Large-aperture transmission type spectrometer using single material and design method thereof

Abstract

The invention relates to a large-aperture transmission type spectrometer using a single material and a design method thereof, and the method comprises the steps: carrying out the linear fitting of a material refractive index n in a target spectral band, and obtaining a fitting refractive index nf; and when only one material is used, the focal length of the convergent lens group meets # imgabs0 #, f is the focal length of the lens group, n is the refractive index of the material, and r2n-1 and r2n are the curvature radiuses of the two surfaces of the nth lens in the lens group respectively. According to the large-aperture transmission type spectrograph using the single material and the design method thereof, under the condition that the refractive index change requirement given by a formula is met, the large-aperture transmission type spectrograph can be applied to spectrometers with various spectral bands and various resolution requirements, and the application field is very wide; and the design of the transmitting mirror group only adopts a single material to correct monochromatic aberration, so that the design difficulty is low.

Description

Technical Field

[0001] The present invention relates to the technical field of spectrum measurement and analysis, and in particular to a large-aperture transmission spectrometer using a single material and a design method thereof. Background Art

[0002] Spectral measurement and analysis technology has become a basic technology in studying the composition and structure of materials. Spectral instruments based on various measurement principles have been developed one after another. Among them, small / micro fiber optic spectrometers are widely used in various fields such as scientific research, agriculture, biomedicine and industrial production due to their low cost, high performance, small size and weight, and small size and convenient use of fiber optic probes, and play an important role. This type of spectrometer technology is relatively mature, and there are many companies at home and abroad that can produce similar products. Internationally, such as Ocean Optics, Bidatech and Hamamatsu Photonics, and domestically, such as Fuxiang Optics and Changguang Grey, all have products with similar spectral measurement ranges, covering ultraviolet to short-wave infrared bands, but they differ in performance such as spectral resolution, relative aperture, spectral stray light and volume and weight; but the overall performance level is not much different, and there is no essential difference.

[0003] The analysis of the optical structure of common grating spectrometers mainly includes spectrometer structures based on curved gratings and spectrometer structures based on plane gratings. Spectrometer structures based on curved gratings include Rowland circle spectrometers, Littrow spectrometers, Offner spectrometers, and Dyson spectrometers. Such spectrometers usually have excellent performances such as larger relative apertures and larger fields of view, but at the cost of using curved gratings for spectroscopy. Curved gratings with different parameters are difficult to be used in spectrometer systems with different performance indicators. At the same time, grating manufacturing and system integration are very difficult, which greatly increases the cost of the spectrometer system. Therefore, for commercialized micro-fiber spectrometers, the cost performance of such curved grating spectrometers is relatively poor.

[0004] At present, the common commercial fiber optic spectrometers on the market are mainly based on the plane grating Czerny-Turner optical structure design. The Czerny-Turner structure spectrometer is a very classic reflective spectrometer structure, which has the advantages of low optical device cost, simple structure, low difficulty in installation and adjustment, and stable performance; but it also has the problems of small field of view and small relative aperture. In addition to the CT structure, the common spectrometer structure based on plane grating is also based on the plane transmission grating spectrometer. According to relevant reports at home and abroad, since the transmission structure can have many optical surfaces, it greatly increases the design variables, so the relative aperture of this type of spectrometer is very large. For example, Hamamatsu, Japan, has a transmission-type micro-fiber spectrometer with a relative aperture of 1 / 2.2 on sale. Transmission-type spectrometers have the following advantages: 1. The structure is symmetrical and the aberration is easy to correct, so the relative aperture of the system is large; 2. Based on the coaxial refraction structure, the processing and adjustment process is relatively simple and mature; 3. The structure is compact, easy to miniaturize, and has good mechanical resistance. Therefore, the transmission-type micro-spectrometer has unique advantages in improving performance and reducing costs, and is one of the future development trends of spectrometers.

