Free space quantum key distribution optical system and communication system

Abstract

The utility model provides a free space quantum key distribution optical system and communication system, comprising a base plate, the base plate is installed on a rotary table, and the base plate is provided with a transmission-type optical telescope, a reflector, a spectroscope, a fine tracking module, a coupling module, a coarse tracking module, a beacon light module and a control module. According to the utility model, the miniaturization and the structure compactness of the system are realized through the ingenious structural design, and the optical telescope adopts a transmission-type optical telescope and a simplified rear optical path terminal, so that the blocking and vignetting phenomena of the secondary mirror can be effectively avoided; the optical telescope system is small in axial size, is lighter than a clamping type reflection telescope in weight under the same aperture, is more suitable for large-scale use in short-distance free space quantum communication, can be carried and deployed by a single person, has an all-time quantum key distribution capability, is better in portability, is simple and convenient to use, and is low in processing and installation cost.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of optical system and device design, concretely relates to a kind of free space quantum key distribution optical system and communication system. BACKGROUND

[0002] The statements in this part only provide background technical information related to the utility model, and do not necessarily constitute prior art.

[0003] The currently practical quantum communication technology is quantum key distribution technology. The current free space quantum communication terminal is mainly large-aperture or multi-aperture transmitting / receiving telescope. The large-aperture telescope is mainly reflective, and the reflective optical receiving system includes a primary concave mirror with an aperture of more than 250 mm and a secondary convex mirror. The primary mirror and the eyepiece are at the rear end of the telescope, and the secondary convex mirror is placed before the focal point of the primary concave mirror. A small hole is left in the center of the primary concave mirror. The light is reflected by the primary concave mirror and the secondary convex mirror twice and then emitted from the small hole to the eyepiece.

[0004] In short-distance free space quantum key distribution, the reflective telescope usually includes a primary mirror and a secondary mirror. The secondary mirror blocks the received light beam, and at the same time, the secondary convex mirror blocks the light beam, causing the energy loss in the central region to be much larger than the proportion of the energy blocked by the secondary convex mirror in the total energy of the light beam. Moreover, the secondary convex mirror blocking also causes vignetting, further leading to energy loss.

[0005] In addition, the reflective telescope has problems such as high weight and large volume, and the processing and integration price is too expensive, making it difficult for the equipment to be popularized. INVENTION CONTENTS

[0006] The utility model discloses in order to solve the above problem, propose a kind of free space quantum key distribution optical system and communication system, the utility model discloses by ingenious structure design, it is realized that the miniaturization of system, compact structure, optical telescope uses small aperture transmission type optical telescope, secondary mirror blocking and vignetting phenomenon can be effectively avoided, optical telescope system axial dimension is smaller and compared with cassette reflective telescope under same aperture weight is lighter, with good portability, it is easy to use, and processing, installation cost is low.

[0007] According to some embodiments, the utility model adopts the following technical scheme:

[0008] A kind of free space quantum key distribution optical system, including bottom plate, the bottom plate is installed on turntable, transmission type optical telescope, reflector, beamsplitter, fine tracking module, coupling module, coarse tracking module, beacon light module and control module are arranged on the bottom plate, wherein:

[0009] The transmission optical telescope, located in the middle of the base plate, is used to emit quantum light and laser communication light, and to receive response beacon light emitted from distant free space, or to receive beacon light, quantum light and laser communication light, and to propagate the received beam to the reflector.

[0010] A reflector, located on one side of a transmission optical telescope, is used to track beacon light or response beacon light, receive quantum light and laser communication light emitted by the coupling module and reflected by the beam splitter's folding mirror, and send them to the transmission optical telescope. Simultaneously, it receives response beacon light propagated by the transmission optical telescope, or receives optical beacon light, quantum light, and laser communication light propagated by the transmission optical telescope, folds and reflects them, and sends them to the beam splitter. The normal of the reflector is at 45° to the optical axis of the transmission optical telescope.

[0011] A beam splitter is positioned between the precision tracking module and the reflector, with its incident optical axis at 90° to the incident optical axis of the transmission optical telescope. It is used to receive quantum light and laser communication light emitted by the coupling module, reflect them to the reflector and the transmission optical telescope, and emit them into free space, or receive the beams after being refracted and reflected by the reflector, and then transmit them to the precision tracking module and the coupling module respectively according to the wavelength band.

[0012] The coupling module, located above the eyepiece of the transmission optical telescope, is used to couple quantum light or laser communication light.

[0013] The beacon light module, located above the objective lens of a transmission optical telescope, is used to emit beacon light;

[0014] The precision tracking module has its incident optical axis at 90° to the incident optical axis of the transmission optical telescope and is connected to the control module;

[0015] The coarse tracking module is located below the transmission optical telescope and is connected to the control module;

[0016] The control module, located at the upper left of the base plate, is used to connect to and control the coarse tracking module, the fine tracking module, and the reflector.

[0017] As an alternative implementation, the transmissive optical telescope includes an objective lens and an eyepiece, both of which are composed of a transmissive spherical lens, an aspherical lens, or a lens group. The focal point of the objective lens coincides with the focal point of the eyepiece, and the focal point is located between the objective lens and the eyepiece.

