1.5 [mu] m erbium-ytterbium co-doped fiber laser amplifier

Abstract

The invention discloses a 1.5 [mu] m erbium-ytterbium co-doped fiber laser amplifier, which belongs to the technical field of fiber laser amplifiers and comprises a pumping source, a pumping coupler, a low-absorption-coefficient gain fiber, a high-absorption-coefficient gain fiber and a cladding light stripper. The low-absorption-coefficient gain optical fiber and the high-absorption-coefficient gain optical fiber are Er < 3 + > and Yb < 3 + > co-doped active optical fibers, the pumping coupler couples externally transmitted 1.5-micron signal light and pumping light output by the pumping source, and 1.5-micron laser amplified by the low-absorption-coefficient gain optical fiber and the high-absorption-coefficient gain optical fiber sequentially passes through the cladding light stripper and then is output. The 1.5 [mu] m erbium-ytterbium co-doped fiber laser amplifier provided by the invention can inhibit generation of 1 [mu] m ASE (Accelerated Solvent Erbium) laser and reduce heat production of a fiber entrance point of a laser, thereby realizing high-power 1.5 [mu] m laser output.

Description

Technical Field

[0001] This invention belongs to the field of fiber laser amplifier technology, specifically relating to a 1.5μm erbium-ytterbium co-doped fiber laser amplifier that can suppress spontaneous emission amplification (ASE) and thermal effects. Background Technology

[0002] 1.5μm band lasers have attracted much attention in fields such as lidar, satellite remote sensing, space optical communication, and precision measurement due to their advantages in atmospheric transmission, eye safety, and low-loss window for fiber optic communication. This is achieved through the use of ytterbium ions (Yb) doped in erbium-ytterbium co-doped fiber (EYDF). 3+ The ion absorbs pump light (such as 976nm, 940nm, 915nm) and then transfers energy to erbium ions (Er). 3+ ), then Er 3+ Radiation-based generation of 1.5μm lasers is currently the mainstream method for generating high-power 1.5μm lasers. In this process, Yb 3+ Absorb pump light energy from ground state 2 F 7 / 2 Transition to excited state 2 F 5 / 2 Then, energy is transferred to Er through the cross-relaxation process. 3+ Thus Er 3+ From the ground state 4 I 15 / 2 Transition to excited state 4 I 11 / 2 .

[0003] However, due to limitations in the properties of optical fiber preform materials and doping processes, Er in commercially available quartz optical fibers... 3+ The doping concentration is difficult to increase significantly, and is far lower than that of Yb. 3+ The achievable doping concentration. Currently, the concentration ratio of the two in commercially available EYDF (Yb...) 3+ Er 3+ The ratio is approximately 10:1, which also leads to the Yb ratio at high pump power. 3+ and Er 3+ Bottleneck effect of energy transfer between: As pump power increases, when Yb 3+ The rate at which pump energy is absorbed is greater than that of Er. 3+ At the rate of cross-relaxation, the excited state Yb 3+ The quantity will continue to increase, eventually leading to the ASE effect. The 1μm ASE light generated in this process is prone to self-oscillation, causing the 1.5μm band laser to be unable to be further amplified or causing damage to the components in the laser.

[0004] To suppress the generation of ASE (associated ester) in 1.5μm EYDF lasers, the main solutions include selective loss methods, peak-shifting pumping methods, and auxiliary signal methods, as exemplified by patents such as CN120453837A and CN120497743A. Peak-shifting pumping is currently the mainstream solution for high-power 1.5μm lasers, employing a 940nm or 915nm semiconductor laser as the pump source to avoid Yb 3+ The absorption peak at 976 nm causes the pump light to be gradually absorbed in longer optical fibers, thereby alleviating the Yb 3+ With Er 3 + Bottleneck effect of energy transfer between spaces.

[0005] However, even with 940nm peak-shifted pumping, 1μm ASE light will still be generated with further increases in pump power. In achieving higher 1.5μm laser output power, 1μm ASE remains a major limiting factor for lasers. Furthermore, in high-power, narrow-linewidth 1.5μm lasers, the shortest possible fiber length is required to suppress stimulated Brillouin scattering (SBS), which necessitates maximizing the absorption coefficient of the gain fiber used. And the higher the absorption coefficient of the EYDF, the more Yb... 3+ The doping concentration also increases accordingly, making it more prone to ASE problems. Simultaneously, due to the large quantum loss in the conversion from 940nm pump light to 1.5μm laser light, the gain fiber generates more heat during amplification. This is especially true near the fiber entry point of the gain fiber in the fiber laser amplifier. 3+ The absorption of pump light is strongest, and the amplification of the 1.5μm signal light is also strongest, leading to severe heat generation at the fiber entry point. Poor heat dissipation can easily cause the fiber entry point to burn out. In summary, the ASE effect and fiber entry point heating are the most significant negative factors affecting the power increase of the 1.5μm EYDF laser amplifier under high pump power conditions. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a 1.5μm erbium-ytterbium co-doped fiber laser amplifier that can suppress ASE and thermal effects. It can suppress the generation of 1μm ASE laser and reduce the heat generation at the laser entry point, thereby achieving high-power 1.5μm laser output.

