detection, the key is to flexibly adjust the central wavelength and bandwidth of the filter channel to accurately match the characteristic spectral peaks of different targets.

[0003] The filter channel is usually composed of multiple layers of thin films with different refractive indices, which produce differences in the spatial and spectral distribution of light through the thin film interference effect. The existing optimization design methods of the filter channel are mainly divided into two categories: analytical method and optimization method. The analytical method relies on a specific film system structure and combines analytical design methods such as equivalent layer method, vector diagram method or equivalent interface method to manually design and adjust the film system. This method is time-consuming and labor-intensive, and requires high basic knowledge of thin film optics and film system design experience of the designer. The optimization method is based on various optimization algorithms. By formulating objective functions, numerical simulation and iterative search are used to minimize the difference between the design and the target spectrum to find the optimal structure. However, the existing optimization methods have limitations: i) parameter scanning or optimization algorithms based on gradient information are prone to fall into local optimal solutions; ii) the existing objective function only includes two index values, rectangularity and corrugation coefficient. Due to the different orders of magnitude of rectangularity and corrugation coefficient, the weight value needs to be repeatedly modified and debugged, and the weight value has a great influence on the accuracy of the optimization algorithm; iii) processing errors and other issues are not fully considered. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to break the limitations of existing filter channel optimization methods, avoid the optimization algorithm from falling into the optimal solution, and customize the filter channels for the spectral characteristic peaks of different targets.

[0005] The present invention provides a method for optimizing and designing a spectral filter channel based on target characteristics, wherein the filter channel comprises a substrate and a plurality of layers stacked on the substrate in sequence. The method comprises the following steps: Step 1. Collect a target spectrum curve of the target; extract the number of characteristic peaks in the target spectrum curve and number them in sequence; Step 2. Select the material of the thin film according to the wavelength range of the target spectral curve; Step 3. Randomly generate each layer of film The candidate solution set of candidate solutions is expressed as: ; In the formula, represents the refractive index of the film, Indicates the thickness of the film, Indicates Layer of thin film The refractive index and thickness of the film of the candidate solution; Step 4. m The candidate solutions are randomly crossed with each other and we get m new candidate solutions, before the crossover m Candidate solutions and new m candidate solutions form a candidate solution set; Step 5. Set the mutation rate to randomly change the material and thickness of all candidate solutions of one layer of the film in the candidate solution set obtained in step 4 to obtain a mutated candidate solution set; Step 6. Construct an objective function including a penalty term , input the mutated candidate solution set into the objective function The individual with the minimum objective function value is selected as the optimal filtering channel.

[0006] Compared with the prior art, the present invention has the following advantages: m The candidate solutions are cross-mutated by combining genetic algorithms to expand the candidate solution set, without repeatedly debugging the weights in the optimization algorithm, simplifying the calculation amount of the optimization algorithm, and then constructing an objective function containing a penalty term based on the diversity of the target characteristic peaks. The optimal film system combination of the filter channel is obtained from the mutated candidate solution set, which enables free control of the central wavelength and bandwidth of the filter channel. At the same time, the coupling overlap between multiple characteristic peaks of the same target is prevented, which effectively overcomes the limitations of the existing optimization algorithm and makes the design results more targeted.

[0007] In a possible implementation manner, the step 6 further includes the following steps: Step 7. Introduce a 1% error into the thickness of each film layer in the optimal filtering channel obtained in step 6, and keep the material of each film layer unchanged; Step 8. Calculate the objective function value of the optimal filtering channel after introducing the error amount and set the threshold , determine the objective function Is the value less than or equal to If so, then the optimal filtering channel before the error is introduced is output. The output optimal filtering channel includes the value and transmittance curve; if not, proceed to step 9; Step 9. Set the number of iterations , , set the maximum number of iterations , determine whether If yes, return to step 3. If no, expand the number of candidate solutions in the candidate set. , and return to step 3.

[0008] In a possible implementation, step 6 constructs an objective function including a penalty term. The calculation formula is: ; In the formula, Indicates the maximum wavelength of the filter channel in the entire wavelength range, Indicates the minimum wavelength of the filter channel in the entire wavelength range; It represents the transmittance of the optimized filter channel. Indicates the transmittance of the target spectral curve.

[0009] In a possible implementation, the objective function in step 6 is based on The calculation formula for selecting the individual with the minimum objective function value as the optimal filtering channel is: Minimize ; Subject to ; In the formula, Minimize means minimization, Subject to means constraint, is the number of the characteristic peak in the target spectrum curve, It represents the transmittance of the optimized filter channel. Indicates the transmittance of the target spectral curve; Indicates The maximum transmittance at each characteristic peak and its corresponding design wavelength range; For the x The design wavelength width corresponding to the transmittance at each characteristic peak is 0.5, 0.8 and 0.05 times the maximum value. Indicates The transmittance at the characteristic peak is 0.5 times the maximum value, which corresponds to the target wavelength range.

