Demonstration of an electric field conjugation algorithm for improved starlight rejection through a single mode optical fiber
Demonstration of an electric field conjugation algorithm for improved starlight rejection through a single mode optical fiber
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DOI：
10.1117/1.jatis.5.1.019004
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发表时间：
2019-03
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通讯作者：
Jorge Llop Sayson;G. Ruane;D. Mawet;N. Jovanovic;B. Calvin;N. Levraud;M. Roberson;J. Delorme;D. Echeverri;N. Klimovich;Y. Xin
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作者：
Jorge Llop Sayson;G. Ruane;D. Mawet;N. Jovanovic;B. Calvin;N. Levraud;M. Roberson;J. Delorme;D. Echeverri;N. Klimovich;Y. Xin
摘要。通过单模光纤将日冕仪与摄谱仪连接起来，是利用当前和未来的地面和太空望远镜详细描述系外行星大气的一条途径。然而，考虑到行星和主星之间的极端亮度比和很小的角距，行星的信噪比可能会受到不必要的星光耦合到光纤中的限制。为了解决这个问题，我们利用一个波前控制回路和一个可变形的镜子，通过测量通过光纤传输的光线来系统地拒绝来自光纤的星光。波前控制算法基于电场共轭（EFC）的形式，在我们的情况下，它解释了光纤的空间模式选择性。这是通过使用控制输出来实现的，该输出是电场与单模光纤基模的重叠积分。这个量可以通过使用可变形镜注入的成对成像平面探头来估计。我们提供的仿真和实验室结果表明，相对于传统的EFC控制器，我们的方法在通过光纤抑制星光方面提供了显着改进。在我们的实验装置中，在角距为4λ / D的光纤中，初始归一化强度为3 × 10−4，通过光纤（100倍抑制因子），在λ = 635 nm的单色光中，我们获得了最终归一化强度为3 × 10−6，在Δλ / λ = 8%的宽带光中，约λ = 625 nm（10倍抑制因子），最终归一化强度为2 × 10−5。基于光纤的方法提高了高对比度下光谱测量的灵敏度，可以作为未来天基系外行星成像任务以及地面仪器的组成部分。
Abstract. Linking a coronagraph instrument to a spectrograph via a single-mode optical fiber is a pathway toward detailed characterization of exoplanet atmospheres with current and future ground- and space-based telescopes. However, given the extreme brightness ratio and small angular separation between planets and their host stars, the planet signal-to-noise ratio will likely be limited by the unwanted coupling of starlight into the fiber. To address this issue, we utilize a wavefront control loop and a deformable mirror to systematically reject starlight from the fiber by measuring what is transmitted through the fiber. The wavefront control algorithm is based on the formalism of electric field conjugation (EFC), which in our case accounts for the spatial mode selectivity of the fiber. This is achieved by using a control output that is the overlap integral of the electric field with the fundamental mode of a single-mode fiber. This quantity can be estimated by pairwise image plane probes injected using a deformable mirror. We present simulation and laboratory results that demonstrate our approach offers a significant improvement in starlight suppression through the fiber relative to a conventional EFC controller. With our experimental setup, which provides an initial normalized intensity of 3 × 10 − 4 in the fiber at an angular separation of 4λ / D, we obtain a final normalized intensity of 3 × 10 − 6 in monochromatic light at λ = 635 nm through the fiber (100 × suppression factor) and 2 × 10 − 5 in Δλ / λ = 8 % broadband light about λ = 625 nm (10 × suppression factor). The fiber-based approach improves the sensitivity of spectral measurements at high contrast and may serve as an integral part of future space-based exoplanet imaging missions as well as ground-based instruments.