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Guillermo Martin

Publications and source records attributed to Guillermo Martin.

At least 19 recordsLinked to original sources
arXiv2026

He'e-Lab: A modular testbed for astrophotonics and wavefront sensing development

Advanced astronomical instrumentation requires accessible, reconfigurable platforms to validate novel technologies and algorithms before on-sky deployment. We present the design, architecture, and alignment validation of the Hawaii Experimental Engineering Lab (He'e-Lab), a state-of-the-art modular testbed dedicated to two complementary research tracks: (A) the integration and characterization of astrophotonics components within a real-time computing loop, and (B) the development of advanced wavefront sensing and control (WFS&C) algorithms. The testbed features a broadband supercontinuum source (500 nm to 2 microns), a high-order 1k-actuator Boston Micromachines deformable mirror, and a 37-segment hexagonal mirror assembly providing piston-tip-tilt control to emulate segmented apertures like Keck and JWST. Downstream capabilities include a HASO 126 Shack-Hartmann sensor, a real-time computing environment driven by the CACAO package, and a modular injection platform coupled to a visible-wavelength spectrograph (R3, 000). We report on the successful system alignment and outline the roadmap for upcoming adaptive optics and photonic device validation frameworks.

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arXiv2026

Characterization and on-sky testing of photonic, AWG-based astronomical spectrographs

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 Bo\"otes) and Betelgeuse (alpha Orionis). This work contributes to assessing the capabilities of photonic spectroscopy for the development of future compact instruments.

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arXiv2024

Spectroscopy using a visible photonic lantern at the Subaru telescope: Laboratory characterization and first on-sky demonstration on Ikiiki ({\alpha} Leo) and `Aua ({\alpha} Ori)

Photonic lanterns are waveguide devices enabling high throughput single mode spectroscopy and high angular resolution. We aim to present the first on-sky demonstration of a photonic lantern (PL) operating in visible light, to measure its throughput and assess its potential for high-resolution spectroscopy of compact objects. We used the SCExAO instrument (a double stage extreme AO system installed at the Subaru telescope) and FIRST mid-resolution spectrograph (R 3000) to test the visible capabilities of the PL on internal source and on-sky observations. The best averaged coupling efficiency over the PL field of view was measured at 51% +/- 10% with a peak at 80%. We also investigate the relationship between coupling efficiency and the Strehl ratio for a PL, comparing them with those of a single-mode fiber (SMF). Findings show that in the AO regime, a PL offers better coupling efficiency performance than a SMF, especially in the presence of low spatial frequency aberrations. We observed Ikiiki (alpha Leo - mR = 1.37) and `Aua (alpha Ori - mR = -1.17) at a frame rate of 200 Hz. Under median seeing conditions (about 1 arcsec measured in H band) and large tip/tilt residuals (over 20 mas), we estimated an average light coupling efficiency of 14.5% +/- 7.4%, with a maximum of 42.8% at 680 nm. We were able to reconstruct both star's spectra, containing various absorption lines. The successful demonstration of this device opens new possibilities in terms of high throughput single-mode fiber-fed spectroscopy in the Visible. The demonstrated on-sky coupling efficiency performance would not have been achievable with a single SMF injection setup under similar conditions, partly because the residual tip/tilt alone exceeded the field of view of a visible SMF (18 mas at 700 nm). Thus emphasizing the enhanced resilience of PL technology to such atmospheric disturbances. The additional

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arXiv2024

Spectral interferometric wavefront sensing: a solution for petalometry at Subaru/SCExAO

The petaling effect, induced by pupil fragmentation from the telescope spider, drastically affects the performance of high contrast instruments by inducing core splitting on the PSF. Differential piston/tip/tilt aberrations within each optically separated fragment of the pupil are poorly measured by commonly used Adaptive Optics (AO) systems. We here pursue a design of dedicated low-order wavefront sensor -- or petalometers -- to complement the main AO. Interferometric devices sense differential aberrations between fragments with optimal sensitivity; their weakness though is their limitation to wrapped phase measurements. We show that by combining multiple spectral channels, we increase the capture range for petaling aberrations beyond several microns, enough to disambiguate one-wave wrapping errors made by the main AO system. We propose here to implement a petalometer from the multi-wavelength imaging mode of the VAMPIRES visible-light instrument, deployed on SCExAO at the Subaru Telescope. The interferometric measurements obtained in four spectral channels through a 7 hole non-redundant mask allow us to effiiently reconstruct diffierential piston between pupil petals.

