Short-distance air-ground quantum key communication telescope transmitting and receiving device

Abstract

The invention relates to the field of quantum communication, and discloses a short-distance air-ground quantum key communication telescope transceiving device which comprises an off-axis three-mirror optical system serving as the front end part of the device and four rear-end optical paths serving as the rear end part of the device. The device has the beneficial effects that the front end of the device adopts an off-axis three-mirror optical system, so that the coaxial and common-caliber design of four optical paths, namely a coarse tracking optical path, a fine tracking optical path, a quantum optical path and a beacon optical path is realized, the optical path structure is optimized, and the single-mode optical fiber coupling adjustment time under different near field communication working conditions is shortened; a coarse-fine tracking integrated design is adopted, so that the capture efficiency of the device is improved while the tracking precision of quantum key communication is ensured; in conclusion, the device remarkably improves the efficiency of quantum key communication on the aspect of overall design.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication, and in particular to a short-range air-to-ground quantum key communication telescope transceiver device. Background Art

[0002] Quantum key communication channels are divided into fiber optic channels and free space channels, and free space quantum communication can be divided into satellite-ground free space channels and space-ground free space channels. The airborne platform for short-range space-ground quantum key communication is usually unmanned aerial vehicle equipment.

[0003] However, existing short-range air-to-ground quantum key communication devices have the following problems: drones, as aerial platforms, usually have a high vibration frequency and are greatly affected by wind disturbances. It is difficult to capture the target in a short time during the initial capture stage of establishing the communication link. Moreover, due to the high-frequency vibration, tracking accuracy is difficult to guarantee, which directly affects the communication reception efficiency. Summary of the Invention

[0004] The present invention aims to improve at least one technical problem in the background technology.

[0005] The present invention provides a short-range air-to-ground quantum key communication telescope transceiver device, comprising: An off-axis three-mirror optical system is provided at the front end of the device and is used to receive external light, fold the light path, and reduce the light beam; A first beam splitter, which is arranged on the outgoing light path of the off-axis three-mirror optical system and splits the light into two parts, namely, transmission and reflection; a coarse tracking lens group, which is arranged on the reflected light path of the first beam splitter and is used for preliminarily tracking and locating the signal source from the air; a piezoelectric fast reflecting mirror, located on the transmission light path of the first beam splitter and used for aligning the optical axis; A second beam splitter, which is arranged on the path of the reflected light of the piezoelectric fast reflector and splits the light into two parts, namely, transmission and reflection; A precision tracking lens assembly, which is arranged on the transmission light path of the second beam splitter and is used to achieve higher precision tracking and positioning; A third beam splitter is provided on the path of the reflected light of the second beam splitter, and splits the light into two parts, namely, reflected and transmitted, for a third time; a quantum light lens, which is arranged on the reflected light path of the third beam splitter and is used to process quantum light; The beacon light lens is arranged on the transmission light path of the third beam splitter and is used to process the beacon light.

[0006] Beneficial effects of the present invention: The present invention provides a short-range air-to-ground quantum key communication device. The front end of the device adopts an off-axis three-mirror optical system, which realizes the coaxial and co-aperture design of four optical paths: coarse tracking optical path, fine tracking optical path, quantum optical path and beacon optical path, optimizes the optical path structure, and shortens the single-mode optical fiber coupling adjustment time under different short-range communication conditions; adopts a coarse-fine tracking integrated design, which improves the capture efficiency of the device while ensuring the tracking accuracy of quantum key communication; in summary, the overall design of the device significantly improves the efficiency of quantum key communication.

[0007] As some sub-solutions of the above technical solution, the off-axis three-mirror optical system includes a primary mirror, a secondary mirror, a first plane reflector, a third mirror and a second plane reflector arranged in sequence along the light propagation path.

[0008] As some sub-solutions of the above technical solution, the mirror surfaces of the primary mirror and the third mirror are quadratic surfaces, and the mirror surface of the secondary mirror is aspherical; the primary mirror and the secondary mirror are concave mirrors, and the third mirror is convex mirrors.

