Co-phase error detection system and method based on broadband spectrum synchronous phase-shifting interference

Abstract

The invention discloses a co-phase error detection system and method based on broadband spectrum synchronous phase-shifting interference. The system comprises an optical path adaptation module, a broadband synchronous phase shift module, a dispersion compensation module, a tilt error detection module and a large dynamic range accurate measurement module. The method comprises the following steps: firstly, carrying out polarization modulation on a broadband light source; performing synchronous phase shift on the interferogram by using a broadband achromatic wave plate, a light splitting prism and a polarization beam splitter, and obtaining four interference fringes by using a single sensor; and then a mass center measurement device and a dispersion device are combined, and a four-step phase-shifting interference measurement method and a multi-wavelength interference spectrum are combined, so that the purposes of wide-range and high-precision measurement of the optical path difference of the two arms can be achieved, and co-phase error measurement of wavefront phases in the two arms is realized. The contradiction between the dynamic range and the precision in the prior art is solved, and the system is compact in structure, high in anti-disturbance capacity, capable of being in seamless joint with an existing optical system and high in engineering landing performance.

Description

Technical Field

[0001] This invention relates to the fields of interferometric phase detection and optical path error measurement, and in particular to a co-phase error detection system and method based on broadband spectral synchronous phase-shifting interferometry. Background Technology

[0002] In the field of astronomy, the angular resolution of conventional single-aperture telescopes is insufficient for observing most stars and other celestial objects of interest. However, increasing the aperture to improve angular resolution is constrained by factors such as manufacturing technology, support structure, materials, and operating costs. Against this backdrop, an important method to resolve this contradiction is to shift from observation by a single telescope to a sparse array composed of two or more telescopes. By adjusting the spacing between the sub-telescopes according to scientific needs, observation capabilities far exceeding the angular resolution of a single sub-telescope can be obtained. This technology is known as optical synthetic aperture imaging.

[0003] When multiple sub-mirrors or apertures are stitched together, inconsistencies in their wavefront phases can lead to a decrease in image quality. This phase inconsistency is called co-phase error. Co-phase error is a critical issue in optical synthetic aperture imaging technology, as it affects the system's resolution and light-gathering ability, thus requiring precise detection and correction. Without the ability to detect and correct high-precision co-phase errors between telescopes, synthetic aperture imaging becomes meaningless.

[0004] Similarly, in astronomical interferometer systems, real-time monitoring of the wavefront state of starlight across different apertures is crucial to ensure the relative parallelism of the wavefronts and the stability of the optical path difference length at the optimal coherence position. This means that, just as with monitoring the co-phase error of aperture mirrors, it is necessary to detect wavefront co-phase errors caused by various errors in starlight.

[0005] Invention patent CN111220072A discloses a device and method for generating digital dispersion fringes for measuring co-phase error. This method involves continuously and linearly changing the transmission wavelength of a tunable filter and sequentially storing light spot arrays on a detector. A spot corresponding to the seam is extracted from each light spot array, and all extracted spots corresponding to the seam are accumulated along a direction parallel to the seam to obtain a one-dimensional light intensity distribution. Finally, all the obtained one-dimensional light intensity distributions are stacked sequentially according to the magnitude of the corresponding tunable wavelengths to obtain digital dispersion fringes. This allows for the simultaneous measurement of the co-phase error corresponding to all seams. Invention patent CN120176991A discloses a method for detecting the co-phase error of sub-mirrors in a spliced ​​telescope. A special mask is designed so that the second-peak values ​​representing the co-phase error of each sub-mirror in the MTF under broadband illumination do not overlap. This allows for the separate calculation of the true second-peak values ​​representing the co-phase error of each sub-mirror in the MTF under broadband illumination. Then, through repeated iterations using a population optimization algorithm, a large-scale, high-precision real-time detection of the three-dimensional co-phase error of each sub-mirror is achieved. However, existing co-phase error measurement techniques still have the following key problems:

[0006] Dynamic range and measurement accuracy are difficult to balance: While single-wavelength phase-shifting interferometry can achieve nanometer-level measurement accuracy, it is limited by... The problem of fuzziness means that the dynamic range of a single-step measurement is usually no more than half a wavelength, which cannot meet the requirements for optical path difference measurement of tens to hundreds of micrometers in measurement. Although the traditional group delay interferometry method can achieve large-range coarse measurement, the measurement accuracy can only reach the wavelength level, which is difficult to meet the requirements of high-precision co-phase control.

[0007] Significant dispersion interference in wide-band: In white light or wide-band observation scenarios, the axial and lateral dispersion of optical elements can lead to a decrease in phase shifting accuracy and fringe distortion. Existing phase shifting technologies are mostly designed for monochromatic light and lack effective wide-band dispersion compensation schemes, which cannot guarantee measurement consistency at different wavelengths.

