A small airborne laser communication terminal based on single-mode launch and multi-mode receive

Abstract

This invention discloses a small airborne laser communication terminal based on single-mode transmission and multi-mode reception, including a signal transmission and beacon transmission module and a signal reception and beacon reception module. The beacon light in the signal transmission and beacon transmission module is emitted at a specific half-divergence angle, and the signal light is also emitted at a specific half-divergence angle. After propagating a certain distance in free space, the signal light and beacon light are received by the receiving telescope, which focuses the beacon light onto the camera target surface. The pointing angle of the three-axis gimbal is driven based on the position error signal of the beacon light spot, completing the bidirectional alignment of the telescope. This invention employs a small and lightweight laser communication system, which improves fiber coupling efficiency, reduces signal light link loss, and has better robustness to atmospheric turbulence and platform vibration, making it suitable for use on UAVs for free-space optical communication experiments.

Description

Technical Field

[0001] This invention relates to the field of free-space laser communication, and more particularly to a small airborne laser communication terminal suitable for use on UAVs for free-space optical communication, based on single-mode transmission and multi-mode reception. Background Technology

[0002] Free-space optical (FSO) communication is a communication technology based on the propagation of light signals in free space. It boasts advantages such as high bandwidth, high speed, and resistance to electromagnetic interference, and is widely used in satellite communication, UAV communication, and high-speed terrestrial communication. Free-space laser communication links established based on UAV platforms also offer advantages such as high mobility and flexible deployment. In existing technologies, large-aperture reflecting telescopes are typically used to achieve free-space optical communication. First, an acquisition, point, and tracking (APT) system is used to align and track the beacon optical link. Then, signal optical communication occurs between the two telescopes. Traditionally, the reflecting telescope is used as an optical antenna to receive the signal light, and then a rear optical path is used to couple the signal light into a single-mode fiber to complete signal reception. However, in practical applications, environmental factors such as vibration and atmospheric turbulence can increase the alignment error between the telescopes, thus reducing the coupling efficiency of the single-mode fiber. Therefore, traditional FSO systems typically require very high alignment accuracy and generally have the disadvantages of large size and weight, making them unsuitable for laser communication on mobile platforms with low payloads, such as UAVs.

[0003] In existing technologies, single-mode fiber has a small mode field diameter, and the alignment accuracy requirements for angle and position during fiber coupling are very high. However, due to interference from complex external environmental factors such as alignment errors, vibration, and atmospheric turbulence, the coupling efficiency of single-mode fiber in practical FSO systems is low, which reduces communication quality and stability. Currently, most optical antennas in FSO systems are relatively bulky and unsuitable for mounting on low-payload mobile platforms such as UAVs for laser communication. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a small airborne laser communication terminal suitable for use on drones for free-space optical communication, based on single-mode transmission and multi-mode reception.

[0005] Technical Solution: The small airborne laser communication terminal based on single-mode transmission and multi-mode reception described in this invention includes a signal transmission and beacon transmission module and a signal reception and beacon reception module. The beacon light in the signal transmission and beacon transmission module is emitted with a half-divergence angle of 1°, and the signal light is emitted with a half-divergence angle of 200 μrad. After the signal light and beacon light propagate a certain distance in free space, they are received by the receiving telescope, which focuses the beacon light onto the camera target surface. The pointing angle of the three-axis gimbal is driven according to the position error signal of the beacon light spot to complete the bidirectional alignment of the telescope.

[0006] Furthermore, the signal receiving and beacon receiving module includes a window, a transmissive optical antenna, a first dichroic beam splitter, a signal light focusing lens group, a beacon light focusing lens, a camera, and a multimode fiber. The signal light receiving and beacon light receiving share a single transmissive optical antenna. After being split by the first dichroic beam splitter, the signal light is coupled into the multimode fiber by the focusing lens group in the transmission path, and the beacon light is focused onto the camera target surface by the beacon light focusing lens in the reflection path.

[0007] Furthermore, both the signal transmission module and the beacon transmission module include an optical fiber ferrule, a glass sleeve, and a Clens. The optical fiber ferrule and the Clens are housed inside the glass sleeve. The signal transmission module uses single-mode optical fiber, which is collimated by the Clens and transmits at a half-divergence angle of 200 μrad. The beacon transmission module uses single-mode optical fiber, which is collimated by the Clens and transmits at a half-divergence angle of 35 mrad.

[0008] Furthermore, the transmissive optical antenna is arranged in sequence with a biconvex lens, a meniscus lens, and a biconcave lens.

[0009] Furthermore, the signal light focusing lens group is arranged in sequence as a biconcave lens and a plano-convex lens.

[0010] Furthermore, in the signal transmission and beacon transmission module, the signal light is emitted from a single-mode optical fiber, passes through a signal transmission lens, a second dichroic beam splitter, and a right-angle prism, and then exits from the center of the telescope's main mirror.

