Snapshot spatial solar spectrum magnetic imaging instrument based on integration of f-p cavity and superlens

Abstract

The application relates to the field of solar magnetic field detection, in particular to a snapshot spatial solar spectrum magnetic imager integrated based on an F-P cavity and a superlens, which comprises, along an optical path, a front filter assembly, a front telescope system, a band-pass filter, a tunable F-P resonant cavity filter, an F-P resonant cavity polarization enhancer and a surface array detector. The polarization enhancer comprises a fixed F-P resonant cavity and a polarization beam splitting superlens embedded in the cavity, the superlens is composed of an anisotropic subwavelength nanostructure array, the anisotropic subwavelength nanostructure array is used for implementing differential phase regulation on light beams of different polarization states, target polarization state light beams are efficiently transmitted by meeting the cavity resonance condition, and non-target polarization state light beams are reflected and suppressed, and the spatial separation and focusing of four polarization components are simultaneously completed in a single exposure. The application can significantly improve the system integration and mechanical stability, effectively suppress the polarization error of the instrument, and improve the adaptability and measurement accuracy of the system in the space environment.

Description

Technical Field

[0001] This invention belongs to the field of solar magnetic field detection technology, and particularly relates to a snapshot-type space solar spectromagnetic imager based on the integration of an FP cavity and a superlens. Background Technology

[0002] The detection of solar magnetic field information is primarily based on the Zeeman effect, where magnetic spectral lines in the solar atmosphere split under the influence of a magnetic field, exhibiting specific polarization characteristics. By precisely measuring the polarization states of these spectral lines, the intensity and direction distribution of the solar vector magnetic field can be retrieved. This detection process requires the use of ultra-high resolution filtering devices to select fine target spectral bands from the solar spectrum, and the use of polarization analysis devices to measure the intensity of all Stokes parameters (I, Q, U, V). Finally, the vector magnetic field information is calculated using an inversion program.

[0003] In existing visible-light solar magnetic imager technical solutions, the filtering module and polarization measurement module constitute the core observation architecture. Existing filtering modules mainly employ various types, including grating spectrometers, Fourier transform spectrometers, Lyot filters, and two-stage filtering systems combining Lyot filters with Fabry-Perot (FP) interferometers. Grating spectrometers utilize diffraction principles for spectral selection, but suffer from large system size and complex optical paths. Fourier transform spectrometers acquire spectral information through the Fourier transform of interferograms, offering high throughput, but also face the challenge of complex system structure. Lyot filters, composed of alternating stacks of multi-stage birefringent crystals and polarizers, achieve narrowband filtering through polarization interference, resulting in a relatively compact structure. The two-stage filtering scheme, combining Lyot filters with Fabry-Perot interferometers, balances a wide free spectral range with extremely high spectral resolution, effectively suppressing sideband transmission while maintaining narrowband filtering performance, making it the mainstream filtering configuration widely adopted in current high-performance solar magnetic imagers.

[0004] Existing polarization measurement modules generally employ time-series modulation techniques, with their core devices primarily falling into two categories: mechanically rotating waveplates and liquid crystal variable phase retarders. The mechanically rotating waveplate scheme uses a stepper motor or servo motor to drive the waveplate rotation, modulating the polarization state of the incident light to varying degrees at different times. A subsequent polarization beam splitter then performs polarization detection, allowing the acquisition of image information with different polarization states sequentially across different time frames. The liquid crystal variable phase retarder scheme utilizes the principle that the birefringence of liquid crystal materials is adjustable under an applied electric field. It rapidly switches the phase delay amount through electronic control, achieving time-series modulation and measurement of the incident light's polarization state. Although these two schemes differ in modulation rate and implementation method, they are essentially time-division multiplexing modulation techniques. This means that multiple frames of images under different polarization modulation states need to be sequentially switched and acquired at different times to combine and calculate the complete Stokes parameters.

[0005] Although the aforementioned existing technical solutions have been widely used in the field of solar magnetic field observation, they still have the following shortcomings in engineering applications for space solar exploration: (1) The system has low integration and complex and large structure. In the existing scheme, the Leo filter relies on the stacking and assembly of multi-level birefringent crystals and polarizers. The polarization analyzer is also built with discrete components such as mechanically rotating waveplates or liquid crystal variable phase retarders. The modules are connected by complex optomechanical structures, resulting in a long optical path and large size. It is difficult to achieve system miniaturization and limits its application in scenarios with strict constraints on payload volume and weight, such as space exploration.

