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

Abstract

This invention provides a fiber optic nutation coupling method, system, and device based on electro-optic crystals, relating to the field of free-space optical communication technology. The device mainly includes: 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 comprises a first electro-optic crystal and a second electro-optic crystal arranged sequentially in the optical path between an external light source and the convex lens. The optical power meter is used to detect the power of the optical signal and convert it into a first electrical signal input to the controller. This invention utilizes the characteristic that the refractive index of the electro-optic crystal changes directionally with the electric field. By modulating the voltage, it can adjust and compensate for the stereo angle error when the laser is incident and coupled to the center of the fiber end face 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 perpendicularly, thereby improving the efficiency, quality, and stability of free-space laser communication. This device has a simple structure, small size, and wide applicability.

Description

Technical Field

[0001] This invention relates to the field of free-space optical communication technology, and in particular to an optical fiber nutation coupling method, system and device based on electro-optic crystals. Background Technology

[0002] Currently, spaceborne laser communication terminal technology is gradually maturing, and satellites and satellite-to-ground connections have been successfully established, leading to an increasingly urgent demand for the commercial application of laser communication terminals.

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

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

[0005] The purpose of this invention is to provide a fiber optic nutation coupling method, system, and apparatus based on electro-optic crystals to solve at least one of the aforementioned technical problems in the prior art.

[0006] In a first aspect, to solve the above-mentioned technical problems, the present invention provides a fiber nutation coupling method based on electro-optic crystals, comprising the following steps:

[0007] Step 1: After the laser is incident on the electro-optic crystal, it converges towards the center of the end face of the fiber input end; the electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged in sequence, which are used to adjust one of the optical path directions in the nutation direction;

[0008] Step 2: Collect the optical power of the laser signal at the output end of the optical fiber, and calculate the angular error of the laser in each nutation direction based on the rate of change of optical power;

[0009] Step 3: Based on the angle error, calculate the modulation voltage applied to each electro-optic crystal electrode, which is used to change the refractive index of the laser in each nutation direction according to the electro-optic effect;

[0010] Step 4: Apply the modulation voltage to each electro-optic crystal electrode to compensate for the angular error of the laser in each nutation direction, and iteratively execute step 2 until the first iteration end condition is met.

[0011] By utilizing the above method and taking advantage of the characteristic that the refractive index of an electro-optic crystal changes directionally with the electric field, the stereo angle error when the laser is incident on the center of the fiber end face can be adjusted and compensated in real time by modulating the voltage. This ensures that the laser is incident on the center of the fiber end face in real time, accurately and perpendicularly, thereby improving the efficiency, quality and stability of free-space laser communication.

[0012] In one feasible embodiment, the electro-optic crystal is a LiTaO3 (lithium tantalate) crystal, which, compared with other electro-optic crystal materials, has advantages such as high optical damage threshold, low birefringence, high transmission bandwidth, high light transmittance, strong sensitivity, wide light transmission range, large electro-optic coefficient, non-hygroscopicity, and stable physicochemical properties.

[0013] In one feasible implementation, the LiTaO3 crystal is cylindrical with several cylindrical electrodes evenly distributed on its circumference, which facilitates the provision of a uniform vertical electric field.

[0014] In one feasible implementation, the electro-optic coefficient matrix r of the LiTaO3 crystal can be represented as follows:

[0015] ;

[0016] in, It represents the principal electro-optic coefficient when an electric field is applied along the Z-axis of the crystal (the length direction of a cylindrical crystal is set as the Y-axis);

[0017] So, the refractive index along the Z-axis of the crystal electric field along the Z-axis of the crystal The relationship can be expressed as:

[0018] ;

[0019] in, It represents the intrinsic refractive index of the material.

[0020] In one feasible implementation, the laser beam is deflected relative to the Y-axis in the LiTaO3 crystal at a certain angle. The calculation formula can be expressed as:

[0021] ;

[0022] in, Indicates the length of the crystal along the Y-axis; Indicates the light aperture radius of the crystal; This represents the initial voltage along the Z-axis.

[0023] In one feasible implementation, The value is 8mm; The value is 2.18; The value is 3.3 x 10 - 11 m / V; If the value is taken as 2.75 mm, then substituting it into and simplifying the above equation yields the deflection rate. :

[0024] ;

[0025] In one feasible implementation, the formula for calculating the modulation voltage can be:

[0026] ;

[0027] in, This represents the angular error of the laser projection onto the XY coordinate plane; This represents the angular error of the laser projection onto the YZ coordinate plane; This represents the modulation voltage along the X-axis of the crystal. This represents the modulation voltage along the Z-axis of the crystal.