[0008] Multiple errors cannot be detected synchronously: Existing technologies usually require separate optical paths to detect tilt error and piston error, which makes the system structure complex, the optical path debugging difficult, and there are detection timing differences, which cannot meet the real-time co-phase control requirements in dynamic environments.

[0009] Insufficient disturbance resistance: Time-modulated phase-shifting technologies, such as piezoelectric ceramic driven lens displacement technology, are sensitive to dynamic disturbances such as mechanical vibration and atmospheric turbulence. Phase drift will seriously affect measurement accuracy and is difficult to adapt to complex dynamic scenarios such as astronomical observation.

[0010] Therefore, developing a co-phase error measurement device that combines wide-band adaptability, high precision, large range, multi-error synchronous detection capability, and strong anti-disturbance performance is key to overcoming the aforementioned technical bottlenecks. It can be applied in various fields such as precision splicing mirror co-phase error measurement, inter-aperture starlight wavefront error measurement in astronomical interferometers, and precision displacement measurement. Summary of the Invention

[0011] The purpose of this invention is to provide a common phase error detection system and method based on broadband spectral synchronous phase-shifting interferometry, which has a wide band adaptation range, high measurement accuracy, large measurement range, strong multi-error synchronous detection capability, and strong anti-disturbance capability.

[0012] The technical solution to achieve the purpose of this invention is: a co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry, including an optical path adaptation module, a broadband synchronous phase-shifting module, a dispersion compensation module, a tilt error detection module, and a large dynamic range precision measurement module;

[0013] The optical path adapter module separates two beams of light from the same light source by amplitude splitting or wavefront splitting using a broadband beam splitter or a dual-aperture beam splitter.

[0014] The broadband synchronous phase-shifting module adopts a Mach-Zehnder interferometer structure, with an achromatic waveplate placed in one arm of the interferometer to introduce aberrations between the orthogonal polarization components of the beam. Phase delay; utilizing the complementary interferogram characteristics of the dual-output ports of the Mach-Zehnder interferometer, combined with a polarization separation component, four phase-separated images are simultaneously acquired. Interference fringes;

[0015] The dispersion compensation module achieves wideband dispersion compensation through "achromatic waveplate + compensation plate of the same material / achromatic waveplate of the same model";

[0016] The tilt error detection module extracts a portion of the beam through a beam splitter after the two arms of the interferometer splits the beam, focuses it through a lens to form a spot, calculates the centroid offset of the spot using the "threshold segmentation + target window locking" centroid method, and combines the focusing focal length to infer the wavefront tilt angle of the two beams, thus realizing real-time detection of tilt error.

[0017] The large dynamic range precision measurement module adopts a collaborative strategy of "coarse measurement to expand the range + fine measurement to improve accuracy". After polarization separation, the four beams of light are incident on the Amitch prism for dispersion to form an interference spectrum. After wavenumber correction to correct the horizontal axis of the spectrum, the number of spectral fringe periods is calculated by the FFT fast Fourier transform algorithm to obtain the coarse optical path difference result. The intensity data of four phase-shifted interference beams of a set wavelength are extracted from the interference spectrum and substituted into the four-step phase-shifting formula to calculate the precise phase. Combined with the dual-wavelength fusion algorithm to eliminate integer ambiguity, the optical path difference result with further precision is obtained. Finally, the fine phase difference is obtained by averaging the single-wavelength phase calculation.

[0018] Furthermore, the co-phase error includes tilt error and piston error. The synchronous detection, dispersion compensation, and coarse and fine measurement processes of the tilt error and piston error are carried out in coordination. When it is necessary to compensate for the co-phase error, the measurement results are fed back to the closed-loop control unit. The co-phase error is compensated in real time through a high-speed tilt mirror and a piezoelectric displacement stage until the co-phase requirement under the detection accuracy is achieved.

[0019] Furthermore, the polarization separation component of the wideband synchronous phase shifting module operates as follows:

[0020] The vertical outgoing light from the two ports of the Mach-Zehnder interferometer is adjusted to be parallel light by a reflector and a right-angle external reflector, and then incident on the optical circuit of the polarizing beam splitter PBS. Two beams of light enter the circuit simultaneously from the incident port of one of the polarizing beam splitters PBS, and are split into four beams: P-beams and S-beams. After being refracted by a high-reflectivity reflector, they are emitted in the same direction from the same beam splitting surface, ensuring that four interferograms are acquired synchronously on the same detector surface. The combination of four reflectors, including two reflectors that cooperate with the right-angle external reflector and two reflectors at the polarizing beam splitter PBS, controls the outgoing direction of the four beams of light.

[0021] Furthermore, the detector employs a high-speed detector to ensure the simultaneous acquisition of four phase-shifted interferograms and interferometric spectra.

