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

Abstract

The invention discloses a high-spatial-resolution solar imager based on optical interference and a working method of the high-spatial-resolution solar imager. The high-spatial-resolution solar imager comprises an aperture pair array with high aperture packing density, a heat dissipation system, a broadband light beam single-mode optical fiber transmission array, a phase fast scanning regulation and control compensation module, a narrow-band light splitting / filtering system, a narrow-band light beam single-mode optical fiber transmission array, an integrated cross-polarization measurement device array and a photoelectric conversion and data acquisition unit. An aperture pair array is used for collecting energy, optical fiber pairing transmission interference is used for measuring mutual intensity information of a sunlight space frequency spectrum, then a sun high-resolution image is reconstructed by means of an algorithm, and the situation that a large-aperture convergence scheme must face large-aperture range light beam distortion and high-energy convergence is effectively avoided. In the aspect of high-spatial-resolution solar imaging, the system has the advantages of being high in expansion capability, low in development cost and the like.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic imaging technology, and in particular to a high spatial resolution solar imager based on optical interference and a working method thereof, which will provide a new technical solution for space weather scientists and astronomers to observe and understand the sun. Background Art

[0002] Obtaining high-resolution observation data of the sun is of great significance for predicting the future destiny of mankind. First, the sun is the master of the solar system, and all the spheres of the earth are affected by the sun. Understanding the sun's temper is conducive to the comfortable life of human beings on Earth. Secondly, the sun is the only star that humans can observe in depth. By observing the sun and studying the changing characteristics of stars, we can deepen our understanding of the formation and evolution of the entire universe, which has significant practical significance and practical value in protecting international livelihoods, maintaining national security, promoting the future development of mankind, and searching for extraterrestrial civilizations.

[0003] To this end, mankind has conducted more than 400 years of research and established more than 60 solar observatories around the world. In recent years, scientists have made great efforts to obtain high-definition solar image data to meet the precise prediction of solar activity. The basic methods currently used to obtain high-definition images are based on the principle of diffraction imaging and are divided into two categories: one is represented by the US "Parker" solar probe, which launches satellites to approach the sun with limited-aperture detection instruments, but there are problems such as high cost, high temperature test, and short life; the other is represented by the US 4.24-meter DKIST and my country's planned 8-meter advanced ground-based solar telescope, which builds ground-based large-aperture detection instruments based on traditional single-aperture technical solutions to improve solar resolution by increasing the optical aperture, but will suffer from a series of problems such as blinding due to strong energy collection and difficulty in breaking through the seeing angle due to atmospheric turbulence.

[0004] In addition, the 8-meter advanced ground-based solar telescope can theoretically only observe the 0.1″-2.6″, average 1.4″ (1000km) of rice-grain structure on the solar surface. Whether there are more delicate structures inside the rice-grain structure requires a solar observation instrument with a larger optical aperture. So far, there has been no research report on solar imaging instruments with a larger aperture and higher resolution.

[0005] Since the discovery of optical interference 200 years ago, optical interference technology has gradually developed from astronomical angle measurement to astronomical computational imaging, and then developed into optical interference computational imaging methods. The biggest technical advantage of optical interference computational imaging methods is that they have ultra-high spatial resolution, and are widely used in the field of extrasolar star observation. The most representative is the Center for High Angular Resolution Astronomy (CHARA) array in the United States, which consists of 6 1m-diameter telescopes arranged in a Y-shaped array, with observation bands ranging from visible light to 2.2μm infrared band. In 2006, CHARA used an interferometer composed of 4 telescopes to capture the surface image of Altair in 3 hours. Six years later, in 2012, scientists at the University of California, Davis, combined integrated optics with optical interference and proposed the Segmented Planar Imaging Detector for EO Reconnaissance (SPIDER), and completed the verification of integrated optical interference computational imaging in the laboratory in 2016. There are no research reports and ideas on the application of this technology to solar observation. At the same time, there are documents that explain that the traditional means of building spliced ​​large-aperture high-resolution observation telescopes, such as synthetic aperture, integrated aperture or spliced ​​aperture, are not suitable for solar imaging observations. For example, Cheng Jingquan's "Principles and Design of Astronomical Telescopes" published by Nanjing University Press states on page 283: "Fortunately, because the Webb Space Telescope is not a coronagraph, the coronagraph needs to use a single primary mirror." Therefore, whether the optical interferometric computational imaging method with aperture segmentation array arrangement can be applied to solar imaging observations still needs to be explored.

