A Variable Beam Divergence Angle Laser Communication Terminal and Its Fast Acquisition Method

Abstract

The present invention discloses a variable beam divergence angle laser communication terminal and a rapid acquisition method thereof, belonging to the technical field of optical communication devices, including a main telescope, a fine tracking fast steering mirror, a beam splitter, a filter, a beam splitter, a beacon receiving lens group, a beacon detector, a signal transmitting mirror group, a pre-aiming fast steering mirror, a signal receiving mirror group, a receiving fiber amplifier, a multi-core fiber splitter, an optical switch, and a transmitting fiber amplifier, which constitute a signal light transmitting optical path, a beacon light receiving optical path, and a signal light receiving optical path; the signal light transmitting optical path provides a transmitting beam through different mode field fibers, and uses different paths of the transmitting mirror group to shape and variably beam-divergence emit the transmitted light, the signal light receiving optical path is used to collect, shape, couple, and optically amplify the input signal light, and the beacon light receiving optical path is used to collect, shape, converge the input signal light, and use an image positioning detector to position the target light spot. The present invention can improve the efficiency of long-distance acquisition.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication devices, and particularly relates to a variable beam divergence angle laser communication terminal and a rapid capture method thereof. Background Art

[0002] Compared with the existing microwave communication technology, satellite laser communication technology has significant advantages such as high data rate, anti-interference, and good confidentiality, and is an effective supplementary technical means for future satellite communication. Compared with the traditional microwave communication system, the laser communication system uses the optical wave band as the information carrier (carrier 10 - 400 THz), has an extremely high communication bandwidth, and at the same time has the outstanding advantages of light weight, small volume, and low power consumption, and is widely used in various occasions such as space, atmosphere, and underwater.

[0003] However, in order to meet the requirements of long-distance communication, the emission beam divergence angle of general laser communication terminals is generally designed to be small, adopting a near diffraction limit design (such as between satellites and between satellite and ground). Due to various factors such as the operating position of the laser communication terminal flight platform, structural deformation, platform attitude, and time synchronization accuracy, there are large aiming errors, large mutual uncertainty regions, and long scanning and capture times during the laser communication link establishment process. Especially in the first link establishment, due to the unknown error characteristics of the uncertainty region, the initial link establishment is more difficult.

[0004] Especially for a beaconless laser communication terminal, since there is no large beam divergence angle beacon optical path independent of the communication band, but through the coarse and fine scanning of the compound axis to achieve coverage of the uncertainty region. This method requires strict synchronization between the transceiver parties, coordinated target response actions, and an extremely short spot response time, all of which result in difficult two-way capture and link establishment and low success rate.

[0005] However, the current traditional terminals have the following problems: 1) low capture and scanning efficiency, 2) long capture time, 3) low capture success rate. Summary of the Invention

[0006] In view of the above problems, the present invention proposes a variable beam divergence angle laser communication terminal and a rapid capture method thereof. Through the variable beam divergence angle design based on a multi-core optical fiber splitter and supplemented by corresponding capture and tracking strategies, it can achieve a 20 - 100-fold increase in the coverage efficiency of the beacon light compared with the traditional laser communication, and at the same time significantly reduce the capture time (reduced to 1 / 5 - 1 / 10), improve the long-distance capture and establishment efficiency, and can be widely used in beacon light / signal light terminals with a small beam divergence angle.

[0007] The above object is achieved by the following technical solutions:

[0008] The present invention first provides a variable beam divergence angle laser communication terminal, which includes the following optical elements: a main telescope, a fine tracking fast steering mirror, a beam splitter, a filter, a beam splitter, a beacon receiving lens group, a beacon detector, a signal transmitting mirror group, an early aiming fast steering mirror, a signal receiving mirror group, a receiving fiber amplifier, a multi-core fiber splitter, an optical switch, a transmitting fiber amplifier. The above optical elements constitute a signal light transmitting optical path, a beacon light receiving optical path, and a signal light receiving optical path; wherein:

[0009] The signal light transmitting optical path provides a transmitting beam through different mode field fibers, and uses different paths of the transmitting mirror group to shape and variably emit the transmitted light, including a main telescope, a fine tracking fast steering mirror, a beam splitter, a signal transmitting mirror group, an early aiming fast steering mirror, a multi-core fiber splitter, an optical switch, a transmitting fiber amplifier; the transmitting fiber amplifier amplifies the input transmitted signal light and outputs it to the optical switch. Under the command control, the optical switch transmits the input amplified beam to fibers with different mode fields / core diameters respectively, and inputs them to the discrete fiber ends of the multi-core fiber splitter through different fibers. The multi-core fiber splitter integrates fibers with multiple different core diameters into the same fiber ceramic core, and inputs it to the optical antenna. The input beam is incident on the signal transmitting mirror group, and after being reflected by the coaxiality adjustment of the early aiming fast steering mirror, it is incident on the main telescope after being tracked and reflected by the beam splitter and the fine tracking fast steering mirror, and finally exits the terminal;

[0010] The signal light receiving optical path is used to collect, shape, couple, and optically amplify the input signal light, including a main telescope, a fine tracking fast steering mirror, a beam splitter, a filter, a beam splitter, a signal receiving mirror group, a receiving fiber amplifier; the beam received by the main telescope is reflected by the fine tracking fast steering mirror, and after being split by the beam splitter, it is incident on the signal receiving mirror group after being reflected by the filter and the beam splitter, and is focused and coupled into the receiving fiber, and is transmitted to the receiving fiber amplifier through the fiber for optical amplification, and is transmitted to the photodetector for optical demodulation;

[0011] The beacon light receiving optical path is used to collect, shape, converge the input signal light, and use an image positioning detector to position the target light spot, including a main telescope, a fine tracking fast steering mirror, a beam splitter, a filter, a beam splitter, a beacon receiving lens group, a beacon detector. The beam received by the main telescope is reflected by the fine tracking fast steering mirror, and after being split by the beam splitter, it is incident on the beacon receiving lens group after being reflected by the filter and the beam splitter, and is focused on the target surface of the beacon detector to realize the identification and positioning of the light spot. The multi-core fiber splitter has two interfaces, a multi-way end and a few-way end.

[0012] Further, the multi-channel end of the multi-core optical fiber splitter uses N optical fiber cores made of ceramics or metals, and each optical fiber core is independent of each other, where N≥2; the few-channel end of the multi-core optical fiber splitter is to integrate multiple optical fiber cores at the multi-channel end onto M optical fiber cores on the same optical fiber connector at the few-channel end, where M≥1 and M<N.

[0013] Further, the deflection stroke L1 of the pre-aiming fast steering mirror satisfies the condition: where dmax represents the adjustment distance of each optical fiber at the few-channel end of the multi-core optical fiber splitter, and f1 is the focal length of the signal transmitting mirror group.

[0014] The present invention also provides a method for fast acquisition using the above variable beam divergence angle laser communication terminal, and the method includes the following steps:

[0015] S1. Select the beam divergence angle φ according to different working distances, and calculate the receivable power P of the beam divergence angle reaching the target beacon detector r :

[0016] P r =P t ·η ot ·L r ·η s ·L PAT ·η or

[0017] In the formula: P r is the detector receiving power; P t is the emission power of the emission light source; η ot is the efficiency of the emission optical unit; L r is the space transmission loss, and its expression is: where D is the receiving aperture, θ is the laser beam divergence angle, and L is the link distance; η s is the power loss caused by the channel; L PAT is the power loss caused by the PAT alignment mismatch; η or is the efficiency of the receiving optical system; in the design, P r should be greater than P CCD-min , P CCD-min is the minimum receivable power that the beacon detector can work, that is, the sensitivity threshold;

[0018] S2. And according to the beam divergence angle, the fiber mode field diameter j of the corresponding output optical fiber at the few-channel end of the multi-core optical fiber splitter can be calculated, where F is the equivalent emission focal length of the signal light emission optical path, and the fiber mode field diameter J of the multi-channel end of the multi-core optical fiber splitter is obtained;

