Mid-infrared tunable pure soliton fiber laser based on cascade amplification

Abstract

The invention discloses a mid-infrared tunable pure soliton fiber laser based on cascade amplification, which comprises: a femtosecond pulse laser, a first-stage fiber amplifier and a second-stage fiber amplifier; the femtosecond pulse laser is used to generate a femtosecond pulse signal and transmit the femtosecond pulse signal to the first-stage fiber amplifier; the first-stage fiber amplifier is used to power amplify the femtosecond pulse signal and generate Raman solitons; the second-stage fiber amplifier is used to recycle background signal light to amplify Raman solitons; the invention can obtain higher output power and pulse energy, wider tunable range and pure Raman soliton pulses by recycling the background signal light to amplify Raman solitons.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, and in particular to a mid-infrared tunable pure soliton optical fiber laser based on cascade amplification. Background Art

[0002] High-power mid-infrared femtosecond lasers are extremely important due to their wide applications in many fields such as molecular spectroscopy, remote sensing, laser surgery, and material processing. Compared with solid-state lasers, mid-infrared femtosecond lasers based on fluoride ZBLAN fibers have obvious advantages in terms of system compactness, environmental reliability, and high beam quality. At present, the nonlinear polarization rotation-based mode-locking technology is an effective means to achieve femtosecond pulse output of mid-infrared fiber lasers, but the mode-locked pulses are limited to a few wavelengths such as 2.8μm, 2.9μm, 3.1μm, and 3.5μm, and their wavelength tunability is limited by the gain bandwidth of fluoride rare earth ions. In many practical applications of molecular spectroscopy and sensor detection, mid-infrared femtosecond lasers with continuously tunable wavelengths over a large range are required.

[0003] The soliton self-frequency shift (SSFS) effect in optical fibers can be used to break through similar wavelength tunability limitations and provide femtosecond pulses with broadband tunability. The SSFS effect can make the original soliton pulse deviate from the Kelly sideband of the mode-locked pulse and shift to the long-wave direction, thereby obtaining very clean and complete Raman solitons. So far, tunable femtosecond lasers based on the SSFS effect have been deeply studied in quartz fiber, tellurite fiber, fluoride fiber and chalcogenide fiber. Among them, due to the high loss in the mid-infrared region, the Raman soliton in quartz fiber is limited to a wavelength of 2.3μm, while the soft glass fiber, thanks to the lower phonon energy, can support the Raman soliton to achieve further frequency shift in the mid-infrared region. In soft glass fiber, compared with tellurite fiber and chalcogenide fiber, fluoride fiber has a lower nonlinear refractive index and larger anomalous dispersion, which makes it possible to generate Raman solitons with high pulse energy and high peak power through fluoride fiber.

[0004] At present, the existing technologies for realizing broadband tunable pulse output in the mid-infrared based on the SSFS effect in fluoride fibers are mainly concentrated in the following aspects: First, using a near-infrared ultrafast laser amplifier as a pump source to generate high-energy ultrashort pulses, and using fluoride fibers as frequency-shifted fibers to achieve mid-infrared tunable ultrafast pulse output. For example, a mid-infrared ultrafast system with a pulse energy of 5nJ and a wavelength tunable range of 2 to 4.3μm is realized by combining an erbium-doped laser amplifier and a highly nonlinear InF3 fiber. Although SSFS can use a more convenient near-infrared fiber laser as a pump source, the mid-infrared fiber laser as a pump source has the advantage of a longer initial pump wavelength, thereby facilitating the realization of a greater pulse energy of Raman soliton pulses at far wavelengths. Second, using a fluoride fiber-based ultrashort pulse oscillator and its amplifier as a mid-infrared pump source, and also using a fluoride fiber as a frequency-shifted fiber mid-infrared tunable ultrafast system, high-energy Raman soliton pulse output is achieved. For example, by using Er:ZBLAN fiber oscillator and its amplifier as pump source, an ultrafast system of watt-level Raman soliton pulses with continuously tunable wavelength from 2.8μm to 3.6μm is realized. However, the above SSFS system is always accompanied by background signal light or second-order Raman solitons, which limits the energy conversion efficiency, Raman frequency shift range and spectral purity. How to select the first-order Raman soliton from the background signal light or the second-order Raman soliton to obtain pure Raman soliton requires further work, which will undoubtedly increase the complexity of the system structure and the difficulty of operation. Summary of the invention

[0005] The main purpose of the present invention is to provide a mid-infrared tunable pure soliton fiber laser based on cascade amplification, which can obtain a high-power mid-infrared broadband tunable pure Raman soliton laser and significantly improve the spectral purity of the mid-infrared Raman soliton fiber laser.

