Low profile laser communication optical system and laser communication alignment method

Abstract

The application discloses a low-profile laser communication optical system and a laser communication alignment method, and belongs to the technical field of space laser communication. The application comprises a total controller, a motor controller, a receiving liquid crystal polarization grating group, a transmitting liquid crystal polarization grating group, a receiving branch and a transmitting branch. The receiving branch comprises a Galileo type beam-reducing system, a first fast mirror, a first dichroic mirror, a tracking optical system, a second fast mirror and a communication receiving system. The transmitting branch comprises a beacon light transmitting module, a signal light transmitting module, a second dichroic mirror, a third fast mirror and a fourth fast mirror. The total controller calculates the offset angle of the liquid crystal polarization grating and the first to fourth fast mirrors through a spot centroid offset amount, and completes the alignment of the laser communication. The application uses the liquid crystal polarization grating group to realize beam deflection, has the advantages of light weight and large angle, and has a low exposed profile, and has a wide application prospect in the field of airborne platform laser communication.

Description

Technical Field

[0001] This invention relates to the field of space laser communication technology, and in particular to a low-profile laser communication optical system and a laser communication alignment method. Background Technology

[0002] Space laser communication technology is a communication technology that uses lasers as the propagation medium to transmit information in space. Due to its many advantages, such as high speed, wide bandwidth, and strong anti-interception capability, it has developed rapidly in recent years in deep space, space-to-ground, and inter-satellite link communication applications.

[0003] Airborne laser communication technology is a research hotspot in space laser communication technology. To meet the stealth performance requirements of aircraft platforms and achieve high-speed communication in various attitudes, airborne communication terminals need to develop towards miniaturization, lightweighting, and conformal design. However, currently mature beam scanning mechanisms such as frame-type and single-mirror-type systems have the problems of large size and high exposed profile, while voice coil mirror-type and MEMS mirror-type systems cannot meet the technical requirements of large scanning angles. Summary of the Invention

[0004] In view of this, the present invention proposes a low-profile laser communication optical system and a laser communication alignment method. This system uses a liquid crystal polarization grating to achieve beam deflection, offering advantages such as lightweight design and large beam angle, while maintaining a low exposed profile, making it promising for broad applications in airborne platform laser communication.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows.

[0006] A low-profile laser communication optical system includes a main controller, a motor controller, a receiving liquid crystal polarization grating group, an emitting liquid crystal polarization grating group, a receiving branch, and an emitting branch. The receiving branch includes a Galilean beam-shrinking system, a first fast mirror, a first dichroic mirror, a tracking optical system, a second fast mirror, and a communication receiving system. The emitting branch includes a beacon light emitting module, a signal light emitting module, a second dichroic mirror, a third fast mirror, and a fourth fast mirror.

[0007] The receiving liquid crystal polarization grating group includes three identical and coaxially cascaded receiving liquid crystal polarization gratings, and the emitting liquid crystal polarization grating group includes three identical and coaxially cascaded emitting liquid crystal polarization gratings; both the receiving and emitting liquid crystal polarization gratings are fabricated using the interference method of two orthogonal circularly polarized beams; the motor control group includes three drive motors, each drive motor is connected to one receiving liquid crystal polarization grating; the other end of each receiving liquid crystal polarization grating is connected to one emitting liquid crystal polarization grating via a synchronous belt, realizing the same angular rotation of the receiving and emitting liquid crystal polarization gratings;

[0008] In the transmitting branch, the main controller controls the beacon light transmitting module to emit beacon light, and simultaneously controls the signal light transmitting module to emit signal light. After the beacon light reaches the second dichroic mirror, it continues to propagate along its original path. The signal light is reflected by the fourth fast reflector to the second dichroic mirror, which then reflects the signal light onto the same path as the beacon light. The two light rays reaching the second dichroic mirror merge into one light ray, which is reflected by the third fast reflector to the emitting liquid crystal polarization grating group. The main controller drives the motor controller to control the rotation of the emitting liquid crystal polarization grating group, causing the light rays reflected to the emitting liquid crystal polarization grating group to undergo diffraction and deflection to be emitted outward.

