A 1907nm single-mode polarization-maintaining all-fiber laser

Abstract

A 1907nm single-mode polarization-maintaining all-fiber laser belongs to the field of optics. The present invention solves the problem of low output power of the existing polarization-maintaining single-mode thulium-doped fiber laser. It includes: a fiber oscillator and a fiber amplifier; a high-reflectivity fiber Bragg grating is sequentially connected to the first forward-pumped optical combiner, the first low-doped single-mode thulium-doped gain fiber and the low-reflectivity fiber Bragg grating, and the first pump light source is connected to the first forward-pumped optical combiner pump fiber; the output end of the low-reflectivity fiber Bragg grating is connected to the input end of the first cladding pump light stripper; the first cladding pump light stripper is sequentially connected to the optical isolator, the mode field adapter, the second forward-pumped optical combiner, the second low-doped single-mode thulium-doped gain fiber and the second cladding pump light stripper, and the second pump light source is connected to the second forward-pumped optical combiner pump fiber; the optical isolator pigtail outputs linearly polarized light on the slow axis; all devices are polarization-maintaining devices. The present invention is used for fiber lasers.

Description

Technical Field

[0001] The invention relates to a 1907nm single-mode polarization-maintaining all-fiber laser, and belongs to the field of optics. Background Art

[0002] Fiber lasers are the third generation of new lasers after traditional gas lasers and solid-state lasers. They have the advantages of compact structure, stable power, long life, maintenance-free, excellent thermal management and good beam quality. Fiber lasers have a wide range of applications, including laser fiber communications, laser space long-distance communications, industrial shipbuilding, automobile manufacturing, laser engraving, laser marking, laser cutting, printing rollers, metal and non-metal drilling / cutting / welding (brass welding, quenching, cladding and deep welding), military defense security, medical equipment, large-scale infrastructure, as a pump source for other lasers, etc. Among them, the more special single-mode polarization-maintaining fiber laser can be mainly used in communications and laser measurement.

[0003] High-power thulium-doped continuous fiber lasers operating in the 1.9μm eye-safe special band have a gain bandwidth covering 1.7 to 2.1μm. Usually, 1.7 to 1.9μm lasers can be obtained by core-pumping thulium-doped fibers using erbium-ytterbium co-doped fiber lasers with an output wavelength of 1550nm. However, the theoretical quantum efficiency of thulium fibers pumped by mature 790nm laser diode cladding is high. Compared with erbium-ytterbium co-doped fiber lasers as pump sources, they have higher electro-optical efficiency and more advantages in output power. Therefore, they have always been one of the important directions in the field of high-power laser technology. At present, randomly polarized multimode thulium-doped fiber amplifiers can achieve kilowatt-level power output, and the power level of randomly polarized single-mode thulium-doped fiber lasers has also been promoted to 300W, which can meet the requirements of many fields such as special material processing, clinical surgery, mid- and long-range laser radar, holmium-doped solid-state lasers, and mid-infrared spectrum generation.

[0004] However, the existing thulium-doped polarization-maintaining single-mode fiber laser has the problem of low output power.

[0005] When the output wavelength of a thulium-doped fiber laser is less than 1950nm, due to the overlap of the absorption spectrum and emission spectrum of the thulium-doped fiber, these wavelengths have reabsorption losses, which reduces the output efficiency of the laser. In contrast, laser wavelengths greater than 1950nm can obtain greater gain, which makes it easy for thulium-doped lasers to generate amplified spontaneous radiation and parasitic oscillations when operating at short wavelengths, and cannot obtain high-power output. At the same time, the existing large mode field gain fibers are all few-mode fibers. High-order modes can exist in the core and obtain gain to achieve amplification. However, in high-power and strong nonlinear working conditions, since the mode field diameter to core diameter ratio (MFD / D) value of this type of fiber is less than 1, the signal light field area on the core cross section is smaller than the core area, the laser energy density is large, and the nonlinear phase difference between multiple modes is associated with power. Self-phase modulation and cross-phase modulation make multiple modes coherently superimposed, which will cause the output spot distribution to no longer be Gaussian linear, and even excite the unstable mode phenomenon. The output laser’s pointing direction and beam quality evolve randomly, limiting the further increase of power. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of low output power of the existing polarization-maintaining single-mode thulium-doped fiber laser, and to provide a 1907nm single-mode polarization-maintaining all-fiber laser.

