Segmented mirror surface channel spectrum determination method

Abstract

The invention relates to a segmented mirror surface channel spectrum determination method, belongs to the technical field of optical measurement, and solves the problems that most of the existing co-phase detection technologies cannot meet the detection requirements of high precision, wide range, real-time performance and the like at the same time, and the difficulty and complexity of a primary mirror system for realizing co-phase are further increased along with the increase of the number of spliced sub-mirrors. The method comprises the following steps that an optical fiber beam combiner is adopted for light source input, coherent light with different wavelengths is combined, and the combined light enters a segmented mirror system; constructing an interference intensity distribution template of the sub-channel spectrum by using the theoretical model; obtaining the central stripe position of each section of channel spectrum; and the step difference of the segmented mirror is obtained by combining the dispersion constant and the spectral center position. According to the method, the spectral side of the segmented mirror surface channel can be accurately measured, and a basis is provided for correction of an active optical system, so that a high-precision spliced mirror in a global coplanar state is obtained.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, and in particular relates to a method for segmented mirror channel spectral measurement. Background Technology

[0002] The Center for High Angular Resolution Astronomy (CHARA) was the earliest planetary interferometer constructed, consisting of six one-meter aperture telescopes. Its longest baseline reached 300 meters, covering the visible and near-infrared bands. The Mark III planetary interferometer consisted of two 0.13-meter telescopes with a 32-meter baseline, employing the ABCD method to solve phase detection problems. It served as the prototype for the Navy Precision Optical Interferometer (NPOI), consisting of six 0.5-meter aperture telescopes. The planetary interferometer formed by these telescopes had a longest baseline of 400 meters. The Keck Telescope consisted of two ten-meter-class telescopes interconnected using single-mode ray tracing to form a 140-meter baseline planetary interferometer. Building upon this, the concept of the Optical Hawaiian Array for Nano-radian Astronomy (OHANA) interferometric array was proposed by connecting multiple telescopes. The European Southern Observatory's Very Large Telescope Interferometer (VLI) consists of four 8.2-meter telescopes and four 1.8-meter telescopes, providing a baseline of hundreds of meters. Through adaptive optics correction of its wavefront, it can achieve beam combining in the visible, near-infrared, and mid-to-long-wavelength bands. Long-baseline interferometry allows for precise measurement of celestial angular features, making it invaluable for exoplanet detection and interstellar environment monitoring. The Large Binoculars Interferometer (LBI) is achieved using two 8.4-meter primary mirrors on a shared tracking frame. Its longest baseline is 22 meters, enabling planetary interferometry in the near-infrared and mid-infrared bands.

[0003] Ground-based planetary interferometers can achieve high-resolution detection, but they face significant challenges in beam collection and synthesis due to external environmental influences and vibrations. Utilizing adaptive optics would greatly increase system complexity, hence the proposal to use space-based systems for planetary interferometry. The US SIM-PlanetQuest mission will use the visible light band to achieve a large field of view measurement with a six-meter baseline, achieving an angular accuracy better than 4 μas at a 15-degree field of view. The US-proposed Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) project, with an eight-meter baseline, consists of two 0.5-meter telescopes, combining Fourier spectroscopy in the long-wave infrared band to ultimately achieve a spatial resolution better than 1 arcsecond.

[0004] Currently, high-precision planetary probes face several major challenges. First, the back-end fringe resolution is limited by the system's pixel resolution. Longer focal lengths significantly increase the system's size and weight, and it becomes more susceptible to external disturbances. Lower pixel resolution also makes it impossible to achieve high phase positioning accuracy. The second problem is that achieving high-contrast imaging requires null-elimination interferometry, necessitating a rearrangement of the wavefront phase. When using bulk optics for beam refraction, this is constrained by size and practical physical limitations, and the number of measurement paths is also limited.

