CN115296125A - A mid-infrared tunable pure soliton fiber laser based on cascaded amplification - Google Patents

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; signal, and transmit the femtosecond pulse signal to the first-stage fiber amplifier; the first-stage fiber amplifier is used to amplify the power of the femtosecond pulse signal and generate Raman soliton; the second-stage fiber amplifier is used to recycle the background signal light Reuse to amplify Raman solitons; the invention can obtain higher output power and pulse energy, wider tunable range and pure Raman soliton pulses by recycling and reusing background signal light to amplify Raman solitons.

Description

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

technical field

The invention relates to the field of fiber laser technology, in particular to a mid-infrared tunable pure soliton fiber laser based on cascade amplification.

Background technique

High-power mid-infrared femtosecond lasers are of great significance because of their wide applications in 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 mode-locking technology based on nonlinear polarization rotation is an effective means to realize femtosecond pulse output of mid-infrared fiber lasers, but the mode-locked pulses are limited to several wavelengths such as 2.8 μm, 2.9 μm, 3.1 μm and 3.5 μm, and its wavelength is tunable. Limited by the gain bandwidth of fluoride rare earth ions. In many practical applications of molecular spectroscopy and sensing detection, mid-infrared femtosecond lasers with continuously tunable wavelength over a wide range are required.

The soliton self-frequency shifting (SSFS) effect in optical fibers can be exploited to break through similar wavelength tunability limitations to provide femtosecond pulses with broadband tunability. The SSFS effect can make the original soliton pulse frequency shift away from the Kelly sideband of the mode-locked pulse to the long-wave direction, thereby obtaining a very clean and complete Raman soliton. So far, tunable femtosecond lasers based on the SSFS effect have been intensively studied in silica fibers, tellurate fibers, fluoride fibers, and chalcogenide fibers. Among them, due to the high loss in the mid-infrared region, the Raman soliton in the silica fiber is limited to a wavelength of 2.3 μm, while the soft glass fiber benefits from the lower phonon energy, which can support the further realization of Raman soliton in the mid-infrared region. frequency shift. Among soft glass fibers, fluoride fibers have lower nonlinear refractive index and larger anomalous dispersion compared to tellurate fibers and chalcogenide fibers, which enable high pulse energy and high peak values to be generated through fluoride fibers Raman soliton power becomes possible.

At present, based on the SSFS effect in the fluoride optical fiber, the existing technologies for mid-infrared broadband tunable pulse output mainly focus on the following aspects: First, the use of near-infrared ultrafast laser amplifiers as pump sources to generate high-energy ultrashort pulses, using fluorine The chemical fiber is used as a frequency-shifting fiber to realize 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 2-4.3μm has been realized through the combination of 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, using a mid-infrared fiber laser as a pump source has a longer initial pump wavelength, which facilitates the realization of Raman soliton pulses at far wavelengths. The advantages. Second, use the ultrashort pulse oscillator and its amplifier based on fluoride fiber as the mid-infrared pump source, and also use the fluoride fiber as the frequency-shifting fiber mid-infrared tunable ultrafast system to achieve high-energy Raman soliton pulse output. For example, by using the Er:ZBLAN fiber oscillator and its amplifier as the pump source, an ultrafast system of watt-level Raman soliton pulses with continuously tunable wavelengths from 2.8 μm to 3.6 μm can be realized. However, the above SSFS systems are always accompanied by background signal light or second-order Raman solitons, which limit the energy conversion efficiency, Raman frequency shift range and spectral purity. How to select the first-order Raman solitons from the background signal light or the second-order Raman solitons to obtain pure Raman solitons requires further work, which will undoubtedly increase the complexity of the system structure and the difficulty of operation.

Contents of the invention

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 improves the spectrum of the mid-infrared Raman soliton fiber laser purity.

