Method for GHz optical helicity modulation by acoustic drum modes on a chip.

Area of Science:

• Acoustics
• Optomechanics
• Nanotechnology

Background:

• GHz acoustic modes are crucial for advanced optomechanical systems.
• Tunable helicity in acoustic modes is key for novel functionalities.
• On-chip acoustic mode generation and control remain challenging.

Purpose of the Study:

• To demonstrate electrical generation of GHz membrane-like helical drum acoustic modes on-chip.
• To propose their application in generating optical beams with tunable orbital angular momentum (OAM).
• To explore acousto-optical chiral functionalities.

Main Methods:

• Utilizing the dependence of Lamb-like acoustic mode frequencies on substrate thickness for lateral confinement.
• Generating modes in disk-shaped regions using piezoelectric resonators.
• Experimentally confirming modes via radio-frequency spectroscopy and surface displacement mapping.
• Creating acoustic vortices with tunable OAM polarity using phased sector-shaped piezoelectric transducers.

Main Results:

• Successfully generated and confined GHz membrane-like helical drum acoustic modes on-chip.
• Demonstrated experimental confirmation of these modes.
• Showcased the transfer of tunable OAM polarity from acoustic vortices to optical beams.
• Developed analytical and finite-element models for acoustic mode coupling.

Conclusions:

• The developed concept enables on-chip electrical generation of tunable helical acoustic modes.
• These modes are applicable for generating optical beams with tunable OAM.
• The platform offers flexible acousto-optical chiral functionalities in the GHz range.
• The findings provide insights for adapting the technology to other material systems.