High spatial resolution solar imager based on optical interference and working method thereof

Abstract

The application discloses a high spatial resolution sun imager based on optical interference and a working method thereof. The high spatial resolution sun imager comprises a high-aperture filling density aperture pair array, a heat dissipation system, a wideband light beam single-mode optical fiber transmission array, a phase fast scanning regulation and compensation module, a narrowband light splitting / filtering system, a narrowband light beam single-mode optical fiber transmission array, an integrated orthogonal polarization measurement device array, an optical-electric conversion and data acquisition unit, and a data processing and image reconstruction unit. The aperture pair array is used to collect energy, the mutual intensity information of the spatial spectrum of the sun light is transmitted by means of optical fiber pairing, and then a high-resolution sun image is reconstructed by means of an algorithm, so that the problems of large-aperture range beam distortion, high-energy convergence and stray light influence, which must be faced by a large-aperture convergence scheme, are effectively avoided. The high spatial resolution sun imager has the advantages of strong expansion capability and low development cost in the aspect of high spatial resolution sun imaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photoelectric imaging technology, and in particular to a high spatial resolution solar imager based on optical interference and a working method thereof. The present application provides a new technical solution for observing and understanding the sun for spatial weather scientists and astronomical scientists. BACKGROUND

[0002] Obtaining high spatial resolution observation data of the sun is of great significance for predicting the future of mankind. First, the sun is the master of the solar system, and each layer of the earth is affected by the sun. Understanding the temperament of the sun is conducive to the comfortable life of mankind on earth; second, the sun is the only star that mankind can possibly observe in depth. By observing the sun, the characteristics of the change of the star can be studied to deepen the cognition of the formation and evolution of the entire universe, which has significant practical significance and practical value for safeguarding international livelihood, maintaining national security, promoting the future development of mankind, and searching for extraterrestrial civilizations.

[0003] Therefore, mankind has carried out research for more than 400 years, and more than 60 solar observatories have been established around the world. In recent years, scientists have made great efforts to obtain high-definition solar image data and meet the needs of accurate solar activity prediction. Currently, the basic methods for obtaining high-definition images are based on the principle of diffraction imaging and can be divided into two categories: one category is represented by the American Parker Solar Probe, which uses a satellite with a limited aperture to approach the sun for observation, but has problems such as high cost, high temperature test, short service life, etc.; the other category is represented by the American 4.24-meter DKIST and the 8-meter advanced ground-based solar telescope being planned in China, which builds a large-aperture detection instrument based on the traditional single-aperture technology scheme to improve the solar resolution by increasing the optical aperture, but will suffer from a series of problems such as strong energy collection blindness, atmospheric turbulence affecting the seeing angle, and difficulty in breaking through.

[0004] In addition, the 8-meter advanced ground-based solar telescope can only meet the observation of the 0.1″-2.6″, average 1.4″(1000km) of the solar surface grain structure in theory. Whether there is a more detailed structure inside the grain structure requires a larger optical aperture solar observation instrument. Currently, there is no research report on a larger aperture and higher resolution solar imager.

[0005] Since the discovery of optical interference phenomenon in 200 years, optical interference technology has gradually developed from astronomical angle measurement to astronomical calculation imaging, and then developed into optical interference calculation imaging method. The biggest technical advantage of optical interference calculation imaging method is that it has super high spatial resolution, which is widely used in exoplanet observation field. The most representative is the Center for High Angular Resolution Astronomy (CHARA) array in the United States, which is composed of 6 1m aperture telescopes arranged in a Y-shaped array, and the observation wavelength ranges from visible light to 2.2 μm infrared band. In 2006, CHARA used an interferometer composed of 4 telescopes to take a surface image of the star Betelgeuse in 3 hours. Six years later, in 2012, scientists at the University of California, Davis, combined integrated optics and optical interference to propose a segmented planar imaging detector for EO reconnaissance (SPIDER) technology, and completed the integrated optical interference calculation imaging verification in the laboratory in 2016. There is no research report or idea about applying this technology to solar observation. At the same time, some documents describe the traditional means of building a large aperture high resolution observation telescope, such as synthetic aperture, integrated aperture or spliced aperture, which is not suitable for solar imaging observation. For example, page 283 of "Astronomical Telescope Principles and Design" published by Nanjing University Press and written by Cheng Jingquan states: "Fortunately, because the Webb Space Telescope is not a coronagraph, the coronagraph needs to use a single main mirror." Therefore, whether the aperture segmented array arrangement optical interference calculation imaging method can be applied to solar imaging observation still needs to be explored.