[0018] Furthermore, the objective lens has a total aperture of 55.9 mm, an effective aperture of 50.8 mm, an incident surface radius of curvature R1 of 114.949 mm, an exit surface R2 that is flat, and a center thickness of 10 mm. The eyepiece has a total aperture of 30 mm, an effective aperture of 3.4 mm, an incident surface radius of curvature R3 of 49.955 mm, an exit surface radius of curvature R4 of -8.975 mm, a center thickness t2 of 1.25 mm, and a lens distance of 231 mm between the objective and eyepiece.

[0019] As an alternative implementation, the transmissive optical telescope includes an objective lens and an eyepiece, both of which are composed of a transmissive spherical lens, an aspherical lens, or a lens group, with the focal point of the objective lens coinciding with the virtual focal point of the eyepiece.

[0020] As a further feature, the objective lens has a total aperture of 55.9 mm, an effective aperture of 50.8 mm, a radius of curvature R1 of the objective lens incident surface of 114.949 mm, an objective lens exit surface R2 that is flat, and a center thickness of t1 = 10 mm; the eyepiece has a total aperture of 30.4 mm, an effective aperture of 3.4 mm, a radius of curvature R3 of the eyepiece incident surface of -8.849 mm, a radius of curvature R4 of the eyepiece exit surface of 60.631 mm, a center thickness of t2 of 1.5 mm, and a lens distance of 200.912 mm between the objective lens and the eyepiece.

[0021] Positive focal length eyepieces can effectively reduce the distance between the mirror and the exit pupil of a transmission optical telescope, increasing the utilization rate of the telescope aperture; negative focal length eyepieces can compress the length of the telescope, making the optical mechanism structure more compact.

[0022] As an alternative implementation, the reflector is installed at 45° to the incident optical axis of the transmission optical telescope to refract and reflect the light beam, and the reflected optical axis is at 90° to the incident optical axis of the transmission optical telescope.

[0023] As an alternative implementation, the beam splitter is mounted at a position 45° to its incident optical axis.

[0024] As a further step, the beam splitter is a dichroic dichroic mirror, with a transmission path wavelength of 500-1100nm and a transmittance T>90%; and a reflection path wavelength of 1100-1600nm and a reflectance R>95%.

[0025] As an alternative implementation, the precision tracking module includes a filter, a precision camera, and a lens. The filter is positioned in front of the lens of the precision camera, and the precision camera is connected to the control module.

[0026] As an alternative implementation, the coupling module includes a filter, a reflective collimator, and a single-mode fiber, with the filter positioned in front of the reflective collimator and the reflective collimator connected to the single-mode fiber.

[0027] As a further step, the incident optical axis of the coupling module is at 180° to the incident optical axis of the transmission optical telescope.

[0028] As an alternative implementation, the coarse tracking module includes a filter, a coarse camera, and a lens. The filter is positioned in front of the lens of the coarse camera, and the coarse camera is connected to the control module.

[0029] As a further step, the optical axis of the coarse tracking module is parallel to the optical axis of the transmission optical telescope.

[0030] As an alternative implementation, the turntable is equipped with a turntable control system, and the movement of the turntable is controlled by the turntable control system.

[0031] The control module is connected to the coarse tracking module, fine tracking module, reflector and turntable control system via a network port.

[0032] A communication system includes at least one free-space quantum key distribution optical system, which serves as a transmitter or a receiver.

[0033] Alternatively, it may include two free-space quantum key distribution optical systems, one of which acts as the transmitter and the other as the receiver.

[0034] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0035] This invention provides a free-space quantum key distribution optical system. By employing a transmission-type common-aperture optical telescope, it eliminates secondary mirror obstruction and vignetting, thereby achieving low energy loss during reception. A reflector and beam splitter are used to connect the transmission-type optical telescope, the precision tracking module, and the coupling module in series, enabling quantum light, laser communication light, and beacon light to form a common optical path for transmission and reception. This design features a rational structural layout, small space occupation, and miniaturization. The small-aperture transmission-type common-aperture optomechanical design utilizes a single-mode transmission and a single-mode fiber reception path after both the transmitting and receiving transmission-type optical telescopes. Furthermore, the compact optomechanical structure improves space utilization efficiency, reduces system weight, and further shrinks the size of the optical system.

[0036] The optical system provided by this invention can be used as both a transmitter and a receiver, and can be used in combination with each other in quantum communication and laser communication.

[0037] This invention achieves system miniaturization through ingenious structural design, resulting in a small size and light weight, enabling portability and rapid deployment. It can be applied to quantum and laser communication between scattered users in special geographical environments, avoiding ground excavation and fiber optic cable laying. It can be used for secure communication in field activities at sea, on land, and in the air. It can also be applied to scenarios where communication base stations are damaged and cannot be repaired in a short time due to sudden disasters, allowing for rapid emergency deployment of the system's communication endpoints.

[0038] This utility model provides a small-aperture transmission telescope. By designing the effective aperture, radius of curvature, center thickness of the lens, and inter-lens spacing of the objective lens and eyepiece, the telescope meets the magnification requirements and can effectively avoid secondary lens obstruction and vignetting. By adjusting the eyepiece parameters, the overall size of the telescope is further reduced, improving space utilization efficiency.