[0005] However, the current design theory of transmission spectrometers is still mainly based on mature optical imaging lens design ideas, and it is necessary to use a variety of optical glass materials to achieve chromatic aberration correction of collimation and convergence lens groups, thereby achieving better collimation and convergence imaging effects. Although this method is relatively mature and reliable, the use of multiple materials will increase the difficulty of design and increase the cost of optical manufacturing and assembly; especially in the infrared band (including short-wave infrared 1-2.5μm, medium-wave infrared 3-5μm and long-wave infrared 7-14μm), there are very few optical materials with good optical and physical and chemical properties, and the realization of infrared band achromatic and apochromatic lenses has put forward higher requirements for design, processing and cost. Therefore, it is necessary to study the possibility of reducing the types of optical materials in transmission spectrometers from the perspective of optical design theory, and expand the application of large-aperture transmission spectrometers in various bands. Summary of the invention

[0006] The present invention aims to solve the technical problems in the prior art and provides a large-aperture transmission spectrometer using a single material and a design method thereof.

[0007] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0008] A design method for a large-aperture transmission spectrometer using a single material, in which a linear fit is performed on the material refractive index n in the target spectral band to obtain the fitted refractive index n f ; The focal length satisfies the formula:

[0009]

[0010] where fs is the focal length of the single lens, n is the refractive index of the material, r1 and r2 are the radii of curvature of the two surfaces of the single lens respectively;

[0011] When only one material is used, the focal length of the converging lens group satisfies:

[0012]

[0013] Where f is the focal length of the lens group, n is the refractive index of the material, and r 2n-1 、r 2n are the curvature radii of the two surfaces of the nth lens in the lens group.

[0014] In the above technical solution, The basis for quantifying and judging the linearity of is:

[0015] calculate The parameter curve is fitted linearly to obtain

[0016] The relative deviation between the actual value and the theoretical value for:

[0017]

[0018] In the above technical solution, when the tilted image plane method is used, the defocus amount caused by the nonlinearity of axial chromatic aberration is:

[0019]

[0020] Where Δ is the defocus amount caused by the nonlinearity of axial chromatic aberration, and f is the focal length of the converging lens group;

[0021] According to the optical lens focal depth estimation formula:

[0022] δ=F w ·S

[0023] Where δ is the semi-focal depth of the optical system, F w is the lens working F number, S is the pixel size;

[0024] If the defocus caused by the axial chromatic aberration of the converging lens group is within the allowable range of the focal depth, it satisfies:

[0025] Δ≤δ.

[0026] A large-aperture transmission spectrometer using a single material is designed according to the above-mentioned design method.

[0027] The present invention has the following beneficial effects:

[0028] The large-aperture transmission spectrometer using a single material and the design method thereof of the present invention are based on a coaxial catadioptric optical system design, with a small number of optical elements and only a single material, no aspheric surface, low manufacturing difficulty, and a relatively more mature and simple coaxial system assembly and adjustment process;

[0029] The large-aperture transmission spectrometer using a single material and the design method thereof of the present invention uses a plane grating as the diffraction spectrometer element, and the device cost and manufacturing difficulty are much lower than those of a spectrometer based on a curved grating.

[0030] The large-aperture transmission spectrometer using a single material and the design method thereof of the present invention can be applied to spectral instruments of various spectral bands and various resolution requirements under the condition of satisfying the refractive index change requirements given by the formula, and has a wide range of applications; and the transmission lens group design only uses a single material to correct monochromatic aberrations, and the design difficulty is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] Figure 1 Schematic diagram of the refractive index variation curve of optical fused quartz from 400 to 2500 nm.

[0033] Figure 2 Schematic diagram of the 1 / (n-1) variation curve of optical fused quartz.

[0034] Figure 3 Schematic diagram of the linearity evaluation of the 1 / (n-1) parameter in the 900-2100nm band of fused quartz.

[0035] Figure 4 Schematic diagram of the optical structure of the all-fused quartz transmission spectrometer.

[0036] Figure 5(a)-5(e) They are the MTF of the fully fused silica transmission spectrometer. They are: 5(a)

[0037] MTF of each field of view at 0.9μm wavelength, 5(b) MTF of each field of view at 1.2μm wavelength, 5(c) MTF of each field of view at 1.5μm wavelength, 5(d) MTF of each field of view at 1.8μm wavelength, 5(e) MTF of each field of view at 2.1μm wavelength.

[0038] Figure 6 Schematic diagram of the optical structure of the reflection collimation-transmission converging spectrometer.

