CN111856644B - Apodized long-period fiber bragg grating inscription device, inscription method and laser system - Google Patents

Abstract

An apodized long period fiber grating writing device, writing method and laser system. The writing device includes a carbon dioxide laser, a beam expansion lens group, a scanning galvanometer, a focusing field lens, and a fiber optic operating mobile platform. The transmission path of the laser output from the carbon dioxide laser is sequentially provided with a beam expansion lens group, a scanning galvanometer, and a focusing field lens. An optical fiber operating mobile platform is provided directly below the field mirror. The optical fiber to be written with apodized long-period fiber grating is installed on the optical fiber operating mobile platform. The laser emitted from the focusing field mirror can be incident on the optical fiber installed on the optical fiber operating mobile platform. Apodized long-period fiber grating writing is achieved. The long-period fiber grating obtained by the above-mentioned writing method is installed in the laser system, and the high loss of the long-period fiber grating in the Raman band is used to suppress stimulated Raman scattering. Using a writing device to write apodized long-period fiber gratings can eliminate the sudden change in refractive index caused by the point-by-point exposure writing method.

Description

Apodized long period fiber grating writing device, writing method and laser system

Technical field

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

Background technique

Fiber gratings are widely used in fields such as fiber lasers, fiber communications, and fiber sensing. Compared with traditional gratings, fiber gratings have the advantages of narrow line width, low insertion loss, strong anti-electromagnetic interference ability, high sensitivity, light weight, small size, easy to implement wavelength division multiplexing and flexible use. The all-fiber laser, which uses fiber gratings to replace traditional optical dichromatic mirrors, has the advantages of high stability and compact structure, making fiber lasers practical. The emergence of fiber gratings has also greatly promoted the development of optical fiber communications and optical fiber sensing.

At present, the main methods for preparing long-period fiber gratings include phase mask method, point-by-point writing method, splicing method and fused tapering method. Among them, the phase mask method usually uses ultraviolet light to irradiate a phase mask to form diffraction stripes, and uses ±1st order diffraction stripes to side-expose a photosensitive optical 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 stripe (the grating period is half of the phase mask stripe period), thus reducing the difficulty of the fiber grating preparation process. The point-by-point writing method is usually used to prepare long-period fiber gratings with relatively large periods. This method is not limited by the light source. Excimer lasers, femtosecond lasers, and carbon dioxide lasers can all be used as light sources for the point-by-point writing method. This method mainly relies on focusing the beam and exposing it point by point on the optical fiber to form periodic modulation of the refractive index. The two most commonly used writing devices are the electric translation method and the galvanometer scanning method.

The point-by-point writing method is used to prepare long-period fiber gratings. Since there is a refractive index mutation between the exposure points at the two ends of the grating area and the ordinary optical fiber, a self-chirp effect occurs, which is manifested by the appearance of serious sidebands in the transmission spectrum and reflection spectrum. , which greatly restricts the application of fiber grating devices. Through long-period fiber grating apodization technology, the amplitude of the refractive index modulation in the grating presents a Gaussian distribution along the grating axis, which can effectively avoid the short-wavelength loss of the fiber and effectively suppress the sidebands of the resonance peak of the transmission spectrum. Since the preparation method of this kind of long-period fiber grating is to write point by point, it is impossible to use an apodized template like Bragg grating to make the substrate refractive index in the entire grating area have a Gaussian distribution.

The writing cycle of the point-by-point writing method is usually controlled by an electric displacement platform. During the entire process, the exposure time of each refractive index modulation point is consistent, so the refractive index modulation amplitude of each exposure position is equal. This results in the refractive index change of the grating area part and the non-grating area part having no gradient, showing a two-level differentiation. This magnitude-differentiated refractive index distribution also leads to the generation of resonance peak sidebands. In some cases, the performance of long-period fiber gratings can be greatly affected.

Contents of the invention

In view of the defects existing in the prior art, the present invention proposes an apodized long-period fiber grating writing device, writing method and laser system.

In order to achieve the above technical objectives, the specific technical solutions adopted by the present invention are as follows:

The invention provides an apodized long-period fiber grating writing device, which includes a carbon dioxide laser, a beam expansion lens group, a scanning galvanometer, a focusing field lens and an optical fiber operating mobile platform. The transmission path of the laser output by the carbon dioxide laser is sequentially provided with beam expansion The lens group, the scanning galvanometer and the focusing field lens are provided with an optical fiber operating mobile platform directly below the focusing field lens. The optical fiber to be written with apodized long-period fiber grating is installed on the optical fiber operating mobile platform, and can be operated on the optical fiber operating mobile platform. Driven by the movement, the laser emitted from the focusing field mirror can be incident on the optical fiber installed on the optical fiber operating mobile platform to achieve apodized long-period fiber grating writing. The optical fiber operation mobile platform is driven by a displacement platform drive motor, and the horizontal movement distance and speed of the optical fiber operation mobile platform are controlled by controlling the displacement platform drive motor.

Further, the scanning galvanometer of the present invention is controlled by a galvanometer driver, and the galvanometer driver controls the marking pattern and marking position of the scanning galvanometer. Further, the galvanometer driver is connected to a computer, and the computer controls the marking pattern and marking position of the scanning galvanometer by controlling the galvanometer driver.

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

Further, the optical fiber operation mobile platform of the present invention includes an optical fiber clamp, a three-dimensional adjustment base and an electric horizontal displacement platform. There are two optical fiber clamps, namely a left optical fiber clamp and a right optical fiber clamp. The apodized long-period optical fiber to be written is The optical fiber of the 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 adjustment base. By adjusting the two three-dimensional adjustment bases, the optical fiber to be written with the apodized long-period fiber grating is Located directly below the focusing field lens; the three-dimensional adjustment bases are installed on an electric horizontal displacement platform, and the electric horizontal displacement platform moves horizontally driven by the displacement platform driving motor. Further, the displacement platform drive motor is connected to a computer, and the computer controls the displacement platform drive motor and thereby controls the horizontal movement distance and speed of the electric horizontal displacement platform.

Further, the light outlet and the beam expansion lens group of the carbon dioxide laser of the present invention are on the same axis. The output laser of the beam expansion lens group is aligned with the center of the input light port of the scanning galvanometer.

Based on the above-mentioned apodized long-period fiber grating writing device, the present invention provides a first apodized long-period fiber grating writing method, which includes the following steps:

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

(2) Cut an optical fiber of appropriate length, coat the area where the apodized long-period fiber grating is to be written with a chemical stripper, then wipe it with alcohol and install the optical fiber on the optical fiber operation mobile platform; adjust the optical fiber operation mobile platform so that The optical fiber to be written with the apodized long-period fiber grating is located directly below the focusing field lens, so that the laser light emitted from the focusing field lens can be incident on the optical fiber installed on the optical fiber operating mobile platform;

(3) Apodized long period fiber grating writing;

(3.1) The marking pattern of the scanning galvanometer is a row of vertical stripes. Set the marking position of the scanning galvanometer and the number of vertical stripes in the initial marking pattern; turn on the carbon dioxide laser and the scanning galvanometer for this exposure scan. Make the laser perform a single exposure on the entire area on the optical fiber to be written with apodized long-period fiber grating according to the set marking pattern, and then turn off the carbon dioxide laser and scanning galvanometer;

(3.2) Reset the marking pattern of the scanning galvanometer. The currently set scanning pattern is to reduce the number of vertical stripes at both ends based on the last scanning pattern. Start the carbon dioxide laser and scanning galvanometer again for this exposure scan. The laser exposure area on the optical fiber in this exposure scan is located in the middle of the laser exposure area in the previous exposure scan, that is, only the middle area of the previous laser exposure area is exposed again;

(3.3) Repeat step (3.2) until the number of vertical stripes in the marking pattern of the scanning galvanometer is lower than the set threshold. Specifically, until the number of vertical stripes in the marking pattern of the scanning galvanometer is lower than 1/3 of the number of vertical stripes in the initial scanning pattern.

