Next Generation OH Suppression Fiber Bragg Gratings: towards Operation on Sky

下一代 OH 抑制光纤布拉格光栅：面向天空运行

• 批准号: 455425131
• 负责人: Professor Dr. Stefan Nolte
• 金额: --
• 依托单位: Leibniz-Institut für Astrophysik Potsdam (AIP)
• 依托单位国家: 德国
• 项目类别: New Instrumentation for Research
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/455425131?language=en
• 关键词: Next; Generation; OH; Suppression; Fiber

Ground-based telescopes like the Extremely Large Telescope ELT operating in the near-infrared are one of the pillars of Astronomy for various science cases such as, e.g., the search for exoplanets, fundamental physics (dark matter, dark energy, universal validity of physics over cosmic time), black holes, nucleosynthesis in stars and the cycle of matter, the formation and evolution of galaxies. While atmospheric disturbances leading to deformations of the wavefront can be counteracted by adaptive optics, the sensitivity of these telescopes is severely hampered by strong atmospheric OH emission lines for low to medium resolution spectroscopy in the NIR. The intensity of these lines is several orders of magnitude larger than the extraterrestrial background of faint stars or galaxies and thus it contributes substantially to the stray light signals inside the spectrograph, making the measurement of the faint extraterrestrial signals very challenging. However, as the spectral width of these emission lines is only a few tens of picometer, narrow notch filters can be used to suppress them and reduce stray light within the instrument. Especially, fiber Bragg gratings (FBG), consisting of a periodic refractive index modulation in the fiber core, offer excellent properties to filter out the OH emission lines, which has been demonstrated before. Yet, in order to filter out a large number of OH emission lines, many individual gratings would have to be realized in series causing significant transmission loss. An alternative to a series of simple FBGs are aperiodic FBGs (AFBGs). The idea of AFBGs is to overlap several gratings with different resonance wavelengths inside the fiber core with a minimized superimposed refractive index modulation. Therefore, a single AFBG can reflect many wavelengths simultaneously to filter out a large number of OH emission lines. The OH-SUPER project aspires to realize a disruptive innovation for OH suppression in the NIR by joining the complementary expertise of the two research institutions involved to develop highly complex aperiodic gratings. A competitive implementation with two types of gratings (written by UV or fs-IR laser structuring) within a joint on-sky demonstrator will convince infrastructure operators such as ESO to implement a follow-up device using the best-performing solution at the telescope. The two major goals of OH-SUPER are, firstly, to develop UV and fs-NIR laser-based inscription techniques to be able to consistently deliver AFBGs suitable for OH suppression at the level of prototypes. Secondly, the resulting filters shall be integrated in an onsky demonstrator as a front-end subsystem to CARMENES at the 3.5m telescope of Calar Alto Observatory, Spain, to allow for a validation and comparative performance study.

地面望远镜，如在近红外线操作的极大望远镜ELT，是天文学的支柱之一，用于各种科学案例，例如，寻找系外行星、基础物理学（暗物质、暗能量、宇宙时间内物理学的普遍有效性）、黑洞、恒星核合成和物质循环、星系的形成和演化。虽然大气扰动导致的波前变形可以抵消自适应光学，这些望远镜的灵敏度是严重阻碍了强大气OH发射线的低至中分辨率光谱在近红外。这些谱线的强度比微弱恒星或星系的地外背景大几个数量级，因此它对光谱仪内的杂散光信号有很大贡献，使得测量微弱的地外信号非常具有挑战性。然而，由于这些发射线的光谱宽度只有几十皮米，因此可以使用窄陷波滤波器来抑制它们并减少仪器内的杂散光。特别是，光纤布拉格光栅（FBG），包括在光纤芯中的周期性折射率调制，提供了优良的性能，以过滤掉OH发射线，这已经证明了之前。然而，为了滤除大量的OH发射线，许多单独的光栅将不得不串联实现，从而导致显著的传输损耗。一系列简单FBG的替代方案是非周期性FBG（AFBG）。AFBG的想法是将具有不同谐振波长的几个光栅重叠在光纤芯内，使叠加的折射率调制最小化。因此，单个AFBG可以同时反射多个波长以滤除大量OH发射线。OH-SUPER项目旨在通过将两个研究机构的互补专业知识结合起来，开发高度复杂的非周期性光栅，实现近红外中OH抑制的颠覆性创新。在联合空中演示器中使用两种类型的光栅（由紫外或fs-IR激光结构写入）的竞争性实施将说服ESO等基础设施运营商在望远镜上使用性能最佳的解决方案来实施后续设备。OH-SUPER的两个主要目标是，首先，开发基于UV和fs-NIR激光的铭文技术，以便能够在原型水平上始终如一地提供适合OH抑制的AFBG。其次，将把得到的滤波器作为前端子系统集成到西班牙卡拉阿尔托天文台3.5米望远镜CARMENES的onsky演示器中，以便进行验证和比较性能研究。