[0011] Furthermore, in the signal transmission and beacon transmission module, the beacon light is emitted from the multimode fiber, passes through the beacon transmission lens, the second dichroic beam splitter, and the right-angle prism, and then also exits from the center of the telescope's main mirror.

[0012] Furthermore, in the signal transmission and beacon transmission module, the optical axis of the signal beam, the optical axis of the beacon beam, and the optical axis of the telescope primary mirror are all coincident.

[0013] Furthermore, the tracking accuracy of the signal receiving and beacon receiving modules is controlled by the angle of the three-axis gimbal, and multimode optical fiber with a large receiving angle is used at the signal receiving end.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0015] (1) The present invention uses a 50 mm small aperture, transmission type optical antenna. The compact optical design makes the overall size and weight of the system very small. The small-lightweight laser communication system can improve the fiber coupling efficiency, reduce the signal optical link loss, and has better robustness to atmospheric turbulence and platform vibration. It is suitable for carrying out free space optical communication experiments on UAVs.

[0016] (2) The present invention adopts a design method of transmitting signal light with single-mode fiber and receiving signal light with multi-mode fiber, which realizes a low-loss optical communication link, reduces the alignment accuracy requirements of the telescope, and at the same time has better suppression of optical link loss fluctuations caused by atmospheric turbulence and platform jitter. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of a laser communication terminal based on multimode fiber reception.

[0018] Figure 2 This is a structural diagram of an 878 nm beacon light emitting module;

[0019] Figure 3 This is a structural diagram of a 1550 nm signal light emitting module. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0021] The small airborne laser communication terminal based on single-mode transmission and multi-mode reception described in this invention utilizes a combination of single-mode fiber and a transmitting lens at the signal transmitting end to reduce the divergence angle of the signal light, enabling the system to perform laser communication over long distances. At the signal receiving end, a transmission-type optical antenna, a focusing lens group, and multi-mode fiber are used to receive the signal light, and the signal light is coupled into the multi-mode fiber with low loss. Compared to single-mode fiber, multi-mode fiber has a larger core diameter and higher nanometer density (NA), which not only effectively improves fiber coupling efficiency but also reduces the accuracy requirements for telescope alignment and provides better robustness to vibrations and atmospheric turbulence in UAV platforms. Furthermore, for a small and lightweight design, this invention employs a compact optical system design, keeping the weight of the entire system below 1 kg.

[0022] The miniaturized and lightweight laser communication system of this invention improves fiber coupling efficiency, reduces signal optical link loss, and exhibits better robustness to atmospheric turbulence and platform vibration, making it particularly suitable for free-space optical communication mounted on UAVs. The overall design parameters of the system are shown in Table 1. Its specific structure mainly includes a signal transmission and beacon transmission module and a signal reception and beacon reception module. A schematic diagram of the entire system is shown below. Figure 1 As shown.

[0023] Table 1

[0024] category parameter Light aperture 50 mm Operating wavelength Signal light @1550 nm; Beacon light @878.6 nm Receiving half field of view Signal light@200 μrad; Beacon light@35 mrad focal length Signal beam @ 108 mm; Beacon beam @ 92.7 mm 1550nm multimode fiber Core diameter: 62.5 μm, NA = 0.22 878nm multimode fiber Core diameter 200 μm, NA=0.22 1550nm single-mode fiber Core diameter: 8.2 μm, NA = 0.12 Output beam half divergence angle Signal light@200 μrad; Beacon light@35 mrad beacon camera Target surface size: 4.97 mm * 3.72 mm; resolution: 720 * 540; pixel size: 6.9 μm

[0025] The signal receiving and beacon receiving module mainly consists of a window, a transmission optical antenna, a first dichroic beam splitter 5, a signal light focusing lens group and a beacon light focusing lens, a camera, and a multimode fiber. The signal light and beacon light receive share a single transmission optical antenna. After being split by the dichroic beam splitter 5, the signal light is coupled into the multimode fiber by the focusing lens group in the transmission path, while the beacon light is focused onto the camera target surface by the beacon light focusing lens in the reflection path.

[0026] The transmissive optical antenna includes a biconvex lens 2, a meniscus lens 3, and a biconcave lens 4. The signal light focusing lens group includes a biconcave lens 6 and a plano-convex lens 7. The beacon light focusing lens is a meniscus lens 8.

[0027] Signal transmitting unit and beacon transmitting unit, such as Figure 2 and Figure 3 As shown, both the signal and beacon transmitting units consist of three parts: fiber optic ferrules, glass sleeves, and a Clens. The end faces of the fiber optic ferrules are designed with an 8° tilt to improve return loss. The signal fiber is single-mode fiber, which, after being collimated by the Clens, is emitted at a half-divergence angle of 200 μrad. The beacon fiber is multimode fiber, which, after being collimated by the Clens, is emitted at a half-divergence angle of 35 mrad.

