Optical fiber nutation coupling method, system and device based on electro-optical crystal

Abstract

The invention provides an optical fiber nutation coupling method, system and device based on an electro-optical crystal, and relates to the technical field of free space optical communication, and the device mainly comprises the electro-optical crystal, a convex lens, an optical fiber, a beam splitter, an optical power meter, a controller and a driver. The electro-optical crystal comprises a first electro-optical crystal and a second electro-optical crystal which are arranged in sequence, and is arranged on a light path between an external light source and the convex lens; the optical power meter is used for detecting the power of an optical signal, converting the power into a first electric signal and inputting the first electric signal to the controller. The characteristic that the refractive index of the electro-optical crystal directionally changes along with an electric field is utilized, the three-dimensional angle error generated when laser is incident and coupled to the center of the optical fiber end face is adjusted and compensated in real time by modulating voltage, and it is ensured that signal laser emitted by an external light source is incident to the center of the optical fiber end face accurately and vertically in real time; therefore, the efficiency, quality and stability of free space laser communication are improved; the device is simple in structure, small in size and wide in application range.

Description

Technical Field

[0001] The present invention relates to the technical field of free space optical communication, and in particular, to a fiber nutation coupling method, system and device based on an electro-optic crystal. Background Art

[0002] At present, the technology of spaceborne laser communication terminals has gradually matured, and links have been successfully established between satellites and between satellite and ground, resulting in an increasingly urgent demand for commercial applications of laser communication terminals.

[0003] However, due to the influence of factors such as optical machining errors, installation and debugging deviations, mechanical structure strain of the satellite platform, satellite platform vibration, and system transceiver coaxial error, it is very difficult to couple the weak signal light entering the optical system into a single-mode fiber with a size of about 9 μm.

[0004] Therefore, an efficient and stable free space optical-single mode fiber coupling method is a prerequisite and guarantee for realizing high-speed and long-distance laser communication technology. How to improve the efficiency, quality and stability of free space laser communication through automatic fiber technology has become a difficult problem in the industry. Summary of the Invention

[0005] The purpose of the present invention is to provide a fiber nutation coupling method, system and device based on an electro-optic crystal to solve at least one of the above technical problems existing in the prior art.

[0006] In a first aspect, to solve the above technical problems, the present invention provides a fiber nutation coupling method based on an electro-optic crystal, including the following steps: Step 1: Make the laser converge towards the center of the end face of the fiber input end after entering the electro-optic crystal; the electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged in sequence, which are respectively used to adjust one optical path direction in the nutation direction; Step 2: Collect the optical power of the laser signal at the fiber output end, and based on the change rate of the optical power, calculate the angular error of the laser in each nutation direction; Step 3: Based on the angular error, calculate the modulation voltage applied to the electrodes of each electro-optic crystal, and use the electro-optic effect to change the refractive index of the laser in each nutation direction; Step 4: Load the modulation voltage on the electrodes of each electro-optic crystal, compensate for the angular error of the laser in each nutation direction, and iteratively execute Step 2 until the first iteration end condition is reached.

[0007] Through the above method, by using the characteristic that the refractive index of the electro-optic crystal changes directionally with the electric field, the modulation voltage is used to adjust and compensate in real time the solid angle error when the laser is incident on the center of the fiber end face, ensuring that the laser is incident on the center of the fiber end face in real time, accurately and vertically, thereby improving the efficiency, quality and stability of free space laser communication.

[0008] In a feasible implementation, the electro-optic crystal is LiTaO 3 (lithium tantalate) crystal, which has the advantages of high optical damage threshold, low birefringence, high transmission bandwidth, high light transmittance, strong sensitivity, wide light transmission range, large electro-optic coefficient, not easy to deliquesce, and stable physical and chemical properties compared with other electro-optic crystal materials.

[0009] In a feasible implementation, the LiTaO 3 crystal is cylindrical, and a plurality of cylindrical electrodes are evenly distributed on the circumferential surface, which is convenient for providing a uniform vertical electric field.

