title: Integrated Tip-Tilt Sensing for Single-Mode Fiber Coupling
creator: Hottinger, Philipp
subject: ddc-520
subject: 520 Astronomy and allied sciences
subject: ddc-530
subject: 530 Physics
description: This thesis presents the development and on-sky tests of the novel Microlens-Ring Tip-Tilt (MLR-TT) sensor. The sensor consists of a micro-lens ring (MLR) that is printed directly on the face of a fiber bundle with a central single-mode fiber (SMF) accepting the light almost unclipped if the beam is aligned. The edge of the beam, however, is refracted by the MLR to couple into six surrounding multi-mode fibers (MMFs). Detecting the flux in these sensor fibers allows reconstruction of the beam position, i.e. the tip and tilt aberrations of the wavefront.    The lenses are manufactured in collaboration with Karlsruhe Institute for Technology (KIT) with state-of-the-art two-proton polymerization, a novel technology that allows the fabrication of very precise and freeform lenses. The sensor is integrated with the instrument’s fiber link and features a small physical size of 380 µm. This novel integration of a sensor into existing components reduced opto-mechanical footprint and complexity, as well as reducing non-common path aberrations (NCPAs) to a bare minimum.    This thesis describes the various steps that were part of this development, starting with designing, optimizing, and characterizing the sensor itself, setting up a corresponding laboratory environment, and developing a control system for on-sky testing. The system is tested on-sky with iLocater fiber coupling front-end (acquisition camera) at the Large Binocular Telescope (LBT). It was found that principle reconstruction is possible but the observed accuracy is ∼0.19 λ/D both for tip and for tilt. With this accuracy, it was not possible to improve the resulting SMF coupling efficiency. A strong correlation between sensor accuracy and the instantaneous Strehl ratio (SR), i.e. residual adaptive optics (AO) aberrations, is found. Additionally, the corresponding power spectral density (PSD) reveals that most of the reconstruction inaccuracy occurs in low temporal frequencies. This suggests that the dominating limitations of the accuracy of the MLR-TT sensor arise from residual AO aberrations and the false signal they introduce in the sensor.    These findings are discussed in detail and the future prospects of further analysis and development are outlined in the context of the most beneficial application environment.
date: 2023
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/33427/1/Hottinger_PhD_final.pdf
identifier: DOI:10.11588/heidok.00033427
identifier: urn:nbn:de:bsz:16-heidok-334276
identifier:   Hottinger, Philipp  (2023) Integrated Tip-Tilt Sensing for Single-Mode Fiber Coupling.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/33427/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng