Fiber grating preparation system and method based on piezoelectric displacement and femtosecond laser direct writing

Abstract

The invention discloses a fiber grating preparation system and method based on piezoelectric displacement and femtosecond laser direct writing. The system comprises a piezoelectric displacement platform, a single-axis high-precision displacement platform, a femtosecond laser device, a piezoelectric controller, a laser controller, a signal generator and an upper computer. According to the system, grid line inscribing bending can be avoided, the efficiency of inscribing the fiber bragg grating line by line by femtosecond laser is improved, and the positioning precision of the grating period is improved. The invention discloses a method for inscribing the fiber grating line by line based on piezoelectric displacement and femtosecond laser, and is based on the system.

Description

Technical Field

[0001] The invention relates to a fiber grating preparation technology, and in particular to a fiber grating preparation system and method based on piezoelectric displacement and femtosecond laser direct writing. Background Art

[0002] Fiber Bragg grating is a diffraction grating formed by axially periodically modulating the refractive index of the optical fiber core through a specific method. It is a passive filter device that plays a very important role in the fields of fiber optic sensing, fiber lasers, and fiber optic communications.

[0003] Femtosecond laser direct writing is a new method for preparing fiber gratings. It fixes the optical fiber on a three-dimensional high-precision displacement platform, keeps the focal position of the focused femtosecond laser unchanged, and uses the three-dimensional high-precision displacement platform to drive the optical fiber to move relative to the focal point of the femtosecond laser, so as to periodically modulate the refractive index inside the optical fiber. The traditional femtosecond laser direct writing method for preparing fiber gratings can be divided into point-by-point grating method and line-by-line grating method. Both methods are highly dependent on the accuracy and repeatability of the three-dimensional high-precision displacement platform, and often require the purchase and use of expensive displacement equipment to achieve fiber grating preparation.

[0004] When the traditional femtosecond laser direct writing method is used to write line-by-line gratings, while the grating lines are being written in the radial direction, the axial direction needs to stop and wait for the grating lines to be finished before the next cycle of engraving can be carried out, which is inefficient. In addition, the platform for controlling radial displacement in the existing technical solution is generally an air-floating electric displacement platform. When the writing speed is increased, the written grating lines will bend (especially in the acceleration and deceleration areas). In addition, the traditional femtosecond laser direct writing method uses a high-precision air-floating displacement platform with a positioning accuracy of sub-micron level. When the above-mentioned femtosecond laser direct writing method is used to write chirped fiber gratings line by line, its accuracy cannot meet the requirements of the small change amount of the chirped grating between two adjacent periods, resulting in poor spectral effect of the prepared chirped fiber grating and the chirp rate is difficult to reduce. Summary of the invention

[0005] In order to solve the above-mentioned deficiencies of the prior art, the present invention provides a fiber grating preparation system and method based on piezoelectric displacement and femtosecond laser direct writing, which can avoid grating line writing bending, improve the efficiency of femtosecond laser writing the fiber grating line by line, and improve the positioning accuracy of the grating period.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solutions: A fiber Bragg grating preparation system based on piezoelectric displacement and femtosecond laser direct writing, comprising a piezoelectric displacement platform, a uniaxial high-precision displacement platform, a femtosecond laser device, a host computer, a signal generator, a piezoelectric controller and a laser controller, wherein The piezoelectric displacement platform and the uniaxial high-precision displacement platform are used to drive the optical fiber to perform uniform displacement. The piezoelectric displacement platform is arranged on the uniaxial high-precision displacement platform. The displacement direction of the uniaxial high-precision displacement platform is parallel to the axial direction of the optical fiber. The displacement direction of the piezoelectric displacement platform is inclined to the displacement direction of the uniaxial high-precision displacement platform. The femtosecond laser device comprises a femtosecond laser, which is used to output femtosecond laser to the optical fiber, so as to write the fiber grating line by line inside the optical fiber; The host computer is used to calculate the signal timing diagram of the piezoelectric displacement platform according to the grating parameters of the target fiber Bragg grating, and provide the signal timing diagram to the signal generator, and control the displacement speed of the single-axis high-precision displacement platform, and is connected to the signal generator and the single-axis high-precision displacement platform respectively; The signal generator is used to generate a pulse signal of the piezoelectric displacement platform according to the signal timing diagram, and output the pulse signal to the piezoelectric controller and the laser controller at the same time, and is connected to the piezoelectric controller and the laser controller respectively; The piezoelectric controller is used to amplify the pulse signal to control the displacement point of the piezoelectric displacement platform, and is connected to the piezoelectric displacement platform; The laser controller is used to control the on and off of the femtosecond laser according to the pulse signal and is connected to the femtosecond laser.