[0039] Figure 7(a)-7(e)They are the MTFs of the reflective collimation-transmission convergence spectrometer, respectively: 7(a) MTF of each field of view at 0.9μm wavelength, 7(b) MTF of each field of view at 1.2μm wavelength, 7(c) MTF of each field of view at 1.5μm wavelength, 7(d) MTF of each field of view at 1.8μm wavelength, and 7(e) MTF of each field of view at 2.1μm wavelength. DETAILED DESCRIPTION

[0040] The inventive concept of the present invention is:

[0041] According to public literature, the main design process of existing transmission spectrometers is as follows: 1. Determine the plane grating parameters, as well as the imaging field of view, imaging resolution, effective spectral band and other design input parameters of the collimating and converging lens group according to the required slit length, spectral dispersion width, spectral range, spectral resolution and relative aperture; 2. Design an imaging lens that can meet the design input requirements based on the mature transmission imaging lens structure method; 3. Invert the designed imaging lens as a collimating lens group and the imaging lens as a converging lens group, and set a prism-grating assembly (or only a transmission grating) between the two, adjust the relative position and angle relationship between the grating, the collimating lens group and the converging lens group to meet the theoretical calculated values, and then set the image plane tilt to better correct the axial chromatic aberration, and slightly optimize the parameters of the collimating and converging lens group and the image plane tilt angle as a whole, so as to complete the design of a common transmission spectrometer.

[0042] There is a hidden theoretical blind spot in this conventional design idea: the wide-band optical imaging lens needs to achieve good convergence of all wavelengths in the wide band at any position on the image plane, so it is necessary to use a variety of optical materials for achromatic design. According to the basic principle of the spectrometer, the optical lens used for the transmission spectrometer only needs to image specific wavelengths of light in different fields of view, so the image plane tilt method can be used to correct the axial chromatic aberration corresponding to different fields of view. So in fact, the wide-band imaging lens and the lens required for the transmission spectrometer have different requirements for chromatic aberration correction: the wide-band imaging lens requires that the chromatic aberration corresponding to the imaging of all wavelengths in the target spectrum is approximately 0, while the converging lens of the transmission spectrometer requires that its axial chromatic aberration is approximately linearly distributed with the field of view angle. The two requirements are essentially different.

[0043] Therefore, it can be seen that the chromatic aberration correction process in the existing transmission spectrometer design is a sufficient condition but not a necessary condition for the spectrometer design. Therefore, in theory, the use of non-achromatic single-material or multi-material lenses can also realize the design of transmission spectrometers, thereby reducing the difficulty of system design and manufacturing costs.

[0044] Based on the above principle analysis, the present invention provides the basic design theory and one embodiment of a single material transmission spectrometer, proves the theoretical feasibility and advantages of the single material transmission spectrometer, and points out its limiting factors.

[0045] The present invention first proves theoretically that the chromatic aberration of the spectrometer convergent lens group only needs to be corrected to make the axial chromatic aberration approximately linearly distributed according to the basic optical principle. Then, taking fused silica material as an example, the nonlinear degree of its dispersion curve distribution is analyzed, and the relationship formula for realizing the linear distribution of chromatic aberration correction by a single material in a certain band is pointed out, and the feasibility of using a single material to realize the design of a transmission spectrometer and the performance limiting factors are demonstrated. Finally, a design example of a 900-2100nm large-aperture short-wave infrared spectrometer using all fused silica materials is given to prove the feasibility and advantages of the present invention.

[0046] The core idea of ​​the present invention is to utilize the characteristic that the dispersion curve of optical materials is approximately linear in a specific spectral range, and to combine the method of correcting the axial chromatic aberration of the converging lens group with the image plane tilt method, so that the design of a transmission spectrometer can be realized with only a single material. Since the refractive index curve of optical materials in the short-wave, medium-wave and long-wave infrared bands is generally highly linear, and there are few high-performance, low-cost materials, the above-mentioned spectrometer converging lens group design method based on a single material has a wide range of application value in the design of infrared spectrometers. However, this does not mean that the present invention can only be used in the infrared band.

[0047] According to the basic design theory described in the present invention, the basis for judging whether the same material can be used to realize a transmission spectrometer is whether the linearity of the material's dispersion curve (or refractive index curve) is sufficiently high within the target spectral band. Therefore, the infrared spectrometer design scheme described in the present invention is only an example of the present invention. This design method can also be used for transmission spectrometers with narrower spectral ranges in the ultraviolet and visible bands, as long as the linearity of the material's refractive index curve within this band is sufficiently high.