[0022] Furthermore, the dispersion compensation scheme of the dispersion compensation module includes two implementation methods:

[0023] (1) Two beams of light are passed through a polarizing beam splitter to adjust the polarization direction to 45°. One beam of light passes through an achromatic waveplate with the fast axis parallel to the polarization direction, and the other beam of light passes through an achromatic waveplate with the fast axis at 45° to the polarization direction. Wide-band phase shifting and dispersion compensation are achieved by using double achromatic waveplates.

[0024] (2) Two beams of light are transmitted and reflected in a selected band by passing them through the same dichroic mirror. In the transmitted light, one beam passes through an achromatic waveplate whose fast axis is parallel to the vertical or horizontal direction, and the other beam passes through a compensation plate of the same material to ensure that axial dispersion compensation and polarization phase shift are achieved in tandem.

[0025] Furthermore, the specific detection steps of the tilt error detection module are as follows:

[0026] (1) Extract the beams of both arms through a beam splitter, and then... A lens with a focal length of 1-2m focuses light to form a spot;

[0027] (2) The area array detector acquires the spot image, and the centroid of the spot is roughly located by binarization processing. The target window is delineated to reduce random device errors.

[0028] (3) Calculate the centroid of the pixels within the window to obtain the centroid offset in the X and Y directions. ;

[0029] (4) Through the formula Calculate the wavefront tilt angle with a detection accuracy of ≤2″.

[0030] Furthermore, the dual Amicis prism consists of two triangular prisms, the first of which is made of medium dispersion glass and the second of which is made of high dispersion glass. The prism angles and materials are optimized so that the outgoing direction of the center wavelength light is parallel to the incident direction, while other wavelengths are deflected according to their dispersion capabilities.

[0031] Furthermore, the specific detection steps of the large dynamic range precision measurement module are as follows:

[0032] (1) Calculate the coarse phase difference using the number of fringe periods, where the number of fringe periods of the dispersive fringe sensor is... Optical path error between the two arms The relationship is:

[0033]

[0034] 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;

[0035] (2) Using dual-wavelength phase calculation avoids the error in calculating the fringe period when the optical path is close to 0, further locking the optical path difference, and using the single-wavelength four-step phase shift calculation result to calculate the accurate phase difference; the specific method of dual-wavelength phase calculation is to use the light intensity at a specific wavelength position of four interference spectra as the input of the four-step phase shift. Its dual wavelengths were obtained The phases of respectively The formulas for calculating phase and optical path difference are as follows:

[0036]

[0037]

[0038] in , ;

[0039] (3) Solving the phase of a single wavelength This serves as the result of the fine cophase error calculation.

[0040] Furthermore, the optical path adaptation module is compatible with multiple light source types, including broadband light sources, lasers, and quasi-monochromatic light. It works with narrowband filters to perform wavenumber position positioning for set band measurements. It is used for phase error measurement of astronomical interferometers, sub-aperture phase detection of optical synthetic aperture telescopes, and displacement detection of high-precision displacement measurement equipment. It is compatible with various light source scenarios such as broadband white light, starlight, lasers, and quasi-monochromatic light.

[0041] A method for detecting co-phase error based on broadband spectral synchronous phase-shifting interferometry, wherein the co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry includes the following steps:

[0042] Step 1: Separate two beams of light from the same source by amplitude splitting or wavefront splitting using a broadband beam splitter or dual-aperture beam splitter.

[0043] Step 2: By using a phase delayer with polarization modulation, orthogonal polarization direction components are obtained in one arm of the interferometer. Phase delay;

[0044] Step 3: Utilize the phase shifting effect of the beam splitter's reflection, the complementarity of the interference patterns at the two output ports of the Mach-Zehnder interferometer, and the inter-polarization components... The phase delay combination, through orthogonal polarization separation at the two output ports of the interferometer, yields four phase shifts with the following values: Interference fringes;

[0045] Step 4: Achieve simultaneous acquisition of four interference spectral fringes by a single detector through optical path modulation;

[0046] Step 5: Split the beam in both arms of the interferometer and simultaneously measure the wavefront tilt change of the two beams by calculating the centroid of the focused spot.

