First on-sky demonstration of an integrated-photonic nulling interferometer: the GLINT instrument

Abstract

The characterisation of exoplanets is critical to understanding planet diversity and formation, their atmospheric composition and the potential for life. This endeavour is greatly enhanced when light from the planet can be spatially separated from that of the host star. One potential method is nulling interferometry, where the contaminating starlight is removed via destructive interference. The GLINT instrument is a photonic nulling interferometer with novel capabilities that has now been demonstrated in onsky testing. The instrument fragments the telescope pupil into sub-apertures that are injected into waveguides within a single-mode photonic chip. Here, all requisite beam splitting, routing and recombination is performed using integrated photonic components. We describe the design, construction and laboratory testing of our GLINT pathfinder instrument. We then demonstrate the efficacy of this method on sky at the Subaru Telescope, achieving a null-depth precision on sky of ∼ 10 −4 and successfully determining the angular diameter of stars (via their null-depth measurements) to milliarcsecond accuracy. A statistical method for analysing such data is described, along with an outline of the next steps required to deploy this technique for cutting-edge science.

Kernel nullers for an arbitrary number of apertures

“…No active long-baseline optical interferometer currently provides more than six sub-apertures. However, the masking of monolithic apertures to produce interferometric arrays is an established practice (Tuthill et al 2010;Jovanovic et al 2012) that may be used in conjunction with nulling interferometry (Norris et al 2020). Therefore, the use of even larger combiners may prove to be a viable alternatives to small inner working angle coronagraphs (Guyon et al 2006).…”

“…Although τ does not have the same robustness to aberrations, there may be ways to use it with the processing methods employed by Hanot et al (2011) and Norris et al (2020) so as to provide additional information on the target in different science cases. The kernel null κ is best suited for the study of high-contrast non-symmetrical features such as planetary companions, while τ may be used to study brighter symmetrical features such as debris disks or stellar envelopes.…”

“…This observing mode takes advantage of the spatial filtering provided by the resolving power of each of the 8 m telescopes of the Very Large Telescope Interferometer (VLTI), coupled into single mode fibers to reach the required contrast. Interferometric nullers (Bracewell 1978;Colavita et al 2009;Serabyn et al 2019;Hoffmann et al 2014;Defrère et al 2015;Norris et al 2020) offer the possibility to explore smaller angular separations through the use of fragmented apertures and long-baseline interferometry. Some combining solutions have been found that optimize the rejection of resolved stars (Angel & Woolf 1997;Guyon et al 2013).…”

“…Some combining solutions have been found that optimize the rejection of resolved stars (Angel & Woolf 1997;Guyon et al 2013). The exploitation of these instruments is still limited by their vulnerability to optical path difference (OPD) errors, and requires sophisticated statistical analysis, like those proposed by Hanot et al (2011) and Defrère et al (2016), and more recently used by Norris et al (2020) to disentangle the off-axis astrophysical signal from the effects of unwanted OPDs.…”

Astronomical Applications of Multi-Core Fiber Technology

“…This means that MCFs may be the ideal fiber technology for applications that require the beams in the cores to be interfered in a downstream instrument. A MCF could be used to collect the light from a segmented pupil (with the aid of a MLA) and route it to a downstream beam combiner in a fashion akin to the pupil remapping interferometers Dragonfly/GLINT [63], [64] and FIRST [65]. These instruments are used to image objects at very small separations from the host star such as dust shells, disks and binaries.…”