A rotating multi-structure spectrometer and its design method

Abstract

The present invention relates to a rotating multi-structure spectrometer and a design method thereof, belonging to the field of spectral measurement technology. The design method comprises the following steps: determining optical system design indicators of the rotating multi-structure spectrometer; determining a detector based on the spectral range and spectral resolution; using a parabolic reflector as a collimating lens group; selecting a plane transmission grating as a light splitting device and determining the incident angle of the plane transmission grating; calculating the wavelength range and central wavelength corresponding to each structure position based on the number of preset structure positions, the spectral range, and the spectral resolution, determining the relative position of each structure position, and deriving an equation representing the axial chromatic aberration between different wavelengths at each structure position; and performing wide-band chromatic aberration correction based on the achromatic aberration equation within each wavelength band and the derived equation representing the axial chromatic aberration between different wavelengths at each structure position. The present invention enables the spectrometer to have both a wide spectrum and high resolution, thereby improving spectral measurement efficiency and reducing measurement costs.

Description

Technical Field

[0001] The present invention relates to the technical field of spectrum measurement, and in particular to a rotating multi-structure spectrometer and a design method thereof. Background Art

[0002] Miniature / micro fiber optic spectrometers, with their low cost, high performance, compact size and weight, and the compact size and ease of use of fiber optic probes, are widely used and play an important role in various fields, including scientific research, agriculture, biomedicine, and industrial production. For example, they have been used to quickly and non-destructively test the quality of crops. By analyzing the relationship between crop infrared spectra and quality parameters and establishing relevant models, crop quality can be assessed. In biomedicine, fiber optic spectrometers are used for protein screening. However, with technological development, the demand for fiber optic spectrometers that combine wide bandwidth and high resolution is increasing.

[0003] Generally speaking, fiber optic spectrometers can be categorized into two types. The first type is a scanning spectrometer, which utilizes a single-point detector in combination with a rotating grating. This type of spectrometer exhibits reduced spectral stray light and superior spectral signal quality. However, due to the presence of moving parts, its structure is complex, its size is large, and the scanning measurement process is lengthy. Therefore, this type of spectrometer is primarily used in large scientific laboratory instruments. The second type is a spectrometer that combines a fixed grating with an array detector. This array detector structure is often used in miniaturized spectrometers. It requires only a single exposure to acquire spectral information within a specific spectral range, resulting in extremely rapid measurement speeds. Consequently, this type of spectrometer utilizing a fixed grating and array detector has seen rapid development and application in a wider range of fields. Array detector spectrometers are available in two types: reflective and transmissive. The reflective type is mainly based on the CT (Czerny-Turner) structure, which has no chromatic aberration, but the numerical aperture is limited, so the energy efficiency is very low. On the contrary, the transmissive structure has the advantage of a large numerical aperture and can achieve high energy efficiency, but the use of lenses requires eliminating chromatic aberration in a wide band.

[0004] Among the factors limiting the performance of array-detector spectrometers, photodetector performance is crucial. Since spectral information across the entire spectral range is acquired through a single exposure, for a fixed detector length and number of pixels, the spectrometer's spectral range and spectral resolution are mutually constrained. For the conventional UV-Vis band, silicon-based detectors are highly mature, and various linear and planar arrays can meet these requirements. However, for the shortwave infrared (SWIR), available detectors are scarce, and performance, such as array size and noise, lags significantly behind silicon-based detector arrays. For the 1-2.5μm SWIR band, for example, currently only two types of array detectors are commonly used: cooled TeCdHg detectors and cooled InGaAs detectors with enhanced spectral range. The former requires a chiller for cooling, resulting in high size, weight, power consumption, and price, but offers relatively better performance. The latter, on the other hand, requires only semiconductor cooling, requiring less size and power consumption while maintaining acceptable performance. Therefore, they are more widely used in conventional SWIR spectrometers. At present, conventional 0.9-2.5μm linear array InGaAs detectors are mainly provided by Hamamatsu Corporation in Japan. The available models and sizes are very limited, and the largest linear array detector size is only 512 pixels, which greatly limits the spectral range and spectral resolution performance of spectrometers. Summary of the Invention

[0005] In order to fully utilize the performance of the spectrometer optical system, the present invention proposes a rotating multi-structure spectrometer and a design method thereof. The method of relative rotation reconstruction of a collimating lens group and a converging lens group is used to achieve fast, high-resolution spectral measurement within a wide spectral band, so as to improve instrument performance, increase measurement efficiency and reduce costs. This solves the problem that for spectrometers combining a fixed grating and an array detector, the spectral range and spectral resolution of the spectrometer are mutually restricted. For reflective spectrometers, a large numerical aperture cannot be achieved, that is, the energy efficiency is low. For refractive spectrometers, it is necessary to balance chromatic aberration in a wide band, and the current array detectors limit the spectral range and spectral resolution performance of spectrometers.