[0047] Compared with the prior art, the significant advantages of this invention are: (1) It adopts a “coarse measurement + fine measurement” collaborative design to achieve a large range of tens or even hundreds of micrometers and a high precision measurement of ≤λ / 30, solving the contradiction between the dynamic range and precision of traditional technology; (2) Through the dispersion compensation scheme of “achromatic waveplate + compensation plate of the same material / waveplate of the same model + optical path matching delay line”, it can synchronously shift phase of multiple wavelengths in a wide spectrum range of 533nm-633nm, adapting to a variety of wide band light sources; (3) It integrates the synchronous detection function of tilt error and piston error, without the need for an additional independent optical path, the system structure is compact, the detection has no time difference, and meets the real-time co-phase control requirements of dynamic environment; (4) It adopts spatial modulation synchronous phase shift technology, and completes four-step phase acquisition in a single frame image, with strong anti-disturbance ability and adaptability to complex scenarios such as astronomical observation; (5) The core optical components are all mature commercial or easy-to-process customized components, the optical path debugging difficulty is low, and it can be seamlessly connected with existing optical systems, with strong engineering implementation. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to the present invention.

[0049] Figure 2 This is a schematic diagram of the co-phase error detection system of the present invention, which uses an internal light source and can be used for precision displacement measurement.

[0050] Figure 3 This is a schematic diagram of the principle of the special compensation plate in this invention.

[0051] Figure 4 This is a schematic diagram illustrating the principle of the special loop-shaped PS optical splitter in this invention.

[0052] Figure 5 This is a schematic diagram illustrating the principle of the direct-view dispersive element and the Zemax simulation results in an embodiment of the present invention.

[0053] Figure 6 This is a schematic diagram of the test results of a single interference spectral fringe in an embodiment of the present invention.

[0054] Figure 7 This is a schematic diagram of the four synchronous phase-shifting interference spectral fringes obtained in an embodiment of the present invention.

[0055] Figure 8 This is a schematic diagram showing the change of light intensity at dual wavelengths of 533nm and 633nm as a function of optical path difference, as measured in an embodiment of the present invention.

[0056] Figure 9 This is a schematic diagram of the measured optical path error and the error introduced by actively modifying the optical path in an embodiment of the present invention. Detailed Implementation

[0057] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0058] like Figure 1 As shown, the present invention discloses a co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry, comprising an optical path adaptation module, a broadband synchronous phase-shifting module, a dispersion compensation module, a tilt error detection module, and a large dynamic range precision measurement module;

[0059] The optical path adapter module separates two beams of light from the same light source by amplitude splitting or wavefront splitting using a broadband beam splitter or a dual-aperture beam splitter.

[0060] The broadband synchronous phase-shifting module adopts a Mach-Zehnder interferometer structure, with an achromatic waveplate placed in one arm of the interferometer. Its fast axis is at 45° to the polarization direction, introducing asymmetric polarization components between the beam paths. Phase delay; utilizing the complementary interferogram characteristics of the dual-output ports of the Mach-Zehnder interferometer, combined with a polarization separation component, four phase-separated images are simultaneously acquired. Interference fringes;

[0061] The dispersion compensation module achieves wide-band dispersion compensation through "achromatic waveplate + compensation plate of the same material / achromatic waveplate of the same model + optical path matching delay line";

[0062] The tilt error detection module extracts a portion of the beam through a beam splitter after the two arms of the interferometer splits the beam, focuses it through a lens to form a spot, calculates the centroid offset of the spot using the "threshold segmentation + target window locking" centroid method, and combines the focusing focal length to infer the wavefront tilt angle of the two beams, thus realizing real-time detection of tilt error.

[0063] The large dynamic range precision measurement module adopts a collaborative strategy of "coarse measurement to expand the range + fine measurement to improve accuracy". After polarization separation, the four beams of light are incident on the Amitch prism for dispersion to form an interference spectrum. After wavenumber correction to correct the horizontal axis of the spectrum, the number of spectral fringe periods is calculated by the FFT fast Fourier transform algorithm to obtain the coarse optical path difference result. The intensity data of four phase-shifted interference beams at specific wavelengths are extracted from the interference spectrum and substituted into the four-step phase-shifting formula to calculate the precise phase. Combined with the dual-wavelength fusion algorithm to eliminate integer ambiguity, the optical path difference result with further precision is obtained. Finally, the fine phase difference is obtained by averaging the single-wavelength phase calculation.

[0064] As a specific example, the co-phase error includes tilt error and piston error. The synchronous detection, dispersion compensation, and coarse and fine measurement processes of the tilt error and piston error are carried out in coordination. When it is necessary to compensate for the co-phase error, the measurement results are fed back to the closed-loop control unit. The co-phase error is compensated in real time through a high-speed tilt mirror and a piezoelectric displacement stage until the co-phase requirement under the detection accuracy is achieved.

[0065] As a specific example, the polarization separation component of the broadband synchronous phase shifting module operates as follows:

[0066] The vertical outgoing light from the two ports of the Mach-Zehnder interferometer is adjusted to be parallel light by a reflector and a right-angle external reflector before being incident on the optical circuit of the polarizing beam splitter PBS. Two beams of light simultaneously enter the circuit from the incident port of one of the polarizing beam splitters PBS, and are split into four beams: P-beams and S-beams. After being refracted by a high-reflectivity reflector, they are emitted in the same direction from the same beam splitting surface, ensuring that four interferograms are acquired synchronously on the same detector surface. The combination of four reflectors, including two reflectors that cooperate with the right-angle external reflector and two reflectors at the polarizing beam splitter PBS, can control the outgoing direction of the four beams of light.

