Self-co-phase detection method for plane diffraction spliced telescope with built-in vortex light

Abstract

The invention discloses a self-co-phase detection method for a plane diffraction spliced telescope with built-in vortex light, and belongs to the technical field of optical imaging telescopes. According to the method, an internal light source of the system is used as beacon light, so that a light beam passes through an optical system in a reverse imaging direction and is emitted in a parallel light form, and then enters the optical system again after being reflected by the front surface of a primary mirror to form a detection light beam carrying co-phase error information; and then, the detection light beam and a vortex light beam in the system generate interference on an image plane, and by acquiring and processing interference fringes in real time and extracting attitude information of the primary mirror under the combined action of forward and reverse errors, decoupling and correction of the piston and tilt errors of the spliced mirror surface can be realized, so that the error correction precision and the overall performance of the system are remarkably improved. In addition, two detectors are arranged in the system, interference fringe detection and system imaging can be achieved at the same time, a beacon light source is taken from the interior of the system, and the defect that a traditional method highly depends on external beacon light is overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging telescopes, and particularly relates to a self - phase - matching detection method for a planar diffraction mosaic telescope with vortex light inside. 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 is an unremitting pursuit of humanity. However, limited by aspects such as launch costs, materials, and processing technologies, it is difficult to infinitely increase the size of a single - piece large - aperture primary mirror in practical applications. To break through the limitations of the existing space telescope aperture, the technology of large - aperture planar diffraction mosaic telescopes has been proposed. This technology uses multiple small - size planar diffraction units to mosaic into an equivalent large - aperture primary mirror, thus theoretically achieving the same ultimate resolution as a large - aperture single - piece primary mirror. Compared with the manufacturing and alignment difficulties of traditional large - aperture reflective or refractive primary mirrors, the planar diffraction mosaic scheme can alleviate the process bottleneck to a certain extent and has great flexibility and scalability during space deployment, thus receiving extensive attention.

[0003] In practical applications, due to factors such as alignment errors, processing errors, and environmental disturbances, each planar diffraction unit sub - mirror cannot always be accurately maintained in the ideal position. Once the sub - mirror undergoes a slight tilt or translation, the entire mosaic telescope system will generate a so - called phase - matching error. The phase - matching error can be further divided into two parts: the focus shift caused by the tilt between sub - apertures and the optical path difference inconsistency caused by the translation between sub - apertures. The former will cause the foci of the sub - apertures to be misaligned, seriously affecting the imaging resolution of the system; the latter results in phase mismatch between sub - apertures and cannot form correct interference superposition on the image plane, thus reducing the imaging quality. Therefore, how to accurately detect and real - time correct the phase - matching error of each sub - aperture is one of the key technologies for large - aperture planar diffraction mosaic telescopes to achieve high - resolution imaging.

[0004] In order to measure and correct the phase - matching error, under laboratory conditions, a collimator with the same aperture is usually used to generate collimated light for detecting the phase - matching error of the sub - mirror. However, as the aperture of the telescope continues to increase, the manufacturing and calibration of large - aperture collimators become very difficult; under space - based observation conditions, stars are mostly used as beacon light sources to calibrate the sub - mirror. The optical system needs to frequently turn, and it is impossible to perform real - time continuous imaging operations on the target, which limits the on - orbit application performance and imaging reliability of the mosaic telescope. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a self - phase - matching detection method for a planar diffractive segmented telescope with an internal vortex light. By using the beacon light generated by the internal light source of the telescope system as the detection light, it is not necessary to additionally introduce an external collimator, and real - time detection and correction of the phase - matching error can be achieved 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 in - orbit phase - matching error detection of large - aperture space telescopes in the future. By interfering the detection beam carrying the system's phase - matching error with the vortex reference beam on the detector and analyzing and processing the formed interference fringes, the piston and tilt postures of each sub - aperture can be obtained in real time under the condition of coupling forward and reverse errors, and the results are fed back to the phase - modulation device for correction, thereby maintaining the high - resolution imaging ability of the entire planar diffractive segmented telescope 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 a self - phase - matching detection method for a planar diffractive segmented telescope with an internal vortex light, and the method includes:

[0008] Step 1: In the planar diffractive segmented telescope system, use a lens to collimate the internal beacon light source, and use a beam splitter to divide the collimated beam into two paths. One path is used as the reference beam, carrying orbital angular momentum information, and the other path is used as the detection beam, which carries the phase - matching error of the telescope's 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, 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's primary mirror.