[0006] (2) The time-series polarization measurement method cannot achieve real-time measurement. Because the current polarization measurement requires switching different polarization modulation states in sequence and acquiring multiple frames of images sequentially, there is an inherent time delay. When observing rapidly evolving solar activity phenomena, this non-simultaneity will introduce significant measurement errors, which seriously restricts the time resolution in dynamic solar magnetic field observation.

[0007] (3) Poor mechanical stability and susceptible to environmental interference. The system contains a large number of discrete mechanical moving parts and precision assembly structures. Under the influence of environmental factors such as vibration, stress or temperature deformation, optical path misalignment and polarization distortion are very likely to occur, which will affect the long-term stability of measurement accuracy. In particular, it is difficult to adapt to the strong vibration and shock during the space launch process and the extreme temperature alternation conditions on orbit.

[0008] (4) The instrument has a large polarization error, and the source of the error is difficult to trace and correct. Due to the large number of discrete components and the complexity of the optical path, static polarization errors such as tilted interface reflection and stress birefringence introduced by each component are difficult to accurately calibrate. More importantly, in the space environment, factors such as mechanical motion, component deformation and temperature drift will induce new dynamic polarization errors. Such errors are difficult to predict completely in the early stage of design and seriously affect the measurement accuracy of solar magnetic field information. Summary of the Invention

[0009] In view of this, the present invention aims to provide a snapshot-type space solar spectromagnetic imager based on the integration of FP cavity and superlens, so as to solve the problems of low system integration, inability to achieve real-time measurement, poor mechanical stability and large instrument polarization error in the prior art.

[0010] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration includes a front filter assembly, a front telescope system, a bandpass filter, a tunable FP resonant cavity filter, an FP resonant cavity polarization enhancer, and an area array detector, arranged sequentially along the incident direction of sunlight; wherein, The pre-filter is used to perform preliminary spectral screening and intensity attenuation of incident sunlight; The front telescope system is used to converge and collimate the incident sunlight; A bandpass filter is used to compress the spectral bandwidth of incident sunlight into a narrow window of the magnetic spectral lines of the nearby target sun. Tunable FP resonant cavity filters are used for spectral scanning and narrowband filtering of target solar magnetic spectral lines; The FP resonant cavity polarization enhancer includes a fixed FP resonant cavity and a polarization beam splitter superlens embedded in the fixed FP resonant cavity. The polarization beam splitter superlens is used to simultaneously separate and independently focus four polarization beams during a single exposure. The fixed FP resonant cavity is used to ensure that the four polarization beams meet the cavity resonance matching condition to achieve transmission enhancement. The area array detector is used to simultaneously receive four polarized beams during a single exposure to obtain all polarization components required to solve the full Stokes parameters.

[0011] Furthermore, the four polarization beams are 0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light, and right-hand circularly polarized light, respectively. The polarization beam splitter is used to focus these four polarization beams onto the four independent detection areas of the array detector.

[0012] Furthermore, the in-plane partitioning method of the polarization beam splitter is either a shared aperture distribution or an interlaced aperture distribution.

[0013] Furthermore, when the polarization beam-splitting superlens has a shared aperture distribution, the polarization beam-splitting superlens has four regions corresponding to 0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light, and right-hand circularly polarized light, respectively.

[0014] Furthermore, the polarization beam-splitting superlens employs an all-dielectric metasurface, specifically composed of a dielectric substrate and an array of anisotropic subwavelength nanostructures arranged on the dielectric substrate.

[0015] Furthermore, the anisotropic subwavelength nanostructures are rectangular, cross-shaped, or L-shaped.

[0016] Furthermore, the tunable FP resonant cavity filter includes an air FP resonant cavity and a driving mechanism. The air FP resonant cavity includes a moving mirror and a stationary mirror. The driving mechanism is a piezoelectric ceramic driving system or a microelectromechanical system, used to drive the moving mirror to adjust the cavity length of the air FP resonant cavity, thereby achieving spectral scanning of the target solar spectrum.

