Phase shift modulation plane diffraction spliced telescope co-phase error active detection method

Abstract

The invention discloses an active detection method for co-phase errors of a phase shift modulation planar diffraction spliced telescope, and belongs to the technical field of optical imaging telescopes. According to the method, a laser emits a beacon light source at the focal point of a spliced telescope and reversely irradiates a primary mirror of the telescope, a beacon light beam passes through the rear surface of the primary mirror, is reflected by a front surface, then passes through the rear surface and returns along an imaging light path, and a phase shift modulator applies a specific delay phase to a reference aperture. Point spread functions under different modulations are collected through a camera so as to solve co-phase errors of the system, and co-phase error correction is carried out through a phase shift modulator. According to the method, the semi-transparent and semi-reflecting mirror is used for dividing an imaging light path into two parts, the laser is arranged at the other focus, the original telescope imaging light path does not need to be damaged, an external light source does not need to be additionally introduced, and the practicability of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging telescopes, and particularly relates to an active detection method for the common phase error of a phase-shift modulation planar diffraction mosaic telescope. Background Art

[0002] According to the Rayleigh criterion, in the visible spectral range, the main factor affecting the ultimate resolution of an astronomical telescope is the aperture of the telescope. The larger the aperture of the telescope, the stronger the energy it collects and the more details it can resolve. Therefore, designing and manufacturing large-aperture astronomical telescopes has been an unremitting goal of mankind. To break through the aperture limitation of existing space telescopes, the technology of large-aperture planar diffraction mosaic telescopes has been proposed. This technology can use many small-sized planar diffraction units to mosaic into an equivalent large-aperture primary mirror to achieve the purpose of obtaining the same ultimate resolution.

[0003] In practical applications, due to reasons such as alignment errors and manufacturing and processing errors, it is difficult to ensure that each sub-mirror of the planar diffraction mosaic mirror is always in an ideal position. Once a sub-mirror tilts or translates, a common phase error will occur in the mosaic telescope system. Generally, the common phase error consists of two parts: tilt error and translation error. On the one hand, the existence of tilt errors between sub-apertures will cause the corresponding focal points of the sub-mirrors to move, and the imaging resolution of the mosaic telescope system cannot be improved, affecting the imaging quality. On the other hand, the existence of translation errors between sub-apertures will cause the optical path difference between sub-mirrors to be non-zero, and the imaging planes of the system cannot be in common phase. Therefore, the detection and correction of the common phase error are the premise for the imaging of large-aperture planar diffraction mosaic telescopes and are of great significance for the telescope system to achieve high-resolution imaging.

[0004] To achieve the common phase of the planar diffraction mosaic telescope, a light source needs to be introduced for the detection of the common phase error. In the alignment test, the common practice is to use a collimator with the same aperture to generate collimated light for calibration and analyze it through a specific method at the image plane of the telescope, so as to obtain the common phase error of each sub-mirror. However, the above method has the following problems: (1) As the aperture of the mosaic telescope increases, it is difficult to manufacture and process a large-aperture collimator; (2) The collimator can only be used for the verification test of the detection and correction of the common phase error of the ground mosaic telescope mirror and cannot achieve the detection and correction of the common phase error of the space mosaic telescope; (3) The telescope cannot achieve real-time common phase detection and calibration during observation. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides an active detection method for the common phase error of a phase-shift modulation plane diffraction mosaic telescope, which can achieve the internal self-common phase error detection of the system without changing the original optical path of the system, and the phase-shift modulator can be used for the correction of the common phase error at the same time. In addition, the beacon light source is placed inside the system, overcoming the high dependence on the external beacon light in the traditional method, enabling this method to complete the real-time common phase error detection in various scenarios, and further improving the practicability and reliability of the system.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] In the first aspect, the present invention proposes an active detection method for the common phase error of a phase-shift modulation plane diffraction mosaic telescope, and the method includes:

[0008] Step 1: Insert a semi-transparent and semi-reflective mirror into the collimation optical path of the mosaic telescope, and place the beacon light source at the focus of the converging optical path behind the beam splitter; the beacon beam emitted by the beacon light source propagates in the opposite direction to the imaging optical path, passes through the beam splitter and the relay secondary mirror in sequence until it reaches the primary mirror of the mosaic telescope, and the beam reflected by the primary mirror carries the common phase error information and returns along the imaging optical path;

[0009] Step 2: The beam carrying the common phase error information enters the phase-shift modulator through the semi-transparent and semi-reflective mirror, and uses the piston displacement of the phase-shift modulator to apply a delay phase to the reference aperture, and performs M modulations. The modulated beam is focused on the detector through the imaging lens to obtain the point spread function, and the corresponding optical transfer function is obtained through Fourier transform;

[0010] Step 3: Multiply the optical transfer function by the corresponding delay phase and linearly superimpose them, calculate the wavefront error of the synthetic aperture telescope system, decouple the common phase error from the wavefront error, and use the phase-shift modulator to correct the common phase error.

