Integrated fiber laser

Abstract

The utility model discloses an integrated optical fiber laser. The optical fiber laser sequentially comprises a pumping source, an active optical fiber coupled with the pumping source, and an optical fiber end cap coupled with the active optical fiber, wherein the active optical fiber is sequentially divided into a first core diameter section, a second core diameter section, a third core diameter section, a fourth core diameter section and a fifth core diameter section according to different fiber core diameters; the first core diameter section is provided with a high-reflectivity fiber grating, and the third core diameter section is provided with a low-reflectivity fiber grating; the fiber core diameter of the second core diameter section is greater than the fiber core diameter of the first core diameter section and the fiber core diameter of the third core diameter section; the fiber core diameter of the fourth core diameter section is larger than the fiber core diameter of the third core diameter section and the fiber core diameter of the fifth core diameter section. According to the integrated fiber laser provided by the utility model, the problem that the output power of the integrated fiber laser prepared in the prior art is limited can be solved.

Description

Technical Field

[0001] The utility model relates to the field of lasers, in particular to an integrated optical fiber laser. Background Art

[0002] All-fiber fiber lasers have been a hot topic in the field of fiber lasers in recent years. Due to the advantages of compact structure, stable performance, high efficiency, and easy maintenance, the laser has broad application prospects in the fields of industry, medicine, and military.

[0003] Traditional fiber lasers usually have two structures, one is a fiber laser oscillator and the other is a fiber laser amplifier.

[0004] The fiber oscillator is characterized by simple structure, low cost and strong anti-echo capability. However, the optical-to-optical conversion efficiency of the device is low, and in the case of high power output, the performance requirements of the fiber Bragg grating in the oscillation cavity are particularly strict.

[0005] Fiber amplifiers have the advantages of high efficiency and high power output, but the reflection of the amplified laser will cause the output power of the master oscillator power amplifier (MOPA) structure laser to fluctuate. When the reflected light passes through the melting point of the optical fiber, it will cause the key components such as the pump source to burn out. Therefore, in industrial applications, special attention should be paid to the anti-return design, which makes the manufacturing process of the laser more complicated.

[0006] In 2021, the National University of Defense Technology studied and verified for the first time the control logic and stability of the oscillation-amplification integrated fiber laser based on the rate equation theory established by the Iran University of Science and Technology and the China Academy of Engineering Physics. It was shown that when the forward and backward pump sources of the laser are turned on at will, the fiber laser with this structure can work stably, but there are problems such as low integration and high production cost.

[0007] Chinese patent publication CN113097843A discloses a method of utilizing an integrated high-efficiency fiber laser without a melting point. In order to control the loss at the melting point, reduce the excitation of high-order modes, and the temperature of the melting point, a process of directly writing a grating in the energy transmission fiber region using a laser is used. This reduces the number of fiber melting points in the fiber laser, solves the process problems existing in current traditional fiber lasers, and increases the threshold of device loss. However, the output power of the laser is still limited. Utility Model Content

[0008] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide an integrated fiber laser to solve the problem of limited output power of the integrated fiber laser prepared by the prior art.

[0009] In order to achieve the above-mentioned purpose and other related purposes, the utility model provides an integrated fiber laser, which comprises: a pump, an active fiber coupled to the pump source, and a fiber end cap coupled to the active fiber; wherein:

[0010] The active optical fiber is divided into a first core diameter section, a second core diameter section, a third core diameter section, a fourth core diameter section and a fifth core diameter section from the input end to the output end according to different core diameters;

[0011] The first core diameter section is provided with a high-reflection fiber Bragg grating, and the third core diameter section is provided with a low-reflection fiber Bragg grating;

[0012] Furthermore, the core diameter of the second core diameter segment is larger than the core diameter of the first core diameter segment and the core diameter of the third core diameter segment; the core diameter of the fourth core diameter segment is larger than the core diameter of the third core diameter segment and the core diameter of the fifth core diameter segment.

[0013] Optionally, the second core diameter segment has the same diameter as the fourth core diameter segment, and the first core diameter segment, the third core diameter segment and the fifth core diameter segment have the same diameter.

[0014] Optionally, the first core diameter segment, the third core diameter segment and the fifth core diameter segment have the same diameter.

[0015] Optionally, the cladding diameter of the first core diameter segment, the cladding diameter of the second core diameter segment, the cladding diameter of the third core diameter segment, the cladding diameter of the fourth core diameter segment and the cladding diameter of the fifth core diameter segment are the same.

[0016] Optionally, the cladding size of the first core diameter segment, the second core diameter segment, the third core diameter segment, the fourth core diameter segment and the fifth core diameter segment is 600 μm, the core diameter size of the first core diameter segment, the third core diameter segment and the fifth core diameter segment is 20 μm, and the core diameter size of the second core diameter segment and the fourth core diameter segment is 30 μm.

