Design method of star magnitude large dynamic range spectrum modulation system

Abstract

The invention relates to a design method of a star magnitude large dynamic range spectrum modulation system. The design method comprises the following steps: S1, adopting a cylindrical collimation beam expanding system, a star magnitude large dynamic range light splitting system and a DMD device; the star magnitude large dynamic range light splitting system is composed of a large dynamic light splitting optical system and an energy modulation optical system. The star isometric large dynamic light splitting optical system is composed of a steering reflecting mirror, a grating and an imaging reflecting mirror. The energy modulation optical system is composed of a steering mirror, a grating and a plane mirror. S2, selecting a DMD device and a grating; and S3, carrying out optimization design on the cylindrical collimation beam expanding system and the star magnitude large dynamic range beam splitting system. According to the invention, the cylindrical collimation and beam expanding system is adopted to replace a physical slit and a collimating mirror in the Czerny-Turner type plane diffraction grating optical structure, so that the imaging quality of the large-dynamic-range spectrum modulation optical system can be improved; and the problem of contradiction between the slit and the imaging quality in the initial structure can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of optical testing, and in particular to a design method for a stellar magnitude large dynamic range spectrum modulation system. Background Art

[0002] At present, the main factor affecting the simulation accuracy of the spectral modulation system is the peak interval. The smaller the peak interval, the higher the spectral simulation accuracy, that is, the higher the spectral resolution of the spectral modulation optical system, the higher the spectral simulation accuracy. Since the wide spectrum beam output by the spectral modulation system cannot be an ideal smooth curve, there will inevitably be peaks locally. Therefore, the spectral radiation distribution of the minimum unit of the spectral simulation output by the stellar magnitude large dynamic range spectral modulation system is somewhat different from the Gaussian distribution. Considering the residual aberration, installation error and design difficulty of the stellar magnitude large dynamic range spectral modulation system, the peak wavelength resolution of the appropriate stellar magnitude large dynamic range spectrometer system is selected to ensure the spectral simulation accuracy and magnitude simulation accuracy of simulating the optical radiation characteristics of stars.

[0003] Therefore, it is necessary to invent a design method for a stellar magnitude large dynamic range spectral modulation system to solve the above problems. Summary of the invention

[0004] The object of the present invention is to provide a design method for a stellar magnitude large dynamic range spectral modulation system for improving the imaging quality of the stellar magnitude large dynamic range spectral modulation optical system.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A design method for a star magnitude large dynamic range spectrum modulation system comprises the following steps:

[0007] S1. A cylindrical collimation beam expansion system, a stellar magnitude large dynamic range spectroscopic system and a DMD device are used; the stellar magnitude large dynamic range spectroscopic system is composed of a large dynamic spectroscopic optical system and an energy modulation optical system; the stellar magnitude large dynamic spectroscopic optical system is composed of a steering reflector, a grating, and an imaging reflector; the energy modulation optical system is composed of a steering reflector, a grating, and a plane reflector;

[0008] S2, select DMD device and grating;

[0009] S3. Optimize the design of the cylindrical collimation beam expansion system and the star magnitude large dynamic range spectrometer system. The steps are as follows:

[0010] 1) Determine the output spot diameter of the continuous laser source;

[0011] 2) Determine the beam expansion multiple of the cylindrical collimation beam expansion system in the non-dispersive direction based on the output spot diameter of the continuous laser light source and the DMD size for

[0012] ;

[0013] In the formula, is the side length of DMD in non-dispersion direction, is the spot diameter of the continuous laser output;

[0014] 3) The spot diameter output by the cylindrical collimation beam expansion system is used as the aperture diameter of the large dynamic range spectrometer system , whose formula is

[0015] ;

[0016] 4) Substitute the number of grating line pairs ;

[0017] 5) Calculate the dispersion angle of each wavelength of the mixed beam after passing through the grating, and use the dispersion angle as the half field angle of the imaging reflector for

[0018] ;

[0019] In the formula, and is the spectral range of the incident beam; is the minimum wavelength dispersion angle; is the maximum wavelength dispersion angle;

[0020] 6) According to the DMD array surface size , calculate the focal length of the imaging mirror , where the DMD array surface size consists of two parts, namely the zero-order diffraction energy compensation area and the negative first-order spectrum modulation area. Since the zero-order diffraction energy compensation area is consistent with the effective aperture of the diffraction grating, the size of the negative first-order spectrum modulation area is , focal length of imaging mirror The calculation formula is

[0021] ;

[0022] In the formula, It is the length of the DMD array surface along the dispersion direction, that is, the length of the zero-order diffraction energy compensation area along the dispersion direction.

