Co-phase adjustment method for spliced telescope

Abstract

The invention relates to the technical field of spliced telescopes, and particularly provides a co-phase adjustment method for a spliced telescope, which comprises the following steps of: acquiring interference patterns of a spliced sub-mirror in the spliced telescope under at least two preset wavelengths, and acquiring a theoretical interference template of the spliced sub-mirror under each preset wavelength, calculating the phase offset of the interference pattern of each spliced sub-mirror relative to the corresponding theoretical interference template, taking the phase offset under each preset wavelength as a known observed quantity, constructing an equation set in combination with dispersion characteristic parameters of the spliced telescope, and calculating to obtain the axial optical path step difference between the spliced sub-mirrors in the spliced telescope; therefore, co-phase adjustment of the spliced telescope is carried out. According to the invention, high-precision and high-reliability co-phase determination and adjustment are realized in a wide spectrum range.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mosaic telescopes, and particularly relates to a co-phasing adjustment method for a mosaic telescope. BACKGROUND

[0002] Large-aperture optical telescopes are the key to improving the angular resolution and light-gathering capability of astronomical observations. In recent years, to break through the manufacturing and launch limitations of single mirror apertures, mosaic mirror technology has been widely used. However, after being mosaicked, the imaging effect of the mirror surface will inevitably decline due to mosaic errors. In the process of mosaicking multiple sub-mirrors, there is a serious co-phasing problem in addition to the current focus adjustment problem. The co-phasing problem arises because there is a small amount of front-back distance, i.e., a height step difference, between the multiple sub-mirrors after mosaicking. This error introduces an optical path difference, causing the optical path of the light incident on different sub-mirrors to be different, which in turn causes the phases to be inconsistent, seriously affecting the imaging quality, especially high-contrast imaging. SUMMARY

[0003] Therefore, the present application aims to provide a co-phasing adjustment method for a mosaic telescope, which realizes multi-wavelength input through wavelength division multiplexing, constructs a theoretical interference template for the segmented channel spectrum using a theoretical model, obtains the center fringe position of each channel spectrum using correlation operation, obtains the segmented mirror step difference by combining the dispersion constant and the spectral center position, and realizes co-phasing measurement and adjustment of the mosaic telescope.

[0004] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: The present application provides a co-phasing adjustment method for a mosaic telescope, comprising: S1: obtaining the interference patterns of the mosaic sub-mirrors in the mosaic telescope at at least two preset wavelengths; S2: calculating the interference patterns of the mosaic sub-mirrors at each preset wavelength under ideal co-phasing conditions according to the optical interference theory, and taking the interference patterns as theoretical interference templates; S3: for each preset wavelength, calculating the phase shift of the interference pattern of each mosaic sub-mirror relative to the corresponding theoretical interference template; S4: taking the phase shift at each preset wavelength as a known observation, combining the dispersion characteristic parameters of the mosaic telescope to construct an equation set, and calculating the axial optical path step difference between the mosaic sub-mirrors in the mosaic telescope; S5: driving each mosaic sub-mirror to perform axial compensation according to the axial optical path step difference between the mosaic sub-mirrors, so as to realize the co-phasing of the mosaic telescope.

[0005] Preferably, in S1, a broadband light source is arranged to generate a broadband light beam, the broadband light beam is transmitted to a wavelength division multiplexer through a multimode optical fiber, the wavelength division multiplexer divides the broadband light beam into multiple channels of incident light of different preset wavelength bands, and controls only one preset wavelength band of incident light to be shot towards the mosaic telescope each time, and a beam splitter is arranged on the light path before the incident light is shot towards the mosaic telescope to split the incident light into a reference light and a detection light, the detection light is shot into a mosaic sub-mirror of the mosaic telescope, the detection light reflected by the mosaic sub-mirror is called signal light, and the reference light and the signal light are interfered to obtain an interference pattern under a corresponding preset wavelength.

[0006] Preferably, in S1, the broadband starlight of an observed celestial body is taken as the incident light, the incident light reflected by the mosaic sub-mirror is called signal light, the signal light is split into a first light beam and a second light beam by the beam splitter, a filter is arranged on the propagation light path of the first light beam to make the first light beam retain only light rays of a preset wavelength, and the light rays of the preset wavelength retained are interfered with the second light beam to obtain an interference pattern under the corresponding preset wavelength.

[0007] Preferably, the interference pattern under each preset wavelength is obtained by switching different filters.