[0009] As some sub-solutions of the above technical solution, the coarse tracking lens group includes three coarse light lenses, and the three coarse light lenses are respectively a convex lens arranged along the propagation direction of the light and a pair of concave lenses arranged oppositely.

[0010] As some sub-solutions of the above technical solution, the precision tracking lens group includes three precision optical lenses, and the three precision optical lenses are respectively a convex lens arranged along the propagation direction of light and a pair of concave lenses arranged oppositely.

[0011] As some sub-solutions of the above technical solution, the two surfaces of the quantum light lens are spherical and aspherical respectively.

[0012] As some sub-solutions of the above technical solution, the quantum light lens is made of quartz glass.

[0013] As some sub-solutions of the above technical solution, the first beam splitter fully transmits light with wavelengths of 1550nm and 671nm, and semi-transmits and semi-reflects light with a wavelength of 532nm; the second beam splitter fully transmits light with a wavelength of 532nm, and fully reflects light with wavelengths of 1550nm and 671nm; the third beam splitter fully transmits light with a wavelength of 671nm, and fully reflects light with a wavelength of 1550nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which: Figure 1 A schematic structural diagram of a telescope device provided in an embodiment of the present invention; Figure 2 The transfer function calculation diagram of the off-axis three-mirror optical system; Figure 3 Design a schematic diagram for the quantum light path; Figure 4 is the quantum light path lattice diagram; Figure 5 Calculation diagram for quantum optical path coupling efficiency.

[0015] In the accompanying drawings: 1-primary mirror; 2-secondary mirror; 3-tertiary mirror; 4-first plane reflector; 5-second plane reflector; 6-first beam splitter; 7-coarse tracking lens group; 8-piezoelectric fast reflector; 9-fine tracking lens group; 10-quantum light lens; 11-beacon light lens; 12-second beam splitter; 13-third beam splitter. DETAILED DESCRIPTION

[0016] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0017] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0018] In the description of the present invention, "several" means an indefinite quantity, "multiple" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, and "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" is solely for the purpose of distinguishing technical features and should not be understood to indicate or imply relative importance, or to implicitly indicate the number or order of the technical features indicated. "And / or" throughout the text represents three parallel solutions. For example, "A and / or B" means a solution where A satisfies, a solution where B satisfies, or a solution where both A and B satisfy.

[0019] In the description of the present invention, if there is a short sentence containing multiple parallel features, the attributive defines the closest feature. For example, "B, C, and E are arranged on A, and are connected to D" means that B is arranged on A and E is connected to D, and does not constitute a limitation on C. However, attributives that express the relationship between features, such as "spaced arrangement" or "circular arrangement", do not fall into this category. If the word "all" is preceded by an attributive, it means that all features in the short sentence are limited. For example, "B, C, and D are all arranged on A" means that B, C, and D are all arranged on A. In a sentence with an omitted subject, the omitted subject is the subject of the previous sentence, that is, "B is arranged on A, including C" means that B is arranged on A and A includes C.

[0020] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0021] The following combination Figures 1 to 5 Embodiments of the present invention are described.

[0022] A short-range space-to-ground quantum key communication telescope transceiver device in this embodiment includes: An off-axis three-mirror optical system is provided at the upstream of the device and is used to receive external light, fold the optical path, and reduce the light beam; A first beam splitter 6 is provided on the outgoing light path of the off-axis three-mirror optical system and is used to split the light into two parts, namely, a transmission part and a reflection part; a coarse tracking lens group 7, which is arranged on the path of the reflected light of the first beam splitter 6 and is used for preliminarily tracking and locating the signal source from the air; a piezoelectric fast reflection mirror 8, located on the transmission light path of the first beam splitter 6, for aligning the optical axis; A second beam splitter 12 is provided on the path of the reflected light of the piezoelectric fast reflector 8 and splits the light into two parts, namely, a transmission part and a reflection part; A precision tracking lens group 9, which is arranged on the transmission light path of the second beam splitter 12, and is used to achieve higher precision tracking and positioning; A third beam splitter 13 is provided on the path of the reflected light of the second beam splitter 12 and splits the light into two parts, namely, reflected and transmitted parts; a quantum light lens 10 , which is arranged on the reflected light path of the third beam splitter 13 and is used to process quantum light; The beacon light lens 11 is arranged on the transmission light path of the third beam splitter 13 and is used to process the beacon light.

