High-power Narrow-linewidth Fiber Lasers Research Articles

5 kW power-level 1050 nm narrow-linewidth fiber amplifier enabled by biconical-tapered active fiber.

Effective wavelength extension is vital in the applications of high-power narrow-linewidth fiber lasers. In this work, we demonstrate a 5-kW power-level narrow-linewidth fiber amplifier at 1050 nm utilizing a homemade biconical-tapered Yb-doped fiber (BT-YDF). Up to ∼4.96 kW fiber laser is achieved with a 3 dB linewidth of ∼0.54 nm and a beam quality factor of Mx 2 = 1.46, My 2 = 1.6. The experimental comparisons reveal that BT-YDF has the advantages of improving a stimulated Raman scattering threshold and balancing transverse mode instability suppression in the fiber amplifier. This work could provide a good reference for extending the operating wavelength of high-power fiber amplifiers.

Key technology analysis and research progress of high-power narrow linewidth fiber laser based on the multi-longitudinal-mode oscillator seed source

Key technology analysis and research progress of high-power narrow linewidth fiber laser based on the multi-longitudinal-mode oscillator seed source

Towards a tapered Yb-doped fiber-based narrow linewidth single-mode fiber laser with a high signal to Raman ratio.

We demonstrate an all-fiber high-power narrow-linewidth fiber laser based on a homemade tapered Yb-doped fiber (T-YDF). The laser performance is investigated and systematically compared with different seed powers and pump manners. The experimental results reveal that the injected seed power requires a trade-off designed to take into account the impact of spectral broadening, nonlinear effects, and transverse mode instability (TMI). Compared with the co-pump manner, the counter-pump manner performs well in inhibiting nonlinearities, spectral broadening, and improving the TMI threshold. Under the counter-pump manner, this narrow-linewidth T-YDF amplifier realized a 2.09 kW output power with a 3 dB spectral linewidth of ∼0.34 nm, a beam quality of M2∼1.28 and a high Raman suppression ratio over 53.5 dB, the highest reported power for such a T-YDF-based narrow-linewidth single-mode laser, to the best of our knowledge. This work provides a promising pathway towards implementing monolithic high-power narrow-linewidth single-mode fiber lasers.

Temporal characteristics of the light output from optical fibers with PRBS-modulated laser injection.

Pseudo-random binary sequence (PRBS) phase modulation is an effective method to promote the stimulated Brillouin scattering (SBS) threshold of high-power narrow linewidth fiber lasers. Most studies focus on the subjects of PRBS pattern selection, filter parameter optimization, threshold promotion, etc. In this paper, the temporal characteristics of the light output from optical fibers with PRBS modulated laser injection are investigated theoretically. We found that serious temporal fluctuations, i.e., high intensity pulses, existed in the output laser and backward Stokes light, even though the time-averaged backward Stokes power is only 1% of the input laser power. Based on the transient three wave coupling equations, through exploring the influence of clock rate and PRBS pattern, we demonstrate that this phenomenon arises from the long dwell times in PRBS patterns. Finally, modified PRBS patterns are proposed to significantly eliminate the intense pulses without decreasing the original SBS threshold.

4 kW narrow-linewidth fiber laser based on a simple one-stage MOPA structure

One-stage master oscillator power amplification (MOPA) structure is a simple and robust way to acquire high-power narrow-linewidth fiber lasers (NLFLs), which have wide applications in spectral/coherent beam combination. In this work, an NLFL system was established based on a home-made fiber oscillator seed. By using this one-stage MOPA system, a 4 kW output power was achieved with 3 dB linewidth of about 0.53 nm and optical-to-optical conversion efficiency of 76.9%. The signal to Raman ratio was ∼22 dB. The measured beam quality (M2 factor) was about 1.6 at the output power of 3780 W then degraded to 2.8 at the maximum power of 4 kW. To the best of our knowledge, the 4 kW is the highest output power for such narrow linewidth one-stage MOPA fiber lasers.

Real-Time Definite Sequence Modulation Based Spectral Broadening Scheme for High-Power Narrow-Linewidth Fiber Laser

High-power narrow-linewidth continuous fiber lasers have wide applications in the fields of power synthesis, nonlinear frequency conversion, and industrial processing. The output power of kW or even MW can be achieved by adopting spectral synthesis. However, in the power amplification process, the nonlinear effect represented by the stimulated Brillouin scattering (SBS) effect limits the further increase of the laser power. And the accompanying self-pulsing effect poses a threat to the safety of the laser system. A high-order phase modulation scheme using a definite time sequence has been proposed to realize the controllable spectral broadening of the seed source, so as to suppress the SBS effect and improve the output power in the amplification stage. In this paper, we demonstrate a real-time definite time sequence generation scheme by using an integrated field-programmable gate array (FPGA) and digital-to-analog converter (DAC). Combined with a single-stage phase modulator, the broadened bandwidth up to 30 GHz and controllable spectral shape can be achieved by adjusting the output waveform of the DAC directly. The generation principles and waveform control methods of real-time sequence are introduced in detail. Proven by a master oscillator power amplifier (MOPA) structure, the laser output power has increased by 30% under the extended bandwidth of 10 GHz compared to the cascaded white noise modulation case. This scheme provides a compact real-time control module for spectral broadening, which lays the foundation for implementing low-cost, compact, and standardized high-power narrow-linewidth fiber lasers.

High Power Narrow-Linewidth Fiber Laser Based on Double-Tapered Fiber

A homemade double-tapered Yb-doped fiber is employed in a high-power narrow-linewidth fiber amplifier to improve the thresholds of nonlinear effects and transverse mode instability (TMI) effect. A bidirectional pumping configuration is employed, and a phase-modulated single-frequency fiber laser serves as the seed laser. As a result, an output power of 3630 W with 0.21 nm linewidth (stimulate Brillouin scattering limited) and an output power of 4180 W with 0.59 nm linewidth (TMI limited) are realized, corresponding to the slope efficiency of ∼77%. The beam quality at the maximum output power is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm M}_{\rm x}^{2}= 1.57, {\rm M}_{\rm y}^{\rm 2} = 1.39$</tex-math></inline-formula> . The results could provide a well reference for the power scaling of narrow-linewidth Yb-doped fiber amplifier.

3.1 kW 1050 nm narrow linewidth pumping-sharing oscillator-amplifier with an optical signal-to-noise ratio of 45.5 dB.

In this paper, the amplified spontaneous emission (ASE) suppression in a 1050 nm fiber laser with a pump-sharing oscillator-amplifier (PSOA) structure is studied theoretically and experimentally. A theoretical model of a fiber laser with a PSOA structure is established. The characteristics of the ASE for the PSOA structure and the pump-independent oscillator-amplifier (PIOA) structure are compared and analyzed. The experimental results show that the ASE can be effectively suppressed by utilizing the PSOA structure, which agree with the simulation results. A 1050 nm high-power narrow-linewidth fiber laser with PSOA structure is demonstrated, in which the gain fiber lengths of the oscillator and amplifier are 1.6 m and 9 m, respectively, to ensure the interconnection of pump power between the oscillator and amplifier. Finally, the maximum output power of 3.1 kW has been achieved, the linewidth is 0.22 nm at 3 dB, the beam quality M2 ≈ 1.33, and the optical signal-to-noise ratio (OSNR) is 45.5 dB.

High-power narrow-linewidth fiber lasers using optical spectrum broadening based on high-order phase modulation of inversion probability-tuning sequence.

Continuous fiber laser with ultra-high power and narrow linewidth is one of the key devices in the field of high-precision industrial processing, beam combining, and nonlinear frequency conversion. Under the premise of ensuring the signal quality, continuously increasing the output power is the focus of high-power narrow-linewidth fiber lasers. Driven by the white noise or pseudo-random binary sequence (PRBS), using cascaded phase modulations to broaden the spectrum of the seed source to suppress the stimulated Brillouin scattering (SBS) effect in the master oscillator power amplifier (MOPA) structure is an effective solution to increase the output power. However, this type of optical spectrum needs to be optimized, and the randomness of the driving signal causes a self-pulsing effect, which limits the further increase of the output power. In this paper, the influence of the frequency interval and randomness of the driving signal on the SBS effect in the laser system is analyzed. The modulated spectral type can be simply adjusted through changing the bit rate and inversion probability. Combining with high-order phase modulation, an approximate rectangular spectral broadening of the seed source with a tunable bandwidth up to 30 GHz is achieved. Compared with the cascaded white noise case, the output power of this scheme is increased by 600 W under the extended bandwidth of 27 GHz. It is fully verified that the seed source spectrum with high in-band flatness and low randomness can effectively suppress the SBS effect in the fiber laser and increase the output power.

Research Progress on Ytterbium-Doped Silica Glass Fiber for High-Power Narrow-linewidth Fiber Lasers

Research Progress on Ytterbium-Doped Silica Glass Fiber for High-Power Narrow-linewidth Fiber Lasers

Six kilowatt record all-fiberized and narrow-linewidth fiber amplifier with near-diffraction-limited beam quality

Abstract In this work, an all-fiberized and narrow-linewidth fiber amplifier with record output power and near-diffraction-limited beam quality is presented. Up to 6.12 kW fiber laser with the conversion efficiency of approximately 78.8% is achieved through the fiber amplifier based on a conventional step-index active fiber. At the maximum output power, the 3 dB spectral linewidth is approximately 0.86 nm and the beam quality factor is M x 2 = 1.43, M y 2 = 1.36. We have also measured and compared the output properties of the fiber amplifier employing different pumping schemes. Notably, the practical power limit of the fiber amplifier could be estimated through the maximum output powers of the fiber amplifier employing unidirectional pumping schemes. Overall, this work could provide a good reference for the optimal design and potential exploration of high-power narrow-linewidth fiber laser systems.

