CN111856644A

CN111856644A - Apodization long period optical fiber grating inscribing device, inscribing method and laser system

Info

Publication number: CN111856644A
Application number: CN202010737644.4A
Authority: CN
Inventors: 王泽锋; 胡琪浩; 王蒙; 李宏业; 田鑫; 赵晓帆; 饶斌裕; 奚小明; 陈子伦; 潘志勇; 王小林; 许晓军; 陈金宝
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2020-07-28
Filing date: 2020-07-28
Publication date: 2020-10-30
Anticipated expiration: 2040-07-28
Also published as: CN111856644B

Abstract

An apodization long period fiber grating writing device, a writing method and a laser system. The engraving device comprises a carbon dioxide laser, a beam expanding lens group, a scanning galvanometer, a focusing field lens and an optical fiber operation moving platform, wherein the beam expanding lens group, the scanning galvanometer and the focusing field lens are sequentially arranged on a transmission path of laser output by the carbon dioxide laser, the optical fiber operation moving platform is arranged under the focusing field lens, optical fibers to be engraved with the apodization long-period optical fiber grating are arranged on the optical fiber operation moving platform, and laser emitted from the focusing field lens can be incident on optical fibers arranged on the optical fiber operation moving platform to realize apodization long-period optical fiber grating engraving. The long-period fiber grating obtained by the writing method is arranged in a laser system, and the stimulated Raman scattering is inhibited by utilizing the high loss factor of the long-period fiber grating in a Raman waveband. The apodization long-period fiber grating is inscribed by the inscription device, so that the refractive index mutation caused by the point-by-point exposure lithography method can be eliminated.

Description

Apodization long period optical fiber grating inscribing device, inscribing method and laser system

Technical Field

The invention relates to the technical field of fiber grating writing and application, in particular to an apodization long-period fiber grating writing device, a writing method and a laser system.

Background

The fiber grating has wide application in the fields of fiber lasers, fiber communication, fiber sensing and the like. Compared with the traditional grating, the fiber grating has the advantages of narrow line width, low insertion loss, strong anti-electromagnetic interference capability, high sensitivity, light weight, small volume, easy realization of wavelength division multiplexing, flexible use and the like. The all-fiber laser formed by replacing the traditional optical dichroic mirror with the fiber grating has the advantages of high stability, compact structure and the like, so that the fiber laser is practical. The advent of fiber gratings has also greatly facilitated the development of fiber optic communications and fiber sensing.

The main methods for preparing the long-period fiber grating at present include a phase mask method, a point-by-point writing method, a splicing method, a fused biconical taper method and the like. In the phase mask method, the phase mask is usually irradiated by ultraviolet light to form diffraction fringes, and the side surface of the diffraction fringes of +/-1 order is exposed to a photosensitive fiber to prepare a grating structure. The period of the fiber grating prepared by the phase mask method only depends on the period of the phase mask stripes (the grating period is half of the period of the phase mask stripes), so that the difficulty of the fiber grating preparation process is reduced. The point-by-point writing method is generally used for preparing long-period fiber gratings with relatively large periods, the method is not limited by a light source, and excimer laser, femtosecond laser and carbon dioxide laser can be used as light sources of the point-by-point writing method. The method mainly forms periodic modulation of refractive index by means of point-by-point exposure on optical fiber after focusing light beams, and two most commonly used writing devices are an electric translation method and a galvanometer scanning method.

The long-period fiber grating prepared by the point-by-point writing method has a self-chirp effect due to a refractive index mutation between the exposure points at the two ends of the grating region and the common fiber, which shows that severe sidebands appear on the transmission spectrum and the reflection spectrum, and greatly restricts the application of the fiber grating device. By the long-period fiber grating apodization technology, the amplitude of the refractive index modulation in the grating presents Gaussian distribution along the axial direction of the grating, so that the short-wave loss of the optical fiber can be effectively avoided, and the side band of the resonance peak of the transmission spectrum can be effectively inhibited. Because the preparation method of the long-period fiber grating is point-by-point writing, the refractive index of the substrate in the whole grating region can not be in Gaussian distribution by using an apodization template like a Bragg grating.

The writing period of the dot-by-dot writing method is usually controlled by an electric displacement platform, and the exposure time of each refractive index modulation point is consistent in the whole process, so that the refractive index modulation amplitude of each exposure position is equal. This results in no gradient in the refractive index change between the grating region portion and the non-grating region portion, exhibiting two-stage differentiation. This order-differentiated refractive index profile also results in the generation of resonance peak sidebands. The performance of long period fiber gratings can be greatly affected in some cases.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides an apodization long-period fiber grating inscribing device, an inscribing method and a laser system.

In order to achieve the technical purpose, the invention adopts the following specific technical scheme:

the invention provides an apodization long-period fiber grating writing device which comprises a carbon dioxide laser, a beam expanding lens group, a scanning galvanometer, a focusing field lens and a fiber operation moving platform, wherein the beam expanding lens group, the scanning galvanometer and the focusing field lens are sequentially arranged on a transmission path of laser output by the carbon dioxide laser, the fiber operation moving platform is arranged right below the focusing field lens, optical fibers of the apodization long-period fiber grating to be written are arranged on the fiber operation moving platform and can move under the driving of the fiber operation moving platform, and the laser emitted from the focusing field lens can be incident on the optical fibers arranged on the fiber operation moving platform to realize apodization long-period fiber grating writing. The optical fiber operation moving platform is driven by a displacement platform driving motor, and the horizontal moving distance and speed of the optical fiber operation moving platform are controlled by controlling the displacement platform driving motor.

Furthermore, the scanning galvanometer is controlled by a galvanometer driver, and the galvanometer driver controls the marking pattern and the marking position of the scanning galvanometer. Furthermore, the galvanometer driver is connected with a computer, and the computer controls the scanning of the marking pattern and the marking position of the galvanometer by controlling the galvanometer driver.

Further, the output power and frequency of the carbon dioxide laser are controlled by a computer.

Furthermore, the optical fiber operation moving platform comprises two optical fiber clamps, a three-dimensional adjusting base and an electric horizontal displacement platform, wherein the two optical fiber clamps are respectively a left optical fiber clamp and a right optical fiber clamp, and an optical fiber of the apodization long-period optical fiber grating to be inscribed is clamped by the left optical fiber clamp and the right optical fiber clamp; the left optical fiber clamp and the right optical fiber clamp are respectively fixed on a three-dimensional adjusting base, and the optical fiber of the apodization long-period optical fiber grating to be inscribed is positioned right below the focusing field lens by adjusting the two three-dimensional adjusting bases; the three-dimensional adjusting base is arranged on the electric horizontal displacement platform, and the electric horizontal displacement platform moves horizontally under the driving of the displacement platform driving motor. Further, the displacement platform driving motor is connected with a computer, and the computer controls the displacement platform driving motor so as to control the horizontal moving distance and speed of the electric horizontal displacement platform.

