An optical system of high sampling efficiency integral field spectrometer and its design method

Abstract

The present invention discloses an optical system of a high sampling efficiency integral field spectrometer and a design method thereof. The optical system includes a slit module, a narrowband filter module, a collimation module and a dispersion module arranged in sequence along the transmission direction of the optical path; the angle between the normal of the collimation module and the normal of the dispersion module is equal to the incident angle of the dispersion module when in use, the angle between the normal of the dispersion module and the normal of the imaging module is equal to the diffraction angle of the dispersion module when the dispersion is used, and the imaging module and the reflection detector module are arranged in a straight line. The present invention can significantly reduce the number of terminal spectrometers of the observation telescope, or increase the size of the observation field when the number of spectrometers is constant; and realize the observation of objects with high time resolution.

Description

Technical Field

[0001] The invention belongs to the technical field of optical equipment, and in particular relates to an optical system of a high sampling efficiency integral field spectrometer and a design method thereof. Background Art

[0002] In recent years, with the rapid development of astronomical technology, many astronomical telescopes at home and abroad currently use IFU to replace the slits in general spectrometers to link telescopes and spectrometer systems to form fiber optic imaging spectrometers. Traditional spectrometer observations are to obtain spectral information. To obtain two-dimensional spatial information, the slit needs to be scanned in space to obtain two-dimensional information. The disadvantage of this method is low temporal resolution. The IFU consists of a microlens array end and a pseudo-slit end. The microlens array end divides the two-dimensional spatial image, which is then transmitted through the optical fiber. The pseudo-slit formed by rearranging the output end is placed at the incident end of the spectrometer for dispersion, thereby achieving simultaneous acquisition of two-dimensional spatial information and one-dimensional spectral information, providing the possibility of high temporal resolution observations. However, when using an integral field of view unit for observation, a large number of optical fibers are required to obtain a large two-dimensional field of view information. Therefore, the development of a high sampling efficiency integral field of view spectrometer is an important guarantee for ensuring high temporal resolution spectral imaging observations. For example, for my country's future large-scale coronagraph, a single IFU contains more than 100,000 spatial sampling points, and the use of paired IFU technology requires more than 200,000 optical fibers. Such a huge number of optical fibers puts forward an urgent need for a high-sampling efficiency integral field-of-view spectrometer.

[0003] Currently, there is no high sampling efficiency integral field spectrometer (or high sampling efficiency fiber spectrometer) that can perform spectral dispersion on thousands of optical fibers simultaneously. Summary of the invention

[0004] In response to the demand for high sampling efficiency integral field spectrometers, the present invention discloses an optical system of a high sampling efficiency integral field spectrometer and a design method thereof. A spectrometer of the present invention can accommodate thousands of optical fibers, and the method will be applied to astronomical telescopes or other spectral equipment that need to use a large number of optical fiber IFUs for high sampling efficiency observations. The method disclosed in the present invention is used to develop a high sampling efficiency integral field spectrometer that can accommodate 7,000 optical fibers for simultaneous dispersion, and the method will also be used in the high sampling efficiency integral field spectrometer of my country's large coronagraph terminal in the future.

[0005] In order to solve the above technical problems, the present invention discloses a high sampling efficiency integral field spectrometer optical system, which includes a slit module, a narrowband filter module, a collimation module and a dispersion module arranged in sequence along the transmission direction of the light path; the angle between the normal of the collimation module and the normal of the dispersion module is equal to the incident angle of the dispersion module when in use, the angle between the normal of the dispersion module and the normal of the imaging module is equal to the diffraction angle of the dispersion module when the dispersion is in use, and the imaging module and the reflection detector module are arranged in a straight line.

[0006] Optionally, the slit module includes a plurality of slit units arranged in parallel, each slit unit includes a first slit mechanism and a second slit mechanism, a 30 mm interval is provided between the first slit mechanism and the second slit mechanism, and each first slit mechanism and the second slit mechanism are composed of the same number of optical fibers.

[0007] Optionally, each of the first slit mechanism and the second slit mechanism comprises 500 optical fibers arranged at intervals of 120 μm, and the length of each of the first slit mechanism and the second slit mechanism is 60 mm; the first slit mechanism, the intervals and the second slit mechanism are on the same straight line.

[0008] Optionally, the narrow-band filter module is a narrow-band filter.

[0009] Optionally, the collimation module includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens arranged in sequence along the light transmission direction; the materials of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are H-ZK6, H-K9L, H-K3, H-F51, FCD100 and LAF3 respectively.

[0010] Optionally, the dispersion module is a ruled reflective grating.

[0011] Optionally, the imaging module includes a seventh lens, an eighth lens, a ninth lens, a tenth lens, an eleventh lens and a twelfth lens arranged in sequence along the diffraction direction of the light path; the materials of the seventh lens, the eighth lens, the ninth lens, the tenth lens, the eleventh lens and the twelfth lens are H-LAK11, H-LAK11, ZF52, Fused silica, ZF52, ZF52 in sequence.