[0028] The specific implementation plan is as follows:

[0029] (1) Signal light and beacon light emission

[0030] A 1550 nm signal beam emerges from a single-mode fiber, passes through a signal transmitting lens 11, a second dichroic beam splitter 10, and a right-angle prism 9, and then exits from the center of the telescope's primary mirror, with a half-divergence angle of 200 μrad. An 878.6 nm beacon beam emerges from a multimode fiber, passes through a beacon transmitting lens 12, a second dichroic beam splitter 10, and a right-angle prism 9, and also exits from the center of the telescope's primary mirror. The optical axes of the signal beam, the beacon beam, and the primary mirror coincide.

[0031] (2) Beacon tracking and signal transmission and reception

[0032] To make the system smaller and lighter, this invention uses a single-stage CMOS closed-loop feedback scheme instead of a multi-stage tracking system, with the three-axis gimbal serving as the sole feedback actuator. Therefore, the tracking accuracy of the system is determined by the angle control accuracy of the three-axis gimbal. Furthermore, to achieve lower signal optical transmission loss in a single-stage tracking feedback loop, a multimode fiber with a larger receiving angle is used at the signal receiver, reducing the tracking system's requirements for tracking accuracy.

[0033] The specific beacon tracking and signal transmission / reception process of this invention is as follows: The beacon light from the transmitting party is emitted with a half-divergence angle of 1°, and the signal light is emitted with a half-divergence angle of 200 μrad. After propagating a certain distance in free space, the signal light and beacon light are received by the receiving telescope, which focuses the beacon light onto the camera target surface. The pointing angle of the three-axis gimbal is driven based on the position error signal of the beacon light spot, completing the bidirectional alignment of the telescope. After the bidirectional alignment of the telescope is completed, the signal light coupling efficiency of the transmission path will also reach its maximum value, achieving low-loss signal light transmission.

Claims

1. A small airborne laser communication terminal based on single-mode transmission and multi-mode reception, characterized in that, It includes a signal transmitting and beacon transmitting module and a signal receiving and beacon receiving module. In the signal transmitting and beacon transmitting module, the beacon light is emitted at a specific half-divergence angle, and the signal light is emitted at a specific half-divergence angle. After the signal light and beacon light propagate a certain distance in free space, they are received by the receiving telescope, which focuses the beacon light onto the camera target surface. The pointing angle of the three-axis gimbal is driven by the position error signal of the beacon light spot to complete the bidirectional alignment of the telescope.

2. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 1, characterized in that, The signal receiving and beacon receiving module includes a window (1), a transmission optical antenna, a first dichroic beam splitter (5), a signal light focusing lens group, a beacon light focusing lens, a camera, and a multimode fiber. The signal light receiving and beacon light receiving share a transmission optical antenna. After being split by the first dichroic beam splitter (5), the signal light is coupled into the multimode fiber by the focusing lens group in the transmission path, and the beacon light is focused on the camera target surface by the beacon light focusing lens in the reflection path.

3. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 1, characterized in that, Both the signal transmission module and the beacon transmission module include an optical fiber ferrule (14), a glass sleeve (15), and a Clens (16). The optical fiber ferrule (14) and the Clens (16) are fitted inside the glass sleeve (15). The optical fiber type of the signal transmission module is single-mode optical fiber, which is collimated by the Clens (16) and then transmitted at a specific half-divergence angle. The optical fiber type of the beacon transmission module is single-mode optical fiber, which is collimated by the Clens (16) and then transmitted at a specific half-divergence angle.

4. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 2, characterized in that, The transmissive optical antenna is arranged in sequence with a biconvex lens (2), a meniscus lens (3), and a biconcave lens (4).

5. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 2, characterized in that, The signal light focusing lens group is arranged in sequence as a biconcave lens (6) and a plano-convex lens (7).

6. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 1, characterized in that, In the signal transmission and beacon transmission module, the signal light is emitted from a single-mode fiber, passes through the signal transmission lens (11), the second dichroic beam splitter (10), and the right-angle prism (9), and then exits from the center of the telescope's main mirror.

7. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 1, characterized in that, In the signal transmission and beacon transmission module, the beacon light is emitted from the multimode fiber, passes through the beacon transmission lens (12), the second dichroic beam splitter (10) and the right-angle prism (9), and then also exits from the center of the telescope's main mirror.

8. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 1, characterized in that, In the signal transmission and beacon transmission module, the optical axes of the signal beam, the beacon beam, and the telescope primary mirror coincide.

9. The small airborne laser communication terminal based on single-mode transmission and multi-mode reception according to claim 1, characterized in that, The tracking accuracy of the signal receiving and beacon receiving modules is controlled by the angle of the three-axis gimbal, and multimode optical fiber with a large receiving angle is used at the signal receiving end.

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