[0017] Furthermore, both the moving mirror and the stationary mirror are distributed Bragg mirrors or metallic mirrors. The distributed Bragg mirror is composed of alternating depositions of high-refractive-index materials and low-refractive-index materials, with an optical thickness of λ / 4 for each layer, where λ is the center wavelength of the target solar magnetic spectral line. The high-refractive-index material is any one of titanium dioxide, tantalum pentoxide, niobium pentoxide, or hafnium oxide, and the low-refractive-index material is silicon dioxide. The metallic mirror is made of silver, aluminum, or gold.

[0018] Furthermore, the bandpass filter is a multilayer dielectric film interference filter or a fixed FP resonant cavity based on distributed Bragg mirrors.

[0019] Furthermore, the pre-filter assembly includes an anti-reflection filter, a cutoff filter, and an attenuation filter arranged sequentially along the incident direction of sunlight.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) The system has high integration, compact structure, and can be miniaturized. This invention integrates a tunable FP resonant cavity filter with a superlens embedded FP resonant cavity polarization enhancer into a single chip-level design. This single-chip device replaces the multi-stage stacked Leo filter and the polarization analyzer built from discrete components in the traditional solution, thus simultaneously achieving ultra-narrowband spectral filtering and parallel separation of multiple polarization states. The size of the single-chip device can be reduced to the micrometer level, and it can be directly integrated with the back-end area array detector. This can significantly reduce the complexity of assembly and adjustment and alignment errors, providing a feasible solution for applications such as space exploration where there are strict constraints on payload volume and weight.

[0021] (2) Snapshot-style real-time measurement with high temporal resolution. This invention uses a polarization beam-splitting superlens to spatially separate beams of different polarization states and independently focus them onto different regions of the array detector. In a single exposure, all polarization components required to calculate the complete Stokes parameters can be acquired in parallel. This fully static, single-exposure working method fundamentally breaks through the inherent limitation of traditional time-series modulation schemes, which require sequential switching of polarization states and sequential acquisition. It eliminates measurement errors introduced by time delay and can significantly improve the temporal resolution of dynamic magnetic field measurements when observing rapidly evolving solar activity phenomena.

[0022] (3) High mechanical stability and minimal environmental interference. The core component of this invention, the FP resonant cavity polarization enhancer, which is responsible for polarization state separation and focusing, is a static structure. Its polarization response characteristics are entirely determined by the geometric parameters of the solidified nanostructure. It does not rely on any moving or active modulation components such as mechanically rotating waveplates, stepper motors, or liquid crystal electronically controlled modulation, thus avoiding optical path misalignment and polarization distortion caused by vibration, stress, or deformation. It is suitable for long-term stable operation in harsh space environments.

[0023] (4) The instrument has small polarization error and strong traceability of error sources. Compared with the complex polarization error chain introduced by a large number of discrete optical components in the traditional scheme, the present invention significantly simplifies the optical path structure and reduces the introduction of static polarization error sources such as tilted interface reflection and stress birefringence from the source. At the same time, by eliminating mechanical moving parts and electronic control modulation units, the dynamic polarization error induced by component deformation, temperature drift and other factors in the on-orbit environment is effectively avoided, making the source of instrument polarization error clearer and easier to complete accurate calibration and modeling in the laboratory stage, thereby significantly improving the measurement accuracy of solar magnetic field information. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the structure of a snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration as described in an embodiment of the present invention; Figure 2 A schematic diagram of the transmission spectrum of the bandpass filter and the tunable FP resonant cavity filter described in the embodiments of the present invention; Figure 3 A planar schematic diagram of the polarization four-quadrant superlens described in an embodiment of the present invention; Figure 4 A schematic diagram of the beam-splitting and focusing optical path of the polarization four-quadrant superlens described in the embodiments of the present invention; Figure 5 A schematic diagram of the structure of the FP resonant cavity polarization enhancer described in the embodiment of the present invention.

