Electrowetting-Based Tunable Liquid Droplet Microresonator

A tunable liquid whispering gallery mode (WGM) resonator based on the electrowetting principle is presented. The liquid resonator consists of a glycerol droplet submerged within an immiscible liquid (dodecane/hexane) bath. The diameter of the droplet is electrically tuned using the electrowetting effect, resulting in a redshift in optical resonance frequency. By applying 35 V, a maximum spectral tuning of 1.44 nm ± 5 pm is achieved. The tuning range achieved is twice the free spectral range (FSR) of the resonator, 0.679 nm. The Q-factor of the resonator with a glycerol droplet in hexane liquid system is measured to be 3.5 × 10
⁶
. This work represents a new on-chip design, fabricated using standard microfabrication techniques, for future physical and biochemical sensing applications.