Distributed pumping optical fiber amplifier

Abstract

The invention discloses a distributed pumping optical fiber amplifier. The amplifier is characterized in that a multi-mode pumping source is injected into a multi-section double-cladding active optical fiber through a pumping / signal light beam combiner to provide pumping light for the amplifier; the low-power seed source is injected into the multi-section double-cladding active optical fiber through the optical fiber isolator and the pumping / signal light beam combiner for power amplification; the multiple sections of long-period fiber bragg gratings and the multiple sections of double-clad active optical fibers are sequentially connected in a crossed manner; the multiple sections of long-period fiber gratings have harmonic peaks at pumping wavelengths, and due to different periods, cladding mode orders corresponding to the harmonic peaks are different; the multi-section long-period fiber bragg grating couples the cladding pump light into the fiber core to perform distributed fiber core pumping on the double-cladding active fiber, the distributed fiber core pumping is combined with cladding pumping to optimize gain distribution and heat distribution of the fiber amplifier, and high-efficiency and high-power amplification of the seed light is realized. While the heat distribution of the amplifier is optimized, the pumping efficiency is improved, the length of the amplification-stage optical fiber is effectively shortened, the nonlinear effect is inhibited, and high-power optical fiber laser amplification is realized.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber laser technology, and in particular to a distributed pumped optical fiber amplifier. Background Art

[0002] High-power fiber lasers have important applications in laser processing, 3D printing and additive manufacturing, and national defense security. High-power fiber amplifiers based on the master oscillator power amplifier (MOPA) structure have significant advantages in maintaining laser wavelength stability, single longitudinal mode operation characteristics, pulse repetition frequency, and pulse width. However, as the power level of fiber lasers increases, the limited mode field area of the fiber waveguide structure causes high-power fiber lasers to experience nonlinear effects such as stimulated Raman scattering, stimulated Brillouin scattering, four-wave mixing, and self-phase modulation. While limiting the laser power level, it also causes performance degradation problems such as laser spectrum broadening, decreased time-domain stability, and decreased beam quality.

[0003] To solve this problem, on the one hand, by designing the transverse and longitudinal structural parameters of the optical fiber and developing ultra-large mode field optical fiber, the laser power density in the optical fiber core is reduced, thereby weakening the accumulation of nonlinear effects in the optical fiber under high-power laser. However, due to the current level of quartz glass refractive index control, the few-mode working characteristics of ultra-large mode field quartz fiber lead to the degradation of laser beam quality; on the other hand, by designing a composite functional fiber with integrated pumping and gain, forward and reverse pumping is combined with a side distributed pumping structure to disperse the thermal effect and reduce the nonlinear effect. However, the composite functional fiber is difficult to manufacture and has a low yield, making it difficult to effectively improve the laser beam quality. In addition, due to the low side pumping absorption coefficient, it is often necessary to use a longer active fiber to obtain sufficient pump absorption, which leads to more serious nonlinear effects of high-power lasers.

[0004] Therefore, in response to the application needs of high-power, high-beam-quality fiber lasers, it is urgent to develop new fiber amplification technologies that can effectively avoid the nonlinear effects of high-power lasers while ensuring high laser beam quality. Summary of the Invention

[0005] The present invention provides a distributed pumped fiber amplifier. This invention addresses the issues of severe nonlinear effects and thermal effects during the power boosting process of high-power fiber lasers, as well as the degradation of the beam quality of ultra-large mode field fiber lasers. By using multiple segments of long-period fiber gratings in the laser amplification stage, cladding pump light of different order modes is gradually coupled into the active fiber core for core pumping. By combining cladding pumping with distributed core pumping, the amplifier's thermal distribution is optimized while improving pumping efficiency, effectively shortening the fiber length of the amplifier stage, suppressing nonlinear effects, and achieving high-power fiber laser amplification. Details are described below:

[0006] A distributed pumped fiber amplifier, comprising a low-power seed source, a fiber isolator, a multimode pump source, a pump / signal optical combiner, multiple sections of double-clad active optical fiber, and multiple sections of long-period fiber gratings with different periods;