[0028] The modulation voltage used to compensate for angular errors can be accurately calculated using the above formula. Applying this modulation voltage to the electrodes of the electro-optic crystal modulates the refractive index of the electro-optic crystal, thereby adjusting the direction of the laser.

[0029] In one feasible implementation, the first iteration ends when the angular error of the laser in each nutation direction is zero.

[0030] Secondly, based on the same inventive concept, this application also provides an optical fiber nutation coupling system based on an electro-optic crystal, including a data receiving module, a data processing module, and a signal generation module:

[0031] The data receiving module is used to receive the optical power of the laser signal at the output end of the optical fiber;

[0032] The data processing module includes an angle error calculation unit and a modulation voltage calculation unit:

[0033] The angle error calculation unit calculates the angle error of the laser in each nutation direction based on the rate of change of the optical power.

[0034] The modulation voltage calculation unit calculates the modulation voltage applied to each electro-optic crystal electrode 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.

[0035] The signal generation module sends the modulation voltage to each electro-optic crystal electrode.

[0036] Thirdly, based on the same inventive concept, this application also provides an optical 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:

[0037] The electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged sequentially in the optical path between the external light source and the convex lens; the convex lens is used to converge the beam output by the electro-optic 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 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 input to the controller; the controller calculates the angular error of the beam in each nutation direction based on the first electrical signal and calculates the modulation voltage applied to the electrode of each electro-optic crystal, and outputs it to the driver; the driver supplies power to the electrode of each electro-optic crystal based on the modulation voltage.

[0038] The above structure utilizes the characteristic that the refractive index of an electro-optic crystal changes directionally with the electric field. By modulating the voltage, the stereo angle error when the laser is incident on the center of the fiber end face can be adjusted and compensated in real time. This ensures that the laser emitted by the external light source is incident on the center of the fiber end face in real time, accurately, and perpendicularly, thereby improving the efficiency, quality, and stability of free-space laser communication. This device has a simple structure, small size, and wide range of applications.

[0039] In one feasible implementation, the device further includes a beam shrinker, which is disposed in the optical path between the external light source and the electro-optic crystal. Through a focusless 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.

[0040] In one feasible implementation, the downstream device includes a communication detector for photoelectric conversion of the input optical signal to obtain a second electrical signal; the second electrical signal is used to transmit communication data.

[0041] In one feasible implementation, the downstream device further includes a demodulator for demodulating the second electrical signal output by the communication detector.

[0042] In one feasible implementation, a half-wave plate is provided in the optical path between the first electro-optic crystal and the second electro-optic crystal to adjust the polarization state of the beam so as to meet the polarization state requirements of the electro-optic crystal.

[0043] In one feasible implementation, the optical fiber is a single-mode optical fiber, which provides a wider transmission bandwidth and a longer transmission distance.

[0044] In one feasible implementation, the spectral ratio is 1:4, 1:9, or 3:7.

[0045] In one feasible implementation, the operation method of the optical fiber nutation coupling device includes a first operation method and a second operation method;

[0046] The first working method operates under the condition that the initial position of the signal is known (at which part or all of the laser can couple into the optical fiber), and specifically includes the following steps:

[0047] Step a1: After the controller receives the initial position data, the fiber optic nutation coupling device enters the working state, and the electro-optic crystal performs two-dimensional scanning; the target orientation information at the fiber input end (from the laser beam entering the optical power meter) is converted into the deflection angle of each electro-optic crystal, and preliminary coupling is performed and judged: if the qualified condition for preliminary coupling is met, step a2 is executed; otherwise, step a1 is executed again.

[0048] Step a2: The deflection angle of the electro-optic crystal is adjusted stepwise by the 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-optic crystal, and then adjusts the deflection angle of the electro-optic crystal again to achieve precise alignment.

[0049] Step a3: The controller determines the offset position of the light spot at the fiber input end in real time according to the magnitude of the optical power value, and fine-tunes each electro-optic crystal until the qualified conditions for stable coupling are met, thereby achieving stable coupling.

[0050] Step a3: Start the communication link and the controller monitors the target location information in real time. If the target location information is lost midway, repeat step a1; otherwise, maintain the communication status until the communication ends.