[0007] The present invention provides a 1907nm single-mode polarization-maintaining all-fiber laser, which comprises: a fiber oscillator and a fiber amplifier;

[0008] The fiber oscillator comprises a high-reflectivity fiber Bragg grating, a first forward pumping optical combiner, a first pumping light source, a first low-doped single-mode thulium-doped gain fiber and a low-reflectivity fiber Bragg grating;

[0009] The optical fiber amplifier comprises a first cladding pump light stripper, a second cladding pump light stripper, an optical isolator, a mode field adapter, a second forward pump light combiner, a second low-doped single-mode thulium-doped gain optical fiber and a second pump light source;

[0010] The output end of the high-reflectivity fiber Bragg grating is connected to the input end of the first forward-pumped optical combiner, the first pump light source is connected to the pump optical fiber of the first forward-pumped optical combiner, the output end of the first forward-pumped optical combiner is connected to one end of the first low-doped single-mode thulium-doped gain optical fiber, and the other end of the first low-doped single-mode thulium-doped gain optical fiber is connected to the input end of the low-reflectivity fiber Bragg grating;

[0011] The output end of the low-reflectivity fiber Bragg grating is connected to the input end of the first cladding pump light stripper;

[0012] The output end of the first cladding pump light stripper is connected to the optical isolator, the output pigtail of the optical isolator is connected to the mode field adapter, the output end of the mode field adapter is connected to the second forward pump light combiner, the second pump light source is connected to the pump fiber of the second forward pump light combiner, the signal light output pigtail of the second forward pump light combiner is connected to one end of the second low-doped single-mode thulium-doped gain fiber, and the other end of the second low-doped single-mode thulium-doped gain fiber is connected to the output end of the second cladding pump light stripper; the optical isolator pigtail outputs linearly polarized light on the slow axis;

[0013] All devices are polarization-maintaining devices.

[0014] Preferably, the high-reflectivity fiber Bragg grating, the low-reflectivity fiber Bragg grating, the first low-doped single-mode thulium-doped gain fiber and the second low-doped single-mode thulium-doped gain fiber are fixed on a heat dissipation base, respectively.

[0015] Preferably, the high-reflectivity fiber Bragg grating and the low-reflectivity fiber Bragg grating are fixedly arranged on different cooling platforms respectively, and the cooling platforms are all cooled by semiconductor refrigerators, and the temperature control range is -5 to 40°C.

[0016] Preferably, the other end of the first low-doped single-mode thulium-doped gain optical fiber is orthogonally fused with the input end of the low-reflectivity fiber Bragg grating;

[0017] The output end of the low-reflectivity fiber Bragg grating is orthogonally fused with the input end of the first cladding pump light stripper;

[0018] Other devices are fused horizontally.

[0019] Preferably, the fast axis Bragg wavelength of the high reflectivity fiber Bragg grating is 1907nm±0.2nm, the reflectivity is>99.5%, the transmission bandwidth is 0.5nm±0.1nm, and the pump power that can be sustained is higher than 200W;

[0020] The slow axis Bragg wavelength of the low-reflectivity fiber Bragg grating is 1907nm±0.2nm, the reflectivity is 10±2%, the reflection bandwidth is 0.3nm±0.1nm, and the maximum signal light power that can be sustained is 50W;

[0021] The spectral side mode suppression ratio is greater than 20dB, and the Bragg wavelength mismatch between the fast axis and the slow axis is less than 0.1nm.

[0022] Preferably, the first forward pump optical combiner is a (6+1)×1 combiner, the pump efficiency is>95%, the signal light transmission loss is<0.7dB, the core diameter and cladding diameter of the combiner signal fiber are 10 / 130μm, and the pump fiber is 105 / 125μm;

[0023] The second forward pump optical combiner is a (6+1)×1 combiner, with a pump efficiency of >95%, a signal light transmission loss of <2dB, a polarization extinction ratio of >18dB, a single-arm power handling power of >150W, a signal fiber of 15 / 250μm, and a pump fiber of 200 / 220μm.