[0023] The telescope assembly first receives light from the outside world (including airborne signal sources) through its front-end off-axis three-mirror optical system. This system not only receives the light but also folds the optical path and focuses the light, reducing its diameter for subsequent processing. After passing through the off-axis three-mirror optical system, the received light is directed toward the first beamsplitter 6. The first beam splitter 6 divides the light into two parts, reflected light and transmitted light. A coarse tracking lens group 7 with a smaller focal length is provided on the reflected light path for quickly capturing the signal source. At the same time, the light transmitted through the first beam splitter 6 continues to propagate along its path and reaches the piezoelectric fast reflector 8 to improve the alignment accuracy of the remaining light path. The light reflected by the piezoelectric fast reflector 8 is split again by the second beam splitter 12. A fine tracking lens group 9 with a larger focal length is provided on the transmitted light path to ensure high-precision alignment of the signal source. The light reflected from the second beam splitter 12 continues to propagate to the third beam splitter 13, which divides the light into two parts, reflected light and transmitted light. A quantum optical lens 10 is provided on the reflected light path for processing quantum optical signals and performing quantum communication tasks such as quantum key distribution. A beacon optical lens 11 is provided on the transmitted light path of the third beam splitter 13 for processing beacon optical signals and establishing and maintaining communication links.

[0024] Throughout the workflow, the coarse tracking lens group 7 and the fine tracking lens group 9 work together to ensure that the device can quickly and accurately capture and track the signal source in the air; the rapid response capability of the piezoelectric fast reflection mirror 8 ensures high-precision alignment of the optical axis, providing a stable foundation for the processing of quantum light and beacon light; finally, the quantum light lens 10 and the beacon light lens 11 process the quantum light signal and the beacon light signal respectively, realizing efficient and accurate quantum key communication.

[0025] Beneficial effects of the present invention: The present invention provides a short-range air-to-ground quantum key communication device. The front end of the device adopts an off-axis three-mirror optical system, which realizes the coaxial and co-aperture design of four optical paths, namely, a coarse optical path, a fine optical path, a quantum optical path, and a beacon optical path. The optical path structure is optimized and the single-mode optical fiber coupling adjustment time under different short-range communication conditions is shortened. The coarse-fine tracking integrated design is adopted to improve the capture efficiency of the device while ensuring the tracking accuracy of quantum key communication. In summary, the overall design of the device significantly improves the efficiency of quantum communication.

[0026] Reference Figure 2 , Figure 2This is the diffraction modulation transfer function (MTF) graph. The diffraction modulation transfer function (MTF) is the ratio of the contrast between the output image and the input image, and is used to reflect the ability of an optical system to transmit sinusoidal modulations of various frequencies. The MTF curve quantitatively describes the clarity of an optical imaging system. The flatter the curve, the better the consistency between the edges and the center, and the closer it is to the diffraction limit of the optical system being measured. Figure 2 The modulation transfer function curve of the short-range air-to-ground quantum key communication device provided by the present invention is demonstrated. The curve has high straightness, is close to the optical diffraction limit design, and has excellent imaging quality and contrast transmission capability.

[0027] Reference Figure 3 and Figure 4 , the quantum light path design of quantum light in the device is as follows Figure 3 As shown, the optical design CodeV software is used to analyze the quantum optical path design, and the following can be obtained: Figure 4 The quantum light path lattice diagram shown, Figure 4 What is shown is the shape of the imaging spot at the focal point after the external incident light passes through the quantum light path.

