arXiv subjects

Andreas Stoll

Publications and source records attributed to Andreas Stoll.

7 recordsLinked to original sources

arXiv2026

Validation and extension of the PAWS Zemax model as a first step in the development of a Compact Arrayed Waveguide Stacked Multi-Object Spectrograph (CAWSMOS)

The linear size of a bulk optical astronomical spectrograph scales with the diameter of the primary mirror of the corresponding telescope. As modern telescopes continue to increase in aperture size, miniaturization of the spectrograph becomes crucial beyond the offered advantages in terms of multifunctional integration and photon efficiency. The presented concept of development for a Compact Arrayed Waveguide Stacked Multi-Object Spectrograph (CAWSMOS) includes the design of the Arrayed Waveguide Grating (AWG) chips, the stacking frame and cross-dispersion optics for the imaging of multiple spectral orders per AWG. It aims to reduce the cost and size of astronomical spectrographs while also improving efficiency. This will bring the AWG technology closer to the realization of its full potential for ground based, airborne and spaceborne astronomical applications. Part of this development is an extension of the Potsdam Arrayed Waveguide Spectrograph (PAWS). To do that, the Zemax model is compared to PAWS calibration data, finding that the position can be matched with the measurement within 28 px in x and 18 px in y-direction. It also shows a discrepancy between the measured PSF size and the Zemax model of around factor five, and that the detector area can only partially accommodate a second chip.

astro-ph.IM↗

arXiv2023

ReWaRD: Retinal Waves for Pre-Training Artificial Neural Networks Mimicking Real Prenatal Development

Computational models trained on a large amount of natural images are the state-of-the-art to study human vision - usually adult vision. Computational models of infant vision and its further development are gaining more and more attention in the community. In this work we aim at the very beginning of our visual experience - pre- and post-natal retinal waves which suggest to be a pre-training mechanism for the primate visual system at a very early stage of development. We see this approach as an instance of biologically plausible data driven inductive bias through pre-training. We built a computational model that mimics this development mechanism by pre-training different artificial convolutional neural networks with simulated retinal wave images. The resulting features of this biologically plausible pre-training closely match the V1 features of the primate visual system. We show that the performance gain by pre-training with retinal waves is similar to a state-of-the art pre-training pipeline. Our framework contains the retinal wave generator, as well as a training strategy, which can be a first step in a curriculum learning based training diet for various models of development. We release code, data and trained networks to build the basis for future work on visual development and based on a curriculum learning approach including prenatal development to support studies of innate vs. learned properties of the primate visual system. An additional benefit of our pre-trained networks for neuroscience or computer vision applications is the absence of biases inherited from datasets like ImageNet.

cs.CV↗

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.

astro-ph.IM↗

arXiv2023

Astrophotonics: photonic integrated circuits for astronomical instrumentation

Photonic Integrated Circuits (PIC) are best known for their important role in the telecommunication sector, e.g. high speed communication devices in data centers. However, PIC also hold the promise for innovation in sectors like life science, medicine, sensing, automotive etc. The past two decades have seen efforts of utilizing PIC to enhance the performance of instrumentation for astronomical telescopes, perhaps the most spectacular example being the integrated optics beam combiner for the interferometer GRAVITY at the ESO Very Large Telescope. This instrument has enabled observations of the supermassive black hole in the center of the Milky Way at unprecedented angular resolution, eventually leading to the Nobel Price for Physics in 2020. Several groups worldwide are actively engaged in the emerging field of astrophotonics research, amongst them the innoFSPEC Center in Potsdam, Germany. We present results for a number of applications developed at innoFSPEC, notably PIC for integrated photonic spectrographs on the basis of arrayed waveguide gratings and the PAWS demonstrator (Potsdam Arrayed Waveguide Spectrograph), PIC-based ring resonators in astronomical frequency combs for precision wavelength calibration, discrete beam combiners (DBC) for large astronomical interferometers, as well as aperiodic fiber Bragg gratings for complex astronomical filters and their possible derivatives in PIC.

astro-ph.IM↗

arXiv2021

Design, simulation and characterization of integrated photonic spectrographs for Astronomy II: Low-aberration Generation-II AWG devices with three stigmatic points

In the second part of our series on integrated photonic spectrographs for astronomy, we present theoretical and experimental results on the design, simulation and characterization of custom-manufactured silica-on-silicon Arrayed Waveguide Gratings (AWGs) constructed using the three-stigmatic-point method. We derive several mid-to-high resolution field-flattened AWG designs, targeting resolving powers of 11,000 - 35,000 in the astronomical H-band, by iterative computation of differential coefficients of the optical path function. We use numerical simulations to study the imaging properties of the designs in a wide wavelength range between 1500 nm and 1680 nm. We theoretically discuss the design-specific degradation of spectral resolving power at far-off-centre wavelengths and suggest possible solutions. In the experimental section, we provide characterization results of seven manufactured AWG devices of varying free spectral range and resolution. We obtain estimates on spectral resolving powers of up to 27,600 for polarized input at 1550 nm from measurements of the channel transmission bandwidth. Furthermore, we numerically predict expected resolving powers of up to 36,000 in polarized mode and up to 24,000 in unpolarized mode for direct continuous imaging of the spectrum.

astro-ph.IM↗

arXiv2021

Design, simulation and characterization of integrated photonic spectrographs for Astronomy I: Generation-I AWG devices based on canonical layouts

We present an experimental study on our first generation of custom-developed arrayed waveguide gratings (AWG) on silica platform for spectroscopic applications in near-infrared astronomy. We provide a comprehensive description of the design, numerical simulation and characterization of several AWG devices aimed at spectral resolving powers of 15,000 - 60,000 in the astronomical H-band. We evaluate the spectral characteristics of the fabricated devices in terms of insertion loss and estimated spectral resolving power and compare the results with numerical simulations. We estimate resolving powers of up to 18,900 from the output channel 3-dB transmission bandwidth. Based on the first characterization results, we select two candidate AWGs for further processing by removal of the output waveguide array and polishing the output facet to optical quality with the goal of integration as the primary diffractive element in a cross-dispersed spectrograph. We further study the imaging properties of the processed AWGs with regards to spectral resolution in direct imaging mode, geometry-related defocus aberration, and polarization sensitivity of the spectral image. We identify phase error control, birefringence control, and aberration suppression as the three key areas of future research and development in the field of high-resolution AWG-based spectroscopy in astronomy.

astro-ph.IM↗

arXiv2020

Performance limits of astronomical arrayed waveguide gratings on silica platform

We present a numerical and experimental study of the impact of phase errors on the performance of large, high-resolution Arrayed Waveguide Gratings (AWG) for applications in astronomy. We use a scalar diffraction model to study the transmission spectrum of an AWG under random variations of the optical waveguide lengths. We simulate phase error correction by numerically trimming the lengths of the optical waveguides to the nearest integer multiple of the central wavelength. The optical length error distribution of a custom-fabricated silica AWG is measured using frequency-domain interferometry and Monte-Carlo fitting of interferogram intensities. In the end, we give an estimate for the phase-error limited size of a waveguide array manufactured using state-of-the-art technology. We show that post-processing eliminates phase errors as a performance limiting factor for astronomical spectroscopy in the H-band.

astro-ph.IM↗