[0012] Optionally, the reflection detector module includes a plane reflector and a detector, the detector includes a first detector and a second detector, and the plane reflector is placed between the detector and the imaging module; the first detector is arranged in parallel with the twelfth lens, and the image of the first slit mechanism in the slit unit is directly irradiated and imaged on the first detector after being emitted from the twelfth lens; the second detector is placed below the plane reflector, and the plane reflector is placed between the second detector and the twelfth lens, at 45° to the second detector and the twelfth lens (5-6), and the image of the second slit mechanism in the slit unit is emitted from the twelfth lens and reflected by the plane reflector and then irradiated and imaged on the second detector.

[0013] The present invention also discloses a design method for the optical system of the high sampling efficiency integral field spectrometer, comprising the following steps:

[0014] Step 1: Determine the grating parameters:

[0015] The grating equation is:

[0016] d(sinα+sinβ)=mλ (1)

[0017] Where m is the diffraction order, λ is the wavelength, d is the grating constant, α is the incident angle of the reflection grating, β is the diffraction angle, α and β have the same sign, indicating that the incident angle and the diffraction angle are on the same side of the grating normal, and different signs indicate that the incident angle and the diffraction angle are on both sides of the grating normal; The resolution expression of the spectrometer is:

[0018]

[0019] Where Δβ is the angle between the two wavelengths λ and λ+Δλ. Then the focal length fs of the imaging system corresponding to the distance s between the two wavelengths λ and λ+Δλ on the spectrometer detector is:

[0020] fs=s / Δβ (3)

[0021] Then the focal length fc of the collimation system in front of the grating is:

[0022] fc=fs / M (4)

[0023] Where M is the magnification of the spectrometer system, which is determined by the detector target size D, the number of optical fibers N required to be imaged on the detector, and the optical fiber arrangement interval L. Its expression is:

[0024] M=D / (N×L) (5)

[0025] The grating size used in the spectrometer is related to the incident light focal ratio Fin, Lg is the length of the grating line direction, and Wg is the length of the grating dispersion direction:

[0026] Lg=fc / Fin (6)

[0027] Wg=Lg / cosα (7)

[0028] In the design of the spectrometer, the spatial arrangement direction of the fiber array at the output end of the integral field unit (IFU) and the dispersion direction of each fiber are perpendicular to the detector; the overall resolution of the spectrometer is determined by multiple factors, including: the resolution of the grating, the width of the slit, the size of the detector and the size of the dispersion spot; in order to achieve the spectral resolution index of the spectrometer design, in the dispersion direction, the distance s between the two wavelengths λ and λ+Δλ on the detector must be at least greater than or equal to the size of the image of an optical fiber on the detector along the dispersion direction; formula (5) is the magnification of the spectrometer in the spatial direction of the optical fiber; the magnification M' of the spectrometer in the dispersion direction is expressed as:

[0029] M'=Mcosα / cosβ (8)

[0030] Then the image size O' of each optical fiber's core diameter on the detector along the dispersion direction is:

[0031] O'=M'×O (9)

[0032] Where O is the optical fiber core diameter; this spectrum design must satisfy the following relationship:

[0033]

[0034] Where η is the size of a single pixel of the detector;

[0035] Based on the detector parameters, slit length and spectrometer resolution requirements, the spectrometer design parameters are calculated and analyzed according to formulas (1)-(10), and the grating parameter size, line density and blaze wavelength in the spectrometer are selected and determined;

[0036] Step 2: Determine the number of slits in slit module 1

[0037] The number of slits in a multi-slit integral field spectrometer is related to many parameters, such as the size of the detector target, spectral resolution, observation band, and other factors. After being dispersed by the spectrometer system, each sub-slit is imaged on the detector target, and the size Nsi occupied along the dispersion direction is:

[0038] Nsi=s·(τ0+τ1+τ2) / Δλ (11)

[0039] Where τ0, τ1, and τ2 represent the central observation band width of the narrowband filter and the band width corresponding to the rising and falling edges of the narrowband filter, respectively; on the detector, the spectra after dispersion of multiple slits cannot overlap, so the number of incident end slits that can be accommodated on the detector is Ns:

[0040] Ns≤ integer (D / (Nsi+Δd)) (12)

[0041] Where Δd is the size of the dark area between the images of two adjacent slits on the detector along the dispersion direction after dispersion;

[0042] From formulas (11) and (12), we know that for narrow-band filters, the smaller τ0, τ1, and τ2 are, the more slits are observed at one time. Therefore, when customizing filters, it is necessary to ensure that τ1 and τ2 are as small as possible, that is, the rising and falling edges of the narrow-band filter's transmittance changing with wavelength are steep;

[0043] Step 3: Adopt refractive optical design: Due to the multi-slit integral field spectrometer design, the object plane size of the spectrometer is too large. In the absence of obstruction, the reflective structure is difficult to achieve a two-dimensional large field of view design; for a 7-slit integral field spectrometer design, the object plane size reaches 60mm×150mm, which puts forward requirements for the glass material of the optical design, because the size of the mirror blank of the general optical material is 160mm in diameter; but considering that the observation band range is not large, the glass materials used in the optical design are all selected from the Chengdu Guangming Large Glass Warehouse;

[0044] Step 4. Considering that the use of the integral field of view unit is to achieve spectral imaging of the observed object, the image needs to be reconstructed, which requires that the light energy loss of each optical fiber be consistent. In the design, the spectrometer system adopts an object-side telecentric optical path design, and the grating is placed at the exit pupil of the collimation system.

