A piezoelectric optical fiber stretcher has been introduced for working point controlling and low-frequency noise suppression of a fiber-optic atmospheric turbulence sensor. It is actuated by a piezoelectric ceramic stack. The rational structure allows the fiber to extend only along the axial direction, which minimizes the nonlinear birefringence effects for the optical phase shift. What is believed to be a novel method has been proposed to measure its phase-shift coefficient. With the use of this device, the fiber-optic atmospheric turbulence sensor has been tested for the air refractive index measurement.

Controlled turbulence simulators in the laboratory have been extensively employed to investigate turbulence effects on light propagation in the atmosphere, driven by some advanced optical engineering such as remote sensing, energy-delivery systems, and free-space optical communication systems. Many studies have achieved rich results on the optical turbulence intensity, scintillation index, and power spectral density characteristics of the light propagation path in the center of a turbulence simulator, but a comprehensive analysis of the optical turbulence characteristics for different spatial locations is still lacking. We simulate turbulence with air as the medium in a classical convective Rayleigh–Bénard turbulence simulator through high-resolution computational fluid dynamics methods, the three-dimensional refractive index distribution is obtained, and the optical properties are analyzed comprehensively. It is found that the hot and cold plumes and the large-scale circulation strongly influence the inhomogeneity of $C_n^2$ in the turbulence tank, making it weak in the middle and strong near the boundary. The refractive index power spectral density at different heights is centrally symmetric, with the slope gradually deviating from the −5/3 scaling power with increasing distance from the central region. Under the log-log plot, the variation of the refractive index variance with height exhibits a three-segmented feature, showing in order: a stable region, a logarithmic profile, and a power-law profile, in the region close to the boundary. These results will contribute to the construction of a suitable turbulence simulator for optical engineering applications.

The application of ultra-high-bandwidth free-space optical (FSO) communication has become a widely researched hotspot. In remote areas without network coverage, the low altitude platform (LAP), such as airships, drones, etc., can provide a low-cost and rapid deployment emergency FSO communication platform covering hundreds of kilometers and has immeasurable application prospects. In our work, we experimentally demonstrated a line rate of 112 Gbit/s FSO communication at a distance of 104.8 km over Qinghai Lake. By adopting the methods of polarization multiplexing (PM), high-order quadrature amplitude modulation (n-QAM), automatic gain optical amplification (AGOA), etc., we have achieved a long-haul and high-bandwidth laser communication in atmospheric link with the optimum bit error rate (BER) of 3E-3 (zero-BER after error-correction) for a time-length of 50 s. It is particularly emphasized that the AGOA effectively can suppress the fluctuation of received optical power caused by atmospheric turbulence scintillation effect in Qinghai Lake, which solved the difficulty of detection-demodulation with ultra-high-speed laser signals. In addition, the efficient soft decision forward error correction (SD-FEC) also improved the stability of the communication link, which played a crucial role in the success of this experiment. Our design of non-adaptive optical (AO) system is very suitable for application in small-scale LAP and will potentially become an important foundation of the large-capacity nonterrestrial network (NTN) based on LAP. To the best of our knowledge, this experiment verified the feasibility of single-wavelength (1556.15 nm) 112 Gbit/s high-bandwidth laser signal transmission with a long-haul of 104.8 km in low-altitude horizontal atmospheric link for the world’s first time. To a large extent, our research findings also have great application value in the field of low-altitude economy.

All roads lead to Rome. In this article we propose a novel theoretical framework to demonstrate vector beams whose degree of polarization does not change on atmospheric propagation. Inspired by the Fresnel equations, we derive the reflected and refracted field of vector beams propagating through a phase screen by employing the continuity of electromagnetic field. We generalize the conventional split-step beam propagation method by considering the vectorial properties in the vacuum diffraction and the refractive properties of a single phase screen. Based on this vectorial propagation model, we extensively calculate the change of degree of polarization (DOP) of vector beams under different beam parameters and turbulence parameters both in free-space and satellite-mediated links. Our result is that whatever in the free-space or satellite-mediated regime, the change of DOP mainly fluctuates around the order of 10⁻¹³ to 10⁻⁶, which is almost negligible.

The idea of projecting a laser beam onto a large area microcrystalline reflective film (3M film) for the visualization and measurement of atmospheric optical turbulence was proposed and investigated. The fold pass propagation of a laser beam by the reflection of a 3M film was theoretically analyzed and numerically simulated, which uncovers that the mechanism of bright dots, random in shape, brightness, and position, appears on the received laser speckle images. Experiments were performed to get the phenomena and explore the applications of the idea. An easy to implement laser speckle imaging system was set up for the qualitative experiments. As the result, the image of laser speckle patterns characterized by random dots and movable shadows were recorded, and the two-dimensional path averaged transverse wind field was retrieved. Also, a high-performance laser speckle imaging system cooperated with two professional optical turbulence monitoring instruments was set up for the qualitative experiments. Using the image data recorded in a clear sunny day, the probability distribution, spatial correlation coefficient, and scintillation index of the light intensity on the laser speckles were estimated. Meanwhile, the refractive index structure constant, aperture averaging factor, and inner scale of optical turbulence field were retrieved and compared with the monitored values and theoretical expectations. All the results are reasonable, which reveals the possibility and verifies the feasibility of using a fold pass laser speckle imaging system for optical turbulence research.

根据广义Huygens-Fresnel原理，推导了von Karman湍流谱条件下激光回波复相干度的理论解析式；基于湍流相位屏分步传输算法和随机粗糙目标表面模型，实现了激光回波光场的仿真计算。首先通过镜面反射回波光场的仿真分析，验证了算法的正确性；然后基于1.1km的均匀传输路径，综合分析了随机粗糙目标表面特性和路径湍流强度对回波光场复相干度的影响。结果表明：回波光场的空间相干性随目标表面高度均方根的增大而降低；随目标表面相关长度的减小而降低，当表面相关长度远小于大气相干长度时，回波相干性会被严重破坏。该研究可为目标表面特性或利用已知表面获取路径湍流状态的相干探测提供有益的参考。