Solar System analog gas giants and habitable-zone terrestrial planets are observationally elusive to conventional exoplanet detection and characterization techniques, i.e. transits, radial velocities, and direct imaging. Long baseline nulling interferometry across multiple apertures suppresses starlight and enables detection of faint planetary signals at higher spatial resolution than traditional coronagraphs on single-aperture telescopes. Leveraging technological advancements from the telecommunications industry, photonic integrated circuits (PICs) offer a promising platform for performing the optical operations necessary for astronomical applications, including phasing and beam combination for nulling interferometry in both long-baseline and cross-aperture configurations. PICs provide compact, scalable architectures with reduced sensitivity to alignment as well as thermal and mechanical perturbations compared to bulk optics. However, their design and manufacturing precision remain insufficient for the stringent requirements of exoplanet instrumentation. Here, we investigate the nulling capabilities of photonic tricouplers, devices composed of three equal-width waveguides that are geometrically predisposed to produce achromatic nulls upon beam combination through their symmetric construction. In the laboratory, we characterize null depths in monochromatic light at 1.55 m with devices on a planar silica-on-silicon platform. In broadband H-band light, we explore chromatic effects from components such as thermo-optic phase modulators used for fine-phasing. Our ongoing efforts towards maturation of PICs for direct detection and atmospheric characterization of exoplanets will support scalable testing and deployment of high-contrast technologies for future space-based observatories, such as the Habitable Worlds Observatory.

High-contrast imaging of Solar System scale exoplanets and protoplanets demands advancements in instrumentation to access deeper starlight suppression at smaller angular separations than today's state-of-the-art. The multi-mode to single-mode conversion capabilities of photonic lanterns (PLs) provide new avenues to implement techniques such as nulling interferometry due to the inherent spatial filtering of single-mode waveguides. In this work, we present laboratory results on an all-fiber-based focal plane nulling interferometer using off-the-shelf components operating at 1550 nm. We demonstrate the implementation of a PL for coupling light into the instrument, and compare it to the case when laser light is directly fed into the interferometer. The integration of a PL with the interferometer evidences their potential for feeding photonic-based science instruments. Additionally, we discuss expanding the concept of the instrument for the detection of accreting protoplanets.

Astrophotonics is central to the next generation of astronomical instrumentation, enabling compact photonic integrated circuits for both ground-based observatories and future space missions. Beam combination for nulling interferometry suppresses starlight, revealing exoplanets and companions. Two-waveguide photonic combiners rely on symmetric evanescent, inherently chromatic, coupling to interfere light. A three-waveguide configuration, or tri-coupler, offers the potential for deeper, broader, and more stable achromatic nulls compared with two-waveguide approaches. This work compares the simulated performance of evanescent tri-couplers and a multimode interference coupler across the 1.5-1.8 micron band, evaluating exoplanet throughput, starlight attenuation, sensing characteristics, and estimations on fabrication tolerance. All three tri-couplers achieved >40dB attenuation over a 270nm bandwidth. Including component loss, the tapered tri-coupler has the highest total throughput, averaging 97 Future designs aim to combine high exoplanet throughput, deep starlight attenuation, and non-degenerate sensing within a single integrated architecture. This work provides a simulation suite for three tri-couplers.

Astrophotonics is a field that intends to meet the needs of next-generation instruments at a small footprint, low cost, and high stability, compared to bulk-optics-based alternatives. Much development effort is driven by the stringent requirements of direct detection and characterization of exoplanets. Our team works in characterizing Arrayed-Waveguide Grating (AWG) chips for photonics-based, high-resolution, near infrared spectro-interferometry. AWG spectrographs allow to test the feasibility of photonic spectro-interferometers for exoplanet characterization, another step towards fully photonic instruments for astronomy. We present the current status of our AWG characterization and a preliminary on-sky qualification campaign at the PAPYRUS AO system. We present the CoLiBRIS-AWG spectrograph prototype built for on-sky testing, and preliminary results using our high-resolution (H band, R 18000) AWG for observations of Arcturus (alpha Boötes) and Betelgeuse (alpha Orionis). This work contributes to assessing the capabilities of photonic spectroscopy for the development of future compact instruments.

Nulling interferometry is a promising method for direct detection and characterization of faint stellar companions such as exoplanets and faint binary sources. The dominant constraint on instrument performance is instability noise from vibrations, thermal expansions, and other systematic sources. Photonic instruments have footprints of a few centimeters and enable advanced light control architectures. Astrophotonic implementations can include active phase control via Mach-Zehnder interferometers (MZIs) to actively minimize residual optical path errors at the location of beam combination. The compact size of photonic chips also makes them a promising solution for space-based applications such as the upcoming Habitable Worlds Observatory. The Center for High Angular Resolution Astronomy (CHARA) Array is equipped with the world's longest baseline in the near-infrared at 330 meters long. CHARA therefore has the most sensitive angular resolution in the near-infrared. A nuller at CHARA would have access to a novel parameter space essential for exoplanet discovery and characterization. The first step in preparing a nulling beam combiner for CHARA is to develop compelling, realistic, and well-defined science cases. Simulation suites quantify the technical requirements to reach such science goals in their respective complex systems. The CHARA Array Response Model (CHARM) is the first-ever simulator built specifically for CHARA, opening up new pathways for instrument simulation. CHARM is a flexible simulation tool of an H-band, self-calibrated astrophotonic nulling beam combiner with active phase control for the CHARA Array. In this paper, we present an update on the development of our photonic nulling beam combiner for CHARA. We include early results from CHARM, demonstrating that the photonic nuller has the potential to detect and characterize a wide range of bright stellar companion systems.

