A fiber laser amplifier based on hierarchical heat dissipation

Abstract

The present invention discloses a fiber laser amplifier based on hierarchical heat dissipation, which relates to the field of high-brightness fiber lasers. The fiber laser amplifier comprises: a fiber laser seed source, a pigtail semiconductor pump source, a first-stage fiber oscillator component, and a second-stage fiber laser amplifier component. The semiconductor pump light and the laser seed light are combined and injected into the first-stage fiber oscillator component, and the low-brightness semiconductor pump light is converted into a higher-brightness transition laser through a laser oscillation process with a lower quantum loss. The second-stage fiber laser amplifier component converts the transition laser into the laser seed light and outputs a high-brightness main laser. Based on the configuration of the pigtail semiconductor pump source, the present invention effectively distributes the heat generated by the quantum loss to two-stage components for heat dissipation, while also reducing the heat concentration on the single-stage component and improving the reliability of the amplifier.

Description

Technical Field

[0001] The present invention relates to the field of high-brightness fiber lasers, and in particular to a fiber laser amplifier based on graded heat dissipation. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Fiber lasers, with their excellent beam quality, compact structure, and high efficiency, are widely used in industrial, medical, and military applications. However, conventional fiber lasers / amplifiers utilize semiconductor pump sources, where the pump wavelength differs significantly from the laser wavelength. This introduces significant quantum loss heat generation during the generation and amplification of high-power fiber lasers. In particular, with the industry's increasing demand for fiber laser power over the past decade, thermal effects in optical fibers, such as thermal lensing and mode instability, have become a major factor limiting the high-brightness output of fiber lasers.

[0004] To reduce the impact of thermal effects on beam quality, the main approach currently used is to adjust the absorption coefficient of the gain fiber or the pump light wavelength to avoid the excessive concentration of heat generation caused by strong particle inversion, thereby achieving the goal of smoothing the distribution of quantum loss heat generation over the entire length of the gain fiber. However, the gain fiber used in this solution is too long, which can easily trigger strong nonlinear effects in the fiber, such as stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and cross-phase modulation (XPM), leading to new reliability risks for the laser system. Summary of the Invention

[0005] The purpose of the present invention is to address the problems existing in the prior art and provide a fiber laser amplifier based on graded heat dissipation. The energy conversion process of the amplifier is divided into two stages on the same laser amplification link. The semiconductor pump light energy is first converted to the transition laser wavelength, and then the transition laser energy is converted to the main laser. Ultimately, the quantum loss heat in the original laser amplification process is released in two stages and heat is dissipated separately, thereby reducing the thermal effect of the main laser amplification process. At the same time, the gain fiber used in this solution adopts a multi-cladding structure. The transition laser and the main laser are coaxially amplified in different areas on the cross section of the gain fiber, and the structure is simpler and more compact, thereby solving the above-mentioned problems.

[0006] The technical solutions of the present invention are as follows:

[0007] A fiber laser amplifier based on graded heat dissipation can reduce the thermal effects of the main laser amplification process by releasing the quantum loss heat during the laser amplification process in two stages and dissipating the heat separately, thereby achieving high-brightness amplification of the fiber laser. Similar to conventional amplifiers, this amplifier only requires the injection of seed laser and semiconductor pump light, which passes through the seed laser in one direction and is amplified to the required power. Specifically, it includes:

[0008] A fiber laser seed source, which is used to generate laser seed light with high beam quality and the same central wavelength as the main laser;

[0009] A pigtail semiconductor pump source, wherein the semiconductor pump light generated by the pigtail semiconductor pump source and the laser seed light are combined through a fiber combiner;

[0010] A first-stage fiber oscillator component, wherein the semiconductor pump light and the laser seed light are combined and injected into the first-stage fiber oscillator component, and the low-brightness semiconductor pump light is used to generate a higher-brightness transition laser in the fiber core and inner cladding through a laser oscillation process with a low quantum loss, and the laser seed light power is not significantly amplified in this process;

[0011] A two-stage fiber laser amplifier component converts transition laser light into laser seed light and outputs high-brightness main laser light.