The long-period fiber grating obtained by the above-mentioned first apodized long-period fiber grating writing method is placed in the fiber laser oscillator cavity, and the high loss of the long-period fiber grating in the Raman band is used to suppress stimulated pulling. Mann scattering. Further, the present invention provides a laser system, including a laser oscillator. A long period fiber grating is provided in the laser oscillator. The long period fiber grating is written using the above-mentioned first apodized long period fiber grating writing method. Become. The laser oscillator is a forward pumped fiber laser oscillator, a backward pumped fiber laser oscillator or a bidirectional pumped fiber laser oscillator. Forward-pumped fiber laser oscillators, backward-pumped fiber laser oscillators, and bidirectionally pumped fiber laser oscillators are divided according to the different pumping methods of the oscillators. The laser oscillator includes a pump light source, a pump light combiner, a highly reflective grating, a doped optical fiber, and a low-reflective grating. The long-period fiber grating is arranged in front of the low-reflective grating in the laser oscillator cavity or is arranged in the fiber laser oscillation After the highly reflective grating in the cavity of the fiber laser oscillator, or the long period fiber grating is directly written on the doped fiber in the fiber laser oscillator cavity. Utilizing the high loss of the long-period fiber grating in the Raman band, it has a good suppression effect on both the forward and backward Raman light inside the fiber laser oscillator, especially the suppression of the backward Raman light, so that due to the high power The risk caused by backward Raman light to the system is greatly reduced, so that the stimulated Raman scattering phenomenon can be observed in the output of the fiber laser oscillator at a higher power level, which greatly increases the upper limit of the power output of the fiber laser oscillator.

Using the above-mentioned first apodized long-period fiber grating writing method to obtain the long-period fiber grating, and setting it into a high-power fiber laser amplifier system, the effect of suppressing stimulated Raman scattering can be achieved. Specifically, the present invention provides a laser system, including a seed source and one or more levels of laser amplifiers. Long-period fiber gratings are provided between the seed source and the laser amplifier and between each level of laser amplifiers. The long-period fiber grating is The fiber grating is written using the above-mentioned first apodized long-period fiber grating writing method. The long-period fiber grating is directly connected between the seed source and the fiber amplifier, and the high loss of the long-period fiber grating in the Raman band is used to filter the seed source, so that the seed source can still output a relatively pure output at a higher power level. signal light. It also improves the working efficiency of the fiber amplifier and increases the Raman threshold of the overall system. Placing long-period fiber gratings between various levels of fiber amplifiers improves the efficiency of each level of fiber amplifiers, increases the overall Raman threshold, and further improves the suppression effect.

Based on the above-mentioned apodized long-period fiber grating writing device, the present invention provides a second apodized long-period fiber grating writing method, which includes the following steps:

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

(2) Cut an optical fiber of appropriate length, coat the area where the apodized long-period fiber grating is to be written with a chemical stripper, then wipe it with alcohol and install the optical fiber on the optical fiber operation mobile platform; adjust the optical fiber operation mobile platform so that The optical fiber to be written with the apodized long-period fiber grating is located directly below the focusing field lens, so that the laser light emitted from the focusing field lens can be incident on the optical fiber installed on the optical fiber operating mobile platform;

(3) Apodized long period fiber grating writing;

(3.1) Turn on the scanning galvanometer and control the scanning galvanometer to output a vertical line in the middle of the marking range; set the moving speed and initial moving distance of the electric horizontal displacement platform; turn on the carbon dioxide laser and the electric displacement platform for the first exposure scan, carbon dioxide When the laser emits light, the electric horizontal displacement platform and the optical fiber on the electric horizontal displacement platform begin to move horizontally, completing a single exposure of the entire area on the optical fiber to be written with apodized long-period fiber gratings. Then the carbon dioxide laser is turned off and the electric displacement platform is moved. reset;

(3.2) Set the turn-on time of the carbon dioxide laser and the electric displacement platform in the next exposure scan so that the laser exposure area on the optical fiber in this exposure scan is located in the middle of the laser exposure area in the previous exposure scan, that is, only the upper The middle area of the laser exposure area is exposed again;

(3.3) Repeat step (3.2) until the current laser exposure area meets the set conditions. 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 above-mentioned second apodized long-period fiber grating writing method is placed in the fiber laser oscillator cavity, and the high loss of the long-period fiber grating in the Raman band is used to suppress stimulated pulling. Mann scattering. Further, the present invention provides a laser system, including a laser oscillator. A long period fiber grating is provided in the laser oscillator. The long period fiber grating is written using the above-mentioned second apodized long period fiber grating writing method. Formed, the laser oscillator is a forward pumped fiber laser oscillator, a backward pumped fiber laser oscillator or a bidirectional pumped fiber laser oscillator; the laser oscillator includes a pump light source, a pump light combiner, a high Reflective grating, doped fiber and low-reflective grating, the long-period fiber grating is arranged in front of the low-reflective grating in the laser oscillator cavity or after the high-reflective grating in the fiber laser oscillator cavity, or the long-period fiber grating is directly Inscribed on the doped fiber inside the fiber laser oscillator cavity. Utilizing the high loss of the long-period fiber grating in the Raman band, it has a good suppression effect on both the forward and backward Raman light inside the fiber laser oscillator, especially the suppression of the backward Raman light, so that due to the high power The risk caused by backward Raman light to the system is greatly reduced, so that the stimulated Raman scattering phenomenon can be observed in the output of the fiber laser oscillator at a higher power level, which greatly increases the upper limit of the power output of the fiber laser oscillator.

The long-period fiber grating obtained by using the above-mentioned second apodized long-period fiber grating writing method can be installed in a high-power fiber laser amplifier system to achieve the effect of suppressing stimulated Raman scattering. Specifically, the present invention provides a laser system, including a seed source and one or more levels of laser amplifiers. Long-period fiber gratings are provided between the seed source and the laser amplifier and between each level of laser amplifiers. The long-period fiber grating is The fiber grating is written using the second apodized long-period fiber grating writing method mentioned above. The long-period fiber grating is directly connected between the seed source and the fiber amplifier, and the high loss of the long-period fiber grating in the Raman band is used to filter the seed source, so that the seed source can still output a relatively pure output at a higher power level. signal light. It also improves the working efficiency of the fiber amplifier and increases the Raman threshold of the overall system. Placing long-period fiber gratings between various levels of fiber amplifiers improves the efficiency of each level of fiber amplifiers, increases the overall Raman threshold, and further improves the suppression effect.