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arXiv2024

Photonic beam-combiner for visible interferometry with SCExAO/FIRST: laboratory characterization and design optimization

Integrated optics are used to achieve astronomical interferometry inside robust and compact materials, improving the instrument's stability and sensitivity. In order to perform differential phase measurements at the H$\alpha$ line (656.3 nm) with the 600-800 nm spectro-interferometer FIRST, a photonic integrated circuit (PIC) is being developed in collaboration with TEEM Photonics. This PIC performs the interferometric combination of the beams coming from sub-apertures selected in the telescope pupil, thus implementing the pupil remapping technique to restore the diffraction limit of the telescope. In this work, we report on the latest developments carried out within the FIRST project to produce a high performance visible PIC. The PICs are manufactured by TEEM Photonics, using their technology based on $K_+:Na_+$ ion exchange in glass. The first part of the study consists in the experimental characterization of the fundamental properties of the waveguides, in order to build an accurate model, which is the basis for the design of more complex functions. In the second part, theoretical designs and their optimization for three types of combiner architectures are presented: symmetric directional coupler, asymmetric directional couplers and ABCD cells including achromatic phase shifters.

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arXiv2024

Photonic chip for visible interferometry: laboratory characterization and comparison with the theoretical model

Integrated optics are used to achieve astronomical interferometry inside robust and compact materials, improving the instruments stability and sensitivity. In order to perform differential phase measurements at the H$\alpha$ line (656.3 nm) with the 600-800 nm spectro-interferometer FIRST, a photonic integrated circuit (PIC) is being developed. This PIC performs the visible combination of the beams coming from the telescope pupil sub-apertures. In this work, TEEM Photonics waveguides fabricated by $K_+:Na_+$ ion exchange in glass are characterized in terms of single-mode range and mode field diameter. The waveguide diffused index profile is modeled on Beamprop software. FIRST beam combiner building blocks are simulated, especially achromatic directional couplers and passive $\pi/2$ phase shifters for a potential ABCD interferometric combination.

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arXiv2024

Visible Photonic Lantern integration, characterization and on-sky testing on Subaru/SCExAO

A Photonic Lantern (PL) is a novel device that efficiently converts a multi-mode fiber into several single-mode fibers. When coupled with an extreme adaptive optics (ExAO) system and a spectrograph, PLs enable high throughput spectroscopy at high angular resolution. The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system of the Subaru Telescope recently acquired a PL that converts its multi-mode input into 19 single-mode outputs. The single mode outputs feed a R~4,000 spectrograph optimized for the 600 to 760 nm wavelength range. We present here the integration of the PL on SCExAO, and study the device performance in terms of throughput, field of view, and spectral reconstruction. We also present the first on-sky demonstration of a Visible PL coupled with an ExAO system, showing a significant improvement of x12 in throughput compared to the use of a sole single-mode fiber. This work paves the way towards future high throughput photonics instrumentation at small angular resolution.

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arXiv2024

L-band nulling interferometry at the VLTI with Asgard/NOTT: status and plans

NOTT (formerly Hi-5) is the L'-band (3.5-4.0~microns) nulling interferometer of Asgard, an instrument suite in preparation for the VLTI visitor focus. The primary scientific objectives of NOTT include characterizing (i) young planetary systems near the snow line, a critical region for giant planet formation, and (ii) nearby main-sequence stars close to the habitable zone, with a focus on detecting exozodiacal dust that could obscure Earth-like planets. In 2023-2024, the final warm optics have been procured and assembled in a new laboratory at KU Leuven. First fringes and null measurements were obtained using a Gallium Lanthanum Sulfide (GLS) photonic chip that was also tested at cryogenic temperatures. In this paper, we present an overall update of the NOTT project with a particular focus on the cold mechanical design, the first results in the laboratory with the final NOTT warm optics, and the ongoing Asgard integration activities. We also report on other ongoing activities such as the characterization of the photonic chip (GLS, LiNbO3, SiO), the development of the exoplanet science case, the design of the dispersion control module, and the progress with the self-calibration data reduction software.