[0019] S3. According to the requirements of different divergence angles φi, repeat the processes of S1 and S2 respectively, and obtain different multi-channel end fiber mode field diameters Ji, and obtain the corresponding relationships (φ1, J1), (φ2, J2) … (φm, Jm);

[0020] S4: Based on different multi-channel end fiber mode field diameters Ji and the quantity, design the fiber distribution topologies with different mode field diameters on the few-channel end fiber end face of the multi-core fiber splitter. The distribution topologies include but are not limited to concentric circle distribution, square distribution, and star distribution;

[0021] S5. The distance from each fiber core at the few-channel end to the geometric center of the fiber end face is di, then the included angle relative to the geometric center of the few-channel end fiber end face is The corresponding angle position for pre-aiming the fast steering mirror is βi (βi = Ωi × η, where η is the angle magnification factor of the pre-aiming fast steering mirror);

[0022] S6. During the operation of the laser terminal, according to the requirements of different divergence angles φ i control the optical switch to switch to the corresponding φi;

[0023] S7. Control the deflection angle position βi of the pre-aiming fast steering mirror, and the laser terminal realizes the beam emission with a divergence angle of φi;

[0024] S8: The total stroke Β of the pre-aiming fast steering mirror should satisfy Β > (βmax - βmin), where βmax is the maximum rotation angle of the pre-aiming fast steering mirror, and βmin is the minimum rotation angle of the pre-aiming fast steering mirror.

[0025] Beneficial effects:

[0026] Through the switching of the optical switch, the selection of the multi-core fiber splitter, and the deflection of the pre-aiming fast steering mirror, the present invention realizes the function of accurately adjustable stepped divergence angles of the emitted beam of the laser communication terminal. This technology can be widely used in various terminals. After testing, it is proved that compared with the traditional laser communication system, the spot coverage efficiency of the present invention is increased by 20 - 100 times, and the acquisition time of both parties is reduced to 1 / 5 - 1 / 10 of the original, significantly improving the link establishment performance of the laser communication terminal. Description of the drawings

[0027] Figure 1 is the system structure diagram of the present invention;

[0028] Figure 2 is the structural schematic diagram of the multi-core fiber splitter of the present invention;

[0029] Description of the reference numerals in the drawings: 1. Main telescope; 2. Fine tracking fast steering mirror; 3. Beam splitter; 4. Filter; 5. Beam splitter; 6. Beacon receiving lens group; 7. Beacon detector; 8. Signal transmitting mirror group; 9. Pre-aiming fast steering mirror; 10. Signal receiving mirror group; 11. Receiving fiber optic amplifier; 12. Multi-core fiber optic splitter; 13. Optical switch; 14. Transmitting fiber optic amplifier. Detailed implementation manners

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] As shown Figure 1 in the figure, a variable beam divergence angle laser communication terminal in this embodiment includes the following optical elements: main telescope 1, fine tracking fast steering mirror 2, beam splitter 3, filter 4, beam splitter 5, beacon receiving lens group 6, beacon detector 7, signal transmitting mirror group 8, pre-aiming fast steering mirror 9, signal receiving mirror group 10, receiving fiber optic amplifier 11, multi-core fiber optic splitter 12, optical switch 13, and transmitting fiber optic amplifier 14. The above optical elements constitute a signal light transmitting optical path, a beacon light receiving optical path, and a signal light receiving optical path; where:

[0032] The signal light transmitting optical path provides a transmitting beam through different mode field fibers, and uses different paths of the transmitting mirror group to shape and variably beam-divergence-emit the transmitted light, including main telescope 1, fine tracking fast steering mirror 2, beam splitter 3, signal transmitting mirror group 8, pre-aiming fast steering mirror 9, multi-core fiber optic splitter 12, optical switch 13, and transmitting fiber optic amplifier 14; the transmitting fiber optic amplifier 14 amplifies the input transmitted signal light and outputs it to the optical switch 13. Under the command control, the optical switch 13 transmits the input amplified beam to fibers with different mode fields / core diameters respectively, and inputs the fibers with different core diameters to the discrete fiber ends of the multi-core fiber optic splitter 12. After the multi-core fiber optic splitter 12 integrates multiple fibers with different core diameters into the same fiber ceramic core, and inputs it to the optical antenna, the input beam is incident on the signal transmitting mirror group 8, and after being reflected by the coaxiality adjustment of the pre-aiming fast steering mirror 9, it is incident on the main telescope 1 after being tracked and reflected by the beam splitter 3 and the fine tracking fast steering mirror 2, and finally exits the terminal;

