Jacopo Siliprandi,1 David G. MacLachlan,1 Calum A. Ross,1 Tarun K. Sharma,2 Lucas Labadie,2 Kalaga Madhavhttps://orcid.org/0000-0002-6711-7137,3 Abani S. Nayak,3 Aline N. Dinkelaker,3 Martin M. Roth,3 Ettore Pedretti,4 Theo A. ten Brummelaar,5 Nicholas J. Scott,5 Vincent Coudé du Foresto,6 Robert R. Thomson,1 Aurélien Benoît1
1Heriot-Watt Univ. (United Kingdom) 2Univ. zu Köln (Germany) 3Leibniz-Institut für Astrophysik Potsdam (Germany) 4UK Research and Innovation (United Kingdom) 5Georgia State Univ. (United States) 6Lab. d'Etudes Spatiales et d'Instrumentation en Astrophysique, Observatoire de Paris, CNRS, UPMC, Univ. Paris Diderot (France)
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We report the ultrafast laser inscription (ULI) of a 2-telescope integrated optic (IO) beam combiner for K-band interferometry in commercial Infrasil glass. The ULI setup used for this work is based on a 1030 nm femtosecond laser which is paired with a spatial-light-modulator (SLM). The SLM controls the numerical aperture of the focused beam used to write waveguides in the substrate. The optimum ULI parameters were found to inscribe straight single-mode waveguides exhibiting an insertion loss of 1.1 ± 0.1 dB for a 17 mm long chip over the entire K-band. To develop optimal directional couplers, we focused our efforts on investigating the effect of varying the core-to-core separation and the effect of detuning the waveguide parameters in the coupler. By doing so, we have identified fabrication parameters that are suitable for the fabrication of a beam combiner integrating an achromatic 3 dB directional coupler and two photometric taps with a splitting ratio of 80:20. These results demonstrate the capability of the ULI fabrication technique to inscribe efficient achromatic directional couplers in the K-band range. A final fabrication step will involve simple assembly of the beam combiner with input/output fibers in preparation for on-sky testing at the CHARA array planned for July 2022.
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Jacopo Siliprandi, David G. MacLachlan, Calum A. Ross, Tarun K. Sharma, Lucas Labadie, Kalaga Madhav, Abani S. Nayak, Aline N. Dinkelaker, Martin M. Roth, Ettore Pedretti, Theo A. ten Brummelaar, Nicholas J. Scott, Vincent Coudé du Foresto, Robert R. Thomson, Aurélien Benoît, "Ultrafast laser inscription of integrated optics two-telescope beam combiners for K-band interferometry at the CHARA array," Proc. SPIE 12183, Optical and Infrared Interferometry and Imaging VIII, 1218314 (26 August 2022); https://doi.org/10.1117/12.2629899