[0024] Preferably, the core / cladding of the first low-doped single-mode thulium-doped gain optical fiber is 10 / 130 μm, the numerical apertures of the core and cladding are 0.14 and 0.46 respectively, the absorption coefficient of the cladding to 793 nm pump light is 4.5-4.7 dB / m, and the length is 1.8 m;

[0025] The core / cladding of the second low-doped single-mode thulium-doped gain optical fiber is 15 / 250 μm, the numerical apertures of the core and cladding are 0.11 and 0.46 respectively, the absorption coefficient of the cladding to 793 nm pump light is 2.0-2.1 dB / m, and the length is 3.0 m.

[0026] Preferably, the core / cladding of the first cladding pump light stripper is 10 / 130 μm, the transmission loss of the signal light is <0.2 dB, the pump light stripping efficiency is >22 dB, and the polarization extinction ratio is >20 dB;

[0027] The core / cladding of the second cladding pump light stripper is 15 / 250 μm, the transmission loss of the signal light is <0.2 dB, the pump light stripping efficiency is >20 dB, and the polarization extinction ratio is >18 dB.

[0028] Preferably, the polarization isolation of the optical isolator is greater than 20 dB, the power withstand of a single arm is 20 W, the core / cladding of the signal fiber is 10 / 130 μm, and the slow axis of the pigtail outputs linearly polarized light.

[0029] Preferably, the extinction ratio of the mode field adapter is >16 dB, the incorporation loss is <0.9 dB, the core / cladding of the input end pigtail is 10 / 130 μm, and the output end is 15 / 250 μm.

[0030] The 1907nm single-mode polarization-maintaining all-fiber laser proposed in the present invention has the following advantages:

[0031] 1. Use polarization-maintaining devices, and use horizontal or orthogonal polarization-maintaining welding between devices. Under the action of polarization-maintaining grating, the output laser is linearly polarized.

[0032] 2. A semiconductor cooler (TEC) is used to control the temperature of the fiber Bragg grating. The spectral offset is optimized by changing the grating cooling temperature, thereby improving the polarization extinction ratio of the thulium-doped fiber laser. At the same time, a certain wavelength tuning can be performed within the grating center wavelength range of 0.5nm.

[0033] 3. Using 790nm laser diode as pump source has more advantages in output power than semiconductor lasers and fiber lasers in the same band.

[0034] 4. The structure of polarization-maintaining large mode field gain fiber is optimized to enable the fiber laser to obtain high-power polarization-maintaining single-mode laser output; by optimizing MFD / D, the laser pumping efficiency and beam quality can also be improved, thereby improving the laser output efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of a 1907nm single-mode polarization-maintaining all-fiber laser according to the present invention;

[0036] Figure 2 This is the polarization selection principle diagram of the polarization-maintaining grating pair with double PM-FBG fused at 0°;

[0037] Figure 3 This is the polarization selection principle diagram of the polarization-maintaining grating pair with double PM-FBG fused at 90°;

[0038] Figure 4 is the output power curve of the seed source of the thulium-doped single-mode polarization-maintaining oscillator in the present invention;

[0039] Figure 5 is the output power curve of the thulium-doped single-mode polarization-maintaining all-fiber amplifier in the present invention;

[0040] Figure 6 This is the output spectrum diagram of the thulium-doped single-mode polarization-maintaining all-fiber amplifier in the present invention;

[0041] Figure 7 It is the beam quality and spot profile of the thulium-doped single-mode polarization-maintaining all-fiber amplifier in the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0045] Embodiment 1:

[0046] Combine the following Figure 1 This embodiment is described. This embodiment describes a 1907nm single-mode polarization-maintaining all-fiber laser, which includes: a fiber oscillator and a fiber amplifier;

[0047] The fiber oscillator comprises a high-reflectivity fiber Bragg grating 1, a first forward pumping optical combiner 3-I, a first pumping light source 5-I, a first low-doped single-mode thulium-doped gain fiber 4-I and a low-reflectivity fiber Bragg grating 2;

[0048] The optical fiber amplifier comprises a first cladding pump light stripper 6-I, a second cladding pump light stripper 6-II, an optical isolator 7, a mode field adapter 8, a second forward pump light combiner 3-II, a second low-doped single-mode thulium-doped gain fiber 4-II and a second pump light source 5-II;

[0049] The output end of the high-reflectivity fiber Bragg grating 1 is connected to the input end of the first forward-pumped optical combiner 3-I, the first pump light source 5-I is connected to the pump optical fiber of the first forward-pumped optical combiner 3-I, the output end of the first forward-pumped optical combiner 3-I is connected to one end of the first low-doped single-mode thulium-doped gain optical fiber 4-I, and the other end of the first low-doped single-mode thulium-doped gain optical fiber 4-I is connected to the input end of the low-reflectivity fiber Bragg grating 2;

[0050] The output end of the low-reflectivity fiber Bragg grating 2 is connected to the input end of the first cladding pump light stripper 6-I;

[0051] The output end of the first cladding pump light stripper 6-I is connected to the optical isolator 7, the output pigtail of the optical isolator 7 is connected to the mode field adapter 8, the output end of the mode field adapter 8 is connected to the second forward pump light combiner 3-II, the second pump light source 5-II is connected to the pump fiber of the second forward pump light combiner 3-II, the signal light output pigtail of the second forward pump light combiner 3-II is connected to one end of the second low-doped single-mode thulium-doped gain fiber 4-II, and the other end of the second low-doped single-mode thulium-doped gain fiber 4-II is connected to the output end of the second cladding pump light stripper 6-II; the optical isolator 7 pigtail outputs linearly polarized light on the slow axis;

[0052] All devices are polarization-maintaining devices.

[0053] Furthermore, the high-reflectivity fiber Bragg grating 1, the low-reflectivity fiber Bragg grating 2, the first low-doped single-mode thulium-doped gain fiber 4-I and the second low-doped single-mode thulium-doped gain fiber 4-II are respectively fixed on the heat dissipation base.

[0054] Furthermore, the high-reflectivity fiber Bragg grating 1 and the low-reflectivity fiber Bragg grating 2 are respectively fixedly arranged on different cooling platforms, and both cooling platforms are cooled by semiconductor refrigerators, and the temperature control range is -5 to 40°C.

[0055] Furthermore, the other end of the first low-doped single-mode thulium-doped gain optical fiber 4-I is orthogonally fused with the input end of the low-reflectivity fiber Bragg grating 2;

[0056] The output end of the low-reflectivity fiber Bragg grating 2 is orthogonally fused with the input end of the first cladding pump light stripper 6-I;

[0057] Other devices are fused horizontally.

[0058] In this embodiment, the slow axis of the first low-doped single-mode thulium-doped gain fiber 4-I is fused with the fast axis of the low-reflectivity fiber Bragg grating 2 pigtail.

[0059] In this embodiment, the slow axis of the low reflectivity fiber Bragg grating 2 pigtail is fused with the fast axis of the first cladding pump light stripper 6 -I.

[0060] In this implementation manner, horizontal fusion splicing is performed between other components, that is, the slow axes of each pigtail are fused to each other, and the fast axes are fused to each other.

[0061] Embodiment 2:

[0062] Combine the following Figure 1 This embodiment is described. This embodiment describes a 1907nm single-mode polarization-maintaining all-fiber laser, which includes: a fiber oscillator and a fiber amplifier;

[0063] The fiber oscillator comprises a high-reflectivity fiber Bragg grating 1, a first forward pumping optical combiner 3-I, a first pumping light source 5-I, a first low-doped single-mode thulium-doped gain fiber 4-I and a low-reflectivity fiber Bragg grating 2;

[0064] The optical fiber amplifier comprises a first cladding pump light stripper 6-I, a second cladding pump light stripper 6-II, an optical isolator 7, a mode field adapter 8, a second forward pump light combiner 3-II, a second low-doped single-mode thulium-doped gain fiber 4-II and a second pump light source 5-II;

[0065] The output end of the high-reflectivity fiber Bragg grating 1 is connected to the input end of the first forward-pumped optical combiner 3-I, the first pump light source 5-I is connected to the pump optical fiber of the first forward-pumped optical combiner 3-I, the output end of the first forward-pumped optical combiner 3-I is connected to one end of the first low-doped single-mode thulium-doped gain optical fiber 4-I, and the other end of the first low-doped single-mode thulium-doped gain optical fiber 4-I is connected to the input end of the low-reflectivity fiber Bragg grating 2;

[0066] The output end of the low-reflectivity fiber Bragg grating 2 is connected to the input end of the first cladding pump light stripper 6-I;

[0067] The output end of the first cladding pump light stripper 6-I is connected to the optical isolator 7, the output pigtail of the optical isolator 7 is connected to the mode field adapter 8, the output end of the mode field adapter 8 is connected to the second forward pump light combiner 3-II, the second pump light source 5-II is connected to the pump fiber of the second forward pump light combiner 3-II, the signal light output pigtail of the second forward pump light combiner 3-II is connected to one end of the second low-doped single-mode thulium-doped gain fiber 4-II, and the other end of the second low-doped single-mode thulium-doped gain fiber 4-II is connected to the output end of the second cladding pump light stripper 6-II; the optical isolator 7 pigtail outputs linearly polarized light on the slow axis;

[0068] All devices are polarization-maintaining devices.

[0069] Furthermore, the fast axis Bragg wavelength of the high reflectivity fiber Bragg grating 1 is 1907nm±0.2nm, the reflectivity is>99.5%, the transmission bandwidth is 0.5nm±0.1nm, and the pump power can be higher than 200W;

[0070] The slow axis Bragg wavelength of the low reflectivity fiber Bragg grating 2 is 1907nm±0.2nm, the reflectivity is 10±2%, the reflection bandwidth is 0.3nm±0.1nm, and the maximum signal light power that can be sustained is 50W;

[0071] The spectral side mode suppression ratio is greater than 20dB, and the Bragg wavelength mismatch between the fast axis and the slow axis is less than 0.1nm.

[0072] Furthermore, the first forward pump optical combiner 3-I is a (6+1)×1 combiner, the pump efficiency is>95%, the signal light transmission loss is<0.7dB, the core diameter and cladding diameter of the combiner signal fiber are 10 / 130μm, and the pump fiber is 105 / 125μm;

[0073] The second forward pumped optical combiner 3-II is a (6+1)×1 combiner with a pumping efficiency of >95%, a signal light transmission loss of <2dB, a polarization extinction ratio of >18dB, a single-arm power handling capacity of >150W, a signal fiber of 15 / 250μm, and a pump fiber of 200 / 220μm.

[0074] Furthermore, the core / cladding of the first low-doped single-mode thulium-doped gain optical fiber 4-I is 10 / 130 μm, the numerical apertures of the core and cladding are 0.14 and 0.46 respectively, the absorption coefficient of the cladding to 793 nm pump light is 4.5-4.7 dB / m, and the length is 1.8 m;

[0075] The core / cladding of the second low-doped single-mode thulium-doped gain fiber 4-II is 15 / 250 μm, the numerical apertures of the core and cladding are 0.11 and 0.46 respectively, the absorption coefficient of the cladding to 793 nm pump light is 2.0-2.1 dB / m, and the length is 3.0 m.

[0076] Furthermore, the core / cladding of the first cladding pump light stripper 6-I is 10 / 130 μm, the transmission loss of the signal light is <0.2 dB, the pump light stripping efficiency is >22 dB, and the polarization extinction ratio is >20 dB;

[0077] The core / cladding of the second cladding pump light stripper 6-II is 15 / 250 μm, the transmission loss of the signal light is <0.2 dB, the pump light stripping efficiency is >20 dB, and the polarization extinction ratio is >18 dB.

[0078] Furthermore, the polarization isolation of the optical isolator 7 is greater than 20 dB, the single arm withstands a power of 20 W, the core / cladding of the signal fiber is 10 / 130 μm, and the slow axis of the pigtail outputs linearly polarized light.

[0079] Furthermore, the extinction ratio of the mode field adapter 8 is greater than 16 dB, the incorporation loss is less than 0.9 dB, the core / cladding of the input end pigtail is 10 / 130 μm, and the output end is 15 / 250 μm.