[0023] Specifically, a Czerny-Turner type plane diffraction grating optical structure is selected as the initial structure of the stellar magnitude large dynamic range spectroscopic system;

[0024] Specifically, the stellar magnitude large dynamic range spectroscopic system adopts a cylindrical collimating beam expansion system to replace the physical slits and collimating reflectors in the Czerny-Turner type plane diffraction grating optical structure.

[0025] The beneficial effects of the present invention are:

[0026] The present application adopts a cylindrical collimating beam expansion system to replace the physical slits and collimating reflectors in the Czerny-Turner type plane diffraction grating optical structure, so as to reduce the relative aperture of the system in the dispersion direction, greatly reduce spherical aberration, and further reduce coma, thereby improving the imaging quality of the stellar magnitude large dynamic range spectral modulation optical system; at the same time, in the non-dispersion direction, the light beam is expanded to fill the entire system, thereby solving the problem of the contradiction between the slit and the imaging quality in the initial structure.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the composition and optical path structure of the star magnitude large dynamic range spectrum modulation system shown in the present invention;

[0029] Figure 2 The optical path structure diagram of the Czerny-Turner type plane diffraction grating optical structure shown in the present invention;

[0030] Figure 3 It is the initial structure optical path diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0031] Figure 4 It is the initial structure light trace diagram of the magnitude large dynamic range spectroscopic system shown in the present invention;

[0032] Figure 5 It is a spot diagram at 450nm in the initial structure of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0033] Figure 6 It is a spot diagram at 750nm in the initial structure of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0034] Figure 7 It is a spot diagram at 1000nm in the initial structure of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0035] Figure 8 The flowchart of the optimization design of the large dynamic range spectral modulation optical system shown in the present invention;

[0036] Fig. 9 This is the optical path diagram of the cylindrical collimation beam expansion system shown in the present invention;

[0037] Fig.10 It is the overall optical path diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0038] Fig.11 It is the minus first-order diffraction light path diagram in the light path diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0039] Fig.12 It is the zero-order diffraction optical path diagram in the optical path diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0040] Fig.13 It is the spot diagram before optimization at 750nm of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0041] Fig.14 This is the optimized spot diagram at 750nm of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0042] Fig.15 It is a curve diagram of the RMS variation of the magnitude large dynamic range spectroscopic system with wavelength shown in the present invention;

[0043] Fig.16 It is a light trace diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0044] Fig.17 It is a local light trace diagram at 450nm in the light trace diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0045] Fig.18 It is a local light trace diagram at 750nm in the light trace diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention;

[0046] Fig.19 It is a local light trace diagram at 1000nm in the light trace diagram of the star magnitude large dynamic range spectroscopic system shown in the present invention; DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work belong to the scope of protection of the present invention. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal connection of two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood in specific situations. In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] See also Figure 1 The present invention proposes a design method for a stellar magnitude large dynamic range spectrum modulation system, including a cylindrical collimation beam expansion system, a stellar magnitude large dynamic range spectroscopic system and a DMD device; the stellar magnitude large dynamic range spectroscopic system is composed of a large dynamic spectroscopic optical system and an energy modulation optical system.

[0049] Specifically, the large dynamic spectroscopic optical system is composed of a steering reflector, a grating, and an imaging reflector; and the energy modulation optical system is composed of a steering reflector, a grating, and a plane reflector.

[0050] Since DMD has pixel-level modulation capability, enough spectral simulation minimum units can modulate a smaller peak interval, that is, for the light beam subdivided by the spectroscopic system, each column of micromirror pixels on the array surface represents a spectral simulation minimum unit, and the resolution of a single column of micromirror pixels is the modulation coefficient of the spectral simulation minimum unit. Therefore, for a stellar magnitude large dynamic range spectroscopic system, the higher the selected DMD spatial resolution, the greater the modulation capability of the system; the larger the selected DMD spatial size, the more conducive to the optimization design of the stellar magnitude large dynamic range spectroscopic system, the larger the area means the increase of the imaging size, and within the same spectral range, the lower the imaging quality requirements for the spectroscopic system. The parameters of several commonly used models of spatial light modulation devices are shown in Table 1.

