Quasi-phase-matched nonlinear optical frequency conversion in on-chip whispering galleries

• DOI: 10.1364/optica.5.000872
• Publication Date: 2018-07-16T20:34:58Z
• Authors: Richard Wolf; Yuechen Jia; Sebastian Bonaus; Christoph S. Werner; Simon J. Herr; Ingo Breunig; Karsten Buse; Hans Zappe
• Keywords: 0103 physical sciences; FOS: Physical sciences; 600; 01 natural sciences; Physics - Optics; Optics (physics.optics)

Chip-integrated whispering-gallery resonators enable compact and wavelength-agile nonlinear optical frequency synthesizers. So far, the most flexible phase-matching technique, i.e. quasi phase matching, has not been applied in this configuration. The reason is the lack of suitable thin films with alternating crystal structure on a low-refractive-index substrate. Here, we demonstrate an innovative method of realizing thin film substrates suitable for quasi phase matching by field-assisted domain engineering of lithium niobate, and subsequent direct bonding and polishing. We are able to fabricate high-Q on-chip WGRs with these substrates by using standard semiconductor manufacturing techniques. The Q-factors of the resonators are up to one million, which allows us to demonstrate quasi-phase-matched second-harmonic generation in on-chip WGRs for the first time. The normalized conversion efficiency is $9\times 10^{-4}\,\textrm{mW}^{-1}$. This method can also be transferred to other material systems.<br/>5 pages, 5 figures<br/>