[0006] To achieve the above object, the present invention provides a mid-infrared tunable pure soliton fiber laser based on cascade amplification, comprising: a femtosecond pulse laser, a first-stage fiber amplifier and a second-stage fiber amplifier;

[0007] The femtosecond pulse laser is used to generate a femtosecond pulse signal and transmit the femtosecond pulse signal to the first-stage optical fiber amplifier; the first-stage optical fiber amplifier is used to power amplify the femtosecond pulse signal and generate Raman solitons; the second-stage optical fiber amplifier is used to recycle the background signal light to amplify the Raman solitons; the first-stage optical fiber amplifier includes: a first polarization-dependent isolator, a first half-wave plate, a first quarter-wave plate, a first pump laser, a first pump light collimating lens, a first pump light laser dichroic mirror, a first pump light laser focusing lens, and a first optical fiber; the first polarization-dependent isolator is connected to the first half-wave plate, the first half-wave plate is connected to the first quarter-wave plate, the first quarter-wave plate is connected to the first pump light laser dichroic mirror, and the first pump light laser focusing lens is connected to the first half-wave plate. The first pump light laser dichroic mirror is connected to the first pump light laser focusing lens, and the first pump light laser dichroic mirror is connected to the first pump light laser focusing lens. The first pump light laser dichroic mirror is used to combine the laser light passing through the quarter wave plate and the pump light passing through the first pump light collimating lens, and transmit them to the first pump light laser focusing lens, and the first pump light laser focusing lens is connected to the first optical fiber; the second-stage optical fiber amplifier includes: a cladding power stripper, a second optical fiber, a first optical fiber output end cap, and a first laser collimating lens; the cladding power stripper is connected to the second optical fiber, the second optical fiber is connected to the first optical fiber output end cap, and the first optical fiber output end cap is connected to the first laser collimating lens.

[0008] Furthermore, the femtosecond pulse laser includes: a second pump laser, a second pump light collimating lens, a second pump light laser dichroic mirror, a second pump light laser focusing lens, a third optical fiber, a second optical fiber output end cap, a second laser collimating lens, a third pump light laser dichroic mirror, a second half wave plate, a polarization beam splitter, a second polarization-dependent isolator, a gold mirror, and a second quarter wave plate; the second pump laser is connected to the second pump light collimating lens; the second pump light collimating lens is connected to the second pump light laser dichroic mirror; the second pump light laser dichroic mirror is connected to the second pump light laser focusing lens and the second quarter wave plate, and is used to combine the pump light and laser from the second pump light collimating lens and the second quarter wave plate, and transmit the pump light and laser from the second pump light collimating lens and the second quarter wave plate. to the second pump light laser focusing lens; the second pump light laser focusing lens is connected to the third optical fiber, the second optical fiber output end cap is connected to the other end of the third optical fiber, the second optical fiber output end cap is also connected to the second laser collimating lens, the second laser collimating lens is connected to the third pump light laser dichroic mirror, the third pump light laser dichroic mirror is connected to the second half wave plate, the second half wave plate is connected to the polarization beam splitter prism, the polarization beam splitter prism is connected to the second polarization-dependent isolator, used to output a femtosecond pulse signal to the first-stage optical fiber amplifier and output laser to the second polarization-dependent isolator, the second polarization-dependent isolator is connected to the gold mirror, and the gold mirror is connected to the second quarter wave plate.

[0009] Furthermore, the first optical fiber is an erbium-doped fluoride optical fiber, and the first optical fiber is a double-clad optical fiber; the second optical fiber is a dysprosium-doped fluoride optical fiber, and the second optical fiber is a single-clad optical fiber.

[0010] Furthermore, the erbium ion doping concentration of the first optical fiber is 7 mol.%, the length is 3.9 m, the core diameter is 15 μm, the numerical aperture is 0.12, the cladding diameter is 260 μm, it is cut by two planes with a spacing of 240 μm, and the cladding numerical aperture is 0.46; the dysprosium ion doping concentration of the second optical fiber is 0.2 mol.%, the length is 11 m, the core diameter is 12.5 μm, the cladding diameter is 125 μm, and the numerical aperture is 0.16.