[0010] In a feasible implementation, the electro-optic coefficient matrix r of the LiTaO 3 crystal can be expressed as follows: ; Among them, represents the main electro-optic coefficient when an electric field is applied in the Z-axis direction of the crystal (the length direction of the cylindrical crystal is set as the Y-axis); Then, the relationship between the refractive index in the Z-axis direction of the crystal and the electric field in the Z-axis direction of the crystal can be: ; Among them, represents the intrinsic refractive index of the material.

[0011] In a feasible implementation, the calculation formula for the deflection angle 3 of the laser in the LiTaO crystal relative to the Y-axis can be expressed as: ; Among them, represents the length of the crystal in the Y-axis direction; represents the radius of the light passing port of the crystal; represents the initial voltage in the Z-axis direction.

[0012] In a feasible implementation, takes a value of 8 mm; takes a value of 2.18; takes a value of 3.3ⅹ10 -11 m / V; takes a value of 2.75 mm; then substituting and simplifying the above equation can obtain the deflection rate : ; In a feasible implementation, the calculation formula for the modulation voltage can be: ; wherein, represents the angular error of the laser projected onto the XY coordinate plane; represents the angular error of the laser projected onto the YZ coordinate plane; represents the modulation voltage in the X-axis direction of the crystal; represents the modulation voltage in the Z-axis direction of the crystal; In this way, through the above formula, the modulation voltage for compensating the angular error can be accurately calculated. By applying this modulation voltage to the electrodes of the electro-optic crystal, the refractive index of the electro-optic crystal can be modulated, thereby adjusting the direction of the laser.

[0013] In a feasible implementation manner, the end condition of the first iteration is that the angular error of the laser in each nutation direction is zero.

[0014] In a second aspect, based on the same inventive concept, the present application further provides a fiber nutation coupling system based on an electro-optic crystal, including a data receiving module, a data processing module, and a signal generating module: The data receiving module is configured to receive the optical power of the laser signal at the output end of the optical fiber; The data processing module includes an angular error resolution unit and a modulation voltage calculation unit: The angular error resolution unit resolves the angular error of the laser in each nutation direction based on the change rate of the optical power; The modulation voltage calculation unit calculates the modulation voltage applied to the electrodes of each electro-optic crystal based on the angular error, for changing the refractive index of the laser in each nutation direction according to the electro-optic effect; The signal generating module sends the modulation voltage to the electrodes of each electro-optic crystal.

[0015] In a third aspect, based on the same inventive concept, the present application further provides a fiber nutation coupling device based on an electro-optic crystal, including an electro-optic crystal, a convex lens, an optical fiber, a beam splitter, an optical power meter, a controller, and a driver: The electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged in sequence, and is disposed on the optical path between the external light source and the convex lens; the convex lens is configured to converge the light beam output by the electro-optic crystal to the center of the end face of the optical fiber input end; the beam splitter is disposed at the output end of the optical fiber, and is configured to output the optical signal to the optical power meter and the subsequent device respectively according to the splitting ratio; the optical power meter is configured to detect the power of the optical signal and convert it into a first electrical signal and input it to the controller; the controller resolves the angular error of the light beam in each nutation direction based on the first electrical signal and calculates the modulation voltage applied to the electrodes of each electro-optic crystal, and outputs it to the driver; the driver supplies power to the electrodes of each electro-optic crystal based on the modulation voltage.

[0016] With the above structure, the characteristic that the refractive index of the electro-optic crystal changes directionally with the electric field can be utilized. By modulating the voltage, the solid angle error when the compensation laser is incident on the center of the fiber end face can be adjusted in real time, ensuring that the laser emitted by the external light source is incident on the center of the fiber end face in real time, accurately, and vertically, thereby improving the efficiency, quality, and stability of free-space laser communication; the structure of this device is simple, the volume is small, and the application range is wide.

[0017] In a feasible implementation manner, this device further includes a beam expander, which is arranged on the optical path between the external light source and the electro-optic crystal. Through an afocal system, the free-space laser is compressed and vertically projected onto the end face of the input end of the electro-optic crystal to filter out stray light.