[0007] Furthermore, when the piezoelectric displacement platform is displaced at a uniform speed, it has a radial component velocity in the radial direction and an axial component velocity in the axial direction, and the axial component velocity is opposite in direction to the displacement velocity of the uniaxial high-precision displacement platform and has the same magnitude.

[0008] Furthermore, each time period T of the signal timing diagram includes a first time period and a second time period. In the first time period, the voltage value of the pulse signal increases linearly from a minimum value to a maximum value, corresponding to the grating time of the fiber Bragg grating. At this time, the femtosecond laser is in an on state, and the piezoelectric displacement platform uniformly displaces from a first displacement point to a second displacement point. At the end of the first time period, the voltage value of the pulse signal is at a maximum value, and at this time, the femtosecond laser switches from an on state to a off state; in the second time period, the voltage value of the pulse signal linearly recovers from a maximum value to a minimum value, corresponding to the non-grating time of the fiber Bragg grating. At this time, the femtosecond laser is in an off state, and the piezoelectric displacement platform uniformly resets from the second displacement point to the first displacement point. At the end of the second time period, the voltage value of the pulse signal is at a minimum value, and at this time, the femtosecond laser switches from an off state to an on state.

[0009] Furthermore, the first time period t1=L / (V1*tanθ), the second time period t2=(Λ*tanθ-L) / (V1*tanθ), L is the grating line length of the fiber grating, Λ is the grating period of the fiber grating, and θ is the inclination angle of the displacement direction of the piezoelectric displacement platform; the frequency f of the signal timing diagram is 1 / (t1+t2)=V1 / Λ.

[0010] Furthermore, if the fiber grating is a Bragg fiber grating, each time period of the signal timing diagram is fixed and unchanged; if the fiber grating is a chirped fiber grating, each time period of the signal timing diagram changes in a chirping manner.

[0011] Furthermore, when the voltage value of the pulse signal output by the signal generator is the maximum value, the level signal output by the laser controller to the femtosecond laser is switched from a high level to a low level to turn off the femtosecond laser; when the voltage value of the pulse signal output by the signal generator is the minimum value, the level signal output by the laser controller to the femtosecond laser is switched from a low level to a high level to turn on the femtosecond laser.

[0012] Furthermore, the fiber Bragg grating preparation system also includes an oscilloscope for detecting the pulse signal, which is connected to the signal generator.

[0013] Furthermore, the inclination angle θ of the displacement direction of the piezoelectric displacement platform is arctan (L / Λ), L is the grating line length of the fiber grating, and Λ is the grating period of the fiber grating.

[0014] Furthermore, the single-axis high-precision displacement platform is an air-floating electric displacement platform.

[0015] A method for preparing a fiber Bragg grating based on piezoelectric displacement and femtosecond laser direct writing comprises the following steps: Step 100: Calculate the signal timing diagram of the piezoelectric displacement platform according to the grating parameters of the target fiber grating; Step 200: adjusting the inclination angle between the displacement direction of the piezoelectric displacement platform and the displacement direction of the uniaxial high-precision displacement platform; Step 300: Generate a pulse signal of the piezoelectric displacement platform according to the signal timing diagram; Step 400: Control the piezoelectric displacement platform to drive the optical fiber to move uniformly along the tilt direction according to the pulse signal, and control the uniaxial high-precision displacement platform to drive the optical fiber to move uniformly along the axial direction, and control the opening and closing of the femtosecond laser according to the pulse signal.