[0011] Furthermore, the first pump laser is a 976nm semiconductor pump laser; the central wavelength of the Raman soliton output by the second-stage optical fiber amplifier is 3.03μm-3.63μm, and the pulse energy is 0.4-31.8nJ.

[0012] Furthermore, the third optical fiber is Er-doped 3+ Fluoride ZBLAN Fiber, Er 3+The ion concentration is 7 mol.%, the length is 2.4 m, the first optical fiber is a double-clad optical fiber with a core diameter of 15 μm, a numerical aperture of 0.12, a cladding diameter of 260 μm, and is cut by two planes with a spacing of 240 μm. The cladding numerical aperture is 0.46.

[0013] Furthermore, the second pump laser is a 976nm semiconductor pump laser; the fiber input end of the first optical fiber, the first optical fiber output end cap, the fiber input end of the third optical fiber, and the second optical fiber output end cap are all cut at an angle of 8°.

[0014] Furthermore, the first optical fiber output end cap and the second optical fiber output end cap are made of zirconium fluoride, with a core diameter of 200 μm, the first optical fiber output end cap and the second optical fiber are connected by fusion splicing, and the second optical fiber output end cap and the third optical fiber are connected by fusion splicing.

[0015] Furthermore, the Raman soliton generated by the first-stage optical fiber amplifier is 3 μm, and the background light is 2.8 μm.

[0016] Furthermore, the first optical fiber and the second optical fiber are connected by fusion splicing, and the power stripper is used to strip the power loss caused by the fusion splicing of the first optical fiber and the second optical fiber and the remaining 976nm pump light of the first pump laser; the femtosecond pulse laser and the first-stage optical fiber amplifier are connected by spatial coupling.

[0017] The present invention provides a mid-infrared tunable pure soliton fiber laser based on cascade amplification, which has the beneficial effect of being able to recycle background signal light to amplify Raman solitons, thereby obtaining higher output power and pulse energy, wider tunable range and pure Raman soliton pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 It is a schematic block diagram of the structure of a mid-infrared tunable pure soliton fiber laser based on cascade amplification according to an embodiment of the present invention;

[0020] Figure 2 It is a schematic diagram of the structure of the first-stage fiber amplifier and the second-stage fiber amplifier of the mid-infrared tunable pure soliton fiber laser based on cascade amplification according to an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of the structure of a femtosecond pulse laser of a mid-infrared tunable pure soliton fiber laser based on cascade amplification according to an embodiment of the present invention;

[0022] Figure 4 This is a spectrum diagram of the output pulse of the first-stage fiber amplifier of the mid-infrared tunable pure soliton fiber laser based on cascade amplification according to an embodiment of the present invention;

[0023] Figure 5 This is a spectrum diagram of the output pulse of the second-stage fiber amplifier of the mid-infrared tunable pure soliton fiber laser based on cascade amplification in an embodiment of the present invention.

[0024] In the accompanying drawings, each reference numeral represents:

[0025] 01. Femtosecond pulse laser; 02. First-stage fiber amplifier; 03. Second-stage fiber amplifier; 1. Second pump laser; 2. Second pump light collimating lens; 3. Second pump light laser dichroic mirror; 4. Second pump light laser focusing lens; 5. Third optical fiber; 6. Second optical fiber output end cap; 7. Second laser collimating lens; 8. Third pump light laser dichroic mirror; 9. Second half-wave plate; 10. Polarization beam splitter; 11. Second polarization-dependent isolator ; 12. gold mirror; 13. second quarter wave plate; 21. first polarization dependent isolator; 22. first half wave plate; 23. first quarter wave plate; 24. first pump laser; 25. first pump light collimating lens; 26. first pump light laser dichroic mirror; 27. first pump light laser focusing lens; 28. first optical fiber; 29. ​​cladding power stripper; 30. second optical fiber; 31. first optical fiber output end cap; 32. first laser collimating lens. DETAILED DESCRIPTION

[0026] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0027] See also Figure 1, which is a mid-infrared tunable pure soliton fiber laser based on cascade amplification, comprising: a femtosecond pulse laser 01, a first-stage fiber amplifier 02 and a second-stage fiber amplifier 03; wherein, the femtosecond pulse laser 01 is used to generate a femtosecond pulse signal and transmit the femtosecond pulse signal to the first-stage fiber amplifier 02; the first-stage fiber amplifier 02 is used to amplify the power of the femtosecond pulse signal and generate Raman solitons; the second-stage fiber amplifier 03 is used to recycle the background signal light to amplify the Raman solitons.

