Lei Wang

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (13)0 Total impact

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    ABSTRACT: The increasing number of spectral survey telescopes that are soon commissioned for exploring the universe will confront us with many new challenges on the use of optical fibers. A fiber-switching problem for telescope's terminal instrument is as important as a well-known problem of positioning fibers on telescope's focal plane. For a modern survey telescope, it generally feeds several terminal instruments with different functions. According to the observation, these instruments are seriously in need of switching fiber-link with telescope as soon as possible. A kind of multi-fiber coupling plugs introduced in this paper will work for switching fiber-link between Multi-object Exoplanet Search Spectral Interferometer (MESSI) and low resolution spectrograph at Guoshoujing telescope (LAMOST). It includes an inserter, a receptor and a socket in general. The number of simultaneously coupling fibers is up to 25 per group, and any broken fiber in a single plug can be replaced by a new standard one soon without wasting entire fiber bundle. In addition, Most of mechanical part can also be individually replaced when a normal loss happens after a long working time. The related test result is given in detail, including the machining precision and coupling efficiency.
    03/2014;
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    ABSTRACT: The design, construction, and preliminary test of an advanced image slicer(AIS) Integral Field Unit(IFU) experiment system is introduced in the paper.The ultimate optimized IFU will be installed for further test on 1m Telescope in Wei Hai. This IFU employs an all-mirror design associated with a classical spectrograph. It operates in the visible wavelength range (380nm -770nm) and divides the telescopic field of view into the nine sub-fields. This paper also describes the components test results and overall IFU system performance. At last, we discuss some possible science applications by using the IFU on Chinese small telescopes.
    Proc SPIE 10/2012;
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    ABSTRACT: Optical interferometry isn't only widely applied into optical workshop, but also makes great contribution in astronomical observation. A multi-object fixed delay Michelson interferometer commissioned to search extra-solar planet (exoplanet) is introduced here. Fixed delay of 1.9mm, which is good for stellar radial velocity measuring precision, is obtained by two interference arms with different materials. This configuration has different refractive indexes and physical characteristics so that supplies wider field of view and better thermal stability. In addition, compact interference component with three glued prisms and smart structure are the other important features. Because of vibration influence, the combination among the prisms is a direct and effective method. And the reason why make the structure as small as possible is of central obscuration under the workspace of interferometer.
    Proc SPIE 10/2012;
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    ABSTRACT: One of the Large Sky Area Multi-Object Spectroscopic Telescope (LAMOST) scientific requirements require the ability of the low resolution spectrograph(LRS) to measure velocities to a accuracy of 4km/s over the entire 5 degree field in 2 hours objects observation. This requirement results in the specification of image movement less than 0.6μm/hours (0.05pixl/hours corresponding to the science detector).There are 16 spectrographs for LAMOST telescope, so we expect the design aspects of the instrument directed towards achieving the stability goal. In this paper we present the last design aspects of the instrument which enable meeting the 4km/s requirement, and the recent test results of the LRS's Stability Performance. The test results show that the stability performance of LAMOST-LRS can meet the the stability goal, the image shift along the direction of dispersion is not influenced by the external factors, and the image shift along vertical dispersion direction meet the technical requirements when the environmental temperature of the spectrograph room is in control.
    Proc SPIE 09/2012;
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    ABSTRACT: It's a very important point that fully open up power of Gou Shoujing telescope (LAMOST) in exoplanet detection field by developing a multi-exoplanet survey system. But it's an indisputable truth in the present astronomy that a traditional type of multi-object high resolution spectrograph is almost impossible to be developed. External Dispersed Interferometry is an effective way to improve the radial velocity measuring accuracy of medium resolution spectrograph. With the using of this technique, Multi-object Exoplanet Search Spectral Interferometer (MESSI) is an exploratory system with medium measuring accuracy based on LAMOST low resolution spectrograph works in medium-resolution mode (R=5,000 - 10,000). And it's believed that will bring some feasible way in the future development of multi-object medium/high resolution spectrograph. After prototype experiment in 2010, a complete configuration is under the development, including a multi-object fixed-delay Michelson interferometer, an iodine cell with multi-fiber optical coupling system and a multi-terminal switching system in an efficient fiber physical coupling way. By some effective improvement, the interferometer has smaller cross section and more stable interference component. Moreover, based on physical and optical fiber coupling technique, it's possible for the iodine cell and the switching system to simultaneously and identically coupling 25 pairs of fibers. In paper, all of the progress is given in detail.