[0006] In order to solve the above problems, the present invention specifically adopts the following technical solutions:

[0007] A design method for a rotating multi-structure spectrometer, the rotating multi-structure spectrometer comprising an incident slit, a collimating lens group, a spectrometer, a converging lens group, and a detector arranged in sequence along an optical path, wherein the converging lens group and the detector can be rotated to a plurality of preset structural positions by a mechanical structure; the design method comprises the following steps:

[0008] Step 1: Determine the optical system design indicators of the rotating multi-structure spectrometer, wherein the optical system design indicators include spectral range, spectral resolution, numerical aperture, slit size, sampling rate and system size;

[0009] Step 2: Determine the detector according to the spectral range and the spectral resolution;

[0010] Step 3: Select a parabolic reflector as the collimating lens group;

[0011] Step 4: Selecting a plane transmission grating as the spectroscopic device and determining the incident angle of the plane transmission grating;

[0012] Step 5: Based on the number of preset structural positions, the spectral range, and the spectral resolution, calculate the wavelength range and central wavelength corresponding to each structural position, determine the relative position of each structural position, and derive an equation representing the axial chromatic aberration between different wavelength bands at each structural position;

[0013] Step 6: Perform wide-band chromatic aberration correction. The specific process includes:

[0014] Step 6.1: Allocate the optical power of each lens in the converging lens assembly that eliminates chromatic aberration in each wavelength band according to the achromatic aberration equation in each wavelength band, and optimize the correction of axial chromatic aberration in each wavelength band;

[0015] Step 6.2: Based on the derived equations for expressing the axial chromatic aberration between different bands at each structural position, jointly optimize and correct the axial chromatic aberration between each band in a wide band to achieve wide-band achromatism.

[0016] Correspondingly, the present invention also proposes a rotating multi-structure spectrometer, which is designed using the above-mentioned design method.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The rotating multi-structure spectrometer designed by the present invention breaks through the restriction of the number of detector pixels on the spectral range / spectral resolution, so that the spectrometer can have both a wide spectral range and high resolution, thereby improving the measurement efficiency of the spectrometer and reducing the measurement cost;

[0019] (2) The numerical aperture of the rotating multi-structure spectrometer of the present invention can reach 0.3 or even larger, which is higher than the numerical aperture of the common CT fiber spectrometer on the market, and has higher energy efficiency;

[0020] (3) The rotating multi-structure spectrometer of the present invention is based on a coaxial catadioptric optical system design, has a small number of optical elements, and has no aspheric surfaces. It uses a plane transmission grating for spectrometry, which is easy to manufacture. The coaxial system assembly and adjustment process is relatively mature and simple, and the cost is low.

[0021] (4) The design method of the rotating multi-structure spectrometer proposed in the present invention can be applied to the design of fiber optic spectrometers with various spectral bands and resolution requirements, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the optical structure of the rotating multi-structure spectrometer in an embodiment of the present invention;

[0023] Figure 2 Flowchart of a design method for a rotating multi-structure spectrometer according to an embodiment of the present invention;

[0024] Figure 3 This is a comparison chart of the optimization effects;

[0025] Figure 4 Result diagram of the optical system design for the rotating multi-structure spectrometer;

[0026] Figure 5 Schematic diagram of the three-dimensional structure of the rotating multi-structure spectrometer;

[0027] Figure 6 MTF diagrams of the rotating multi-structure spectrometer at different wavelengths. The corresponding wavelengths in the figures are: (a) 900nm, (b) 1083nm, (c) 1265nm, (d) 1263nm, (e) 1435nm, (f) 1610nm, (g) 1608nm, (h) 1765nm, (i) 1925nm, (j) 1923nm, (k) 2055nm, (l) 2190nm, (m) 2188nm, (n) 2292nmand, (o) 2400nm;

[0028] Figure 7 Point diagrams of the rotating multi-structure spectrometer at different wavelengths. The corresponding wavelengths in the figures are: (a) 900 nm, (b) 1083 nm, (c) 1265 nm, (d) 1263 nm, (e) 1435 nm, (f) 1610 nm, (g) 1608 nm, (h) 1765 nm, (i) 1925 nm, (j) 1923 nm, (k) 2055 nm, (l) 2190 nm, (m) 2188 nm, (n) 2292 nm and (o) 2400 nm.

