“…They are fabricated on-chip with photolithographic techniques in different materials systems and in large sensor arrays [24, 40, 50, 52, 53, 89, 130, 131, 162–168]. For example, ring, racetrack and disk resonators can be fabricated in silica, silicon [24, 50, 89, 111, 166, 168] and organic polymers [52, 165, 167, 169, 170]. Early biosensing demonstrations proposed a high-finesse (low loss) WGM disk resonator [130] and utilized a vertically coupled glass microring resonator with Q of about 12000 [111] as well an integrated silicon nitride (Si x N y /SiO 2 ) ring resonator [53].…”