Demonstration of a speckle nulling algorithm and Kalman filter estimator with a fiber injection unit for observing exoplanets with high-dispersion coronagraphy

J. Astron. Telesc. Instrum. Syst.

Ruane

Mawet

et al. 2019

Demonstration of an electric field conjugation algorithm for improved starlight rejection through a single mode optical fiber,"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 ¼ 635 nm through the fiber (100× suppression factor) and 2 × 10 −5 in Δλ∕λ ¼ 8% broadband light about λ ¼ 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.

Section: Perspectivesmentioning

confidence: 99%

Demonstration of an electric field conjugation algorithm for improved starlight rejection through a single mode optical fiber

J. Astron. Telesc. Instrum. Syst.

Ruane

Mawet

et al. 2019

“…Below is a recap of the results from Xin et al 2018, the experiments of which were conducted using the same laboratory setup.…”

Section: Previous Resultsmentioning

confidence: 99%

“…Using all 500 iterations, a contrast improvement of 10% was found. 5 Figure 6. The raw contrast readings for speckle nulling both with and without the Kalman filter.…”

Section: Previous Resultsmentioning

confidence: 99%

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Novel implementation of a Kalman filter for speckle nulling with a fiber injection unit

Zhang

Techniques and Instrumentation for Detection of Exoplanets IX

Jovanović

et al. 2019

Self Cite

High dispersion coronagraphy (HDC) is a technique that combines high contrast imaging techniques with high spectral resolution spectroscopy to directly characterize exoplanets and provide key information such as chemical composition, temperature, and rotational velocity. A consequence of adaptive optics systems used in direct imaging is the formation of residual bright spots of star lights, called speckles, in the final image. Due to the large difference in brightness between host stars and their planets, these speckles can easily obscure potential exoplanets. In a previous demonstration, it was shown that using monochromatic light and a fiber injection unit (FIU), simulated exoplanet light can be directed to a high-resolution spectrograph. The method had speckle suppression that exceeding conventional image-based speckle nulling. With a previous Kalman filter estimator implementation, we found that with the implementation of the algorithm, speckle suppression was even more stable and outperformed traditional speckle nulling. In this update to the estimator, progress has been made in terms of a new filter design, and better estimates of the physical parameters in the laboratory, resulting in a higher speckle nulling performance.

“…A Kalman Filter was implemented for Speckle Nulling by Xin et al in these proceedings, 9 in which the control history, and previous measurements, were used to achieve a more stable null through the SMF, and an overall better raw contrast, in the order of 10% improvement. A Kalman Filter Estimator for EFC was proven Figure 7.…”

Section: Future Work and Conclusionmentioning

confidence: 99%

Wavefront control for minimization of speckle coupling into a fiber injection unit based on the electric field conjugation algorithm

Adaptive Optics Systems VI

Mawet

Ruane

et al. 2018

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