[0016] The present invention has the following beneficial effects: The fiber grating preparation system of the present invention uses the piezoelectric displacement platform to control the displacement of the optical fiber in the radial direction, and uses the uniaxial high-precision displacement platform to control the displacement of the optical fiber in the axial direction when writing the fiber grating line by line. The displacement direction of the piezoelectric displacement platform is inclined to the displacement direction of the uniaxial high-precision displacement platform. At the same time, the laser controller is used to control the synchronous opening and closing of the femtosecond laser according to the pulse signal of the piezoelectric displacement platform. It has at least the following beneficial effects: 1. The piezoelectric displacement platform drives the displacement of the optical fiber based on piezoelectric deformation. The voltage value of the pulse signal is directly related to the displacement point of the piezoelectric displacement platform. One voltage value corresponds to one displacement point. Therefore, the signal generator can achieve uniform displacement of the optical fiber by outputting a linearly changing pulse signal, and can achieve instantaneous resetting of the optical fiber by outputting an instantaneously changing pulse signal. The piezoelectric displacement platform has good high-frequency vibration characteristics, which can ensure good linearity under high-frequency vibration, and solves the problem of grating line bending when the existing solution writes the optical fiber grating at high speed. 2. The displacement direction of the piezoelectric displacement platform is tilted to the displacement direction of the uniaxial high-precision displacement platform. The verticality of the grating line to the axial direction can be controlled by adjusting the tilt angle of the piezoelectric displacement platform and the speed ratio between the piezoelectric displacement platform and the uniaxial high-precision displacement platform. At the same time, the uniaxial high-precision displacement platform does not need to stop and wait when writing the grating line, which greatly improves the efficiency of femtosecond laser writing the fiber grating line by line, so that the efficiency of writing the fiber grating line by line can be comparable to the efficiency of writing the fiber grating point by point; 3. The laser controller controls the femtosecond laser to turn on and off synchronously according to the pulse signal of the piezoelectric displacement platform, so that the single-axis high-precision displacement platform can always maintain a state of uniform displacement, and then locate the grating period of the fiber Bragg grating through the switching time of the femtosecond laser to avoid affecting the positioning of the grating period due to insufficient start-stop accuracy of the single-axis high-precision displacement platform, thereby improving the positioning accuracy of the fiber Bragg grating. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the principle structure of the fiber Bragg grating preparation system provided by the present invention.

[0018] Figure 2 A schematic diagram of the writing path inside the optical fiber of the optical fiber Bragg grating preparation system provided by the present invention.

[0019] Figure 3 This is a signal timing diagram of the piezoelectric displacement platform of the fiber grating preparation system provided by the present invention.

[0020] Figure 4 This is a time displacement diagram of the piezoelectric displacement platform of the fiber grating preparation system provided by the present invention.

[0021] Figure 5 This is a control signal diagram of the femtosecond laser of the fiber grating preparation system provided by the present invention.

[0022] Figure 6 A flowchart of the steps of the fiber grating preparation method provided by the present invention. DETAILED DESCRIPTION

[0023] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments, examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0024] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are 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 should not be understood as a limitation on the present invention.

