A wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source

Abstract

This invention discloses a broadband tunable mid-infrared high-energy femtosecond pulsed fiber laser source, comprising a laser pump source, a laser pump source pigtail, a first lens, a dichroic mirror, a second lens, an active fiber, and a third lens connected in sequence. A seed laser source is connected to the dichroic mirror, and the active fiber is a double-clad Er-type fiber. 3+ Dy 3+ A co-doped InF3 fiber is used; by adjusting the power of the laser pump source, the femtosecond pulsed laser generated by the seed laser source is amplified and frequency-shifted in the active fiber to obtain a continuously tunable high-energy femtosecond pulsed laser in the 3μm–5μm band. This invention utilizes a double-clad Er 3+ Dy 3+ Co-doped InF3 fiber was used as the gain medium, while Er... 3+ middle 4 F 9 / 2 → 4 I 9 / 2 Leap, Dy 3+ middle 6 H 13 / 2 → 6 H 15 / 2 Leap and 6 H 11 / 2 → 6 H 13 / 2 The transition achieves radiation in three transition bands, realizes full-band gain compensation, and finally obtains a high-energy femtosecond pulse laser that is continuously tunable in the 3μm to 5μm band.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser, in particular to a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source. BACKGROUND

[0002] 3-5um mid-infrared waveband is an important wavelength interval, it is not only the atmospheric low-loss transmission window, but also covers a number of molecular and chemical bond absorption peaks, so the mid-infrared laser source located in the wavelength interval has important application value in the fields of gas detection, polymer processing, infrared countermeasure, atmospheric communication and the like. In recent years, with the continuous improvement of infrared fiber drawing process and pumping technology, the mid-infrared fiber laser technology has made a great progress, especially the femtosecond pulse with narrow time domain width and high peak power has been widely concerned. Mode locking is the most commonly used technical means to generate femtosecond pulse, however, limited by the bandwidth of rare earth gain medium, the pulse operating wavelength is relatively fixed or can only be tuned in a relatively narrow range, and the widest tuning range of the current mid-infrared femtosecond mode-locked fiber laser is only 55nm, which greatly limits the application of the laser, therefore, the wavelength broadband tunable mid-infrared femtosecond fiber laser source has become a research hotspot, among which the femtosecond fiber laser source based on fiber Raman soliton self-frequency shift effect has been widely concerned due to its simple structure and flexible wavelength tuning capability.

[0003] In 2016, a research team of Cornell University in the United States used 2um femtosecond pulse as excitation and InF3 passive fiber as nonlinear medium to realize the generation of 2um-4.3um wavelength continuously tunable femtosecond pulse, however, due to the lack of gain compensation in the process of pulse frequency shift, the pulse energy is only at the level of several nJ; in the same year, a research team of Laval University in Canada used 2.8um femtosecond pulse as seed, combined with Er 3+ ZrF4 fiber amplification and frequency shift to realize the output of 2.8um-3.6um wavelength tunable femtosecond pulse, and the pulse energy reached 37nJ; recently, they optimized the length of Er 3+ ZrF4 fiber and spliced a passive InF3 fiber at the rear to expand the femtosecond pulse wavelength to 4.8um, however, due to the lack of long-wave gain, not only the long-wave pulse energy is low (several nJ), but also the wavelength cannot be further expanded, which cannot realize the full coverage of 3um-5um. SUMMARY

[0004] The present application aims to overcome the problem that the femtosecond pulse laser cannot realize the full coverage of 3um-5um in the prior art, and provides a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] The application provides a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source, which comprises a laser pumping source, a laser pumping source tail fiber, a first lens, a dichroic mirror, a second lens, an active optical fiber and a third lens which are sequentially connected. 3+ , Dy 3+ and InF3 fiber.

[0007] The power of the laser pumping source is adjusted, the femtosecond pulse laser generated by the seed laser source is amplified and frequency-shifted in the active optical fiber, and a 3-5 mu m wavelength band continuous tunable high-energy femtosecond pulse laser is obtained.

[0008] In one example, the wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is used for generating red light laser with a wavelength of 645-655 nm.

[0009] In one example, the wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is used for generating femtosecond pulse laser with a wavelength of 3 mu m.

[0010] In one example, the wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is used for generating red light laser with a wavelength of 645-655 nm.

[0011] In one example, the wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is used for generating femtosecond pulse laser with a wavelength of 3 mu m.

[0012] In one example, the wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is used for generating femtosecond pulse laser with a wavelength of 3 mu m.

[0013] The first radiation band is generated by Er 3+ in the active optical fiber, the second radiation band and the third radiation band are generated by Dy 3+ in the active optical fiber.

[0014] In one example, the wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is used for generating femtosecond pulse laser with a wavelength of 3 mu m. 3+ in the active optical fiber, the second radiation band and the third radiation band are generated by Dy 4 .

[0015] 9 / 2 . 4 . 9 / 2The transition realizes laser amplification in a wavelength range of 3.2-3.9 mu m.

[0016] In one example, a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is provided, which is pumped by a Dy 3+ Generating a second radiation band comprises:

[0017] Dy 3+ In 6 H 13 / 2 → 6 H 15 / 2 The transition realizes laser amplification in a wavelength range of 3-3.4 mu m.

[0018] In one example, a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is provided, which is pumped by a Dy 3+ Generating a third radiation band comprises:

[0019] 6 H 11 / 2 → 6 H 13 / 2 The transition realizes laser amplification in a wavelength range of 4-5 mu m.

[0020] In one example, a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is provided, which is pumped by a Dy

[0021] It should be further explained that the technical features corresponding to the above options can be combined or replaced with each other to form new technical solutions without conflict.

[0022] Compared with the prior art, the beneficial effects of the present application are:

[0023] (1) The active fiber of the present application is a double-clad Er 3+ , Dy 3+ co-doped InF3 fiber, which uses a double-clad Er 3+ , Dy 3+ co-doped InF3 fiber as a gain medium, and simultaneously utilizes the Er 3+ In 4 F 9 / 2 → 4 I 9 / 2 transition, Dy 3+ In 6 H 13 / 2 → 6 H 15 / 2 transition and 6 H 11 / 2 → 6 H 13 / 2The transition realizes three transition band radiations, realizes full-band gain compensation, and finally obtains a 3-5 mu m band continuous tunable high-energy femtosecond pulse laser, which takes into account wavelength broadband tuning and high-energy operation.

[0024] (2) The double-clad Er 3+ , Dy 3+ co-doped InF3 optical fiber used in the application not only can provide wideband gain in the range of 3-5 mu m, solve the problem of too low pulse energy of the tunable femtosecond fiber laser source caused by lack of long-wave gain, but also can provide a suitable transmission medium for wavelength frequency shift of femtosecond pulses. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A structure schematic diagram of a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source is shown for an embodiment of the application.

[0026] Figure 2 An energy level transition schematic diagram is shown for an embodiment of the application.

[0027] Figure 3 A radiation band schematic diagram is shown for an embodiment of the application.

[0028] In the figure: 1, laser pump source; 2, laser pump source tail fiber; 3, pump light input; 4, first lens; 5, dichroic mirror; 6, seed laser source; 7, second lens; 8, active optical fiber; 9, third lens; 10, laser output; 11, 4 I 15 / 2 energy level; 12, 4 I 13 / 2 energy level; 13, 4 I 11 / 2 energy level; 14, 4 I 9 / 2 energy level; 15, 4 F 9 / 2 energy level; 16, first upper transition; 17, first lower transition; 18, second lower transition; 19, first energy transfer process; 20, second energy transfer process; 21, 6 H 15 / 2 energy level; 22, 6 H 13 / 2 energy level; 23, 6 H 11 / 2 energy level; 24, 6 H 9 / 2, 6 F 11 / 2 energy level; 25, 6 H 7 / 2, 6 F 9 / 2Energy level; 26, third lower transition; 27, fourth lower transition; 28, fifth lower transition; 29 sixth lower transition. DETAILED DESCRIPTION

[0029] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0030] In the description of the present application, it should be noted that the directions or positional relationships indicated by "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like are described based on the directions or positional relationships described in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0031] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, "mounting", "connection" and "connection" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above-mentioned terms in the present application can be understood according to the specific circumstances.

[0032] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0033] Reference Figure 1 In an exemplary embodiment, the present application provides a wavelength broadband tunable mid-infrared high-energy femtosecond pulse fiber laser source, comprising laser pump source 1, laser pump source tail fiber 2, first lens 4, dichroic mirror 5, second lens 7, active optical fiber 8, third lens 9 and laser output 10 connected in sequence, wherein the seed laser source 6 is connected on the dichroic mirror 5, the active optical fiber 8 is a double-clad Er 3+ , Dy 3+ co-doped InF3 optical fiber;

[0034] Adjust the power of the laser pump source 1, the femtosecond pulse laser generated by the seed laser source 6 is amplified and frequency shifted in the active optical fiber 8, and a 3-5 μm band continuous tunable high-energy femtosecond pulse laser is obtained.

[0035] Specifically, the laser pump source 1 is used to generate red laser light with a wavelength of 645nm to 655nm as pump light; the laser pump source pigtail 2 is a multimode fiber used to output red laser light with a wavelength of 645nm to 655nm, and the red laser light with a wavelength of 645nm to 655nm is output to the first lens 4 through the pump light input 3. The first lens 4 is used to collimate the output of the pump light, and the dichroic mirror 5 has high transmittance for red laser light with a wavelength of 645nm to 655nm.

[0036] Furthermore, the seed laser source 6 is used to generate a femtosecond pulse laser with a wavelength of 3μm. The dichroic mirror 5 is highly reflective of the femtosecond pulse laser with a wavelength of 3μm, and combines the pump laser and the femtosecond pulse laser. Then, the second lens 7 focuses and couples the pump laser and the femtosecond pulse laser generated by the seed laser source 6 into the inner cladding and core of the active optical fiber 8, respectively. Specifically, the pump light output from the laser pump source pigtail 2 is coupled into the inner cladding of the active optical fiber 8, and the laser generated by the seed laser source 6 is coupled into the core of the active optical fiber 8.

[0037] Among them, the active optical fiber 8 is a double-clad Er 3+ Dy 3+ Co-doped InF3 fiber is used to amplify femtosecond pulse laser with a wavelength of 3μm and use the soliton self-frequency shift effect to shift the frequency to a longer wavelength; then the femtosecond pulse laser generated in the core of the active fiber 8 is collimated by the third lens 9 and output through the laser output 10.

[0038] Furthermore, as the power of the laser pump source 1 increases, the seed laser undergoes amplification and frequency shift in the active fiber 8, ultimately generating a tunable femtosecond pulse laser with a wavelength of 3μm to 5μm.

[0039] In one example, the femtosecond pulsed laser generated by the seed laser source is amplified and frequency-shifted in the active optical fiber, including:

[0040] Through Er in active optical fiber 3+ The first radiation band is generated, which passes through the active optical fiber in the Dy 3+ This generates a second and a third radiation belt.

[0041] Specifically, such as Figure 2 As shown, 4 I 15 / 2 Energy level 11 is Er in active optical fiber 8 3+ The first energy level of the ion, 4 I 13 / 2 Energy level 12 is Er in active optical fiber 8 3+ The second energy level of an ion; 4 I 11 / 2 Energy level 13 is Er in active optical fiber3+ a third ion energy level; 4 I 9 / 2 Energy level 14 is an Er 3+ a fourth ion energy level; 4 F 9 / 2 Energy level 15 is an Er 3+ a fifth ion energy level; a first up transition 16 is generated between 4 I 15 / 2 energy level 11 and 4 F 9 / 2 energy level 15, 4 I 15 / 2 the ion on energy level 11 absorbs the pumping light and jumps to 4 F 9 / 2 energy level 15, wherein red light laser with wavelength of 645nm-655nm is selected as the pumping light, corresponding to the strong absorption region of the first up transition 16;

[0042] Further, a first down transition 17 is generated between 4 F 9 / 2 energy level 15 and 4 I 9 / 2 energy level 14, a second down transition 18 is generated between 4 I 9 / 2 energy level 14 and 4 I 11 / 2 energy level 13, 4 I 9 / 2 the ion on energy level 14 jumps to 4 I 11 / 2 energy level 13 by multi-phonon relaxation; a first energy transfer process 19 occurs between 4 I 11 / 2 energy level 13 and 6 H 7 / 2, 6 F 9 / 2 energy level 25, so that 4 I 11 / 2 the ion on energy level 13 rapidly jumps back to 4 I 15 / 2 energy level 11, while 6 H 15 / 2 the ion on energy level 21 absorbs 4 I 11 / 2 the energy released by the ion on energy level 13 jumps to 6 H 7 / 2 , 6 F 9 / 2 energy level 25; a second energy transfer process 20 occurs between 4 I 13 / 2 energy level 12 and 6 H 11 / 2 energy level 23, so that4 I 13 / 2 The ions on energy level 12 rapidly transition back 4 I 15 / 2 energy level 11, while 6 H 15 / 2 The ions on energy level 21 absorb 4 I 13 / 2 The energy transition of the ions on energy level 12 releases 6 H 11 / 2 energy level 23; wherein 6 H 15 / 2 Energy level 21 is the first energy level of Dy 3+ ions in the active optical fiber 8, 6 H 13 / 2 Energy level 22 is the second energy level of Dy 3+ ions in the active optical fiber 8, 6 H 11 / 2 Energy level 23 is the third energy level of Dy 3+ ions in the active optical fiber 8; 6 H 9 / 2 , 6 F 11 / 2 Energy level 24 is the fourth energy level of Dy 3+ ions in the active optical fiber 8; 6 H 7 / 2 , 6 F 9 / 2 Energy level 25 is the fifth energy level of Dy 3+ ions in the active optical fiber 8, the third lower transition 26 being between 6 H 7 / 2 , 6 F 9 / 2 energy level 25 and 6 H 9 / 2 , 6 F 11 / 2 energy level 24, 6 H 7 / 2 , 6 F 9 / 2 The ions on energy level 25 transition to 6 H 9 / 2 , 6 F 11 / 2 energy level 24 by way of a multi-phonon relaxation; the fourth lower transition 27 being between 6 H 9 / 2 , 6 F 11 / 2 energy level 24 and 6 H 11 / 2 energy level 23, 6 H 9 / 2 , 6 F 11 / 2 The ions on energy level 24 transition to6 H 11 / 2 Energy level 23 (upper); fifth lower jump 28 (lower). 6 H 11 / 2 Energy level 23 and 6 H 13 / 2 It occurs between energy levels 22, and the sixth lower transition occurs at energy level 29. 6 H 13 / 2 Energy level 22 and 6 H 15 / 2 It arises between energy levels 21. 6 H 9 / 2 , 6 F 11 / 2 Energy level 24 and 6 H 7 / 2 , 6 F 9 / 2 Level 25 is the merging of two levels, meaning that the two levels are very close together and can be treated as one level.

[0043] Furthermore, red laser light with a wavelength of 645nm to 655nm will be used in active optical fiber 8. 4 I 15 / 2 Ion pumping at energy level 11 4 F 9 / 2 At energy level 15, achieve 4 F 9 / 2 Level 15 and the lower level 4 I 9 / 2 Population inversion between energy levels 14 4 F 9 / 2 Ions at energy level 15 rapidly transfer to energy level 17 via the first lower transition 17. 4 I 9 / 2 At energy level 14, the first lower transition 17 amplifies laser light with wavelengths ranging from 3.2 μm to 3.9 μm through stimulated emission. Subsequently... 4 I 9 / 2 Ions at energy level 14 rapidly transfer via a second lower transition 18 to 4 I 11 / 2 Energy level 13 and above.

[0044] Immediately afterwards, 6 H 15 / 2 Partial ion absorption at energy level 21 4 I 11 / 2 Ion transitions at energy level 13 back to 4 I 15 / 2 The energy released at energy level 11 then jumps to 6 H 7 / 2 , 6 F 9 / 2 At energy level 25, the first energy transfer process 19 is completed; 6 H 15 / 2The part of ions on the energy level 21 absorbs 4 I 13 / 2 The ions on the energy level 12 jump back to 4 I 15 / 2 The energy released on the energy level 11, and then jump to 6 H 11 / 2 The energy level 23, completing the second energy transfer process 20. After the two energy transfer processes are completed, 6 H 7 / 2 , 6 F 9 / 2 The ions on the energy level 25 are rapidly transferred to 6 H 9 / 2 , 6 F 11 / 2 The energy level 24, 6 H 9 / 2 , 6 F 11 / 2 The ions on the energy level 24 are rapidly transferred to 6 H 11 / 2 The energy level 23, realizing 6 H 11 / 2 The population inversion between the energy level 23 and the lower energy level 6 H 13 / 2 The energy level 22, 6 H 11 / 2 The ions on the energy level 23 are rapidly transferred to 6 H 13 / 2 The energy level 22, amplifying the laser with the wavelength of 4 μm ~ 5 μm by stimulated emission. At the same time, 6 H 13 / 2 The population inversion between the energy level 22 and the lower energy level 6 H 15 / 2 The energy level 21, 6 H 13 / 2 The ions on the energy level 22 are rapidly transferred to 6 H 15 / 2 The energy level 21, amplifying the laser with the wavelength of 3 μm ~ 3.4 μm by stimulated emission.

[0045] When the seed laser source 6 enters the active optical fiber 8, the signal light with the wavelength of 3 μm will be frequency-shifted to the long wavelength direction under the action of the Raman soliton self-frequency shift effect, and when the wavelength is frequency-shifted to the wavelength of the active optical fiber 8, 6 H 13 / 2 The energy level 22 and 6 H 15 / 2 The energy level 21, 4 F 9 / 2 The energy level 15 and 4 I 9 / 2 The energy level 14, and 6 H11 / 2 Energy level 23 and 6 H 13 / 2 Energy level 22 transition wavelength corresponding to the time, will experience effective amplification to achieve energy enhancement, ultimately through the control of laser pump source 1 power, can realize 3 ~ 5 mu m wavelength tunable high energy femtosecond pulse laser output.