[0011] In the second aspect, the present invention provides an electronic device, including: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors are enabled to implement the foregoing active detection method for the common phase error of a phase-shift modulation plane diffraction mosaic telescope.

[0012] In the third aspect, the present invention provides a computer-readable storage medium, on which executable instructions are stored, and when the instructions are executed by a processor, the processor can be enabled to implement the foregoing active detection method for the common phase error of a phase-shift modulation plane diffraction mosaic telescope.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention can complete the detection and correction of the co-phase error of the segmented telescope without the need to additionally introduce a collimator to simulate an infinitely distant target; the actively detected beacon light source will not damage the original structure of the segmented telescope, and the segmented telescope can simultaneously achieve imaging and co-phase error detection and correction, with high practicality. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of an implementation scheme of an active detection method for the co-phase error of a phase-shift modulation planar diffraction segmented telescope.

[0016] Reference Signs:

[0017] 1 is the primary mirror of the telescope, 2 is the relay secondary mirror, 3 is the beacon light source, 4 is the beam splitter, 5 is the detector, and 6 is the phase shifter. Detailed Embodiments

[0018] The present invention will be further described below in conjunction with the drawings and embodiments.

[0019] As Figure 1 shown, it is a schematic diagram of an implementation scheme of an active detection method for the co-phase error of a phase-shift modulation planar diffraction segmented telescope. The method includes:

[0020] Step 1. Assume that the wavelength of the beacon beam emitted by the built-in beacon light source 3 is , the number of sub-apertures of the segmented primary mirror of the synthetic aperture telescope system is N (N shown in Figure 1 is 8), the radius of each sub-aperture is R, and its pupil function can be expressed as:

[0021] (1)

[0022] where x and y represent the spatial coordinates on the segmented primary mirror.

[0023] Insert a beam splitter 4 into the convergent optical path of the segmented telescope, and place the beacon light source 3 at the focal point of the optical path behind the beam splitter 4. The beam splitter 4 can be a semi-transmissive and semi-reflective mirror or a planar beam splitter;

[0024] The beacon beam emitted by the beacon light source 3 propagates along the reverse imaging direction, passes through the beam splitter 4 and the relay secondary mirror 2 in sequence until it reaches the primary mirror 1 of the planar diffraction segmented telescope. The light reflected back from the outer surface of the telescope primary mirror 1 is used as the beacon light to achieve co-phase error detection.

[0025] Without loss of generality, the imaging optical path mentioned in this article refers to the forward optical path from the telescope primary mirror 1 to the camera. In this method, the detection beam passes through the optical system twice in the forward and reverse directions.

[0026] The beacon beam passes through the rear surface of the primary mirror 1 of the telescope, is reflected by the front surface of the primary mirror, passes through the rear surface again, and returns along the original imaging optical path direction, thereby carrying back the possible common phase error information to the detection end. The complex amplitude distribution on the rear surface of the primary mirror after reflection can be expressed as:

[0027] (2)

[0028] Where represents the pupil function of the reference aperture, represents the wavefront error of the nth sub-aperture, i represents the imaginary unit, and represent the central coordinates of the nth sub-aperture.

[0029] Step 2: The detection beam with common phase error information is collimated by the relay secondary mirror 2 and then reaches the phase shift modulator 6. The piston displacement of the phase shift modulator 6 is used to apply a delay phase to the reference aperture. After M modulations, the delay phase for the mth modulation can be expressed as:

[0030] (3)

[0031] The modulated beam is focused on the detector 5 by the imaging lens. The point spread function collected by the detector 5 after the reflected light passes through the optical system is:

[0032] (4)

[0033] Where, represents the point spread function of the system during the mth modulation and can be expressed as:

[0034] (5)

[0035] After Fourier transform, the optical transfer function of the corresponding synthetic aperture telescope system is obtained as:

[0036] (6)

[0037] Step 3: Multiply the optical transfer function of the above synthetic aperture telescope system by the corresponding delay phase factors and linearly superimpose them to obtain expression C:

[0038] (7)

[0039] Where,[[]] represents the convolution operation. The common phase error of the system can be obtained through the following formula:

[0040] (8)

[0041] Among them, Im[ ] and Re[ ] respectively represent the imaginary part and the real part of a complex number. Thus, the wavefront errors of each sub-aperture of the synthetic aperture telescope system relative to the reference aperture are obtained.