[0029] Explanation of the accompanying symbols: 1. Incident slit; 2. Collimating lens group; 3. Spectral element; 4. Converging lens group; 5. Detector. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments.

[0031] In one embodiment, the present invention provides a design method for a rotating multi-structure spectrometer, wherein the optical structure of the rotating multi-structure spectrometer is as follows: Figure 1As shown, the spectrometer primarily comprises an entrance slit 1, a collimating lens assembly 2, a spectrometer 3, a converging lens assembly 4, and a detector 5, which are sequentially arranged along the optical path. The converging lens assembly 4 and the detector 5 can be rotated to multiple preset positions via a mechanical structure, each corresponding to a substructure of the rotating multi-structure spectrometer. In this rotating multi-structure spectrometer, optical design ensures that the converging lens assembly 4 provides good, uniform imaging quality for light incident at different angles within a certain wavelength range and aperture range. By arranging the converging lens assembly 4 and the detector 5 to different preset angles, i.e., multiple preset positions, the existing mechanical structure enables rapid, high-resolution scanning detection across a wide spectral band using the same set of optical components and the same array detector.

[0032] like Figure 2 As shown, the design method of the rotating multi-structure spectrometer of this embodiment includes the following steps:

[0033] Step 1: Determine the optical system design indicators of the rotating multi-structure spectrometer.

[0034] When designing the optical structure of the rotating multi-structure spectrometer, the main design indicators of the system are shown in Table 1.

[0035] Table 1 Design indicators of the optical system of the rotating multi-structure spectrometer

[0036] index parameter spectral range 0.9-2.4μm Spectral resolution ≤0.8nm Numerical aperture ～0.3 Slit size 25μm×0.5mm Sampling rate 1:1 System size ~155×120×45mm

[0037] Step 2: Detector selection.

[0038] Based on the target spectral measurement band (i.e., the spectral range in step 1) and spectral resolution, a Hamamatsu G11478-512WB linear array InGaAs detector was selected as detector 5. This detector has 512 pixels, a 25μm pixel size, a photosensitive surface length of 12.8mm, and a spectral response range of 0.9-2.55μm. It should be noted that detector 5 may also be other types of linear or planar array photodetectors with different response bands and pixel sizes.

[0039] Step 3: Design of collimating lens assembly.

[0040] The function of the collimator lens assembly 2 is to collimate the incident light guided by the optical fiber and then illuminate the spectrometer 3. For such a wide spectral range of 0.9-2.5 μm, chromatic aberration correction is more complex if a refractive structure is used, generally requiring at least three or four lenses made of different materials to achieve effective results. However, a reflective structure eliminates the need for chromatic aberration correction and only requires a single parabolic reflector, reducing complexity and making its processing and inspection easier. Therefore, the collimator lens assembly 2 in this embodiment is implemented using a single parabolic reflector.

[0041] The relative aperture of the optical system needs to be matched, so a large-aperture fiber spectrometer must be used with a correspondingly large numerical aperture fiber. Currently, commercially available large numerical aperture quartz fibers have an NA of 0.5 or higher (corresponding to a relative aperture of 1 / 0.87), thus meeting the requirements for the large relative aperture fiber spectrometer of the present invention.

[0042] Step 4: Design of optical splitter device.

[0043] Gratings have much better spectroscopic linearity than prisms, so this embodiment uses a plane transmission grating as the spectroscopic device 3. In addition, there are many standard plane grating products with low cost and good performance. In order to ensure that there is no obstruction or interference between the collimated and converging light paths, a spectrometer structure with a plane transmission grating structure is selected. Since the diffraction angle distribution of the grating is uneven within a large diffraction angle range, the line density of the plane transmission grating cannot be too high. The present invention uses a plane transmission grating with a line density of 554g / mm and uses +1 order diffracted light. At the same time, in order to ensure that the plane transmission grating has a high diffraction efficiency within the entire wavelength range, the central wavelength should meet the Bragg condition:

[0044] 2d sinθ=mλ center (1)

[0045] Where d is the grating period, θ is the grating incident angle, m is the grating diffraction order, and λ center is the center wavelength of the entire spectral range.