[0051] The second working method operates under the condition of unknown initial signal position, and specifically includes the following steps:

[0052] Step b1: Drive the electro-optic crystal to perform a trajectory scan with a preset large deflection angle and make a judgment: if a laser signal is present, proceed to step b2; otherwise, proceed to step b1.

[0053] Step b2: Drive the electro-optic crystal to complete several unidirectional trajectory scans with a preset small deflection angle. Based on the preset trajectory and the magnitude of the target feedback signal, calculate and judge the initial position of the signal light: if there is an initial position of the signal light, then execute b3; otherwise, continue to execute b2.

[0054] Step b3: Perform the first working method.

[0055] In one feasible implementation, the specific method for the initial coupling in step a1 includes:

[0056] Step c1: Set the current modulation voltage in each nutation direction. (Right now or ),make , This represents the initial modulation voltage. For nutation coupling, the initial modulation voltage is generally the voltage applied after the system's static error is compensated.

[0057] Step c2: Generate a random voltage that follows a Bernoulli distribution. ;

[0058] Step c3, Positive superposition The performance evaluation function is calculated using the following formula:

[0059] ;

[0060] in, This represents a positive performance evaluation function value;

[0061] Step c4, Negative superposition The performance evaluation function is calculated using the following formula:

[0062] ;

[0063] in, This represents a negative performance evaluation function value;

[0064] Step c5: Calculate the change in the performance evaluation function. The specific formula is as follows:

[0065] ;

[0066] Step c6: Iteratively calculate the new modulation voltage The specific formula is as follows:

[0067] ;

[0068] in, Indicates the gain coefficient;

[0069] make After updating the modulation voltage, step c2 is executed until the optical power meets the second iteration termination condition.

[0070] In one feasible implementation, the second iteration termination condition is that the coupling efficiency reaches 50%.

[0071] By adopting the above technical solution, the present invention has the following beneficial effects:

[0072] This invention provides a fiber optic nutation coupling method, system, and device based on electro-optic crystals. Utilizing the characteristic that the refractive index of an electro-optic crystal changes directionally with the electric field, the stereo angle error when the laser incident on the fiber end face is easily and in real-time adjusted and compensated by (unidirectional) adjusting the modulation voltage. This ensures that the signal laser emitted from an external light source is incident on the fiber end face center in real-time, accurately, and perpendicularly, thereby improving the efficiency, quality, and stability of free-space laser communication. The device has a simple structure, small size, and wide applicability. Attached Figure Description

[0073] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0074] Figure 1 A flowchart of an optical fiber nutation coupling method based on an electro-optic crystal is provided for an embodiment of the present invention;

[0075] Figure 2 This is a diagram showing the electro-optic crystal electrode layout provided in an embodiment of the present invention;

[0076] Figure 3 This is a schematic diagram of the electro-optic crystal optical path provided in an embodiment of the present invention;

[0077] Figure 4 A diagram of an optical fiber nutation coupling system based on an electro-optic crystal is provided for an embodiment of the present invention;

[0078] Figure 5 A schematic diagram of the layout of an optical fiber nutation coupling device based on an electro-optic crystal provided for an embodiment of the present invention;

[0079] Figure 6 This is a schematic diagram of the internal layout of the electro-optic crystal provided in an embodiment of the present invention;

[0080] Figure label:

[0081] 1-Beam shrinker; 2-Electro-optic crystal; 3-Convex lens; 4-Fiber optic cable; 5-Beam splitter; 6-Optical power meter; 7-Controller; 8-Driver; 9-Communication detector; 10-Half-wave plate. Detailed Implementation

[0082] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0083] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0084] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0085] To facilitate understanding of the following embodiments of the invention, the design concept of the invention is briefly described below:

[0086] To address the various technical problems in the background art, this invention considers utilizing the characteristic that the refractive index of an electro-optic crystal changes directionally with the electric field. By modulating the voltage, the stereo angle error when the laser 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 perpendicularly, thereby improving the efficiency, quality, and stability of free-space laser communication.

[0087] The present invention will be further explained below with reference to specific embodiments.

[0088] It should also be noted that the specific embodiments or implementation methods described below are a series of optimized settings listed by the present invention to further explain the specific content of the invention, and these settings can be combined or used in conjunction with each other.