[0039] The optical system used in this invention can be connected to existing miniaturized fiber optic quantum key distribution transmitter / receiver terminals, enabling the entire system to be carried and established by a single person.

[0040] The optical system of this invention has a small receiving field of view, and by combining it with high-precision narrowband filtering devices, the application scenarios of free-space quantum key distribution can be extended from nighttime to daytime.

[0041] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0042] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments of this utility model and their descriptions are used to explain this utility model and do not constitute an improper limitation of this utility model.

[0043] Figure 1 This is a schematic diagram of a transmission optical telescope structure according to one embodiment;

[0044] Figure 2 This is a schematic diagram of a transmission optical telescope structure according to another embodiment;

[0045] Figure 3 A schematic diagram of the structure of a quantum key distribution optical system according to one embodiment;

[0046] Figure 4 This is a schematic diagram of another embodiment of a quantum key distribution optical system;

[0047] Figure 5 This is a schematic diagram of the system accessories in one embodiment;

[0048] Figure 6 This is a physical schematic diagram of a quantum key distribution optical system according to one embodiment.

[0049] Wherein, A is the objective lens, B is the eyepiece, and C is the focal point;

[0050] 1. Base plate, 2. Beacon optical module, 3. Transmission optical telescope, 4. Coarse tracking module, 5. Mirror, 6. Beam splitter, 7. Fine tracking module, 8. Coupling module, 9. Control module. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0052] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0053] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0054] Where there is no conflict, the embodiments and features described in this application may be combined with each other.

[0055] Example 1

[0056] As mentioned in the background section, setting up a large-aperture receiving telescope in free-space quantum and laser communication terminals presents challenges such as high weight and large size. Furthermore, telescope installation requires pre-selection of a site and construction of a proportionally sized base, thus hindering portability and rapid deployment. The manufacturing and installation costs are also prohibitively high, making widespread adoption difficult. In addition, the presence of the aperture in the primary mirror and the central blind zone in the secondary mirror weakens the telescope's received energy. This results in significant power loss during short-range communication, making Cassette reflector telescopes with central obstructions unsuitable for use as receiving telescopes in short-range quantum and laser communication.

[0057] This embodiment provides a free-space quantum key distribution optical system. The optical telescope is a transmission-type telescope, which effectively avoids secondary mirror obstruction and vignetting. The optical telescope system has a smaller axial dimension and is lighter than a Cassette reflector telescope of the same aperture, making it more suitable for large-scale use in short-range free-space quantum communication. It can be carried and deployed by a single person and has all-weather quantum key distribution capabilities. Furthermore, the transmitting and receiving telescopes are interchangeable, meaning the system can function as both a transmitter and a receiver, extending quantum communication coverage to areas inaccessible by fiber optics and satellites, and enabling rapid deployment in various emergency situations. Compared to the high cost of satellites and the extensive deployment of fiber optics, the small-aperture transmission-type portable terminal designed in this solution has lower production, usage, and maintenance costs.

[0058] Transmission optical telescopes, such as Figure 1 As shown, it includes eyepiece B and objective lens A, both of which use positive power design, with focal point C located between objective lens A and eyepiece B.

[0059] This embodiment designs a small-aperture transmission optical telescope with an effective objective lens diameter of 40–150 mm and a beam reduction ratio of 10–30. It can simultaneously meet the magnification requirements and the wavelength requirements of both quantum communication and laser communication (e.g., 1310 nm–1350 nm for laser communication and 1530 nm–1570 nm for quantum communication). Specific design parameters are as follows:

[0060] Objective lens A has a total aperture of 55.9 mm, an effective aperture of 50.8 mm, a radius of curvature R1 = 114.949 mm, and R2 is a flat plane. The center thickness of objective lens A is t1 = 10 mm. Eyepiece B has a total aperture of 30 mm, an effective aperture of 3.4 mm, a radius of curvature R3 = 49.955 mm, a radius of curvature R4 = -8.975 mm, and a center thickness of t2 = 1.25 mm. The inter-lens distance between objective lens A and eyepiece B is d = 231 mm. Both objective lens A and eyepiece B are made of H-K9L material.

[0061] like Figure 1 As shown, the parallel beam of light is converged to focal point C by objective lens A and then diverges. After being converged and collimated by eyepiece B, the beam is reduced to parallel light and emitted. The focal point of objective lens A and the focal point of eyepiece B are located between the two lenses and are confocal.

[0062] In this embodiment, the focal point C of the transmission optical telescope is located between the objective lens A and the eyepiece B. The distance between objective lens A and eyepiece B is relatively long. To further reduce the size of the optical telescope, improvements are made to this design, such as... Figure 2As shown, in another embodiment of the transmission optical telescope, the eyepiece B is a negative lens. The objective lens A and the eyepiece B in this system are the same virtual focal point C of the positive and negative lenses. The system has a smaller axial dimension and is lighter than the Cassette reflector telescope of the same aperture.

