Mechanical and Electric Control of Photonic Modes in Random Dielectrics

Random dielectrics defines a class of non‐absorbing materials where the index of refraction is randomly arranged in space. Whenever the transport mean free path is sufficiently small, light can be confined in modes with very small volume. Random photonic modes have been investigated for their basic physical insights, such as Anderson localization, and recently several applications have been envisioned in the field of renewable energies, telecommunications, and quantum electrodynamics. An advantage for optoelectronics and quantum source integration offered by random systems is their high density of photonic modes, which span a large range of spectral resonances and spatial distributions, thus increasing the probability to match randomly distributed emitters. Conversely, the main disadvantage is the lack of deterministic engineering of one or more of the many random photonic modes achieved. This issue is solved by demonstrating the capability to electrically and mechanically control the random modes at telecom wavelengths in a 2D double membrane system. Very large and reversible mode tuning (up to 50 nm), both toward shorter or longer wavelength, is obtained for random modes with modal volumes of the order of few tens of (λ/n)³.     

Squeezed-state generation via atomic collisions in a Bose–Einstein condensate inside an optical cavity

In this paper, we investigate theoretically a system consisting of a one-dimensional Bose–Einstein condensate trapped inside the optical lattice of an optical cavity. In the weak-interaction regime and under the Bogoliubov approximation, the wave function of the Bose–Einstein condensate can be described by a classical field (condensate mode) having some quantum fluctuations (the Bogoliubov mode) about the mean value. Such a system behaves as a so-called atomic parametric amplifier, similar to an optical parametric amplifier, where the condensate and the Bogoliubov modes play, respectively, the roles of the pump field and the signal mode in the degenerate parametric amplifier and the s-wave scattering frequency of atom–atom interaction plays the role of the nonlinear gain parameter. We show that using the nonlinear effect of atomic collisions, how one can manipulate and control the state of the Bogoliubov mode and produce squeezed states.     

制备空间光机结构件的高体份SiC/Al复合材料

采用无压浸渗复合新方法和自行研制的专用工艺设备,低成本地制备了用作空间光机结构件的高体份(55%~57%)SiC/Al复合材料大尺寸坯锭,并对其微观结构特征、基本的力学及热物理性能和断裂机制予以表征。此外,还通过线切割、电火花成型等特种加工手段将该种复合材料制造成反射镜背板、焦面板等一系列空间光机结构用典型样件。研究结果表明,该材料既有优异的结构承载功能(弹性模量213 GPa,而比模量则比铝合金、钛合金及钢高出近两倍),又有卓越的热控功能(其热膨胀系数比钛合金还要低,热导率接近纯铝,达到235 W/m·K),若以其替代钛合金用于空间光机结构可望获得显著的轻量化效果并降低热控负荷、改善热控效果。     

NURBS自由曲面在光机设计和分析中的应用

针对光学曲面要求面形描述能力和拟合精度高以及光线追迹速度快的要求,研究了NURBS作为自由曲面的拟合、坐标空间转换和光线追迹算法。首先使用多分辨率B样条拟合方法浅度非球面,深度非球面和Peaks自由曲面进行NURBS拟合,RMS误差均小于10 nm,表现出很好的适应性。其次研究了NURBS曲面的参数空间到坐标空间的转化算法,与传统曲面求导方法相比,速度提高了3倍以上。在提出合理迭代初值计算方法的基础上,将计算每个曲面点的时间缩短至0.3 ms。最后通过NURBS曲面在自由曲面头盔系统的光机分析中和CODEV用户自定义曲面中的成功运用,证明了NURBS曲面能很好地满足光机设计、分析和加工的要求。     

Photostrictive Effect: Characterization Techniques,Materials, and Applications

Photostrictive effect exhibits a fascinating ability to directly convert light into mechanical strain, which enables a facile and straightforward approach to realize the wireless and remote control of the micro-electromechanical systems (MEMS). It provides a great potential to upgrade the existing electric-driven mechanical devices to optomechanical devices by replacing or integrating electrostriction, piezoelectric effect, or magnetostriction. Although this effect can be dated back to the 1960s, it should not be overlooked as a unique photophysical phenomenon. Especially in the passing decade, it has regained widespread attention, triggered by the emerging characterization techniques and new material systems, as well as the booming progress of MEMS. The recent progress of this fast-growing field is summarized by emphasizing the up-to-date characterization techniques and several new material systems. Furthermore, the potential applications of the photostrictive effect are also comprehensively reviewed. It is hoped that this article will promote the development of photostrictive effect, to not only deepen the research on the underlying mechanisms, but also accelerate the exploration of high-performance photostrictive materials, so as to meet the upcoming challenges faced by light as a major energy source in the foreseeable future.     

Conformational Freedom-Enhanced Optomechanical Energy Conversion Efficiency in Bulk Azo-Polyimides

Azobenzene-doped glassy polyimides (azo-polyimides) offer some of the most efficient optomechanical power densities to date rivaling electrostrictive polymers. Despite such potential attributes, the optomechanical efficiency remains low in comparison to other smart materials. Using high-fidelity coarse-grained molecular dynamics simulations, the authors reconcile both experimental and theoretical challenges to understand the limiting factors for the optomechanical conversion in photostrictive polymers. Interestingly, the ideal optomechanical efficiency of 10–24% for a single-chain azo-imide monomer predicted here is equal to or a little higher than experimental reports, suggesting experimental design space. The time-dependent optomechanical efficiency of bulk azo-polyimide is quantified, for the first time, to be strongly correlated with the initial free volumes, a measure of polymer conformational freedom. This trend is elaborated by conformational order parameters and viscoelastic relaxation moduli. Resembling the role of porosity in azobenzene-contained metal/covalent organic frameworks to enhance the photo-switching efficiency, a larger conformational freedom enables >10 times increase in optomechanical efficiency comparing to existing experiments. This is primarily due to facilitated viscoelastic relaxation after photo-switching which alleviates residual stresses quickly and reduces heat dissipation. These findings suggest opportunities to improve the optomechanical performance through targeted strategies, such as porosity control and thermal annealing.