[0046] Therefore, according to the above formula, the incident angle of the plane transmission grating is determined to be 27.197°.

[0047] Step 5: Design of converging lens assembly.

[0048] After determining the grating incident angle, the number of pre-set structural positions for the spectrometer and the angle corresponding to each structural position need to be determined. To ensure that the spectral resolution at each structural position is less than or equal to 0.8nm, at least five structural positions are required. It should be noted that for spectrometer systems with different spectral ranges and spectral resolution levels, those skilled in the art can adjust the number of structural positions or substructures based on actual conditions.

[0049] First, determine the band range at each structural position. The five structural positions of the spectrometer correspond to five structures, namely substructure 1, substructure 2, substructure 3, substructure 4, and substructure 5. Since the diffraction angle distribution of the grating is uneven within a large diffraction angle range, the spectral angular resolution increases with the increase of the diffraction angle, so the spectral range covered by each substructure is designed to be different. The band range at each structural position is divided based on the equal diffraction angle, so as to ensure that the detector length is not wasted. After the entire spectral range and the grating parameters are known, the difference in diffraction angles within the entire spectral range can be calculated, and the wavelength value of the corresponding band can be inferred based on the equal diffraction angle difference as the standard. Therefore, the end wavelength λ of the band range of each structural position is n It can be expressed as:

[0050]

[0051] Where d represents the grating period, m represents the diffraction order, and q represents the number of preset structural positions, where q = 5. a Indicates the starting wavelength of the total band range, λ b The wavelength of the total wavelength range is defined as the end wavelength, θ is the grating incident angle, and n' represents the corresponding structure position, with n' = 1, 2, 3, 4, or 5. After determining the wavelength range corresponding to each structure position, a 2nm spectral overlap is added to each band to prevent errors in the edge wavelength at each position. The relative position of each substructure, or structure position, can be determined based on the center wavelength of each band.

[0052] Next, in order to achieve achromatism within a wide spectral range, the rotating multi-structure spectrometer must first ensure that achromatism is achieved within the band range at each structural position. Therefore, the achromatism equation must be satisfied in each band:

[0053]

[0054] Where, is the focal power of the i-th lens; is the optical power of the rotating multi-structure spectrometer optical system; ω 1i 、ω 2i ,…,ω ni are the dispersion powers of the i-th lens in different bands, and their values ​​are related to the refractive index of the central wavelength of each band; are the focal lengths of the i-th lens in different wavelength bands; h i is the paraxial ray height at the i-th lens; k represents the number of lenses in the optical system of the rotating multi-structure spectrometer; n represents the number of spectrometer structures, i.e., the number of preset structural positions; Δl'1, Δl'2, ..., Δl' n They are the axial chromatic aberration within the band at different structural positions.

[0055] According to formula (3), the axial chromatic aberration in each band at each structural position of the spectrometer can be eliminated. However, for the wide-band spectrometer proposed in the present invention, since the positions of the converging lens group 4 and the detector 5 need to be kept relatively unchanged, when the converging lens group 4 and the detector 5 are rotated to different structural positions, the central wavelength of the system is equivalent to a change. According to the above formula (3), it cannot be guaranteed that the optical system has good imaging quality for multiple different bands at the same image plane position. Therefore, it is necessary to discuss the characterization and correction of chromatic aberration between different bands at each structural position of the rotating multi-structure spectrometer.

[0056] The following is the derivation of the axial chromatic aberration equation between each band. Here, the subscript cw is used to represent the central wavelength at a certain structural position. For example, λ 1cw Indicates the central wavelength of the entire band at the first structural position. Similarly, l 1cw 、l' 1cw 、n 1cw 、 They respectively represent the object distance, image distance, material refractive index and lens power of the central wavelength of the entire band at the first structural position.

[0057] According to the thin lens imaging relationship, we can get:

[0058]

[0059] Where l' is the image distance, l is the object distance, n is the material refractive index, R1 is the radius of curvature of the first lens surface, R2 is the radius of curvature of the second lens surface, and f is the focal length of the lens.