[0010] In a possible implementation manner, the transmittance of the optimized filter channel is The calculations include: Calculate first k Transmission matrix of the filter channel composed of layers of thin films M： ; In the formula, Indicates i Thin film No. The phase thickness of the candidate solution, 、 Indicates Layer of thin film The refractive index of the candidate solution and the thickness refractive index of the film, Indicates wavelength; Indicates Layer of thin film The optical admittance of the candidate solution, Indicates The beam passes through the candidate solution The incident angle of the thin film, represents the refractive index of the incident medium; Next, the transmittance of the optimized filter channel is The calculation formula is: . BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 is a structural diagram of the filter channel of the present invention; Figure 3 A comparison diagram of the design of the filter channel using dual characteristic peaks and the target spectrum curve in a specific embodiment of the present invention; Figure 4 These are the design parameters of the optimal filtering channel for the dual characteristic peaks outputted by the specific embodiment of the present invention. DETAILED DESCRIPTION

[0012] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0013] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0014] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0015] The present application is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] See also Figure 1 , the present application embodiment discloses a spectral filter channel optimization design method based on target characteristics, such as Figure 2 As shown, the filter channel includes a substrate and sequentially stacked on the substrate. The method comprises the following steps: Step 1. Collect the target spectrum curve of the target; extract the number of characteristic peaks in the target spectrum curve and number them in sequence; the target of this specific embodiment is leaves, and the target spectrum curve of the leaves is obtained by using a spectrophotometer, such as Figure 3 As shown by the dotted line in the figure, set it at 400 nm -445 nm and 481 nm -580 nm The transmittance is 0 in the wavelength range, and nm -480 nm and 581 nm -590 nm The transmittance within the wavelength range is 1; and the wavelength range 446 nm -480 nm The peak is extracted as characteristic peak 1, and the wavelength range is 581 nm -590 nm The characteristic peak 2 is extracted from the target spectrum curve. It is a prior art to identify the characteristic peak, which will not be described in detail here. Step 2: Select the material of the film according to the wavelength range of the target spectrum curve; the wavelength range of the target spectrum curve in this specific embodiment is 400 nm -700 nm Regarding the selection of film materials, the principle is to follow that the wavelength range of the film material falls within the wavelength range of the target spectrum curve; this specific embodiment is suitable for 400 nm -700 nm The material of wavelength range is TiO 2 and SiO 2 ; Step 3. Randomly generate each layer of film The candidate solution set of candidate solutions is expressed as: ; In the formula, represents the refractive index of the film, Indicates the thickness of the film, Indicates Layer of thin film The refractive index and thickness of the film of the candidate solution; Step 4. Randomly cross the candidate solutions of the same film layer. For example, , Perform crossover to generate new candidate solutions , ; In this specific embodiment, after randomly selecting two candidate solutions to cross-generate new candidate solutions, two more candidate solutions are randomly selected from the remaining candidate solutions to continue cross-generating, and the 3000 candidate solutions before the cross-generation and the new 3000 candidate solutions generated after the cross-generation are added together to form a candidate solution set with 6000 candidate solutions; Step 5. Set the mutation rate to 0.01 to randomly change the material and thickness of all candidate solutions for a layer of film in the candidate solution set obtained in step 4 to obtain a mutated candidate solution set; Step 6. Construct an objective function including a penalty term , input the mutated candidate solution set into the objective function The individual with the minimum objective function value is selected as the optimal filtering channel; where the objective function The calculation formula is: ; In the formula, Indicates the maximum wavelength of the filter channel in the entire wavelength range, Indicates the minimum wavelength of the filter channel in the entire wavelength range; It represents the transmittance of the optimized filter channel. Indicates the transmittance of the target spectral curve; Based on the objective function The calculation formula for selecting the individual with the minimum objective function value as the optimal filtering channel is: Minimize ; Subject to ; In the formula, Minimize means minimization, Subject to means constraint, is the number of the characteristic peak in the target spectrum curve, It represents the transmittance of the optimized filter channel. Indicates the transmittance of the target spectral curve; Indicates The maximum transmittance at each characteristic peak and its corresponding design wavelength range; For the x The design wavelength width corresponding to the transmittance at each characteristic peak is 0.5, 0.8 and 0.05 times the maximum value. Indicates The transmittance at the characteristic peak is 0.5 times the maximum value, which corresponds to the target wavelength range.

[0017] The transmittance of the optimized filter channel is The calculations include: Calculate first k Transmission matrix of the filter channel composed of layers of thin films M： ; In the formula, Indicates i Thin film No. The phase thickness of the candidate solution, 、 Indicates Layer of thin film The refractive index of the candidate solution and the thickness refractive index of the film, Indicates wavelength; Indicates Layer of thin film The optical admittance of the candidate solution, Indicates The beam passes through the candidate solution The incident angle of the thin film, Represents the refractive index of the incident medium.

