Optical fiber nutation coupling device and use method thereof

Abstract

The invention provides an optical fiber nutation coupling device and a use method thereof, and relates to the technical field of laser communication, the device mainly comprises a light splitting module, a light spot position monitoring module, an optical fiber coupling adjustment module, a nutation scanning module, a receiving optical fiber and a main base; the system is initialized and calibrated through the light splitting module, the light spot position monitoring module and the optical fiber coupling adjustment module, a light beam entering the nutation scanning module is restrained in a determined small-range area, and then the light beam is coupled into a receiving optical fiber through nutation scanning. The device can solve the problem that free space light is difficult to efficiently and stably couple to the single-mode fiber in the prior art. Meanwhile, the device adopts a modular design concept, a nutation coupling system is highly integrated, the structure is compact, the size is small, the weight is light, the power consumption is low, and system debugging and assembling are convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of laser communication, and particularly to an optical fiber nutation coupling device and a method for using the same. Background Art

[0002] In recent years, with the increasing maturity of the spaceborne laser communication terminal technology, the commercialization demand for laser communication terminals has become more and more urgent. Considering factors such as optical machining, alignment deviation, on-orbit temperature and stress changes of the satellite platform leading to micro-deformation of the mechanical structure, platform vibration and system transceiver non-coaxiality, etc., it is undoubtedly very difficult to couple the weak signal light entering the optical system into a single-mode optical fiber with a diameter of 9um. Therefore, an efficient and stable free-space light-single-mode optical fiber coupling technology is the prerequisite and guarantee for the realization of high-speed and long-distance laser communication technology, and is also a key technology in space laser communication. At the same time, due to reasons such as optical machining, alignment and vibration, the coupled light beam will have problems such as tilt, defocus or other aberrations, resulting in a significant decrease in the coupling quality of free-space light-single-mode optical fiber. Therefore, the industry urgently needs to develop an automatic optical fiber coupling technology to improve the coupling efficiency and thus ensure the quality of free-space laser communication.

[0003] A patent application with the publication number CN110401483A and the name of a laser communication device and method uses a fast steering mirror as a nutation coupling mirror for single-mode optical fiber nutation coupling. When performing optical fiber nutation coupling, the position of the light spot cannot be determined. This uncertainty in the position of the light spot results in the need to perform a large-range scan near the uncertain position before the signal light can be coupled into the optical fiber. Therefore, the efficiency and effect of this optical fiber coupling scheme are not good. Summary of the Invention

[0004] The purpose of the present invention is to provide an optical fiber nutation coupling device and a method for using the same to solve the problem in the prior art that it is difficult to efficiently and stably couple free-space light into a single-mode optical fiber.

[0005] To solve the above technical problems, the present invention provides an optical fiber nutation coupling device, which includes a beam splitting module, a light spot position monitoring module, an optical fiber coupling alignment module, a nutation scanning module, a receiving optical fiber and a main base.

[0006] The beam splitting surface of the beam splitting module is fixed at 45 degrees to the main base. The incident light is incident perpendicularly on the incident surface of the beam splitting module. After being split by the beam splitting surface, the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light. When the light beam is incident perpendicularly on the first surface of the beam splitting module, it is incident on the beam splitting surface at an incident angle of 45 degrees. According to the law of reflection of light, the incident angle is equal to the reflection angle, so the reflected light is perpendicular to the incident light. According to the law of refraction of light, when light enters a transparent medium in a perpendicular incidence (i.e., the incident angle is 0 degrees and the light is perpendicular to the surface of the medium), the direction of the transmitted light does not change, so the transmitted light can enter the nutation scanning module along the original optical path direction.

[0007] The spot position monitoring module includes a position detection focusing mirror and a position detector, and is used to monitor the spot position of the reflected light. The reflected light is incident on the position detector through the position detection focusing mirror. The position detection focusing mirror and the position detector are respectively connected to the main base through a bolt-fastened sliding adjustable structure (including at least a fastening bolt groove) for adjusting the focal length of the spot position monitoring module. Through the beam splitting module and the reflected light spot position monitoring module, an image of the receiving optical fiber and the transmitted light spot is formed. By adjusting and monitoring the optical path of the reflected light, the spot position of the reflected light is limited within a certain small range, and thus the spot of the transmitted light is also limited within a certain small range.

[0008] The nutation scanning module includes a nutation coupling fast steering mirror and a fast steering mirror controller. The fast steering mirror controller is used to control the nutation coupling fast steering mirror to scan within the coupling scanning area.

[0009] The optical fiber coupling and alignment module includes an optical fiber coupling focusing mirror, an incident lens barrel, an optical fiber flange, a three-point adjustment disk and an L-shaped support plate. The optical fiber flange is arranged at one end of the incident lens barrel for installing the receiving optical fiber. The other end of the incident lens barrel passes through the vertical surface of the L-shaped support plate and the three-point adjustment disk and is inserted into the lens barrel of the optical fiber coupling focusing mirror. The three-point adjustment disk is installed on the vertical surface of the L-shaped support plate. The horizontal plane of the L-shaped support plate and the optical fiber coupling focusing mirror are respectively connected to the main base through a bolt-fastened sliding adjustable structure for adjusting the focal length of the optical fiber coupling and alignment module.

[0010] The transmitted light is reflected by the nutation coupling fast steering mirror and then enters the optical fiber coupling focusing mirror, and then enters the receiving optical fiber through the incident lens barrel. The whole incident lens barrel of the optical fiber coupling and alignment module is inserted into the optical fiber coupling focusing mirror, which can prevent the interference of stray light.

[0011] Further, the three-point adjustment disk is installed on the vertical plate of the L-shaped support plate through studs.

