CN100452572C - Mid-infrared high-power laser source based on erbium-ytterbium co-doped double-clad fiber - Google Patents

Abstract

A mid-infrared high-power laser light source based on erbium and ytterbium co-doped double-clad fiber, which consists of: a high-power semiconductor laser and an energy-transmitting fiber arranged sequentially from the output end of the high-power semiconductor laser, a first fiber grating, and a third fiber grating. Two fiber gratings, erbium and ytterbium co-doped double-clad fibers, collimating lenses, focusing lenses, nonlinear crystals and collimating output lenses. The erbium and ytterbium co-doped double-clad optical fiber is spliced with a first fiber grating and a second fiber grating that have high reflectivity for wavelength λ ₁ near 1.06 μm and wavelength λ ₂ near 1.56 μm and erbium and ytterbium co-doped double cladding. The end face of the other end of the optical fiber forms a resonant cavity, thereby achieving high-power laser output with wavelengths λ ₁ and λ ₂ and focusing on the nonlinear crystal through the achromatic lens. The difference frequency is performed in the nonlinear crystal and output through the collimated output lens. Mid-infrared light high-power laser. The invention has the advantages of high laser conversion efficiency, simple structure, small size, light weight, and high system stability.

Description

Mid-infrared high-power laser source based on erbium-ytterbium co-doped double-clad fiber

technical field

The invention relates to a high-power mid-infrared laser source, in particular to a mid-infrared high-power laser source based on erbium-ytterbium co-doped double-clad fiber.

Background technique

In recent years, the extension of the output wavelength of lasers to the mid-infrared has received more and more attention, not only because the absorption line intensity of gas molecules in the mid-infrared wavelength region is several orders of magnitude higher than that in the near-infrared region, so the mid-infrared laser Spectral technology has a very important application prospect, and because the 3-5μm band is the window band of the atmosphere, in this band the laser has a strong penetrating power to the fog and smoke, and the transmission on the sea level is less affected by the scattering of gas molecules. , so it is suitable for use in lidar, photoelectric countermeasures and other fields. At present, the technologies for obtaining mid-infrared lasers in this wavelength range mainly include direct generation of fluorine-deuterium chemical lasers, optical parametric oscillator (OPO) and difference frequency (DFG) generation, etc. to obtain lasers in this wavelength range. . The energy distribution of chemical lasers is in a wide spectral range, but the structure is huge and expensive; the output light energy of optical parametric oscillators is low, and the beam quality is poor; compared with optical parametric oscillators and chemical lasers, the difference frequency has many advantages , such as flexible tunable range, compact all-cured structure, high output energy, etc.

In the prior art of generating mid-infrared laser by difference frequency, two Nd:YAG lasers with different output wavelengths are required to generate mid-infrared laser in the 4 μm band. See the prior art [Optics and Optoelectronics Technology. 3: 26-28, 2005], the efficiency of the solid Nd:YAG laser is relatively low, and the laser beam quality is low during high power operation, resulting in low difference frequency conversion efficiency; in addition, due to Two lasers are used, the cost of the system is high, and the stability is not high. In the prior art, the erbium-ytterbium co-doped fiber is used as the laser medium, and the laser with a wavelength of 1.5 μm is obtained by suppressing the laser oscillation of 1.06 μm, and the spectral bandwidth of the output laser is relatively large. See the prior art [OPTICSEXPRESS.14: 3936-3941, 2006]. In this technology, since the resonant cavity is formed by the coated cavity plate, the full-fiber laser cannot be realized, and its popularization and application are limited.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the above-mentioned prior art, and provide a mid-infrared high-power laser source based on erbium-ytterbium co-doped double-clad fiber, so as to improve the conversion efficiency and output stability of the laser source, and obtain high Mid-infrared laser output with high power and high beam quality realizes structural fiber optics to facilitate the miniaturization of laser light sources.

The basic idea of the present invention is to use a high-power semiconductor laser to pump an erbium-ytterbium co-doped double-clad fiber that is fused with two fiber gratings to realize the simultaneous output of dual-wavelength lasers near 1.06 μm and 1.56 μm, and then use non- The linear crystal realizes the difference frequency of two wavelength lasers to obtain high-power mid-infrared laser output.