[0051]

[0052] Theoretically, the DLP9000 model DMD with higher resolution and larger imaging size is an ideal spatial light modulation device for partition modulation, but DLP9000 is difficult to purchase. Therefore, this application uses the DLP6500 with the highest resolution currently available on the market as the modulation device for system design. Its resolution is 1920×1080 and the single pixel size is 7.56μm. Therefore, according to the DMD use requirements and the rationalization of the arrangement of optical elements in engineering, the resolution 1920 direction is used as the dispersion direction and the resolution 1080 direction is used as the modulation direction.

[0053] The spectral resolution of the grating determines the spectral resolution of the large dynamic range spectral modulation system. The larger the grating constant, the higher the dispersion ability. The formula for the grating spectral resolution is:

[0054] ; (1-1)

[0055] ; (1-2)

[0056] In the formula, is the grating diffraction surface width; is the grating constant; is the total number of grooves in the entire grating; is the diffraction order, and this paper takes ; is the resolving power of the grating.

[0057] Taking into account the design and adjustment of the stellar magnitude large dynamic range spectrum modulation system, the spectral resolution of the stellar magnitude large dynamic range spectrometer system is set to be better than 5nm. Therefore, the grating diffraction surface size is selected as 3.6mm×10mm in this application. According to formulas (1-1) and (1-2), the grating logarithm can be calculated as , so this paper selects the grating constant as .

[0058] After selecting the DMD device and grating, the cylindrical collimation beam expansion system and the stellar magnitude large dynamic range spectrometer system are optimized and designed.

[0059] The stellar magnitude large dynamic range spectrum modulation system uses the zero-order diffraction of the grating for base energy compensation and the negative first-order diffraction for spectrum modulation. Therefore, the stellar magnitude large dynamic range spectroscopic system uses a plane diffraction grating as a dispersion element. At present, the main plane diffraction grating optical system structures are Littrow self-collimation type, Ebert-Fastie type and Czerny-Turner type. Their advantages and disadvantages are shown in Table 2.

[0060]

[0061] According to Table 2, the Czerny-Turner structure has more degrees of freedom in optical design, better ability to correct aberrations, and the plane grating is easy to process, the system is simple to assemble and adjust, and the system has good spectral resolution and imaging quality. Therefore, the Czerny-Turner plane diffraction grating optical structure is selected as the initial structure of the large dynamic range spectroscopic system.

[0062] See also Figure 2 The aberrations existing in the Czerny-Turner type plane diffraction grating optical structure are mainly spherical aberration, coma and astigmatism. Among them, spherical aberration affects the clarity of the spectral line profile, reducing the spectral resolution of the system; coma produces unilateral diffusion of the spectral line profile, causing the spectral line to be clearly imaged on one side and blurred on the other side, which also affects the spectral resolution of the system; at the same time, astigmatism will cause the spectral line to be extended to hundreds of microns, millimeters or even larger along the length of the slit. The existence of astigmatism affects the spatial resolution along the length of the slit. Since the large dynamic range spectroscopic system of star magnitude only requires the spectral line images to be arranged in sequence on the DMD array surface, that is, only the two-dimensional spectral resolution of the spectral line images is required, the spatial resolution of the spectral line images is not required to be high. When designing the large dynamic range spectroscopic system of star magnitude, the correction of spherical aberration and coma should be considered first, and the requirements for astigmatism can be appropriately relaxed. Therefore, in the Czerny-Turner type optical structure, spherical aberration and coma must be strictly corrected.

[0063] In the Czerny-Turner initial structure, the main reason for spherical aberration is the relative aperture of the collimating mirror, and the aperture of the collimating mirror is also the aperture of the system, that is, the beam aperture of the monochromatic light on the imaging mirror after beam splitting. Spherical aberration can be corrected by the collimating mirror; the main reason for coma is the beam width, and coma can be corrected by the imaging mirror. The initial structure design process of the large dynamic range spectroscopic system of magnitude is as follows:

[0064] (1) First determine the off-axis angle of the collimating mirror , Collimating mirror curvature radius , the curvature radius of the imaging mirror , the angle between the incident light beam and the normal line of the grating surface (incident angle) and the diffraction angle of the central wavelength .

