A phase adjustable nulling interferometer system

Abstract

The application discloses a phase-adjustable nulling interference system and relates to the field of photoelectric measurement, which comprises a first telescope and a second telescope, a first collimating lens, a second collimating lens, a phase adjusting device, multiple plane mirrors, a beam splitter, a convex lens, a detector and a control device. Incident light passes through the first and second telescopes and is converted into parallel light beams by the first and second collimating lenses. One of the light beams is subjected to phase adjustment by the phase adjusting device, and then the two light beams continue to transmit through the multiple plane mirrors. At the beam splitter, the two light beams are coherently superposed to generate an interference pattern. The pattern is focused on the plane of the detector by the convex lens to form an interference image available for analysis. The detector receives the image and transmits it to the control device, the control device processes and analyzes the image and controls the phase adjusting device to adjust the phase difference between the two light beams, so that the movement of the interference fringes is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photoelectric measurement, and relates to a phase-adjustable nulling interference system. BACKGROUND

[0002] Nulling interference is an interference measurement technique mainly applied to high-precision observations in astronomy. This technique is particularly suitable for observing dark and weak celestial bodies around extremely bright stars, such as exoplanets. By eliminating the interference of starlight, nulling interference can more clearly detect planets orbiting around stars.

[0003] Based on the principle of light interference, when two coherent light beams meet, the combined light intensity depends on the phase difference Δφ. The combined light intensity can be represented as:

[0004] ,

[0005] Where I1 and I2 are the intensities of the two light beams. When Δφ = π, cos(Δφ) = -1, so the light intensity reaches a minimum:

[0006] ,

[0007] However, for light from a planet, due to its slight deviation in angular position from the star, it does not fully meet the condition for destructive interference. Therefore, the planet light is not completely eliminated at the center of interference, and there is still a certain light intensity, which makes it possible to extract the planet light in a high-contrast environment.

[0008] The core of the nulling interference technique lies in effectively eliminating errors and dealing with noise interference. The main challenges currently include wavefront errors, atmospheric turbulence, detector noise, mechanical vibration and thermal deformation, etc. To address these challenges, adaptive optics systems, high-order deformable mirrors and advanced wavefront sensors are used to significantly improve wavefront errors; lucky imaging technology and post-processing algorithms are used to mitigate the effects of atmospheric turbulence; low-noise devices are developed and ultra-low temperature refrigeration technology is applied to reduce detector noise; precise vibration isolation systems and structural optimization design are used to suppress mechanical vibration; and active thermal management systems are implemented and low-expansion materials are used to control thermal deformation. In addition, advanced coronagraph technology enhances the ability to suppress stray light, and differential imaging technology and machine learning algorithms greatly improve the ability to extract weak signals in data processing. However, despite the significant progress made, error elimination and noise suppression still face many challenges.

[0009] Traditional nulling interference systems usually only produce a phase of π, resulting in a limited number of dark fringes in the image, and the information obtained at the dark fringes is relatively less, which is easily affected by noise and has low detection accuracy. Therefore, the number of dark fringes needs to be increased to obtain more effective data. SUMMARY

[0010] The technical problem solved by the present application is that the phase-adjustable nulling interferometric system can move the dark fringes to different positions by adjusting the phase of the interference fringes, thereby obtaining planet signals at different positions, increasing the data richness in the phase dimension, and improving the resolution and detection accuracy of the system.

[0011] The technical solution adopted by the present application to solve the technical problem is a phase-adjustable nulling interferometric system, which comprises a telescope, a collimating lens, a plane mirror, a beam splitter, a phase adjustment device, a convex lens, a detector, and a control device. The system uses two telescopes to receive incident light signals. The incident light is collected and focused by the telescopes to form preliminary light signals. These light signals are then collimated by the collimating lens to convert them into two parallel light beams. One of the light beams passes through the phase adjustment device to accurately change the phase of the light beam, thereby controlling the phase difference between the two light beams when they interfere. The adjustment of the phase difference can be achieved by changing the optical path difference, which satisfies the following relationship:

[0012] ,

[0013] where Δφ is the phase difference between the two light beams, λ is the wavelength of the light, and ΔL is the optical path difference. By accurately controlling the optical path difference ΔL, the phase difference Δφ can be accurately controlled.