[0028] Figure 4 In the , Airy radius refers to the diffraction-limited spot size, which is a theoretical limit of the optical system performance; RMS radius refers to the root mean square result of different light position offsets, and the RMS radius is used to quantify the discreteness or stability of the light spot. The smaller the RMS value, the more concentrated the light position and the more stable the light spot; GEO radius refers to the maximum position offset, which is used to evaluate the light position offset in the worst case; the units of Airy radius, RMS radius and GEO radius are all microns. Figure 4 In the present invention, the RMS radius of the light spot is smaller than the Airy radius, which proves that the quantum light path designed by the present invention has been optimized to the diffraction limit, and the maximum position offset of the light is very small, with high energy concentration, meeting the requirements of high efficiency of single-mode fiber coupling.

[0029] Reference Figure 5 , focusing on the actual working state of short-range air-to-ground quantum key communication, the efficiency attenuation at a distance of 1 km was analyzed; without considering the influence of beam jitter and atmospheric turbulence, the quantum light output was simulated as a Gaussian beam with a beam wavelength of 1.5500 μm (1550 nm), and the simulation analysis was performed according to the refraction condition of the medium refractive index of 1; the simulation calculation shows that the output beam width of the present invention is X = 1.05386E-02 mm and Y = 1.08662E-02 mm, which is close to the mode field diameter of 10.4 μm; its theoretical coupling efficiency is 56% at a distance of 1 km, which is relatively high and meets the coupling requirements of single-mode fiber; the coupling efficiency refers to the efficiency of external incident light coupling to the receiving optical fiber after passing through the short-range air-to-ground quantum key communication device provided by the present invention; Figure 5 In the figure, peak irradiance and total power are used to indicate the power and maximum irradiance of the quantum light output; X width and Y height are used to indicate the size of the analysis interface (the blue area in the figure) in the X and Y directions.

[0030] Specifically, the off-axis three-mirror optical system includes a primary mirror 1, a secondary mirror 2, a first plane reflector 4, a third mirror 3 and a second plane reflector 5 which are arranged in sequence along the light propagation path.

[0031] The primary mirror 1 serves as the first reflecting surface of the off-axis three-mirror optical system, capturing the light from the observed target and performing the initial reflection; the secondary mirror 2 serves as the second reflecting surface of the off-axis three-mirror optical system, responsible for reflecting the light from the object for the second time, helping to correct the aberration introduced by the primary mirror 1; the first plane mirror 4 is used to change the propagation direction of the light and fold the light path; the third mirror 3 serves as the last key reflecting surface of the off-axis three-mirror optical system, reflecting the light that has passed the first two reflections again; the second plane mirror 5 is similar to the first plane mirror 4, and is also used to change the propagation direction of the light, fold the light path, and finally reflect the light out of the optical system; the off-axis three-mirror optical system can achieve high-resolution imaging to meet the needs of precise observation of target details; the off-axis system can eliminate the problem of center obstruction; the use of the first plane mirror 4 and the second plane mirror 5 increases the flexibility of the system, allowing light to enter and leave the system at different angles; the off-axis three-mirror front-end afocal beam reduction system greatly saves space size and structural weight through multiple folding light path designs, making the device adaptable to small equipment such as drones.

[0032] Specifically, the mirror surfaces of primary mirror 1 and tertiary mirror 3 are quadratic surfaces, while the mirror surface of secondary mirror 2 is aspherical. Primary mirror 1 and secondary mirror 2 are concave mirrors, while tertiary mirror 3 is convex. The aspherical surface of secondary mirror 2 provides more complex reflection characteristics, which can significantly improve the imaging quality of the optical system and reduce aberrations and distortion. The mirror surface of primary mirror 1 is a quadratic surface with a curvature radius of -214.59mm; the mirror surface of secondary mirror 2 is an aspherical surface with a curvature radius of -81.37mm; and the mirror surface of tertiary mirror 3 is a quadratic surface with a curvature radius of 143.18mm. The primary mirror 1, secondary mirror 2, and tertiary mirror 3 form an afocal beam reduction system. When parallel light rays enter the afocal beam reduction system, they are first converged by primary mirror 1 and secondary mirror 2. Then, through the divergence effect of tertiary mirror 3, the light beam is compressed and directed to the output end of the system. The afocal beam reduction system has a beam reduction ratio of 4 and a real exit pupil. The afocal beam reduction system improves the measurement accuracy and stability of the entire device.