To achieve the above object, the present invention provides a mid-infrared tunable pure soliton fiber laser based on cascade amplification, including: 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 transmits the femtosecond pulse signal to the first-stage fiber amplifier; the first-stage fiber amplifier is used to power the femtosecond pulse signal Amplifying and generating Raman solitons; the second-stage fiber amplifier is used to recycle background signal light to amplify the Raman solitons; the first-stage fiber amplifier includes: a first polarization-dependent isolator, a first A half-wave plate, a first quarter-wave plate, a first pump laser, a first pump light collimator lens, a first pump light laser dichroic mirror, a first pump light laser focusing lens, The 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, and the first half-wave plate is connected to the first quarter-wave plate. The first quarter-wave plate is connected with the first pumping light laser dichroic mirror, and the opposite sides of the pumping light collimating to the lens are connected with the first pumping laser and the first pumping laser respectively. The light laser dichroic mirror is connected, the first pump light laser dichroic mirror is connected with the first pump light laser focusing lens, and the first pump light laser dichroic mirror is used to pass through the quadrant The laser light from one of the wave plates is combined with the pumping light passing through the first pumping light collimating lens, and transmitted to the first pumping light laser focusing lens, and the first pumping light laser focusing lens is combined with the first pumping light laser focusing lens The first optical fiber is connected; 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 first optical fiber Two optical fibers are connected, 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.

Further, the femtosecond pulsed laser includes: a second pump laser, a second pump light collimator lens, a second pump light laser dichroic mirror, a second pump light laser focusing lens, a third optical fiber, a first Two fiber output end caps, the second laser collimator lens, the third pump light laser dichroic mirror, the second half-wave plate, the polarization beam splitter prism, the second polarization-dependent isolator, the gold mirror, the second quarter splitter A wave plate; the second pump laser is connected to the second pump light collimator lens; the second pump light collimator lens is connected to the second pump light laser dichroic mirror; the The second pumping light laser dichroic mirror is connected with the second pumping light laser focusing lens and the second quarter-wave plate, and is used to collimate the pumping light from the second pumping light collimating lens and the first The pumping light and laser light of the two quarter-wave plates are combined, and transmitted to the second pumping light laser focusing lens; the second pumping light laser focusing lens is connected to the third optical fiber, and the The second optical fiber output end cap is connected to the other end of the third optical fiber, and the second optical fiber output end cap is also connected to the second laser collimating lens, and the second laser collimating lens is connected to the third optical fiber. The pump light laser dichroic mirror is connected, the third pump light laser dichroic mirror is connected to the second half-wave plate, and the second half-wave plate is connected to the polarization beam splitter prism , the polarization beam splitter is connected to the second polarization-dependent isolator for outputting femtosecond pulse signals to the first-stage fiber amplifier, and outputting laser light to the second polarization-dependent isolator, the second The polarization-dependent isolator is connected to the gold mirror, and the gold mirror is connected to the second quarter-wave plate.

Further, the first optical fiber is an erbium-doped fluoride optical fiber, and the first optical fiber is a double-layer clad optical fiber; the second optical fiber is a dysprosium-doped fluoride optical fiber, and the second optical fiber is a single-layer clad optical fiber .

Further, the erbium ion doping concentration of the first optical fiber is 7mol.%, the length is 3.9m, the core diameter is 15μm, the numerical aperture is 0.12, the cladding diameter is 260μm, and it is separated by two planes with an interval of 240μm. The cladding numerical aperture is 0.46; the dysprosium ion doping concentration of the second optical fiber is 0.2mol.%, the length is 11m, the core diameter is 12.5μm, the cladding diameter is 125μm, and the numerical aperture is 0.16.

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

Further, the third optical fiber is an Er ³⁺ fluoride-doped ZBLAN optical fiber, the concentration of Er ³⁺ ions is 7 mol.%, and the length is 2.4 m, and the first optical fiber is a double-clad optical fiber with a core diameter of 15 μm. The numerical aperture is 0.12, the diameter of the cladding is 260 μm, and is cut by two planes with an interval of 240 μm, and the numerical aperture of the cladding is 0.46.

Further, the second pump laser is a 976nm semiconductor pump laser; the fiber input end of the first fiber, the first fiber output cap, the fiber input end of the third fiber, the second Fiber output end caps are cut at an 8° angle.

Further, the material of the first optical fiber output end cap and the second optical fiber output end cap is zirconium fluoride, and the core diameter is 200 μm, and the first optical fiber output end cap and the second optical fiber are welded together The second optical fiber output end cap and the third optical fiber are connected by fusion splicing.

Further, the Raman soliton generated by the first-stage fiber amplifier is 3 μm, and the background light is 2.8 μm.

Further, the first optical fiber and the second optical fiber are connected by fusion splicing, and the power stripper is used to strip the lost power caused by the fusion splicing of the first optical fiber and the second optical fiber and the power of the first pump The remaining 976nm pumping light of the pump laser; the femtosecond pulse laser and the first-stage fiber amplifier are connected through spatial coupling.

The present invention provides a mid-infrared tunable pure soliton fiber laser based on cascaded amplification, which has the beneficial effect of being able to recycle and reuse background signal light to amplify Raman solitons, thereby obtaining higher output power and pulse energy, and more Wide tunable range and pulses of pure Raman solitons.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without creative work.

1 is a schematic block diagram of a mid-infrared tunable pure soliton fiber laser based on cascaded amplification according to an embodiment of the present invention;

2 is a schematic structural diagram of a first-stage fiber amplifier and a second-stage fiber amplifier of a mid-infrared tunable pure soliton fiber laser based on cascaded amplification according to an embodiment of the present invention;

3 is a schematic structural diagram of a femtosecond pulsed laser based on a mid-infrared tunable pure soliton fiber laser based on cascaded amplification according to an embodiment of the present invention;

Fig. 4 is the spectrogram 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 the embodiment of the present invention;

Fig. 5 is a spectrum diagram of output pulses of the second-stage fiber amplifier of the mid-infrared tunable pure soliton fiber laser based on cascaded amplification according to an embodiment of the present invention.

In the accompanying drawings, each reference sign indicates:

01. Femtosecond pulse laser; 02. First-stage fiber amplifier; 03. Second-stage fiber amplifier; 1. Second pump laser; 2. Second pump collimator lens; 3. Second pump laser Dichroic mirror; 4. The second pump light laser focusing lens; 5. The third optical fiber; 6. The second optical fiber output end cap; 7. The second laser collimator lens; 8. The third pump light laser dichroic mirror ; 9, the second half-wave plate; 10, the polarization beam splitter prism; 11, the second polarization-dependent isolator; 12, the gold mirror; 13, the second quarter-wave plate; 21, the first polarization-dependent isolation 22, the first half-wave plate; 23, the first quarter-wave plate; 24, the first pump laser; 25, the first pump light collimator lens; 26, the first pump light Laser dichroic mirror; 27. The first pump light laser focusing lens; 28. The first optical fiber; 29. The cladding power stripper; 30. The second optical fiber; 31. The output end cap of the first optical fiber; 32. The first laser collimating lens.

Detailed ways

In order to make the purpose, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described The embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to Figure 1, which is a mid-infrared tunable pure soliton fiber laser based on cascade amplification, including: femtosecond pulse laser 01, first-stage fiber amplifier 02 and second-stage fiber amplifier 03; among them, femtosecond pulse laser 01 is used to generate the 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 optical fiber Amplifier 03 is used to recycle background signal light to amplify Raman solitons.

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

Referring to Fig. 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 Pumping light collimating lens 25, first pumping light laser dichroic mirror 26, first pumping light laser focusing lens 27, first optical fiber 28; first polarization dependent isolator 21 and first half-wave plate 22 is connected, the first half-wave plate 22 is connected with the first quarter-wave plate 23, the first quarter-wave plate 23 is connected with the first pumping light laser dichroic mirror 26, the first pumping The opposite sides of the light collimating lens 25 are respectively connected with the first pump laser 24 and the first pump laser dichroic mirror 26, and the first pump laser dichroic mirror 26 is connected with the first pump laser focusing lens 27. Connected, the first pump light laser dichroic mirror 26 is used to combine the laser light passing through the first quarter-wave plate 23 and the pump light passing through the first pump light collimating lens 25, and transmit to the first pump light The pump laser focusing lens 27, the first pump laser focusing lens 27 is connected with the first optical fiber 28.

