In this paper, a two-stage phase control method was proposed to increase the control bandwidth of the target-in-the-loop coherent beam combining (CBC) system. Firstly, the principle of the target-in-the-loop CBC system based on two-stage phase control was introduced. In order to verify the feasibility of two-stage phase control technology, then a 7-channel fiber laser array beam combining system was established. The experimental research showed that when the phase noise in the fibers and on the transmission path from the collimators was controlled by two phase controllers respectively, the laser array coherently combined in the far field stably. The power in bucket was 11.4% in the close-loop, which was 70.1% of the theoretical value. The normalized mean voltage detected by the photoelectric detector increased from 0.107 to 0.648, with an increase of 6.1 times. This experiment initially verified the feasibility of the two-stage phase control method, which will be helpful for the control bandwidth increasing in the target-in-the-loop CBC system.
Transceiver collimator is an advanced component in high power fiber lasers long distance transmission. Here, based on fiber weak taper technology, an all-fiber laser emitting and target detecting transceiver collimator is proposed. Meanwhile, a (18+1)-channel optical fiber bundle detection experiment was succeed build.With a home-made signal processing circuit, the on-line dynamic tracking image display was achieved, and the target detection and transceiver collimator was experimental demonstrated.
The pulse shape from the pulsed amplifier always distorts because of gain saturation effect, an effective method is active control the output pulse shape by reshaping the pulse shape of the laser seed. We demonstrated a new method for active temporal pulse shape control of fiber amplifier with adaptive proportional control. We numerically researched three proportional control methods, including static proportional control, adaptive proportional control and piecewise adaptive proportional control. The results show that proportional control can generate arbitrary temporal pulse shape with high accuracy and less iterations even if parameters of the fiber amplifier are unknown.
We present the laboratory experiments of phase locking of a 37-channel tiled fiber array using a stochastic parallel gradient descent (SPGD) feedback controller. The experimental setup comprises a hexagonally close-packed array of thirty-seven 23-mm-diameter fiber collimator sub-apertures. The fraction of the output laser power within a solid angle of 1.22λ/D was measured in open loop state and then in closed loop state. The results show that the power in the bucket was increased from 0.028 in open loop to 0.890 in closed loop. When the 37 beams were phase-locked, the residual phase error was λ/23. The power ratio in the bucket (PIB) was 28% that improved 32 times than the open loop state.
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