Dynamic astronomical light interference fringe tracking system and method for beam combination rear-end polarization modulation

Abstract

The invention discloses a dynamic astronomical light interference fringe tracking system and method for beam combination rear-end polarization modulation. The system comprises a first cat eye system delay system, a second cat eye system delay system, a first achromatic half-wave plate, a second achromatic half-wave plate, a first polarization splitting prism, a second polarization splitting prism, a first reflector, a second reflector, a third reflector, a fourth reflector, a fifth reflector, a first cat eye reflector, a second cat eye reflector and a right-angle outer reflector. The method comprises the following steps: firstly, performing interference beam combination of astronomical light by using a first polarization splitting prism; then, carrying out polarization modulation after interference beam combination by adopting a beam combination rear-end polarization modulation method; carrying out polarization component extraction on the light beam subjected to polarization modulation by using a second polarization splitting prism to obtain four interferogram images with phase intervals; and finally, obtaining a piston error and a tilt error through spectrum period calculation, four-step phase shift calculation of monochromatic light and light spot measurement after light splitting. The precision requirement of a polarization modulation device is reduced, the astronomical light interference fringe tracking precision is improved, the disturbance rejection capability is high, the system structure is compact, broadband work is supported, and engineering implementation is easy.

Description

Technical Field

[0001] This invention relates to the field of astronomical optical interferometry and high-precision phase detection technology, and in particular to a dynamic astronomical optical interferometric fringe tracking system and method with beam combining back-end polarization modulation. Background Technology

[0002] In astronomical observation, the angular resolution of traditional single-aperture telescopes is insufficient to meet the demands of observing the fine structures of numerous stars and other celestial objects. Increasing the resolution by enlarging a single aperture faces limitations in manufacturing processes, support structures, materials, and cost. Therefore, astronomical optical interferometry has emerged. This technique involves arranging multiple smaller-aperture telescopes in a sparse array and adjusting the baseline lengths between the sub-telescopes to achieve a much higher angular resolution than a single sub-telescope. However, due to factors such as atmospheric turbulence, rapid relative tilting and optical path disturbances occur between the wavefronts of starlight received by different sub-telescopes. These are called tilt errors and piston errors, or co-phase errors. Co-phase errors are a critical issue in optical synthetic aperture imaging systems. They represent the wavefront phase difference between multiple sub-apertures or sub-mirrors. This error disrupts the system's interference effect, leading to image blurring or reduced resolution, and severely decreasing the visibility of interference fringes. Accurate measurement and real-time compensation of co-phase errors between two interfering beams, including piston errors and wavefront tilt, are fundamental prerequisites for achieving high-resolution observations. Effective astronomical optical interferometry imaging cannot be achieved without high-precision detection and correction of low-order aberrations, especially tilt and piston errors, between the beams of each sub-aperture. Therefore, any astronomical optical interferometer must be equipped with a co-phase detection fringe tracking subsystem that meets the requirements of high detection frequency, wide dynamic range, and high measurement accuracy.

[0003] However, existing co-phase error measurement and fringe tracking techniques have several key bottlenecks that limit their application in dynamic astronomical observation environments:

[0004] 1. Dispersion interference during wide-band operation: In white light or wide-band observation scenarios, the axial dispersion of optical elements, especially phase-shifting elements, introduces additional wavelength-related phase errors, leading to decreased phase-shifting accuracy and interference fringe distortion. Existing phase-shifting techniques often perform polarization modulation at the beam combiner front end, which makes dispersion compensation difficult and presents challenges in achieving high-precision element surface configurations, thus making it difficult to guarantee measurement consistency across the entire observation band.