[0018] In a feasible implementation manner, the subsequent device includes a communication detector, which is used to perform photoelectric conversion on the input optical signal to obtain a second electrical signal; the second electrical signal is used to transmit communication data.

[0019] In a feasible implementation manner, the subsequent device further includes a demodulator, which is used to demodulate the second electrical signal output by the communication detector.

[0020] In a feasible implementation manner, a half-wave plate is arranged on the optical path between the first electro-optic crystal and the second electro-optic crystal to adjust the polarization state of the light beam so as to meet the polarization state requirements of the electro-optic crystal.

[0021] In a feasible implementation manner, the optical fiber is a single-mode optical fiber, so that the transmission bandwidth is wider and the transmission distance is farther.

[0022] In a feasible implementation manner, the splitting ratio is 1:4 or 1:9 or 3:7.

[0023] In a feasible implementation manner, the working method of the optical fiber nutation coupling device includes a first working method and a second working method; The first working method works under the condition of knowing the initial position of the signal (at this position, part or all of the laser can be coupled into the optical fiber), and specifically includes the following steps: Step a1: After the controller receives the signal initial position data, the optical fiber nutation coupling device enters the working state, and the electro-optic crystal performs two-dimensional scanning; the target azimuth information of the optical fiber input end (from the laser beam entering the optical power meter) is converted into the deflection angles of each electro-optic crystal, and preliminary coupling is performed and judged: if the qualified condition for preliminary coupling is reached, step a2 is executed; otherwise, step a1 is executed again; Step a2: Steplessly adjust the deflection angle of the electro-optical crystal through a driver. The controller records the optical power value (feedback signal) of the optical power meter and converts it into the modulation voltage of each electro-optical crystal, and then adjusts the deflection angle of the electro-optical crystal again to achieve precise alignment. Step a3: The controller determines the offset orientation of the light spot at the fiber input end in real time according to the magnitude of the optical power value, and finely adjusts each electro-optical crystal until the qualified condition of stable coupling is reached, so as to achieve stable coupling. Step a3: Turn on the communication link, and the controller monitors the target orientation information in real time. If the target orientation information is lost midway, then re-execute Step a1; otherwise, maintain the communication state until the communication ends. The second working method works in the case where the initial position of the unknown signal is unknown, and specifically includes the following steps: Step b1: Drive the electro-optical crystal to perform a trajectory scan with a preset large deflection angle and make a judgment. If a laser signal exists, then execute Step b2; otherwise, execute Step b1. Step b2: Drive the electro-optical crystal to complete several one-way trajectory scans with a preset small deflection angle, calculate the initial position of the signal light based on the preset trajectory and the magnitude of the target feedback signal, and make a judgment. If the initial position of the signal light exists, then execute b3; otherwise, continue to execute b2. Step b3: Execute the first working method. In a feasible implementation manner, the specific method for preliminary coupling in Step a1 includes: Step c1: Set the current modulation voltage in each nutation direction (i.e., or ), and let , represents the initial modulation voltage. For nutation coupling, the initial modulation voltage is generally the voltage applied after the system static error compensation. Step c2: Generate a random voltage that follows a Bernoulli distribution . Step c3: Positively superimpose on , and calculate the performance evaluation function. The specific formula is: . Among them, represents the positive performance evaluation function value. Step c4: Negatively superimpose on , and calculate the performance evaluation function. The specific formula is: . Among them, Represents the negative value of the performance evaluation function; Step c5, calculate the change in the performance evaluation function , and the specific formula is: ; Step c6, iteratively calculate the new modulation voltage , and the specific formula is: ; Among them, represents the gain coefficient; Let , and after updating the modulation voltage, execute step c2 until the optical power meets the second iteration termination condition.

[0024] In a feasible implementation manner, the second iteration termination condition is that the coupling efficiency reaches 50%.