This thesis work presents the conceptual design and experimental characterization of the Photonic Lantern Nuller instrument, which uses a multimode-to-single-mode demultiplexing waveguide to cancel out starlight while maintaining planet light, allowing for the direct characterization of planets at a telescope's diffraction limit. The PLN was experimentally characterized in the lab, where it was further enhanced using common-path wavefront sensing and control techniques, and then demonstrated on sky at the Subaru Telescope. Highlights include measured in-lab null-depths of ∼ 10^-4 in three out of four ports simultaneously and on-sky null-depths of approximately ∼ 10^-1 (limited by jitter and atmospheric residuals). We provide an overview of these results and discuss avenues for future work.

Astrophotonics will be central to the next generation of astronomical instrumentation, enabling lightweight, compact, and environmentally stable photonic integrated circuits for both ground-based observatories and future space missions. One key application is beam combination for nulling interferometry, which suppresses starlight to reveal exoplanets and companions. Compact, broadband photonic beam combiners are essential for enabling complex circuitry on a single chip and for scalable solutions for single- and multi-telescope instruments, and are investigated herein. Two-waveguide photonic combiners rely on symmetric evanescent coupling to interfere light, which is inherently chromatic and requires modification for broadband operation. A three-waveguide configuration, or tri-coupler, offers the potential for deeper, broader, and more stable achromatic nulls compared with two-waveguide approaches. This work compares the simulated performance of two evanescent tri-couplers and a multimode interference coupler (MMI) across the 1.5-1.8 µm band, evaluating exoplanet throughput, starlight attenuation, sensing characteristics, and estimations on fabrication tolerance. All three tri-couplers achieved >40 dB attenuation over a ≥270 nm bandwidth. However, the standard tri-coupler was outperformed by both a bespoke tapered tri-coupler and the MMI, each of which achieved exoplanet throughput >85% across the band, excluding component losses. Including component loss, the tapered tri-coupler has the highest total throughput, averaging ∼96%. The standard tri-coupler began with an equivalent exoplanet throughput, falling to 50% at the band edges. The tapered tri-coupler was further redesigned to achieve a non-degenerate sensing state. The MMI, while limited to a starlight attenuation of 40 dB (10-4) by uncoupled light, showed the greatest tolerance to fabrication errors, offering strong practical potential. Future designs aim to combine high exoplanet throughput, deep starlight attenuation, and non-degenerate sensing within a single integrated architecture. This work provides a simulation suite for three tri-couplers. They can be selected based on robustness to common fabrication tolerances (the MMI), exoplanet throughput (the tapered tri-coupler), and/or the sensing performance (the tapered tri-coupler).

The Photonic Lantern Nuller (PLN) is an instrument concept designed to characterize exoplanets within a single beam-width from its host star. The PLN leverages the spatial symmetry of a mode-selective photonic lantern (MSPL) to create nulled ports, which cancel out on-axis starlight but allow off-axis exoplanet light to couple. The null-depths are limited by wavefront aberrations in the system as well as by imperfections in the lantern. We show that the implicit electric field conjugation algorithm can be used to reduce the stellar coupling through the PLN by orders of magnitude while maintaining the majority of the off-axis light, leading to deeper null depths ( 10^-4) and thus higher sensitivity to potential planet signals. We discuss a theory for the tradeoff we observed between the different ports, where iEFC improves the nulls of some ports at the expense of others, and show that targeting one port alone can lead to deeper starlight rejection through that port than when targeting all ports at once. We also observe different levels of stability depending on the port and discuss the implications for practically implementing this technique for science observations.

Here we present an optical cross-dispersion setup for an astrophotonic spectrograph in the near-IR H-band (1460-1630 nm). In this spectrograph, the arrayed waveguide grating (AWG) chip acts as the main dispersing element. An AWG produces a 1D spectrum with overlapping spectral orders, and we designed a cross-dispersion setup that can cross-disperse these overlapping spectral orders perpendicular to the 1D spectral output. This setup consists of a collimating lens, a grating, and a focusing lens. The cross-dispersed 2D spectrum is then imaged onto a near-IR detector array. The AWG we used for this project has a spectral resolution of (lambda/delta lambda) of similar to 1000 and a free spectral range of 10 nm. An on-sky solar test was performed and analyzed, demonstrating the potential of this setup.