[0012] Furthermore, the wavelength of the transition laser is between the wavelength of the semiconductor pump light and the wavelength of the main laser.

[0013] Furthermore, the first-stage fiber oscillator assembly includes:

[0014] High reflection fiber Bragg grating, first-order gain fiber, low reflection fiber Bragg grating.

[0015] Furthermore, the secondary fiber laser amplifier assembly comprises:

[0016] Secondary gain fiber and cladding pump stripper.

[0017] Furthermore, the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating both adopt multi-clad passive fibers matched with the first-order gain optical fiber, and the two constitute a fiber Bragg grating pair.

[0018] Furthermore, the reflectivity of the high-reflection fiber Bragg grating is greater than 90%, and the low-reflection fiber Bragg grating is partially reflective;

[0019] The central wavelength of the fiber Bragg grating pair corresponds to the transition laser wavelength, which is longer than the wavelength of the semiconductor pump light and shorter than the wavelength of the main laser.

[0020] Furthermore, the primary gain fiber and the secondary gain fiber are both multi-clad fibers, and the transition laser and the main laser are gained and transmitted through different fiber cross-sectional areas of the two gain fibers respectively. The processes are relatively independent, and the two-stage components dissipate heat separately.

[0021] Furthermore, the primary gain fiber is a multi-cladding structure with 4 or more layers, specifically comprising:

[0022] a primary gain optical fiber core having no gain;

[0023] At least two inner cladding layers, the inner cladding layers being coaxial with the primary gain fiber core, and comprising: a gain region composed of doped elements having a gain effect and a confinement region for confining the transition laser to transmit within the gain region; the gain region is used for gain amplification and stable transmission of the transition laser;

[0024] The outer cladding of the first-order gain fiber is used to confine the semiconductor pump light;

[0025] The primary gain optical fiber protective layer is located at the outermost layer and plays a protective role.

[0026] Furthermore, the secondary gain optical fiber is a multi-cladding structure with 4 or more layers, specifically comprising:

[0027] A secondary gain fiber core, wherein the secondary gain fiber core is doped with an element having a gain effect to form a gain region, and the diameter, refractive index, and numerical aperture of the secondary gain fiber core are consistent with those of the primary gain fiber core;

[0028] At least two inner claddings, said inner claddings being coaxial with the core of the secondary gain fiber and having no gain, comprising: an inner conduction region for conducting semiconductor pump light and transition laser light, and an outer conduction region for conducting only semiconductor pump light; the minimum diameter and numerical aperture of each level of inner cladding being greater than or equal to the maximum diameter and numerical aperture of the same level of inner cladding in the primary gain fiber;

[0029] The outer cladding of the secondary gain fiber is used to confine the semiconductor pump light;

[0030] The secondary gain optical fiber protective layer is located at the outermost layer and plays a protective role.

[0031] Furthermore, the primary gain fiber and the secondary gain fiber are non-polarization-maintaining fibers or polarization-maintaining fibers;

[0032] The shape of the inner cladding includes: circular, D-shaped, and polygonal;

[0033] The doping element of the gain region is germanium, phosphorus, cerium, ytterbium, erbium, thulium, holmium or a combination of the above.

[0034] Compared with the existing technology, the beneficial effects of the present invention are:

[0035] 1. A fiber laser amplifier based on graded heat dissipation, based on the pigtail semiconductor pump source configuration, effectively divides the heat generated by quantum loss into two stages of components for heat dissipation, while also reducing the heat concentration on a single-stage component and improving the reliability of the amplifier.

[0036] 2. A fiber laser amplifier based on graded heat dissipation, in which the main laser is amplified only in the secondary fiber laser amplifier component. The quantum loss in this amplification process is smaller than that in existing semiconductor direct-pumped fiber MOPA lasers, effectively reducing the impact of thermal effects during laser amplification and helping to maintain high beam quality output.

