An active detection method for common phase error in phase-shift modulated plane diffraction spliced ​​telescopes

Abstract

The application discloses a phase shift modulation plane diffraction spliced telescope common phase error active detection method and belongs to the technical field of optical imaging telescopes. The method utilizes a laser to emit a beacon light source at a focal point of a spliced telescope and reversely irradiate a main mirror of the telescope. The beacon light beam passes through a rear surface of the main mirror, is reflected by a front surface, passes through the rear surface again, and returns along an imaging light path. A specific delay phase is applied to a reference aperture by a phase shift modulator. A point spread function under different modulations is collected by a camera, so that common phase errors of the system are solved, and the common phase errors are corrected by the phase shift modulator. The method divides the imaging light path into two parts by using a half-transmission half-reflection mirror. The laser is arranged at the other focal point, so that the original imaging light path of the telescope is not 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 in particular relates to a method for actively detecting common phase errors in a phase-shift modulated plane diffraction splicing telescope. Background Art

[0002] According to the Rayleigh criterion, the primary factor affecting the ultimate resolution of an astronomical telescope in the visible spectrum is its aperture. The larger the telescope's aperture, the more energy it collects and the greater the detail it can resolve. Therefore, the design and construction of large-aperture astronomical telescopes remains a persistent goal. To overcome the limitations of existing space telescope apertures, researchers have proposed large-aperture planar diffraction splicing telescopes. This technology utilizes numerous small-scale planar diffraction units to create an equivalent large-aperture primary mirror, achieving the same ultimate resolution.

[0003] In practical applications, due to errors in assembly and manufacturing, it is difficult to ensure that the sub-mirrors of a plane diffraction spliced ​​telescope are always in the ideal position. Once a sub-mirror tilts or shifts, the spliced ​​telescope system will produce a common phase error. Typically, the common phase error consists of two parts: tilt error and translation error. On the one hand, the existence of tilt error between sub-apertures will cause the focus of the corresponding sub-mirror to move, and the imaging resolution of the spliced ​​telescope system will not be improved, affecting the image quality. On the other hand, the existence of translation error between sub-apertures will cause the optical path difference between the sub-mirrors to be non-zero, and the system imaging plane will not be in phase. Therefore, the detection and correction of common phase error is a prerequisite for imaging in large-aperture plane diffraction spliced ​​telescopes and is of great significance for achieving high-resolution imaging in telescope systems.

[0004] In order to achieve the common phase of a plane diffraction spliced ​​telescope, a light source needs to be introduced to detect the common phase error. In the assembly test, people usually use collimated light generated by a collimated tube of the same diameter for calibration, and analyze it at the image plane of the telescope through a specific method to obtain the common phase error of each sub-mirror. However, the above method has the following problems: (1) As the aperture of the spliced ​​telescope increases, large-aperture collimators are difficult to manufacture and process; (2) Collimators can only be used for common phase error detection and correction tests of ground-based spliced ​​telescopes, and cannot be used to detect and correct the common phase error of space-based spliced ​​telescopes; (3) The telescope cannot achieve real-time common phase detection and calibration during observation. Summary of the Invention

[0005] To address the aforementioned technical issues, the present invention provides a method for actively detecting common-phase errors in a phase-shift-modulated planar diffraction spliced ​​telescope. This method achieves internal common-phase error detection without changing the system's existing optical path, and the phase-shift modulator can also be used to correct the common-phase error. Furthermore, by placing the beacon light source within the system, this overcomes the traditional method's heavy reliance on external beacon light. This enables real-time common-phase error detection in a variety of scenarios, further improving the system's practicality and reliability.

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

[0007] In a first aspect, the present invention proposes a method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope, the method comprising:

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

[0009] Step 2: The light beam carrying the common phase error information enters the phase shift modulator through a semi-transparent and semi-reflective mirror. The piston displacement of the phase shift modulator applies a delayed phase to the reference aperture, performing M modulations. The modulated light beam is converged to the detector through an imaging lens to obtain a point spread function. The corresponding optical transfer function is obtained through Fourier transform.

[0010] Step 3: Multiply the optical transfer functions by the corresponding delay phases and linearly superpose them to calculate the wavefront error of the synthetic aperture telescope system, decouple the common phase error from the wavefront error, and correct the common phase error using a phase shift modulator.

[0011] In a second aspect, the present invention provides an electronic device comprising: one or more processors; and 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 aforementioned method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope.

[0012] In a third aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope.