[0006] The intense activity of the sun that has a harmful effect on the earth is generally called "magnetic storm", which is a kind of activity driven by magnetic field. The magnetic field activity is hidden in the polarization characteristics of sunlight, so the current solar imaging pursues high spatial resolution on one hand and focuses on the polarization light measurement of specific spectral width that can reflect the characteristics of magnetic field on the other hand.

[0007] The application of optical interference calculation imaging method to solar high spatial resolution imaging faces the following problems: 1) long baseline range transient imaging: the sun is burning fiercely all the time, and high spatial resolution imaging of the sun needs to be completed in an instant, that is, the solar imager needs to accurately detect the sunlight information in a large scale range of equivalent aperture meter level or even dozens of meters with high time efficiency. The existing ground-based interferometric high spatial resolution telescope based on the principle of optical interference calculation imaging all uses the relative position motion between stars to complete the high spatial frequency sampling rate cross-correlation intensity collection in the long baseline range through long time accumulation, which cannot meet the instantaneous imaging demand; therefore, the invention needs to propose a long baseline transient imaging technical scheme.

[0008] 2) Polarization data transient measurement: The existing solar imager is based on the diffraction image plane direct imaging method, and uses a traditional polarization element such as a polarizer to measure the solar magnetic field. The working principle of the optical interference calculation imaging method is different from that of the diffraction image plane direct imaging method, so the existing polarization measurement method cannot be directly borrowed, and a multi-polarization state transient measurement method based on the optical interference calculation imaging method needs to be invented to complete the measurement of the polarization intensity reflecting the solar magnetic field information.

[0009] 3) Optical path difference problem caused by atmospheric turbulence or long baseline stability: For high spatial resolution imaging instruments, the equivalent aperture or baseline scale is large, and is affected by environmental vibration or temperature field changes. The stability of the optical path difference corresponding to the optical interference arm will be affected, which will further affect the accuracy of the interference signal detection. In addition, when ground-based optical observation instruments observe the sun, they will inevitably encounter atmospheric turbulence, which will cause the wavefront of the solar beam to be distorted, and then the optical path difference of the interference light path will change, which will further affect the accuracy of the interference signal detection. Therefore, imaging instruments based on the principle of optical interference calculation imaging need to take certain technical measures to control or compensate for the changes in the interference optical path difference caused by various factors, and to improve the accuracy of interference information measurement.

[0010] 4) Temperature field control problem: The solar imager works on the sun, and the solar beam directly enters the interior of the optical instrument, so it is impossible to avoid solar heating. The temperature field of the optical and mechanical components changes, causing thermal deformation of the optical and mechanical components, which further affects the working performance of the solar imager. Therefore, the important component of the solar imager is the heat dissipation module.

[0011] 5) Stray light suppression problem: High spatial resolution solar imagers often have a small field of view and work in the local area of the sun. The radiation from the surface of the sun located at the edge of the field of view can easily enter the suppression angle of the instrument and enter the imaging light path as stray light, affecting the imaging effect. Especially for coronal imaging observation instruments, when the field of view is relatively weak, the radiation from the photosphere layer of the solar disk is stronger and enters the coronal instrument as stray light, which seriously affects the imaging. Therefore, the suppression of stray light is an important design content in the design of coronal imaging observation instruments. SUMMARY

[0012] For the first problem, the imaging instrument based on the principle of optical interference calculation imaging is used, such as the chessboard imaging instrument (CN202010965700.X, application date 2020.09.15), SPIDER (US8913859B1, publication date 2014.12.16) and the aperture arrangement mode of the honeycomb imaging instrument. The aperture pair array is used for solar light collection with high aperture filling density, and the collected light is transmitted into the optical fiber array with long distance transmission capability. The aperture pair beam is paired and transmitted through the optical fiber, realizing high-density sampling of the high spatial frequency domain in the long baseline scale range of the sunlight information, and minimizing the information loss caused by aperture segmentation, that is, realizing the long baseline range transient acquisition of the sunlight information. At the same time, due to the use of optical fiber for beam transmission, the optical path is unstable, which brings difficulties to the phase measurement of the spatial frequency mutual intensity based on optical interference measurement. Therefore, a phase recovery algorithm (eg. On Fienup Methods for Sparse Phase Retrieval, Digital Object Identifier 10.1109 / TSP.2017.2780044) is needed to reconstruct the solar image.

