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Opto-Electronic Advances 第2卷 第10期

Author Affiliations
Abstract
Opto-Electronic Advances
2019, 2(10): 1
Tao Tang 1,2Shuaixu Niu 1,2,3Jiaguang Ma 1,2Bo Qi 1,2,*[ ... ]Yongmei Huang 1,2
Author Affiliations
Abstract
1 Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
2 Key Laboratory of Optical Engineering, Chinese Academy of Sciences, Chengdu 610209, China
3 University of Chinese Academy of Sciences, Beijing 100049, China
Structural vibrations in Tip-Tilt modes usually affect the closed-loop performance of astronomically optical telescopes. In this paper, the state of art control methods—proportional integral (PI) control, linear quadratic Gaussian (LQG) control, disturbance feed forward (DFF) control, and disturbance observer control (DOBC) of Tip-Tilt mirror to reject vibrations are first reviewed, and then compared systematically and comprehensively. Some mathematical transformations allow PI, LQG, DFF, and DOBC to be described in a uniform framework of sensitivity function that expresses their advantages and disadvantages. In essence, feed forward control based-inverse model is the main idea of current techniques, which is dependent on accuracies of models in terms of Tip-Tilt mirror and vibrations. DOBC can relax dependences on accuracy model, and therefore this survey concentrates on concise tutorials of this method with clear descriptions of their features in the control area of disturbance rejections. Its applications in various conditions are reviewed with emphasis on the effectiveness. Finally, the open problems, challenges and research prospects of DOBC of Tip-Tilt mirror are discussed.
structural vibrations astronomical telescope Q-filter error-based DOBC Tip-Tilt mirror 
Opto-Electronic Advances
2019, 2(10): 190011
Author Affiliations
Abstract
School of Engineering, University of Tokyo, Tokyo 113-8656, Japan
Silicon dominates the contemporary electronic industry. However, being an indirect band-gap material, it is a poor absorber of light, which decreases the efficiency of Si-based photodetectors and photovoltaic devices. This review highlights recent studies performed towards improving the optical absorption of Si. A summary of recent theoretical approaches based on the first principle calculation has been provided. It is followed by an overview of recent experimental approaches including scattering, plasmon, hot electron, and near-field effects. The article concludes with a perspective on the future research direction of Si-based photodetectors and photovoltaic devices.
Si indirect band gap plasmon first principle calculation near-field effect 
Opto-Electronic Advances
2019, 2(10): 190023

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