[0065] (2) Then according to the coma correction condition , find the off-axis angle of the imaging mirror At this time, the spectroscopic system only corrects the coma for the central wavelength. Due to the diffraction effect of the grating, the off-axis angles of the imaging reflector for different wavelengths are different, so the wavelength and Coma and Have the smallest possible off-axis angle.

[0066] See also Figure 3 , Figure 3 The initial structure optical path diagram of the magnitude large dynamic range spectrometer system designed for this application and the initial structure parameter design results are shown in Table 3.

[0067]

[0068] See also Figure 4~Figure 7 ,according to Figure 4 It can be seen that the resolution is about 20nm and there is a spectral line bending phenomenon. Figure 5~Figure 7 It can be seen that there are relatively serious spherical aberrations at 450nm, 750nm and 1000nm. In addition to spherical aberration at 450nm, coma is also relatively serious. Therefore, the imaging quality of the initial structure is average and needs further optimization.

[0069] The present application adopts a cylindrical collimation beam expansion system to replace the physical slit and collimation reflector in the initial structure of the Czerny-Turner system. The cylindrical collimation beam expansion system can reduce the relative aperture of the system in the dispersion direction, greatly reduce spherical aberration, and further reduce coma, thereby improving the imaging quality of the large dynamic range spectral modulation optical system; at the same time, in the non-dispersion direction, the light beam is expanded to fill the entire system, solving the problem of the contradiction between the slit and the imaging quality in the initial structure.

[0070] See also Figure 8 According to the above analysis, the specific design method for optimizing the optical system of stellar magnitude and large dynamic range spectrum modulation is as follows:

[0071] (1) Determine the output spot diameter of the continuous laser source;

[0072] (2) Determine the beam expansion factor of the cylindrical collimation beam expansion system in the non-dispersive direction based on the output spot diameter of the continuous laser light source and the DMD size. for

[0073] ; (1-3)

[0074] In the formula, is the side length of DMD in non-dispersion direction, is the spot diameter of the continuous laser output;

[0075] (3) The spot diameter output by the cylindrical collimation beam expansion system is used as the aperture diameter of the large dynamic range spectrometer system , whose formula is

[0076] ; (1-4)

[0077] (4) Substitute the number of grating line pairs ;

[0078] (5) Calculate the dispersion angle of each wavelength of the mixed light beam after it passes through the grating, and use the dispersion angle as the half-field angle of the imaging reflector for

[0079] ; (1-5)

[0080] In the formula, and is the spectral range of the incident beam; is the minimum wavelength dispersion angle; is the maximum wavelength dispersion angle;

[0081] (6) According to the DMD array surface size , calculate the focal length of the imaging mirror , where the DMD array surface size consists of two parts, namely the zero-order diffraction energy compensation area and the negative first-order spectrum modulation area. Since the zero-order diffraction energy compensation area is consistent with the effective aperture of the diffraction grating, the size of the negative first-order spectrum modulation area is , focal length of imaging mirror The calculation formula is

[0082] ; (1-6)

[0083] In the formula, It is the length of the DMD array surface along the dispersion direction, that is, the length of the zero-order diffraction energy compensation area along the dispersion direction.

[0084] The cylindrical collimating beam expansion system designed in this paper is an afocal system, which adopts the "negative + positive" optical structure, that is, the combination of the front group negative lens and the rear group positive lens. The "negative + positive" combination can effectively correct the spherical aberration of the system and shorten the length of the cylindrical collimating beam expansion system. According to the principle of collimating beam expansion, the greater the beam expansion ratio, the better the collimation of the light beam. Therefore, it is more conducive to improving the imaging quality of the large dynamic range spectroscopic system with star magnitude.

[0085] The cylindrical collimation and beam expansion system designed in this application is as follows Fig. 9 As shown in the figure, the focal length of the front lens group is -15.73mm, the focal length of the rear lens group is 76.86mm, the interval is 60mm, and the beam expansion factor is 5 times. In the non-dispersive direction, after the light beam is collimated and expanded, the parallelism of the output light is shown in Table 4, and the divergence half angle is reduced from 0.043° (the divergence angle of the continuous laser light source) to 0.0128°.