Furthermore, the light outlet of the carbon dioxide laser and the beam expanding lens group are positioned on the same axis. The output laser of the beam expanding lens group is aligned with the right center of the input optical port of the scanning galvanometer.

Based on the apodization long period fiber grating writing device, the invention provides a first apodization long period fiber grating writing method, which comprises the following steps:

(1) setting parameters of a carbon dioxide laser, including the repetition frequency and the voltage of the carbon dioxide laser;

(2) intercepting an optical fiber with proper length, coating the area of the apodization long-period optical fiber grating to be inscribed with a chemical stripping agent, wiping with alcohol, and then installing the optical fiber on an optical fiber operation moving platform; adjusting the optical fiber operation moving platform to enable the optical fiber of the apodization long-period fiber grating to be engraved and written to be positioned under the focusing field lens, so that the laser emitted from the focusing field lens can be incident on the optical fiber arranged on the optical fiber operation moving platform;

(3) apodizing long period fiber grating inscription;

(3.1) the marking pattern of the scanning galvanometer is a row of vertical line stripes, and the marking position of the scanning galvanometer and the number of the vertical line stripes in the initial marking pattern are set; starting a carbon dioxide laser and a scanning galvanometer to carry out exposure scanning, enabling the laser to carry out single exposure on the whole area of the apodization long-period fiber grating to be inscribed on the optical fiber according to a set marking pattern, and then closing the carbon dioxide laser and the scanning galvanometer;

(3.2) resetting the marking pattern of the scanning galvanometer, wherein the currently set scanning pattern is that the number of vertical line stripes at two ends of the currently set scanning pattern is reduced on the basis of the previous scanning pattern, the carbon dioxide laser and the scanning galvanometer are restarted to carry out the exposure scanning, and the laser exposure area on the optical fiber in the exposure scanning is positioned in the middle of the laser exposure area in the previous exposure scanning, namely, only the middle area of the laser exposure area in the previous exposure scanning is subjected to the exposure again;

and (3.3) repeating the step (3.2) until the number of vertical line stripes in the marking pattern of the scanning galvanometer is lower than a set threshold value. Specifically, until 1/3 where the number of vertical lines in the marking pattern of the scanning galvanometer is lower than the number of vertical lines in the initial scanning pattern.

The long-period fiber grating obtained by the first apodization long-period fiber grating inscription method is arranged in a fiber laser oscillator cavity, and the high loss of the long-period fiber grating in a Raman waveband is utilized to suppress stimulated Raman scattering. Further, the present invention provides a laser system, comprising a laser oscillator, wherein a long-period fiber grating is arranged in the laser oscillator, and the long-period fiber grating is formed by the first apodized long-period fiber grating writing method. The laser oscillator is a forward pumping fiber laser oscillator, a backward pumping fiber laser oscillator or a bidirectional pumping fiber laser oscillator. The forward pump fiber laser oscillator, the backward pump fiber laser oscillator, and the bidirectional pump fiber laser oscillator are divided according to the pumping mode of the oscillators. The laser oscillator comprises a pump light source, a pump light beam combiner, a high-reflection grating, a doped fiber and a low-reflection grating, wherein the long-period fiber grating is arranged in front of the low-reflection grating in the laser oscillator cavity or behind the high-reflection grating in the fiber laser oscillator cavity or directly inscribed on the doped fiber in the fiber laser oscillator cavity. By utilizing the high loss of the long-period fiber grating in the Raman band, the fiber laser oscillator has a good inhibition effect on the forward and backward Raman light in the fiber laser oscillator, especially on the backward Raman light, so that the risk of the high-power backward Raman light on the system is greatly reduced, the stimulated Raman scattering phenomenon can be observed in the output of the fiber laser oscillator at a higher power level, and the upper limit of the power output of the fiber laser oscillator is greatly improved.

The long-period fiber grating obtained by the first apodization long-period fiber grating inscribing method is arranged in a high-power fiber laser amplifier system, and the effect of suppressing stimulated Raman scattering can be achieved. Specifically, the invention provides a laser system, which comprises a seed source and more than one stage of laser amplifiers, wherein long-period fiber gratings are arranged between the seed source and the laser amplifiers and between the laser amplifiers at all stages, and the long-period fiber gratings are formed by adopting the first apodization long-period fiber grating inscribing method. The long-period fiber grating is directly connected between the seed source and the fiber amplifier, and the seed source is filtered by utilizing the high loss factor of the long-period fiber grating in a Raman wave band, so that the seed source can still output relatively pure signal light at a higher power level. And the working efficiency of the optical fiber amplifier is improved, and the Raman threshold of the whole system is improved. The long-period fiber grating is arranged between each stage of fiber amplifiers, so that the working efficiency of each stage of fiber amplifiers is improved, the integral Raman threshold is improved, and the suppression effect is further improved.

Based on the apodization long period fiber grating writing device, the invention provides a second apodization long period fiber grating writing method, which comprises the following steps:

(3) apodizing long period fiber grating inscription;

(3.1) starting the scanning galvanometer, and controlling the scanning galvanometer to output a vertical line in the middle of the marking range; setting the moving speed and the initial moving distance of the electric horizontal displacement platform; starting a carbon dioxide laser and an electric displacement platform to carry out first exposure scanning, enabling the carbon dioxide laser to emit light, enabling the electric horizontal displacement platform and optical fibers on the electric horizontal displacement platform to start to move horizontally, completing single exposure on the whole area to be subjected to apodization long-period optical fiber grating writing on the optical fibers, then closing the carbon dioxide laser and resetting the electric displacement platform;

(3.2) setting the starting time of the carbon dioxide laser and the electric displacement platform in the next exposure scanning so that the laser exposure area on the optical fiber in the exposure scanning is positioned in the middle of the laser exposure area in the previous exposure scanning, namely only exposing the middle area of the laser exposure area in the previous exposure scanning again;

and (3.3) repeating the step (3.2) until the current laser exposure area meets the set condition. Specifically, until the current exposure area is less than 1/3 of the laser exposure area in the first exposure scan.