[0037] 3. A fiber laser amplifier based on graded heat dissipation, in which the output fiber of the first-stage fiber oscillator assembly is fused with the input fiber of the second-stage fiber laser amplifier assembly. That is, the high-brightness transition laser generated by the first-stage fiber oscillator assembly directly enters the next-stage amplifier, avoiding the brightness degradation caused by pump beam combining. As a result, the gain fiber length is also shortened, reducing the accumulation of fiber nonlinear effects.

[0038] 4. A fiber laser amplifier based on graded heat dissipation. Except for the first-stage fiber oscillator component and the second-stage gain fiber, the remaining components can use either corresponding matching passive fibers or general-purpose fiber components. The design is more flexible and only requires the injection of seed laser and semiconductor pump light with the same wavelength as the main laser. It is comparable to existing fiber laser amplifier solutions, and the system is simpler and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the structure of a fiber laser amplifier based on hierarchical heat dissipation;

[0040] Figure 2 is the cross section of the first-level gain fiber in the embodiment of the present invention;

[0041] Figure 3 : is the cross section of the secondary gain fiber in the embodiment of the present invention.

[0042] Figure 1: Fiber laser seed source, 2: pigtail semiconductor pump source, 3: fiber combiner, 4: first-order fiber oscillator assembly, 41: first-order gain fiber, 42: high-reflection fiber Bragg grating, 43: low-reflection fiber Bragg grating, 5: second-order fiber laser amplifier assembly, 51: second-order gain fiber, 52: cladding pump stripper, 411: first-order gain fiber core, 412: first-order gain fiber first inner cladding, 413: second-order gain fiber second inner cladding, 414: first-order gain fiber outer cladding, 415: first-order gain fiber protective layer, 511: second-order gain fiber core, 512: first-order gain fiber first inner cladding, 513: second-order gain fiber second inner cladding, 514: second-order gain fiber outer cladding, 515: second-order gain fiber protective layer. DETAILED DESCRIPTION

[0043] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0044] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0045] Example 1

[0046] See also Figure 1 , a fiber laser amplifier based on hierarchical heat dissipation, specifically comprising:

[0047] A fiber laser seed source 1, wherein the fiber laser seed source 1 is used to generate laser seed light with high beam quality and the same central wavelength as the main laser;

[0048] A pigtail semiconductor pump source 2, wherein the semiconductor pump light generated by the pigtail semiconductor pump source 2 and the laser seed light are combined through a fiber combiner 3;

[0049] The first-stage fiber oscillator component 4 is configured such that the semiconductor pump light is combined with the laser seed light and injected into the first-stage fiber oscillator component 4, and the low-brightness semiconductor pump light is used to generate a higher-brightness transition laser in the fiber core and inner cladding through a laser oscillation process with a lower quantum loss, and the laser seed light power is not significantly amplified in this process; that is, the laser seed light is combined with the semiconductor pump light via the fiber combiner 3 and injected into the first-stage fiber oscillator component 4;

[0050] A secondary fiber laser amplifier assembly 5, which converts the transition laser light into a laser seed light and outputs a high-brightness main laser light;

[0051] It should be noted that all connections between components are direct fusion splicing of input / output optical fibers.

[0052] In this embodiment, specifically, the wavelength of the transition laser is between the wavelength of the semiconductor pump light and the wavelength of the main laser;

[0053] That is, during the main laser amplification process, the semiconductor pump light is first converted into a transition laser with a wavelength between the semiconductor pump light wavelength and the main laser wavelength through the first-level fiber oscillator component 4, and then converted into a laser seed light through the second-level fiber laser amplifier component 5; the transition laser and the laser seed light are respectively amplified and transmitted through different fiber cross-sectional areas of the gain fiber, and the processes are relatively independent, and the two-level components dissipate heat separately; this process divides the quantum loss heat in the laser amplification process into two stages for release, reducing the influence of the thermal effect of the main laser amplification process, thereby ensuring that the final output laser has good beam quality.