Please continue to refer to Fig. 2, the second-stage optical fiber amplifier 03 includes: cladding power stripper 29, the second optical fiber 30, the first optical fiber output end cap 31, the first laser collimating lens 32; cladding power stripper 29 and the first The two optical fibers 30 are connected, 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 .

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

The erbium ion doping concentration of the first optical fiber 28 is 7mol.%, the length is 3.9m, the core diameter is 15 μm, the numerical aperture is 0.12, and the cladding diameter is 260 μm, which is cut by two planes with an interval of 240 μm. The numerical aperture is 0.46; the dysprosium ion doping concentration of the second optical fiber 30 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. Wherein, the erbium ion is the trivalent erbium ion Er ³⁺ , and the dysprosium ion is the trivalent dysprosium ion Dy ³⁺ .

In this embodiment, the pulse output of the femtosecond pulsed laser 01 passes through the first polarization-dependent isolator 21 to prevent the reflected light from the cascaded amplifier from affecting the femtosecond pulsed 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, and the pump light and the seed pulse laser pass through the first After the pump light is combined with the laser dichroic mirror 26, the first pump light laser focusing lens 27 is coupled into the first optical fiber 28 to form a forward pump structure.

Among them, the Raman soliton generated by the first-stage fiber amplifier 02 is 3 μm, and the background light is 2.8 μm.

In this embodiment, the first-stage fiber amplifier 02 is used as an amplifier to increase the optical power of a 2.8 μm femtosecond pulse signal and a frequency shifter to generate a 3 μm Raman soliton. Then inject the 3 μm Raman soliton and 2.8 μm background signal light into the second-stage fiber amplifier 03 , and use the cladding power stripper 29 to strip the remaining 976nm pump light.

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 lost power caused by the fusion of the first optical fiber 28 and the second optical fiber 30; femtosecond pulse laser 01 and The first-stage optical fiber amplifier 02 is connected through spatial coupling.

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 of the two optical fibers, the actual signal light transmission transmittance of the fusion splicing point is measured to be 82%. The power resulting in losses is also stripped by the cladding power stripper 29 .

Please refer to Fig. 3, in one embodiment, the femtosecond pulsed laser 01 comprises: the second pump laser 1, the second pump light collimator lens 2, the second pump light laser dichroic mirror 3, the second pump light Optical laser focusing lens 4, third optical fiber 5, second optical fiber output end cap 6, second laser collimating lens 7, third pumping light laser dichroic mirror 8, second half-wave plate 9, polarization splitter A prism 10 , a second polarization-dependent isolator 11 , a gold mirror 12 , and a second quarter-wave plate 13 .

Wherein, the second pumping laser 1 is connected with the second pumping light collimating lens 2; the second pumping light collimating lens 2 is connected with the second pumping light laser dichroic mirror 3; the second pumping light laser dichroic mirror The mirror 3 is connected with the second pumping light laser focusing lens 4 and the second quarter-wave plate 13 for pumping from the second pumping light collimating lens 2 and the second quarter-wave plate 13 The light and the laser light are combined and transmitted to the second pumping light laser focusing lens 4; the second pumping 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 Connect, the second fiber output end cap 6 is also connected with the second laser collimator lens 7, the second laser collimator lens 7 is connected with the third pump light laser dichroic mirror, the third pump light laser dichroic mirror is connected with the first laser dichroic mirror The second half-wave plate 9 is connected, the second half-wave plate 9 is connected with the polarization splitter prism 10, and the polarization splitter prism 10 is connected with the second polarization-dependent isolator 11 for outputting to the first-stage optical fiber amplifier 02 femtosecond pulse signal, and output laser light 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.

Wherein, the third optical fiber 5 is a ZBLAN fiber doped with Er ³⁺ fluoride, the concentration of Er ³⁺ ions is 7 mol.%, and the length is 2.4 m. The first optical fiber 28 is a double-clad optical fiber with a core diameter of 15 μm and a numerical aperture of 0.12, the diameter of the cladding is 260 μm, cut by two planes with an interval of 240 μm, and the numerical aperture of the cladding is 0.46.

The second pump laser 1 is a 976nm semiconductor pump laser, emitting continuous pump light with a wavelength of 976nm, which is focused to the third optical fiber 5 by the second pump light collimator lens 2 and the second pump light laser focusing lens 4 in the inner cladding. The second pump light laser dichroic mirror 3 and the third pump light laser dichroic mirror are used to combine and separate 2.8 μm laser light and 976 nm 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 forms a passive mode-locking device with the second half-wave plate 9 and the second quarter-wave plate 13 to start and maintain mode-locked 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. Femtosecond pulsed laser 01 obtains mode-locked pulses working in the soliton region with a pulse width of 257 fs.

In this embodiment, both the first pump laser 24 and the second pump laser 1 are 976nm semiconductor pump lasers, which are fiber-coupled multimode semiconductor lasers.

In one embodiment, the material of the first optical fiber output end cap 31 and the second optical fiber output end cap 6 is zirconium fluoride, the core diameter is 200 μm, and the first optical fiber output end cap 31 and the first optical fiber 28 are welded together Connection, the second optical fiber output end cap 6 and the second optical fiber 30 are connected by fusion splicing.

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

The output end cap 6 of the second optical fiber cut at an angle of 8° is fused to the output end of the third optical fiber 5 to prevent damage to the end face of the optical fiber caused by long-term operation of the laser, and its length is about 350 μm.

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

Please refer to Figure 4. Figure 4 shows the spectral evolution of the output pulse of the first-stage fiber amplifier 02. As the pump power increases, the power of the 2.8 μm femtosecond pulse is amplified and Raman solitons are formed at 3 μm, and gradually move toward Longer wavelength regions shift. The center wavelength of the Raman soliton output by the first-stage fiber amplifier 02 is always within the radiation section of the second fiber 30, which is beneficial for the second-stage fiber amplifier 03 to amplify the Raman soliton by recycling the 2.8 μm background signal light.

Please refer to Figure 5. Figure 5 shows the spectral evolution of the output pulse of the second-stage fiber amplifier 03. As the pump power increases, the central wavelength of the Raman soliton can be continuously tuned from 3.03 μm to 3.63 μm. No 2.8μm background signal light or second-order Raman solitons are observed in the output spectrum, and the state of pure Raman solitons with high-quality spectral purity is always maintained. Finally, at a pump power of 20W, the pure Raman soliton with a center wavelength of 3.63μm achieves a pulse energy of 31.8nJ and a pulse duration of 210fs, corresponding to a peak power of 151kW.

The mid-infrared tunable pure soliton fiber laser based on cascaded amplification provided in this embodiment shows that the present invention creatively amplifies Raman solitons by recycling and reusing background signal light based on cascaded amplification. Pulsed fiber lasers with high pulse energy, broadband wavelength tunability, and pure Raman solitons provide an effective approach.

It should be noted that the above embodiments are examples for describing the technical solution of the present invention in detail rather than limitation. The present invention can also be applied to other SSFS-based pure Raman soliton fiber laser systems, such as Er3 ^+-doped and Tm3 ^+-doped fiber cascade-amplified fiber lasers, Tm3 ⁺ -doped and Ho3 ⁺ -doped fiber cascade-amplified fiber lasers fiber lasers and more. All modifications and changes made by those skilled in the art that do not depart from the spirit of the technical solution of the present invention shall be covered by the protection scope of the appended claims of the present invention.

In the foregoing embodiments, the descriptions of each embodiment have their own emphases, and for parts not described in detail in a certain embodiment, reference may be made to relevant descriptions of other embodiments.

The above is a description of a mid-infrared tunable pure soliton fiber laser based on cascaded amplification provided by the present invention. For those skilled in the art, based on the ideas of the embodiments of the present invention, they will understand both the specific implementation and the scope of application. There are changes, and in summary, the contents of this specification should not be construed as limiting the present invention.