[0063] Based on the above requirements, the parameters of another embodiment of the transmission optical telescope can be as follows:

[0064] Objective lens A has a total aperture of 55.9 mm, an effective aperture of 50.8 mm, a radius of curvature R1 = 114.949 mm, a flat surface R2, and a center thickness t1 = 10 mm. Eyepiece B has a total aperture of 30.4 mm, an effective aperture of 3.4 mm, a radius of curvature R3 = -8.849 mm, a radius of curvature R4 = 60.631 mm, and a center thickness t2 = 1.5 mm. Both objectives A and eyepiece B are made of H-K9L material. The distance between objectives A and eyepiece B is d = 200.912 mm. Based on the effective aperture of objective lens A and eyepiece B, the system meets the magnification requirements.

[0065] like Figure 2 As shown, after the parallel beam passes through objective lens A, it is converged by objective lens A, and then collimated and reduced by eyepiece B, exiting as parallel light. The focal point of objective lens A coincides with the virtual focal point of eyepiece B.

[0066] In this embodiment of the transmissive optical telescope structure, both objective lens A and eyepiece B adopt a transmissive design. Transmissive spherical lenses, aspherical lenses, or lens groups can be selected, which can effectively avoid light energy loss caused by secondary lens obstruction.

[0067] Based on the aforementioned small-aperture transmission optical telescope, this embodiment provides a free-space quantum key distribution optical system. The system comprises eight parts: a transmission optical telescope 3, a reflector 5, a beam splitter 6, a coupling module 8, a coarse tracking module 4, a fine tracking module 7, a beacon optical module 2, and a control module 9. The system is suitable for quantum communication and laser communication.

[0068] The free-space quantum key distribution optical system is a transceiver integrated system, which can be used as both a transmitter and a receiver, and can be used in combination with each other.

[0069] Employing a transmissive common-aperture design, a single telescope is used to receive beacon light, quantum light, and laser communication light. The transmissive optical telescope 3 eliminates secondary mirror obstruction and vignetting, achieving low energy loss during reception. A reflector 5 and a beam splitter 6 connect the transmissive optical telescope 3, the precision tracking module 7, and the coupling module 8 in series, enabling the quantum light, laser communication light, and beacon light to share a common optical path for transmission and reception. This design features a rational structural layout, minimal space occupation, and miniaturization. The small-aperture transmissive common-aperture optomechanical design utilizes single-mode transmission and a single-mode fiber reception in the rear optical paths of both the transmitting and receiving transmissive optical telescopes, resulting in a compact optomechanical structure, improved space utilization efficiency, reduced system mass, and further miniaturization of the optical system.

[0070] System structure such as Figure 3 As shown, taking the receiving end as an example, the specific details are as follows:

[0071] The transmission-type optical telescope 3 mainly consists of objective lens A and eyepiece B. Objective lens A has a full aperture of 55.9 mm and an effective aperture of 50.8 mm, while eyepiece B has a full aperture of 30.4 mm and an effective aperture of 3.4 mm. Both objective lens A and eyepiece B are composed of transmission-type spherical mirrors. The transmission-type structure design avoids secondary mirror obstruction and reduces beam energy loss. The transmission-type optical telescope is responsible for receiving beacon light, quantum light, and laser communication light, and propagating the received beams to reflector 5.

[0072] The reflector 5, measuring 25.4 mm, is mounted at a 45° angle to the incident optical axis of the transmission optical telescope. It is responsible for refraction and reflection of the light beam, with the reflected optical axis forming a 90° angle with the incident optical axis of the transmission optical telescope. The results are fed back to the control module 9 via the precision camera in the precision tracking module 7. The refraction angle of the reflector is adjustable to track the beacon light in real time. The reflector 5 receives the light beam propagated from the transmission optical telescope, refracts and reflects it, and then sends it to the beam splitter 6, achieving high coupling efficiency of quantum light.

[0073] Beam splitter 6, based on the design of a transmission optical telescope, has a size of 25.4 mm. Its incident optical axis forms a 90° angle with the incident optical axis of the transmission optical telescope, and it is mounted at a 45° angle to the incident optical axis. Beam splitter 6 is a dichroic mirror; the transmission path has a wavelength range of 500-1100 nm with a transmittance T > 90%; the reflection path has a wavelength range of 1100-1600 nm with a reflectivity R > 95%. Beam splitter 6 receives the beam transmitted by reflector 5, splits it according to the wavelength range, and then transmits it to the precision tracking module 7 and the coupling module 8 respectively.

[0074] The fine tracking module 7 receives the beacon light (e.g., 650nm wavelength) through the transmission path of the beam splitter 6. The fine tracking module 7 consists of a 1550nm filter, a fine camera, and a lens. The camera software identifies the position of the beacon light spot relative to the calibration point and feeds it back to the control module 9, which then adjusts the reflector 5 to track the beacon light, thus achieving fine tracking. The position of the calibration point is set according to the position of the beacon light spot in the fine camera when the quantum optical coupling efficiency is highest during the assembly and adjustment stage.

[0075] The coupling module 8 receives quantum light (e.g., 1550nm wavelength) or laser communication light after reflection by the beam splitter 6. The coupling module 8 includes a 1550nm filter, a reflective collimator, and a single-mode fiber. The quantum light or laser communication light is coupled into the single-mode fiber via the reflective collimator for subsequent data collection and processing. In the optical system structure layout, the coupling module 8 is located above the eyepiece B end of the transmission optical telescope, and the incident optical axis of the coupling module 8 is at 180° with the incident optical axis of the transmission optical telescope 3.