[0005] Astronomical photonics, a newly emerging discipline in recent years, has significantly improved the measurement throughput and cost-effectiveness of long-baseline interferometers through technologies such as optical communication, while reducing the system's size and weight, making it more suitable for space-based interferometry systems. The next generation of planetary interferometers will adopt astronomical photonics, using photonic devices for beam splitting, aperture rearrangement, and interferometry to achieve high-resolution and high-contrast imaging. Regarding the system architecture, the front-end beam collection section will still utilize a large-aperture telescope for beam collection. After alignment and adjustment, the beam is coupled into the waveguide.

[0006] Large-aperture segmented space optical systems are advanced scientific payloads involving optics, materials science, mechanics, and control science. For their spliced ​​mirrors to achieve the same imaging capability as an equivalent single mirror, the reflecting surfaces of the sub-mirrors must be in a co-phase state. Clearly, the pose accuracy of the optomechanical structure directly affects the imaging performance of the segmented space optical system, and the required level of positional accuracy depends on the telescope, wavelength, and mission. However, many factors can cause positional errors in the deployed primary mirror components, including assembly errors, deployment accuracy, and shape changes caused by environmental loads, resulting in a decline in system imaging quality. Currently, effectively measuring and correcting mechanical misalignments caused by changes in the complex space environment, thereby achieving higher pose accuracy in situ, is crucial to ensuring the normal operation of the space optical system.

[0007] Conventional ground-based measurement methods, such as laser trackers and interferometers, perform poorly in the long-term operational environment of space telescopes. Furthermore, to ensure image quality, deployed or planned optical systems demand extremely high positioning accuracy for their optomechanical structures, posing a significant challenge to existing conventional measurement methods. Therefore, designing an effective in-situ measurement system to accurately measure the misalignment of the optomechanical structure is crucial for ensuring the final imaging quality of space optical systems.

[0008] Most existing co-phase detection technologies cannot simultaneously meet the requirements of high precision, large range, and real-time performance. Furthermore, as the number of segmented mirrors increases, the difficulty and complexity of achieving co-phase detection in the primary mirror system further increases, posing a significant challenge to traditional detection and analysis methods. Therefore, there is an urgent need to develop a large-range, high-precision segmented mirror pose error measurement technology for use in active optics systems for correction and control, obtaining a globally coplanar state of the segmented mirror to maintain its performance while performing spectral dispersion. Summary of the Invention

[0009] To address the above problems, this invention provides a method for segmented mirror channel spectral measurement.

[0010] A method for segmented mirror channel spectroscopy includes the following steps:

[0011] For the light source input, an optical fiber combiner is used to combine coherent light of different wavelengths and then incident it into the segmented mirror system.

[0012] A template for the interference intensity distribution of the channel spectrum is constructed using a theoretical model;

[0013] The position of the center fringe in each channel spectrum is obtained using correlation calculations;

[0014] By combining the dispersion constant and the spectral center position, the step difference of the segmented mirror is obtained.

[0015] The beneficial effects of this invention are:

[0016] This invention enables accurate measurement of the spectral side of segmented mirror channels, providing a basis for the calibration of active optical systems, thereby obtaining high-precision splicing mirrors with a globally coplanar state. Attached Figure Description

[0017] Figure 1 This is a flowchart of a segmented mirror channel spectral measurement method according to an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the segmented mirror system;

[0019] Figure 3This is a schematic diagram of the channel spectral dispersion process based on aperture coding.

[0020] Figure 4 The figure shows the results of the field experiment. In the figure, (a) is the light intensity distribution in front of the focal point, (b) is the intensity distribution behind the focal point, and (c) is the wavefront solution result.

[0021] Figure 5 This is a schematic diagram of the structure of an optical local high-dimensional edge sensor;

[0022] Figure 6 This is a flowchart of edge spectrum processing. Detailed Implementation

[0023] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and preferred embodiments.

