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

Abstract

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.

Experimental demonstration of single-mode fiber coupling using adaptive fiber coupler

“…A photodetector (PD) is located behind the tail of SMF to detect coupled optical power. Stochastic parallel gradient descent (SPGD) algorithm [10][11][12][13][14][15] is employed as the control strategy, where the detected power from PD is used as metric function J and the algorithm's iteration rate is 625 Hz. HVA is a highvoltage amplifier by which control signals are amplified one hundred times.…”

“…In recent years, Geng from the Key Laboratory on Adaptive Optics, Chinese Academy of Sciences (CAS) developed the adaptive fiber-optics collimator (AFOC) for tip/tilt control in beam combining applications. [10][11][12][13][14][15] Compared with FSM, the AFOC drives fiber tip directly with advantages of precise control, small inertia, high resonance-frequency, compactness, and convenience for assembling and integration. Based on the principle of optical reversibility, the AFOC has the potential for adaptive laser coupling.…”