The beneficial effects of the present invention are as follows:

(1) The present invention provides an apodized long-period fiber grating writing device. Using this device to write apodized long-period fiber gratings can eliminate the refractive index mutation caused by the point-by-point exposure writing method.

(2) Using the apodized long-period fiber grating writing device provided by the present invention, two apodized long-period fiber grating writing methods can be realized. The first apodization long-period fiber grating writing method provided by the present invention can realize different apodization functions by flexibly adjusting the marking position of the scanning galvanometer and the number of vertical stripes in the marking pattern, thereby realizing different types of cutting. Preparation of inscribed fiber gratings.

(3) The apodized long-period fiber grating writing device provided by the present invention can not only realize the writing of long-period fiber gratings by scanning with a scanning galvanometer, but also can only output a vertical line in the middle when the scanning galvanometer does not scan. , relying on the movement of the electric horizontal displacement platform to achieve the inscription of long-period fiber gratings. This method can also form apodization by controlling the electric horizontal displacement platform to gradually reduce the refractive index modulation at both ends of the grating.

(4) The long-period fiber grating obtained by the apodized long-period fiber grating writing method provided by the present invention is installed in the fiber laser system. For example, if it is placed in the laser oscillator cavity, the high loss of long-period fiber grating in the Raman band can be used to suppress stimulated Raman scattering. The introduction of long-period fiber gratings into the fiber laser oscillator cavity has a stronger suppression effect than outside the cavity and can increase the Raman threshold of the fiber laser oscillator to a greater extent. At the same time, the suppression ratio can be flexibly adjusted by controlling the number of added long-period fiber gratings.

If it is installed in a high-power fiber laser amplifier system, the effect of suppressing stimulated Raman scattering can be achieved. The introduction of long-period fiber gratings into high-power fiber laser amplifier systems can improve the overall Raman threshold of the system, while also having a certain filtering effect, inhibiting backward Raman light, and providing good protection for fiber devices. . At the same time, the suppression ratio can be flexibly adjusted by controlling the number of added long-period fiber gratings. Since the working mechanism of long-period fiber grating is the coupling between the core mode and the cladding mode, its temperature rise coefficient is smaller when used in fiber lasers and has greater application potential.

The long-period fiber grating of the present invention is easy to produce, and its parameters can be flexibly adjusted according to actual needs to match different suppression bands. Long-period fiber gratings have low insertion loss, are easy to prepare on different types of optical fibers, have good stability, and have a wide range of applications.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without exerting creative efforts.

Figure 1 is a schematic structural diagram of an apodized long period fiber grating writing device in Embodiment 1;

Figure 2 is a schematic diagram of the marking pattern of the scanning galvanometer provided in Embodiment 2;

Figure 3 is a schematic structural diagram of Embodiment 4;

Figure 4 is a schematic structural diagram of Embodiment 5;

Figure 5 is a schematic structural diagram of Embodiment 6;

Figure 6 is a schematic structural diagram of Embodiment 7;

Figure 7 is a schematic structural diagram of Embodiment 8;

Figure 8 is a schematic structural diagram of Embodiment 9;

Figure 9 is a schematic structural diagram of Embodiment 10;

Figure 10 is a schematic structural diagram of Embodiment 11;

Figure 11 is a schematic structural diagram of Embodiment 12;

Figure 12 is a schematic structural diagram of Embodiment 13;

Figure 13 is a schematic structural diagram of Embodiment 14;

Figure 14 is a schematic structural diagram of Embodiment 15.

Description of numbers in the figure:

1. Carbon dioxide laser; 2. Beam expansion lens group; 3. Scanning galvanometer; 4. Focusing field lens; 5. Fiber optic clamp; 6. Three-dimensional adjustment base; 7. Electric horizontal displacement platform; 8. Displacement platform drive motor; 9 , Computer; 10. Galvanometer driver.

101. Pump LD light source; 102. Pump combiner; 103. High reflection grating; 104. Doped fiber; 105. Low reflection grating; 106. Long period fiber grating; 107. Melting point; 108. Seed source; 109 , 1st level optical fiber amplifier; 110. 2nd level optical fiber amplifier; nth level optical fiber amplifier.

Detailed ways

In order to make the technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

Example 1:

An apodized long-period fiber grating writing device includes a carbon dioxide laser 1, a beam expansion lens group 2, a scanning galvanometer 3, a focusing field lens 4, an optical fiber operating mobile platform and a computer 9.

The emission spot of the carbon dioxide laser 1 is circular, and the light energy distribution is relatively uniform. A beam expansion lens group 2, a scanning galvanometer 3 and a focusing field lens 4 are arranged in sequence on the transmission path of the laser output by the carbon dioxide laser 1. The central axis of the beam expansion lens group 2 and the carbon dioxide laser are located on the same straight line, and the output laser of the beam expansion lens group 2 is aligned with the center of the input light port of the scanning galvanometer 3.

An optical fiber operating mobile platform is provided directly below the focusing field lens 4 . The optical fiber 11 to be written with apodized long-period fiber grating is installed on the optical fiber operating mobile platform. The laser emitted from the focusing field lens 4 can be incident on the optical fiber 11 installed on the optical fiber operating mobile platform to achieve apodized long-period optical fiber grating writing. , The optical fiber operation mobile platform is driven by a displacement platform drive motor 8, and by controlling the displacement platform drive motor 8, the horizontal movement distance and speed of the optical fiber operation mobile platform are controlled. Specifically, the optical fiber operation mobile platform includes an optical fiber clamp 5 , a three-dimensional adjustment base 6 and an electric horizontal displacement platform 7 . The optical fiber clamp 5 is provided with two, namely a left optical fiber clamp and a right optical fiber clamp. The optical fiber 11 to be written with apodized 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 adjustment base 6. In this embodiment, the three-dimensional adjustment base 6 is manually adjusted. Place both ends of the optical fiber 11 into the V-shaped grooves of the left fiber optic clamp and the right fiber optic clamp, and manually adjust the two three-dimensional adjustment bases 6 so that the optical fiber 11 to be written with the apodized long-period fiber grating is located directly below the focusing field lens 4. The two three-dimensional adjustment bases 6 are installed on the electric horizontal displacement platform 7. The electric horizontal displacement platform 7 moves horizontally driven by the displacement platform drive motor 8. The displacement platform drive motor 8 is connected to the computer 9, and the computer 9 controls the displacement platform drive motor 8. Then, the horizontal movement distance and speed of the electric horizontal displacement platform 7 are controlled. The light outlet of the carbon dioxide laser 1 and the beam expansion lens group 2 are on the same axis, ensuring that the output laser energy can be output normally. The scanning galvanometer 3 can be a mature commercial product, such as Qinlong galvanometer. The laser light emitted from the scanning galvanometer 3 is focused by the focusing field lens 4 and then converged at the location of the optical fiber 11 . The electric horizontal displacement platform 7 is an existing technology, for example, a PI electric displacement platform can be used.