The long-period fiber grating obtained by the second apodization long-period fiber grating inscription method is arranged in a fiber laser oscillator cavity, and the high loss of the long-period fiber grating in a Raman waveband is utilized to suppress stimulated Raman scattering. Further, the present invention provides a laser system, comprising a laser oscillator, wherein a long-period fiber grating is arranged in the laser oscillator, the long-period fiber grating is formed by using the second apodization long-period fiber grating writing method, and the laser oscillator is a forward pumping fiber laser oscillator, a backward pumping fiber laser oscillator or a bidirectional pumping fiber laser oscillator; the laser oscillator comprises a pump light source, a pump light beam combiner, a high-reflection grating, a doped fiber and a low-reflection grating, wherein the long-period fiber grating is arranged in front of the low-reflection grating in the laser oscillator cavity or behind the high-reflection grating in the fiber laser oscillator cavity or directly inscribed on the doped fiber in the fiber laser oscillator cavity. By utilizing the high loss of the long-period fiber grating in the Raman band, the fiber laser oscillator has a good inhibition effect on the forward and backward Raman light in the fiber laser oscillator, especially on the backward Raman light, so that the risk of the high-power backward Raman light on the system is greatly reduced, the stimulated Raman scattering phenomenon can be observed in the output of the fiber laser oscillator at a higher power level, and the upper limit of the power output of the fiber laser oscillator is greatly improved.

The long-period fiber grating obtained by the second apodization long-period fiber grating inscribing method is arranged in a high-power fiber laser amplifier system, and the effect of suppressing stimulated Raman scattering can be achieved. Specifically, the invention provides a laser system, which comprises a seed source and more than one stage of laser amplifiers, wherein long-period fiber gratings are arranged between the seed source and the laser amplifiers and between the laser amplifiers at all stages, and the long-period fiber gratings are formed by adopting the second apodization long-period fiber grating inscribing method. The long-period fiber grating is directly connected between the seed source and the fiber amplifier, and the seed source is filtered by utilizing the high loss factor of the long-period fiber grating in a Raman wave band, so that the seed source can still output relatively pure signal light at a higher power level. And the working efficiency of the optical fiber amplifier is improved, and the Raman threshold of the whole system is improved. The long-period fiber grating is arranged between each stage of fiber amplifiers, so that the working efficiency of each stage of fiber amplifiers is improved, the integral Raman threshold is improved, and the suppression effect is further improved.

The invention has the following beneficial effects:

(1) the invention provides an apodization long-period fiber grating writing device, which is used for writing apodization long-period fiber gratings and can eliminate the refractive index mutation caused by a point-by-point exposure lithography method.

(2) The apodization long period fiber grating writing device provided by the invention can realize two apodization long period fiber grating writing methods. According to the first apodization long-period fiber grating inscription method provided by the invention, different apodization functions can be realized by flexibly adjusting the inscription position of the scanning galvanometer and the number of vertical line stripes in the inscription pattern, so that the inscription preparation of different types of apodization fiber gratings can be realized.

(3) The apodization long-period fiber grating inscription device provided by the invention can not only realize the inscription of the long-period fiber grating by means of scanning of the scanning vibrating mirror, but also realize the inscription of the long-period fiber grating by means of the movement of the electric horizontal displacement platform under the condition that the scanning vibrating mirror does not scan and only outputs one vertical line in the middle. The method can also form apodization by controlling the electric horizontal displacement platform to gradually reduce the refractive index modulation at two ends of the grating.

(4) The long-period fiber grating obtained by the apodization long-period fiber grating writing method provided by the invention is arranged in a fiber laser system. If it is set in the cavity of laser oscillator, the high loss of long-period fiber grating in Raman band is used to suppress stimulated Raman scattering. The long-period fiber grating is introduced into the cavity of the fiber laser oscillator, and compared with the fiber laser oscillator outside the cavity, the long-period fiber grating has a stronger inhibition effect, and the Raman threshold of the fiber laser oscillator can be improved to a greater extent. Meanwhile, the suppression ratio is flexibly adjusted by controlling the number of the added long-period fiber gratings.

If the fiber laser amplifier is arranged in a high-power fiber laser amplifier system, the effect of suppressing the stimulated Raman scattering can be achieved. The long-period fiber grating is introduced into the high-power fiber laser amplifier system, so that the overall Raman threshold of the system can be improved, a certain filtering effect is achieved, backward Raman light is inhibited, and the fiber device can be well protected. Meanwhile, the suppression ratio is flexibly adjusted by controlling the number of the added long-period fiber gratings. The working mechanism of the long-period fiber grating is the coupling between a fiber core mode and a cladding mode, so that the temperature rise coefficient is small when the long-period fiber grating is applied to a fiber laser, and the long-period fiber grating has larger application potential.

The long-period fiber grating is simple and convenient to manufacture, and parameters can be flexibly adjusted according to actual requirements so as to match different suppression wave bands. The long-period fiber grating has small insertion loss, is convenient to prepare on different types of optical fibers, and has good stability and wide application range.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

FIG. 1 is a schematic diagram of a structure of an apodized long period fiber grating writing device according to embodiment 1;

FIG. 2 is a schematic diagram showing a marking pattern of the scanning galvanometer provided in example 2;

FIG. 3 is a schematic structural view of example 4;

FIG. 4 is a schematic structural view of example 5;

FIG. 5 is a schematic structural view of example 6;

FIG. 6 is a schematic structural view of example 7;

FIG. 7 is a schematic structural view of example 8;

FIG. 8 is a schematic structural view of example 9;

FIG. 9 is a schematic structural view of example 10;

FIG. 10 is a schematic structural view of example 11;

FIG. 11 is a schematic structural view of example 12;

FIG. 12 is a schematic structural view of example 13;

FIG. 13 is a schematic structural view of example 14;

FIG. 14 is a schematic structural view of example 15.

The reference numbers in the figures illustrate:

1. a carbon dioxide laser; 2. a beam expanding lens group; 3. scanning a galvanometer; 4. a focusing field lens; 5. an optical fiber clamp; 6. a three-dimensional adjusting base; 7. an electric horizontal displacement platform; 8. a displacement platform drive motor; 9. a computer; 10. a galvanometer driver.

101. A pump LD light source; 102. a pump combiner; 103. high-reflection grating; 104. doping the optical fiber; 105. a low-reflection grating; 106. a long-period fiber grating; 107. melting point; 108. a seed source; 109. a 1 st stage fiber amplifier; 110. a 2 nd stage fiber amplifier; and the nth stage of optical fiber amplifier.

Detailed Description

In order to make the technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1:

an apodization long period optical fiber grating writing device comprises a carbon dioxide laser 1, a beam expanding lens group 2, a scanning galvanometer 3, a focusing field lens 4, an optical fiber operation moving platform and a computer 9.

The emergent light spot of the carbon dioxide laser 1 is circular, and the light energy distribution is more uniform. The transmission path of the laser output by the carbon dioxide laser 1 is sequentially provided with a beam expanding lens group 2, a scanning galvanometer 3 and a focusing field lens 4. The central axis of the beam expanding lens group 2 and the carbon dioxide laser are positioned on the same straight line, and the output laser of the beam expanding lens group 2 is aligned with the right center of the input optical port of the scanning galvanometer 3.