[0045] Compared with the prior art, the present invention can achieve the following technical effects:

[0046] 1) The high sampling efficiency integral field spectrometer proposed in the present invention can significantly reduce the number of observation telescope terminal spectrometers using IFU equipment, or increase the size of the observation field of view (ie, the number of optical fibers) when the number of spectrometers is constant.

[0047] 2) The present invention adopts a core technical solution of combining a multi-slit unit and two-slit sections, matching the bandpass filter and the detector front reflector to achieve high sampling efficiency spectral observation, and realizing an integral field of view spectrometer that can simultaneously obtain a large field of view two-dimensional spatial information and one-dimensional spectral information, thereby achieving high temporal resolution observation of objects (such as the sun).

[0048] 3) For telescope equipment that requires a large number of optical fibers for observation at the same time, such as my country's future large-scale coronagraph, this high sampling efficiency integral field spectrometer can significantly reduce the number of terminal spectrometers and the size of terminal equipment of the observation telescope.

[0049] Of course, any product implementing the present invention does not necessarily need to achieve all of the above-mentioned technical effects at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0051] Figure 1 It is a structural schematic diagram of the optical system of the high sampling efficiency integral field spectrometer of the present invention;

[0052] Figure 2 The present invention Figure 1 A magnified view of middle;

[0053] Figure 3 is a schematic structural diagram of a slit module of the present invention;

[0054] Figure 4 The present invention Figure 1 Enlarged view of middle B;

[0055] Figure 5 This is a diagram of the image points on the detector of the optical system of the high sampling efficiency integral field spectrometer provided by the present invention at a wavelength of 519.85nm; wherein the black circle represents the size of the Airy spot;

[0056] Figure 6 This is a diagram of the image particles on the detector of the optical system of the high sampling efficiency integral field spectrometer provided by the present invention at a wavelength of 525.15nm; wherein the black circle represents the size of the Airy spot;

[0057] Figure 7 This is a diagram of the image particles on the detector of the optical system of the high sampling efficiency integral field spectrometer provided by the present invention at a wavelength of 530.45nm; wherein the black circle represents the size of the Airy spot;

[0058] Figure 8 It is a schematic diagram of the spectral resolution capability of the optical system of the high sampling efficiency integrating field spectrometer provided by the present invention (satisfying R=5800@530nm). DETAILED DESCRIPTION

[0059] The following will describe the implementation methods of the present invention in detail with reference to examples, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0060] The present invention provides a high sampling efficiency integral field spectrometer optical system, which is a technical solution combining multiple slits and two-stage slits, and simultaneously matching the bandpass filter and the detector front reflector to improve the sampling efficiency of the spectrometer from two dimensions of the spectrometer dispersion direction and the spatial direction. Figure 1 As shown, along the transmission direction of the optical path, it includes a slit module 1, a narrowband filter module 2, a collimation module 3, and a dispersion module 4 arranged in sequence; the angle between the normal line of the collimation module 3 and the normal line of the dispersion module 4 is equal to the incident angle corresponding to the grating in the dispersion module 4 when in use (α in formula (1)); the angle between the normal line of the dispersion module 4 and the normal line of the imaging module 5 is equal to the diffraction angle corresponding to the grating in the dispersion module 4 when in use (β in formula (1)), and the imaging module 5 and the reflection detector module 6 are arranged in a straight line.

[0061] Among them, the slit module 1 includes a plurality of parallel arranged slit units 1-1, each slit unit 1-1 includes a first slit mechanism 1-2 and a second slit mechanism 1-3, a 30mm interval 1-4 is arranged between the first slit mechanism 1-2 and the second slit mechanism 1-3, and each first slit mechanism 1-2 and the second slit mechanism 1-3 are composed of the same number of optical fibers 1-5.

[0062] The slit module 1 adopts a technical solution combining multiple slits and two-stage slits. Multiple slit units are arranged in parallel at intervals and each single slit is further divided into two sub-slits (the first slit mechanism 1-2 and the second slit mechanism 1-3) with an interval of 30 mm to improve the sampling efficiency of the spectrometer from two dimensions: the dispersion direction and the spatial direction of the spectrometer.

[0063] The narrowband filter module 2 is a narrowband filter whose transmittance changes with wavelength with rising and falling edges as steep as possible. The narrowband filter is placed between the slit module 1 and the collimation module 3 .

[0064] All slits pass through the same narrow-band filter to ensure that the spectra dispersed by multiple slits do not overlap on the detector, thus ensuring the validity of the spectral data.

[0065] The collimation module 3 includes a first lens 3-1, a second lens 3-2, a third lens 3-3, a fourth lens 3-4, a fifth lens 3-5 and a sixth lens 3-6 which are arranged in sequence along the spectral transmission direction; the materials of the first lens 3-1, the second lens 3-2, the third lens 3-3, the fourth lens 3-4, the fifth lens 3-5 and the sixth lens 3-6 are H-ZK6, H-K9L, H-K3, H-F51, FCD100 and LAF3 respectively; the collimation module 3 is placed after the narrow-band filter module 2.

[0066] Collimation module: The light emitted from all slit segments is collimated into parallel light by the same collimation system and then irradiated onto the same reflection grating.

