Dual-wavelength cascade-pumped 4.3-micron mid-infrared fiber laser and laser high-efficiency generation method

Abstract

The application discloses a kind of 4.3 μm mid-infrared fiber laser of dual-wavelength cascade pumping and laser high-efficiency generation method, comprising the following steps: S1, first pump laser generates first pump light;S2, second pump laser generates second pump light;S3, first pump light is coupled into the core of dysprosium-doped indium fluoride gain optical fiber by first dichroic mirror, convex lens;Second pump light is coupled into the core of dysprosium-doped indium fluoride gain optical fiber by mirror, convex lens;S4, the laser generated by oscillation in optical resonant cavity is output by second fiber bragg grating, and first pump light not absorbed by dysprosium-doped indium fluoride gain optical fiber is filtered out using second dichroic mirror, to obtain 4.3 μm laser output.The application can avoid laser self-termination effect and small quantum loss, and 4.3 μm laser with optical-to-optical conversion efficiency up to 38% can be obtained, which significantly improves the generation efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser, and particularly relates to a 4.3-micron mid-infrared fiber laser of dual-wavelength cascade pumping and a laser efficient generation method. BACKGROUND

[0002] The 4.3-micron mid-infrared band laser has great application value and demand in the fields of environmental monitoring, biological medicine, molecular spectroscopy and national defense. However, due to the rapid increase of the non-radiative transition rate and the light transmission loss with the increase of the maximum phonon energy of the substrate material, the direct generation of the 4-micron laser above still faces challenges. The indium fluoride fiber has low phonon energy and can be doped with high-concentration dysprosium ions, and has great potential in the generation of 4.3-micron laser. In 2018, Majewski et al. of Macquarie University in Australia first observed the fluorescence spectrum of 4.1-4.5 microns in the dysprosium-doped indium fluoride fiber by 1.7-micron single-wavelength laser direct pumping ([1] M.R. Majewski, et al. "Emission beyond 4 microns and mid-infrared lasing in a dysprosium-doped indium fluoride (InF3) fiber," Opt. Lett., 2018, 43(8): 1926-1929). However, due to the short lifetime of the upper level of dysprosium ions 6 H 11 / 2 the lifetime of the lower level 6 H 13 / 2 , the single-wavelength pumping faces the problem of laser self-termination. The scheme of 1.7-micron and 2.3-micron dual-wavelength pumping can solve the problem of laser self-termination, and theoretically can obtain a maximum light-light conversion efficiency of 26%. However, due to the 1.7-micron pumping mode not being the same band pumping, the laser generation efficiency is limited by a large quantum loss. In order to obtain a 4.3-micron laser with higher efficiency, the laser generation method needs to be improved. SUMMARY

[0003] In order to realize the efficient generation of the dysprosium-doped indium fluoride fiber laser, the application provides a 4.3-micron mid-infrared fiber laser of dual-wavelength cascade pumping and a laser efficient generation method, which can avoid the effect of laser self-termination and has small quantum loss, and can obtain a 4.3-micron laser with a light-light conversion efficiency of 38%, thereby significantly improving the generation efficiency of the 4.3-micron mid-infrared fiber laser.

[0004] The technical scheme for solving the above problems is: a dual-wavelength cascade-pumped 4.3-micron mid-infrared fiber laser, comprising a first pump laser for generating first pump light, a second pump laser for generating second pump light; further comprising a first dichroic mirror, a second dichroic mirror, a mirror, a convex lens, an aluminum fluoride end cap, a dysprosium-doped indium fluoride gain fiber, a first fiber Bragg grating, a second fiber Bragg grating, and a third fiber Bragg grating;

[0005] The first fiber Bragg grating and the second fiber Bragg grating jointly form an optical resonant cavity; the dysprosium-doped indium fluoride gain fiber is located in the optical resonant cavity; the first pump light and the second pump light are both coupled into the core of the dysprosium-doped indium fluoride gain fiber through the convex lens; the laser oscillating in the optical resonant cavity is output through the second fiber Bragg grating, and the first pump light not absorbed by the dysprosium-doped indium fluoride gain fiber is filtered out by the second dichroic mirror, thereby obtaining 4.3-micron laser output;

[0006] The third fiber Bragg grating is located behind the second fiber Bragg grating, and reflects the residual second pump light back into the optical resonant cavity; the first dichroic mirror is located behind the first pump laser, and is used for reflecting the second pump light reflected by the third fiber Bragg grating, so that the second pump light is completely absorbed by the dysprosium-doped indium fluoride gain fiber.