    Proc SPIE 09/2012;
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    ABSTRACT: The China-made telescope, LAMOST, consists of 16 Spectrographs to detect stellar spectra via 4000 optical fibers. In each spectroscope, many movable parts work in phase. Those parts are real-time controlled and managed by field controllers based on FPGA. The master control board of controllers currently being used is constructed by Altera's Cyclone II Development Kit. However, now Altera no longer produce such Kits. As the needs for maintenance and improvement, a backup control board is developed, so that once any field controller is broken, another can changed in time to ensure the control system not being interrupted. Using the newer Altera FPGA chip 3C40 as master control chip can minimize the change in the original design frame of the control structure so as to reduce the workload of software and hardware migration. This paper describes the design process of the Spectrographs backup field controller based on Cyclone 3C40 and gives the problems and solutions encountered during migration for controller hardware and software. The improved field controller not only retains the original controller functions, but also can serve for more motors and sensors due to the increase of input and output pins. Besides, no commodity supply limits, which saves expenses. The FPGA-field controller can also be used in other telescopes, astronomical instruments and industrial control systems as well.
    Proc SPIE 09/2012;
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    ABSTRACT: The 16 low resolution spectrographs (LRS) have been successfully commissioned for the LAMOST. The LRS design employs a dual-beamed and bench-mounted, with large-beamed, fast Schmidt cameras and Volume Phase Holographic (VPH) transmission gratings. The design wavelength range is 370-900nm, at resolutions of R=1000and R=10000. Each spectrograph is fed by 250 fibers with 320 micron in diameter (corresponding 3.3 arcsec), composed of one F/4 Schmidt collimator, a dichroic beam-splitter, four VPH gratings, articulating Schmidt cameras that are optimized at blue band (370-590 nm) and red band (570-900 nm), and field lens near the focal plane service as the vacuum window of CCD detector cryogenic head. In this paper, we present the testing result of the LRS on the image quality, spectra resolution, efficiency and observing spectra.
    Proc SPIE 07/2010;
  • Kai Zhang, Yongtian Zhu, Lei Wang
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    ABSTRACT: Chinese national science project-LAMOST successfully received its official blessing in June, 2009. Its aperture is about 4m, and its focal plane of 1.75m in diameter, corresponding to a 5° field of view, can accommodate as many as 4000 optical fibers, and feed 16 multi-object low-medium resolution spectrometers (LRS). In addition, a new technique called External Dispersed Interferometry (EDI) is successfully used to enhance the accuracy of radial velocity measurement by heterodyning an interference spectrum with absorption lines. For further enhancing the survey power of LAMOST, a major astronomical project, Multi-object Exoplanet Survey System (MESS) based on this advanced technique, is being developed by Nanjing Institute of Astronomical Optics and Technology (NIAOT) and National Astronomical Observatories of China (NAOC), and funded by Joint Fund of Astronomy, which is set up by National Natural Sciences Foundation of China (NSFC) and Chinese Academy of Sciences (CAS). This system is composed of a multi-object fixed delay Michelson interferometer (FDMI) and a multi-object medium resolution spectrometer (R=5000). In this paper, a prototype design of FDMI is given, including optical system and mechanical structure.
    Proc SPIE 07/2010;
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    ABSTRACT: The China-made telescope, LAMOST, consists of 16 spectroscopes to detect stellar spectra via 4000 optical fibers. In each spectroscope, many movable parts work in phase. Those parts are real-time controlled and managed by field controllers based on FPGA. This paper mainly introduces how to use DSP Builder module library in MATLAB / Simulink to construct the IP control core on FPGA chip. This method can also be used to design the control core of PID arithmetic, to carry out arithmetic simulation and generate VHDL language file, as well as to integrate it into SOPC developing environment so as to repeatedly use. In this way, the design period of the control system may be shortened and design process simplified. Finally due to the reversibility and programmability of the IP control core ,a system on a chip for field controllers of spectroscope is realized, which meets astronomical control requirements, providing an effective scheme for embedded system in astronomical instrument applications.