[0042] The wavefront error includes forward error and reverse error. According to the non-linear action relationship of the forward and reverse errors on the wavefront, the decoupling of the forward and reverse errors can be realized. The forward error is the common phase error of the system.

[0043] The common phase error of the system is corrected by using the piston and tilt attitude adjustment of the phase shift modulator 6.

[0044] Furthermore, the built-in light source of the system is used as the detection light source. The built-in light source is coupled into the optical system by using a beam splitter. The beam splitter 4 can be a crystal beam splitter, a flat plate beam splitter, or other coupling devices.

[0045] Furthermore, a beacon beam is emitted by a laser at the focus of the primary mirror 1 of the segmented telescope and is irradiated back to the primary mirror 1 of the telescope in the reverse direction. The beacon beam passes through the rear surface of the primary mirror 1 of the telescope, is reflected by the front surface and then passes through the rear surface again, and returns along the imaging optical path. The modulated point spread function is received by the detector 5 and the common phase error is calculated.

[0046] Furthermore, a specific delay phase is generated for the reference aperture by using the phase shift modulator 6, which can be modulated 3 times, 4 times or more times.

[0047] Furthermore, the phase shift modulator 6 can be used to apply the delay phase of the reference aperture and can also be used for the correction of the common phase error of the system.

[0048] Furthermore, the phase shift modulator 6 can be placed before the optical path coupling device or after the optical path coupling. If it is placed before the optical path coupler, the optical path will pass through the phase modulator twice, which avoids the problem of decoupling the forward and reverse errors. However, since it modulates the optical path twice, its delay phase needs to be recalculated.

[0049] Furthermore, the segmented telescope should be a transmissive telescope. The beacon beam needs to enter the medium inside the primary mirror 1 of the telescope and be reflected by the front surface before it can contain the segmented error information. It can be a glass mirror or a thin film mirror in terms of materials.

[0050] Furthermore, the phase shift modulator 6 can adopt a reflective liquid crystal spatial light modulation device, a transmissive liquid crystal phase retarder, or devices such as a three-dimensional fast steering mirror and a six-degree-of-freedom displacement stage.

[0051] Furthermore, the detector 5 can be a CCD camera, a CMOS camera or other area array detectors that meet the conditions.

[0052] Embodiment

[0053] The object measured in this implementation scheme is a large-aperture diffractive segmented telescope composed of eight diffractive optical elements (DOEs). A fiber laser with a wavelength of 635 nm is used as the built-in beacon light to detect the phase error of the segmented telescope. The specific implementation steps are as follows:

[0054] Insert a beam splitter in the converging optical path of the eight-plane diffractive segmented telescope, and place the beacon light source at the focus of the optical path behind the beam splitter;

[0055] The beacon beam emitted by the laser propagates in the opposite direction to the imaging optical path, passes through the beam splitter, the secondary mirror in turn until it reaches the eight segmented diffractive primary mirrors;

[0056] The beacon beam passes through the rear surface of the eight segmented diffractive primary mirrors, is reflected by the front surface and then passes through the rear surface again, and returns along the imaging optical path;

[0057] The beam containing the phase error information of the segmented primary mirror enters the phase shift modulator through the beam splitter. Select aperture No. 1 as the reference aperture, and use the piston attitude adjustment of the phase shift modulator to apply a delay phase to aperture No. 1, and perform 4 modulations. The applied delay phases are (0, π / 2, π, 3π / 2);

[0058] The point spread functions collected by the CCD camera under the four modulations are respectively: (PSF1, PSF2, PSF3, PSF4). Through Fourier transform, the corresponding optical transfer functions of the synthetic aperture telescope system are respectively (OTF1, OTF2, OTF3, OTF4);

[0059] Multiply the optical transfer functions of the above synthetic aperture telescope system by the corresponding delay phases and linearly superimpose them to obtain expression C, and then calculate the wavefront error of the synthetic aperture telescope system from formula (8).

[0060] According to the non-linear relationship between the forward and reverse errors, use the least squares method to decouple the forward error from the mixed forward and reverse wavefront errors, that is, the phase error of the system.

[0061] Use the piston and tilt attitude adjustments of the phase shift modulator to correct the solved phase error.