[0054] In this embodiment, specifically, the first-stage fiber oscillator assembly 4 includes:

[0055] The high-reflection fiber Bragg grating 42, the primary gain fiber 41, and the low-reflection fiber Bragg grating 43; that is, the high-reflection fiber Bragg grating 42, the primary gain fiber 41, and the low-reflection fiber Bragg grating 43 constitute a cladding pumped oscillator.

[0056] In this embodiment, specifically, the secondary fiber laser amplifier assembly 5 includes:

[0057] Secondary gain fiber 51 and cladding pump stripper 52.

[0058] In this embodiment, specifically, the high-reflection fiber Bragg grating 42 and the low-reflection fiber Bragg grating 43 are both made of multi-clad passive fibers that match the primary gain fiber 41 , and the two constitute a fiber Bragg grating pair.

[0059] In this embodiment, specifically, the reflectivity of the high-reflection fiber Bragg grating 42 is greater than 90%, and the low-reflection fiber Bragg grating 43 is partially reflective;

[0060] The central wavelength of the fiber Bragg grating pair corresponds to the transition laser wavelength, which is longer than the wavelength of the semiconductor pump light and shorter than the wavelength of the main laser;

[0061] In this embodiment, preferably, the output end optical fiber of the low-reflection fiber Bragg grating 43 is directly fused with the secondary gain optical fiber 51 of the secondary fiber laser amplifier assembly 5;

[0062] The transition laser and the residual semiconductor pump light are respectively transmitted in the inner cladding of the secondary gain fiber 51 and provide energy for the main laser amplification process; the quantum loss heat generation of this process is about half or less than that of the semiconductor direct pumping amplification method of the main laser, thereby ultimately outputting a high-brightness main laser.

[0063] In this embodiment, specifically, the first-level gain fiber 41 and the second-level gain fiber 51 are both multi-clad fibers, and the transition laser and the main laser are respectively gained and transmitted through different fiber cross-sectional areas of the two gain fibers. The processes are relatively independent, and the two-level components dissipate heat separately.

[0064] In this embodiment, specifically, the primary gain fiber 41 is a multi-cladding structure with 4 or more layers, specifically including:

[0065] A primary gain fiber core 411, wherein the primary gain fiber core 411 has no gain and mainly plays a role in transmitting the main laser light; preferably, the diameter of the primary gain fiber core 411 is between 10 μm and 50 μm;

[0066] At least two inner claddings, the inner claddings being coaxial with the primary gain fiber core 411, and comprising: a gain region formed by doping elements having a gain effect, and a confinement region for confining the transition laser to propagate within the gain region; the gain region is used for gain amplification and stable conduction of the transition laser; that is, the inner cladding with a smaller diameter is doped with elements having a gain effect to form the gain region for gain amplification and stable conduction of the transition laser, and the inner cladding with a larger diameter is used to confine the transition laser to propagate within the inner cladding with a smaller diameter; preferably, the gain region is annular and has an outer diameter between 20 μm and 250 μm;

[0067] The primary gain fiber outer cladding 414 is used to confine the semiconductor pump light, that is, to confine the semiconductor pump light to be transmitted within the inner cladding with the largest diameter;

[0068] The primary gain fiber protection layer 415 is located at the outermost layer and plays a protective role.

[0069] In this embodiment, specifically, the secondary gain fiber 51 is a multi-cladding structure with 4 or more layers, specifically including:

[0070] A secondary gain fiber core 511, wherein the secondary gain fiber core 511 is doped with an element having a gain effect to form a gain region, and the diameter, refractive index, and numerical aperture of the secondary gain fiber core 511 are consistent with those of the primary gain fiber core 411; and the passive fibers matched to the two also have the same refractive index distribution parameter requirements;

[0071] At least two inner cladding layers, the inner cladding layers being coaxial with the secondary gain fiber core 511 and having no gain, comprising: an inner conduction region for conducting semiconductor pump light and transition laser light, and an outer conduction region for conducting only semiconductor pump light; that is, the inner cladding layers having a smaller diameter conduct the semiconductor pump light and transition laser light, while the inner cladding layers having a larger diameter conduct only the semiconductor pump light;

[0072] The minimum diameter and numerical aperture of each level of inner cladding are greater than or equal to the maximum diameter and numerical aperture of the same level of inner cladding in the first-level gain fiber 41;

[0073] The secondary gain fiber outer cladding 514 is used to confine the semiconductor pump light;

[0074] The secondary gain fiber protection layer 515 is located at the outermost layer and plays a protective role.

