Layer pumping grating preparation system based on rotary etching process

Abstract

The invention relates to a preparation system of a layer pumping grating based on a rotary etching process. The preparation system comprises a first linear electric displacement table, a second linear electric displacement table and a third linear electric displacement table. The first linear electric displacement table is used for controlling a cylindrical lens and a phase mask to move in the Z-axis direction. The second linear electric displacement table is used for controlling the cladding pumping optical fiber to move in the Y-axis direction; the electric rotating clamp is used for controlling the cladding pumping optical fiber to rotate around the Y axis; and the controller is used for controlling the first linear electric displacement table and the electric rotating clamp to complete etching of one refractive index modulation area, controlling the second linear electric displacement table to translate the cladding pumping optical fiber, and continuously controlling the first linear electric displacement table and the electric rotating clamp to complete etching of the next refractive index modulation area after translation. And the process is repeatedly executed until etching of all the refractive index modulation regions is completed, so that effective expansion of the cladding gate region area can be realized while core region attributes can be perfectly reserved.

Description

Technical Field

[0001] The invention relates to the field of laser technology, and in particular to a preparation system of a layer pumped grating based on a spin engraving process. Background Art

[0002] Cladding pumping technology has unprecedentedly improved the output power of fiber lasers. In fiber lasers, the gain medium is the laser rare earth ions doped in the fiber core. The laser signal within the gain spectrum of the rare earth ions will be guided in the fiber core and continuously absorb the pump light bound in the cladding. Therefore, cladding pumping technology successfully realizes the conversion of low-quality cladding pump light into core signal light with high beam quality.

[0003] However, as the demand for laser output power continues to rise, the pump power required by the system is also increasing accordingly. At present, people can provide sufficient pump light injection, but limited by the pump absorption coefficient of the gain fiber, the fiber cannot complete sufficient pump absorption conversion, which ultimately leads to excessive pump residue and a series of safety issues. In order to achieve higher pump absorption, a larger pump absorption coefficient and a longer fiber length are required. However, limited by the photon darkening effect, the rare earth ion doping concentration of the gain fiber cannot be effectively improved, and the excessive absorption coefficient will cause the gain fiber near the pump end to overheat. Therefore, long-distance gain fibers (>20m) with low absorption coefficients are usually used to achieve stronger pump absorption. However, the very long gain fiber length not only directly leads to an increase in system cost, but also leads to obvious fiber nonlinear effects. In summary, how to achieve higher pump absorption conversion efficiency at a constant gain fiber length is of great significance.

[0004] The grating preparation process based on femtosecond light source can overcome the shortcomings of traditional ultraviolet light sources, and the preparation of grating devices is no longer limited by the size and photosensitivity of optical fibers. With the continuous development and maturity of femtosecond lasers, people can use femtosecond light sources to etch cladding pump reflection gratings CPG (Cladding Pump Grating, CPG) in large-mode field double / triple-cladding optical fibers. The grating can effectively return the residual pump light in the cladding to the gain fiber to achieve effective secondary absorption extraction. The implantation of this device can effectively reduce the required gain fiber length under the same pump injection situation, directly reduce the cost of the gain fiber, and weaken the nonlinear effect of the system, and finally break through the output upper limit of the existing laser system. However, the existing cladding grating etching process will cause additional damage and insertion loss in the core area, making this technology only suitable for low-power optical fiber sensing fields, which seriously limits the application and promotion of this technology in higher power. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a system for preparing a layer-pumped grating based on a spin-etching process, which solves the technical problem in the prior art of additional damage to the core region caused by the modified region simultaneously covering the core.

[0007] (II) Technical solution

[0008] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0009] In a first aspect, an embodiment of the present invention provides a preparation system of a layer pump grating based on a spin-engraving process, the preparation system comprising: a cladding pump grating comprising a plurality of periodic refractive index modulation regions, and each refractive index modified region does not cover a core region of a cladding pump fiber; the preparation system comprises: a first linear electric translation stage, a cylindrical lens and a phase mask are arranged on the first linear electric translation stage, and the first linear electric translation stage is arranged on one side of the cladding pump fiber, and the cylindrical lens is arranged on a side of the first linear electric translation stage away from the cladding pump fiber, and the phase mask is arranged on a side of the first linear electric translation stage close to the cladding pump fiber, and the first linear electric translation stage is used to control the movement of the cylindrical lens and the phase mask in the Z-axis direction; a second linear electric translation stage, A second linear electric translation stage is arranged at the other side of the cladding pump fiber, and the second linear electric translation stage is used to control the movement of the cladding pump fiber in the Y-axis direction; an electric rotary clamp is used to clamp the cladding pump fiber and control the cladding pump fiber to rotate around the Y-axis; a controller is electrically connected to the first linear electric translation stage, the second linear electric translation stage and the electric rotary clamp respectively, and the controller is used to control the first linear electric translation stage and the electric rotary clamp to complete the etching of a refractive index modulation zone, and control the second linear electric translation stage to translate the cladding pump fiber, and after the translation, continue to control the first linear electric translation stage and the electric rotary clamp to complete the etching of the next refractive index modulation zone, and repeat the above process until the etching of all refractive index modulation zones is completed.

