Acta Photonica Sinica, Volume. 52, Issue 5, 0552212(2023)

Multi-objects Spectroscopy with Compact Arranged Optical Waveguides

Dong LIN1,2,3, Zhuangzhuang ZHU1,2,3, Jijun FENG4, and Jinping HE1,2,3,5、*
Author Affiliations
  • 1National Astronomical Observatories/Nanjing Institute of Astronomical Optics & Technology, Laboratory of Solar and Space Instrument, Nanjing 210042, China
  • 2CAS Key Laboratory of Astronomical Optics & Technology, Nanjing 210042, China
  • 3University of Chinese Academy of Sciences, Beijing 100049, China
  • 4University of Shanghai for Science and Technology, School of Optical-Electrical and Computer Engineering, Shanghai 200093, China
  • 5College of Nanjing, University of Chinese Academy of Science, Nanjing 211135, China
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    Multi-object spectroscopic detection has become one of the most important tools in astronomical observation, as it can simultaneously obtain a large amount of spectral information from celestial bodies. Astronomers have developed numerous research achievements in galaxy structure and evolution, outer planet detection and research, and cosmic large-scale structures and evolution through massive spectral data. The astronomical community has set up multiple large-scale spectral survey dedicated telescopes, obtaining tens of millions of spectral information in the past few decades. However, compared to the vast number of celestial bodies in the universe, the current amount of spectral data is still insignificant. For instance, the number of galaxies alone may exceed 100 billion, with an extremely large number of celestial bodies in each galaxy, such as the 100 billion to 400 billion stars in our Milky Way galaxy. Therefore, there is still much more unknown information waiting for exploration. In recent years, China has been actively promoting the second-phase project of survey telescopes and the establishment of new large-scale survey telescopes to maintain its world-leading position in large-scale spectroscopic survey technology and corresponding astronomical scientific research. This requires a significant increase in the number of multi-object spectroscopic detections. However, observing so many celestial spectra at the same time still presents significant technological and cost challenges. Currently, multi-object spectroscopy is generally based on fiber optic spectrographs. After collecting multi-object signals at the telescope focal plane, numerous fibers form a one-dimensional array at the entrance slit of the spectrograph, ultimately achieving multi-target spectral detection on a single instrument. With the same physical field of view, known large multi-object fiber optic spectrographs can measure hundreds of celestial spectra simultaneously due to their close to 300 mm aperture. However, only synchronously observing several hundred targets is far from sufficient when compared to the vast number of observation targets. Enlarging the aperture requires the use of large optical components, which not only brings about technical issues in manufacturing, modulation, and control but also causes an exponential increase in cost. Moreover, the spatial arrangement of input fibers in multi-object fiber optic spectrographs has reached a theoretical limit. When light energy propagates through optical fibers, it is mainly localized in the core, while the coating layer that each fiber independently possesses restricts further narrowing of the core distance, which may affect the pixel utilization efficiency of the astronomical detector, whose price is extremely high. In the observation environment with minimal disturbances from space and atmospheric turbulence, coupling efficiency can be achieved with small fiber cores, making the problem of detector utilization efficiency more serious. Therefore, at present, the method to enhance the observing quantity mainly relies on building more telescopes and terminal instruments, which will also exponentially increase costs, making it equally unacceptable. To solve this problem, this research uses dense waveguide photonic chips as the multi-object input mechanism and verifies in experiments that this device can effectively reduce the influence of large fiber cladding on fiber spatial arrangement, improving the detection efficiency of multi-object spectroscopy by at least four times, and the chip's optical efficiency can be greater than 90%. The waveguides used in this paper adopt mature planar waveguide technology, combined with end-face coupling technology of fiber-optic-waveguide, have the potential for large-scale production, and do not incur additional technical costs. Since all input channels are integrated into the chip, all target spectra have negligible relative spatial movement on the detector, making the relative spectral drift between different channels almost zero, improving the wavelength accuracy or radial velocity detection accuracy.In addition, based on waveguide rearrangement, multi-object spectroscopic detection also has advantages in two-dimensional layout and greater design freedom, providing a competitive multi-object input mechanism solution for extremely large-scale observation, especially for spatially large-scale spectroscopic surveys or integral field astronomical observation.

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    Dong LIN, Zhuangzhuang ZHU, Jijun FENG, Jinping HE. Multi-objects Spectroscopy with Compact Arranged Optical Waveguides[J]. Acta Photonica Sinica, 2023, 52(5): 0552212

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    Paper Information

    Category: Special Issue for Advanced Science and Technology of Astronomical Optics

    Received: Mar. 6, 2023

    Accepted: Apr. 28, 2023

    Published Online: Jul. 19, 2023

    The Author Email: HE Jinping (jphe@niaot.ac.cn)

    DOI:10.3788/gzxb20235205.0552212

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