Rotary multi-structure spectrometer and design method thereof

Abstract

The invention relates to a rotary multi-structure spectrometer and a design method thereof, and belongs to the technical field of spectral measurement, and the design method comprises the following steps: determining an optical system design index of the rotary multi-structure spectrometer; determining a detector according to the spectral range and the spectral resolution; the parabolic reflector is used as a collimating mirror group; selecting a plane transmission grating as a light splitting device, and determining an incident angle of the plane transmission grating; according to the number of the preset structure positions, the spectral range and the spectral resolution, the waveband range and the central wavelength corresponding to each structure position are calculated, the relative position of each structure position is determined, and an axial chromatic aberration expression equation between different wavebands at each structure position is deduced; and performing broadband chromatic aberration correction based on the achromatic equation in each waveband and the deduced axial chromatic aberration expression equation between different wavebands at each structure position. According to the invention, the spectrometer can have wide spectrum and high resolution at the same time, the spectral measurement efficiency is improved, and the measurement cost is reduced.

Description

Technical Field

[0001] The 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] Small / micro fiber optic spectrometers are widely used in various fields such as scientific research, agriculture, biomedicine, and industrial production, and play an important role due to their low cost, high performance, small size and weight, small size of fiber optic probes, and convenient use. For example, they have been used to quickly and non-destructively detect the quality of crops. By analyzing the relationship between the infrared spectrum of crops and quality parameters, relevant models are established to evaluate the quality of crops. In biomedicine, fiber optic spectrometers are used for protein screening. However, with the development of technology, the demand for fiber optic spectrometers that take into account both wide band and high resolution is increasing.

[0003] Generally speaking, the structure of fiber optic spectrometers can be divided into two types. One is a scanning spectrometer that uses a single-point detector and a rotating grating. This type of spectrometer has the characteristics of less spectral stray light and better spectral signal quality. However, because it is equipped with moving parts, its structure is complicated, its volume is large, and the scanning measurement process is quite long, so this type of spectrometer is mostly used in large scientific instruments and equipment in laboratories. The second is a spectrometer composed of a fixed grating and an array detector. Most miniaturized spectrometers use this array detector structure, which only requires a single exposure operation to obtain spectral information within a specific spectrum band, and the measurement speed is extremely fast. For this reason, this spectrometer structure using a fixed grating and an array detector has achieved faster development at present and has been applied in a wider range of fields. For array detector type spectrometers, there are 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 the elimination of chromatic aberration in a wide band.

[0004] Among the factors that limit the performance of array detector spectrometers, the performance of photodetectors is crucial. Since spectral information in the entire spectral range is obtained through a single exposure, the spectral range and spectral resolution of the spectrometer are mutually restricted for a fixed detector length and number of pixels. For conventional ultraviolet-visible bands, silicon-based detectors are already very mature, and various linear and planar array detectors can meet the requirements of use. However, for short-wave infrared, there are very few available detectors, and the performance of detector arrays, such as scale and noise, is still far behind that of silicon-based detector arrays. Taking the 1-2.5μm short-wave infrared band as an example, the commonly used array detectors are only two types: cooled TeCdHg detectors and cooled InGaAs detectors with enhanced spectral range. The former requires a refrigerator for cooling, and has high volume, weight, power consumption and price, but relatively better performance. The latter only requires semiconductor cooling, has lower requirements for volume and power consumption, and has acceptable performance, so it is more widely used in the field of conventional short-wave infrared spectrometers. At present, conventional 0.9-2.5μm band 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 the spectrometer. Summary of the invention

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

[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 spectroscopic device, a converging lens group and a detector arranged in sequence along an optical path, and the converging lens group and the detector can be rotated to a plurality of preset structural positions through 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 mirror group;

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

[0012] Step 5: According to the number of preset structural positions, the spectral range, and the spectral resolution, the band range and central wavelength corresponding to each structural position are calculated, the relative position of each structural position is determined, and the axial chromatic aberration expression equation between different bands at each structural position is derived;

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

[0014] Step 6.1: Distribute the optical power of each lens in the converging lens group for eliminating chromatic aberration in each band according to the achromatic aberration equation in each band, and optimize the correction of axial chromatic aberration in each band;