[0018] Next, the transmittance of the optimized filter channel is The calculation formula is: ; Step 7. Introduce a 1% error into the thickness of each film layer in the optimal filtering channel obtained in step 6, and keep the material of each film layer unchanged; Step 8. Calculate the objective function of the optimal filtering channel after introducing the error value, and set the threshold , determine the objective function Is the value less than or equal to If so, then the optimal filtering channel before the error is introduced is output. The output optimal filtering channel includes the value and transmittance curve; if not, proceed to step 9; Step 9. Set the number of iterations , , set the maximum number of iterations , determine whether If yes, return to step 3. If no, expand the number of candidate solutions in the candidate set. , and return to step 3.

[0019] The present invention generates a plurality of thin films on each filter channel. m The candidate solutions are cross-mutated by combining genetic algorithms to expand the candidate solution set, without repeatedly debugging the weights in the optimization algorithm, simplifying the calculation amount of the optimization algorithm, and then constructing an objective function containing a penalty term based on the diversity of the target characteristic peaks. The optimal film system combination of the filter channel is obtained from the mutated candidate solution set, which enables free control of the central wavelength and bandwidth of the filter channel. At the same time, the coupling overlap between multiple characteristic peaks of the same target is prevented, which effectively overcomes the limitations of the existing optimization algorithm and makes the design results more targeted.

[0020] In the description of the embodiments of the present application, it should be noted that in the description of the present application, terms such as "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description, and does not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present application.

[0021] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0022] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for optimizing and designing a spectral filter channel based on target characteristics, wherein the filter channel comprises a substrate and a plurality of layers stacked on the substrate in sequence. A thin film, characterized in that The following steps are involved: Step 1. Collect a target spectrum curve of the target; extract the number of characteristic peaks in the target spectrum curve and number them in sequence; Step 2. Select the material of the thin film according to the wavelength range of the target spectral curve; Step 3. Randomly generate a The candidate solution set of candidate solutions is expressed as: ； In the formula, represents the refractive index of the film, Indicates the thickness of the film, Indicates Layer of thin film The refractive index and thickness of the film of the candidate solution; Step 4. Place the same layer of film m The candidate solutions are randomly crossed with each other and we get m new candidate solutions, crossing the m Candidate solutions and new m candidate solutions form a candidate solution set; Step 5. Set the mutation rate to randomly change the material and thickness of all candidate solutions of one layer of the film in the candidate solution set obtained in step 4 to obtain a mutated candidate solution set; Step 6. Construct an objective function including a penalty term , input the mutated candidate solution set into the objective function The individual with the minimum objective function value is selected as the optimal filtering channel.

2. The method for optimizing the spectral filtering channel based on target characteristics according to claim 1 is characterized in that: The step 6 further includes the following steps: Step 7. Introduce a 1% error into the thickness of each film layer in the optimal filtering channel obtained in step 6, and keep the material of each film layer unchanged; Step 8. Calculate the objective function value of the optimal filtering channel after introducing the error amount and set the threshold , determine the objective function Is the value less than or equal to If so, then the optimal filtering channel before the error is introduced is output. The output optimal filtering channel includes the value and transmittance curve; if not, proceed to step 9; Step 9. Set the number of iterations , , set the maximum number of iterations , determine whether If yes, return to step 3. If no, expand the number of candidate solutions in the candidate set. , and return to step 3.

3. The method for optimizing the spectral filtering channel based on target characteristics according to claim 1, characterized in that: Step 6 constructs an objective function including a penalty term The calculation formula is: ； In the formula, Indicates the maximum wavelength of the filter channel in the entire wavelength range, Indicates the minimum wavelength of the filter channel in the entire wavelength range; It represents the transmittance of the optimized filter channel. Indicates the transmittance of the target spectral curve.

4. The method for optimizing the spectral filtering channel based on target characteristics according to claim 3 is characterized in that: In step 6, based on the objective function The calculation formula for selecting the individual with the minimum objective function value as the optimal filtering channel is: Minimize ； Subject to ； In the formula, Minimize means minimization, Subject to means constraint, is the number of the characteristic peak in the target spectrum curve, It represents the transmittance of the optimized filter channel. Indicates the transmittance of the target spectral curve; Indicates The maximum transmittance at each characteristic peak and its corresponding design wavelength range; For the x The design wavelength width corresponding to the transmittance at each characteristic peak is 0.5, 0.8 and 0.05 times the maximum value. Indicates The transmittance at the characteristic peak is 0.5 times the maximum value, which corresponds to the target wavelength range.

5. The method for optimizing the design of spectral filtering channels based on target characteristics according to claim 4, characterized in that: The transmittance of the optimized filter channel is The calculations include: Calculate first k Transmission matrix of the filter channel composed of layers of thin films M : ； In the formula, Indicates i Thin film No. The phase thickness of the candidate solution, 、 Indicates Layer of thin film The refractive index of the candidate solution and the thickness refractive index of the film, Indicates wavelength; Indicates Layer of thin film The optical admittance of the candidate solution, Indicates The beam passes through the candidate solution The incident angle of the thin film, represents the refractive index of the incident medium; Next, the transmittance of the optimized filter channel is The calculation formula is: 。

Images