Observing Exoplanets with High-dispersion Coronagraphy. II. Demonstration of an Active Single-mode Fiber Injection Unit

Abstract

High-dispersion coronagraphy (HDC) optimally combines high-contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a critical pathway toward fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we demonstrate an innovative concept for injecting the directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). Our laboratory demonstration includes three key milestones: close-to-theoretical injection efficiency, accurate pointing and tracking, and on-fiber coherent modulation and speckle nulling of spurious starlight signal coupling into the fiber. Using the extreme modal selectivity of single-mode fibers, we also demonstrated speckle suppression gains that outperform conventional image-based speckle nulling by at least two orders of magnitude.

Vortex fiber nulling for exoplanet observations: conceptual design, theoretical performance, and initial scientific yield predictions

“…[22][23][24][25] Coronagraph instruments are also starting to take advantage of SMFs for improving the rejection of stellar speckles in cases where the planet is spatially resolved from the star. 26,27 Thus, the optics required for VFN are readily available and may be commonplace in future adaptive optics (AO) instruments designed for exoplanet science.…”

Nulling at short wavelengths: theoretical performance constraints and a demonstration of faint companion detection inside the diffraction limit with a rotating-baseline interferometer

“…2), the NSC algorithm can be seen as the interferometric "dark fringe" analog of coronagraphic dark-speckle companion-detection techniques that operate at intensity minima within coronagraphic dark holes (Labeyrie 1995). Indeed, the coupling of SM fibers to specific locations within dark holes serves to complete the analogy (Mawet et al 2017). The two techniques differ mainly in the number of subapertures contributing to the dark field, ranging from the number of deformable-mirror elements in the coronagraphic case to a pair of much larger apertures in the single-baseline nulling interferometer case.…”

High-contrast Demonstration of an Apodized Vortex Coronagraph

“…A fiber injection unit is planned for HCST, with which we will perform WFSC through a single mode fiber (SMF) with the purpose of paving the way for high-dispersion corona-graphy (Sparks & Ford 2002;de Kok et al 2014;Kawahara et al 2014;Snellen et al 2015;Mawet et al 2017;Wang et al 2017). Indeed, using an SMF to recover the planet signal improves the sensitivity to planet signal in the presence of starlight noise by virtue of the modal selectivity of the fiber.…”