Technical solution of the present invention is as follows:

A mid-infrared high-power laser light source based on erbium-ytterbium co-doped double-clad fiber, which consists of: a high-power semiconductor laser and sequentially arranged from the output end of the high-power semiconductor laser: an energy transmission fiber, a first fiber grating, The second fiber grating, erbium-ytterbium co-doped double-clad fiber, collimating lens, focusing lens, nonlinear crystal and collimating output lens, the output end of the erbium-ytterbium co-doped double-clad fiber is located at the collimating The front focus of the lens, the back focus of the focusing lens and the front focus of the collimating output lens are confocal, the focus is located in the nonlinear crystal, and the pumping light emitted by the high-power semiconductor laser passes through the The energy fiber is coupled to the erbium-ytterbium co-doped double-clad fiber, and between the energy-transmitting fiber and the erbium-ytterbium co-doped double-clad fiber, there are respectively the first high-reflection to the center wavelength λ ₁ and the center wavelength λ ₂ The fiber grating and the second fiber grating are respectively used as resonant cavity mirrors for the λ ₁ and λ ₂ laser wavelengths of the erbium-ytterbium co-doped double-clad fiber laser, and the other end of the erbium-ytterbium co-doped double-clad fiber is cut vertically as a resonant cavity output mirror.

The core of the erbium-ytterbium co-doped double-clad fiber is circular, with a diameter of 20 μm and a core numerical aperture of 0.07; its inner cladding is hexagonal or octagonal, with a diameter of 200 μm or 400 μm, and the inner cladding numerical aperture is 0.46.

The first fiber grating is a double-clad fiber grating with a central wavelength of λ ₁ =1.06 μm and a high reflectivity, and its fiber grating is only written in the circular core area, with a reflectivity greater than 90%; its core and inner cladding The diameter and numerical aperture are the same as the corresponding parameters of the erbium-ytterbium co-doped double-clad fiber.

The second fiber grating is a double-clad fiber grating with a central wavelength of λ ₂ =1.56 μm and a high reflectivity. The fiber grating is only written in the circular core area, and the reflectivity is greater than 90%. The core and inner cladding The diameter and numerical aperture are the same as those of the erbium-ytterbium co-doped double-clad fiber.

The central wavelength of the high-power semiconductor laser matches the absorption wavelength of the erbium-ytterbium co-doped double-clad fiber, which is 975nm or 915nm. The high-power semiconductor laser is a combination of multiple semiconductor laser arrays or multiple single-tube combination of semiconductor lasers.

Described collimating lens is the collimating lens that is made of a spherical lens group to wavelength λ ₁ and λ ₂ achromatism, and its each surface all is coated with the anti-reflection film of these two wavelengths, realizes the high-resolution of two wavelength lasers efficiency collimated output.

Described focusing lens is the focusing lens to wavelength λ ₁ and λ ₂ achromats that is made of a spherical lens group, or is the achromatic lens that is made of aspheric lens, and it is all coated with these two wavelengths on each surface anti-reflection coating. The dual-wavelength laser generated by the erbium-ytterbium co-doped double-clad fiber can be more effectively focused into the nonlinear crystal to realize efficient difference frequency conversion.

The nonlinear crystal is LiNbO ₃ crystal, MgO:LiNbO ₃ crystal or other nonlinear crystal. The nonlinear crystal has a high laser damage threshold and a large nonlinear coefficient. It can achieve phase matching by adjusting the angle or temperature control in the wavelength range of 1 μm to 4 μm. Through its difference frequency conversion of wavelengths λ1 and λ2, Obtain high-efficiency, high-power mid-infrared laser output.

Technical effect of the present invention:

The present invention uses a high-power semiconductor laser to pump an erbium-ytterbium co-doped double-clad fiber that is welded with two fiber gratings, and realizes the simultaneous output of high-power, high-beam-quality lasers of 1.06 μm and 1.56 μm dual-wavelength lasers, while in In the prior art, two lasers must be used in order to obtain two wavelengths of laser output. Therefore, the present invention has the advantages of simple system structure and high efficiency, and can greatly reduce system cost.