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

[0014] The present invention can complete the common-phase error detection and correction of the spliced ​​telescope without the need to additionally introduce a parallel light tube to simulate an infinite point target; the active detection beacon light source will not destroy the original structure of the spliced ​​telescope, and the spliced ​​telescope can simultaneously realize imaging and common-phase error detection and correction, and has high practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing an implementation plan for an active detection method of common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope.

[0016] Reference numerals:

[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 shift modulator. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the accompanying drawings and examples.

[0019] like Figure 1 FIG. 1 is a diagram showing an implementation scheme of a method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope, the method comprising:

[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 spliced ​​primary mirror of the synthetic aperture telescope system is N ( Figure 1 The N shown in the figure is 8), the radius of each sub-aperture is R, and its pupil function can be expressed as:

[0021] (1)

[0022] Among them, x and y represent the spatial coordinates on the spliced ​​primary mirror.

[0023] Insert a beam splitter 4 into the converging optical path of the spliced ​​telescope, and place the beacon light source 3 at the focus of the optical path behind the beam splitter 4. The beam splitter 4 can use a semi-transparent and semi-reflective mirror or a flat beam splitter;

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

[0025] Without loss of generality, the imaging light path mentioned in this article refers to the forward light 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 telescope primary mirror 1, is reflected by the front surface of the primary mirror, passes through the rear surface again, and returns along the original imaging optical path, thereby carrying possible common phase error information back to the detection end. The complex amplitude distribution of the rear surface of the primary mirror after reflection can be expressed as:

[0027] (2)

[0028] in represents the pupil function of the reference aperture, represents the wavefront error of sub-aperture No. n, i represents the imaginary unit, and Represents the center coordinate of sub-aperture number n.

[0029] Step 2: The probe 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 delayed phase to the reference aperture. M modulations are performed. The delayed phase for the mth modulation can be expressed as:

[0030] (3)

[0031] The modulated light beam is converged onto the detector 5 through 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] in, The point spread function of the system at the mth modulation can be expressed as:

[0034] (5)

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

[0036] (6)

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

[0038] (7)

[0039] in, Represents the convolution operation. The common phase error of the system can be obtained by the following formula:

[0040] (8)

[0041] Here, Im[ ] and Re[ ] represent the imaginary and real parts of the complex number, respectively. Thus, the wavefront errors of each subaperture 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 nonlinear relationship between the forward and reverse errors on the wavefront, the forward and reverse errors can be decoupled. The forward error is also the common phase error of the system.

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

[0044] Furthermore, the system has a built-in light source as a detection light source, and a beam splitter is used to couple the built-in light source into the optical system. The beam splitter 4 can be a crystal beam splitter, a flat beam splitter, or other coupling devices.

[0045] Furthermore, a laser is used to emit a beacon beam at the focus of the spliced ​​telescope primary mirror 1 to illuminate the telescope primary mirror 1 in reverse. The beacon beam passes through the rear surface of the telescope primary mirror 1, is reflected by the front surface, 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 solved.

[0046] Furthermore, the phase shift modulator 6 is used to generate a specific delayed phase for the reference aperture, which may be modulated three times, or four times or more.

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

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

[0049] Furthermore, the spliced ​​telescope should be a transmission telescope. The beacon beam needs to enter the medium of the telescope's primary mirror 1 and be reflected by the front surface before it can contain splicing error information. According to the material, it can be a glass mirror or a thin film mirror.

[0050] Furthermore, the phase shift modulator 6 may be a reflective liquid crystal spatial light modulator, a transmissive liquid crystal phase retarder, or a three-dimensional fast mirror, a six-degree-of-freedom displacement stage or other devices.

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

[0052] Example

[0053] This implementation targets a large-aperture diffractive spliced ​​telescope consisting of eight diffractive optical elements (DOEs). A fiber laser with a wavelength of 635 nm is used as a built-in beacon light to detect the common phase error of the spliced ​​telescope. The specific implementation steps are as follows:

[0054] Insert a semi-transparent and semi-reflective mirror into the converging light path of the eight-piece plane diffraction spliced ​​telescope, and place the beacon light source at the focus of the light path behind the beam splitter;

[0055] The beacon beam emitted by the laser propagates in the opposite direction of the imaging optical path, passing through the semi-transparent and semi-reflective mirrors, the secondary mirrors, and finally reaching the eight-piece spliced ​​diffraction primary mirrors.

