Aiming for suppressing side-mode and spectrum broadening, a slit beam-shaping method and super-Gaussian apodization processing for femtosecond laser point-by-point (PbP) inscription technology of fiber Bragg gratings (FBGs) are reported here. High-quality FBGs, featuring narrow bandwidth of less than 0.3 nm, high reflectivity above 85%, low insertion loss (0.21 dB), and low cladding loss (0.82 dB), were obtained successfully. By a semi-automatic PbP inscription process, an array consisting of six FBGs, exhibiting almost no side-mode peaks with high suppression ability and narrow bandwidth, was fabricated along three independently developed single-mode fibers with an interval of 20 mm.

In this study, we propose an underwater ghost-imaging scheme using a modulation pattern combining offset-position pseudo-Bessel-ring (OPBR) and random binary (RB) speckle pattern illumination. We design the experiments based on modulation rules to order the OPBR speckle patterns. We retrieve ghost images by OPBR beam with different modulation speckle sizes. The obtained ghost images have a better contrast-to-noise rate compared to RB beam ghost imaging under the same conditions. We verify the results both in the experiment and simulation. In addition, we also check the image quality at different turbidities. Furthermore, we demonstrate that the OPBR speckle pattern also provides better image quality in other objects. The proposed method promises wide applications in highly scattering media, atmosphere, turbid water, etc.

二氧化钒具有从金属相到绝缘体相发生可逆相变的特性，在68℃，分子结构从单斜结构转换成金红石结构，同时伴随着光学、电学和热学性质的快速突变，使得二氧化钒被广泛应用于热光调控、光学防护、红外伪装、离子电池和化学传感等领域。本文总结了二氧化钒薄膜新颖的制备技术、研究现状以及各种技术的优缺点，分析了应力、掺杂、缺陷等因素对二氧化钒相变特性的显著影响，归纳了二氧化钒的相变机理和支持相关相变机理的证据，列举了二氧化钒在不同热门领域中的应用，并对二氧化钒的发展方向和应用前景进行了总结和展望。

针对水下目标探测应用场景，给出了相应的532 nm波长激光雷达系统参数，结合条纹管激光雷达和载波调制激光雷达的优点，设计研制了一套水下三维成像增程激光雷达原理样机。相对于常见的微波调制激光产生高频脉冲的方案，该原理样机采取调Q技术压缩激光脉冲，再结合F-P腔的特性产生高频激光脉冲，具有峰值功率高和输出能量高的优点。实验结果表明，该原理样机在清水环境中成像距离优于20 m，能够捕捉到13 m处直径9 mm的目标细节；在浊水环境中的信号处理增程能力达到81.4%，相对距离分辨误差为0.01 m。所获得的实验结果为进一步提升水下激光雷达的成像距离和分辨率进而发展水下成像装备奠定了基础。

Ultrashort pulsed Bessel beams with intrinsic nondiffractive character and potential strong excitation confinement down to 100 nm can show a series of advantages over Gaussian beams in fabricating efficient Bragg grating waveguides (BGWs). In this work, we focus on parameter management for the inscription of efficient BGWs using the point-by-point method employing Bessel beams. Due to their high aspect ratio, the resulting one-dimensional void-like structures can section the waveguides and interact efficiently with the optical modes. Effective first-order BGWs with low birefringence can then be fabricated in bulk fused silica. By controlling the size and the relative location of grating voids via the Bessel pulse energy and scan velocities, the resonant behaviors of BGWs can be well regulated. A high value of 34 dB for 8 mm length is achieved. A simple predictive model for BGWs is proposed for analyzing the influences of processing parameters on the performance of BGWs. The technique permits multiplexing several gratings in the same waveguide. Up to eight grating traces were straightforwardly inscribed into the waveguide in a parallel-serial combined mode, forming the multiplex BGWs. As an application, the multiplex BGW sensor with two resonant peaks is proposed and fabricated for improving the reliability of temperature detection.