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

[0007] The application of optical interferometric computational imaging methods to high spatial resolution solar imaging faces the following problems: 1) Long baseline range transient imaging: The sun is burning fiercely all the time, and its high spatial resolution imaging needs to be completed in an instant, that is, the solar imager needs to detect and obtain sunlight information in a timely and accurate manner at an equivalent aperture of meters or even tens of meters. Existing ground-based interferometric high spatial resolution telescopes based on the principle of optical interferometric computational imaging all use the relative position movement between stars to complete the cross-correlation intensity acquisition of high spatial frequency sampling rate within a long baseline range through long-term accumulation, which cannot meet the needs of instant imaging; therefore, the present invention needs to propose a long baseline transient imaging technical solution.

[0008] 2) Transient measurement of polarization data: Existing solar imagers are all based on the direct imaging method of the diffraction image plane, using traditional polarization elements such as polarizers to measure the solar magnetic field. The working principle of the optical interferometric computational imaging method is different from that of the direct imaging method of the diffraction image plane, so the existing polarization measurement method cannot be directly borrowed. It is necessary to invent a multi-polarization state transient measurement method based on the optical interferometric computational imaging method to complete the measurement of the polarization intensity that reflects the solar magnetic field information.

[0009] 3) The 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 the stability of the optical path difference corresponding to the optical interferometer arm will be affected by the vibration of the working environment or the change of the temperature field, which will 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 that causes the wavefront distortion of the solar beam, which will lead to changes in the optical path difference of the interference light path, and thus affect the accuracy of the interference signal detection. Therefore, imagers based on the principle of optical interferometric computational 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 improve the accuracy of interference information measurement.

[0010] 4) Temperature field control problem: When the solar imager is working, it faces the sun and the solar beams directly enter the interior of the optical instrument. The heating by the sunlight cannot be avoided. The temperature field of the optomechanical components changes, causing thermal deformation of the optomechanical components, which in turn affects the working performance of the solar imager. Therefore, the heat dissipation module is an important component of the solar imager.

[0011] 5) Stray light suppression problem: High spatial resolution solar imagers often have a small working field of view. During operation, the radiation from the solar surface in the area facing the sun and at the edge of the working field can easily enter the suppression angle of the instrument and enter the imaging optical path as stray light, affecting the imaging effect. This is especially true for observation instruments for corona imaging. When the working field is used to image the relatively weak corona, the photosphere beam with stronger radiation from the solar disk enters the coronagraph as a stray light source, causing serious effects on imaging. Therefore, in the design of observation instruments for corona imaging, stray light suppression is an important design content. Summary of the invention

[0012] In response to the first problem mentioned above, the long baseline transient imaging problem, the present invention borrows the aperture arrangement of imagers based on the principle of optical interference computational imaging, such as chessboard imagers (CN202010965700.X application date 2020.09.15), SPIDER (US8913859B1, publication date 2014.12.16) and cellular imagers, and adopts an aperture array with a high aperture filling density to collect sunlight, and collect it into an optical fiber array with long-distance transmission capability. The aperture pair beams are paired and transmitted through the optical fiber to achieve high-density sampling of the high spatial frequency domain within the long baseline scale range of sunlight information, minimize the information loss caused by aperture segmentation, and realize transient acquisition of sunlight information in the long baseline range. However, at the same time, due to the instability of the optical path of the optical fiber for beam transmission, it brings difficulties to the phase measurement of the spatial frequency mutual intensity based on optical interferometry measurement. Therefore, it is necessary to introduce a phase recovery algorithm (eg. On Fienup Methods for Sparse Phase Retrieval, Digital Object Identifier 10.1109 / TSP.2017.2780044) to reconstruct the solar image.

