密排光波导多目标光谱探测技术研究

Multi-objects Spectroscopy with Compact Arranged Optical Waveguides

利用密排波导光子芯片作为多目标输入机构,将多目标光谱仪同步探测能力提高至少4倍,且芯片光学效率大于90%。另外,由于各输入信道均被集成在芯片内,所有目标光谱在探测器上几无相对空间移动,有利于获取高光谱稳定性。本文研究有望为极多目标观测,尤其是空间大规模光谱巡天或积分视场天文观测提供有竞争力的多目标输入机构解决方案。

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 multiobject 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.