[0048] The present invention is described in detail below with reference to the accompanying drawings.

[0049] 1. Design principle of transmission spectrometer based on single optical material

[0050] For a transmission type plane grating spectrometer, since the different field angles of the converging lens group only need to image the light of a specific direction and wavelength diffracted by the grating, and the wavelength λ is proportional to the diffraction angle θ, the axial chromatic aberration of the converging lens group can be corrected by tilting the image plane. However, the collimation and converging lens group design of the current conventional transmission spectrometer is still based on the achromatic design method using different optical materials, and the achromatic ability of the tilted image plane method is not fully utilized. The following takes the refractive index change of fused quartz material as an example to illustrate the feasibility of designing a transmission spectrometer using a single material.

[0051] Figure 1 The figure shows the refractive index variation curve of fused quartz at 400-2500nm. It can be seen that the refractive index of fused quartz material is highly nonlinear in the UV-visible band, and its variation tends to be linear as the wavelength increases. Without considering other aberrations, the refractive index n of the material can be linearly fitted in the target spectral band to obtain the fitted refractive index n f Because for a thin lens made of a single material, its focal length satisfies the formula:

[0052]

[0053] where f s is the focal length of the single lens, n is the refractive index of the material, and r1 and r2 are the radii of curvature of the two surfaces of the single lens respectively.

[0054] Accordingly, when only one material is used, the focal length of the converging lens group satisfies:

[0055]

[0056] Where f is the focal length of the lens group, n is the refractive index of the material, and r 2n-1 、r 2n are the curvature radii of the two surfaces of the nth lens in the lens group.

[0057] Therefore, when only one material is used, it can be known that the focal length of the converging lens group is proportional to Therefore, if the optical material is within a certain spectral band If the change of is close to linear, it is possible to achieve better imaging effect by using the same material and combining the image plane tilt method.

[0058] Taking fused quartz as an example, discuss the parameters related to its refractive index Law of change. Figure 2 Shown are the parameters of fused quartz in the range of 400-2500nm From the changes, it can be seen that the refractive index changes dramatically and nonlinearly in the visible-near infrared band, while the refractive index changes tend to be linear in the short-wave infrared band.

[0059] Next, give The linearity of the image plane can be quantified and judged to determine whether the axial chromatic aberration can be corrected by the image plane tilt method. Taking the fused quartz within the range of 900-2100nm as an example, the calculation The parameter curve is fitted linearly to obtain The results are as follows Figure 3 (a) The curve can represent the theoretical nonlinear distribution of the image plane of the lens group, and its linear fitting result represents the position of the actual tilted image plane. The relative deviation between the actual value and the theoretical value like Figure 3 (b) as shown:

[0060]

[0061] The relative deviation It can characterize the relative defocus degree between the actual tilted image plane and the theoretical curved image plane.

[0062] Still taking fused quartz in the range of 900-2100nm as an example, if the focal length of the spectrometer converging lens group at a wavelength of 1500nm is 50mm, then when using the tilted image plane method, the defocus amount caused by its axial chromatic aberration nonlinearity can be estimated as:

[0063]

[0064] Where Δ is the defocus amount caused by the nonlinearity of axial chromatic aberration, and f is the focal length of the converging lens group.

[0065] According to the optical lens focal depth estimation formula:

[0066] δ=F w ·S (5)

[0067] Where δ is the semi-focal depth of the optical system, F w is the lens working F number, and S is the pixel size.

[0068] Therefore, if the defocus caused by the axial chromatic aberration of the converging lens group is within the allowable range of the focal depth, it satisfies:

[0069] Δ≤δ (6)

[0070] It can be judged that within a given spectral range, using a single material and tilted image plane method can achieve better imaging quality. Taking fused quartz as an example, according to Figure 3 (b) It can be seen that when a single fused quartz material is used to design the converging lens group of the transmission spectrometer, within the range of 900-2100nm, the relative defocus caused by the nonlinear distribution of axial chromatic aberration is within ±0.093%; if the focal length of the converging lens group is 50mm and the F number is 2, then Δ=50×0.093%=0.00465mm, and δ=2×0.0025=0.005mm, which meets the requirement that the defocus Δ is less than the semi-focal depth δ, that is, fused quartz can be used as a material combined with a tilted image plane to realize the design of a transmission spectrometer within this range.