[0076] Before receiving quantum light and laser communication light, the optical system needs to perform coarse positioning of the beacon light by capturing it through the coarse tracking module 4. The coarse tracking module 4 consists of a 650nm filter, a coarse camera, and a lens. It identifies the relative position of the light spot through camera software and feeds it back to the control module 9 for coarse positioning. In the optical system structure layout, the coarse tracking module 4 is installed side by side below the transmission optical telescope, that is, the optical axis of the coarse tracking module 4 is parallel to the optical axis of the transmission optical telescope 3.

[0077] The aforementioned camera software all utilizes existing technology.

[0078] Beacon light module 2 emits 650nm visible red light from a beacon laser and is used for capture, tracking, and alignment of inter-system link communication. That is, coarse tracking module 4 and fine tracking module 7 use beacon light to capture, track, and align the link.

[0079] Control module 9 is the logical control center of the entire system, responsible for the control of the entire experimental process, data processing and status monitoring.

[0080] In this embodiment, each module is mounted on the base plate 1, which is mounted on the turntable. The turntable is controlled by a turntable control system (not shown in the figure).

[0081] Control module 9 is connected to the fine tracking camera, coarse tracking camera, and turntable control system via a network port, enabling inter-system communication for acquisition, tracking, and alignment. In the optical system layout, control module 9 is located in the upper left corner of the entire system.

[0082] The coupling module 8 and the fine tracking module 7 share a transmission optical telescope 3 to receive quantum light, laser communication light, and beacon light, respectively. The miniaturized free-space quantum key distribution optical system is a transceiver integrated system, which can function as both a transmitter and a receiver.

[0083] In other embodiments, the system acts as a transmitter, such as... Figure 4 As shown, it includes:

[0084] The transmission-type optical telescope 3 mainly consists of objective lens A and eyepiece B. Objective lens A has a full aperture of 55.9 mm and an effective aperture of 50.8 mm, while eyepiece B has a full aperture of 30.4 mm and an effective aperture of 3.4 mm. Both objective lens A and eyepiece B are composed of transmission-type spherical mirrors. The transmission structure design avoids secondary mirror obstruction and reduces beam energy loss. The laser source propagates as a parallel beam in free space through the coupling module, and reaches the transmission-type telescope module 3 after passing through the reflector 5. The transmission-type optical telescope 3 is responsible for emitting quantum light and laser communication light, and receiving beacon light emitted from distant free space, which is then propagated to the reflector 5.

[0085] The reflector 5 has a size of 25.4 mm and is installed at 45° to the incident optical axis of the transmission optical telescope 3. In some embodiments, the reflector 5 is mounted on a piezoelectric controller and is responsible for refraction and reflection of the light beam. The reflected optical axis is at 90° to the incident optical axis of the telescope.

[0086] The precision camera in the precision tracking module 7 feeds back the results to the control module 9, which in turn activates the piezoelectric control mirror 5 to track the response beacon light in real time. Simultaneously, the mirror 5 receives the beam emitted by the coupling module 8 and reflected by the beam splitter 6, and sends it to the transmission optical telescope 3. It also receives the response beacon light propagated by the transmission optical telescope 3.

[0087] Of course, the piezoelectric controller mentioned above can be selected from existing equipment.

[0088] Beam splitter 6, based on the design of the transmission optical telescope 3, has a size of 25.4 mm. The incident optical axis of beam splitter 6 is at 90° to the incident optical axis of the transmission optical telescope 3, and it is mounted at 45° to the incident optical axis of beam splitter 6. Beam splitter 6 is a dichroic mirror; the transmission path has a wavelength range of 500-1100 nm and a transmittance T > 90%; the reflection path has a wavelength range of 1100-1600 nm and a reflectance R > 95%. Beam splitter 6 receives the response beacon light transmitted by the transmission optical telescope 3 and the reflector 5, and transmits it through the transmission path to the precision tracking module 7. Simultaneously, beam splitter 6 receives quantum light and laser communication light emitted by the coupling module 8, and reflects them through the reflection path to the reflector 5 and the transmission optical telescope 3, and then emits them into free space.

[0089] The fine tracking module 7 receives the response beacon light (e.g., 650nm wavelength) through the beam splitter transmission path. The fine tracking module 7 consists of a 1550nm filter, a fine camera, and a lens. The camera software identifies the position of the response beacon light spot relative to the calibration point and feeds it back to the control module 9, which then adjusts the reflector to track the response beacon light to achieve fine tracking. The calibration point position is set according to the position of the beacon light spot in the fine camera when the quantum optical coupling efficiency is highest during the assembly and adjustment stage.

[0090] The coupling module 8 includes a 1550nm filter, a reflective collimator, and a single-mode fiber. Light sources such as quantum light (e.g., 1550nm wavelength) and laser communication light are emitted as parallel beams into free space after passing through the single-mode fiber and reflective collimator. The beams are then reflected by the reflective path of the beam splitter 6 to the reflector 5 and the transmission optical telescope 3, and then emitted into free space. In the optical system layout diagram, the coupling module 8 is located above the eyepiece end of the transmission optical telescope 3, and the optical axis of the coupling module 8 forms a 180° angle with the incident optical axis of the transmission optical telescope 3.