Evolution of Relative Intensity Noise in High-Power Narrow-Linewidth Fiber Laser Systems

In this work, we carry out a systematic study on the evolution of relative intensity noise (RIN) in a high-power narrow-linewidth fiber laser system based on phase-modulated single-frequency seed laser. The experimental results clarify that enhancement of the RIN mainly occurs when the seed laser gets amplified from low power to medium power. In addition, further power scaling could lead to reduction of the RIN until it reaches saturation on the condition that the transverse mode instability (TMI) effect is effectively suppressed. Apart from the power scaling process, the phase-modulation would also lead to enhancement of the RIN at specific frequencies corresponded to the modulation frequency. More importantly, the contrast experiments reveal that the TMI effect could lead to obvious enhancement of the RIN of the signal laser during amplification well below the TMI threshold defined by the traditional method. Therefore, apart from degeneration of the RIN during amplification, potential enhancement of the RIN induced by the phase-modulation or the TMI effect below its traditional threshold should be carefully considered and controlled to achieve high-power low-noise fiber laser. Overall, our experimental results could provide a well reference for design of high-power low-noise fiber lasers and high-power narrow-linewidth fiber lasers.

Suppressing stimulated Raman scattering by adopting a composite cavity in a narrow linewidth fiber oscillator

The master oscillator power amplifier structure has been widely employed to realize high-power and narrow-linewidth output in fiber lasers. However, the stimulated Raman scattering (SRS) effect would appear in high-power operation and even become an important limitation on further power scaling, especially when the seed lasers are based on a fiber Bragg grating (FBG) pair. In order to improve SRS suppressing ability, a composite cavity structure was demonstrated by employing an additional wide-bandwidth low-reflectivity FBG outside the conventional oscillator. After passing through a piece of 50 m SMF-28e fiber, thanks to the improved temporal stability of the composite oscillator, the proportion of Raman Stokes light dropped dramatically compared with the proportion in a conventional fiber oscillator. This composite cavity design could provide a simple and compact approach for SRS suppression in a high-power narrow-linewidth fiber laser system.

Brillouin gain spectrum characterization in Ge-doped large-mode-area fibers* *Project supported by the Key-Area Research and Development Program of Guangdong Province, China (Grant No. 2018B090904001), the National Natural Science Foundation of China (Grant Nos. 61805261, 61405202, and 61705243), and the Youth Innovation Promotion Association, Chinese Academy of Sciences (Grant No. 2020252).

The dependence of Brillouin gain spectrum (BGS) characteristics, including the Brillouin frequency shift (BFS) and the BGS bandwidth, on germanium concentration in large-mode-area Ge-doped passive fibers is investigated theoretically and experimentally. The simulation results show that the BFS is inversely proportional to GeO2 concentration, and the BGS bandwidth initially increases with the augment of GeO2 concentration, and then decreases. The BGSs of four fibers with core diameters of 10μm and 20μm for different GeO2 concentrations are compared experimentally. Experimental results demonstrate that with the same core diameter, the variations of BFS and BGS bandwidths with GeO2 concentration accord with the simulation results. Additionally, the BGS characteristics of three large-mode-area passive fibers with diameters of 10μm, 25μm, and 30μm are measured, which confirm that the increasing of the fiber diameters will cause the BGS bandwidth to broaden. We believe that these results can provide valuable references for modulating the high-power narrow-linewidth fiber lasers and Brillouin fiber amplifiers.

All-fiberized and narrow-linewidth 5 kW power-level fiber amplifier based on a bidirectional pumping configuration

Abstract In this paper, an all-fiberized and narrow-linewidth 5 kW power-level fiber amplifier is presented. The laser is achieved based on the master oscillator power amplification configuration, in which the phase-modulated single-frequency laser is applied as the seed laser and a bidirectional pumping configuration is applied in the power amplifier. The stimulated Brillouin scattering, stimulated Raman scattering, and transverse mode instability effects are all effectively suppressed in the experiment. Consequently, the output power is scaled up to 4.92 kW with a slope efficiency of as high as approximately 80%. The 3-dB spectral width is about 0.59 nm, and the beam quality is measured to be M2∼1.22 at maximum output power. Furthermore, we have also conducted a detailed spectral analysis on the spectral width of the signal laser, which reveals that the spectral wing broadening phenomenon could lead to the obvious decrease of the spectral purity at certain output power. Overall, this work could provide a reference for obtaining and optimizing high-power narrow-linewidth fiber lasers.