[0005] 2. Difficulty in simultaneously achieving dynamic range and measurement accuracy: While time-series phase-shifting interferometry based on single wavelengths can achieve nanometer-level measurement accuracy, it is limited by the phase solution. The ambiguity problem means that the unambiguous measurement range is usually no more than half a wavelength, making it difficult to meet the requirements for optical path difference measurements of tens to hundreds of micrometers under initial capture or large disturbances. While measurement methods based on group delay channel interferometric spectroscopy can achieve large-range coarse measurements, their accuracy is usually only on the order of wavelength, which cannot meet the requirements of high-precision closed-loop control.

[0006] 3. Multiple types of errors cannot be detected synchronously: Existing solutions usually require the construction of independent optical paths to detect tilt error and piston error separately, resulting in complex system structure and difficulty in optical path debugging. Furthermore, due to the asynchronous detection timing, it is difficult to provide completely consistent error information for real-time co-phase control in a dynamically changing environment.

[0007] 4. Insufficient resistance to environmental disturbances: Phase-shifting techniques that rely on time modulation, such as phase-shifting techniques that drive the reference mirror to move in steps using piezoelectric ceramics, are extremely sensitive to instantaneous disturbances such as mechanical vibration and atmospheric turbulence during their multiple sampling intervals. This can easily introduce significant phase measurement errors and make it difficult to adapt to complex and dynamic working environments such as observatories.

[0008] Therefore, developing an astronomical optical interferometry fringe tracking method that can simultaneously achieve wide-band adaptability, high measurement accuracy, large range, simultaneous detection of tilt and piston errors, and strong anti-disturbance capability has become the key to breaking through current technical bottlenecks and promoting the development of astronomical optical interferometry and synthetic aperture technology. Summary of the Invention

[0009] The purpose of this invention is to provide a dynamic astronomical optical interferometric fringe tracking system and method with strong anti-interference capability, high precision and large range, and easy engineering implementation, which features beam combining back-end polarization modulation.

[0010] The technical solution to achieve the purpose of this invention is: a dynamic astronomical light interferometric fringe tracking system with beam combining back-end polarization modulation, comprising a first cat's eye system delay system, a second cat's eye system delay system, a first polarizing beam splitter, a first achromatic half-wave plate, an achromatic quarter-wave plate, a second achromatic half-wave plate, a second polarizing beam splitter, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, a fourth reflecting mirror, a right-angle external reflecting mirror, a fifth reflecting mirror, a first cat's eye reflecting mirror, and a second cat's eye reflecting mirror;

[0011] Collimated starlight beams 1 and 2 from the two sub-telescopes pass through the first cat's eye system delay system and the second cat's eye system delay system, respectively. The two beams pass through the first reflector and the second reflector, respectively, and are incident on the first polarizing beam splitter at a set angle. The first polarizing beam splitter combines the S component of beam 1 with the P component of beam 2, and at the same time combines the P component of beam 1 with the S component of beam 2.

[0012] The S component of beam 1 and the P component of beam 2 are polarized by the first achromatic half-wave plate and the achromatic quarter-wave plate, and the P component of beam 1 and the S component of beam 2 are polarized by the second achromatic half-wave plate.

[0013] The first and second achromatic half-wave plates modulate the incident orthogonally polarized components into four linearly polarized lights in the +45° and -45° directions, respectively. The achromatic quarter-wave plate introduces a fixed polarization between the two linearly polarized lights of the first achromatic half-wave plate. Relative phase delay; the modulated beam, after being reflected by the third, fourth, and right-angle external mirrors, is split into four paths by the second polarizing beam splitter. Two of these paths are reflected by the fifth mirror, resulting in four beams with a phase interval of [missing information]. The interferogram image was obtained, and then the phase was extracted using spatial modulation synchronous phase shifting technology.

[0014] Furthermore, all modulation elements are located in the common optical path after beam combining, and their effects on the two interfering beams are completely consistent. Therefore, they have common-mode suppression capabilities for the surface shape error, assembly tolerance, and dispersion introduced when working with white light.

