A super-spectral resolution spectrometer based on Fabry-Perot interferometer

Abstract

The present invention provides a hyperspectral resolution spectrometer based on a Fabry-Perot interferometer, comprising an optical introduction system, a primary Fabry-Perot interferometer spectrometer system, a secondary spectral order selection system, and a two-dimensional array detection system. The optical introduction system is configured to receive a light beam to be measured and enter the spectrometer system, and project the light beam into the primary spectrometer system through a collimating lens. The primary Fabry-Perot interferometer spectrometer system is configured to receive parallel light beams at different angles from the collimating lens and perform primary spectrometry based on the angular dependence of the interference spectrum. The secondary spectral order selection system is configured to perform secondary selection on the aliased spectrum separated by the primary spectrometer system in a single spatial dimension. The two-dimensional array detection system is configured to receive coarse-resolution spectral signals and high-resolution spectral signals. The advantages of the present invention are high spectral resolution, a wide spectral range, relatively low cost, and a relatively small size.

Description

Technical Field

[0001] The present invention relates to the field of spectral technology, and in particular to a hyperspectral resolution spectrometer based on a Fabry-Perot interferometer. Background Art

[0002] Spectroscopic instruments are widely used in physical and chemical analysis, biological sample testing, semiconductor material testing, optical testing, material testing and environmental monitoring.

[0003] Existing spectroscopic instruments mainly include grating spectrometers, prism spectrometers, and Fourier spectrometers. Among them, grating spectrometers mainly rely on low-order interference spectroscopy of diffraction gratings, and the spectral resolution is limited by the number of diffraction grating lines, the focal length of the focusing lens, and the size of the detector. High-resolution grating spectrometers often require dense grating lines combined with large-size gratings and long focusing lenses, resulting in large size and high cost. At the same time, the spectral range is limited by the size of the detector, making it difficult to achieve high spectral resolution over a wide band. Prism spectrometers rely on refraction spectroscopy and will not cause spectral aliasing, but the resolution is also poor. Fourier spectrometers rely on interference spectroscopy and perform Fourier transform on the interference intensity to achieve high spectral resolution, but the instrument requires high-precision mechanical control, is generally large in size, and is expensive.

[0004] Therefore, there is an urgent need to develop a spectral instrument with high spectral resolution, wide spectral range, relatively low cost and relatively small size. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a hyper-spectral resolution spectrometer based on a Fabry-Perot interferometer. The spectrometer combines the first-level light splitting system and the second-level spectral order selection system of the Fabry-Perot interferometer, and uses a two-dimensional detector to receive a two-dimensional high-resolution spectrum image to realize a hyper-spectral resolution spectrometer, which effectively solves the problems of existing spectroscopic instruments that are difficult to achieve high spectral resolution and wide spectral range, and are relatively high in cost and relatively large in size.

[0006] The present invention adopts the following technical solutions to solve the above technical problems:

[0007] A hyperspectral resolution spectrometer based on Fabry-Perot interferometer, comprising an optical introduction system, a first-level spectral splitting system of Fabry-Perot interferometer, a second-level spectral order selection system and a two-dimensional array detection system;

[0008] The optical introduction system includes an incident slit and a collimating lens; the incident slit is used to receive the light beam to be measured and enter the spectrometer system, and project the light beam into the first-level spectroscopic system of the Fabry-Perot interferometer through the collimating lens;

[0009] The Fabry-Perot interferometer primary light splitting system includes a Fabry-Perot interferometer; the Fabry-Perot interferometer is used to receive parallel light beams at different angles from a collimating lens and perform primary light splitting based on the angular dependence of the interference spectrum;

[0010] The secondary spectral order selection system includes a grating or a filter device for performing secondary selection on the aliased spectrum separated by the primary optical splitting system of the Fabry-Perot interferometer in one spatial dimension;

[0011] The two-dimensional array detection system is used to receive the coarse-resolution spectrum signal from the secondary spectrum order selection system and the high-resolution spectrum signal filtered out by the primary spectroscopic system of the Fabry-Perot interferometer.

[0012] As one of the preferred embodiments of the present invention, the entrance slit of the optical introduction system is located at the focal plane of the collimating lens; light beams entering from different spatial positions of the entrance slit are formed into parallel light beams of different angles through the collimating lens.

