This paper proposes a method used to calculate centroid for Shack-Hartmann wavefront sensor (SHWFS) in adaptive optics (AO) systems that suffer from strong environmental light and noise pollutions. In these extreme situations, traditional centroid calculation methods are invalid. The proposed method is based on the artificial neural networks that are designed for SHWFS, which is named SHWFS-Neural Network (SHNN). By transforming spot detection problem into a classification problem, SHNNs first find out the spot center, and then calculate centroid. In extreme low signal-noise ratio (SNR) situations with peak SNR ($SN{R}_p$) of 3, False Rate of SHNN-50 (SHNN with 50 hidden layer neurons) is 6%, and that of SHNN-900 (SHNN with 900 hidden layer neurons) is 0%, while traditional methods’ best result is 26 percent. With the increase of environmental light interference’s power, the False Rate of SHNN-900 remains around 0%, while traditional methods’ performance decreases dramatically. In addition, experiment results of the wavefront reconstruction are presented. The proposed SHNNs achieve significantly improved performance, compared with the traditional method, the Root Mean Square (RMS) of residual decreases from 0.5349 um to 0.0383 um. This method can improve SHWFS’s robustness.

A two-frame phase-shifting interferometric wavefront reconstruction method based on deep learning is proposed. By learning from a large number of simulation data based on a physical model, the wrapped phase can be calculated accurately from two interferograms with an unknown phase step. The phase step can be any value excluding the integral multiples of π and the size of interferograms can be flexible. This method does not need a pre-filtering to subtract the direct-current term, but only needs a simple normalization. Comparing with other two-frame methods in both simulations and experiments, the proposed method can achieve better performance.

The stochastic parallel gradient descent (SPGD) algorithm is usually employed as the control strategy for phase-locking in fiber laser phased array systems. However, the convergence speed of the SPGD algorithm will slow down as the number of array elements increases. To improve the control bandwidth, the convolutional neural network is introduced to quickly calculate the initial piston aberration in a single step. In addition, the irrationality of the commonly used Mean Square Error (MSE) evaluation function in existing convolutional neural networks is analyzed. A new evaluation function NPCD (Normalized Phase Cosine Distance) is proposed to improve the accuracy of the neural networks. The results show that the piston aberration residual is 0.005 and the normalized power in the bucket (PIB) is 0.993 in the simulation and 0.933 in the experiment after accurate preliminary compensation, which means that the system directly enters the co-phase state. We also demonstrate the robustness and scalability by expanding the scale of the array.

Free-space optical communication is an effective alternative solution to address the “last mile” bottleneck in fiber-optic communication systems. However, its practical performance is significantly affected by phase perturbations and intensity scintillation induced by atmospheric turbulence effects. This paper proposes a multi-aperture adaptive fiber-coupled communication architecture, systematically investigating the optical transmission characteristics in turbulent channels through a combined approach of theoretical modeling and experimental validation. Utilizing the Gamma-Gamma turbulence channel model, quantitative analyses are conducted to elucidate the relationships between the scintillation index, the number of transmitting apertures, and the bit error rate. By establishing an outdoor 2.1 km experimental platform, we demonstrate that multi-aperture diversity transmission combined with closed-loop control reduces the scintillation index by 60% while achieving 10 Gbit/s error-free communication under weak turbulence conditions. Experimental results indicate that the proposed architecture enhances coupling power while maintaining high communication quality. Its modular design ensures high compatibility with mature fiber-optic communication components, providing a solution for constructing low-complexity, high-reliability hybrid optical communication systems in urban environments.

Fiber coupling plays an important role in applications such as free-space optical communication (FSOC) and self-referencing interferometry. However, the coupling efficiency is often affected by turbulence and platform vibrations, which requires dynamic coupling with optimization algorithms. In this paper, to further mitigate the effects of sudden disturbances and to expand the effective range of fiber coupling systems, we propose a new method called the advanced root mean square propagation with warm-up (ARW) algorithm. By adaptively adjusting both the gain rate and the perturbation rate with warm-up operations, the ARW algorithm can achieve higher effective range and acceptable steady-state coupling efficiency simultaneously. Simulation and experimental results demonstrate that the proposed method requires only 36.4% of the iterations of the SPGD algorithm to deal with sudden disturbances. Moreover, the effective range of the ARW algorithm is 530.50µrad in the specific coupling platform, which is 20% higher than the effective range of SPGD.

We first demonstrate atmospheric turbulence compensation and optical coherent combining using a phased fiber laser array with the largest channels of sub-apertures. With multi-dimensional control of piston and tip/tilt phases on each sub-aperture, the co-phasing and adaptive fiber coupling of receiving beamlets have been achieved in all-fiber structure, and the mean received power increased by about 12 times and the scintillation index caused by turbulence decreased from 0.275 to 0.041 compared with open loop. This experiment shows the practicability and adaptive optics ability of the phased fiber laser array and suggests the great potential of its applications in urban free-space optical communications.