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arXiv2024

Asgard/NOTT: L-band nulling interferometry at the VLTI. II. Warm optical design and injection system

Asgard/NOTT (previously Hi-5) is a European Research Council (ERC)-funded project hosted at KU Leuven and a new visitor instrument for the Very Large Telescope Interferometer (VLTI). Its primary goal is to image the snow line region around young stars using nulling interferometry in the L-band (3.5 to 4.0)$\mu$m, where the contrast between exoplanets and their host stars is advantageous. The breakthrough is the use of a photonic beam combiner, which only recently allowed the required theoretical raw contrast of $10^{-3}$ in this spectral range. Nulling interferometry observations of exoplanets also require a high degree of balancing between the four pupils of the VLTI in terms of intensity, phase, and polarization. The injection into the beam combiner and the requirements of nulling interferometry are driving the design of the warm optics and the injection system. The optical design up to the beam combiner is presented. It offers a technical solution to efficiently couple the light from the VLTI into the beam combiner. During the coupling, the objective is to limit throughput losses to 5% of the best expected efficiency for the injection. To achieve this, a list of different loss sources is considered with their respective impact on the injection efficiency. Solutions are also proposed to meet the requirements on beam balancing for intensity, phase, and polarization. The different properties of the design are listed, including the optics used, their alignment and tolerances, and their impact on the instrumental performances in terms of throughput and null depth. The performance evaluation gives an expected throughput loss of less than <6.4% of the best efficiency for the injection and a null depth of $\sim2.10^{-3}$, mainly from optical path delay errors outside the scope of this work.

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arXiv2023

2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

Photonics offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile. Integrated astrophotonic devices stand to offer critical advantages for instrument development, including extreme miniaturization, as well as integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including for example the development of photonic lanterns, complex aperiodic fiber Bragg gratings, complex beam combiners to enable long baseline interferometry, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of (1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient integration of photonics with detectors, to name a few. In this roadmap, we identify 24 areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional instruments will be realized leading to novel observing capabilities for both ground and space platforms.

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arXiv2023

Photonic spectro-interferometry with SCExAO/FIRST at the Subaru Telescope: towards H-alpha imaging of protoplanets

FIRST is a post Extreme Adaptive-Optics (ExAO) spectro-interferometer operating in the Visible (600-800 nm, R~400). Its exquisite angular resolution (a sensitivity analysis of on-sky data shows that bright companions can be detected down to 0.25lambda/D) combined with its sensitivity to pupil phase discontinuities (from a few nm up to dozens of microns) makes FIRST an ideal self-calibrated solution for enabling exoplanet detection and characterization in the future. We present the latest on-sky results along with recent upgrades, including the integration and on-sky test of a new spectrograph (R~3,600) optimized for the detection of H-alpha emission from young exoplanets accreting matter.

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arXiv2023

Single-aperture spectro-interferometry in the visible at the Subaru telescope with FIRST: First on-sky demonstration on Keho'oea ({\alpha} Lyrae) and Hokulei ({\alpha} Aurigae)

FIRST is a spectro-interferometer combining, in the visible, the techniques of aperture masking and spatial filtering thanks to single-mode fibers. This instrument aims to deliver high contrast capabilities at spatial resolutions that are inaccessible to classical coronagraphic instruments. The technique implemented is called pupil remapping: the telescope is divided into subpupils by a segmented deformable mirror conjugated to a micro-lens array injecting light into single-mode fibers. The fiber outputs are rearranged in a nonredundant configuration, allowing simultaneous measurement of all baseline fringe patterns. The fringes are also spectrally dispersed, increasing the coherence length and providing precious spectral information. The optical setup of the instrument has been adapted to fit onto the SCExAO platform at the Subaru Telescope. We present the first on-sky demonstration of the FIRST instrument at the Subaru telescope. We used eight subapertures, each with a diameter of about 1 m. Closure phase measurements were extracted from the interference pattern to provide spatial information on the target. We tested the instrument on two types of targets : a point source (Keho'oea) and a binary system (Hokulei). An average accuracy of 0.6 degree is achieved on the closure phase measurements of Keho'oea, with a statistical error of about 0.15 degree at best. We estimate that the instrument can be sensitive to structures down to a quarter of the telescope spatial resolution. We measured the relative positions of Hokulei Aa and Ab with an accuracy about 1 mas. FIRST opens new observing capabilities in the visible wavelength range at the Subaru Telescope. With SCExAO being a testing platform for high contrast imaging instrumentation for future 30-meter class telescopes, FIRST is an important stepping stone for future interferometric instrumentation on extremely large telescopes.