The present invention adopts two fiber gratings as resonant cavity mirrors of two lasers with different wavelengths to realize the simultaneous output of two wavelengths of lasers. The adoption of fiber gratings makes the dual-wavelength fiber lasers realize full-fiberization, and is beneficial to narrow-spectrum line lasers. The output improves the nonlinear difference frequency conversion efficiency.

In the present invention, LiNbO ₃ crystal or MgO:LiNbO ₃ crystal is used to perform frequency difference between two wavelength lasers with high beam quality, and high-power mid-infrared laser output with a wavelength of about 3.3 μm can be realized.

Description of drawings

Fig. 1 is a schematic structural diagram of a mid-infrared high-power laser source based on Erbium-Ytterbium co-doped double-clad fiber of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Please refer to FIG. 1 first. FIG. 1 is a schematic structural diagram of a mid-infrared high-power laser source based on an Er-Yb co-doped double-clad fiber according to the present invention. As can be seen from the figure, the composition of the mid-infrared high-power laser light source based on the erbium-ytterbium co-doped double-clad fiber of the present invention includes a high-power semiconductor laser 1 and sequentially arranged from the output end of the high-power semiconductor laser 1: energy transmission fiber 2 , a first fiber grating 3, a second fiber grating 4, an erbium-ytterbium co-doped double-clad fiber 5, a collimating lens 6, a focusing lens 7, a nonlinear crystal 8 and a collimating output lens 9, and the erbium-ytterbium co-doping The output end 10 of the double-clad fiber 5 is located at the front focus of the collimator lens 6, and the rear focus of the focus lens 7 is confocal with the front focus of the collimator output lens 9, and the focus is located at the nonlinear In the crystal 8, the pump light emitted by the high-power semiconductor laser 1 is coupled to the erbium-ytterbium co-doped double-clad fiber 5 through the energy-transfer fiber 2, and the energy-transfer fiber 2 and the erbium-ytterbium co-doped double-clad fiber Between the layers of optical fibers 5, the first fiber grating 3 and the second fiber grating 4 that are highly reflective to the central wavelength λ ₁ and the central wavelength λ ₂ are spliced respectively, and are respectively used as λ ₁ and λ of the erbium-ytterbium co-doped double-clad fiber laser. The resonant cavity mirror of ₂ laser wavelengths, the other end 10 of the erbium-ytterbium co-doped double-clad fiber 5 is cut perpendicular to the axis, and serves as the output mirror of the resonant cavity.

The pumping light emitted by the high-power semiconductor laser 1 is coupled to the erbium-ytterbium co-doped double-clad fiber 5 through the energy-transfer optical fiber 2, which provides the particle population inversion of the erbium-ytterbium co-doped double-clad fiber core, and in the energy transmission Between the optical fiber 2 and the erbium-ytterbium co-doped double-clad fiber 5, the first fiber grating and 4 with high reflectivity to the wavelength λ ₁ and λ ₂ are fused, respectively, as resonant cavity mirrors of the λ ₁ and λ ₂ laser wavelengths , λ ₁ is around 1.06 μm, λ ₂ is around 1.56 μm, the other end of the optical fiber is cut vertically, as _the output mirror ₁₀ of laser light; After the lenses are collimated, they are then collectively focused on the nonlinear crystal 8 through the focusing lens, and the two wavelengths of laser light pass through the difference frequency in the nonlinear crystal 8 to generate a wavelength of (λ ₁ ×λ ₂ )/(λ ₂ -λ ₁ ) mid-infrared laser, and achieve collimated output through the collimated output lens.