[0067] As a specific example, the detector employs a high-speed detector to ensure the simultaneous acquisition of four phase-shifted interferograms and interferometric spectra.

[0068] As a specific example, the dispersion compensation scheme of the dispersion compensation module includes two implementation methods:

[0069] (1) Two beams of light are passed through a polarizing beam splitter to adjust the polarization direction to 45°. One beam of light passes through an achromatic waveplate with the fast axis parallel to the polarization direction, and the other beam of light passes through an achromatic waveplate with the fast axis at 45° to the polarization direction. Wide-band phase shifting and dispersion compensation are achieved by using double achromatic waveplates.

[0070] (2) Two beams of light are transmitted and reflected in a selected band by passing them through the same dichroic mirror. In the transmitted light, one beam passes through an achromatic waveplate whose fast axis is parallel to the vertical or horizontal direction, and the other beam passes through a specially made compensation plate of the same material to ensure that axial dispersion compensation and polarization phase shift are achieved in tandem.

[0071] As a specific example, the specific detection steps of the tilt error detection module are as follows:

[0072] (1) Extract the beams of both arms through a beam splitter, and then... A lens with a focal length of 1-2m focuses light to form a spot;

[0073] (2) The area array detector acquires the spot image, and the centroid of the spot is roughly located by binarization processing. The target window is delineated to reduce random device errors.

[0074] (3) Calculate the centroid of the pixels within the window to obtain the centroid offset in the X and Y directions. ;

[0075] (4) Through the formula Calculate the wavefront tilt angle with a detection accuracy of ≤2″.

[0076] As a specific example, the dual Amicis prism consists of two triangular prisms, the first of which is made of medium dispersion glass and the second of which is made of high dispersion glass. The prism angles and materials are optimized so that the outgoing direction of the center wavelength light is parallel to the incident direction, while other wavelengths are deflected according to their dispersion capabilities, thus reducing assembly difficulty.

[0077] As a specific example, the specific detection steps of the large dynamic range precision measurement module are as follows:

[0078] (1) Calculate the coarse phase difference using the number of fringe periods, where the number of fringe periods of the dispersive fringe sensor is... Optical path error between the two arms The relationship is:

[0079]

[0080] 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;

[0081] (2) Using dual-wavelength phase calculation avoids the error in calculating the fringe period when the optical path is close to 0, further locking the optical path difference, and using the single-wavelength four-step phase shift calculation result to calculate the accurate phase difference; the specific method of dual-wavelength phase calculation is to use the light intensity at a specific wavelength position of four interference spectra as the input of the four-step phase shift. Its dual wavelengths can be obtained The phases of respectively The formulas for calculating phase and optical path difference are as follows:

[0082]

[0083]

[0084] in , ;

[0085] (3) Solving the phase of a single wavelength As the solution result.

[0086] As a specific example, the optical path adapter module is compatible with various light source types, including broadband light sources, lasers, and quasi-monochromatic light. When used with a narrowband filter, it can perform wavenumber position positioning for specific band measurements. It can be used for phase error measurement of astronomical interferometers, sub-aperture phase detection of optical synthetic aperture telescopes, and displacement detection of high-precision displacement measurement equipment. It is compatible with various light source scenarios such as broadband white light, starlight, lasers, and quasi-monochromatic light.

[0087] This invention also provides a method for detecting co-phase error based on broadband spectral synchronous phase-shifting interferometry, comprising the following steps:

[0088] Step 1: Separate two beams of light from the same source by amplitude splitting or wavefront splitting using a broadband beam splitter or dual-aperture beam splitter.

[0089] Step 2: By using a phase delayer with polarization modulation, orthogonal polarization direction components are obtained in one arm of the interferometer. Phase delay;

[0090] Step 3: Utilize the phase shifting effect of the beam splitter's reflection, the complementarity of the interference patterns at the two output ports of the Mach-Zehnder interferometer, and the inter-polarization components... The phase delay combination, through orthogonal polarization separation at the two output ports of the interferometer, yields four phase shifts with the following values: Interference fringes;

[0091] Step 4: Achieve simultaneous acquisition of four interference spectral fringes by a single detector through optical path modulation;

[0092] Step 5: Split the beam in both arms of the interferometer and simultaneously measure the wavefront tilt change of the two beams by calculating the centroid of the focused spot.

