Distributed side pumped fiber bragg grating, preparation device and method and fiber laser

Abstract

The invention discloses a distributed side pumped fiber bragg grating, a preparation device and method and a fiber laser, and relates to the technical field of fiber lasers, before preparation, an LED illumination part and a CCD camera are controlled to work, a rotary fiber clamp and a three-axis displacement table are controlled to work based on a shot image obtained by the CCD camera, and the fiber bragg grating is prepared. During preparation, a femtosecond laser, an optical switch and a three-axis displacement table are controlled to work, the signal fiber is inscribed until a first reflectivity grating is formed at the first end of the signal fiber, and a second reflectivity grating is formed at the second end of the signal fiber; and a second reflectivity grating is formed at the second end of the signal fiber. According to the invention, the grating can be inscribed on the distributed side-pumped fiber, the distributed side-pumped fiber grating can be prepared, fusion points are prevented from appearing in an oscillator, and the problem that the final performance of a fiber laser is affected due to the appearance of the fusion points is solved.

Description

Technical Field

[0001] The present application relates to the technical field of fiber lasers, and in particular to a distributed side-pumped fiber grating, a preparation device, a method and a fiber laser. Background Art

[0002] Fiber lasers are lasers that use rare earth-doped glass fibers as gain media. They have the advantages of good beam quality, high conversion efficiency, compact structure, and excellent thermal management. They are widely used in military defense, industrial processing, and other fields. With the deepening of application needs in military defense, industrial processing, and other fields, fiber lasers need to develop in the direction of higher power. High-power fiber lasers based on distributed side-pumped fibers are one of the current research hotspots. They are not limited by the performance of fiber combiners, and they also have more uniform thermal distribution, which has unique advantages in achieving single-fiber output of tens of kilowatts of power.

[0003] At present, since it is impossible to well engrave gratings on distributed side-pumped optical fibers, one can only engrave ordinary double-clad fiber gratings first, and then fuse the ordinary double-clad fiber gratings with the distributed side-pumped optical fibers to integrate the oscillators (also called oscillation cavities) in the fiber lasers. This complex integration process often greatly increases the difficulty of integration and engineering of fiber lasers, and the fusion points are easily damaged, which limits the output power of the oscillator and affects the ultimate performance of the fiber laser. Summary of the invention

[0004] The purpose of the present application is to provide a distributed side-pumped fiber grating, a preparation device, a method and a fiber laser, which can write a grating on a distributed side-pumped fiber to prepare a distributed side-pumped fiber grating, avoid the occurrence of a fusion point in the oscillator, and solve the problem that the final performance of the fiber laser is affected by the occurrence of a fusion point.

[0005] To achieve the above objectives, this application provides the following solutions.

[0006] In a first aspect, the present application provides a preparation device for a distributed side-pumped fiber grating, the preparation device for a distributed side-pumped fiber grating comprising: a rotating fiber clamp, a three-axis translation stage, an LED lighting component, a laser focusing component, a CCD camera, a femtosecond laser, an optical switch and a control component, the three-axis translation stage comprising an x-axis translation stage, a y-axis translation stage and a z-axis translation stage; The rotating fiber clamp is installed on the x-axis translation stage; the rotating fiber clamp is used to clamp the distributed side pumping fiber and drive the distributed side pumping fiber to rotate; the laser focusing component is installed on the z-axis translation stage; the three-axis translation stage is used to drive the distributed side pumping fiber to move along the x-axis direction and the y-axis direction, and drive the laser focusing component to move along the z-axis direction; The LED lighting component is used to emit lighting light, and the lighting light is incident on the distributed side pumping optical fiber, and the outgoing light obtained by the distributed side pumping optical fiber transmitting or reflecting the lighting light is incident on the CCD camera; the CCD camera is used to image the outgoing light to obtain a captured image; The femtosecond laser is used to emit a femtosecond laser; the optical switch and the laser focusing component are sequentially arranged on the output optical path of the femtosecond laser according to the transmission direction of the femtosecond laser; the optical switch is used to selectively shield the femtosecond laser; the laser focusing component is used to direct the femtosecond laser emitted by the optical switch into the distributed side pumping optical fiber; The control component is connected to the rotating fiber clamp, the three-axis translation stage, the LED lighting component, the CCD camera, the femtosecond laser and the optical switch drive; the control component is used to control the LED lighting component and the CCD camera to work before preparation, and control the rotating fiber clamp to work based on the captured image obtained by the CCD camera until the signal fiber in the distributed side pumping fiber is in a preparable position; control the three-axis translation stage to work based on the captured image obtained by the CCD camera until the focus or focal line of the femtosecond laser is in the core of the signal fiber in the distributed side pumping fiber; during preparation, the femtosecond laser, the optical switch and the three-axis translation stage are controlled to work, and the signal fiber is written until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber; wherein the preparable position is a position where the signal fiber is not blocked by the pump fiber in the distributed side pumping fiber and the signal fiber can be written; the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value.

[0007] Optionally, when the preparation device for the distributed side-pumped fiber grating is prepared based on a direct writing method, the laser focusing component includes: an oil immersion objective lens; When the distributed side-pumped fiber grating preparation device is prepared based on the fiber mask method, the laser focusing component includes: a cylindrical lens and a phase mask, which are sequentially arranged on the output light path of the femtosecond laser according to the transmission direction of the femtosecond laser.

[0008] Optionally, when the laser focusing component includes a cylindrical lens and a phase mask, the LED lighting component is a first LED lighting assembly; the first LED lighting assembly is used to emit lighting light; the laser focusing component is arranged on an exit light path of the first LED lighting assembly, the laser focusing component is used to incident the lighting light onto a distributed side pumping optical fiber, and incident the reflected light obtained by the distributed side pumping optical fiber reflecting the lighting light onto a CCD camera; the CCD camera is used to image the reflected light to obtain a captured image; When the laser focusing component includes an oil immersion objective lens, the LED lighting component is a second LED lighting assembly; the second LED lighting assembly is used to emit illumination light; the laser focusing component is used to direct the transmitted light after the illumination light passes through the distributed side-pumped optical fiber to be incident on the CCD camera; the CCD camera is used to image the transmitted light to obtain a captured image.

[0009] Optionally, the preparation device of the distributed side-pumped fiber grating further includes: an optical attenuator, a reflector, a first dichroic mirror and a second dichroic mirror; The optical attenuator, the reflector and the first dichroic mirror are all located between the optical switch and the laser focusing component, and the optical attenuator, the reflector and the first dichroic mirror are sequentially arranged on the outgoing optical path of the femtosecond laser according to the transmission direction of the femtosecond laser; When the LED lighting component is a first LED lighting assembly, the first dichroic mirror and the second dichroic mirror are both located between the first LED lighting assembly and the laser focusing component, and the second dichroic mirror and the first dichroic mirror are sequentially arranged on an exit light path of the first LED lighting assembly according to a transmission direction of the illumination light; When the LED lighting component is a second LED lighting assembly, the first dichroic mirror and the second dichroic mirror are both located between the laser focusing component and the CCD camera, and the first dichroic mirror and the second dichroic mirror are sequentially arranged according to the transmission direction of the transmitted light after the illumination light passes through the distributed side pumping optical fiber; The first dichroic mirror is used to reflect the femtosecond laser to the laser focusing component, transmit the illumination light emitted by the first LED lighting component to the laser focusing component, transmit the reflected light of the illumination light emitted by the first LED lighting component to the second dichroic mirror, and transmit the transmitted light of the illumination light emitted by the second LED lighting component to the second dichroic mirror; the second dichroic mirror is used to reflect the illumination light emitted by the first LED lighting component to the first dichroic mirror, transmit the reflected light of the illumination light emitted by the first LED lighting component to the CCD camera, and transmit the transmitted light of the illumination light emitted by the second LED lighting component to the CCD camera.