The optical fiber clamp 5 has a V-shaped groove, and the flip cover of the V-shaped groove can be screwed onto the clamp, thereby fixing the optical fiber as stably as possible.

In this embodiment, the position of the optical fiber 11 can be fine-tuned by the three-dimensional adjustment base 6. The three-dimensional adjustment frame 6 can be appropriately adjusted for optical fibers with 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, quantity, and number of marking patterns of the marking pattern.

As a general control system, the computer 9 controls the marking pattern of the scanning galvanometer, the output optical power and frequency of the laser, the moving speed and distance of the electric horizontal displacement platform, etc.

Example 2:

Using the apodized long-period fiber grating writing device provided in Embodiment 1, this embodiment provides an apodized long-period fiber grating writing method, which includes the following steps:

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

(2) Cut an optical fiber of appropriate length (select large mode field double-clad fiber), coat the area where the apodized long-period fiber grating is to be written with a chemical stripper, wipe it with alcohol, and then install the optical fiber in the optical fiber operation mobile on the platform; adjust the optical fiber operation mobile platform so that the optical fiber to be written with apodized long-period fiber grating is located directly below the focusing field lens, so that the laser emitted from the focusing field lens can be incident on the optical fiber installed on the optical fiber operation mobile platform;

(3) Apodized long period fiber grating writing;

(3.1) The default marking pattern of the scanning galvanometer is a row of vertical stripes, as shown in Figure 3, where the optical fiber is placed horizontally, and the output marking pattern will mark periodic notches on the optical fiber. Figure 3 shows the marking pattern set in the multiple exposure scan. The initial marking pattern is the top row of vertical stripes in Figure 3, and the second row of vertical stripes from top to bottom are the ones set in the second exposure scan. The set marking pattern, the third row of vertical stripes is the marking pattern set in the third exposure scan, and so on.

In this embodiment, the initial marking pattern set in the initial exposure scan is the top row of vertical stripes in Figure 3; the carbon dioxide laser and the scanning galvanometer are turned on for this exposure scan, so that the laser follows the set marking pattern. Perform a single exposure on the entire area on the optical fiber where the apodized long-period fiber grating is to be written, and then turn off the carbon dioxide laser and scanning galvanometer;

(3.2) Reset the marking pattern of the scanning galvanometer. The marking pattern set in the second exposure scan is the second row of vertical stripes from top to bottom in Figure 3. The currently set scanning pattern is the one set in the last exposure scan. On the basis of the scanning pattern, reduce the number of vertical stripes at both ends, and start the carbon dioxide laser and scanning galvanometer again for this exposure scan. The laser exposure area on the optical fiber in this exposure scan is located at the laser exposure area in the previous exposure scan. Middle, that is, only the middle area of the last laser exposure area is re-exposed;

(3.3) Repeat step (3.2) until the number of vertical stripes in the marking pattern of the scanning galvanometer is lower than the set threshold. Specifically, until the number of vertical stripes in the marking pattern of the scanning galvanometer is lower than 1/3 of the number of vertical stripes in the initial scanning pattern.

Example 3:

Using the apodized long-period fiber grating writing device provided in Embodiment 1, this embodiment provides a method for writing apodized long-period fiber gratings by controlling an electric horizontal displacement platform to write apodized long-period fiber gratings, including the following steps :

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

(2) Cut an optical fiber of appropriate length (select large mode field optical fiber), coat the area where the apodized long-period fiber grating is to be written with a chemical stripper, then wipe it with alcohol and install the optical fiber on the optical fiber operating mobile platform; Adjust the optical fiber operation mobile platform so that the optical fiber to be written with apodized long-period fiber grating is located directly below the focusing field lens, so that the laser emitted from the focusing field lens can be incident on the optical fiber installed on the optical fiber operation mobile platform. Connect one end of the optical fiber to the broadband light source, and the other end to the online detection system (spectrum analyzer), and detect it through the online detection system.

(3) Apodized long period fiber grating writing;

(3.1) Turn on the scanning galvanometer and control the scanning galvanometer to output a vertical line in the middle of the marking range; set the moving speed and initial moving distance of the electric horizontal displacement platform; turn on the carbon dioxide laser and the electric displacement platform for the first exposure scan, carbon dioxide When the laser emits light, the electric horizontal displacement platform and the optical fiber on the electric horizontal displacement platform begin to move horizontally, completing a single exposure of the entire area on the optical fiber to be written with apodized long-period fiber gratings. Then the carbon dioxide laser is turned off and the electric displacement platform is moved. reset;

(3.2) Set the turn-on time of the carbon dioxide laser and the electric displacement platform in the next exposure scan so that the laser exposure area on the optical fiber in this exposure scan is located in the middle of the laser exposure area in the previous exposure scan, that is, only the upper The middle area of the laser exposure area is exposed again;

(3.3) Repeat step (3.2) until the current laser exposure area meets the set conditions. 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 above-mentioned first or second apodized long-period fiber grating writing method is placed in the fiber laser oscillator cavity, and the high loss of the long-period fiber grating in the Raman band is used to achieve Suppression of stimulated Raman scattering. The following Embodiment 4 to Embodiment 12 respectively provide a laser system, each including a laser oscillator. A long-period fiber grating is provided in the laser oscillator. The long-period fiber grating adopts the above-mentioned first or third method. It is written by two apodized long period fiber grating writing methods, the details are as follows:

Example 4:

Figure 3 is a schematic structural diagram of Embodiment 4; in this embodiment, it is a forward-pumped fiber laser oscillator. A laser system includes a pump LD light source 101, a pump combiner 102, a high-reflective grating 103, a doped optical fiber 104, and a low-reflective grating 105. The long period fiber grating 106 is arranged in front of the low reflection grating 105 in the fiber laser oscillator cavity.

There are multiple pump LD light sources 101 , and the output pigtails of each pump LD light source 101 are connected to each pump arm of the pump combiner 2 . For common fiber laser oscillators, the pump source wavelength can be selected as 976nm or 915nm, and the output power is in the hundreds of watts range. In actual use, the parameters, selected wavelength, output power, number of units used, etc. of the pump LD light source 101 vary according to needs, and there are no special requirements. The pump combiner 102 in the forward pump fiber laser oscillator is usually a 7*1 pump combiner. The backward pumped fiber laser oscillator is usually a 6+1*1 pump combiner. The output pigtail of the pump combiner 102 is a large mode field fiber. The output pigtail of the pump combiner 102 is then connected to a high-reflective grating 103, a doped grating 104, a long-period fiber grating 106 and a low-reflective grating 105 in sequence. In this embodiment, the long period fiber grating 106 and the low reflection grating 105 are fabricated on the same optical fiber, where the long period fiber grating 106 is located in front of the low reflection grating 105 with a certain distance between them to optimize the oscillator performance. The output pigtail of the pump combiner 102 and the high-reflective grating 103, the high-reflective grating 103 and the doped grating 104, and the doped optical fiber 104 and the long-period fiber grating 106 are all connected by welding. A melting point 107 is formed at the welding location. A fiber laser oscillator composed of a pump LD light source 101, a pump combiner 102, a high reflective grating 103, a doped optical fiber 104, a long period fiber grating 106, a low reflective grating 105 and a melting point 107.