[0075] In this embodiment, specifically, the primary gain fiber 41 and the secondary gain fiber 51 are non-polarization-maintaining fibers or polarization-maintaining fibers;

[0076] The shape of the inner cladding includes: circular, D-shaped, polygonal or other shapes, which are not limited in this embodiment;

[0077] The doping elements of the gain region are germanium (Ge), phosphorus (P), cerium (Ce), ytterbium (Yb), erbium (Er), thulium (Tm), holmium (Ho), or co-doping of the above.

[0078] Specifically, the main laser seed light output by the fiber laser seed source 1 is transmitted unidirectionally in the amplifier, passing through the first-stage fiber oscillator component 4 and the second-stage fiber laser amplifier component 5 in sequence, and is always transmitted in the fiber core of the main optical path; the transition laser generated by the first-stage fiber oscillator component 4 is transmitted in the core and inner cladding of the first-stage fiber oscillator component 4 and the second-stage fiber laser amplifier component 5.

[0079] Example 2

[0080] The second embodiment is a specific example of a fiber laser amplifier based on graded heat dissipation proposed in the first embodiment.

[0081] See also Figure 1-3An erbium-doped fiber laser amplifier based on graded heat dissipation comprises an erbium-doped fiber laser source, a 915nm pigtail semiconductor pump source 2, a (6+1)×1 fiber combiner 3, a first-stage erbium-ytterbium co-doped fiber oscillator component, and a second-stage erbium-doped fiber laser amplifier component.

[0082] The erbium-doped fiber laser source outputs low-power, near-diffraction-limited fiber laser with a central wavelength of 1562nm, and the output fiber is a conventional 1.5μm band single-mode fiber.

[0083] The (6+1)×1 fiber combiner 3 combines the output light of multiple pigtailed semiconductor pump sources 2 with a central wavelength of 915 nm and an erbium-doped fiber laser source into a conventional double-clad optical fiber with parameters of 25 / 300NA0.09.

[0084] The reflectivity of the high-reflection fiber Bragg grating 42 of the first-stage erbium-ytterbium co-doped fiber oscillator assembly is greater than 99%, the reflectivity of the low-reflection fiber Bragg grating 43 is 10%, and the reflection center wavelength is 1535nm. The optical fiber for writing the fiber Bragg grating pair is the matching passive fiber of the first-stage gain fiber 41.

[0085] The structure of the first-order gain fiber 41 is as follows: Figure 2 As shown, the first-level gain fiber 41 adopts a ring-doped structure; in the figure, 411 is the first-level gain fiber core, with a diameter of 25μm, NA0.09, and no erbium and ytterbium elements doped, which mainly plays a role in laser conduction; 412 is the first inner cladding of the first-level gain fiber, with a diameter of 105μm, NA0.22, and is co-doped with erbium and ytterbium, which is the gain region of the fiber (shown by the shadow); 413 is the second inner cladding of the first-level gain fiber, with a diameter of 300μm and NA greater than 0.46, which mainly plays a role in further confining the transition laser and transmitting the semiconductor pump light at the same time; 414 is the outer cladding of the first-level gain fiber, with a refractive index slightly smaller than that of the second inner cladding of the first-level gain fiber, which plays a role in confining the semiconductor pump light; 415 is the protective layer of the first-level gain fiber.