[0025] Adopting the above technical solution, the present invention has the following beneficial effects: A fiber nutation coupling method, system and device based on an electro-optic crystal provided by the present invention can utilize the characteristic that the refractive index of the electro-optic crystal changes directionally with the electric field. By (unidirectionally) adjusting the modulation voltage, the three-dimensional angle error when compensating the laser incident coupling to the center of the fiber end face can be simply and real-time adjusted, ensuring that the signal laser emitted by the external light source is incident on the center of the fiber end face in real time, accurately and vertically, thereby improving the efficiency, quality and stability of free space laser communication; the structure of this device is simple, small in size and wide in application range. Description of the Drawings

[0026] 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 use in 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.

[0027] Figure 1 Is a flowchart of a fiber nutation coupling method based on an electro-optic crystal provided by an embodiment of the present invention; Figure 2 Is an electrode layout diagram of an electro-optic crystal provided by an embodiment of the present invention; Figure 3 Is an optical path schematic diagram of an electro-optic crystal provided by an embodiment of the present invention; Figure 4 Is a system diagram of a fiber nutation coupling based on an electro-optic crystal provided by an embodiment of the present invention; Figure 5Schematic layout diagram of an optical fiber nutation coupling device based on an electro-optic crystal provided by an embodiment of the present invention; Figure 6 Schematic internal layout diagram of the electro-optic crystal provided by an embodiment of the present invention; Reference numerals: 1 - beam expander; 2 - electro-optic crystal; 3 - convex lens; 4 - optical fiber; 5 - beam splitter; 6 - optical power meter; 7 - controller; 8 - driver; 9 - communication detector; 10 - half-wave plate. Specific embodiments

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. 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.

[0029] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0030] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0031] For the convenience of understanding the following embodiments of the present invention, the design concept of the present invention is briefly described as follows: In order to solve the technical problems in the background art, the present invention considers using the characteristic that the refractive index of the electro-optic crystal changes directionally with the electric field, and by modulating the voltage, the solid angle error when the compensated laser is incident and coupled to the center of the fiber end face is adjusted in real time, ensuring that the signal laser emitted by the external light source is incident on the center of the fiber end face in real time, accurately, and vertically, thereby improving the efficiency, quality, and stability of free-space laser communication.

[0032] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0033] It should also be noted that the following specific embodiments or specific implementation manners are a series of optimized setting manners listed by the present invention to further explain the specific invention content, and these setting manners can be combined with each other or used in association with each other.

[0034] Embodiment 1: As Figure 1 shown, this embodiment provides a fiber optic nutation coupling method based on an electro-optic crystal, including the following steps: Step 1: Make the laser converge to the center of the end face of the fiber optic input end after entering the electro-optic crystal; the electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged in sequence, which are respectively used to adjust one optical path direction in the nutation direction; Step 2: Collect the optical power of the laser signal at the fiber optic output end, and based on the change rate of the optical power, calculate the angular error of the laser in each nutation direction; Step 3: Based on the angular error, calculate the modulation voltage applied to the electrodes of each electro-optic crystal, and use the electro-optic effect to change the refractive index of the laser in each nutation direction; Step 4: Load the modulation voltage on the electrodes of each electro-optic crystal, compensate for the angular error of the laser in each nutation direction, and iteratively execute Step 2 until the iteration end condition is reached.