[0014] After phase adjustment, the two light beams are reflected by a series of plane mirrors to propagate along the designed path and accurately overlap in space. At the beam splitter, the two light beams are coherently superimposed to produce an interference effect. The interfered light beam is focused by the convex lens onto the plane of the detector. After receiving the interference pattern, the detector converts the optical signal into an electrical signal and transmits it to the control device. The control device processes and analyzes the received interference image. First, the interference pattern is preprocessed, such as denoising and smoothing. Then, the sine fitting method is used to analyze the distribution of the interference fringes to determine the center positions of the bright and dark fringes. The data of the dark fringe center positions are recorded, and further analysis is performed based on the phase difference and fringe position information to provide a basis for subsequent fringe movement. The intensity distribution of the interference fringes can be represented as:

[0015] ,

[0016] where I(x) is the light intensity at position x, I0is the average light intensity, V is the contrast of the fringe, Λ is the fringe period, φ0is the initial phase, a is the attenuation coefficient, and x0is the center of the fringe envelope. By fitting the experimental data, the position of the center of each dark fringe, i.e., the position where the light intensity reaches the minimum value, can be accurately extracted. After obtaining the light intensity at the center of the dark fringe, i.e., the planet signal, the control device analyzes the information such as the position and contrast of the fringe. According to the current phase difference and the position of the fringe, combined with the parameters of the system and the characteristics of the target, the direction and distance that the fringe needs to move are determined.

[0017] In order to obtain a complete planet image, the system needs to fit and reconstruct the light intensity distribution of the planet. The reconstruction process uses a fitting method, which assumes that the light intensity distribution of the planet can be represented by a Gaussian distribution:

[0018]

[0019] where I0is the peak light intensity of the planet, (x0, y0) is the center position of the planet, and σ is the standard deviation of the spot. By fitting the measured (I p (n), x(n), y(n)) at the center of the dark fringe, the parameters I0, x0, y0, and σ can be solved, thereby determining the position and characteristics of the planet.

[0020] Since a single measurement can only obtain limited spatial information, the control device adjusts the phase adjustment device to change the phase difference Δφ of the two light beams, thereby moving the interference fringes. After each phase adjustment, the position of the dark fringes in the interference pattern changes, and the new dark fringe center position corresponds to the position where the star light is suppressed. By adjusting the phase difference multiple times, the control device extracts pixel information at each new dark fringe center position, accumulates multiple measurement data, and obtains the planet light intensity values and corresponding position coordinates under different phase conditions.

[0021] In order to move the fringes, the control device adjusts the phase adjustment device to change the optical path difference ΔL, thereby adjusting the phase difference Δφ. After each phase adjustment, the moved fringe position is recaptured, and new dark fringe center position data is extracted. By adjusting the phase difference multiple times and moving the fringes, the fringe position data obtained under different phase conditions is accumulated to form rich measurement data. The movement Δx of the fringe and the change of the phase difference satisfy the following relationship:

[0022]

[0023] ​Wherein, f is the focal length of the null interference system, d is the distance between the first telescope and the second telescope. By precisely controlling Δφ, the interference fringes can be moved as expected. The moved fringes are captured by the detector again, and the control device extracts the position data of the dark fringe center again. By adjusting the phase difference, moving the fringes and extracting data for many times, the fringe position data under different phase conditions are obtained, and the abundance of the measurement data is increased.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] The present application can move the dark fringes to different positions, obtain the planetary signals at different positions, increase the phase dimension data abundance, and improve the system resolution and detection accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A schematic diagram of a phase-adjustable null interference system;

[0027] Figure 2 A star-planet system observation result diagram;

[0028] Figure 3 An observation result X-direction cross-section diagram;

[0029] Figure 4 A planetary position fitting result.

[0030] In the figure, the reference numerals are: the first telescope 1, the second telescope 2, the first collimating lens 3, the second collimating lens 4, the phase adjusting device 5, the first plane mirror 6, the second plane mirror 7, the third plane mirror 8, the fourth plane mirror 9, the fifth plane mirror 10, the beam splitter 11, the convex lens 12, the detector 13, and the control device 14. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other. In order to achieve the above purpose, the present application adopts the following technical scheme.

