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Quasi-phase matching in integrated lithium-niobate whispering galleries
Author(s): Ingo Breunig; Karsten Buse
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Paper Abstract

Whispering-gallery resonators (WGRs) made of lithium niobate are very attractive for nonlinear-optical frequency conversion due to their small mode volumes and high Q-factors. To achieve phase matching, methods like birefringent phase matching and quasi phase matching (QPM) have been employed in millimeter-sized bulk WGRs. Among these, the latter provides ultimate flexibility in terms of wavelengths and polarization of the interacting waves. Integrated on-chip WGRs are in particular very appealing due to the possibility of building photonic circuits and the usage of highly-parallel and thus scalable semiconductor manufacturing techniques. Integrated WGRs are, however, fabricated on thin-film substrates. This leads to one major drawback: QPM is hard to achieve, since it is difficult to realize periodically-poled thin films by field-assisted domain inversion. We report on a method to resolve this issue. First, we do domain engineering in bulk material. Next, we bond this sample on a quartz substrate by direct wafer bonding and finally we polish the lithium niobate to a 2-μm-thick film. By lithography and reactive-ion etching we structure waveguide rings with 200 μm diameter into the thin film. Subsequent polishing of the waveguide sidewalls decreases surface-scattering losses and enables on-chip WGRs with quality factors exceeding one million. This allowed us to demonstrate for the first time quasi-phase matched second-harmonic generation in integrated WGRs, pumped by light with 1550 nm wavelength, obtaining a normalized conversion efficiency of 0.9 ‰/mW. Being now able to deploy type-0 and type-ii phase matching opens entirely new possibilities for frequency conversion with on-chip WGRs.

Paper Details

Date Published: 4 March 2019
PDF: 6 pages
Proc. SPIE 10904, Laser Resonators, Microresonators, and Beam Control XXI, 1090403 (4 March 2019); doi: 10.1117/12.2509835
Show Author Affiliations
Ingo Breunig, Univ. of Freiburg (Germany)
Fraunhofer-Institut für Physikalische Messtechnik (Germany)
Karsten Buse, Univ. of Freiburg (Germany)
Fraunhofer-Institut für Physikalische Messtechnik (Germany)

Published in SPIE Proceedings Vol. 10904:
Laser Resonators, Microresonators, and Beam Control XXI
Alexis V. Kudryashov; Alan H. Paxton; Vladimir S. Ilchenko, Editor(s)

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