[0008] Preferably, the process of calculating the phase shift of the interference pattern of each mosaic sub-mirror relative to the corresponding theoretical interference template is as follows: the normalized cross-correlation function of the interference pattern and the corresponding theoretical interference template is calculated, the peak position of the normalized cross-correlation function is determined as the position shift of the central fringe of the interference pattern, and the position shift of the central fringe is converted into the phase shift.

[0009] Preferably, in S4, based on the physical relationship between the optical path difference, the phase and the wavelength, combined with the dispersion characteristic parameters of the mosaic telescope, the axial optical path step difference between the sub-mirrors causing the phase shift is solved according to the phase shift of the central fringe under each preset wavelength.

[0010] Preferably, the physical relationship between the optical path difference, the phase and the wavelength is as follows: ; Wherein, represents the phase, represents the initial phase, represents the wavelength, represents the optical path difference.

[0011] Compared with the prior art, the application can achieve the following beneficial effects: The present application realizes high-precision and high-efficiency determination and adjustment of axial step difference between sub-mirrors of a spliced large-aperture telescope by adopting multi-wavelength spectral interference matching, and based on the physical relationship between optical path difference, phase and wavelength, and high-precision and high-reliability co-phasing control is realized in a wide spectral range by using multiple discrete wavelength information to check each other, which provides a co-phasing adjustment basis for high-resolution imaging of a large space spliced mirror telescope.

[0012] In addition, the present application can be applied to the scene of constructing a wavelength division multiplexing light source in a laboratory environment, and also applied to the scene of using starlight as a light source in actual work, so as to ensure that the method can be used for laboratory precision assembly and adjustment, and can also adapt to real-time co-phasing maintenance of on-orbit observation, and has high application flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0013] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The accompanying drawings do not constitute an inappropriate limitation of the present application. In the accompanying drawings: Figure 1 is a co-phasing adjustment method flowchart of a spliced telescope according to an embodiment of the present application; Figure 2 is a co-phasing adjustment schematic diagram of a spliced telescope when a wavelength division multiplexing light source is used in a laboratory environment according to an embodiment of the present application; Figure 3 is a co-phasing adjustment schematic diagram of a spliced telescope when starlight is used as a light source in actual work according to an embodiment of the present application; Figure 4 is an axial optical path step difference schematic diagram according to an embodiment of the present application; Figure 5 is an interference pattern schematic diagram of a single spliced sub-mirror according to an embodiment of the present application; Figure 6 is a main mirror interference pattern schematic diagram of a spliced telescope according to an embodiment of the present application.

[0014] The reference signs in the drawings include: Spliced telescope 1, main mirror 11, sub-mirror 12, wideband light source 2, multimode optical fiber 3, wavelength division multiplexer 4, beam splitter 5, reflecting mirror 6, interference surface 7, optical filter 8. DETAILED DESCRIPTION

[0015] For the purpose of making the object, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application. In different embodiments, similar elements are associated with similar element labels. In the following embodiments, many details are described in order to make the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials, methods. In some cases, some operations related to the present application are not shown or described in the specification in order to avoid the core part of the present application being overwhelmed by too much description, and it is not necessary to describe these related operations in detail for those skilled in the art according to the description in the specification and general technical knowledge in the art.

[0016] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other to form various embodiments without conflict. At the same time, each step or action in the method description can also be sequentially adjusted or adjusted in a manner obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for the purpose of clearly describing a certain embodiment, and do not mean a necessary sequence, unless otherwise stated that a certain sequence must be followed.

[0017] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0018] In the description of the present application, it should be noted that unless specifically defined and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0019] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0020] Please refer to Figure 1 In an embodiment of the present application, a method for co-phasing a mosaic telescope is provided, comprising the following steps: S1: obtaining the interference patterns of the mosaic sub-mirrors in the mosaic telescope at least two preset wavelengths; S2: according to the optical interference theory, the interference patterns of the mosaic sub-mirrors at each preset wavelength under the ideal co-phasing state are calculated and used as the theoretical interference templates; S3: for each preset wavelength, the phase offset of the interference pattern of each mosaic sub-mirror relative to the corresponding theoretical interference template is calculated; S4: the phase offset at each preset wavelength is taken as a known observation, and an equation set is constructed in combination with the dispersion characteristic parameters of the mosaic telescope, and the axial optical path step difference between each mosaic sub-mirror in the mosaic telescope is calculated; S5: according to the axial optical path step difference between each mosaic sub-mirror, each mosaic sub-mirror is driven for axial compensation to realize the co-phasing of the mosaic telescope.