[0032] As Figure 1As shown, the present application provides a phase-adjustable nulling interferometric system, which includes a first telescope 1 and a second telescope 2, a first collimating lens 3 and a second collimating lens 4, a phase adjustment device 5, a first to a fifth plane mirror 6-10, a beam splitter 11, a convex lens 12, a detector 13 and a control device 14. The incident light passes through the first and second telescopes 1, 2 respectively, and is converted into parallel light beams by the first and second collimating lenses 3, 4. One of the light beams is adjusted in phase by the phase adjustment device 5, and then the two light beams continue to transmit through the multiple plane mirrors 6-10. At the beam splitter 11, the two light beams are coherently superimposed to generate an interference pattern. The pattern is focused on the plane of the detector 13 by the convex lens 12, forming an interference image that can be analyzed. The detector 13 receives the image and transmits it to the control device 14, which processes and analyzes the image and controls the phase adjustment device 5 to adjust the phase difference of the two light beams, achieving the movement of the interference fringes.

[0033] The control device 14 acquires the image collected by the detector 13, analyzes the interference pattern using a sine fitting method, and determines the center position of the dark fringes, i.e., the position of the lowest light intensity. The data of the center position of the dark fringes is recorded, and further analysis is performed based on the phase difference and fringe position information to provide a basis for subsequent fringe movement. Combined with the current position and other parameters, the direction and distance of the fringe movement are determined, and then the phase adjustment device 5 is controlled to adjust the phase difference of the two light beams, achieving the movement of the interference fringes.

[0034] The phase adjustment device 5 is adjusted by the control device 14 to change the optical path difference to adjust the phase difference, so that the interference fringes move in the predetermined direction and distance. After each phase adjustment, the position of the moved fringes is recaptured, and the new center position data of the dark fringes is extracted. By adjusting the phase difference and moving the fringes multiple times, the fringe position data obtained under different phase conditions is accumulated to form rich measurement data. These accumulated data are further used to fit a Gaussian distribution model to fit and reconstruct the light intensity distribution of the planet, thereby obtaining complete image information of the planet.

[0035] One of the light beams passes through the phase adjustment device 5 to accurately change the phase of the light beam, so as to control the phase difference of the two light beams when they interfere. The adjustment of the phase difference can be achieved by changing the optical path difference, satisfying the following relationship:

[0036] ,

[0037] where Δφ is the phase difference of the two light beams, λ is the wavelength of the light, and ΔL is the optical path difference. By accurately controlling the optical path difference ΔL, the phase difference Δφ can be accurately controlled.

[0038] After phase adjustment, the two beams of light are reflected by a series of plane mirrors 6-10, so that the light beams propagate along the designed path and are accurately superimposed in space. At the beam splitter 11, the two beams of light are coherently superimposed to produce interference effects. The light beams after interference are focused by the convex lens 12 onto the plane of the detector 13. After receiving the interference pattern, the detector 13 converts the optical signal into an electrical signal and transmits it to the control device 14. The control device 14 processes and analyzes the received interference image. First, the interference pattern is preprocessed, such as denoising and smoothing, and then the distribution of interference fringes is analyzed by using the sine fitting method to determine the center position of bright and dark fringes. The data of the dark fringe center position are recorded, and further analysis is performed according to the phase difference and fringe position information to provide a basis for subsequent fringe movement. The intensity distribution of the interference fringes can be expressed as:

[0039] ,

[0040] where I(x) is the light intensity at position x, I0 is the average light intensity, V is the visibility (contrast) of the fringe, Λ is the fringe period, φ0 is the initial phase, α is the attenuation coefficient, and x0 is the center of the fringe envelope. By fitting the experimental data, the position of the dark fringe center, i.e., the position where the light intensity reaches a minimum, can be accurately extracted. After obtaining the light intensity at the dark fringe center position, i.e., the planet signal, the control device 14 analyzes the position, contrast, and other information of the fringe. According to the current phase difference and fringe position, combined with the parameters of the system and the characteristics of the target, the direction and distance of the fringe movement are determined.

[0041] In order to obtain a complete planet image, the system needs to fit and reconstruct the light intensity distribution of the planet. The reconstruction process uses a fitting method, which assumes that the light intensity distribution of the planet can be represented by a Gaussian distribution:

[0042] ,

[0043] where I0 is the peak light intensity of the planet, (x0, y0) is the center position of the planet, and σ is the standard deviation of the spot. By fitting the (I p (n), x(n), y(n)) measured by the dark fringe center, the parameters I0, x0, y0, and σ can be solved, thereby determining the position and characteristics of the planet.

