Su Rongtao

Coherent beam combination of adaptive fiber laser array with tilt-tip and phase-locking control

We present an experimental study on tilt-tip (TT) and phase-locking (PL) control in a coherent beam combination (CBC) system of adaptive fiber laser array. The TT control is performed using the adaptive fiber-optics collimator (AFOC), and the PL control is realized by the phase modulator (PM). Cascaded and simultaneous controls of TT and PL using stochastic parallel gradient descent (SPGD) algorithm are investigated in this paper. Two-fiber-laser-, four-fiber-laser-, and six-fiber-laser-arrays are employed to study the TT and PL control. In the cascaded control system, only one high-speed CMOS camera is used to collect beam data and a computer is used as the controller. In a simultaneous control system one high-speed CMOS camera and one photonic detector (PD) are employed, and a computer and a control circuit based on field programmable gate array (FPGA) are used as the controllers. Experimental results reveal that both cascaded and simultaneous controls of TT using AFOC and PL using PM in fiber laser array are feasible and effective. Cascaded control is more effective in static control situation and simultaneous control can be applied to the dynamic control system directly The control signals of simultaneous PL and TT disturb each other obviously and TT and PL control may compete with each other, so the control effect is limited.

Passive Coherent Beam Combining Four Channels of Nanosecond Pulsed Laser Using All-Fiber Feedback Loop

We present an all-fiber configuration of passive beam combining using an all-fiber feedback loop and demonstrate passive coherent combining of a four-channel nanosecond pulsed laser. The output power, pulse characteristics, polarization extinction ratio and far field laser intensities of the combined output laser are investigated. The experimental results validate that passive phasing using an all-fiber feedback loop provides a simple while robust method for coherent beam combining of pulsed lasers. If replacing the fiber coupler used into a high power tapered fused bundle fiber combiner, this scheme is promising to scale the output power up to the kW level.

Adaptive Polarization Control of Fiber Amplifier Based on SPGD Algorithm

We demonstrate an adaptive polarization control system of a 10.2 W non-polarization-maintaining fiber amplifier based on stochastic parallel gradient decent (SPGD) algorithm. The experimental investigation shows that the system can used to compensate for the polarization fluctuation of the fiber amplifier effectively and perform well over a long-time observation. When the adaptive polarization control system is in closed loop, the extinction ratio increases from 2.28 dB to 11.54 dB, and more than 93.4% of the total power in desired polarization direction is achieved.

Comparative study on the power scaling performance of three different coherent polarization beam combination system structures

Coherent polarization beam combination (CPBC) is a new kind of coherent beam combination configuration with high combining efficiency and excellent beam quality. In order to extend the CPBC system to a large scale, we provide a comparative study on the power scaling performance of three different coherent polarization beam combination system structures. It is found that the pairwise structure has high tolerance to aberrations and has the potential to extend to a large scale with high combining efficiency. In consideration of all the aberrations, the combining efficiency of the pairwise structure can be attained as high as 90% when the combined beams are more than 200. Some instructive suggestions are given to extend the CPBC system to a large scale.