AstroPIC: Architecture options and trades for integrated photonic coronagraphy

The Habitable Worlds Observatory (HWO) is the leading recommendation of the Astro2020 decadal survey. The HWO flagship, to be launched in the early 2040s, will directly survey ~100 of the nearest stellar systems and their habitable zones with the goal of detecting and spectroscopically characterizing ~25 potentially "Earth-like planets" (or "Exo-Earths"). The HWO telescope will feature a >6-m diameter aperture and a coronagraph that will suppress starlight by ten orders of magnitude to reveal the reflected light from orbiting dim, rocky exoplanets at the small angular separations that span the host star's habitable zone. There is an efficiency gap between current baseline coronagraph designs and theoretical limits that optimally suppress on-axis starlight modes with a fundamental trade-off between contrast, throughput, inner-working angle, and jitter-robustness. To close this efficiency gap, improve risk margins, and increase the science yield for HWO, coronagraphs will need to adopt novel technological solutions. Photonics technology driven primarily by market demand in the telecommunications and related industries represents a paradigm shift in the generation, control, and detection of light. In particular, a photonic integrated chip (or "PIC") offers the opportunity to miniaturize and integrate functionality for traditional astronomical instrumentation in a small-form factor in the emerging astrophotonics field. We present the potential improvements capable with a photonic coronagraph operating at the optimal limit across a range of telescope apertures. We will also review architecture options for a PIC-based coronagraph ("AstroPIC"). This will span photonic components such as a microlens array and gratings to couple the optical beam from the telescope to the PIC with low throughput losses, Mach-Zehnder Interferometric mesh options to enable photonic nulling theoretically capable of reaching optimal limits, and coupling onto a science detector. In addition we will compare coronagraphic architecture options that include hybrid photonic/traditional coronagraph systems and a fully-photonic coronagraph depending on the number of available modes on the PIC. Finally, we will review the state of the art in photonic nulling capabilities demonstrated to date including achieved suppression, throughput, and bandwidth