Chao Geng

As a type of optical phased array technology, phased fiber laser array (PFLA) manipulates the phase of multiple beams to achieve high-power laser output and high-speed beam control. In this paper, a PFLA of cascaded microlens array scanners (MLAS) is proposed for the first time, and the wide-angle scanning and combining characteristics of the array light field are theoretically studied by using the multi-stage phase cooperative control theory of tip/tilt-piston phase. At the same time, using a seven-aperture array system as an example, the paper compares and analyzes the properties of using piston phase control, tip/tilt phase control, and tip/tilt-piston phase cooperative control to achieve scanning and combining beams. The results indicate that the proposed PFLA technology with cascaded MLAS can achieve continuous and stable beam scanning in a wide field of view. Moreover, this technology adopts a flexible distributed design with the characteristics of large aperture transmission and reception. In addition, each device is independent of each other, without coupling crosstalk, and the control is simple. This technology provides a solution for the integration of coherent combining and electronically controlled beam scanning, and is expected to be widely used in fields such as free-space optical communication and laser atmospheric transmission.

Free space optical communication (FSOC) is a promising technology for 6G wireless networks with the advantages of high bandwidth and low cost. However, atmospheric turbulence severely degrades receiver coupling efficiency, especially in small-aperture MIMO systems. These systems simplify the correction of high-order atmospheric aberrations by decomposing them into low-order tip/tilt aberration using concatenated small-aperture receivers. However, current correction strategies without any consideration for device delays and the random, time-varying nature of turbulence limit their effectiveness. In this paper, we propose a neural network-based pre-correction model that utilizes LSTM to anticipate the evolving characteristics of tip/tilt aberration induced by atmospheric turbulence, thereby allowing valuable response time for the correction device to execute precise adjustments. Testing under five turbulence conditions demonstrated an average improvement of 4.54 dB in coupling power (CP), with bit error rates reduced from 0.068 to near zero, achieving telecom-grade performance. This work offers a cost-effective solution for enhancing FSOC systems and provides insights for aberration correction in dynamic environments.

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.

Phased fiber laser arrays provide an effective means to mitigate atmospheric turbulence and achieve high-quality beams, where efficient combiners play a crucial role in achieving phase coherence among sub-beams and generating high-power output beams. This paper focuses on investigation of a silicon-based beam combiner with 19 input channels, which employs a structure comprised of cascaded 2 × 1 multi-mode interference couplers and 2 × 1 Mach-Zehnder interferometers on a silicon chip. According to the thermo-optic effect of silicon material, the square of the control voltage is linearly related to the phase change. In response, the modified stochastic parallel gradient descent (SPGD) algorithm is proposed, and parameters are analyzed. Experimental results confirm that the silicon-based beam combiner with the modified SPGD algorithm can combine laser beams effectively. Under static conditions, after about 0.09 s of iteration, the output power of the silicon-based beam combiner reaches the average value detected by photodetector (PD), with a phase-locking accuracy of approximately λ/36. Under dynamic disturbance conditions, after about 0.3 s of iteration, the output power reaches the average value detected by PD, with a phase-locking accuracy of approximately λ/32.

Microlens array scanning (MLAS) has emerged as a promising semi-solid micromechanical beam scanning technology, which has significant potential in fields such as LIDAR and free-space optical communication. Beam quality is a crucial performance index in MLAS, which directly affects the overall performance of the system. To better evaluate and optimize the performance of the MLAS system, we investigate the effect of aberrations on this critical parameter of MLAS beam quality. This paper commences by constructing a model of the Kepler-structured MLAS system affected by aberrations based on the wave aberration theory. A detailed examination is conducted on the influence of both uniform and non-uniform wave aberrations within the MLAS on the beam quality. This paper investigates the effects of defocus, astigmatism, coma, and spherical aberration on the far-field intensity distribution of the MLAS system by using the Zernike aberration decomposition technique. Employing the Strehl ratio (SR) and power-in-the-bucket (PIB) as quantitative evaluation indices of beam quality, this study calculates the aberration-induced alterations in far-field focusing ability and energy concentration. The findings of this study provide valuable insights for the design optimization, manufacturing, and assembly testing of MLAS technologies.

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.

Coherent beam combining (CBC) with closely arranged centrosymmetric arrays is a promising way to obtain a high-brightness laser. An essential task in CBC is to actively control the piston phases of the input beams, maintaining the correct phasing to maximize the combination efficiency. By applying the neural network, the nonlinear mapping relationship between the far-field image and the piston phase could be established, so that the piston phase can be corrected quickly with one step, which caused widespread concern. However, there exists a piston-type phase ambiguity problem in the CBC system with centrosymmetric arrays, which means that multiple different piston phases may generate the same far-field image. This will prevent the far-field image from correctly reflecting the phase information, which will result in a performance degradation of the image-based intelligent algorithms. In this paper, we make a theoretical analysis of phase ambiguity. A method to solve phase ambiguity is proposed, which requires no additional optical devices. We designed simulations to verify our conclusions and methods. We believe that our work solves the phase ambiguity problem in theory and is conducive to improving the performance of image-based algorithms.

We propose an imaging method based on optical fiber bundle combined with micro-scanning technique for improving image quality without complex image reconstruction algorithms. In the proposed method, a piezoelectric-ceramic-chip is used as the micro-displacement driver of the optical fiber bundle, which has the advantages of small volume, fast response speed and high precision. The corresponding displacement of the optical fiber bundle can be generated by precise voltage controlling. An optical fiber bundle with core/cladding diameter 4/80 μm and hexagonal arrangement is used to scan the 1951 USAF target. The scanning step is 1 μm, which is equivalent to the diffraction limit resolution of the optical system. The corresponding information is recorded at high speed through photo-detectors and a high-resolution image is obtained by image stitching processing. The minimum distinguishable stripe width of the proposed imaging technique with piezoelectric-ceramic-chip driven micro-scanning is approximately 2.1 μm, which is 1 time higher than that of direct imaging with a CCD camera whose pixel size is close to the fiber core size. The experimental results indicate that the optical fiber bundle combined with piezoelectric-ceramic-chip driven micro-scanning is a high-speed and high-precision technique for high-resolution imaging.