In recent years, machine learning, especially various deep neural networks, as an emerging technique for data analysis and processing, has brought novel insights into the development of fiber lasers, ...in particular complex, dynamical, or disturbance-sensitive fiber laser systems. This paper highlights recent attractive research that adopted machine learning in the fiber laser field, including design and manipulation for on-demand laser output, prediction and control of nonlinear effects, reconstruction and evaluation of laser properties, as well as robust control for lasers and laser systems. We also comment on the challenges and potential future development.
Quasi-continuous wave (QCW) laser has a very broad application in the industrial field, especially in additive manufacturing, surface treatment, laser cutting, laser cleaning, and laser drilling. ...Compared with the unidirectional fiber laser, the bidirectional output can be achieved two ports high power output with only one resonator, which can greatly reduce the industrial cost. However, there are few researches on QCW fiber lasers with bidirectional output. Here, we optimized and demonstrated a bidirectional output QCW laser with output power of 2 × 4.5 kW based on a double-clad ytterbium-doped fiber with a core/cladding diameter of 25/400 μm. The peak power at both ends reached 4515 W and 4694 W, respectively. The Raman suppression ratio at both ends of A and B is about 12 dB, and the beam quality factor M2 is about 1.37 and 1.42, respectively. The corresponding optical-to-optical efficiency is 79%. To the best of our knowledge, this is the highest peak power of QCW laser with near-single-mode beam quality in a bidirectional structure laser.
Concave gold bipyramids (CAuBPs) exhibit enhanced saturable absorption characteristics due to their large electromagnetic-field enhancement, large third order nonlinearity and fast recovery time. In ...this paper, the CAuBPs are synthetized through a seed-mediated wet-chemical growth method, and a 1018 nm passively Q-switched fiber laser exploiting CAuBPs saturable absorber (SA) is demonstrated in a ring cavity. The maximum average output power of 9.61 mW is obtained under the pump power of 270 mW in Q-switched regime. The minimum pulse width is 1.83 μs at the pulse repetition rate of 97.47 kHz. The results prove that CAuBP is a promising SA with potential for important applications in the field of pulsed lasers.
Agile mode switching between LP 01 and LP 11 modes in an all-fiber laser is demonstrated by exploiting an acoustically induced fiber grating within the laser cavity. The laser exploits a cladding ...pump configuration and can deliver up to 5.85 W of stable output power in LP 11 mode at 1070.07 nm and 6.06 W in LP 01 mode at 1070.48 nm, with a slope efficiency near 50%. Complete mode-switching speed with 250 Hz and partial mode-switching speed with 1 kHz are demonstrated. Based on the obtained switching time between LP 11 and LP 01 mode, the maximum complete mode-switching speed is calculated to be ∼555.56 Hz. Moreover, variable output beam profiles could be obtained by adjusting the frequency of the modulation signal applied on the acoustically induced fiber grating. This paper could provide an example of realizing a high-power, mode-switchable fiber laser source for practical use.
Fiber lasers with flexible spectral manipulation property could provide a flexible tool for scenes where the temporal coherence property accounts, for example, coherent sensing/communication and ...nonlinear frequency conversion. Due to the good laser performance and relative simplicity of implementation, random fiber lasers (RFLs) based on random distributed feedback and Raman gain have earned more and more attention in the past few years, and a variety of RFLs with substantially different spectral properties have been developed. In this presentation, we demonstrate a high power linearly polarized RFL with flexible spectral manipulation property, in which the central wavelength and the linewidth of the spectrum can be tuned independently through a bandwidth-adjustable tunable optical filter (BA-TOF). The central wavelength of the RFL can be continuously tuned from 1095 to 1115 nm, while the full width at half-maximum (FWHM) linewidth has a maximal tuning range from ~0.6 to more than 2 nm. Moreover, the output power of 1102.5-1112.5 nm reaches ~23 W with polarization extinction ratio (PER) value > 20 dB. To the best of our knowledge, this is the first demonstration of a powerful linearly polarized RFL with both wavelength and linewidth tunability.
Fiber laser has been developed to the point where the average power scaling can reach several kilowatts readily for oscillators and more for amplifiers. In the meanwhile, the thermal effects inside ...the fiber laser also become prominent. Temperature rise of the fiber core caused by thermal effects has a conspicuous impact on laser performance. In this paper, the spectral properties of superfluorescent fiber sources at low temperature have been studied experimentally and theoretically. We observe a significant flattening of the arc top of the spectra and a broadening to the short-wave direction as the gain fiber temperature decreases from 25 °C to −95 °C. The corresponding 10 dB bandwidth and 20 dB bandwidth increased by 7.216 and 4.004 nm, respectively. The 10 dB center position and the 20 dB center position of the spectrum also move 6.1 nm and 4.2 nm towards short-wave direction, respectively. The absorption and emission cross-sections at different temperatures, calculated based on Lorenz fitting theory, are used to simulate the experimental phenomena, and the results are consistent with the experiment. Additionally, the small signal gain coefficient at low temperature is calculated to help explain the observed phenomena in the experiment.
Transverse mode instability (TMI) has been recognized as onse of the primary limiting factors for the average power scaling of high-brightness fiber lasers. In this work, a static model of the TMI ...effect based on stimulated thermal Rayleigh scattering (STRS) is established while considering the four-wave mixing (FWM) effect. The focus of the model is to theoretically investigate the TMI phenomenon and threshold power dominated by FWM. The gain saturation effect and fiber laser system parameters, such as seed power, pumping direction, and core numerical aperture, which have not been considered in the previous perturbation theory model, are also investigated. This work will enrich the perturbation theory model and extend its application scope in TMI mitigation strategies, providing guidance for understanding and suppressing TMI.
Traditional ytterbium-doped high-power fiber lasers generally use a unidirectional output structure. To reduce the cost and improve the efficiency of the fiber laser, we propose a bidirectional ...output fiber laser (BOFL). The BOFL has many advantages over that of the traditional unidirectional output fiber laser (UOFL) and has a wide application in the industrial field. In theory, the model of the BOFL is established, and a comparison of the nonlinear effect in the traditional UOFL and the BOFL is studied. Experimentally, high-power continuous wave (CW) and quasi-continuous wave (QCW) BOFLs are demonstrated. In the continuous laser, we first combine the BOFL with the oscillating amplifying integrated structure, and a near-single-mode bidirectional 2 × 4 kW output with a total power of above 8 kW is demonstrated. Then, with the simple BOFL, a CW bidirectional 2 × 5 kW output with a total power of above 10 kW is demonstrated. By means of pump source modulation, a QCW BOFL is developed, and the output of a near-single mode QCW laser with a peak output of 2 × 4.5 kW with a total peak power of more than 9 kW is realized. Both CW and QCW output BOFL are the highest powers reported at present.
We demonstrate a high power linearly polarized Raman fiber laser (RFL) pumped by an amplified spontaneous emission (ASE) source. Temporal-stable operation of RFL could be ensured owing to the ...employment of ASE, which mitigates the inherent intensity noise compared with the classic scheme adopting laser oscillator as pump source. In this experiment, the RFL has up to 119.5 W output power, with central wavelength of 1129.2 nm, and full width at half maximum (FWHM) linewidth of about 4.18 nm. The polarization extinction ratio (PER) of the Raman laser is about 23 dB. Moreover, this laser has excellent long-term and short-term stabilities in terms of the output power and time domain.
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