[0017] Optionally, the ratio of the cladding diameter to the core diameter of the first core diameter segment, the ratio of the cladding diameter to the core diameter of the second core diameter segment, the ratio of the cladding diameter to the core diameter of the third core diameter segment, the ratio of the cladding diameter to the core diameter of the fourth core diameter segment, and the ratio of the cladding diameter to the core diameter of the fifth core diameter segment are the same.

[0018] Optionally, the cladding size of the first core diameter segment, the third core diameter segment and the fifth core diameter segment is 400μm, and the core diameter size of the first core diameter segment, the third core diameter segment and the fifth core diameter segment is 20μm; the cladding size of the second core diameter segment and the fourth core diameter segment is 600μm, and the core diameter size of the second core diameter segment and the fourth core diameter segment is 30μm.

[0019] Optionally, the fifth core segment is provided with a cladding light stripper.

[0020] Optionally, the output end of the fifth core segment is formed by cladding etching to form the cladding light stripper.

[0021] Optionally, a tapered transition section is provided between each adjacent core diameter section.

[0022] As described above, the utility model provides an integrated fiber laser, in which the active fiber adopts a multi-diameter variable fiber, in which different core diameter segments are respectively provided with different optical elements, a high-reflection fiber grating is engraved on the first core diameter segment, the second core diameter segment is used to generate signal light under stimulation, a low-reflection fiber grating is engraved on the third core diameter segment, the fourth core diameter segment is used to amplify the signal light, and the fifth core diameter segment outputs laser; the core diameters of the second core diameter segment and the fourth core diameter segment are relatively large, and the core diameters of the first core diameter segment, the third core diameter segment and the fifth core diameter segment are relatively small, which can effectively balance the nonlinear effect of the narrow core diameter and the mode instability of the wide core diameter, obtain high-quality beam output, and improve conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more embodiments are exemplarily described by pictures in the corresponding drawings, and these exemplified descriptions do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0024] Figure 1 It is a schematic structural diagram of an integrated fiber laser with a constant active fiber core ratio provided in this embodiment.

[0025] Figure 2 It is a schematic structural diagram of an integrated fiber laser with a variable active fiber core ratio provided in this embodiment. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the utility model, the utility model is described in more detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that when an element is described as "fixed to" another element, it can be directly on another element, or there can be one or more centered elements therebetween. When an element is described as "connected" to another element, it can be directly connected to another element, or there can be one or more centered elements therebetween. The orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "bottom" and the like used in this specification is based on the orientation or positional relationship shown in the accompanying drawings, only for the convenience of describing the utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the utility model. In addition, the terms "first", "second", "third" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0027] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art in the technical field of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not used to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more related listed items.

[0028] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] like Figure 1 As shown, this embodiment provides an integrated fiber laser 1, which includes: a pump source 10, an active fiber 20 coupled to the pump source 10, and a fiber end cap 30 coupled to the active fiber 20.

[0030] Among them, the active optical fiber 20 is divided into a first core diameter segment 21, a second core diameter segment 22, a third core diameter segment 23, a fourth core diameter segment 24 and a fifth core diameter segment 25 from the input end to the output end according to different core diameters; the first core diameter segment 21 is provided with a high-reflection fiber grating 211, and the third core diameter segment is provided with a low-reflection fiber grating 231; and the core diameter of the second core diameter segment 22 is larger than the core diameter of the first core diameter segment 21 and the core diameter of the third core diameter segment 23; the core diameter of the fourth core diameter segment 24 is larger than the core diameter of the third core diameter segment 23 and the core diameter of the fifth core diameter segment 25.

[0031] In this embodiment, the first core segment 21, the second core segment 22 and the third core segment 23 of the active optical fiber 20 constitute a resonant cavity structure 20a of the optical fiber laser 1.

[0032] Among them, the high-reflection fiber grating 211 is directly engraved on the first core diameter section 21, and the low-reflection fiber grating 231 is directly engraved on the third core diameter section 230. Compared with the method of fusing an external grating fiber, the grating is directly engraved inside the active fiber 20, which can avoid the problems of heat concentration and power loss caused by the grating fiber and the active fiber fusing; the third core diameter section 23, the fourth core diameter section 24 and the fifth core diameter section 25 of the active fiber 20 constitute the amplifier structure 20b of the fiber laser 1. The resonant cavity structure 20a and the amplifier structure 20b are prepared on the same active fiber, which can avoid the problems of power loss and heat concentration caused by the fiber fusion of the resonant cavity structure and the amplifier structure. In addition, the fifth core diameter section 25 of the active fiber also assumes the function of an energy transmission fiber, which is directly coupled and connected to the fiber end cap 30, which can avoid the problems of power loss and heat concentration caused by the fusion of the energy transmission fiber and the amplifier structure.