[0015] A dynamic astronomical optical interferometric fringe tracking method with beam combining back-end polarization modulation includes the following steps:

[0016] Step 1: Use the first polarizing beam splitter to perform interference beam combining of astronomical light;

[0017] Step 2: Using the beam combining post-polarization modulation method, polarization modulation is performed after interference beam combining by using the first achromatic half-wave plate, the achromatic quarter-wave plate, and the second achromatic half-wave plate;

[0018] Step 3: For the polarization-modulated beam, use the second polarization beam splitter to extract the polarization components, obtaining four beams with a phase spacing of [missing information]. Interferogram image;

[0019] Step 4: By combining spectral period calculation with four-step phase shift calculation of monochromatic light and measurement of the spot after spectral dispersion, the piston error and tilt error are obtained.

[0020] Furthermore, the interference and beam combining of astronomical light using the first polarizing beam splitter described in step 1 is as follows:

[0021] The sub-aperture beams collected by each astronomical interferometer array at the front end are adjusted so that the polarization components in the vertical and horizontal directions are the same. No adjustment is needed for randomly polarized light that is close to natural light. For astronomical light with partial polarization, an achromatic half-wave plate is used to adjust the polarization direction. Then, the beams are combined on the first polarization beam splitter through cross transmission, and the two outgoing beams maintain a common optical path.

[0022] Furthermore, the polarization modulation method at the back end of the beam combiner described in step 2 involves polarization modulation after interference beam combining using a first achromatic half-wave plate, an achromatic quarter-wave plate, and a second achromatic half-wave plate, as detailed below:

[0023] Beams 1 and 2 are split into four beams—P1, S1, P2, and S2—by the first polarizing beam splitter. Beams P1 and S2 share a common optical path, and beams P2 and S1 share a common optical path. After passing through the first achromatic half-wave plate, the angle between the fast axis of beam P2 and the vertical direction... =22.5° becomes linearly polarized light along the -45° direction; the S1 light passes through the first achromatic half-wave plate, and the angle between the fast axis and the vertical direction is... =22.5° becomes linearly polarized light along the 45° direction; P1 light becomes linearly polarized light along the -45° direction after passing through the second achromatic half-wave plate, and S2 light becomes linearly polarized light along the 45° direction after passing through the second achromatic half-wave plate; then P2 light and S1 light are passed through an achromatic quarter-wave plate, with the fast axis making an angle of 45° with the vertical direction, introducing a 90° phase delay in the two linearly polarized lights at 45° and -45°.

[0024] Furthermore, in step 3, the polarization components of the polarized beam are extracted using a second polarizing beam splitter to obtain four beams with a phase spacing of [missing information]. The interferogram image is as follows:

[0025] For the four polarized beams that have undergone polarization modulation, the beams are further split using a second polarization beam splitter. After passing through the second polarization beam splitter, beams P1 and S2 are obtained as interference patterns I1 and I3 with phase shifts of 0° and 180°, respectively. After passing through the second polarization beam splitter, beams P2 and S1 are obtained as interference patterns I2 and I4 with phase shifts of 90° and 270°, respectively. Finally, four interference pattern images with phases of 0°, 90°, 180°, and 270° are output.

[0026] Furthermore, step 4, by combining the spectral period calculation with the four-step phase-shifting calculation of monochromatic light, yields the piston error and tilt error, as detailed below:

[0027] Step 4.1: Calculate the phase using a four-step phase-shifting algorithm, as shown in the following formula:

[0028]

[0029] Where I1, I2, I3, and I4 are the light intensity values ​​of the four interference images, and their theoretical phases differ sequentially. ;

[0030] Step 4.2: Calculate the piston error. The formula for optical path difference is:

[0031]

[0032] in, Wavelength;

[0033] Step 4.3: After the beams are polarized and modulated by the QWP and HWP, a low-reflectivity beam splitter or dichroic mirror is added to the subsequent optical path to separate some of the energy. The two sampled beams pass through a shared focusing lens and form two separate, clear light spots on the same CCD. The positional offset of the two light spots is calculated using a real-time image processing algorithm. The formula for calculating the wavefront tilt angle is:

[0034] .