An optical fiber operation moving platform is arranged right below the focusing field lens 4. The optical fiber 11 to be etched and written with the apodization long-period fiber grating is arranged on the optical fiber operation moving platform, laser emitted from the focusing field lens 4 can be incident on the optical fiber 11 arranged on the optical fiber operation moving platform to realize the apodization long-period fiber grating etching, the optical fiber operation moving platform is driven by the displacement platform driving motor 8, and the horizontal moving distance and the horizontal moving speed of the optical fiber operation moving platform are further controlled by controlling the displacement platform driving motor 8. Specifically, the optical fiber operation moving platform comprises an optical fiber clamp 5, a three-dimensional adjusting base 6 and an electric horizontal displacement platform 7. The optical fiber clamps 5 are respectively a left optical fiber clamp and a right optical fiber clamp, and the optical fiber 11 to be inscribed with the apodization long-period fiber grating is clamped by the left optical fiber clamp and the right optical fiber clamp. The left optical fiber clamp and the right optical fiber clamp are respectively fixed on a three-dimensional adjusting base 6. The three-dimensional adjustment base 6 in this embodiment is manually adjusted. Two ends of the optical fiber 11 are placed in V-shaped grooves of the left optical fiber clamp and the right optical fiber clamp, and the optical fiber 11 to be inscribed with the apodization long-period optical fiber grating is positioned right below the focusing field lens 4 by manually adjusting the two three-dimensional adjusting bases 6. Two three-dimensional regulation bases 6 are all installed on electronic horizontal displacement platform 7, and electronic horizontal displacement platform 7 horizontal migration under the drive of displacement platform driving motor 8, and displacement platform driving motor 8 is connected with computer 9, and computer 9 control displacement platform driving motor 8 and then control electronic horizontal displacement platform 7's horizontal migration distance and speed. The light outlet of the carbon dioxide laser 1 and the beam expanding lens group 2 are positioned on the same axis, so that the energy of output laser can be normally output. The scanning galvanometer 3 may be a commercially available product such as, for example, a Qinlong galvanometer. The laser emitted from the scanning galvanometer 3 is focused by the focusing field lens 4 and then is collected at the position of the optical fiber 11. The electric horizontal displacement platform 7 is a conventional one, and for example, a PI electric displacement platform may be used.

The fiber clamp 5 has a V-groove, and the flip of the V-groove can be screwed onto the clamp, whereby the fiber can be fixed as stably as possible.

In this embodiment, the position of the optical fiber 11 can be finely adjusted by the three-dimensional adjusting base 6, and the three-dimensional adjusting frame 6 can be properly adjusted for optical fibers of different diameters to optimize the exposure effect of the carbon dioxide laser.

In this example, the scanning galvanometer 3 can be flexibly controlled by the computer 9, including the period, length, number and marking times of the marked patterns.

The computer 9 is used as a general control system for controlling the marking pattern of the scanning galvanometer, the output light power and frequency of the laser, the moving speed and distance of the electric horizontal displacement platform and the like.

Example 2:

by using the apodization long period fiber grating writing device provided in embodiment 1, this embodiment provides an apodization long period fiber grating writing method, which includes the following steps:

(2) intercepting an optical fiber with proper length (a large mode field double-clad optical fiber is selected), coating a region of an apodization long-period optical fiber grating to be engraved and written with a chemical stripping agent, wiping with alcohol, and then installing the optical fiber on an optical fiber operation moving platform; adjusting the optical fiber operation moving platform to enable the optical fiber of the apodization long-period fiber grating to be engraved and written to be positioned under the focusing field lens, so that the laser emitted from the focusing field lens can be incident on the optical fiber arranged on the optical fiber operation moving platform;

(3) apodizing long period fiber grating inscription;

(3.1) the preset marking pattern of the scanning galvanometer is a row of vertical line stripes, as shown in fig. 3, wherein the optical fiber is horizontally placed, and the output marking pattern marks periodic nicks on the optical fiber. Fig. 3 shows the marking pattern set in the multiple exposure scanning, where the initial marking pattern is the uppermost row of vertical line stripes in fig. 3, the second row of vertical line stripes from top to bottom is the marking pattern set in the second exposure scanning, the third row of vertical line stripes is the marking pattern set in the third exposure scanning, and so on.

In this embodiment, the initial marking pattern set in the initial exposure scan is the uppermost row of vertical lines in fig. 3; starting a carbon dioxide laser and a scanning galvanometer to carry out exposure scanning, enabling the laser to carry out single exposure on the whole area of the apodization long-period fiber grating to be inscribed on the optical fiber according to a set marking pattern, and then closing the carbon dioxide laser and the scanning galvanometer;

(3.2) resetting a marking pattern of the scanning galvanometer, wherein the marking pattern set in the second exposure scanning is a second row of vertical line stripes from top to bottom in the graph 3, the number of the vertical line stripes at two ends of the scanning galvanometer is reduced on the basis of the previous scanning pattern in the currently set scanning pattern, the carbon dioxide laser and the scanning galvanometer are restarted to carry out the exposure scanning, and a laser exposure area on the optical fiber in the exposure scanning is positioned in the middle of the laser exposure area in the previous exposure scanning, namely only the middle area of the previous laser exposure area is subjected to the exposure again;

Example 3:

by using the apodization long period fiber grating writing device provided in embodiment 1, this embodiment provides an apodization long period fiber grating writing method, which performs the writing of an apodization long period fiber grating by controlling an electric horizontal displacement platform, and includes the following steps:

(2) intercepting an optical fiber with a proper length (selecting a large mode field optical fiber), coating a region of an apodization long-period optical fiber grating to be inscribed with a chemical stripping agent, wiping with alcohol, and then installing the optical fiber on an optical fiber operation moving platform; and adjusting the optical fiber operation moving platform to enable the optical fiber of the apodization long-period fiber grating to be engraved and written to be positioned under the focusing field lens, so that the laser emitted from the focusing field lens can be incident on the optical fiber arranged on the optical fiber operation moving platform. One end of the optical fiber is connected with a broadband light source, and the other end of the optical fiber is connected with an online detection system (a spectrum analyzer) for detection.

