Ultrafast laser fabrication of a K-band integrated optic 2-telescope beam combiner for astronomical interferometry

This dissertation explores the vast potential of the ultrafast laser inscription (ULI) fabrication technique for astrophotonics applications. A fibre-connectorised K-band 2-telescope integrated optics (IO) beam combiner is designed and fabricated in commercial Infrasil® glass (IG) to update the existing JouFLU beam combiner at the Center for High Angular Resolution Astronomy (CHARA) array. A liquid crystal on silicon phase-only spatial light modulator (SLM) is integrated into a conventional ULI fabrication system to control the laser phase profile at the objective plane. During the fabrication runs, the SLM is used to provide dynamic control of the virtual numerical aperture of the writing objective. The investigation begins by determining the ULI parameters which optimise the guiding properties of straight single mode waveguides. The insertion losses of the waveguides were measured at 1.1 ± 0.1 dB over a 17 mm IG chip, which corresponds to 78 % of global throughput over the whole K-band. The prototype IO beam combiner incorporates three asymmetric directional couplers: a 3 dB coupler for interferometric measurements and two photometric taps for calibration purposes. When tested in the lab, the interferometry contrast of the ULI fabricated bare beam combiner provided a high figure of ≈ 87 % when input polarisation was controlled. Furthermore, the fibre-connectorised beam combiner prototype presented consistent interferometric performance under the same conditions and produced an interferometric contrast of ≈ 92 %, marking a significant result in the field of near-infrared (NIR) interferometry. This achievement opens new opportunities for driving exoplanet research and expanding the capabilities of the K-band instruments. The successful implementation of this fibre-connectorised IO beam combiner highlights the potential of ULI to produce highly efficient and versatile devices for astronomical applications. The findings of this research contribute to the ongoing development of state-of-the-art astronomical instruments, uncovering new possibilities for exploring celestial phenomena. The knowledge obtained from this study along with the beneficial partnership with our partners at, contributed to establishing the groundwork for a potential joint project that seeks to further develop this capability.

Grantor dc:publisher

Heriot-Watt University

Year dc:date.issued

2024

Author dc:creator

• Siliprandi, Jacopo

Advisor dc:contributor.advisor

• Thomson, Robert

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/10399/5088

OAI identifier oai:identifier

oai:ros.hw.ac.uk:10399/5088