Claims (10)

1. A mid-infrared tunable pure soliton fiber laser based on cascaded amplification, comprising: a femtosecond pulsed laser, a first-order fiber amplifier and a second-order fiber amplifier; The femtosecond pulse laser is used to generate a femtosecond pulse signal, and transmits the femtosecond pulse signal to the first-stage fiber amplifier; the first-stage fiber amplifier is used to power the femtosecond pulse signal Amplifying and generating Raman solitons; the second-stage fiber amplifier is used to recycle background signal light to amplify the Raman solitons; 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 collimator lens, a first A 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, and the first half wave plate A wave plate is connected with the first quarter-wave plate, the first quarter-wave plate is connected with the first pump light laser dichroic mirror, and the pump light is directed to the opposite side of the lens. The two sides are respectively connected with the first pump laser and the first pump laser dichroic mirror, and the first pump laser dichroic mirror is connected with the first pump laser focusing lens, so 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 to the first pump light A pump laser focusing lens, the first pump 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 collimator lens; the cladding power stripper is connected to the second optical fiber, and 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, wherein the femtosecond pulsed laser comprises: The second pump laser, the second pump light collimator lens, the second pump light laser dichroic mirror, the second pump light laser focusing lens, the third optical fiber, the second optical fiber output end cap, the second laser collimator A 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 collimator lens; the second pump light collimator lens is connected to the second pump light laser dichroic mirror; the second pump light The light laser dichroic mirror is connected with the second pump light laser focusing lens and the second quarter wave plate, and is used to collimate the pump light from the second pump light through the collimating lens and the second quarter wave plate. The pumping light and laser light of the wave plate are combined and transmitted to the second pumping light laser focusing lens; the second pumping light laser focusing lens is connected to the third optical fiber, and the output end of the second optical fiber The cap is connected to the other end of the third optical fiber, and the second optical fiber output end cap is also connected to the second laser collimating lens, and the second laser collimating lens is connected to the third pumping laser two The color mirror is connected, the third pump light laser dichroic mirror is connected with the second half-wave plate, the second half-wave plate is connected with the polarization beam splitter prism, and the polarization beam splitter The prism is connected with the second polarization-dependent isolator, and is used to output femtosecond pulse signal to the first-stage fiber amplifier, and output laser to the second polarization-dependent isolator, and the second polarization-dependent isolator and The gold mirror is connected, and the gold mirror is connected to the second quarter-wave plate. 3. the mid-infrared tunable pure soliton fiber laser based on cascaded 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-layer clad optical fiber; The second optical fiber is a dysprosium-doped fluoride optical fiber, and the second optical fiber is a single-layer clad optical fiber. 4. the mid-infrared tunable pure soliton fiber laser based on cascaded amplification according to claim 3, characterized in that, The erbium ion doping concentration of the first optical fiber is 7mol.%, the length is 3.9m, the core diameter is 15μm, the numerical aperture is 0.12, and the cladding diameter is 260μm, which is cut by two planes with an interval of 240μm. Layer numerical aperture is 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 cascaded amplification according to claim 1, characterized in that, 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 3.03 μm-3.63 μm, and the pulse energy is 0.4-31.8 nJ. 6. The mid-infrared tunable pure soliton fiber laser based on cascaded amplification according to claim 2, characterized in that, The third optical fiber is a ZBLAN fiber doped with Er ³⁺ fluoride, the concentration of Er ³⁺ ions is 7mol.%, and the length is 2.4m. The first optical fiber is a double-clad optical fiber with a core diameter of 15 μm and a numerical aperture of 0.12, the diameter of the cladding is 260 μm, cut by two planes with an interval of 240 μm, and the numerical aperture of the cladding is 0.46. 7. 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 976nm semiconductor pump laser; The optical fiber input end of the first optical fiber, the first optical fiber output end cap, the third optical fiber input end, and the second optical fiber output end cap all have an 8° angle cut. 8. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 2, characterized in that, The material of the first optical fiber output end cap and the second optical fiber output end cap is 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, The second optical fiber output end cap is connected to the second optical fiber by fusion splicing. 9. The mid-infrared tunable pure soliton fiber laser based on cascade amplification according to claim 1, characterized in that, The Raman soliton generated by the first-stage optical fiber amplifier is 3 μm, and the background light is 2.8 μm. 10. 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, and the power stripper is used to strip the lost power caused by the fusion of the first optical fiber and the second optical fiber and the first pumping laser The remaining 976nm pump light; The femtosecond pulsed laser and the first-stage fiber amplifier are connected through spatial coupling.

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