[0021] The mosaic telescope usually adopts the optical structure of a primary mirror and a secondary mirror, wherein the primary mirror is a super-large aperture mosaic mirror surface composed of a large number of mosaic sub-mirrors, and the co-focus and co-phase of the mosaic sub-mirrors will seriously affect the imaging quality of the mosaic telescope. Among them, the co-focus means that each mosaic sub-mirror can reflect the light beam to the same focal point, and the co-phase means that the light path of each mosaic sub-mirror is the same, and the mosaic sub-mirror strictly follows the standard mirror distribution, and there is no distance difference between the adjacent mosaic sub-mirrors in the axial direction.

[0022] As an optional embodiment, in step S1, as Figure 2As shown, in the process of assembling and adjusting the sub-mirror of the telescope in the laboratory, a wavelength division multiplexing light source is used to provide multiple preset wavelengths of incident light. Specifically, a broadband light source 2 is provided to generate a broadband light beam covering the working wavelength range, the broadband light beam provided by the broadband light source 2 is transmitted through a multi-mode optical fiber 3, and a wavelength division multiplexer 4 is arranged on the multi-mode optical fiber 3. The broadband light beam is separated in the spectrum by the wavelength division multiplexer 4 to form multiple independent output channels, each channel corresponding to a preset wavelength of incident light, thereby generating multiple incident lights with different center wavelengths. A light path selection and control unit (such as an optical switch) is used to control the selection of only one preset wavelength of incident light at a time, which is emitted from the light outlet of the multi-mode optical fiber 3. A beam splitter 5 is arranged on the light path from the light outlet of the multi-mode optical fiber 3 to the primary mirror 11 of the telescope, which splits the preset wavelength of incident light into two paths: one as reference light, which is directly guided to the interference surface 7 by optical elements, such as a mirror 7 for changing the transmission direction; the other as probe light, which is directed to the primary mirror 11 of the telescope, and the probe light is reflected by each sub-mirror on the primary mirror 11 and returns, the reflected light carries the surface shape and phase error information of each sub-mirror, which is called signal light, and is guided to the interference surface 7 by optical elements, and the signal light and the reference light interfere to form an interference pattern on the interference surface 7. By controlling the unit to switch different wavelength channels in turn, different preset wavelengths of incident light are provided to the telescope, and the above process is repeated to obtain interference patterns at multiple preset wavelengths, providing complete multi-wavelength data for subsequent template matching and phase calculation.

[0023] As an optional embodiment, a broadband light source with low temporal coherence can be used for confocal adjustment before phase adjustment to ensure the accuracy of focus adjustment. When adjusting the phase, the broadband light source 2 uses a high-coherence broadband light source.

[0024] As an optional embodiment, in order to eliminate the influence of non-interference background light and improve the signal-to-noise ratio, background light intensity correction can be performed during the acquisition of the interference pattern. The intensity distribution data of the two reference lights and the signal light are obtained before the interference fringes are acquired, and the non-interference part of the two lights is obtained based on the interference principle. This part is the non-interference background. By subtracting the non-interference part of the two lights from the interference pattern obtained by the interference surface 7, the pure interference data can be obtained. The interference data without the non-interference background is used as the final interference pattern, which can greatly improve the sub-pixel accuracy and noise resistance of the phase calculation.

[0025] As an optional embodiment, in step S1, as Figure 3As shown, in actual on-orbit operation, starlight is used as the incident light. Specifically, starlight is directly incident on the primary mirror 11 of the mosaic telescope 1. The incident starlight reflected by the mosaic sub-mirror on the primary mirror 11 is referred to as signal light. The primary mirror 11 reflects the signal light to the secondary mirror 12, and the secondary mirror 12 further reflects the signal light. At this time, the signal light is split into a first light beam and a second light beam by the beam splitter 5. A narrow-band filter 8 is arranged for the image point region of the mosaic sub-mirror in the propagation path of the first light beam, so that the first light beam only retains light of a predetermined wavelength. The light of the predetermined wavelength and the second light beam are guided to the interference surface 7 by the optical structure such as the mirror 7, and interference is performed between the light of the predetermined wavelength and the second light beam. The interference pattern corresponding to the predetermined wavelength is obtained on the interference surface 7. By replacing the filter 8 with a filter having a different filtering bandwidth, the above process is repeated to obtain the interference pattern at each predetermined wavelength. As shown in FIG. 6, Figure 5 is the actual interference pattern obtained by a single mosaic sub-mirror, Figure 6 is the actual interference pattern obtained by all the mosaic sub-mirrors on the entire mosaic mirror surface.

