Man Hu

10.8 kW spectral beam combination of eight all-fiber superfluorescent sources and their dispersion compensation.

We report an 8-element spectral beam combination of Yb-doped all fiber superfluorescent sources around 1070 nm wavelength. Each source consists of a 60 mW front-end and a 1.5 kW three-stage fiber amplifier chain. The eight output beamlets are spectrally combined using a home-made polarization-independent multilayer dielectric reflective diffraction grating. 10.8 kW output power is achieved with an efficiency of 94%. Besides, both theoretical and experimental studies of dual grating dispersion compensation scheme have been performed, which is proved to be a prospective way for high brightness spectral beam combination.

Passive coherent beam combining of four Yb-doped fiber amplifier chains with injection-locked seed source.

An injection-locked fiber laser is introduced to the passive fiber laser coherent beam combination with all-optical feedback loop. A coherent beam combining system with two-dimensional four Yb-doped fiber amplifier chains is established, and the injection-locked fiber laser works as a switchable seed source. The 1064 nm output laser of the injection-locked fiber laser is extinguished automatically as the feedback injection power is high enough, and the injection-locked fiber laser acts as an amplifier for the feedback laser with 7.4 dB gains. We find that the phase-locked far-field interference pattern of our system with seed laser extinguished is stable, and the visibility is up to 91.5%, which is slightly higher than the prevalent method with auxiliary seed laser (88.2%).

Dammann-grating-based passive phase locking by an all-optical feedback loop

A Dammann grating is used as a spatial filter for a passive coherent beam combination (CBC) of three Yb-doped fiber amplifiers with an all-optical feedback loop. Using this diffractive-optics-based spatial filtering technique, we demonstrate CBC with 20 W output power, and the visibility of the far-field interference pattern is up to 88.7%. Measurements suggest that this approach is robust with respect to laboratory environment perturbations, and it can scale to high powers and large arrays.

High-Peak Power, All-Fiber Passively Q-Switched Laser Using a Sm-Doped Fiber Saturable Absorber

An all-fiber passively Q-switched Yb-doped fiber laser with fiber saturable absorber (SA) based on a piece of Sm-doped fiber is presented. For the first time, we observe the fast stimulated Brillouin scattering Q-switched process in an Yb/Sm all-fiber laser and obtain 41 ns pulses and 1.7 kW maximum peak power. Compared with the reported traditional SA Q-switched process, the pulse energy and peak power are both improved an order of magnitude. Furthermore, a traditional SA Q-switched process with 450 ns pulsewidth and 7.5 W peak power is also obtained in the same structure by increasing the feedback of cavitys output end.

Widely tunable repetition-rate and pulse-duration nanosecond pulses from two spectral beam combined fiber amplifiers

Nanosecond pulses with a widely tunable repetition-rate and pulse-duration at 1 μm wavelength are obtained by spectrally combining two pulse fiber amplifiers using a home-made polarization-independent multilayer dielectric reflective diffraction grating. The width of the combined pulses can be tuned from 4 ns to 800 ns, and the pulse repetition-rate can be ranged from 1 MHz to 200 MHz. Thanks to the spectral beam combining system, the maximum repetition-rate and pulse-duration of the combined pulses are doubled, compared to the single pulse fiber amplifier, by setting a proper temporal delay between the two pulse channels.

Raman Suppression in a Kilowatt Narrow-Band Fiber Amplifier*

A novel technique to suppress stimulated Raman scattering in a high power narrow-band fiber amplifier is reported. By seeding with a combination of a broadband amplified spontaneous emission seed and a narrowband master oscillator seed, the Raman Stokes components can be reduced about 16 dB at a total output power of 1 kW. Raman suppression results are depicted in a different wavelengths seeding case and the same wavelength seeding case, respectively, with different seed power ratios.

Experiments and Perturbative Analysis of Dammann-Grating-Based Aperture Filling in a Passive Coherent Beam Combination

A Dammann-grating-based aperture filling technology is demonstrated in a passive coherent beam combination fiber amplifier array, which is phase-locked using an all-optical feedback loop. The maximum output power is 206 W. The combined efficiency of a three channels aperture filling is discussed and demonstrated to vary with the output power. Perturbative factors leading to the loss of the combined efficiency are theoretically simulated and the key factor is the residual phase error. Theoretical and experimental results show that this technology has good potential to achieve higher brightness in a single beam.

Effective dispersion compensation of variable-linewidth fiber amplifier by single-multilayer dielectric grating

We achieve effective dispersion compensation by employing a single-multilayer dielectric diffraction grating and a variable-linewidth fiber amplifier. Both theoretical and experimental studies on the diffracted beam quality have been performed. The experimental results show that when the linewidth reaches 0.41 nm the beam quality in the dispersive plane reduces dramatically from 5.4 for the first-time diffracted beam to 2.08 for the second-time diffracted beam. This dispersion compensation technology relaxes the requirement on the linewidth of the incident beam source, which is beneficial for high-brightness spectral beam combining.

Passive Phase Locking of Three Nanosecond Fiber Amplifiers Using a Dammann Grating Spatial Filter

A passive coherent beam combination of three nanosecond Yb-doped fiber amplifiers by an all-optical feedback loop is realized by a Dammann grating intracavity spatial filter. By using this diffractive-optics-based spatial filtering technique, three tile-aperture laser beams are phase-locked with a peak power of 1.02 kW. The width of the combined pulses is 9.6 ns, and the repetition frequency is 2.208 MHz. The visibility of the far-field interference pattern is up to 82.9%. The results show that this approach can scale to larger arrays and higher powers.

Coherent Beam Combining of Fiber Amplifiers by means of Dammann Grating Spatial Filter

Passive coherent beam combining of three Yb-doped fiber amplifiers is achieved by Dammann grating spatial filter. We demonstrate 20 W phase locking of tiled-aperture beamlets, and the visibility of the far-field interference pattern is 88.7%.