[0091] The coarse tracking module 4 is used to coarsely locate the response beacon light before the quantum light and laser communication light are emitted. The coarse tracking module 4 consists of a 650nm filter, a coarse camera, and a lens. It identifies the relative position of the light spot using camera software and feeds this information back to the control module 9 for coarse positioning. In the optical system layout diagram, the coarse tracking module 4 is installed parallel to the transmission telescope 3 below it, meaning that the coarse tracking module 4 is parallel to the optical axis of the transmission telescope 3.

[0092] Beacon optical module 2 emits 650nm visible red light from a beacon laser and is used for capture, tracking, and alignment of inter-system link communication. That is, coarse tracking module 4 and fine tracking module 7 use beacon light to capture, track, and align the link.

[0093] Control module 9 is the logical control center of the entire system, responsible for the control of the entire experimental process, data processing, and status monitoring. It connects via Ethernet to the camera in fine tracking module 7, the camera in coarse tracking module 4, the piezoelectric controller, and the turntable control system (not shown in the figure), enabling inter-system communication for acquisition, tracking, and alignment. In the optical system layout diagram, the control module is located in the upper left corner of the entire system.

[0094] In addition, in this embodiment, the optical system can be connected to an existing miniaturized fiber optic quantum key distribution transmitter / receiver terminal, enabling the entire system to be carried and established by a single person; the quantum light or laser communication light is coupled into the single-mode fiber through the reflective collimator of the coupling module, and then narrowband filtering and quantum light detection and laser communication detection are performed, which can extend the application scenario of free space quantum key distribution from nighttime to daytime.

[0095] In some embodiments, the systems serving as transmitters and receivers can be used together to form a communication system.

[0096] The specific working method of a communication system can be as follows: Figure 5 As shown, the transmitting end calculates the location of the receiving end based on GPS coordinates and other methods, and simultaneously transmits a beacon light. Control module 9 controls the turntable to rotate, pointing the beacon light towards the receiving end. The receiving end calculates the location of the transmitting end based on GPS coordinates and other methods, and control module 9 controls the turntable to rotate, so as to capture the beacon light. The receiving end's coarse tracking module detects the beacon light transmitted by the transmitting end, and the receiving end rotates the turntable to align with the transmitting end, bringing the light spot in the coarse camera of the coarse tracking module as close as possible to the center of the camera target surface, completing the acquisition process. After capturing the beacon light, the receiving end transmits a beacon light back to the transmitting end as a response beacon light. After the transmitting end detects the response beacon light emitted by the receiving end from the coarse tracking module, it also rotates the turntable to bring the light spot on the coarse camera of the coarse tracking module closer to the center of the camera target surface. Thus, the coarse tracking process is completed.

[0097] In the rear optical path of both the transmitter and receiver, there is a reflector 5 and a fine tracking module 7. Through the cooperation of the reflector 5 and the turntable, the beacon light transmitted through the transmission optical telescope 3 to the rear optical path is imaged onto the calibration point of the fine camera. The calibration point of the fine camera is the point where the quantum optical coupling efficiency is highest as determined by the system. This completes the fine tracking process. Throughout the communication process, the coarse tracking module 3 / fine tracking module 7 and the control module 9 will continue to operate to ensure the smooth operation of the communication link and to ensure that the quantum optical coupling efficiency transmitted through the transmission optical telescope 3 to the rear optical path is at its highest.

[0098] When the free-space quantum key distribution optical system is used as both the transmitter and receiver, it can be used as a terminal system for free-space quantum communication. One end can be placed on the ground, and the other end can be placed in any location with an unobstructed view, such as the ground, buildings, mountains, or the air, to conduct free-space quantum communication.

[0099] In some embodiments, the free-space quantum key distribution optical system can function as either an independent transmitter or receiver terminal system.

[0100] The above control processes can all employ existing control methods, software, or programs.

[0101] In this embodiment, the overall optical system structure layout is as follows: Figure 3As shown, with the transmission optical telescope 3 as the main center, the beacon light module 2 is located above the objective lens A of the transmission optical telescope, serving as the optical path guide during rapid link establishment, bidirectional loop closure, and acquisition tracking. The coarse tracking module 4 is located below the transmission optical telescope 3, performing coarse acquisition tracking of the beacon light during terminal link establishment. The reflector 5 is located at the right end of the eyepiece B of the transmission optical telescope 3, and the normal of the reflector 5 forms a 45° angle with the optical axis of the transmission optical telescope 3.

[0102] In this embodiment, the beam splitter 6 is located between the reflecting mirror 5 and the fine tracking module 7, with its incident optical axis forming a 90° angle with the incident optical axis of the transmission optical telescope 3. The fine tracking module 7 is located at the upper right of the overall optical system, with its incident optical axis forming a 90° angle with the optical axis of the transmission optical telescope 3. The control module 9 is located at the upper left of the overall optical system. The coupling module 8 is located above the eyepiece B end of the transmission optical telescope 3 and is installed between the control module 9 and the fine tracking module 7.

[0103] Of course, in other embodiments, the placement of the modules can be changed or adjusted according to their physical size and structure, such as... Figure 6 As shown, as long as the positional relationship meets the optical path requirements, it's acceptable. These are the ones that are easy to think of.