[0010] Optionally, the preparation device of the distributed side-pumped fiber grating further includes: a y-axis scanning galvanometer; The y-axis scanning galvanometer is located between the optical switch and the laser focusing component, and the y-axis scanning galvanometer is set on the output light path of the femtosecond laser. The control component is connected to the y-axis scanning galvanometer drive; the y-axis scanning galvanometer is used to make the femtosecond laser incident on different positions of the signal fiber in the y-axis direction.

[0011] In a second aspect, the present application provides a method for preparing a distributed side-pumped fiber grating, which is applied to a preparation device for a distributed side-pumped fiber grating as described in any one of the above, and the preparation method for a distributed side-pumped fiber grating comprises: Control the operation of LED lighting components and CCD cameras; Acquire a captured image obtained by a CCD camera, and determine whether the signal fiber in the distributed side pumping optical fiber is in a preparable position based on the captured image; determine whether the focus or focal line of the femtosecond laser is located at the core position of the signal fiber in the distributed side pumping optical fiber based on the captured image; the preparable position is a position where the signal fiber is not blocked by the pump fiber in the distributed side pumping optical fiber and the signal fiber can be written; If not, the rotating optical fiber fixture is controlled to work, driving the distributed side pumping optical fiber to rotate, the three-axis translation stage is controlled to work, driving the distributed side pumping optical fiber to move, and the process returns to the step of "obtaining the captured image obtained by the CCD camera"; If so, the LED lighting component and the CCD camera are controlled to stop working, and the femtosecond laser, the optical switch and the three-axis translation stage are controlled to work to write the signal fiber until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber; the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value.

[0012] Optionally, controlling a femtosecond laser, an optical switch, and a three-axis translation stage to work and write on the signal fiber until a first reflectivity grating is formed at a first end of the signal fiber and a second reflectivity grating is formed at a second end of the signal fiber, specifically includes: Control the operation of femtosecond laser; The optical switch is controlled to not allow the femtosecond laser to pass through, and the three-axis translation stage is controlled to work, so as to drive the distributed side pumping optical fiber to move along the x-axis direction, so that the femtosecond laser can be incident on the grating surface to be written of the signal fiber; the grating surface to be written is one of the first reflectivity grating and the second reflectivity grating; Control the optical switch to allow the femtosecond laser to pass through, control the three-axis translation stage to work, drive the distributed side pumping optical fiber to move along the y-axis and z-axis directions, and write on the grating surface to be written on the signal fiber; Determining whether all grating surfaces of the first reflectivity grating and the second reflectivity grating have been written; If yes, the writing is stopped, and at this time, a first reflectivity grating is formed at the first end of the signal fiber, and a second reflectivity grating is formed at the second end of the signal fiber; If not, one of the unwritten grating surfaces of the first reflectivity grating and the second reflectivity grating is selected as the grating surface to be written in the next iteration, and the process returns to the step of "controlling the optical switch to not allow the femtosecond laser to pass through".

[0013] In a third aspect, the present application provides a distributed side-pumped fiber grating, which is prepared based on the preparation device of the distributed side-pumped fiber grating described in any one of the above, and is prepared by the preparation method of the distributed side-pumped fiber grating described in any one of the above, wherein the distributed side-pumped fiber grating comprises: an outer cladding, a signal fiber and at least one pump fiber, the signal fiber and the pump fiber are bonded together, and the outer cladding covers the signal fiber and the pump fiber; The first end of the signal fiber is engraved with a first reflectivity grating, and the second end of the signal fiber is engraved with a second reflectivity grating; the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value.

[0014] In a fourth aspect, the present application provides a fiber laser, the fiber laser comprising: an integrated oscillator module, a filter module and an amplification module; The integrated oscillator module includes a first pump laser and an oscillator, the oscillator adopts the above-mentioned distributed side-pumped fiber grating, and the first pump laser is connected to the pump fiber in the distributed side-pumped fiber grating; The input end of the filter module is connected to the output end of the integrated oscillator module; the filter module is used to filter the laser output by the integrated oscillator module to obtain filtered laser; The input end of the amplifying module is connected to the output end of the filtering module; the amplifying module is used to amplify the filtered laser output by the filtering module to obtain the amplified laser.

[0015] Optionally, the filter module includes a tilted grating and a cladding light filter connected in sequence; the amplification module includes a second pump laser and a distributed side pump fiber, and the second pump laser is connected to a pump fiber in the distributed side pump fiber.

[0016] According to the specific embodiments provided in this application, this application discloses the following technical effects: The present application provides a distributed side-pumped fiber grating, a preparation device, a method and a fiber laser, wherein the preparation device comprises: a rotating fiber fixture, a three-axis translation stage, an LED lighting component, a laser focusing component, a CCD camera, a femtosecond laser, an optical switch and a control component. Before preparation, the LED lighting component and the CCD camera are controlled to work, and the rotating fiber fixture is controlled to work based on the captured image obtained by the CCD camera until the signal fiber in the distributed side-pumped fiber is in a preparable position, which is a position where the signal fiber is not blocked by the pump fiber in the distributed side-pumped fiber and can be written, and the three-axis translation stage is controlled to work based on the captured image obtained by the CCD camera until the focus or focal line of the femtosecond laser is in the core of the signal fiber in the distributed side-pumped fiber. During preparation, the femtosecond laser, optical switch and three-axis translation stage are controlled to work, and the signal fiber is written until a first reflectivity grating is formed at the first end of the signal fiber, and a second reflectivity grating is formed at the second end of the signal fiber, the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value. The present application uses an innovatively designed preparation device to write a grating on a distributed side-pumped optical fiber, prepare a distributed side-pumped optical fiber grating, avoid the appearance of a fusion point in the oscillator, and solve the problem that the appearance of a fusion point affects the final performance of the optical fiber laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of a (1+1) type distributed side-pumped optical fiber provided in this application.

[0019] Figure 2 A schematic structural diagram of a fiber laser based on distributed side-pumped fiber provided in this application.

[0020] Figure 3 This is a schematic diagram of the structure of the device for preparing the distributed side-pumped fiber grating provided in Example 1 of the present application.

[0021] Figure 4 This is a schematic diagram of the structure of a rotating fiber clamp and a three-axis translation stage in the preparation device for a distributed side-pumped fiber grating provided in Example 1 of the present application.

[0022] Figure 5Schematic diagram of the three-axis surface-by-surface scanning writing effect of the distributed side-pumped fiber grating provided in Example 1 of the present application.

[0023] Figure 6 A schematic flow chart of the method for preparing a distributed side-pumped fiber grating provided in Example 2 of the present application.

[0024] Figure 7 This is a schematic diagram of the structure of the distributed side-pumped fiber Bragg grating provided in Example 3 of the present application.

[0025] Figure 8 This is a micrograph of the grating structure of the distributed side-pumped fiber grating provided in Example 3 of the present application.

[0026] Fig. 9 This is a grating spectrum diagram of the distributed side-pumped fiber Bragg grating provided in Example 3 of the present application.

[0027] Fig.10 This is a schematic diagram of the structure of the fiber laser provided in Example 4 of the present application.

[0028] Fig.11 A schematic diagram of the simplified structure of a fiber laser based on a distributed side-pumped fiber grating provided in Example 4 of the present application.