[0025] In addition, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0026] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix", "set" and the like 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 a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] Embodiment 1 like Figure 1 and 2As shown, a fiber Bragg grating preparation system based on piezoelectric displacement and femtosecond laser direct writing includes a piezoelectric displacement platform 6, a single-axis high-precision displacement platform 7, a femtosecond laser device, a host computer 9, a signal generator 10, a piezoelectric controller 8 and a laser controller 12, wherein The piezoelectric displacement platform 6 and the uniaxial high-precision displacement platform 7 are used to drive the optical fiber to perform uniform displacement. The piezoelectric displacement platform 6 is arranged on the uniaxial high-precision displacement platform 7. The displacement direction of the uniaxial high-precision displacement platform 7 is parallel to the axial direction X of the optical fiber. The displacement direction of the piezoelectric displacement platform 6 is inclined to the displacement direction of the uniaxial high-precision displacement platform 7. The femtosecond laser device comprises a femtosecond laser 1, which is used to output femtosecond laser to the optical fiber, so as to write the fiber grating line by line inside the optical fiber; The host computer 9 is used to calculate the signal timing diagram of the piezoelectric displacement platform 6 according to the grating parameters of the target fiber grating, and provide the signal timing diagram to the signal generator 10, and control the displacement speed of the single-axis high-precision displacement platform 7, and is connected to the signal generator 10 and the single-axis high-precision displacement platform 7 respectively; The signal generator 10 is used to generate a pulse signal of the piezoelectric displacement platform 6 according to the signal timing diagram, and output the pulse signal to the piezoelectric controller 8 and the laser controller 12 at the same time, and is connected to the piezoelectric controller 8 and the laser controller 12 respectively; The piezoelectric controller 8 is used to amplify the pulse signal to control the displacement point of the piezoelectric displacement platform 6 and is connected to the piezoelectric displacement platform 6; The laser controller 12 is used to control the on and off of the femtosecond laser 1 according to the pulse signal, and is connected to the femtosecond laser 1 .

[0028] The fiber grating preparation system of the present invention uses the piezoelectric displacement platform 6 to control the displacement of the optical fiber in the radial direction Y, and uses the uniaxial high-precision displacement platform 7 to control the displacement of the optical fiber in the axial direction X when writing the fiber grating line by line. The displacement direction of the piezoelectric displacement platform 6 and the displacement direction of the uniaxial high-precision displacement platform 7 are arranged obliquely, and the laser controller 12 is used to control the synchronous opening and closing of the femtosecond laser 1 according to the pulse signal of the piezoelectric displacement platform 6, which has at least the following beneficial effects: 1. The piezoelectric displacement platform 6 drives the displacement of the optical fiber based on piezoelectric deformation. The voltage value of the pulse signal is directly related to the displacement point of the piezoelectric displacement platform 6. One voltage value corresponds to one displacement point. Therefore, the signal generator 10 can achieve uniform displacement of the optical fiber by outputting a linearly changing pulse signal, and can achieve instantaneous resetting of the optical fiber by outputting an instantaneously changing pulse signal. The piezoelectric displacement platform 6 has good high-frequency vibration characteristics, and can ensure good linearity under high-frequency vibration, which solves the problem of grating line bending when the existing solution writes the optical fiber grating at high speed. 2. The displacement direction of the piezoelectric displacement platform 6 is tilted with respect to the displacement direction of the uniaxial high-precision displacement platform 7. The verticality of the grating line to the axial direction X can be controlled by adjusting the tilt angle of the piezoelectric displacement platform 6 and the speed ratio between the piezoelectric displacement platform 6 and the uniaxial high-precision displacement platform 7. At the same time, the uniaxial high-precision displacement platform 7 does not need to stop and wait when writing the grating line, which greatly improves the efficiency of femtosecond laser writing the fiber Bragg grating line by line, so that the efficiency of writing the fiber Bragg grating line by line can be comparable to the efficiency of writing the fiber Bragg grating point by point; 3. The laser controller 12 controls the femtosecond laser 1 to turn on and off synchronously according to the pulse signal of the piezoelectric displacement platform 6, so that the single-axis high-precision displacement platform 7 can always maintain a state of uniform displacement, and then locate the grating period of the fiber Bragg grating through the switching time of the femtosecond laser 1, so as to avoid the positioning of the grating period due to the insufficient start-stop accuracy of the single-axis high-precision displacement platform 7, thereby improving the positioning accuracy of the fiber Bragg grating.