[0033] Specifically, the coarse tracking lens assembly 7 comprises three coarse optical lenses, each consisting of a convex lens and a pair of concave lenses arranged in the direction of light propagation. Coarse tracking lens assembly 7 transmits 532nm light. This configuration helps effectively converge and diverge incident light, thereby optimizing the light transmission path. The focal length of the coarse tracking optical path is 345mm, and the focal length of the lens assembly is 86.25mm, as determined by the afocal system's beam reduction ratio. The coarse tracking field of view is 1.44°. This wide field of view enables the system to quickly acquire targets over a wide range, increasing the probability of target capture.

[0034] Specifically, the fine tracking lens assembly 9 comprises three precision optical lenses: a convex lens and a pair of concave lenses arranged in opposite directions along the light propagation direction. The precision tracking lens assembly 9 transmits 532nm light. This configuration helps effectively converge and diverge the incident light, thereby optimizing the light transmission path. The lens assembly features real-time focal length adjustment, enabling precise adjustments based on target distance and lighting conditions, enabling high-precision tracking. The focal length of the fine tracking optical path is 900mm, while the afocal system's reduction ratio yields a 225mm focal length for the precision optical lens assembly, ensuring clear imaging and accurate tracking during high-precision tracking.

[0035] Specifically, the two surfaces of the Quantum Optical Lens 10 are spherical and aspherical, respectively. The focal length of the Quantum Optical Lens 10 is 61mm. The lens's two surfaces are designed as spherical and aspherical, with curvature radii of 1.00E+18mm and -27.08mm, respectively, and a semi-aperture of 6.5mm. The aspherical design enhances the lens's adaptability to different incident angles and wavelengths and improves its focusing performance. Compared with complex dual aspherical or higher-order aspherical designs, the single aspherical design significantly reduces costs. The combined spherical and aspherical design can also effectively correct for various aberrations.

[0036] Specifically, the quantum light lens 10 is made of quartz glass. Quartz glass has good stability and excellent light transmittance in the visible and near-infrared bands, which can ensure the efficient transmission of quantum light in the lens and can withstand large laser shocks, ensuring the reliability and durability of the system.

[0037] Specifically, the first beam splitter 6 fully transmits light with wavelengths of 1550nm and 671nm, and semi-transmits and semi-reflects light with a wavelength of 532nm; the second beam splitter 12 fully transmits light with a wavelength of 532nm, and fully reflects light with wavelengths of 1550nm and 671nm; the third beam splitter 13 fully transmits light with a wavelength of 671nm, and fully reflects light with a wavelength of 1550nm. After the four light paths pass through the first beam splitter 6, the 1550nm quantum light and the 671nm beacon light are fully transmitted, and the 532nm light is semi-transmitted and semi-reflected; the reflected 532nm light enters the coarse tracking lens group 7, and the transmitted 532nm light, 1550nm quantum light, and 671nm beacon light are reflected by the piezoelectric fast reflection mirror 8 onto the second beam splitter 12 and are separated again. The second beam splitter 12 fully transmits the remaining 532nm light, allowing the 532nm light to enter the fine tracking lens group 9. The second beam splitter 12 The 1550nm quantum light and the 671nm beacon light are totally reflected, reaching the third beam splitter 13; the third beam splitter 13 fully transmits the 671nm beacon light and totally reflects the 1550nm quantum light, allowing all the 1550nm quantum light to enter the quantum light lens 10 and be emitted; through the careful setting of the beam splitter, the system can efficiently separate and merge four paths of light with different wavelengths, ensuring that each path of light can propagate along the predetermined path, avoiding mutual interference of light, and thus improving the overall performance and stability of the system.