[0029] Fig.12 A schematic diagram of the simplified structure of a fiber laser based on a distributed side-pumped fiber provided in Example 4 of the present application.

[0030] Reference numerals: 1-femtosecond laser; 2-optical switch; 3-optical attenuator; 4-reflector; 5-y-axis scanning galvanometer; 6-first dichroic mirror; 7-laser focusing component; 8-distributed side pumping fiber; 9-rotating fiber clamp; 10-x-axis translation stage; 11-y-axis translation stage; 12-z-axis translation stage; 13-first LED lighting assembly; 14-CCD camera; 15-second dichroic mirror; 16-second LED lighting assembly; 17-outer cladding; 1 8-pump fiber; 19-signal fiber; 20-signal fiber core; 21-first reflectivity grating; 22-second reflectivity grating; 23-pump light; 24-laser signal; 25-high reflectivity fiber Bragg grating; 26-low reflectivity fiber Bragg grating; 27-pump laser; 28-first pump laser; 29-tilted grating; 30-cladding light filter; 31-second pump laser; 32-output head; 33-subsequent module; 34-passive optical fiber. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] Example 1.

[0033] Typical distributed side-pumped fibers and fiber lasers based on distributed side-pumped fibers are shown in Figure 2. Figure 1 and Figure 2 The distributed side-pumped optical fiber is usually composed of an active signal fiber 19 and at least one passive pump fiber 18 tightly fitted together, and the two are jointly coated by an outer cladding 17. Figure 1 It is a schematic diagram of a (1+1) type distributed side-pumped optical fiber, in which the signal fiber 19 and the pump fiber 18 are both one fiber. Figure 2 Schematic diagram of a 10kW-class fiber laser based on distributed side-pumped fiber. The seed source is an oscillator based on an ordinary double-clad fiber Bragg grating (i.e., a high-reflectivity fiber Bragg grating 25 and a low-reflectivity fiber Bragg grating 26) and an integrated distributed side-pumped fiber 8. The distributed side-pumped fiber 8 is pumped by a pump laser 27. That is, the oscillator includes a high-reflectivity fiber Bragg grating 25, Figure 2 The first distributed side pumping fiber 8 and the low reflectivity fiber grating 26 in the amplifier are only composed of the distributed side pumping fiber 8, that is, the amplifier includes Figure 2 The second distributed side pumping fiber 8 in the figure, where "×" is the fusion point between the ordinary double-clad fiber grating and the distributed side pumping fiber 8. Since it is currently impossible to well engrave the grating on the distributed side pumping fiber 8, we can only engrave the ordinary double-clad fiber grating first, and then fuse the ordinary double-clad fiber grating with the distributed side pumping fiber 8 to integrate the oscillator. This complex integration process often greatly increases the difficulty of integration and engineering of the fiber laser, and the fusion point is easily damaged, which limits the output power of the oscillator and affects the final performance of the fiber laser.

[0034] The reason why it is impossible to write gratings directly on distributed side-pumped optical fibers is that the currently widely used high-power grating writing method is the ultraviolet laser grating method (phase mask method). This method requires that the optical fiber must be a germanium-doped hydrogen-loaded sensitized optical fiber, and the optical fiber coating must be removed during writing. The signal fiber of the distributed side-pumped optical fiber is an ytterbium-doped active optical fiber, which has poor photosensitivity and is difficult to carry out hydrogen loading, making it difficult to effectively write gratings. In addition, the emerging femtosecond laser grating method in recent years has a different mechanism from the ultraviolet laser grating method. This method can directly write gratings on non-sensitive optical fibers without the need to carry hydrogen and remove the coating of the optical fiber. The femtosecond laser grating method is divided into two types: the phase mask method and the direct writing method. However, due to the limitations of the existing preparation equipment and preparation methods, no matter which method is used, there is currently no public report on the realization of femtosecond grating on distributed side-pumped optical fibers. The reasons are, firstly, that the core diameter of the signal fiber of the distributed side-pumped optical fiber is very large, and it is difficult to write a high-reflectivity grating to meet the index requirements; secondly, it is difficult to achieve the search and focusing of the ultra-large core diameter signal fiber and its core.

[0035] Since it is impossible to write gratings directly on distributed side-pumped optical fibers, currently the only way is to write gratings based on commercial double-clad optical fibers, which are then fused with the signal fiber of the distributed side-pumped optical fibers to form an oscillator. However, this fusion point is the main difficulty of fiber lasers, which causes fiber lasers to face the following problems.

[0036] (1) Fiber laser engineering is difficult.

[0037] First, the power of the load transmitted through the end face at the fusion point is extremely large. Second, the special structure of the distributed side-pumped fiber itself makes the fusion process extremely complicated, making it difficult to effectively control the fusion quality. There is a greater risk of thermal damage caused by fusion loss and substandard cleanliness. In addition, the size and performance parameters of the passive double-clad fiber used in general commercial fiber gratings are difficult to match with the active signal fiber of the distributed side-pumped fiber. The asymmetric fusion of the two is difficult to integrate, and it is even more difficult to withstand high power. In the oscillator, there are two such fusion points, which are difficult to engineer.

[0038] (2) The output power of the fiber laser oscillator is limited.

[0039] The two asymmetric welding points are both inside the oscillator. The welding points are directly subjected to the very high cladding power in the cavity. The welding points are easily damaged, which limits the output power of the oscillator.

[0040] (3) The ultimate output power of fiber lasers is limited.

[0041] Due to the damage threshold of the fusion point, the difficulty of integration and the power of the oscillator itself, the laser power that can be effectively injected into the amplifier is limited, thus affecting the final output power of the fiber laser.

[0042] In order to solve the above problems, this embodiment provides a distributed side-pumped fiber grating preparation device, which can prepare a grating on the signal fiber of the distributed side-pumped fiber to avoid the occurrence of a fusion point in the oscillator of the fiber laser. Figure 3 As shown, the preparation device of the distributed side-pumped fiber grating includes: a rotating fiber clamp 9, a three-axis translation stage, an LED lighting component, a laser focusing component 7, a CCD camera 14, a femtosecond laser 1, an optical switch 2 and a control component, and the three-axis translation stage includes an x-axis translation stage 10, a y-axis translation stage 11 and a z-axis translation stage 12.

[0043] The rotating fiber clamp 9 is mounted on the x-axis translation stage 10. The rotating fiber clamp 9 is used to clamp the distributed side pumping fiber 8 and drive the distributed side pumping fiber 8 to rotate.

[0044] The laser focusing component 7 is mounted on the z-axis translation stage 12. The three-axis translation stage is used to drive the distributed side pumping optical fiber 8 to move along the x-axis direction and the y-axis direction, and drive the laser focusing component 7 to move along the z-axis direction.

[0045] The LED lighting component is used to emit lighting light, and the lighting light is incident on the distributed side pumping optical fiber 8, and the outgoing light obtained by the distributed side pumping optical fiber 8 transmitting or reflecting the lighting light is incident on the CCD camera 14. The CCD camera 14 is used to image the outgoing light to obtain a captured image.

[0046] The femtosecond laser 1 is used to emit a femtosecond laser. The optical switch 2 and the laser focusing component 7 are sequentially arranged on the output optical path of the femtosecond laser 1 according to the transmission direction of the femtosecond laser. The optical switch 2 is used to selectively block the femtosecond laser, and the laser focusing component 7 is used to direct the femtosecond laser emitted by the optical switch 2 to the distributed side pumping optical fiber 8.