[0062] In a second aspect, the present invention provides an electronic device, including: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the foregoing active detection method for the phase error of a phase shift modulation plane diffractive segmented telescope.

[0063] In a third aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, and when the instructions are executed by a processor, the processor can implement the foregoing active detection method for the common phase error of a phase-shift modulation planar diffraction stitching telescope.

[0064] In the specific embodiments described above, the objectives, technical solutions, and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An active detection method for the common phase error of a phase-shift modulation planar diffraction mosaic telescope, characterized in that, The method includes: Step 1: Insert a semi-transparent and semi-reflective mirror into the collimation optical path of the segmented telescope, and place the beacon light source at the focal point of the converging optical path behind the beam splitter; the beacon beam emitted by the beacon light source propagates in the direction opposite to the imaging optical path, passes through the beam splitter and the relay secondary mirror in sequence until it reaches the primary mirror of the segmented telescope, and the beam reflected by the primary mirror carries the co-phasing error information and returns along the imaging optical path; Step 2: The beam carrying the co-phasing error information enters the phase-shift modulator through the semi-transparent and semi-reflective mirror, and uses the piston displacement of the phase-shift modulator to apply a delay phase to the reference aperture and perform M modulations. The modulated beam is focused on the detector through the imaging lens to obtain the point spread function, and the corresponding optical transfer function is obtained through Fourier transform; Step 3: Multiply the optical transfer function by the corresponding delay phase and linearly superimpose them to calculate the wavefront error of the synthetic aperture telescope system, decouple the co-phasing error from the wavefront error, and use the phase-shift modulator to correct the co-phasing error.

2. The active detection method for the common phase error of a phase-shift modulation planar diffraction mosaic telescope according to claim 1, wherein The said Step 1 includes: The beacon beam passes through the rear surface of the primary mirror of the telescope, is reflected by the front surface of the primary mirror and then passes through the rear surface again, and returns along the original imaging optical path direction.

3. A method for actively detecting the common phase error of a phase-shift modulation planar diffraction mosaic telescope according to claim 1, characterized in that In the said Step 2, the delay phase of the m-th modulation is expressed as: （3） The point spread function collected by the detector after the reflected light passes through the optical system is: （4） Among them, represents the point spread function of the system during the m-th modulation, and is expressed as: （5） where B r is the pupil function of the reference aperture, and B T is the pupil function of the remaining apertures. n represents the aperture number of the primary mirror of the segmented telescope, and N represents the total number of apertures of the primary mirror of the segmented telescope. represents the wavefront error on the nth sub-aperture, represents the spatial coordinates on the segmented primary mirror, represents the central coordinates of the nth sub-aperture, and i represents the imaginary unit; After Fourier transform, the corresponding optical transfer function of the synthetic aperture telescope system is: （6）。 4. The active detection method for the common phase error of a phase-shift modulation planar diffraction stitching telescope according to claim 1, characterized in that The said Step 3 includes using the least squares method to decouple the forward error, that is, the co-phasing error, from the forward and reverse mixed wavefront error, and using the piston and tilt attitude of the phase-shift modulator to correct the co-phasing error.

5. The active detection method for the common phase error of a phase-shift modulation planar diffraction mosaic telescope according to claim 3, characterized in that In the said Step 3, multiply the optical transfer function of the synthetic aperture telescope system by the corresponding delay phase factor and linearly superimpose them to obtain the expression C: （7） Among them, represents a convolution operation.

6. The active detection method for the common phase error of a phase-shift modulation planar diffraction mosaic telescope according to claim 5, characterized in that, The co-phasing error of the system is obtained through the following formula: （8） wherein, Im[ ] and Re[ ] respectively represent taking the imaginary part and real part of a complex number.

7. A method for actively detecting the common phase error of a phase-shift modulation planar diffraction mosaic telescope according to claim 1, characterized in that The said segmented telescope is a transmissive telescope.

8. A method for actively detecting the common phase error of a phase shift modulation planar diffraction mosaic telescope according to claim 1, characterized in that, The phase-shift modulator adopts a reflective liquid crystal spatial light modulation device, a transmissive liquid crystal phase retarder, or a three-dimensional fast steering mirror, a six-degree-of-freedom displacement stage.

9. An electronic device, characterized in that, It includes: One or more processors; A memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement an active detection method for the co-phasing error of a phase-shift modulation plane diffraction segmented telescope according to any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, Stored thereon are executable instructions, which when executed by a processor can enable the processor to implement an active detection method for the co-phasing error of a phase-shift modulation plane diffraction segmented telescope according to any one of claims 1-8.

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