[0086] The output end of the low-reflection fiber Bragg grating 43 is directly fused with the secondary gain fiber 51, which adopts a central doping structure, such as Figure 3 As shown in the figure, 511 is a secondary gain fiber. The secondary gain fiber 51 is erbium-doped, has a diameter of 25μm, and an NA of 0.09, and is the gain region of the fiber (shown in shaded form). 512 is the first inner cladding of the secondary gain fiber, with a diameter of 105μm and an NA of 0.22. 513 is the second inner cladding of the secondary gain fiber, with a diameter of 300μm and an NA greater than 0.46. 514 is the outer cladding of the secondary gain fiber, which serves to confine the semiconductor pump light. 515 is the protective layer of the secondary gain fiber. The output of the secondary gain fiber 51 is fiber-spliced ​​to a 25 / 300NA 0.09 fiber cladding pump stripper 52, which removes all pump light and transition laser light.

[0087] Example 3

[0088] The third embodiment is another specific example of a fiber laser amplifier based on graded heat dissipation proposed in the first embodiment.

[0089] See also Figure 1-3 A thulium-doped fiber laser amplifier based on graded heat dissipation comprises a thulium-doped fiber laser source, a 793nm pigtail semiconductor pump source 2, a (6+1)×1 fiber combiner 3, a first-stage thulium-doped fiber oscillator component and a second-stage thulium-doped fiber laser amplifier component.

[0090] The thulium-doped fiber laser source outputs a low-power, near-diffraction-limited fiber laser with a central wavelength of 2020nm, and the output fiber is a conventional 2μm band single-mode fiber.

[0091] A conventional (6+1)×1 fiber combiner 3 is used to combine the output light from multiple fiber-pigtailed semiconductor pump sources 2 with a central wavelength of 793 nm and a thulium-doped fiber oscillator into a passive multi-clad fiber matched with a first-stage gain fiber 41. The high-reflection fiber Bragg grating 42 of the first-stage thulium-doped fiber oscillator assembly has a reflectivity greater than 99%, while the low-reflection fiber Bragg grating 43 has a reflectivity of approximately 10%. Both reflect at a central wavelength of 1940 nm. The fiber used to write the fiber Bragg grating pair also uses the passive fiber matched to the first-stage gain fiber 41.

[0092] The structure of the first-order gain fiber 41 is as follows: Figure 2 As shown, the first-stage gain fiber 41 adopts a ring-doped structure. In the figure, 411 is the first-stage gain fiber core 411, with a diameter of 25μm and an NA of 0.09. It is undoped with thulium and primarily functions as a laser conductor. 412 is the first inner cladding 412 of the first-stage gain fiber, with a diameter of 105μm and an NA of 0.22. It is primarily doped with rare earth elements that provide gain and represents the gain region of the fiber (shown in shaded form). 413 is the second inner cladding of the first-stage gain fiber, with a diameter of 400μm and an NA greater than 0.46. It primarily serves to further confine the transition laser while also transmitting the semiconductor pump light. 414 is the outer cladding of the first-stage gain fiber, with a refractive index slightly lower than that of the second inner cladding, which serves to confine the semiconductor pump light. 415 is the protective layer of the first-stage gain fiber.

[0093] The output end of the low-reflection fiber Bragg grating 43 is directly fused with the secondary gain fiber 51, which adopts a central doping structure, such as Figure 3As shown in the figure, 511 is a secondary gain fiber. The secondary gain fiber 51 is doped with thulium, has a diameter of 25μm, and an NA of 0.09, and represents the gain region of the fiber (shown in shaded area). 512 is the first inner cladding of the secondary gain fiber, with a diameter of 105μm and an NA of 0.22. 513 is the second inner cladding of the secondary gain fiber, with a diameter of 400μm and an NA greater than 0.46. 514 is the outer cladding of the secondary gain fiber, which serves to confine the semiconductor pump light. 515 is the protective layer of the secondary gain fiber. The output of the secondary gain fiber 51 is fiber-spliced ​​to a conventional 25 / 400NA 0.09 fiber cladding pump stripper 52, which removes all pump light and transition laser light.

[0094] Example 4

[0095] The fourth embodiment is another specific example of a fiber laser amplifier based on graded heat dissipation proposed in the first embodiment.