[0044] Since only limited spatial information can be obtained in a single measurement, the control device 14 changes the phase difference Δφ of the two light beams by adjusting the phase adjustment device, so as to realize the movement of the interference fringes. After each phase adjustment, the position of the dark fringes in the interference pattern changes, and the new dark fringe center position corresponds to the position where the light of the new star is suppressed. By adjusting the phase difference multiple times, the control device extracts pixel information at each new dark fringe center position, accumulates multiple measurement data, and obtains the planet light intensity value and the corresponding position coordinate under different phase conditions.

[0045] In order to realize the movement of the fringes, the control device 14 adjusts the phase adjustment device 5 to change the optical path difference ΔL, so as to adjust the phase difference Δφ. After each phase adjustment, the position of the moved fringes is recaptured, and the data of the new dark fringe center position is extracted. By adjusting the phase difference multiple times and moving the fringes, the fringe position data obtained under different phase conditions is accumulated to form rich measurement data. The movement amount Δx of the fringes and the change of the phase difference satisfy the following relationship:

[0046]

[0047] Wherein, f is the focal length of the null interference system, and d is the distance between the first telescope and the second telescope. By accurately controlling Δφ, the interference fringes can be moved as expected. The moved fringes are captured by the detector 13 again, and the control device 14 reextracts the position data of the dark fringe center. By adjusting the phase difference multiple times, moving the fringes and extracting data, the fringe position data under different phase conditions is obtained, and the richness of the measurement data is increased.

[0048] The embodiment constructs a null interference system composed of a first telescope 1 and a second telescope 2 with an aperture of 20 mm and a focal length of 2 m, and the baseline length is set to 0.1 m. In order to verify the performance of the system, a typical star-planet system is simulated as an observation target, and the main star light source is located at the center of the picture, and the planet light source is located at the left side of the main star by 0.4 angular seconds. The intensity of the planet light source is set to be one tenth of the main star light source, that is, I planet = 0.1I star . The observation data is obtained by a simulated high-resolution detector, and the pixel size of the detector is set to 1.1x1.1 microns. According to the system parameters, it is calculated that the theoretical position of the planet should be located at the left side of the image center by 3.64 pixels. At the same time, a direct current bias term is added to the signal to simulate the background response of the detector 13, and noise is introduced to simulate the noise influence in the real observation environment. The noise level is set to a signal-to-noise ratio (SNR) of 5 to reflect the real observation conditions. 10000 images are read continuously and superimposed to simulate long-time exposure to improve the signal-to-noise ratio. Subsequently, the superimposed image is normalized to obtain the relative brightness distribution. Figure 2The simulated observation image is shown, with the horizontal and vertical axes representing the pixel positions in the X and Y directions, respectively.

[0049] To further analyze the intensity distribution of the spot, one-dimensional intensity data is extracted from the middle row of the image, i.e. Figure 3 the position of the white horizontal line in (a). The resulting data represent the relative intensity distribution in the X direction, as shown in the scatter plot in (b). Figure 3

[0050] For the extracted one-dimensional data, a Gaussian function is used for fitting to determine the center position and related parameters of the spot. The mathematical expression of the Gaussian function is:

[0051] ,

[0052] This formula is used to intercept one-dimensional data to prepare for the following fringe fitting, where A represents the peak amplitude, x0 is the center position, and σ is the standard deviation of the spot. Through the fitting result, the center position x0 and the standard deviation σ of the spot are obtained. Based on this, the data within a range of 3σ on the left and right of the center of the spot are intercepted to reduce the influence of background noise and improve the purity of the signal.

[0053] Within the intercepted 3σ range, a sinusoidal function containing eight harmonics is used for fitting to more finely describe the characteristics of the interference fringes. This model can accurately capture the periodic changes of the interference fringes, and its mathematical form is:

[0054] ,

[0055] where I(x) is the light intensity at position x, I0 is the average light intensity, V is the visibility (contrast) of the fringes, Λ is the fringe period, φ0 is the initial phase, α is the attenuation coefficient, and x0 is the center of the fringe envelope. Through the fitting of the data, the accurate model of the interference fringes is obtained. Subsequently, using a local minimum detection algorithm, the dark fringe positions in the interference fringes are extracted, which correspond to the positions where the main star light is weakened by interference, i.e., the planet signal.

[0056] To further determine the position of the planet, a Gaussian function is fitted to the extracted planet signal. The light intensity distribution of the planet can be represented by a Gaussian distribution:

[0057] ,

[0058] where I0 is the peak light intensity of the planet, (x0, y0) is the center position of the planet, and σ is the standard deviation of the spot. The fitting result is shown in Figure 4 ​As shown in (a), the center position x0 of the Gaussian function is the pixel position of the planet in the X direction. Based on the fitting parameters, the planet is calculated to be located 3.14 pixels to the left of the image center, with a relative error of 13.7%.