[0024] See Figures 1 to 6 This embodiment provides a method for segmented mirror channel spectroscopy measurement, which includes the following steps:

[0025] For the light source input, an optical fiber combiner is used to combine coherent light of different wavelengths and then incident it into the segmented mirror system; such as Figure 2 As shown, the segmented mirror system includes two cylindrical lenses, a dispersive element, a mask, and segmented mirrors;

[0026] A template for the interference intensity distribution of the channel spectrum is constructed using a theoretical model;

[0027] The position of the center fringe in each channel spectrum is obtained using correlation calculations;

[0028] By combining the dispersion constant and the spectral center position, the step difference of the segmented mirror is obtained.

[0029] Taking a large-aperture survey telescope with a prime focus as an example, its prime focus component camera terminal has a built-in misaligned curvature sensor (which uses two detectors located in front of and behind the prime focus to simultaneously collect defocus images), and the light source illumination intensity is assumed to be unsaturated.

[0030] For mirror co-phase testing, this invention further combines aperture coding and a small-aperture sampling strategy, the specific process of which is as follows: Figure 3As shown. First, a digital micromirror device (DMD) is used to quickly select and locate the sampling positions corresponding to each sub-aperture. Based on the system response requirements, a single-aperture fast scanning mode and a multi-aperture fine detection mode are flexibly configured to achieve complete coverage of the system's frequency response. In actual measurements, in addition to the modulation fringes introduced by the optical path difference, residual aberrations also significantly affect the straightness and slope of the fringes. Therefore, this invention starts from the holographic intensity distribution, systematically analyzes the influence mechanism of residual aberrations on the fringe tilt angle, and effectively improves the contrast of the interference fringes through aberration correction methods. Regarding the co-phase error suppression strategy, firstly, the fringe envelope generated by white light interference is used to achieve coarse co-phase detection to obtain the approximate range of the initial step error between sub-mirrors; then, the segmented mirror channel spectrum measurement method proposed in this invention is introduced. Through the precise extraction of the center position of the channel spectrum interference fringes, a precise connection from coarse co-phase to fine co-phase is achieved, ultimately completing high-resolution suppression of the residual step error between sub-mirrors near the working center wavelength. This scheme organically integrates aperture coding sampling with channel spectral measurement, which not only ensures the real-time performance and dynamic range of cophase detection, but also achieves nanoscale precision cophase control, providing reliable technical support for active optical correction of large-aperture spliced ​​mirror systems.

[0031] Furthermore, such as Figure 5 As shown, an optical local high-dimensional edge sensor is used to measure the tilt angle of the segmented mirror. A thin beam of light from the telescope gantry is used as feedback to replace the local optical closed loop and replace the local high-dimensional sensor.

[0032] This invention applies to two types of spectrometers: seamless spectrometers and fiber optic spectrometers. The seamless spectrometer includes a telescope matting device (TMD) used to encode the positions of the telescope seams to obtain the system's state. The fiber optic spectrometer is primarily used for spectral dispersion, followed by an internal lens array (Hartmann), which assigns a microlens to each sub-lens to control the pose of each sub-lens.

[0033] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0034] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for segmented mirror channel spectroscopy determination, characterized in that, Includes the following steps: For the light source input, an optical fiber combiner is used to combine coherent light of different wavelengths and then incident it into the segmented mirror system. A template for the interference intensity distribution of the channel spectrum is constructed using a theoretical model; Obtain the position of the center fringe in the spectrum of each channel; By combining the dispersion constant and the spectral center position, the step difference of the segmented mirror is obtained.

2. The method for segmented mirror channel spectroscopy measurement according to claim 1, characterized in that, The segmented mirror system includes two cylindrical lenses, a dispersive element, a mask, and a segmented mirror.

3. The method for segmented mirror channel spectroscopy measurement according to claim 1, characterized in that, The tilt angle of the segmented mirror is measured by an optical local high-dimensional edge sensor, with a fine beam of light coming from the truss as feedback, replacing the local optical closed loop to replace the local high-dimensional sensor.

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