[0007] Further, the first pump light output by the first pump laser has a wavelength of 2.83 microns, and the second pump light output by the second pump laser has a wavelength of 2.3 microns.

[0008] Further, the dual-wavelength cascade-pumped 4.3-micron mid-infrared fiber laser, wherein the working wavelengths of the first fiber Bragg grating and the second fiber Bragg grating are both 4.3 microns.

[0009] Further, the dual-wavelength cascade-pumped 4.3-micron mid-infrared fiber laser, wherein the working wavelength of the third fiber Bragg grating is 2.3 microns.

[0010] Further, the first pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the first dichroic mirror and the convex lens in sequence; and the second pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the mirror and the convex lens in sequence.

[0011] Further, the dysprosium-doped indium fluoride gain fiber is fused with the aluminum fluoride end cap at the pump end face, so as to improve the damage threshold of the fiber.

[0012] Further, the dysprosium ion doping concentration in the dysprosium-doped indium fluoride gain fiber is 2000 ppm, and the core diameter of the dysprosium-doped indium fluoride gain fiber is 12 microns, and the length is 6 cm to 20 cm.

[0013] The laser oscillated in the optical resonant cavity is output through the second fiber Bragg grating, and the first pump light not absorbed by the dysprosium-doped indium fluoride gain fiber is filtered out by the second dichroic mirror to obtain 4.3 mu m laser output.

[0014] A laser efficient generation method of the 4.3 mu m mid-infrared fiber laser using the above-mentioned dual-wavelength cascade pumping, comprising the following steps:

[0015] S1, a first pump laser generates first pump light;

[0016] S2, a second pump laser generates second pump light;

[0017] S3, the first pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the first dichroic mirror and the convex lens; the second pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the mirror and the convex lens;

[0018] S4, the laser oscillated in the optical resonant cavity is output through the second fiber Bragg grating, and the first pump light not absorbed by the dysprosium-doped indium fluoride gain fiber is filtered out by the second dichroic mirror to obtain 4.3 mu m laser output.

[0019] The beneficial effects of the present application are that a dual-wavelength cascade pumped 4.3 mu m mid-infrared fiber laser and a laser efficient generation method are provided, the first pump light is pumped by the same band, the particles on the energy level 6 H 15 / 2 are pumped to the energy level 6 H 13 / 2 ; the second pump light further pumps the particles on the energy level 6 H 13 / 2 to the energy level 6 H 9 / 2 + 6 F 11 / 2 ; since 6 H 9 / 2 + 6 F 11 / 2 The energy level lifetime is very short, and the fast multi-photon relaxation makes the dysprosium ions jump to the energy level 6 H 11 / 2 accumulation; the stimulated radiation between the energy level 6 H 11 / 2 and the energy level 6 H 13 / 2 produces 4.3 mu m laser. This scheme can avoid the laser self-termination effect and has small quantum loss, and can obtain 4.3 mu m laser with optical-to-optical conversion efficiency up to 38%, which significantly improves the generation efficiency of 4.3 mu m mid-infrared fiber laser. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments description will be briefly introduced as follows. Obviously, the drawings in the following description are only typical embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings. Among them:

[0021] Figure 1 The structural schematic diagram of the embodiment of the present application is shown in the figure.

[0022] Figure 2 The figure is a graph of the variation of the output power of the laser with the second pump power obtained by theoretical calculation of the embodiment of the present application.

[0023] Figure 3 The specific flow chart of the laser generation method provided by the embodiment of the present application is shown in the figure.

[0024] In the figure: 1. first pump laser; 2. first dichroic mirror; 3. reflecting mirror; 4. second pump laser; 5. convex lens; 6. aluminum fluoride end cap; 7. first fiber Bragg grating; 8. dysprosium-doped indium fluoride gain fiber; 9. second fiber Bragg grating; 10. third fiber Bragg grating; 11. second dichroic mirror. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described below are only used to explain the present application, and are not used to limit the present application.