[0086]

[0087] The cylindrical mirror is introduced into the initial structure of the large dynamic range spectrometer system to replace the slit and collimating reflector. According to the coma elimination condition, the system is optimized and designed, with the imaging reflector as the main optimization parameter to balance the system coma. The structural parameters of the large dynamic range spectrometer system designed by ZEMAX are shown in Table 5. The optical path of the large dynamic range spectrometer system is as follows: Figure 10~Figure 12 shown.

[0088]

[0089] See also Figure 13~Figure 19 , the spherical aberration and coma of the large dynamic range spectroscopic system optimized and designed in this application are compared and analyzed, such as Figure 13~Figure 14 As shown, Take the example of the comparative analysis. Fig.13 is the spectral point diagram of the Czerny-Turner initial structure, Fig.14 This is the spectral point diagram of the stellar magnitude large dynamic range spectroscopic system with a collimating beam expansion system. By comparison, it can be seen that the spherical aberration and coma of the system are greatly reduced. Fig.15 The curve of the RMS radius of the large dynamic range spectrometer system with the change of wavelength is shown in the figure. According to the data in the figure, the RMS radius of the system along the Y direction is less than 26μm. Figure 16~Figure 19 As shown, it can be seen that the spectral resolution of the star-magnitude large dynamic range spectroscopic system is better than 2nm, which meets the design requirement of a spectral resolution better than 5nm.

[0090] 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.

[0091] 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 stellar magnitude large dynamic range spectrum modulation system, characterized in that: The steps include: S1. A cylindrical collimation beam expansion system, a stellar magnitude large dynamic range spectroscopic system and a DMD device are used; the stellar magnitude large dynamic range spectroscopic system is composed of a large dynamic spectroscopic optical system and an energy modulation optical system; the stellar magnitude large dynamic spectroscopic optical system is composed of a steering reflector, a grating, and an imaging reflector; the energy modulation optical system is composed of a steering reflector, a grating, and a plane reflector; S2, select DMD device and grating; S3. Optimize the design of the cylindrical collimation beam expansion system and the star magnitude large dynamic range spectrometer system. The steps are as follows: 1) Determine the output spot diameter of the continuous laser source; 2) Determine the beam expansion multiple of the cylindrical collimation beam expansion system in the non-dispersive direction based on the output spot diameter of the continuous laser light source and the DMD size for ； In the formula, is the side length of DMD in the non-dispersive direction, is the spot diameter of the continuous laser output; 3) The spot diameter output by the cylindrical collimation beam expansion system is used as the aperture diameter of the large dynamic range spectrometer system , whose formula is ； 4) Substitute the number of grating line pairs ; 5) Calculate the dispersion angle of each wavelength of the mixed beam after passing through the grating, and use the dispersion angle as the half field angle of the imaging reflector for ； In the formula, and is the spectral range of the incident beam; is the minimum wavelength dispersion angle; is the maximum wavelength dispersion angle; 6) According to the DMD array surface size , calculate the focal length of the imaging mirror , where the DMD array surface size consists of two parts, namely the zero-order diffraction energy compensation area and the negative first-order spectrum modulation area. Since the zero-order diffraction energy compensation area is consistent with the effective aperture of the diffraction grating, the size of the negative first-order spectrum modulation area is , focal length of imaging mirror The calculation formula is ； In the formula, It is the length of the DMD array surface along the dispersion direction, that is, the length of the zero-order diffraction energy compensation area along the dispersion direction.

2. The design method of a star magnitude large dynamic range spectrum modulation system as claimed in claim 1, characterized in that: The Czerny-Turner type plane diffraction grating optical structure is selected as the initial structure of the stellar magnitude large dynamic range spectrometer system.

3. The design method of a star magnitude large dynamic range spectrum modulation system as claimed in claim 2, characterized in that: The stellar magnitude large dynamic range spectrometer system adopts a cylindrical collimating beam expansion system to replace the physical slits and collimating mirrors in the Czerny-Turner type plane diffraction grating optical structure.

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