[0089] Example 1:

[0090] like Figure 1As shown, this embodiment provides a fiber optic nutation coupling method based on electro-optic crystals, including the following steps:

[0091] Step 1: After the laser is incident on the electro-optic crystal, it converges towards the center of the end face of the fiber input end; the electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged in sequence, which are used to adjust one of the optical path directions in the nutation direction;

[0092] Step 2: Collect the optical power of the laser signal at the output end of the optical fiber, and calculate the angular error of the laser in each nutation direction based on the rate of change of optical power;

[0093] Step 3: Based on the angle error, calculate the modulation voltage applied to each electro-optic crystal electrode, which is used to change the refractive index of the laser in each nutation direction according to the electro-optic effect;

[0094] Step 4: Apply the modulation voltage to each electro-optic crystal electrode to compensate for the angular error of the laser in each nutation direction, and iteratively execute step 2 until the iteration end condition is met.

[0095] Furthermore, the electro-optic crystal is a LiTaO3 (lithium tantalate) crystal, which, compared with other electro-optic crystal materials, has advantages such as high optical damage threshold, low birefringence, high transmission bandwidth, high light transmittance, strong sensitivity, wide light transmission range, large electro-optic coefficient, non-hygroscopicity, and stable physicochemical properties.

[0096] Furthermore, such as Figure 2 As shown, the LiTaO3 crystal is cylindrical with four cylindrical electrodes evenly distributed on its circumference. This provides a more uniform vertical electric field compared to the traditional two electrodes at the top and bottom.

[0097] Furthermore, the electro-optic coefficient matrix r of the LiTaO3 crystal can be represented as follows:

[0098] ;

[0099] in, It represents the principal electro-optic coefficient when an electric field is applied along the Z-axis of the crystal (the length direction of a cylindrical crystal is set as the Y-axis);

[0100] So, the refractive index along the Z-axis of the crystal electric field along the Z-axis of the crystal The relationship can be expressed as:

[0101] ;

[0102] in, Indicates the intrinsic refractive index of the material;

[0103] Furthermore, such as Figure 3As shown, the deflection angle of the laser relative to the Y-axis in the LiTaO3 crystal. The calculation formula can be expressed as:

[0104] ;

[0105] in, Indicates the length of the crystal along the Y-axis; Indicates the light aperture radius of the crystal; Indicates the initial voltage in the Z-axis direction;

[0106] Understandable. Figure 3 In this diagram, E represents the direction of the electric field, H represents the direction of the magnetic field, K represents the direction of the beam; α represents the equivalent virtual wedge angle; and D represents the crystal diameter.

[0107] Further, The value is 8mm; The value is 2.18; The value is 3.3 x 10 -11 m / V; If the value is taken as 2.75 mm, then substituting it into and simplifying the above equation yields the deflection rate. :

[0108] ;

[0109] Furthermore, the formula for calculating the modulation voltage can be:

[0110] ;

[0111] in, This represents the angular error of the laser projection onto the XY coordinate plane; This represents the angular error of the laser projection onto the YZ coordinate plane; This represents the modulation voltage along the X-axis of the crystal. This represents the modulation voltage along the Z-axis of the crystal.

[0112] Furthermore, the iteration termination condition is that the angular error of the laser in each nutation direction is zero.

[0113] Example 2:

[0114] like Figure 4 As shown, this embodiment provides an optical fiber nutation coupling system based on electro-optic crystals, including a data receiving module, a data processing module, and a signal generation module:

[0115] The data receiving module is used to receive the optical power of the laser signal at the output end of the optical fiber;

[0116] The data processing module includes an angle error calculation unit and a modulation voltage calculation unit:

[0117] The angle error calculation unit calculates the angle error of the laser in each nutation direction based on the rate of change of the optical power.

[0118] The modulation voltage calculation unit calculates the modulation voltage applied to each electro-optic crystal electrode 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.

[0119] The signal generation module sends the modulation voltage to each electro-optic crystal electrode.

[0120] Example 3:

[0121] like Figure 5 As shown, this embodiment provides an optical fiber nutation coupling device based on an electro-optic crystal, including a beam shrinking mirror 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.

[0122] The beam shrinking mirror 1 is placed in the optical path between the external light source and the electro-optic crystal 2. Through the focusless system, it compresses the free space laser and is used to filter out stray light.

[0123] The electro-optic crystal 2 includes a first electro-optic crystal and a second electro-optic crystal arranged sequentially, positioned in the optical path between the external light source and the convex lens 3. The convex lens 3 is used to converge the beam output from 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 located 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 input to the controller 7. The controller 7, based on the first electrical signal, calculates the angular error of the beam in each nutation direction 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.