[0012] Furthermore, three adjusting set screws are provided on the three-point adjusting disc. By using the set screws of the three-point adjusting disc to make minute position and angle adjustments to the receiving optical fiber and the incident lens barrel, adjustments can be achieved at the micron level.

[0013] By adjusting the adjustable structure in the above device, the device is initialized and calibrated. After initialization and calibration, the optical axis of the incident light entering the spot position monitoring module and the optical axis of the transmitted light reflected by the nutation scanning fast steering mirror and entering the fiber coupling alignment module achieve high-precision coincidence.

[0014] In a feasible implementation manner, the nutation coupling device further includes a light baffle, which is fixed outside the gap between the nutation coupling fast steering mirror and the fiber coupling focusing lens for excluding interfering light.

[0015] In a feasible implementation manner, the beam splitting module includes a cube beam splitting prism. The cube beam splitting prism has stable beam splitting performance, regular shape, small volume, and compact structure, which is helpful for integration and installation and debugging.

[0016] Preferably, the reflection / transmission ratio of the beam splitting surface of the cube beam splitting prism is set to 50 / 50.

[0017] In a feasible implementation manner, the position detector includes a spot imaging sensor, a detector encapsulation cover, and a detector window. The spot imaging sensor and the detector window are respectively arranged at the central positions at both ends of the detector encapsulation cover. One end of the detector encapsulation cover with the detector window is inserted into the lens barrel of the position detection focusing lens. The fastening bolt groove of the position detector is arranged at the corresponding positions of the detector encapsulation cover base and the main base. The spot imaging sensor uses a Charge-Coupled Device (CCD for short) to collect spot images in real time.

[0018] The CCD includes a photosensitive pixel array, a charge transfer channel, and a readout circuit, which converts the optical signal into a voltage signal, forms a digital image through amplification and analog-to-digital conversion (ADC), and calculates the spot center coordinates through the pixel gray values. The CCD has the characteristics of high sensitivity and low noise. The detector encapsulation cover is connected to the position detection focusing lens barrel through the detector window, so that the reflected light is not interfered by external light, further improving the precision.

[0019] In a feasible implementation manner, fastening bolt grooves are provided at the bases of the L-shaped support plate, the fiber coupling focusing lens, and the position detection focusing lens, respectively, for performing lateral position sliding adjustment and fixation on the fiber coupling alignment module, the fiber coupling focusing lens, and the position detection focusing lens. The fastening bolt groove of the position detector is set as an axially oblong shape for performing axial position adjustment and fixation on the position detector, so that the spot of the reflected light remains at the central position of the position detector.

[0020] In the overall structural design of the present device, the optical paths of the light spot position monitoring module and the optical fiber coupling assembly and alignment module are parallel on the same horizontal plane. Through the setting of the fastening bolt slots, the focal lengths of the two modules can be adjusted more precisely respectively.

[0021] In a feasible implementation manner, the optical fiber coupling focusing mirror includes a first focusing mirror base, a first focusing mirror, and a first narrow-band filter. The first focusing mirror and the first narrow-band filter are respectively arranged in the middle and one end of the barrel of the first focusing mirror base. The incident light enters the first focusing mirror after being filtered by the first narrow-band filter. The other end of the barrel is used for inserting the incident barrel. The fastening bolt slots of the optical fiber coupling focusing mirror are arranged at the corresponding positions of the main base and the first focusing mirror base.

[0022] Similarly, the position detection focusing mirror includes a second focusing mirror base, a second focusing mirror, and a second narrow-band filter. The second focusing mirror and the second narrow-band filter are respectively arranged in the middle and one end of the barrel of the second focusing mirror base. The incident light enters the second focusing mirror after being filtered by the second narrow-band filter. The other end of the barrel is used for inserting one end of the position detector encapsulation cover provided with a detector window. The fastening bolt slots of the position detection focusing mirror are arranged at the corresponding positions of the main base and the second focusing mirror base.

[0023] In another feasible implementation manner, the first narrow-band filter, the second narrow-band filter, and the narrow-band filter of the detector window can all be replaced with plane mirrors.

[0024] In a feasible implementation manner, the nutation coupling fast steering mirror includes a fast steering mirror base, a fast steering mirror pedestal, a fast steering mirror amplification structure, a piezoelectric ceramic, a lens holder, a flexure hinge, a reflecting lens, and a gland. The fast steering mirror base is an L-shaped panel. The horizontal plane of the L-shaped panel is fixed on the upper surface of the fast steering mirror controller. The fast steering mirror pedestal is fixed on the vertical surface of the L-shaped panel through a bolt-fastened sliding adjustable structure. The fast steering mirror amplification structure includes four triangular linkages with the same structure. The horizontal rods of the triangular linkages are all fixed on the fast steering mirror base and are at equal distances from the center of the bottom surface of the fast steering mirror pedestal. The inclined struts of the triangular linkages form an acute angle with the horizontal rods. The piezoelectric ceramic is arranged between the horizontal rod and the inclined strut of the triangular linkage. The lens holder is installed on the tops of the four inclined struts. The reflecting lens is installed on the lens holder through a flexure hinge. The gland is an annular structure and is installed on the top of the fast steering mirror pedestal to encapsulate the fast steering mirror amplification structure, the piezoelectric ceramic, the lens holder, the flexure hinge, and the reflecting lens in the fast steering mirror pedestal.

[0025] When a voltage is applied to the piezoelectric ceramic, the piezoelectric ceramic generates a displacement change, thereby changing the angle between the inclined strut and the horizontal rod of the corresponding triangular linkage, causing the position at the top of the inclined strut to rise or fall, driving the corresponding mirror holder and reflecting lens to move accordingly, and thus changing the angle of the reflecting lens.