[0013] As one of the preferred embodiments of the present invention, the beam angle is determined by Formula 1:

[0014] α=arctan(d / f) Formula 1;

[0015] Where d is the height of the spatial point on the incident slit, f is the focal length of the collimating lens, and α is the beam angle.

[0016] As one of the preferred embodiments of the present invention, the Fabry-Perot interferometer primary spectroscopic system is located behind the optical introduction system, and spectrum selection is performed according to Formula II:

[0017]

[0018] Where α is the angle of the light beam entering the Fabry-Perot interferometer, R is the mirror reflectivity of the Fabry-Perot interferometer, d is the mirror spacing of the Fabry-Perot interferometer, and T is the spectral transmittance;

[0019] After passing through the Fabry-Perot interferometer, different spatial positions receive spectra transmitted at different angles, and then ultra-high resolution spectral information is extracted.

[0020] As one of the preferred embodiments of the present invention, the secondary spectral order selection system is located behind the primary spectroscopic system of the Fabry-Perot interferometer, and uses the grating or filter device to separate the aliased high-resolution spectrum from the primary spectroscopic system of the Fabry-Perot interferometer.

[0021] As one of the preferred embodiments of the present invention, the two-dimensional array detection system has two spatial dimensions, one of which is used to receive a coarse-resolution spectral selection signal from a grating or filter device in the secondary spectral order selection system, and the other is used to receive a high-resolution spectral signal filtered out by the spectral angle dependence of the Fabry-Perot interferometer in the primary spectroscopic system of the Fabry-Perot interferometer.

[0022] As one of the preferred embodiments of the present invention, a broadband high-resolution spectrum is obtained by splicing the high-resolution spectrum and the coarse-resolution spectrum received by the two-dimensional area array detection system.

[0023] As one of the preferred embodiments of the present invention, an optical coupling system is further provided between the primary optical splitting system and the secondary spectral order selection system of the Fabry-Perot interferometer.

[0024] As one of the preferred embodiments of the present invention, the optical coupling system includes a coupling lens, a secondary slit and a secondary collimating lens; the coupling lens converges spatial light at different angles from the first-level spectroscopic system of the Fabry-Perot interferometer to the secondary slit; the secondary slit is located at the focus of the secondary collimating lens, limiting the received spatial light at different angles from entering the secondary spectral order selection system in the form of parallel light after being collimated by the secondary collimating lens.

[0025] Working principle:

[0026] A primary spectral selection is performed using high-order interference of Fabry-Perot interferometer, and the angular dependence of the transmission spectrum of the Fabry-Perot interferometer is used to focus high-order aliasing spectra of different wavelengths on different spatial points. A secondary spectral selection is performed using a grating / filter device, and low-order spectral filtering is performed in a spatial dimension in one direction. Finally, a two-dimensional spectrum containing ultra-high-resolution spectral information is received on a two-dimensional detector. The high-resolution spectrum within a single free spectral range of the Fabry-Perot interferometer is spliced ​​with the wide-band spectrum of the grating / filter device to obtain wide-band, high-spectral-resolution spectral information.

[0027] The advantages of the present invention over the prior art are:

[0028] (1) The grating / filter device only serves as a spectral order selection device, and fine spectral resolution is provided by high-order interference of the Fabry-Perot interferometer (FP). Therefore, compared with spectrometers that increase the spectral resolution by increasing the number of grating lines, the present invention has a lower implementation cost;

[0029] (2) Traditional high-resolution spectrometers can only provide high-resolution spectra within a narrow band (by increasing the focal length of the focusing lens). The present invention uses a grating / filter device to perform coarse-resolution spectral selection and a Fabry-Perot interferometer (FP) to further subdivide the spectrum within a single grating spectral channel, which can achieve high-resolution spectral acquisition within a wide band and has a small size (no long-focal-length focusing lens is required). BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 3D schematic diagram of the structure of the hyper-spectral resolution spectrometer based on Fabry-Perot interferometer in Example 1;

[0031] Figure 2 1 is a schematic diagram of the front view structure of the hyper-spectral resolution spectrometer based on Fabry-Perot interferometer in Example 1;

