Using astrophotonics to design new components for future telescopes

With the Extremely Large Telescopes (ELTs) currently under construction we are entering a new era of challenging requirements, which drive spectrograph designs towards techniques that more efficiently use a facility’s light feed. If the spectrograph can operate close to the diffraction limit, this reduces the footprint of the instrument compared to a conventional high resolution spectrograph and mitigates problems and cost issues caused by the use of large optics. By using adaptive optics (AO) to address the wavefront distortions caused by the Earth’s atmospheric turbulence, we can provide diffraction limited starlight to the telescope’s focal plane. Using astrophotonic spatial reformatters and custom optical fibers to manage the AO output, we can increase the starlight coupled into the instrument. In the first part of the thesis, simulation models are compared to manufactured and on-sky tested astrophotonic reformatters. Re-designing of the structures allowed their simulated performance to be further optimised. This is complemented by the laboratory characterisation of multiple different reformatters. In the second part of the thesis, everything discussed thus far is combined, leading to the design, manufacture and on-sky test of a novel instrument concept. This new instrument is composed of a multi-core fiber (MCF) with 3D printed micro-optics on its cores, which increase the coupling of light into them. The custom fiber is used to feed starlight from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument at the 8.2 m Subaru telescope in Hawaii to a diffraction-limited high resolution spectrograph. The results are promising and highlight the instrument’s potential to change the paradigm with which high resolution spectrographs are built, in particular in the near infrared (NIR), for telescopes equipped with powerful AO systems. This study complements recent work in the field and provides crucial insight for optimising future astrophotonic devices

Optimizing astrophotonic spatial reformatters using simulated on-sky performance

One of the most useful techniques in astronomical instrumentation is image slicing. It enables a spectrograph to have a more compact angular slit, whilst retaining throughput and increasing resolving power. Astrophotonic components like the photonic lanterns and photonic reformatters can be used to replace bulk optics used so far. This study investigates the performance of such devices using end-to-end simulations to approximate realistic on-sky conditions. It investigates existing components, tries to optimize their performance and aims to understand better how best to design instruments to maximize their performance. This work complements the recent work in the field and provides an estimation for the performance of the new components.Comment: Conference proceedings in SPIE 2018 Austin Texa

On-sky results for the integrated microlens ring tip-tilt sensor

We present the first on-sky results of the microlens ring tip-tilt sensor. This sensor uses a 3D printed microlens ring feeding six multimode fibers to sense misaligned light, allowing centroid reconstruction. A tip-tilt mirror allows the beam to be corrected, increasing the amount of light coupled into a centrally positioned single-mode (science) fiber. The sensor was tested with the iLocater acquisition camera at the Large Binocular Telescope in Tucson, Arizona, in November 2019. The limit on the maximum achieved rms reconstruction accuracy was found to be 0.19/D in both tip and tilt, of which approximately 50% of the power originates at frequencies below 10 Hz. We show the reconstruction accuracy is highly dependent on the estimated Strehl ratio and simulations support the assumption that residual adaptive optics aberrations are the main limit to the reconstruction accuracy. We conclude that this sensor is ideally suited to remove post-adaptive optics noncommon path tip-tilt residuals. We discuss the next steps for concept development, including optimization of the lens and the fiber, tuning of the correction algorithm, and selection of optimal science cases

An innovative integral field unit upgrade with 3D-printed micro-lenses for the RHEA at Subaru

In the new era of Extremely Large Telescopes (ELTs) currently under construction, challenging requirements drive spectrograph designs towards techniques that efficiently use a facility's light collection power. Operating in the single-mode (SM) regime, close to the diffraction limit, reduces the footprint of the instrument compared to a conventional high-resolving power spectrograph. The custom built injection fiber system with 3D-printed micro-lenses on top of it for the replicable high-resolution exoplanet and asteroseismology spectrograph at Subaru in combination with extreme adaptive optics of SCExAO, proved its high efficiency in a lab environment, manifesting up to ~77% of the theoretical predicted performance

Multi-core fibre-fed integral-field unit (MCIFU):Overview and first-light

The Multi-Core Integral-Field Unit (MCIFU) is a new diffraction-limited near-infrared integral-field unit for exoplanet atmosphere characterization with extreme adaptive optics (xAO) instruments. It has been developed as an experimental pathfinder for spectroscopic upgrades for SPHERE+/VLT and other xAO systems. The wavelength range covers 1.0 um to 1.6um at a resolving power around 5000 for 73 points on-sky. The MCIFU uses novel astrophotonic components to make this very compact and robust spectrograph. We performed the first successful on-sky test with CANARY at the 4.2 meter William Herschel Telescope in July 2019, where observed standard stars and several stellar binaries. An improved version of the MCIFU will be used with MagAO-X, the new extreme adaptive optics system at the 6.5 meter Magellan Clay telescope in Chile. We will show and discuss the first-light performance and operations of the MCIFU at CANARY and discuss the integration of the MCIFU with MagAO-X.</p

Diffraction-limited integral-field spectroscopy for extreme adaptive optics systems with the multicore fiber-fed integral-field unit

International audienceDirect imaging instruments have the spatial resolution to resolve exoplanets from their host star. This enables direct characterization of the exoplanets atmosphere, but most direct imaging instruments do not have spectrographs with high enough resolving power for detailed atmospheric characterization. We investigate the use of a single-mode diffraction-limited integral-field unit that is compact and easy to integrate into current and future direct imaging instruments for exoplanet characterization. This achieved by making use of recent progress in photonic manufacturing to create a single-mode fiber-fed image reformatter. The fiber link is created with three-dimensional printed lenses on top of a single-mode multicore fiber that feeds an ultrafast laser inscribed photonic chip that reformats the fiber into a pseudoslit. We then couple it to a first-order spectrograph with a triple stacked volume phase holographic grating for a high efficiency over a large bandwidth. The prototype system has had a successful first-light observing run at the 4.2-m William Herschel Telescope. The measured on-sky resolving power is between 2500 and 3000, depending on the wavelength. With our observations, we show that single-mode integral-field spectroscopy is a viable option for current and future exoplanet imaging instruments

Status of the SCExAO instrument: recent technology upgrades and path to a system-level demonstrator for PSI

International audienc