[0056] The beacon beam passes through the rear surface of the eight-piece spliced ​​diffraction primary mirror, is reflected by the front surface, passes through the rear surface again, and returns along the imaging optical path;

[0057] The beam containing the common phase error information of the spliced ​​primary mirror passes through a half-transparent half-reflective mirror and enters the phase shift modulator. Aperture No. 1 is selected as the reference aperture. The piston posture adjustment of the phase shift modulator is used to apply a delayed phase to aperture No. 1. Four modulations are performed, and the applied delayed phases are (0, π / 2, π, 3π / 2).

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

[0059] The optical transfer functions of the above-mentioned synthetic aperture telescope system are multiplied by the corresponding delay phases and linearly superimposed to obtain the expression C. The wavefront error of the synthetic aperture telescope system is then calculated using formula (8).

[0060] According to the nonlinear relationship between the forward and reverse errors, the least square method is used to decouple the forward error, that is, the common phase error of the system, from the mixed forward and reverse wavefront errors.

[0061] The solved common phase error is corrected using the piston and tilt attitude adjustment of the phase shift modulator.

[0062] In a second aspect, the present invention provides an electronic device comprising: one or more processors; and 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 aforementioned method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope.

[0063] In a third aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope.

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

Claims

1. A method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope, characterized in that: The method comprises: Step 1: Insert a semi-transparent, semi-reflective mirror into the collimating optical path of the spliced ​​telescope, and place the beacon light source at the focus of the converging optical path behind the beam splitter. The beacon light beam emitted by the beacon light source propagates in the opposite direction of the imaging optical path, passing through the beam splitter and the relay secondary mirror in sequence until it reaches the primary mirror of the spliced ​​telescope. The light beam reflected by the primary mirror carries the common phase error information and returns along the imaging optical path. Step 2: The beam carrying the common phase error information enters the phase shift modulator through a semi-transparent and semi-reflective mirror. The piston displacement of the phase shift modulator applies a delayed phase to the reference aperture, performing M modulations. The modulated beam is converged to the detector through an imaging lens, obtaining M point spread functions. By performing Fourier transform on the point spread functions, the corresponding M optical transfer functions are obtained. Step 3: Multiply the M optical transfer functions by the corresponding delay phases and linearly superpose them to obtain a complex amplitude distribution containing a common phase error. By performing an arctangent operation on the complex amplitude distribution, the wavefront error of each subaperture relative to the reference subaperture is separated, and the common phase error is decoupled from the wavefront error. Finally, the common phase error is corrected using a phase shift modulator; wherein, The step 1 comprises: the beacon beam passes through the rear surface of the telescope primary mirror, is reflected by the front surface of the primary mirror, passes through the rear surface again, and returns along the original imaging optical path; In step 2, the delayed phase of the m-th modulation is expressed as: （3） The point spread function of the reflected light collected by the detector after passing through the optical system is: （4） in, represents the point spread function of the system at the mth modulation, which is expressed as: （5） Where B r is the pupil function of the reference aperture, B T is the pupil function of the remaining apertures, n represents the aperture number of the main mirror of the spliced ​​telescope, N represents the total number of main mirror apertures of the spliced ​​telescope, represents the wavefront error on the nth sub-aperture, represents the spatial coordinates on the spliced ​​primary mirror, represents the center coordinate of the nth subaperture, i represents the imaginary unit; After Fourier transform, the optical transfer function of the corresponding telescope system is obtained as: （6）； In step 3, the optical transfer function of the telescope system is multiplied by the corresponding delay phase factor and linearly superimposed to obtain the expression C: （7） in, Represents the convolution operation; The common phase error of the system is obtained by the following formula: （8） Among them, Im[ ] and Re[ ] represent the imaginary part and real part of the complex number respectively.

2. The method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope according to claim 1, characterized in that: The step 3 also includes correcting the common phase error using the piston and tilt posture of the phase shift modulator.

3. The method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​telescope according to claim 1, characterized in that: The spliced ​​telescope is a transmission telescope.

4. The method for actively detecting common phase errors in a phase-shift modulated plane diffraction spliced ​​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 reflection mirror and a six-degree-of-freedom displacement stage.

5. An electronic device, characterized in that: include: one or more processors; a memory for storing one or more programs; Wherein, when one or more programs are executed by the one or more processors, the one or more processors implement the method for actively detecting common phase errors of a phase-shift modulated plane diffraction spliced ​​telescope as described in any one of claims 1 to 4.

6. A computer-readable storage medium, characterized in that Executable instructions are stored thereon, and when the instructions are executed by the processor, the processor can implement the active detection method for common phase error of a phase-shift modulated plane diffraction spliced ​​telescope as described in any one of claims 1 to 4.

Images