[0071] 2. Design example of single material transmission fiber optic spectrometer

[0072] Based on the basic design principle of a single-material transmission spectrometer, a design example of a short-wave infrared full-transmission optical fiber spectrometer using a single fused silica material is given below to demonstrate the effectiveness and advantages of the present invention.

[0073] 2.1 Design indicators of short-wave infrared transmission spectrometer

[0074] The detector used is Hamamatsu G11477-512WB linear array InGaAs detector (response range 0.9-2.15μm), and the main design specifications are shown in Table 1.

[0075] Table 1 Short-wave infrared fiber spectrometer optical system design indicators

[0076] index parameter Spectral range 0.9-2.1μm Spectral resolution 4.7nm Relative aperture 1 / 2.0 Slit width 25μm×5mm Sampling rate 2:1 Dispersion Width 12.6mm Grating line density 200lp / mm

[0077] 2.2 Design Process

[0078] Grating component design

[0079] Generally speaking, there is a restrictive relationship between the focal length, field of view and relative aperture of an optical system. Based on the experience of optical design, taking into account the system image plane size, the field of view of the converging light path, the system relative aperture, the size of the optical system and the difficulty of design, the focal length of the collimating and converging light path is selected to be 50mm, and the transmission grating line density is 200lp / mm; at this time, according to the grating equation, it can be calculated that the 0.9-2.1μm spectrum dispersion angle is about 14.4°, corresponding to a theoretical dispersion length of 12.64mm.

[0080] Converging light path design

[0081] The function of the converging optical path is to converge the parallel light of different fields diffracted by the grating at different positions on the focal plane to form a spectral image of the slit. According to the design indicators and combined with the experience of optical design, the main parameters of the converging optical path are determined as follows: focal length 50mm, relative aperture 1 / 2, field of view greater than ±7.2°, spectral range 0.9-2.1μm, and image quality requirement MTF at 20lp / mm to reach above 0.5.

[0082] Double Gaussian objective lenses are widely used due to their symmetrical structure, easy aberration correction, large relative aperture, large field of view, and long back working distance. Therefore, the converging optical path is designed with a double Gaussian objective lens with a relative aperture of 1 / 2 as the initial structure. And because there is no need to apochromatize the converging lens group, only one fused quartz material is used to correct the monochromatic aberration of the central wavelength of 1.5μm; then the residual axial chromatic aberration can be corrected by combining the image plane tilt method. After the initial optimization design is completed, the aperture of the double Gaussian converging objective lens is set to the front and the system is optimized and fine-tuned again to dock with the collimation and splitter optical path.

[0083] Collimated optical path design

[0084] The function of the collimating optical path is to collimate the incident divergent light and irradiate it onto the spectrometer. If it is used in scenes that require a longer slit, such as spectral imaging, it is necessary to better correct the off-axis light aberration. In this case, the converging lens group can be directly inverted and used as a collimating lens group. In this case, the optical design results of the single-material spectrometer are as follows: Figure 4 As shown, the MTF of each wavelength is Figure 5(a)~5(e) As shown in the figure, the collimation and convergence paths of this design each have 7 lenses, the slit length is 5mm, the relative aperture is 1 / 2.0, the system is made entirely of fused quartz material, the total optical length is 170mm, the back intercept is 11.9mm, the image plane is tilted 15.88°, the dispersion length is 12.6mm, and the corresponding spectral resolution can reach 4.7nm (sampling rate 2:1), and the MTF of each wavelength is better than 0.65 at 20lp / mm, which well meets the design index requirements.

[0085] If used in fiber optic spectrometers and other situations where only aberration correction is required for a very small paraxial field of view, a single hyperbolic mirror can be used to replace the collimating lens group to achieve high-quality isochoric collimation in a small paraxial area, greatly simplifying the system structure. At this time, the slit length is 0.6mm, and other parameters remain unchanged. The overall optical structure is as follows Figure 6 As shown, the system MTF is Figure 7(a)~7(e) As shown in the figure. The collimating optical path of this design is composed of a hyperbolic reflector, and the converging optical path contains 6 fused silica lenses. The slit length is 0.6mm, which is enough to cover the conventional fiber core diameter size; the total optical length is 133mm, the relative aperture is 1 / 2.0, the back intercept is 11.9mm, the image plane is tilted 7.36°, the dispersion length is 12.6mm, and the corresponding spectral resolution can reach 4.7nm (sampling rate 2:1). The MTF of each wavelength is better than 0.65 at 20lp / mm, which well meets the design index requirements.