[0007] The multimode pump source is injected into the multiple sections of double-clad active optical fiber through the pump / signal optical combiner to provide pump light for the amplifier; the low-power seed source is injected into the multiple sections of double-clad active optical fiber through the optical fiber isolator and the pump / signal optical combiner for power amplification; the multiple sections of long-period fiber gratings are sequentially cross-connected with the multiple sections of double-clad active optical fiber;

[0008] The multiple sections of long-period fiber gratings all have resonance peaks at the pump wavelength, and due to different periods, the cladding mode orders corresponding to the resonance peaks are different; the multiple sections of long-period fiber gratings couple the cladding pump light into the fiber core to perform distributed core pumping on the double-clad active optical fiber, and combine with the cladding pumping to optimize the gain distribution and thermal distribution of the optical fiber amplifier, thereby achieving high-efficiency and high-power amplification of the seed light.

[0009] The grating periods of each section of the long-period fiber grating increase along the propagation direction of the signal light, and the order of the cladding mode corresponding to the resonance peak of the pump light decreases.

[0010] The long-period fiber grating is inscribed in a passive double-clad optical fiber and fused with the double-clad active optical fiber to achieve coupling of the cladding pump light to the double-clad active optical fiber core, or is inscribed in the double-clad active optical fiber to directly achieve coupling of the cladding pump light to the active optical fiber core.

[0011] Wherein, the amplifier adopts a forward pumping mode or a reverse pumping mode.

[0012] The beneficial effects of the technical solution provided by the present invention are:

[0013] 1. The present invention introduces multiple long-period fiber gratings with different periods into the optical fiber amplifier stage, coupling the cladding pump light into the active optical fiber core for core pumping. Combined with cladding pumping, this can effectively shorten the optical fiber length of the amplifier stage, increase the nonlinear effect threshold, and achieve an increase in the power level of the optical fiber amplifier.

[0014] 2. The present invention optimizes the grating period of a long-period fiber Bragg grating (LPB) to achieve coupling of different-order cladding pump light modes to the fiber core. Based on the signal power evolution characteristics of the fiber amplifier, a decreasing order distribution of the cladding modes corresponding to the grating resonance peak is designed. While ensuring efficient amplification of the signal light, the thermal load distribution characteristics of the high-power fiber amplifier are optimized to avoid the risk of decreased operating stability or even burnout of the laser system caused by a relatively concentrated thermal load distribution in the high-power fiber laser system.

[0015] 3. The present invention achieves high-power amplification of signal light by introducing a long-period grating into the optical fiber amplifier stage. The optical fiber amplification system does not need to adopt a complex optical fiber structure design. The system structure is simple and easy to implement and integrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural diagram of a distributed pumped fiber amplifier.

[0017] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0018] 1: Low power seed source; 2: Fiber optic isolator;

[0019] 3: Multimode pump source; 4: Pump / signal optical combiner;

[0020] 5: Double-clad active optical fiber; 6: Long-period fiber grating. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0022] Example 1

[0023] A distributed pumped fiber amplifier, see Figure 1 The amplifier includes: a low-power seed source 1, an optical fiber isolator 2, a multi-mode pump source 3, a pump / signal optical combiner 4, multiple sections of double-clad active optical fiber 5, and multiple sections of long-period fiber gratings 6 with different periods.

[0024] The low-power seed source 1 is a continuous wave fiber laser with a central wavelength of 1080 nm and an output power of 30 W. It is injected into the fiber optic isolator 2 and the (18+1)×1 980 nm / 1080 nm fiber combiner 4 to form a 650 μm 2 , a double-clad active fiber 5 (i.e., a double-clad ytterbium-doped fiber) with a pump absorption coefficient of 1 dB / m, multiple 980nm multimode pump sources 3 with a maximum output power of 250W are coupled to the double-clad ytterbium-doped fiber 5 through a beam combiner 4 to amplify the signal light. The resonance peaks correspond to the cladding mode orders LP 07 LP 06 LP 05 LP 04 The multi-segment long period fiber Bragg grating 6 is cross-connected with the multi-segment double-clad ytterbium-doped fiber to couple the corresponding order cladding pump light into the ytterbium-doped fiber core to amplify the seed light power, achieving a power of ≥ 6kW and a beam quality factor (M 2 )≤1.3 high-power single-mode laser output.