[0036] Furthermore, by incorporating a dispersive fringe sensor, breakthroughs can be achieved across the entire spectrum compared to single-wavelength methods. Fuzzy constraints enable measurement ranges exceeding half a wavelength, as detailed below:

[0037] For four interferograms emitted in the same direction, by adding a dispersive prism and then a focusing prism, the spectral channel fringe pattern of the interference is obtained, and the number of fringes is calculated to extend the measurement range.

[0038] The optical path difference between the two arms is calculated using the number of fringe periods in the interference spectrum, where the number of fringe periods in the dispersive fringe sensor is [not specified]. Optical path error between the two arms The relationship is:

[0039]

[0040] in, The number of fringe periods in a specific band on the sensor. It is the upper limit of wavelength. It is the lower limit of wavelength. It is the optical path difference. Step 4.1 involves selecting the light intensity at four specific wavelength spectral positions on the dispersive fringe sensor to maintain a large dynamic range and achieve high precision.

[0041] Furthermore, the tilt detection module and the piston detection module share part of the optical path, and the detection beam is extracted after polarization modulation by a beam splitter to ensure the spatiotemporal synchronization of tilt and piston detection.

[0042] Furthermore, the method also supports working in conjunction with a delay line system to obtain a delay system without left or right sway through the first cat's eye system delay system and the second cat's eye system delay system for delay compensation in measurement. If the disturbance exceeds the upper limit threshold, the first cat's eye system delay system and the second cat's eye system delay system as a whole are moved. If the disturbance is below the lower limit threshold, the first cat's eye reflector and the second cat's eye reflector are moved.

[0043] Compared with the prior art, the present invention has the following significant advantages: (1) It adopts common optical path polarization modulation after beam combining, which avoids the axial dispersion problem caused by polarization modulation when the beam is separated. No additional dispersion compensation mechanism is required, and the requirements for the surface accuracy and thickness accuracy of the polarization modulation device are low; (2) It adopts spatial modulation synchronous phase shifting technology, and completes four-step phase acquisition in a single frame image. It has strong anti-disturbance ability and is suitable for complex scenarios such as astronomical observation; (3) It integrates the synchronous detection function of tilt error and piston error, which does not require an additional independent optical path. The system structure is compact, the detection has no timing difference, and meets the real-time common phase control requirements of dynamic environment; (4) All phase shifting elements are located in the common optical path, which reduces the difficulty of assembly and adjustment and the sensitivity of aberration. It supports wide band operation and can be realized through existing commercial products. No processing or customization is required, and it is easy to implement in engineering. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a dynamic astronomical optical interferometric fringe tracking system with beam combining back-end polarization modulation according to the present invention.

[0045] Figure 2 This is a schematic diagram of the polarization direction of the P-light and S-light after back-end polarization modulation in this invention.

[0046] Figure 3 This is a schematic diagram of the optional tilt measurement and extended range stripe dispersive spectroscopy module in this invention. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0048] like Figure 1 As shown, the present invention discloses a dynamic astronomical light interferometric fringe tracking system with beam combining back-end polarization modulation, comprising a first cat's eye system delay system 1, a second cat's eye system delay system 2, a first polarizing beam splitter prism 3, a first achromatic half-wave plate 4, an achromatic quarter-wave plate 5, a second achromatic half-wave plate 6, a second polarizing beam splitter prism 7, a first reflecting mirror 8, a second reflecting mirror 9, a third reflecting mirror 10, a fourth reflecting mirror 11, a right-angle external reflecting mirror 12, a fifth reflecting mirror 13, a first cat's eye reflecting mirror 14, and a second cat's eye reflecting mirror 15;

[0049] Collimated starlight beams 1 and 2 from the two sub-telescopes pass through the first cat's eye system delay system 1 and the second cat's eye system delay system 2, respectively. The two beams pass through the first reflector 8 and the first reflector 9, respectively, and are incident on the first polarizing beam splitter 3 at a set angle. The first polarizing beam splitter 3 combines the S component of beam 1 with the P component of beam 2, and at the same time combines the P component of beam 1 with the S component of beam 2.