[0096] See also Figure 1-3 A Raman fiber laser amplifier based on graded heat dissipation includes a Raman fiber laser source, a 976nm pigtail semiconductor pump source 2, a (6+1)×1 fiber combiner 3, a first-stage ytterbium-doped fiber oscillator component, and a second-stage Raman fiber laser amplifier component.

[0097] The Raman fiber laser source outputs low-power, near-diffraction-limited fiber laser with a central wavelength of 1240nm, and the output fiber is a conventional 1μm band single-mode fiber.

[0098] A conventional (6+1)×1 fiber combiner 3 is used to combine the output light from multiple fiber-pigtailed semiconductor pump sources 2 with a central wavelength of 976 nm and an ytterbium-doped fiber oscillator into a passive multi-clad fiber matched with a first-stage gain fiber 41. The first-stage ytterbium-doped fiber oscillator assembly includes a high-reflection fiber Bragg grating (FBG) 42 with a reflectivity greater than 99%, and a low-reflection fiber Bragg grating (FBG) 43 with a reflectivity of approximately 10%. Both reflect at a central wavelength of 1064 nm. The fiber used to write the FBG pair also uses the passive fiber matched to the first-stage gain fiber 41.

[0099] The structure of the first-order gain fiber 41 is as follows: Figure 2As shown, the fiber adopts a ring-doped structure. In the figure, 411 is the first-level gain fiber core 411, with a diameter of 14μm, an NA of 0.08, and no ytterbium doping, which mainly functions as laser conduction; 412 is the first inner cladding 412 of the first-level gain fiber, with a diameter of 62.5μm, an NA of 0.22, and mainly doped with ytterbium, which is the gain region of the fiber (shown in shaded form); 413 is the second inner cladding of the first-level gain fiber, with a diameter of 250μm and an NA greater than 0.46, which mainly serves to further confine the transition laser and simultaneously transmit the semiconductor pump light; 414 is the outer cladding of the first-level gain fiber, with a refractive index slightly lower than that of the second inner cladding, which serves to confine the semiconductor pump light; and 415 is the protective layer of the first-level gain fiber.

[0100] The output end of the low-reflection fiber Bragg grating 43 is directly fused with the secondary gain fiber 51, which adopts a central doping structure, such as Figure 3 As shown. In the figure, 511 is a secondary gain fiber. The secondary gain fiber 51 is doped with phosphorus, has a diameter of 14μm, and an NA of 0.08. It is the gain region of the fiber (shown in shadow); 512 to 514 are all fiber claddings, which are not doped with phosphorus. 512 is the first inner cladding of the secondary gain fiber, with a diameter of 62.5μm and an NA of 0.22; 513 is the second inner cladding of the secondary gain fiber, with a diameter of 250μm and an NA greater than 0.46; 514 is the outer cladding of the secondary gain fiber, which serves to confine the semiconductor pump light; 515 is the protective layer of the secondary gain fiber. The output fiber of the secondary gain fiber 51 is fused with a conventional 14 / 250NA0.08 fiber cladding pump stripper 52 to strip off all pump light and transition laser light.

[0101] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, and all such variations and improvements fall within the scope of protection of the present application.

[0102] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of the description in this section that did not constitute prior art at the time of filing are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A fiber laser amplifier based on hierarchical heat dissipation, characterized in that: include: A fiber laser seed source (1), wherein the fiber laser seed source (1) is used to generate laser seed light with high beam quality and the same central wavelength as the main laser; A pigtail semiconductor pump source (2), wherein the semiconductor pump light generated by the pigtail semiconductor pump source (2) and the laser seed light are combined through a fiber combiner (3); A first-stage fiber oscillator component (4), wherein the semiconductor pump light and the laser seed light are combined and injected into the first-stage fiber oscillator component (4), and the low-brightness semiconductor pump light is used to generate a higher-brightness transition laser in the fiber core and the inner cladding through a laser oscillation process with a lower quantum loss, and the laser seed light power is not significantly amplified in this process; A secondary fiber laser amplifier component (5) converts the transition laser light into laser seed light and outputs a high-brightness main laser light; The wavelength of the transition laser is between the wavelength of the semiconductor pump light and the wavelength of the main laser; The first-stage fiber oscillator assembly (4) comprises: High-reflection fiber Bragg grating (42), first-order gain fiber (41), low-reflection fiber Bragg grating (43); The secondary fiber laser amplifier assembly (5) comprises: A secondary gain fiber (51) and a cladding pump stripper (52); The output end optical fiber of the low-reflection fiber grating (43) is directly fused with the secondary gain optical fiber (51) of the secondary optical fiber laser amplifier component (5).