(3) Apodizing long period fiber grating inscription;

The long-period fiber grating obtained by the first or second apodization long-period fiber grating inscription method is arranged in a fiber laser oscillator cavity, and the high loss factor of the long-period fiber grating in a Raman waveband is utilized to inhibit stimulated Raman scattering. Embodiments 4 to 12 below provide laser systems, each including a laser oscillator, in which a long-period fiber grating is disposed, and the long-period fiber grating is formed by using the first or second apodized long-period fiber grating writing method, specifically as follows:

example 4:

FIG. 3 is a schematic structural view of example 4; in this embodiment, a forward pumped fiber laser oscillator. A laser system comprises a pump LD light source 101, a pump beam combiner 102, a high reflection grating 103, a doped fiber 104 and a low reflection grating 105. A long period fiber grating 106 is placed in front of the low-reflection grating 105 in the fiber laser oscillator cavity.

The number of the pump LD light sources 101 is plural, and an output pigtail of each pump LD light source 101 is connected to each pump arm of the pump combiner 2. For a common fiber laser oscillator, the pump source wavelength can be selected to be 976nm or 915nm, and the output power is in the order of hundreds of watts. In the actual use process, parameters, selected wavelengths, output powers, the number of used pump LD light sources 101, and the like are different according to requirements, and there is no special requirement. The pump combiner 102 in a forward pumped fiber laser oscillator is typically a 7 x 1 pump combiner. Backward pumped fiber laser oscillator which is typically a 6+1 x 1 pump combiner. The output pigtail of the pump combiner 102 is a large mode field fiber. The output tail fiber of the pump beam combiner 102 is sequentially connected with a high reflective grating 103, a doped grating 104, a long-period fiber grating 106 and a low reflective grating 105. In this embodiment, the long-period fiber grating 106 and the low reflective grating 105 are fabricated on the same fiber, wherein the long-period fiber grating 106 is located in front of the low reflective grating 105 and the two are spaced apart from each other to optimize the performance of the oscillator. The output tail fiber of the pump beam combiner 102 is connected with the high reflecting grating 103, the high reflecting grating 103 is connected with the doped grating 104, and the doped fiber 104 is connected with the long-period fiber grating 106 in a fusion mode, and a melting point 107 is formed at the fusion position. A pump LD light source 101, a pump beam combiner 102, a high reflection grating 103, a doped fiber 104, a long period fiber grating 106, a low reflection grating 105 and a melting point 107.

The high-reflection grating 103 has reflectivity of more than 99% at the working wavelength of the fiber laser oscillator, and 3dB bandwidth of 2-4nm, and is prepared on the same fiber as the output fiber of the pump beam combiner. The doped fiber 104 should be selected to match the highly reflective grating 103. The output low reflectivity grating 105 is typically no more than 10%, the 3dB bandwidth is typically no more than 1nm, and the center wavelength of the output low reflectivity grating should be no more than ± 0.4nm from the center wavelength of the output high reflectivity grating 103.

The pump LD light source 101 provides pump light necessary for generating laser light, and the pump light is coupled to the high-reflection grating 103 via the pump beam combiner 102. The high reflectivity grating 103 and the low reflectivity grating 105 only reflect at the signal light wavelength, e.g., 1080nm, and do not reflect at the pump light wavelength, with only losses. The pump light is injected into the doped fiber 104 via the high-reflectivity grating 103. The doped fiber 104 is typically doped with a rare earth element such as ytterbium, which is capable of absorbing the pump light and exciting the signal light, and outputting the signal light via the low reflective grating.

Due to the high energy density in the oscillator cavity, losses have a large effect on its efficiency. The long-period fiber grating 106 and the low-reflection grating 105 are prepared on the same optical fiber, so that no melting point exists between the long-period fiber grating and the low-reflection grating, the loss of the oscillation cavity is further reduced, and the output efficiency is improved. The optical fiber used for the long-period fiber grating 106 needs to match the fiber laser oscillator. When the intensity of signal light in the fiber laser oscillator exceeds a certain threshold, the SBS effect is generated, and the signal light generated after the pump light which is continuously injected at the moment is rapidly converted into the Stokes light through the SRS effect to form stronger Stokes light.

In the normal working process of the fiber laser oscillator, laser generated by doping the fiber in the fiber laser oscillator cavity comprises two components of signal light and Stokes light as shown by hollow arrows in the figure. When the long-period fiber grating 106 passes through the long-period fiber grating, due to the unique mode coupling characteristics of the long-period fiber grating, the Stokes light transmitted in the fiber core and the modes in the cladding are coupled with each other, so that the Stokes light is coupled to the fiber cladding and is scattered, a loss spectrum with a wide bandwidth exists at the wavelength of the Stokes light of the long-period fiber grating 106, and the intensity of the Stokes light signal in the laser is attenuated, as shown by the solid arrows in the figure. Therefore, in the actual output laser of the fiber laser oscillator, as shown by the solid dovetail arrow in the figure, the Stokes light has few components, so that the stimulated Raman process can be generated only under the condition of higher pump power, the generation of the stimulated Raman process is inhibited, and the effect of improving the Raman threshold is achieved. Meanwhile, because the laser path in the fiber laser oscillator cavity is a reciprocating oscillation process, when the backward returning light passes through the long-period fiber grating 106, the intensity of the Stokes light signal in the backward returning light still generates attenuation; meanwhile, if the pumping power is high, strong raman signals are very likely to exist in the cavity. The stimulated raman process is a bidirectional process, the Stokes light transmitted backwards can generate a large risk to the system after being amplified, the Stokes light is still subjected to loss filtering when passing through the long-period fiber grating 106, as shown by a reverse solid arrow in the figure, the stimulated raman process can be further inhibited from being generated, the efficiency of an oscillator is improved, a certain isolation effect is achieved, a strong attenuation effect is achieved on backward raman signals, and a protection effect is achieved on an optical fiber device. In the actual process, the suppression effect is best achieved by adjusting parameters such as the grating period, the inclination angle, the chirp rate, the modulation depth and the like of the long-period fiber grating 106.

In order to further enhance the SRS suppression effect of the fiber laser oscillator, a plurality of long-period fiber gratings having the same parameter may be connected in series by fusion splicing and then connected to the fiber laser oscillator, and the suppression ratio thereof corresponds to the superposition of the suppression ratios of the plurality of long-period fiber gratings. The flexible adjustment of the suppression ratio can be realized by controlling the number of the long-period fiber gratings.

Example 5:

FIG. 4 is a schematic structural view of example 5; in this embodiment, a backward pumping fiber laser oscillator. A laser system comprises a pump LD light source 101, a pump beam combiner 102, a high reflection grating 103, a doped fiber 104 and a low reflection grating 105. A long period fiber grating 106 is placed in front of the low-reflection grating 105 in the fiber laser oscillator cavity. Embodiment 5 differs from embodiment 4 in the pumping manner, and the arrangement of the long-period fiber grating and the requirements and arrangement of other optical components are the same as those in embodiment 4, and are not described herein again.