[0033] The signal light receiving optical path is used to collect, shape, couple, and optically amplify the input signal light, and includes a main telescope 1, a fine tracking fast steering mirror 2, a beam splitter 3, a filter 4, a beam splitter 5, a signal receiving mirror group 10, and a receiving fiber amplifier 11; the light beam received by the main telescope 1 is reflected by the fine tracking fast steering mirror 2, and after being split by the beam splitter 3, it is incident on the signal receiving mirror group 10 after being reflected by the filter 4 and the beam splitter 5 and then focused and coupled into the receiving optical fiber, and is transmitted through the optical fiber to the receiving fiber amplifier 11 for optical amplification, and is transmitted to the photodetector for optical demodulation;

[0034] The beacon light receiving optical path is used to collect, shape, and converge the input signal light, and use the image positioning detector to position the target light spot, and includes a main telescope 1, a fine tracking fast steering mirror 2, a beam splitter 3, a filter 4, a beam splitter 5, a beacon receiving lens group 6, and a beacon detector 7. The light beam received by the main telescope 1 is reflected by the fine tracking fast steering mirror 2, and after being split by the beam splitter 3, it is incident on the beacon receiving lens group 6 after being reflected by the filter 4 and the beam splitter 5 and then focused on the target surface of the beacon detector 7 to realize the identification and positioning of the light spot.

[0035] In this embodiment, the multi-core fiber splitter 12 has two interfaces, a multi-path end and a few-path end. The multi-path end uses N ceramic or metal optical fiber cores, and each optical fiber core is independent of each other, and the number N≥2; the few-path end is to integrate the multiple optical fiber cores at the multi-path end into M optical fiber cores on the same optical fiber connector of the few-path end, where M≥1 and M<N. In this embodiment, the forms of the optical fiber connectors on both sides of the multi-core fiber splitter 12 are not limited to the FC interface, and can be various interfaces such as SMA, SC, LC, etc. For example Figure 2 as shown Figure 2 in the multi-core fiber splitter 12, the few-path end M is 1, and the multi-path end has N1, N2...Ni.

[0036] In this embodiment, the deflection stroke L1 of the pre-aiming fast steering mirror 9 satisfies the condition: where dmax represents the adjustment distance of each optical fiber at the few-path end of the multi-core fiber splitter 12, and f1 is the focal length of the signal transmitting mirror group 8.

[0037] The optical switch 13 in this embodiment is not limited to the applicable type, and it is advisable to meet the output power requirement. The switching number of the optical switch 13 is based on the number of multi-path ends of the multi-core fiber splitter 12 at the rear end, and the switching number of the optical switch is designed according to different numbers.

[0038] A method for rapid acquisition using the above variable beam divergence angle laser communication terminal, the method comprising the following steps:

[0039] S1. Select the beam divergence angle φ according to different working distances, and calculate the receivable power Pr of the beam divergence angle reaching the target beacon detector:

[0040] P r = P t ·η ot ·L r ·η s ·L PAT ·η or

[0041] Where: P r is the received power of the detector; P t is the transmitted power of the transmitting light source; η ot is the efficiency of the transmitting optical unit; L r is the space transmission loss, and its expression is: where D is the receiving aperture, θ is the laser beam divergence angle, and L is the link distance; η s is the power loss caused by the channel; L PAT is the power loss caused by the PAT alignment mismatch; η or is the efficiency of the receiving optical system; in the design, P r should be greater than P CCD-min , P CCD-min is the lowest working received power of the beacon detector 7, that is, the sensitivity threshold;

[0042] S2. And according to the beam divergence angle, the fiber mode field diameter j of the corresponding output fiber at the few-path end of the multi-core fiber splitter 12 can be calculated, where F is the equivalent emission focal length of the signal light emission optical path, and the multi-path end fiber mode field diameter J of the multi-core fiber splitter 12 is obtained;