[0093] Example

[0094] This implementation example Figure 1 As shown, collimated artificial light or natural parallel light passes through two sub-aperture or beam-splitting prisms to obtain beams beam1 and beam2. These beams then pass through a polarization beam splitter or wavelength-splitting beam splitter 1, one beam entering the tilt detection module for tilt error detection. The other two beams pass through the achromatic waveplate / compensation plate of the polarization control module and are then incident on the Mach-Zehnder interferometer unit. After beam combining, they are output as four synchronously phase-shifting interference beams via a polarization separation component. The interference beams are dispersed by an Amigh prism and then enter the detection camera for coarse and fine piston error measurement. When compensation is required, the measurement data is fed back to the control system, where error correction is completed using a high-speed tilt mirror and a piezoelectric displacement stage. The common-phase error measurement includes the following steps:

[0095] (1) Two beams split from the same light source pass through a dichroic mirror beam splitter 1 and a telephoto lens 2 into the pointing detection system. The pointing detection method is used to correct the tilt error. By focusing the two sub-beams onto the detection camera, the tilt error is calculated using the centroid extraction method. The area array detector acquires the spot image, and the centroid of the spot is roughly located through binarization processing. The target window is delineated to reduce random device errors. The centroid of the pixels within the window is calculated to obtain the centroid offset in the X and Y directions. ; through formula The wavefront tilt angle is calculated, and the actual measurement accuracy is ≤2″.

[0096] (2) Adjust the two beams to be parallel, and the incident light after beam splitting is incident on the polarization phase shifting element achromatic waveplate 7; adjust the fast axis direction of the achromatic waveplate 7 so that the fast axis is in the horizontal 0° or vertical 90° direction; place a compensation plate 8 in another path to compensate for the axial dispersion caused by the achromatic waveplate 7. The two compensation schemes are as follows: Figure 3 As shown, the goal is to introduce polarization phase shift into one beam of light while compensating for dispersion in another beam without changing the polarization state. The principle of the specially designed compensation plate is as follows: Figure 3 As shown, axial dispersion can be controlled even when the polarization is not changed by controlling the angle between the cutting direction and the optical axis. In the polarization-controlled beams, one p-beam and the s-beam maintain their original phase, while the other beam has a 90° polarization phase separation.

[0097] (3) The two beams are split and combined on the surface of the beam splitter and combiner prism 9, resulting in four beams and two interference patterns. At this time, the p-component and s-component in the two interference patterns are not separated. The two interference patterns are output in the same direction by an external reflecting mirror and two plane mirrors 10 and 11. The incident light is a special loop-shaped optical path composed of polarizing beam splitters PBS (12 and 13) and reflecting mirrors 14 and 15. The principle is as follows: Figure 4 A beam of polarized or unpolarized light is incident on the aforementioned loop-shaped optical path. Due to the presence of the PBS film, the light passing through the first film in one polarization direction is reflected and propagates perpendicularly, returning to the second prism. At this point, the polarization state of the light determines that it can only be reflected by the second PBS film, not transmitted. The light in the other orthogonally polarized state passes through the film twice. The light exiting in the same direction as the previous light passes through the dispersive system, which uses a pair of Amigh prisms 16. The principle is as follows: Figure 5 Through special design, direct-view spectral dispersion is ensured. For the non-ideal lateral dispersion of the Amighi prism, including dispersion angle and wavenumber nonlinearity, prediction is performed using simple ray tracing calculations, and calibration is then performed in subsequent dispersion fringes. Nonlinear dispersion is a problem encountered by all prism-based dispersion sensors, including dispersion fringe sensors (DFS), spectrometers, and wavefront detectors. To ensure the usability of the DFS over a wide wavelength range or with non-ideal prisms, dispersion wavenumber correction is necessary. The core objective of this correction is to reduce the actual nonlinearity... The mapping correction achieves the theoretically required linear relationship, making Re-established. Among them... Indicates the current wavenumber position. Indicates the position of the next wave number. As a linear invariant, it can be achieved using coordinate transformation and coordinate interpolation. If the wavenumber... If the light source is a single variable, wavenumber correction is required, which can be achieved through theoretical ray tracing. In addition, the spectral profile of the light source also needs correction; both aim to restore the sinusoidal or cosine distribution of the interference fringe periods on the fringe sensor surface. The corrected spectrum is then analyzed in the frequency domain using an FFT algorithm to extract the number of fringe periods. , , 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.

[0098] (4) In order to overcome the limitations of single-wavelength measurement The blurring problem is solved using the dispersive interference spectral fringes obtained from an achromatic lens 17, as shown below. Figure 6As shown, the accuracy of the single-step displacement testing system is demonstrated. The scatter plots represent the test data, the straight lines and broken lines represent the ideal curve, and another red broken line graph close to 0 represents the error between the system and the ideal line. The displacement test was performed under a single spectrum. By actively introducing optical path difference through one arm, the test results were good within a range of nearly 30 micrometers.

