A wavelength calibration method for dispersion common phase detection of spliced ​​telescope system

Abstract

The present invention relates to a method for calibrating the wavelength of dispersion co-phase detection of a segmented telescope system, including: Step S1, constructing a segmented telescope system; Step S2, keeping the central sub-mirror stationary, and the initial absolute optical path difference between the central sub-mirror and the i-th non-central sub-mirror is h i ; Step S3, applying a corresponding driving voltage to the driver of the i-th non-central sub-mirror to drive the i-th non-central sub-mirror to translate, so that the absolute optical path difference between the i-th non-central sub-mirror and the central sub-mirror becomes h i +n*S i , collecting the n-th frame of dispersion interference fringe image #imgabs0# between the i-th non-central sub-mirror and the central sub-mirror; Step S4, obtaining all frames of dispersion interference fringe images between the i-th non-central sub-mirror and the central sub-mirror; Step S5, calibrating the wavelength of the dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror; Step S6, completing the wavelength calibration of the dispersion interference fringes between all non-central sub-mirrors and the central sub-mirror.

Description

Technical Field

[0001] The invention relates to the field of spliced ​​telescopes, and more specifically to a method for calibrating wavelengths of dispersion common-phase detection of a spliced ​​telescope system. Background Art

[0002] As human beings' understanding and exploration of the universe become more urgent, they need optical telescopes with higher resolution. As we all know, the resolution of a telescope is proportional to its aperture. If you need to observe the details of the surface of a star, the angular resolution of the telescope is required to be better than 0.01 arc seconds; if you observe in the near-infrared band, the telescope aperture is required to be more than 20 meters. Limited by current manufacturing technology, material costs and other factors, the maximum aperture of a single-mirror telescope that can be built so far is 8.4 meters. In addition, an overly large aperture increases the difficulty of the telescope's primary mirror support design and the transportation, installation and commissioning of the primary mirror. Under existing technical conditions, it is technically and economically very difficult to manufacture a telescope with a single aperture of tens of meters.

[0003] Spliced ​​telescope technology is an effective way to achieve high resolution of telescopes. Spliced ​​telescopes use multiple sub-mirrors and achieve equivalent aperture resolution through beam synthesis. The mirror size of a single sub-mirror is small, light, low-cost, and flexible in arrangement. A typical representative of spliced ​​telescopes is GMT, which consists of 7 sub-mirrors with an aperture of 8.4 meters. After co-phasing, it can obtain the resolution of a telescope with an equivalent aperture of 25.4 meters. This telescope does not require long-stroke delay line detection and optical path difference compensation, has a compact structure, and can directly image instantly. Each sub-beam from the spliced ​​sub-mirror must be coherently superimposed in phase on the focal plane of the system, and its phase difference needs to be controlled within one-tenth of the wavelength. This is a prerequisite for the spliced ​​telescope to achieve interferometric imaging and obtain resolution close to the diffraction limit. Translation error detection and control technology in spliced ​​telescopes has become one of the hot topics in related research fields, and co-phasing detection based on dispersion interference fringes is one of the best methods that takes into account both measurement accuracy and measurement range.

[0004] Fang Shi et al. from the Jet Propulsion Laboratory of California Institute of Technology first proposed a common phase detection method based on dispersed interference fringes for common phase detection between sub-mirrors of the Keck spliced ​​telescope (see: Experimental verification of dispersed fringe sensing as a segment phasing technique using the Keck telescope, Applied Optics Vol. 43, Issue 23, pp. 4474-4481 (2004)). Simulation calculations and experimental results show that this method has a large measurement range and a measurement accuracy better than 0.1 μm. However, this method requires accurate calibration of the wavelength in the dispersion direction in advance, and the specific calibration method is not given in the article.

[0005] In the Chinese patent application with application number 200810000577.7, a two-dimensional dispersion fringe analysis method for absolute distance measurement is proposed, which can be used to splice telescope systems to achieve common phase detection. This method has a large measurement range and high measurement accuracy. However, in actual use, this method also requires accurate wavelength calibration of the interference fringes in the dispersion direction, and the patent does not provide a specific calibration method.

[0006] In the Chinese patent application with application number 201610288401.0, a common phase control device and control method for a spliced ​​telescope are proposed, which can effectively realize the real-time detection and compensation correction of translation, tilt and high-order aberrations, with a large measurement range and high measurement accuracy. However, in actual use, this method also requires accurate wavelength calibration of the interference fringes on the dispersion side, and the patent does not provide a specific calibration method.

