Double-clad tapered gradient refractive index gain optical fiber

Abstract

The present invention provides a double-clad tapered gradient refractive index gain optical fiber. In the double-clad tapered gradient refractive index gain optical fiber, the refractive index of the core in the first direction is distributed in a gradient manner, so that the double-clad tapered gradient refractive index gain optical fiber has a self-cleaning effect, and solves the problem of mode instability. In addition, the orthographic projection area of ​​the cross section of the core in the first direction gradually decreases, so that the shape of the core is a tapered structure. Compared with a uniform optical fiber of ordinary specifications, the equivalent core diameter of this structure becomes larger, the threshold of nonlinear effects such as stimulated Raman scattering and stimulated Brillouin scattering in the process of high-power laser amplification is increased, the influence of stimulated Raman scattering and stimulated Brillouin scattering on high-power laser transmission in the optical fiber is reduced, the power limitation of the current high-power laser is solved, and the output power of the existing high-power fiber laser is increased.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber technology, and more particularly to a double-clad tapered gradient refractive index gain optical fiber. Background Art

[0002] Due to the special waveguide structure of the optical fiber itself, the fiber laser has the advantages of high efficiency, compact structure, low thermal effect, strong anti-interference ability, etc., and has important applications in laser processing, optical fiber communication and other fields. With the continuous research in recent years, the power, brightness, and application range of fiber lasers have been greatly developed; the practical application in fields such as national defense and industry has also led to an increasing demand for high-power fiber lasers; however, due to the small core diameter of the optical fiber, the further improvement of the power of high-power fiber lasers also faces many challenges.

[0003] The transmission of high-power lasers in micron-sized fiber cores will cause a series of problems such as thermal damage. Although the damage threshold can be reduced and the output power can be effectively increased in a certain stage of development by increasing the fiber core diameter, such as replacing single-mode fiber with multi-mode fiber, as people's requirements for the beam quality of high-power fiber lasers increase, the mode instability problem caused by multi-mode fiber with a larger mode field area is still difficult to solve; at the same time, the nonlinear effects in high-power fiber lasers will also affect the laser output.

[0004] Therefore, there is an urgent need for a gain fiber to solve the power limitation problem of current high-power fiber lasers. Summary of the invention

[0005] In view of this, in order to solve the above problems, the present invention provides a double-clad tapered gradient refractive index gain optical fiber, and the technical solution is as follows:

[0006] The double-clad tapered gradient refractive index gain optical fiber comprises:

[0007] The core, inner cladding, and outer cladding;

[0008] The inner cladding wraps the core; the outer cladding wraps the inner cladding;

[0009] The fiber core includes a first end and a second end; in a first direction, the refractive index of the fiber core is distributed in a gradient manner, and the first direction is a direction from the first end to the second end;

[0010] The orthographic projection area of ​​the cross section of the fiber core in the first direction gradually decreases, and the plane where the cross section of the fiber core is located is perpendicular to the first direction.

[0011] Optionally, in the above double-clad tapered gradient refractive index gain optical fiber, the core is doped with rare earth ions.

[0012] Optionally, in the above double-clad tapered gradient refractive index gain optical fiber, the rare earth ions are ytterbium, erbium or thulium.

[0013] Optionally, in the above double-clad tapered gradient refractive index gain optical fiber, the minimum refractive index of the core is greater than the refractive index of the inner cladding.

[0014] Optionally, in the above double-clad tapered gradient refractive index gain optical fiber, the refractive index of the inner cladding is greater than the refractive index of the outer cladding.

[0015] Optionally, in the above double-clad tapered gradient refractive index gain optical fiber, the core is located at the center of the area surrounded by the inner cladding.

[0016] Optionally, in the above-mentioned double-clad tapered gradient refractive index gain optical fiber, the shape of the cross section of the inner cladding is the same as the shape of the cross section of the outer cladding, which is circular, elliptical or hexagonal;

[0017] Wherein, the plane where the cross section of the inner cladding lies and the plane where the cross section of the outer cladding lies are both perpendicular to the first direction.

[0018] Optionally, in the above double-clad tapered gradient refractive index gain optical fiber, the double-clad tapered gradient refractive index gain optical fiber further includes:

[0019] A coating layer wraps the outer cladding layer.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a double-clad tapered gradient refractive index gain optical fiber, which comprises a core, an inner cladding and an outer cladding; the inner cladding wraps the core; the outer cladding wraps the inner cladding; wherein the core comprises a first end and a second end; in a first direction, the refractive index of the core is distributed in a gradient manner, and the first direction is the direction from the first end to the second end; the orthographic projection area of ​​the cross section of the core in the first direction gradually decreases, and the plane where the cross section of the core is located is perpendicular to the first direction.