[0009] In the receiving branch, the light emitted by the distant antenna is diffracted and deflected after entering the receiving liquid crystal polarization grating. The diffracted light then enters the Galilean beam-shrinking system. The beam-shrinking light is reflected by the first fast reflector to the first dichroic mirror. The first dichroic mirror splits the light into two paths. The first path enters the tracking optical system directly along its original path, while the second path is reflected by the first dichroic mirror to the second fast reflector. The second fast reflector then reflects the second path to the communication receiving system. The light output from both the tracking optical system and the communication receiving system is sent to the main controller for tracking and communication.

[0010] Furthermore, the Galilean beam-shrinking system includes a biconvex lens with a positive focal length and a biconcave lens with a negative focal length. The light rays that have been diffracted and deflected after passing through the receiving liquid crystal polarization grating are first sent to the biconvex lens, and then converged by the biconvex lens and transmitted to the biconcave lens for output.

[0011] Furthermore, the tracking optical system includes a first filter, a first converging lens, and a CMOS sensor; the communication receiving system includes a second filter, a second converging lens, and an APD detector;

[0012] The light rays input to the tracking optical system sequentially enter the first filter and the first converging lens before being input to the CMOS sensor, and then output by the CMOS sensor;

[0013] The light entering the communication receiving system sequentially enters the second filter and the second converging lens before entering the avalanche photodiode detector, which then outputs the light.

[0014] Furthermore, the beacon light emitting module includes a beacon laser, a first collimating lens, a first half-wave plate, and a first quarter-wave plate; the signal light emitting module includes a signal laser, a second collimating lens, a second half-wave plate, and a second quarter-wave plate.

[0015] The beacon light emitted by the beacon laser sequentially enters the first collimating lens, the first half-wave plate, and the first quarter-wave plate before being transmitted to the second dichroic mirror;

[0016] The signal light emitted by the signal laser sequentially enters the second collimating lens, the second half-wave plate, and the second quarter-wave plate before being transmitted to the fourth fast reflector.

[0017] Furthermore, the initial working angles of the first to fourth fast reflectors and the first to second dichroic mirrors are all 45° with the x-direction and 0° with the y-direction; wherein the x-direction is the direction of the grating line of the liquid crystal polarizing grating group, and the y-direction is the direction perpendicular to the grating line of the liquid crystal polarizing grating group.

[0018] A laser communication alignment method, implemented based on a low-profile laser communication optical system as described in any of the above, includes the following steps:

[0019] Step 1: The main controller controls the transmitting branch to emit light to the outside;

[0020] Step 2: The main controller drives the motor controller to control the rotation of the liquid crystal polarization grating group, thereby guiding the light emitted by the transmitting branch to scan around a certain range until the main controller captures the light from the receiving branch.

[0021] Step 3: The main controller calculates the centroid deviation of the tracking optical system, and calculates the offset angle of each of the three receiving liquid crystal polarization gratings based on the centroid deviation.

[0022]

[0023]

[0024] Where, Φ x To achieve the desired light spot centroid deviation in the x-direction during receiver branch light acquisition, Φ y The deviation of the spot centroid in the y-direction when capturing light from the receiving branch; δ1, δ2, and δ3 are the wavelength grating pitch ratios of the three receiving liquid crystal gratings, respectively; These are the offset angles of the three receiving liquid crystal gratings, respectively;

[0025] Based on the relationship between the offset angles of the three receiving liquid crystal gratings, the set of data with the smallest rotation angle is selected, and the corresponding drive motor driving amount is further calculated. The main controller controls the receiving liquid crystal polarization grating to rotate to the specified position according to the drive motor driving amount, and makes the transmitting liquid crystal polarization grating rotate by the same angle through the synchronous belt to achieve coarse tracking.

[0026] Step 4: The main controller recalculates the centroid deviation of the tracking optical system, and calculates the offset angle between the first and third fast-reflecting mirrors based on the centroid deviation.

[0027]

[0028]

[0029] Where α is the deviation of the spot centroid in the x-direction after coarse tracking, b is the deviation of the spot centroid in the y-direction after coarse tracking, and f is the focal length of the first converging lens; x Let α be the offset of the first and third fast mirrors in the x-direction. y Let α be the offset angle between the first and third fast reflecting mirrors in the y-direction; according to α x and α y Adjust the first and third fast reflectors to the correct positions to achieve precise tracking;

[0030] Step 5: The main controller calculates the required dispersion offset angles between the second and fourth fast mirrors based on the rotation angle of the liquid crystal polarization grating group.