[0046] Further, as Figure 3 indicated, the first lower transition 17, the fifth lower transition 28 and the sixth lower transition 29 generate three radiation bands, wherein the first lower transition 17 provides amplification gain for laser of 3.2 ~ 3.9 mu m through Er 3+ The first radiation band is generated, 4 F 9 / 2 → 4 I 9 / 2 Transition; the sixth lower transition 29 provides amplification gain for laser of 3 ~ 3.4 mu m through Dy 3+ The second radiation band is generated, and Dy 3+ The third radiation band is generated, 6 H 13 / 2 → 6 H 15 / 2 Transition; the fifth lower transition 28 provides amplification gain for laser of 4 ~ 5 mu m through Dy 3+ The third radiation band is generated, 6 H 11 / 2 → 6 H 13 / 2 Transition.

[0047] The application utilizes red light laser diode with wavelength of 645 ~ 655 nm to pump double-clad Er 3+ , Dy 3+ Co-doped InF3 optical fiber, simultaneously excites Er 3+ and Dy 3+ The three transition bands of 4 F 9 / 2 → 4 I 9 / 2 , 6 H 11 / 2 → 6 H 13 / 2 and 6 H 13 / 2 → 6 H 15 / 2 radiation greatly expand the gain bandwidth. At the same time, the double-clad Er 3+ , Dy 3+ Co-doped InF3 optical fiber can not only provide broadband gain in the range of 3 ~ 5 mu m, but also utilize red light laser diode with wavelength of 645 ~ 655 nm to pump double-clad Er 3+ / Dy 3+The co-doped InF3 optical fiber serves as a femtosecond pulse wavelength frequency shift and broadband amplification medium, and provides a suitable transmission medium for wavelength frequency shift of femtosecond pulses.

[0048] Further, the first lens and the third lens are both collimating lenses, and the laser pump source tail fiber is a multimode optical fiber.

[0049] The above detailed description of the embodiments is a detailed explanation of the present application, and cannot be deemed as limiting the embodiments of the present application to the above description. For those skilled in the art of the present application, without departing from the concept of the present application, a number of simple deductions and substitutions can be made, which should be deemed as falling within the protection scope of the present application.

Claims

1. A broadband tunable mid-infrared high-energy femtosecond pulsed fiber laser source, characterized in that, The system comprises, in sequence, a laser pump source, a laser pump source pigtail, a first lens, a dichroic mirror, a second lens, an active optical fiber, and a third lens. A seed laser source is connected to the dichroic mirror, and the active optical fiber is a double-clad Er-type fiber. 3+ Dy 3+ Co-doped InF3 fiber; the second lens is used to couple the pump light output from the laser pump source pigtail into the inner cladding of the active fiber, and to couple the laser generated by the seed laser source into the core of the active fiber. By adjusting the power of the laser pump source, the femtosecond pulsed laser generated by the seed laser source is amplified and frequency-shifted in the active optical fiber to obtain a continuously tunable high-energy femtosecond pulsed laser in the 3µm~5µm band; the amplification and frequency shifting of the femtosecond pulsed laser generated by the seed laser source in the active optical fiber includes: Through Er in active optical fiber 3+ The first radiation band is generated, which passes through the active optical fiber in the Dy 3+ The second and third radiation bands are generated; the Er in the active optical fiber 3+ The first radiation band is generated, including: 4 F 9 / 2 → 4 I 9 / 2 The transition enables laser amplification in the wavelength range of 3.2µm to 3.9µm; The active optical fiber Dy 3+ The second radiation band is generated, including: Dy 3+ middle 6 H 13 / 2 → 6 H 15 / 2 The transition enables laser amplification in the wavelength range of 3µm to 3.4µm; The active optical fiber Dy 3+ The third radiation belt is generated, including: 6 H 11 / 2 → 6 H 13 / 2 The transition enables laser amplification in the wavelength range of 4µm to 5µm.

2. The broadband tunable mid-infrared high-energy femtosecond pulsed fiber laser source according to claim 1, characterized in that, The laser pump source is used to generate red laser light with a wavelength of 645nm~655nm.

3. The broadband tunable mid-infrared high-energy femtosecond pulsed fiber laser source according to claim 1, characterized in that, The seed laser source is used to generate femtosecond pulsed lasers with a wavelength of 3 μm.

4. The wavelength-wide tunable mid-infrared high-energy femtosecond pulsed fiber laser source according to claim 1, characterized in that, Both the first lens and the third lens are collimating lenses.

5. A wavelength-wide tunable mid-infrared high-energy femtosecond pulsed fiber laser source according to claim 1, characterized in that, The laser pump source pigtail is a multimode fiber.

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