Closed-Loop Control of Photonic Ring Resonators by Means of Photo-Thermal Plasmonic Sensors

This paper highlights the effectiveness of photo-thermal plasmonic sensors in enabling real-time closed-loop stabilization of photonic devices. To assess the waveguided optical power, the in-line detector leverages the photo-thermal resistance variation of a micrometric plasmonic strip in contact with the waveguide. The generated signal is used to lock to resonance a ring resonator against wavelength and temperature variations, in a silicon-based technology. Thanks to the high sensitivity of the detector and its limited penalty on the waveguide loss, automatic re-tuning of the ring resonator with a recovery time of
$20 \,\mathrm{m}\mathrm{s}$
has been successfully achieved. The micrometric dimensions of the sensor, its technological simplicity, and the delivered signal (proportional to the optical power) make the photo-thermal plasmonic sensor an attractive in-line candidate for closed-loop control of optical devices, regardless of the technology employed for the photonic chip fabrication.