Below is the physical parameter of a specific embodiment of the present invention:

As shown in FIG. 1 , the central wavelength of the high-power semiconductor laser 1 is 975nm. After beam shaping by multiple semiconductor laser arrays, the high-power semiconductor laser 1 is coupled and output through the energy-transmitting optical fiber 2, and the output laser power reaches 300W. The core diameter of the energy transmission fiber 2 is 400 μm, and the numerical aperture is 0.44. The energy transmission fiber 2 is directly fused with the first fiber Bragg grating 3, the center wavelength of the first fiber Bragg grating 3 is λ ₁ =1064nm, and the reflectivity is 97%. The diameter is 20 μm, the numerical aperture is 0.06, the inner cladding layer is circular, the diameter is 400 μm, and the numerical aperture is 0.46. The other end of the first fiber grating 3 is welded with the second fiber grating 4, the center wavelength λ ₂ of the second fiber grating 4=1565nm, and the reflectivity is 97%. The second fiber grating 4 is also a double-clad fiber grating. Layer and core parameters are the same as those of the first fiber grating 3 . The other end of the second fiber grating 4 is welded to the erbium-ytterbium co-doped double-clad fiber 5 .

The erbium-ytterbium co-doped double-clad fiber 5 is a double-clad fiber with a large mode field area. Erbium ions and ytterbium ions are co-doped in a certain proportion in the fiber core, the concentration of Yb ³⁺ is 1wt%, and the concentration of Er ³⁺ It is 0.125wt%. The doped fiber core is circular with a diameter of 20 μm and a numerical aperture of about 0.06. The inner cladding is octagonal in shape with a diameter of 400 μm and a numerical aperture of about 0.46; one end is welded to the fiber grating 4, and the other end is directly cut perpendicular to the axis of the fiber. As the output terminal 10 of the laser. The erbium-ytterbium co-doped double-clad fiber 5 absorbs about 2 dB/m of small signals at 975 nm, and the length of the fiber is 6.5 m. The 975nm pump light emitted by the high-power semiconductor laser 1 is efficiently coupled into the erbium-ytterbium co-doped double-clad fiber 5 through the energy-transmitting fiber 2, the first fiber grating 3 and the second fiber grating 4, and is the doped fiber core. The particle population inversion provides energy, the second fiber grating 4 and the fiber end face 10 form a pair of laser resonators with λ ₂ =1565nm, and the first fiber grating 3 and the fiber end face 10 form another pair of laser resonators with λ ₁ =1064nm , so that the simultaneous operation of two wavelength lasers of 1064nm and 1565nm can be realized.

The dual-wavelength laser output from the fiber end face 10 is collimated by the achromatic composite collimating lens 6 with a focal length f=8mm, and then focused on the nonlinear crystal 8 by the achromatic composite focusing lens 7 with a focal length f=40mm, and the collimating lens 6 And each surface of the focusing lens 7 is coated with anti-reflection coatings for wavelength λ ₁ and λ ₂ . The nonlinear crystal 8 is LiNbO ₃ , its nonlinear coefficient d _eff =0.88×10 ^-8 esu, and the corresponding crystal cutting angle is θ=48.5°, , the length of the nonlinear crystal 8 is 12mm. The laser beam of wavelength λ ₁ =1064nm and the laser beam of wavelength λ ₂ =1565nm injected into the nonlinear crystal 8 are frequency-differenced in LiNbO ₃ to obtain the mid-infrared wavelength of (λ1×λ2)/(λ2-λ1)=3.3μm For the laser, the focal length of the collimating output lens 9 for a wavelength of 3.3 μm is 40 mm, so as to realize the collimation of the mid-infrared laser. The mid-infrared laser light source based on the erbium-ytterbium co-doped double-clad fiber of this embodiment, when the output power of the high-power semiconductor laser is 300W, will be able to achieve a wavelength of 3.3 μm near 20W high-power, high-beam quality medium Infrared laser output.

In summary, the present invention is based on the mid-infrared high-power laser source of erbium-ytterbium co-doped double-clad fiber, using two high-reflectivity fiber gratings as resonant cavity mirrors with a wavelength near 1.06 μm and a wavelength near 1.56 μm respectively. A high-power semiconductor laser is used as the pump source, and a section of erbium-ytterbium co-doped double-clad fiber is used as the laser gain medium. Two wavelengths of high-power laser output are realized from an all-fiber fiber laser; two high-beam quality The laser with two wavelengths is frequency-differenced by a nonlinear crystal to obtain a mid-infrared laser output with high power and high beam quality. Compared with the prior art, the invention has the characteristics of simple structure, good stability and high conversion efficiency, and can obtain mid-infrared laser output with high power and high beam quality.

