Abstract
Microring resonators made of materials with a zinc-blend or diamond lattice allow exploiting their 4-bar symmetry to achieve quasi-phase matching condition for second-order optical nonlinearities. However, fabrication tolerances impose severe limits on the quasi-phase matching condition, which in turn degrades the generation efficiency. Here, we present a method to mitigate these limitations. As an example, we studied the geometry and the pump wavelength conditions to induce the second-harmonic generation in silicon-based microrings with a second-order susceptibility χzxy(2)≠0. We found the best compromises between performances and experimental requirements, and we unveil a strategy to minimize the impacts of fabrication defects. The method can be easily transferred to other material systems.
Highlights
Ranging from the frequency conversion to photon pair emission, the second-order nonlinear phenomena are fundamental tools in integrated photonics
We studied various microresonator geometries, allowing second-harmonic generation (SHG) to find the best compromise between performances and experimental requirements
Note that we use dashed curves in the figure to underline that the SHG conditions are not continuous, since the microrings have separate resonances—i.e., the azimuthal number is an integer
Summary
Ranging from the frequency conversion to photon pair emission, the second-order nonlinear phenomena are fundamental tools in integrated photonics. In 2015, optical frequency comb generation has been demonstrated in silicon microring resonators by using four wave mixing and self-phase modulation [2]. Due to these nonlinear processes, the frequency comb generation was limited in its frequency span. To extend this span beyond one octave, the use of both second-order and third-order nonlinearities was shown in MgO:LiNbO3 microcavities [3]. Second-order nonlinearities can directly produce simultaneous octave-distant
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