[0013] For the second problem, the integrated optical 2D optical waveguide orthogonal modulation coupler array used by SPIDER is abandoned, and an integrated orthogonal polarization measurement device array is used to measure the solar polarization data of the aperture pair beam paired transmission optical fiber array. Each integrated orthogonal polarization measurement device includes an aperture pair beam collection end 701, two 1x2 beam splitting and polarizing units 702, two polarization direction Ix beam transmission units 703, two polarization direction Iy beam transmission units 704, two same polarization state beam 2x1 beam combining interference units 705 and an orthogonal polarization state beam output end 706. The optical paths of the four light paths in the device from the beam splitting and polarizing starting point to the beam combining ending point are consistent. The sunlight is coupled into the aperture pair beam collection end 701, and each is divided into two orthogonal polarized light through the 1x2 beam splitting and polarizing unit 702. Then, the polarization direction Ix beam transmission unit 703 and the polarization direction Iy beam transmission unit 704 are transmitted. After that, the same polarization state beams are paired into the 2x1 beam combining interference unit 705 for interference, and finally output from the orthogonal polarization state beam output end 706.

[0014] For the third problem above, the change of optical path difference caused by atmospheric turbulence or instability of long baseline fiber, the application configures a phase fast scanning regulation compensation module in the light beam transmission path of the aperture pair light beam matching transmission fiber array, regulates the optical path difference of each pair of matching transmission fiber, compensates the change of interference path difference caused by atmospheric turbulence, environmental vibration and temperature, and further ensures accurate measurement of the mutual correlation intensity of different spatial spectrum and different polarization state of sunlight.

[0015] For the fourth problem above, the temperature field control problem, the application uses the aperture array to collect energy, each sub-aperture collects energy independently, avoids high-density energy convergence of a single point in a large aperture range, and reduces the energy density; in addition, a heat conduction heat dissipation method is adopted to regulate the temperature field of the aperture array and the entire imaging instrument, so that a relatively stable imaging working temperature field environment is obtained.

[0016] For the fifth problem above, the stray light suppression problem, on the one hand, the application uses a single-mode optical fiber to collect energy, uses the working aperture characteristics of the single-mode optical fiber to achieve 100% suppression efficiency of energy outside the working field of view, and on the other hand, uses the characteristics that stray light is difficult to meet the interference condition, and filters the stray light as part of the direct current when extracting the interference signal.

[0017] Based on the above series of solutions, the application discloses a high spatial resolution solar imager based on optical interference. The imager includes an aperture pair array 1 with high aperture filling density, a heat dissipation system 2, a wideband light beam single-mode fiber transmission array 3, a phase fast scanning regulation compensation module 4, a narrowband light splitting / filtering system 5, a narrowband light beam single-mode fiber transmission array 6, an integrated orthogonal polarization measurement device array 7, a photoelectric conversion device and data acquisition unit 8, and a data processing and image reconstruction unit 9. The sunlight to be measured is collected by the aperture pair array 1, and is sequentially transmitted through the wideband light beam single-mode fiber transmission array 3, the phase fast scanning regulation compensation module 4, the narrowband light splitting / filtering system 5, the narrowband light beam single-mode fiber transmission array 6, and the integrated orthogonal polarization measurement device array 7, and is transmitted in pairs to enter the photoelectric conversion device and data acquisition unit 8, is converted into an electrical signal and stored, and finally is processed and inverted by the data processing and image reconstruction unit 9 to reconstruct the high spatial resolution image of the sunlight in two orthogonal polarization states.

[0018] Wherein, the integrated orthogonal polarization measurement device array is composed of several integrated orthogonal polarization measurement devices, each of which includes an aperture pair light beam collection end 701, two 1x2 light splitting and polarizing units 702, two polarization direction Ix light beam transmission units 703, two polarization direction Iy light beam transmission units 704, two same polarization state light beam 2x1 beam combining interference units 705, and an orthogonal polarization state light beam output end 706. The optical paths of the four light beams in the device from the light splitting and polarization starting point to the beam combining ending point are consistent. The sunlight is coupled into the aperture pair light beam collection end 701, and each is divided into two orthogonal polarized lights by the 1x2 light splitting and polarizing unit 702. Then, the two orthogonal polarized lights are transmitted by the polarization direction Ix light beam transmission unit 703 and the polarization direction Iy light beam transmission unit 704. After that, the two same polarization state light beams are paired into the 2x1 beam combining interference unit 705 for interference. Finally, the two orthogonal polarization state light beams are output from the orthogonal polarization state light beam output end 706, and the contrast measurement of the mutual intensity of the two orthogonal polarization light information Ix and Iy of the sunlight is completed by photoelectric conversion.