[0025] Figure reference numerals: 1. Front filter assembly; 2. Front telescope system; 3. Bandpass filter; 4. Tunable FP resonant cavity filter; 4. Air FP resonant cavity; 41. Drive mechanism; 42. FP resonant cavity polarization enhancer; 5. Fixed FP resonant cavity; 51. Polarizing beam splitter; 52. Substrate; 53. Bottom DBR; 54. Lower spacer layer; 55. Upper spacer layer; 56. Top DBR; 57. Area array detector; 6. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0028] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] like Figures 1-5 As shown, the snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration provided by the present invention includes a front filter assembly 1, a front telescope system 2, a bandpass filter 3, a tunable FP resonant cavity filter 4, an FP resonant cavity polarization enhancer 5, and an area array detector 6.

[0032] The pre-filter assembly 1 is positioned at the very front of the optical path, directly receiving incident sunlight and performing preliminary spectral filtering and intensity attenuation on the incident sunlight. The pre-filter assembly 1 is composed of an anti-reflection filter, a cutoff filter, and an attenuation filter. The anti-reflection filter reduces surface reflection loss over a wide wavelength range (typically 400–900 nm, covering the visible to near-infrared band), improving light energy utilization. The cutoff filter blocks stray light outside the target wavelength range, initially limiting the spectral range (e.g., 580–660 nm, bandwidth approximately 80 nm). The attenuation filter appropriately attenuates the incident light intensity (typically reducing the total transmittance to 0.1%–1%, corresponding to optical density OD1–3), further controlling the energy entering subsequent systems. Through this combined filtering, stray light is effectively suppressed, heat load is reduced, and the system's signal-to-noise ratio is improved.

[0033] The front telescope system 2 is located at the rear end of the front filter assembly 1. As the optical front end of the entire magnetic imager, the front telescope system 2 is responsible for converging, shaping, and collimating far-field sunlight. The front telescope system 2 uses a Cassegrain telescope to converge parallel-incident sunlight. At the same time, through optical design (such as using aspherical mirrors and achromatic lens groups), it suppresses stray light and various aberrations, shaping the beam into a collimated beam that meets the requirements of subsequent filtering and polarization analysis.

[0034] The bandpass filter 3 is located at the rear end of the front telescope system 2. Based on the broadband pre-screening completed by the front filter assembly 1, the bandpass filter 3 is used to further compress the spectral bandwidth and accurately lock the narrow band window near the target magnetic spectral line (e.g., about 2nm bandwidth near the 617nm spectral line), providing spectrally clean input light for the rear tunable FP resonant cavity filter 4.

[0035] In this embodiment, the bandpass filter 3 can be a multilayer dielectric film interference filter, which is formed by alternating deposition of dielectric thin film layers with different refractive indices, achieving narrowband transmission through interference effects. Alternatively, the bandpass filter 3 can also be a fixed FP resonant cavity structure based on a distributed Bragg mirror (DBR) to achieve a better balance between bandwidth compression and energy transmission efficiency.

[0036] Figure 2 The transmission spectra of bandpass filter 3 and tunable FP resonant cavity filter 4 are shown under extremely low loss conditions. Figure 2 As shown, the transmission curve of bandpass filter 3 has a broad peak, a center wavelength of 617nm, and a full width at half maximum (FWHM) of about 2nm; the transmission curve of tunable FP resonant cavity filter 4 shows an extremely narrow transmission peak in the bandpass range, with a FWHM of less than 0.01nm.

[0037] The tunable FP resonant cavity filter 4 is located at the rear end of the bandpass filter 3 and is the core device for realizing ultra-high resolution spectral scanning in this invention.

[0038] The tunable FP resonant cavity filter 4 includes an air FP resonant cavity 41 and a driving mechanism 42. The air FP resonant cavity 41 is composed of a moving mirror, a stationary mirror, and an air gap between the moving mirror and the stationary mirror. The moving mirror and the stationary mirror, as cavity mirrors of the air FP resonant cavity 41, both adopt distributed Bragg reflectors.