[0010] In a possible embodiment, the cross-section of each refractive index modulation region is annular, and the inner ring of the annular region does not overlap with the core region.

[0011] In a possible embodiment, the controller is used to control the electric rotating fixture to rotate at least one circle when the femtosecond beam is focused in the optical fiber cladding after passing through the cylindrical lens and the phase mask, and after the rotation is completed, control the first linear electric translation stage to move to adjust the distance between the focusing spot and the core of the cladding pump optical fiber, and after the adjustment is completed, continue to control the electric rotating fixture to rotate at least one circle, and repeat the above process until the etching of a refractive index modulation area is completed. Wherein, at least one circle includes one or more circles.

[0012] In a possible embodiment, the calculation expression of the period of the phase mask is:

[0013]

[0014] Where Λ represents the period of the phase mask; λ B represents the Bragg wavelength of the cladding pump grating; n represents the order of the diffracted beam formed after passing through the phase mask; n eff Represents the effective refractive index of the cladding mode of the optical fiber.

[0015] In one possible embodiment, the cladding pumped fiber includes a gain fiber.

[0016] In a second aspect, an embodiment of the present invention provides a high-power fiber resonant cavity, comprising a gain fiber, and the gain fiber is the gain fiber described in the first aspect.

[0017] In a third aspect, an embodiment of the present invention provides a high-power optical fiber amplifier, comprising a gain optical fiber, and the gain optical fiber is the gain optical fiber described in the first aspect.

[0018] (III) Beneficial effects

[0019] The beneficial effects of the present invention are:

[0020] The embodiment of the present application provides a preparation system for a layer-pumped grating based on a spin-etching process. Compared with the existing transmission-type grating process, the cladding-pumped grating prepared by the preparation system of the present application can perfectly retain the core region properties while achieving effective expansion of the cladding grating area.

[0021] In order to make the above-mentioned objectives, features and advantages to be achieved by the embodiments of the present application more obvious and understandable, the following specifically cites preferred embodiments and describes them in detail with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 A schematic diagram of the operation of a cladding pumped optical fiber is shown;

[0024] Figure 2 A schematic diagram of the structure of a conventional lower cladding pump grating is shown;

[0025] Figure 3A cross-sectional view of a conventional engraved grid system provided in an embodiment of the present application is shown;

[0026] Figure 4 The cross-sectional schematic diagram of CPG prepared based on the traditional process provided in the embodiment of the present application is shown;

[0027] Figure 5 A schematic diagram of a system for preparing a layer pumped grating based on a spin etching process provided in an embodiment of the present application is shown;

[0028] Figure 6 A cross-sectional view of a preparation system provided in an embodiment of the present application is shown;

[0029] Figure 7 A schematic cross-sectional view of a CPG prepared by a femtosecond spin etching process according to an embodiment of the present application is shown;

[0030] Figure 8 A schematic diagram of a high-power optical fiber resonant cavity provided in an embodiment of the present application is shown;

[0031] Fig. 9 A schematic diagram of a high-power optical fiber amplifier provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0032] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0033] See also Figure 1 , Figure 1 FIG. 2 shows a schematic diagram of the operation of a cladding pumped optical fiber. Figure 1 As shown, a large-angle pump light (11) is injected into the cladding of the optical fiber (12), and the type and injection method of the pump light are not limited (injection through a pump signal combiner or injection through end-face space coupling are both considered in this solution). In the optical fiber channel, the pump light is continuously absorbed in the cladding and converted into high-quality core signal light (13). Due to the limitations of the absorption capacity and length of the optical fiber, some residual pump light (14) is output from another port and requires additional stripping process treatment. The residual pump not only directly causes energy waste but also increases the complexity of the system process.

[0034] And, continue to see Figure 2 , Figure 2 FIG. 1 shows a schematic diagram of the structure of a conventional lower cladding pump grating. Figure 2 As shown, the optical fiber is composed of a core region (15), a cladding region (16) and a coating region (17), and the grating is realized by a periodic refractive index modified surface (18).

