Spectrometer bandwidth expansion method based on Fabry-Perot etalon

Abstract

The invention belongs to the technical field of optical metrology testing, and particularly relates to a spectrograph bandwidth expansion method based on a Fabry-Perot etalon. The method comprises the following steps: S1, acquiring an initial wavelength and a maximum wavelength of a spectrometer, and calculating a maximum diffraction order of a Fabry-Perot etalon; s2, calculating the thickness of the Fabry-Perot etalon based on the calculation result of the step S1; s3, based on the calculation result of the step S2, calculating the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order, and calculating the maximum incident angle of the m diffraction order corresponding to the minimum wavelength value of the m diffraction order; and S4, judging whether the incident angles of the adjacent diffraction orders are overlapped or not, if so, adjusting the thickness of the Fabry-Perot etalon, and executing the step S3, otherwise, completing the expansion of the bandwidth of the spectrograph. Under the condition that spectrum aliasing does not exist, the bandwidth of the system can be increased, and therefore the system requirement is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical metrology and testing, and in particular relates to a method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon. Background Art

[0002] Spectral imaging technology is a remote sensing technology that emerged in the 1980s. Because spectral imaging technology can obtain spectral information of the target, it has developed rapidly in recent years.

[0003] In the field of spectral imaging remote sensing, there are two main methods for acquiring target spectral information: dispersive and interferometric. Dispersive methods include grating dispersion and prism dispersion; interferometric methods primarily utilize the optical path differences generated by various optical components and utilize Fourier transforms to achieve spectral demodulation. The Fabry-Perot (FP) interferometer is a multi-beam interferometer that, compared to dispersive spectrometers, offers greater light energy utilization and significantly higher spectral resolution than interferometric spectrometers. However, the spectral resolution and free spectral range (FSR) of an FP interferometer are mutually restricted: the larger the FP spacing, the higher the spectral resolution but the smaller the FSR. This makes it impossible to use an FP etalon as a key component of a spectrometer when the system bandwidth is known and exceeds the FSR of the FP etalon. This is because once the spectral range exceeds its FSR, spectral aliasing occurs, significantly limiting the application of FP etalons. Currently, FP etalons cannot be used as key components of spectrometers when the system bandwidth exceeds the FSR, significantly limiting their application. Summary of the Invention

[0004] In view of this, the present invention aims to provide a method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon, so as to solve the problem that when the system bandwidth exceeds the free spectral range of the FP etalon, the FP etalon cannot be used as a key component of the spectrometer, which limits the application of the FP etalon. The present invention can increase the system bandwidth in the absence of spectral aliasing, thereby meeting system requirements.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows: A method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon comprises the following steps: S1: Get the starting wavelength of the spectrometer and maximum wavelength , and calculate the maximum diffraction order of the Fabry-Perot etalon; S2: Calculate the thickness of the Fabry-Perot etalon based on the calculation result of step S1; S3: Based on the calculation result of step S2, calculate the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order, and calculate the maximum incident angle of the m diffraction order corresponding to the minimum wavelength value of the m diffraction order; S4: Determine whether the incident angles of adjacent diffraction orders overlap. If so, adjust the thickness of the Fabry-Perot etalon and execute step S3. Otherwise, complete the expansion of the spectrometer bandwidth.

[0006] Furthermore, in step S1, the starting wavelength of the spectrometer is used as the minimum wavelength value of the m diffraction order, and the maximum wavelength of the spectrometer is used as the maximum wavelength value of the m-1 diffraction order, and the maximum diffraction order m of the Fabry-Perot etalon is calculated: ; ; ; Where, d is the thickness of the Fabry-Perot etalon, is the minimum wavelength of the m diffraction order, is the maximum wavelength of the m-1 diffraction order, is the starting wavelength of the spectrometer The corresponding incident angle, is the maximum wavelength of the spectrometer The corresponding angle of incidence.

[0007] Furthermore, in step S2, the thickness of the Fabry-Perot etalon is calculated by the following formula: ; ; ; in, It is an intermediate variable and has no physical meaning.

[0008] Furthermore, in step S3, the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order is calculated. The formula used is: ; Calculate the maximum incident angle of the m diffraction order corresponding to the minimum wavelength value of the m diffraction order The formula used is: .

[0009] Furthermore, the incident angle corresponding to the current diffraction order is the angle between the incident light of the spectrometer and the normal of the incident surface of the FP etalon.

[0010] Compared with the prior art, the present invention can achieve the following beneficial effects: The present invention creates a method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon, which enables the spectrometer to meet the bandwidth requirements while avoiding order aliasing, and has a wide range of engineering application value for FP etalon. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 A schematic flow chart of a method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon according to an embodiment of the present invention; Figure 2 The present invention is a schematic diagram of the principle of the method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon according to an embodiment of the present invention. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0013] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0014] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0015] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0016] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0017] like Figure 1 As shown, the present invention proposes a method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon, which specifically includes the following steps: S1: Get the starting wavelength of the spectrometer and maximum wavelength , and calculate the maximum diffraction order of the Fabry-Perot etalon; S2: Calculate the thickness of the Fabry-Perot etalon based on the calculation result of step S1; S3: Based on the calculation result of step S2, calculate the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order, and calculate the maximum incident angle of the m diffraction order corresponding to the minimum wavelength value of the m diffraction order; S4: Determine whether the incident angles of adjacent diffraction orders overlap. If so, adjust the thickness of the Fabry-Perot etalon and execute step S3. Otherwise, complete the expansion of the spectrometer bandwidth.