[0029] In this embodiment, the single-axis high-precision displacement platform 7 is an air-floating electric displacement platform.

[0030] The femtosecond laser device further comprises an optical attenuator 2, a two-way color mirror 3, a CCD camera 4, and a focusing lens 5. The optical attenuator 2 and the two-way color mirror 3 are sequentially arranged in front of the emission end of the femtosecond laser 1, the CCD camera 4 is arranged in front of the transmission end of the two-way color mirror 3, and the focusing lens 5 is arranged in front of the reflection end of the two-way color mirror 3. After the power of the femtosecond laser beam emitted by the femtosecond laser 1 is attenuated by the optical attenuator 2, it is divided into two beams by the two-way color mirror 3. One femtosecond laser beam is focused by the focusing lens 5 and then writes the fiber grating in the optical fiber, and the other femtosecond laser beam is imaged on the CCD camera 4 to obtain the writing track of the fiber grating. Of course, the femtosecond laser device is not limited to the structure in this embodiment.

[0031] The fiber Bragg grating preparation system further includes an oscilloscope 11 for detecting the pulse signal, which is connected to the signal generator 10 .

[0032] When the piezoelectric displacement platform 6 is displaced at a uniform speed, it has a radial component velocity in the radial direction Y and an axial component velocity in the axial direction X. The radial component velocity during displacement is used to realize the uniform displacement of the optical fiber in the radial direction Y when writing the grating lines, and the axial component velocity during displacement is used to offset the displacement velocity of the uniaxial high-precision displacement platform 7 when writing the grating lines. When the axial component velocity during displacement and the displacement velocity of the uniaxial high-precision displacement platform 7 are opposite in direction and have the same magnitude, that is, V1=V2*cosθ, V1 is the displacement velocity of the uniaxial high-precision displacement platform 7, V2 is the displacement velocity of the piezoelectric displacement platform 6, and θ is the inclination angle of the displacement direction of the piezoelectric displacement platform 6. After the two offset each other, the focal position of the optical fiber in the axial direction X relative to the femtosecond laser remains fixed.

[0033] When the piezoelectric displacement platform 6 is quickly reset, it has a radial component velocity in the radial direction Y and an axial component velocity in the axial direction X. The radial component velocity during reset is used to achieve rapid reset of the optical fiber in the radial direction Y when the grating lines are not being written, and the axial component velocity during reset is used to superimpose with the displacement velocity of the uniaxial high-precision displacement platform 7 when the grating lines are not being written, so as to control the period between two adjacent grating lines, that is, the grating period.

[0034] like Figure 3-5 As shown, each time period T of the signal timing diagram includes a first time period t1 and a second time period t2. In the first time period t1, the voltage value of the pulse signal increases linearly from a minimum value min to a maximum value max, corresponding to the grating time of the fiber Bragg grating. At this time, the femtosecond laser 1 is in an on state, and the piezoelectric displacement platform 6 uniformly displaces from the first displacement point D1 to the second displacement point D2. At the end of the first time period t1, the voltage value of the pulse signal is at a maximum value max, and the femtosecond laser 1 is switched from an on state to a off state; in the second time period t2, the voltage value of the pulse signal linearly recovers from a maximum value max to a minimum value min, corresponding to the non-grating time of the fiber Bragg grating. At this time, the femtosecond laser 1 is in an off state, and the piezoelectric displacement platform 6 uniformly resets from the second displacement point D2 to the first displacement point D1. At the end of the second time period t2, the voltage value of the pulse signal is at a minimum value min, and the femtosecond laser 1 is switched from an off state to an on state. During the entire grating writing time, the single-axis high-precision displacement platform 7 always maintains a uniform displacement.