[0047] The control component is connected to the rotating fiber fixture 9, the three-axis translation stage, the LED lighting component, the CCD camera 14, the femtosecond laser 1 and the optical switch 2. The control component is used to control the LED lighting component and the CCD camera 14 to work before preparation, control the rotating fiber fixture 9 to work based on the captured image obtained by the CCD camera 14 until the signal fiber in the distributed side pumping fiber 8 is in a preparation position, and control the three-axis translation stage to work based on the captured image obtained by the CCD camera 14 until the focus or focal line of the femtosecond laser is in the core of the signal fiber in the distributed side pumping fiber 8; during preparation, control the femtosecond laser 1, the optical switch 2 and the three-axis translation stage to work, and write the signal fiber until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber. Among them, the prepareable position is a position where the signal fiber is not blocked by the pump fiber in the distributed side pump fiber 8 and can be written on the signal fiber, the reflectivity of the first reflectivity grating is greater than the first preset value, the reflectivity of the second reflectivity grating is less than the second preset value, and the first preset value is greater than the second preset value.

[0048] In this embodiment, the first reflectivity grating is a high reflectivity grating, the second reflectivity grating is a low reflectivity grating, and the first preset value and the second preset value can be set according to user needs.

[0049] In this embodiment, when the preparation device of the distributed side-pumped fiber grating is prepared based on the direct writing method, the laser focusing component 7 includes: an oil immersion objective lens; when the preparation device of the distributed side-pumped fiber grating is prepared based on the fiber mask method, the laser focusing component 7 includes: a cylindrical lens and a phase mask, and the cylindrical lens and the phase mask are sequentially arranged on the output light path of the femtosecond laser 1 according to the transmission direction of the femtosecond laser.

[0050] In this embodiment, when preparing a distributed side-pumped fiber grating, a phase mask method can be used, in which the grating is engraved after the coating layer is stripped. Although this increases the process steps and time, it reduces the difficulty of the engraving process and can also achieve the effect of avoiding the occurrence of fusion points in the oscillator. Since the phase mask method is difficult to achieve coating separation processing, in order to further improve the processing efficiency, a direct writing method can be used.

[0051] In the phase mask method, because the light transmittance of the phase mask is too strong, the reflected light should be observed. In the direct writing method, because the light transmittance of the oil immersion objective is small, the transmitted light should be observed.

[0052] When the laser focusing component 7 includes a cylindrical lens and a phase mask, the LED lighting component is a first LED lighting assembly 13, and the first LED lighting assembly 13 is used to emit lighting light. The laser focusing component 7 is arranged on the exit light path of the first LED lighting assembly 13, and the laser focusing component 7 is used to incident the lighting light onto the distributed side pumping optical fiber 8, and incident the reflected light obtained by the distributed side pumping optical fiber 8 reflecting the lighting light onto the CCD camera 14. The CCD camera 14 is used to image the reflected light to obtain a captured image.

[0053] When the laser focusing component 7 includes an oil immersion objective lens, the LED lighting component is a second LED lighting assembly 16, and the second LED lighting assembly 16 is used to emit lighting light, and the transmitted light after the lighting light passes through the distributed side pumping optical fiber 8 is incident on the CCD camera 14 through the laser focusing component 7, that is, the laser focusing component 7 is used to make the transmitted light after the lighting light passes through the distributed side pumping optical fiber 8 be incident on the CCD camera 14. The CCD camera 14 is used to image the transmitted light to obtain a captured image.

[0054] In this embodiment, the manufacturing device of the distributed side-pumped fiber grating further includes: an optical attenuator 3 , a reflector 4 , a first dichroic mirror 6 and a second dichroic mirror 15 .

[0055] The optical attenuator 3, the reflector 4 and the first dichroic mirror 6 are all located between the optical switch 2 and the laser focusing component 7, and are sequentially arranged on the outgoing light path of the femtosecond laser 1 according to the transmission direction of the femtosecond laser.

[0056] When the LED lighting component is the first LED lighting assembly 13, the first dichroic mirror 6 and the second dichroic mirror 15 are both located between the first LED lighting assembly 13 and the laser focusing component 7, and the second dichroic mirror 15 and the first dichroic mirror 6 are sequentially arranged on the output light path of the first LED lighting assembly 13 according to the transmission direction of the illumination light.

[0057] When the LED lighting component is the second LED lighting assembly 16, the first dichroic mirror 6 and the second dichroic mirror 15 are both located between the laser focusing component 7 and the CCD camera 14, and the first dichroic mirror 6 and the second dichroic mirror 15 are arranged in sequence according to the transmission direction of the transmitted light after the illumination light passes through the distributed side-pumped optical fiber 8.

[0058] The first dichroic mirror 6 is used to reflect the femtosecond laser to the laser focusing component 7, transmit the illumination light emitted by the first LED lighting component 13 to the laser focusing component 7, transmit the reflected light of the illumination light emitted by the first LED lighting component 13 to the second dichroic mirror 15, and transmit the transmitted light of the illumination light emitted by the second LED lighting component 16 to the second dichroic mirror 15; the second dichroic mirror 15 is used to reflect the illumination light emitted by the first LED lighting component 13 to the first dichroic mirror 6, transmit the reflected light of the illumination light emitted by the first LED lighting component 13 to the CCD camera 14, and transmit the transmitted light of the illumination light emitted by the second LED lighting component 16 to the CCD camera 14.

[0059] In this embodiment, the preparation device of the distributed side-pumped fiber Bragg grating further includes: a y-axis scanning galvanometer 5, which is located between the optical switch 2 and the laser focusing component 7, and is arranged on the output light path of the femtosecond laser 1, and the control component is drivingly connected to the y-axis scanning galvanometer 5. The y-axis scanning galvanometer 5 is used to make the femtosecond laser incident on different positions of the signal fiber in the y-axis direction.

[0060] In this embodiment, the femtosecond laser 1 can be a femtosecond fiber laser, which can also be called a fiber femtosecond laser, and the femtosecond laser 1 is used to generate a femtosecond laser. Preferably, a femtosecond laser 1 in the visible light band or infrared band is used, that is, the femtosecond laser is a femtosecond laser in the visible light band or infrared band. Since the material of the coating layer of the distributed side-pumped optical fiber 8 generally has a strong absorption of ultraviolet light, it is difficult to use a commonly used ultraviolet laser to achieve the purpose of writing a grating on the distributed side-pumped optical fiber 8 through the coating layer. The use of a femtosecond laser 1 in the visible light band or infrared band can effectively avoid this problem and successfully achieve the writing of the coating layer of the distributed side-pumped optical fiber grating.

[0061] In this embodiment, the optical switch 2 is an electric optical switch. The optical switch 2 is an optical device with one or more optional transmission ports. Its function is to perform physical switching or logical operations on optical signals in an optical transmission line or an integrated optical circuit. When the optical switch 2 is driven to be turned on, the femtosecond laser can be transmitted backward through the optical switch 2; when the optical switch 2 is driven to be turned off, the femtosecond laser will not be transmitted backward.

[0062] In this embodiment, the optical attenuator 3 may be an electric optical attenuator. The optical attenuator 3 is a device for attenuating optical power, and is specifically used to attenuate the optical power of the femtosecond laser emitted by the optical switch 2 .

[0063] In this embodiment, the reflector 4 may be any existing reflector as long as it can reflect the femtosecond laser emitted by the optical attenuator 3 to the subsequent y-axis scanning galvanometer 5 .