[0035] Furthermore, the electro-optic crystal is a LiTaO 3 (lithium tantalate) crystal, which has the advantages of high optical damage threshold, low birefringence, high transmission bandwidth, high light transmittance, strong sensitivity, wide light transmission range, large electro-optic coefficient, not easy to deliquesce, and stable physical and chemical properties compared with other electro-optic crystal materials; Furthermore, as Figure 2 shown, the LiTaO 3 crystal is cylindrical, and four cylindrical electrodes are evenly distributed on the circumferential surface. In this way, compared with the traditional upper and lower two electrodes, a more uniform vertical electric field can be provided; Furthermore, the electro-optic coefficient matrix r of the LiTaO 3 crystal can be expressed as follows: ; Among them, represents the main electro-optic coefficient when an electric field is applied in the Z-axis direction of the crystal (the length direction of the cylindrical crystal is set as the Y-axis); Then, the relationship between the refractive index in the Z-axis direction of the crystal and the electric field in the Z-axis direction of the crystal can be: ; Among them, represents the intrinsic refractive index of the material; Furthermore, as Figure 3 shown, the deflection angle 3 of the laser with respect to the Y-axis in the LiTaO crystal can be calculated by the formula: ; Among them, represents the length of the crystal in the Y-axis direction; represents the radius of the light-transmitting port of the crystal; represents the initial voltage in the Z-axis direction; It can be understood that Figure 3 in, E represents the direction of the electric field, H represents the direction of the magnetic field, K represents the direction of the light beam; α represents the included angle of the equivalent virtual wedge plate; D represents the diameter of the crystal; Furthermore, takes the value of 8 mm; takes the value of 2.18; takes the value of 3.3ⅹ10 -11 m / V; takes the value of 2.75 mm; then substituting and simplifying the above equation can obtain the deflection rate : ; Furthermore, the calculation formula of the modulation voltage can be: ; Among them, represents the angular error of the laser projected onto the XY coordinate plane; represents the angular error of the laser projected onto the YZ coordinate plane; represents the modulation voltage in the X-axis direction of the crystal; represents the modulation voltage in the Z-axis direction of the crystal; Furthermore, the iteration end condition is that the angular error of the laser in each nutation direction is zero.

[0036] Example 2: As Figure 4 shown, this embodiment provides a fiber optic nutation coupling system based on an electro-optic crystal, including a data receiving module, a data processing module, and a signal generating module: The data receiving module is used to receive the optical power of the laser signal at the output end of the optical fiber; The data processing module includes an angular error calculation unit and a modulation voltage calculation unit: The angular error calculation unit calculates the angular error of the laser in each nutation direction based on the change rate of the optical power; The modulation voltage calculation unit calculates the modulation voltage applied to the electrodes of each electro-optic crystal based on the angle error, and is used to change the refractive index of the laser in each nutation direction according to the electro-optic effect; The signal generation module sends the modulation voltage to the electrodes of each electro-optic crystal.

[0037] Embodiment 3: As Figure 5 shown, this embodiment provides a fiber optic nutation coupling device based on an electro-optic crystal, including a beam expander 1, an electro-optic crystal 2, a convex lens 3, an optical fiber 4, a beam splitter 5, an optical power meter 6, a controller 7, a driver 8, and a communication detector 9: The beam expander 1 is arranged on the optical path between the external light source and the electro-optic crystal 2, and compresses the free space laser through an afocal system to filter out stray light; The electro-optic crystal 2 includes a first electro-optic crystal and a second electro-optic crystal arranged in sequence, and is arranged on the optical path between the external light source and the convex lens 3; the convex lens 3 is used to converge the light beam output by the electro-optic crystal 2 to the center of the end face of the input end of the optical fiber 4; the beam splitter 5 is arranged at the output end of the optical fiber 4, and is used to output 20% of the optical signal to the optical power meter 6 and 80% of the optical signal to the communication detector 9 according to a 1:4 splitting ratio; the optical power meter 6 is used to detect the power of the optical signal and convert it into a first electrical signal and input it to the controller 7; the controller 7 calculates the angle error of the light beam in each nutation direction based on the first electrical signal and calculates the modulation voltage applied to each electrode in the electro-optic crystal 2, and outputs it to the driver 8; the driver 8 supplies power to each electrode of the electro-optic crystal 2 based on the modulation voltage; The communication detector 9 is used to perform optoelectronic conversion on the input optical signal to obtain a second electrical signal for transmitting communication data backward.

[0038] Further, as Figure 6 shown, a half-wave plate 10 is arranged on the optical path between the first electro-optic crystal and the second electro-optic crystal to adjust the polarization state of the light beam to meet the polarization state requirements of the electro-optic crystal.

[0039] Further, the optical fiber 4 is a single-mode optical fiber: its numerical aperture (NA) ranges from 0.12 to 0.14; the mode field diameter (1 / e 2 ) is about 10.4 microns when the wavelength is 1550 nm; in this way, this device can match the common optical fiber core diameters and has wide versatility.