[0080] Combine the following Figure 1 The working principle of the present invention is described:

[0081] According to the single-mode optical fiber mode field diameter formula:

[0082]

[0083] From the above formula, we can see that there is a monotonically decreasing relationship between the mode field diameter to core diameter ratio (MFD / D) and the normalized frequency V. In order to obtain single-mode laser output, we first need to ensure that the core V value is less than 2.4048. The calculation shows that the MFD / D value is 1.099 at this time, which is the optimal mode matching achievable in the single-mode fiber category.

[0084] Taking the common large mode area thulium-doped fiber as an example, the typical core NA value is 0.09, so the maximum core diameter to ensure 1900nm laser single-mode transmission is about 16.2μm. Considering that the laser transmission signal light is linearly polarized, too large MFD / D will cause most of the signal light to be transmitted in the cladding, reducing its polarization extinction ratio. Therefore, the core diameter of the customized single-mode fiber needs to comprehensively consider both MFD / D and polarization extinction ratio.

[0085] In order to obtain higher laser efficiency, the core needs to be finely designed to obtain a higher doping concentration while reducing the NA. However, low NA and high doping concentration are contradictory. The design requirements of efficient thulium-doped fiber components for large mode area and low NA are long-standing technical difficulties in the manufacture of thulium-doped fiber. This is the design difficulty of highly doped fiber and one of the main reasons that limit the efficiency of current thulium-doped fiber lasers to be much smaller than the theoretical quantum efficiency. In order to improve the pump absorption efficiency and light-to-light conversion efficiency, the doping concentration and core-to-clad diameter ratio can be appropriately increased. However, too high a doping concentration makes it more difficult to manufacture low-core NA fiber, and photon darkening occurs, degrading the fiber efficiency. At the same time, considering that the core NA is too small, it is not conducive to the transmission of cladding pump light in the core when the fiber laser is integrated, affecting the absorption efficiency of the pump. If the NA is designed to be 0.096, the maximum single-mode core diameter design value that ensures single-mode transmission of light energy with a wavelength greater than 1.9μm is 15.1μm. Therefore, we designed the fiber parameters in this research plan as follows: core NA = 0.08, core diameter 15μm, cladding NA = 0.48, inner cladding diameter 250μm, mode field diameter MFD = 16.4μm, V value is about 2.0. Considering the thermal management, ASE suppression and efficiency issues of the gain fiber area, the gain fiber cladding absorption coefficient is designed to be 2.00dB / m@793nm.

[0086] The present invention achieves 207.6W continuous laser output when injecting 793nm pump light power of 475W, the laser center wavelength is 1907.8nm, the optical-to-optical conversion efficiency is 43.7%, the polarization extinction ratio is 16.6dB, and the beam quality is 1.52.

[0087] Combine the following Figure 2 and Figure 3 Explain the principle of dual FBG polarization selection:

[0088] Writing FBG in the core region of polarization-maintaining fiber is equivalent to writing FBG with the same grating period along the fast and slow principal axes. The inherent high birefringence of polarization-maintaining fiber makes the Bragg wavelength λ of the fast and slow principal axes F and λ S Slightly different, there is a small Bragg wavelength shift Δλ B , and Δλ B =2BΛ, where B is the mode birefringence of the polarization-maintaining fiber, B = Δn = n s -n f , n s and n f are the modal refractive indices of polarization states on the slow axis and fast axis, respectively, and B is on the order of 10 -4 , dimensionless. The magnitude of Λ is 10 2 nm, Δλ BThe typical value distribution range is 0.1 to 0.6 nm. Since the two wavelengths appear on the fast and slow axes respectively, the wavelengths show polarization-dependent characteristics.

[0089] In a dual PM-FBG linear cavity fiber continuous laser, if the dual PM-FBG is fused at 0°, such as Figure 2 As shown, ignoring the error introduced during the production process, λ F B-HR =λ F B-LR ,λ S B-HR =λ S B-LR , according to the dual FBG wavelength selection, there will be a pair of equal intensity and wavelength interval Δλ B The dual-wavelength characteristic spectrum, the short wavelength corresponds to the fast axis of the dual PM-FBG, the long wavelength corresponds to the slow axis of the dual PM-FBG, the output laser is elliptically polarized light, even if the dual FBG is located at different positions in the cavity, the pump light power is different, the nonlinearity of the two is different, but because the dual wavelength intensity is similar, the dual wavelengths appear basically at the same time, and the dual wavelengths can be separated by a polarization beam splitter.