[0033] For the resonant cavity structure 20a, since the core diameter of the second core diameter segment 22 is larger than the core diameter of the first core diameter segment 21 and the core diameter of the third core diameter segment 23, the first core diameter segment 21 and the third core diameter segment 23 with relatively narrow cores have lower mode field areas, which can suppress high-order modes and mode instability effects. However, correspondingly, the smaller the core size, the easier it is to produce nonlinear effects, such as stimulated Raman scattering effects. Strong nonlinear effects can damage devices and cause energy loss; and the influence of Raman scattering effects will accumulate with the increase of optical fiber length. Therefore, the second core diameter segment 22 set after the first core diameter segment 21 can reduce the power density in the core and prevent the accumulation of nonlinear effects; the third core diameter segment 23 set after the second core diameter segment 22 can ensure the beam quality of the output laser and prevent the occurrence of mode instability effects.

[0034] For the amplifier structure 20b, since the core diameter of the fourth core segment 24 is larger than the core diameter of the third core segment 23, the power density of the laser amplified therein can be effectively reduced, and the accumulation of nonlinear effects can be prevented. At the same time, the core diameter of the fifth core segment 25 is smaller than the core diameter of the fourth core segment 24, which can ensure the beam quality of the amplified light beam at output and prevent mode instability.

[0035] It should be noted that if Figure 1 and Figure 2As shown, the active optical fiber 20 is prepared by using a plurality of sections of taper from a prefabricated optical fiber. There is a core diameter gradient section between each core diameter section with different core diameters. The minimum length of each core diameter gradient section is determined by the taper ratio between adjacent core diameter sections. When the length of the core diameter gradient section is long enough, the transmission efficiency of the taper section can be effectively improved. Since the taper ratio between each adjacent core diameter section can be controlled separately, each core diameter gradient section can have a different length, and at the same time, the core diameter of each core diameter section can also have a different size ratio. As an example, the fourth core diameter section needs to gain the power of the laser formed by the second core diameter section, so the core diameter of the fourth core diameter section is set to be larger than the core diameter of the second core diameter section. As another example, the first core diameter section, the third core diameter section and the fifth core diameter section support the same number of modes of laser transmission, and the core diameter is the same.

[0036] In some embodiments, Figure 1 As shown, when preparing core diameter segments with different core diameters, the cladding of the active optical fiber 20 and the core are tapered synchronously at the same ratio. Therefore, the ratio of the cladding diameter to the core diameter of each core diameter segment formed by the tapering remains unchanged, and the preparation method of the active optical fiber 20 is relatively simple.

[0037] As an example, the cladding sizes of the first core diameter segment 21, the third core diameter segment 23 and the fifth core diameter segment 25 are the same, which are all 400μm, the core sizes of the first core diameter segment 21, the third core diameter segment 23 and the fifth core diameter segment 25 are also the same, which are all 20μm, and the cladding ratio is 20:1; the cladding sizes of the second core diameter segment 22 and the fourth core diameter segment 24 are the same, which are all 600μm, the core sizes of the second core diameter segment 22 and the fourth core diameter segment 24 are also the same, which are all 30μm, and the cladding ratio is also 20:1.

[0038] In some embodiments, Figure 2 As shown, although different core diameter segments have different core diameters, they have the same cladding diameter. The pump light emitted by the pump source 10 is transmitted in the cladding, and the change in the core diameter does not affect the transmission efficiency of the pump light.

[0039] As an example, the cladding sizes of the first core diameter segment 21, the second core diameter segment 22, the third core diameter segment 23, the fourth core diameter segment 24 and the fifth core diameter segment 25 are the same, which is 600 μm, the core sizes of the first core diameter segment 21, the third core diameter segment 23 and the fifth core diameter segment 25 are the same, which is 20 μm, and the core sizes of the second core diameter segment 22 and the fourth core diameter segment 24 are the same, which is 30 μm, and the cladding-to-core ratios are 30:1 and 20:1 respectively.

[0040] In some embodiments, the high-reflection fiber Bragg grating 211 and the low-reflection fiber Bragg grating 231 are both fiber Bragg gratings prepared by femtosecond laser; the reflectivity of the high-reflection fiber Bragg grating 211 is greater than 90%; the reflectivity of the low-reflection fiber Bragg grating 231 is in the range of 4% to 50%. The central wavelengths of the high-reflection fiber Bragg grating 211 and the low-reflection fiber Bragg grating 231 are matched, and the central wavelength range of the fiber Bragg grating is 1000nm to 1100nm;

[0041] In some embodiments, the fourth core segment and the fifth core segment are used to enhance the power and intensity of the laser signal to meet specific application requirements. The core diameter should be between 10 μm and 400 μm, the cladding diameter should be between 200 μm and 1 mm, and the total length should be between 1 m and 30 m.