[0007] In the Chinese patent application with application number 201910248039.8, a high-precision wavelength calibration method based on an interference imaging spectrometer is proposed. This method requires the use of several monochromatic lights of different wavelengths as light sources to collect enough data for wavelength calibration. It is costly and complex to implement, and it is difficult to directly use it for the wavelength calibration of the spliced ​​telescope system to achieve common phase detection.

[0008] Therefore, it is necessary to develop a wavelength calibration method for dispersion common phase detection of a spliced ​​telescope system. Summary of the invention

[0009] In order to solve the above problems in the prior art, the present invention provides a dispersion common phase detection wavelength calibration method for a spliced ​​telescope system to overcome the shortcomings of the existing dispersion common phase detection wavelength calibration technology and reduce the implementation complexity and cost.

[0010] The present invention provides a method for calibrating wavelength of dispersion common phase detection of a spliced ​​telescope system, comprising:

[0011] Step S1, constructing a spliced ​​telescope system, including a spliced ​​telescope, a translation error detector and a wavefront controller, wherein the spliced ​​telescope includes a spliced ​​sub-mirror group, and the spliced ​​sub-mirror group includes a central sub-mirror and a plurality of non-central sub-mirrors arranged in a circle around the central sub-mirror;

[0012] Step S2, keep the central sub-mirror still, set i=1, and the initial absolute optical path difference between the central sub-mirror and the i-th non-central sub-mirror is h i ;

[0013] Step S3, let n = 1, apply a corresponding driving voltage to the driver of the ith non-central sub-mirror through the wavefront controller, drive the ith non-central sub-mirror to translate, so that the absolute optical path difference between the ith non-central sub-mirror and the central sub-mirror becomes h i +n*S i At the same time, the translation error detector is used to collect the nth frame of dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror

[0014] Step S4, determine whether n is equal to M, M = the stroke of the driver of the non-center sub-mirror / the resolution of the driver of the non-center sub-mirror, if yes, proceed to step S5; if not, set n = n + 1, and repeat step S3;

[0015] Step S5, collecting the dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror Perform wavelength calibration;

[0016] Step S6, let i=i+1, and repeat steps S3-S5 until the dispersion interference fringes of all non-central sub-mirrors and the central sub-mirror complete the wavelength calibration.

[0017] Furthermore, S i Greater than or equal to twice the driver resolution of the non-central sub-mirror.

[0018] Furthermore, the step S5 comprises:

[0019] Step S51, for the nth frame of dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror A coordinate system is established with the dispersion direction as the x-axis and the baseline direction of the spliced ​​sub-mirror formed by the i-th non-central sub-mirror and the central sub-mirror as the y-axis, and the y-axis direction includes N one-dimensional sub-stripes;

[0020] Step S52, let j = 1, let n = 1, calculate the n-th frame dispersion interference fringe image The peak ratio of the positive and negative information of the translation error contained in the jth one-dimensional sub-fringe

[0021] Step S53, determine whether n is equal to M, if so, proceed to step S54; if not, set n=n+1, repeat step S52, and obtain multiple frames of data at the position of the j-th one-dimensional sub-strip;

[0022] Step S54: construct a one-dimensional signal sequence for the multi-frame data at the position of the j-th one-dimensional sub-strip. Get the wavelength corresponding to the j-th one-dimensional sub-fringe;

[0023] Step S55, determine whether j is equal to N, if so, proceed to step S56; if not, set j = j + 1, and repeat steps S52 to S54 until the wavelength data λ corresponding to all one-dimensional sub-fringe are obtained. j (j=1, ..., N);

[0024] Step S56: the wavelength data λ corresponding to all one-dimensional sub-fringe j (j=1, ..., N) to perform linear fitting to obtain the final wavelength calibration result.

[0025] Furthermore, the peak value ratio of the positive and negative information of the translation error contained in the j-th one-dimensional sub-fringe in step S52 is The limit is calculated according to the following formula:

[0026]

[0027] Among them, I 2 (j) represents the second peak intensity of the jth one-dimensional sub-fringe, y 2 (j) represents the second peak position, I 3 (j) represents the third peak intensity, y 3 (j) represents the third peak position, and sign[] is the sign function.

[0028] After the spliced ​​telescope realizes the coarse common phase, the present invention sequentially drives each non-central sub-mirror to produce translation, collects the two-dimensional dispersion interference fringes between each non-central sub-mirror and the central sub-mirror, and calculates and analyzes the multi-frame dispersion interference fringes, thereby realizing the wavelength calibration of the dispersion interference fringes. The present invention does not need to make any improvement to the original telescope system, reduces the cost and reduces the complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of a spliced ​​telescope system to which the dispersion common phase detection wavelength calibration method of the spliced ​​telescope system of the present invention is applicable.