[0064] In this embodiment, the y-axis scanning galvanometer 5 is an excellent vector scanning device with a displacement accuracy of sub-nanometer level. It is used to make the femtosecond laser incident on different positions of the signal fiber in the y-axis direction, which is equivalent to driving the signal fiber to move in the y-axis direction. It has the same function as the y-axis translation stage 11 in the three-axis translation stage. The y-axis scanning galvanometer 5 is used to directly control the femtosecond laser for y-axis scanning, which is more efficient than directly using the y-axis translation stage 11 to move the distributed side pump fiber 8 for y-axis scanning.

[0065] The characteristic of a dichroic mirror is that it almost completely transmits light of a certain wavelength, but almost completely reflects light of other wavelengths. In this embodiment, the first dichroic mirror 6 is used to reflect the femtosecond laser to the laser focusing component 7 .

[0066] During preparation, the femtosecond laser emitted by the femtosecond laser 1 is incident on the optical attenuator 3 through the optical switch 2, is incident on the reflector 4 through the optical attenuator 3, is reflected by the reflector 4 to the y-axis scanning galvanometer 5, is incident on the first dichroic mirror 6 through the y-axis scanning galvanometer 5, is reflected by the first dichroic mirror 6 to the laser focusing component 7, and is incident on the distributed side pumping fiber 8 through the laser focusing component 7.

[0067] In this embodiment, the rotating optical fiber clamp 9 may adopt an existing structure as long as it has the function of clamping the distributed side pumping optical fiber 8 and driving the distributed side pumping optical fiber 8 to rotate.

[0068] like Figure 4 As shown, in this embodiment, the displacement accuracy of the three-axis translation stage is in the sub-nm level, and the three-axis translation stage includes an x-axis translation stage 10, a y-axis translation stage 11, and a z-axis translation stage 12. The x-axis translation stage 10 is mounted on the y-axis translation stage 11, the y-axis translation stage 11 is mounted on a black base, and the z-axis translation stage 12 is mounted on a black bracket. The x-axis translation stage 10 is used to drive the distributed side pumping optical fiber 8 to move along the x-axis direction, the y-axis translation stage 11 is used to drive the distributed side pumping optical fiber 8 to move along the y-axis direction, and the z-axis translation stage 12 is used to drive the laser focusing component 7 to move along the z-axis direction. Figure 3 The z-axis translation stage 12 shown is fixed on the black bracket, driving the structure composed of the first dichroic mirror 6 and the laser focusing component 7 to move, changing the distance between the laser focusing component 7 and the distributed side pumping fiber 8, which is equivalent to driving the distributed side pumping fiber 8 to move along the z-axis direction. Compared with the situation where the translation stages of the three axes are all connected to the black base, the adjustable range is larger and the load-bearing capacity is stronger.

[0069] This embodiment adds an x, y, z three-axis translation stage and a y-axis scanning galvanometer 5 that are linked to the optical switch 2. The three-axis translation stage and the y-axis scanning galvanometer 5 form a scanning module, and the displacement accuracy is in the sub-nm level. The three-axis translation stage can realize precise adjustment of the grating optical path to ensure that the femtosecond laser focuses on the signal fiber core. When engraving the grating, the y-axis scanning galvanometer 5, the x-axis translation stage 10, and the z-axis translation stage 12 are combined with the optical switch 2 to perform three-axis scanning simultaneously according to the set logic to achieve face-by-face writing of ultra-large core diameters, increase the refractive index modulation area of ​​the optical fiber cross section, increase the coupling efficiency, and improve the reflectivity. The specific three-axis face-by-face scanning effect is as follows: Figure 5 The specific grating process is as follows: first, the optical switch 2 is turned on, and the y-axis scanning galvanometer 5 moves back and forth in the y-axis direction and the z-axis translation stage 12 moves unidirectionally in the z-axis direction ( Figure 5 In the example from A to B in FIG2 , a grating plane scan is performed in the signal fiber core of the distributed side-pumped optical fiber 8. The scanning length of the y-axis scanning galvanometer 5 is greater than the core diameter, and the movement distance (AB) of the z-axis translation stage 12 is greater than the core diameter, so that the grating plane with refractive index modulation fully covers the core. Next, the optical switch 2 is turned off, the x-axis translation stage 10 moves the grating period length Λ, the z-axis returns to position A, and then the optical switch 2 is turned on for the next grating plane scan. This process is repeated until the required number of grating periods and indicators are obtained, and the grating writing is completed. During the writing process, high-reflectivity gratings and low-reflectivity gratings are formed respectively by adjusting the length, energy and frequency of the writing. The length, energy and frequency of the high-reflectivity grating are higher than the length, energy and frequency of the low-reflectivity grating. The specific parameters can be set according to user needs.

[0070] In this embodiment, the first LED lighting assembly 13 and the second LED lighting assembly 16 may be LED lamps for emitting lighting light.

[0071] In this embodiment, the first dichroic mirror 6 is used to transmit the illumination light emitted by the first LED lighting component 13 to the laser focusing component 7, transmit the reflected light of the illumination light emitted by the first LED lighting component 13 to the second dichroic mirror 15, and transmit the transmitted light of the illumination light emitted by the second LED lighting component 16 to the second dichroic mirror 15; the second dichroic mirror 15 is used to reflect the illumination light emitted by the first LED lighting component 13 to the first dichroic mirror 6, transmit the reflected light of the illumination light emitted by the first LED lighting component 13 to the CCD camera 14, and transmit the transmitted light of the illumination light emitted by the second LED lighting component 16 to the CCD camera 14.

[0072] In this embodiment, the CCD camera 14 is used to image the reflected light of the illumination light emitted by the first LED illumination assembly 13 or the transmitted light of the illumination light emitted by the second LED illumination assembly 16 .

[0073] Before preparation, when the phase mask method is used for writing, the first LED lighting assembly 13 emits illumination light, which is reflected to the first dichroic mirror 6 by the second dichroic mirror 15, transmitted to the laser focusing component 7 by the first dichroic mirror 6, and incident to the distributed side pumping fiber 8 by the laser focusing component 7. The reflected light reflected by the distributed side pumping fiber 8 to the illumination light is incident to the first dichroic mirror 6 by the laser focusing component 7, transmitted to the second dichroic mirror 15 by the first dichroic mirror 6, and transmitted to the CCD camera 14 by the second dichroic mirror 15. The CCD camera 14 images the reflected light to obtain a captured image.

[0074] When direct writing is used for engraving, the second LED lighting assembly 16 emits illumination light, which is incident on the distributed side pumping optical fiber 8, transmitted through the distributed side pumping optical fiber 8 to the laser focusing component 7, transmitted through the laser focusing component 7 to the first dichroic mirror 6, transmitted through the first dichroic mirror 6 to the second dichroic mirror 15, and transmitted through the second dichroic mirror 15 to the CCD camera 14. The CCD camera 14 images the transmitted light to obtain a captured image.

[0075] This embodiment adds a large-diameter rotating optical fiber clamp 9 specially designed for the distributed side pump optical fiber 8, and cooperates with a visual module composed of a CCD camera 14 and an LED lighting component to judge the position of the distributed side pump optical fiber 8 by observing the number of imaged fiber cores. If the image shows two fiber cores, the signal fiber and the pump fiber are in a relatively horizontal position and will not block each other. If only one fiber core is imaged, that is, the image shows one fiber core, the signal fiber and the pump fiber have an upper and lower position relationship and will block each other. The position of the distributed side pump optical fiber 8 can be rotated to adjust the signal fiber so that the signal fiber is not blocked by the pump fiber. At the same time, combined with a three-axis translation stage, it is convenient to find and focus on the signal fiber core position, thereby improving the writing accuracy.