[0050] The S component of beam 1 and the P component of beam 2 are polarized by the first achromatic half-wave plate 4 and the achromatic quarter-wave plate 5, and the P component of beam 1 and the S component of beam 2 are polarized by the second achromatic half-wave plate 6.

[0051] The first achromatic half-wave plate 4 and the second achromatic half-wave plate 6 modulate the incident orthogonally polarized components P and S light into four linearly polarized lights in the +45° and -45° directions, respectively. The achromatic quarter-wave plate 5 introduces a fixed [polarity] between the two linearly polarized lights of the first achromatic half-wave plate 4. Relative phase delay; the modulated beam, after being reflected by the third reflecting mirror 10, the fourth reflecting mirror 11, and the right-angle external reflecting mirror 12, is split into four paths by the second polarizing beam splitter 7. Two of these paths are reflected by the fifth reflecting mirror 13, resulting in four beams with a phase interval of [missing information]. The interferogram image was obtained, and then the phase was extracted using spatial modulation synchronous phase shifting technology.

[0052] As a specific example, all modulation elements are located in the common optical path after beam combining, and their effects on the two interfering beams are completely consistent. Therefore, they have a natural common-mode suppression capability for the surface shape error, assembly tolerance, and dispersion introduced when working with white light, which reduces the requirements for component processing accuracy and system assembly.

[0053] A dynamic astronomical optical interferometric fringe tracking method with beam combining back-end polarization modulation includes the following steps:

[0054] Step 1: Use the first polarizing beam splitter 3 to perform interference beam combining of astronomical light, as detailed below:

[0055] The sub-aperture beams collected by each astronomical interferometer array at the front end are adjusted so that their polarization components in the vertical and horizontal directions are close. Randomly polarized light that is close to natural light does not need to be adjusted. For astronomical light with partial polarization, an achromatic half-wave plate is used to adjust its polarization direction. Then, the beams are combined on the first polarization beam splitter 3 through cross transmission, and the two outgoing beams maintain a common optical path.

[0056] Step 2: Using the beam combining post-polarization modulation method, polarization modulation is performed after interference beam combining using the first achromatic half-wave plate 4, the achromatic quarter-wave plate 5, and the second achromatic half-wave plate 6, as follows: Figure 2 As shown, the details are as follows:

[0057] Beams 1 and 2 are split into four beams—P1, S1, P2, and S2—by the first polarizing beam splitter 3. Beams P1 and S2 share a common optical path, and beams P2 and S1 share a common optical path. After passing through the first achromatic half-wave plate 4, the angle between the fast axis of beam P2 and the vertical direction... =22.5° becomes linearly polarized light along the -45° direction; the S1 light passes through the first achromatic half-wave plate 4, and the angle between the fast axis and the vertical direction is... =22.5° becomes linearly polarized light along the 45° direction; P1 light becomes linearly polarized light along the -45° direction after passing through the second achromatic half-wave plate 6, and S2 light becomes linearly polarized light along the 45° direction after passing through the second achromatic half-wave plate 6; then P2 light and S1 light are passed through the achromatic quarter-wave plate 5, with the fast axis making an angle of 45° with the vertical direction, introducing a 90° phase delay in the two linearly polarized lights at 45° and -45°.