[0067] The dispersion module 4 is a reflective grating. The incident light beam from the slit module 1 is collimated by the collimation module 3 and then irradiated on the reflective grating in the dispersion module 4 for dispersion. The light beam diffracted by the grating enters the imaging module 5 .

[0068] The imaging module 5 comprises a seventh lens 5-1, an eighth lens 5-2, a ninth lens 5-3, a tenth lens 5-4, an eleventh lens 5-5 and a twelfth lens 5-6 which are sequentially arranged along the diffraction direction of the optical path; the materials of the seventh lens 5-1, the eighth lens 5-2, the ninth lens 5-3, the tenth lens 5-4, the eleventh lens 5-5 and the twelfth lens 5-6 are H-LAK11, H-LAK11, ZF52, Fused silica, ZF52 and ZF52 respectively; the imaging system module 5 is located in the optical path of the diffracted light of the dispersion module 4 in the emitting direction, and converges the diffracted light to form an image on the detector in the reflection detector module 6.

[0069] The reflection detector module 6 includes a plane reflector 6-1 and a detector, and the detector includes a first detector 6-2 and a second detector 6-3. The plane reflector 6-1 is placed between the detector and the imaging module 5; the first detector 6-2 is arranged in parallel with the twelfth lens 5-6, and the image of the first slit mechanism 1-2 in the slit unit 1-1 is directly irradiated and imaged on the first detector 6-2 after being emitted from the twelfth lens 5-6; the second detector 6-3 is placed below the plane reflector 6-1, and the plane reflector 6-1 is placed between the second detector 6-3 and the twelfth lens 5-6, and is 45° to the second detector 6-3 and the twelfth lens 5-6. The image of the second slit mechanism 1-3 in the slit unit 1-1 is emitted from the twelfth lens 5-6 and reflected by the plane reflector 6-1 and then irradiated and imaged on the second detector 6-3.

[0070] Among them, the reflection detector module: uses a plane reflector 6-1 to separately image the sub-slits (the first slit mechanism 1-2 and the second slit mechanism 1-3) divided into two sections onto the first detector 6-2 and the second detector 6-3.

[0071] The slit module 1 of the optical system of the present invention uses a plurality of slit units 1-1 arranged side by side in combination with a narrowband filter 2 to ensure that the spectrum after dispersion of each slit does not overlap on the detector, and the plane reflector 6-1 placed in front of the final detector separates the diffracted imaging light of the two slits (the first slit mechanism 1-2 and the second slit mechanism 1-3) and images them on the first detector 6-2 and the second detector 6-3, thereby improving the sampling efficiency of the spectrometer from two dimensions: the dispersion direction and the spatial direction of the spectrometer. The slits at all incident ends of the spectrometer are collimated by the same collimation system 3, and then irradiated on the reflection grating 4 for diffraction. The diffracted light beams are then imaged by the same imaging system 5. Because all optical systems are shared, it is truly realized that one spectrometer is equivalent to the work of two spectrometers. It should be noted that since the front slit adopts a combination of multiple slits and two-stage slits, the grating of this scheme cannot work under Littrow conditions, that is, the grating incident light and diffracted light cannot share a set of optical systems, and a double-pass structure cannot be used.

[0072] The present invention also discloses a design method for an optical system of a high sampling efficiency integral field spectrometer, comprising the following steps:

[0073] Step 1, the incident end of the spectrometer (slit module 1) adopts a technical solution combining multiple slit units 1-1 and two-segment slit first slit mechanism 1-2 and second slit mechanism 1-3. Multiple slit units 1-1 are arranged in parallel at a certain interval along the dispersion direction of the spectrometer to improve the sampling efficiency, and along the spatial direction of the slit, each slit unit 1-1 is further divided into a first slit mechanism 1-2 and a second slit mechanism 1-3 with an interval of 30 mm to improve the sampling efficiency; Figure 3 Schematic diagram of the slit arrangement at the incident end of the spectrometer shown.

[0074] Step 2: Combine the slit module 1 with the narrowband filter module 2. The front end of the spectrometer adopts a multi-slit design. It is necessary to match the appropriate narrowband bandpass filter to ensure that the spectra after dispersion of each slit do not overlap on the detector, ensure the validity of the spectral data, and improve the sampling efficiency of the spectrometer from the dispersion direction of the spectrometer. The number of slits in the spectrometer is related to the size of the detector target, the instrument resolution, and the observation bandwidth. The specific relationship is shown in formulas (11)-(12).

[0075] Step 3: Each slit is divided into two sections ( Figure 3The first slit mechanism 1-2 and the second slit mechanism 1-3 in the detector are used in combination with the flat reflector 6-1 in front of the detector to ensure that the spectra dispersed by the two segmented slits enter two different detectors (the first detector 6-2 and the second detector 6-3) respectively. The incident light of all the slits at the incident end of the entire spectrometer passes through the same set of narrow-band filter modules 2, collimation modules 3, dispersion modules 4 and imaging systems 5, so that one spectrometer can truly realize the functions of two spectrometers, greatly reducing the number and size of spectrometers; and improving the sampling efficiency of the spectrometer along the spatial direction of the spectrometer.