[0031]

[0032]

[0033] Where λ1 is the wavelength of the beacon light, λ2 is the wavelength of the signal light, Λ is the grating pitch of the liquid crystal polarization grating, and θ x Let θ be the dispersion offset angle between the second and fourth fast mirrors in the x-direction. y Let θ be the dispersion shift angle between the second and fourth fast mirrors in the y-direction. x and θ y Adjust the second and fourth fast reflectors to the correct positions to complete the alignment of the laser communication.

[0034] Due to the adoption of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0035] 1. The present invention uses three liquid crystal polarization gratings to form a beam deflection device, and the diffraction efficiency of a single liquid crystal polarization grating can reach 100% under ideal conditions.

[0036] 2. This invention enables large-range dynamic scanning by controlling the polarization direction of the incident light and the rotation angle of each of the three liquid crystal polarization gratings.

[0037] 3. This invention has significant advantages such as lightweight, large angle, high precision and low profile, and has great application prospects in the field of airborne platform laser communication. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of a low-profile laser communication optical system according to an embodiment of the present invention;

[0039] Figure 2 This describes the beam deflection principle of the liquid crystal polarization grating group in this embodiment of the invention. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] A low-profile laser communication optical system, such as Figure 1 As shown, it includes a main controller, a motor controller, a receiving liquid crystal polarization grating group, an emitting liquid crystal polarization grating group, a receiving branch, and an emitting branch. The receiving branch includes a Galilean beam-shrinking system, a first fast reflector, a first dichroic mirror, a tracking optical system, a second fast reflector, and a communication receiving system. The emitting branch includes a beacon light emitting module, a signal light emitting module, a second dichroic mirror, a third fast reflector, and a fourth fast reflector.

[0042] The receiving liquid crystal polarization grating group includes three identical and coaxially cascaded receiving liquid crystal polarization gratings, and the emitting liquid crystal polarization grating group includes three identical and coaxially cascaded emitting liquid crystal polarization gratings; both the receiving and emitting liquid crystal polarization gratings are fabricated using the interference method of two orthogonal circularly polarized beams; the motor control group includes three drive motors, each drive motor is connected to one receiving liquid crystal polarization grating; the other end of each receiving liquid crystal polarization grating is connected to one emitting liquid crystal polarization grating via a synchronous belt, realizing the same angular rotation of the receiving and emitting liquid crystal polarization gratings;

[0043] Specifically, in this embodiment, the receiving liquid crystal polarization grating group has a period of 5μm, the maximum deflection angle of the diffracted light is 35°, and the aperture is 60mm; the emitting liquid crystal polarization grating group has a period of 5μm, the maximum deflection angle of the diffracted light is 35°, and the aperture is 30mm.

[0044] The direction opposite to the perpendicular incidence of light into the liquid crystal polarization grating group is the positive z-axis. The rotation angles of the three liquid crystal polarization gratings around the positive z-axis are respectively...

[0045] In the transmitting branch, the main controller controls the beacon light emitting module to emit a 1540nm laser, and simultaneously controls the signal light emitting module to emit a 1560nm laser. The 1540nm laser continues to propagate along its original path after reaching the second dichroic mirror. The 1560nm laser is reflected by the fourth fast reflector back to the second dichroic mirror, which then reflects the 1560nm laser onto the same path as the 1540nm laser. The two beams of light reaching the second dichroic mirror merge into one beam, which is then reflected by the third fast reflector to the emitting liquid crystal polarization grating. The main controller drives the motor controller to control the rotation of the emitting liquid crystal polarization grating, causing the light reflected from the emitting liquid crystal polarization grating to be diffracted and deflected outward.

[0046] In the receiving branch, the light emitted by the distant antenna is diffracted and deflected after entering the receiving liquid crystal polarization grating. The diffracted light then enters the Galilean beam-shrinking system, and the beam-shrinking light is reflected by the first fast reflector to the first dichroic mirror. The first dichroic mirror splits the light into two paths. The first path of light enters the tracking optical system directly along its original path, while the second path of light is reflected by the first dichroic mirror to the second fast reflector. The second fast reflector then reflects the second path of light to the communication receiving system. The light output from both the tracking optical system and the communication receiving system is sent to the main controller for tracking and communication.