[0030] Figure 2The present invention is a flow chart of a method for calibrating wavelength of dispersion common phase detection of a spliced ​​telescope system according to an embodiment of the present invention.

[0031] Figure 3 It is a schematic diagram of the light intensity distribution of dispersive interference fringes and the light intensity distribution of one-dimensional sub-fringe.

[0032] Figure 4 This is a schematic diagram of the signal sequence constructed at the location of the first one-dimensional sub-stripe.

[0033] Figure 5 is in accordance with Figure 2 Schematic diagram of the error in calibrating the wavelength of dispersion interference fringes using the method shown. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0035] The present invention provides a method for calibrating wavelength of dispersion common phase detection of a spliced ​​telescope system, which is used for Figure 1 Wavelength calibration of dispersive co-phase detection of a tiled telescope system is shown.

[0036] like Figure 1 As shown, the spliced ​​telescope system includes: a spliced ​​telescope 10, a first beam splitter 4, a second beam splitter 5, an imaging system 6, a wavefront detector 7, a translation error detector 8 and a wavefront controller 9.

[0037] The spliced ​​telescope 10 is used to receive incident light (such as starlight or ordinary broadband light) from the object to be measured in the periphery, and generate parallel (or substantially parallel) outgoing light. In this embodiment, the spliced ​​telescope 10 is a Cassegrain type reflecting telescope, which includes a separate deformable secondary mirror 1 with a driver, a spliced ​​sub-mirror group 2 and an eyepiece 3. Among them, the spliced ​​sub-mirror group 2 is used to receive and reflect the incident light, including a central sub-mirror and a plurality of surrounding sub-mirrors arranged in a circle around the central sub-mirror, and each surrounding sub-mirror and the central sub-mirror form a pair of spliced ​​sub-mirrors. The separate deformable secondary mirror 1 is used to receive the incident light reflected by the spliced ​​sub-mirror, and reflect the incident light again to converge in front of the spliced ​​sub-mirror. In this embodiment, the separate deformable secondary mirror 1 may include a plurality of independent deformable mirrors (each deformable mirror has multiple drivers to correct high-order aberrations), and the arrangement of these deformable mirrors is consistent with the arrangement of the spliced ​​sub-mirror group 2. Each sub-mirror of the spliced ​​sub-mirror group 2 also has a driver for coarse confocality and coarse co-phase. In addition, the driver of the separated deformable secondary mirror 1 has nanometer-level precision and millimeter-level travel, and can correct translation, tilt, and high-order aberrations. The eyepiece 3 is used to receive the incident light reflected again by the separated deformable secondary mirror 1 and generate an outgoing light.

[0038] The first beam splitter 4 is used to receive the outgoing light from the spliced ​​telescope 10 , and transmit the first split light beam to the wavefront detector 7 , and transmit the second split light beam to the second beam splitter 5 .

[0039] The second beam splitter 5 is used to receive the second sub-beam, and transmit the third sub-beam to the translation error detector 8, and transmit the fourth sub-beam to the imaging system 6 for observation.

[0040] The wavefront detector 7 is used to detect the first sub-beam and obtain the system aberration data on the transmission path of each spliced ​​sub-mirror and the wavefront distortion aberration data (including translation, tilt and high-order aberration) caused by atmospheric turbulence.

[0041] The translation error detector 8 is used to detect the third sub-beam and collect the dispersion interference fringes between the spliced ​​sub-mirrors.

[0042] In this embodiment, the centers of the spliced ​​telescope 10, the first beam splitter 4, the second beam splitter 5, and the imaging system 6 are located on the same optical axis, the second beam splitter and the fourth beam splitter are beam splitters passing through the first beam splitter 4 and the second beam splitter 5, respectively, and the first beam splitter and the third beam splitter are beam splitters reflected by the first beam splitter 4 and the second beam splitter 5, respectively.

[0043] The wavefront controller 9 is respectively connected to the wavefront detector 7, the translation error detector 8 and the driver of the separated deformable secondary mirror 1. On the one hand, it receives and outputs a first driving voltage to the driver of the separated deformable secondary mirror 1 according to the system aberration data on the transmission path of each spliced ​​sub-mirror and the wavefront distortion aberration data caused by atmospheric turbulence, so as to drive the separated deformable secondary mirror 1 to produce corresponding deformation to compensate and correct the system aberration on the transmission path of each spliced ​​sub-mirror and the wavefront distortion aberration caused by atmospheric turbulence; on the other hand, it receives and calculates the phase translation error between each spliced ​​sub-mirror according to the dispersion interference fringes between each spliced ​​sub-mirror, and outputs a second driving voltage to the driver of the separated deformable secondary mirror 1 according to the phase translation error between each spliced ​​sub-mirror, so as to drive the separated deformable secondary mirror 1 to produce translation to compensate and correct the phase translation error between each spliced ​​sub-mirror. In this common phase detection process, the wavelength of the dispersion interference fringes needs to be calibrated in advance.