[0028] The mid-infrared tunable pure soliton fiber laser based on cascade amplification provided in this embodiment obtains higher output power and pulse energy, wider tunable range and pure Raman soliton pulses by recycling background signal light to amplify Raman solitons. This solution will solve the problem that SSFS cannot directly provide mid-infrared broadband tunable femtosecond pulses with sufficiently high spectral purity.

[0029] See also Figure 2 The first-stage fiber amplifier 02 includes: a first polarization-dependent isolator 21, a first half-wave plate 22, a first quarter-wave plate 23, a first pump laser 24, a first pump light collimating lens 25, a first pump light laser dichroic mirror 26, a first pump light laser focusing lens 27, and a first optical fiber 28; the first polarization-dependent isolator 21 is connected to the first half-wave plate 22, the first half-wave plate 22 is connected to the first quarter-wave plate 23, the first quarter-wave plate 23 is connected to the first pump light laser dichroic mirror 26, and the first pump light laser focusing lens 27. The first pump light laser dichroic mirror 26 is connected to the first pump light collimating lens 25, the opposite sides of the first pump light collimating lens 25 are respectively connected to the first pump laser 24 and the first pump light laser dichroic mirror 26, the first pump light laser dichroic mirror 26 is connected to the first pump light laser focusing lens 27, the first pump light laser dichroic mirror 26 is used to combine the laser passing through the first quarter wave plate 23 and the pump light passing through the first pump light collimating lens 25, and transmit them to the first pump light laser focusing lens 27, and the first pump light laser focusing lens 27 is connected to the first optical fiber 28.

[0030] Please continue reading Figure 2 The second-stage optical fiber amplifier 03 includes: a cladding power stripper 29, a second optical fiber 30, a first optical fiber output end cap 31, and a first laser collimating lens 32; the cladding power stripper 29 is connected to the second optical fiber 30, the second optical fiber 30 is connected to the first optical fiber output end cap 31, and the first optical fiber output end cap 31 is connected to the first laser collimating lens 32.

[0031] In this embodiment, the first optical fiber 28 is an erbium-doped fluoride optical fiber, and the first optical fiber 28 is a double-clad optical fiber; the second optical fiber 30 is a dysprosium-doped fluoride optical fiber, and the second optical fiber 30 is a single-clad optical fiber.

[0032] The first optical fiber 28 has an erbium ion doping concentration of 7 mol.%, a length of 3.9 m, a core diameter of 15 μm, a numerical aperture of 0.12, a cladding diameter of 260 μm, and is cut by two planes with a spacing of 240 μm, and a cladding numerical aperture of 0.46; the second optical fiber 30 has a dysprosium ion doping concentration of 0.2 mol.%, a length of 11 m, a core diameter of 12.5 μm, a cladding diameter of 125 μm, and a numerical aperture of 0.16. Among them, the erbium ion is a trivalent erbium ion Er 3+ , the dysprosium ion is trivalent dysprosium ion Dy 3+ .

[0033] In this embodiment, the pulse output of the femtosecond pulse laser 01 passes through the first polarization-dependent isolator 21 to prevent the reflected light from the cascade amplifier from affecting the femtosecond pulse laser 01. The first half-wave plate 22 and the first quarter-wave plate 23 are used to adjust the polarization state of the seed pulse input to the cascade amplifier. The first pump light collimating lens 25 is used to collimate the pump light output by the first pump laser 24, wherein the first pump laser 24 is a 976nm semiconductor pump laser. After the pump light and the seed pulse laser pass through the combination of the first pump light laser dichroic mirror 26, they are coupled into the first optical fiber 28 by the first pump light laser focusing lens 27 to form a forward pumping structure.

[0034] The Raman soliton generated by the first-stage optical fiber amplifier 02 is 3μm, and the background light is 2.8μm.

[0035] In this embodiment, the first-stage fiber amplifier 02 is used as an amplifier to increase the optical power of the 2.8μm femtosecond pulse signal and as a frequency shifter to generate 3μm Raman solitons. The 3μm Raman solitons and 2.8μm background signal light are then injected into the second-stage fiber amplifier 03, and the cladding power stripper 29 is used to strip the remaining 976nm pump light.