[0047] Specifically, such as Figure 2 As shown, light emitted from a distant antenna is incident on a liquid crystal polarization grating and undergoes diffraction. The diffraction formula is as follows:

[0048]

[0049]

[0050] Where η0 is the zero-order diffraction efficiency of the grating, η ±1 denoted by s'3, where s is the diffraction efficiency of the first order of the grating, s'3 is the normalized Stokes constant, Δn is the refractive index variation coefficient, d is the grating thickness, and λ is the wavelength of the incident light.

[0051] Furthermore, the Galilean beam-shrinking system includes a biconvex lens with a positive focal length and a biconcave lens with a negative focal length. The light rays that have been diffracted and deflected after passing through the receiving liquid crystal polarization grating are first sent to the biconvex lens, and then converged by the biconvex lens and transmitted to the biconcave lens for output.

[0052] Furthermore, the tracking optical system includes a first filter, a first converging lens, and a CMOS sensor; the communication receiving system includes a second filter, a second converging lens, and an avalanche photodiode detector.

[0053] Specifically, in this embodiment, the focal length of both the first and second converging lenses is 10mm, the center wavelength of the first filter is 1560mm, and the center wavelength of the second filter is 1540mm.

[0054] The light rays input to the tracking optical system sequentially enter the first filter and the first converging lens before being input to the CMOS sensor, and then output by the CMOS sensor;

[0055] The light entering the communication receiving system sequentially enters the second filter and the second converging lens before entering the avalanche photodiode detector, which then outputs the light.

[0056] Furthermore, the beacon light emitting module includes a 1540nm band light laser, a first collimating lens, a first half-wave plate, and a first quarter-wave plate; the signal light emitting module includes a 1560nm band light laser, a second collimating lens, a second half-wave plate, and a second quarter-wave plate.

[0057] The beacon light emitted by the beacon laser sequentially enters the first collimating lens, the first half-wave plate, and the first quarter-wave plate before being transmitted to the second dichroic mirror;

[0058] The signal light emitted by the signal laser sequentially enters the second collimating lens, the second half-wave plate, and the second quarter-wave plate before being transmitted to the fourth fast reflector.

[0059] Furthermore, the initial working angles of the first to fourth fast reflectors and the first to second dichroic mirrors are all 45° with the x-direction and 0° with the y-direction; wherein the x-direction is the direction of the grating line of the liquid crystal polarizing grating group, and the y-direction is the direction perpendicular to the grating line of the liquid crystal polarizing grating group.

[0060] A laser communication alignment method, implemented based on a low-profile laser communication optical system as described in any of the above, includes the following steps:

[0061] Step 1: The main controller controls the transmitting branch to emit light to the outside;

[0062] Step 2: The main controller drives the motor controller to control the rotation of the liquid crystal polarization grating group, thereby guiding the light emitted by the transmitting branch to scan around a certain range until the main controller captures the light from the receiving branch.

[0063] Step 3: The main controller calculates the centroid deviation of the tracking optical system, and calculates the offset angle of each of the three receiving liquid crystal polarization gratings based on the centroid deviation.

[0064]

[0065]

[0066] Where, Φ x To achieve the desired light spot centroid deviation in the x-direction during receiver branch light acquisition, Φ y The deviation of the spot centroid in the y-direction when capturing light from the receiving branch; δ1, δ2, and δ3 are the wavelength grating pitch ratios of the three receiving liquid crystal gratings, respectively; These are the offset angles of the three receiving liquid crystal gratings, respectively;

[0067] Based on the relationship between the offset angles of the three receiving liquid crystal gratings, the set of data with the smallest rotation angle is selected, and the corresponding drive motor driving amount is further calculated. The main controller controls the receiving liquid crystal polarization grating to rotate to the specified position according to the drive motor driving amount, and makes the transmitting liquid crystal polarization grating rotate by the same angle through the synchronous belt to achieve coarse tracking.