[0015] Step 6.2: Based on the derived equations for representing the axial chromatic aberration between different bands at each structural position, jointly optimize and correct the axial chromatic aberration between bands in a wide band range 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 spectrum 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-type 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 surface. It uses a plane transmission grating for light splitting, has low manufacturing difficulty, and the coaxial system assembly and adjustment process is relatively more mature and simple, and has a low cost;

[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 application fields. 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 A flow chart 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 effect;

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

[0026] Figure 5 It is a 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 This is a point diagram of the rotating multi-structure spectrometer at different wavelengths. The corresponding wavelengths in the figure 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.

[0029] Explanation of the reference numerals: 1. Entrance slit; 2. Collimating lens group; 3. Spectral splitter; 4. Converging lens group; 5. Detector. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be described in detail below in conjunction with 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, it mainly includes an incident slit 1, a collimating lens group 2, a spectrometer 3, a converging lens group 4 and a detector 5 which are sequentially arranged along the 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, and each structural position corresponds to a substructure of a rotating multi-structure spectrometer. In the rotating multi-structure spectrometer, the converging lens group 4 is ensured to have good and uniform imaging quality for incident light of a certain wavelength range, a certain aperture range and different angles through optical design, and then the converging lens group 4 and the detector 5 are rotated to different preset angles, that is, to a plurality of preset structural positions through the existing mechanical structure, so that fast and high-resolution scanning detection in a wide spectral band can be achieved by the same group of optical devices 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 indexes 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 Dimensions ~155×120×45mm

[0037] Step 2: Detector selection.

[0038] According to the target spectral measurement band (i.e., the spectral range in step 1) and the spectral resolution, the Hamamatsu G11478-512WB linear array indium gallium arsenide detector is selected as the detector 5, which has 512 pixels, a pixel size of 25 μm, a photosensitive surface length of 12.8 mm, and a spectral response range of 0.9-2.55 μm. It should be pointed out that the detector 5 can also select other types of linear arrays, planar array photoelectric detectors, etc. with different response bands and different pixel sizes.

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

[0040] The function of the collimator lens group 2 is to collimate the incident light introduced by the optical fiber and then irradiate it onto the spectrometer 3. For such a wide spectral range of 0.9-2.5μm, if a refractive structure is used, the chromatic aberration correction is relatively complicated, and generally at least 3-4 lenses of different materials are required to achieve it well; if a reflective structure is used, there is no need to correct the chromatic aberration, and only one parabolic reflector is needed to achieve it, which can reduce the complexity and the difficulty of its processing and detection is also relatively low. Therefore, the collimator lens group 2 in this embodiment is implemented by a 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 corresponding large numerical aperture fiber. The NA of the currently available large numerical aperture quartz fiber can reach more than 0.5 (corresponding to a relative aperture of 1 / 0.87), so it can meet the use of the large relative aperture fiber spectrometer of the present invention.

[0042] Step 4: Design of optical splitter.

[0043] The grating has much better spectroscopic linearity than the prism, so the present embodiment adopts a plane transmission grating as the spectroscopic device 3. In addition, there are many standard products of plane gratings, with low cost and good performance. In order to ensure that there is no obstruction and 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 adopts 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: Converging lens assembly design.

[0048] After determining the grating incident angle, it is necessary to determine the number of preset structural positions of the spectrometer and the angle corresponding to each structural position. In order to ensure that the spectral resolution at each structural position is less than or equal to 0.8nm, at least 5 structural positions need to be set. It should be pointed out that for spectrometer systems with different spectral ranges and spectral resolution levels, those skilled in the art can set the number of structural positions or substructures according to 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, which ensures that the length of the detector is not wasted. After the entire spectral range and grating parameters are known, the difference in diffraction angles in 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 at each structural position is n It can be expressed as:

[0050]

[0051] Wherein, 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 Indicates the end wavelength of the total band range, θ indicates the grating incident angle, and n' indicates the corresponding structural position, n' = 1, 2, 3, 4, 5. After determining the band range corresponding to each structural position, each band adds 2nm of spectral overlap to prevent errors in the edge wavelength of each position. According to the central wavelength of each band, the relative position of each substructure, that is, each structural position, can be determined.

