A self-phase detection method for plane diffraction spliced ​​telescope with built-in vortex light

Abstract

The present invention discloses a self-phase detection method for a plane diffraction splicing telescope with built-in vortex light, which belongs to the technical field of optical imaging telescopes. The method uses the internal light source of the system as a beacon light, so that the light beam first passes through the optical system in the opposite direction of imaging and is emitted in the form of parallel light, and then re-enters the optical system after being reflected by the front surface of the main mirror, forming a detection light beam carrying the common phase error information; then, the detection light beam and the vortex light beam in the system interfere with each other on the image plane, and the attitude information of the main mirror is extracted under the joint action of the positive and negative errors by acquiring and processing the interference fringes in real time, so as to realize the decoupling and correction of the piston and tilt error of the splicing mirror, thereby significantly improving the accuracy of error correction and the overall performance of the system. In addition, the configuration of two detectors in the system can realize interference fringe detection and system imaging at the same time, and the beacon light source is taken from the inside of the system, which overcomes the high dependence of the traditional method on external beacon light.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging telescopes, and in particular relates to a self-co-phase detection method for a plane diffraction splicing telescope with built-in vortex light. Background Art

[0002] According to the Rayleigh criterion, the primary factor affecting the limiting 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, designing and manufacturing large-aperture astronomical telescopes is a relentless pursuit. However, due to limitations such as launch costs, materials, and processing techniques, the size of a single, large primary mirror cannot be increased indefinitely in practical applications. To overcome the limitations of existing space telescope apertures, large-aperture planar diffraction splicing telescopes has been proposed. This technology utilizes multiple small-scale planar diffraction elements to create an equivalent large-aperture primary mirror, theoretically achieving the same limiting resolution as a single large-aperture primary mirror. Compared to the manufacturing and assembly challenges of traditional large-aperture reflective or refractive primary mirrors, the planar diffraction splicing approach can alleviate process bottlenecks to a certain extent and offers greater flexibility and scalability for space deployment, thus attracting widespread attention.

[0003] In practical applications, due to factors such as installation errors, processing errors, and environmental disturbances, the individual sub-mirrors of the plane diffraction unit cannot always be precisely maintained in the ideal position. Once the sub-mirrors undergo a slight tilt or translation, the entire stitched telescope system will produce the so-called common phase error. The common phase error can be further divided into two parts: focus offset caused by tilt between sub-apertures and inconsistent optical path differences caused by translation between sub-apertures. The former will cause the focus of the sub-aperture to be misaligned, seriously affecting the imaging resolution of the system; the latter will cause phase mismatch between sub-apertures, making it impossible to form correct interference superposition on the image plane, thereby reducing image quality. Therefore, how to accurately detect and correct the common phase error of each sub-aperture in real time is one of the key technologies for achieving high-resolution imaging in large-aperture plane diffraction stitched telescopes.

[0004] To measure and correct for common-phase error, collimators of equal aperture are typically used in the laboratory to generate collimated light for common-phase error detection of the sub-mirrors. However, as telescope apertures continue to increase, the manufacture and calibration of large-aperture collimators have become increasingly difficult. In space observations, common-phase calibration of sub-mirrors is often performed using stars as beacon light sources. This requires frequent steering of the optical system, making it impossible to achieve real-time continuous imaging of the target, limiting the on-orbit performance and imaging reliability of the segmented telescope. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a self-phase detection method for a plane diffraction splicing telescope with built-in vortex light, which uses the beacon light generated by the internal light source of the telescope system as the detection light. There is no need to introduce an external parallel light tube, and it can realize real-time detection and correction of the common phase error during the normal observation of the telescope. This not only greatly reduces the dependence on the external test optical path, but also lays a feasible technical foundation for the on-orbit common phase error detection of future large-aperture space telescopes. By interfering the detection beam carrying the system common phase error with the vortex reference beam on the detector, and analyzing and processing the interference fringes formed, the piston and tilt attitude of each sub-aperture can be obtained in real time under the condition of coupling the forward error and the reverse error, and the results are fed back to the common phase modulator for correction, thereby maintaining the high-resolution imaging capability of the entire plane diffraction splicing telescope system.