[0060] For the rotating multi-structure spectrometer of this embodiment, only the center wavelengths at the left and right edge structures and the center wavelength at the center structure need to be corrected for axial chromatic aberration. The center wavelengths at the left, right and center structure positions are selected and recorded as λ respectively. lcw ,λ rcw and λ ccw .

[0061] According to formula (4), we can get:

[0062]

[0063] in, is the focal length of the lens corresponding to the central wavelength at the right edge structure position, is the focal length of the lens corresponding to the central wavelength at the left edge structure position.

[0064] Subtracting equation (5) from equation (6), we get:

[0065]

[0066] Consider l' rcw ≈l' lcw =l',l rcw ≈l lcw = l, we can get:

[0067]

[0068] Where C is the inter-band axial chromatic aberration coefficient, is the focal length of the lens corresponding to the central wavelength of the entire spectral range, and:

[0069]

[0070] Let the axial chromatic aberration between bands be Δl' c , and multiply both sides of equation (8) by y 2 , then:

[0071]

[0072] Where, Δl c '=l' lcw -l' rcw , Δl c Indicates the difference in object distance corresponding to the central wavelength at the left and right edge structure positions, that is, Δl c =l lcw -l rcw , y is the height at which the light reaches the lens, is the object aperture angle, is the image side aperture angle.

[0073] If the converging lens group 4 has k lenses, and each lens has formula (10), then:

[0074]

[0075] Adding the left and right sides of equation (11) (“Lens design fundamentals”, Rudolf Kingslake, Institute of Optics University of Rochester), we can obtain:

[0076]

[0077] Where Δl' ck is the inter-band axial chromatic aberration of the k-th lens, u' k is the image-side aperture angle of the kth lens, Δl c1 is the difference in object distances between the center wavelengths of the first lens at the left and right edge structures, u1 is the object side aperture angle of the first lens, and y iis the height at which the light reaches the i-th lens, C i is the inter-band axial chromatic aberration coefficient of the i-th lens, is the focal power of the i-th lens.

[0078] Formula (12) is the calculation formula for the inter-band axial chromatic aberration of the rotating multi-structure spectrometer of the thin lens model. If the object plane is considered to be at infinity, Formula (12) can be written as:

[0079]

[0080] Therefore, the inter-band axial chromatic aberration caused by the difference in the dispersion characteristics of the material between the two bands can be expressed as:

[0081]

[0082] So far, the equation for expressing the inter-band axial chromatic aberration of the rotating multi-structure spectrometer has been derived.

[0083] Step 6: Broadband chromatic aberration correction.

[0084] Specifically in the actual optical design process, when performing wide-band chromatic aberration correction, the following steps are included:

[0085] Step 6.1: First, the focal lengths of the lenses in the converging lens assembly 4 that eliminate chromatic aberration in each wavelength band are allocated according to the achromatic aberration equation in each wavelength band, i.e., formula (3), and the axial chromatic aberration in each wavelength band is optimized and corrected using a computer;

[0086] Step 6.2: Based on the derived equation for expressing the axial chromatic aberration between different bands at each structural position, i.e., formula (14), the axial chromatic aberration between each band in the wide band range is jointly optimized and corrected to achieve the purpose of achromatization in the wide band range.

[0087] from Figure 3 The comparison of the optimization effects of the two optimization methods shown in the figure shows that when only the chromatic aberration correction within each band is considered, the optimization effect is as follows: Figure 3 As shown in (a), it can be seen that the chromatic aberration within each band has been optimized very well, but the chromatic aberration is still large for the entire wide band. When combined with the derived wide band chromatic aberration correction equation for joint optimization, the optimization effect is as follows: Figure 3 As shown in (b), the chromatic aberration correction within each band is good, and the chromatic aberration within a wide band is also relatively good, which proves that the wide-band chromatic aberration correction theory proposed in this step is effective for the chromatic aberration correction of the rotating multi-structure spectrometer.

[0088] After the designed collimating lens group 2, spectrometer 3 and converging lens group 4 are docked, the spectrometer 3, converging lens group 4 and detector 5 are rotated to five specific structural positions by setting multiple structural functions, thereby covering the target spectral range and obtaining relatively uniform imaging quality.

