Permanent mitigation of loss in ultrathin silicon-on-insulator high-Q resonators using ultraviolet light

Mitigation of optical losses is of prime importance for the performance of integrated micro-photonic devices. In this paper, we demonstrate strip-loaded guiding optical components realized on a 27 nm ultra-thin silicon-on-insulator (SOI) platform. The absence of physically etched boundaries within the guiding core majorly suppresses the scattering loss, as shown by us previously for a silicon nitride (Si3N4) platform. Unexpectedly, the freshly fabricated Si devices showed large losses of 5.1 dB/cm originating from absorption by free carriers, accumulated under the positively charged Si3N4 loading layer. We show how ultraviolet (UV, 254 nm) light exposure can progressively and permanently neutralize Si3N4’s bulk charge, associated with diamagnetic + defects. Consequently, the net decrease of electron concentration in the SOI layer reduces the propagation loss down to 0.9 dB/cm. Accurate cavity linewidth measurements demonstrate how the intrinsic cavity’s boosts from 70,000 up to 500,000 after UV illumination. Our results may open routes towards engineering of new functionalities in photonic devices employing UV modification of space-charge-associated local electric fields, unveil the origin of induced optical nonlinearities in Si3N4/Si micro-photonic systems, as well as envisage possible integration of these with both standard and ultra-thin SOI electronics.