[0026] The nutation-coupled fast steering mirror has a simple and compact structure, is easy to integrate, assemble, disassemble, repair, and has a high sensitivity to the regulation of the reflection angle.

[0027] In a feasible implementation manner, the method for initializing and calibrating the nutation coupling device is as follows: Step a1: Control the incident light to be normally incident on the incident surface of the beam splitting module, so that the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light. Step a2: Adjust the positions of the position detection focusing mirror and the position detector by tightening the sliding adjustable structure with bolts, so that the reflected light is focused on the central position of the position detector and remains stationary. Step a3: Set the nutation-coupled fast steering mirror to be stationary at the zero position, and adjust the position of the receiving optical fiber in the vertical plane through the L-shaped support plate and the three-point adjustment disc, so that the incident light enters the receiving optical fiber and the optical power reaches the maximum value. Step a4: By changing the front and rear positions of the incident lens barrel extending into the lens barrel of the fiber coupling focusing mirror and adjusting the focal length with the three-point adjustment disc, make the optical power of the light incident on the receiving optical fiber the largest. Step a5: Adjust the position of the nutation-coupled fast steering mirror in the vertical plane, so that the incident light enters the receiving optical fiber and the received optical power reaches the maximum value, and record the current position of the nutation-coupled fast steering mirror as the ground reference zero position. Step a6: Fix the sliding adjustable structures to keep the positions of the modules stationary, determine the coupling scanning area of the nutation-coupled fast steering mirror, and set it through the fast steering mirror controller. Step a7: After the device is launched into orbit, according to the ground reference zero position, fine-tune the nutation-coupled fast steering mirror again through the fast steering mirror controller, so that the optical power of the light incident on the receiving optical fiber reaches the maximum, and set the position of the nutation-coupled fast steering mirror at this time as the on-orbit reference zero position.

[0028] After initializing and calibrating the device using the above method, the optical axes of the spot position monitoring module and the receiving optical fiber are parallel on the same horizontal plane, and the light beams are respectively focused on the central position of the position monitor and a determined small range area centered on the core of the receiving optical fiber, that is, the coupling scanning area. The reference zero position and the coupling scanning area of the nutation scanning fast steering mirror are set through the fast steering mirror controller to complete the initial calibration.

[0029] In a feasible implementation manner, the specific method for using the nutation coupling device provided by the present invention to receive free space light into an optical fiber includes: Step b1: Make the free space light be normally incident on the incident surface of the beam splitting module. After being split by the beam splitting surface, the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light. Step b2: Adjust the free-space light so that the spot of the reflected light remains at the center position of the spot position monitoring module. Meanwhile, the transmitted light enters the fiber coupling focusing mirror and the incident lens barrel through the nutation-coupled fast steering mirror, and the spot is within the coupling scanning area. Step b3: Control the nutation-coupled fast steering mirror to scan within the coupling scanning area through the fast steering mirror controller, so that the spot is coupled into the optical fiber. The coupling scanning area refers to the area with the strongest fiber coupling within a predetermined range near the reference zero position of the nutation-coupled fast steering mirror calibrated through initial calibration.

[0030] Adopting the above technical solution, the present invention has the following beneficial effects: The present invention provides an optical fiber nutation coupling device and its usage method. The device is initialized and calibrated through a beam splitting module, a spot position detector, and an optical fiber coupling installation and adjustment module, which can pre-calibrate the position with the strongest fiber coupling, control the change in coupling efficiency caused by nutation within a certain small range area, and then quickly and efficiently couple the beam into the core of the receiving optical fiber through nutation scanning. The device of the present invention can solve the technical problem in the prior art that it is difficult to efficiently and stably couple free-space light into a single-mode optical fiber. At the same time, the device of the present invention adopts a modular design concept, highly integrates the nutation coupling system, has a compact structure, small volume, light weight, and low power consumption, and is convenient for system assembly, debugging, and maintenance. Description of the Drawings

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a three-dimensional structure diagram of the optical fiber nutation coupling device provided by the embodiment of the present invention; Figure 2 It is a top view of the structure of the optical fiber nutation coupling device provided by the embodiment of the present invention; Figure 3 It is a three-dimensional structure diagram of the optical fiber coupling installation and adjustment module provided by the embodiment of the present invention; Figure 4 It is a top view of the structure of the optical fiber coupling installation and adjustment module provided by the embodiment of the present invention; Figure 5 It is an exploded view of the structure of the nutation-coupled fast steering mirror provided by the embodiment of the present invention; Figure 6This is a comparison diagram of the spot positions detected by the position detector before and after initialization calibration provided by an embodiment of the present invention. Among them, figure (a) shows the spot position detected by the position detector before initialization calibration; figure (b) shows the spot position detected by the position detector after initialization calibration; Figure 7 This is a flowchart of a method for initializing and calibrating an optical fiber nutation coupling device provided by an embodiment of the present invention; Figure 8 This is a flowchart of a method for using an optical fiber nutation coupling device to receive free space light into a single-mode optical fiber provided by an embodiment of the present invention; Reference numerals: 1 - optical fiber flange; 2 - incident lens barrel; 3 - L-shaped support plate; 4 - three-point adjustment disk; 5 - first focusing lens holder; 6 - first focusing lens; 7 - first spacer; 8 - first narrow-band filter; 9 - second spacer; 10 - light shield; 11 - fast steering mirror base; 12 - nutation coupling fast steering mirror; 13 - fast steering mirror controller; 14 - beam splitter prism base; 15 - beam splitter prism; 16 - third spacer; 17 - second narrow-band filter; 18 - fourth spacer; 19 - second focusing lens; 20 - second focusing lens holder; 21 - detector encapsulation cover; 22 - spot imaging sensor; 23 - detector window; 24 - main base; 25 - sliding adjustable structure; 26 - stud; 1201 - fast steering mirror base; 1202 - fast steering mirror amplification structure; 1203 - piezoelectric ceramic; 1204 - lens holder; 1205 - flexible hinge; 1206 - gland; 1207 - reflecting lens. Detailed implementation manners

[0033] Next, the technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. 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.

