Huawei Jiang

Kilowatt Ytterbium-Raman fiber laser.

A kilowatt-level Raman fiber laser is demonstrated with an integrated Ytterbium-Raman fiber amplifier architecture. A high power Ytterbium-doped fiber master oscillator power amplifier at 1080 nm is seeded with a 1120 nm fiber laser at the same time. By this way, a kilowatt-level Raman pump laser at 1080 nm and signal laser at 1120 nm is combined in the fiber core. The subsequent power conversion from 1080 nm to 1120 nm is accomplished in a 70 m long passive fiber. A 1.28 kW all-fiber Raman amplifier at 1120 nm with an optical efficiency of 70% is demonstrated, limited only by the available pump power. To the best of our knowledge, this is the first report of Raman fiber laser with over one kilowatt output.

Ultra-wide wavelength tuning of a cascaded Raman random fiber laser

An ultra-broadband tunable cascaded Raman random fiber laser pumped by a tunable (1020-1080 nm) ytterbium-doped fiber laser is investigated. By continuously adjusting the pump laser wavelength, the Raman random laser tunes accordingly due to the Raman gain competition. By increasing the pump power, up to the 5th order Raman random laser is achieved. As a result, 300 nm of continuous wavelength tuning from 1070 to 1370 nm is achieved by adjusting the pump wavelength and power altogether. The highest output power is 1.8 W at 1360 nm with an optical efficiency of 15% from 1080 nm. To the best of our knowledge, this is the widest wavelength tuning range reported for a random fiber laser so far.

Integrated ytterbium-Raman fiber amplifier.

An integrated ytterbium-Raman fiber amplifier architecture is proposed for power scaling of a Raman fiber laser. It is an ytterbium (Yb) fiber amplifier seeded with a double or multiple wavelength laser and followed by a passive Raman fiber. The bluest wavelength light gets amplified in the Yb fiber and the power is transferred to redder wavelengths in the following Raman fiber. A proof of principle experiment demonstrates a 300 W all-fiber linearly polarized single mode amplifier at 1120 nm with an optical efficiency of 70%, limited only by available pump power. The amplifier consists of 4 m of Yb-doped fiber and 20 m of germanium-doped fiber, and seeded with a laser emitting at 1070 and 1120 nm. The power evolution of the 1070 and 1120 nm light inside the amplifier is investigated, both numerically and experimentally. The possibility of power scaling to over kilowatt levels is discussed.

Nearly-octave wavelength tuning of a continuous wave fiber laser

The wavelength tunability of conventional fiber lasers are limited by the bandwidth of gain spectrum and the tunability of feedback mechanism. Here a fiber laser which is continuously tunable from 1 to 1.9 μm is reported. It is a random distributed feedback Raman fiber laser, pumped by a tunable Yb doped fiber laser. The ultra-wide wavelength tunability is enabled by the unique property of random distributed feedback Raman fiber laser that both stimulated Raman scattering gain and Rayleigh scattering feedback are available at any wavelength. The dispersion property of the gain fiber is used to control the spectral purity of the laser output.

Actively mode-locked Raman fiber laser

Active mode-locking of Raman fiber laser is experimentally investigated for the first time. An all fiber connected and polarization maintaining loop cavity of ~500 m long is pumped by a linearly polarized 1120 nm Yb fiber laser and modulated by an acousto-optic modulator. Stable 2 ns width pulse train at 1178 nm is obtained with modulator opening time of > 50 ns. At higher power, pulses become longer, and second order Raman Stokes could take place, which however can be suppressed by adjusting the open time and modulation frequency. Transient pulse evolution measurement confirms the absence of relaxation oscillation in Raman fiber laser. Tuning of repetition rate from 392 kHz to 31.37 MHz is obtained with harmonic mode locking.

High-Power Single-Frequency 1336 nm Raman Fiber Amplifier

A high power, single frequency, quasi-continuous-wave 1336 nm laser is achieved by Raman amplification of an external cavity diode laser in a variably strained polarization maintaining silica fiber. The pump laser is a 1256 nm Ytterbium-Raman integrated fiber amplifier with a maximum output peak power of 235 W. The 1336 nm amplifier produces square-shaped pulses with tunable repetition rate and duration. The peak power is as high as 53 W, which remains constant during the tuning. A polarization extinction ratio of >25 dB is achieved due to the all polarization maintaining fiber configuration. The laser is locked precisely at 1336.63 nm for future application in laser cooling of 27Al+ after 8th harmonic generation.

Power scaling of Raman fiber lasers

Raman fiber laser is an efficient way to expand the spectral coverage of fiber lasers. In recent years, output power of Raman fiber laser has been scaled quickly. There is a great potential in further power scaling, technical innovations, and scientific applications. An integrated ytterbium-Raman fiber amplifier architecture was proposed, which allows power scaling of Raman fiber laser to over kilowatt and more. Hundred watt level single frequency Raman fiber amplifier was achieved, which allows the generation of high power sodium guide star laser. New scheme of cladding pumped Raman fiber laser is studied in order to improve the brightness enhancement. Furthermore, possible application in spectral beam combing is discussed.

Cascaded-cladding-pumped cascaded Raman fiber amplifier

The conversion efficiency of double-clad Raman fiber laser is limited by the cladding-to-core area ratio. To get high conversion efficiency, the inner-cladding-to-core area ratio has to be less than about 8, which limits the brightness enhancement. To overcome the problem, a cascaded-cladding-pumped cascaded Raman fiber laser with multiple-clad fiber as the Raman gain medium is proposed. A theoretical model of Raman fiber amplifier with multiple-clad fiber is developed, and numerical simulation proves that the proposed scheme can improve the conversion efficiency and brightness enhancement of cladding pumped Raman fiber laser.

Over 50 W 589 nm single frequency laser by frequency doubling of single Raman fiber amplifier

300 W CW linearly-polarized 1120 nm laser is achieved with an integrated Yb-Raman fiber amplifier. 86 W 1178 nm single frequency Raman fiber amplifier is generated and frequency doubled to 589 nm with power up to 52.7 W.

A 1.3 kW Raman fiber laser

A high efficiency 1.3 kW Raman fiber laser at 1120 nm is demonstrated with an integrated Ytterbium-Raman fiber amplifier architecture limited only by the available pump power.