[0035] Continue to see Figure 3 , Figure 3 FIG. 2 shows a cross-sectional view of a conventional grid system provided by an embodiment of the present application. Figure 3 As shown, after collimation and beam expansion, the femtosecond beam (32) sequentially passes through the cylindrical lens (31) and the phase mask (33) and is focused in the fiber cladding. When a conventional weak focusing cylindrical lens (i.e., a long focal cylindrical lens) is used, the focused light spot (34) is elongated in the Z direction. At this time, the optical fiber is controlled to translate in the X direction through the existing electric translation stage (35), and finally a nearly rectangular distribution of the modified surface is achieved on the cross section of the optical fiber. For details, see Figure 4 ,and Figure 4 The cross-sectional schematic diagram of a CPG prepared based on a traditional process provided by an embodiment of the present application is shown. Although the etching method can quickly achieve large-area scanning coverage, since the modified surface also covers the fiber core, it will cause additional damage to the core area, thereby introducing additional signal light loss, and this loss is acceptable for low-power fiber sensing applications, but it is not suitable for kilowatt or even 10,000-watt high-fiber laser scenarios.

[0036] Based on this, an embodiment of the present application provides a preparation system for a layer-pumped grating based on a spin etching process. Compared with the existing transmission grating process, the cladding pumped grating prepared by the preparation system of the present application can perfectly retain the core region properties while achieving effective expansion of the cladding gate region area.

[0037] In order to better understand the above technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0038] First embodiment

[0039] Continue to see Figure 5 , Figure 5 FIG. 1 is a schematic diagram of a system for preparing a layer pumped grating based on a spin etching process provided in an embodiment of the present application. Figure 5 As shown, the cladding pump grating includes a plurality of periodic refractive index modulation regions (or grating modulation regions), and each refractive index modulation region does not cover the core region of the cladding pump optical fiber; the preparation system includes:

[0040] A first linear electric translation stage (38), on which a cylindrical lens (31) and a phase mask (33) are arranged, and the first linear electric translation stage (38) is arranged on one side of the cladding pump optical fiber (40), and the cylindrical lens (31) is arranged on a side of the first linear electric translation stage (38) away from the cladding pump optical fiber (40), and the phase mask (33) is arranged on a side of the first linear electric translation stage (38) close to the cladding pump optical fiber (40), and the first linear electric translation stage (38) is used to control the movement of the cylindrical lens (31) and the phase mask (33) in the Z-axis direction;

[0041] A second linear electric displacement stage (37), which is arranged on the other side of the cladding pump optical fiber (40), and is used to control the movement of the cladding pump optical fiber (40) in the Y-axis direction;

[0042] An electric rotating fixture (39), the electric rotating fixture (39) is used to clamp the cladding pump optical fiber (40) and control the cladding pump optical fiber (40) to rotate around the Y axis;

[0043] A controller (not shown) is electrically connected to the first linear electric translation stage (38), the second linear electric translation stage (37) and the electric rotating fixture (39) respectively. The controller is used to control the first linear electric translation stage (38) and the electric rotating fixture (39) to complete the etching of one refractive index modified zone, and control the second linear electric translation stage to translate the cladding pump optical fiber (40), and after the translation, continue to control the first linear electric translation stage (38) and the electric rotating fixture (39) to complete the etching of the next modified zone, and repeat the above process until the etching of all periodic refractive index modified zones is completed. That is to say, the first linear electric translation stage (38) is used to control the depth R of the focused light spot, and the electric rotating clamp (39) is used to rotate the optical fiber, so that the first linear electric translation stage (38) and the electric rotating clamp (39) are combined to realize the etching of a modified surface, and the second linear electric translation stage (37) is used to translate the optical fiber, and the subsequent combination of the first linear electric translation stage (38) and the electric rotating clamp (39) can realize the replication of multiple periodic modified surfaces.

[0044] It should be understood that the etching process of a refractive index modulation area in the grating can be set according to actual needs, and the embodiments of the present application are not limited to this.

[0045] Alternatively, if Figure 5 and Figure 6As shown, when the femtosecond beam (32) is focused in the optical fiber cladding after passing through the cylindrical lens (31) and the phase mask (33), the distance R between the focusing spot (36) and the core of the cladding pump optical fiber (40) is controlled by the controller to rotate the electric rotating fixture (39) 360 degrees, so that a single-turn modified zone can be realized, and after the rotation is completed, the first linear electric translation stage is controlled to move, thereby changing the position of the focusing spot (36), and then adjusting the distance R (for example, gradually reducing R, etc., that is, achieving the control of the distance R). After the adjustment is completed, the electric rotating fixture is continued to be controlled, and the above process is repeated until the etching of a refractive index modified zone is completed. Among them, the specific number of rotations is determined according to the process parameters.

