The investigation on metalenses have been rapidly developing, aiming to bring compact optical devices with superior properties to the market. Realizing miniature optics at the UV frequency range in particular has been challenging as the available transparent materials have limited range of dielectric constants. In this work we introduce a low absorption loss and low refractive index dielectric material magnesium oxide, MgO, as an ideal candidate for metalenses operating at UV frequencies. We theoretically investigate metalens designs capable of efficient focusing over a broad UV frequency range (200–400 nm). The presented metalenses are composed of sub-wavelength MgO nanoblocks, and characterized according to the geometric Pancharatnam–Berry phase method using FDTD method. The presented broadband metalenses can focus the incident UV light on tight focal spots (182 nm) with high numerical aperture ( $$\hbox {NA}\approx 0.8$$NA ≈ 0.8 ). The polarization conversion efficiency of the metalens unit cell and focusing efficiency of the total metalens are calculated to be as high as 94%, the best value reported in UV range so far. In addition, the metalens unit cell can be hybridized to enable lensing at multiple polarization states. The presented highly efficient MgO metalenses can play a vital role in the development of UV nanophotonic systems and could pave the way towards the world of miniaturization.

We theoretically investigate a multi-resonant plasmonic metamaterial perfect absorber operating between 600 and 950 nm wavelengths. The presented device generates 100% absorption at two resonance wavelengths and delivers an ultra-narrow band (sub-20 nm) and high quality factor $(Q=44)$ resonance. The studied perfect absorber is a metal–insulator–metal configuration where a thin MgF${}_2$ spacer is sandwiched between an optically thick gold layer and uniformly patterned gold circular nanodisc antennas. The localized and propagating nature of the plasmonic resonances are characterized and confirmed theoretically. The origin of the perfect absorption is investigated using the impedance matching and critical coupling phenomenon. We calculate the effective impedance of the perfect absorber and confirm the matching with the free space impedance. We also investigate the scattering properties of the top antenna layer and confirm the minimized reflection at resonance wavelengths by calculating the absorption and scattering cross sections. The excitation of plasmonic resonances boost the near-field intensity by three orders of magnitude which enhances the interaction between the metamaterial surface and the incident energy. The refractive index sensitivity of the perfect absorber could go as high as $S=500$ nm/RIU. The presented optical characteristics make the proposed narrow-band multi-resonant perfect absorber a favorable platform for biosensing and contrast agent based bioimaging.

Integration of polarization sensing into conventional imaging devices can uncover crucial information, unlocking applications across a wide range of scientific domains from biomedical imaging to remote sensing and astronomy. Rapid progress in nanofabrication technology has driven the trend of pixel downscaling in imaging devices, leading to improved device functionality and performance. For polarization imaging to engage with high-resolution image sensor a further scaling of per-pixel polarizing objects is needed, while maintaining the optical throughput. In this paper, we propose a design for an ultracompact polarization splitting device based on a vertical dielectric waveguide architecture, compatible with sub-micron pixel sizes (560 nm), which is close to the state-of-the-art CMOS imager sensor resolution. The device implements an adiabatic mode converter to effectively separate orthogonal linear polarization states of incident light across the entire visible spectrum. Moreover, we demonstrate the design versatility by expanding its polarization splitting functionality across the entire linear polarization space (0°–180°), enabling robust polarization detection for advanced polarization imaging applications.