We report results of the impact of fiber fusion splicing on Focal Ratio Degradation (FRD) and transmission loss of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) fiber system. We test at f/5 input f-ratio conditions, the influence of fiber fusion splicing on FRD and transmission respectively in the laboratory. A precision test system was designed to reduce the system error and human error. The measurement accuracy of the system reaches micron scale. The fiber end surface was prepared by large core fiber cutter, grinder and fusion splicing workstation. The fiber surface roughness is less than 1 micron and the surface angle is less than 0.5°. By optimize the cutting and polish process, adjusted the fusion parameters, a satisfactory results of optical fiber fusion obtained in the laboratory. The maximum transmission increase caused by the fiber fusion is less than 3%, average value is about 1%; while the maximum FRD increase is about 0.12°. We repaired 14 damaged optical fibers of LAMOST fiber system by use fiber fusion method, and the average peak light intensity of the repaired fiber reaches more than 90% of the peak light intensity of the normal use fiber in action. Our results indicate that fiber fusion technology can be adopted for repair failure optical fiber, replace the fiber clips and astronomical instrument construction.
LAMOST is a special Schmidt telescope with 16 spectrographs. Through these spectrographs, it can detect 4000 stellar spectra via optical fibers. Before the year of 2017 LAMOST’s spectrograph only work on low resolution spectrograph(LRS) mode, and recently we have finished the update of optical, mechanical structure and control system of these 16 spectrographs which could switch working mode between low resolution and middle resolution spectrograph(MRS) to meet the needs of LAMOST Phase II Sky Survey. Due to the strict optical performance requirements and the close arrangement of the optical equipment on the spectrograph platform, the control system must be quite accurate, stable and reliable. In this paper, we mainly describe the design and improvements of the spectrograph control system of the LAMOST’s spectrographs, including shutter sub-system control, back-illuminate sub-system control, LRS/MRS switch sub-system control, camera lens electric focus sub-system control, and some other sub-systems in LAMOST’s spectrograph control system. What’s more, there are also some connections between different sub-systems. As a result, we use FPGA chip as the main spectrograph controller, and make some improvements not only on host-computer software program, but also on slave-FPGA controller software and hardware design. The FPGA controller does some logical judgements according to the feedback information provided by the position sensor and the working mode designed to suit for different working condition. In this way, we make the spectrograph work more accurate and stable, and make it more safety and reliable especially on switching between LRS mode and MRS mode. Through those design and improvements on spectrograph’s control system mentioned in this paper, LAMOST could get more high-quality star spectral data from its 16 spectrographs.
We report results of the impact of fiber fusion splicing on Focal Ratio Degradation and transmission loss. Experiment use formed beam methods at wavelengths between 400 and 1000nm of Polymicro fiber. We test at five input f-ratio (f/2.5, f/3.75, f/5, f/75, f/10) conditions, the influence of fiber fusion splicing on FRD respectively, and test at f/5 input fratio condition, the influence of fiber fusion splicing on fiber transmission loss. A precision test system was designed to reduce the system error and human error. The measurement accuracy of the system reaches micron scale. The fiber end surface was prepared by large core fiber cutter, grinder and fusion splicing workstation. The fiber surface roughness is less than 1 micron and the surface angle is less than 0.5 deg. By optimize the cutting and polish process, adjusted the fusion parameters, a satisfactory results of optical fiber fusion obtained in the laboratory. The maximum transmission increase caused by the fiber fusion is less than 2%, average value is less than 1%; while the maximum FRD increase is less than 0.16 degrees. Our results indicate that fiber fusion technology can be adopted for repair failure optical fiber, replace the fiber clips and astronomical instrument construction.
The non-redundant aperture masking techniques transforms telescope into a Fizeau interferometer by a simple action of placing an aperture mask over the pupil, the limited resolution set by atmospheric fluctuations can be overcome by closure phase techniques to obtain diffraction-limited images. For binary stars, the closure phases can not only eliminate the influence of atmospheric fluctuations on ground-based optical telescope, but also have a functional relationship with contrast and angular separation of binary stars. In this paper, basing on the mathematical model of non-redundant aperture masking detecting binary stars, we carry out the computer simulation and laboratory experiment by using the Golay-6 mask.
The LAMOST completed its first five years of operation in June 2017, and 9 million low resolution spectra are obtained. The spectrographs have been upgraded in 2017, and the resolution can reach up to 7500(with 2/3 slit). In the midresolution mode, the wavelength can cover 495nm-535nm(blue band) and 630nm-680nm(red band). The LAMOST will carry out the middle resolution spectroscopic survey in September 2018, and 3 million middle resolution spectra will be obtained. This paper describes the requirements, optical design and mechanical design of the LAMOST-MRS (the LAMOST middle resolution spectrograph)
Exoplanet detection, a highlight in the current astronomy, will be part of puzzle in astronomical and astrophysical future,
which contains dark energy, dark matter, early universe, black hole, galactic evolution and so on. At present, most of the
detected Exoplanets are confirmed through methods of radial velocity and transit. Guo shoujing Telescope well known
as LAMOST is an advanced multi-object spectral survey telescope equipped with 4000 fibers and 16 low resolution fiber
spectrographs. To explore its potential in different astronomical activities, a new radial velocity method named
Externally Dispersed Interferometry (EDI) is applied to serve Exoplanet detection through combining a fixed-delay
interferometer with the existing spectrograph in medium spectral resolution mode (R=5,000-10,000). This new
technology has an impressive feature to enhance radial velocity measuring accuracy of the existing spectrograph through
installing a fixed-delay interferometer in front of spectrograph. This way produces an interference spectrum with higher
sensitivity to Doppler Effect by interference phase and fixed delay. This relative system named Multi-object Exoplanet
Search Spectral Interferometer (MESSI) is composed of a few parts, including a pair of multi-fiber coupling sockets, a
remote control iodine subsystem, a multi-object fixed delay interferometer and the existing spectrograph. It covers from
500 to 550 nm and simultaneously observes up to 21 stars. Even if it’s an experimental instrument at present, it’s still
well demonstrated in paper that how MESSI does explore an effective way to build its own system under the existing
condition of LAMOST and get its expected performance for multi-object Exoplanet detection, especially instrument
stability and its special data reduction. As a result of test at lab, inside temperature of its instrumental chamber is stable
in a range of ±0.5degree Celsius within 12 hours, and the direct instrumental stability without further observation
correction is equivalent to be ±50m/s every 20mins.
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.
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
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.
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.
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.
This paper presents details of a novel photoelectric system for intelligent structural health monitoring in aircrafts.
Through light intensity-based experiments about loads and damages of an aircraft composite structure conducted in this
paper, the potential for structural health monitoring of the composite material is discussed. Firstly, the paper
demonstrates the design of a novel photoelectric system including an optical part and a circuit part. The former part
consists of a light resource group and fiber optical sensors. And the latter part of this system is composed of a monitoring
host and a computer, both of which work together under the instructions given by self-designed software. The schematic
hardware diagram and the flow chart of the main program of the software are specified in this paper. In order to assess
the monitoring effect, the loads experiments are carried out at different locations of a test object in which special optical
fibers are buried. Finally, the degrees of loads and damages are measured and the experimental results are discussed.
Results obtained offer feasibilities of employing the proposed photoelectric system as a monitoring device for load and
damage detection in intelligent composite structures.