The highly reflective grating 103 has a reflectivity usually greater than 99% at the operating wavelength of the fiber laser oscillator, a 3dB bandwidth usually 2-4nm, and is prepared on the same fiber as the output fiber of the pump combiner. The doped optical fiber 104 should be selected to match the highly reflective grating 103 . The reflectivity of the low-reflective grating 105 used for output is usually not greater than 10%, the 3dB bandwidth is usually not greater than 1nm, and the difference between its center wavelength and the center wavelength of the high-reflective grating 103 should be no greater than ±0.4nm.

The pump LD light source 101 provides the pump light necessary for generating laser light, and the pump light is coupled to the highly reflective grating 103 via the pump beam combiner 102 . The high-reflective grating 103 and the low-reflective grating 105 only have reflection at the signal light wavelength, such as 1080 nm, and there is no reflection at the pump light wavelength, only loss. The pump light is injected into the doped optical fiber 104 through the highly reflective grating 103. The doped optical fiber 104 is usually doped with rare earth elements such as ytterbium, which can absorb pump light and excite signal light, and output it through a low-reflection grating.

Due to the high energy density in the oscillator cavity, losses have a greater impact on its efficiency. Since the long-period fiber grating 106 and the low-reflection grating 105 are prepared on the same optical fiber, there is no melting point between them, so as to further reduce the loss of the oscillation cavity and improve the output efficiency. The optical fiber used in the long period fiber grating 106 needs to match the fiber laser oscillator. When the signal light intensity in the fiber laser oscillator exceeds a certain threshold, the SBS effect will occur. At this time, the signal light generated after the continued injection of pump light will quickly transform into Stokes light from the SRS effect, forming stronger Stokes light.

During the normal operation of the fiber laser oscillator, the laser generated by the doped fiber in the fiber laser oscillator cavity, as shown by the hollow arrow in the figure, contains two components: signal light and Stokes light. When it passes through the long-period fiber grating 106, due to its unique mode coupling characteristics, the Stokes light transmitted in the fiber core will couple with the mode in the cladding, causing it to couple to the fiber cladding and be lost, causing the long-period The fiber grating 106 has a loss spectrum with a wider bandwidth at the Stokes light wavelength, and the Stokes light signal intensity in the laser will be attenuated, as shown by the solid arrow 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 component is very small, so that the stimulated Raman process can only be generated under higher pump power conditions, thereby suppressing the stimulated Raman process. The generation of excited Raman process achieves the effect of increasing the Raman threshold. At the same time, since the laser path in the fiber laser oscillator cavity is a reciprocating oscillation process, when the reverse return light passes through the long period fiber grating 106, the Stokes optical signal intensity will still be attenuated; at the same time, if the pump power is high, , it is very likely that there is a strong Raman signal in the cavity. The stimulated Raman process is a two-way process. The backward transmitted Stokes light will cause greater risks to the system after amplification. It is still lost and filtered by the long period fiber grating 106, as indicated by the reverse solid arrow in the figure. It is shown that this can further suppress the generation of the stimulated Raman process, improve the oscillator efficiency, and at the same time play a certain isolation role, have a strong attenuation effect on the backward Raman signal, and protect the optical fiber device. In the actual process, by adjusting the grating period, tilt angle, chirp rate, modulation depth and other parameters of the long period fiber grating 106, the suppression effect is achieved to the best.

In order to further improve the SRS suppression effect of the fiber laser oscillator, multiple long-period fiber gratings with the same parameters can be connected in series through welding and then connected to the fiber laser oscillator. The suppression ratio is equivalent to the suppression ratio of multiple long-period fiber gratings. Overlay. By controlling the number of long-period fiber gratings, the suppression ratio can be flexibly adjusted.

Example 5:

Figure 4 is a schematic structural diagram of Embodiment 5; in this embodiment, it is a backward-pumped fiber laser oscillator. A laser system includes a pump LD light source 101, a pump combiner 102, a high-reflective grating 103, a doped optical fiber 104, and a low-reflective grating 105. The long period fiber grating 106 is arranged in front of the low reflection grating 105 in the fiber laser oscillator cavity. Except that the pumping method of Embodiment 5 is different from that of Embodiment 4, the settings of the long-period fiber grating and the requirements and settings of other optical components are consistent with Embodiment 4, and will not be described again here.

Example 6:

Figure 5 is a schematic structural diagram of Embodiment 6; in this embodiment, it is a bidirectional pump fiber laser oscillator. A laser system includes a pump LD light source 101, a pump combiner 102, a high-reflective grating 103, a doped optical fiber 104, and a low-reflective grating 105. The long period fiber grating 106 is arranged in front of the low reflection grating 105 in the fiber laser oscillator cavity. Except that the pumping method of Embodiment 6 is different from that of Embodiment 4, the settings of the long period fiber grating and the requirements and settings of other optical components are consistent with Embodiment 4, and will not be described again here.

Example 7 to Example 9:

Figure 6 is a schematic structural diagram of Embodiment 7; Figure 7 is a schematic structural diagram of Embodiment 8; Figure 8 is a schematic structural diagram of Embodiment 9; Embodiment 7 is a forward-pumped fiber laser oscillator. Embodiment 8 is a backward-pumped fiber laser oscillator. Except that the pumping method is different from that in Embodiment 7, the arrangement of the long period fiber grating is the same as that in Embodiment 7. Embodiment 9 is a bidirectional pump fiber laser oscillator. Except that the pumping method is different from that in Embodiment 7, the arrangement of the long period fiber grating is the same as that in Embodiment 7. The fiber laser oscillator is composed of a pump LD light source 101, a pump combiner 102, a high reflective grating 103, a long period fiber grating 106, a doped fiber 104, a low reflective grating 105 and a melting point 107. Embodiments 7, 8 and 9 all dispose the long period fiber grating 106 behind the highly reflective grating 103 in the fiber laser oscillator cavity. Due to the high energy density in the oscillator cavity, losses have a greater impact on its efficiency. In Embodiments 7, 8 and 9, the high-reflective grating 103 and the long-period fiber grating 106 are prepared on the same optical fiber, so there is no melting point between them, so as to further reduce the loss of the oscillation cavity and improve the output efficiency. The high-reflective grating 103 has a higher energy density than the low-reflective grating 105. Placing the long-period fiber grating 106 behind the high-reflective grating 103 suppresses the initial Raman signal and improves the overall stimulated tension. Mann process has better suppression effect.