[0022] In the double-clad tapered gradient refractive index gain fiber, the refractive index of the core in the first direction is distributed in a gradient manner, so that the double-clad tapered gradient refractive index gain fiber has a self-cleaning effect and solves the problem of mode instability; in addition, the orthographic projection area of ​​the cross section of the core in the first direction gradually decreases, so that the shape of the core is a tapered structure. Compared with a uniform optical fiber of ordinary specifications, this structure has a larger equivalent core diameter, improves the threshold of nonlinear effects such as stimulated Raman scattering and stimulated Brillouin scattering in the process of high-power laser amplification, reduces the influence of stimulated Raman scattering and stimulated Brillouin scattering on high-power laser transmission in the optical fiber, solves the power limitation of the current high-power laser, and improves the output power of the existing high-power fiber laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0024] Figure 1 A schematic structural diagram of a cross-section of a double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention;

[0025] Figure 2 A schematic structural diagram of a core of a double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention;

[0026] Figure 3 A refractive index distribution diagram of a fiber core provided by an embodiment of the present invention;

[0027] Figure 4 A schematic structural diagram of a cross section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention;

[0028] Figure 5 A schematic structural diagram of a cross section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention;

[0029] Figure 6 A schematic structural diagram of a cross section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention;

[0030] Figure 7 A schematic structural diagram of a cross section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention;

[0031] Figure 8A schematic structural diagram of a cross section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] refer to Figure 1 , Figure 1 A schematic diagram of the cross-sectional structure of a double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention; Figure 2 , Figure 2 A schematic structural diagram of a core of a double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention.

[0035] The double-clad tapered gradient refractive index gain optical fiber comprises:

[0036] Fiber core 01, inner cladding 02 and outer cladding 03.

[0037] The inner cladding 02 wraps the core 01 ; the outer cladding 03 wraps the inner cladding 02 .

[0038] The fiber core 01 includes a first end 05 and a second end 06 ; in a first direction M, the refractive index of the fiber core 01 is gradiently distributed, and the first direction M is the direction from the first end 05 to the second end 06 .

[0039] The orthographic projection area of ​​the cross section of the fiber core 01 in the first direction M gradually decreases, and the plane where the cross section of the fiber core 01 is located is perpendicular to the first direction M.

[0040] Specifically, Figure 2As shown, the core 01 of the double-clad tapered gradient refractive index gain optical fiber includes a first end 05 and a second end 06, the direction from the first end 05 to the second end 06 is a first direction M, the plane where the cross section of the core 01 is located is perpendicular to the first direction M, the cross section of the core 01 can be circular, and in the first direction M, the orthographic projection area of ​​the cross section of the core 01 gradually decreases, that is, the orthographic projection area of ​​the cross section at the first end 05 is larger than the orthographic projection area of ​​the cross section at the second end 06, and when the cross section of the core 01 is circular, the core 01 forms a cone in the first direction M.

[0041] It should be noted that compared with ordinary uniform optical fibers, this conical structure has a larger equivalent core diameter, which increases the threshold of nonlinear effects such as stimulated Raman scattering and stimulated Brillouin scattering during high-power laser amplification, reduces the influence of stimulated Raman scattering and stimulated Brillouin scattering on high-power laser transmission in optical fibers, solves the power limitation of current high-power lasers, and increases the output power of existing high-power fiber lasers.

[0042] In the first direction M, the refractive index of the core 01 is distributed in a gradient manner, referring to Figure 3 , Figure 3 The refractive index distribution diagram of the fiber core provided by the embodiment of the present invention is as follows: Figure 3 As shown, as the radius of the cross section of the fiber core 01 gradually decreases, the refraction first increases to a maximum preset value and then gradually decreases; that is, from the first end 05 of the fiber core 01 to the second end 06 of the fiber core 01, the refractive index of the fiber core 01 gradually increases, and after increasing to the maximum preset value, the refractive index of the fiber core 01 gradually decreases.

[0043] It should be noted that the refractive index of the core 01 is in a gradient distribution, which makes the double-clad tapered gradient refractive index gain fiber have a self-cleaning effect and solves the problem of mode instability.

[0044] It should also be noted that the refractive index of the core 01 region is gradient distributed, which can support multi-mode transmission. Compared with ordinary single-mode cores, it can improve the efficiency of pump light coupling into the core 01, thereby improving the efficiency of pump light absorption by doped rare earth ions; at the same time, when a multi-mode beam is transmitted in a gain fiber with a gradient refractive index distribution, due to the Kerr effect and inter-mode four-wave mixing, the high-order mode will be converted into a single fundamental mode, and the energy will be irreversibly transferred from the high-order mode to the fundamental mode. After propagating for a certain distance, the multi-mode input beam will be converted into a single-mode fundamental mode output, which solves the problem of reduced output beam quality of high-power fiber lasers caused by unstable output mode.