[0058] Step 3: For the polarization-modulated beam, the polarization components are extracted using the second polarization beam splitter 7, resulting in four beams with a phase spacing of [missing information]. The interferogram image is as follows:

[0059] For the four polarized beams that have undergone polarization modulation, the beams are further split using the second polarization beam splitter 7. After passing through the second polarization beam splitter 7, the P1 beam and the S2 beam obtain interference patterns I1 and I3 with phase shifts of 0° and 180°, respectively. After passing through the second polarization beam splitter 7, the P2 beam and the S1 beam obtain interference patterns I2 and I4 with phase shifts of 90° and 270°, respectively. Finally, four interference pattern images with phases of 0°, 90°, 180°, and 270° are output.

[0060] Step 4: By combining spectral period calculation with the four-step phase shift calculation of monochromatic light, high-precision piston error and tilt error are obtained, as detailed below:

[0061] Step 4.1: Calculate the phase using a four-step phase-shifting algorithm, as shown in the following formula:

[0062]

[0063] Wherein, I1, I2, I3, and I4 are the light intensity values ​​of the four interference images, and their theoretical phases differ sequentially. ;

[0064] Step 4.2: Calculate the high-precision piston error. The formula for optical path difference is:

[0065]

[0066] in, Wavelength;

[0067] Step 4.3: After the beams are polarized and modulated by the QWP and HWP, a low-reflectivity beam splitter or dichroic mirror is added to the subsequent optical path to separate some of the energy. The two sampled beams pass through a shared focusing lens and form two separate, clear light spots on the same CCD. The positional offset of the two light spots is calculated using a real-time image processing algorithm. The formula for calculating the wavefront tilt angle is:

[0068]

[0069] As a concrete example, breakthroughs in single-wavelength detection can be achieved across the entire spectrum by incorporating a dispersive fringe sensor. Fuzzy constraints enable measurement ranges exceeding half a wavelength, as detailed below:

[0070] For four interferograms emitted in the same direction, by adding a dispersive prism and then a focusing prism, the spectral channel fringe pattern of the interference is obtained, and the number of fringes is calculated to extend its measurement range.

[0071] The optical path difference between the two arms is calculated using the number of fringe periods in the interference spectrum, where the number of fringe periods in the dispersive fringe sensor is [not specified]. Optical path error between the two arms The relationship is:

[0072]

[0073] in, The number of fringe periods in a specific band on the sensor. It is the upper limit of wavelength. It is the lower limit of wavelength. The optical path difference is used to select the light intensity at four specific wavelength spectral positions on the dispersive fringe sensor in step 4.1 to maintain a large dynamic range and achieve high precision.

[0074] As a specific example, the tilt detection module and the piston detection module share part of the optical path. The detection beam is extracted after polarization modulation by a beam splitter to ensure the spatiotemporal synchronization of tilt and piston detection and avoid control lag caused by timing differences.

[0075] As a specific example, the method also supports working in conjunction with a delay line system. A delay system without left or right sway is obtained through the first cat's eye system delay system 1 and the second cat's eye system delay system 2, which can be used for delay compensation in measurement. Large-scale disturbances involve moving the first cat's eye system delay system 1 and the second cat's eye system delay system 2 as a whole, while small-scale movements involve moving the first cat's eye reflector 14 and the second cat's eye reflector 15.