[0090] If two PM-FBGs are welded at 90°, Figure 3 As shown in the figure, the slow axis λ of HR-FBG can be ensured by carefully designing the fast and slow axis Bragg wavelengths and bandwidths or by applying temperature control to FBG. S B-HR and the fast axis λ of LR-FBG F B-LR Correspondingly, the fast axis λ of HR-FBG can be suppressed at the same time F B-HR and the slow axis λ of LR-FBG S B-LR The final output is a linearly polarized light that oscillates between the HR-FBG slow axis and the LR-FBG fast axis.

[0091] Combine the following Figure 4 , Figure 5 , Figure 6 and Figure 7 The output parameters of the present invention are described as follows:

[0092] Figure 4 The output power curve of the seed source oscillator in the present invention is shown, the horizontal axis represents the pump power of the semiconductor laser injected into the beam combiner, and the vertical axis represents the output power of the 1907nm single-mode polarization-maintaining all-fiber oscillator. When the injected 793nm pump light power is 33.7W, the output power of the oscillator is 12.5W, the slope efficiency is 41.1%, the laser wavelength at this time is 1907.78nm, and the polarization extinction ratio after ISO is 19.6dB.

[0093] Figure 5 This is the output curve of the 1907nm single-mode polarization-maintaining all-fiber amplifier, where the abscissa represents the pump power absorbed by the amplifier stage, and the ordinate represents the output power of the amplifier. When the injected 793nm pump light power is 475W, the present invention achieves a continuous laser output of 207.6W, with a slope efficiency of 43.4%.

[0094] Figure 6 The abscissa represents the laser wavelength of the amplifier, the ordinate represents the wavelength, and the dimensionless spectral intensity. The central wavelength of the amplifier is the same as that of the oscillator, which is stable at 1907.8nm. The half-wave full width of the spectrum is 0.19nm, and the polarization extinction ratio at the highest power is 16.6dB.

[0095] Figure 7 It represents the beam quality and spot distribution at the highest power of the amplifier. The horizontal axis represents the position in the laser transmission direction, and the vertical axis represents the spot radius. The beam quality is measured by the knife-edge method. The fitting curve shows that the beam quality in the x-direction at the highest power of the amplifier is 1.52, and the beam quality in the y-direction is 1.50.

[0096] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A 1907nm single-mode polarization-maintaining all-fiber laser, characterized in that: It includes: Fiber oscillators and fiber amplifiers; The fiber oscillator comprises a high-reflectivity fiber Bragg grating (1), a first forward pumping optical combiner (3-I), a first pumping light source (5-I), a first low-doped single-mode thulium-doped gain fiber (4-I) and a low-reflectivity fiber Bragg grating (2); The optical fiber amplifier comprises a first cladding pump light stripper (6-I), a second cladding pump light stripper (6-II), an optical isolator (7), a mode field adapter (8), a second forward pump light combiner (3-II), a second low-doped single-mode thulium-doped gain optical fiber (4-II) and a second pump light source (5-II); The output end of the high-reflectivity fiber Bragg grating (1) is connected to the input end of the first forward-pumped optical combiner (3-I), the first pumping light source (5-I) is connected to the pumping optical fiber of the first forward-pumped optical combiner (3-I), the output end of the first forward-pumped optical combiner (3-I) is connected to one end of a first low-doped single-mode thulium-doped gain optical fiber (4-I), and the other end of the first low-doped single-mode thulium-doped gain optical fiber (4-I) is connected to the input end of the low-reflectivity fiber Bragg grating (2); The output end of the low-reflectivity fiber Bragg grating (2) is connected to the input end of the first cladding pump light stripper (6-I); The output end of the first cladding pump light stripper (6-I) is connected to the optical isolator (7), the output pigtail of the optical isolator (7) is connected to the mode field adapter (8), the output end of the mode field adapter (8) is connected to the second forward pump light combiner (3-II), the second pump light source (5-II) is connected to the pump fiber of the second forward pump light combiner (3-II), the signal light output pigtail of the second forward pump light combiner (3-II) is connected to one end of the second low-doped single-mode thulium-doped gain fiber (4-II), and the other end of the second low-doped single-mode thulium-doped gain fiber (4-II) is connected to the output end of the second cladding pump light stripper (6-II); the optical isolator (7) pigtail outputs linearly polarized light on the slow axis; All devices are polarization-maintaining devices; The other end of the first low-doped single-mode thulium-doped gain optical fiber (4-I) is orthogonally fused with the input end of the low-reflectivity fiber Bragg grating (2); The output end of the low-reflectivity fiber Bragg grating (2) is orthogonally fused with the input end of the first cladding pump light stripper (6-I); Other devices are fused horizontally.