Example 6:

FIG. 5 is a schematic structural view of example 6; in this embodiment, a bidirectional pump fiber laser oscillator. A laser system comprises a pump LD light source 101, a pump beam combiner 102, a high reflection grating 103, a doped fiber 104 and a low reflection grating 105. A long period fiber grating 106 is placed in front of the low-reflection grating 105 in the fiber laser oscillator cavity. Embodiment 6 differs from embodiment 4 in the pumping manner, and the arrangement of the long-period fiber grating and the requirements and arrangement of other optical components are the same as those in embodiment 4, and are not described herein again.

Example 7 to example 9:

FIG. 6 is a schematic structural view of example 7; FIG. 7 is a schematic structural view of example 8; FIG. 8 is a schematic structural view of example 9; example 7 is a forward pump fiber laser oscillator. In example 8, the backward pump fiber laser oscillator is used. The arrangement of the long period fiber grating was the same as that of example 7 except that the pumping manner was different from that of example 7. Example 9 is a bidirectional pump fiber laser oscillator. The arrangement of the long period fiber grating was the same as that of example 7 except that the pumping manner was different from that of example 7. The fiber laser oscillator comprises a pump LD light source 101, a pump beam combiner 102, a high reflecting grating 103, a long-period fiber grating 106, a doped fiber 104, a low reflecting grating 105 and a melting point 107. Examples 7, 8 and 9 each have a long-period fiber grating 106 disposed behind a high-reflection grating 103 in a fiber laser oscillator cavity. Due to the high energy density in the oscillator cavity, losses have a large effect on its efficiency. In examples 7, 8 and 9, the high reflective grating 103 and the long-period fiber grating 106 are prepared on the same optical fiber, so that no melting point exists between the high reflective grating and the long-period fiber grating, thereby further reducing the loss of the oscillation cavity and improving the output efficiency. Compared with the low reflective grating 105, the high reflective grating 103 has higher energy density, and the long-period fiber grating 106 is placed on the high reflective grating 103 to initially suppress the initial raman signal, so that the overall stimulated raman process is well suppressed.

In the normal working process of the fiber laser oscillator, laser generated by doping the fiber in the fiber laser oscillator cavity comprises two components of signal light and Stokes light as shown by hollow arrows in the figure. When the long-period fiber grating 106 passes through the long-period fiber grating, due to the unique mode coupling characteristics of the long-period fiber grating, the Stokes light transmitted in the fiber core and the modes in the cladding are coupled with each other, so that the Stokes light is coupled to the fiber cladding and is scattered, a loss spectrum with a wide bandwidth exists at the wavelength of the Stokes light of the long-period fiber grating 106, and the intensity of the Stokes light signal in the laser is attenuated, as shown by the solid arrows in the figure. Therefore, in the actual output laser of the fiber laser oscillator, as shown by a solid dovetail arrow in the figure, the Stokes light has few components, so that the stimulated Raman process can be generated only under the condition of higher pumping power, the generation of the stimulated Raman process is inhibited, the effect of improving the Raman threshold is achieved, a certain isolation effect is achieved, and the fiber device is protected. Meanwhile, because the laser path in the cavity of the fiber laser oscillator is a reciprocating oscillation process, when the backward returning light passes through the long-period fiber grating 106, the intensity of the Stokes light signal still generates attenuation, as shown by a backward solid arrow in the figure, so that the generation of the stimulated Raman process can be further inhibited, and the efficiency of the oscillator is improved. In the actual process, the suppression effect is best by adjusting parameters such as the grating period and the modulation depth of the long-period fiber grating 106.

Example 10 to example 12:

FIG. 9 is a schematic structural view of example 10; FIG. 10 is a schematic structural view of example 11; FIG. 11 is a schematic structural view of example 12. Example 10 is a forward pump fiber laser oscillator. The backward pump fiber laser oscillator in example 11 was the same as that in example 10 except that the pumping method was different from that in example 10, and the arrangement of the long period fiber grating 106 was the same as that in example 10. Example 12 is a bidirectional pump fiber laser oscillator. The arrangement of the long period fiber grating 106 is the same as that of example 10 except that the pumping manner is different from that of example 10. A pump LD light source 101, a pump beam combiner 102, a high reflection grating 103, a doped fiber 104, a long period fiber grating 106, a low reflection grating 105 and a melting point 107. Examples 10, 11 and 12 all write a long period fiber grating 106 directly onto a doped fiber 104 within a fiber laser oscillator cavity. Due to the high energy density in the oscillator cavity, losses have a large effect on its efficiency. In the process of actually building the oscillator, the fiber gratings are all packaged, so that the fiber gratings are inconvenient to write, and the long-period fiber gratings 106 can be directly written on the doped fibers 104 in the fiber laser oscillator cavity, so that the loss of the oscillator cavity is further reduced, the output efficiency is improved, and the stimulated Raman phenomenon in the oscillator is inhibited. The working principle of the embodiments 10, 11, 12 is similar to that of the previous embodiment and will not be described again.

Experiments prove that when the fiber laser oscillator is connected into the long-period fiber grating, the Raman light proportion in output is obviously reduced along with the increase of the pumping power, and the Raman light proportion can be further reduced along with the increase of the number of fusion connection series of the long-period fiber grating.

The long-period fiber grating obtained by the first apodized long-period fiber grating writing method provided in embodiment 2 or the second apodized long-period fiber grating writing method provided in embodiment 3 is arranged in a high-power fiber laser amplifier system, so that the effect of suppressing the stimulated raman scattering can be achieved. The high loss performance of the long-period fiber grating in a Raman waveband is utilized to inhibit stimulated Raman scattering. Embodiments 13 to 15 below provide laser systems, each including a seed source and more than one stage of laser amplifiers, and long-period fiber gratings are disposed between the seed source and the laser amplifiers and between the laser amplifiers at each stage, and the long-period fiber gratings are formed by the second apodization long-period fiber grating writing method. The long-period fiber grating is directly connected between the seed source and the fiber amplifier, and the seed source is filtered by utilizing the high loss factor of the long-period fiber grating in a Raman wave band, so that the seed source can still output relatively pure signal light at a higher power level. And the working efficiency of the optical fiber amplifier is improved, and the Raman threshold of the whole system is improved. The long-period fiber grating is arranged between each stage of fiber amplifiers, so that the working efficiency of each stage of fiber amplifiers is improved, the integral Raman threshold is improved, and the suppression effect is further improved.