[0043] S3. According to different beam divergence angle φi requirements, the processes of S1 and S2 are respectively repeated, and different multi-path end fiber mode field diameters Ji are obtained, and the corresponding relationships (φ1, J1), (φ2, J2)... (φm, Jm) are obtained;

[0044] S4: Based on different multi-path end fiber mode field diameters Ji and quantities, the fiber distribution topologies with different mode field diameters on the few-path end fiber end face of the multi-core fiber splitter 12 are designed, and the distribution topologies include but are not limited to concentric circle distribution, square distribution, and star distribution;

[0045] S5. The distance from each fiber core at the few-path end to the geometric center of the fiber end face is di, then the angle relative to the geometric center of the few-path end fiber end face is The corresponding angle position for aiming at the fast steering mirror 9 in advance is βi (βi = Ωi × η, where η is the angle magnification factor of the fast steering mirror for pre-aiming);

[0046] S6. The laser terminal works according to different beam divergence angles φ iAccording to the requirements, control the optical switch 13 to switch to the corresponding φi;

[0047] S7. Control the deflection angle position βi of the pre-aiming fast steering mirror 9, and the laser terminal realizes the beam emission with a divergence angle of φi;

[0048] S8: The total stroke Β of the pre-aiming fast steering mirror 9 should satisfy Β > (βmax - βmin), where βmax is the maximum rotation angle of the pre-aiming fast steering mirror, and βmin is the minimum rotation angle of the pre-aiming fast steering mirror.