[0039] When a distributed Bragg reflector is used as the cavity mirror, it is formed by alternating deposition of high-refractive-index and low-refractive-index materials on the substrate material. The optical thickness of each layer is λ / 4, where λ is the center wavelength of the target solar magnetic spectral line. The high-refractive-index material can be any one of titanium dioxide, tantalum pentoxide, niobium pentoxide, or hafnium oxide, while the low-refractive-index material is silicon dioxide. High reflectivity (typically above 99%) is achieved through constructive interference, thus ensuring that the air FP resonator 41 has high spectral resolution. The substrate material is selected from fused silica or silicon wafers, with a surface roughness of less than 1 nm and a flatness better than λ / 10, to ensure the parallelism and surface quality of the cavity mirror.

[0040] In addition to using distributed Bragg mirrors, endoscopic mirrors can also use high-reflectivity metal mirrors, such as thin-film metal mirrors made of silver, aluminum, or gold.

[0041] The drive mechanism 42 can employ a piezoelectric ceramic (Lead Zirconate Titanate, PZT) drive system or a micro-electro-mechanical system (MEMS). The piezoelectric ceramic drive system utilizes the piezoelectric effect to generate micrometer-level displacement when a voltage is applied, offering advantages such as fast response speed (millisecond level) and high displacement accuracy (nanometer level). The MEMS is manufactured using microfabrication technology, integrating the moving mirror and drive mechanism 42 on a single chip, resulting in smaller size, lower power consumption, and suitability for mass production.

[0042] The moving mirror translates along the optical axis under the drive of a piezoelectric ceramic drive system or a microelectromechanical system, thereby adjusting the cavity length of the air FP resonator 41. A small change in the cavity length will cause a corresponding shift in the transmission peak wavelength of the air FP resonator 41, thereby achieving high-resolution spectral scanning of the target solar spectrum.

[0043] In this embodiment, the specific parameters for the tunable FP resonant cavity filter 4 to achieve spectral scanning are as follows: the scanning wavelength range is 616.338 nm to 618.336 nm, the corresponding cavity length adjustment range is 94915.57 nm to 95223.30 nm, the total adjustment is 307.73 nm, the total number of scanning steps is 333 steps, and the required step resolution is approximately 0.924 nm / step. These parameters meet the requirements for fine scanning of the 617 nm magnetic spectral line.

[0044] The FP resonant cavity polarization enhancer 5 is located at the rear end of the tunable FP resonant cavity filter 4 and is the core device for realizing snapshot polarization measurement in this invention. For example... Figure 5 As shown, the FP resonant cavity polarization enhancer 5 includes a fixed FP resonant cavity 51 and a polarization beam-splitting superlens 52. The fixed FP resonant cavity 51 is a solid-state resonant cavity with a constant cavity length. Specifically, it includes two cavity mirrors, which are distributed Bragg mirrors or metal mirrors, with a solid medium between them. The polarization beam-splitting superlens 52 is embedded in the solid medium of the fixed FP resonant cavity 51.

[0045] The polarizing beam splitter 52 can be sequentially and uniformly fabricated on a single chip along with the fixed FP resonant cavity 51 using semiconductor processes (especially MOCVD deposition combined with electron beam lithography). For example: a bottom DBR 54 and a lower spacer layer 55 (usually silicon dioxide) are sequentially deposited on a substrate 53 (usually BK7 glass); the polarizing beam splitter 52 is fabricated on the surface of the lower spacer layer 55 using electron beam lithography and etching processes; then an upper spacer layer 56 (usually silicon dioxide) is deposited to completely cover the polarizing beam splitter 52; a top DBR 57 is then deposited on top of the upper spacer layer 56, thereby encapsulating the polarizing beam splitter 52 between the lower spacer layer 55 and the upper spacer layer 56.

[0046] The polarization beam splitter 52 is used to simultaneously separate the incident sunlight into 0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light and right-hand circularly polarized light during a single exposure, and independently focus these four polarized beams onto four independent detection areas of the array detector 6, thereby achieving snapshot-style synchronous detection of the four polarized beams.

[0047] The polarizing beam-splitting superlens 52 can be divided into two in-plane partitioning methods: a shared aperture distribution or an interlaced aperture distribution. A shared aperture distribution means that different functional areas jointly cover the entire light-transmitting aperture, seamlessly spliced ​​together without overlapping. It's like dividing a complete circular lens into several independent areas, all of which fill the entire incident window and jointly receive the entire incident beam.