[0036] In one embodiment, the first optical fiber 28 and the second optical fiber 30 are connected by fusion splicing, and the power stripper is used to strip the power lost due to the fusion splicing of the first optical fiber 28 and the second optical fiber 30; the femtosecond pulse laser 01 and the first-stage optical fiber amplifier 02 are connected by spatial coupling.

[0037] In this embodiment, the first optical fiber 28 and the second optical fiber 30 are connected by using fusion splicing technology. Due to the slight mode field mismatch between the two optical fibers, the actual signal light transmission transmittance of the fusion splicing point is measured to be 82%, and the power loss caused by fusion splicing is also stripped off by the cladding power stripper 29.

[0038] See also Figure 3In one embodiment, the femtosecond pulse laser 01 includes: a second pump laser 1, a second pump light collimating lens 2, a second pump light laser dichroic mirror 3, a second pump light laser focusing lens 4, a third optical fiber 5, a second optical fiber output end cap 6, a second laser collimating lens 7, a third pump light laser dichroic mirror 8, a second half wave plate 9, a polarization beam splitter prism 10, a second polarization-dependent isolator 11, a gold mirror 12, and a second quarter wave plate 13.

[0039] Among them, the second pump laser 1 is connected to the second pump light collimating lens 2; the second pump light collimating lens 2 is connected to the second pump light laser dichroic mirror 3; the second pump light laser dichroic mirror 3 is connected to the second pump light laser focusing lens 4 and the second quarter wave plate 13, and is used to combine the pump light and laser from the second pump light collimating lens 2 and the second quarter wave plate 13, and transmit them to the second pump light laser focusing lens 4; the second pump light laser focusing lens 4 is connected to the third optical fiber 5, and the second optical fiber output end cap 6 is connected to the other end of the third optical fiber 5, and the second The optical fiber output end cap 6 is also connected to the second laser collimating lens 7, the second laser collimating lens 7 is connected to the third pump light laser dichroic mirror, the third pump light laser dichroic mirror is connected to the second half wave plate 9, the second half wave plate 9 is connected to the polarization splitter prism 10, the polarization splitter prism 10 is connected to the second polarization-dependent isolator 11, and is used to output a femtosecond pulse signal to the first-stage optical fiber amplifier 02 and output a laser to the second polarization-dependent isolator 11, the second polarization-dependent isolator 11 is connected to the gold mirror 12, and the gold mirror 12 is connected to the second quarter wave plate 13.

[0040] Among them, the third optical fiber 5 is Er-doped 3+ Fluoride ZBLAN Fiber, Er 3+ The ion concentration is 7 mol.%, the length is 2.4 m, the first optical fiber 28 is a double-clad optical fiber with a core diameter of 15 μm, a numerical aperture of 0.12, a cladding diameter of 260 μm, and is cut by two planes with a spacing of 240 μm. The cladding numerical aperture is 0.46.

[0041] The second pump laser 1 is a 976nm semiconductor pump laser, emitting continuous pump light with a wavelength of 976nm, which is focused into the inner cladding of the third optical fiber 5 through the second pump light collimating lens 2 and the second pump light laser focusing lens 4. The second pump light laser dichroic mirror 3 and the third pump light laser dichroic mirror are used to combine and separate the 2.8μm laser and the 976nm pump light, respectively. The second polarization-dependent isolator 11 is used to ensure the unidirectional circulation of the laser in the ring cavity, and at the same time, it forms a passive mode-locking device with the second half-wave plate 9 and the second quarter-wave plate 13 to start and maintain the mode-locking operation. The polarization beam splitter prism 10 is used as a pulse output port, and the gold mirror 12 makes the optical path form a ring laser resonant cavity. The femtosecond pulse laser 01 obtains a mode-locked pulse working in the soliton region with a pulse width of 257fs.

[0042] In this embodiment, the first pump laser 24 and the second pump laser 1 are both 976 nm semiconductor pump lasers, which are multi-mode semiconductor lasers with fiber-coupled outputs.

[0043] In one embodiment, the first optical fiber output end cap 31 and the second optical fiber output end cap 6 are made of zirconium fluoride, and the core diameter is 200 μm. The first optical fiber output end cap 31 and the first optical fiber 28 are connected by fusion splicing, and the second optical fiber output end cap 6 and the second optical fiber 30 are connected by fusion splicing.