[0089] According to the design calculation results, the angle between the optical axis of the converging lens group corresponding to substructure 1 of the rotating multi-structure spectrometer and the grating normal is 8.202°. This substructure 1 covers a spectral range of 0.9-1.265μm, corresponding to a spectral resolution of 0.72nm. The angle between the optical axis of the converging lens group corresponding to substructure 2 of the rotating multi-structure spectrometer and the grating normal is 19.752°. This substructure 2 covers a spectral range of 1.263-1.610μm, corresponding to a spectral resolution of 0.69nm. The angle between the optical axis of the converging lens group corresponding to substructure 3 of the rotating multi-structure spectrometer and the grating normal is 31.383°. This substructure 3 covers a spectral range of 1.608-1.925μm, corresponding to a spectral resolution of 0.63nm. The angle between the optical axis of the converging lens group and the grating normal corresponding to substructure 4 of the rotating multi-structure spectrometer is 42.955°. This substructure 4 covers a spectral range of 1.923-2.190μm, corresponding to a spectral resolution of 0.53nm. The angle between the optical axis of the converging lens group and the grating normal corresponding to substructure 5 of the rotating multi-structure spectrometer is 54.390°. This substructure 5 covers a spectral range of 2.188-2.400μm, corresponding to a spectral resolution of 0.42nm. The spectral resolution within each structure is less than 0.8nm.

[0090] The collimating lens assembly 2 in the present invention can be implemented using a spherical reflector. The converging lens assembly 4 consists of six lenses, where the lens materials, from incident light to outgoing light, are H-ZPK7, FK5, PK51A, SF15, N-SSK5, and N-LASF40, respectively. These materials are all common optical glass. The system back focus is approximately 10 mm, sufficient for focal plane adjustment. The image plane is always perpendicular to the optical axis of the converging lens assembly, making adjustment relatively easy. The optical system measures approximately 155 × 120 × 45 mm and is a coaxial transmission structure with a relatively compact structure and mature adjustment technology.

[0091] Furthermore, the collimating lens group 2 and the converging lens group 4 in the rotating multi-structure spectrometer can be replaced with other forms of refraction, reflection or catadioptric hybrid systems.

[0092] Furthermore, the spectrometer 3 in the rotating multi-structure spectrometer can also be replaced by various spectrometers such as a reflection grating, a spectroscopic prism, etc., and its principle and design concept are similar to those of the plane transmission grating.

[0093] The design results of the optical system of the rotating multi-structure spectrometer obtained by the design method of the present invention and the schematic diagram of the three-dimensional structure are shown in the following figures: Figure 4and Figure 5 As shown, the MTF diagram and point diagram at each wavelength are as follows Figure 6 and Figure 7 As shown. Figure 6 and Figure 7 It can be seen from the figure that the MTF of each substructure, each wavelength, and each field of view of the reconfigurable spectrometer optical system of the present invention is greater than 0.65, the imaging quality is good, good spectral resolution can be achieved, and the design index requirements can be met.

[0094] The present invention further provides a rotating multi-structure spectrometer, which is designed using the design method of the rotating multi-structure spectrometer described in the aforementioned embodiment. For details, please refer to the aforementioned method embodiment, which will not be repeated here.

[0095] The present invention mainly has the following beneficial effects:

[0096] (1) The rotating multi-structure spectrometer designed by the present invention breaks through the restriction of the number of detector pixels on the spectral range / spectral resolution, so that the spectrometer can have both a wide spectral range and high resolution, thereby improving the measurement efficiency of the spectrometer and reducing the measurement cost;

[0097] (2) The numerical aperture of the rotating multi-structure spectrometer of the present invention can reach 0.3 or even larger, which is higher than the numerical aperture of the common CT fiber spectrometer on the market, and has higher energy efficiency;

[0098] (3) The rotating multi-structure spectrometer of the present invention is based on a coaxial catadioptric optical system design, with a small number of optical elements, no aspheric surfaces, and uses a plane grating for light splitting, which is easy to manufacture. In addition, the coaxial system assembly and adjustment process is relatively mature and simple, and the cost is low.

[0099] (4) The design method of the rotating multi-structure spectrometer proposed in the present invention can be applied to the design of fiber optic spectrometers with various spectral bands and resolution requirements, and has a wide range of applications.

