Ultrafast laser inscription of asymmetric integrated waveguide 3 dB couplers for astronomical K-band interferometry at the CHARA array

Aurélien Benoît, Fraser A. Pike, Tarun K. Sharma, David G. MacLachlan, Aline N. Dinkelaker, Abani S. Nayak, Kalaga Madhav, Martin M. Roth, Lucas Labadie, Ettore Pedretti, Theo A. ten Brummelaar, Nic Scott, Vincent Coudé du Foresto, Robert R. Thomson

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Abstract

We present the fabrication and characterization of 3 dB asymmetric directional couplers for the astronomical K-band at wavelengths between 2.0 and 2.4 µm. The couplers were fabricated in commercial Infrasil silica glass using an ultrafast laser operating at 1030 nm. After optimizing the fabrication parameters, the insertion losses of straight single-mode waveguides were measured to be ∼1.2 ± 0.5 dB across the full K-band. We investigate the development of asymmetric 3 dB directional couplers by varying the coupler interaction lengths and by varying the width of one of the waveguide cores to detune the propagation constants of the coupled modes. In this manner, we demonstrate that ultrafast laser inscription is capable of fabricating asymmetric 3 dB directional couplers for future applications in K-band stellar interferometry. Finally, we demonstrate that our couplers exhibit an interferometric fringe contrast of >90%. This technology paves the path for the development of a two-telescope K-band integrated optic beam combiner for interferometry to replace the existing beam combiner (MONA) in Jouvence of the Fiber Linked Unit for Recombination (JouFLU) at the Center for High Angular Resolution Astronomy (CHARA) telescope array.

Original languageEnglish
Pages (from-to)2455-2464
Number of pages10
JournalJournal of the Optical Society of America B: Optical Physics
Volume38
Issue number9
Early online date4 Aug 2021
DOIs
Publication statusPublished - 1 Sep 2021

ASJC Scopus subject areas

  • Statistical and Nonlinear Physics
  • Atomic and Molecular Physics, and Optics

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