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

[0053]

[0054] In the formula, is the focal power of the i-th lens; is the focal length of the rotating multi-structure spectrometer optical system; ω 1i ,ω 2i ,…,ω ni are the dispersion power 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 light 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 being changed. 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 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 represents the central wavelength of the entire band at the first structural position. 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] Among them, 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 surface of the lens, R2 is the radius of curvature of the second surface of the lens, and f is the focal length of the lens.

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

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

[0062]

[0063] in, is the lens focal length corresponding to the central wavelength at the right edge structure position, is the lens optical power 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] Among them, Δl c '=l' lcw -l' rcw , Δl c It represents the difference in object distance corresponding to the central wavelength at the left and right edge structures, i.e. 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 get:

[0076]

[0077] Among them, Δl' ck is the inter-band axial chromatic aberration of the kth lens, u' k is the image-side aperture angle of the kth lens, Δl c1 is the difference in object distances corresponding to the central wavelengths of the first lens at the left and right edge structures, u1 is the object side aperture angle of the first lens, 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 length 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 length of each lens in the converging lens group 4 for eliminating chromatic aberration in each band is allocated according to the achromatic aberration equation in each band, i.e., formula (3), and the axial chromatic aberration in each band is optimized and corrected by 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 bands in a wide band is jointly optimized and corrected to achieve the purpose of achromatization in a wide band.

[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 in 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 in each band is good, and the chromatic aberration in the 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, the spectrometer 3 and the converging lens group 4 are connected, the spectrometer 3, the converging lens group 4 and the detector 5 are rotated to five specific structural positions by setting multiple structural functions, so as to cover the target spectral range and obtain relatively uniform imaging quality.

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

[0090] The collimating lens group 2 in the present invention can be realized by a spherical reflector. 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. The selected materials are all common optical glass materials. The back intercept of the system is about 10mm, which is sufficient for focal plane adjustment. The image plane is always perpendicular to the optical axis of the converging lens group, and adjustment is relatively easy. The size of the optical system is about 155×120×45mm, and the overall structure is a coaxial transmission mechanism with a relatively compact structure and a mature adjustment process.

[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 spectroscopic device 3 in the rotating multi-structure spectrometer can also be replaced by various spectroscopic devices such as a reflection grating and a spectroscopic prism, and the principle and design concept thereof are similar to those of a 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 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 described in detail 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 spectrum 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-type 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 surface, and a plane grating for light splitting, which is easy to manufacture, and the coaxial system assembly and adjustment process is relatively mature and simple, with low cost;

[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 application fields.

[0100] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached 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 spectroscopic device (3), a converging lens group (4) and a detector (5) which are sequentially arranged 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 lens group (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: According to the number of preset structural positions, the spectral range, and the spectral resolution, the band range and central wavelength corresponding to each structural position are calculated, the relative position of each structural position is determined, and the axial chromatic aberration expression equation between different bands at each structural position is derived; 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 representing the axial chromatic aberration between different bands at each structural position, jointly optimize and correct the axial chromatic aberration between bands in a wide band range 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 length of the i-th lens, is the focal length of the rotating multi-structure spectrometer optical system, ω 1i ,ω 2i ,…,ω ni are the dispersion power 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 light 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 structural 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: Among them, Δl c ' represents the axial chromatic aberration between bands, represents the focal length 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 first structural position corresponds to a covered spectral range of 0.9-1.265 μm, and the corresponding spectral resolution is 0.72 nm; the second structural position corresponds to a covered spectral range of 1.263-1.610 μm, and the corresponding spectral resolution is 0.69 nm; the third structural position corresponds to a covered spectral range of 1.608-1.925 μm, and the corresponding spectral resolution is 0.63 nm; the fourth structural position corresponds to a covered spectral range of 1.923-2.190 μm, and the corresponding spectral resolution is 0.53 nm; the fifth structural position corresponds to a covered spectral range of 2.188-2.400 μm, and the corresponding spectral resolution is 0.42 nm.

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 line density of the planar transmission grating is 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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