Claims (8)

1, a kind of based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, be characterised in that its formation comprise high-power semiconductor laser (1) and certainly the output of this high-power semiconductor laser (1) set gradually: energy-transmission optic fibre (2), first fiber grating (3), second fiber grating (4), erbium ytterbium co doped double clad fiber (5), collimating lens (6), condenser lens (7), nonlinear crystal (8) and collimation output lens (9), the output (10) of described erbium ytterbium co doped double clad fiber (5) is positioned at the front focus of described collimating lens (6), the front focus of the back focus of described condenser lens (7) and collimation output lens (9) is confocal, this focus is positioned among the described nonlinear crystal (8), the pump light that described high-power semiconductor laser (1) sends is coupled to erbium ytterbium co doped double clad fiber (5) by energy-transmission optic fibre (2), between described energy-transmission optic fibre (2) and erbium ytterbium co doped double clad fiber (5), welding has respectively to central wavelength lambda ₁And central wavelength lambda ₂High anti-described first fiber grating (3) and described second fiber grating (4) are made the λ of erbium ytterbium co doped double clad fiber laser respectively ₁And λ ₂The resonator mirror of optical maser wavelength, output (10) the vertical axis cutting of erbium ytterbium co doped double clad fiber (5) is as the outgoing mirror of resonant cavity.

2, according to claim 1 based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, the fibre core that it is characterized in that described erbium ytterbium co doped double clad fiber (5) is for circular, and diameter is 20 μ m, and the fibre core numerical aperture is 0.07; The inner cladding of described erbium ytterbium co doped double clad fiber (5) is hexagon or octangle, and diameter is 200 μ m or 400 μ m, and the inner cladding numerical aperture is 0.46.

3, according to claim 1 based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, it is characterized in that described first fiber grating (3) is a central wavelength lambda ₁=1.06 μ m, have the doubly clad optical fiber grating of high reflectance, its fiber grating only is scribed at the circular core zone, and reflectivity is greater than 90%; The diameter of its fibre core and inner cladding is identical with the relevant parameter of described erbium ytterbium co doped double clad fiber (5) with numerical aperture.

4, according to claim 1 based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, it is characterized in that described second fiber grating (4) is a central wavelength lambda ₂=1.56 μ m, have the doubly clad optical fiber grating of high reflectance, its fiber grating only is scribed at the circular core zone, and reflectivity is greater than 90%; The diameter of its fibre core and inner cladding is identical with the relevant parameter of described erbium ytterbium co doped double clad fiber (5) with numerical aperture.

5, according to claim 1 based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, the absorbing wavelength that it is characterized in that the same erbium ytterbium co doped double clad fiber of centre wavelength (5) of described high-power semiconductor laser (1) is complementary, be 975nm or 915nm, described high-power semiconductor laser (1) is the combination of a plurality of semiconductor laser arraies or the combination of a plurality of single tube semiconductor lasers

6, according to claim 1 based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, it is characterized in that described collimating lens (6) be by a spherical lens group constitute to wavelength X ₁And λ ₂Achromatic collimating lens, its each face all plates the anti-reflection film of two wavelength, realizes the high efficiency collimation output of two wavelength lasers.

7, according to claim 1 based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, it is characterized in that described condenser lens (7) be by a spherical lens group constitute to wavelength X ₁And λ ₂Achromatic condenser lens, or the achromatic lens that constitutes by non-spherical lens, and its each face is all plated the anti-reflection film of two wavelength.

8, according to claim 1 based on infrared high power laser sources in the erbium ytterbium co doped double clad fiber, it is characterized in that described nonlinear crystal (8) is LiNbO3 crystal, MgO:LiNbO ₃Crystal or other nonlinear crystal.

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