[0076] The distributed side-pumped fiber grating of this embodiment can be prepared by using a femtosecond grating device optimized and improved for the distributed side-pumped fiber 8. Compared with the general femtosecond grating device, the preparation device of this embodiment mainly targets the writing requirements of the distributed side-pumped fiber 8, and makes innovative improvements on the femtosecond grating device, so that the distributed side-pumped fiber grating can be prepared.

[0077] Example 2.

[0078] This embodiment provides a method for preparing a distributed side-pumped fiber Bragg grating, which is applied to the preparation device for the distributed side-pumped fiber Bragg grating described in Example 1. Figure 6 As shown, the preparation method of the distributed side-pumped fiber grating includes the following steps.

[0079] S1: Control the LED lighting components and CCD camera.

[0080] S2: Acquire a captured image obtained by a CCD camera, and determine whether the signal fiber in the distributed side-pumped optical fiber is in a preparable position based on the captured image; determine whether the focus or focal line of the femtosecond laser is located at the core position of the signal fiber in the distributed side-pumped optical fiber based on the captured image; the preparable position is a position where the signal fiber is not blocked by the pump fiber in the distributed side-pumped optical fiber and the signal fiber can be written.

[0081] S3: If not, control the rotating fiber fixture to drive the distributed side pumping fiber to rotate, control the three-axis translation stage to drive the distributed side pumping fiber to move, and return to the step of "obtaining the captured image obtained by the CCD camera".

[0082] S4: If so, control the LED lighting component and the CCD camera to stop working, control the femtosecond laser, the optical switch and the three-axis translation stage to work, and write the signal fiber until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber; the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value.

[0083] In S4, the femtosecond laser, the optical switch and the three-axis translation stage are controlled to work, and the signal fiber is written until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber, which specifically includes the following steps.

[0084] (1) Control the operation of femtosecond laser.

[0085] (2) Control the optical switch to prevent the femtosecond laser from passing through, control the three-axis translation stage to work, drive the distributed side pumping fiber to move along the x-axis direction, and enable the femtosecond laser to be incident on the grating surface to be written of the signal fiber; the grating surface to be written is one of the first reflectivity grating and the second reflectivity grating.

[0086] (3) Control the optical switch to allow the femtosecond laser to pass through, control the three-axis translation stage to work, drive the distributed side pumping fiber to move along the y-axis and z-axis directions, and write on the grating surface to be written on the signal fiber.

[0087] Optionally, the step of "controlling the three-axis translation stage to drive the distributed side pumping fiber to move along the y-axis and z-axis directions" can be replaced by the step of "controlling the y-axis scanning galvanometer to make the femtosecond laser incident on different positions of the signal fiber in the y-axis direction, controlling the three-axis translation stage to drive the distributed side pumping fiber to move along the z-axis direction".

[0088] The movement in the y-axis direction needs to cover two boundaries of the signal fiber on the y-axis, and the movement in the z-axis direction needs to cover two boundaries of the signal fiber on the z-axis.

[0089] (4) Determine whether all grating surfaces of the first reflectivity grating and the second reflectivity grating have been written.

[0090] (5) If yes, stop writing. At this time, a first reflectivity grating is formed at the first end of the signal fiber, and a second reflectivity grating is formed at the second end of the signal fiber.

[0091] (6) If not, select one of the unwritten grating surfaces of the first reflectivity grating and the second reflectivity grating as the grating surface to be written in the next iteration, and return to the step of "controlling the optical switch to not allow the femtosecond laser to pass through".

[0092] When selecting the grating surface to be written, the selection is performed in the order of the x-coordinates of the grating surfaces in the first reflectivity grating and the second reflectivity grating from large to small or from small to large.

[0093] Example 3.

[0094] This embodiment provides a distributed side-pumped fiber Bragg grating, which is prepared based on the preparation device of the distributed side-pumped fiber Bragg grating described in Example 1 and the preparation method of the distributed side-pumped fiber Bragg grating described in Example 2. Figure 7 As shown, the distributed side-pumped fiber grating includes: an outer cladding 17 , a signal fiber 19 and at least one pump fiber 18 , the signal fiber 19 and the pump fiber 18 are in close contact with each other, and the outer cladding 17 covers the signal fiber 19 and the pump fiber 18 .

[0095] A first reflectivity grating 21 is engraved on the first end of the signal fiber 19, and a second reflectivity grating 22 is engraved on the second end of the signal fiber 19. The reflectivity of the first reflectivity grating 21 is greater than a first preset value, and the reflectivity of the second reflectivity grating 22 is less than a second preset value. The first preset value is greater than the second preset value.

[0096] Figure 7The whole is a distributed side pumping fiber, wherein 17 is the outer cladding of the distributed side pumping fiber 8, 18 is the pump fiber of the distributed side pumping fiber 8, 19 is the signal fiber of the distributed side pumping fiber 8, 20 is the signal fiber core, 21 is the first reflectivity grating (i.e., high reflectivity grating) inscribed in the signal fiber core 20, 22 is the second reflectivity grating (i.e., low reflectivity grating) inscribed in the signal fiber core 20, and 23 is the pumping light injected into the distributed side pumping fiber 8. After side pumping coupling, the generated laser is amplified in the linear oscillator constructed by the distributed side pumping fiber grating, and finally the laser signal 24 is output. The distributed side pumping fiber grating is directly inscribed into the signal fiber 19 of the distributed side pumping fiber 8 through the outer cladding 17, so there is no fusion point in the oscillator, which greatly simplifies the integration steps, reduces the integration difficulty, facilitates the engineering of fiber lasers, and can also avoid damage to the fusion point and improve the output power of the oscillator. At the same time, processing gratings through coating can simplify the grating preparation process. There is no need to peel off long distances of coating, and there is no need to worry about the quality of the coating fracture inside the oscillator and the heat caused by cleaning, which reduces the preparation difficulty and reduces the grating preparation time.

[0097] The grating structure micrograph and grating spectrum of the distributed side-pumped fiber Bragg grating are shown in Figure 2. Figure 8 and Fig. 9 shown.

[0098] Example 4.

[0099] This embodiment provides a fiber laser, such as Fig.10 As shown, the fiber laser includes: an integrated oscillator module, a filter module and an amplification module.

[0100] The integrated oscillator module includes a first pump laser 28 and an oscillator. The oscillator adopts the distributed side-pumped fiber grating described in Example 3. The first pump laser 28 is connected to the pump fiber in the distributed side-pumped fiber grating.

[0101] The input end of the filter module is connected to the output end of the integrated oscillator module, and the filter module is used to filter the laser output by the integrated oscillator module to obtain filtered laser.

[0102] The input end of the amplifying module is connected to the output end of the filtering module. The amplifying module is used to amplify the filtered laser output by the filtering module to obtain the amplified laser.

[0103] In this embodiment, the filter module includes a tilted grating 29 and a cladding light filter 30 connected in sequence. The amplification module includes a second pump laser 31 and a distributed side pump fiber 8, and the second pump laser 31 is connected to the pump fiber in the distributed side pump fiber 8.

