Spectrally tunable liquid resonator based on electrowetting.

Area of Science:

• Photonics
• Microfluidics
• Materials Science

Background:

• On-chip optical resonators are crucial for integrated photonic circuits.
• Environmental fluctuations often limit the performance of micro-resonators.
• Achieving tunable and stable high-Q resonators remains a challenge.

Purpose of the Study:

• To present a novel tunable on-chip liquid resonator.
• To demonstrate spectral tuning using the electrowetting effect.
• To explore the integration potential with standard semiconductor fabrication.

Main Methods:

• Fabrication of a glycerol droplet resonator within an immiscible liquid bath using semiconductor techniques.
• Utilizing tapered fiber for coupling light into the resonator.
• Employing the electrowetting effect for spectral tuning by altering droplet diameter.
• 2D axisymmetric finite-element simulations for mode analysis.

Main Results:

• Achieved a high Q-factor of 10^5 on-chip due to a smooth liquid-liquid interface.
• Demonstrated spectral tuning of 1.44 nm ± 5 pm by applying 35 V.
• Observed a tuning range twice the free spectral range (0.679 nm).
• Simulations predicted resonance modes and tuning speeds of 20 nm/s.

Conclusions:

• The developed liquid resonator offers a stable, tunable platform for on-chip photonic devices.
• Standard semiconductor fabrication enables future integration of photonic components.
• The electrowetting-induced tuning mechanism provides a viable method for spectral control.