2. The fiber laser amplifier based on hierarchical heat dissipation according to claim 1, characterized in that: The high-reflection fiber Bragg grating (42) and the low-reflection fiber Bragg grating (43) both adopt multi-clad passive fibers matched with the first-order gain optical fiber (41), and the two form a fiber Bragg grating pair.

3. The fiber laser amplifier based on hierarchical heat dissipation according to claim 2, characterized in that: The reflectivity of the high-reflection fiber Bragg grating (42) is greater than 90%, and the low-reflection fiber Bragg grating (43) is partially reflective; The central wavelength of the fiber Bragg grating pair corresponds to the transition laser wavelength, which is longer than the wavelength of the semiconductor pump light and shorter than the wavelength of the main laser.

4. The fiber laser amplifier based on hierarchical heat dissipation according to claim 1, characterized in that: The first-level gain fiber (41) and the second-level gain fiber (51) are both multi-clad fibers, and the transition laser and the main laser are respectively gained and transmitted through different fiber cross-sectional areas of the two gain fibers, the processes are relatively independent, and the two-level components dissipate heat separately.

5. The fiber laser amplifier based on hierarchical heat dissipation according to claim 4, characterized in that: The primary gain optical fiber (41) is a multi-cladding structure with 4 or more layers, specifically comprising: a first-level gain optical fiber core (411), wherein the first-level gain optical fiber core (411) has no gain; At least two inner cladding layers are coaxial with the primary gain optical fiber core (411), and include: a gain region composed of doped elements having a gain effect and a confinement region for confining the transition laser to transmit within the gain region; the gain region is used for gain amplification and stable transmission of the transition laser; A first-order gain fiber outer cladding (414) for confining semiconductor pump light; A primary gain optical fiber protective layer (415) is located at the outermost layer and plays a protective role.

6. The fiber laser amplifier based on hierarchical heat dissipation according to claim 5, characterized in that: The secondary gain optical fiber (51) is a multi-cladding structure with 4 or more layers, specifically comprising: a secondary gain fiber core (511), wherein the secondary gain fiber core (511) is doped with an element having a gain effect to form a gain region, and the diameter, refractive index and numerical aperture of the secondary gain fiber core (511) are consistent with those of the primary gain fiber core (411); At least two inner claddings, the inner claddings being coaxial with the secondary gain optical fiber core (511), having no gain, and comprising: an inner conduction region for conducting semiconductor pump light and transition laser light, and an outer conduction region for conducting only semiconductor pump light; the minimum diameter and numerical aperture of each level of inner cladding being greater than or equal to the maximum diameter and numerical aperture of the same level of inner cladding in the primary gain optical fiber (41); A secondary gain fiber outer cladding (514) for confining semiconductor pump light; The secondary gain optical fiber protective layer (515) is located at the outermost layer and plays a protective role.

7. The fiber laser amplifier based on hierarchical heat dissipation according to claim 6, characterized in that: The primary gain optical fiber (41) and the secondary gain optical fiber (51) are non-polarization maintaining optical fibers or polarization maintaining optical fibers; The shape of the inner cladding includes: circular, D-shaped, and polygonal; The doping element of the gain region is germanium, phosphorus, cerium, ytterbium, erbium, thulium, holmium or a combination of the above.

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