[0035] Among them, the inclination angle θ of the displacement direction of the piezoelectric displacement platform 6 is arctan (L / Λ), L is the grating line length of the fiber grating, Λ is the grating period of the fiber grating, and V1 is the displacement speed of the uniaxial high-precision displacement platform; the first time period t1 is L / (V1*tanθ), the second time period t2 is (Λ*tanθ-L) / (V1*tanθ), L is the grating line length of the fiber grating, Λ is the grating period of the fiber grating; the frequency f of the signal timing diagram is 1 / (t1+t2)=V1 / Λ.

[0036] If the fiber grating is a Bragg fiber grating, each time period T of the signal timing diagram is fixed; if the fiber grating is a chirped fiber grating, each time period T of the signal timing diagram changes in a chirping manner.

[0037] When the voltage value of the pulse signal output by the signal generator 10 is the maximum value max, the level signal output by the laser controller 12 to the femtosecond laser 1 changes from the high level V H Switch to low level V L , so that the femtosecond laser 1 is turned off, when the voltage value of the pulse signal output by the signal generator 10 is the minimum value min, the level signal output by the laser controller 12 to the femtosecond laser 1 changes from the low level V L Switch to high level V H , so that the femtosecond laser 1 is turned on.

[0038] Embodiment 2 like Figure 6 As shown, a method for preparing a fiber Bragg grating based on piezoelectric displacement and femtosecond laser direct writing is applied to the fiber Bragg grating preparation system described in Example 1, and comprises the following steps: Step 100: Calculate the signal timing diagram of the piezoelectric displacement platform 6 according to the grating parameters of the target fiber grating; Step 200: adjusting the inclination angle between the displacement direction of the piezoelectric displacement platform 6 and the displacement direction of the uniaxial high-precision displacement platform 7; Step 300: Generate a pulse signal of the piezoelectric displacement platform 6 according to the signal timing diagram; Step 400: Control the piezoelectric displacement platform 6 to drive the optical fiber to move uniformly along the tilt direction according to the pulse signal, and control the uniaxial high-precision displacement platform 7 to drive the optical fiber to move uniformly along the axial direction X, and control the opening and closing of the femtosecond laser 1 according to the pulse signal.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention rather than to limit them. Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the embodiments of the present invention can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber Bragg grating preparation system based on piezoelectric displacement and femtosecond laser direct writing, characterized in that: It includes a piezoelectric displacement platform, a uniaxial high-precision displacement platform, a femtosecond laser device, a host computer, a signal generator, a piezoelectric controller and a laser controller. The piezoelectric displacement platform and the uniaxial high-precision displacement platform are used to drive the optical fiber to perform uniform displacement. The piezoelectric displacement platform is arranged on the uniaxial high-precision displacement platform. The displacement direction of the uniaxial high-precision displacement platform is parallel to the axial direction of the optical fiber. The displacement direction of the piezoelectric displacement platform is inclined to the displacement direction of the uniaxial high-precision displacement platform. The femtosecond laser device comprises a femtosecond laser, which is used to output femtosecond laser to the optical fiber, so as to write the fiber grating line by line inside the optical fiber; The host computer is used to calculate the signal timing diagram of the piezoelectric displacement platform according to the grating parameters of the target fiber Bragg grating, and provide the signal timing diagram to the signal generator, and control the displacement speed of the single-axis high-precision displacement platform, and is connected to the signal generator and the single-axis high-precision displacement platform respectively; The signal generator is used to generate a pulse signal of the piezoelectric displacement platform according to the signal timing diagram, and output the pulse signal to the piezoelectric controller and the laser controller at the same time, and is connected to the piezoelectric controller and the laser controller respectively; The piezoelectric controller is used to amplify the pulse signal to control the displacement point of the piezoelectric displacement platform, and is connected to the piezoelectric displacement platform; The laser controller is used to control the on and off of the femtosecond laser according to the pulse signal and is connected to the femtosecond laser.

