Selective Linewidth Control in a Micro-Resonator With a Resonant Interferometric Coupler

Optical microresonators are characterized by a comb of resonances that preserve similar characteristics over a broad spectral interval. However, for many applications it is beneficial to selectively control of the quality factor (Q) of one or only some resonances. In this work we propose and experimentally validate the use of a resonant interferometric coupler to selectively change the Q-factor of a target resonance in an integrated silicon nitride microresonator. We show that its loaded Q-factor can be continuously tuned from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$6.5\times 10^{4}$</tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3\times 10^{6}$</tex-math></inline-formula>, leaving the not-target resonances uperturbed. Our design can be scaled to independently control several resonances, and offers improved wavelength selectivity, reduced power consumption, and decreased thermal cross-talk compared to the sole use of an interferometric coupler.