[0034] The following further explains the present invention in conjunction with specific implementation manners.

[0035] The design concept of the device of the present invention is based on the principle of light reflection and the law of light refraction. A beam splitting module, a spot position detection module, and an optical fiber coupling alignment module are added to the traditional nutation coupling device. Using the spot position of the reflected light that is homologous to the received light source as a reference, the position with the strongest optical fiber coupling is pre-calibrated through initialization calibration, and the change in coupling efficiency caused by nutation is controlled within a certain small range. Then, through nutation scanning, free space light is quickly and efficiently coupled into the core of the receiving optical fiber.

[0036] Embodiment 1 AsFigure 1 and Figure 2 The front view and the top cross-sectional view of the structural diagram of the fiber optic nutation coupling device provided by the embodiment of the present invention are shown respectively, which mainly include a beam splitting module, a spot position monitoring module, a fiber optic coupling alignment module, a nutation scanning module, a receiving optical fiber, and a main base 24; The beam splitting surface of the beam splitting module is fixed at 45 degrees with the main base 24. The incident light is normally incident on the incident surface of the beam splitting module. After being split by the beam splitting surface, the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light; The spot position monitoring module includes a position detection focusing mirror and a position detector, and is used to monitor the spot position of the reflected light. The reflected light is incident on the position detector through the position detection focusing mirror. The position detection focusing mirror and the position detector are respectively connected to the main base 24 through a bolt-fastened sliding adjustable structure 25, which is used to adjust the focal length of the spot position monitoring module; The nutation scanning module includes a nutation coupling fast steering mirror 12 and a fast steering mirror controller 13. The fast steering mirror controller 13 is used to control the nutation coupling fast steering mirror 12 to perform nutation scanning within the coupling scanning area; In this embodiment, the fiber optic coupling alignment module includes a fiber optic coupling focusing mirror, an incident lens barrel 2, a fiber optic flange 1, a three-point adjustment disk 4, and an L-shaped support plate 3. The fiber optic flange 1 is arranged at one end of the incident lens barrel 2 and is used to install the receiving optical fiber. The other end of the incident lens barrel 2 passes through the vertical surface of the L-shaped support plate 3 and the three-point adjustment disk 4 and is inserted into the lens barrel of the fiber optic coupling focusing mirror. The three-point adjustment disk 4 is installed on the vertical surface of the L-shaped support plate 3. The horizontal plane of the L-shaped support plate 3 and the fiber optic coupling focusing mirror are respectively connected to the main base 24 through a bolt-fastened sliding adjustable structure 25, which is used to adjust the focal length of the fiber optic coupling alignment module; The three-point adjustment disk 4 is installed on the vertical plate of the L-shaped support plate 3 through a stud 26. Three adjustment set screws are arranged on the three-point adjustment disk 4. By adjusting the set screws of the three-point adjustment disk 4, the receiving optical fiber and the incident lens barrel 2 can be finely adjusted in position and angle, and the adjustment can reach the micron level.

[0037] The transmitted light is reflected by the nutation coupling fast steering mirror 12 and then enters the fiber optic coupling focusing mirror, and then enters the receiving optical fiber through the incident lens barrel 2.

[0038] In this embodiment, in addition to the above-mentioned modules, the device further includes a light shield 10, which is fixed outside the gap between the nutating coupled fast steering mirror 12 and the fiber-coupled focusing mirror, and is used to exclude interfering light and block ambient light (such as sunlight) or internal system reflected light from entering the fiber-coupled alignment module. A triangular support plate with a bottom plate is provided on the back of the light shield 10, and is fixed on the upper surface of the fast steering mirror controller 13 or the main base 24 by screws, making the overall structure of the device more stable. The light shield 10 is preferably made of a metal material, and the surface of the light shield 10 is blackened for absorbing stray light.

[0039] The main base 24 is used to fix each module, compactly combine each module together, and at the same time make the overall structure more stable and improve the accuracy of the system.

[0040] In this embodiment, the beam splitting module uses a cube beam splitting prism 15. The function of the beam splitting prism 15 is to split the incident light into two paths, one path enters the spot position monitoring module, and the other path passes through the nutating scanning module, the fiber-coupled alignment module and the receiving optical fiber and enters the coupled optical fiber, and the splitting ratio is 1:1 or 2:8.

[0041] In a specific implementation, the beam splitting prism 15 is formed by gluing two right-angled prisms, and a beam splitting film is plated at the interface to achieve splitting of the incident light into reflection and transmission; the beam splitting film selects different coating designs according to the laser wavelength.

[0042] Further, to protect the beam splitting prism body and facilitate fixing, a protective cover is provided outside the beam splitting prism 15. Windows are left on three sides of the protective cover for the incident light to enter and the transmitted light and the reflected light to exit respectively. The bottom surface is fixed on the beam splitting prism base 14 to keep the centers of the modules in the device on the same horizontal plane, ensuring the consistency of the optical path. The other surfaces are preferably made of light-shielding materials to reduce the interference of stray light on the signal light.