[0045] The inner cladding 02 wraps the core 01, and the inner cladding 02 is used to transmit the pump light; the outer cladding 03 wraps the inner cladding 02, and the outer cladding 03 is used to constrain the pump light transmitted in the inner cladding 02; since the orthographic projection area of ​​the cross section of the core 01 in the first direction M gradually decreases, the orthographic projection area of ​​the cross section of the inner cladding 02 wrapping the core 01 in the first direction M also gradually decreases, and the orthographic projection area of ​​the cross section of the outer cladding 03 wrapping the inner cladding 02 in the first direction M also gradually decreases. When the cross section is circular, the structure of the gain optical fiber forms a cone as a whole. It should be noted that the cone angle of the formed cone can be controlled by changing the drawing speed and other methods.

[0046] It should be noted that the structure of the inner cladding 02 and the outer cladding 03 can efficiently couple high-power pump light into the gain medium, and high-power and high-efficiency pumping makes high-power amplification possible; and the gain fiber forms a conical structure. Since the equivalent core diameter of the conical core 01 is larger, the conical gain fiber with corresponding parameters can match the large mode field fiber of corresponding size, and can support higher-power laser propagation; and the gain fiber with a conical double-cladding structure can also reduce the requirements for pump brightness, effectively improving the output power of the high-power laser while ensuring high-purity single-mode output, thereby improving the output quality of the light beam.

[0047] Optionally, in another embodiment of the present invention, the double-clad tapered gradient refractive index gain optical fiber further includes:

[0048] The coating layer 04 wraps the outer cladding layer 03 .

[0049] Specifically, Figure 1 As shown, the coating layer 04 wraps the outer cladding layer 03, and the area of ​​the orthographic projection of the cross section of the coating layer 04 in the first direction M gradually decreases; the coating layer 04 is used to protect the double-clad tapered gradient refractive index gain optical fiber.

[0050] Optionally, in another embodiment of the present invention, the fiber core 01 is doped with rare earth ions.

[0051] Optionally, in another embodiment of the present invention, the rare earth ion is ytterbium, erbium or thulium.

[0052] Specifically, the signal light is transmitted in the core 01 of the double-clad tapered gradient refractive index gain optical fiber. When the pump light is transmitted in the inner cladding 02, part of the pump light enters the core 01 for transmission and is effectively absorbed by the doped rare earth ions. The doped rare earth ions may be ytterbium, erbium, thulium, etc., and the doping method may be flat-top doping, parabolic doping, etc.

[0053] It should be noted that the doped rare earth ions include but are not limited to ytterbium, erbium, thulium, etc., and the doping methods include but are not limited to flat-top doping and parabolic doping.

[0054] Optionally, in another embodiment of the present invention, the minimum refractive index of the core 01 is greater than the refractive index of the inner cladding 02 .

[0055] Optionally, in another embodiment of the present invention, the refractive index of the inner cladding 02 is greater than the refractive index of the outer cladding 03 .

[0056] Specifically, the refractive index of the core 01 is gradient distributed and has a relatively large refractive index, and is used to transmit signal light. The minimum refractive index of the core 01 is greater than the refractive index of the inner cladding 02, and the inner cladding 02 is used to transmit pump light. The refractive index of the inner cladding 02 is greater than the refractive index of the outer cladding 03, and the outer cladding 03 is used to limit the overflow of the pump light.

[0057] It should be noted that the inner cladding 02 has a relatively large numerical aperture and can support multiple modes of transmission at the same time, effectively increasing the upper limit of the power of the pump light.

[0058] Optional, reference Figure 4 , Figure 4 A schematic diagram of the cross-section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention; Figure 5 , Figure 5 A schematic diagram of the cross-section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention; Figure 6 , Figure 6 A schematic structural diagram of the cross-section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention; in another embodiment of the present invention, the shape of the cross-section of the inner cladding 02 is the same as the shape of the cross-section of the outer cladding 03, which is circular, elliptical or hexagonal.

[0059] The plane where the cross section of the inner cladding 02 is located and the plane where the cross section of the outer cladding 03 is located are both perpendicular to the first direction M.

[0060] Specifically, the cross-sectional shape of the inner cladding 02 is the same as the cross-sectional shape of the outer cladding 03, such as Figure 4 As shown, the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are both hexagonal. Figure 5 As shown, the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are both elliptical. Figure 6 As shown, the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are both "D" shaped; Figure 7 , Figure 7A schematic diagram of the cross-section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention is shown in FIG. Figure 7 As shown, the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 can also be octagonal; the plane where the cross-sectional plane of the inner cladding 02 and the plane where the cross-sectional plane of the outer cladding 03 are located are both perpendicular to the first direction M.

[0061] It should be noted that the shape of the cross section of the inner cladding 02 and the shape of the cross section of the outer cladding 03 are only the same in shape, and the size is not specifically limited; and the shape of the cross section of the inner cladding 02 and the shape of the cross section of the outer cladding 03 are not specifically limited.