[0044] Based on this, Figure 2 As shown, the method for calibrating wavelength of dispersion common phase detection of a spliced ​​telescope system provided by the present invention comprises the following steps:

[0045] Step S1, constructing the above-mentioned spliced ​​telescope system.

[0046] Step S2, keep the central sub-mirror (also called central sub-aperture, the central sub-mirror is a reflector with a light-clearing hole) stationary, let i = 1, the initial absolute optical path difference between the central sub-mirror and the i-th non-central sub-mirror (the non-central sub-mirror is the above-mentioned surrounding sub-mirror) is h i .

[0047] Step S3, let n = 1, apply a corresponding driving voltage to the driver of the ith non-central sub-mirror through the wavefront controller 9, drive the ith non-central sub-mirror to translate, so that the absolute optical path difference between the ith non-central sub-mirror and the central sub-mirror becomes h i +n*S i At the same time, the translation error detector 8 is used to collect the n-th frame of dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror n is the frame number of the dispersion interference fringe image.

[0048] The relationship between the driving voltage applied by the driver of the sub-mirror and the translation of the sub-mirror is accurately calibrated when the driver leaves the factory. The minimum driving voltage of the driver causes the sub-mirror to produce the minimum translation, which is the resolution of the driver. The changed optical path difference is twice the translation. Therefore, S i Greater than or equal to twice the driver resolution of the non-central sub-mirror, in nm. i The smaller it is, the higher the sampling rate is, and the more accurate the wavelength calibration result is. i =2.5nm.

[0049] Step S4, determine whether n is equal to M, M = the stroke of the driver of the non-center sub-mirror / the resolution of the driver of the non-center sub-mirror. If so, proceed to step S5; if not, set n = n + 1 and repeat step S3. That is, for the i-th non-center sub-mirror, step S3 is executed M times in total, and the final absolute optical path difference of the i-th non-center sub-mirror is h i +M*S i In this embodiment, M=10000.

[0050] Step S5, collecting the dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror Perform wavelength calibration.

[0051] Step S6, let i=i+1, and repeat steps S3-S5 until the dispersion interference fringes of all non-central sub-mirrors and the central sub-mirror complete the wavelength calibration.

[0052] Wherein, step S5 comprises:

[0053] Step S51, for the nth frame of dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror A coordinate system is established with the dispersion direction as the x-axis and the baseline direction of the spliced ​​sub-mirror formed by the i-th non-central sub-mirror and the central sub-mirror as the y-axis; Figure 3 As shown, the two-dimensional dispersion interference fringe image It includes N one-dimensional sub-stripes along the y-axis direction (N depends on the width of the dispersion interference stripes on the translation error detector 8, which is expressed in the number of pixels, that is, N pixels). In this embodiment, N=1000.

[0054] Step S52, let j = 1, let n = 1, calculate the n-th frame dispersion interference fringe image The peak ratio of the positive and negative information of the translation error contained in the jth one-dimensional sub-fringe

[0055] The peak ratio of the positive and negative information of the translation error contained in the jth one-dimensional sub-fringe Calculated according to the following formula:

[0056]

[0057] Among them, I 2 (j) represents the second peak intensity of the jth one-dimensional sub-fringe, y 2 (j) represents the second peak position, I 3 (j) represents the third peak intensity, y 3 (j) represents the third peak position, and sign[] is the sign function. Since the sub-stripe data is a one-dimensional vector data, I 2 (j), y 2 (j) I 3 (j), y 3 (j) correspond respectively to the second maximum value, the vector index of the second maximum value, the third maximum value and the vector index of the third maximum value of the vector.

[0058] Step S53, determine whether n is equal to M, if so, proceed to step S54; if not, set n=n+1, repeat step S52, and obtain multiple frames of data at the position of the jth one-dimensional sub-strip.

[0059] Step S54: construct a one-dimensional signal sequence for the multi-frame data at the position of the j-th one-dimensional sub-strip. Its sampling rate is 1 / S i , using the Fourier transform method, we can calculate its period as T j , then the wavelength λ corresponding to the jth one-dimensional sub-fringe j =T j .

[0060] The signal sequence x constructed at the wavelength position of the first one-dimensional sub-fringe 1 (m) Figure 4As shown, the horizontal axis is the sampling number, with a total of M = 10000 samples, and the vertical axis is the peak ratio calculated by formula (1).