[0048] Interwoven aperture distribution refers to the finely interwoven arrangement of different functional regions in a checkerboard or pixel-like pattern, with anisotropic subwavelength nanostructures corresponding to each function uniformly distributed throughout the aperture. Interwoven aperture distribution does not involve each region being divided into a large, complete area; instead, each functional unit is broken down into numerous tiny units, arranged alternately like a woven mesh.

[0049] In this embodiment, the anisotropic subwavelength nanostructure array of the polarization beam-splitting superlens 52 adopts a shared aperture distribution. For example... Figure 3 and Figure 4 As shown, the polarization beam-splitting superlens 52 has four regions, labeled as regions 1, 2, 3, and 4, respectively, corresponding to 0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light, and right-hand circularly polarized light. The polarization beam-splitting superlens 52 employs an all-dielectric metasurface, fabricated based on an array of anisotropic subwavelength nanostructures (typically titanium dioxide, tantalum pentoxide, or hydrogenated amorphous silicon) on a dielectric substrate (usually silicon dioxide). The anisotropic subwavelength nanostructures are rectangular, cross-shaped, or L-shaped. By precisely controlling the geometric dimensions (such as length, width, and height), spatial orientation (such as rotation angle), and arrangement (such as period and spacing) of anisotropic subwavelength nanostructures, and integrating them with the principles of propagation phase modulation, geometric phase modulation, and reverse design, the required phase distribution can be achieved independently in each region. This allows four polarization beams—0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light, and right-hand circularly polarized light—to be independently focused into four independent detection regions 1, 2, 3, and 4 of the array detector 6.

[0050] When the light beam is incident on the FP resonant cavity polarization enhancer 5: For the target polarized beam: the anisotropic subwavelength nanostructure in the region corresponding to the polarization beam splitter 52 introduces a specific phase distribution into the target polarized beam, shaping its wavefront into a converging spherical wave; simultaneously, the equivalent optical path of the target polarized beam within the fixed FP resonant cavity 51 satisfies the resonance condition, resulting in constructive interference of multiple beams and a peak transmittance (approaching 100%). The converged transmitted light is directly focused onto the detection region corresponding to the area array detector 6.

[0051] For non-target polarization states: the phase distribution introduced by the anisotropic subwavelength nanostructure in the region corresponding to the polarization beam splitter 52 cannot effectively focus the non-target polarization beam; more importantly, the equivalent optical path of the non-target polarization beam in the fixed FP resonant cavity 51 deviates from the resonance condition, the multi-beam interference cancels out, the transmittance drops sharply (<1%), and most of the energy is blocked by reflection.

[0052] This coupling mechanism of polarization modulation and resonance enhancement not only achieves spatial separation and independent focusing of beams with different polarization states, but also improves the polarization extinction ratio of each channel without the need for additional polarization optical elements, effectively suppresses crosstalk between channels, thereby enhancing the detection capability of weak magnetic field signals and improving the calculation accuracy of the full Stokes parameters, thus improving the measurement accuracy of solar magnetic field information.

[0053] Based on the FP resonance enhancement mechanism and the polarization-selective response of the polarization-splitting superlens 52, this invention can effectively improve the transmission efficiency of the target polarization state and suppress orthogonal polarization components, thereby achieving high polarization extinction performance. In this embodiment, the polarization extinction ratio preferably reaches above 20 dB.

[0054] The array detector 6 is located at the rear end of the FP resonant cavity polarization enhancer 5. The array detector 6 has four independent detection areas, which respectively receive four polarization beams: 0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light, and right-hand circularly polarized light, in order to obtain all polarization components required to solve the full Stokes parameters and realize snapshot-type synchronous detection of the four polarization components.

[0055] The FP resonant cavity polarization enhancer 5 in this invention can be integrated with the area array detector 6 through wafer-level bonding, flip-chip bonding, or transparent adhesive encapsulation. In specific implementation, a high-precision alignment process is used to mount the FP resonant cavity polarization enhancer 5 on top of the CMOS or InGaAs area array detector, so that each polarization enhancement sub-region is precisely matched with the corresponding detection region.