[0062] Optionally, in another embodiment of the present invention, the fiber core 01 is located at the center of the area enclosed by the inner cladding 02 .

[0063] Specifically, Figure 1 As shown, the core 01 may be located at the center of the area enclosed by the inner cladding 02; the core 01 may also not be located at the center of the area enclosed by the inner cladding 02; Figure 8 , Figure 8 A schematic structural diagram of a cross section of another double-clad tapered gradient refractive index gain optical fiber provided in an embodiment of the present invention.

[0064] It should be noted that the position of the core 01 is not specifically limited. For example, if the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are circular, the core 01 is located at the center of the area enclosed by the inner cladding 02; if the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are circular, the core 01 is not located at the center of the area enclosed by the inner cladding 02; if the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are hexagonal, the core 01 is located at the inner cladding 0 2; the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are elliptical, and the core 01 is located at the center of the area enclosed by the inner cladding 02; the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are octagonal, and the core 01 is located at the center of the area enclosed by the inner cladding 02; the cross-sectional shape of the inner cladding 02 and the cross-sectional shape of the outer cladding 03 are "D" shaped, and the core 01 is located at the center of the area enclosed by the inner cladding 02, etc.

[0065] It should be noted that the double-clad tapered gradient refractive index gain optical fiber has a tapered structure including but not limited to a linear change in the relationship between the optical fiber diameter and the optical fiber position.

[0066] In this embodiment, the double-clad tapered gradient refractive index gain fiber can efficiently couple high-power pump light into the gain medium, and high-power and high-efficiency pumping makes high-power amplification possible; and the double-clad tapered gradient refractive index gain fiber forms a tapered structure. Since the equivalent core diameter of the tapered core 01 is larger, the tapered gain fiber with corresponding parameters can match the large mode field fiber of corresponding size, and can support higher-power laser propagation; and the gain fiber with a tapered double-cladding structure can also reduce the requirements for pump brightness, effectively improving the output power of the high-power laser while ensuring high-purity single-mode output, thereby improving the output quality of the light beam.

[0067] It should be noted that the present invention solves the power limitation of current high-power lasers caused by pump brightness limitation, optical fiber thermal damage, nonlinear effect and mode instability, and improves the output power of existing optical fiber lasers.

[0068] The above is a detailed introduction to a double-clad tapered gradient refractive index gain optical fiber provided by the present invention. Specific examples are used in this article to illustrate the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

[0069] It should be noted that each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0070] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device that includes a series of elements is inherent to the elements, or also includes elements inherent to these processes, methods, articles or devices. In the absence of further restrictions, the elements defined by the sentence "including a..." do not exclude the presence of other identical elements in the process, method, article or device that includes the elements.

[0071] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A double-clad tapered gradient refractive index gain optical fiber, characterized in that: The double-clad tapered gradient refractive index gain optical fiber comprises: The core, inner cladding, and outer cladding; The inner cladding wraps the core; the outer cladding wraps the inner cladding; The fiber core includes a first end and a second end; in a first direction, the refractive index of the fiber core is distributed in a gradient manner, and the first direction is a direction from the first end to the second end; The orthographic projection area of ​​the cross section of the fiber core in the first direction gradually decreases, and the plane where the cross section of the fiber core is located is perpendicular to the first direction; the refractive index of the fiber core is gradiently distributed, including: as the radius of the cross section of the fiber core gradually decreases, the refraction of the fiber core first increases to a maximum preset value and then gradually decreases.

2. The double-clad tapered gradient refractive index gain optical fiber according to claim 1, characterized in that: The core is doped with rare earth ions.

3. The double-clad tapered gradient refractive index gain optical fiber according to claim 2, characterized in that: The rare earth ion is ytterbium, erbium or thulium.

4. The double-clad tapered gradient refractive index gain optical fiber according to claim 1, characterized in that: The minimum refractive index of the core is greater than the refractive index of the inner cladding.

5. The double-clad tapered gradient refractive index gain optical fiber according to claim 1, characterized in that: The refractive index of the inner cladding is greater than the refractive index of the outer cladding.

6. The double-clad tapered gradient refractive index gain optical fiber according to claim 1, characterized in that: The fiber core is located at the center of the area surrounded by the inner cladding.

7. The double-clad tapered gradient refractive index gain optical fiber according to claim 1, characterized in that: The cross-sectional shape of the inner cladding is the same as that of the outer cladding, which is circular, elliptical or hexagonal; Wherein, the plane where the cross section of the inner cladding lies and the plane where the cross section of the outer cladding lies are both perpendicular to the first direction.

8. The double-clad tapered gradient refractive index gain optical fiber according to claim 1, characterized in that: The double-clad tapered gradient refractive index gain optical fiber further comprises: A coating layer wraps the outer cladding layer.

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