    Proc SPIE 07/2010;
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    ABSTRACT: A large Schmitt reflector telescope, Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST), is being built in China, which has effective aperture of 4 meters and can observe the spectra of as many as 4000 objects simultaneously. To fit such a large amount of observational objects, the dispersion part is composed of a set of 16 multipurpose fiber-fed double-beam Schmidt spectrographs, of which each has about ten of moveable components realtimely accommodated and manipulated by a controller. An industrial Ethernet network connects those 16 spectrograph controllers. The light from stars is fed to the entrance slits of the spectrographs with optical fibers. In this paper, we mainly introduce the design and realization of our real-time controller for the spectrograph, our design using the technique of System On Programmable Chip (SOPC) based on Field Programmable Gate Array (FPGA) and then realizing the control of the spectrographs through NIOSII Soft Core Embedded Processor. We seal the stepper motor controller as intellectual property (IP) cores and reuse it, greatly simplifying the design process and then shortening the development time. Under the embedded operating system muC/OS-II, a multi-tasks control program has been well written to realize the real-time control of the moveable parts of the spectrographs. At present, a number of such controllers have been applied in the spectrograph of LAMOST.
    Proc SPIE 08/2008;
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    ABSTRACT: The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project is one of the National Major Scientific Projects undertaken by the Chinese Academy of Science. There are 16 low resolution multipurpose fiber-fed spectrographs in total, enabling it to obtain the spectrum of celestial objects as faint as down to 20.5. Building auto-focusing systems for the spectrographs is important due to the popularity of instruments. The system enables the optical system to automatically compensate changes in accordance to external variables, such as temperature, timidity, to ensure the spectrum collected more reliably. Image-based algorithm is utilized to calculate the departure of CCD plane from optical focal plane. The calculation also aids to regulation of the system. The defocus value is transformed to the controlling computer of each spectrograph. A driving step-motor performs refocusing function by moving the fiber slit unit to its right position.
    Proc SPIE 11/2007;
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    ABSTRACT: A multipurpose fiber-fed double-beam Schmidt spectrograph using VPHG (volume phase holographic gratings) is under construction for LAMOST (The Large Sky Area Multi-Object Fiber Spectroscopic Telescope). There are 16 such spectrographs (hereafter referred to as LRSs) for the project. The spectrographs are designed with wavelength coverage from 370 to 900 nm, with spectral resolutions of 1000-10000, and with multi-object capability over a 5 degrees field of view. Each spectrograph will be accommodating 250 fibers of 320 microns diameter (corresponding 3.3 arcsecs). The 200 mm diameter collimated beam is split into two separate channels. The blue channel is optimized for 370nm-590nm, and the red channel for 570nm-900nm. The LRS can work in several varied resolution modes. The optical design and performance is described. The spectrograph is of simple design with moderate image quality and good throughput. Progress on the construction of LRS is reported as well.
    Proc SPIE 01/2006;
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    ABSTRACT: A preliminary design study for a high-resolution echelle spectrograph to be used for LAMOST (The large Sky Area Multi-Object Fiber Spectroscopic Telescope) that is currently under construction is presented. In order to obtain a resolution-slit product of about 40000 as required by science case, the less expensive design used a 105mm beam feeding a 408mm deep Echelle is good solution. The optical design of high resolution Echelle spectrograph for LAMOST is given. This spectrograph will be more powerful tool for astrophysical research using high-resolution spectroscopy in China. Some new technology and novel design concepts have been adopted in this spectrograph, such as white pupil collimator system, R4 Echelle with large blaze angle, and the fold and off-axial Schimidt camera without center obstruction and so on.
    Proc SPIE 09/2004;