[0061] Step S55, determine whether j is equal to N, if so, proceed to step S56; if not, set j = j + 1, and repeat steps S52 to S54 until the wavelength data λ corresponding to all one-dimensional sub-fringe are obtained. j (j=1,…,N).

[0062] Step S56: the wavelength data λ corresponding to all one-dimensional sub-fringe j (j=1, ..., N) for linear fitting, that is The coefficients a and b are calculated using the least squares method based on N discrete data. The final wavelength calibration result is given by Calculation given.

[0063] In this embodiment, a wavelength of 550nm-650nm is used as the bandwidth light. The absolute error between the final wavelength calibration result and its true value is as follows: Figure 5 As shown in the figure, the absolute error of wavelength calibration of each dispersion fringe is less than 0.1nm, which meets the requirements of practical applications.

[0064] The present invention effectively solves the wavelength calibration problem of the spliced ​​telescope system dispersion common phase detection, and does not require hardware changes to the original system, making it simple and convenient to implement. In addition, the present invention can achieve wavelength calibration using broadband light, without switching light sources of different wavelengths, and has high measurement accuracy.

[0065] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A wavelength calibration method for dispersion and common phase detection of spliced ​​telescope system, It is characterized in that include: Step S1, constructing a spliced ​​telescope system, including a spliced ​​telescope, a translation error detector and a wavefront controller, wherein the spliced ​​telescope includes a spliced ​​sub-mirror group, and the spliced ​​sub-mirror group includes a central sub-mirror and a plurality of non-central sub-mirrors arranged in a circle around the central sub-mirror; Step S2, keep the central sub-mirror still, set i=1, and the initial absolute optical path difference between the central sub-mirror and the i-th non-central sub-mirror is h i ; Step S3, let n = 1, apply a corresponding driving voltage to the driver of the ith non-central sub-mirror through the wavefront controller, drive the ith non-central sub-mirror to translate, so that the absolute optical path difference between the ith non-central sub-mirror and the central sub-mirror becomes h i +n*S i At the same time, the translation error detector is used to collect the nth frame of dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror Step S4, determine whether n is equal to M, M = the stroke of the driver of the non-center sub-mirror / the resolution of the driver of the non-center sub-mirror, if yes, proceed to step S5; if not, set n = n + 1, and repeat step S3; Step S5, collecting the dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror Perform wavelength calibration; include: Step S51, for the nth frame of dispersion interference fringe image between the i-th non-central sub-mirror and the central sub-mirror A coordinate system is established with the dispersion direction as the x-axis and the baseline direction of the spliced ​​sub-mirror formed by the i-th non-central sub-mirror and the central sub-mirror as the y-axis, and the y-axis direction includes N one-dimensional sub-stripes; Step S52, let j = 1, let n = 1, calculate the n-th frame dispersion interference fringe image The peak ratio of the positive and negative information of the translation error contained in the jth one-dimensional sub-fringe Step S53, determine whether n is equal to M, if so, proceed to step S54; if not, set n=n+1, repeat step S52, and obtain multiple frames of data at the position of the j-th one-dimensional sub-strip; Step S54: construct a one-dimensional signal sequence for the multi-frame data at the position of the j-th one-dimensional sub-strip. Get the wavelength corresponding to the j-th one-dimensional sub-fringe; Step S55, determine whether j is equal to N, if so, proceed to step S56; if not, set j = j + 1, and repeat steps S52 to S54 until the wavelength data λ corresponding to all one-dimensional sub-fringe are obtained. j (j=1,…,N); Step S56: the wavelength data λ corresponding to all one-dimensional sub-fringe j (j=1,…,N) to perform linear fitting and obtain the final wavelength calibration result; Step S6, let i=i+1, and repeat steps S3-S5 until the dispersion interference fringes of all non-central sub-mirrors and the central sub-mirror complete the wavelength calibration.

2. The method for calibrating wavelength of dispersion common phase detection of a spliced ​​telescope system according to claim 1, It is characterized in that S i Greater than or equal to twice the driver resolution of the non-central sub-mirror.

3. The method for calibrating wavelength of dispersion common phase detection of a spliced ​​telescope system according to claim 1, It is characterized in that In step S52, the peak value ratio of the positive and negative information of the translation error contained in the j-th one-dimensional sub-fringe Calculated according to the following formula: Among them, I 2 (j) represents the second peak intensity of the jth one-dimensional sub-fringe, y 2 (j) represents the second peak position, I 3 (j) represents the third peak intensity, y 3 (j) represents the third peak position, and sign[] is the sign function.

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