[0019] In order to ensure that the solar imager still works normally when the sun is directly opposite the sun, the high spatial resolution solar imager further includes a heat dissipation system 2, which provides temperature control function for the entire imaging light path, especially provides heat dissipation function for the aperture pair array 1 directly facing the sun.

[0020] The broadband light beam single-mode fiber transmission array 3 uses single-mode fiber to suppress stray light, especially near-field stray light which is difficult to suppress in traditional solar imagers, by the effective numerical aperture angle of the fiber.

[0021] The phase fast scanning regulation and compensation module 4 is used to regulate and control the optical path difference of the paired light path, compensate for the change of the optical path difference of the interference light path caused by atmospheric turbulence, environmental vibration and temperature, and realize fast scanning near zero optical path difference of the paired light path in the process of information acquisition, so as to obtain the mutual intensity information of the two orthogonal polarization state spatial frequencies. According to the range and accuracy of the optical path compensation, a spatial phase modulator or a fiber stretching type phase modulator (fiber delay line) can be selected.

[0022] The narrowband light splitting / filtering system 5 realizes the demand for spectral selection filtering of the scientific observation target of the sun.

[0023] The integrated orthogonal polarization measurement device array 7 divides the single-mode light beams collected and transmitted by the front end into two orthogonal polarized light beams according to the polarization direction, and further realizes the measurement of the two orthogonal polarization state sunlight information.

[0024] The integrated orthogonal polarization measurement device array 7 is located between the narrowband light beam single-mode fiber transmission array 6 and the photoelectric conversion and data acquisition unit 8, and completes the contrast measurement of the mutual intensity of the two orthogonal polarization light information Ix and Iy of the sunlight.

[0025] The data processing and image reconstruction unit 9 has a spatial frequency domain phase recovery and image reconstruction function.

[0026] For the high spatial resolution solar imager for ground-based application, the aperture pair array is adopted, each sub-aperture of which has a small aperture, about millimeter level, so that the wavefront distortion caused by atmospheric turbulence in the range of each sub-aperture aperture can be ignored. The baseline of each aperture pair is not equal, and the length of the baseline of the aperture pair is from millimeter level to meter level. The beam wavefront distortion caused by atmospheric turbulence between any aperture pair, especially between long baseline aperture pairs, cannot be ignored, so the phase fast scanning regulation and compensation module 4 is needed to compensate for the change of the optical path difference between the aperture pairs. At the same time, due to the influence of vibration or temperature field change on the relative position relationship of any baseline paired aperture pair, the optical path difference between the aperture pairs changes, so the phase fast scanning regulation and compensation module also needs to compensate.

[0027] For the high spatial resolution solar imager for space-based application, although there is no influence of atmospheric turbulence, the relative position relationship of any baseline paired aperture pair cannot be avoided due to the influence of vibration or temperature field change, so the phase fast scanning regulation and compensation module 4 is also a core component unit for the high spatial resolution solar imager based on optical interference for space-based observation.

[0028] In application, in order to utilize the existing conventional single-aperture solar imager and reduce the cost of building a new high-resolution solar imager based on interference, the aperture pair array 1 with high aperture filling density can be default to the short baseline interference information acquisition part, that is, form the hollow part 11, and the corresponding light receiving and imaging capability is completed by the single-aperture solar imager 10 with an aperture and a short baseline, and the imaging information obtained is transmitted to the data processing and image reconstruction unit 9, and the data obtained by the long baseline interference information acquisition part is fused, and finally the high spatial resolution solar image of two orthogonal polarization states is processed and reconstructed by the data processing and image reconstruction unit 9.

[0029] A working method of a high spatial resolution solar imager based on optical interference, the working method is suitable for the high spatial resolution solar imager based on optical interference, and is characterized by comprising the following steps:

[0030] First step, the sun imager starts, the phase fast scanning control compensation module 4 and the photoelectric conversion and data acquisition unit 8 open the working mode, the scanning of the phase fast scanning control compensation module 4 is used to compensate the optical path difference change caused by atmospheric turbulence, working environment vibration or temperature field change and other factors, so that the photoelectric conversion and data acquisition unit 8 can collect the maximum value of the interference envelope of each matched transmission interference light path of the aperture pair array, and then the zero optical path difference position of each matched transmission interference light path of the aperture pair array of the sun imager is judged, and the phase fast scanning control compensation module 5 is set near the zero optical path difference position of each matched transmission interference light path of the aperture pair array;