[0032] Figure 3 2 is a schematic diagram of the front view structure of the hyper-spectral resolution spectrometer based on Fabry-Perot interferometer in Example 2;

[0033] Figure 4 Schematic diagram of the top view of the hyper-spectral resolution spectrometer based on Fabry-Perot interferometer in Example 2;

[0034] Figure 5 3 is a schematic diagram of the front view structure of the hyper-spectral resolution spectrometer based on Fabry-Perot interferometer in Example 3;

[0035] Figure 6 is the spectral transmittance of the Fabry-Perot interferometer in Examples 1, 2, and 3;

[0036] Figure 7 is a graph showing the variation of spectral transmittance of the Fabry-Perot interferometer with angle in Examples 1, 2, and 3;

[0037] Figure 8 It is a spectrum diagram of the grating spectrometer received by the two-dimensional detector image plane in Examples 1 and 2 and the hyper-spectral resolution spectrometer based on the Fabry-Perot interferometer.

[0038] In the figure: 1 is the optical introduction system, 11 is the incident slit, 12 is the collimating lens, 2 is the first-level spectroscopic system of Fabry-Perot interferometer, 21 is the Fabry-Perot interferometer, 3 is the second-level spectral order selection system, 31 is the diffraction grating, 32 is the focusing lens, 33 is the focusing lens, 34 is the linear gradient filter, 4 is the two-dimensional array detection system, 41 is the two-dimensional detector, 5 is the optical coupling system, 51 is the coupling lens, 52 is the secondary slit, and 53 is the secondary collimating lens. DETAILED DESCRIPTION

[0039] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0040] Example 1

[0041] like Figure 1-2 As shown, a hyperspectral resolution spectrometer based on a Fabry-Perot interferometer according to this embodiment includes, in order along the optical path, an optical introduction system 1, a first-level Fabry-Perot interferometer light splitting system 2, a second-level spectral order selection system 3, and a two-dimensional array detection system 4. The optical introduction system 1 includes an input slit 11 and a collimating lens 12; the first-level Fabry-Perot interferometer light splitting system 2 includes a Fabry-Perot interferometer 21; the second-level spectral order selection system 3 includes a diffraction grating 31 and a focusing lens 32; and the two-dimensional array detection system 4 includes a two-dimensional detector 41.

[0042] Furthermore, in this embodiment, the input slit 11 is located at the focal plane of the collimating lens 12, which is used to receive the measured light beam into the spectrometer system. The input slit 11 limits the light beam to a linear shape, which is then collimated by the collimating lens 12 into parallel light perpendicular to the direction of the input slit 11. The angle of the light beam parallel to the direction of the input slit 11 varies with the spatial position of the input slit 11.

[0043] The light beams entering from different spatial positions of the incident slit 11 are formed into parallel beams of different angles through the collimating lens 12. The beam angle is determined by formula 1:

[0044] α=arctan(d / f) Formula 1;

[0045] Wherein, d is the height of the spatial point on the incident slit 11, f is the focal length of the collimating lens 12, and α is the beam angle.

[0046] Furthermore, in this embodiment, the Fabry-Perot interferometer 21 is located behind the collimating lens 12 and is used to receive parallel light beams at different angles from the collimating lens 12 and perform primary light splitting based on the angular dependence of the interference spectrum.

[0047] Specifically, the Fabry-Perot interferometer 21 disperses light entering at different angles into different wavelengths according to Formula II (Fabry-Perot interferometer transmittance formula):

[0048]

[0049] Wherein, α is the angle of the light beam entering the Fabry-Perot interferometer 21, R is the mirror reflectivity of the Fabry-Perot interferometer 21, d is the mirror spacing of the Fabry-Perot interferometer 21, and T is the spectral transmittance.

[0050] The transmittance of the Fabry-Perot interferometer 21 in this embodiment is as follows: Figures 6-7 As shown, the first-order light splitting by the Fabry-Perot interferometer 21 generates an aliased spectrum with high spectral resolution.

[0051] Furthermore, in this embodiment, the diffraction grating 31 performs secondary spectral order selection on the high spectral resolution aliased spectrum from the Fabry-Perot interferometer 21, and selects a focusing lens 32 with a suitable angle according to Formula III (grating line dispersion formula) to disperse light of different wavelengths to different spatial positions. Only the transmission peak spectrum corresponding to the wavelength range of the diffraction grating 31 diffraction spectrum and the transmission peak position of the spectrum of the Fabry-Perot interferometer 21 can pass through.