[0068] Step 4: The main controller recalculates the centroid deviation of the tracking optical system, and calculates the offset angle between the first and third fast-reflecting mirrors based on the centroid deviation.

[0069]

[0070]

[0071] Where α is the deviation of the spot centroid in the x-direction after coarse tracking, b is the deviation of the spot centroid in the y-direction after coarse tracking, and f is the focal length of the first converging lens; x Let α be the offset of the first and third fast mirrors in the x-direction. y Let α be the offset angle between the first and third fast reflecting mirrors in the y-direction; according to α x and α y Adjust the first and third fast reflectors to the correct positions to achieve precise tracking;

[0072] Step 5: The main controller calculates the required dispersion offset angles between the second and fourth fast mirrors based on the rotation angle of the liquid crystal polarization grating group.

[0073]

[0074]

[0075] Where λ1 is the wavelength of the beacon light, λ2 is the wavelength of the signal light, Λ is the grating pitch of the liquid crystal polarization grating, and θ x Let θ be the dispersion offset angle between the second and fourth fast mirrors in the x-direction. yLet θ be the dispersion shift angle between the second and fourth fast mirrors in the y-direction. x and θ y Adjust the second and fourth fast reflectors to the correct positions to complete the alignment of the laser communication.

[0076] In summary, this method uses a liquid crystal polarization grating to achieve beam deflection, which has the advantages of being lightweight and having a large angle, while also having a low exposed profile, and has broad application prospects in the field of airborne platform laser communication.

[0077] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and does not limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the present invention as defined in the appended claims should be included within the protection scope of the present invention.

Claims

1. A low-profile laser communication optical system, characterized in that, It includes a main controller, a motor controller, a receiving liquid crystal polarization grating group, an emitting liquid crystal polarization grating group, a receiving branch, and an emitting branch. The receiving branch includes a Galilean beam-shrinking system, a first fast reflector, a first dichroic mirror, a tracking optical system, a second fast reflector, and a communication receiving system. The emitting branch includes a beacon light emitting module, a signal light emitting module, a second dichroic mirror, a third fast reflector, and a fourth fast reflector. The receiving liquid crystal polarization grating group includes three identical and coaxially cascaded receiving liquid crystal polarization gratings, and the emitting liquid crystal polarization grating group includes three identical and coaxially cascaded emitting liquid crystal polarization gratings; both the receiving and emitting liquid crystal polarization gratings are fabricated using the interference method of two orthogonal circularly polarized beams; the motor control group includes three drive motors, each drive motor is connected to one receiving liquid crystal polarization grating; the other end of each receiving liquid crystal polarization grating is connected to one emitting liquid crystal polarization grating via a synchronous belt, realizing the same angular rotation of the receiving and emitting liquid crystal polarization gratings; In the transmitting branch, the main controller controls the beacon light transmitting module to emit beacon light, and simultaneously controls the signal light transmitting module to emit signal light. After the beacon light reaches the second dichroic mirror, it continues to propagate along its original path. The signal light is reflected by the fourth fast reflector to the second dichroic mirror, which then reflects the signal light onto the same path as the beacon light. The two light rays reaching the second dichroic mirror merge into one light ray, which is reflected by the third fast reflector to the emitting liquid crystal polarization grating group. The main controller drives the motor controller to control the rotation of the emitting liquid crystal polarization grating group, causing the light rays reflected to the emitting liquid crystal polarization grating group to undergo diffraction and deflection to be emitted outward. In the receiving branch, the light emitted by the distant antenna is diffracted and deflected after entering the receiving liquid crystal polarization grating group. The diffracted light enters the Galilean beam-shrinking system, and the beam-shrinking light is reflected by the first fast reflector to the first dichroic mirror. The first dichroic mirror splits the light into two paths. The first path of light enters the tracking optical system directly along its original path, and the second path of light is reflected by the first dichroic mirror to the second fast reflector. Then, the second fast reflector reflects the second path of light to the communication receiving system. The light rays output from both the tracking optical system and the communication receiving system are sent to the main controller for tracking and communication.