[0043] In this embodiment, the position detector includes a spot imaging sensor 22, a detector encapsulation cover 21 and a detector window 23. The spot imaging sensor 22 and the detector window 23 are respectively arranged at the central positions at both ends of the detector encapsulation cover 21. One end of the detector encapsulation cover 21 provided with the detector window 23 is inserted into the lens barrel of the position detection focusing mirror. The fastening bolt groove of the position detector is arranged at the corresponding positions of the base of the detector encapsulation cover 21 and the main base 24. The spot imaging sensor 22 uses a CCD to collect spot images in real time. The position of the spot can be viewed and monitored in real time through an external device or software. The photosensitive pixel size of the CCD can reach the micron level, meeting the high-resolution requirements in optical fiber communication.

[0044] Further, the detector encapsulation cover 21 of the position detector uses a light-shielding material.

[0045] Furthermore, a narrow-band filter is provided at the detector window 23 to suppress the interference of stray light and improve the quality of the signal light.

[0046] As Figure 3 and Figure 4 shown in the front view and the top sectional view of the fiber optic coupling and alignment module structure diagram, sliding adjustable structures 25 are provided at the bases of the L-shaped support plate 3, the fiber optic coupling focusing mirror, and the position detection focusing mirror, respectively, for laterally sliding and fixing the fiber optic coupling and alignment module, the fiber optic coupling focusing mirror, and the position detection focusing mirror.

[0047] In this embodiment, the fiber optic coupling focusing mirror includes a first focusing mirror base 5, a first focusing mirror 6, and a first narrow-band filter 8. The first focusing mirror 6 and the first narrow-band filter 8 are respectively disposed in the middle and one end of the barrel of the first focusing mirror base 5. The incident light enters the first focusing mirror 6 after being filtered by the first narrow-band filter 8. The other end of the barrel is used to insert into the incident barrel 2. The sliding adjustable structure 25 of the fiber optic coupling focusing mirror is disposed at the corresponding positions of the main base 24 and the first focusing mirror base 5.

[0048] Furthermore, the first focusing mirror 6 and the first narrow-band filter 8 are respectively fixed at the middle position of the barrel of the fiber optic coupling focusing mirror and the end where the signal light enters through the first spacer 7 and the second spacer 9. A reserved position is provided at the other end of the barrel for inserting the incident barrel 2. The focal length of the first focusing mirror 6 can be adjusted by adjusting the inserted length of the incident barrel 2.

[0049] Similarly, the position detection focusing mirror includes a second focusing mirror base 20, a second focusing mirror 19, and a second narrow-band filter 17. The second narrow-band filter 17 and the second focusing mirror 19 are respectively fixed at the middle and one end of the barrel of the position detection focusing mirror through the third spacer 16 and the fourth spacer 18. The incident light enters the second focusing mirror 19 after being filtered by the second narrow-band filter 17. The other end of the barrel is used to insert into one end of the detector package cover 21 provided with the detector window 23. The sliding adjustable structure 25 of the position detection focusing mirror is disposed at the corresponding positions of the main base 24 and the second focusing mirror base 20.

[0050] Furthermore, the first narrow-band filter 8, the second narrow-band filter 17, and the narrow-band filter of the detector window 23 can be configured or replaced according to the wavelength of the signal light to enhance the suppression of interference waves and improve the quality of the signal light.

[0051] As Figure 5 shown, in this embodiment, the nutation-coupled fast steering mirror 12 includes a fast steering mirror base 11, a fast steering mirror base 1201, a fast steering mirror amplification structure 1202, a piezoelectric ceramic 1203, a lens holder 1204, a flexure hinge 1205, a reflecting lens 1207, and a gland 1206.

[0052] Further, the fast steering mirror base 11 is an L-shaped panel. The horizontal plane of the L-shaped panel is fixed on the upper surface of the fast steering mirror controller 13. The fast steering mirror base 1201 is fixed on the vertical surface of the L-shaped panel through the bolt-fastened sliding adjustable structure 25. The fast steering mirror amplification structure 1202 includes four triangular linkages with the same structure. The horizontal bars of the triangular linkages are all fixed on the fast steering mirror base 11 and are equidistant from the center of the bottom surface of the fast steering mirror base 1201. The diagonal braces of the triangular linkages form an acute angle with the horizontal bars. The piezoelectric ceramics 1203 are arranged between the horizontal bars and the diagonal braces of the triangular linkages. The lens holder 1204 is installed at the tops of the four diagonal braces. The reflecting lens 1207 is installed on the lens holder 1204 through the flexible hinge 1205. The gland 1206 is of an annular structure and is installed on the top of the fast steering mirror base 1201 to encapsulate the fast steering mirror amplification structure 1202, the piezoelectric ceramics 1203, the lens holder 1204, the flexible hinge 1205 and the reflecting lens 1207 in the fast steering mirror base 1201.

[0053] Further, fastening bolt grooves of the bolt-fastened sliding adjustable structure 25 are arranged on the bottom of the fast steering mirror base 1201 and / or on the vertical surface of the fast steering mirror base 11 for adjusting the position of the fast steering mirror base 1201 in the vertical plane (including the longitudinal X direction and the Y direction).

[0054] Further, a high-precision displacement sensor is arranged on the piezoelectric ceramics 1203 to feed back the displacement generated by the piezoelectric ceramics 1203 to the fast steering mirror controller 13, so that the fast steering mirror controller 13 can adaptively control the nutation-coupled fast steering mirror 12 to complete the coupling of the signal light to the receiving optical fiber.

[0055] As Figure 7 shown, in this embodiment, the method for initializing and calibrating the optical fiber nutation coupling device is as follows: Step a1, control the incident light to be normally incident on the incident surface of the beam splitting module, so that the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light.