[0046] Further, based on the above steps, a cross section of a refractive index modulation region is generated as follows: Figure 7 As shown, the cross-section of each refractive index modulation zone is annular, and the inner ring of the annular zone does not overlap with the core zone.

[0047] That is to say, the cladding modified surface (29) achieved by the rotary etching process of the present application is annular, and compared with the traditional process, the area of ​​the modified area accounts for a larger proportion, and the core area is well protected.

[0048] Further, see Figure 5 ,,After the incident femtosecond light beam (32) is collimated and expanded, it passes through the cylindrical lens (31) and the phase mask (33) in sequence, and then diffracts below the phase mask (33), wherein the nth order diffracted light beam overlaps with the -nth order diffracted light beam, and interference fringes (42) are generated in the overlapping area (41). Also, the focusing position of the interference fringes (42) in the optical fiber can be achieved by changing the relative position of the focusing cylindrical lens (31) and the optical fiber through the first linear electric displacement stage (38), and after the etching of the local grating area is completed, the etching expansion of the entire grating area is achieved through the second linear electric displacement stage (37) of the Y axis. It can be known from the grating equation that the period Λ of the phase mask (53), the order n of the diffracted light beam formed after the phase mask, and the Bragg wavelength λ of the cladding pump grating B The following quantitative relationship is followed:

[0049]

[0050] Where Λ represents the period of the phase mask; λ B represents the Bragg wavelength of the cladding pump grating; n represents the order of the diffracted beam formed after passing through the phase mask; n eff Represents the effective refractive index of the cladding mode of the gain fiber.

[0051] Based on the above formula, the first-order diffracted beam is usually used, and the pump wavelength λ is given BIn this case, the required mask period can be calculated.

[0052] It should be noted here that the parameters involved in the preparation system can be set according to actual needs, and the embodiments of the present application are not limited to this.

[0053] For example, the pump wavelength λ B The specific wavelength, the rotation speed of the gain optical fiber (54), and the way of changing the R distance (for example, gradually increasing and gradually decreasing) can all be set according to actual needs, and the embodiments of the present application are not limited thereto.

[0054] It should be understood that the above-mentioned system for preparing layer pumped gratings based on spin etching process is only exemplary, and those skilled in the art can make various modifications according to the above-mentioned method, and the modified schemes also fall within the protection scope of the present application.

[0055] Second embodiment

[0056] It should be noted here that the cladding pumped optical fiber prepared by the first embodiment includes a gain optical fiber (85).

[0057] Continue to see Figure 8 , Figure 8 FIG. 1 is a schematic diagram of a high-power optical fiber resonant cavity provided in an embodiment of the present application. Figure 8 As shown, the resonant cavity includes a gain fiber (85) and a high-reflection grating (84) and a low-reflection grating (86) on both sides. A pump source (88) connected to a pump signal combiner (87) and a cladding pump grating (82) are distributed at both ends of the resonant cavity, and finally the laser output is realized through an output head (89) on a passive optical fiber (81). Among them, each device is connected by a corresponding connection coupling means, and the node (83) can be a melting point, which also includes a spatial coupling situation. The proposed high-efficiency resonant cavity has two main features: CPG is used to recover the residual cladding pump and reflect it to the resonant cavity; the reflection direction of the CPG is opposite to the emission direction of the pump source. Figure 8 Only the reverse pumping case is given, and the CPG is located outside the resonant cavity, but for other simple deformation cases, any solution that meets the above two main features should be within the scope of protection of this patent.

[0058] It should be noted here that the relevant preparation contents of CPG (82) can be found in the relevant description of the first embodiment, and will not be repeated here.

[0059] It should be understood that the above-mentioned high-power optical fiber resonant cavity is only exemplary, and those skilled in the art may make various modifications according to the above-mentioned method, and the modified scheme also falls within the protection scope of the present application.

[0060] Third embodiment

[0061] It should be noted here that the cladding pumped optical fiber prepared by the first embodiment includes a gain optical fiber (93).