During the normal operation of the fiber laser oscillator, the laser generated by the doped fiber in the fiber laser oscillator cavity, as shown by the hollow arrow in the figure, contains two components: signal light and Stokes light. When it passes through the long-period fiber grating 106, due to its unique mode coupling characteristics, the Stokes light transmitted in the fiber core will couple with the mode in the cladding, causing it to couple to the fiber cladding and be lost, causing the long-period The fiber grating 106 has a loss spectrum with a wider bandwidth at the Stokes light wavelength, and the Stokes light signal intensity in the laser will be attenuated, as shown by the solid arrow 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 component is very small, so that the stimulated Raman process can only be generated under higher pump power conditions, thereby suppressing the stimulated Raman process. The generation of the excited Raman process can increase the Raman threshold, play a certain isolation role, and protect optical fiber devices. At the same time, since the laser path in the fiber laser oscillator cavity is a reciprocating oscillation process, when the reverse return light passes through the long period fiber grating 106, the Stokes optical signal intensity will still be attenuated, as shown by the reverse solid arrow in the figure. , which can further suppress the generation of stimulated Raman processes and improve the oscillator efficiency. In the actual process, by adjusting the grating period, modulation depth and other parameters of the long period fiber grating 106, the suppression effect is maximized.

Example 10 to Example 12:

Figure 9 is a schematic structural diagram of Embodiment 10; Figure 10 is a schematic structural diagram of Embodiment 11; Figure 11 is a schematic structural diagram of Embodiment 12. Embodiment 10 is a forward-pumped fiber laser oscillator. Embodiment 11 is a backward-pumped fiber laser oscillator. Except that the pumping method is different from that of Embodiment 10, the arrangement of its long-period fiber grating 106 is consistent with that of Embodiment 10. Embodiment 12 is a bidirectionally pumped fiber laser oscillator. Except that the pumping method is different from that in Embodiment 10, the arrangement of the long period fiber grating 106 is consistent with that in Embodiment 10. A fiber laser oscillator composed of a pump LD light source 101, a pump combiner 102, a high reflective grating 103, a doped optical fiber 104, a long period fiber grating 106, a low reflective grating 105 and a melting point 107. In Embodiments 10, 11 and 12, the long period fiber grating 106 is directly written on the doped optical fiber 104 in the fiber laser oscillator cavity. Due to the high energy density in the oscillator cavity, losses have a greater impact on its efficiency. During the actual construction of the oscillator, the fiber gratings have been packaged and it is inconvenient to write the fiber grating. The long period fiber grating 106 can be directly written on the doped fiber 104 in the fiber laser oscillator cavity to further reduce the loss of the oscillation cavity. , improve the output efficiency and suppress the stimulated Raman phenomenon inside the oscillator. The working principles of Embodiments 10, 11, and 12 are similar to the previous embodiments and will not be described again.

Experiments have proven that when the fiber laser oscillator is connected to a long-period fiber grating, as the pump power increases, the proportion of Raman light in the output decreases significantly, and as the number of long-period fiber gratings welded in series increases, the proportion of Raman light in the output decreases. The proportion of Manguang can be further reduced.

The long period fiber grating obtained by using 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 placed in a high power fiber laser In amplifier systems, the effect of suppressing stimulated Raman scattering can be achieved. The high loss of long period fiber grating in the Raman band is used to suppress stimulated Raman scattering. The following Embodiments 13 to 15 respectively provide a laser system, each including a seed source and one or more levels of laser amplifiers. Long-period devices are provided between the seed source and the laser amplifiers and between each level of laser amplifiers. Fiber grating, the long-period fiber grating is written using the above-mentioned second apodized long-period fiber grating writing method. The long-period fiber grating is directly connected between the seed source and the fiber amplifier, and the high loss of the long-period fiber grating in the Raman band is used to filter the seed source, so that the seed source can still output a relatively pure output at a higher power level. signal light. It also improves the working efficiency of the fiber amplifier and increases the Raman threshold of the overall system. Placing long-period fiber gratings between various levels of fiber amplifiers improves the efficiency of each level of fiber amplifiers, increases the overall Raman threshold, and further improves the suppression effect.

Figure 12 is a schematic structural diagram of Embodiment 13; it includes a seed source and a fiber amplifier, and the long period fiber grating 106 is connected between the seed source and the fiber amplifier. The seed source includes a pump LD light source 101, a pump combiner 102, a high-reflective grating 103, a doped optical fiber 104, and a low-reflective grating 105. There are multiple pump LD light sources, and the output pigtails of each pump LD light source are connected to on each pump arm of the pump combiner 102. The parameters, selected wavelength, output power, etc. of the pump LD light source vary depending on the actual situation, and there are no special requirements. The output pigtail of the pump combiner 102 is connected to the high reflective grating 103, the doped grating 104 and the low reflective grating 105 in sequence. Between the output pigtail of the pump combiner 102 and the high reflective grating 103, the high reflective grating 103 The doped optical fiber 104 and the low-reflective grating 105 are connected by welding, and a melting point 107 is formed at the welding position. The fiber oscillator composed of pump LD light source 101, pump combiner 102, high reflective grating 103, doped optical fiber 104, low reflective grating 105 and melting point 107 serves as the seed source 108 of the high power fiber laser amplifier system. In Embodiment 13, a 1-stage optical fiber amplifier is introduced, that is, n=1. The long period fiber grating 106 is connected between the seed source 108 and the first-stage fiber amplifier 109 through fusion splicing.

Among them: At present, the most commonly used pump source wavelengths are 976nm and 915nm. The pump LD light source 101 can use these two wavelength LD pump sources, and their output power is in the order of hundreds of watts. The pump combiner 102 is a 7*1 fiber pump combiner. The output pigtails of the 976nm and 915nm LD pump sources in the pump LD light source 101 are connected to the pump arm of the pump combiner 102 through welding. Connected, the output fiber of the pump combiner 102 is a large mode field fiber. The reflectivity of the highly reflective grating 103 at the laser operating wavelength, such as the commonly used wavelength of 1080nm, is usually greater than 99%, and the 3dB bandwidth is usually 2-4nm. The highly reflective grating 103 is prepared on the same optical fiber as the output fiber of the pump combiner 102 . The doped optical fiber 104 should be selected to match the fiber size and numerical aperture of the highly reflective grating 103. The low-reflective grating 105 is used as the output fiber of the seed source. The reflectivity of the low-reflective grating 105 is usually not greater than 10%, and the 3dB bandwidth is usually not greater than 1 nm. The difference between the center wavelength of the low-reflective grating 105 and the center wavelength of the high-reflective grating 103 is no more than 10%. Greater than ±0.4nm.

The output laser light of the seed source 108, as shown by the hollow arrow in Figure 12, contains two components: signal light and Stokes light. When it passes through the long period fiber grating 106, since the long period fiber grating 106 has a loss spectrum with a wider bandwidth at the Stokes wavelength, the Stokes light in the laser passes through the long period fiber grating 106. According to the mode coupling characteristics of the long period fiber grating , the Stokes light transmitted in the fiber core will couple with the mode in the cladding, causing the Stokes light to couple to the fiber cladding and be lost, and the Stokes light intensity will attenuate, as shown by the solid arrow in Figure 12. Therefore, in the actual input laser of the first-stage amplifier 109, as shown by the solid dovetail arrow in the figure, the Stokes light component is very small, so that the stimulated Raman process can be generated under a higher first-stage amplification power condition, thereby suppressing the stimulated Raman process. The generation of excited Raman process achieves the effect of increasing the Raman threshold. In the actual process, by adjusting the grating period, modulation depth and other parameters of the long period fiber grating 106, the suppression effect is maximized.