[0026] As an optional embodiment, in any of the above scenarios, after obtaining the interference patterns at at least two predetermined wavelengths, an accurate digital simulation model of the mosaic telescope 1 is established in the computer based on the optical interference theory. In the model, all the mosaic sub-mirrors are set to be in an ideal in-phase state, that is, it is assumed that there is no any axial position error between the mosaic sub-mirrors, and the reflected wavefronts constitute a perfect continuous phase front. Under this ideal condition, the incident light of each predetermined wavelength is simulated to be incident on the primary mirror 11 of the mosaic telescope 1. Similarly, by splitting and interfering, the ideal interference pattern of the mosaic sub-mirror at each predetermined wavelength is simulated and obtained as a theoretical interference template.

[0027] As an optional embodiment, in step S3, for each mosaic sub-mirror on the primary mirror 11, the normalized cross-correlation function between the actually obtained interference pattern and the corresponding theoretical interference template is calculated. The position offset of the central fringe of the interference pattern and the theoretical interference template is determined by finding the peak position of the peak position of the cross-correlation function. This position offset is caused by the movement of the interference fringes due to the relative axial distance difference between adjacent mosaic sub-mirrors. According to the relationship between the phase and the position offset, the position offset of the central fringe can be converted into the phase offset, that is, each mosaic sub-mirror can obtain its corresponding phase offset.

[0028] As an optional embodiment, in step S5, as shown in FIG. 8, Figure 4 For any mosaic sub-mirror, when the incident light is of any predetermined wavelength, there is a physical relationship between the phase, the wavelength, and the optical path difference caused by the mosaic sub-mirror as follows: ; wherein, denotes the phase, denotes the initial phase, denotes the wavelength, denotes the optical path difference.

[0029] To obtain the optical path difference , the dispersion characteristic parameters of the stitching telescope 1 need to be corrected so that the optical path difference can be approximately a linear function of the wavelength in a narrow waveband, wherein the dispersion characteristic parameters are known system parameters which can be obtained by previous calibration. Further, the phase offset at each preset wavelength is taken as a known observation, and an equation is constructed in combination with the dispersion characteristic parameters of the stitching telescope 1. Different preset wavelengths can obtain different equations, and the optical path differences in these equations are the same. Thus, these equations can be combined to form an equation group, and a numerical optimization algorithm such as the least squares method is used to solve the equation group, so as to solve the optical path difference of the adjacent two stitching sub-mirrors. Different equation groups can be obtained by different stitching sub-mirror position offsets, and the optical path differences between all adjacent stitching sub-mirrors can be obtained by solving all equation groups. Thus, the phase inversion can be realized, and the axial optical path step difference of all stitching sub-mirrors can be obtained, so as to realize the absolute measurement of the step difference in the sub-wavelength level and large dynamic range, and overcome the problem that the optical path difference is difficult to measure in the traditional phase calibration process.

[0030] As an optional embodiment, after obtaining the axial optical path step difference in step S5, the axial optical path step difference between each stitching sub-mirror is taken as an error signal of the stitching sub-mirror, and the actuators driving each stitching sub-mirror are controlled to perform axial displacement compensation, so that the fringes in the interference pattern obtained on the interference surface 7 are continuous, so as to realize the co-phasing adjustment of the stitching sub-mirrors of the primary mirror 11 of the stitching telescope 1.

[0031] As an optional embodiment, in the co-phasing adjustment process, in order to eliminate the interference fringe distortion caused by system noise, the position and posture of the stitching sub-mirror can be actively adjusted to introduce a large wavefront tilt during the adjustment process of the stitching sub-mirror, so that dense and delicate interference fringes are generated in the interference field. In this case, the interference fringes are extremely sensitive to local phase changes, and since the fringe period is small, the contrast is less affected by the uniform background light and low-frequency stray light, so that a high-contrast and high-signal-to-noise ratio interference pattern can be obtained.

[0032] After obtaining the dense interference fringes, the stitching sub-mirror is gradually adjusted in the reverse direction to reduce and eliminate the overall tilt introduced before. In this process, the interference fringes gradually become sparse and the fringe spacing becomes larger, and finally form low-frequency fringes with a larger width. At this time, the residual error of the low-frequency fringes is mainly caused by the phase jump of the stitching sub-mirror. At this time, the axial actuator driving the stitching sub-mirror is adjusted to gradually reduce and eliminate the fringe dislocation problem until the fringes on all stitching sub-mirrors are continuous and pass through the entire stitching mirror surface.