[0018] It should be noted that in a spectrometer based on a Fabry-Perot etalon, the Fabry-Perot etalon of a single diffraction order has a limitation in the free spectral range (FSR). When the FSR of a single order cannot meet the spectrometer design requirements, the spectrum design task cannot be completed, that is, "it is known that one order cannot meet" the system's requirement for spectral bandwidth. In order to break through the limitation of a single order, the core idea of ​​the present invention is to make two orders exist in the system when it is known that one order cannot meet the requirement, but there is no aliasing between the two orders, so that the system bandwidth can be increased. Therefore, the focus is to prevent aliasing between the two orders through system design. As Figure 2As shown, the principle of the method for increasing the bandwidth of a spectrometer based on a Fabry-Perot etalon is as follows: calculate whether a single diffraction order can meet the bandwidth in the absence of order aliasing. If so, the spectrometer design can be completed using a single diffraction order. If a single diffraction order cannot meet the bandwidth, the method of the present invention is used to calculate the orders m and m-1 existing in the Fabry-Perot etalon; first calculate the thickness of the Fabry-Perot etalon; then calculate the range of incident angles corresponding to each diffraction order; finally determine the total bandwidth of the spectrometer and verify whether order aliasing exists under this thickness.

[0019] In some embodiments, in step S1, the starting wavelength of the spectrometer is used as the minimum wavelength value of the m diffraction order, and the maximum wavelength of the spectrometer is used as the maximum wavelength value of the m-1 diffraction order to calculate the maximum diffraction order m of the Fabry-Perot etalon: ; ; ; Where, d is the thickness of the Fabry-Perot etalon, is the minimum wavelength of the m diffraction order, is the maximum wavelength of the m-1 diffraction order, is the starting wavelength of the spectrometer The corresponding incident angle, is the maximum wavelength of the spectrometer The corresponding angle of incidence.

[0020] It should be noted that the key method to increase the bandwidth of a Fabry-Perot etalon spectrometer is to ensure that there are two diffraction orders in the system, but there is no aliasing between the two orders, so that the system bandwidth can be increased. Therefore, it is crucial to determine the number of these two orders. , , we can know the minimum wavelength of the m diffraction order and the maximum wavelength of the m-1 diffraction order.

[0021] Furthermore, in step S2, the thickness of the Fabry-Perot etalon is calculated by the following formula: ; ; ; in, It is an intermediate variable and has no physical meaning.

[0022] Furthermore, in step S3, the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order is calculated. The formula used is: ; Calculate the maximum incident angle of the m diffraction order corresponding to the minimum wavelength value of the m diffraction order The formula used is: .

[0023] Furthermore, the incident angle corresponding to the current diffraction order is the angle between the incident light of the spectrometer and the normal of the incident surface of the FP etalon.

[0024] It should be noted that in order to increase the bandwidth of the spectrometer, there must be neither diffraction order aliasing (i.e., one incident angle corresponds to multiple diffraction order information) nor wavelength overlap between two adjacent diffraction orders. Therefore, is the minimum wavelength of the m-1 diffraction order and the maximum wavelength of the m diffraction order. According to this principle, using the formula , we can get the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order The maximum incident angle of the m diffraction order corresponding to the minimum wavelength of the m diffraction order .

[0025] Furthermore, the incident angle corresponding to the current diffraction order is the angle between the incident light of the spectrometer and the normal of the incident surface of the FP etalon.

[0026] It should be noted that for the m diffraction order, the spectrometer bandwidth is , after introducing the (m-1) diffraction order, the total system bandwidth is , increasing the system bandwidth. In order to ensure that there is no level aliasing, it is necessary to calculate the mth level and the m-1th level. arrive The incident angles corresponding to the wavelength ranges are compared to see if there is any overlap. If there is overlap, the thickness d needs to be adjusted and the incident angles corresponding to the starting wavelength and maximum wavelength of the spectrometer bandwidth need to be recalculated.

[0027] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0028] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon, characterized by: The specific steps include: S1: Get the starting wavelength of the spectrometer and maximum wavelength , and calculate the maximum diffraction order of the Fabry-Perot etalon; S2: Calculate the thickness of the Fabry-Perot etalon based on the calculation result of step S1; S3: Based on the calculation result of step S2, calculate the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order, and calculate the maximum incident angle of the m diffraction order corresponding to the minimum wavelength value of the m diffraction order; S4: Determine whether the incident angles of adjacent diffraction orders overlap. If so, adjust the thickness of the Fabry-Perot etalon and execute step S3. Otherwise, complete the expansion of the spectrometer bandwidth.

2. The method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon according to claim 1, wherein: In step S1, the starting wavelength of the spectrometer is used as the minimum wavelength value of the m diffraction order, and the maximum wavelength of the spectrometer is used as the maximum wavelength value of the m-1 diffraction order, and the maximum diffraction order m of the Fabry-Perot etalon is calculated: ； ； ； Where, d is the thickness of the Fabry-Perot etalon, is the minimum wavelength of the m diffraction order, is the maximum wavelength of the m-1 diffraction order, is the starting wavelength of the spectrometer The corresponding incident angle, is the maximum wavelength of the spectrometer The corresponding angle of incidence.

3. The method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon according to claim 2, wherein: In step S2, the thickness of the Fabry-Perot etalon is calculated by the following equations: ； ； ； in, It is an intermediate variable and has no physical meaning.

4. The method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon according to claim 3, wherein: In step S3, the minimum incident angle of the m-1 diffraction order corresponding to the maximum wavelength value of the m-1 diffraction order is calculated. The formula used is: ； Calculate the maximum incident angle of the m diffraction order corresponding to the minimum wavelength value of the m diffraction order The formula used is: 。 5. The method for extending the bandwidth of a spectrometer based on a Fabry-Perot etalon according to claim 3, wherein: The incident angle corresponding to the current diffraction order is the angle between the incident light of the spectrometer and the normal of the incident surface of the FP etalon.

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