[0007] This invention achieves this objective through the following technical solution: A 1.5μm erbium-ytterbium co-doped fiber laser amplifier includes a pump source, a pump coupler, a low absorption coefficient gain fiber, a high absorption coefficient gain fiber, and a cladding stripper. Both low-absorption-coefficient gain fibers and high-absorption-coefficient gain fibers are Er 3+ Yb 3+Co-doped active optical fibers The pump coupler couples the externally transmitted 1.5μm signal light with the pump light output from the pump source. The 1.5μm laser light, amplified sequentially by a low-absorption-coefficient gain fiber and a high-absorption-coefficient gain fiber, is then output after passing through a cladding stripper.

[0008] Preferably, the pump coupler is a signal pump combiner or a wavelength division multiplexer.

[0009] Preferably, the pump coupler is coupled to the gain fiber using fiber fusion coupling or spatial optical focusing coupling.

[0010] Preferably, the low-absorption-coefficient gain fiber and the high-absorption-coefficient gain fiber are of the same type, the transmission mode is single-mode fiber or multi-mode fiber, and the cladding structure is single-clad fiber or double-clad fiber.

[0011] Preferably, the absorption coefficient of low-absorption-coefficient gain fiber for 915nm pump light is smaller than that of high-absorption-coefficient gain fiber.

[0012] Preferably, the core diameter and core numerical aperture of low absorption coefficient gain fiber are less than or equal to those of high absorption coefficient gain fiber.

[0013] Preferably, the cladding diameter and cladding numerical aperture of the low absorption coefficient gain fiber are less than or equal to those of the high absorption coefficient gain fiber.

[0014] Preferably, the low-absorption-coefficient gain fiber and the high-absorption-coefficient gain fiber are coupled by direct fusion splicing.

[0015] Preferably, the pump source is one of a fiber laser, a solid-state laser, or a semiconductor laser, and the laser mode adopts a fundamental transverse mode or multiple transverse modes, with an emission wavelength in the Yb range. 3+ Within the absorption wavelength range.

[0016] Preferably, the 1.5μm laser generating device for generating signal light is one of fiber laser, solid-state laser, or semiconductor laser, and the laser mode adopts fundamental transverse mode or multiple transverse mode, with the signal wavelength in the range of 1.5μm to 1.6μm.

[0017] Compared with the prior art, the beneficial effects of this invention are as follows: 1. By fusion splicing two types of EYDFs—one with low absorption coefficient and the other with high absorption coefficient—to serve as the gain fiber for a laser amplifier, the pump light and signal light first enter the low-absorption-coefficient EYDF, thus suppressing Yb in the front gain fiber. 3+ Excessive absorption of high-power-density pump light prevents it from being fully directed to Er. 3+The ASE effect is caused by transmission. Since the front gain fiber has absorbed part of the pump light, the pump light power density in the rear high absorption coefficient EYDF has been reduced, which also suppresses the occurrence of the ASE effect.

[0018] 2. The use of high absorption coefficient EYDF in the rear gain fiber shortens the total length of the gain fiber used, which helps to suppress the SBS effect during laser amplification with a narrow linewidth of 1.5μm.

[0019] 3. The gain fiber at the fiber entry point uses a low absorption coefficient EYDF, which reduces the pump light absorbed at this point, and thus also reduces the signal light generated by the conversion at this point. The reduced signal light conversion at this point also reduces the heat generated by quantum defects at the fiber entry point, making the heat distribution of the entire gain fiber more uniform and improving the laser amplifier's ability to withstand thermal effects. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of an embodiment of the present invention.

[0021] In the figure, the labels are: 1-pump source, 2-pump coupler, 3-low absorption coefficient gain fiber, 4-high absorption coefficient gain fiber, 5-cladding stripper. Detailed Implementation

[0022] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] The power increase of 1.5μm erbium-ytterbium co-doped fiber (EYDF) lasers is mainly limited by the amount of ytterbium ions (Yb). 3+ To mitigate the effects of spontaneous emission amplification (ASE) and thermal effects, this invention proposes a 1.5μm EYDF laser amplifier that suppresses ASE and thermal effects. By fusion splicing two EYDF fibers with different absorption coefficients as gain fibers, the signal light and pump light are first amplified by the low-absorption-coefficient EYDF before entering the high-absorption-coefficient EYDF, thereby reducing the Yb in the initial amplification stage. 3+The excessive absorption of pump light causes the ASE effect; at the same time, the use of high absorption coefficient EYDF in the back section reduces the total length of the gain fiber used in the laser amplifier, thereby suppressing the SBS effect during narrow linewidth laser amplification; furthermore, the use of low absorption coefficient EYDF in the gain fiber at the fiber entry point reduces the absorption of pump light at this point, and the conversion of less pump light into signal light also reduces the heat generation at the fiber entry point, improving the laser amplifier's ability to withstand thermal effects.