[0040] Further, the working method of the fiber optic nutation coupling device includes a first working method and a second working method; The first working method operates when the initial position of the known signal (where part or all of the laser can be coupled into the optical fiber) is known, that is, it is known where the signal is. The specific steps are as follows: Step a1: After the controller 7 receives the data of the signal initial position, the fiber nutation coupling device enters the working state, and the electro-optic crystal 2 performs two-dimensional scanning; the target azimuth information at the fiber input end (from the laser beam entering the optical power meter) is converted into the deflection angle of the electro-optic crystal 2 for preliminary coupling and determination: If the qualified condition for preliminary coupling is reached (for example, the coupling efficiency ≥ 10%), then step a2 is executed; otherwise, step a1 is executed again; Step a2: Through the driver, the deflection angle of the electro-optic crystal 2 is adjusted step by step (for example, 1 - 5 urad); the controller 7 records the optical power value (feedback signal) of the optical power meter 6 and converts it into the modulation voltage of the electro-optic crystal 2, and then adjusts the deflection angle of the electro-optic crystal 2 again to achieve precise alignment; Step a3: The controller 7 determines the offset azimuth of the light spot at the fiber input end in real time according to the magnitude of the optical power value, and finely adjusts the electro-optic crystal 2 until the qualified condition for stable coupling is reached (for example, the coupling efficiency ≥ 50%) to achieve stable coupling; Step a3: Turn on the communication link, and the controller 7 monitors the target azimuth information in real time: If the target azimuth information is lost midway, then step a1 is executed again; otherwise, the communication state is maintained until the communication ends; The second working method operates when the initial position of the unknown signal is unknown, that is, it is not known where the signal is. The specific steps are as follows: Step b1: Drive the electro-optic crystal 2 to perform a trajectory scan with a preset large deflection angle and make a judgment: If a laser signal exists, then step b2 is executed; otherwise, step b1 is executed; Step b2: Drive the electro-optic crystal 2 to complete several times (for example, 4 - 5 times) of one-way (for example, forward) trajectory scans with a preset small deflection angle, calculate the initial position of the signal light (for example, the maximum value of the laser signal can be calculated, and the target azimuth information corresponding to the maximum value of the laser signal is used as the initial position of the signal light) based on the preset trajectory and the magnitude of the target feedback signal, and make a judgment: If the initial position of the signal light exists, then b3 is executed; otherwise, b2 is continued to be executed; Step b3: Execute the first working method. Further, the specific method for preliminary coupling in step a1 includes: Step c1: Set the current modulation voltage in each nutation direction (that is or ), let , Denote the initial modulation voltage. For nutation coupling, the initial modulation voltage is generally the voltage applied after compensating for the system static error; Step c2: Generate a random voltage that follows a Bernoulli distribution ; Step c3: Superimpose positively on and calculate the performance evaluation function. The specific formula is: ; where, denotes the positive performance evaluation function value; Step c4: Superimpose negatively on and calculate the performance evaluation function. The specific formula is: ; where, denotes the negative performance evaluation function value; Step c5: Calculate the change in the performance evaluation function , and the specific formula is: ; Step c6: Iteratively calculate the new modulation voltage , and the specific formula is: ; where, denotes the gain coefficient; Let , update the modulation voltage and then execute step c2 until the optical power satisfies the second iteration termination condition.

[0041] Furthermore, the second iteration termination condition is that the coupling efficiency reaches 50%.

[0042] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber nutation coupling method based on electro-optical crystal, characterized in that: include: Step 1, after the laser is incident on the electro-optical crystal, it converges toward the center of the end face of the optical fiber input end; the electro-optical crystal includes a first electro-optical crystal and a second electro-optical crystal which are arranged in sequence, and are respectively used to adjust one optical path direction in the nutation direction; Step 2, collecting the optical power of the laser signal at the output end of the optical fiber, and solving the angular error of the laser in each nutation direction based on the rate of change of the optical power; Step 3: Based on the angle error, calculate the modulation voltage applied to each electro-optic crystal electrode to change the refractive index of the laser in each nutation direction according to the electro-optic effect; the specific calculation formula is: ； Wherein, the length direction of the crystal is defined as the Y axis; Indicates the angular error of the laser projection onto the XY coordinate plane; Indicates the angular error of the laser projection to the YZ coordinate plane; Represents the modulation voltage in the X-axis direction of the crystal; Represents the modulation voltage in the Z-axis direction of the crystal; represents the deflection rate; Step 4: Load the modulation voltage on each electro-optical crystal electrode to compensate for the angle error of the laser in each nutation direction, and iteratively execute step 2 until the iteration end condition is reached.