[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 provides a method for self-phase detection of a plane diffraction spliced ​​telescope with built-in vortex light, the method comprising:

[0008] Step 1: Use a lens to collimate the built-in beacon light source in the plane diffraction splicing telescope system, and use a beam splitter to split the collimated light beam into two paths. One path is used as a reference beam, carrying orbital angular momentum information, and the other path is used as a detection beam, which carries the common phase error of the telescope primary mirror after being reflected by the outer surface of the primary mirror;

[0009] Step 2: extract the coordinates of the interference fringes generated by the reference beam and the detection beam on the second detector, and use the least squares method to fit the parameters of the deformed Fermat spiral curve to solve the radial tilt, tangential tilt error, and piston error of the telescope primary mirror;

[0010] Step 3: The radial tilt, tangential tilt error, and piston error information are transmitted to the phase modulator to calculate the piston and tilt posture that need to be compensated for each sub-aperture, and the piston and tilt of the phase modulator are used to achieve accurate compensation of the common phase error and clear imaging without common phase error.

[0011] In a second aspect, the present invention provides an electronic device comprising: 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 aforementioned self-phase detection method of a plane diffraction spliced ​​telescope with built-in vortex light.

[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 self-phase detection method of a plane diffraction spliced ​​telescope with built-in vortex light.

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

[0014] The present invention utilizes the reflective properties of the outer surface of the plane diffraction spliced ​​primary mirror and sets a light source inside the telescope system. After the light beam emitted by the light source passes through the primary mirror, part of its reflected light is used as beacon light for system self-common phase detection, reducing dependence on external beacon light. The measurement and correction of common phase errors can also be completed independently in a space environment, with higher flexibility and applicability.

[0015] The detection beam and the reference beam in the present invention generate interference fringes on the telescope image plane. The interference pattern is acquired by the detector and calculated in real time, which can quickly solve and correct the common phase error between each sub-mirror. This process does not need to interrupt the normal observation of the telescope, and realizes real-time common phase error detection and correction.

[0016] By using a vortex beam with orbital angular momentum as a reference beam and analyzing the deformation of the characteristic Fermat spiral interference fringes, the tilt of the sub-mirror and the piston posture can be directly decoupled without distinguishing between forward and reverse errors, and the back-end compensation system can be used to achieve real-time correction of the common phase error. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a diagram showing the implementation of a self-phase detection method for a plane diffraction splicing telescope with built-in vortex light according to the present invention.

[0018] Reference numerals

[0019] 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 spiral phase plate, 6 is the first reflector, 7 is the second reflector, 8 is the phase modulator, 9 is the converging lens, 10 is the first detector, and 11 is the second detector. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings and examples.

[0021] like Figure 1 FIG. 1 is a diagram showing an implementation scheme of a self-phase detection method for a plane diffraction spliced ​​telescope with built-in vortex light according to the present invention, the method comprising:

[0022] Step 1: In a plane diffraction splicing telescope system, a lens is used to collimate the built-in beacon light source, and a beam splitter is used to split the collimated light beam into two paths, one of which is used as a reference beam and carries orbital angular momentum information, and the other is used as a detection beam and carries the common phase error of the telescope primary mirror after being reflected by the outer surface of the primary mirror; the plane diffraction splicing telescope system includes a telescope primary mirror, a relay secondary mirror, a beam splitter, and a second detector arranged in sequence along the imaging direction, and a phase modulator arranged between the beam splitter and the second detector along the reverse imaging direction; specifically:

[0023] In a plane diffraction splicing telescope system, a laser is used to emit a beacon light source 3 at the focus of the plane diffraction splicing telescope to illuminate the telescope primary mirror in reverse. A lens is used to collimate the built-in beacon light source 3, and a beam splitter 4 splits the collimated light beam into two paths. The plane diffraction splicing telescope system includes a telescope primary mirror 1 and a relay secondary mirror 2 placed in sequence along the optical path. The beam splitter is a flat beam splitter or a crystal beam splitter.

[0024] Among them, it passes through the spiral phase plate 5 and is modulated into a vortex beam with a topological charge of m. Since the vortex beam has orbital angular momentum information, it is used as a reference beam for detection. The light field distribution of the vortex light can be expressed as:

[0025] (1)

[0026] Where m represents the topological charge of the vortex light, represents the azimuth, represents the initial phase of the reference beam, i represents the imaginary unit, k represents the wave vector, z represents the beam propagation distance, and E1 represents the vortex light amplitude. The vortex beam passes through the first reflector 6 and the second reflector 7 before being received by the second detector 11. The second reflector 7 modulates the phase of the reference beam by adjusting its propagation distance, ensuring that interference fringes are generated between the reference beam and the probe beam.