[0033] In general, the above description is only preferred embodiments of the present specification, and is not intended to limit the protection range of the present specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present specification shall be included in the protection range of the present specification.

[0034] The system, apparatus, module or unit illustrated by one or more embodiments described above can be specifically implemented by a computer chip or entity, or by a product with certain functions. A typical implementation device is a computer. Specifically, the computer may, for example, be a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0035] It should also be noted that the terms "comprising", "including", or any other variation thereof are intended to cover non-exclusive inclusions, such that processes, methods, articles, or devices including a series of elements include not only those elements, but also other elements not explicitly listed, or other elements inherent in such processes, methods, articles, or devices. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or device including the element.

[0036] Each of the embodiments in the present specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments. In particular, for system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and the relevant parts can be referred to the part of the method embodiment.

Claims

1. A method for co-phase adjustment of a spliced ​​telescope, characterized in that, include: S1: Obtain the interference patterns of the splicing sub-mirrors in the splicing telescope at at least two preset wavelengths; S2: Based on the optical interference theory, calculate the interference pattern of the splicing sub-mirrors under each preset wavelength in an ideal co-phase state, and use it as a theoretical interference template; S3: For each preset wavelength, calculate the phase offset of the interference pattern of each splicing sub-mirror relative to the corresponding theoretical interference template; S4: Using the phase offset at each preset wavelength as a known observation, and combining it with the dispersive characteristic parameters of the spliced ​​telescope, construct a set of equations to calculate the axial optical path step difference between each spliced ​​sub-mirror in the spliced ​​telescope. S5: Drive each splicing sub-mirror to perform axial compensation based on the axial optical path step difference between each splicing sub-mirror, so as to achieve the co-phase of the splicing telescope.

2. The method for co-phase adjustment of the spliced ​​telescope according to claim 1, characterized in that, In step S1, a broadband light source is set up to generate a broadband beam. The broadband beam is transmitted to a wavelength division multiplexer through a multimode fiber. The wavelength division multiplexer splits the broadband beam into multiple paths of incident light in different preset wavelength bands. At each time, only one preset wavelength band of incident light is controlled to be directed toward the splicing telescope. A beam splitter is set in the optical path before the incident light is directed toward the splicing telescope to split the incident light into a reference beam and a probe beam. The probe beam is directed toward the splicing sub-mirror of the splicing telescope. The probe beam reflected by the splicing sub-mirror is called the signal beam. The reference beam and the signal beam are interfered with to obtain an interference pattern at the corresponding preset wavelength.

3. The method for co-phase adjustment of a spliced ​​telescope according to claim 1, characterized in that, In step S1, the broadband starlight of the observed celestial body is used as the incident light, and the incident light reflected by the splicing sub-mirror is called the signal light. The signal light is split into a first beam and a second beam using a beam splitter. A filter is set on the propagation path of the first beam so that the first beam retains only a preset wavelength of light. The reserved preset wavelength of light is interfered with the second beam to obtain an interference pattern at the corresponding preset wavelength.

4. The method for co-phase adjustment of the spliced ​​telescope according to claim 3, characterized in that, Interference patterns at each preset wavelength are obtained by switching different filters.

5. The method for co-phase adjustment of the spliced ​​telescope according to claim 1, characterized in that, The process of calculating the phase offset of the interference pattern of each splicing sub-mirror relative to the corresponding theoretical interference template is as follows: calculate the normalized cross-correlation function between the interference pattern and the corresponding theoretical interference template, determine the peak position of the normalized cross-correlation function as the position offset of the center fringe of the interference pattern, and convert the position offset of the center fringe into the phase offset.

6. The method for co-phase adjustment of a spliced ​​telescope according to claim 1, characterized in that, In step S4, based on the physical relationship between optical path difference, phase, and wavelength, and combined with the dispersion characteristic parameters of the spliced ​​telescope, the axial optical path step difference between the sub-mirrors that causes the phase shift is calculated according to the phase shift of the central fringe at each preset wavelength.

7. The method for co-phase adjustment of a spliced ​​telescope according to claim 1, characterized in that, The physical relationship between optical path difference, phase, and wavelength is as follows: ； in, Indicates phase, Indicates the initial phase. Indicates wavelength. This indicates the optical path difference.

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