[0013] In response to the second problem mentioned above, that is, the problem of transient measurement of polarization data, the present invention abandons the integrated optical 2D optical waveguide orthogonal modulation coupler array used in SPIDER, adopts an integrated orthogonal polarization measurement device array, and docks the aperture pair beam pairing transmission fiber array to measure the polarization data of sunlight, wherein each integrated orthogonal polarization measurement device includes an aperture pair beam collection end 701, two 1×2 light splitting polarizing units 702, two polarization direction Ix beam transmission units 703, two polarization direction Iy beam transmission units 704, and two same polarization state light The 2×1 beam combining interference unit 705 and the orthogonal polarization state beam output terminal 706 have the same optical path lengths of the four optical paths from the starting point of the beam polarization and splitting to the end point of the beam combining. The sunlight is coupled into the aperture beam collecting end 701, and each is divided into two orthogonal polarized lights by the 1×2 beam splitting and polarizing unit 702, and then transmitted through the polarization direction Ix beam transmission unit 703 and the polarization direction Iy beam transmission unit 704. After that, the beams with the same polarization state are paired in pairs and enter the 2×1 beam combining interference unit 705 for interference. Finally, they are output from the orthogonal polarization state beam output terminal 706.

[0014] In response to the third problem mentioned above - the problem of changes in optical path difference caused by atmospheric turbulence or long-baseline optical fiber instability, the present invention configures a phase fast scanning control and compensation module in the beam transmission optical path of the aperture beam pairing transmission optical fiber array to control the optical path difference of each pair of paired transmission optical fibers, thereby compensating for changes in the optical path difference of the interference optical path caused by atmospheric turbulence, environmental vibration and temperature, thereby ensuring accurate measurement of the cross-correlation intensity of different polarization states of different spatial spectra of sunlight.

[0015] In response to the fourth problem mentioned above - the temperature field control problem, the present invention uses an aperture pair array to collect energy, and each sub-aperture collects energy independently, avoiding the high-density concentration of energy at a single point in a large aperture range and reducing the energy density; in addition, a thermal conduction heat dissipation method is used to control the temperature field of the aperture pair array and the entire imaging instrument, thereby obtaining a relatively stable imaging working temperature field environment.

[0016] In response to the fifth problem mentioned above - the problem of stray light suppression, the present invention, on the one hand, adopts single-mode optical fiber for energy collection, and utilizes the working aperture characteristics of single-mode optical fiber to achieve 100% suppression efficiency of energy outside the working field of view, and on the other hand, utilizes the characteristic that stray light is difficult to meet the interference conditions, and filters it out as part of the direct current when extracting the interference signal.

[0017] Based on the above series of solutions, the present invention 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 broadband beam single-mode fiber transmission array 3, a phase fast scanning control compensation module 4, a narrow-band light splitting / filtering system 5, a narrow-band 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 sequentially passes through the broadband beam single-mode fiber transmission array 3, the phase fast scanning control compensation module 4, the narrow-band light splitting / filtering system 5, the narrow-band beam single-mode fiber transmission array 6, and the integrated orthogonal polarization measurement device array 7, and is transmitted in pairs into the photoelectric conversion device and data acquisition unit 8, converted into electrical signals and stored, and finally processed by the data processing and image reconstruction unit 9 to invert and reconstruct the solar high spatial resolution image of two orthogonal polarization states.

[0018] The integrated orthogonal polarization measurement device array is composed of a number of integrated orthogonal polarization measurement devices, each of which includes an aperture pair beam collection end 701, two 1×2 beam splitting polarization units 702, two polarization direction Ix beam transmission units 703, two polarization direction Iy beam transmission units 704, two same polarization state beam 2×1 beam combining interference units 705 and an orthogonal polarization state beam output end 706. The optical paths of the four optical paths from the beam polarization splitting start point to the beam combining end point in the device are consistent. The sunlight is coupled into the aperture pair beam collection end 701, and each is divided into two orthogonal polarized lights by the 1×2 beam splitting polarization unit 702, and then transmitted by the polarization direction Ix beam transmission unit 703 and the polarization direction Iy beam transmission unit 704. After that, the same polarization state beams are paired in pairs and enter the 2×1 beam combining interference unit 705 for interference. Finally, they are output from the orthogonal polarization state 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 through photoelectric conversion.

[0019] In order to ensure that the solar imager can still work normally when facing the sun, the high spatial resolution solar imager also includes a heat dissipation system 2, which provides a temperature control function for the entire imaging optical path, especially provides a heat dissipation function for the aperture array 1 facing the sun;

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

[0021] The phase fast scanning control and compensation module 4 is used to control the optical path difference of the paired optical path, and compensate for the change of the optical path difference of the interference optical path caused by atmospheric turbulence, environmental vibration and temperature. In the process of information acquisition, a fast scan near the zero optical path difference of the paired optical path is realized by means of a closed-loop control technology, so as to obtain the mutual intensity information of the spatial frequencies of two orthogonal polarization states. It can select a spatial phase modulator or a fiber stretching phase modulator (fiber delay line) according to the different optical path compensation range and accuracy;

[0022] The narrow-band spectroscopic / filtering system 5 realizes the requirements of spectrum selection and filtering for solar observation scientific objectives;

[0023] The integrated orthogonal polarization measurement device array 7 divides the single-mode light beam collected and transmitted at the front end into two orthogonal polarization light beams according to the polarization direction, thereby realizing the measurement of sunlight information in two orthogonal polarization states;

[0024] The integrated orthogonal polarization measurement device array 7 is located between the narrowband beam single-mode optical 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 sunlight.