FIG. 12 is a schematic structural view of example 13; including a seed source and a fiber amplifier, with a long period fiber grating 106 connected between the seed source and the fiber amplifier. The seed source comprises a plurality of pump LD light sources 101, a pump beam combiner 102, a high-reflection grating 103, a doped fiber 104 and a low-reflection grating 105, and the output tail fiber of each pump LD light source is connected to each pump arm of the pump beam combiner 102. Parameters, selected wavelengths, output powers and the like of the pump LD light source are different from reality, and no special requirements are required. The high-reflection grating 103, the doped grating 104 and the low-reflection grating 105 are sequentially connected behind the output tail fiber of the pumping beam combiner 102, the output tail fiber of the pumping beam combiner 102 is connected with the high-reflection grating 103, the high-reflection grating 103 is connected with the doped grating 104, and the doped fiber 104 is connected with the low-reflection grating 105 in a fusion mode, and a melting point 107 is formed at the fusion position. The fiber oscillator is composed of a pump LD light source 101, a pump beam combiner 102, a high reflection grating 103, a doped fiber 104, a low reflection grating 105 and a melting point 107, and serves as a seed source 108 of the high-power fiber laser amplifier system. In example 13, a 1-stage fiber amplifier was introduced, i.e., n is 1. The long period fiber grating 106 is connected between the seed source 108 and the stage 1 fiber amplifier 109 by means of fusion splicing.

Wherein: currently, the most commonly used pump source wavelengths are 976nm and 915 nm. The pump LD light source 101 may be an LD pump source with two wavelengths, and the output power thereof is in the order of hundreds of watts. The pumping beam combiner 102 is a 7 × 1 optical fiber pumping beam combiner, output pigtails of 976nm and 915nmLD pumping sources in the pumping LD light source 101 are connected with a pumping arm of the pumping beam combiner 102 in a fusion welding mode, and an output optical fiber of the pumping beam combiner 102 is a large mode field optical fiber. The reflectivity of the high reflection grating 103 is usually more than 99% at the laser working wavelength, such as the common wavelength of 1080nm, the 3dB bandwidth is usually 2-4nm, and the high reflection grating 103 is prepared on the same optical fiber as the output optical fiber of the pump beam combiner 102. The doped fiber 104 should be selected to match the size and numerical aperture of the highly reflective grating 103. The low reflecting grating 105 is used as an output optical fiber of a seed source, the reflectivity of the low reflecting grating 105 is usually not more than 10%, the 3dB bandwidth is usually not more than 1nm, and the difference between the central wavelength of the low reflecting grating 105 and the central wavelength of the high reflecting grating 103 is not more than +/-0.4 nm.

The output laser of the seed source 108, as indicated by the hollow arrow in FIG. 12, contains both signal light and Stokes light components. When the long-period fiber grating 106 passes through the long-period fiber grating 106, since the long-period fiber grating 106 has a loss spectrum with a wide bandwidth at the Stokes wavelength, the Stokes light in the laser passes through the long-period fiber grating 106, and the Stokes light transmitted in the fiber core and the mode in the cladding are mutually coupled according to the mode coupling characteristics of the long-period fiber grating, so that the Stokes light is coupled to the fiber cladding and is scattered, and the Stokes light intensity is attenuated, as shown by the solid arrows in fig. 12. Therefore, in the actual input laser of the primary amplifier 109, as shown by the solid dovetail arrow in the figure, the Stokes light has very few components, so that the stimulated raman process can be generated under the condition of higher primary amplification power, thereby inhibiting the generation of the stimulated raman process and achieving the effect of improving the raman threshold. In the actual process, the suppression effect is best by adjusting parameters such as the grating period and the modulation depth of the long-period fiber grating 106.

In order to further improve the stimulated raman scattering suppression effect of the high-power fiber laser amplifier system, a plurality of long-period fiber gratings with the same parameters can be connected in series in a welding mode, namely, the long-period fiber grating 6 can be formed by welding and connecting a plurality of long-period fiber gratings in series, and the suppression ratio of the long-period fiber grating is equivalent to the superposition of the suppression ratios of the plurality of long-period fiber gratings. The flexible adjustment of the suppression ratio can be realized by controlling the number of the long-period fiber gratings.

FIG. 13 is a schematic structural view of example 14; in this example, a 2 nd stage optical fiber amplifier, i.e., n is 2, is introduced on the basis of the embodiment shown in fig. 12. The long-period fiber grating 106 is connected between the seed source 108 and the 1 st-stage fiber amplifier 109 and between the 1 st-stage fiber amplifier 109 and the 2 nd-stage fiber amplifier 110 by fusion.

After the amplification by the level 1 fiber amplifier 109, the output laser power of the level 1 fiber amplifier 109 is already high, and may even reach the raman threshold, and the Stokes light intensity thereof is high, as shown by the hollow arrow in the figure, and includes two components of the signal light and the Stokes light. When it passes through the long-period fiber grating 106 between the 1 st-order fiber amplifier 109 and the 2 nd-order fiber amplifier 110, the Stokes light intensity in the laser is attenuated due to the wide-bandwidth loss spectrum of the long-period fiber grating 106 at the Stokes wavelength, as shown by the solid arrows. Therefore, in the actual input laser of the 2 nd-stage fiber amplifier 110, as shown by the solid dovetail arrow in the figure, the Stokes light has very few components, so that the stimulated raman process can be generated under the condition of higher second-stage amplification power, the generation of the stimulated raman process is suppressed, and the effect of improving the raman threshold is achieved. Meanwhile, after the second-stage amplification by the 2 nd-stage optical fiber amplifier 110, the laser power is high, and the 2 nd-stage optical fiber amplifier 110 has a high possibility of having a strong raman signal. Whereas the stimulated raman process is a bi-directional process. After the long-period fiber grating 106 is added between the 1 st-stage fiber amplifier 109 and the 2 nd-stage fiber amplifier 110, the Stokes light transmitted backwards can still be filtered, as shown by a solid arrow in the figure, so that the efficiency of the second-stage amplifier can be improved, a certain interstage isolation effect can be achieved, a strong attenuation effect on backward Raman signals can be achieved, and both the seed source 108 and the 1 st-stage fiber amplifier 109 can be protected.

In the actual process, the suppression effect is best achieved by adjusting parameters such as the grating period, the inclination angle, the chirp rate, the modulation depth and the like of the long-period fiber grating 106.

In order to further improve the stimulated raman scattering suppression effect of the high-power fiber laser amplifier system, a plurality of long-period fiber gratings with the same parameters can be connected in series in a welding mode, that is, the long-period fiber grating 106 can be formed by welding and connecting a plurality of long-period fiber gratings in series, and the suppression ratio of the long-period fiber grating is equivalent to the superposition of the suppression ratios of the plurality of long-period fiber gratings. The flexible adjustment of the suppression ratio can be realized by controlling the number of the long-period fiber gratings.