[0076] Step 4. This solution is suitable for using a refractive structure, but not for using a reflective structure, that is, the collimation system and the imaging system optical elements are both designed with a lens refractive structure. This is because the core technology used in this spectrometer is the combination of multiple slits and two-stage slits. Because of this structure, the incident end of the spectrometer is no longer a traditional single slit, or multiple slits arranged in a row, but a two-dimensional object surface. If a reflective structure is used, in order to avoid light being blocked in the spectrometer system, an off-axis reflective structure must be used, and the off-axis reflective structure is not conducive to imaging of large-size two-dimensional objects. Therefore, in terms of design, the collimation system and the imaging system use a refractive structure.

[0077] Example 1

[0078] The embodiment of the present invention adopts the above-mentioned high sampling efficiency integral field spectrometer optical system. This embodiment is mainly aimed at the solar corona observation band of 519.85nm-530.45nm. In addition, there are also abundant solar chromosphere and photosphere spectral lines within this band, and the observation of solar photosphere and chromosphere can also be realized. After successful development, it will be installed at the rear end of the FASOT-1B telescope at the Lijiang Astronomical Observatory of the Yunnan Astronomical Observatory of the Chinese Academy of Sciences. It can increase the current telescope observation field by nearly 30 times, and is used for in-depth research and understanding of solar activities, and to solve the core problems of solar physics such as the mechanism of violent activity of the solar atmosphere, solar wind acceleration and coronal heating. In addition, the high sampling efficiency integral field spectrometer optical system is also the first high sampling efficiency integral field spectrometer prototype that meets the requirements of the future development of my country's 1.2-meter world's largest refractive coronagraph. This high sampling efficiency integrating field spectrometer is mainly used to observe the coronal spectral lines. Considering the weak energy of the corona, in order to avoid too long exposure time, the spectral resolution meets 5800@530nm; the observation band is: 519.85nm-530.45nm.

[0079] The present invention adopts a method of combining multiple slits and two-stage slits to complete the design of the optical system of the high sampling efficiency integral field spectrometer. The grating is the core component of the spectrometer (i.e., the optical system of the high sampling efficiency integral field spectrometer, the same below). First, a suitable grating must be selected. The grating equation is:

[0080] d(sinα+sinβ)=mλ (1)

[0081] Where m is the diffraction order, λ is the wavelength, d is the grating constant, α is the incident angle of the reflection grating, β is the diffraction angle, and α and β have the same sign, indicating that the incident angle and diffraction angle are on the same side of the grating normal, and different signs indicate that the incident angle and diffraction angle are on both sides of the grating normal. Spectrometer resolution expression:

[0082]

[0083] Where Δβ is the angle between the two wavelengths λ and λ+Δλ. Then the focal length fs of the imaging system corresponding to the distance s between the two wavelengths λ and λ+Δλ on the spectrometer detector is:

[0084] fs=s / Δβ (3)

[0085] Then the focal length fc of the collimation system in front of the grating is:

[0086] fc=fs / M (4)

[0087] Where M is the magnification of the spectrometer system, which is determined by the detector target size D, the number of optical fibers N required to be imaged on the detector, and the optical fiber arrangement interval L. Its expression is:

[0088] M=D / (N×L) (5)

[0089] The grating size used in the spectrometer is related to the incident light focal ratio Fin, Lg is the length of the grating line direction, and Wg is the length of the grating dispersion direction:

[0090] Lg=fc / Fin (6)

[0091] Wg=Lg / cosα (7)

[0092] In the design of the spectrometer, the spatial arrangement direction of the optical fiber array at the IFU output end and the dispersion direction of each optical fiber are perpendicular to the detector. The overall resolution of the spectrometer is determined by a variety of factors, including: the resolution of the grating, the width of the slit, the size of the detector and the size of the dispersion spot. In order to achieve the spectral resolution index of the spectrometer design, in the dispersion direction, the distance s separating the two wavelengths λ and λ+Δλ on the detector must be at least greater than or equal to the size of the image of an optical fiber on the detector along the dispersion direction. Equation (5) is the magnification of the spectrometer in the spatial direction of the optical fiber. Due to the particularity of the grating itself, the magnification of the spectrometer in the optical fiber dispersion direction is different from that in its spatial direction. The magnification M' of the spectrometer in the dispersion direction is expressed as:

[0093] M'=Mcosα / cosβ (8)

[0094] Then the image size O' of each optical fiber's core diameter on the detector along the dispersion direction is:

[0095] O'=M'×O (9)

[0096] Where O is the fiber core diameter. Of the four factors mentioned above that affect the resolution of the spectrometer, the factor with the lowest resolution plays a decisive role. Generally, when they are similar, the resolution is the square root of the sum of their squares. Because the grating itself has a high resolution and will not limit the resolution of the spectrometer, the spectrum design must satisfy the following relationship:

[0097]

[0098] Where η is the size of a single pixel in the detector. The most reasonable design is to match these factors with each other, especially not to affect the original resolution ability because of the detector.