[0076] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dynamic astronomical optical interferometric fringe tracking system with beam combining back-end polarization modulation, characterized in that, It includes a first cat's eye system delay system (1), a second cat's eye system delay system (2), a first polarizing beam splitter (3), a first achromatic half-wave plate (4), an achromatic quarter-wave plate (5), a second achromatic half-wave plate (6), a second polarizing beam splitter (7), a first reflector (8), a second reflector (9), a third reflector (10), a fourth reflector (11), a right-angle external reflector (12), a fifth reflector (13), a first cat's eye reflector (14), and a second cat's eye reflector (15); The collimated starlight beams 1 and 2 from the two sub-telescopes pass through the first cat's eye system delay system (1) and the second cat's eye system delay system (2), respectively. The two beams pass through the first reflector (8) and the first reflector (9) respectively and are incident on the first polarizing beam splitter (3) at a set angle. The first polarizing beam splitter (3) combines the S component of beam 1 with the P component of beam 2, and at the same time combines the P component of beam 1 with the S component of beam 2. The S component of beam 1 and the P component of beam 2 are polarized by the first achromatic half-wave plate (4) and the achromatic quarter-wave plate (5), and the P component of beam 1 and the S component of beam 2 are polarized by the second achromatic half-wave plate (6). The first achromatic half-wave plate (4) and the second achromatic half-wave plate (6) modulate the incident orthogonally polarized components P and S light into four linearly polarized lights in the +45° and -45° directions, respectively. The achromatic quarter-wave plate (5) introduces a fixed [interval] between the two linearly polarized lights modulated by the first achromatic half-wave plate (4). Relative phase delay; the modulated beam, after being reflected by the third mirror (10), the fourth mirror (11), and the right-angle external mirror (12), is split into four paths by the second polarizing beam splitter (7), two of which are reflected by the fifth mirror (13), resulting in four beams with a phase interval of . The interferogram image was obtained, and then the phase was extracted using spatial modulation synchronous phase shifting technology.

2. The dynamic astronomical interferometric fringe tracking system with beam combining back-end polarization modulation according to claim 1, characterized in that, All modulation elements are located in the common optical path after beam combining, and their effects on the two interfering beams are completely consistent. Therefore, they have common-mode suppression capabilities for the surface shape error, assembly tolerance, and dispersion introduced when working with white light.

3. A method for tracking dynamic astronomical interferometric fringe patterns using polarization modulation at the back end of beam combining, characterized in that, Includes the following steps: Step 1: Use the first polarizing beam splitter (3) to perform interference beam combining of astronomical light; Step 2: Using the beam combining back-end polarization modulation method, polarization modulation is performed after interference beam combining by the first achromatic half-wave plate (4), the achromatic quarter-wave plate (5), and the second achromatic half-wave plate (6); Step 3: For the polarization-modulated beam, the polarization components are extracted using the second polarization beam splitter (7) to obtain four beams with a phase spacing of [missing information]. Interferogram image; Step 4: By combining spectral period calculation with four-step phase shift calculation of monochromatic light and measurement of the spot after spectral dispersion, the piston error and tilt error are obtained.

4. The dynamic astronomical interferometric fringe tracking method with beam combining back-end polarization modulation according to claim 3, characterized in that, The interference and beam combining of astronomical light using the first polarizing beam splitter (3) described in step 1 is as follows: The sub-aperture beams collected by each astronomical interferometer array at the front end are adjusted so that the polarization components in the vertical and horizontal directions are the same. No adjustment is needed for random polarized light that is close to natural light. For astronomical light with partial polarization, an achromatic half-wave plate is used to adjust the polarization direction. Then, the beams are combined on the first polarization beam splitter (3) through cross transmission, and the two emitted beams maintain the same optical path.

5. The dynamic astronomical interferometric fringe tracking method with beam combining back-end polarization modulation according to claim 3, characterized in that, Step 2 describes the post-beam combining polarization modulation method, which uses a first achromatic half-wave plate (4), an achromatic quarter-wave plate (5), and a second achromatic half-wave plate (6) to perform polarization modulation after interference beam combining, as detailed below: Beam 1 and beam 2 are split into four beams, P1, S1, P2, and S2, by the first polarizing beam splitter (3). Among them, P1 and S2 share the same optical path, and P2 and S1 share the same optical path. After passing through the first achromatic half-wave plate (4), the angle between the fast axis and the vertical direction of P2 beam is... =22.5° becomes linearly polarized light along the -45° direction; the S1 light passes through the first achromatic half-wave plate (4), and the angle between the fast axis and the vertical direction is... =22.5° becomes linearly polarized light along the 45° direction; P1 light becomes linearly polarized light along the -45° direction after passing through the second achromatic half-wave plate (6), and S2 light becomes linearly polarized light along the 45° direction after passing through the second achromatic half-wave plate (6); then P2 light and S1 light are passed through the achromatic quarter-wave plate (5), with the fast axis and the vertical direction at an angle of 45°, introducing a 90° phase delay in the two linearly polarized lights at 45° and -45°.