2. The method according to claim 1, characterized in that The specific calculation formula of the deflection rate is: ； in, represents the intrinsic refractive index of the material; It represents the principal electro-optic coefficient when an electric field is applied in the Z-axis direction of the crystal; Indicates the length of the crystal along the Y axis; Represents the radius of the light opening of the crystal.

3. The method according to claim 1, characterized in that The iteration end condition is that the angle error of the laser in each nutation direction is zero.

4. An optical fiber nutation coupling system based on electro-optical crystal, characterized in that: Including data receiving module, data processing module and signal generating module: The data receiving module is used to receive the optical power of the laser signal at the output end of the optical fiber; The data processing module includes an angle error solving unit and a modulation voltage calculating unit: The angle error solving unit solves the angle error of the laser in each nutation direction based on the rate of change of the optical power; The modulation voltage calculation unit calculates the modulation voltage applied to each electro-optic crystal electrode based on the angle error, so as to change the refractive index of the laser in each nutation direction according to the electro-optic effect; the specific calculation formula is: ； Wherein, the length direction of the crystal is defined as the Y axis; Indicates the angular error of the laser projection onto the XY coordinate plane; Indicates the angular error of the laser projection to the YZ coordinate plane; Represents the modulation voltage in the X-axis direction of the crystal; Represents the modulation voltage in the Z-axis direction of the crystal; represents the deflection rate; The signal generating module sends the modulation voltage to each electro-optical crystal electrode.

5. An optical fiber nutation coupling device based on an electro-optical crystal, characterized in that: Including electro-optical crystal, convex lens, optical fiber, beam splitter, optical power meter, controller and driver: The electro-optic crystal comprises a first electro-optic crystal and a second electro-optic crystal which are arranged in sequence and are arranged on the optical path between the external light source and the convex lens; The convex lens is used to converge the light beam output by the electro-optical crystal to the center of the end face of the optical fiber input end; The beam splitter is arranged at the output end of the optical fiber, and is used to output the optical signal to the optical power meter and the subsequent equipment respectively according to the splitting ratio; The optical power meter is used to detect the power of the optical signal and convert it into a first electrical signal to input into the controller; The controller, based on the first electrical signal, calculates the angle error of the light beam in each nutation direction and calculates the modulation voltage applied to each electro-optical crystal electrode, and outputs it to the driver; The specific calculation formula is: ； Wherein, the length direction of the crystal is defined as the Y axis; Indicates the angular error of the laser projection onto the XY coordinate plane; Indicates the angular error of the laser projection to the YZ coordinate plane; Represents the modulation voltage in the X-axis direction of the crystal; Represents the modulation voltage in the Z-axis direction of the crystal; represents the deflection rate; The driver supplies power to electrodes of each electro-optical crystal based on the modulation voltage.

6. The device according to claim 5, characterized in that It also includes a beam reducing mirror, which is arranged on the optical path between the external light source and the electro-optical crystal.

7. The device according to claim 5, characterized in that The subsequent device includes a communication detector, which is used to perform photoelectric conversion on the input optical signal to obtain a second electrical signal; the second electrical signal is used to transmit communication data.

8. The device according to claim 7, characterized in that The post-stage device also includes a demodulator for demodulating the second electrical signal output by the communication detector.

9. The device according to claim 5, characterized in that A half-wave plate is arranged on the optical path between the first electro-optical crystal and the second electro-optical crystal.

10. The device according to claim 5, characterized in that The optical fiber is a single-mode optical fiber.

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