Hening Yang

1.5 kW Incoherent Beam Combining of Four Fiber Lasers Using Adaptive Fiber-Optics Collimators

We demonstrate the incoherent beam combining (BC) of four high-power single-mode fiber lasers. Adaptive fiber-optics collimators (AFOC) of 0.5 kW-level are developed to correct the tip/tilt-type phase errors among beamlets. The maximum deflection angle of the AFOC is about 0.29 mrad. A stochastic parallel gradient descent algorithm is employed as the tip/tilt control strategy. The tip/tilt control makes four separate laser beams overlap with each other in the far-field, and the average of normalized power-in-bucket increases from 0.171 in open loop to 0.798 in closed loop when 1.5-kW total output power is achieved. The precise tracking ability and control accuracy of this BC system are investigated. Experimental results expose that thermal-blooming effect disturbs BC seriously when the total output power is up to kW-level, which could be mitigated by inducing air flow near the laser output.

126 W fiber laser at 1018 nm and its application in tandem pumped fiber amplifier

We report on a 126 W fiber laser operating at 1018 nm with an optical efficiency of 75%. The optimal length for such a fiber laser is theoretically analyzed using steady-state rate equations including amplified spontaneous emission. Excellent agreement on the maximum output power is achieved between the numerical result and the experimental counterpart. Furthermore, a monolithic tandem pumped fiber amplifier is established by using conventional 30/250 μm double clad ytterbium-doped fiber, and 185 W output power with 85% optical efficiency is realized.

Numerical analysis of large mode area segmented cladding fibers

We analyze numerically the dependence of segmented cladding fibers (SCF) characters, including the effective V-number, the effective fundamental mode area and the permissible bending radius of fundamental mode, on the structure parameters of the fiber and the signal wavelength with the methods of radial effective index and transmission matrix. The results show that a single mode and large mode area fiber with an acceptable permissible bending radius can be obtained when we design SCF with optimized structure parameters. The effective fundamental area is as large as 1948.93μm2 with proper fiber parameters. It will benefit the fabrication of the SCF for applications in high power fiber lasers.

Output performance of gain guided and index antiguided fiber lasers pumped by different methods

The output performance of Yb3+ doped gain guided and index antiguided (GG-IAG) fiber lasers pumped by different methods are compared by numerically solving rate equations (REs) with additional leakage losses. Three pump models, including forward pump, backward pump and bidirectional pump are established combined with REs model. Calculation results show that the output powers and slope efficiencies of GG-IAG fiber from high to low under the same condition are obtained by bidirectional pump, backward pump and forward pump in sequence. The upper energy level particle population density N2(z) and thermal distribution along the fiber generated by bidirectional pump are more uniform than that by other two pump methods. It benefits the lasing of GG-IAG fiber most.