Off-axis bifocal metalens for displacement measurement

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Metasurfaces are advanced micro-optical elements capable of precisely controlling electromagnetic waves.
• Dielectric structures within metasurfaces can be geometrically tuned to modulate wave properties.

Purpose of the Study:

• To design and demonstrate a bifocal metalens for potential application in displacement measurement.
• To explore the use of metasurfaces for high-precision sensing applications.

Main Methods:

• Designed a bifocal metalens using a phase modulation approach based on optical holography.
• Utilized polarization-insensitive TiO2 cylinders as structural units with varying radii for phase control.
• Fabricated the metalens using electron beam lithography and atomic layer deposition.

Main Results:

• Successfully designed a metalens with two distinct focal spots (900 μm and 1100 μm) not aligned on the same optical axis.
• Experimental measurements confirmed a linear differential signal, demonstrating effective displacement measurement capabilities.
• Achieved a linear interval for displacement sensing using the bifocal differential method.

Conclusions:

• The designed bifocal metalens shows promise for accurate displacement measurement.
• The semiconductor-compatible fabrication process allows for easy integration into miniaturized devices.
• Potential applications include miniaturized displacement sensors, micro-resonators, and acceleration measurements.