[0052]

[0053] Where f is the focal length of the focusing lens, m is the grating interference order, θ is the grating diffraction angle, λ is the wavelength, and l is the distance between adjacent spectral lines.

[0054] Furthermore, in this embodiment, the two-dimensional detector 41 has two spatial dimensions, one of which receives a coarse-resolution spectral selection channel from the secondary spectral order selection system 3, and the other receives a high-resolution spectral signal filtered out by the spectral angle dependence of the Fabry-Perot interferometer 21 in the primary spectroscopic system 2 of the Fabry-Perot interferometer.

[0055] The spectrum of the grating spectrometer received by the image plane of the two-dimensional detector 41 in this embodiment and the spectrum of the super spectral resolution spectrometer based on the Fabry-Perot interferometer 21 is as follows: Figure 8 shown.

[0056] By splicing the high-resolution spectrum and the coarse-resolution spectrum received by the two-dimensional detector 41, a broadband high-resolution spectrum is obtained.

[0057] Example 2

[0058] like Figure 3-4 As shown, a hyperspectral resolution spectrometer based on a Fabry-Perot interferometer according to this embodiment includes, in order along the optical path, an optical introduction system 1, a primary Fabry-Perot interferometer light splitting system 2, an optical coupling system 5, a secondary spectral order selection system 3, and a two-dimensional array detection system 4. Specifically, the optical introduction system 1 includes an input slit 11 and a collimating lens 12; the primary Fabry-Perot interferometer light splitting system 2 includes a Fabry-Perot interferometer 21; the secondary spectral order selection system 3 includes a diffraction grating 31 and a focusing lens 32; the two-dimensional array detection system 4 includes a two-dimensional detector 41; and the optical coupling system 5 includes a coupling lens 51, a secondary slit 52, and a secondary collimating lens 53.

[0059] Furthermore, in this embodiment, the input slit 11 is located at the focal plane of the collimating lens 12, which is used to receive the measured light beam into the spectrometer system. The input slit 11 limits the light beam to a linear shape, which is then collimated by the collimating lens 12 into parallel light perpendicular to the direction of the input slit 11. The angle of the light beam parallel to the direction of the input slit 11 varies with the spatial position of the input slit 11.

[0060] The light beams entering from different spatial positions of the incident slit 11 are formed into parallel beams of different angles through the collimating lens 12. The beam angle is determined by formula 1:

[0061] α=arctan(d / f) Formula 1;

[0062] Wherein, d is the height of the spatial point on the incident slit 11, f is the focal length of the collimating lens 12, and α is the beam angle.

[0063] Furthermore, in this embodiment, the Fabry-Perot interferometer 21 is located behind the collimating lens 12 and is used to receive parallel light beams at different angles from the collimating lens 12 and perform primary light splitting based on the angular dependence of the interference spectrum.

[0064] Specifically, the Fabry-Perot interferometer 21 disperses light entering at different angles into different wavelengths according to Formula II (Fabry-Perot interferometer transmittance formula):

[0065]

[0066] Wherein, α is the angle of the light beam entering the Fabry-Perot interferometer 21, R is the mirror reflectivity of the Fabry-Perot interferometer 21, d is the mirror spacing of the Fabry-Perot interferometer 21, and T is the spectral transmittance.

[0067] The transmittance of the Fabry-Perot interferometer 21 in this embodiment is as follows: Figures 6-7 As shown, the first-order light splitting by the Fabry-Perot interferometer 21 generates an aliased spectrum with high spectral resolution.

[0068] Furthermore, in this embodiment, the coupling lens 51 converges the spatial light at different angles from the Fabry-Perot interferometer 21 to the secondary slit 52; the secondary slit 52 is located at the focus of the secondary collimating lens 53, limiting the received spatial light at different angles to enter the secondary spectral order selection system 3 behind it in the form of parallel light after being collimated by the secondary collimating lens 53.