[0026] Due to the limitation of the laser self-termination effect, it is difficult for the dysprosium-doped indium fluoride fiber laser pumped by single wavelength to generate 4.3 μm mid-infrared laser. The 1.7 μm and 2.3 μm dual-wavelength pumping mode can solve the problem of laser self-termination, but is limited by large quantum loss, and the generation efficiency of the laser is low. In order to solve the above problems, the present application provides a 4.3 μm mid-infrared fiber laser pumped by dual-wavelength cascade, as shown in the figure. Figure 1The 4.3 μm mid-infrared fiber laser of the present application comprises: a first pump laser 1, a second pump laser 4, a first dichroic mirror 2, a second dichroic mirror 11, a mirror 3, a convex lens 5, an aluminum fluoride end cap 6, a dysprosium-doped indium fluoride gain fiber 8, a first fiber Bragg grating 7, a second fiber Bragg grating 9, and a third fiber Bragg grating 10. The first pump laser 1 and the second pump laser 4 generate first pump light with a wavelength of 2.83 μm and second pump light with a wavelength of 2.3 μm, respectively. The first pump light is focused by the convex lens 5 and coupled into the core of the dysprosium-doped indium fluoride gain fiber 8 after passing through the first dichroic mirror 2. The second pump light is focused by the convex lens 5 and coupled into the core of the dysprosium-doped indium fluoride gain fiber 8 after being reflected by the mirror 3. The first fiber Bragg grating 7 and the second fiber Bragg grating 9 together form an optical resonant cavity. The dysprosium-doped indium fluoride gain fiber generates 4.3 μm laser light in the fiber resonant cavity under the cascade pumping of the first pump light and the second pump light. The third fiber Bragg grating 10 reflects the residual second pump light back into the optical resonant cavity. The first dichroic mirror 2 is used to reflect the second pump light reflected by the third fiber Bragg grating, so that the second pump light is completely absorbed by the dysprosium-doped indium fluoride gain fiber 8. The dysprosium-doped indium fluoride gain fiber 8 is fused with the aluminum fluoride end cap 6 at the pump end to improve the damage threshold of the fiber. The laser light formed by oscillation in the optical resonant cavity is output through the second fiber Bragg grating, and the first pump light not absorbed by the dysprosium-doped indium fluoride gain fiber 8 is filtered out using the second dichroic mirror 11 to obtain 4.3 μm laser output.

[0027] In specific implementation, the first dichroic mirror has a transmittance of greater than 95% for 2.83 μm laser light and a reflectance of greater than 99.5% for 2.3 μm laser light.

[0028] In specific implementation, the convex lens 5 is a broadband antireflection-coated aspheric lens.

[0029] Preferably, the convex lens 5 has a transmittance of greater than 98% in the wavelength range of 2.2 μm-4.5 μm.

[0030] In specific implementation, the mirror 3 is a metal-dielectric mirror with a reflectance of greater than 99.5%.

[0031] In specific implementation, the dysprosium-doped indium fluoride gain fiber 8 has a doping concentration of 2000 ppm and a core diameter of 12 μm.

[0032] In specific implementation, the first fiber Bragg grating 7 has a reflectance of greater than 99% for 4.3 μm laser light and a working bandwidth of less than 1 nm.

[0033] In specific implementation, the second fiber Bragg grating 9 has a reflectance of between 80% and 90% for 4.3 μm laser light and a working bandwidth of less than 1 nm.

[0034] In practice, the third fiber Bragg grating 10 reflects the residual portion of the second pump light back into the optical resonant cavity, so that the second pump light is completely absorbed by the dysprosium-doped indium fluoride gain fiber 8.

[0035] Preferably, the third fiber Bragg grating 10 has a reflectivity of more than 99% for 2.3μm laser light and an operating bandwidth of less than 1nm.

[0036] In practice, an aluminum fluoride end cap 6 is fused to the pump end face of the dysprosium-doped indium fluoride gain fiber 8.

[0037] In practice, the second dichroic mirror 11 has a reflectivity of more than 99.5% for 2.83μm laser and a transmittance of more than 95% for 4.3μm laser, so as to filter out the first pump light that is not absorbed by the dysprosium-indium fluoride gain fiber 8, and the 4.3μm laser is transmitted and output from the second dichroic mirror 11.

[0038] Theoretical calculations show that high-efficiency laser output can be obtained by optimizing the length of the dysprosium-doped fluoride gain fiber 8, the reflectivity of the second fiber Bragg grating 9, and the first pump power. Figure 2 The figure shows the variation of laser output power with second pump power under the conditions of 6cm dysprosium-doped fluoride gain fiber, 80% reflectivity of the second fiber Bragg grating, and 0.15W first pump power. When the second pump power is 40W, the laser output power is 15.2W, and the optical-to-optical conversion efficiency reaches 38%.