6. The dynamic astronomical interferometric fringe tracking method with beam combining back-end polarization modulation according to claim 3, characterized in that, Step 3 describes extracting the polarization components of the polarization-modulated beam using a second polarization beam splitter (7) to obtain four beams with a phase spacing of [missing information]. The interferogram image is as follows: For the four polarized lights that have undergone polarization modulation, the second polarization beam splitter (7) is used to further split the light. After passing through the second polarization beam splitter (7), the P1 light and the S2 light are obtained as interference patterns I1 and I3 with phase shifts of 0° and 180°, respectively. After passing through the second polarization beam splitter (7), the P2 light and the S1 light are obtained as interference patterns I2 and I4 with phase shifts of 90° and 270°, respectively. Finally, four interference pattern images with phases of 0°, 90°, 180° and 270° are output.

7. The dynamic astronomical interferometric fringe tracking method with beam combining back-end polarization modulation according to claim 3, characterized in that, Step 4, which combines spectral period calculation with the four-step phase-shifting calculation of monochromatic light, yields the piston error and tilt error, as detailed below: Step 4.1: Calculate the phase using a four-step phase-shifting algorithm, as shown in the following formula: ； Where I1, I2, I3, and I4 are the light intensity values ​​of the four interference images, and their theoretical phases differ sequentially. ; Step 4.2: Calculate the piston error. The formula for optical path difference is: ； in, Wavelength; Step 4.3: After the beams are polarized and modulated by the QWP and HWP, a low-reflectivity beam splitter or dichroic mirror is added to the subsequent optical path to separate some of the energy. The two sampled beams pass through a shared focusing lens and form two separate, clear light spots on the same CCD. The positional offset of the two light spots is calculated using a real-time image processing algorithm. The formula for calculating the wavefront tilt angle is: 。 8. The dynamic astronomical interferometric fringe tracking method with beam combining back-end polarization modulation according to claim 3, characterized in that, By incorporating a dispersive fringe sensor, breakthroughs can be achieved across the entire spectrum, overcoming the limitations of single-wavelength detection. Fuzzy constraints enable measurement ranges exceeding half a wavelength, as detailed below: For four interferograms emitted in the same direction, by adding a dispersive prism and then a focusing prism, the spectral channel fringe pattern of the interference is obtained, and the number of fringes is calculated to extend the measurement range. The optical path difference between the two arms is calculated using the number of fringe periods in the interference spectrum, where the number of fringe periods in the dispersive fringe sensor is [not specified]. Optical path error between the two arms The relationship is: ； in, The number of fringe periods in a specific band on the sensor. It is the upper limit of wavelength. It is the lower limit of wavelength. It's the optical path difference.

9. The dynamic astronomical interferometric fringe tracking method with beam combining back-end polarization modulation according to claim 3, characterized in that, The tilt detection module and the piston detection module share part of the optical path. The detection beam is extracted after polarization modulation by a beam splitter to ensure the spatiotemporal synchronization of tilt and piston detection.

10. The dynamic astronomical interferometric fringe tracking method with beam combining back-end polarization modulation according to claim 3, characterized in that, The method also supports working in conjunction with a delay line system, obtaining a delay system without left or right sway through the first cat-eye system delay system (1) and the second cat-eye system delay system (2) for delay compensation of measurement. If the disturbance exceeds the upper limit threshold, the first cat-eye system delay system (1) and the second cat-eye system delay system (2) are moved as a whole. If the disturbance is below the lower limit threshold, the first cat-eye reflector (14) and the second cat-eye reflector (15) are moved.

Images