[0031] Second step, the phase fast scanning control compensation module 4 and the photoelectric conversion and data acquisition unit 8 open the working mode, the sun imager phase fast scanning control compensation module 4 scans through the zero optical path difference near each matched transmission interference light path, and the photoelectric conversion and data acquisition unit 8 records the mutual intensity interference data of the two orthogonal polarization light information Ix, Iy of sunlight obtained by the integrated orthogonal polarization measuring device array;

[0032] Third step, by means of the data processing and image reconstruction unit 9, the direct current is filtered out, the peak and average values of the two orthogonal polarization light information Ix, Iy mutual intensity interference data of the sun imager are calculated, the contrast of the two orthogonal polarization state spatial spectrum mutual intensity is obtained, and the sun high spatial resolution image is reconstructed by means of the phase recovery and image reconstruction algorithm.

[0033] In summary, the application discloses a high spatial resolution sun imaging method based on the optical interference calculation imaging principle, utilizes the aperture array with high aperture filling density to collect sunlight, collects the sunlight into the optical fiber array for long baseline beam transmission, then transmits into the polarization detector array with two orthogonal polarization state detection functions, utilizes the numerical aperture of the single-mode optical fiber and the optical interference condition to suppress the influence of near-field stray light, completes the polarization data transient measurement of the sun by means of the phase difference control module and the high-speed photoelectric detector, and finally reconstructs the high spatial resolution image of the sun by means of the algorithm inversion.

[0034] The application discloses a high spatial resolution sun imaging method based on the optical interference calculation imaging principle, utilizes the aperture array with high aperture filling density to collect sunlight, collects the sunlight into the optical fiber array for long baseline beam transmission, then transmits into the polarization detector array with two orthogonal polarization state detection functions, utilizes the numerical aperture of the single-mode optical fiber and the optical interference condition to suppress the influence of near-field stray light, completes the polarization data transient measurement of the sun by means of the phase difference control module and the high-speed photoelectric detector, and finally reconstructs the high spatial resolution image of the sun by means of the algorithm inversion. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The application discloses a high spatial resolution sun imaging method based on the optical interference calculation imaging principle, utilizes the aperture array with high aperture filling density to collect sunlight, collects the sunlight into the optical fiber array for long baseline beam transmission, then transmits into the polarization detector array with two orthogonal polarization state detection functions, utilizes the numerical aperture of the single-mode optical fiber and the optical interference condition to suppress the influence of near-field stray light, completes the polarization data transient measurement of the sun by means of the phase difference control module and the high-speed photoelectric detector, and finally reconstructs the high spatial resolution image of the sun by means of the algorithm inversion.

[0036] Figure 2 Figure 1 is a schematic diagram of the integrated orthogonal polarization measurement device function structure, i.e. the integrated orthogonal polarization measurement device composition and the orthogonal polarization state optical information measurement module function structure schematic diagram.

[0037] Figure 3 Figure 2 is a solar surface image input for simulation in embodiment 1, which is derived from an image collected by the Visible Broadband Imager (VBI) of the Daniel K. Inouye Solar Telescope (DKIST) funded by the National Science Foundation.

[0038] Figure 4 Figure 3 is a solar surface reconstructed image output for simulation in embodiment 1, at this time the system N = 60, the minimum baseline length Bmin = 0.0036 mm, and the maximum baseline length Bmax = 0.2175 m.

[0039] Figure 5 Figure 4 is a solar surface reconstructed image output for simulation in embodiment 1, at this time the system N = 260, the minimum baseline length Bmin = 0.0036 mm, and the maximum baseline length Bmax = 0.9360 m.

[0040] Figure 6 Figure 5 is a single-aperture + long-baseline interference combined high spatial resolution solar imager in embodiment 1, which includes a conventional single-aperture solar imager, and a long-baseline solar imager based on optical interference with a shorter baseline that does not cover the default single-aperture diameter.

[0041] Figure 7 Figure 6 is the imaging simulation effect of the high-resolution solar imager in embodiment 2.

[0042] Figure 1 is a schematic diagram of the integrated orthogonal polarization measurement device function structure, i.e. the integrated orthogonal polarization measurement device composition and the orthogonal polarization state optical information measurement module function structure schematic diagram. DETAILED DESCRIPTION

[0043] The application will be further described below with reference to the specific embodiments. It should be understood that these embodiments are only used to explain the application and not to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content of the application, and these equivalent forms also fall within the scope defined by the appended claims.