[0010] Step 3: Transmit the radial tilt, tangential tilt error, and piston error information to the phase - modulation device, calculate the piston and tilt postures that need to be compensated for each sub - aperture, and achieve precise compensation of the phase - matching error and clear imaging without phase - matching error through the piston and tilt of the phase - modulation device.

[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 implement the aforementioned self - phase - matching detection method for a planar diffractive segmented telescope with an internal vortex light.

[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 implement the aforementioned self - phase - matching detection method for a planar diffractive segmented telescope with an internal vortex light.

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

[0014] By utilizing the reflection characteristics of the outer surface of the planar diffractive segmented primary mirror, a light source is arranged inside the telescope system. After the light beam emitted by the light source passes through the primary mirror, a part of the reflected light is used as the beacon light for the self-phase conjugation detection of the system, reducing the dependence on external beacon light. The measurement and correction of the phase conjugation error can also be independently completed in the space environment, with higher flexibility and applicability.

[0015] In the present invention, the detection beam and the reference beam generate interference fringes on the image plane of the telescope. By acquiring the interference pattern through a detector and performing real-time calculations, the phase conjugation error between each sub-mirror can be quickly solved and corrected. This process does not require interrupting the normal observation of the telescope, realizing real-time detection and correction of the phase conjugation error.

[0016] By using the vortex beam with orbital angular momentum as the reference beam, and analyzing the deformation amount of the characteristic Fermat spiral interference fringes, the tilt and piston postures of the sub-mirrors can be directly decoupled without distinguishing between forward and reverse errors, and the real-time correction of the phase conjugation error can be realized by using the backend compensation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of an implementation scheme of a self-phase conjugation detection method for a planar diffractive segmented telescope with an internal vortex light in the present invention.

[0018] REFERENCE SIGNS

[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 OF THE EMBODIMENTS

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

[0021] As Figure 1 shown, it is a schematic diagram of an implementation scheme of a self-phase conjugation detection method for a planar diffractive segmented telescope with an internal vortex light in the present invention. The method includes:

[0022] Step 1: In a planar diffractive segmented telescope system, a lens is used to collimate the built-in beacon light source, and a beam splitter divides the collimated beam into two paths. One path serves as the reference beam, carrying orbital angular momentum information, and the other path serves as the detection beam, which carries the phase error of the telescope primary mirror after being reflected by the outer surface of the primary mirror. The planar diffractive segmented 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. Specifically:

[0023] In the planar diffractive segmented telescope system, a laser is used to emit a beacon light source 3 at the focus of the planar diffractive segmented telescope and irradiate the telescope primary mirror in the reverse direction. A lens is used to collimate the built-in beacon light source 3, and a beam splitter 4 divides the collimated beam into two paths. The planar diffractive segmented telescope system includes a telescope primary mirror 1 and a relay secondary mirror 2 arranged in sequence along the optical path. The beam splitter uses a flat beam splitter or a crystal beam splitter.

[0024] One of the paths passes through a 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 the reference beam for detection. The optical field distribution of the vortex light can be expressed as:

[0025] (1)

[0026] where m represents the topological charge number of the vortex light, represents the azimuth angle, represents the initial phase of the reference beam, i represents the imaginary unit, k represents the wave vector, z represents the propagation distance of the beam, and E1 represents the amplitude of the vortex light. The vortex beam passes through a first mirror 6 and a second mirror 7 in sequence and is received by a second detector 11. The second mirror 7 modulates the phase by adjusting the propagation distance of the reference beam to ensure that the reference beam and the detection beam generate interference fringes.

[0027] The other path is coupled into the optical system through the beam splitter 4 and propagates along the reverse imaging direction of the planar diffractive segmented telescope system. It passes through the relay secondary mirror 2 and the telescope primary mirror 1 in sequence and exits in the form of parallel light. Since the outer surface of the telescope primary mirror 1 is a planar structure, part of the 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 system imaging direction. It passes through the beam splitter 4 and a converging lens 9 and interferes with the reference beam on the second detector 11. At this time, the reflected light carries the phase error of the telescope primary mirror 1, and this reflected light is regarded as the detection beam. The optical 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 beam, and E2 represents the amplitude of the spherical wave.

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

[0031] (3)

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

[0033] Step 2: Extract the coordinates of the interference fringes generated by the reference beam and the probe beam at 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; specifically:

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

[0035] (4)

[0036] where, .

