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Chen F.,Beijing Institution of Space Mechanics and Electricity | Xu P.-M.,Beijing Institution of Space Mechanics and Electricity
Guangxue Jingmi Gongcheng/Optics and Precision Engineering | Year: 2011

The interference between the optical paths in a broadband astignatism-free Gzerny-Turner spectrometer which uses spherical optics and a plane grating was introduced theoretically. To eliminate the interference, the zeroth-order and first-order astigmatism-free conditions of the Czerny-Turner spectrometer was researched and several situations of optical path interference satisfied the astigmatism-free conditions were analyzed. Based on the astigmatism-free conditions and avoidance conditions of optical structure interference, the selection principles of the incidence angles θC and θF were deduced, and the optimization approach was summarized. Then, the optical system of Czerny-Turner spectrometer which will be loaded on a spacecraft was designed according to the method whose selection principle was verified by using ray-tracing method. The results show that the obtained imaging quality has a good spectral resolution, which validates that the Czerny-Turner spectrometer can satisfy the requirements both for eliminating astigmatism and for avoiding optical structure interference. In conclusion, the method can help the spectrometer more compact and more efficient. Source


Wu C.,Beijing Institution of Space Mechanics and Electricity | Lin Z.,Beijing Institution of Space Mechanics and Electricity
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Inertially stabilized platform (ISP) is indispensable for various imaging systems to segregate the base angular movement and achieve high LOS (Line-Of-Sight) stability. The disturbance rejection ratio and command following performance are of primary concern in designing ISP control systems. In this paper, the redundant gimbals ISP system is considered and it is shown to experience complex disturbance and parameter variation during operation. To meet advanced LOS stabilization requirement, a disturbance observer based (DOB) dual-loop controller design for ISP is proposed of which the DOB is the internal-loop. Using a nominal plant model and a low-pass filter, the disturbance signal is estimated and used as a cancellation input added to the current command of torque motor. If the DOB works well, the disturbance torque and mismatch between nominal plant and actual plant will be compensated and the internal-loop will behave as nominal model parameters. On the other hand, the external-loop will be designed for nominal model parameters to meet stabilization requirements. This paper will mainly focus on the DOB design method. Since the low-pass filter of DOB determines the sensitivity and complementary sensitivity function as will be shown in this paper, designing the filter is the most important consideration. In this paper, an optimal low-pass filter design method is proposed. The method is intuitive, simple to implement and allows on-line tuning. Simulation results show the performance enhancement of our control structure in the presence of disturbance and measurement noise. © 2012 SPIE. Source


Chen F.,Beijing Institution of Space Mechanics and Electricity | Xu P.,Beijing Institution of Space Mechanics and Electricity
Guangxue Xuebao/Acta Optica Sinica | Year: 2014

With the wide application of broadband imaging spectrometer in the ocean remote sensor, the depolarizer in front of the optical system must satisfy the high requirement. Based on the theory of matrix optics, Lyot depolarizer is introduced. According to the numerical analysis, the relationship between the residual polarization and the angle and thickness of the depolarizer is analyzed in the wide wavelength range. Combined with the residual polarization and resolution requirement of the optical system, a depolarizer used in a broadband imaging spectrometer is designed. With in the wavelength from 400 nm to 950 nm, when the spectral resolution is 4 nm, the residual polarizations of the depolarizer are less than 2% for arbitrary polarization of linear polarized. Source


Chen F.,Beijing Institution of Space Mechanics and Electricity | Li M.,Beijing Institution of Space Mechanics and Electricity | Xu P.,Beijing Institution of Space Mechanics and Electricity
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

With the wide application of broadband imaging spectrometer in the ocean remote sensor, the depolarizer in front of the optical system must satisfy the high requirement. Based on the character of simple structure and good stability, Lyot depolarizer is widely used in the fiber and grating spectrometer in which the polarization should be controlled strictly. Nowadays the design method of Lyot depolarizer based on the coherent condition is mostly used for laser and sensors of narrow band, not suitable for the broadband and high spectral resolution. According to the theory of matrix optics, the relationship between the residual polarization and the angle and thickness of the depolarizer has been analyzed in the wide wavelength range. The formula is too complicated to get an analysis solver. With the numerical results, as the wedge angle increasing the residual polarization dying oscillates to a stable value. As the crystal thickness increasing the value of residual polarization is oscillating to zero. As a result, increasing the wedge angle and the thickness both could reduce the residual polarization of the depolarizer, but considering the dimension and the resolution of the optical system the wedge angle and the thickness of the depolarizer have restrictions. The design process of Lyot depolarizer used for broadband are summarized as follows: 1. Using the numerical solution the variability of the residual polarization along the wedge angle and thickness are analyzed; 2. According to the requirement of the spectral resolution the wedge angle could be chosen; 3. While the wedge angle is curtained, based on the numerical results the suitable thickness could be solved satisfying the requirement of the residual polarization. This method can be widely applied to the depolarizer design in imaging spectrometer of broadband which can cover several hundred nanometers and high spectral resolution which is to several nanometers. In this article a Lyot depolarizer has been designed for a broadband imaging spectrometer used in ocean observation. In the wavelength from 400nm to 950nm, the residual polarizations of the depolarizer are less than 2%. This is necessary for the instrument to obtain the accurate radiance data of the target. © 2012 SPIE. Source

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