In order to further improve the stimulated Raman scattering suppression effect of the high-power fiber laser amplifier system, multiple long-period fiber gratings with the same parameters can be connected in series through welding. That is, the long-period fiber grating 6 can be made by welding and connecting multiple long-period fiber gratings in series. The suppression ratio is equivalent to the superposition of the suppression ratios of multiple long period fiber gratings. By controlling the number of long-period fiber gratings, the suppression ratio can be flexibly adjusted.

Figure 13 is a schematic structural diagram of Embodiment 14; in this embodiment, based on the implementation shown in Figure 12, a second-stage optical fiber amplifier is introduced, that is, n=2. The long period fiber grating 106 is connected between the seed source 108 and the first-stage optical fiber amplifier 109, and between the first-stage optical fiber amplifier 109 and the second-stage optical fiber amplifier 110 by fusion splicing.

After being amplified by the first-stage optical fiber amplifier 109, the output laser power of the first-stage optical fiber amplifier 109 is already high, and may even have reached the Raman threshold, and its Stokes light intensity is high, as shown by the hollow arrow in the figure, including the signal. Two components: light and Stokes light. When it passes through the long-period fiber grating 106 between the first-stage fiber amplifier 109 and the second-stage fiber amplifier 110, since the long-period fiber grating 106 has a loss spectrum with a wider bandwidth at the Stokes wavelength, the Stokes light in the laser The intensity is attenuated, as shown by the solid arrows in the figure. Therefore, in the actual input laser of the second-stage fiber amplifier 110, as shown by the solid dovetail arrow in the figure, the Stokes light component is very small, so that the stimulated Raman process can be generated under a higher second-stage amplification power condition, thus It inhibits the generation of stimulated Raman processes and improves the Raman threshold. At the same time, after the second-stage amplification of the second-stage optical fiber amplifier 110, the laser power is relatively high, and the second-stage optical fiber amplifier 110 is likely to have a strong Raman signal. The stimulated Raman process is a two-way process. After the long-period fiber grating 106 is added between the first-stage fiber amplifier 109 and the second-stage fiber amplifier 110, it can still filter the backward transmitted Stokes light, as shown by the solid arrow in the figure. In this way, It can improve the efficiency of the second-stage amplifier, and at the same time, it can play a certain role in inter-stage isolation, has a strong attenuation effect on the backward Raman signal, and plays a protective role on both the seed source 108 and the first-stage optical fiber amplifier 109.

In the actual process, by adjusting the grating period, tilt angle, chirp rate, modulation depth and other parameters of the long period fiber grating 106, the suppression effect is achieved to the best.

In order to further improve the stimulated Raman scattering suppression effect of the high-power fiber laser amplifier system, multiple long-period fiber gratings with the same parameters can be connected in series through welding. That is, the long-period fiber grating 106 can be formed by welding and connecting multiple long-period fiber gratings in series. The suppression ratio is equivalent to the superposition of the suppression ratios of multiple long period fiber gratings. By controlling the number of long-period fiber gratings, the suppression ratio can be flexibly adjusted.

Figure 14 is a schematic structural diagram of Embodiment 15. In this embodiment, an n-level fiber amplifier 111 is introduced into the high-power fiber laser amplifier system. The fiber amplifiers at all levels are connected through long-period fiber gratings, that is, between the first-level fiber amplifier and the second-level optical fiber amplifier, between the second-level optical fiber amplifier and the third-level optical fiber amplifier...n-1 The first-stage optical fiber amplifier and the n-th stage optical fiber amplifier 111 are connected through long-period fiber gratings 106. The long-period fiber grating 106 is connected between various levels of fiber amplifiers through fusion splicing to attenuate the Stokes light and at the same time isolate the backward return light. This can improve the working efficiency of fiber amplifiers at all levels, increase the overall Raman threshold, and further improve the suppression effect.

In the actual process, by adjusting the grating period, tilt angle, chirp rate, modulation depth and other parameters of the long period fiber grating 106, the suppression effect is achieved to the best.

In order to further improve the stimulated Raman scattering suppression effect of the high-power fiber laser amplifier system, multiple long-period fiber gratings with the same parameters can be connected in series through welding. That is, the long-period fiber grating 106 can be formed by welding and connecting multiple long-period fiber gratings in series. The suppression ratio is equivalent to the superposition of the suppression ratios of multiple long period fiber gratings. By controlling the number of long-period fiber gratings, the suppression ratio can be flexibly adjusted.

In this embodiment, an n-level fiber amplifier is introduced into the high-power fiber laser amplifier system. The fiber amplifiers at all levels are connected through long-period fiber gratings, that is, between the first-level fiber amplifier and the second-level optical fiber amplifier, between the second-level optical fiber amplifier and the third-level optical fiber amplifier...n-1 The first-level optical fiber amplifier and the n-th level optical fiber amplifier are connected through long period fiber grating 106. The long-period fiber grating 106 is connected between various levels of fiber amplifiers through fusion splicing to attenuate the Stokes light and at the same time isolate the backward return light. This can improve the working efficiency of fiber amplifiers at all levels, increase the overall Raman threshold, and further improve the suppression effect.

In the actual process, by adjusting the grating period, tilt angle, chirp rate, modulation depth and other parameters of the long period fiber grating 106, the suppression effect is achieved to the best.

In order to further improve the stimulated Raman scattering suppression effect of the high-power fiber laser amplifier system, multiple long-period fiber gratings with the same parameters can be connected in series through welding. That is, the long-period fiber grating 6 can be made by welding and connecting multiple long-period fiber gratings in series. The suppression ratio is equivalent to the superposition of the suppression ratios of multiple long period fiber gratings. By controlling the number of long-period fiber gratings, the suppression ratio can be flexibly adjusted.

In summary, although the present invention has been disclosed above in terms of preferred embodiments, they are not intended to limit the present invention. Any person of ordinary skill in the art can make various modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims (13)

1. The method for writing the apodized long-period fiber bragg grating is characterized by comprising the following steps of:

(1) The method comprises the steps that an apodization long-period fiber bragg grating inscribing device is built, the apodization long-period fiber bragg grating inscribing device comprises a carbon dioxide laser, a beam expanding lens group, a scanning vibrating mirror, a focusing field lens and a fiber bragg grating operating moving platform, the beam expanding lens group, the scanning vibrating mirror and the focusing field lens are sequentially arranged on a laser transmission path output by the carbon dioxide laser, the fiber bragg grating operating moving platform is arranged right below the focusing field lens, an optical fiber of the apodization long-period fiber bragg grating to be inscribed is arranged on the fiber bragg grating operating moving platform and can move under the driving of the fiber bragg grating operating moving platform, laser emitted from the focusing field lens can be incident on the optical fiber arranged on the fiber bragg grating operating moving platform to inscribe inscribed, the fiber bragg grating operating moving platform is driven by a displacement platform driving motor, and then the horizontal moving distance and the horizontal moving speed of the fiber bragg grating operating moving platform are controlled by controlling the displacement platform driving motor;