[0024] Pump light and signal light are input into a low-absorption-coefficient gain fiber through a pump coupler, and then fused together and coupled into a high-absorption-coefficient gain fiber.

[0025] Both low-absorption-coefficient gain fibers and high-absorption-coefficient gain fibers are Er 3+ Yb 3+ Co-doped active optical fiber, Yb 3+ Absorb pump light energy and transfer it to Er through a cross-relaxation process. 3+ , making Er 3+ It provides gain for 1.5μm band signal light; both gain fibers are of the same type, and the transmission mode uses single-mode or multimode fiber, and the cladding structure uses single-clad or double-clad fiber; the absorption coefficient of the low absorption coefficient gain fiber for 915nm pump light is less than that of the high absorption coefficient gain fiber; the core diameter and core numerical aperture of the low absorption coefficient gain fiber are less than or equal to those of the high absorption coefficient gain fiber; the cladding diameter and cladding numerical aperture of the low absorption coefficient gain fiber are less than or equal to those of the high absorption coefficient gain fiber.

[0026] Low-absorption-coefficient gain fiber and high-absorption-coefficient gain fiber are coupled by direct fusion splicing.

[0027] The signal light comes from a 1.5μm laser generating device outside the laser amplifier, which can be a fiber laser, a solid-state laser, or a semiconductor laser. The laser mode can be a fundamental transverse mode or multiple transverse modes, and the signal wavelength is between 1.5μm and 1.6μm.

[0028] The pump light originates from a pump source, which can be a fiber laser, a solid-state laser, or a semiconductor laser. The laser mode can be the fundamental transverse mode or multiple transverse modes, and the emission wavelength is in the Yb range. 3+ Within the absorption wavelength range, it can be absorbed to generate laser gain.

[0029] A pump coupler can be a signal pump combiner or a wavelength division multiplexer, which couples the signal light and pump light into the gain fiber. The coupling method can be fiber fusion coupling or spatial light focusing coupling.

[0030] The following provides a specific embodiment of a 1.5μm erbium-ytterbium co-doped fiber laser amplifier that can suppress ASE and thermal effects, such as... Figure 1As shown. The laser amplifier includes: a pump source 1, a pump coupler 2, a low absorption coefficient gain fiber 3, a high absorption coefficient gain fiber 4, and a cladding stripper 5.

[0031] Pump source 1 is a 940nm semiconductor laser with fiber-coupled output. The core / cladding diameter of the pigtail is 105μm / 125μm (hereinafter referred to as "105 / 125 fiber"). The maximum average output power of a single pump source is 100W. Pump coupler 2 is a (2+1)×1 forward signal pump combiner. The pump arm fiber is a 105 / 125 single-clad fiber, and the signal arm is a double-clad fiber. The core / inner cladding diameter of the fiber is 25μm / 300μm (hereinafter referred to as "25 / 300 fiber"). Low absorption coefficient gain fiber 3 is a 25 / 300 double-clad fiber. 3+ Yb 3+ Co-doped, the core has an absorption coefficient of 85 dB / m at 1535 nm, the cladding has an absorption coefficient of 2.5 dB / m at 915 nm, and a length of 2.1 m; the high-absorption-coefficient gain fiber 4 is a 25 / 300 double-clad fiber, Er 3+ Yb 3+ The fiber is co-doped, with a core absorption coefficient of 90 dB / m for 1535 nm light and a cladding absorption coefficient of 3.0 dB / m for 915 nm light, and a length of 3.7 m. The cladding stripper 5 uses a 25 / 300 double-clad fiber pigtail, with the output end cut at an 8° angle. The above devices are sequentially fused together according to their serial numbers. In this embodiment, the signal light coupled into the signal arm of the signal pump combiner is a continuous narrow-linewidth laser with a center wavelength of 1550 nm, a linewidth of 0.04 nm, and an average power of 8 W.