[0124] The communication detector 9 is used to perform photoelectric conversion on the input optical signal to obtain a second electrical signal, which is used to transmit communication data.

[0125] Furthermore, such as Figure 6 As shown, a half-wave plate 10 is provided in the optical path between the first electro-optic crystal and the second electro-optic crystal to adjust the polarization state of the beam so as to meet the polarization state requirements of the electro-optic crystal.

[0126] Furthermore, 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 at a wavelength of 1550 nm is (1 / e 2 The core diameter is approximately 10.4 micrometers; thus, this device can be matched with commonly used fiber core diameters, and has wide versatility.

[0127] Furthermore, the operating method of the optical fiber nutation coupling device includes a first operating method and a second operating method;

[0128] The first working method operates under the condition that the initial position of the signal is known (at which part or all of the laser can couple into the optical fiber), that is, the location of the signal is known, and specifically includes the following steps:

[0129] Step a1: After the controller 7 receives the initial position data, the fiber optic nutation coupling device enters the working state, and the electro-optic crystal 2 performs two-dimensional scanning; the target orientation 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, and preliminary coupling is performed and judged: if the qualified conditions for preliminary coupling are met (e.g., coupling efficiency ≥ 10%), then step a2 is executed; otherwise, step a1 is executed again.

[0130] Step a2: The deflection angle of the electro-optic crystal 2 is adjusted stepwise (e.g., 1~5 urad) by the driver; 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;

[0131] Step a3: The controller 7 determines the offset position of the light spot at the optical fiber input end in real time according to the magnitude of the optical power value, and fine-tunes the electro-optic crystal 2 until the qualified conditions for stable coupling are met (e.g., coupling efficiency ≥ 50%), thereby achieving stable coupling.

[0132] Step a3: Start the communication link. Controller 7 monitors the target location information in real time. If the target location information is lost midway, step a1 is executed again. Otherwise, the communication status is maintained until the communication ends.

[0133] The second working method operates under the condition that the initial position of the signal is unknown, that is, the location of the signal is unknown, and specifically includes the following steps:

[0134] 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 is present, proceed to step b2; otherwise, proceed to step b1.

[0135] Step b2: Drive the electro-optic crystal 2 to complete several (e.g., 4-5) unidirectional (e.g., forward) trajectory scans with a preset small deflection angle. Based on the preset trajectory and the magnitude of the target feedback signal, calculate the initial position of the signal light (e.g., calculate the maximum value of the laser signal and use the target orientation information corresponding to the maximum value of the laser signal as the initial position of the signal light) and make a judgment: If there is an initial position of the signal light, then execute b3; otherwise, continue to execute b2.

[0136] Step b3: Perform the first working method.

[0137] Furthermore, the specific method for preliminary coupling in step a1 includes:

[0138] Step c1: Set the current modulation voltage in each nutation direction. (Right now or ),make , This represents the initial modulation voltage. For nutation coupling, the initial modulation voltage is generally the voltage applied after the system's static error is compensated.

[0139] Step c2: Generate a random voltage that follows a Bernoulli distribution. ;

[0140] Step c3, Positive superposition The performance evaluation function is calculated using the following formula:

[0141] ;

[0142] in, This represents a positive performance evaluation function value;

[0143] Step c4, Negative superposition The performance evaluation function is calculated using the following formula:

[0144] ;

[0145] in, This represents a negative performance evaluation function value;

[0146] Step c5: Calculate the change in the performance evaluation function. The specific formula is as follows:

[0147] ;

[0148] Step c6: Iteratively calculate the new modulation voltage The specific formula is as follows:

[0149] ;

[0150] in, Indicates the gain coefficient;

[0151] make After updating the modulation voltage, step c2 is executed until the optical power meets the second iteration termination condition.

[0152] Furthermore, the second iteration termination condition is that the coupling efficiency reaches 50%.