[0099] For the optical system of high sampling efficiency integral field spectrometer, the detector is the SCOMS camera with the largest target surface in China, with a chip of 6144 pixels×6144 pixels, a single pixel size of 10μm / pixel, and a detector target surface size of 61.44 mm. The total length of the incident end slits 1-2, 1-3 and 1-4 is 150mm, of which the lengths of 1-2 and 1-3 are 60mm respectively (corresponding to 500 optical fibers arranged at intervals of 120μm), and are imaged on two detectors respectively. In the spatial direction of the optical fiber arrangement, the system magnification M=61.44 / 60=1.024. Considering the spectral bending, a part of the dark area should be left around the detector target surface, and the magnification value is M=0.95. The two wavelengths λ and λ+Δλ that meet the spectral resolution R=5800@530nm are separated by a distance s of 37μm on the detector, and the incident angle ratio of the spectrometer system is Fin / 5. Based on the above detector parameters, slit length and spectrometer resolution, according to the spectrometer design calculation and analysis formulas (1)-(10), the grating is a commercial Richardson grating, model 53-260 commercial ruled grating. Other specific parameters of the optical system are as follows: 1) Collimation system focal length fc = 720mm, imaging system focal length fs = 685mm, 2) Grating incident angle: α = 22°, diffraction angle: β = -3.245 (530nm). 3) Grating size: Lg = 144mm, Wg = 155mm. 4) Magnification M' in the dispersion direction = 0.88.

[0100] Secondly, calculate the number of slits that the spectrometer can accommodate. After each sub-slit is dispersed by the spectrometer system, it is imaged on the detector target surface, and the size Nsi occupied along the dispersion direction is:

[0101] Nsi=s·(τ0+τ1+τ2) / Δλ (11)

[0102] Where τ0, τ1, and τ2 represent the central observation band width of the narrowband filter and the band width corresponding to the rising and falling edges of the narrowband filter, respectively. On the detector, the spectra after dispersion of multiple slits cannot overlap, so the number of incident end slits that can be accommodated on the detector is Ns:

[0103] Ns≤take an integer ((D+(τ1+τ1) / Δλ) / (Nsi+Δd)) (12)

[0104] Where Δd is the size of the dark area between the images of two adjacent slits on the detector along the dispersion direction after dispersion.

[0105] From formulas (11) and (12), we can see that for narrow-band filters, the smaller τ0, τ1, and τ2 are, the more slits can be observed at one time. Therefore, when customizing filters, it is necessary to ensure that τ1 and τ2 are as small as possible, that is, the rising and falling edges of the narrow-band filter transmittance as the wavelength changes are steep. At present, the rising and falling edge transmittance of domestic filters has reached 10 －5 Tmax, the corresponding τ1 and τ2 are 5nm. The observation band τ0 is 10.6nm, Δd is 20 pixels on the detector, and Ns≤7.3 can be obtained by formula (11)-(12), and the integer Ns=7. Therefore, the optical system of the high sampling efficiency integral field spectrometer has a total of 7 slits, each of which is divided into two sections, which can accommodate 7×500×2=7000 optical fibers.

[0106] Considering the later observation requirements of the optical system of the high sampling efficiency integral field spectrometer, it can be matched with different telescopes for observation. The spectrometer is required to be easy to move, compact in structure, and not too large in size. In addition, the object size of the spectrometer composed of 7 slits is too large. In the absence of obstruction, it is difficult for the reflective structure to achieve a 4.8°×11.8° large field of view design. Based on the above two points, the optical design of this project adopts a refractive optical design. Since the object size is 60mm×150mm, requirements are put forward for the glass material of the optical design, because the size of the mirror blank of general optical materials is 160mm in diameter. However, considering that the observation band range is not large, it also provides the possibility of using refractive optical design. The glass materials used in the optical design are all selected from the Chengdu Guangming Large Glass Library. In addition, considering that the use of the integral field unit is to realize the spectral imaging of the observed object, the image needs to be reconstructed, which requires that the light energy loss of each optical fiber be consistent. The spectrometer system in the design adopts the object telecentric optical path design, and the grating is placed at the exit pupil of the collimation system.

[0107] The optical system design of the high sampling efficiency integral field spectrometer of the embodiment of the present invention is as follows: Figure 1 shown. Figure 1The middle slit 1 is a pseudo-slit composed of 7000 optical fibers arranged at intervals of 120 μm (e.g. Figure 3 As shown in the figure, the slit uses 7 slit units, each of which is divided into two sections. The interval between the two sub-slits (the first slit mechanism 1-2 and the second slit mechanism 1-3) is 30mm, which can accommodate 7000 optical fibers in total. The incident light from the 7 slits in the slit module 1 first passes through the bandpass filter 2, and then is collimated by the collimation module 3 composed of 6 large lenses and irradiated on the dispersion module 4 for dispersion. The dispersed spectrum is then imaged on the detector in the reflection detector module 6 through the imaging module 5 composed of 6 large lenses. A reflector 6-1 is placed at a distance of 150mm from the front end of the reflection detector module 6 to separate the diffracted imaging light of the sub-slit divided into two sections at the incident end and imaged on two different detectors 6-2 and 6-3. This achieves the effect of one spectrometer being equivalent to the work of two spectrometers.

[0108] Figure 5-Figure 7 This is the image quality point diagram on the detector of the optical system of the high sampling efficiency integral field spectrometer. The point diagrams of the first, fourth and seventh slits in slit 1 at wavelengths of 519.85nm, 525.15nm and 530.45nm are given. Only the image quality diagram on one detector is shown here, and the other is consistent with it. The black circle in the figure represents the size of the Airy spot under the diffraction limit condition. The point diagram of the optical system design of the spectrometer is basically within the Airy disk, close to the diffraction limit imaging, and the optical system has a very good image quality.