[0025] The data processing and image reconstruction unit 9 has the functions of spatial frequency domain phase recovery and image reconstruction.

[0026] For high spatial resolution solar imagers for ground-based applications, the present invention uses an aperture pair array, and the aperture of each sub-aperture is relatively small, about the order of millimeters, so the wavefront distortion caused by atmospheric turbulence within the aperture range of each sub-aperture can be ignored. Each aperture pair baseline is not equal, and the aperture pair baseline length ranges from the order of millimeters to the order of meters. Between any aperture pairs, especially between long-baseline aperture pairs, the wavefront distortion of the light beam caused by atmospheric turbulence cannot be ignored, so a phase rapid scanning control compensation module 4 is required to compensate for the change in the optical path difference between the aperture pairs. At the same time, since the relative position relationship of the aperture pairs of any baseline pairing is affected by vibration or temperature field changes, resulting in changes in the optical path difference between the aperture pairs, a phase rapid scanning control compensation module is also required to compensate for it.

[0027] For high spatial resolution solar imagers for space-based applications, although there is no influence of atmospheric turbulence, the relative position relationship of the aperture pairs of any baseline pairing is inevitably affected by vibration or temperature field changes. Therefore, the phase fast scanning control compensation module 4 is also a core component unit for the high spatial resolution solar imager based on optical interferometry used for space-based observations.

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

[0029] A working method of a high spatial resolution solar imager based on optical interferometry, the working method being applicable to the above-mentioned high spatial resolution solar imager based on optical interferometry, characterized in that:

[0030] The first step is to turn on the solar imager, and start the working mode of the phase rapid scanning control compensation module 4 and the photoelectric conversion and data acquisition unit 8. The phase rapid scanning control compensation module 4 is used to scan to compensate for the optical path difference changes caused by factors such as atmospheric turbulence, working environment vibration or temperature field changes, so that the photoelectric conversion and data acquisition unit 8 can collect the maximum value of the interference envelope of each paired transmission interference light path of the aperture pair array, and then judge the zero optical path difference position of each paired transmission interference light path of each aperture pair array of the solar imager, and set the phase rapid scanning control compensation module 5 near the zero optical path difference position of each paired transmission interference light path of each aperture pair array;

[0031] In the second step, the phase rapid scanning control compensation module 4 and the photoelectric conversion and data acquisition unit 8 start the working mode, the solar imager phase rapid scanning control compensation module 4 scans through the zero optical path difference of each paired 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 and Iy of the sunlight obtained by the integrated orthogonal polarization measurement device array;

[0032] The third step is to filter out the direct current with the help of the data processing and image reconstruction unit 9, complete the calculation of the peak-to-valley value and average value of the mutual intensity interference data of the two orthogonal polarized light information Ix and Iy of the solar imager, obtain the contrast of the mutual intensity of the spatial spectrum of the two orthogonal polarization states, and reconstruct the high spatial resolution image of the sun through phase recovery and image reconstruction algorithms.

[0033] In summary, the present invention discloses a high spatial resolution solar imaging method based on the principle of optical interference computational imaging, which uses an aperture array with a high aperture filling density to collect solar light, and collects it into an optical fiber array for long baseline beam transmission, and then transmits it into a polarization detector array with two orthogonal polarization state detection functions. The single-mode optical fiber numerical aperture and optical interference conditions are used to suppress the influence of near-field stray light, and with the help of a phase difference control module and a high-speed photoelectric detector, the transient measurement of solar polarization data is completed, and finally a high spatial resolution image of the sun is reconstructed with the help of algorithm inversion.