[0044] Specific embodiment 1: ground-based high spatial resolution solar imager

[0045] The ground-based high spatial resolution solar imager adopts the rectangular array aperture arrangement scheme of the checkerboard imager (ZL201711000143.2) to realize continuous non-redundant sampling in the maximum baseline scale range, and the system parameters are shown in the following table. The optical fiber adopts a single-mode polarization maintaining optical fiber, and the polarization direction of the optical fiber array is aligned with one of the polarization directions (Ix direction) of the integrated orthogonal polarization measurement device array. In theory, at this time, the optical path only collects light in the x polarization direction, and the output light energy in the y polarization direction is 0.

[0046] Table 1: System parameters of the ground-based high spatial resolution solar imaging scheme

[0047] Item Parameter Operating wavelength 450.287 nm Operating bandwidth 0.406 nm Aperture-to-array arrangement scheme Chessboard type Minimum baseline length Bmin 0.0036 mm Array size (2N+1) x (2N+1) Long-baseline beam transmission fiber type Single-mode polarization-maintaining fiber Fiber array polarization direction x polarization Heat dissipation system Metallic material as the main support material + active system such as water cooling Phase fast scanning regulation compensation module Spatial large-range phase regulation + fiber type fine phase regulation Integration time 1 ms

[0048] The aperture pair array and the optical fiber transmission array are supported by a support structure made of metal material with high specific stiffness and good thermal conductivity such as invar titanium alloy. The support structure is connected with the active thermal control system such as water cooling to ensure the stability of the structure while making the system have a stable temperature field. The phase fast scanning control compensation module adopts a combination of spatial large-range phase control and optical fiber fine phase control, and realizes coarse adjustment of the optical path difference of the paired aperture pair array in the range of ±3mm, high-precision adjustment of 10 microns in any area and 20 nanometers by means of closed-loop control circuit. Before exposure to the sun surface, the fast scanning of each optical path difference position of each aperture pair array in the large optical path difference range is searched, and then the fast scanning in the wavelength range of zero optical path difference position is performed to compensate the optical path difference of the aperture pair caused by atmospheric turbulence and other factors. At the same time, the interference fringes of each spatial frequency corresponding to each aperture pair are collected and recorded by photoelectric exposure. Based on the interference fringe data, the contrast of each spatial frequency mutual intensity of the x polarization direction of the sun light is calculated, and finally the high spatial resolution image of the x polarization direction of the sun light is inversed and reconstructed by means of the phase recovery and image reconstruction algorithm of the data processing and image reconstruction unit.

[0049] One of the images collected by the visible broadband imager (VBI) of the Daniel K. Inouye Solar Telescope (DKIST) funded by the National Science Foundation of the United States (DKIST) is taken as a simulation image, which is input into the simulation model of the imaging system. When the system N=60, i.e. the maximum baseline length Bmax=0.2175m, the inversed and reconstructed image is as shown in Figure 3 Figure 4 ​As shown, when N = 260, i.e. the maximum baseline length Bmax= 0.9360m, the image reconstructed by inversion is as shown in Figure 5 .

[0050] Wherein, the short baseline solar imager can be replaced by a traditional single aperture solar imager with an aperture comparable to the short baseline, i.e. as shown in Figure 6 As shown, the high resolution solar imager can be composed of a traditional single aperture solar imager with a relatively small aperture and a short baseline, and an interferometric solar imager with a relatively long baseline. Figure 6 The high aperture filling density aperture pair array 1 of the interferometric solar imager with a relatively long baseline is missing the short baseline interferometric information acquisition part, forming a hollow part 11. The light collection and imaging capability corresponding to the hollow part 11 is completed by the single aperture solar imager 10 with an aperture comparable to the short baseline. The imaging data obtained by the single aperture solar imager 10 is transmitted to the data processing and image reconstruction unit 9, and is fused with the data obtained by the interferometric solar imager with a relatively long baseline, and finally processed by the data processing and image reconstruction unit 9 to reconstruct high spatial resolution solar images in two orthogonal polarization states, which is equivalent to a long baseline solar imager. In this example, N = 60, the maximum baseline length Bmax= 0.2175m can be replaced by a traditional single aperture solar imager with an equivalent aperture D = 0.2175m, which is combined with an interferometric imager with a baseline range of 0.2175m ~ 0.9360m to obtain the same imaging effect as the solar imager with N = 260 and the maximum baseline length Bmax= 0.9360m.