[0025] Example 2

[0026] Another embodiment of a distributed pumped fiber amplifier structure and Figure 1 The low-power seed source 1 is a continuous wave fiber laser with a central wavelength of 1950nm and an output power of 10W. It is injected into a double-clad thulium-doped fiber 5 with a core / cladding diameter of 25 / 400μm and a pump absorption coefficient of 1.2dB / m through a fiber isolator 2 and a (18+1)×1 793nm / 1950nm fiber combiner 4. Multiple 793nm multimode pump sources 3 with a maximum output power of 240W are coupled into the double-clad thulium-doped fiber 5 through the combiner 4 to amplify the signal light. The resonance peaks correspond to the cladding mode orders LP and LP, respectively. 07 LP 06 LP 04 The multi-segment long period fiber Bragg grating 6 is cross-connected with the multi-segment double-clad ytterbium-doped fiber to couple the corresponding order cladding pump light into the thulium-doped fiber core to amplify the seed light power, achieving a power of ≥ 500W and a beam quality factor (M 2 )≤1.3 in the 2μm band high-power single-mode laser output.

[0027] In summary, the distributed pumped fiber amplifier proposed in the embodiments of the present invention introduces multiple long-period fiber gratings with different periods into the fiber amplifier stage, coupling the cladding pump light into the active fiber core to efficiently amplify the signal light. While effectively shortening the amplifier stage fiber length and increasing the nonlinear effect threshold, the embodiments of the present invention optimize the thermal load distribution of high-power fiber lasers, thereby achieving high-power, high-beam-quality laser output.

[0028] Unless otherwise specified, the embodiments of the present invention do not limit the models of the components. Any component that can perform the above functions may be used.

[0029] Those skilled in the art will understand that the accompanying drawings are only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A distributed pumped fiber amplifier, characterized in that: The amplifier is composed of a low-power seed source, an optical fiber isolator, a multi-mode pump source, a pump / signal optical combiner, multiple sections of double-clad active optical fiber, and multiple sections of long-period fiber gratings with different periods; The multimode pump source is injected into the multiple sections of double-clad active optical fiber through the pump / signal optical combiner to provide pump light for the amplifier; the low-power seed source is injected into the multiple sections of double-clad active optical fiber through the optical fiber isolator and the pump / signal optical combiner for power amplification; the multiple sections of long-period fiber gratings are sequentially cross-connected with the multiple sections of double-clad active optical fiber; The multiple sections of long-period fiber gratings all have resonance peaks at the pump wavelength, and due to different periods, the cladding mode orders corresponding to the resonance peaks are different; the multiple sections of long-period fiber gratings couple the cladding pump light into the fiber core to perform distributed core pumping on the double-clad active optical fiber, and combine with the cladding pumping to optimize the gain distribution and thermal distribution of the optical fiber amplifier, thereby achieving high-efficiency and high-power amplification of the seed light.

2. A distributed pumped fiber amplifier according to claim 1, characterized in that: The grating period of each section of the long-period fiber grating increases along the propagation direction of the signal light, and the order of the cladding mode corresponding to the pump light resonance peak decreases.

3. The distributed pumped fiber amplifier according to claim 1, wherein: The long-period fiber grating is inscribed in a passive double-clad optical fiber and fused with the double-clad active optical fiber to achieve coupling of the cladding pump light to the double-clad active optical fiber core, or is inscribed in the double-clad active optical fiber to directly achieve coupling of the cladding pump light to the active optical fiber core.

4. The distributed pumped fiber amplifier according to claim 1, wherein: The amplifier adopts a forward pumping mode or a reverse pumping mode.

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