[0027] The other path is coupled into the optical system through the beam splitter 4, propagates along the reverse imaging direction of the plane diffraction splicing telescope system, passes through the relay secondary mirror 2 and the telescope primary mirror 1 in sequence, and is emitted as parallel light; since the outer surface of the telescope primary mirror 1 is a planar structure, part of the light beam will be reflected by the outer surface of the telescope primary mirror 1 to the relay secondary mirror 2, and pass through the optical system again along the imaging direction of the system, through the beam splitter 4 and the converging lens 9, and interfere with the reference beam on the second detector 11. At this time, the reflected light carries the common phase error of the telescope primary mirror 1, and the reflected light is regarded as the detection beam. The light field distribution of the detection beam can be expressed as:

[0028] (2)

[0029] Where R represents the radius of curvature of the spherical wave, represents the initial phase of the probe beam, represents the common phase error of the primary mirror, r represents the radial propagation distance of the light beam, and E2 represents the spherical wave amplitude.

[0030] Since the probe beam passes through the primary mirror in both the forward and reverse directions, it is necessary to consider the impact of these two transmission processes on the common phase error. After integration, the common phase error can be expressed as:

[0031] (3)

[0032] in, represents the phase distribution caused by piston error, represents the phase error caused by the radial tilt of the sub-mirror, represents the phase error caused by the tangential tilt of the sub-mirror, They represent the piston error, radial tilt error and tangential tilt error of the sub-mirror respectively, Indicates the distance of the sub-mirror from the axis, Indicates the radial distance from a point on the sub-mirror to the center of the sub-mirror, represents the tangential distance from this point to the center of the sub-mirror, f represents the focal length of the primary mirror, and x, y represent the coordinates of the primary mirror in space.

[0033] Step 2: Extract the coordinates of the interference fringes generated by the reference beam and the detection beam on the second detector, use the least squares method to fit the parameters of the deformed Fermat spiral curve, and solve the radial tilt, tangential tilt error, and piston error of the telescope primary mirror; specifically:

[0034] When the detection beam and the reference beam interfere with each other on the second detector 11, assuming that the intermediate parameter , the interference light intensity can be expressed as:

[0035] (4)

[0036] in, .

[0037] The bright fringe distribution on the second detector 11 can be expressed as follows according to formula (4):

[0038] (5)

[0039] This distribution can be viewed as a deformed Fermat spiral curve, where n represents an integer. When the common phase error term in formula (3) is substituted into formula (5), the following formula can be obtained:

[0040] (6)

[0041] in, represents the unit vector pointing from the origin to the subaperture center coordinate, represents the unit tangent vector pointing from the origin to the subaperture center coordinate, These are the undetermined coefficients introduced when fitting the bright fringes in the interference fringes to a Fermat spiral curve using the least squares method. These coefficients characterize the quadratic term, tilt term, and constant phase term in the wavefront error.

[0042] After extracting the coordinates of the interference bright fringes and converting them into polar coordinates, the relevant parameters can be fitted by the least squares fitting algorithm. Perform fitting. The parameters obtained by fitting , the radial tilt and tangential tilt errors of the sub-aperture can be further solved:

[0043] (7)

[0044] When the radial tilt of the sub-mirror is known and parameters After that, the piston error is further solved. It is known that when there is no piston error, the interference fringes are distributed in the form of a Fermat spiral, but the piston error and radial tilt error will cause the Fermat spiral curve to rotate, which is reflected in The amount of change .according to The amount of change The piston error of the primary mirror can be solved:

[0045] (8)

[0046] In summary, the piston and tilt attitudes of the primary mirror are extracted from the common phase errors generated by the forward and reverse couplings and the coupling of the piston error and the tilt error.

[0047] Step 3: The radial tilt, tangential tilt error, and piston error information are transmitted to the phase modulator to calculate the piston and tilt posture required to be compensated for each sub-aperture, and the piston and tilt of the phase modulator are used to achieve accurate compensation of the common phase error and clear imaging without common phase error.

[0048] The primary mirror's piston and tilt attitude information is transmitted to the phase modulator 8, which calculates the piston and tilt attitude required for compensation for each subaperture of the phase modulator 8. Accurate compensation for common phase error is achieved through the piston and tilt of the phase modulator 8. After the common phase error is compensated by the phase modulator 8, clear imaging without common phase error can be achieved on the first detector 10.

[0049] Furthermore, a laser is used to emit a beacon beam at the focal point of the spliced ​​telescope, illuminating the telescope's primary mirror in reverse. Because the primary mirror's outer surface is planar, part of the beam is reflected and passes through the optical system again along the imaging direction. The reflected light carries the common phase error of the primary mirror and can be considered a probe beam.