[0039] In summary, this embodiment employs a cascaded pumping method with 2.83μm and 2.3μm wavelengths. The first pump light is pumped through a co-band pump to enhance the gain fiber energy levels. 6 H 15 / 2 Particles are pumped to the energy level 6 H 13 / 2 The second pump light will reduce the energy level 6 H 13 / 2 The particles on the surface are further pumped to the energy level. 6 H 9 / 2 + 6 F 11 / 2 ,because 6 H 9 / 2 + 6 F 11 / 2 The energy level lifetime is very short, and rapid multiphonon relaxation allows dysprosium ions to transition to the energy level. 6 H 11 / 2 Accumulation, energy level 6 H 11 / 2 and energy level 6 H 13 / 2The stimulated radiation between the two wavelengths generates 4.3 μm laser radiation. This dual-wavelength cascade pumping method can not only solve the problem of laser self-termination, but also significantly improve the generation efficiency of 4.3 μm mid-infrared fiber laser, and the optical-to-optical conversion efficiency reaches 38%.

[0040] In addition, the embodiment of the present application also provides a laser high-efficiency generation method of the above-mentioned dual-wavelength cascade pumped 4.3 μm mid-infrared fiber laser, as shown in the following formula (I): Figure 3 The method comprises the following steps:

[0041] S1, a first pump laser generates first pump light;

[0042] S2, a second pump laser generates second pump light;

[0043] S3, the first pump light is coupled into the core of a dysprosium-doped indium fluoride gain optical fiber through a first dichroic mirror and a convex lens; and the second pump light is coupled into the core of the dysprosium-doped indium fluoride gain optical fiber through the mirror and the convex lens;

[0044] S4, the laser generated by oscillation in the optical resonant cavity is output through a second fiber Bragg grating, and the first pump light not absorbed by the dysprosium-doped indium fluoride gain optical fiber is filtered out by using a second dichroic mirror, so as to obtain 4.3 μm laser output.

[0045] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A dual-wavelength cascade-pumped 4.3 pm mid-infrared fiber laser, comprising a first pump laser generating a first pump light, a second pump laser generating a second pump light; characterized in that: It also includes a first dichroic mirror, a second dichroic mirror, a mirror, a convex lens, an aluminum fluoride end cap, a dysprosium-doped indium fluoride gain fiber, a first fiber Bragg grating, a second fiber Bragg grating, and a third fiber Bragg grating. The first fiber Bragg grating and the second fiber Bragg grating together form an optical resonant cavity, and the dysprosium-doped indium fluoride gain fiber is located in the optical resonant cavity; the first pump light and the second pump light are both coupled into the core of the dysprosium-doped indium fluoride gain fiber through the convex lens; the laser oscillating in the optical resonant cavity is output through the second fiber Bragg grating, and the first pump light not absorbed by the dysprosium-doped indium fluoride gain fiber is filtered out by the second dichroic mirror to obtain 4.3 μm laser output; The third fiber Bragg grating is located behind the second fiber Bragg grating to reflect the residual second pump light back into the optical resonant cavity; the first dichroic mirror is located behind the first pump laser to reflect the second pump light reflected by the third fiber Bragg grating, so that the second pump light is completely absorbed by the dysprosium-doped indium fluoride gain fiber; The first pump light output by the first pump laser has a wavelength of 2.83 μm, and the second pump light output by the second pump laser has a wavelength of 2.3 μm; The working wavelength of the first fiber Bragg grating and the second fiber Bragg grating is 4.3 μm; The working wavelength of the third fiber Bragg grating is 2.3 μm; The first pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the first dichroic mirror and the convex lens in sequence; and the second pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the mirror and the convex lens in sequence; The end face of the dysprosium-doped indium fluoride gain fiber is fused with the aluminum fluoride end cap to improve the damage threshold of the fiber. 2.The dual-wavelength cascade-pumped 4.3-μm mid-infrared fiber laser of claim 1, wherein: The dysprosium ion doping concentration of the dysprosium-doped indium fluoride gain fiber is 2000 ppm, and the length of the dysprosium-doped indium fluoride gain fiber is 6 cm to 20 cm.

3. A method for efficient generation of laser light using the 4.3 pm mid-infrared fiber laser of any one of claims 1-2, characterized in that: The method comprises the following steps: S1, a first pump laser generates first pump light with a wavelength of 2.83 μm; S2, a second pump laser generates second pump light with a wavelength of 2.3 μm; S3, the first pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the first dichroic mirror and the convex lens, and the second pump light is coupled into the core of the dysprosium-doped indium fluoride gain fiber through the mirror and the convex lens; S4, the laser oscillating in the optical resonant cavity is output through the second fiber Bragg grating, and the first pump light not absorbed by the dysprosium-doped indium fluoride gain fiber is filtered out by the second dichroic mirror to obtain 4.3 μm laser output.

Images