2. A 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The high-reflectivity fiber Bragg grating (1), the low-reflectivity fiber Bragg grating (2), the first low-doped single-mode thulium-doped gain fiber (4-I) and the second low-doped single-mode thulium-doped gain fiber (4-II) are respectively fixed on a heat dissipation base.

3. The 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The high-reflectivity fiber Bragg grating (1) and the low-reflectivity fiber Bragg grating (2) are respectively fixedly arranged on different cooling platforms, and both cooling platforms are cooled by semiconductor refrigerators, and the temperature control range is -5 to 40°C.

4. The 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The high-reflectivity fiber Bragg grating (1) has a fast-axis Bragg wavelength of 1907nm±0.2nm, a reflectivity of >99.5%, a transmission bandwidth of 0.5nm±0.1nm, and can withstand a pump power of more than 200W; The slow axis Bragg wavelength of the low reflectivity fiber Bragg grating (2) is 1907nm±0.2nm, the reflectivity is 10±2%, the reflection bandwidth is 0.3nm±0.1nm, and the maximum signal light power that can be tolerated is 50W; The spectral side mode suppression ratio is greater than 20dB, and the Bragg wavelength mismatch between the fast axis and the slow axis is less than 0.1nm.

5. The 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The first forward pump optical combiner (3-I) is a (6+1)×1 combiner, the pump efficiency is >95%, the signal light transmission loss is <0.7dB, the core diameter and cladding diameter of the combiner signal fiber are 10 / 130μm, and the pump fiber is 105 / 125μm; The second forward pumped optical combiner (3-II) is a (6+1)×1 combiner with a pumping efficiency of >95%, a signal light transmission loss of <2dB, a polarization extinction ratio of >18dB, a single-arm power handling power of >150W, a signal fiber of 15 / 250μm, and a pump fiber of 200 / 220μm.

6. The 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The first low-doped single-mode thulium-doped gain optical fiber (4-I) has a core / cladding ratio of 10 / 130 μm, a core and cladding numerical aperture of 0.14 and 0.46 respectively, an absorption coefficient of the cladding for 793 nm pump light of 4.5-4.7 dB / m, and a length of 1.8 m; The core / cladding of the second low-doped single-mode thulium-doped gain fiber (4-II) is 15 / 250 μm, the numerical apertures of the core and cladding are 0.11 and 0.46 respectively, the absorption coefficient of the cladding to 793 nm pump light is 2.0-2.1 dB / m, and the length is 3.0 m.

7. The 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The core / cladding of the first cladding pump light stripper (6-I) is 10 / 130 μm, the transmission loss of the signal light is <0.2 dB, the pump light stripping efficiency is >22 dB, and the polarization extinction ratio is >20 dB; The core / cladding of the second cladding pump light stripper (6-II) is 15 / 250 μm, the transmission loss of the signal light is <0.2 dB, the pump light stripping efficiency is >20 dB, and the polarization extinction ratio is >18 dB.

8. The 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The polarization isolation of the optical isolator (7) is greater than 20 dB, the power withstood by a single arm is 20 W, the core / cladding of the signal fiber is 10 / 130 μm, and linearly polarized light is output on the slow axis of the pigtail.

9. The 1907nm single-mode polarization-maintaining all-fiber laser according to claim 1, characterized in that: The extinction ratio of the mode field adapter (8) is greater than 16 dB, the incorporation loss is less than 0.9 dB, the core / cladding of the input end pigtail is 10 / 130 μm, and the core / cladding of the output end is 15 / 250 μm.

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