基于半导体光放大器交叉偏振调制效应实现正、反相波长变换

利用琼斯矩阵,对基于半导体光放大器中的交叉偏振调制效应实现全光波长变换进行了理论分析.结果表明,利用这种机制可以实现同相与反相波长变换.在实验上同时实现了10Gb/s归零信号的正相与反相波长变换,输出消光比分别达到了6.9 dB和8.1 dB.     

基于P3近似的空间分辨漫反射研究

光源附近组织的空间分辨漫反射是近年来生物医学光子学领域的一个研究热点,其目的是发展一种能够测定活体生物组织光学参量的新技术。漫射近似理论研究光源附近组织的空间分辨漫反射具有很大局限性。P3近似理论考虑了相函数的三阶矩,能较准确地描述光源附近组织的光辐射分布。研究了基于P3近似的空间分辨漫反射,从输运理论的PN方程组出发,导出了P3近似方程组和P3近似的格林函数解;阐述了漫射近似与P1近似的关系,给出了外推边界条件下,准直光束近似后的P3近似漫反射率的完整表示,讨论了相函数二阶参量对P3近似漫反射的影响,并与漫射近似和蒙特卡罗模拟结果进行了比较,指出了P3近似的应用范围。     

克尔介质中双原子与场拉曼作用系统的腔场谱

研究了含克尔介质腔中两个耦合二能级原子与双模光场拉曼相互作用过程的腔场谱。通过求解本征方程导出了腔场谱的计算公式,给出了双模初始光场均处于数态时的数值计算结果。发现在两模初始场均为弱场时,克尔效应不仅使峰位右移,还使峰的强度、个数和频率发生改变,破坏峰结构的对称性。在克尔效应较强时,原子之间的耦合对腔场的影响被抑制,谱结构主要由克尔效应决定。在强场条件下,无克尔介质加入时,原子间的耦合作用使各峰的强度都得到加强;随克尔效应的增强,靠近中心频率的主峰迅速增长并很快达到饱和,而远离中心频率的边峰则被抑制并产生劈裂。     

Convergence analysis of a block preconditioned steepest descent eigensolver with implicit deflation

Gradient-type iterative methods for solving Hermitian eigenvalue problems can be accelerated by using preconditioning and deflation techniques. A preconditioned steepest descent iteration with implicit deflation (PSD-id) is one of such methods. The convergence behavior of the PSD-id is recently investigated based on the pioneering work of Samokish on the preconditioned steepest descent method (PSD). The resulting non-asymptotic estimates indicate a superlinear convergence of the PSD-id under strong assumptions on the initial guess. The present paper utilizes an alternative convergence analysis of the PSD by Neymeyr under much weaker assumptions. We embed Neymeyr's approach into the analysis of the PSD-id using a restricted formulation of the PSD-id. More importantly, we extend the new convergence analysis of the PSD-id to a practically preferred block version of the PSD-id, or BPSD-id, and show the cluster robustness of the BPSD-id. Numerical examples are provided to validate the theoretical estimates.     

A instrument for measuring solution concentration

Optical Review - In this paper, a set of devices, including hardware and software systems, is designed based on the basic principle of Michelson interferometry to measure solution concentration,...     

Dual Lewis Acid-Base Sites Regulate Silver-Copper Bimetallic Oxide Nanowires for Highly Selective Photoreduction of Carbon Dioxide to Methane

Highly selective photoreduction of CO₂ to valuable hydrocarbons is of great importance to achieving a carbon-neutral society. Precisely manipulating the formation of the Metal₁⋅⋅⋅C=O⋅⋅⋅Metal₂ (M₁⋅⋅⋅C=O⋅⋅⋅M₂) intermediate on the photocatalyst interface is the most critical step for regulating selectivity, while still a significant challenge. Herein, inspired by the polar electronic structure feature of CO₂ molecule, we propose a strategy whereby the Lewis acid-base dual sites confined in a bimetallic catalyst surface are conducive to forming a M₁⋅⋅⋅C=O⋅⋅⋅M₂ intermediate precisely, which can promote selectivity to hydrocarbon formation. Employing the Ag₂Cu₂O₃ nanowires with abundant Cu⋅⋅⋅Ag Lewis acid-base dual sites on the preferred exposed {110} surface as a model catalyst, 100 % selectivity toward photoreduction of CO₂ into CH₄ has been achieved. Subsequent surface-quenching experiments and density functional theory (DFT) calculations verify that the Cu⋅⋅⋅Ag Lewis acid-base dual sites do play a vital role in regulating the M₁⋅⋅⋅C=O⋅⋅⋅M₂ intermediate formation that is considered to be prone to convert CO₂ into hydrocarbons. This study reports a highly selective CO₂ photocatalyst, which was designed on the basis of a newly proposed theory for precise regulation of reaction intermediates. Our findings will stimulate further research on dual-site catalyst design for CO₂ reduction to hydrocarbons.