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

[0038] (5)

[0039] This distribution form can be regarded as a deformed Fermat spiral curve, and n represents an integer. When substituting the common phase error term in formula (3) into formula (5), the formula can be obtained:

[0040] (6)

[0041] where, denotes the unit vector pointing from the origin to the center coordinates of the sub-aperture, denotes the unit tangential vector pointing from the origin to the center coordinates of the sub-aperture, are the undetermined coefficients introduced when fitting the bright fringes in the interference fringes to the 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 to the polar coordinate system, the relevant parameters can be fitted through the least squares fitting algorithm. The parameters obtained through fitting can be further used to solve the radial tilt and tangential tilt errors of the sub-aperture:

[0043] (7)

[0044] When the radial tilt of the secondary mirror and the parameter are known, its piston error can be further solved. When there is no piston error, the interference fringes are distributed in a Fermat spiral, but the piston error and radial tilt error will cause the rotation of the Fermat spiral curve, which is reflected in the change amount . According to the change amount of

[0045] (8)

[0046] In summary, the piston and tilt postures of the primary mirror are extracted from the co-phase errors generated by the forward and reverse coupling, as well as the coupling of the piston error and tilt error.

[0047] Step 3: Transmit the radial tilt, tangential tilt error, and piston error information to the phase modulator, calculate the piston and tilt postures that each sub-aperture needs to compensate, and achieve precise compensation of the co-phase error and clear imaging without co-phase error through the piston and tilt of the phase modulator. Specifically:

[0048] Transmit the piston and tilt posture information of the primary mirror to the phase modulator 8, calculate the piston and tilt postures that each sub-aperture of the phase modulator 8 needs to compensate, and achieve precise compensation of the co-phase error through the piston and tilt of the phase modulator 8. After the co-phase error is compensated by the dependent modulator 8, clear imaging without co-phase error can be achieved on the first detector 10.

[0049] Furthermore, a beacon beam is emitted by a laser at the focus of the spliced telescope and is irradiated back onto the primary mirror of the telescope. Since the outer surface of the primary mirror is a planar structure, part of the beam will be reflected by the outer surface of the primary mirror and pass through the optical system again along the system imaging direction. The reflected light carries the phase error of the primary mirror, and this reflected light can be regarded as the detection 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 as the reference beam through a specific modulator. The beacon light can be modulated into a vortex beam using a spiral phase plate, or other devices such as a spatial light modulator can also be used. The other path is coupled into the optical system through the beam splitter. The beam splitter can be a planar beam splitter or a crystal beam splitter;

[0051] Furthermore, an interference optical path similar to a Mach-Zehnder interferometer is built. The vortex beam with angular momentum serves as the reference beam, and the spherical wave carrying the phase error serves as the detection beam. Interference occurs on the detector. The optical path can adopt an optical path similar to that of a Mach-Zehnder interferometer, or other optical paths such as a Michelson interferometer can also be used for interference;

[0052] Furthermore, a converging lens 9 is inserted into the detection optical path to adjust the spacing of the Fermat spiral curve. Other forms can also be used to adjust the spacing of the Fermat spiral curve by changing the curvature radius of the spherical wave;

[0053] Furthermore, a mirror is used in the reference optical path to adjust the optical path difference to ensure that interference fringes can be generated on the image plane between the reference light and the detection beam;

[0054] Furthermore, the topological charge number of the vortex light can be selected as 1, or 2 or higher can be selected, but the spacing of the Fermat spiral curve and the extraction accuracy need to be taken into account;

[0055] Furthermore, after extracting the interference fringes, the bright fringes can be fitted, or the dark fringes can be fitted; The least squares method can be used to fit the parameters for fitting, or other algorithms can also be used to for fitting;

[0056] Furthermore, the phase modulator 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.

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

[0058] Embodiment

[0059] 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 632.8 nm is used as the light source, and this light source is used as the beacon light to detect the phase error of the segmented telescope. The specific implementation steps are as follows:

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

[0061] One of the paths passes through a 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 the reference beam for detection;

[0062] The vortex beam is reflected twice by the first mirror 6 and the second mirror 7 in sequence, and after passing through the beam splitter, it is received by the second detector 11. The second mirror 7 modulates the phase by adjusting the propagation distance of the reference beam to ensure that the reference beam and the detection beam generate interference fringes;

[0063] The other path is coupled into the optical system through the beam splitter 4 and propagates along the reverse imaging direction of the plane diffractive segmented telescope system. After passing through the optical system, it exits in the form of parallel light;

[0064] Since the outer surface of the telescope primary mirror 1 is a plane 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 system imaging direction. It passes through the beam splitter and the converging lens 9 and interferes with the reference beam on the second detector 11. At this time, the reflected light carries the 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 show a deformed Fermat spiral distribution;

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

[0067] ;

[0068] Here, are the undetermined 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 coordinates of the bright fringes in the polar coordinate system.