[0038] In this embodiment, the beacon light band is 671nm, and the beacon light is emitted by defocused emission, that is, the emission position of the light source is adjusted so that its emission position is not at the focus, so that the emitted beacon light has a larger divergence angle, thereby covering more areas.

[0039] The above specifically describes the preferred embodiments of the present invention, but the present disclosure is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of the present disclosure.

Claims

1. A short-range space-to-ground quantum key communication telescope transceiver, characterized in that: include: An off-axis three-mirror optical system is arranged at the front end of the device and is used to receive external light, fold the light path and reduce the light beam; A first beam splitter (6), which is arranged on the outgoing light path of the off-axis three-mirror optical system and divides the light into two parts, a transmission part and a reflection part, for the first time; A coarse tracking lens group (7), which is arranged on the path of the reflected light of the first beam splitter (6) and is used for preliminarily tracking and locating a signal source from the air; A piezoelectric fast reflection mirror (8), which is located on the transmission light path of the first beam splitter (6) and is used for aligning the optical axis; A second beam splitter (12), which is arranged on the reflected light path of the piezoelectric fast reflector (8) and splits the light into two parts, a transmission part and a reflection part; A precision tracking lens group (9), which is arranged on the transmission light path of the second beam splitter (12) and is used to achieve higher precision tracking and positioning; A third beam splitter (13), which is arranged on the reflected light path of the second beam splitter (12) and splits the light into two parts, a reflected part and a transmitted part, for a third time; A quantum light lens (10), which is arranged on the reflected light path of the third beam splitter (13) and is used to process quantum light; A beacon light lens (11) is arranged on the transmission light path of the third beam splitter (13) and is used to process the beacon light.

2. The short-distance space-to-ground quantum key communication telescope transceiver device according to claim 1 is characterized in that: The off-axis three-mirror optical system comprises a primary mirror (1), a secondary mirror (2), a first plane reflector (4), a third mirror (3) and a second plane reflector (5) which are arranged in sequence along a light propagation path.

3. The short-distance space-to-ground quantum key communication telescope transceiver device according to claim 2 is characterized in that: The mirror surfaces of the primary mirror (1) and the third mirror (3) are quadratic curved surfaces, and the mirror surface of the secondary mirror (2) is an aspherical surface; the primary mirror (1) and the secondary mirror (2) are concave mirrors, and the third mirror (3) is a convex mirror.

4. The short-distance space-to-ground quantum key communication telescope transceiver device according to claim 1 is characterized in that: The coarse tracking lens group (7) comprises three coarse light lenses, wherein the three coarse light lenses are respectively a convex lens arranged along the light propagation direction and a pair of concave lenses arranged oppositely.

5. The short-distance space-to-ground quantum key communication telescope transceiver device according to claim 1 is characterized in that: The precision tracking lens group (9) comprises three precision light lenses, wherein the three precision light lenses are respectively a convex lens arranged along the light propagation direction and a pair of concave lenses arranged oppositely.

6. The short-distance space-to-ground quantum key communication telescope transceiver device according to claim 1 is characterized by: The two surfaces of the quantum optical lens (10) are respectively a spherical surface and an aspherical surface.

7. The short-distance space-to-ground quantum key communication telescope transceiver device according to claim 1 is characterized by: The material of the quantum light lens (10) is quartz glass.

8. The short-distance space-to-ground quantum key communication telescope transceiver device according to claim 1 is characterized by: The first beam splitter (6) fully transmits light with wavelengths of 1550 nm and 671 nm, and semi-transmits and semi-reflects light with a wavelength of 532 nm; the second beam splitter (12) fully transmits light with a wavelength of 532 nm, and fully reflects light with wavelengths of 1550 nm and 671 nm; the third beam splitter (13) fully transmits light with a wavelength of 671 nm, and fully reflects light with a wavelength of 1550 nm.

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