[0069] Furthermore, in this embodiment, the diffraction grating 31 performs secondary spectral order selection on the high spectral resolution aliased spectrum from the optical coupling system 5, and selects a focusing lens 32 with a suitable angle according to Formula III (grating line dispersion formula) to disperse light of different wavelengths to different spatial positions. Only the transmission peak spectrum corresponding to the wavelength band of the diffraction grating 31 and the transmission peak position of the spectrum of the Fabry-Perot interferometer 21 can pass through.

[0070]

[0071] Where f is the focal length of the focusing lens, m is the grating interference order, θ is the grating diffraction angle, λ is the wavelength, and l is the distance between adjacent spectral lines.

[0072] Furthermore, in this embodiment, the two-dimensional detector 41 has two spatial dimensions, one of which receives a coarse-resolution spectral selection channel from the secondary spectral order selection system 3, and the other receives a high-resolution spectral signal filtered out by the spectral angle dependence of the Fabry-Perot interferometer 21 in the primary spectroscopic system 2 of the Fabry-Perot interferometer.

[0073] The spectrum of the grating spectrometer received by the image plane of the two-dimensional detector 41 in this embodiment and the spectrum of the super spectral resolution spectrometer based on the Fabry-Perot interferometer 21 is as follows: Figure 8 shown.

[0074] By splicing the high-resolution spectrum and the coarse-resolution spectrum received by the two-dimensional detector 41, a broadband high-resolution spectrum is obtained.

[0075] Example 3

[0076] like Figure 5 As shown, a hyperspectral resolution spectrometer based on a Fabry-Perot interferometer according to this embodiment includes, in order along the optical path, an optical introduction system 1, a first-level Fabry-Perot interferometer light splitting system 2, a second-level spectral order selection system 3, and a two-dimensional array detection system 4. The optical introduction system 1 includes an input slit 11 and a collimating lens 12; the first-level Fabry-Perot interferometer light splitting system 2 includes a Fabry-Perot interferometer 21; the second-level spectral order selection system 3 includes a focusing lens 33 and a linear gradient filter 34; and the two-dimensional array detection system 4 includes a two-dimensional detector 41.

[0077] Furthermore, in this embodiment, the input slit 11 is located at the focal plane of the collimating lens 12, which is used to receive the measured light beam into the spectrometer system. The input slit 11 limits the light beam to a linear shape, which is then collimated by the collimating lens 12 into parallel light perpendicular to the direction of the input slit 11. The angle of the light beam parallel to the direction of the input slit 11 varies with the spatial position of the input slit 11.

[0078] The light beams entering from different spatial positions of the incident slit 11 are formed into parallel beams of different angles through the collimating lens 12. The beam angle is determined by formula 1:

[0079] α=arctan(d / f) Formula 1;

[0080] Wherein, d is the height of the spatial point on the incident slit 11, f is the focal length of the collimating lens 12, and α is the beam angle.

[0081] Furthermore, in this embodiment, the Fabry-Perot interferometer 21 is located behind the collimating lens 12 and is used to receive parallel light beams at different angles from the collimating lens 12 and perform primary light splitting based on the angular dependence of the interference spectrum.

[0082] Specifically, the Fabry-Perot interferometer 21 disperses light entering at different angles into different wavelengths according to Formula II (Fabry-Perot interferometer transmittance formula):

[0083]

[0084] Wherein, α is the angle of the light beam entering the Fabry-Perot interferometer 21, R is the mirror reflectivity of the Fabry-Perot interferometer 21, d is the mirror spacing of the Fabry-Perot interferometer 21, and T is the spectral transmittance.

[0085] The transmittance of the Fabry-Perot interferometer 21 in this embodiment is as follows: Figures 6-7 As shown, the first-order light splitting by the Fabry-Perot interferometer 21 generates an aliased spectrum with high spectral resolution.

[0086] Furthermore, in this embodiment, the focusing lens 33 converges spatial light from different angles of the first-level spectroscopic system 2 of the Fabry-Perot interferometer onto the target surface of the two-dimensional detector 41; the linear gradient filter 34 is located in front of the two-dimensional detector 41, and linearly separates the pixels of the two-dimensional detector 41 according to the wavelength in one spatial dimension. Pixels at different spatial positions receive light intensities in different bands, and the high-spectral-resolution transmission spectrum separated by the angle of the Fabry-Perot interferometer 21 performs a secondary subdivision on the coarse-resolved spectral channel of the linear gradient filter 34 in another spatial dimension.

