Continuous angle-tunable birefringence with freeform metasurfaces for arbitrary polarization conversion

Area of Science:

• Optics and Photonics
• Materials Science
• Metamaterials

Background:

• Birefringence, where light polarization affects refractive index, is crucial for optical elements like wave plates.
• Conventional bulk crystals exhibit limited linear birefringence.
• Metamaterials offer potential for engineered optical anisotropy.

Purpose of the Study:

• To demonstrate arbitrary birefringence using topology-optimized metasurfaces.
• To engineer optical anisotropy for arbitrary-linear, circular, or elliptical eigen-polarization states.
• To achieve angle-tunable birefringence from linear to elliptical.

Main Methods:

• Utilizing topology-optimized metasurfaces with freeform meta-atoms.
• Engineering optical anisotropy to control refractive indices for different polarization states.
• Investigating the continuous tunability of birefringence by changing the angle of incidence.

Main Results:

• Successful demonstration of arbitrary birefringence.
• Achieved continuous tuning from linear to elliptical birefringence with angle of incidence.
• Showcased a single metasurface functioning as multiple parallel wave plates for diverse polarization transformations.

Conclusions:

• Angle-tunable arbitrary birefringence expands possibilities in polarization optics.
• Enables compact and versatile polarization operations, reducing the need for multiple optical elements.
• Potential applications in polarization imaging, quantum optics, and other fields.