[0100] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A design method for a rotating multi-structure spectrometer, characterized in that: The rotating multi-structure spectrometer comprises an incident slit (1), a collimating lens group (2), a spectrometer (3), a converging lens group (4), and a detector (5) arranged in sequence along an optical path, and the converging lens group (4) and the detector (5) can be rotated to a plurality of preset structural positions through a mechanical structure; the design method comprises the following steps: Step 1: Determine the optical system design indicators of the rotating multi-structure spectrometer, wherein the optical system design indicators include spectral range, spectral resolution, numerical aperture, slit size, sampling rate and system size; Step 2: Determine the detector (5) according to the spectral range and the spectral resolution; Step 3: Selecting a parabolic reflector as the collimating mirror assembly (2); Step 4: Selecting a plane transmission grating as the light splitting device (3), and determining the incident angle of the plane transmission grating; Step 5: Based on the number of preset structural positions, the spectral range, and the spectral resolution, calculate the wavelength range and central wavelength corresponding to each structural position, determine the relative position of each structural position, and derive an equation representing the axial chromatic aberration between different wavelength bands at each structural position; Step 6: Perform wide-band chromatic aberration correction. The specific process includes: Step 6.1: allocating the optical power of each lens in the converging lens group (4) for eliminating chromatic aberration in each wavelength band according to the achromatic aberration equation in each wavelength band, and optimizing the correction of axial chromatic aberration in each wavelength band; Step 6.2: Based on the derived equations for expressing the axial chromatic aberration between different bands at each structural position, jointly optimize and correct the axial chromatic aberration between each band in a wide band to achieve wide-band achromatism.

2. The design method of a rotating multi-structure spectrometer according to claim 1, characterized in that: The achromatic equation in each band is: in, is the focal power of the i-th lens, is the optical power of the rotating multi-structure spectrometer optical system, ω 1i 、ω 2i ,…,ω ni are the dispersion powers of the i-th lens in different bands, are the focal lengths of the i-th lens in different wavelength bands, h i is the paraxial ray height at the i-th lens, k represents the number of lenses in the optical system of the rotating multi-structure spectrometer, n represents the number of preset structure positions, Δl'1, Δl'2, ..., Δl' n They are the axial chromatic aberration within the band at different structural positions.

3. The design method of a rotating multi-structure spectrometer according to claim 1 or 2, characterized in that: The equation for the axial chromatic aberration between different bands at each structural position is: Where, Δl c ' represents the axial chromatic aberration between bands, represents the optical power of the rotating multi-structure spectrometer optical system, h i represents the paraxial ray height at the i-th lens, C i represents the inter-band axial chromatic aberration coefficient of the i-th lens, represents the focal length of the i-th lens, and k represents the number of lenses in the converging lens group (4).

4. The design method of a rotating multi-structure spectrometer according to claim 1 or 2, characterized in that: The spectral range is 0.9-2.4 μm, the spectral resolution is less than or equal to 0.8 nm, the numerical aperture is 0.3, the slit size is 25 μm×0.5 mm, the sampling rate is 1:1, and the system size is 155×120×45 mm.

5. The design method of a rotating multi-structure spectrometer according to claim 4, characterized in that: The number of the structural positions is 5, the coverage spectral range corresponding to the first structural position is 0.9-1.265μm, and the corresponding spectral resolution is 0.72nm; the coverage spectral range corresponding to the second structural position is 1.263-1.610μm, and the corresponding spectral resolution is 0.69nm; the coverage spectral range corresponding to the third structural position is 1.608-1.925μm, and the corresponding spectral resolution is 0.63nm; the coverage spectral range corresponding to the fourth structural position is 1.923-2.190μm, and the corresponding spectral resolution is 0.53nm; the coverage spectral range corresponding to the fifth structural position is 2.188-2.400μm, and the corresponding spectral resolution is 0.42nm.

6. The design method of a rotating multi-structure spectrometer according to claim 1 or 2, characterized in that: The converging lens group (4) is composed of 6 lenses, wherein the lens materials are H-ZPK7, FK5, PK51A, SF15, N-SSK5, and N-LASF40 in order from the direction of incident light to the direction of outgoing light.

7. The design method of a rotating multi-structure spectrometer according to claim 1 or 2, characterized in that: The detector (5) adopts a Hamamatsu G11478-512WB linear array indium gallium arsenide detector.

8. The design method of a rotating multi-structure spectrometer according to claim 1 or 2, characterized in that: The planar transmission grating has a line density of 554 g / mm.

9. The design method of a rotating multi-structure spectrometer according to claim 1 or 2, characterized in that: The plane transmission grating is replaced by a reflection grating or a beam splitter prism.

10. A rotating multi-structure spectrometer, characterized in that: The method is designed according to any one of claims 1 to 9.

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