FIG. 14 is a schematic structural view of example 15. In the embodiment, the high-power fiber laser amplifier system introduces an n-stage fiber amplifier 111. The optical fiber amplifiers of all stages are connected through the long-period fiber grating, namely … … n-1 stage optical fiber amplifier and n-stage optical fiber amplifier 111 are connected between the 1 st stage optical fiber amplifier and the 2 nd stage optical fiber amplifier and between the 2 nd stage optical fiber amplifier and the 3 rd stage optical fiber amplifier through the long-period fiber grating 106. The long-period fiber grating 106 is connected between each stage of fiber amplifiers in a fusion mode, and is used for attenuating Stokes light and isolating backward return light. Therefore, the working efficiency of each stage of optical fiber amplifier can be improved, the integral Raman threshold value is improved, and the suppression effect is further improved.

In the embodiment, an n-stage optical fiber amplifier is introduced into the high-power optical fiber laser amplifier system. The optical fiber amplifiers of all stages are connected through the long-period fiber grating, namely … … between the 1 st stage optical fiber amplifier and the 2 nd stage optical fiber amplifier, and between the 2 nd stage optical fiber amplifier and the 3 rd stage optical fiber amplifier are connected through the long-period fiber grating 106. The long-period fiber grating 106 is connected between each stage of fiber amplifiers in a fusion mode, and is used for attenuating Stokes light and isolating backward return light. Therefore, the working efficiency of each stage of optical fiber amplifier can be improved, the integral Raman threshold value is improved, and the suppression effect is further improved.

In summary, although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. An apodization long period fiber grating inscribing device which characterized in that: including carbon dioxide laser ware, beam expanding lens group, scanning galvanometer, focus field lens and optic fibre operation moving platform, set gradually beam expanding lens group, scanning galvanometer and focus field lens on the transmission path of the laser of carbon dioxide laser ware output, be provided with optic fibre operation moving platform under the focus field lens, the optic fibre of waiting to write apodization long period fiber grating is installed at optic fibre operation moving platform, can move under optic fibre operation moving platform's drive, realizes apodization long period fiber grating on can inciding the optic fibre of installing on optic fibre operation moving platform from the laser of focus field lens outgoing and carves, and optic fibre operation moving platform adopts displacement platform driving motor drive, and then controls optic fibre operation moving platform's horizontal migration distance and speed through control displacement platform driving motor.

2. The apodized long period fiber grating writing apparatus according to claim 1, wherein: the scanning galvanometer is controlled by a galvanometer driver, and the galvanometer driver controls the marking pattern and the marking position of the scanning galvanometer.

3. The apodized long period fiber grating writing apparatus according to claim 2, wherein: the output power and frequency of the carbon dioxide laser are controlled by the computer; the galvanometer driver is connected with a computer, and the computer controls the marking pattern and the marking position of the scanning galvanometer by controlling the galvanometer driver.

4. The apodized long period fiber grating writing device according to claim 3, wherein the fiber operation moving platform comprises two fiber clamps, a three-dimensional adjusting base and an electric horizontal displacement platform, the two fiber clamps are respectively a left fiber clamp and a right fiber clamp, and the fiber to be written with the apodized long period fiber grating is clamped by the left fiber clamp and the right fiber clamp; the left optical fiber clamp and the right optical fiber clamp are respectively fixed on a three-dimensional adjusting base, and the optical fiber of the apodization long-period optical fiber grating to be inscribed is positioned right below the focusing field lens by adjusting the two three-dimensional adjusting bases; the three-dimensional adjusting base is installed on the electric horizontal displacement platform, the electric horizontal displacement platform moves horizontally under the driving of the displacement platform driving motor, the displacement platform driving motor is connected with the computer, and the computer controls the displacement platform driving motor so as to control the horizontal movement distance and speed of the electric horizontal displacement platform.

5. The apodization long period fiber grating writing device according to any one of claims 1 to 4, wherein the light outlet of the carbon dioxide laser and the beam expanding lens group are on the same axis, and the output laser of the beam expanding lens group is aligned with the exact center of the input light port of the scanning galvanometer.

6. An apodized long period fiber grating inscribing method is characterized by comprising the following steps:

(3) apodizing long period fiber grating inscription;

and (3.3) repeating the step (3.2) until the number of vertical line stripes in the marking pattern of the scanning galvanometer is lower than a set threshold value.

7. The method according to claim 6, wherein the threshold value set in step (3.3) is 1/3 of the number of vertical lines in the initial scanning pattern.

8. A laser system, characterized by: the laser oscillator is internally provided with a long-period fiber grating, the long-period fiber grating is formed by adopting the apodization long-period fiber grating writing method according to claim 6 or 7, and the laser oscillator is a forward pumping fiber laser oscillator, a backward pumping fiber laser oscillator or a bidirectional pumping fiber laser oscillator; the laser oscillator comprises a pump light source, a pump light beam combiner, a high-reflection grating, a doped fiber and a low-reflection grating, wherein the long-period fiber grating is arranged in front of the low-reflection grating in the laser oscillator cavity or behind the high-reflection grating in the fiber laser oscillator cavity or directly inscribed on the doped fiber in the fiber laser oscillator cavity.

9. A laser system, characterized by: the method comprises a seed source and more than one stage of laser amplifiers, wherein long-period fiber gratings are arranged between the seed source and the laser amplifiers and between the laser amplifiers at all stages, and the long-period fiber gratings are formed by the apodization long-period fiber grating writing method according to claim 6 or 7.

10. An apodized long period fiber grating inscribing method is characterized by comprising the following steps:

(3) apodizing long period fiber grating inscription;

and (3.3) repeating the step (3.2) until the current laser exposure area meets the set condition.

11. The method according to claim 10, wherein the conditions set in step (3.3) are: the current exposure area is less than 1/3 of the laser exposure area in the first exposure scan.

12. A laser system, characterized by: the laser oscillator is provided with a long-period fiber grating, the long-period fiber grating is formed by adopting the apodization long-period fiber grating writing method according to claim 10 or 11, and the laser oscillator is a forward pumping fiber laser oscillator, a backward pumping fiber laser oscillator or a bidirectional pumping fiber laser oscillator; the laser oscillator comprises a pump light source, a pump light beam combiner, a high-reflection grating, a doped fiber and a low-reflection grating, wherein the long-period fiber grating is arranged in front of the low-reflection grating in the laser oscillator cavity or behind the high-reflection grating in the fiber laser oscillator cavity or directly inscribed on the doped fiber in the fiber laser oscillator cavity.

13. A laser system, characterized by: the method comprises a seed source and more than one stage of laser amplifiers, wherein long-period fiber gratings are arranged between the seed source and the laser amplifiers and between the laser amplifiers at all stages, and the long-period fiber gratings are formed by the apodization long-period fiber grating writing method according to claim 10 or 11.