[0062] Continue to see Fig. 9 , Fig. 9 FIG. 1 is a schematic diagram of a high-power optical fiber amplifier provided in an embodiment of the present application. Fig. 9 As shown, the amplifier system includes a signal source (91) injected at the front stage, a cladding pump grating (92), a gain fiber (93), a pump signal combiner (94) and a pump module (95), and the pump light is injected into the gain fiber (93) through the pump signal combiner (94) so ​​that the signal at the front stage is gain-amplified, and the residual cladding pump returns to the gain fiber (93) again through the cladding pump grating (92) to achieve secondary absorption, and the final amplified signal is output through the output head (96). The main feature of the proposed high-efficiency amplifier is that the residual pump is reused by using the cladding pump grating (92), and the pump injection direction is opposite to the grating reflection direction. Therefore, any deformation method that meets the above two main features still falls within the protection scope of this patent, such as using a forward pumping method and placing the cladding pump grating (92) at the output end of the amplifier at the same time, or using multiple series-connected cladding pump gratings (92).

[0063] It should be noted here that the relevant preparation contents of the cladding pump grating (92) can be found in the relevant description of the first embodiment, and will not be repeated here.

[0064] It should be understood that the above-mentioned high-power fiber amplifier is only exemplary, and those skilled in the art may make various modifications based on the above-mentioned method, and the modified scheme also falls within the protection scope of the present application.

[0065] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] The present invention is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments of the present invention. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions.

[0067] It should be noted that in the claims, any reference numerals placed between brackets shall not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention may be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In the claims enumerating several means, several of these means may be embodied by the same hardware. The use of the words first, second, third, etc., is for convenience of expression only and does not indicate any order. These words may be understood as part of the component name.

[0068] In addition, it should be noted that, in the description of this specification, the description of the terms "one embodiment", "some embodiments", "embodiment", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0069] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments after knowing the basic creative concept. Therefore, the claims should be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0070] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention should also include these modifications and variations.

Claims

1. A system for preparing a layer pumped grating based on a spin etching process, characterized in that: The cladding pump grating includes a plurality of periodic refractive index modulation regions, and none of the plurality of refractive index modulation regions covers the core region of the cladding pump optical fiber; the preparation system includes: A first linear electric translation stage, wherein a cylindrical lens and a phase mask are arranged on the first linear electric translation stage, and the first linear electric translation stage is arranged on one side of the cladding pump fiber, and the cylindrical lens is arranged on a side of the first linear electric translation stage away from the cladding pump fiber, and the phase mask is arranged on a side of the first linear electric translation stage close to the cladding pump fiber, and the first linear electric translation stage is used to control the cylindrical lens and the phase mask to move in the Z-axis direction; A second linear electric translation stage, which is disposed on the other side of the cladding pump fiber and is used to control the movement of the cladding pump fiber in the Y-axis direction; An electric rotating fixture, wherein the electric rotating fixture is used to clamp the cladding pump optical fiber and control the cladding pump optical fiber to rotate around the Y axis; A controller, wherein the controller is electrically connected to the first linear electric translation stage, the second linear electric translation stage and the electric rotation fixture respectively, and the controller is used to control the first linear electric translation stage and the electric rotation fixture to complete the etching of one refractive index modulation zone, and control the second linear electric translation stage to translate the cladding pump optical fiber, and after the translation, continue to control the first linear electric translation stage and the electric rotation fixture to complete the etching of the next refractive index modulator, and repeat the above process until the etching of all the periodic modulation zones is completed.

2. The preparation system according to claim 1, characterized in that: The cross section of each refractive index modulation region is annular, and the inner ring of the annular region does not overlap with the core region.

3. The preparation system according to claim 1 or 2, characterized in that: The controller is used to control the electric rotating fixture to rotate at least one circle when the femtosecond beam is focused in the optical fiber cladding after passing through the cylindrical lens and the phase mask, and to control the first linear electric translation stage to move after the rotation is completed to adjust the distance between the focusing spot and the core of the cladding pump optical fiber. After the adjustment is completed, the electric rotating fixture is continued to be controlled to rotate at least one circle, and the above process is repeated until the etching of one of the annular refractive index modulation zones is completed.

4. The preparation system according to claim 1, characterized in that: The calculation expression of the period of the phase mask is: Wherein, Λ represents the period of the phase mask; λ B represents the Bragg wavelength of the cladding pump grating; n represents the order of the diffracted beam formed after passing through the phase mask; n eff represents the effective refractive index of the cladding mode of the optical fiber.

5. The preparation system according to claim 1, characterized in that: The cladding pumped optical fiber includes a gain optical fiber.

6. A high-power optical fiber resonant cavity, characterized in that: The invention comprises a gain optical fiber, and the gain optical fiber is the gain optical fiber according to claim 5.

7. A high power optical fiber amplifier, characterized in that: The invention comprises a gain optical fiber, and the gain optical fiber is the gain optical fiber according to claim 5.

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