[0104] The purpose of this embodiment is to overcome the shortcomings of the prior art and provide a high-power fiber laser based on a distributed side-pumped fiber grating integrated high-power oscillator, which has the characteristics of low engineering difficulty, high output power, high reliability, etc. Fig.10 As shown, it is a schematic diagram of the structure of the high-power fiber laser designed in this embodiment. The fiber laser is formed by connecting an integrated oscillator module, a filter module and an amplifier module in sequence, and the entire fiber laser is constructed based on a distributed side-pumped fiber. Specifically, the oscillator of the integrated oscillator module is composed of only one distributed side-pumped fiber grating, and the grating is directly engraved on both ends of the active signal fiber of the distributed side-pumped fiber 8 to form an oscillator. There is no fusion point in the cavity. The pump fiber of the distributed side-pumped fiber grating is connected to the first pump laser 28. The first pump laser 28 provides pump light for the oscillator, and a unidirectional or bidirectional pumping method can be used. Fig.10 The figure shows a bidirectional pumping mode. The filter module is composed of an ultra-wideband (>20nm) and ultra-high suppression ratio (>30dB) tilted grating 29 for Raman suppression and a cladding light filter 30 for cladding light filtering. The amplification module is composed of a distributed side pumping fiber 8, a second pumping laser 31 and an output head 32, and adopts a unidirectional or bidirectional same-band pumping mode.

[0105] In this embodiment, the integrated oscillator module or the amplifier module may also be a multi-stage cascade pumping structure, that is, a cascade pumping method may be used to increase the pumping power and the output laser power.

[0106] The integrated oscillator module in this embodiment can be used as a pre-stage of a high-power fiber laser, and can also be directly used as a high-power fiber laser to output laser light.

[0107] The distributed side-pumped optical fiber used in the distributed side-pumped fiber grating and fiber laser can be of (1+1) type or (N+1) type. The (N+1) type refers to N pump fibers and 1 signal fiber.

[0108] Fig.11 and Fig.12 It is a comparison diagram of the main parts of this embodiment and the prior art. Fig.11 and Fig.12 In the figure, 33 is a subsequent module and 34 is a passive optical fiber. The main difference is that the grating in this embodiment is directly engraved in the signal fiber of the distributed side pumping optical fiber to form an integrated oscillator without a fusion point, while in the prior art, the grating is engraved on the passive optical fiber and then fused and integrated with the distributed side pumping optical fiber to form an oscillator. Comparing the two, the high-power fiber laser based on the distributed side pumping fiber grating has the following advantages.

[0109] (1) The difficulty of fiber laser integration is greatly reduced: an oscillator based on an integrated distributed side-pumped fiber grating without a welding point can be constructed, avoiding the most difficult injection point welding, simplifying the fiber laser integration steps, reducing the integration difficulty, and reducing the fiber laser integration cost.

[0110] (2) The actual cladding power (i.e., pump power) borne by the fiber laser welding point is lower. Under the same damage threshold, the oscillator output power of the fiber laser is higher: In the prior art, the welding point is inside the oscillator. The welding point will be subjected to very high cladding power, and the welding quality requirements are high, and it is easy to be damaged. In this embodiment, the welding point is outside the oscillator. The cladding power that the welding point outside the oscillator needs to withstand will be an order of magnitude lower than the cladding power borne by the welding point inside the oscillator. Therefore, for the welding point using the same integration process and precision control, this embodiment will be able to withstand higher cladding power, and the oscillator output power will be higher.

[0111] (3) Improve the final output power of the fiber laser, such as Fig.10 As shown, the output power of the integrated oscillator module of the front stage is higher: in the prior art, the oscillator based on the distributed side pumped fiber is generally only in the hundreds of watts. Even if the distributed side cascade pumping solution is adopted, the maximum output power of the oscillator is only about 3 kilowatts due to the heating of the fusion point in the oscillator. In this embodiment, the oscillator based on the distributed side pumped fiber grating can directly reach the high power output of 10,000 watts, simplifying the structure of the 10,000 watt laser. The high-power oscillator can also be used as a front stage to provide seeds for the amplification module according to demand, realizing a high-power laser output of tens of thousands of watts.

[0112] (4) The filter module uses an ultra-wideband and ultra-high suppression ratio tilted grating to filter out Raman light, which greatly increases the nonlinear effect threshold of the fiber laser and improves the final output power of the fiber laser.

[0113] This embodiment uses an improved and optimized femtosecond direct writing device and a face-by-face writing method to directly write gratings in the signal fiber of the distributed side-pumped optical fiber. It can be processed directly through the optical fiber coating layer, or it can be processed after the coating layer is stripped off. The structure of the high-power, non-melting-point integrated optical fiber oscillator based on the distributed side-pumped optical fiber grating can eliminate the fusion points in the cavity that bear the high cladding power, leaving only the ordinary fusion points outside the cavity, reducing the difficulty of integration, and increasing the output power of the oscillator from the existing single-cavity maximum of 2 or 3 kilowatts to the 10,000-watt level. The integrated non-melting-point oscillator provides high-quality and high-power seeds. The filter module effectively suppresses the Raman nonlinear effect, greatly increases the nonlinear effect threshold of the optical fiber laser, and increases the final output power of the optical fiber laser. The amplification module adopts a unidirectional / bidirectional same-band pumping structure, and can ultimately output tens of thousands of watts of high-power laser.

[0114] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A preparation device for a distributed side-pumped fiber Bragg grating, characterized in that: The preparation device of the distributed side-pumped fiber grating comprises: a rotating fiber fixture, a three-axis translation stage, an LED lighting component, a laser focusing component, a CCD camera, a femtosecond laser, an optical switch and a control component, wherein the three-axis translation stage comprises an x-axis translation stage, a y-axis translation stage and a z-axis translation stage; The rotating fiber clamp is installed on the x-axis translation stage; the rotating fiber clamp is used to clamp the distributed side pumping fiber and drive the distributed side pumping fiber to rotate; the laser focusing component is installed on the z-axis translation stage; the three-axis translation stage is used to drive the distributed side pumping fiber to move along the x-axis direction and the y-axis direction, and drive the laser focusing component to move along the z-axis direction; The LED lighting component is used to emit lighting light, and the lighting light is incident on the distributed side pumping optical fiber, and the outgoing light obtained by the distributed side pumping optical fiber transmitting or reflecting the lighting light is incident on the CCD camera; the CCD camera is used to image the outgoing light to obtain a captured image; The femtosecond laser is used to emit a femtosecond laser; the optical switch and the laser focusing component are sequentially arranged on the output optical path of the femtosecond laser according to the transmission direction of the femtosecond laser; the optical switch is used to selectively shield the femtosecond laser; the laser focusing component is used to direct the femtosecond laser emitted by the optical switch into the distributed side pumping optical fiber; The control component is connected to the rotating fiber clamp, the three-axis translation stage, the LED lighting component, the CCD camera, the femtosecond laser and the optical switch drive; the control component is used to control the LED lighting component and the CCD camera to work before preparation, and control the rotating fiber clamp to work based on the captured image obtained by the CCD camera until the signal fiber in the distributed side pumping fiber is in a preparable position; control the three-axis translation stage to work based on the captured image obtained by the CCD camera until the focus or focal line of the femtosecond laser is in the core of the signal fiber in the distributed side pumping fiber; during preparation, the femtosecond laser, the optical switch and the three-axis translation stage are controlled to work, and the signal fiber is written until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber; wherein the preparable position is a position where the signal fiber is not blocked by the pump fiber in the distributed side pumping fiber and the signal fiber can be written; the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value.

2. The manufacturing device of distributed side-pumped fiber Bragg grating according to claim 1, characterized in that: When the preparation device for the distributed side-pumped fiber grating is prepared based on the direct writing method, the laser focusing component includes: an oil immersion objective lens; When the distributed side-pumped fiber grating preparation device is prepared based on the fiber mask method, the laser focusing component includes: a cylindrical lens and a phase mask, which are sequentially arranged on the output light path of the femtosecond laser according to the transmission direction of the femtosecond laser.