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

(3) Intercepting an optical fiber with proper length, coating a region to be inscribed with an apodized long-period optical fiber grating with a chemical stripping agent, wiping the optical fiber with alcohol, and then mounting the optical fiber on an optical fiber operation moving platform; adjusting the optical fiber operation moving platform to enable the optical fiber of the optical fiber grating with the apodization long period to be inscribed to be positioned right below the focusing field lens, so that laser emitted from the focusing field lens can be incident on the optical fiber arranged on the optical fiber operation moving platform;

(4) Apodization long period fiber bragg grating inscription;

(4.1) 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 perform exposure scanning, enabling laser to perform single exposure on the whole area to be inscribed of the apodization long-period fiber grating on the optical fiber according to a set marking pattern, and then closing the carbon dioxide laser and the scanning galvanometer;

(4.2) resetting the marking pattern of the scanning galvanometer, wherein the currently set scanning pattern is to reduce the number of vertical line stripes at two ends of the scanning galvanometer on the basis of the last scanning pattern, starting the carbon dioxide laser and the scanning galvanometer again to perform 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 last exposure scanning, namely, only the middle area of the last laser exposure area is subjected to re-exposure;

(4.3) repeating the step (4.2) until the number of vertical line stripes in the marking pattern of the scanning galvanometer is lower than a set threshold.

2. The method for writing an apodized long period fiber grating 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 method for writing an apodized long period fiber grating according to claim 2, wherein: the carbon dioxide laser also comprises a computer, wherein the output power and the 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 method for writing an apodized long-period fiber grating according to claim 3, wherein 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 apodized long-period fiber grating to be written 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 fibers of the optical fiber gratings with the apodization long periods to be inscribed are positioned under 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, the electric horizontal displacement platform horizontally moves 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 to further control the horizontal movement distance and speed of the electric horizontal displacement platform.

5. The method of any one of claims 1 to 4, wherein the light exit 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 center of the input light port of the scanning galvanometer.

6. The method of writing an apodized long period fiber grating according to claim 1, wherein the threshold set in step (4.3) is 1/3 of the number of vertical line stripes in the initial scan pattern.

7. A laser system, characterized by: the method comprises a laser oscillator, wherein a long-period fiber bragg grating is arranged in the laser oscillator, the long-period fiber bragg grating is inscribed by the apodization long-period fiber bragg grating inscribing method according to claim 1 or 2 or 3 or 4 or 6, 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 pumping light source, a pumping beam combiner, a high-reflection grating, a doped optical fiber and a low-reflection grating, wherein the long-period optical fiber grating is arranged in front of the low-reflection grating in the cavity of the laser oscillator or behind the high-reflection grating in the cavity of the optical fiber laser oscillator or directly inscribes the long-period optical fiber grating on the doped optical fiber in the cavity of the optical fiber laser oscillator.

8. A laser system, characterized by: the method comprises the steps of providing a seed source and more than one stage of laser amplifier, and providing long-period fiber gratings between the seed source and the laser amplifier and between the stages of laser amplifiers, wherein the long-period fiber gratings are inscribed by the apodization long-period fiber grating inscribing method according to claim 1 or 2 or 3 or 4 or 6.

9. The method for writing the apodized long-period fiber bragg grating is characterized by comprising the following steps of:

(1) The method comprises the steps that an apodization long-period fiber bragg grating inscription device is built, the apodization long-period fiber bragg grating inscription device comprises a carbon dioxide laser, a beam expanding lens group, a scanning galvanometer, a focusing field lens, a fiber bragg grating operation moving platform and a computer, 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 bragg grating operation moving platform is arranged right below the focusing field lens, an optical fiber of the apodization long-period fiber bragg grating to be inscribed is arranged on the fiber bragg grating operation moving platform and can move under the driving of the fiber bragg grating operation moving platform, laser emitted from the focusing field lens can be incident on the optical fiber arranged on the fiber bragg grating operation moving platform to inscribe inscribed, the fiber bragg grating operation moving platform is driven by a displacement platform driving motor, and the horizontal moving distance and the speed of the fiber bragg grating operation moving platform are controlled by controlling the displacement platform driving motor; 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; the output power and the frequency of the carbon dioxide laser are controlled by a computer; the vibrating mirror driver is connected with the computer, and the computer controls the marking pattern and the marking position of the scanning vibrating mirror by controlling the vibrating mirror driver; 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 optical fibers of the optical fiber gratings with long periods of apodization to be inscribed are 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 fibers of the optical fiber gratings with the apodization long periods to be inscribed are positioned under the focusing field lens by adjusting the two three-dimensional adjusting bases; the three-dimensional adjusting bases are all arranged on an electric horizontal displacement platform, the electric horizontal displacement platform horizontally moves under the drive of a displacement platform driving motor, the displacement platform driving motor is connected with a computer, and the computer controls the displacement platform driving motor to further control the horizontal movement distance and speed of the electric horizontal displacement platform;

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

(3) Intercepting an optical fiber with proper length, coating a region to be inscribed with an apodized long-period optical fiber grating with a chemical stripping agent, wiping the optical fiber with alcohol, and then mounting the optical fiber on an optical fiber operation moving platform; adjusting the optical fiber operation moving platform to enable the optical fiber of the optical fiber grating with the apodization long period to be inscribed to be positioned right below the focusing field lens, so that laser emitted from the focusing field lens can be incident on the optical fiber arranged on the optical fiber operation moving platform;

(4) Apodization long period fiber bragg grating inscription;

(4.1) 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 perform 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 of the whole area to be inscribed with apodized long-period optical fiber gratings on the optical fibers, closing the carbon dioxide laser, and resetting the electric displacement platform;

(4.2) 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 current exposure scanning is positioned in the middle of the laser exposure area in the last exposure scanning, namely, only the middle area of the last laser exposure area is subjected to re-exposure;

(4.3) repeating the step (4.2) until the current laser exposure area meets the set condition.

10. The method for writing an apodized long period fiber grating according to claim 9, wherein the light outlet of the carbon dioxide laser and the beam expanding lens group are positioned on the same axis, and the output laser of the beam expanding lens group is aligned to the center of the input light port of the scanning galvanometer.

11. The method of writing an apodized long period fiber grating 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 method comprises a laser oscillator, wherein a long-period fiber bragg grating is arranged in the laser oscillator, the long-period fiber bragg grating is inscribed by the apodization long-period fiber bragg grating inscribing method according to claim 9, 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 pumping light source, a pumping beam combiner, a high-reflection grating, a doped optical fiber and a low-reflection grating, wherein the long-period optical fiber grating is arranged in front of the low-reflection grating in the cavity of the laser oscillator or behind the high-reflection grating in the cavity of the optical fiber laser oscillator or directly inscribes the long-period optical fiber grating on the doped optical fiber in the cavity of the optical fiber laser oscillator.

13. A laser system, characterized by: the method comprises the steps of providing a seed source and more than one stage of laser amplifier, and providing long-period fiber gratings between the seed source and the laser amplifier and between the stages of laser amplifiers, wherein the long-period fiber gratings are inscribed by the apodization long-period fiber grating inscribing method according to claim 9, 10 or 11.