[0056] The position of the beam splitting prism 15 is fixed. The incident light can be adjusted by the autocollimation method to ensure that the light is normally incident on the first surface of the beam splitting prism 15. The reflection surface of the beam splitting prism 15 is fixed at 45 degrees to ensure that the reflected light is perpendicular to the incident light.

[0057] Step a2, adjust the positions of the position detection focusing lens and the position detector through the bolt-fastened sliding adjustable structure 25 to make the reflected light focus on the center position of the position detector and keep it stationary.

[0058] After the incident light is split by the beam splitting module, the reflected light passes through the position detection focusing mirror and forms a reflected light spot at the center of the spot imaging sensor 22 of the position detector. The optical path of the reflected light is adjusted by the bolt-fastened sliding adjustable structure 25 on the position detection focusing mirror and the position detector, so that the light spot of the reflected light is focused at the center of the spot imaging sensor 22. The position of the range light spot is monitored by a monitoring device or software. Using CCD imaging technology, a resolution of the micron level can be achieved. The position of the reflected light spot remains stationary and is used as a reference benchmark for subsequent calibration steps.

[0059] Step a3: Set the nutation-coupled fast steering mirror 12 at the zero position without movement. Adjust the position of the receiving optical fiber in the vertical plane through the L-shaped support plate 3 and the three-point adjustment disk 4, so that the incident light enters the receiving optical fiber and the optical power reaches the maximum value. The receiving optical fiber is fixed on the optical fiber flange 1, and the position of the receiving optical fiber is adjusted by finely moving the optical fiber flange 1 to adjust the spot focusing.

[0060] Step a4: By changing the front and rear positions of the incident lens barrel 2 extending into the lens barrel of the fiber coupling focusing mirror and adjusting the focal length with the three-point adjustment disk 4, the optical power incident on the receiving optical fiber is maximized.

[0061] After the incident light is split by the beam splitting module, the transmitted light is reflected by the nutation-coupled fast steering mirror 12 and then enters the fiber coupling focusing mirror, and then enters the receiving optical fiber through the incident lens barrel 2. However, since the end face of the optical fiber core is very small (at the micron level), the light beam cannot be accurately aligned with the end face of the optical fiber. The design concept of the device of the present invention overcomes various errors brought by the objective environment as much as possible through high-precision initial calibration, and controls the received light beam within a small range near the end face of the optical fiber. Therefore, in the design of the fiber coupling alignment module, in addition to adjusting the positions of the L-shaped support plate 3 and the fiber coupling focusing mirror through the bolt-fastened sliding adjustable structure 25, a three-point adjustment disk 4 is also designed to finely adjust the receiving optical path, and a resolution of the micron level can be achieved.

[0062] In steps a3 and a4, the position of the nutation-coupled fast steering mirror 12 is first determined, and then the positions of the receiving optical fiber are adjusted in the vertical plane and the axial direction respectively, so that the received light is incident on the end face of the receiving optical fiber as perpendicularly as possible.

[0063] The three-point adjustment disk 4 is used to finely adjust the position of the receiving optical fiber. During the system alignment process, the initial position of the receiving optical fiber is adjusted by the three set screws on the three-point adjustment disk 4, so that the center of the received light spot of the light spot position detector is coaxial with the optical path of the receiving optical fiber under static conditions.

[0064] Step a5: Adjust the position of the nutation-coupled fast steering mirror 12 in the vertical plane so that the incident light enters the receiving optical fiber and the received optical power reaches the maximum value. Record the current position of the nutation-coupled fast steering mirror 12 as the ground reference zero position; Adjust the position of the fast steering mirror base 1201 in the vertical plane, including the longitudinal X direction and the Y direction, through the fastening bolt slots of the bolt fastening sliding adjustable structure 25 provided on the bottom of the fast steering mirror base 1201 and / or on the vertical surface of the fast steering mirror pedestal 11.

[0065] Step a6, fix each of the sliding adjustable structures 25 so that the positions of the modules remain unchanged, determine the coupled scanning area of the nutation coupled fast steering mirror 12, and set it through the fast steering mirror controller 13.

[0066] In a specific implementation, any step in steps a1 - a6 can be adjusted repeatedly according to the actual situation until the preset standard for the initial calibration of the device is reached. Finally, fix the positions of the various components in the device and no longer change. Keep the position detector consistent with the optical axis of the fiber core and maximize the optical power entering the receiving fiber. Through the above process, the ground initialization calibration of the device of the present invention is completed.

[0067] Step a7, after the device is launched into orbit, according to the ground reference zero position, fine - tune the nutation coupled fast steering mirror 12 again through the fast steering mirror controller 13 to maximize the optical power incident on the receiving fiber, and set the position of the nutation coupled fast steering mirror 12 at this time as the on - orbit reference zero position.

[0068] In the above steps, the process of confirming the reference zero position is realized through the output voltage setting of the fast steering mirror controller 13. Different positions of the nutation coupled fast steering mirror 12 correspond to different control voltages, and the range of control voltage values corresponding to different nutation coupled fast steering mirrors 12 is different. Exemplarily, for a nutation coupled fast steering mirror 12 with an input voltage range of - 10V to 10V, the scanning range is - 2mrad to + 2mrad (i.e., the position range of the nutation coupled fast steering mirror 12). After the initialization calibration is completed, the corresponding initialization configuration is completed through the fast steering mirror controller 13. In addition to the setting of the reference zero position and the coupled scanning area, it also includes the setting of parameters such as the scanning path, scanning speed, and scanning mode.

[0069] From the ground to on - orbit, various objective reasons such as mechanical structure micro - deformation and huge environmental temperature changes will cause small changes in the position of the received light spot, affecting the alignment efficiency and accuracy between the receiving fiber and the received light spot. Therefore, in the on - orbit environment, it is necessary to calibrate the reference zero position of the nutation coupled fast steering mirror 12 and the coupled scanning area corresponding to the new reference zero position again to improve the alignment efficiency and accuracy.