[0104] In other embodiments, the above modules can be arranged in a more compact layout through structural and positional configurations.

[0105] Similarly, in other embodiments, the wavelength of light in this embodiment can also be adjusted according to quantum key distribution requirements, and is not limited to the parameter range provided in this embodiment.

[0106] To enable those skilled in the art to better understand this system, its working method is described as follows:

[0107] When the system acts as a transmitter, the working process is as follows:

[0108] The beacon light (using the 650 GHz band as an example) is emitted in free space by beacon light module 2;

[0109] After the coarse tracking camera detects the response beacon light emitted by the receiver, the control module 9 controls the rotating turntable to bring the light spot on the coarse camera closer to the center of the camera target surface, thus completing the coarse tracking process.

[0110] In the fine tracking stage, the response beacon light passes through the transmission optical telescope 3 and is incident on the reflector 5. After being reflected by the reflector 5, it reaches the beam splitter 6. After being transmitted through the beam splitter 6, the response beacon light reaches the fine tracking module 7. The beam is converged by the lens and responds on the target surface of the fine camera. The fine tracking module 7 detects and captures the position of the response beacon light in real time and performs real-time precise tracking of the response beacon light.

[0111] The optical path of the quantum light before emission: The quantum light emitted by the quantum laser is collimated in free space after passing through a single-mode fiber and coupling module 8. Specifically, the collimator of coupling module 8 emits collimated quantum light, which is reflected by beam splitter 6 and then reaches reflector 5. After being reflected by reflector 5, it reaches transmission optical telescope 3. The quantum light then passes through eyepiece B and objective lens A in sequence before being expanded and emitted.

[0112] The optical path of the laser communication light before transmission: The laser communication light emitted by the laser is collimated in free space after passing through a single-mode fiber and coupling module 8. Specifically, the collimator of coupling module 8 emits collimated laser communication light, which is reflected by beam splitter 6 and then reaches reflector 5. After reflection by reflector 5, it reaches transmission optical telescope 3. The laser communication light then passes through eyepiece B and objective lens A in sequence before being expanded and emitted.

[0113] When the system acts as a receiver, the working process is as follows:

[0114] The optical path of the beacon light emitted by the beacon light module 2 at the transmitting end is as follows: In the coarse tracking stage, the beacon light emitted from the distant transmitting end is focused on the coarse camera target surface by the lens of the coarse tracking module 4. The control module 9 calculates and controls the turntable to perform coarse positioning, capture and track the beacon light. After the beacon light is captured, the beacon light module 2 emits the beacon light back to the transmitting end as a response beacon light. In the fine tracking stage, the beacon light passes through the objective lens A and eyepiece B of the transmission optical telescope 3 in sequence. The parallel light after beam contraction is incident on the reflector 5. After being reflected by the reflector 5, it reaches the beam splitter 6. The transmission path of the beam splitter 6 is 500nm-1100nm. After being transmitted through the beam splitter 6, the beacon light reaches the fine tracking module 7. The beam is focused by the lens and responds on the fine camera target surface. The fine tracking module 7 detects and captures the position of the beacon light at the transmitting end in real time. The control module 9 controls the turntable and reflector 5 to perform real-time and precise tracking of the beacon light.

[0115] The above calculation and control processes can all be performed using existing methods or software.

[0116] The optical path of the quantum light received by the receiver: The quantum light passes sequentially through the objective lens A and eyepiece B of the transmission optical telescope 3. The parallel light after beam contraction is incident on the reflector 5. After being reflected by the reflector 5, it reaches the beam splitter 6. The reflection path of the beam splitter 6 is 1100nm-1600nm. After being reflected by the beam splitter 6, the quantum light reaches the coupling module 8. It is coupled into the single-mode fiber by the reflective collimator and then processed to realize the coupling of the quantum light.

[0117] The optical path of the laser communication light received by the receiver: The laser communication light passes through the objective lens A and eyepiece B of the transmission optical telescope 3 in sequence. The parallel light after beam contraction is incident on the reflector 5. After being reflected by the reflector 5, it reaches the beam splitter 6. After being reflected by the beam splitter 6, it reaches the coupling module 8 for subsequent processing. The laser communication light is coupled through a single-mode fiber to achieve coupling of the laser communication light.