[0044] The fiber input end of the first optical fiber 28, the first optical fiber output end cap 31, the fiber input end of the third optical fiber 5, and the second optical fiber output end cap 6 all have an 8° cut angle.

[0045] The second optical fiber output end cap 6 cut at an 8° angle is fused to the output end of the third optical fiber 5 to prevent the optical fiber end face from being damaged due to long-term operation of the laser. Its length is about 350 μm.

[0046] The first optical fiber output end cap 31 cut at an 8° angle is spliced ​​onto the output end of the second optical fiber 30 to prevent the optical fiber output end from being damaged under high-power pulse output. 3+ The output beam of the fluoride fiber amplifier is collimated by a first laser collimating lens 32 for data measurement.

[0047] See also Figure 4 , Figure 4 The spectral evolution of the output pulse of the first-stage fiber amplifier 02 is shown. As the pump power increases, the power of the 2.8μm femtosecond pulse is amplified and Raman solitons are formed at 3μm, and gradually move to a longer wavelength region. The central wavelength of the Raman soliton output by the first-stage fiber amplifier 02 is always within the radiation cross section of the second optical fiber 30, which is conducive to the second-stage fiber amplifier 03 to amplify the Raman soliton by recycling and reusing the 2.8μm background signal light.

[0048] See also Figure 5 , Figure 5 The spectral evolution of the output pulse of the second-stage fiber amplifier 03 is shown. With the increase of pump power, the central wavelength of the Raman soliton can be continuously tuned from 3.03μm to 3.63μm. No 2.8μm background signal light or second-order Raman soliton is observed in the output spectrum, and the pure Raman soliton state with high-quality spectral purity is always maintained. Finally, at a pump power of 20W, the pure Raman soliton with a central wavelength of 3.63μm achieves a pulse energy of 31.8nJ and a pulse duration of 210fs, corresponding to a peak power of 151kW.

[0049] The mid-infrared tunable pure soliton fiber laser based on cascade amplification provided in this embodiment shows that the present invention innovatively amplifies Raman solitons by recycling background signal light based on cascade amplification, providing an effective way to develop high-power, high-pulse energy, broadband wavelength tunable and pure Raman soliton pulse fiber lasers.

[0050] It should be noted that the above embodiments are for the purpose of illustrating the technical solution of the present invention in detail rather than limiting the present invention. The present invention can also be applied to other pure Raman soliton fiber laser systems based on SSFS, such as Er-doped 3+ and Tm 3+ Fiber cascade amplified fiber laser, Tm-doped 3+ and Ho 3+ Fiber lasers with fiber cascade amplification, etc. Any changes and modifications made by those skilled in the art that do not depart from the spirit of the technical solution of the present invention should be included in the protection scope of the appended claims of the present invention.

[0051] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0052] The above is a description of a mid-infrared tunable pure soliton fiber laser based on cascade amplification provided by the present invention. For those skilled in the art, according to the concept of the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A mid-infrared tunable pure soliton fiber laser based on cascade amplification, characterized in that: include: Femtosecond pulse laser, first-stage fiber amplifier, and second-stage fiber amplifier; The femtosecond pulse laser is used to generate a femtosecond pulse signal and transmit the femtosecond pulse signal to the first-stage optical fiber amplifier; the first-stage optical fiber amplifier is used to amplify the power of the femtosecond pulse signal and generate Raman solitons; the second-stage optical fiber amplifier is used to recycle the background signal light to amplify the Raman solitons; wherein the Raman solitons generated by the first-stage optical fiber amplifier are 3μm, and the background light is 2.8μm; the central wavelength of the Raman solitons output by the second-stage optical fiber amplifier is 3.03μm-3.63μm, and the pulse energy is 0.4-31.8nJ; The first-stage fiber amplifier includes: a first polarization-dependent isolator, a first half-wave plate, a first quarter-wave plate, a first pump laser, a first pump light collimating lens, a first pump light laser dichroic mirror, a first pump light laser focusing lens, and a first optical fiber; the first polarization-dependent isolator is connected to the first half-wave plate, the first half-wave plate is connected to the first quarter-wave plate, the first quarter-wave plate is connected to the first pump light laser dichroic mirror, the opposite sides of the pump light collimating lens are respectively connected to the first pump laser and the first pump light laser dichroic mirror, the first pump light laser dichroic mirror is connected to the first pump light laser focusing lens, the first pump light laser dichroic mirror is used to combine the laser passing through the quarter-wave plate and the pump light passing through the first pump light collimating lens, and transmit them to the first pump light laser focusing lens, and the first pump light laser focusing lens is connected to the first optical fiber; wherein the first pump laser is 976 nm semiconductor pump laser; the second-stage optical fiber amplifier comprises: a cladding power stripper, a second optical fiber, a first optical fiber output end cap, and a first laser collimating lens; the cladding power stripper is connected to the second optical fiber, the second optical fiber is connected to the first optical fiber output end cap, and the first optical fiber output end cap is connected to the first laser collimating lens.

2. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 1, characterized in that: The femtosecond pulse laser comprises: a second pump laser, a second pump light collimating lens, a second pump light laser dichroic mirror, a second pump light laser focusing lens, a third optical fiber, a second optical fiber output end cap, a second laser collimating lens, a third pump light laser dichroic mirror, a second half wave plate, a polarization beam splitter prism, a second polarization-dependent isolator, a gold mirror, and a second quarter wave plate; The second pump laser is connected to the second pump light collimating lens; the second pump light collimating lens is connected to the second pump light laser dichroic mirror; the second pump light laser dichroic mirror is connected to the second pump light laser focusing lens and the second quarter wave plate, and is used to combine the pump light and laser from the second pump light collimating lens and the second quarter wave plate, and transmit them to the second pump light laser focusing lens; the second pump light laser focusing lens is connected to the third optical fiber, the second optical fiber output end cap is connected to the other end of the third optical fiber, the second optical fiber output end cap is also connected to the second laser collimating lens, the second laser collimating lens is connected to the third pump light laser dichroic mirror, the third pump light laser dichroic mirror is connected to the second half wave plate, the second half wave plate is connected to the polarization beam splitter prism, the polarization beam splitter prism is connected to the second polarization-dependent isolator, and is used to output a femtosecond pulse signal to the first-stage optical fiber amplifier and output laser to the second polarization-dependent isolator, the second polarization-dependent isolator is connected to the gold mirror, and the gold mirror is connected to the second quarter wave plate.

3. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 1, characterized in that: The first optical fiber is an erbium-doped fluoride optical fiber, and the first optical fiber is a double-clad optical fiber; The second optical fiber is a dysprosium-doped fluoride optical fiber, and the second optical fiber is a single-clad optical fiber.

4. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 3, characterized in that: The first optical fiber has an erbium ion doping concentration of 7 mol.%, a length of 3.9 m, a core diameter of 15 μm, a numerical aperture of 0.12, a cladding diameter of 260 μm, is cut by two planes with a spacing of 240 μm, and a cladding numerical aperture of 0.46; The second optical fiber has a dysprosium ion doping concentration of 0.2 mol%, a length of 11 m, a core diameter of 12.5 μm, a cladding diameter of 125 μm, and a numerical aperture of 0.

16.

5. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 2, characterized in that: The third optical fiber is Er-doped 3+ Fluoride ZBLAN Fiber, Er 3+ The ion concentration is 7 mol.%, the length is 2.4 m, the first optical fiber is a double-clad optical fiber with a core diameter of 15 μm, a numerical aperture of 0.12, a cladding diameter of 260 μm, and is cut by two planes with a spacing of 240 μm. The cladding numerical aperture is 0.

46.

6. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 2, characterized in that: The second pump laser is a 976 nm semiconductor pump laser; The optical fiber input end of the first optical fiber, the first optical fiber output end cap, the optical fiber input end of the third optical fiber, and the second optical fiber output end cap all have an 8° cut angle.

7. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 2, characterized in that: The first optical fiber output end cap and the second optical fiber output end cap are made of zirconium fluoride, and the core diameter is 200 μm. The first optical fiber output end cap and the first optical fiber are connected by fusion splicing, and the second optical fiber output end cap and the second optical fiber are connected by fusion splicing.

8. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 1, characterized in that: The first optical fiber and the second optical fiber are connected by fusion splicing, and the cladding power stripper is used to strip the power lost due to the fusion splicing of the first optical fiber and the second optical fiber and the remaining 976nm pump light of the first pump light laser; The femtosecond pulse laser and the first-stage optical fiber amplifier are connected by spatial coupling.

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