[0070] In other embodiments, during the daily maintenance of the device of the present invention, the reference zero position of the nutation coupled fast steering mirror 12 can also be periodically and automatically calibrated through the program control of the fast steering mirror controller 13, or a calibration instruction can be sent from the ground to the fast steering mirror controller 13 for reference zero calibration to maintain the effectiveness of the coupled scanning area.

[0071] The coupled scanning area refers to the area with the strongest fiber coupling within a predetermined range near the reference zero position of the nutation-coupled fast steering mirror 12 calibrated through initial calibration. In this embodiment, the range of the coupled scanning area corresponding to the scanning of the fast steering mirror is within a maximum of ±200 μrad near the reference zero position. To further improve the coupling efficiency, the normal coupled scanning area is restricted to within ±50 μrad near the reference zero position. If the received power does not reach the predetermined standard within the range of ±50 μrad, the scanning range is gradually expanded, with the maximum range being ±200 μrad.

[0072] For the nutation-coupled device that has completed initial calibration through the above initial calibration method, when receiving an optical signal into the receiving optical fiber, it can ensure that when the spot of the reflected light is located at the center position of the spot position detection module, the spot position of the transmitted light reflected by the nutation-coupled fast steering mirror and entering the fiber coupling and alignment module is also within the coupled scanning area. If the light beam cannot enter the initialized fiber coupling area as scheduled, the device needs to be re-initialized and calibrated to ensure that under normal operating conditions, the device of the present invention can quickly, efficiently, and stably receive spatial light into a single-mode optical fiber within the coupled scanning area, thereby ensuring the stable operation of the communication system.

[0073] Embodiment 2 As Figure 8 shown, this embodiment provides a specific method for receiving free-space light into a single-mode optical fiber using the above nutation-coupled device, including: Step b1, making the free-space light normally incident on the incident surface of the beam splitting module. After being split by the beam splitting surface, the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light; Step b2, adjusting the free-space light to keep the spot of the reflected light at the center position of the spot position monitoring module. At the same time, the transmitted light enters the fiber coupling focusing mirror and the incident barrel through the nutation-coupled fast steering mirror, and the spot is within the coupled scanning area; Step b3, controlling the nutation-coupled fast steering mirror to scan within the coupled scanning area through the fast steering mirror controller to couple the spot into the optical fiber; The coupled scanning area refers to the area with the strongest fiber coupling within a predetermined range near the reference zero position of the nutation-coupled fast steering mirror calibrated through initial calibration.

[0074] When receiving free-space light, before the light beam enters the beam splitting module, it is also necessary to shape the light beam to enhance the optical signal quality.

[0075] As Figure 6As shown, it is a comparison diagram of the spot positions detected by the position detector before and after initialization calibration. Figure (a) is the moving trajectory of the spot position detected and recorded by the position detector before initialization calibration. After initialization calibration, the spot trajectory is as shown in Figure (b). It can be seen that the device of the present invention can control the spot within a certain small range near the center position of the position detector after initialization calibration. Since the receiving optical path of the receiving optical fiber is coaxial with the receiving optical path of the spot of the position detector, it can be determined that the position of the receiving optical fiber and the receiving spot will also be controlled within a certain small range, thereby reducing the uncertainty of the nutation-coupled fast steering mirror capturing the receiving spot and greatly improving the coupling efficiency and accuracy of nutation scanning.

[0076] The fiber nutation coupling device and method provided by the present invention work in combination with the traditional laser communication terminal acquisition and tracking scheme, which can further reduce the tracking residual of the traditional laser communication terminal and effectively improve the communication stability of the space laser communication terminal.

[0077] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An optical fiber nutation coupling device, characterized in that, It includes a beam splitting module, a spot position monitoring module, an optical fiber coupling assembly and alignment module, a nutation scanning module, a receiving optical fiber, and a main base; The beam splitting surface of the beam splitting module is fixed at 45 degrees to the main base. The incident light is normally incident on the incident surface of the beam splitting module. After being split by the beam splitting surface, the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light; The spot position monitoring module includes a position detection focusing mirror and a position detector, and is used to monitor the spot position of the reflected light. The reflected light is incident on the position detector through the position detection focusing mirror. The position detection focusing mirror and the position detector are respectively connected to the main base through a bolt-fastened sliding adjustable structure, and are used to adjust the focal length of the spot position monitoring module; The nutation scanning module includes a nutation coupling fast steering mirror and a fast steering mirror controller. The fast steering mirror controller is used to control the nutation coupling fast steering mirror to perform nutation scanning within the coupling scanning area; The optical fiber coupling assembly and alignment module includes an optical fiber coupling focusing mirror, an incident lens barrel, an optical fiber flange, a three-point adjustment disc, and an L-shaped support plate. The optical fiber flange is arranged at one end of the incident lens barrel and is used to install the receiving optical fiber. The other end of the incident lens barrel passes through the vertical surface of the L-shaped support plate and the three-point adjustment disc and is inserted into the lens barrel of the optical fiber coupling focusing mirror. The three-point adjustment disc is installed on the vertical surface of the L-shaped support plate. The horizontal surface of the L-shaped support plate and the optical fiber coupling focusing mirror are respectively connected to the main base through a bolt-fastened sliding adjustable structure, and are used to adjust the focal length of the optical fiber coupling assembly and alignment module; The transmitted light is reflected by the nutation coupling fast steering mirror and then enters the optical fiber coupling focusing mirror, and then enters the receiving optical fiber through the incident lens barrel.

