In this study, technologies including beam combination structures, uncoupled two-dimensional adjustment, optical axis detection, and consistency control in fiber laser phased arrays are investigated. During the experiment implementation, seven fiber laser beams are placed in a regular hexagonal arrangement by adopting a “6 +1” array. Beam expansion is achieved by placing an expanding lens behind the fiber rod for each fiber beam, and two-dimensional adjustment is obtained by adopting high-precision uncoupled adaptive fiber optic collimator (AFOC) adjustment devices. Intelligent cameras are used to detect the reflected beam and control the optical axis in the closed loop, which provides an important guarantee of the coherent combination of the seven fiber lasers. The dynamic range of the AFOC is larger than ±230 μrad, the optical axis pointing accuracy is better than 1 μrad, the effective spot size of a single beam laser in the beam combination device is 85 mm, and the area duty cycle is 56.2%. The capability of beam combination, dynamic adjustment, and optical axis consistency control of the seven-beam laser combination device is fully verified by a number of full power experiments, and the average power-in-the-bucket after the phase close loop is 4.8 times that of the open loop.

The combination device adopts an optical fiber rod and a beam-expanding lens to collimate and expand a single laser beam. The reflective far-field detection system has three built-in charge coupled devices (CCDs) to detect the centroids of the seven fiber lasers. After calculating the optical axis shift, the control parameters are amplified by a proportional-integral-derivative (PID) control algorithm and loaded onto the AFOC for translation control to realize the optical axis pointing consistency control of multiple lasers, as shown in Figs. 2?4. By adopting large-thrust piezoelectric ceramics for high-precision adjustment, the AFOC can realize displacement amplification, and a two-dimensional uncoupled design can achieve high-precision control over a large dynamic range. The modal frequency and structural stability of the AFOC are improved through simulation optimization, as shown in Figs. 5?10. The beam combination device adopts a frame structure that integrates the AFOC, built-in CCD, beam expanding lens, weak mirror, and other components, and carries out an integrated lightweight design. Its layout is “6+1”, that is, a center light beam is surrounded by six light beams arranged in a regular hexagon. Invar rods are used for series-fixing and stiffening the plates to enhance their structural strength. The stability of the device is improved through simulations and design optimization. The structural diagram and simulation results are shown in Figs. 11?15.

The effective output aperture of a single laser beam is 85 mm, the area duty cycle of seven lasers is 56.2% ( Fig. 15), and the dynamic range of the AFOC is greater than ±230 μrad (Figs. 20 and 21). Prior to the experiment, the zero point of the beam combination device is calibrated using a far-field sensing device. The calibrated device is used in multiple rounds of experiments. During the experiment, the AFOC is closed to ensure pointing consistency of the seven fiber lasers. After the closed loop, the optical axis pointing accuracy is better than 1 μrad. During coherent combining, the average power-in-the-bucket after the phase closed loop is 4.8 times that of the open loop (Fig. 23), which verifies the dynamic adjustment ability and optical axis pointing control ability of the beam combination device.

A “6+1” layout is used to assemble seven fiber lasers with a phased array. A built-in CCD is used to detect the optical axis in different regions, and the consistency of optical axis pointing is adjusted in real time through a low-coupling and high-thrust AFOC. The performance test shows that the dynamic range of the AFOC is more than 230 μrad, and the resolution is better than 10 μrad. Finally, the experiment verifies the beam combination and optical axis consistency control abilities of the seven-fiber laser phased array combination device. The average power-in-the-bucket after the phase closed loop is 4.8 times that of the open loop.