High-power narrow-linewidth fiber laser technology

In this paper, the research progress of single-frequency fiber oscillators are introduced in the terms of wavelength expansion, the development of single frequency fiber amplifiers are introduced in the terms of power scaling. Besides, the research achievements of 1 μm-band high-power narrow-linewidth fiber laser are summarized based on the techniques of generating narrow-linewidth seed sources. Then the development trend and main challenges of high-power single-frequency and narrow-linewidth fiber laser are analyzed. The key technologies of high-power narrow-linewidth fiber laser are summarized and discussed. Finally, applications in various fields based on the current development status of high-power narrow-linewidth fiber laser are introduced.

Kilowatt-level ytterbium-Raman fiber amplifier with a narrow-linewidth and near-diffraction-limited beam quality.

By focusing on a typical emitting wavelength of 1120 nm as an example, we present the first, to the best of our knowledge, demonstration of a high-efficiency, narrow-linewidth kilowatt-level all-fiber amplifier based on hybrid ytterbium-Raman (Yb-Raman) gains. Notably, two temporally stable, phase-modulated single-frequency lasers operating at 1064 nm and 1120 nm, respectively, were applied in the fiber amplifier, to simultaneously alleviate the spectral broadening of the 1120 nm signal laser and suppress the stimulated Brillouin scattering effect. An over 1 kW narrow-linewidth 1120 nm signal laser was obtained with slope efficiency of ${\sim}{77}\% $∼77% and beam quality of ${\rm M}_x^2\sim {1.25}$Mx2∼1.25, ${\rm M}_y^2 \sim {1.17}$My2∼1.17. The amplified spontaneous emission (ASE) noise in the fiber amplifier was effectively suppressed by incorporating an ASE-filtering system between the seed laser and the main amplifier. Furthermore, the experimental results demonstrate that the spectral linewidth broadening effect is tightly related to the injected power ratios between the two seed lasers. Overall, this setup could provide a reference on obtaining and optimizing high-power narrow-linewidth fiber lasers operating in the long wavelength extreme of the Yb gain spectrum.

Yb-Doped Aluminophosphosilicate Triple-Clad Laser Fiber With High Efficiency and Excellent Laser Stability

We fully demonstrated an ytterbium (Yb) doped triple-clad laser fiber with intense pump absorption, high efficiency, and laser stability. P5+/Al3+ molar ratio in the central region of fiber core was specially designed to be ∼1.08 for compensating P2O5 evaporation, while the ratio in the outer region was set as ∼0.92 for obtaining a flattened refractive index profile. Applying a two-stage deposition process, one-time collapse technique, low-temperature multi-times sintering, and suitable flow of pure POCl3 during sintering and collapsing process were instrumental in decreasing and offsetting element evaporation. Measured in an all-fiber master oscillator power amplifier configuration, the 7-m-long fiber obtained 1.39 kW near-single-mode laser output at 1079.6 nm with a slope efficiency of 85.2% and a beam quality M 2 of 1.36. Output laser spectrum with no sign of nonlinear-related peaks and a narrow 3-dB-bandwidth of ∼0.33 nm was obtained. The fiber-based laser setup was kept at the maximum power for 1 h with power degradation less than 0.21%. The results demonstrated Yb-doped aluminophosphosilicate triple-clad fiber is a highly competitive candidate for commercial high-power laser and high-power narrow-linewidth fiber laser.

780 W narrow linewidth all fiber laser

High-power narrow linewidth fiber lasers are extensively applied in coherent detection and power-spectrum beam combination etc. The suppressing method of stimulated Brillouin scattering is analyzed. And the theory of sinusoidal phase modulation is analyzed also. A single frequency laser is broadened to become a 2.9 GHz linewidth seed by sinusoidal phase modulation technology. The power of the seed is then boosted from 50 mW to 780 W through a three-stage power amplifiber configuration. Central wavelength and linewidth of the laser are 1064.34 nm and 2.9 GHz respectively, with an optical-optical efficiency being 79%. And the beam quality is Mx2 =1.44 and My2 =1.43. The output powers before and after phase modulation are compared with each other. And the reason why output power increases is analyzed. The stimulated Brillouin scattering threshold is promoted by added longitudinal mode. Finally, the output power is promoted after phase modulation, so that the output power of this laser is only limited by the pump power. If the pump power is increased, the higher output power of narrow linewidth fiber laser will be achieved.