[0109] The system resolution is 5800@530nm, that is, after the light beam emitted from any optical fiber at the slit is dispersed by the grating, the optical fiber image with a wavelength of 530nm (λ) can be distinguished from the optical fiber image with a wavelength of 530+530 / 5800=530.091379nm (λ+dλ) on the detector. Figure 8 This is a schematic diagram of the spectrometer's resolution. Each grid in the figure corresponds to 10μm. The three wavelengths of 530nm (λ), 530.091379nm (λ+dλ) and 529.908621nm (λ-dλ) emitted from a point on the slit are separated by 36μm on the detector. The maximum size of the imaging point diffuse spot diameter (RMS value) is 4.5μm. The ideal imaging size (point object into point image) of the 35μm fiber core diameter on the detector along the dispersion direction is 30μm. Therefore, the imaging size (along the dispersion direction) of the λ wavelength (530nm) corresponding to the 35μm fiber core diameter on the detector is (The distance between λ and λ+dλ on the detector). Therefore, the three wavelengths of 530nm, 530.091379nm and 529.908621nm emitted from the same optical fiber can be separated on the detector, meeting the design requirement of R=5800@530nm resolution.

[0110] This embodiment can accommodate a high sampling efficiency integral field spectrometer optical system for simultaneous sampling of 7000 optical fibers arranged at an interval of 120 μm. The high sampling efficiency integral field spectrometer optical system has been put into engineering processing. At the same time, the developed high sampling efficiency integral field spectrometer will solve the core technology of the world's largest 1.2-meter refractive coronagraph in the future, and provide technical support for the high sampling efficiency spectrometer required by its terminal.

[0111] The above description shows and describes several preferred embodiments of the invention, but as mentioned above, it should be understood that the invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. Changes and modifications made by those skilled in the art should be within the scope of protection of the claims attached to the invention without departing from the spirit and scope of the invention.

Claims

1. A high sampling efficiency integral field spectrometer, characterized in that: Along the transmission direction of the optical path, it comprises a slit module (1), a narrowband filter module (2), a collimation module (3), a dispersion module (4), an imaging module (5), and a reflection detector module (6) which are arranged in sequence; the angle between the normal line of the collimation module (3) and the normal line of the dispersion module (4) is equal to the incident angle of the dispersion module (4) when in use, the angle between the normal line of the dispersion module (4) and the normal line of the imaging module (5) is equal to the diffraction angle of the dispersion module (4) when in dispersion use, and the imaging module (5) and the reflection detector module (6) are arranged in a straight line; The slit module (1) comprises a plurality of slit units (1-1) arranged in parallel, each slit unit (1-1) comprises a first slit mechanism (1-2) and a second slit mechanism (1-3), a gap (1-4) is arranged between the first slit mechanism (1-2) and the second slit mechanism (1-3), and each first slit mechanism (1-2) and the second slit mechanism (1-3) are composed of the same number of optical fibers (1-5); The first slit mechanism (1-2), the interval (1-4) and the second slit mechanism (1-3) are on the same straight line; The reflection detector module (6) comprises a plane reflection mirror (6-1) and a detector, wherein the detector comprises a first detector (6-2) and a second detector (6-3), and the plane reflection mirror (6-1) is disposed between the detector and the imaging module (5); the twelfth lens (5-6) is the last lens of the imaging module (5); the first detector (6-2) and the twelfth lens (5-6) are arranged in parallel, and the image of the first slit mechanism (1-2) in the slit unit (1-1) is directly emitted from the twelfth lens (5-6) The second detector (6-3) is placed below the plane reflector (6-1), and the plane reflector (6-1) is placed between the second detector (6-3) and the twelfth lens (5-6), and is at an angle of 45° to both the second detector (6-3) and the twelfth lens (5-6). The image of the second slit mechanism (1-3) in the slit unit (1-1) is emitted from the twelfth lens (5-6), reflected by the plane reflector (6-1), and then irradiated and imaged on the second detector (6-3); The imaging module (5) is located in the optical path of the diffracted light of the dispersion module (4) in the emitting direction, and converges the diffracted light to form an image on a detector in the reflection detector module (6).

2. The high sampling efficiency integral field spectrometer according to claim 1, characterized in that: Each of the first slit mechanism (1-2) and the second slit mechanism (1-3) comprises 500 optical fibers (1-5) arranged at intervals of 120 μm, and each of the first slit mechanism (1-2) and the second slit mechanism (1-3) has a length of 60 mm.

3. The high sampling efficiency integral field spectrometer according to claim 1, characterized in that: The narrow-band filter module (2) is a narrow-band filter.

4. The high sampling efficiency integral field spectrometer according to claim 1, characterized in that: The collimating module (3) comprises a first lens (3-1), a second lens (3-2), a third lens (3-3), a fourth lens (3-4), a fifth lens (3-5) and a sixth lens (3-6) which are sequentially arranged along the light transmission direction; the materials of the first lens (3-1), the second lens (3-2), the third lens (3-3), the fourth lens (3-4), the fifth lens (3-5) and the sixth lens (3-6) are H-ZK6, H-K9L, H-K3, H-F51, FCD100 and LAF3 respectively.