[0056] During a single exposure, light intensity signals corresponding to the polarization state are simultaneously acquired from four detection areas. The raw light intensity signals acquired from each area are then transmitted to the data processing module, where they undergo dark current subtraction, responsivity normalization, and system accuracy calibration to obtain the complete Stokes parameters (I, Q, U, V). Combined with a pre-calibrated inversion program and based on the polarization-magnetic field mapping relationship, the intensity and direction distribution information of the solar vector magnetic field are further calculated. The specific calculation process is existing technology and will not be elaborated here.

[0057] Because the four polarization components are acquired simultaneously, the time resolution is limited only by the CMOS exposure time (which can reach the millisecond level), fundamentally eliminating the time-division measurement error caused by the rapid changes in the solar magnetic field.

[0058] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0059] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration, characterized in that, It includes a front-view filter assembly, a front-view telescope system, a bandpass filter, a tunable FP resonant cavity filter, an FP resonant cavity polarization enhancer, and an area array detector, arranged sequentially along the incident direction of sunlight; among which, The pre-filter is used to perform preliminary spectral screening and intensity attenuation of incident sunlight; The front telescope system is used to converge and collimate the incident sunlight; A bandpass filter is used to compress the spectral bandwidth of incident sunlight into a narrow window of the magnetic spectral lines of the nearby target sun. Tunable FP resonant cavity filters are used for spectral scanning and narrowband filtering of target solar magnetic spectral lines; The FP resonant cavity polarization enhancer includes a fixed FP resonant cavity and a polarization beam splitter superlens embedded in the fixed FP resonant cavity. The polarization beam splitter superlens is used to simultaneously separate and independently focus four polarization beams during a single exposure. The fixed FP resonant cavity is used to ensure that the four polarization beams meet the cavity resonance matching condition to achieve transmission enhancement. The area array detector is used to simultaneously receive four polarized beams during a single exposure to obtain all polarization components required to solve the full Stokes parameters.

2. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 1, characterized in that, The four polarization beams are 0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light, and right-hand circularly polarized light. The polarization beam splitter is used to focus these four polarization beams onto the four independent detection areas of the array detector.

3. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 1 or 2, characterized in that, The in-plane partitioning method of the polarization beam splitter is either a shared aperture distribution or an interlaced aperture distribution.

4. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 3, characterized in that, When the polarization beam splitter is distributed with a shared aperture, the polarization beam splitter has four regions corresponding to 0° linearly polarized light, 90° linearly polarized light, 135° linearly polarized light, and right-hand circularly polarized light, respectively.

5. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 3, characterized in that, The polarization beam-splitting superlens employs an all-dielectric metasurface, specifically composed of a dielectric substrate and an array of anisotropic subwavelength nanostructures arranged on the dielectric substrate.

6. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 5, characterized in that, The anisotropic subwavelength nanostructures are rectangular, cross-shaped, or L-shaped.

7. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 1, characterized in that, The tunable FP resonant cavity filter includes an air FP resonant cavity and a driving mechanism. The air FP resonant cavity includes a moving mirror and a stationary mirror. The driving mechanism is a piezoelectric ceramic driving system or a microelectromechanical system, used to drive the moving mirror to adjust the cavity length of the air FP resonant cavity, thereby achieving spectral scanning of the target solar spectrum.

8. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 7, characterized in that, Both the moving mirror and the stationary mirror are distributed Bragg mirrors or metallic mirrors. The distributed Bragg mirror is composed of alternating depositions of high-refractive-index materials and low-refractive-index materials, with an optical thickness of λ / 4 for each layer, where λ is the center wavelength of the target solar magnetic spectral line. The high-refractive-index material is any one of titanium dioxide, tantalum pentoxide, niobium pentoxide, or hafnium oxide, and the low-refractive-index material is silicon dioxide. The metallic mirror is made of silver, aluminum, or gold.

9. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 1, characterized in that, The bandpass filter is a multilayer dielectric film interference filter or a fixed FP resonant cavity based on distributed Bragg mirrors.

10. The snapshot-type space solar spectromagnetic imager based on FP cavity and superlens integration according to claim 1, characterized in that, The pre-filter assembly includes an anti-reflection filter, a cutoff filter, and an attenuation filter arranged sequentially along the incident direction of sunlight.

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