High-power and high-brightness Er:Yb codoped fiber MOPA operating at 1535 nm.

In this paper, we study the emerging 1535 nm Er: Yb codoped fiber MOPA with high power and high brightness. To characterize the interstage influence of this ASE-sensitive system, we conduct an interstage numerical model based on steady energy transfer model, where the seed and amplifier converge together. We analyze the amplifier setup, the seed pumping scheme, and feedback from inner reflection based on the model. Afterwards, we experimentally demonstrate a 1535 nm all fiber large mode area Er: Yb codoped fiber MOPA with the output power of 174.5 W, the brightness of 13.97 W/µm2sr, and ASE suppression ratio of 45 dB. To the best of our knowledge, this is the highest power and brightness of 1535 nm fiber lasers to date.

Spectral pedestal during the kilowatt-level amplification of a random fiber laser operating near the lasing threshold.

The amplification of random fiber lasers (RFLs) attracts much attention due to their unique characteristics such as wavelength flexibility and low coherence. We present that, in the kilowatt-level amplification of RFL operating near its lasing threshold, a broad and flat spectral pedestal can co-exist with the narrow spectral peak of RFL. This phenomenon is different from the case in the amplification of fixed-cavity laser seeds. Time-domain measurements show that the broad and flat spectral pedestal, which extends to long wavelengths, is composed of temporal pulses, while few temporal pulses exist in the narrow spectral peak. We attribute the spectral pedestal to intensity fluctuations from the random seed laser and modulation instability in the amplification stage. Control experiments reveal that the working status of the random seed laser and the effective length of the amplifier can influence the spectral bandwidth. By taking advantage of this phenomenon, we propose a novel approach to achieve a high-power broadband light source through the amplification of RFLs operating near the lasing threshold.

219.6 W large-mode-area Er:Yb codoped fiber amplifier operating at 1600 nm pumped by 1018 nm fiber lasers.

We demonstrate, to the best of our knowledge, the first high-power large-mode-area Er:Yb codoped fiber amplifier pumped by 1018 nm fiber lasers. The output power reaches 219.6 W, which is the highest power operating at 1600 nm with near-diffraction-limitation beam quality. The 1018 nm pumping scheme contributes to the mitigation of Er,Yb fiber bottlenecking, improvement in signal gain, and reduction of heat generation. Also, we inject co-propagating C-band amplified spontaneous emission (ASE) into the master amplifier to avoid unwanted backward-propagating ASE.

Power scalability of a continuous-wave high-power Er-Yb co-doped fiber amplifier pumped by Yb-doped fiber lasers.

The power scaling of Er-Yb co-doped fiber lasers and amplifiers has been limited by the bottleneck effect of energy-transfer saturation between Yb ions and Er ions. The emerging method of Er-Yb co-doped fiber amplifiers pumped by Yb-doped fiber lasers is considered as an approach to enhance the threshold of the bottleneck effect. In this paper, we quantitatively characterize the threshold of the bottleneck effect via the method of extreme value analysis of the second-order derivative. The method facilitates the optimization of the amplifier configuration. Afterward, we numerically investigate the bottleneck effect of various Er-Yb co-doped fiber amplifiers off-peak cladding-pumped by 10××nm Yb-doped fiber lasers for what we believe, to the best of our knowledge, is the first time. The result shows that the most optimal configuration is long gain fiber over 20 m pumped by a 1020-1025 nm fiber laser, with more than two times the output limit of a conventional laser diode pumping scheme. The essential factors of an amplifier are discussed afterward, including the pump-launching direction, the optimization of large-mode-area fiber, the core-cladding ratio, the concentration of doping ions, the nonlinearity limit, and the distribution of the heat load.

Influence of shriveling on berry composition and antioxidant activity of Cabernet Sauvignon grapes from Shanxi vineyards.

BACKGROUND: Berry shrivel (BS), a berry development disorder, appears soon after veraison. It occurs worldwide and affects the quality of grape berries and wine. However, it had not been reported in China until recently. This study aimed to investigate the changes in berry composition and antioxidant activity of Cabernet Sauvignon grapes from Xiangning Valley, Shanxi Province, China, during BS. RESULTS: Shrinkage contributed to an increase in the concentration of basic grape ingredients such as sugar and acid. An appropriate degree of shrinkage was apparently helpful in improving the phenolic content and increasing the antioxidant activity, but the berries that continued to shrivel showed a low antioxidant activity. Further, the results indicated distinct differences between the berries harvested from the southern side of the canopy and those harvested from the northern side, presumably due to variations in sunlight exposure. CONCLUSION: Moderate BS was beneficial since it increased berry quality and antioxidant activity of Cabernet Sauvignon grapes from Shanxi vineyards.