[0153] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber optic nutation coupling method based on electro-optic crystals, characterized in that, include: Step 1: After the laser is incident on the electro-optic crystal, it converges towards the center of the end face of the fiber input end; the electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged in sequence, which are used to adjust one of the optical path directions in the nutation direction; Step 2: Collect the optical power of the laser signal at the output end of the optical fiber, and calculate the angular error of the laser in each nutation direction based on the rate of change of optical power; Step 3: Based on the aforementioned angular error, calculate the modulation voltage applied to each electro-optic crystal electrode, which is used to change the refractive index of the laser in each nutation direction according to the electro-optic effect; the specific calculation formula is as follows: ； The length direction of the crystal is defined as the Y-axis; This represents the angular error of the laser projection onto the XY coordinate plane; This represents the angular error of the laser projection onto the YZ coordinate plane; This represents the modulation voltage along the X-axis of the crystal. This represents the modulation voltage along the Z-axis of the crystal. Indicates the deflection rate; The specific formula for calculating the deflection rate is as follows: ； in, Indicates the intrinsic refractive index of the material; This represents the principal electro-optic coefficient when an electric field is applied along the Z-axis of the crystal; Indicates the length of the crystal along the Y-axis; Indicates the light aperture radius of the crystal; Step 4: Apply the modulation voltage to each electro-optic crystal electrode to compensate for the angular error of the laser in each nutation direction, and iteratively execute Step 2 until the iteration termination condition is met; The method also includes a preliminary coupling method, specifically including: Step c1: Set the current modulation voltage in each nutation direction. ,make , Indicates the initial modulation voltage; Step c2: Generate a random voltage that follows a Bernoulli distribution. ; Step c3, Positive superposition The performance evaluation function is calculated using the following formula: ； in, This represents a positive performance evaluation function value; Step c4, Negative superposition The performance evaluation function is calculated using the following formula: ； in, This represents a negative performance evaluation function value; Step c5: Calculate the change in the performance evaluation function. The specific formula is as follows: ； Step c6: Iteratively calculate the new modulation voltage The specific formula is as follows: ； in, Indicates the gain coefficient; make After updating the modulation voltage, step c2 is executed until the optical power meets the second iteration termination condition.

2. The method according to claim 1, characterized in that, The iteration ends when the angular error of the laser in each nutation direction is zero.

3. A fiber optic nutation coupling system based on an electro-optic crystal, employing the method described in any one of claims 1-2, characterized in that, It includes a data receiving module, a data processing module, and a signal generation 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 calculation unit and a modulation voltage calculation unit: The angle error calculation unit calculates 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, which is used to change the refractive index of the laser in each nutation direction according to the electro-optic effect; the specific calculation formula is as follows: ； The length direction of the crystal is defined as the Y-axis; This represents the angular error of the laser projection onto the XY coordinate plane; This represents the angular error of the laser projection onto the YZ coordinate plane; This represents the modulation voltage along the X-axis of the crystal. This represents the modulation voltage along the Z-axis of the crystal. Indicates the deflection rate; The signal generation module sends the modulation voltage to each electro-optic crystal electrode.

4. A fiber optic nutation coupling device based on an electro-optic crystal, employing the method described in any one of claims 1-2, characterized in that, Includes electro-optic crystals, convex lenses, optical fibers, beam splitters, optical power meters, controllers, and drivers: The electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal arranged sequentially, and is disposed in the optical path between the external light source and the convex lens; The convex lens is used to focus the beam output from the electro-optic crystal onto the center of the end face of the fiber input end. The beam splitter is located at the output end of the optical fiber and is used to output the optical signal to the optical power meter and subsequent equipment 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 input to the controller; The controller, based on the first electrical signal, calculates the angular error of the beam in each nutation direction and calculates the modulation voltage applied to each electro-optic crystal electrode, and outputs it to the driver. The specific calculation formula is as follows: ； The length direction of the crystal is defined as the Y-axis; This represents the angular error of the laser projection onto the XY coordinate plane; This represents the angular error of the laser projection onto the YZ coordinate plane; This represents the modulation voltage along the X-axis of the crystal. This represents the modulation voltage along the Z-axis of the crystal. Indicates the deflection rate; The driver supplies power to the electrodes of each electro-optic crystal based on the modulation voltage.

5. The apparatus according to claim 4, characterized in that, It also includes a beam shrinker, which is placed in the optical path between the external light source and the electro-optic crystal.

6. The apparatus according to claim 4, characterized in that, The downstream device includes a communication detector for photoelectric conversion of the input optical signal to obtain a second electrical signal; the second electrical signal is used to transmit communication data.

7. The apparatus according to claim 6, characterized in that, The downstream device also includes a demodulator for demodulating the second electrical signal output by the communication detector.

8. The apparatus according to claim 4, characterized in that, A half-wave plate is placed in the optical path between the first electro-optic crystal and the second electro-optic crystal.

9. The apparatus according to claim 4, characterized in that, The optical fiber is a single-mode optical fiber.

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