Specular Effects on the GPU: State of the Art

This survey reviews algorithms that can render specular, i.e. mirror reflections, refractions, and caustics on the GPU. We establish a taxonomy of methods based on the three main different ways of representing the scene and computing ray intersections with the aid of the GPU, including ray tracing in the original geometry, ray tracing in the sampled geometry, and geometry transformation. Having discussed the possibilities of implementing ray tracing, we consider the generation of single reflections/refractions, interobject multiple reflections/refractions, and the general case which also includes self-reflections or refractions. Moving the focus from the eye to the light sources, caustic effect generation approaches are also examined.     

The Beam Radiance Estimate for Volumetric Photon Mapping

We present a new method for efficiently simulating the scattering of light within participating media. Using a theoretical reformulation of volumetric photon mapping, we develop a novel photon gathering technique for participating media. Traditional volumetric photon mapping samples the in‐scattered radiance at numerous points along the length of a single ray by performing costly range queries within the photon map. Our technique replaces these multiple point‐queries with a single beam‐query, which explicitly gathers all photons along the length of an entire ray. These photons are used to estimate the accumulated in‐scattered radiance arriving from a particular direction and need to be gathered only once per ray. Our method handles both fixed and adaptive kernels, is faster than regular volumetric photon mapping, and produces images with less noise.     

基于光纤四波混频效应的2R全光再生方法研究

提出了一种基于光纤中四波混频(FWM)效应实现对光信号的再放大和再整形的2R再生功能的方法,分析了该方法的工作原理,设计了一种基于光纤FWM效应实现光信号2R再生的光纤传输仿真系统。仿真结果表明,2R再生信号良好,系统Q值达到21.59,验证了该方法的可行性。所设计的2R再生方案中,泵浦光的波长与功率是影响FWM效率和2R再生性能的主要因素,对其进行了扫参研究,得出泵浦波长为1 548nm、功率为40dBm时,2R再生性能最优。     

Stable single photon sources in the near C-band range above 400 K

The intrinsic characteristics of single photons became critical issues since the early development of quantum mechanics. Nowadays, acting as flying qubits, single photons are shown to play important roles in the quantum key distribution and quantum networks. Many different single photon sources (SPSs) have been developed. Point defects in silicon carbide (SiC) have been shown to be promising SPS candidates in the telecom range. In this work, we demonstrate a stable SPS in an epitaxial 3CSiC with the wavelength in the near C-band range, which is very suitable for fiber communications. The observed SPSs show high single photon purity and stable fluorescence at even above 400 K. The lifetimes of the SPSs are found to be almost linearly decreased with the increase of temperature. Since the epitaxial 3C-SiC can be conveniently nanofabricated, these stable near Cband SPSs would find important applications in the integrated photonic devices.     

Controlling Red Color–Based Multicolor Upconversion through Selective Photon Blocking

Photon upconversion multiplexing has attracted increasing interest in recent years; however, realizing the red color–based multicolor‐tunable output in upconversion nanoparticles (UCNPs) at a fixed composition remains a huge challenge. Here, a novel and versatile approach to fine‐control upconversion luminescence (UCL) colors from UCNPs through selectively confining specific excitation energy by the photon blocking effect is reported. Four types of dual‐color switchable UCNPs capable of emitting red‐blue and red‐green emissions are successfully designed following this strategy, and their UCL performance shows a multiwavelength (808/980/1550 nm) excitable feature that is well sustained in a wide range of excitation power density. The use of the photon blocking effect further enables the dynamically switchable red‐green‐blue UCL with 808/980 nm excitations. These findings provide a general method to achieve multicolor‐tunable UCL at a single nanoparticle level. Moreover, the UCNPs with red‐based multicolor emissions in this work enriches the upconversion system and should have potential applications in display, anti‐counterfeiting, and bioimaging.     

NIR‐II Excitable Conjugated Polymer Dots with Bright NIR‐I Emission for Deep In Vivo Two‐Photon Brain Imaging Through Intact Skull

Methods for noninvasive brain imaging are highly desirable to study brain structures in neuroscience. Two‐photon fluorescence microscopy (2PFM) with near‐infrared (NIR) light excitation is a relatively noninvasive approach commonly used to study brain with high spatial resolution and large imaging depth. However, most of the current studies require cranial window implantation or skull‐thinning methods due to attenuation of excitation light. 2PFM through intact mouse skull is challenging due to strong scattering induced by skull bone. Herein, NIR‐II light excitable single‐chain conjugated polymer dots (CPdots) with bright fluorescence in NIR‐I region (peak at ≈725 nm and quantum yield of 20.6 ± 1.0%) are developed for deep in vivo two‐photon fluorescence (2PF) imaging of intact mouse brain. The synthesized CPdots exhibit good biocompatibility, high photostability, and large two‐photon absorption cross section. The CPdots allow 2PF images acquired upon excitation at 800, 1040 and 1200 nm with the highest signal‐to‐background ratio of 208 demonstrated for 1200 nm excitation. Moreover, a 3D reconstruction of the brain blood vessel network is obtained with a large vertical depth of 400 µm through intact skull. This work demonstrates great potential of bright NIR fluorophores for in vivo deep tissue imaging.     

Small‐Molecule‐Doped Organic Crystals with Long‐Persistent Luminescence

Traditional long‐persistent luminescence (LPL) materials, which are based on inorganic systems containing rare elements and with preparation temperatures of at least 1000 °C, exhibit afterglow times of more than 10 h and can be tuned for different applications. However, the development of this field is hindered due to the large thermal energy consumption and the need for nonrenewable resources. Thus, the development of a “green” design and preparation of LPL materials is of some importance. A doped‐crystalline material based on two metal‐free organic small molecules is easily prepared through ultrasonic crystallization at room temperature. It has a high‐quality, single‐crystalline structure, and visible LPL performance with a duration of more than 6 s upon low‐energy photoexcitation. A green, flexible, and convenient screen‐printing technology for controllable pattern anticounterfeiting is then developed from this purely organic material, which improves the prospects for commercial utilization in the future.     

全光纤单频光纤放大器实现550W近衍射极限输出

通过引入长锥形增益光纤综合抑制受激布里渊散射和模式不稳定效应,兼顾1030nm波段信号光放大的高模式不稳定阈值特性,基于全光纤放大器实现了550W的近衍射极限单频光纤激光输出,整个放大器的斜率效率达80%,最高功率时的光束质量测量值M^2约为1.47;系统亮度的进一步提升受限于热致模式不稳定效应。