3. The manufacturing device of distributed side-pumped fiber Bragg grating according to claim 2, characterized in that: When the laser focusing component includes a cylindrical lens and a phase mask, the LED lighting component is a first LED lighting assembly; the first LED lighting assembly is used to emit lighting light; the laser focusing component is arranged on the output light path of the first LED lighting assembly, the laser focusing component is used to incident the lighting light onto the distributed side pumping optical fiber, and incident the reflected light obtained by the distributed side pumping optical fiber reflecting the lighting light onto the CCD camera; the CCD camera is used to image the reflected light to obtain a captured image; When the laser focusing component includes an oil immersion objective lens, the LED lighting component is a second LED lighting assembly; the second LED lighting assembly is used to emit illumination light; the laser focusing component is used to direct the transmitted light after the illumination light passes through the distributed side-pumped optical fiber to be incident on the CCD camera; the CCD camera is used to image the transmitted light to obtain a captured image.

4. The manufacturing device of distributed side-pumped fiber Bragg grating according to claim 3, characterized in that: The manufacturing device of the distributed side-pumped fiber grating further includes: an optical attenuator, a reflector, a first dichroic mirror and a second dichroic mirror; The optical attenuator, the reflector and the first dichroic mirror are all located between the optical switch and the laser focusing component, and the optical attenuator, the reflector and the first dichroic mirror are sequentially arranged on the outgoing optical path of the femtosecond laser according to the transmission direction of the femtosecond laser; When the LED lighting component is a first LED lighting assembly, the first dichroic mirror and the second dichroic mirror are both located between the first LED lighting assembly and the laser focusing component, and the second dichroic mirror and the first dichroic mirror are sequentially arranged on an exit light path of the first LED lighting assembly according to a transmission direction of the illumination light; When the LED lighting component is a second LED lighting assembly, the first dichroic mirror and the second dichroic mirror are both located between the laser focusing component and the CCD camera, and the first dichroic mirror and the second dichroic mirror are sequentially arranged according to the transmission direction of the transmitted light after the illumination light passes through the distributed side pumping optical fiber; The first dichroic mirror is used to reflect the femtosecond laser to the laser focusing component, transmit the illumination light emitted by the first LED lighting component to the laser focusing component, transmit the reflected light of the illumination light emitted by the first LED lighting component to the second dichroic mirror, and transmit the transmitted light of the illumination light emitted by the second LED lighting component to the second dichroic mirror; the second dichroic mirror is used to reflect the illumination light emitted by the first LED lighting component to the first dichroic mirror, transmit the reflected light of the illumination light emitted by the first LED lighting component to the CCD camera, and transmit the transmitted light of the illumination light emitted by the second LED lighting component to the CCD camera.

5. The manufacturing device of distributed side-pumped fiber Bragg grating according to claim 1, characterized in that: The distributed side-pumped fiber grating preparation device further includes: a y-axis scanning galvanometer; The y-axis scanning galvanometer is located between the optical switch and the laser focusing component, and the y-axis scanning galvanometer is set on the output light path of the femtosecond laser. The control component is connected to the y-axis scanning galvanometer drive; the y-axis scanning galvanometer is used to make the femtosecond laser incident on different positions of the signal fiber in the y-axis direction.

6. A method for preparing a distributed side-pumped fiber Bragg grating, applied to the preparation device for the distributed side-pumped fiber Bragg grating according to any one of claims 1 to 5, characterized in that: The preparation method of the distributed side-pumped fiber grating comprises: Control the operation of LED lighting components and CCD cameras; Acquire a captured image obtained by a CCD camera, and determine whether the signal fiber in the distributed side pumping optical fiber is in a preparable position based on the captured image; determine whether the focus or focal line of the femtosecond laser is located at the core position of the signal fiber in the distributed side pumping optical fiber based on the captured image; the preparable position is a position where the signal fiber is not blocked by the pump fiber in the distributed side pumping optical fiber and the signal fiber can be written; If not, the rotating fiber fixture is controlled to work, driving the distributed side pumping fiber to rotate, the three-axis translation stage is controlled to work, driving the distributed side pumping fiber to move, and the process returns to the step of "obtaining the captured image obtained by the CCD camera"; If so, the LED lighting component and the CCD camera are controlled to stop working, and the femtosecond laser, the optical switch and the three-axis translation stage are controlled to work to write the signal fiber until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber; the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value.

7. The method for preparing a distributed side-pumped fiber Bragg grating according to claim 6, characterized in that: Controlling the femtosecond laser, the optical switch and the three-axis translation stage to write the signal fiber until a first reflectivity grating is formed at the first end of the signal fiber and a second reflectivity grating is formed at the second end of the signal fiber, specifically comprising: Control the operation of femtosecond laser; The optical switch is controlled to not allow the femtosecond laser to pass through, and the three-axis translation stage is controlled to work, so as to drive the distributed side pumping optical fiber to move along the x-axis direction, so that the femtosecond laser can be incident on the grating surface to be written of the signal fiber; the grating surface to be written is one of the first reflectivity grating and the second reflectivity grating; Control the optical switch to allow the femtosecond laser to pass through, control the three-axis translation stage to work, drive the distributed side pumping optical fiber to move along the y-axis and z-axis directions, and write on the grating surface to be written on the signal fiber; Determining whether all grating surfaces of the first reflectivity grating and the second reflectivity grating have been written; If yes, the writing is stopped, and at this time, a first reflectivity grating is formed at the first end of the signal fiber, and a second reflectivity grating is formed at the second end of the signal fiber; If not, one of the unwritten grating surfaces of the first reflectivity grating and the second reflectivity grating is selected as the grating surface to be written in the next iteration, and the process returns to the step of "controlling the optical switch to not allow the femtosecond laser to pass through".

8. A distributed side-pumped fiber Bragg grating, prepared by the preparation method of the distributed side-pumped fiber Bragg grating according to any one of claims 6 to 7 based on the preparation device of the distributed side-pumped fiber Bragg grating according to any one of claims 1 to 5, characterized in that: The distributed side-pumped fiber grating comprises: an outer cladding, a signal fiber and at least one pump fiber, the signal fiber and the pump fiber are attached to each other, and the outer cladding covers the signal fiber and the pump fiber; The first end of the signal fiber is engraved with a first reflectivity grating, and the second end of the signal fiber is engraved with a second reflectivity grating; the reflectivity of the first reflectivity grating is greater than a first preset value, the reflectivity of the second reflectivity grating is less than a second preset value, and the first preset value is greater than the second preset value.

9. A fiber laser, characterized in that: The fiber laser comprises: an integrated oscillator module, a filter module and an amplification module; The integrated oscillator module comprises a first pump laser and an oscillator, the oscillator adopts the distributed side-pumped fiber grating as claimed in claim 8, and the first pump laser is connected to the pump fiber in the distributed side-pumped fiber grating; The input end of the filter module is connected to the output end of the integrated oscillator module; the filter module is used to filter the laser output by the integrated oscillator module to obtain filtered laser; The input end of the amplifying module is connected to the output end of the filtering module; the amplifying module is used to amplify the filtered laser output by the filtering module to obtain the amplified laser.

10. The optical fiber laser according to claim 9, characterized in that: The filter module includes a tilted grating and a cladding light filter connected in sequence; the amplification module includes a second pump laser and a distributed side pump optical fiber, and the second pump laser is connected to the pump fiber in the distributed side pump optical fiber.

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