[0042] In some embodiments, the first core segment, the second core segment, and the third core segment need to increase the input light gain to above a threshold value so that it forms a laser output. To ensure that the laser can produce stable and continuous laser output, the core diameter of the first core segment, the second core segment, and the third core segment is between 10 μm and 400 μm, the cladding diameter is between 200 μm and 1 mm, and the total length of the first core segment, the second core segment, and the third core segment is between 1 m and 30 m.

[0043] In some embodiments, a cladding light stripper is further provided in the fifth core segment 25. The cladding light stripper is used to strip the pump light that is not completely absorbed and the signal light that is strayed into the cladding. The light beams in the cladding not only affect the light beam quality, but also cause serious heating at the fiber coupling end. Stripping the cladding light by the cladding light stripper can effectively reduce the heating at the coupling position between the output end of the active optical fiber 20 and the end cap. Preferably, a laser etching process is used to etch the output end of the fifth core segment 25, destroy the total reflection structure, and form a cladding light stripper.

[0044] In summary, the utility model describes an integrated fiber laser, the active fiber uses a multi-diameter optical fiber, in which different core diameter segments are respectively provided with different optical elements, the first core diameter segment is engraved with a high-reflection fiber grating, the second core diameter segment is used to generate signal light under stimulation, the third core diameter segment is engraved with a low-reflection fiber grating, the fourth core diameter segment is used to amplify the signal light, and the fifth core diameter segment outputs laser; the second core diameter segment and the fourth core diameter segment have a larger core diameter, and the first core diameter segment, the third core diameter segment and the fifth core diameter segment have a smaller core diameter, which can effectively balance the nonlinear effect of the narrow core diameter and the mode instability of the wide core diameter, obtain high-quality beam output, and improve conversion efficiency. Therefore, the utility model effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0045] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An integrated fiber laser, characterized in that: The fiber laser comprises in sequence: a pump source, an active fiber coupled to the pump source, and a fiber end cap coupled to the active fiber; wherein: The active optical fiber is divided into a first core diameter section, a second core diameter section, a third core diameter section, a fourth core diameter section and a fifth core diameter section in sequence according to different core diameters; The first core diameter section is provided with a high-reflection fiber Bragg grating, and the third core diameter section is provided with a low-reflection fiber Bragg grating; Furthermore, the core diameter of the second core diameter segment is larger than the core diameter of the first core diameter segment and the core diameter of the third core diameter segment; the core diameter of the fourth core diameter segment is larger than the core diameter of the third core diameter segment and the core diameter of the fifth core diameter segment.

2. The integrated fiber laser according to claim 1, characterized in that: The second core diameter segment has a core diameter smaller than that of the fourth core diameter segment.

3. The integrated fiber laser according to claim 1, characterized in that: The core diameters of the first core diameter segment, the third core diameter segment, and the fifth core diameter segment are the same.

4. The integrated fiber laser according to claim 1, characterized in that: The cladding diameter of the first core diameter segment, the cladding diameter of the second core diameter segment, the cladding diameter of the third core diameter segment, the cladding diameter of the fourth core diameter segment, and the cladding diameter of the fifth core diameter segment are the same.

5. The integrated fiber laser according to claim 4, characterized in that: The cladding size of the first core diameter segment, the second core diameter segment, the third core diameter segment, the fourth core diameter segment and the fifth core diameter segment is 600 μm, the core diameter size of the first core diameter segment, the third core diameter segment and the fifth core diameter segment is 20 μm, and the core diameter size of the second core diameter segment and the fourth core diameter segment is 30 μm.

6. The integrated fiber laser according to claim 1, characterized in that: The ratio of the cladding diameter to the core diameter of the first core diameter segment, the ratio of the cladding diameter to the core diameter of the second core diameter segment, the ratio of the cladding diameter to the core diameter of the third core diameter segment, the ratio of the cladding diameter to the core diameter of the fourth core diameter segment, and the ratio of the cladding diameter to the core diameter of the fifth core diameter segment are the same.

7. The integrated fiber laser according to claim 6, characterized in that: The cladding size of the first core diameter segment, the third core diameter segment and the fifth core diameter segment is 400μm, and the core diameter size of the first core diameter segment, the third core diameter segment and the fifth core diameter segment is 20μm; the cladding size of the second core diameter segment and the fourth core diameter segment is 600μm, and the core diameter size of the second core diameter segment and the fourth core diameter segment is 30μm.

8. The integrated fiber laser according to claim 1, characterized in that: The fifth core diameter section is provided with a cladding light stripper.

9. The integrated fiber laser according to claim 8, characterized in that: The output end of the fifth core segment is formed into the cladding light stripper by cladding etching.

10. The integrated fiber laser according to any one of claims 1 to 9, characterized in that: A core diameter gradient section is also provided between adjacent core diameter sections of the active optical fiber.

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