2. The low-profile laser communication optical system according to claim 1, characterized in that, The Galilean beam-shrinking system includes a biconvex lens with a positive focal length and a biconcave lens with a negative focal length. The light rays that have been diffracted and deflected after passing through the receiving liquid crystal polarization grating are first sent to the biconvex lens, and then converged by the biconvex lens and transmitted to the biconcave lens for output.

3. The low-profile laser communication optical system according to claim 1, characterized in that, The tracking optical system includes a first filter, a first converging lens, and a CMOS sensor; the communication receiving system includes a second filter, a second converging lens, and an avalanche photodiode detector. The light rays input to the tracking optical system sequentially enter the first filter and the first converging lens before being input to the CMOS sensor, and then output by the CMOS sensor; The light entering the communication receiving system sequentially enters the second filter and the second converging lens before entering the avalanche photodiode detector, which then outputs the light.

4. The low-profile laser communication optical system according to claim 1, characterized in that, The beacon light emitting module includes a beacon laser, a first collimating lens, a first half-wave plate, and a first quarter-wave plate; the signal light emitting module includes a signal laser, a second collimating lens, a second half-wave plate, and a second quarter-wave plate. The beacon light emitted by the beacon laser sequentially enters the first collimating lens, the first half-wave plate, and the first quarter-wave plate before being transmitted to the second dichroic mirror; The signal light emitted by the signal laser sequentially enters the second collimating lens, the second half-wave plate, and the second quarter-wave plate before being transmitted to the fourth fast reflector.

5. A low-profile laser communication optical system according to claim 1, characterized in that, The initial working angles of the first to fourth fast reflectors and the first to second dichroic mirrors are all 45° with the x-direction and 0° with the y-direction; wherein the x-direction is the direction of the grating line of the liquid crystal polarizing grating group, and the y-direction is the direction perpendicular to the grating line of the liquid crystal polarizing grating group.

6. A laser communication alignment method, characterized in that, The implementation of a low-profile laser communication optical system based on any one of claims 1-5 includes the following steps: Step 1: The main controller controls the transmitting branch to emit light to the outside; Step 2: The main controller drives the motor controller to control the rotation of the liquid crystal polarization grating group, thereby guiding the light emitted by the transmitting branch to scan around a certain range until the main controller captures the light from the receiving branch. Step 3: The main controller calculates the centroid deviation of the tracking optical system, and calculates the offset angle of each of the three receiving liquid crystal polarization gratings based on the centroid deviation. Where, Φ x To achieve the desired light spot centroid deviation in the x-direction during receiver branch light acquisition, Φ y The deviation of the spot centroid in the y-direction when capturing light from the receiving branch; δ1, δ2, and δ3 are the wavelength grating pitch ratios of the three receiving liquid crystal gratings, respectively; These are the offset angles of the three receiving liquid crystal gratings, respectively; Based on the relationship between the offset angles of the three receiving liquid crystal gratings, the data with the smallest rotation angle is selected, and the corresponding drive motor driving amount is further calculated. The main controller controls the receiving liquid crystal polarization grating to rotate to the specified position according to the drive motor driving amount, and makes the transmitting liquid crystal polarization grating rotate by the same angle through the synchronous belt to achieve coarse tracking. Step 4: The main controller recalculates the centroid deviation of the tracking optical system, and calculates the offset angle between the first and third fast-reflecting mirrors based on the centroid deviation. Where α is the deviation of the spot centroid in the x-direction after coarse tracking, b is the deviation of the spot centroid in the y-direction after coarse tracking, and f is the focal length of the first converging lens; x Let α be the offset of the first and third fast mirrors in the x-direction. y Let α be the offset angle between the first and third fast reflecting mirrors in the y-direction; according to α x and α y Adjust the first and third fast reflectors to the correct positions to achieve precise tracking; Step 5: The main controller calculates the required dispersion offset angles between the second and fourth fast mirrors based on the rotation angle of the liquid crystal polarization grating group. Where λ1 is the wavelength of the beacon light, λ2 is the wavelength of the signal light, Λ is the grating pitch of the liquid crystal polarization grating, and θ x Let θ be the dispersion offset angle between the second and fourth fast mirrors in the x-direction. y Let θ be the dispersion shift angle between the second and fourth fast mirrors in the y-direction. x and θ y Adjust the second and fourth fast reflectors to the correct positions to complete the alignment of the laser communication.

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