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Q-factor enhancement of integrated lithium-niobate-on-insulator ridge waveguide whispering-gallery-mode resonators by surface polishing

: Wolf, Richard; Breunig, Ingo; Zappe, Hans; Buse, Karsten


Kudryashov, A.V. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Laser Resonators, Microresonators, and Beam Control XIX : San Francisco, California, United States, January 28, 2017
Bellingham, WA: SPIE, 2017 (Proceedings of SPIE 10090)
ISBN: 978-1-5106-0621-0
Paper 1009002, 6 pp.
Conference "Laser Resonators, Microresonators, and Beam Control" <19, 2017, San Francisco/Calif.>
Bundesministerium für Bildung und Forschung BMBF
Modenkontrolle in optisch-parametrischen Flüstergalerie-Resonatoren zur Ermöglichung günstiger, kompakter und durchstimmbarer Laserlichtquellen
Conference Paper
Fraunhofer IPM ()
whispering Gallery Resonator; integrated optics; Lithium-Niobate-on-Insulator

Whispering-gallery resonators (WGRs) are most promising for nonlinear-optical frequency-conversion due to their intensity enhancement by small mode volumes and high Q-factors. This has been shown frequently by millimeter-sized diamond-blade cut and polished bulk WGRs. For reproducible batch fabrication, however, the integration of WGRs into lithium-niobate-on-insulator (LNOI) substrates became of great interest. Here we report on integrated WGRs made by batch processes like lithography and reactive-ion etching. Since the Qfactor of integrated WGRs is limited by scattering losses, we focused on developing a polishing process for the waveguide sidewalls that allowed us to enhance the unloaded Q-factors already to more than 106 with room for further improvements. Furthermore we employ a coupling scheme with two waveguide chips, one comprising a linear coupling waveguide and one with the integrated WGR. By adjusting the distance between the coupling waveguide and the WGR, we can reproducibly and stably tune the coupling-efficiency between 0 and 95 %.