The dynamic gain of a few-mode erbium-doped fiber amplifier (FM-EDFA) is vital for the long-haul mode division multiplexing (MDM) transmission. Here, we investigate the mode-dependent dynamic gain of an FM-EDFA under various manipulations of the pump mode. First, we numerically calculate the gain variation with respect to the input signal power, where a mode-dependent saturation input power occurs under different pump modes. Even under the fixed intensity profile of the pump laser, the saturation input power of each spatial mode is different. Moreover, high-order mode pumping leads to a compression of the linear amplification region, even though it is beneficial for the mitigation of the differential modal gain (DMG) arising in all guided modes. Then, we develop an all-fiber 3-mode EDFA, where the fundamental mode of the pump laser can be efficiently converted to the LP₁₁ mode using the all-fiber mode-selective coupler (MSC). In comparison with the traditional LP₀₁ pumping scheme, the DMG at 1550 nm can be mitigated from 1.61 dB to 0.97 dB under the LP₁₁ mode pumping, while both an average gain of 19.93 dB and a DMG of less than 1 dB can be achieved from 1530 nm to 1560 nm. However, the corresponding signal input saturation powers are reduced by 0.3 dB for the LP₀₁ mode and 1.6 dB for the LP₁₁ mode, respectively. Both theoretical and experimental results indicate that a trade-off occurs between the DMG mitigation and the extension of the linear amplification range when the intensity profile of pump laser is manipulated.

Realizing high-fidelity optical information transmission through a scattering medium is of vital importance in both science and applications, such as short-range fiber communication and optical encryption. Theoretically, an input wavefront can be reconstructed by inverting the transmission matrix of the scattering medium. However, this deterministic method for retrieving light field information encoded in the wavefront has not yet been experimentally demonstrated. Herein, we demonstrate light field information transmission through different scattering media with near-unity fidelity. Multi-dimensional optical information can be delivered through either a multimode fiber or a ground glass without relying on any averaging or approximation, where their Pearson correlation coefficients can be up to 99%.

We proposed and experimentally demonstrated an all-fiber sensor for measuring bend with high sensitivity based on a ring core fiber (RCF) modal interferometer. The sensor was fabricated by splicing a segment of RCF between two pieces of multimode fiber (MMF) and single-mode fiber (SMF) at the ends of the MMF as lead-in and lead-out. Due to the first segment of the MMF, the transmitted light is coupled into the ring core, silica center, and cladding of the RCF, exciting multiple modes in the RCF. By the modal interferences in the structure, bending sensing can be realized by interrogating the intensity of the interference dip. Experimental results show a high bending sensitivity of -25.63dB/m-1 in the range of 1.0954m-1 to 1.4696m-1. In addition, the advantages of the bend sensor, such as small size, low temperature sensitivity, and simple fabrication process, can be used for curvature measurement in building health monitoring.

基于布里渊光时域分析（Brillouin optical time-domain analysis, BOTDA）测量技术分别研究了单模光纤、光子晶体光纤和镀金光纤在1100 ℃、1200 ℃和1000 ℃的高温传感特性，通过对石英光纤的布里渊频移（Brillouin frequency shift, BFS）跳跃现象和涂覆层燃烧现象进行研究，指出石英光纤均需要退火才能够达到热稳定状态。退火后，三种光纤的布里渊频移随温度呈非线性变化。其中，单模光纤和光子晶体光纤高温状态下涂覆层气化，二氧化硅发生晶化导致其机械强度大幅下降，因此仅能作为一次性高温传感器；镀金光纤由于金涂层具有较高的熔点和良好的气密性，高温退火后仍然能够保持良好的机械强度，因此可以作为一种重复使用的高温传感器。该研究有望为高温传感应用（如涡轮发动机内部温度监测）提供一种技术参考。

近年来，我国海洋发展战略逐步兴起，水下成像技术在海洋工程、海洋资源开发及海洋环境保护等领域发挥日益重要的作用。同时，深度学习技术在图像处理领域获得广泛应用。本文在介绍深度学习基本概念的基础上，对其在水下成像技术中的最新应用研究进展进行了系统综述，针对深度学习在水下图像增强技术、水下图像复原技术、水下偏振成像技术、水下关联成像技术、水下光谱成像技术、水下压缩感知成像技术、水下激光成像技术及水下全息成像技术等典型水下成像场景中的应用特点及不足进行了分析对比，并对该技术的未来发展方向进行了展望。