[0034] This invention abandons the traditional single-aperture diffraction image plane direct imaging technology solution, adopts aperture array energy collection, and uses fiber optic paired transmission interference to measure the mutual intensity information of the sunlight spatial spectrum, and then reconstructs the high-resolution image of the sun with the help of an algorithm, effectively avoiding the large-aperture range beam distortion, high-energy convergence, and stray light influence problems that large-aperture convergence solutions must face, and has the advantages of strong expansion capabilities and low development costs in high spatial resolution solar imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a diagram of the composition of a high spatial resolution solar imager based on optical interferometry, that is, the composition of a high spatial resolution solar imager.

[0036] Figure 2 It is a schematic diagram of the functional structure of an integrated orthogonal polarization measurement device, that is, a schematic diagram of the functional structure of an integrated orthogonal polarization measurement device and an orthogonal polarization state optical information measurement module.

[0037] Figure 3 The solar surface image input for simulation in the specific embodiment 1 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 of the United States.

[0038] Figure 4 This is the reconstructed image of the solar surface output by simulation in the specific 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 This is the reconstructed image of the solar surface output by simulation in the specific 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 The single aperture + long baseline interference combined high spatial resolution solar imager in the specific embodiment 1 includes a traditional single aperture solar imager and a long baseline solar imager based on optical interference with a shorter baseline covered by a default single aperture diameter.

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

[0042] In the figure: 1. Aperture pair array; 2. Heat dissipation system; 3. Broadband beam single-mode fiber transmission array; 4. Phase fast scanning control compensation module; 5. Narrowband splitting / filtering system; 6. Narrowband beam single-mode fiber transmission array; 7. Integrated orthogonal polarization measurement device array; 701. Aperture pair beam collection end; 702. 1×2 splitting polarization unit to realize the separation of sunlight into two polarized lights in orthogonal directions; 703. One polarization direction Ix beam transmission unit; 704. Another polarization direction Iy beam transmission unit; 705. 2×1 beam combining interference unit for beams in the same polarization state; 706. Orthogonal polarization state beam output end, wherein, in the device development, it is necessary to ensure that the optical path lengths of the four optical paths from the beam splitting starting point (i.e. 702) to the beam combining end point (i.e. 705) are consistent; 8. Photoelectric conversion device and data acquisition unit; 9. Data processing and image reconstruction unit; 10. Traditional single-aperture solar imager in the prior art; 11. Hollow part. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[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 pair arrangement scheme of the chessboard imager (ZL201711000143.2) to achieve continuous non-redundant sampling in the maximum baseline scale range. The system parameters are shown in the following table. The optical fiber adopts 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 and transmits light in the x polarization direction, and the output light energy in the y polarization direction is 0.

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

[0047] project parameter Working center wavelength 450.287nm Working bandwidth 0.406nm Aperture pair array arrangement scheme Checkerboard Minimum baseline length Bmin 0.0036mm Array size (2N+1)×(2N+1) Long Baseline Beam Delivery Fiber Types Single Mode Polarization Maintaining Fiber Fiber array polarization direction x-Polarization Cooling System Metal material as the main supporting material + water cooling and other active systems Phase fast scanning control compensation module Spatial large-range phase control + optical fiber fine phase control Integration time 1ms

[0048] The aperture pair array and the optical fiber transmission array adopt metal materials with high specific stiffness and good thermal conductivity such as Invar titanium alloy as the support structure. The support structure is connected to active thermal control systems 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. With the help of a closed-loop control circuit, the optical path difference of the paired aperture pair array is coarsely adjusted in the range of ±3mm, and the high-precision adjustment of 10 microns and 20 nanometers in any area is realized. Before the exposure of the solar surface imaging, the optical path difference position of each aperture pair array is scanned quickly in a large optical path difference range, and then a fast scan is performed within a few wavelengths of the zero optical path difference position to compensate for the optical path difference of the aperture pair interference arm caused by atmospheric turbulence and other factors. At the same time, the photoelectric exposure collects and records 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-polarization direction of the sunlight is calculated. Finally, the high spatial resolution image of the sunlight in the x-polarization direction is inverted and reconstructed with the help of the phase recovery and image reconstruction algorithms of the data processing and image reconstruction unit.

[0049] One of the images collected by the Visible Broadband Imager (VBI) on the Daniel K. Inouye Solar Telescope (DKIST) funded by the National Science Foundation ( Figure 3 ) is used as the simulation image and input into the simulation model of the imaging system. When the system N = 60, that is, the maximum baseline length Bmax = 0.2175m, the inverted and reconstructed image is as follows Figure 4As shown in Figure 2, when N = 260, that is, the maximum baseline length Bmax = 0.9360 m, the inverted reconstructed image is as follows: Figure 5 shown.