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arXiv2022

L-band nulling interferometry at the VLTI with Asgard/Hi-5: status and plans

Hi-5 is the L'-band (3.5-4.0 $\mu$m) high-contrast imager of Asgard, an instrument suite in preparation for the visitor focus of the VLTI. The system is optimized for high-contrast and high-sensitivity imaging within the diffraction limit of a single UT/AT telescope. It is designed as a double-Bracewell nulling instrument producing spectrally-dispersed (R=20, 400, or 2000) complementary nulling outputs and simultaneous photometric outputs for self-calibration purposes. In this paper, we present an update of the project with a particular focus on the overall architecture, opto-mechanical design of the warm and cold optics, injection system, and development of the photonic beam combiner. The key science projects are to survey (i) nearby young planetary systems near the snow line, where most giant planets are expected to be formed, and (ii) nearby main sequence stars near the habitable zone where exozodiacal dust that may hinder the detection of Earth-like planets. We present an update of the expected instrumental performance based on full end-to-end simulations using the new GRAVITY+ specifications of the VLTI and the latest planet formation models.

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arXiv2020

FIRST, a Pupil-Remapping Fiber Interferometer at the Subaru Telescope: on-sky results

FIRST, the Fibered Imager foR a Single Telescope, is a spectro-imager using single-mode fibers for pupil remapping, allowing measurements beyond the telescope diffraction limit. Integrated on the Subaru Coronagraphic Extreme Adaptive Optics instrument at the Subaru Telescope, it benefits from a very stable visible light wavefront allowing to acquire long exposure and operate on significantly fainter sources than previously possible. On-sky results demonstrated the ability of the instrument to detect stellar companions separated 43mas in the case of the Capella binary system. A similar approach on an extremely large telescope would offer unique scientific opportunities for companion detection and characterization at very high angular resolution.

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arXiv2020

Capabilities of a fibered imager on an extremely large telescope

FIRST, the Fibered Imager foR a Single Telescope instrument, is an ultra-high angular resolution spectro-imager, able to deliver calibrated images and measurements beyond the telescope diffraction limit, a regime that is out of reach for conventional AO imaging. FIRST achieves sensitivity and accuracy by coupling the full telescope to an array of single mode fibers. Interferometric fringes are spectrally dispersed and imaged on an EMCCD. An 18-Fiber FIRST setup is currently installed on the Subaru Coronographic Extreme Adaptive Optics instrument at Subaru telescope. It is being exploited for binary star system study. In the late 2020 it will be upgraded with delay lines and an active LiNb03 photonic beam-combining chip allowing phase modulation to nanometer accuracy at MHz. On-sky results at Subaru Telescope have demonstrated that, thanks to the ExAO system stabilizing the visible light wavefront, FIRST can acquire long exposure and operate on significantly fainter sources than previously possible. A similar approach on a larger telescope would therefore offer unique scientific opportunities for galactic (stellar physics, close companions) and extragalactic observations at ultra-high angular resolution. We also discuss potential design variations for nulling and high contrast imaging.

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arXiv2016

Astronomical photonics in the context of infrared interferometry and high-resolution spectroscopy

We review the potential of Astrophotonics, a relatively young field at the interface between photonics and astronomical instrumentation, for spectro-interferometry. We review some fundamental aspects of photonic science that drove the emer- gence of astrophotonics, and highlight the achievements in observational astrophysics. We analyze the prospects for further technological development also considering the potential synergies with other fields of physics (e.g. non-linear optics in condensed matter physics). We also stress the central role of fiber optics in routing and transporting light, delivering complex filters, or interfacing instruments and telescopes, more specifically in the context of a growing usage of adaptive optics.

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