[0050] Furthermore, a beam splitter is used to split the collimated beacon light into two paths. One path is converted into a vortex beam with orbital angular momentum by a specific modulator as a reference beam. The beacon light can be modulated into a vortex beam using a spiral phase plate, or other devices such as a spatial light modulator. The other path is coupled into the optical system through a beam splitter. The beam splitter can be a flat plate beam splitter or a crystal beam splitter.

[0051] Furthermore, an interference optical path similar to a Mach-Zehnder interferometer was built, with a vortex beam with angular momentum as the reference beam and a spherical wave carrying a common phase error as the detection beam, which interfere on the detector. The optical path can be similar to that of a Mach-Zehnder interferometer or other optical paths such as Michelson.

[0052] Furthermore, a converging lens 9 is inserted into the detection optical path to adjust the pitch of the Fermat spiral curve. Alternatively, the pitch of the Fermat spiral curve can be adjusted by changing the radius of curvature of the spherical wave in other ways.

[0053] Furthermore, a reflector is used in the reference light path to adjust the optical path difference, ensuring that the reference light and the detection beam can generate interference fringes on the image plane;

[0054] Furthermore, the vortex optical topological charge can be selected as 1, 2, or even higher, but the spacing of the Fermat spiral curve and the extraction accuracy must be taken into consideration.

[0055] Furthermore, after extracting the interference fringes, the bright fringes can be fitted, as well as the dark fringes. The least squares method can be used to fit the parameters. Other algorithms can also be used to fit Perform fitting;

[0056] Furthermore, the common phase modulator may adopt a reflective liquid crystal spatial light modulation device, a transmissive liquid crystal phase retarder, or a three-dimensional fast reflection mirror, a six-degree-of-freedom displacement stage or other devices.

[0057] Furthermore, the imaging device may be a CCD camera, or a CMOS camera, or other area array detectors that meet the requirements.

[0058] Example

[0059] The measurement object of this implementation is a large-aperture diffraction spliced ​​telescope composed of eight diffractive optical elements (DOEs). A fiber laser with a wavelength of 632.8 nm is used as the light source. This light source is used as the beacon light to detect the common phase error of the spliced ​​telescope. The specific implementation steps are as follows:

[0060] The built-in beacon light source 3 is collimated using a lens, and the collimated light beam is split into two paths using a beam splitter 4;

[0061] One path passes through the spiral phase plate 5, which modulates it into a vortex beam with a topological charge of m. Since the vortex beam has orbital angular momentum information, it is used as a reference beam for detection;

[0062] The vortex beam is reflected twice by the first reflector 6 and the second reflector 7, and then passes through the beam splitter and is received by the second detector 11. The second reflector 7 modulates the phase of the reference beam by adjusting the propagation distance of the reference beam to ensure that the reference beam and the detection beam produce interference fringes.

[0063] The other path is coupled into the optical system through the beam splitter 4, propagates along the reverse imaging direction of the plane diffraction splicing telescope system, and is emitted as parallel light after passing through the optical system;

[0064] Since the outer surface of the telescope primary mirror 1 is a planar structure, part of the light beam will be reflected by the outer surface of the telescope primary mirror 1 and pass through the optical system again along the imaging direction of the system, through the beam splitter and the converging lens 9, and interfere with the reference beam on the second detector 11. At this time, the reflected light carries the common phase error of the telescope primary mirror 1, and this reflected light can be regarded as the detection beam;

[0065] Interference fringes are received on the second detector 11, and the fringes are distributed in a deformed Fermat spiral pattern;

[0066] Extract the coordinates of the bright fringes in the interference fringes and convert them into polar coordinates. Use the least squares method to fit the deformed Fermat spiral curve:

[0067] ;

[0068] here, are the unknown coefficients introduced when fitting the bright fringes in the interference fringes to the Fermat spiral curve. These coefficients characterize the quadratic term, tilt term, and constant phase term in the wavefront error. Represents the polar coordinates of the bright fringe.

[0069] Determine using the least squares method The parameters obtained by fitting , the radial tilt and tangential tilt errors of the sub-aperture can be further solved;

[0070] When the radial tilt of the sub-mirror is known and parameters After that, the piston error is further solved. The piston error and radial tilt error will cause the Fermat spiral curve to rotate, which is reflected in According to the change of The change in can be used to solve the piston error of the primary mirror;

[0071] In summary, the piston and tilt attitudes of the primary mirror are extracted from the common phase errors generated by the forward and reverse couplings as well as the couplings between the piston error and the tilt error.

[0072] Finally, the primary mirror's piston and tilt attitude information is transmitted to the phase modulator 8, which calculates the piston and tilt attitudes required for compensation for each subaperture of the phase modulator 8. Accurate compensation for common phase error is achieved through the piston and tilt of the phase modulator 8. After the common phase error is compensated by the phase modulator 8, clear imaging without common phase error can be achieved on the detector 10.