[0050] Among them, the short baseline solar imager can be replaced by a traditional single-aperture solar imager with the same aperture as the short baseline, such as Figure 6 As shown, a high-resolution solar imager can be composed of a traditional single-aperture solar imager with a relatively small aperture equivalent to a short baseline, and an interferometric solar imager with a relatively long baseline. Figure 6 The aperture pair array 1 of the interferometric solar imager with a relatively long baseline with a high aperture filling density has omitted the short baseline interferometric information acquisition part, forming a hollow part 11. The light collection and imaging capabilities corresponding to the hollow part 11 are completed by the single-aperture solar imager 10 with an aperture equivalent 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. Finally, the data processing and image reconstruction unit 9 processes and inverts and reconstructs the solar high spatial resolution image of two orthogonal polarization states, and its effect is equivalent to that of the long baseline solar imager. For example, 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 covering 0.2175m to 0.9360m to obtain the same imaging effect as the solar imager with N = 260 and a maximum baseline length Bmax = 0.9360m.

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

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

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

[0054] project parameter Working wavelength 629.4nm Aperture pair array arrangement scheme Checkerboard Minimum baseline length 0.0051mm Array size (2N+1)×(2N+1) Long Baseline Beam Delivery Fiber Types Single mode fiber Cooling System Metal material as the main supporting material + water cooling and other active systems Integration time 1ms Polarization direction x and y

[0055] The aperture pair array and the optical fiber transmission array adopt metal materials with high specific stiffness and good thermal conductivity such as Invar titanium alloy as the support structure. The support structure is connected to active thermal control systems 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 adjustment and optical fiber fine phase adjustment. With the help of a closed-loop control circuit, the optical path difference of the paired aperture pair array is coarsely adjusted in the range of ±3mm, and the high-precision adjustment of 10 microns and 20 nanometers in any area is achieved. Before the exposure of the solar surface imaging, the optical path difference position of each aperture pair array is scanned quickly in a large optical path difference range, and then a fast scan is performed within a few wavelengths of the zero optical path difference position to compensate for the optical path difference of the aperture pair interference arm caused by atmospheric turbulence and other factors. At the same time, the photoelectric exposure collects and records 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 sunlight is calculated, and finally the high spatial resolution image of the sunlight in the x and y polarization directions is inverted and reconstructed with the help of a data processing algorithm.

[0056] Two arbitrary x-polarization and y-polarization images collected by the visible light spectropolarimeter (VISP) of the Daniel K. Inouye Solar Telescope (DKIST) funded by the National Science Foundation of the United States are used as simulation images and input into the simulation model of the imaging system. When the system N = 30, that is, the maximum baseline length Bmax = 0.1523m, the PSNRs of the images reconstructed by the inversion of the x and y polarizations are 33.9 and 40.0 respectively; when the system N = 60, that is, the maximum baseline length Bmax = 0.3046, the PSNRs of the images reconstructed by the inversion of the x and y polarizations are 40.4 and 39.6 respectively. For details, see Figure 7 .

[0057] PSNR is an indicator for evaluating image quality by comparing the difference between the original input image and the interferometric imaging reconstructed image. The higher the value, the higher the fidelity of the image. The simulation results of this example show that the reconstructed solar image of the high spatial resolution solar imager based on optical interferometry is very fidelity to the input original image, proving that the technical solution disclosed in the patent of this invention can be applied to solar imaging observation.

[0058] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A high spatial resolution solar imager based on optical interferometry, characterized in that: The high spatial resolution solar imager comprises an aperture pair array (1) with a high aperture filling density, a heat dissipation system (2), a broadband beam single-mode optical fiber transmission array (3), a phase rapid scanning control 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 sequentially passes through the broadband beam single-mode optical fiber transmission array (3), the phase rapid scanning control 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), and is transmitted in pairs into the photoelectric conversion device and data acquisition unit (8), converted into electrical signals and stored, and finally processed by the data processing and image reconstruction unit (9) to invert and reconstruct the solar high spatial resolution image in two orthogonal polarization states. At the same time, the heat dissipation system (2) provides a stable temperature field environment for each group of components.