2. The fiber Bragg grating preparation system according to claim 1, characterized in that: When the piezoelectric displacement platform is displaced at a uniform speed, it has a radial component velocity in the radial direction and an axial component velocity in the axial direction. The axial component velocity is opposite in direction to the displacement velocity of the uniaxial high-precision displacement platform and has the same magnitude.

3. The fiber Bragg grating preparation system according to claim 1 or 2, characterized in that: Each time period T of the signal timing diagram includes a first time period and a second time period. In the first time period, the voltage value of the pulse signal increases linearly from a minimum value to a maximum value, corresponding to the grating time of the fiber Bragg grating. At this time, the femtosecond laser is in an on state, and the piezoelectric displacement platform uniformly displaces from a first displacement point to a second displacement point. At the end of the first time period, the voltage value of the pulse signal is at a maximum value, and at this time, the femtosecond laser switches from an on state to a off state; in the second time period, the voltage value of the pulse signal linearly recovers from a maximum value to a minimum value, corresponding to the non-grating time of the fiber Bragg grating. At this time, the femtosecond laser is in an off state, and the piezoelectric displacement platform uniformly resets from the second displacement point to the first displacement point. At the end of the second time period, the voltage value of the pulse signal is at a minimum value, and at this time, the femtosecond laser switches from an off state to an on state.

4. The fiber Bragg grating preparation system according to claim 3, characterized in that: The first time period t1=L / (V1*tanθ), the second time period t2=(Λ*tanθ-L) / (V1*tanθ), L is the grating line length of the fiber grating, V1 is the displacement speed of the single-axis high-precision displacement platform, Λ is the grating period of the fiber grating, θ is the inclination angle of the displacement direction of the piezoelectric displacement platform, and V1 is the displacement speed of the single-axis high-precision displacement platform; the frequency f of the signal timing diagram is V1 / Λ.

5. The fiber Bragg grating preparation system according to claim 3, characterized in that: If the fiber grating is a Bragg fiber grating, each time period of the signal timing diagram is fixed and unchanged; if the fiber grating is a chirped fiber grating, each time period of the signal timing diagram changes in a chirping manner.

6. The fiber Bragg grating preparation system according to claim 3, characterized in that: When the voltage value of the pulse signal output by the signal generator is the maximum value, the level signal output by the laser controller to the femtosecond laser is switched from a high level to a low level to turn off the femtosecond laser; when the voltage value of the pulse signal output by the signal generator is the minimum value, the level signal output by the laser controller to the femtosecond laser is switched from a low level to a high level to turn on the femtosecond laser.

7. The fiber Bragg grating preparation system according to claim 1, characterized in that: The fiber grating preparation system also includes an oscilloscope, which is used to detect the pulse signal and is connected to the signal generator.

8. The fiber Bragg grating preparation system according to claim 1, characterized in that: The inclination angle θ of the displacement direction of the piezoelectric displacement platform is arctan (L / Λ), L is the grating line length of the fiber grating, and Λ is the grating period of the fiber grating.

9. The fiber Bragg grating preparation system according to claim 1, characterized in that: The single-axis high-precision displacement platform is an air-floating electric displacement platform.

10. A method for preparing fiber Bragg gratings based on piezoelectric displacement and femtosecond laser direct writing, characterized in that: The steps include: Step 100: Calculate the signal timing diagram of the piezoelectric displacement platform according to the grating parameters of the target fiber grating; Step 200: adjusting the inclination angle between the displacement direction of the piezoelectric displacement platform and the displacement direction of the uniaxial high-precision displacement platform; Step 300: Generate a pulse signal of the piezoelectric displacement platform according to the signal timing diagram; Step 400: Control the piezoelectric displacement platform to drive the optical fiber to move uniformly along the tilt direction according to the pulse signal, and control the uniaxial high-precision displacement platform to drive the optical fiber to move uniformly along the axial direction, and control the opening and closing of the femtosecond laser according to the pulse signal.

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