5. The high sampling efficiency integral field spectrometer according to claim 1, characterized in that: The dispersion module (4) is a ruled reflective grating.

6. The high sampling efficiency integral field spectrometer according to claim 1, characterized in that: The imaging module (5) comprises a seventh lens (5-1), an eighth lens (5-2), a ninth lens (5-3), a tenth lens (5-4), an eleventh lens (5-5) and a twelfth lens (5-6) which are sequentially arranged along the diffraction direction of the optical path; the materials of the seventh lens (5-1), the eighth lens (5-2), the ninth lens (5-3), the tenth lens (5-4), the eleventh lens (5-5) and the twelfth lens (5-6) are H-LAK11, H-LAK11, ZF52, Fused silica, ZF52 and ZF52 respectively.

7. A design method for a high sampling efficiency integral field spectrometer according to claim 1, characterized in that: The following steps are involved: Step 1: Determine the grating parameters: The grating equation is: d(sinα+sinβ)=mλ (1) Where m is the diffraction order, λ is the wavelength, d is the grating constant, α is the incident angle of the reflection grating, β is the diffraction angle, α and β have the same sign, indicating that the incident angle and the diffraction angle are on the same side of the grating normal, and different signs indicate that the incident angle and the diffraction angle are on both sides of the grating normal; The resolution expression of the spectrometer is: Where Δβ is the angle between the two wavelengths λ and λ+Δλ; then the focal length fs of the imaging system corresponding to the distance s between the two wavelengths λ and λ+Δλ on the spectrometer detector is: fs=s / Δβ (3) Then the focal length fc of the collimation system in front of the grating is: fc=fs / M (4) Where M is the magnification of the spectrometer system, which is determined by the detector target size D, the number of optical fibers N required to be imaged on the detector, and the optical fiber arrangement interval L. Its expression is: M=D / (N×L) (5) The grating size used in the spectrometer is related to the incident light focal ratio Fin, Lg is the length of the grating line direction, and Wg is the length of the grating dispersion direction: Lg=fc / Fin (6) Wg=Lg / cosα (7) In the design of the spectrometer, the spatial arrangement direction of the optical fiber array at the output end of the integral field of view unit and the dispersion direction of each optical fiber are perpendicular to the detector; the overall resolution of the spectrometer is determined by the following factors: the resolution of the grating, the width of the slit, the size of the detector and the size of the dispersion spot; in the dispersion direction, the distance s between the two wavelengths λ and λ+Δλ on the detector is at least greater than or equal to the size of the image of an optical fiber on the detector along the dispersion direction; formula (5) is the magnification of the spectrometer in the spatial direction of the optical fiber; the magnification M' of the spectrometer in the dispersion direction is expressed as: M′=M cosα / cosβ (8) Then the image size O' of each optical fiber's core diameter on the detector along the dispersion direction is: O'=M'×O (9) Where O is the optical fiber core diameter; this spectrum design must satisfy the following relationship: Where η is the size of a single pixel of the detector; Based on the detector parameters, slit length and spectrometer resolution requirements, the spectrometer design parameters are calculated and analyzed according to formulas (1)-(10), and the grating parameter size, line density and blaze wavelength in the spectrometer are selected and determined; Step 2: Determine the number of slits in the slit module (1) The number of slits in a multi-slit integral field spectrometer is related to the following parameters: the size of the detector target, the spectral resolution, and the bandwidth of the observation band; each sub-slit is imaged on the detector target after being dispersed by the spectrometer system, and the size Nsi occupied along the dispersion direction is: Nsi=s·(τ0+τ1+τ2) / Δλ (11) Where τ0, τ1, and τ2 represent the central observation band width of the narrowband filter and the band width corresponding to the rising and falling edges of the narrowband filter, respectively; on the detector, the spectra after dispersion of multiple slits cannot overlap, so the number of incident end slits that can be accommodated on the detector is Ns: Ns≤ integer (D / (Nsi+Δd)) (12) Where Δd is the size of the dark area between the images of two adjacent slits on the detector along the dispersion direction after dispersion; From formulas (11) and (12), we know that for narrow-band filters, the smaller τ0, τ1, and τ2 are, the more slits are observed at one time. Therefore, when customizing filters, it is necessary to ensure that τ1 and τ2 are as small as possible, that is, the rising and falling edges of the narrow-band filter's transmittance changing with wavelength are steep; Step 3: Adopt refractive optical design: Due to the multi-slit integral field spectrometer design, the object plane size of the spectrometer is too large. In the absence of obstruction, the reflective structure is difficult to achieve a two-dimensional large field of view design; for a 7-slit integral field spectrometer design, the object plane size reaches 60mm×150mm, which puts forward requirements for the glass material of the optical design, because the size of the mirror blank of the general optical material is 160mm in diameter; but considering that the observation band range is not large, the glass materials used in the optical design are all selected from the Chengdu Guangming Large Glass Warehouse; Step 4. Considering that the use of the integral field of view unit is to achieve spectral imaging of the observed object, the image needs to be reconstructed, which requires that the light energy loss of each optical fiber be consistent. In the design, the spectrometer system adopts an object-side telecentric optical path design, and the grating is placed at the exit pupil of the collimation system.

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