[0086] Figure 4 , Figure 5(a)~5(e) , Figure 6 as well as Figure 7(a)~7(e) They are the design result and full-field MTF of the single-material short-wave infrared spectrometer of the present invention. It can be seen that the design method of the single-material transmission spectrometer of the present invention is feasible, and the imaging quality of the designed infrared spectrometer optical system is good, which can fully meet the design index requirements; at the same time, it also has the advantages of low design difficulty, low cost and small size.

[0087] Specifically, the fiber optic spectrometer solution of the present invention can be modified according to different design index requirements, and this situation should also be considered to fall within the scope of protection of the claims of the present invention. The modifiable components mainly include:

[0088] 1. The collimating objective lens in the spectrometer system can be replaced with other forms of refraction, reflection or catadioptric hybrid systems;

[0089] 2. The optical material of the lens can be any other material as long as it meets the refractive index approximate linear condition proposed by the present invention;

[0090] 3. The system's optical splitter can also use a reflective grating, as long as the optical path is not blocked. Other principles and design ideas are similar to those of the solution described in the present invention.

[0091] 4. When the system spectrometer uses a transmission spectrometer, various devices such as prism, prism-grating, prism-grating-prism, etc. can be used. Other principles and design ideas are similar to the solution described in the present invention;

[0092] 5. The detector can be replaced with other types of linear array or planar array photoelectric detectors with different response bands and different pixel sizes;

[0093] 6. Other components not mentioned can be replaced with devices with similar functions according to corresponding needs.

[0094] The large-aperture transmission spectrometer using a single material and the design method thereof of the present invention are based on a coaxial catadioptric optical system design, with a small number of optical elements and only a single material, no aspheric surface, low manufacturing difficulty, and a relatively more mature and simple coaxial system assembly and adjustment process;

[0095] The large-aperture transmission spectrometer using a single material and the design method thereof of the present invention uses a plane grating as the diffraction spectrometer element, and the device cost and manufacturing difficulty are much lower than those of a spectrometer based on a curved grating.

[0096] The large-aperture transmission spectrometer using a single material and the design method thereof of the present invention can be applied to spectral instruments of various spectral bands and various resolution requirements under the condition of satisfying the refractive index change requirements given by the formula, and has a wide range of applications; and the transmission lens group design only uses a single material to correct monochromatic aberrations, and the design difficulty is low.

[0097] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A design method for a large aperture transmission spectrometer using a single material, characterized in that: Perform a linear fit on the material refractive index n within the target spectral band to obtain the fitted refractive index n f ; The focal length satisfies the formula: where f s is the focal length of the single lens, n is the refractive index of the material, r1 and r2 are the radii of curvature of the two surfaces of the single lens respectively; When only one material is used, the focal length of the converging lens group satisfies: Where f is the focal length of the lens group, n is the refractive index of the material, and r 2n-1 、r 2n are the curvature radii of the two surfaces of the nth lens in the lens group.

2. The design method of a large aperture transmission spectrometer using a single material according to claim 1, characterized in that: The basis for quantifying and judging the linearity of is: calculate The parameter curve is fitted linearly to obtain The relative deviation between the actual value and the theoretical value for:

3. The design method of a large aperture transmission spectrometer using a single material according to claim 1, characterized in that: When using the tilted image plane method, the defocus amount caused by axial chromatic aberration nonlinearity is: Where Δ is the defocus amount caused by the nonlinearity of axial chromatic aberration, and f is the focal length of the converging lens group; According to the estimation formula of the focal depth of the optical lens: δ=F w ·S Where δ is the semi-focal depth of the optical system, F w is the lens working F number, S is the pixel size; If the defocus caused by the axial chromatic aberration of the converging lens group is within the allowable range of the focal depth, it satisfies: Δ≤δ.

4. A large aperture transmission spectrometer using a single material, characterized in that: The large-aperture transmission spectrometer is designed according to the design method described in any one of claims 1-3.

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