High-contrast demonstrations with the AstroPIC integrated photonic coronagraph

Abstract

Integrated photonics is a promising coronagraph technology option for exoplanet-imaging missions such as NASA’s Habitable Worlds Observatory flagship. It is theoretically capable of achieving near-optimal coronagraphic performance because arrays of integrated interferometers can be controlled to implement any linear optical function with a device that is orders of magnitude smaller than the bulk optics equivalent. However, photonic coronagraphs require significant maturation to be ready for a space telescope mission. The AstroPIC project is advancing this technology by developing a proof of concept integrated photonic coronagraph based on silicon photonic integrated circuit (PIC) technology. In this paper, we summarize the design and implementation of the PIC coronagraph testbed at Ames, which is designed to be capable of measuring the target 100 dB extinction ratio required to observe an Earth-like planet around a Sun-like star. We present experimental results with the testbed that demonstrate a record-breaking on-chip extinction of a single input channel to 3.83±0.8×10−10, or over 94 dB, using a nine-channel full triangular photonic mesh illuminated with 1550 nm wavelength light. We also demonstrate reimaging a circular pupil onto the input to the chip and implementing a mode sorting algorithm to achieve a contrast ratio of 8.7±1.1×10−8, or over 70 dB, of the stellar source with a measured planet throughput of over 40% into the high-contrast channel.