3D holoscopic image coding scheme using HEVC with Gaussian process regression

3D holoscopic image, also known as integral imaging, light field imaging and plenoptic imaging, can provide a natural and fatigue-free 3D visualization. However, a large amount of data is required to represent the 3D holoscopic content. Therefore, efficient coding schemes for such particular type of image are needed. In this paper, we propose a Gaussian process regression based prediction scheme to compress the 3D holoscopic image. In the proposed scheme, the coding block and its prediction supports are modeled as a Gaussian process (GP) and Gaussian process regression (GPR) is used to obtain a better prediction of the coding block. Limited searching windows in horizontal and vertical directions are used to obtain the prediction supports, and a filtration method is designed to judge the reliability of the obtained prediction supports. Moreover, in order to alleviate the high complexity caused by GPR, a sparsification method is also put forward. Experimental results demonstrate the advantage of the proposed scheme for 3D holoscopic image coding in terms of different quality metrics as well as the visual quality of the views rendered from decompressed 3D holoscopic content, compared to the HEVC intra-prediction method and several other prediction methods in this field.     

二维抗反射亚波长周期结构光栅的设计分析

利用严格耦合波理论(RCWA)和等效介质理论(EMT)研究了二维抗反射亚波长周期结构光栅的设计问题.以立方体和柱状单台阶网格光栅和金字塔形及圆锥形多台阶光栅为例,主要研究了占空比和表面面形对反射率的影响.通过计算发现,当光栅周期足够小的时候,光栅面形对反射率没有影响,同时占空比严重影响着光栅的特性,这对设计制造抗反射光栅非常有用.同时也研究了等效介质理论的适用性.     

Multimode oscillation Q-switched erbium-doped fiber laser with a few-mode fiber cavity

We propose and demonstrate experimentally a multimode oscillation Q-switched erbium-doped fiber laser with a few-mode fiber cavity. The different coupling processes of reflection peaks of fiber Bragg gratings (FBGs) which act as cavity mirrors allow the different oscillating states. We obtain microsecond light pulse output states whose oscillation and output beams have different mode compositions, including high order mode. Such a structure enables the high order mode oscillation in the whole cavity with an all-fiber structure, which has potential applications in mode-division multiplexed systems and research of multimode nonlinear effect.     

Fiber laser twist sensor with hybrid few-mode tilted Bragg grating and few-mode long period grating

A twist sensor with hybrid few-mode tilted fiber Bragg grating (FM-TFBG) and few-mode long period grating (FM-LPG) in fiber laser cavity is demonstrated. The FM-LPG is utilized to excite LP11 core mode. The FM-TFBG is used for sensing. The transverse modes at 1 553.9 nm and 1 550.5 nm are LP01 and LP21 core modes, respectively, which are coupled from forward-propagating LP11 core mode. These two excitation wavelengths have opposite variation tendencies, which participate in sensing. The twist sensitivity of 0.16 dB/° from ?40° to 40° is achieved. The proposed sensor has potentially used for structure monitoring in many areas.     

利用梯度下降极小惯量法的脑中线偏离度算法

大脑受到创伤后往往会伴随着结构的移位,而脑中线的移位程度对医生预估脑内压强、脑疝等脑部创伤后并发症的重要标准。本文以两位脑创伤患者在接受治疗期间内的影响资料为对象,研究了用梯度下降的极小惯量法计算大脑的理想对称轴,并与患者的实际脑中线相比较,归一化后脑中线偏离度随时间变化的趋势图与临床的症状完全吻合,因而对医生的临床判断具有重要意义。     

Unrevealing Temporal Mechanoluminescence Behaviors at High Frequency via Piezoelectric Actuation

Mechanoluminescence (ML) materials present widespread applications. Empirically, modulation for a given ML material is achieved by application of programmed mechanical actuation with different amplitude, repetition velocity and frequency. However, to date modulation on the ML is very limited within several to a few hundred hertz low-frequency actuation range, due to the paucity of high-frequency mechanical excitation apparatus. The universality of temporal behavior and frequency response is an important aspect of ML phenomena, and serves as the impetus for much of its applications. Here, we push the study on ML into high-frequency range (∼250 kHz) by combining with piezoelectric actuators. Two representative ML ZnS:Mn and ZnS:Cu, Al phosphors were chosen as the research objects. Time-resolved ML of ZnS:Mn and ZnS:Cu, Al shows unrevealed frequency-dependent saturation and quenching, which is associated with the dynamic processes of traps. From the point of applications, this study sets the cut-off frequency for ML sensing. Moreover, by in-situ tuning the strain frequency, ZnS:Mn exhibits reversible frequency-induced broad red-shift into near-infrared range. These findings offer keen insight into the photophysics nature of ML and also broaden the physical modulation of ML by locally adjusting the excitation frequency.     

飞秒激光加工红磷的实验研究

为了验证飞秒激光加工含能材料的安全性,本文 以红磷作为含能材料替代物,从理论和实验上说明飞 秒激光加工红磷“冷加工”和“热加工”的可控性。利用有限元软件分析了单脉冲飞秒激光 作用到红磷表 面后样品的径向和轴向温度分布,得到了红磷的热影响区域。通过实验结果验证了飞秒激光 加工红磷样品 时具有“冷加工”和“热加工”两个区域,分析了激光通量对“冷加工”和“热加工”的影 响,确定了加 工红磷样品的“冷加工”的激光通量范围,并计算得到了红磷样品的烧蚀阈值和脉冲累积因 子。     

High Mobility 3D Dirac Semimetal (Cd3As2) for Ultrafast Photoactive Terahertz Photonics

The Dirac semimetal cadmium arsenide (Cd₃As₂), a 3D electronic analog of graphene, has sparked renewed research interests for its novel topological phases and excellent optoelectronic properties. The gapless nature of its 3D electronic band facilitates strong optical nonlinearity and supports Dirac plasmons that are of particular interest to realize high-performance electronic and photonic devices at terahertz (1 THz = 4.1 meV) frequencies, where the performance of most dynamic materials are limited by the tradeoff between power-efficiency and switching speed. Here, all-optical, low-power, ultrafast broadband modulation of terahertz waves using an ultrathin film (100 nm, λ/3000) of Cd₃As₂ are experimentally demonstrated through active tailoring of the photoconductivity. The measurements reveal the photosensitive metallic behavior of Cd₃As₂ with high terahertz electron mobility of 7200 cm² (Vs)⁻¹. In addition, optical fluence dependent ultrafast charge carrier relaxation (15.5 ps), terahertz mobility, and long momentum scattering time (157 fs) comparable to superconductors that invoke kinetic inductance at terahertz frequencies are demonstrated. These remarkable properties of 3D Dirac topological semimetal envision a new class of power-efficient, high speed, compact, tunable electronic, and photonic devices.