Geometric-phase metalens to be used for tunable optical tweezers in microfluidics

ABSTRACT

Geometric-phase dielectric meta-lenses made of silicon with high numerical aperture and short focal lengths are fabricated and characterised. For circularly polarised light, the same meta-lens can act as a converging or diverging lens, depending on the handedness of the circular polarisation. This effect enables application for optical tweezers that trap or release µm-size polymer beads floating in a microfluidic channel on demand. An electrically addressable polarisation converter based on liquid crystals may be used to switch between the two states of polarisation, at which the light transmitted through the meta-lens is focused (trapping) or defocussed (releasing), respectively.

GRAPHICAL ABSTRACT

KEYWORDS:

• Dielectric meta-surface
• geometric phase
• liquid crystal
• microfluidics

Acknowledgements

The authors would like to thank Christian Schlickriede for his assistance in some of the measurements. R. G. and T. Z. acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; TRR142, grant no. 231447078, project B09). H. K. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG, project LO 1922/4-1).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Deutsche Forschungsgemeinschaft [LO 1922/4-1,TRR142, grant no. 231447078, project B09].