[0099] (5) A dual-wavelength fusion algorithm is used to eliminate integer ambiguity. Two characteristic wavelengths, 533nm and 633nm, are selected. The phase four-step phase shift input is calculated, and its dual-wavelength fusion algorithm is obtained. The phases of respectively The optical path difference is: ,in , Furthermore, the optical path difference can be calculated more precisely to within half a wavelength.

[0100] (6) By adjusting the two mirrors that cooperate with the external mirror and the mirrors in the loop-shaped optical path, four staggered interference spectra can be obtained on the image plane. From the four phase-shifted interferograms acquired by the detector camera, the light intensity data of the two characteristic wavelengths, 533nm and 633nm, are extracted and denoted as follows: as well as

[0101] ,like Figure 7 As shown, substitute the values ​​into the four-step phase-shifting formula to calculate the characteristic wavelength phase:

[0102]

[0103] The precise optical path difference was calculated using the averaging method: the measurement accuracy was ≤30nm (λ / 30, λ=632.8nm).

[0104] (7) If external compensation is required, the control system will convert the tilt error and the measured optical path difference into compensation signals and send them to the high-speed tilt mirror and the piezoelectric displacement stage to adjust the 5th and 6th retroreflection delay lines respectively, and adjust the beam direction and optical path in real time.

[0105] Figure 8 To measure the relative point light intensity change during the four-step phase-shifting data acquisition, the left figure shows the light intensity at 633nm, and the right figure shows the light intensity at 533nm. Figure 9 Four spectral synchronous phase-shifting step test curves are presented, where scatter points represent test data, and broken lines represent the ideal curve. The left graph is at a wavelength of 633 nm, the right graph is at a wavelength of 533 nm, and another broken line graph close to 0 on the right axis represents the error between the data and the ideal curve. Figure 2 This diagram shows another alternative scheme that uses an internal light source instead of an external light source for precise displacement measurement. Both schemes employ the same technical principle.

[0106] 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 co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry, characterized in that, It includes an optical path adaptation module, a wideband synchronous phase shifting module, a dispersion compensation module, a tilt error detection module, and a large dynamic range precision measurement module; The optical path adapter module separates two beams of light from the same light source by amplitude splitting or wavefront splitting using a broadband beam splitter or a dual-aperture beam splitter. The broadband synchronous phase-shifting module adopts a Mach-Zehnder interferometer structure, with an achromatic quarter-wave plate placed in one arm of the interferometer to introduce achromatic polarization between the orthogonal polarization components of the beam. Phase delay; utilizing the complementary interferogram characteristics of the dual-output ports of the Mach-Zehnder interferometer, combined with a polarization separation component, four phase-separated images are simultaneously acquired. Interference fringes; The dispersion compensation module achieves wideband dispersion compensation through "achromatic waveplate + compensation plate of the same material / achromatic waveplate of the same model"; The tilt error detection module extracts a portion of the beam after the two arms of the interferometer split the beam, focuses it through a lens to form a spot, calculates the centroid offset of the spot using the "threshold segmentation + target window locking" centroid method, and combines the focusing focal length to infer the wavefront tilt angle of the two beams, thus realizing real-time detection of tilt error. The large dynamic range precision measurement module adopts a collaborative strategy of "coarse measurement to expand the range + fine measurement to improve accuracy". After polarization separation, the four beams of light are incident on the Amitch prism for dispersion to form an interference spectrum. After wavenumber correction to correct the horizontal axis of the spectrum, the number of spectral fringe periods is calculated by the FFT fast Fourier transform algorithm to obtain the coarse optical path difference result. The intensity data of four phase-shifted interference beams of a set wavelength are extracted from the interference spectrum and substituted into the four-step phase-shifting formula to calculate the precise phase. Combined with the dual-wavelength fusion algorithm to eliminate integer ambiguity, the optical path difference result with further precision is obtained. Finally, the fine phase difference is obtained by averaging the single-wavelength phase calculation.

2. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 1, characterized in that, The co-phase error includes tilt error and piston error. The synchronous detection, dispersion compensation, and coarse and fine measurement processes of the tilt error and piston error are carried out in coordination. When it is necessary to compensate for the co-phase error, the measurement results are fed back to the closed-loop control unit. The co-phase error is compensated in real time through a high-speed tilt mirror and a piezoelectric displacement stage until the co-phase requirement under the detection accuracy is achieved.

3. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 1, characterized in that, The polarization separation component of the broadband synchronous phase shifting module operates as follows: The vertical outgoing light from the two ports of the Mach-Zehnder interferometer is adjusted to be parallel light by a reflector and a right-angle external reflector before being incident on the optical circuit of the polarizing beam splitter PBS. Two beams of light simultaneously enter the circuit from the incident port of one of the polarizing beam splitters PBS, and are split into four beams: P-beams and S-beams. After being refracted by a high-reflectivity reflector, they are emitted in the same direction from the same beam splitting surface, ensuring that four interferograms are acquired synchronously on the same detector surface. The combination of four reflectors, including two reflectors that cooperate with the right-angle external reflector and two reflectors at the polarizing beam splitter PBS, controls the outgoing direction of the four beams of light.

4. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 3, characterized in that, The detector is a high-speed detector, which ensures the simultaneous acquisition of four phase-shifted interferograms and interferometric spectra.

5. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 1, characterized in that, The dispersion compensation scheme of the dispersion compensation module includes two implementation methods: (1) Two beams of light are passed through a polarization beam splitter or extinction element, and the polarization direction is adjusted to 45°. One beam of light passes through an achromatic waveplate with the fast axis parallel to the polarization direction, and the other beam of light passes through an achromatic waveplate with the fast axis at 45° to the polarization direction. Wide-band phase shifting and dispersion compensation are achieved by using double achromatic waveplates. (2) Two beams of light are transmitted and reflected in a selected band by passing them through the same dichroic mirror. In the transmitted light, one beam passes through an achromatic waveplate whose fast axis is parallel to the vertical or horizontal direction, and the other beam passes through a compensation plate of the same material to ensure that axial dispersion compensation and polarization phase shift are achieved in tandem.

6. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 1, characterized in that, The specific detection steps of the tilt error detection module are as follows: (1) Extract the beams of both arms through a beam splitter, and then... A lens with a focal length of 1-2m focuses light to form a spot; (2) The area array detector acquires the spot image, and the centroid of the spot is roughly located by binarization processing. The target window is delineated to reduce random device errors. (3) Calculate the centroid of the pixels within the window to obtain the centroid offset in the X and Y directions. ; (4) Through the formula Calculate the wavefront tilt angle with a detection accuracy of ≤2″.

7. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 1, characterized in that, The dual Amicis prism consists of two triangular prisms, the first of which is made of medium dispersion glass and the second of which is made of high dispersion glass. The prism angles and materials are optimized so that the outgoing direction of the center wavelength light is parallel to the incident direction, while other wavelengths are deflected according to their dispersion capabilities.

8. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 1, characterized in that, The specific detection steps of the large dynamic range precision measurement module are as follows: (1) Calculate the coarse phase difference using the number of fringe periods, where the number of fringe periods of the dispersive fringe sensor is... Optical path error between the two arms The relationship is: ； 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; (2) Using dual-wavelength phase calculation avoids the error in calculating the fringe period when the optical path is close to 0, further locking the optical path difference, and using the single-wavelength four-step phase shift calculation result to calculate the accurate phase difference; the specific method of dual-wavelength phase calculation is to use the light intensity at a specific wavelength position of four interference spectra as the input of the four-step phase shift. Its dual wavelengths were obtained The phases of respectively The formulas for calculating phase and optical path difference are as follows: ； ； in , ; (3) Solving the phase of a single wavelength As the solution result.

9. The co-phase error detection system based on broadband spectral synchronous phase-shifting interferometry according to claim 1, characterized in that, The optical path adaptation module is compatible with multiple light source types, including broadband light sources, lasers, and quasi-monochromatic light. It works with narrowband filters to perform wavenumber position positioning for set band measurements. It is used for phase error measurement of astronomical interferometers, sub-aperture phase detection of optical synthetic aperture telescopes, and displacement detection of high-precision displacement measurement equipment. It is compatible with various light source scenarios, including broadband white light, starlight, lasers, and quasi-monochromatic light.

10. A method for detecting co-phase error based on broadband spectral synchronous phase-shifting interferometry, characterized in that, This method, based on the broadband spectral synchronous phase-shifting interferometry co-phase error detection system according to any one of claims 1 to 9, includes the following steps: Step 1: Separate two beams of light from the same source by amplitude splitting or wavefront splitting using a broadband beam splitter or dual-aperture beam splitter. Step 2: By using a phase delayer with polarization modulation, orthogonal polarization direction components are obtained in one arm of the interferometer. Phase delay; Step 3: Utilize the phase shifting effect of the beam splitter's reflection, the complementarity of the interference patterns at the two output ports of the Mach-Zehnder interferometer, and the inter-polarization components... The phase delay combination, through orthogonal polarization separation at the two output ports of the interferometer, yields four phase shifts with the following values: Interference fringes; Step 4: Achieve simultaneous acquisition of four interference spectral fringes by a single detector through optical path modulation; Step 5: Split the beam in both arms of the interferometer and simultaneously measure the wavefront tilt change of the two beams by calculating the centroid of the focused spot.

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