[0118] The above description is merely a preferred embodiment of this utility model and is not intended to limit the scope of this utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, or improvements made by those skilled in the art without creative effort within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A free-space quantum key distribution optical system, characterized by, The application relates to a quantum optical communication system, which comprises a base plate installed on a rotating table, a transmission optical telescope, a mirror, a light splitter, a fine tracking module, a coupling module, a coarse tracking module, a beacon light module and a control module arranged on the base plate. The transmission optical telescope is arranged in the middle of the base plate and is used for transmitting quantum light and laser communication light and receiving response beacon light from a remote free space or receiving beacon light, quantum light and laser communication light and transmitting the received light beams to the mirror. The mirror is arranged on one side of the transmission optical telescope and is used for tracking beacon light or response beacon light, receiving quantum light and laser communication light transmitted by the coupling module and reflected by the light splitter and transmitting the light beams to the transmission optical telescope, receiving response beacon light transmitted by the transmission optical telescope or receiving beacon light, quantum light and laser communication light transmitted by the transmission optical telescope, reflecting the light beams to the light splitter, and the normal line of the mirror is at an angle of 45 degrees with the optical axis of the transmission optical telescope. The light splitter is arranged between the fine tracking module and the mirror and has an incident optical axis at an angle of 90 degrees with the incident optical axis of the transmission optical telescope and is used for receiving quantum light and laser communication light transmitted by the coupling module, reflecting the light beams to the mirror and the transmission optical telescope and transmitting the light beams to the free space or receiving the light beams reflected by the mirror, respectively transmitting the light beams to the fine tracking module and the coupling module after wavelength division. The coupling module is arranged above the ocular end of the transmission optical telescope and is used for coupling quantum light or laser communication light. The beacon light module is arranged above the objective end of the transmission optical telescope and is used for transmitting beacon light. The fine tracking module has an incident optical axis at an angle of 90 degrees with the incident optical axis of the transmission optical telescope and is connected with the control module. The coarse tracking module is arranged below the transmission optical telescope and is connected with the control module. The control module is arranged on the upper left side of the base plate and is used for connecting and controlling the coarse tracking module, the fine tracking module and the mirror.

2. A free-space quantum key distribution optical system as claimed in claim 1, characterized in that The transmission optical telescope comprises an objective and an ocular, the objective and the ocular are composed of transmission spherical lenses, aspherical lenses or lens groups, the focal point of the objective coincides with the virtual focal point of the ocular, and the focal points are arranged between the objective and the ocular.

3. A free-space quantum key distribution optical system as claimed in claim 2, characterized in that The full aperture of the objective is 55.9 mm, the effective aperture is 50.8 mm, the curvature radius R1 of the incident surface of the objective is 114.949 mm, the exit surface R2 of the objective is a plane, the central thickness of the objective is 10 mm, the full aperture of the ocular is 30 mm, the effective aperture is 3.4 mm, the curvature radius R3 of the incident surface of the ocular is 49.955 mm, the curvature radius R4 of the exit surface of the ocular is -8.975 mm, the central thickness t2 of the ocular is 1.25 mm, and the mirror spacing of the objective and the ocular is 231 mm.

4. A free-space quantum key distribution optical system as claimed in claim 1, characterized in that The transmission optical telescope comprises an objective and an ocular, the objective and the ocular are composed of transmission spherical lenses, aspherical lenses or lens groups, the focal point of the objective coincides with the virtual focal point of the ocular.

5. A free-space quantum key distribution optical system as claimed in claim 4, characterized in that The full aperture of the objective lens is 55.9 mm, the effective aperture is 50.8 mm, the curvature radius R1 of the objective lens entrance surface is 114.949 mm, the objective lens exit surface R2 is a plane, and the center thickness is t1=10 mm; the full aperture of the eyepiece is 30.4 mm, the effective aperture is 3.4 mm, the curvature radius R3 of the eyepiece entrance surface is-8.849 mm, the curvature radius R4 of the eyepiece exit surface is 60.631 mm, the center thickness t2 is 1.5 mm, and the mirror spacing of the objective lens and the eyepiece is 200.912 mm.

6. A free-space quantum key distribution optical system as claimed in claim 1, characterized in that The mirror is installed at an angle of 45° with the incident optical axis of the transmission optical telescope, and is used for folding and reflecting the light beam, and the reflected optical axis is at an angle of 90° with the incident optical axis of the transmission optical telescope.

7. A free-space quantum key distribution optical system as claimed in claim 1, characterized in that, The beamsplitter is installed at a position at an angle of 45° with the incident optical axis thereof. Alternatively, the beamsplitter is a dichroic beamsplitter, the wavelength range of the transmission path is 500-1100 nm, the transmittance T is greater than 90%, and the wavelength range of the reflection path is 1100-1600 nm, the reflectivity R is greater than 95%.

8. A free-space quantum key distribution optical system as claimed in claim 1, characterized in that, The fine tracking module comprises a filter, a fine camera and a lens, the filter is arranged in front of the lens of the fine camera, and the fine camera is connected with the control module. The coarse tracking module comprises a filter, a coarse camera and a lens, the filter is arranged in front of the lens of the coarse camera, and the coarse camera is connected with the control module. The optical axis of the coarse tracking module is parallel to the optical axis of the transmission optical telescope.

9. A free-space quantum key distribution optical system as claimed in claim 1, characterized in that, The coupling module comprises a filter, a reflective collimator and a single-mode optical fiber, the filter is arranged in front of the reflective collimator, and the reflective collimator is connected with the single-mode optical fiber. Alternatively, the incident optical axis of the coupling module is at an angle of 180° with the incident optical axis of the transmission optical telescope.

10. A free-space quantum key distribution optical system as claimed in claim 1, characterized in that, The turntable is provided with a turntable control system, and the movement of the turntable is controlled by the turntable control system. The control module is connected with the coarse tracking module, the fine tracking module, the mirror and the turntable control system through a network port.

11. A communication system characterized by The system comprises at least one free-space quantum key distribution optical system as claimed in any one of claims 1-10, which serves as a transmitting end or a receiving end. Alternatively, the system comprises two free-space quantum key distribution optical systems as claimed in any one of claims 1-10, one of which serves as a transmitting end and the other serves as a receiving end.

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