2. The device according to claim 1, wherein It also includes a light shield, which is fixed outside the gap between the nutation coupling fast steering mirror and the optical fiber coupling focusing mirror and is used to exclude interfering light.

3. The device according to claim 1, characterized in that, The beam splitting module uses a cube beam splitting prism.

4. The device according to claim 3, characterized in that, The position detector includes a spot imaging sensor, a detector encapsulation cover, and a detector window. The spot imaging sensor and the detector window are respectively arranged at the center positions of both ends of the detector encapsulation cover. One end of the detector encapsulation cover with the detector window is inserted into the lens barrel of the position detection focusing mirror. The sliding adjustable structure of the position detector is arranged at the corresponding positions of the detector encapsulation cover base and the main base. The spot imaging sensor uses a charge-coupled device to collect spot images in real time.

5. The device according to claim 4, characterized in that, Sliding adjustable structures are arranged at the bases of the L-shaped support plate, the optical fiber coupling focusing mirror, and the position detection focusing mirror, and are respectively used for lateral position sliding adjustment and fixation of the optical fiber coupling assembly and alignment module, the optical fiber coupling focusing mirror, and the position detection focusing mirror.

6. The device according to claim 5, characterized in that, The optical fiber coupling focusing mirror includes a first focusing mirror base, a first focusing mirror, and a first narrowband filter. The first focusing mirror and the first narrowband filter are respectively arranged in the middle and at one end of the lens barrel of the first focusing mirror base. The incident light passes through the first narrowband filter and then enters the first focusing mirror. The other end of the lens barrel is used to insert the incident lens barrel. The sliding adjustable structure of the optical fiber coupling focusing mirror is arranged at the corresponding positions of the main base and the first focusing mirror base.

7. The device according to claim 1, characterized in that, The nutation-coupled fast steering mirror includes a fast steering mirror base, a fast steering mirror pedestal, a fast steering mirror amplification structure, a piezoelectric ceramic, a lens holder, a flexure hinge, a reflecting lens, and a gland.

8. The device according to claim 7, characterized in that, The fast steering mirror base is an L-shaped panel. The horizontal plane of the L-shaped panel is fixed on the upper surface of the fast steering mirror controller. The fast steering mirror pedestal is fixed on the vertical surface of the L-shaped panel through a bolt-fastened sliding adjustable structure. The fast steering mirror amplification structure includes four triangular linkages with the same structure. The horizontal bars of the triangular linkages are all fixed on the fast steering mirror base and are equidistant from the center of the bottom surface of the fast steering mirror pedestal. The diagonal struts of the triangular linkages form an acute angle with the horizontal bars. The piezoelectric ceramic is arranged between the horizontal bar and the diagonal strut of the triangular linkage. The lens holder is installed at the top of the four diagonal struts. The reflecting lens is installed on the lens holder through a flexure hinge. The gland is of an annular structure and is installed on the top of the fast steering mirror pedestal to encapsulate the fast steering mirror amplification structure, the piezoelectric ceramic, the lens holder, the flexure hinge, and the reflecting lens in the fast steering mirror pedestal.

9. The device according to claim 8, wherein The method for initializing and calibrating the device is as follows: Step a1: Control the incident light to be normally incident on the incident surface of the beam splitting module, so that the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light. Step a2: Adjust the positions of the position detection focusing lens and the position detector through the bolt-fastened sliding adjustable structure, so that the reflected light is focused on the central position of the position detector and remains stationary. Step a3: Set the nutation-coupled fast steering mirror to be stationary at the zero position. Adjust the position of the receiving optical fiber in the vertical plane through the L-shaped support plate and the three-point adjustment disk, so that the incident light enters the receiving optical fiber and the optical power reaches the maximum value. Step a4: By changing the front and rear positions of the incident lens barrel extending into the lens barrel of the fiber coupling focusing lens and adjusting the focal length of the three-point adjustment disk, make the optical power of the light incident on the receiving optical fiber the maximum. Step a5: Adjust the position of the nutation-coupled fast steering mirror in the vertical plane, so that the incident light enters the receiving optical fiber and the received optical power reaches the maximum value. Record the current position of the nutation-coupled fast steering mirror as the ground reference zero position. Step a6: Fix the sliding adjustable structures to keep the positions of the modules stationary, determine the coupling scanning area of the nutation-coupled fast steering mirror, and set it through the fast steering mirror controller. Step a7: After the device is launched into orbit, according to the ground reference zero position, fine-tune the nutation-coupled fast steering mirror again through the fast steering mirror controller, so that the optical power of the light incident on the receiving optical fiber reaches the maximum, and set the position of the nutation-coupled fast steering mirror at this time as the on-orbit reference zero position.

10. The device according to any one of claims 1-9, characterized in that, The specific method for the device to receive free space light into the optical fiber includes: Step b1: Make the free space light normally incident on the incident surface of the beam splitting module. After being split by the beam splitting surface, the reflected light enters the spot position monitoring module perpendicular to the incident light, and the transmitted light enters the nutation scanning module along the direction of the incident light. Step b2: Adjust the free space light so that the spot of the reflected light remains at the central position of the spot position monitoring module. At the same time, the transmitted light enters the fiber coupling focusing lens and the incident lens barrel through the nutation-coupled fast steering mirror, and the spot is within the coupling scanning area. Step b3: Control the nutation-coupled fast steering mirror to scan within the coupling scan area through the fast steering mirror controller, so that the light spot is coupled into the optical fiber; The coupling scan area refers to the area with the strongest optical fiber coupling within a predetermined range near the reference zero position of the nutation-coupled fast steering mirror calibrated through initial calibration.

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