All-fiber, single-frequency, and single-mode Er3+:Yb3+ fiber amplifier at 1556 nm core-pumped at 1018 nm

Extended L-band 4-Core Er/Yb co-doped fiber amplifier based on 1018 nm cladding pumping

The extended L-band 4-core Er/Yb co-doped fiber and amplifier (MC-EYDFA) is first proposed and demonstrated, to the best of our knowledge, for space division multiplexing combined with wavelength division multiplexing application. The fiber core co-doped with Er/Yb/P is adopted for bandwidth expansion, and the long wavelength extends to 1625 nm. Numerical simulations further show that efficient amplification and higher saturation power are achieved with the 1018 nm cladding pumping. Based on the integrated 4-core fiber amplifier, an average gain of ∼22 dB covering 1575-1625 nm is experimentally obtained with a 4 W pump power and a 3 dBm total signal power, and the max core-dependent gain (CDG) variation is measured to be 1.7 dB.

Over 250 W low noise core-pumped single-frequency all-fiber amplifier

A high-power linearly-polarized all-fiber single-frequency amplifier at 1 µm based on tandem core-pumping is demonstrated by using a large-mode-area Ytterbium-doped fiber with a core diameter of 20 µm, which nicely balances the stimulated Brillouin scattering effect, thermal load, and output beam quality. A maximum output power of more than 250 W with a corresponding slope efficiency of >85% is achieved at the operating wavelength of 1064 nm without being constrained by the saturation and nonlinear effects. Meanwhile, a comparable amplification performance is realized with a lower injection signal power of the wavelength near the peak gain of the Yb-doped fiber. The polarization extinction ratio and the M² factor of the amplifier are respectively measured to be >17 dB and 1.15 under the maximal output power. In addition, by virtue of the single-mode 1018 nm pump laser, the intensity noise of the amplifier under maximal output power is measured to be comparable to that of the single-frequency seed laser at frequencies higher than 2 kHz, except for the emergence of parasitic peaks that can be eliminated by optimizing the driving electronics of the pump lasers, while the deterioration of the amplification process to the frequency noise and linewidth of the laser is negligible. To the best of our knowledge, this is the highest output power of a single-frequency all-fiber amplifier based on the core-pumping scheme.

A 102 W High-Power Linearly-Polarized All-Fiber Single-Frequency Laser at 1560 nm

A 1560 nm high-power linearly-polarized all-fiber single-frequency narrow-linewidth laser with near diffraction-limited beam quality is demonstrated. The Yb–Er energy transfer efficiency and the ability of the signal laser to capture pump light have been improved by specifically choosing the pumping wavelength and the input signal power in the final power amplifier stage of this laser system. Under the off-peak absorption pumping wavelength of 940 nm, along with the maximum input signal power of 6 W, a maximum output power of 102 W with a slope efficiency of 40.5% is acquired. At the highest output power status, a polarization extinction ratio (PER) of 15.5 dB, a linewidth of 3.05 kHz, and a beam quality of Mx2 = 1.14, My2 = 1.06 are obtained, respectively. This advanced single-frequency fiber laser has great potential for the long-range coherent Doppler lidar and the next generation of gravitational wave detection.

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.

Optimal design of high-power cascade co-pumping Er/Yb-codoped fiber lasers

The Yb-ASE problem has been a main obstacle to the power scaling of Er/Yb-codoped fiber lasers (EYDFLs). In this Letter, cascade co-pumping high-power EYDFLs, i.e., EYDFLs with an Yb-band resonant cavity, are proposed and systematically analyzed, for the first time to the best of our knowledge. A high-Q Yb-band cavity is introduced in an EYDFL to lock and recycle the Yb band energy. The oscillation wavelength of the Yb cavity, the reflectivity of the output fiber grating, and the length of the fiber are optimized numerically. Thermal effects are also considered in the study. The simulation results show that compared to ordinary EYDFLs, the introduction of an appropriate Yb cavity can not only effectively suppress the Yb-ASE, increase the output power, and improve the pump conversion efficiency, but can also greatly shorten the optimal gain fiber length. Cascade co-pumping is a promising way to improve the performance of high-power EYDFLs.