2. The high spatial resolution solar imager based on optical interferometry according to claim 1, characterized in that: 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 1×2 light splitting polarization units (702), two polarization direction Ix beam transmission units (703), two polarization direction Iy beam transmission units (704), two same polarization state beam 2×1 beam combining interference units (705) and an orthogonal polarization state beam output end (706). The optical paths of the four optical paths from the beam polarization splitting start point to the beam combining end point in the device are consistent. Sunlight is coupled into the aperture pair beam collection end (701) and each is divided into two orthogonal polarized lights by the 1×2 light splitting polarization unit (702), and then transmitted by the polarization direction Ix beam transmission unit (703) and the polarization direction Iy beam transmission unit (704). After that, the same polarization state beams are paired in pairs and enter the 2×1 beam combining interference unit (705) for interference. Finally, they are output from the orthogonal polarization state beam output end (706).

3. The high spatial resolution solar imager based on optical interferometry according to claim 1, characterized in that: The heat dissipation system (2) provides a temperature control function for the entire imaging optical path, especially for dissipating heat for the aperture pair array (1) facing the direct sunlight. The broadband beam single-mode optical fiber transmission array (3) adopts a single-mode optical fiber, and suppresses stray light, especially near-field stray light, through the effective numerical aperture angle of the optical fiber. The phase fast scanning control compensation module (4) is used to control the optical path difference of the paired optical path, and compensate for the change of the optical path difference of the interference optical path caused by atmospheric turbulence, environmental vibration and temperature. In the process of information acquisition, a fast scan near the zero optical path difference of the paired optical path is realized by means of a closed-loop control technology, so as to obtain the mutual intensity information of the spatial frequencies of two orthogonal polarization states. The narrowband spectroscopic / filtering system (5) realizes the requirements of solar observation scientific objectives for spectral selection and filtering. The integrated orthogonal polarization measurement device array (7) divides the single-mode light beam collected and transmitted at the front end into two orthogonal polarization light beams according to the polarization direction, thereby realizing the measurement of sunlight information of two orthogonal polarization states. The data processing and image reconstruction unit (9) has the functions of spatial frequency domain phase recovery and image reconstruction.

4. The high spatial resolution solar imager based on optical interferometry according to claim 1, characterized in that: The aperture pair array (1) with a high aperture filling density can omit the short baseline interference acquisition information acquisition part, that is, form a hollow part (11), and its corresponding light collection and imaging capabilities are completed by a single aperture solar imager (10) with an aperture equivalent to the short baseline, and the imaging information obtained is transmitted to the data processing and image reconstruction unit (9), and is fused with the data obtained by the long baseline interference acquisition information acquisition part, and finally processed by the data processing and image reconstruction unit (9) to invert and reconstruct a high spatial resolution solar image in two orthogonal polarization states.

5. A working method of a high spatial resolution solar imager based on optical interferometry, the working method being applicable to a high spatial resolution solar imager based on optical interferometry as claimed in any one of claims 1 to 3, characterized in that: The first step is to turn on the solar imager, and start the working mode of the phase rapid scanning control compensation module (4) and the photoelectric conversion and data acquisition unit (8). The phase rapid scanning control compensation module (4) scans to compensate for the optical path difference change caused by factors such as atmospheric turbulence, working environment vibration or temperature field change, so that the photoelectric conversion and data acquisition unit (8) can collect the maximum value of the interference envelope of each paired transmission interference light path of the aperture pair array (1), and then judge the zero optical path difference position of each paired transmission interference light path of each aperture pair array (1) of the solar imager, and set the phase rapid scanning control compensation module (4) near the zero optical path difference position of each paired transmission interference light path of each aperture pair array; In the second step, the phase rapid scanning control compensation module (4) and the photoelectric conversion and data acquisition unit (8) start the working mode, the solar imaging device phase rapid scanning control compensation module (4) scans through the vicinity of the zero optical path difference of each paired 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 and Iy of the sunlight obtained by the integrated orthogonal polarization measurement device array; The third step is to filter out direct current with the help of the data processing and image reconstruction unit (9), complete the calculation of the peak-to-valley value and average value 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 spatial spectrum of the two orthogonal polarization states, and reconstruct a high spatial resolution image of the sun through phase recovery and image reconstruction algorithms.

6. The working method of a high spatial resolution solar imager based on optical interference according to claim 5, characterized in that: The integrated orthogonal polarization measurement device array (7) is located between the narrow-band beam single-mode optical 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 sunlight.

Images