[0087] Furthermore, in this embodiment, the two-dimensional detector 41 has two spatial dimensions, one of which receives a coarse-resolution spectral selection channel from the linear gradient filter 34 in the secondary spectral order selection system 3, and the other receives a high-resolution spectral signal filtered out by the spectral angle dependence of the Fabry-Perot interferometer 21 in the primary spectroscopic system 2 of the Fabry-Perot interferometer.

[0088] By splicing the high-resolution spectrum and the coarse-resolution spectrum received by the two-dimensional detector 41, a broadband high-resolution spectrum is obtained.

[0089] Matters not covered by the present invention are known technologies.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A hyperspectral resolution spectrometer based on Fabry-Perot interferometer, characterized in that: It includes an optical introduction system, a first-level Fabry-Perot interferometer spectrometer system, a second-level spectral order selection system, and a two-dimensional array detection system; The optical introduction system includes an incident slit and a collimating lens; the incident slit is used to receive the light beam to be measured and enter the spectrometer system, and project the light beam into the first-level spectroscopic system of the Fabry-Perot interferometer through the collimating lens; The Fabry-Perot interferometer primary light splitting system includes a Fabry-Perot interferometer; the Fabry-Perot interferometer is used to receive parallel light beams at different angles from a collimating lens and perform primary light splitting based on the angular dependence of the interference spectrum; The secondary spectral order selection system includes a grating or a filter device for performing secondary selection on the aliased spectrum separated by the primary optical splitting system of the Fabry-Perot interferometer in one spatial dimension; The two-dimensional array detection system is used to receive a coarse-resolution spectrum signal from a secondary spectral order selection system and a high-resolution spectrum signal filtered by a primary spectroscopic system of a Fabry-Perot interferometer; a broadband high-resolution spectrum is obtained by splicing the high-resolution spectrum and the coarse-resolution spectrum received by the two-dimensional array detection system; The incident slit of the optical introduction system is located at the focal plane of the collimating lens; the light beams entering from different spatial positions of the incident slit are formed into parallel light beams of different angles through the collimating lens; the beam angle is determined by Formula I: Formula I; Where, is the height of the spatial point on the incident slit, is the focal length of the collimating lens, is the beam angle; The Fabry-Perot interferometer primary spectroscopic system is located behind the optical introduction system and performs spectrum selection according to Formula II: Formula II; Where, is the angle of the light beam entering the Fabry-Perot interferometer, R is the mirror reflectivity of the Fabry-Perot interferometer, d is the mirror spacing of the Fabry-Perot interferometer, and T is the spectral transmittance.

2. The hyperspectral resolution spectrometer based on Fabry-Perot interferometer according to claim 1, characterized in that: The secondary spectral order selection system is located behind the primary spectroscopic system of the Fabry-Perot interferometer, and utilizes the grating or filter device to separate the aliased high-resolution spectrum from the primary spectroscopic system of the Fabry-Perot interferometer.

3. The hyperspectral resolution spectrometer based on Fabry-Perot interferometer according to claim 1, characterized in that: The two-dimensional array detection system has two spatial dimensions, one of which is used to receive a coarse-resolution spectral selection signal from a grating or filter device in the secondary spectral order selection system, and the other is used to receive a high-resolution spectral signal filtered out by the spectral angle dependence of the Fabry-Perot interferometer in the primary spectroscopic system of the Fabry-Perot interferometer.

4. The hyperspectral resolution spectrometer based on Fabry-Perot interferometer according to any one of claims 1 to 3, characterized in that: An optical coupling system is also provided between the primary light splitting system and the secondary spectrum order selection system of the Fabry-Perot interferometer.

5. The hyperspectral resolution spectrometer based on Fabry-Perot interferometer according to claim 4, characterized in that: The optical coupling system includes a coupling lens, a secondary slit and a secondary collimating lens; the coupling lens converges spatial light of different angles from the primary spectroscopic system of the Fabry-Perot interferometer to the secondary slit; the secondary slit is located at the focus of the secondary collimating lens, limiting the spatial light of different angles received from the secondary spectral order selection system to enter the secondary spectral order selection system in the form of parallel light after being collimated by the secondary collimating lens.

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