Realization of highly efficient trifocal metalens architecture with the blend of Pancharatnam–Berry and propagation phase effect

Light-matter interaction at the micron scale enables unprecedented control over different intrinsic properties of electromagnetic waves. Recently emerged ultrathin metamaterials (metasurfaces) featuring periodic nanoantennas are capable of controlling the amplitude, phase, and polarization states of the incident light and open up new avenues for a variety of exotic nanophotonic applications. Integrating multiple optical phenomena into a single nano-optical device has become a hotspot to increase the multi-functionality of the metasurfaces for functional multiplexing, notably reducing the intricacy of the existing optical setups. Herein, a multifunctional metalens operating at ultraviolet regime λ_d = 300 nm is reported, exploiting the approach of merging the Pancharatnam–Berry (PB) and propagation phases into a single meta-device. Through interleaving the different subwavelength rectangular and cylindrical shaped nanoantennas of silicon nitride (Si3N4) patterned on sapphire (Al2O3) substrate, the proposed meta-device results in a multifunctional metalens capable of focusing the incident light at three different focal spots on the same focal plane. The geometric parameters of both the nanoantennas (rectangular bar and cylindrical pillar) are optimized in such a way to achieve the maximum possible transmission intensity and complete phase coverage requirements for higher resolution focusing on making nanoscale features distinguishable. This attractive design topology of merging the multiple phases into a single device to realize a multifunctional meta-device can envision its promising application in imaging and optical communication.