Claims

1. A method for rapid acquisition using a variable beam divergence angle laser communication terminal, the variable beam divergence angle laser communication terminal comprising the following optical elements: a main telescope (1), a fine tracking fast steering mirror (2), a beam splitter (3), a filter (4), a beam splitter (5), a beacon receiving lens group (6), a beacon detector (7), a signal transmitting mirror group (8), a pre-aiming fast steering mirror (9), a signal receiving mirror group (10), a receiving fiber amplifier (11), a multi-core fiber splitter (12), an optical switch (13), a transmitting fiber amplifier (14), characterized in that, The above optical elements constitute a signal light emission optical path, a beacon light reception optical path, and a signal light reception optical path; where: The signal light emission optical path provides an emission beam through different mode field optical fibers, and uses different paths of the emission mirror group to shape and change the beam divergence angle of the emitted light, including a main telescope (1), a fine tracking fast steering mirror (2), a beam splitter (3), a signal emission mirror group (8), a pre-aiming fast steering mirror (9), a multi-core fiber splitter (12), an optical switch (13), and an emission fiber amplifier (14); the emission fiber amplifier (14) amplifies the input emission signal light and outputs it to the optical switch (13). Under the command control, the optical switch (13) transmits the input amplified beam to optical fibers with different mode fields / core diameters respectively, and inputs it to the discrete fiber ends of the multi-core fiber splitter (12) through different optical fibers. The multi-core fiber splitter (12) integrates optical fibers with multiple different core diameters into the same fiber ceramic core, and inputs it to the optical antenna. The input beam is incident on the signal emission mirror group (8), and after being reflected by the coaxiality adjustment of the pre-aiming fast steering mirror (9), it is incident on the main telescope (1) after being tracked and reflected by the beam splitter (3) and the fine tracking fast steering mirror (2), and finally exits the terminal; The signal light reception optical path is used to collect, shape, couple, and optically amplify the input signal light, including a main telescope (1), a fine tracking fast steering mirror (2), a beam splitter (3), a filter (4), a beam splitting plate (5), a signal reception mirror group (10), and a reception fiber amplifier (11); the beam received by the main telescope (1) is reflected by the fine tracking fast steering mirror (2), and after being split by the beam splitter (3), it is incident on the signal reception mirror group (10) after being reflected by the filter (4) and the beam splitting plate (5), and is focused and coupled into the reception optical fiber. It is transmitted through the optical fiber to the reception fiber amplifier (11) for optical amplification, and is transmitted to the photodetector for optical demodulation; The beacon light reception optical path is used to collect, shape, and converge the input signal light, and use an image positioning detector to position the target light spot, including a main telescope (1), a fine tracking fast steering mirror (2), a beam splitter (3), a filter (4), a beam splitting plate (5), a beacon reception lens group (6), and a beacon detector (7). The beam received by the main telescope (1) is reflected by the fine tracking fast steering mirror (2), and after being split by the beam splitter (3), it is incident on the beacon reception lens group (6) after being reflected by the filter (4) and the beam splitting plate (5), and is focused on the target surface of the beacon detector (7) to realize the identification and positioning of the light spot; The multi-core fiber splitter (12) has two interfaces, a multi-path end and a few-path end; It is characterized in that the method includes the following steps: S1. Select the beam divergence angle φ according to different working distances, and calculate the receivable power P of the beam divergence angle reaching the target beacon detector r : P r = P t · η ot · L r · η s · L PAT · η or Where: P r is the received power of the detector; P t is the transmitted power of the transmitting light source; η ot is the efficiency of the transmitting optical unit; L r is the space transmission loss, and its expression is: where D is the receiving aperture, θ is the laser beam divergence angle, and L is the link distance; η s is the power loss caused by the channel; L PAT is the power loss caused by the PAT alignment mismatch; η or is the efficiency of the receiving optical system; in the design, P r should be greater than P CCD-min , P CCD-min is the minimum received power for the operation of the beacon detector (7), that is, the sensitivity threshold; S2. And according to the divergence angle, the fiber mode field diameter j of the output optical fiber corresponding to the few-path end of the multi-core optical fiber splitter (12) can be calculated. Where F is the equivalent emission focal length of the signal light emission optical path, and the multi-path end fiber mode field diameter J of the multi-core optical fiber splitter (12) is obtained. S3. According to different requirements of the beam divergence angle φi, repeat the processes of S1 and S2 respectively, and obtain different multi-path end fiber mode field diameters Ji, and obtain the corresponding relationships (φ1, J1), (φ2, J2)... (φm, Jm); S4: Based on different multi-path end fiber mode field diameters Ji and quantities, design the fiber distribution topologies with different mode field diameters on the end face of the few-path end fiber of the multi-core fiber splitter (12). The distribution topologies include concentric circle distribution, square distribution, and star distribution; At the minor path end, if the distance from each optical fiber core to the geometric center of the optical fiber end face is di, then the angle relative to the geometric center of the minor path end optical fiber end face is Ωi. The corresponding angular position for aiming at the fast steering mirror (9) in advance is βi, where βi = Ωi × η, and η is the angular magnification factor of the fast steering mirror for advance aiming. S6. During operation, the laser terminal controls the optical switch (13) to switch to the corresponding φi according to the requirements of different beam divergence angles φ i ; S7. Control the deflection value angle position βi of the pre-aiming fast steering mirror (9), and the laser terminal realizes the beam emission with a divergence angle of φi; S8: In the total stroke Β of the pre-aiming fast steering mirror (9), it should satisfy Β > (βmax - βmin), where βmax is the maximum rotation angle of the pre-aiming fast steering mirror, and βmin is the minimum rotation angle of the pre-aiming fast steering mirror.

2. The method for rapid acquisition using a variable beam divergence angle laser communication terminal according to claim 1, wherein The multi-path end of the multi-core fiber splitter (12) uses N ceramic or metal fiber cores, and each fiber core is independent of each other, with N ≥ 2; the few-path end of the multi-core fiber splitter (12) is to integrate multiple fiber cores at the multi-path end into M fiber cores on the same fiber connector at the few-path end, where M ≥ 1 and M < N.

3. The method for rapid acquisition using a variable beam divergence angle laser communication terminal according to claim 2, wherein The deflection stroke L1 of the aforesaid early aiming quick-responding mirror (9) meets the condition that: wherein dmax represents the adjustment distance of each optical fiber at the fewer-path end of the multi-core optical fiber splitter (12), and f1 is the focal length of the signal transmitting mirror group (8).

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