[0032] The 940nm pump light emitted from pump source 1 is coupled into the low-absorption-coefficient gain fiber 3 via pump coupler 2, and propagates in the inner cladding and core; during propagation, it excites the Yb in the gain fiber. 3+ To the excited state, and then through cross-relaxation Er 3+ The 1.5μm signal light generated by the laser amplifier preamplifier is coupled into the low-absorption-coefficient gain fiber 3 through the signal arm of the pump coupler 2 and propagates in the fiber core; during propagation, it carries away the Er from the upper laser level. 3+ The energy in the signal is thus amplified. The remaining pump light and the amplified 1.5μm signal light are transmitted through the low-absorption-coefficient gain fiber 3 to the high-absorption-coefficient gain fiber 4 via fusion coupling. The pump light continues to undergo a cross-relaxation process to amplify the Er in the high-absorption-coefficient gain fiber 4. 3+The signal light is excited to an upper energy level, allowing the 1.5μm signal light to be further amplified. The residual pump light after passing through the high-absorption-coefficient gain fiber 4 is filtered out by the cladding light stripper 5, and the 1.5μm signal light retained in the fiber core is output from the 8° pigtail of the cladding light stripper 5.

[0033] By sequentially fusion-splicing two types of gain fibers—low-absorption-coefficient and high-absorption-coefficient—the ASE and SBS effects in the 1.5μm EYDF laser amplifier were suppressed, and the thermal effects at the fiber entry point were reduced. Since the pump light and signal light are first injected into the low-absorption-coefficient gain fiber after passing through the pump coupler, excessive 940nm pump light is avoided from being concentrated and absorbed by the front gain fiber, thus preventing the ASE effect caused by excessive excited-state Yb3+. Simultaneously, the reduced amplification of the 1.5μm signal light at the front of the gain fiber also reduces heat generation in the gain fiber after the fiber entry point, preventing laser damage caused by overheating at the fiber entry point. Under the parameters of this embodiment, the laser amplifier achieved a 104W, 1550nm narrow-linewidth laser output with a slope efficiency of 48% at a pump power of 200W. No significant ASE or SBS generation was observed in the output spectrum, and the temperature at the fiber entry point was approximately 50℃ under 23℃ water cooling conditions.

[0034] The present invention has been described in detail above through embodiments, but the content described is only an exemplary embodiment of the present invention and should not be considered as limiting the scope of the present invention. The scope of protection of the present invention is defined by the claims. Any technical solutions designed by those skilled in the art using the technical solutions described in the present invention, or similar technical solutions designed by those skilled in the art under the inspiration of the technical solutions of the present invention, within the substance and scope of protection of the present invention, to achieve the above-mentioned technical effects, or equivalent changes and improvements made to the scope of the application, should still fall within the patent protection scope of the present invention. It should be noted that, for clarity, descriptions of some components and processes that are not directly and obviously related to the scope of protection of the present invention but are known to those skilled in the art have been omitted in the description of the present invention.

Claims

1. A 1.5μm erbium-ytterbium co-doped fiber laser amplifier, characterized in that, Includes pump source, pump coupler, low absorption coefficient gain fiber, high absorption coefficient gain fiber and cladding stripper; Both low-absorption-coefficient gain fibers and high-absorption-coefficient gain fibers are Er 3+ Yb 3+ Co-doped active optical fibers The pump coupler couples the externally transmitted 1.5μm signal light with the pump light output from the pump source. The 1.5μm laser light, amplified sequentially by a low-absorption-coefficient gain fiber and a high-absorption-coefficient gain fiber, is then output after passing through a cladding stripper.

2. The 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 1, characterized in that, The pump coupler is a signal pump combiner or wavelength division multiplexer.

3. The 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 1, characterized in that, The pump coupler is coupled to the gain fiber using either fiber fusion coupling or spatial optical focusing coupling.

4. The 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 1, characterized in that, Low-absorption-coefficient gain fiber and high-absorption-coefficient gain fiber are of the same type, and the transmission mode is single-mode fiber or multi-mode fiber, and the cladding structure is single-clad fiber or double-clad fiber.

5. A 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 1, characterized in that, The absorption coefficient of low-absorption-coefficient gain fiber for 915nm pump light is less than that of high-absorption-coefficient gain fiber.

6. A 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 4, characterized in that, The core diameter and core numerical aperture of low-absorption-coefficient gain fibers are less than or equal to those of high-absorption-coefficient gain fibers.

7. A 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 4, characterized in that, The cladding diameter and cladding numerical aperture of low-absorption-coefficient gain fibers are less than or equal to those of high-absorption-coefficient gain fibers.

8. A 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 1, characterized in that, Low-absorption-coefficient gain fiber and high-absorption-coefficient gain fiber are coupled by direct fusion splicing.

9. A 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 1, characterized in that, The pump source is one of fiber lasers, solid-state lasers, or semiconductor lasers. The laser mode uses either the fundamental transverse mode or multiple transverse modes, and the emission wavelength is in the Yb range. 3+ Within the absorption wavelength range.

10. A 1.5μm erbium-ytterbium co-doped fiber laser amplifier according to claim 1, characterized in that, The 1.5μm laser generating device for generating signal light is one of fiber laser, solid-state laser, or semiconductor laser. The laser mode adopts the fundamental transverse mode or multiple transverse modes, and the signal wavelength is between 1.5μm and 1.6μm.

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