[0051] Specific embodiment 2: high spatial resolution solar imager

[0052] The high spatial resolution solar imager adopts a rectangular array aperture pair arrangement scheme of a chessboard imager, and the system parameters are shown in the following table. The optical fiber is a single mode optical fiber, which collects and transmits light in x polarization and y polarization directions.

[0053] Table 2: System parameters of high spatial resolution solar imaging scheme

[0054] Item Parameter Operating wavelength 629.4 nm Aperture-to-array arrangement scheme Chessboard type Minimum baseline length 0.0051 mm Array size (2N+1) x (2N+1) Long-baseline beam transmission fiber type Single-mode fiber Heat dissipation system Metallic material as the main support material + active system such as water cooling Integration time 1 ms Polarization direction x and y

[0055] The aperture pair array and the fiber transmission array adopt a metal material with high equivalent stiffness and good thermal conductivity, such as stainless steel titanium alloy, as a support structure. The support structure is connected with a water cooling active thermal control system to ensure the stability of the structure and make the system have a stable temperature field. The phase fast scanning compensation module adopts a combination of a space type large range phase control and a fiber type fine phase control, and realizes the coarse adjustment of the optical path difference of the aperture pair array within the range of ±3mm, the high-precision adjustment of 10 microns in any area and 20 nanometers by means of a closed-loop control circuit. Before exposure to the sun surface, the fast scanning is performed in the large optical path difference range to search the optical path difference position of each aperture pair array, and then the fast scanning is performed in the wavelength range of the zero optical path difference position to compensate the aperture pair interference arm optical path difference caused by atmospheric turbulence and other factors. At the same time, the photoelectric exposure is collected and recorded to obtain the interference fringes of each spatial frequency corresponding to each aperture pair. Based on the interference fringe data, the contrast of the mutual intensity of each spatial frequency in the x and y polarization directions of the sun light is calculated, and finally the high spatial resolution images in the x and y polarization directions of the sun light are reconstructed by means of the data processing algorithm.

[0056] Any x-polarization and y-polarization images in the images collected by the visible light spectro-polarimeter (VISP) of the Daniel K. Inouye Solar Telescope (DKIST) funded by the National Science Foundation of the United States are taken as simulation images, which are input into the simulation model of the imaging system. When the system N=30, i.e. the maximum baseline length Bmax=0.1523m, the PSNR of the images reconstructed in the x and y polarization directions is 33.9 and 40.0 respectively; when the system N=60, i.e. the maximum baseline length Bmax=0.3046, the PSNR of the images reconstructed in the x and y polarization directions is 40.4 and 39.6 respectively. For details, see Figure 7 .

[0057] The PSNR is an index for evaluating the image quality by comparing the difference between the original input image and the interference imaging reconstructed image, and the higher the value is, the higher the fidelity of the image is. The simulation results of the present example show that the reconstructed sun image based on the optical interference high spatial resolution sun imager has high fidelity with the input original image, which proves that the technical scheme disclosed in the present application can be applied to the sun imaging observation.

[0058] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent flow transformation made by using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A high spatial resolution sun imager based on optical interference, characterized in that: The high spatial resolution solar imager comprises a high-aperture filling density aperture pair array (1), a heat dissipation system (2), a wideband beam single-mode optical fiber transmission array (3), a phase fast scanning regulation compensation module (4), a narrowband light splitting / filtering system (5), a narrowband beam single-mode optical fiber transmission array (6), an integrated orthogonal polarization measurement device array (7), a photoelectric conversion and data acquisition unit (8), and a data processing and image reconstruction unit (9). The solar light to be measured is collected by the aperture pair array (1), and is transmitted into the photoelectric conversion device and the data acquisition unit (8) in pairs through the wideband beam single-mode optical fiber transmission array (3), the phase fast scanning regulation compensation module (4), the narrowband light splitting / filtering system (5), the narrowband beam single-mode optical fiber transmission array (6), and the integrated orthogonal polarization measurement device array (7) in sequence, is converted into an electric signal and stored, and finally, the high spatial resolution solar image of two orthogonal polarization states is processed and reconstructed by the data processing and image reconstruction unit (9), while the heat dissipation system (2) provides a stable temperature field environment for each component. The integrated orthogonal polarization measurement device array (7) is composed of a series of integrated orthogonal polarization measurement devices, wherein each integrated orthogonal polarization measurement device comprises an aperture pair beam collection end (701), two 1x2 light splitting and polarization units (702), two polarization direction Ix beam transmission units (703), two polarization direction Iy beam transmission units (704), two same polarization state beam 2x1 beam combination interference units (705), and an orthogonal polarization state beam output end (706). The optical paths of the four light paths in the device from the light splitting and polarization starting point to the beam combination ending point are consistent. The sunlight is coupled into the aperture pair beam collection end (701), and is respectively split into two orthogonal polarization lights by the 1x2 light splitting and polarization unit (702), is transmitted by the polarization direction Ix beam transmission unit (703) and the polarization direction Iy beam transmission unit (704), is then paired into the 2x1 beam combination interference unit (705) for interference, and finally is output from the orthogonal polarization state beam output end (706).