[0059] To improve the accuracy and robustness of the measurement, this embodiment introduces a phase modulation method. By changing the phase difference of the interferometric system, 50 equally spaced phase values ​​are taken within the range of 0 to 2π. For each phase difference, the above data acquisition and processing process is repeated to obtain local minimum data under different phase conditions. The mathematical expression for phase modulation is:

[0060]

[0061] Where N=50 is the total number of phase samples. By accumulating local minimum data at different phases, the statistical characteristics of the signal are enhanced, and the impact of noise interference is reduced.

[0062] The local minimum data under all phase conditions are summarized, and a Gaussian function is used for fitting again. For example... Figure 4 As shown in (b), the fitted curves demonstrate a comprehensive estimate of the planet's position. Ultimately, the planet's center was calculated to be 3.65 pixels to the left of the image center. The phase modulation method achieved a relative error of 0.2%, significantly improving positioning accuracy compared to single-measurement results.

[0063] It should be understood that the embodiments described above are only for illustrating the method and application of the present invention, and other improvements and modifications based on the concept of the present invention are still within the protection scope of the present invention. Therefore, the protection scope of the present invention is not limited to the specific embodiments described above, but covers all equivalent solutions and techniques based on the concept of the present invention.

Claims

1. A phase-adjustable null-elimination interference system, characterized in that, The system includes a first telescope and a second telescope, a first collimating lens and a second collimating lens, a phase adjustment device, multiple plane mirrors, a beam splitter, a convex lens, a detector, and a control device. One incident light beam passes through the first telescope and is converted into a parallel beam by the first collimating lens. The other incident light beam passes through the second telescope and is converted into a parallel beam by the second collimating lens. One of the beam beams undergoes phase adjustment by the phase adjustment device. Subsequently, the two beam beams continue to be transmitted through multiple plane mirrors. At the beam splitter, the two beam beams coherently superimpose, producing an interference pattern. This pattern is focused onto the detector plane by the convex lens, forming an interference image that can be analyzed. The detector receives the image and transmits it to the control device. The control device processes and analyzes the image and controls the phase adjustment device to adjust the phase difference between the two beams, thereby moving the interference fringes. The control device acquires the image collected by the detector and analyzes the interference pattern using a sine fitting method. The fringe intensity distribution of the interference pattern is expressed as: Where I(x) is the light intensity at position x, I0 is the average light intensity, V is the contrast of the fringe, Λ is the fringe period, φ0 is the initial phase, α is the attenuation coefficient, and x0 is the center of the fringe envelope; the center position of each dark fringe is determined by fitting, that is, the position with the lowest light intensity, and the light intensity and position of the center of the dark fringe (I) are recorded. p (n), x(n), y(n)), and further analysis is performed based on the phase difference and fringe position information to provide a basis for subsequent fringe movement. Combined with the current position parameters, the direction and distance of fringe movement are determined. Then, the phase adjustment device is controlled to adjust the phase difference between the two light rays to realize the movement of the interference fringes. The system fits and reconstructs the light intensity distribution of the planet. The reconstruction process uses a fitting method, assuming that the light intensity distribution of the planet is represented by a Gaussian distribution: Where I0 is the peak light intensity of the planet, (x0, y0) is the center position of the planet, and σ is the standard deviation of the light spot, obtained by measuring the center of the dark fringe. p By fitting the parameters (n), x(n), y(n)), we can solve for the parameters I0, x0, y0 and σ, and thus determine the position and characteristics of the planet. The phase difference Δφ is adjusted by changing the optical path difference ΔL through the control device, so that the interference fringes move in a predetermined direction and distance. The amount of fringe movement Δx and the change in phase difference Δφ satisfy the following relationship: Where f is the focal length of the nulling interference system, and d is the distance between the first telescope and the second telescope; After each phase adjustment, the moved fringe position is recaptured, and new dark fringe center position data is extracted. By adjusting the phase difference and moving the fringe multiple times, the fringe position data obtained under different phase conditions are accumulated to form rich measurement data. This accumulated data is used to fit a Gaussian distribution model to fit and reconstruct the planet's light intensity distribution, thereby obtaining complete planetary image information.

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