[0073] In a second aspect, the present invention provides an electronic device comprising: 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 aforementioned self-phase detection method of a plane diffraction spliced ​​telescope with built-in vortex light.

[0074] 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 self-phase detection method of a plane diffraction spliced ​​telescope with built-in vortex light.

[0075] 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 self-phase detection method for a plane diffraction splicing telescope with built-in vortex light, characterized in that: The method comprises: Step 1: In the plane diffraction splicing telescope system, a lens is used to collimate the built-in beacon light source, and a beam splitter is used to split the collimated light beam into two paths, one of which is used as a reference beam, carrying orbital angular momentum information, and the other is used as a detection beam, which carries the common phase error of the telescope primary mirror after being reflected by the outer surface of the primary mirror; the plane diffraction splicing telescope system includes a telescope primary mirror, a relay secondary mirror, a beam splitter, a second detector arranged in sequence along the imaging direction, and a phase modulator arranged between the beam splitter and the second detector along the reverse imaging direction; a laser is used to emit the beacon light source reflection at the focus of the plane diffraction splicing telescope The beam splitter splits the collimated beacon light source into two paths, one of which is modulated into a vortex beam by a spiral phase plate. The vortex beam is received by the second detector after passing through the first reflector and the second reflector in sequence as a reference beam. The other path propagates along the reverse imaging direction of the plane diffraction splicing telescope system, passes through the relay secondary mirror and the telescope primary mirror in sequence, and is emitted as parallel light. Part of the beam is reflected by the outer surface of the telescope primary mirror to the relay secondary mirror, and passes through the optical system again as a detection beam along the imaging direction of the system, and interferes with the reference beam on the second detector through the beam splitter and the converging lens. Step 2: extract the coordinates of the interference fringes generated by the reference beam and the detection beam on the second detector, and use the least squares method to fit the parameters of the deformed Fermat spiral curve to solve the radial tilt, tangential tilt error, and piston error of the telescope primary mirror; Step 3: The radial tilt, tangential tilt error, and piston error information are transmitted to the phase modulator to calculate the piston and tilt posture that need to be compensated for each sub-aperture, and the piston and tilt of the phase modulator are used to achieve accurate compensation of the common phase error and clear imaging without common phase error.

2. The method for self-phase detection of a plane diffraction spliced ​​telescope with built-in vortex light according to claim 1, characterized in that: The beam splitter is a flat plate beam splitter or a crystal beam splitter.

3. The method for self-phase detection of a plane diffraction spliced ​​telescope with built-in vortex light according to claim 1, characterized in that: The second reflector modulates the phase by adjusting the propagation distance of the reference beam to ensure that interference fringes are generated between the reference beam and the detection beam.

4. The method for self-phase detection of a plane diffraction spliced ​​telescope with built-in vortex light according to claim 1, characterized in that: The converging lens is used to adjust the spacing of the Fermat spiral curve.

5. The method for self-phase detection of a plane diffraction spliced ​​telescope with built-in vortex light according to claim 1, characterized in that: The step 2 includes: The fringe image formed by the interference of the reference beam and the detection beam is captured on the second detector, the pixel coordinates of the bright fringe are extracted, and the coordinates are converted into coordinates in the polar coordinate system. The deformed Fermat spiral curve is obtained using the least squares method; The common phase error carried by the detection beam during the forward and reverse propagation processes along the plane diffraction stitching telescope system is calculated, and the deformed Fermat spiral curve is introduced to solve the fitting parameters to obtain the radial tilt error, tangential tilt error, and piston error.

6. The method for self-phase detection of a plane diffraction spliced ​​telescope with built-in vortex light according to claim 5, characterized in that: After extracting the fringe image, the dark fringes are fitted.

7. The method for self-phase detection of a plane diffraction spliced ​​telescope with built-in vortex light according to claim 1, characterized in that: In step 3, the phase modulator is any one of a reflective liquid crystal spatial light modulation device, a transmissive liquid crystal phase retarder, a three-dimensional fast reflection mirror, and a six-degree-of-freedom displacement stage device.

8. 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 self-phase detection method of a plane diffraction spliced ​​telescope with built-in vortex light as described in any one of claims 1-7.

9. A computer-readable storage medium, characterized in that Executable instructions are stored thereon, which, when executed by a processor, enable the processor to implement the self-phase detection method of a plane diffraction spliced ​​telescope with built-in vortex light as described in any one of claims 1 to 7.

Images