2. The high spatial resolution sun imager based on optical interference according to claim 1, characterized in that: The heat dissipation system (2) provides temperature control function for the whole imaging light path, especially for the aperture pair array (1) directly facing the sunlight; the broadband beam single-mode fiber transmission array (3) uses single-mode fiber to suppress stray light, especially near-field stray light, through the effective numerical aperture angle of the fiber; the phase fast scanning regulation and compensation module (4) is used to regulate and control the optical path difference of the matched light path, to compensate for the change of the optical path difference of the interference light path caused by atmospheric turbulence, environmental vibration and temperature, and to realize fast scanning near the zero optical path difference of the matched light path in the process of information acquisition by means of closed-loop control technology, so as to obtain the mutual intensity information of two orthogonal polarization states of spatial frequency; the narrow-band light splitting / filtering system (5) realizes the requirement of spectral selection filtering for the scientific objective of solar observation; the integrated orthogonal polarization measurement device array (7) divides the single-mode light beams collected and transmitted at the front end into two orthogonal polarization beams according to the polarization direction, and then realizes the measurement of the information of two orthogonal polarization states of solar light; the data processing and image reconstruction unit (9) has the functions of spatial frequency domain phase recovery and image reconstruction.

3. The high spatial resolution sun imager based on optical interference according to claim 1, characterized in that: The aperture pair array (1) with high aperture filling density can default the short-baseline interference information acquisition part, i.e. form a hollow part (11), and the corresponding light collection and imaging capability is completed by the single-aperture solar imager (10) with an aperture comparable to the short baseline, and the imaging information obtained is transmitted to the data processing and image reconstruction unit (9) to be fused with the data obtained by the long-baseline interference information acquisition part, and finally the high spatial resolution images of two orthogonal polarization states of the sun are processed and reconstructed by the data processing and image reconstruction unit (9).

4. A working method of a high spatial resolution solar imager based on optical interference, the working method being applicable to the high spatial resolution solar imager based on optical interference according to any one of claims 1 to 3, and characterized in that: In the first step, the solar imager is started, the phase fast scanning regulation and compensation module (4) and the photoelectric conversion and data acquisition unit (8) are started in the working mode, the change of the optical path difference caused by atmospheric turbulence, working environment vibration or temperature field change is compensated through the scanning of the phase fast scanning regulation and compensation module (4), so that the photoelectric conversion and data acquisition unit (8) can collect the maximum value of the interference envelope of each matched transmission interference light path of the aperture pair array (1), and then the zero optical path difference position of each matched transmission interference light path of the aperture pair array (1) of the solar imager is judged, and the phase fast scanning regulation and compensation module (4) is set near the zero optical path difference position of each matched transmission interference light path of the aperture pair array; In the second step, the phase fast scanning regulation and compensation module (4) and the photoelectric conversion and data acquisition unit (8) are started in the working mode, the phase fast scanning regulation and compensation module (4) of the solar imager scans near the zero optical path difference of each matched transmission interference light path, and the photoelectric conversion and data acquisition unit (8) records the mutual intensity interference data of the two orthogonal polarization light information Ix, Iy of the sun obtained by the integrated orthogonal polarization measurement device array. Thirdly, the data processing and image reconstruction unit (9) is used to filter out the direct current, calculate the peak and average values of the mutual intensity interference data of the two orthogonal polarization light information Ix and Iy of the solar imager, obtain the contrast of the mutual intensity of the two orthogonal polarization states, and reconstruct the high spatial resolution image of the sun through the phase recovery and image reconstruction algorithm.

5. The method of operating a high spatial resolution sun imager based on optical interference according to claim 4, characterized in that: The integrated orthogonal polarization measurement device array (7) is located between the narrow-band beam single-mode fiber transmission array (6) and the photoelectric conversion and data acquisition unit (8), and the integrated orthogonal polarization measurement device array (7) completes the contrast measurement of the mutual intensity of the two orthogonal polarization light information Ix and Iy of the sun.

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