[0069] Use the least squares method to determine the values. Through the parameters obtained by fitting, the radial tilt and tangential tilt errors of the sub-aperture can be further solved;

[0070] With the known radial tilt of the sub - mirror and parameters After that, further solve its piston error. The piston error and the radial tilt error will cause the rotation of the Fermat spiral curve, which is reflected in the change amount of According to the change amount of

[0071] In summary, from the co - phase errors generated by the forward and reverse coupling, as well as the coupling of the piston error and the tilt error, the piston and tilt postures of the primary mirror are extracted;

[0072] Finally, the piston and tilt posture information of the primary mirror is transmitted to the phase modulator 8, and the piston and tilt postures that each sub - aperture of the phase modulator 8 needs to compensate are calculated. Through the piston and tilt of the phase modulator 8, precise compensation of the co - phase error is achieved. After the co - phase error is compensated by the dependent modulator 8, clear imaging without co - phase error can be achieved on the detector 10.

[0073] 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 self - co - phase detection method of a planar diffraction mosaic telescope with an internally - built vortex light.

[0074] In a 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 implement the foregoing self - co - phase detection method of a planar diffraction mosaic telescope with an internally - built vortex light.

[0075] The above - described specific embodiments have further detailed the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above - described are only specific embodiments of the present invention and are not used to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light, characterized in that, The method includes: Step 1: In a planar diffractive segmented telescope system, a lens is used to collimate the built-in beacon light source, and a beam splitter divides the collimated beam into two paths. One path serves as a reference beam carrying orbital angular momentum information, and the other path serves as a detection beam that carries the phase error of the telescope primary mirror after being reflected by the outer surface of the primary mirror. The planar diffractive segmented 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. 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 for the radial tilt, tangential tilt error, and piston error of the telescope primary mirror. Step 3: Transmit the radial tilt, tangential tilt error, and piston error information to the phase modulator, calculate the piston and tilt attitudes that need to be compensated for each sub-aperture, and achieve precise compensation of the phase error and clear imaging without phase error through the piston and tilt of the phase modulator.

2. The self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light according to claim 1, characterized in that, In Step 1, a laser is used to emit a beacon light source at the focus of the planar diffractive segmented telescope to irradiate the telescope primary mirror in the reverse direction. The beam splitter divides the collimated beacon light source into two paths. One path is modulated by a spiral phase plate into a vortex beam, and the vortex beam serves as a reference beam and is received by the second detector after passing through the first mirror and the second mirror in sequence. The other path propagates along the reverse imaging direction of the planar diffractive segmented telescope system, passes through the relay secondary mirror and the telescope primary mirror in sequence, and exits in the form of parallel light. Among them, part of the beam is reflected by the outer surface of the telescope primary mirror to the relay secondary mirror, and again serves as a detection beam through the optical system along the system imaging direction, and interferes with the reference beam on the second detector through the beam splitter and the converging lens.

3. The self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light according to claim 2, characterized in that, The beam splitter uses a planar beam splitter or a crystal beam splitter.

4. The self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light according to claim 2, characterized in that, The second mirror modulates the phase by adjusting the propagation distance of the reference beam to ensure that the reference beam and the detection beam generate interference fringes.

5. The self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light according to claim 2, characterized in that, The converging lens is used to adjust the spacing of the Fermat spiral curve.

6. The self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light according to claim 2, characterized in that, Step 2 includes: Capture the fringe image formed by the interference of the reference beam and the detection beam on the second detector, extract the pixel coordinates of the bright fringes, and convert them into coordinates in the polar coordinate system. Use the least squares method to obtain the deformed Fermat spiral curve. Calculate the phase error carried by the detection beam during the forward and reverse propagation processes along the planar diffractive segmented telescope system, and substitute it into the deformed Fermat spiral curve to solve for the fitting parameters to obtain the radial tilt, tangential tilt error, and piston error.

7. The self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light according to claim 6, characterized in that, After extracting the fringe image, the dark fringes can also be fitted.

8. The self - phase - matching detection method for a planar diffraction - splicing telescope with an internally - built vortex light according to claim 1, characterized in that, In Step 3, the phase modulator can use a reflective liquid crystal spatial light modulation device, a transmissive liquid crystal phase retarder, or a three-dimensional fast steering mirror or a six-degree-of-freedom displacement stage device.

9. An electronic device, characterized in that, Includes: 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 are caused to implement a self-phase-matching detection method for a planar diffractive mosaic telescope with an internally built-in vortex light 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 cause the processor to implement a self-phase-matching detection method for a planar diffractive mosaic telescope with an internally built-in vortex light according to any one of claims 1-8.

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